Alzheimer's Risk Factors Age, APOE Genotype, and Sex Drive Distinct Molecular Pathways.
Evidence suggests interplay among the three major risk factors for Alzheimer's disease (AD): age, APOE genotype, and sex. Here, we present comprehensive datasets and analyses of brain transcriptomes and blood metabolomes from human apoE2-, apoE3-, and apoE4-targeted replacement mice across young, middle, and old ages with both sexes. We found that age had the greatest impact on brain transcriptomes highlighted by an immune module led by Trem2 and Tyrobp, whereas APOE4 was associated with upregulation of multiple Serpina3 genes. Importantly, these networks and gene expression changes were mostly conserved in human brains. Finally, we observed a significant interaction between age, APOE genotype, and sex on unfolded protein response pathway. In the periphery, APOE2 drove distinct blood metabolome profile highlighted by the upregulation of lipid metabolites. Our work identifies unique and interactive molecular pathways underlying AD risk factors providing valuable resources for discovery and validation research in model systems and humans.
CD49f Is a Novel Marker of Functional and Reactive Human iPSC-Derived Astrocytes.
Barbar Lilianne,Jain Tanya,Zimmer Matthew,Kruglikov Ilya,Sadick Jessica S,Wang Minghui,Kalpana Kriti,Rose Indigo V L,Burstein Suzanne R,Rusielewicz Tomasz,Nijsure Madhura,Guttenplan Kevin A,di Domenico Angelique,Croft Gist,Zhang Bin,Nobuta Hiroko,Hébert Jean M,Liddelow Shane A,Fossati Valentina
New methods for investigating human astrocytes are urgently needed, given their critical role in the central nervous system. Here we show that CD49f is a novel marker for human astrocytes, expressed in fetal and adult brains from healthy and diseased individuals. CD49f can be used to purify fetal astrocytes and human induced pluripotent stem cell (hiPSC)-derived astrocytes. We provide single-cell and bulk transcriptome analyses of CD49f hiPSC-astrocytes and demonstrate that they perform key astrocytic functions in vitro, including trophic support of neurons, glutamate uptake, and phagocytosis. Notably, CD49f hiPSC-astrocytes respond to inflammatory stimuli, acquiring an A1-like reactive state, in which they display impaired phagocytosis and glutamate uptake and fail to support neuronal maturation. Most importantly, we show that conditioned medium from human reactive A1-like astrocytes is toxic to human and rodent neurons. CD49f hiPSC-astrocytes are thus a valuable resource for investigating human astrocyte function and dysfunction in health and disease.
Impact of TREM2R47H variant on tau pathology-induced gliosis and neurodegeneration.
Gratuze Maud,Leyns Cheryl Eg,Sauerbeck Andrew D,St-Pierre Marie-Kim,Xiong Monica,Kim Nayeon,Serrano Javier Remolina,Tremblay Marie-Ève,Kummer Terrance T,Colonna Marco,Ulrich Jason D,Holtzman David M
The Journal of clinical investigation
Alzheimer's disease (AD) is characterized by plaques containing amyloid-β (Aβ) and neurofibrillary tangles composed of aggregated, hyperphosphorylated tau. Beyond tau and Aβ, evidence suggests that microglia play an important role in AD pathogenesis. Rare variants in the microglia-expressed triggering receptor expressed on myeloid cells 2 (TREM2) gene increase AD risk 2- to 4-fold. It is likely that these TREM2 variants increase AD risk by decreasing the response of microglia to Aβ and its local toxicity. However, neocortical Aβ pathology occurs many years before neocortical tau pathology in AD. Thus, it will be important to understand the role of TREM2 in the context of tauopathy. We investigated the impact of the AD-associated TREM2 variant (R47H) on tau-mediated neuropathology in the PS19 mouse model of tauopathy. We assessed PS19 mice expressing human TREM2CV (common variant) or human TREM2R47H. PS19-TREM2R47H mice had significantly attenuated brain atrophy and synapse loss versus PS19-TREM2CV mice. Gene expression analyses and CD68 immunostaining revealed attenuated microglial reactivity in PS19-TREM2R47H versus PS19-TREM2CV mice. There was also a decrease in phagocytosis of postsynaptic elements by microglia expressing TREM2R47H in the PS19 mice and in human AD brains. These findings suggest that impaired TREM2 signaling reduces microglia-mediated neurodegeneration in the setting of tauopathy.
Endothelial activation of caspase-9 promotes neurovascular injury in retinal vein occlusion.
Central nervous system ischemic injury features neuronal dysfunction, inflammation and breakdown of vascular integrity. Here we show that activation of endothelial caspase-9 after hypoxia-ischemia is a critical event in subsequent dysfunction of the blood-retina barrier, using a panel of interrelated ophthalmic in vivo imaging measures in a mouse model of retinal vein occlusion (RVO). Rapid nonapoptotic activation of caspase-9 and its downstream effector caspase-7 in endothelial cells promotes capillary ischemia and retinal neurodegeneration. Topical eye-drop delivery of a highly selective caspase-9 inhibitor provides morphological and functional retinal protection. Inducible endothelial-specific caspase-9 deletion phenocopies this protection, with attenuated retinal edema, reduced inflammation and preserved neuroretinal morphology and function following RVO. These results reveal a non-apoptotic function of endothelial caspase-9 which regulates blood-retina barrier integrity and neuronal survival, and identify caspase-9 as a therapeutic target in neurovascular disease.
Restoring metabolism of myeloid cells reverses cognitive decline in ageing.
Ageing is characterized by the development of persistent pro-inflammatory responses that contribute to atherosclerosis, metabolic syndrome, cancer and frailty. The ageing brain is also vulnerable to inflammation, as demonstrated by the high prevalence of age-associated cognitive decline and Alzheimer's disease. Systemically, circulating pro-inflammatory factors can promote cognitive decline, and in the brain, microglia lose the ability to clear misfolded proteins that are associated with neurodegeneration. However, the underlying mechanisms that initiate and sustain maladaptive inflammation with ageing are not well defined. Here we show that in ageing mice myeloid cell bioenergetics are suppressed in response to increased signalling by the lipid messenger prostaglandin E (PGE), a major modulator of inflammation. In ageing macrophages and microglia, PGE signalling through its EP2 receptor promotes the sequestration of glucose into glycogen, reducing glucose flux and mitochondrial respiration. This energy-deficient state, which drives maladaptive pro-inflammatory responses, is further augmented by a dependence of aged myeloid cells on glucose as a principal fuel source. In aged mice, inhibition of myeloid EP2 signalling rejuvenates cellular bioenergetics, systemic and brain inflammatory states, hippocampal synaptic plasticity and spatial memory. Moreover, blockade of peripheral myeloid EP2 signalling is sufficient to restore cognition in aged mice. Our study suggests that cognitive ageing is not a static or irrevocable condition but can be reversed by reprogramming myeloid glucose metabolism to restore youthful immune functions.
Innate immunity stimulation via CpG oligodeoxynucleotides ameliorates Alzheimer's disease pathology in aged squirrel monkeys.
Patel Akash G,Nehete Pramod N,Krivoshik Sara R,Pei Xuewei,Cho Elizabeth L,Nehete Bharti P,Ramani Margish D,Shao Yongzhao,Williams Lawrence E,Wisniewski Thomas,Scholtzova Henrieta
Brain : a journal of neurology
Alzheimer's disease is the most common cause of dementia and the only illness among the top 10 causes of death for which there is no disease-modifying therapy. The failure rate of clinical trials is very high, in part due to the premature translation of successful results in transgenic mouse models to patients. Extensive evidence suggests that dysregulation of innate immunity and microglia/macrophages plays a key role in Alzheimer's disease pathogenesis. Activated resident microglia and peripheral macrophages can display protective or detrimental phenotypes depending on the stimulus and environment. Toll-like receptors (TLRs) are a family of innate immune regulators known to play an important role in governing the phenotypic status of microglia. We have shown in multiple transgenic Alzheimer's disease mouse models that harnessing innate immunity via TLR9 agonist CpG oligodeoxynucleotides (ODNs) modulates age-related defects associated with immune cells and safely reduces amyloid plaques, oligomeric amyloid-β, tau pathology, and cerebral amyloid angiopathy (CAA) while promoting cognitive benefits. In the current study we have used a non-human primate model of sporadic Alzheimer's disease pathology that develops extensive CAA-elderly squirrel monkeys. The major complications in current immunotherapeutic trials for Alzheimer's disease are amyloid-related imaging abnormalities, which are linked to the presence and extent of CAA; hence, the prominence of CAA in elderly squirrel monkeys makes them a valuable model for studying the safety of the CpG ODN-based concept of immunomodulation. We demonstrate that long-term use of Class B CpG ODN 2006 induces a favourable degree of innate immunity stimulation without producing excessive or sustained inflammation, resulting in efficient amelioration of both CAA and tau Alzheimer's disease-related pathologies in association with behavioural improvements and in the absence of microhaemorrhages in aged elderly squirrel monkeys. CpG ODN 2006 has been well established in numerous human trials for a variety of diseases. The present evidence together with our earlier, extensive preclinical research, validates the beneficial therapeutic outcomes and safety of this innovative immunomodulatory approach, increasing the likelihood of CpG ODN therapeutic efficacy in future clinical trials.
Fatty acids and evolving roles of their proteins in neurological, cardiovascular disorders and cancers.
Mallick Rahul,Basak Sanjay,Duttaroy Asim K
Progress in lipid research
The dysregulation of fat metabolism is involved in various disorders, including neurodegenerative, cardiovascular, and cancers. The uptake of long-chain fatty acids (LCFAs) with 14 or more carbons plays a pivotal role in cellular metabolic homeostasis. Therefore, the uptake and metabolism of LCFAs must constantly be in tune with the cellular, metabolic, and structural requirements of cells. Many metabolic diseases are thought to be driven by the abnormal flow of fatty acids either from the dietary origin and/or released from adipose stores. Cellular uptake and intracellular trafficking of fatty acids are facilitated ubiquitously with unique combinations of fatty acid transport proteins and cytoplasmic fatty acid-binding proteins in every tissue. Extensive data are emerging on the defective transporters and metabolism of LCFAs and their clinical implications. Uptake and metabolism of LCFAs are crucial for the brain's functional development and cardiovascular health and maintenance. In addition, data suggest fatty acid metabolic transporter can normalize activated inflammatory response by reprogramming lipid metabolism in cancers. Here we review the current understanding of how LCFAs and their proteins contribute to the pathophysiology of three crucial diseases and the mechanisms involved in the processes.
Cellular senescence at the crossroads of inflammation and Alzheimer's disease.
Guerrero Ana,De Strooper Bart,Arancibia-Cárcamo I Lorena
Trends in neurosciences
Aging is a key risk factor for Alzheimer's disease (AD), but the reasons for this association are not well understood. Senescent cells accumulate in aged tissues and have been shown to play causal roles in age-related pathologies through their proinflammatory secretome. The question arises whether senescence-induced inflammation might contribute to AD and bridge the gap between aging and AD. Here, we highlight the role of cellular senescence as a driver of the aging phenotype, and discuss the current evidence that connects senescence with AD and neurodegeneration.
Microglial Calhm2 regulates neuroinflammation and contributes to Alzheimer's disease pathology.
Alzheimer's disease (AD) is the most common neurodegenerative disease in the world. Neuronal calcium dysfunction and microglial-mediated neuroinflammation are closely associated with the development of AD. However, it remains unknown whether calcium dysfunction contributes to microglial activation and, in turn, AD pathology in vivo. In this study, we demonstrated that the expression of calcium homeostasis modulator family protein 2 (Calhm2) is increased in an AD mouse model. In mice carrying five familial AD gene mutations, both conventional knockout of and conditional microglial knockout of significantly reduced amyloid β deposition, neuroinflammation, and cognitive impairments. Mechanistically, knockout of inhibited microglial proinflammatory activity but increased phagocytic activity, leading to restoration of the balance between inflammation and phagocytosis. In addition, knockout of reduced acute LPS-induced neuroinflammation. These results highlight an important role for Calhm2 in microglial activation and provide a potential therapeutic target for diseases related to microglia-mediated neuroinflammation.
Exploiting dynamic enhancer landscapes to decode macrophage and microglia phenotypes in health and disease.
The development and functional potential of metazoan cells is dependent on combinatorial roles of transcriptional enhancers and promoters. Macrophages provide exceptionally powerful model systems for investigation of mechanisms underlying the activation of cell-specific enhancers that drive transitions in cell fate and cell state. Here, we review recent advances that have expanded appreciation of the diversity of macrophage phenotypes in health and disease, emphasizing studies of liver, adipose tissue, and brain macrophages as paradigms for other tissue macrophages and cell types. Studies of normal tissue-resident macrophages and macrophages associated with cirrhosis, obese adipose tissue, and neurodegenerative disease illustrate the major roles of tissue environment in remodeling enhancer landscapes to specify the development and functions of distinct macrophage phenotypes. We discuss the utility of quantitative analysis of environment-dependent changes in enhancer activity states as an approach to discovery of regulatory transcription factors and upstream signaling pathways.
Emerging roles of Dectin-1 in noninfectious settings and in the CNS.
Trends in immunology
Dectin-1 is a C-type lectin receptor (CLR) expressed on the surface of various mammalian myeloid cells. Dectin-1 recognizes β-glucans and elicits antifungal proinflammatory immune responses. Recent studies have begun to examine the biology of Dectin-1 in previously less explored settings, such as homeostasis, sterile inflammation, and in the central nervous system. Indeed, in certain contexts, Dectin-1 is now known to promote tolerance, and anti-inflammatory and neuroprotective responses. In this review, we provide an overview of the current understanding of the roles of Dectin-1 in immunology beyond the context of fungal infections, mainly focusing on in vivo neuroimmunology studies, which could reveal new therapeutic approaches to modify innate immune responses in neurologic disorders.
Plasma soluble TREM2 is associated with white matter lesions independent of amyloid and tau.
Tsai Hsin-Hsi,Chen Ya-Fang,Yen Ruoh-Fang,Lo Yen-Ling,Yang Kai-Chien,Jeng Jiann-Shing,Tsai Li-Kai,Chang Che-Feng
Brain : a journal of neurology
Cerebral small vessel disease is one of the most common causes of cognitive decline and stroke. While several lines of evidence have established a relationship between inflammation and cerebrovascular pathology, the mechanistic link has not yet been elucidated. Recent studies suggest activation of immune mediators, including the soluble form of triggering receptor expressed on myeloid cells 2 (TREM2), may be critical regulators. In this study, we compared the plasma levels of soluble TREM2 and its correlations with neuroimaging markers and cerebral amyloid load in 10 patients with Alzheimer's disease and 66 survivors of spontaneous intracerebral haemorrhage with cerebral amyloid angiopathy or hypertensive small vessel disease, two of the most common types of sporadic small vessel disease. We performed brain MRI and 11C-Pittsburgh compound B PET for all participants to evaluate radiological small vessel disease markers and cerebral amyloid burden, and 18F-T807 PET in a subgroup of patients to evaluate cortical tau pathology. Plasma soluble TREM2 levels were comparable between patients with Alzheimer's disease and small vessel disease (P = 0.690). In patients with small vessel disease, plasma soluble TREM2 was significantly associated with white matter hyperintensity volume (P < 0.001), but not with cerebral amyloid load. Among patients with Alzheimer's disease and cerebral amyloid angiopathy, plasma soluble TREM2 was independently associated with a tau-positive scan (P = 0.001) and white matter hyperintensity volume (P = 0.013), but not amyloid load (P = 0.221). Our results indicate plasma soluble TREM2 is associated with white matter hyperintensity independent of amyloid and tau pathology. These findings highlight the potential utility of plasma soluble TREM2 as a strong predictive marker for small vessel disease-related white matter injury and hold clinical implications for targeting the innate immune response when treating this disease.
Microglial activation elicits a negative affective state through prostaglandin-mediated modulation of striatal neurons.
Klawonn Anna M,Fritz Michael,Castany Silvia,Pignatelli Marco,Canal Carla,Similä Fredrik,Tejeda Hugo A,Levinsson Julia,Jaarola Maarit,Jakobsson Johan,Hidalgo Juan,Heilig Markus,Bonci Antonello,Engblom David
Microglia are activated in many neurological diseases and have been suggested to play an important role in the development of affective disorders including major depression. To investigate how microglial signaling regulates mood, we used bidirectional chemogenetic manipulations of microglial activity in mice. Activation of microglia in the dorsal striatum induced local cytokine expression and a negative affective state characterized by anhedonia and aversion, whereas inactivation of microglia blocked aversion induced by systemic inflammation. Interleukin-6 signaling and cyclooxygenase-1 mediated prostaglandin synthesis in the microglia were critical for the inflammation-induced aversion. Correspondingly, microglial activation led to a prostaglandin-dependent reduction of the excitability of striatal neurons. These findings demonstrate a mechanism by which microglial activation causes negative affect through prostaglandin-dependent modulation of striatal neurons and indicate that interference with this mechanism could milden the depressive symptoms in somatic and psychiatric diseases involving microglial activation.
Anti-inflammatory dopamine- and serotonin-based endocannabinoid epoxides reciprocally regulate cannabinoid receptors and the TRPV1 channel.
The endocannabinoid system is a promising target to mitigate pain as the endocannabinoids are endogenous ligands of the pain-mediating receptors-cannabinoid receptors 1 and 2 (CB1 and CB2) and TRPV1. Herein, we report on a class of lipids formed by the epoxidation of N-arachidonoyl-dopamine (NADA) and N-arachidonoyl-serotonin (NA5HT) by epoxygenases. EpoNADA and epoNA5HT are dual-functional rheostat modulators of the endocannabinoid-TRPV1 axis. EpoNADA and epoNA5HT are stronger modulators of TRPV1 than either NADA or NA5HT, and epoNA5HT displays a significantly stronger inhibition on TRPV1-mediated responses in primary afferent neurons. Moreover, epoNA5HT is a full CB1 agonist. These epoxides reduce the pro-inflammatory biomarkers IL-6, IL-1β, TNF-α and nitrous oxide and raise anti-inflammatory IL-10 cytokine in activated microglial cells. The epoxides are spontaneously generated by activated microglia cells and their formation is potentiated in the presence of anandamide. Detailed kinetics and molecular dynamics simulation studies provide evidence for this potentiation using the epoxygenase human CYP2J2. Taken together, inflammation leads to an increase in the metabolism of NADA, NA5HT and other eCBs by epoxygenases to form the corresponding epoxides. The epoxide metabolites are bioactive lipids that are potent, multi-faceted molecules, capable of influencing the activity of CB1, CB2 and TRPV1 receptors.
Insomnia symptom severity and cognitive performance: Moderating role of APOE genotype.
Alzheimer's & dementia : the journal of the Alzheimer's Association
INTRODUCTION:We evaluated whether insomnia symptom severity was associated with cognitive function, and whether this relationship was modified by biomarkers associated with Alzheimer's disease risk. METHODS:We examined insomnia symptoms and neuropsychological performance 3.4 years later in 511 dementia-free Framingham Heart Study participants (62.65 ± 8.7 years, 50.9% male). Additionally, we explored insomnia symptoms combined with self-reported short habitual sleep duration and effect modification by apolipoprotein E (APOE) ε4 allele status. RESULTS:More severe insomnia symptoms were associated with lower performance on global cognition, and immediate and delayed Logical Memory recall, especially when insomnia symptoms were combined with short sleep duration. The association between insomnia symptoms and poorer memory recall was more pronounced in APOE ε4 allele carriers. DISCUSSION:Insomnia symptom severity was associated with worse subsequent global cognitive and memory performance, which was especially apparent in APOE ε4 allele carriers, suggesting that poor sleep might be particularly detrimental when the brain is already vulnerable to neurodegeneration.
Type I interferon response drives neuroinflammation and synapse loss in Alzheimer disease.
Roy Ethan R,Wang Baiping,Wan Ying-Wooi,Chiu Gabriel,Cole Allysa,Yin Zhuoran,Propson Nicholas E,Xu Yin,Jankowsky Joanna L,Liu Zhandong,Lee Virginia M-Y,Trojanowski John Q,Ginsberg Stephen D,Butovsky Oleg,Zheng Hui,Cao Wei
The Journal of clinical investigation
Type I interferon (IFN) is a key cytokine that curbs viral infection and cell malignancy. Previously, we demonstrated a potent IFN immunogenicity of nucleic acid-containing (NA-containing) amyloid fibrils in the periphery. Here, we investigated whether IFN is associated with β-amyloidosis inside the brain and contributes to neuropathology. An IFN-stimulated gene (ISG) signature was detected in the brains of multiple murine Alzheimer disease (AD) models, a phenomenon also observed in WT mouse brain challenged with generic NA-containing amyloid fibrils. In vitro, microglia innately responded to NA-containing amyloid fibrils. In AD models, activated ISG-expressing microglia exclusively surrounded NA+ amyloid β plaques, which accumulated in an age-dependent manner. Brain administration of rIFN-β resulted in microglial activation and complement C3-dependent synapse elimination in vivo. Conversely, selective IFN receptor blockade effectively diminished the ongoing microgliosis and synapse loss in AD models. Moreover, we detected activated ISG-expressing microglia enveloping NA-containing neuritic plaques in postmortem brains of patients with AD. Gene expression interrogation revealed that IFN pathway was grossly upregulated in clinical AD and significantly correlated with disease severity and complement activation. Therefore, IFN constitutes a pivotal element within the neuroinflammatory network of AD and critically contributes to neuropathogenic processes.
Alzheimer's-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia.
Andreone Benjamin J,Przybyla Laralynne,Llapashtica Ceyda,Rana Anil,Davis Sonnet S,van Lengerich Bettina,Lin Karin,Shi Ju,Mei Yuan,Astarita Giuseppe,Di Paolo Gilbert,Sandmann Thomas,Monroe Kathryn M,Lewcock Joseph W
Human genetic data indicate that microglial dysfunction contributes to the pathology of Alzheimer's disease (AD), exemplified by the identification of coding variants in triggering receptor expressed on myeloid cells 2 (TREM2) and, more recently, in PLCG2, a phospholipase-encoding gene expressed in microglia. Although studies in mouse models have implicated specific Trem2-dependent microglial functions in AD, the underlying molecular mechanisms and translatability to human disease remain poorly defined. In this study, we used genetically engineered human induced pluripotent stem cell-derived microglia-like cells to show that TREM2 signals through PLCγ2 to mediate cell survival, phagocytosis, processing of neuronal debris, and lipid metabolism. Loss of TREM2 or PLCγ2 signaling leads to a shared signature of transcriptional dysregulation that underlies these phenotypes. Independent of TREM2, PLCγ2 also signals downstream of Toll-like receptors to mediate inflammatory responses. Therefore, PLCγ2 activity regulates divergent microglial functions via distinct TREM2-dependent and -independent signaling and might be involved in the transition to a microglial state associated with neurodegenerative disease.
Pre-symptomatic Caspase-1 inhibitor delays cognitive decline in a mouse model of Alzheimer disease and aging.
Flores Joseph,Noël Anastasia,Foveau Bénédicte,Beauchet Olivier,LeBlanc Andréa C
Early therapeutic interventions are essential to prevent Alzheimer Disease (AD). The association of several inflammation-related genetic markers with AD and the early activation of pro-inflammatory pathways in AD suggest inflammation as a plausible therapeutic target. Inflammatory Caspase-1 has a significant impact on AD-like pathophysiology and Caspase-1 inhibitor, VX-765, reverses cognitive deficits in AD mouse models. Here, a one-month pre-symptomatic treatment of Swedish/Indiana mutant amyloid precursor protein (APP) J20 and wild-type mice with VX-765 delays both APP- and age-induced episodic and spatial memory deficits. VX-765 delays inflammation without considerably affecting soluble and aggregated amyloid beta peptide (Aβ) levels. Episodic memory scores correlate negatively with microglial activation. These results suggest that Caspase-1-mediated inflammation occurs early in the disease and raise hope that VX-765, a previously Food and Drug Administration-approved drug for human CNS clinical trials, may be a useful drug to prevent the onset of cognitive deficits and brain inflammation in AD.
Immunometabolism in the Brain: How Metabolism Shapes Microglial Function.
Bernier Louis-Philippe,York Elisa M,MacVicar Brian A
Trends in neurosciences
Immune cells react to their environment by flexibly reprogramming intracellular metabolic pathways that subsequently alter immune function, in a process called immunometabolism. However, in the CNS, the impact of metabolic reprogramming on microglia, neuroinflammation, and subsequently on brain function is poorly understood. As brain-resident macrophages, microglia are the CNS immune effectors and share similarities with peripheral immune cells. New tools for studying immunometabolism now allow the analysis of bioenergetic regulation with cellular resolution and, as a result, have uncovered previously unappreciated roles for microglial immunometabolism in shaping neuroinflammation. This review highlights evidence that microglia metabolism adapts to changes in brain energy homeostasis and that metabolic reprogramming regulates microglial polarization, thereby impacting pathological inflammatory responses in the brain.
A Novel Targeted and High-Efficiency Nanosystem for Combinational Therapy for Alzheimer's Disease.
Yang Han,Mu Weihang,Wei Daohe,Zhang Yue,Duan Yue,Gao Jun-Xiao,Gong Xiao-Qun,Wang Han-Jie,Wu Xiao-Li,Tao Huaying,Chang Jin
Advanced science (Weinheim, Baden-Wurttemberg, Germany)
Alzheimer's disease (AD) remains the most prevalent neurodegenerative disease, and no effective treatment is available yet. Metal-ion-triggered aggregates of amyloid-beta (A) peptide and acetylcholine imbalance are reported to be possible factors in AD pathogenesis. Thus, a combination therapy that can not only inhibit and reduce A aggregation but also simultaneously regulate acetylcholine imbalance that can serve as a potential treatment for AD is needed. Here, clioquinol (metal-ion chelating agent) and donepezil (acetylcholinesterase (AChE) inhibitor) co-encapsulated human serum albumin (HSA) nanoparticles (dcHGT NPs) are designed, which are modified with transcriptional activator protein (TAT) and monosialotetrahexosylganglioside (GM1). The GM1 lipid and TAT peptide endow this drug delivery nanosystem with high brain entry efficiency and long-term retention capabilities through intranasal administration. It is found that dcHGT NPs can significantly inhibit and eliminate A aggregation, relieve acetylcholine-related inflammation in microglial cells, and protect primary neurons from A oligomer-induced neurotoxicity in vitro. The alleviation of A-related inflammation and AChE-inhibited effect further synergistically adjust acetylcholine imbalance. It is further demonstrated that dcHGT NPs reduce A deposition, ameliorate neuron morphological changes, rescue memory deficits, and greatly improve acetylcholine regulation ability in vivo. This multifunctional synergetic nanosystem can be a new candidate to achieve highly efficient combination therapy for AD.
Glial cells and adaptive immunity in frontotemporal dementia with tau pathology.
Hartnell Iain J,Blum David,Nicoll James A R,Dorothee Guillaume,Boche Delphine
Brain : a journal of neurology
Neuroinflammation is involved in the aetiology of many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and motor neuron disease. Whether neuroinflammation also plays an important role in the pathophysiology of frontotemporal dementia is less well known. Frontotemporal dementia is a heterogeneous classification that covers many subtypes, with the main pathology known as frontotemporal lobar degeneration. The disease can be categorized with respect to the identity of the protein that causes the frontotemporal lobar degeneration in the brain. The most common subgroup describes diseases caused by frontotemporal lobar degeneration associated with tau aggregation, also known as primary tauopathies. Evidence suggests that neuroinflammation may play a role in primary tauopathies with genome-wide association studies finding enrichment of genetic variants associated with specific inflammation-related gene loci. These loci are related to both the innate immune system, including brain resident microglia, and the adaptive immune system through possible peripheral T-cell involvement. This review discusses the genetic evidence and relates it to findings in animal models expressing pathogenic tau as well as to post-mortem and PET studies in human disease. Across experimental paradigms, there seems to be a consensus regarding the involvement of innate immunity in primary tauopathies, with increased microglia and astrocyte density and/or activation, as well as increases in pro-inflammatory markers. Whilst it is less clear as to whether inflammation precedes tau aggregation or vice versa; there is strong evidence to support a microglial contribution to the propagation of hyperphosphorylated in tau frontotemporal lobar degeneration associated with tau aggregation. Experimental evidence-albeit limited-also corroborates genetic data pointing to the involvement of cellular adaptive immunity in primary tauopathies. However, it is still unclear whether brain recruitment of peripheral immune cells is an aberrant result of pathological changes or a physiological aspect of the neuroinflammatory response to the tau pathology.
Meningeal lymphatics affect microglia responses and anti-Aβ immunotherapy.
Alzheimer's disease (AD) is the most prevalent cause of dementia. Although there is no effective treatment for AD, passive immunotherapy with monoclonal antibodies against amyloid beta (Aβ) is a promising therapeutic strategy. Meningeal lymphatic drainage has an important role in the accumulation of Aβ in the brain, but it is not known whether modulation of meningeal lymphatic function can influence the outcome of immunotherapy in AD. Here we show that ablation of meningeal lymphatic vessels in 5xFAD mice (a mouse model of amyloid deposition that expresses five mutations found in familial AD) worsened the outcome of mice treated with anti-Aβ passive immunotherapy by exacerbating the deposition of Aβ, microgliosis, neurovascular dysfunction, and behavioural deficits. By contrast, therapeutic delivery of vascular endothelial growth factor C improved clearance of Aβ by monoclonal antibodies. Notably, there was a substantial overlap between the gene signature of microglia from 5xFAD mice with impaired meningeal lymphatic function and the transcriptional profile of activated microglia from the brains of individuals with AD. Overall, our data demonstrate that impaired meningeal lymphatic drainage exacerbates the microglial inflammatory response in AD and that enhancement of meningeal lymphatic function combined with immunotherapies could lead to better clinical outcomes.
Non-productive angiogenesis disassembles Aß plaque-associated blood vessels.
Alvarez-Vergara Maria I,Rosales-Nieves Alicia E,March-Diaz Rosana,Rodriguez-Perinan Guiomar,Lara-Ureña Nieves,Ortega-de San Luis Clara,Sanchez-Garcia Manuel A,Martin-Bornez Miguel,Gómez-Gálvez Pedro,Vicente-Munuera Pablo,Fernandez-Gomez Beatriz,Marchena Miguel A,Bullones-Bolanos Andrea S,Davila Jose C,Gonzalez-Martinez Rocio,Trillo-Contreras Jose L,Sanchez-Hidalgo Ana C,Del Toro Raquel,Scholl Francisco G,Herrera Eloisa,Trepel Martin,Körbelin Jakob,Escudero Luis M,Villadiego Javier,Echevarria Miriam,de Castro Fernando,Gutierrez Antonia,Rabano Alberto,Vitorica Javier,Pascual Alberto
The human Alzheimer's disease (AD) brain accumulates angiogenic markers but paradoxically, the cerebral microvasculature is reduced around Aß plaques. Here we demonstrate that angiogenesis is started near Aß plaques in both AD mouse models and human AD samples. However, endothelial cells express the molecular signature of non-productive angiogenesis (NPA) and accumulate, around Aß plaques, a tip cell marker and IB4 reactive vascular anomalies with reduced NOTCH activity. Notably, NPA induction by endothelial loss of presenilin, whose mutations cause familial AD and which activity has been shown to decrease with age, produced a similar vascular phenotype in the absence of Aß pathology. We also show that Aß plaque-associated NPA locally disassembles blood vessels, leaving behind vascular scars, and that microglial phagocytosis contributes to the local loss of endothelial cells. These results define the role of NPA and microglia in local blood vessel disassembly and highlight the vascular component of presenilin loss of function in AD.
Beclin1-driven autophagy modulates the inflammatory response of microglia via NLRP3.
Houtman Judith,Freitag Kiara,Gimber Niclas,Schmoranzer Jan,Heppner Frank L,Jendrach Marina
The EMBO journal
Alzheimer's disease is characterized not only by extracellular amyloid plaques and neurofibrillary tangles, but also by microglia-mediated neuroinflammation. Recently, autophagy has been linked to the regulation of the inflammatory response. Thus, we investigated how an impairment of autophagy mediated by BECN1/Beclin1 reduction, as described in Alzheimer's disease patients, would influence cytokine production of microglia. Acutely stimulated microglia from mice exhibited increased expression of IL-1beta and IL-18 compared to wild-type microglia. mice also contained enhanced IL-1beta levels. The investigation of the IL-1beta/IL-18 processing pathway showed an elevated number of cells with inflammasomes and increased levels of NLRP3 and cleaved CASP1/Caspase1 in microglia. Super-resolation microscopy revealed a very close association of NLRP3 aggregates and LC3-positive vesicles. Interestingly, CALCOCO2 colocalized with NLRP3 and its downregulation increased IL-1beta release. These data support the notion that selective autophagy can impact microglia activation by modulating IL-1beta and IL-18 production via NLRP3 degradation and thus present a mechanism how impaired autophagy could contribute to neuroinflammation in Alzheimer's disease.
miRNAs Identify Shared Pathways in Alzheimer's and Parkinson's Diseases.
Sadlon Angélique,Takousis Petros,Alexopoulos Panagiotis,Evangelou Evangelos,Prokopenko Inga,Perneczky Robert
Trends in molecular medicine
Despite the identification of several dozens of common genetic variants associated with Alzheimer's disease (AD) and Parkinson's disease (PD), most of the genetic risk remains uncharacterised. Therefore, it is important to understand the role of regulatory elements, such as miRNAs. Dysregulated miRNAs are implicated in AD and PD, with potential value in dissecting the shared pathophysiology between the two disorders. miRNAs relevant to both neurodegenerative diseases are related to axonal guidance, apoptosis, and inflammation, therefore, AD and PD likely arise from similar underlying biological pathway defects. Furthermore, pathways regulated by APP, L1CAM, and genes of the caspase family may represent promising therapeutic miRNA targets in AD and PD since they are targeted by dysregulated miRNAs in both disorders.
The pathophysiological role of astrocytic endothelin-1.
Hostenbach Stéphanie,D'haeseleer Miguel,Kooijman Ron,De Keyser Jacques
Progress in neurobiology
In the normal central nervous system, endothelin-1 (ET-1) is found in some types of neurons, epithelial cells of the choroid plexus, and endothelial cells of microvessels, but it is usually not detectable in glial cells. However, in different pathological conditions, astrocytes adapting a reactive phenotype express high levels of ET-1 and its receptors, mainly the ETB receptor. ET-1 released by reactive astrocytes appears mainly to have neurodeleterious effects by mechanisms that include constriction of cerebral arterioles leading to impairment of the cerebral microcirculation, increase of blood brain barrier permeability, inflammation, excitotoxicity, impairment of fast axonal transport, and astrogliosis. A few studies in rodents found that ET-1 increased the astrocytic expression of brain-derived neurotrophic factor, glial cell-line derived neurotrophic factor and neurotropin-3, and the production of endocannabinoids. However, whether this occurs in physiological or pathological conditions is unclear. This review summarizes current knowledge about the role of the astrocytic ET-1 system in acute and chronic neurological conditions, including multiple sclerosis, ischemic stroke and hypoxic/ischemic brain injury, traumatic brain injury, subarachnoid hemorrhage, Alzheimer's disease, Binswanger's disease and post-stroke dementia, amyotrophic lateral sclerosis, and CNS infections. Counteracting the harmful effects of astrocytic ET-1 may represent a promising therapeutic target for mitigating secondary brain damage in a variety of neurological diseases. We also briefly address the role of astrocytic ET-1 in astrocytic tumors and pain.
The FTD-like syndrome causing TREM2 T66M mutation impairs microglia function, brain perfusion, and glucose metabolism.
Kleinberger Gernot,Brendel Matthias,Mracsko Eva,Wefers Benedikt,Groeneweg Linda,Xiang Xianyuan,Focke Carola,Deußing Maximilian,Suárez-Calvet Marc,Mazaheri Fargol,Parhizkar Samira,Pettkus Nadine,Wurst Wolfgang,Feederle Regina,Bartenstein Peter,Mueggler Thomas,Arzberger Thomas,Knuesel Irene,Rominger Axel,Haass Christian
The EMBO journal
Genetic variants in the triggering receptor expressed on myeloid cells 2 (TREM2) increase the risk for several neurodegenerative diseases including Alzheimer's disease and frontotemporal dementia (FTD). Homozygous TREM2 missense mutations, such as p.T66M, lead to the FTD-like syndrome, but how they cause pathology is unknown. Using CRISPR/Cas9 genome editing, we generated a knock-in mouse model for the disease-associated Trem2 p.T66M mutation. Consistent with a loss-of-function mutation, we observe an intracellular accumulation of immature mutant Trem2 and reduced generation of soluble Trem2 similar to patients with the homozygous p.T66M mutation. Trem2 p.T66M knock-in mice show delayed resolution of inflammation upon lipopolysaccharide stimulation and cultured macrophages display significantly reduced phagocytic activity. Immunohistochemistry together with TSPO small animal positron emission tomography (μPET) demonstrates an age-dependent reduction in microglial activity. Surprisingly, perfusion magnetic resonance imaging and FDG-μPET imaging reveal a significant reduction in cerebral blood flow and brain glucose metabolism. Thus, we demonstrate that a TREM2 loss-of-function mutation causes brain-wide metabolic alterations pointing toward a possible function of microglia in regulating brain glucose metabolism.
The role of NLRP3-CASP1 in inflammasome-mediated neuroinflammation and autophagy dysfunction in manganese-induced, hippocampal-dependent impairment of learning and memory ability.
Wang Diya,Zhang Jianbin,Jiang Wenkai,Cao Zipeng,Zhao Fang,Cai Tongjian,Aschner Michael,Luo Wenjing
Central nervous system (CNS) inflammation and autophagy dysfunction are known to be involved in the pathology of neurodegenerative diseases. Manganese (Mn), a neurotoxic metal, has the potential to induce microglia-mediated neuroinflammation as well as autophagy dysfunction. NLRP3 (NLR family, pyrin domain containing 3)- CASP1 (caspase 1) inflammasome-mediated neuroinflammation in microglia has specific relevance to neurological diseases. However, the mechanism driving these phenomena remains poorly understood. We demonstrate that Mn activates the NLRP3-CASP1 inflammasome pathway in the hippocampus of mice and BV2 cells by triggering autophagy-lysosomal dysfunction. The autophagy-lysosomal dysfunction is induced by lysosomal damage caused by excessive Mn accumulation, damaging the structure and normal function of these organelles. Additionally, we show that the release of lysosomal CTSB (cathepsin B) plays an important role in Mn-induced NLRP3-CASP1 inflammasome activation, and that the increased autophagosomes in the cytoplasm are not the main cause of NLRP3-CASP1 inflammasome activation. The accumulation of proinflammatory cytokines, such as IL1B (interleukin 1 β) and IL18 (interleukin 18), as well as the dysfunctional autophagy pathway may damage hippocampal neuronal cells, thus leading to hippocampal-dependent impairment in learning and memory, which is associated with the pathogenesis of Alzheimer disease (AD).
NLR members NLRC4 and NLRP3 mediate sterile inflammasome activation in microglia and astrocytes.
Freeman Leslie,Guo Haitao,David Clément N,Brickey W June,Jha Sushmita,Ting Jenny P-Y
The Journal of experimental medicine
Inflammation in the brain accompanies several high-impact neurological diseases including multiple sclerosis (MS), stroke, and Alzheimer's disease. Neuroinflammation is sterile, as damage-associated molecular patterns rather than microbial pathogens elicit the response. The inflammasome, which leads to caspase-1 activation, is implicated in neuroinflammation. In this study, we reveal that lysophosphatidylcholine (LPC), a molecule associated with neurodegeneration and demyelination, elicits NLRP3 and NLRC4 inflammasome activation in microglia and astrocytes, which are central players in neuroinflammation. LPC-activated inflammasome also requires ASC (apoptotic speck containing protein with a CARD), caspase-1, cathepsin-mediated degradation, calcium mobilization, and potassium efflux but not caspase-11. To study the physiological relevance, and mice are studied in the cuprizone model of neuroinflammation and demyelination. Mice lacking both genes show the most pronounced reduction in astrogliosis and microglial accumulation accompanied by decreased expression of the LPC receptor G2A, whereas MS patient samples show increased G2A. These results reveal that NLRC4 and NLRP3, which normally form distinct inflammasomes, activate an LPC-induced inflammasome and are important in astrogliosis and microgliosis.
Neuroprotective exendin-4 enhances hypothermia therapy in a model of hypoxic-ischaemic encephalopathy.
Brain : a journal of neurology
Hypoxic-ischaemic encephalopathy remains a global health burden. Despite medical advances and treatment with therapeutic hypothermia, over 50% of cooled infants are not protected and still develop lifelong neurodisabilities, including cerebral palsy. Furthermore, hypothermia is not used in preterm cases or low resource settings. Alternatives or adjunct therapies are urgently needed. Exendin-4 is a drug used to treat type 2 diabetes mellitus that has also demonstrated neuroprotective properties, and is currently being tested in clinical trials for Alzheimer's and Parkinson's diseases. Therefore, we hypothesized a neuroprotective effect for exendin-4 in neonatal neurodisorders, particularly in the treatment of neonatal hypoxic-ischaemic encephalopathy. Initially, we confirmed that the glucagon like peptide 1 receptor (GLP1R) was expressed in the human neonatal brain and in murine neurons at postnatal Day 7 (human equivalent late preterm) and postnatal Day 10 (term). Using a well characterized mouse model of neonatal hypoxic-ischaemic brain injury, we investigated the potential neuroprotective effect of exendin-4 in both postnatal Day 7 and 10 mice. An optimal exendin-4 treatment dosing regimen was identified, where four high doses (0.5 µg/g) starting at 0 h, then at 12 h, 24 h and 36 h after postnatal Day 7 hypoxic-ischaemic insult resulted in significant brain neuroprotection. Furthermore, neuroprotection was sustained even when treatment using exendin-4 was delayed by 2 h post hypoxic-ischaemic brain injury. This protective effect was observed in various histopathological markers: tissue infarction, cell death, astrogliosis, microglial and endothelial activation. Blood glucose levels were not altered by high dose exendin-4 administration when compared to controls. Exendin-4 administration did not result in adverse organ histopathology (haematoxylin and eosin) or inflammation (CD68). Despite initial reduced weight gain, animals restored weight gain following end of treatment. Overall high dose exendin-4 administration was well tolerated. To mimic the clinical scenario, postnatal Day 10 mice underwent exendin-4 and therapeutic hypothermia treatment, either alone or in combination, and brain tissue loss was assessed after 1 week. Exendin-4 treatment resulted in significant neuroprotection alone, and enhanced the cerebroprotective effect of therapeutic hypothermia. In summary, the safety and tolerance of high dose exendin-4 administrations, combined with its neuroprotective effect alone or in conjunction with clinically relevant hypothermia make the repurposing of exendin-4 for the treatment of neonatal hypoxic-ischaemic encephalopathy particularly promising.
Sensory lesioning induces microglial synapse elimination via ADAM10 and fractalkine signaling.
Gunner Georgia,Cheadle Lucas,Johnson Kasey M,Ayata Pinar,Badimon Ana,Mondo Erica,Nagy M Aurel,Liu Liwang,Bemiller Shane M,Kim Ki-Wook,Lira Sergio A,Lamb Bruce T,Tapper Andrew R,Ransohoff Richard M,Greenberg Michael E,Schaefer Anne,Schafer Dorothy P
Microglia rapidly respond to changes in neural activity and inflammation to regulate synaptic connectivity. The extracellular signals, particularly neuron-derived molecules, that drive these microglial functions at synapses remain a key open question. Here we show that whisker lesioning, known to dampen cortical activity, induces microglia-mediated synapse elimination. This synapse elimination is dependent on signaling by CX3CR1, the receptor for microglial fractalkine (also known as CXCL1), but not complement receptor 3. Furthermore, mice deficient in CX3CL1 have profound defects in synapse elimination. Single-cell RNA sequencing revealed that Cx3cl1 is derived from cortical neurons, and ADAM10, a metalloprotease that cleaves CX3CL1 into a secreted form, is upregulated specifically in layer IV neurons and in microglia following whisker lesioning. Finally, inhibition of ADAM10 phenocopies Cx3cr1 and Cx3cl1 synapse elimination defects. Together, these results identify neuron-to-microglia signaling necessary for cortical synaptic remodeling and reveal that context-dependent immune mechanisms are utilized to remodel synapses in the mammalian brain.
Systemic inflammation impairs microglial Aβ clearance through NLRP3 inflammasome.
Tejera Dario,Mercan Dilek,Sanchez-Caro Juan M,Hanan Mor,Greenberg David,Soreq Hermona,Latz Eicke,Golenbock Douglas,Heneka Michael T
The EMBO journal
Alzheimer's disease is the most prevalent type of dementia and is caused by the deposition of extracellular amyloid-beta and abnormal tau phosphorylation. Neuroinflammation has emerged as an additional pathological component. Microglia, representing the brain's major innate immune cells, play an important role during Alzheimer's. Once activated, microglia show changes in their morphology, characterized by a retraction of cell processes. Systemic inflammation is known to increase the risk for cognitive decline in human neurogenerative diseases including Alzheimer's. Here, we assess for the first time microglial changes upon a peripheral immune challenge in the context of aging and Alzheimer's in vivo, using 2-photon laser scanning microscopy. Microglia were monitored at 2 and 10 days post-challenge by lipopolysaccharide. Microglia exhibited a reduction in the number of branches and the area covered at 2 days, a phenomenon that resolved at 10 days. Systemic inflammation reduced microglial clearance of amyloid-beta in APP/PS1 mice. NLRP3 inflammasome knockout blocked many of the observed microglial changes upon lipopolysaccharide, including alterations in microglial morphology and amyloid pathology. NLRP3 inhibition may thus represent a novel therapeutic target that may protect the brain from toxic peripheral inflammation during systemic infection.
Counteracting the effects of TNF receptor-1 has therapeutic potential in Alzheimer's disease.
Steeland Sophie,Gorlé Nina,Vandendriessche Charysse,Balusu Sriram,Brkic Marjana,Van Cauwenberghe Caroline,Van Imschoot Griet,Van Wonterghem Elien,De Rycke Riet,Kremer Anneke,Lippens Saskia,Stopa Edward,Johanson Conrad E,Libert Claude,Vandenbroucke Roosmarijn E
EMBO molecular medicine
Alzheimer's disease (AD) is the most common form of dementia, and neuroinflammation is an important hallmark of the pathogenesis. Tumor necrosis factor (TNF) might be detrimental in AD, though the results coming from clinical trials on anti-TNF inhibitors are inconclusive. TNFR1, one of the TNF signaling receptors, contributes to the pathogenesis of AD by mediating neuronal cell death. The blood-cerebrospinal fluid (CSF) barrier consists of a monolayer of choroid plexus epithelial (CPE) cells, and AD is associated with changes in CPE cell morphology. Here, we report that TNF is the main inflammatory upstream mediator in choroid plexus tissue in AD patients. This was confirmed in two murine AD models: transgenic APP/PS1 mice and intracerebroventricular (icv) AβO injection. TNFR1 contributes to the morphological damage of CPE cells in AD, and TNFR1 abrogation reduces brain inflammation and prevents blood-CSF barrier impairment. In APP/PS1 transgenic mice, TNFR1 deficiency ameliorated amyloidosis. Ultimately, genetic and pharmacological blockage of TNFR1 rescued from the induced cognitive impairments. Our data indicate that TNFR1 is a promising therapeutic target for AD treatment.
Neuroprotective Effect of Nerve Growth Factor Loaded in Porous Silicon Nanostructures in an Alzheimer's Disease Model and Potential Delivery to the Brain.
Zilony-Hanin Neta,Rosenberg Michal,Richman Michal,Yehuda Ronen,Schori Hadas,Motiei Menachem,Rahimipour Shai,Groisman Alexander,Segal Ester,Shefi Orit
Small (Weinheim an der Bergstrasse, Germany)
Nerve growth factor (NGF) plays a vital role in reducing the loss of cholinergic neurons in Alzheimer's disease (AD). However, its delivery to the brain remains a challenge. Herein, NGF is loaded into degradable oxidized porous silicon (PSiO ) carriers, which are designed to carry and continuously release the protein over a 1 month period. The released NGF exhibits a substantial neuroprotective effect in differentiated rat pheochromocytoma PC12 cells against amyloid-beta (Aβ)-induced cytotoxicity, which is associated with Alzheimer's disease. Next, two potential localized administration routes of the porous carriers into murine brain are investigated: implantation of PSiO chips above the dura mater, and biolistic bombardment of PSiO microparticles through an opening in the skull using a pneumatic gene gun. The PSiO -implanted mice are monitored for a period of 8 weeks and no inflammation or adverse effects are observed. Subsequently, a successful biolistic delivery of these highly porous microparticles into a live-mouse brain is demonstrated for the first time. The bombarded microparticles are observed to penetrate the brain and reach a depth of 150 µm. These results pave the way for using degradable PSiO carriers as potential localized delivery systems for NGF to the brain.
Development of new treatments for Alzheimer's disease based on the modulation of translocator protein (TSPO).
Arbo B D,Ribeiro M F,Garcia-Segura L M
Ageing research reviews
The increase in life expectancy of the world population is associated with a higher prevalence of neurodegenerative diseases. Alzheimer's Disease (AD) is the most common neurodegenerative disease, affecting currently 43 million people over the world. To date, most of the pharmacological interventions in AD are intended for the alleviation of some of its symptoms, and there are no effective treatments to inhibit the progression of the disease. Translocator protein (TSPO) is present in contact points between the outer and the inner mitochondrial membranes and is involved in the control of steroidogenesis, inflammation and apoptosis. In the last decade, studies have shown that TSPO ligands present neuroprotective effects in different experimental models of AD, both in vitro and in vivo. The aim of this review is to analyze the data provided by these studies and to discuss if TSPO could be a viable therapeutic target for the development of new treatments for AD.
Acute systemic inflammation exacerbates neuroinflammation in Alzheimer's disease: IL-1β drives amplified responses in primed astrocytes and neuronal network dysfunction.
Alzheimer's & dementia : the journal of the Alzheimer's Association
Neuroinflammation contributes to Alzheimer's disease (AD) progression. Secondary inflammatory insults trigger delirium and can accelerate cognitive decline. Individual cellular contributors to this vulnerability require elucidation. Using APP/PS1 mice and AD brain, we studied secondary inflammatory insults to investigate hypersensitive responses in microglia, astrocytes, neurons, and human brain tissue. The NLRP3 inflammasome was assembled surrounding amyloid beta, and microglia were primed, facilitating exaggerated interleukin-1β (IL-1β) responses to subsequent LPS stimulation. Astrocytes were primed to produce exaggerated chemokine responses to intrahippocampal IL-1β. Systemic LPS triggered microglial IL-1β, astrocytic chemokines, IL-6, and acute cognitive dysfunction, whereas IL-1β disrupted hippocampal gamma rhythm, all selectively in APP/PS1 mice. Brains from AD patients with infection showed elevated IL-1β and IL-6 levels. Therefore, amyloid leaves the brain vulnerable to secondary inflammation at microglial, astrocytic, neuronal, and cognitive levels, and infection amplifies neuroinflammatory cytokine synthesis in humans. Exacerbation of neuroinflammation to produce deleterious outcomes like delirium and accelerated disease progression merits careful investigation in humans.
Long noncoding RNA lncKdm2b is required for ILC3 maintenance by initiation of Zfp292 expression.
Liu Benyu,Ye Buqing,Yang Liuliu,Zhu Xiaoxiao,Huang Guanling,Zhu Pingping,Du Ying,Wu Jiayi,Qin Xiwen,Chen Runsheng,Tian Yong,Fan Zusen
Innate lymphoid cells (ILCs) communicate with other hematopoietic and nonhematopoietic cells to regulate immunity, inflammation and tissue homeostasis. How ILC lineages develop and are maintained remains largely unknown. In this study we observed that a divergent long noncoding RNA (lncRNA), lncKdm2b, was expressed at high levels in intestinal group 3 ILCs (ILC3s). LncKdm2b deficiency in the hematopoietic system led to reductions in the number and effector functions of ILC3s. LncKdm2b expression sustained the maintenance of ILC3s by promoting their proliferation through activation of the transcription factor Zfp292. Mechanistically, lncKdm2b recruited the chromatin organizer Satb1 and the nuclear remodeling factor (NURF) complex onto the Zfp292 promoter to initiate its transcription. Deletion of Zfp292 or Bptf also abrogated the maintenance of ILC3s, leading to susceptibility to bacterial infection. Therefore, our findings reveal that lncRNAs may represent an additional layer of regulation of ILC development and function.
Extracellular DAMPs in Plants and Mammals: Immunity, Tissue Damage and Repair.
De Lorenzo Giulia,Ferrari Simone,Cervone Felice,Okun Eitan
Trends in immunology
Innate immune receptors, well known mediators of response to non-self-molecules and inflammation, also act as mediators of immunity triggered by 'damage-associated molecular patterns' (DAMPs). Pathogen-associated molecular patterns (PAMPs) cause inflammation in mammals and a rapid immune response in plants, while DAMPs trigger more complex responses, including immunity, tissue maintenance and repair. DAMPs, their receptors and downstream transduction mechanisms are often conserved within a kingdom or, due to convergent evolution, are similar across the kingdoms of life. Herein, we describe the dynamics and functionality of specific extracellular DAMP classes and their receptors in immunity, inflammation and repair of tissue damage in plants and mammals.
Neurotoxic reactive astrocytes are induced by activated microglia.
Liddelow Shane A,Guttenplan Kevin A,Clarke Laura E,Bennett Frederick C,Bohlen Christopher J,Schirmer Lucas,Bennett Mariko L,Münch Alexandra E,Chung Won-Suk,Peterson Todd C,Wilton Daniel K,Frouin Arnaud,Napier Brooke A,Panicker Nikhil,Kumar Manoj,Buckwalter Marion S,Rowitch David H,Dawson Valina L,Dawson Ted M,Stevens Beth,Barres Ben A
Reactive astrocytes are strongly induced by central nervous system (CNS) injury and disease, but their role is poorly understood. Here we show that a subtype of reactive astrocytes, which we termed A1, is induced by classically activated neuroinflammatory microglia. We show that activated microglia induce A1 astrocytes by secreting Il-1α, TNF and C1q, and that these cytokines together are necessary and sufficient to induce A1 astrocytes. A1 astrocytes lose the ability to promote neuronal survival, outgrowth, synaptogenesis and phagocytosis, and induce the death of neurons and oligodendrocytes. Death of axotomized CNS neurons in vivo is prevented when the formation of A1 astrocytes is blocked. Finally, we show that A1 astrocytes are abundant in various human neurodegenerative diseases including Alzheimer's, Huntington's and Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis. Taken together these findings help to explain why CNS neurons die after axotomy, strongly suggest that A1 astrocytes contribute to the death of neurons and oligodendrocytes in neurodegenerative disorders, and provide opportunities for the development of new treatments for these diseases.
β-Synuclein-reactive T cells induce autoimmune CNS grey matter degeneration.
Lodygin Dmitri,Hermann Moritz,Schweingruber Nils,Flügel-Koch Cassandra,Watanabe Takashi,Schlosser Corinna,Merlini Arianna,Körner Henrike,Chang Hsin-Fang,Fischer Henrike J,Reichardt Holger M,Zagrebelsky Marta,Mollenhauer Brit,Kügler Sebastian,Fitzner Dirk,Frahm Jens,Stadelmann Christine,Haberl Michael,Odoardi Francesca,Flügel Alexander
The grey matter is a central target of pathological processes in neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. The grey matter is often also affected in multiple sclerosis, an autoimmune disease of the central nervous system. The mechanisms that underlie grey matter inflammation and degeneration in multiple sclerosis are not well understood. Here we show that, in Lewis rats, T cells directed against the neuronal protein β-synuclein specifically invade the grey matter and that this is accompanied by the presentation of multifaceted clinical disease. The expression pattern of β-synuclein induces the local activation of these T cells and, therefore, determined inflammatory priming of the tissue and targeted recruitment of immune cells. The resulting inflammation led to significant changes in the grey matter, which ranged from gliosis and neuronal destruction to brain atrophy. In humans, β-synuclein-specific T cells were enriched in patients with chronic-progressive multiple sclerosis. These findings reveal a previously unrecognized role of β-synuclein in provoking T-cell-mediated pathology of the central nervous system.
The Microglial Innate Immune Receptor TREM2 Is Required for Synapse Elimination and Normal Brain Connectivity.
Filipello Fabia,Morini Raffaella,Corradini Irene,Zerbi Valerio,Canzi Alice,Michalski Bernadeta,Erreni Marco,Markicevic Marija,Starvaggi-Cucuzza Chiara,Otero Karel,Piccio Laura,Cignarella Francesca,Perrucci Fabio,Tamborini Matteo,Genua Marco,Rajendran Lawrence,Menna Elisabetta,Vetrano Stefania,Fahnestock Margaret,Paolicelli Rosa Chiara,Matteoli Michela
The triggering receptor expressed on myeloid cells 2 (TREM2) is a microglial innate immune receptor associated with a lethal form of early, progressive dementia, Nasu-Hakola disease, and with an increased risk of Alzheimer's disease. Microglial defects in phagocytosis of toxic aggregates or apoptotic membranes were proposed to be at the origin of the pathological processes in the presence of Trem2 inactivating mutations. Here, we show that TREM2 is essential for microglia-mediated synaptic refinement during the early stages of brain development. The absence of Trem2 resulted in impaired synapse elimination, accompanied by enhanced excitatory neurotransmission and reduced long-range functional connectivity. Trem2 mice displayed repetitive behavior and altered sociability. TREM2 protein levels were also negatively correlated with the severity of symptoms in humans affected by autism. These data unveil the role of TREM2 in neuronal circuit sculpting and provide the evidence for the receptor's involvement in neurodevelopmental diseases.
Magnesium Regulates Endothelial Barrier Functions through TRPM7, MagT1, and S1P1.
Zhu Donghui,You Jing,Zhao Nan,Xu Huaxi
Advanced science (Weinheim, Baden-Wurttemberg, Germany)
Mg-deficiency is linked to hypertension, Alzheimer's disease, stroke, migraine headaches, cardiovascular diseases, and diabetes, etc., but its exact role in these pathophysiological conditions remains elusive. Mg can regulate vascular functions, yet the mechanistic insight remains ill-defined. Data show that extracellular Mg enters endothelium mainly through the TRPM7 channel and MagT1 transporter. Mg can act as an antagonist to reduce Ca signaling in endothelium. Mg also reduces the intracellular reactive oxygen species (ROS) level and inflammation. In addition, Mg-signaling increases endothelial survival and growth, adhesion, and migration. Endothelial barrier integrity is significantly enhanced with Mg-treatment through S1P1-Rac1 pathways and barrier-stabilizing mediators including cAMP, FGF1/2, and eNOS. Mg also promotes cytoskeletal reorganization and junction proteins to tighten up the barrier. Moreover, Mg-deficiency enhances endothelial barrier permeability in mice, and Mg-treatment rescues histamine-induced transient vessel hyper-permeability in vivo. In summary, Mg-deficiency can cause deleterious effects in endothelium integrity, and Mg-treatment may be effective in the prevention or treatment of vascular dysfunction.
Regulator of calcineurin 1 is a novel RNA-binding protein to regulate neuronal apoptosis.
Posttranscriptional regulation of gene expression plays an important role in the maturation, transport, stability and translation of coding and noncoding RNAs. RNA-binding protein (RBP) is a key factor of the regulation. Regulator of calcineurin 1 (RCAN1) is a multifunctional protein involved in neurodegeneration, mitochondrial dysfunction, inflammation and protein glycosylation, and plays an important role in the pathogenesis of Down syndrome and Alzheimer's disease. In this report, we discovered that RCNA1 is a novel RNA-binding protein. A 23 nucleotide sequence of adenine nucleotide translocator (ANT1) mRNA was identified as the binding motif of RCAN1. Furthermore, we found that R1SR13, as the RNA aptamer of RCAN1 identified by SELEX, blocked RCAN1-induced inhibition of the nuclear factor of activated T cells (NFAT) and NF-κB signaling pathways, and reduced neuronal apoptosis. Taken together, our results demonstrate that RCAN1 is a novel RNA-binding protein and the RNA aptamer of RCAN1 plays a neuroprotective role.
Nuclear Receptors as Therapeutic Targets for Neurodegenerative Diseases: Lost in Translation.
Moutinho Miguel,Codocedo Juan F,Puntambekar Shweta S,Landreth Gary E
Annual review of pharmacology and toxicology
Neurodegenerative diseases are characterized by a progressive loss of neurons that leads to a broad range of disabilities, including severe cognitive decline and motor impairment, for which there are no effective therapies. Several lines of evidence support a putative therapeutic role of nuclear receptors (NRs) in these types of disorders. NRs are ligand-activated transcription factors that regulate the expression of a wide range of genes linked to metabolism and inflammation. Although the activation of NRs in animal models of neurodegenerative disease exhibits promising results, the translation of this strategy to clinical practice has been unsuccessful. In this review we discuss the role of NRs in neurodegenerative diseases in light of preclinical and clinical studies, as well as new findings derived from the analysis of transcriptomic databases from humans and animal models. We discuss the failure in the translation of NR-based therapeutic approaches and consider alternative and novel research avenues in the development of effective therapies for neurodegenerative diseases.
Melatonin induces mechanisms of brain resilience against neurodegeneration.
Corpas Rubén,Griñán-Ferré Christian,Palomera-Ávalos Verónica,Porquet David,García de Frutos Pablo,Franciscato Cozzolino Silvia M,Rodríguez-Farré Eduard,Pallàs Mercè,Sanfeliu Coral,Cardoso Bárbara R
Journal of pineal research
Melatonin is an endogenous pleiotropic molecule which orchestrates regulatory functions and protective capacity against age-related ailments. The increase in circulating levels of melatonin through dietary supplements intensifies its health benefits. Investigations in animal models have shown that melatonin protects against Alzheimer's disease (AD)-like pathology, although clinical studies have not been conclusive. We hypothesized that melatonin induces changes in the brain that prevent or attenuate AD by increasing resilience. Therefore, we treated healthy nontransgenic (NoTg) and AD transgenic (3xTg-AD) 6-month-old mice with a daily dose of 10 mg/kg of melatonin until 12 months of age. As expected, melatonin reversed cognitive impairment and dementia-associated behaviors of anxiety and apathy and reduced amyloid and tau burden in 3xTg-AD mice. Remarkably, melatonin induced cognitive enhancement and higher wellness level-related behavior in NoTg mice. At the mechanism level, NF-κB and proinflammatory cytokine expressions were decreased in both NoTg and 3xTg-AD mice. The SIRT1 pathway of longevity and neuroprotection was also activated in both mouse strains after melatonin dosing. Furthermore, we explored new mechanisms and pathways not previously associated with melatonin treatment such as the ubiquitin-proteasome proteolytic system and the recently proposed neuroprotective Gas6/TAM pathway. The upregulation of proteasome activity and the modulation of Gas6 and its receptors by melatonin were similarly displayed by both NoTg and 3xTg-AD mice. Therefore, these results confirm the potential of melatonin treatment against AD pathology, by way of opening new pathways in its mechanisms of action, and demonstrating that melatonin induces cognitive enhancement and brain resilience against neurodegenerative processes.
ApoE attenuates unresolvable inflammation by complex formation with activated C1q.
Yin Changjun,Ackermann Susanne,Ma Zhe,Mohanta Sarajo K,Zhang Chuankai,Li Yuanfang,Nietzsche Sandor,Westermann Martin,Peng Li,Hu Desheng,Bontha Sai Vineela,Srikakulapu Prasad,Beer Michael,Megens Remco T A,Steffens Sabine,Hildner Markus,Halder Luke D,Eckstein Hans-Henning,Pelisek Jaroslav,Herms Jochen,Roeber Sigrun,Arzberger Thomas,Borodovsky Anna,Habenicht Livia,Binder Christoph J,Weber Christian,Zipfel Peter F,Skerka Christine,Habenicht Andreas J R
Apolipoprotein-E (ApoE) has been implicated in Alzheimer's disease, atherosclerosis, and other unresolvable inflammatory conditions but a common mechanism of action remains elusive. We found in ApoE-deficient mice that oxidized lipids activated the classical complement cascade (CCC), resulting in leukocyte infiltration of the choroid plexus (ChP). All human ApoE isoforms attenuated CCC activity via high-affinity binding to the activated CCC-initiating C1q protein (K~140-580 pM) in vitro, and C1q-ApoE complexes emerged as markers for ongoing complement activity of diseased ChPs, Aβ plaques, and atherosclerosis in vivo. C1q-ApoE complexes in human ChPs, Aβ plaques, and arteries correlated with cognitive decline and atherosclerosis, respectively. Treatment with small interfering RNA (siRNA) against C5, which is formed by all complement pathways, attenuated murine ChP inflammation, Aβ-associated microglia accumulation, and atherosclerosis. Thus, ApoE is a direct checkpoint inhibitor of unresolvable inflammation, and reducing C5 attenuates disease burden.
Fibrin-targeting immunotherapy protects against neuroinflammation and neurodegeneration.
Ryu Jae Kyu,Rafalski Victoria A,Meyer-Franke Anke,Adams Ryan A,Poda Suresh B,Rios Coronado Pamela E,Pedersen Lars Østergaard,Menon Veena,Baeten Kim M,Sikorski Shoana L,Bedard Catherine,Hanspers Kristina,Bardehle Sophia,Mendiola Andrew S,Davalos Dimitrios,Machado Michael R,Chan Justin P,Plastira Ioanna,Petersen Mark A,Pfaff Samuel J,Ang Kenny K,Hallenbeck Kenneth K,Syme Catriona,Hakozaki Hiroyuki,Ellisman Mark H,Swanson Raymond A,Zamvil Scott S,Arkin Michelle R,Zorn Stevin H,Pico Alexander R,Mucke Lennart,Freedman Stephen B,Stavenhagen Jeffrey B,Nelson Robert B,Akassoglou Katerina
Activation of innate immunity and deposition of blood-derived fibrin in the central nervous system (CNS) occur in autoimmune and neurodegenerative diseases, including multiple sclerosis (MS) and Alzheimer's disease (AD). However, the mechanisms that link disruption of the blood-brain barrier (BBB) to neurodegeneration are poorly understood, and exploration of fibrin as a therapeutic target has been limited by its beneficial clotting functions. Here we report the generation of monoclonal antibody 5B8, targeted against the cryptic fibrin epitope γ, to selectively inhibit fibrin-induced inflammation and oxidative stress without interfering with clotting. 5B8 suppressed fibrin-induced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and the expression of proinflammatory genes. In animal models of MS and AD, 5B8 entered the CNS and bound to parenchymal fibrin, and its therapeutic administration reduced the activation of innate immunity and neurodegeneration. Thus, fibrin-targeting immunotherapy inhibited autoimmunity- and amyloid-driven neurotoxicity and might have clinical benefit without globally suppressing innate immunity or interfering with coagulation in diverse neurological diseases.
Orchestration of NLRP3 Inflammasome Activation by Ion Fluxes.
Gong Tao,Yang Yanqing,Jin Tengchuan,Jiang Wei,Zhou Rongbin
Trends in immunology
The assembly of the NLRP3 inflammasome can promote the release of IL-1β/IL-18 and initiate pyroptosis. Accordingly, the dysregulation of NLRP3 inflammasome activation is involved in a variety of human diseases, including gout, diabetes, and Alzheimer's disease. NLRP3 can sense a variety of structurally unrelated pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs) to trigger inflammation, but the unifying mechanism of NLRP3 activation is still poorly understood. Increasing evidence suggests that intracellular ions, such as K, Ca, and Cl, have a significant role in NLRP3 inflammasome activation. Here, we review the current knowledge about the role of ionic fluxes in NLRP3 inflammasome activation and discuss how disturbances in intracellular ionic levels orchestrate different signaling events upstream of NLRP3.
Perivascular macrophages in health and disease.
Lapenna Antonio,De Palma Michele,Lewis Claire E
Nature reviews. Immunology
Macrophages are a heterogeneous group of cells that are capable of carrying out distinct functions in different tissues, as well as in different locations within a given tissue. Some of these tissue macrophages lie on, or close to, the outer (abluminal) surface of blood vessels and perform several crucial activities at this interface between the tissue and the blood. In steady-state tissues, these perivascular macrophages maintain tight junctions between endothelial cells and limit vessel permeability, phagocytose potential pathogens before they enter tissues from the blood and restrict inappropriate inflammation. They also have a multifaceted role in diseases such as cancer, Alzheimer disease, multiple sclerosis and type 1 diabetes. Here, we examine the important functions of perivascular macrophages in various adult tissues and describe how these functions are perturbed in a broad array of pathological conditions.
Aggregated Tau activates NLRP3-ASC inflammasome exacerbating exogenously seeded and non-exogenously seeded Tau pathology in vivo.
Stancu Ilie-Cosmin,Cremers Niels,Vanrusselt Hannah,Couturier Julien,Vanoosthuyse Alexandre,Kessels Sofie,Lodder Chritica,Brône Bert,Huaux François,Octave Jean-Noël,Terwel Dick,Dewachter Ilse
Brains of Alzheimer's disease patients are characterized by the presence of amyloid plaques and neurofibrillary tangles, both invariably associated with neuroinflammation. A crucial role for NLRP3-ASC inflammasome [NACHT, LRR and PYD domains-containing protein 3 (NLRP3)-Apoptosis-associated speck-like protein containing a CARD (ASC)] in amyloid-beta (Aβ)-induced microgliosis and Aβ pathology has been unequivocally identified. Aβ aggregates activate NLRP3-ASC inflammasome (Halle et al. in Nat Immunol 9:857-865, 2008) and conversely NLRP3-ASC inflammasome activation exacerbates amyloid pathology in vivo (Heneka et al. in Nature 493:674-678, 2013), including by prion-like ASC-speck cross-seeding (Venegas et al. in Nature 552:355-361, 2017). However, the link between inflammasome activation, as crucial sensor of innate immunity, and Tau remains unexplored. Here, we analyzed whether Tau aggregates acting as prion-like Tau seeds can activate NLRP3-ASC inflammasome. We demonstrate that Tau seeds activate NLRP3-ASC-dependent inflammasome in primary microglia, following microglial uptake and lysosomal sorting of Tau seeds. Next, we analyzed the role of inflammasome activation in prion-like or templated seeding of Tau pathology and found significant inhibition of exogenously seeded Tau pathology by ASC deficiency in Tau transgenic mice. We furthermore demonstrate that chronic intracerebral administration of the NLRP3 inhibitor, MCC950, inhibits exogenously seeded Tau pathology. Finally, ASC deficiency also decreased non-exogenously seeded Tau pathology in Tau transgenic mice. Overall our findings demonstrate that Tau-seeding competent, aggregated Tau activates the ASC inflammasome through the NLRP3-ASC axis, and we demonstrate an exacerbating role of the NLRP3-ASC axis on exogenously and non-exogenously seeded Tau pathology in Tau mice in vivo. The NLRP3-ASC inflammasome, which is an important sensor of innate immunity and intensively explored for its role in health and disease, hence presents as an interesting therapeutic approach to target three crucial pathogenetic processes in AD, including prion-like seeding of Tau pathology, Aβ pathology and neuroinflammation.
Elevated plasma ferritin in elderly individuals with high neocortical amyloid-β load.
Goozee K,Chatterjee P,James I,Shen K,Sohrabi H R,Asih P R,Dave P,ManYan C,Taddei K,Ayton S J,Garg M L,Kwok J B,Bush A I,Chung R,Magnussen J S,Martins R N
Ferritin, an iron storage and regulation protein, has been associated with Alzheimer's disease (AD); however, it has not been investigated in preclinical AD, detected by neocortical amyloid-β load (NAL), before cognitive impairment. Cross-sectional analyses were carried out for plasma and serum ferritin in participants in the Kerr Anglican Retirement Village Initiative in Aging Health cohort. Subjects were aged 65-90 years and were categorized into high and low NAL groups via positron emission tomography using a standard uptake value ratio cutoff=1.35. Ferritin was significantly elevated in participants with high NAL compared with those with low NAL, adjusted for covariates age, sex, apolipoprotein E ɛ4 carriage and levels of C-reactive protein (an inflammation marker). Ferritin was also observed to correlate positively with NAL. A receiver operating characteristic curve based on a logistic regression of the same covariates, the base model, distinguished high from low NAL (area under the curve (AUC)=0.766), but was outperformed when plasma ferritin was added to the base model (AUC=0.810), such that at 75% sensitivity, the specificity increased from 62 to 71% on adding ferritin to the base model, indicating that ferritin is a statistically significant additional predictor of NAL over and above the base model. However, ferritin's contribution alone is relatively minor compared with the base model. The current findings suggest that impaired iron mobilization is an early event in AD pathogenesis. Observations from the present study highlight ferritin's potential to contribute to a blood biomarker panel for preclinical AD.
Neuropathological correlates and genetic architecture of microglial activation in elderly human brain.
Felsky Daniel,Roostaei Tina,Nho Kwangsik,Risacher Shannon L,Bradshaw Elizabeth M,Petyuk Vlad,Schneider Julie A,Saykin Andrew,Bennett David A,De Jager Philip L
Microglia, the resident immune cells of the brain, have important roles in brain health. However, little is known about the regulation and consequences of microglial activation in the aging human brain. Here we report that the proportion of morphologically activated microglia (PAM) in postmortem cortical tissue is strongly associated with β-amyloid, tau-related neuropathology, and the rate of cognitive decline. Effect sizes for PAM measures are substantial, comparable to that of APOE ε4, the strongest genetic risk factor for Alzheimer's disease, and mediation models support an upstream role for microglial activation in Alzheimer's disease via accumulation of tau. Further, we identify a common variant (rs2997325) influencing PAM that also affects in vivo microglial activation measured by [C]-PBR28 PET in an independent cohort. Thus, our analyses begin to uncover pathways regulating resident neuroinflammation and identify overlaps of PAM's genetic architecture with those of Alzheimer's disease and several other traits.
Microglia emerge as central players in brain disease.
Salter Michael W,Stevens Beth
There has been an explosion of new findings recently giving us insights into the involvement of microglia in central nervous system (CNS) disorders. A host of new molecular tools and mouse models of disease are increasingly implicating this enigmatic type of nervous system cell as a key player in conditions ranging from neurodevelopmental disorders such as autism to neurodegenerative disorders such as Alzheimer's disease and chronic pain. Contemporaneously, diverse roles are emerging for microglia in the healthy brain, from sculpting developing neuronal circuits to guiding learning-associated plasticity. Understanding the physiological functions of these cells is crucial to determining their roles in disease. Here we focus on recent developments in our rapidly expanding understanding of the function, as well as the dysfunction, of microglia in disorders of the CNS.
Eliminating microglia in Alzheimer's mice prevents neuronal loss without modulating amyloid-β pathology.
Spangenberg Elizabeth E,Lee Rafael J,Najafi Allison R,Rice Rachel A,Elmore Monica R P,Blurton-Jones Mathew,West Brian L,Green Kim N
Brain : a journal of neurology
In addition to amyloid-β plaque and tau neurofibrillary tangle deposition, neuroinflammation is considered a key feature of Alzheimer's disease pathology. Inflammation in Alzheimer's disease is characterized by the presence of reactive astrocytes and activated microglia surrounding amyloid plaques, implicating their role in disease pathogenesis. Microglia in the healthy adult mouse depend on colony-stimulating factor 1 receptor (CSF1R) signalling for survival, and pharmacological inhibition of this receptor results in rapid elimination of nearly all of the microglia in the central nervous system. In this study, we set out to determine if chronically activated microglia in the Alzheimer's disease brain are also dependent on CSF1R signalling, and if so, how these cells contribute to disease pathogenesis. Ten-month-old 5xfAD mice were treated with a selective CSF1R inhibitor for 1 month, resulting in the elimination of ∼80% of microglia. Chronic microglial elimination does not alter amyloid-β levels or plaque load; however, it does rescue dendritic spine loss and prevent neuronal loss in 5xfAD mice, as well as reduce overall neuroinflammation. Importantly, behavioural testing revealed improvements in contextual memory. Collectively, these results demonstrate that microglia contribute to neuronal loss, as well as memory impairments in 5xfAD mice, but do not mediate or protect from amyloid pathology.
Pharmacological targeting of CSF1R inhibits microglial proliferation and prevents the progression of Alzheimer's-like pathology.
Olmos-Alonso Adrian,Schetters Sjoerd T T,Sri Sarmi,Askew Katharine,Mancuso Renzo,Vargas-Caballero Mariana,Holscher Christian,Perry V Hugh,Gomez-Nicola Diego
Brain : a journal of neurology
The proliferation and activation of microglial cells is a hallmark of several neurodegenerative conditions. This mechanism is regulated by the activation of the colony-stimulating factor 1 receptor (CSF1R), thus providing a target that may prevent the progression of conditions such as Alzheimer's disease. However, the study of microglial proliferation in Alzheimer's disease and validation of the efficacy of CSF1R-inhibiting strategies have not yet been reported. In this study we found increased proliferation of microglial cells in human Alzheimer's disease, in line with an increased upregulation of the CSF1R-dependent pro-mitogenic cascade, correlating with disease severity. Using a transgenic model of Alzheimer's-like pathology (APPswe, PSEN1dE9; APP/PS1 mice) we define a CSF1R-dependent progressive increase in microglial proliferation, in the proximity of amyloid-β plaques. Prolonged inhibition of CSF1R in APP/PS1 mice by an orally available tyrosine kinase inhibitor (GW2580) resulted in the blockade of microglial proliferation and the shifting of the microglial inflammatory profile to an anti-inflammatory phenotype. Pharmacological targeting of CSF1R in APP/PS1 mice resulted in an improved performance in memory and behavioural tasks and a prevention of synaptic degeneration, although these changes were not correlated with a change in the number of amyloid-β plaques. Our results provide the first proof of the efficacy of CSF1R inhibition in models of Alzheimer's disease, and validate the application of a therapeutic strategy aimed at modifying CSF1R activation as a promising approach to tackle microglial activation and the progression of Alzheimer's disease.
Inflammatory markers and the risk of dementia and Alzheimer's disease: A meta-analysis.
Darweesh Sirwan K L,Wolters Frank J,Ikram M Arfan,de Wolf Frank,Bos Daniel,Hofman Albert
Alzheimer's & dementia : the journal of the Alzheimer's Association
INTRODUCTION:Inflammatory markers are often elevated in patients with dementia, including Alzheimer's disease (AD). However, it remains unclear whether inflammatory markers are associated with the risk of developing dementia. METHODS:We searched PubMed, Embase, and Cochrane library for prospective population-based studies reporting associations between inflammatory markers and all-cause dementia or AD. We used random effects meta-analyses to obtain pooled hazard ratios (HRs) and 95% confidence intervals of inflammatory markers (highest vs. lowest quantile) for all-cause dementia and AD. RESULTS:Fifteen articles from 13 studies in six countries reported data that could be meta-analyzed. C-reactive protein (HR = 1.37 [1.05; 1.78]), interleukin-6 (HR = 1.40 [1.13; 1.73]), α1-antichymotrypsin (HR = 1.54 [1.14; 2.80]), lipoprotein-associated phospholipase A2 activity (HR = 1.40 [1.03; 1.90]), and fibrinogen were each associated with all-cause dementia, but neither was significantly associated with AD. DISCUSSION:Several inflammatory markers are associated with an increased risk of all-cause dementia; however, these markers are not specific for AD. Whether inflammatory markers closely involved in AD pathology are associated with the risk of AD remains to be elucidated.
Fenamate NSAIDs inhibit the NLRP3 inflammasome and protect against Alzheimer's disease in rodent models.
Daniels Michael J D,Rivers-Auty Jack,Schilling Tom,Spencer Nicholas G,Watremez William,Fasolino Victoria,Booth Sophie J,White Claire S,Baldwin Alex G,Freeman Sally,Wong Raymond,Latta Clare,Yu Shi,Jackson Joshua,Fischer Nicolas,Koziel Violette,Pillot Thierry,Bagnall James,Allan Stuart M,Paszek Pawel,Galea James,Harte Michael K,Eder Claudia,Lawrence Catherine B,Brough David
Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase-1 (COX-1) and COX-2 enzymes. The NLRP3 inflammasome is a multi-protein complex responsible for the processing of the proinflammatory cytokine interleukin-1β and is implicated in many inflammatory diseases. Here we show that several clinically approved and widely used NSAIDs of the fenamate class are effective and selective inhibitors of the NLRP3 inflammasome via inhibition of the volume-regulated anion channel in macrophages, independently of COX enzymes. Flufenamic acid and mefenamic acid are efficacious in NLRP3-dependent rodent models of inflammation in air pouch and peritoneum. We also show therapeutic effects of fenamates using a model of amyloid beta induced memory loss and a transgenic mouse model of Alzheimer's disease. These data suggest that fenamate NSAIDs could be repurposed as NLRP3 inflammasome inhibitors and Alzheimer's disease therapeutics.
Senolytic therapy alleviates Aβ-associated oligodendrocyte progenitor cell senescence and cognitive deficits in an Alzheimer's disease model.
Zhang Peisu,Kishimoto Yuki,Grammatikakis Ioannis,Gottimukkala Kamalvishnu,Cutler Roy G,Zhang Shiliang,Abdelmohsen Kotb,Bohr Vilhelm A,Misra Sen Jyoti,Gorospe Myriam,Mattson Mark P
Neuritic plaques, a pathological hallmark in Alzheimer's disease (AD) brains, comprise extracellular aggregates of amyloid-beta (Aβ) peptide and degenerating neurites that accumulate autolysosomes. We found that, in the brains of patients with AD and in AD mouse models, Aβ plaque-associated Olig2- and NG2-expressing oligodendrocyte progenitor cells (OPCs), but not astrocytes, microglia, or oligodendrocytes, exhibit a senescence-like phenotype characterized by the upregulation of p21/CDKN1A, p16/INK4/CDKN2A proteins, and senescence-associated β-galactosidase activity. Molecular interrogation of the Aβ plaque environment revealed elevated levels of transcripts encoding proteins involved in OPC function, replicative senescence, and inflammation. Direct exposure of cultured OPCs to aggregating Aβ triggered cell senescence. Senolytic treatment of AD mice selectively removed senescent cells from the plaque environment, reduced neuroinflammation, lessened Aβ load, and ameliorated cognitive deficits. Our findings suggest a role for Aβ-induced OPC cell senescence in neuroinflammation and cognitive deficits in AD, and a potential therapeutic benefit of senolytic treatments.
Microglia-derived ASC specks cross-seed amyloid-β in Alzheimer's disease.
Venegas Carmen,Kumar Sathish,Franklin Bernardo S,Dierkes Tobias,Brinkschulte Rebecca,Tejera Dario,Vieira-Saecker Ana,Schwartz Stephanie,Santarelli Francesco,Kummer Markus P,Griep Angelika,Gelpi Ellen,Beilharz Michael,Riedel Dietmar,Golenbock Douglas T,Geyer Matthias,Walter Jochen,Latz Eicke,Heneka Michael T
The spreading of pathology within and between brain areas is a hallmark of neurodegenerative disorders. In patients with Alzheimer's disease, deposition of amyloid-β is accompanied by activation of the innate immune system and involves inflammasome-dependent formation of ASC specks in microglia. ASC specks released by microglia bind rapidly to amyloid-β and increase the formation of amyloid-β oligomers and aggregates, acting as an inflammation-driven cross-seed for amyloid-β pathology. Here we show that intrahippocampal injection of ASC specks resulted in spreading of amyloid-β pathology in transgenic double-mutant APPPSEN1 mice. By contrast, homogenates from brains of APPPSEN1 mice failed to induce seeding and spreading of amyloid-β pathology in ASC-deficient APPPSEN1 mice. Moreover, co-application of an anti-ASC antibody blocked the increase in amyloid-β pathology in APPPSEN1 mice. These findings support the concept that inflammasome activation is connected to seeding and spreading of amyloid-β pathology in patients with Alzheimer's disease.
C/EBPβ regulates delta-secretase expression and mediates pathogenesis in mouse models of Alzheimer's disease.
Wang Zhi-Hao,Gong Ke,Liu Xia,Zhang Zhentao,Sun Xiaoou,Wei Zheng Zachory,Yu Shan Ping,Manfredsson Fredric P,Sandoval Ivette M,Johnson Peter F,Jia Jianping,Wang Jian-Zhi,Ye Keqiang
Delta-secretase cleaves both APP and Tau to mediate the formation of amyloid plaques and neurofibrillary tangle in Alzheimer's disease (AD). However, how aging contributes to an increase in delta-secretase expression and AD pathologies remains unclear. Here we show that a CCAAT-enhancer-binding protein (C/EBPβ), an inflammation-regulated transcription factor, acts as a key age-dependent effector elevating both delta-secretase (AEP) and inflammatory cytokines expression in mediating pathogenesis in AD mouse models. We find that C/EBPβ regulates delta-secretase transcription and protein levels in an age-dependent manner. Overexpression of C/EBPβ in young 3xTg mice increases delta-secretase and accelerates the pathological features including cognitive dysfunctions, which is abolished by inactive AEP C189S. Conversely, depletion of C/EBPβ from old 3xTg or 5XFAD mice diminishes delta-secretase and reduces AD pathologies, leading to amelioration of cognitive impairment in these AD mouse models. Thus, our findings support that C/EBPβ plays a pivotal role in AD pathogenesis via increasing delta-secretase expression.
Single-cell transcriptomic analysis of Alzheimer's disease.
Mathys Hansruedi,Davila-Velderrain Jose,Peng Zhuyu,Gao Fan,Mohammadi Shahin,Young Jennie Z,Menon Madhvi,He Liang,Abdurrob Fatema,Jiang Xueqiao,Martorell Anthony J,Ransohoff Richard M,Hafler Brian P,Bennett David A,Kellis Manolis,Tsai Li-Huei
Alzheimer's disease is a pervasive neurodegenerative disorder, the molecular complexity of which remains poorly understood. Here, we analysed 80,660 single-nucleus transcriptomes from the prefrontal cortex of 48 individuals with varying degrees of Alzheimer's disease pathology. Across six major brain cell types, we identified transcriptionally distinct subpopulations, including those associated with pathology and characterized by regulators of myelination, inflammation, and neuron survival. The strongest disease-associated changes appeared early in pathological progression and were highly cell-type specific, whereas genes upregulated at late stages were common across cell types and primarily involved in the global stress response. Notably, we found that female cells were overrepresented in disease-associated subpopulations, and that transcriptional responses were substantially different between sexes in several cell types, including oligodendrocytes. Overall, myelination-related processes were recurrently perturbed in multiple cell types, suggesting that myelination has a key role in Alzheimer's disease pathophysiology. Our single-cell transcriptomic resource provides a blueprint for interrogating the molecular and cellular basis of Alzheimer's disease.
Selective disruption of TLR2-MyD88 interaction inhibits inflammation and attenuates Alzheimer's pathology.
The Journal of clinical investigation
Induction of TLR2 activation depends on its association with the adapter protein MyD88. We have found that TLR2 and MyD88 levels are elevated in the hippocampus and cortex of patients with Alzheimer's disease (AD) and in a 5XFAD mouse model of AD. Since there is no specific inhibitor of TLR2, to target induced TLR2 from a therapeutic angle, we engineered a peptide corresponding to the TLR2-interacting domain of MyD88 (TIDM) that binds to the BB loop of only TLR2, and not other TLRs. Interestingly, WT TIDM peptide inhibited microglial activation induced by fibrillar Aβ1-42 and lipoteichoic acid, but not 1-methyl-4-phenylpyridinium, dsRNA, bacterial lipopolysaccharide, flagellin, or CpG DNA. After intranasal administration, WT TIDM peptide reached the hippocampus, reduced hippocampal glial activation, lowered Aβ burden, attenuated neuronal apoptosis, and improved memory and learning in 5XFAD mice. However, WT TIDM peptide was not effective in 5XFAD mice lacking TLR2. In addition to its effects in 5XFAD mice, WT TIDM peptide also suppressed the disease process in mice with experimental allergic encephalomyelitis and collagen-induced arthritis. Therefore, selective targeting of the activated status of 1 component of the innate immune system by WT TIDM peptide may be beneficial in AD as well as other disorders in which TLR2/MyD88 signaling plays a role in disease pathogenesis.
A Breakdown in Metabolic Reprogramming Causes Microglia Dysfunction in Alzheimer's Disease.
Baik Sung Hoon,Kang Seokjo,Lee Woochan,Choi Hayoung,Chung Sunwoo,Kim Jong-Il,Mook-Jung Inhee
Reactive microglia are a major pathological feature of Alzheimer's disease (AD). However, the exact role of microglia in AD pathogenesis is still unclear. Here, using metabolic profiling, we found that exposure to amyloid-β triggers acute microglial inflammation accompanied by metabolic reprogramming from oxidative phosphorylation to glycolysis. It was dependent on the mTOR-HIF-1α pathway. However, once activated, microglia reached a chronic tolerant phase as a result of broad defects in energy metabolisms and subsequently diminished immune responses, including cytokine secretion and phagocytosis. Using genome-wide RNA sequencing and multiphoton microscopy techniques, we further identified metabolically defective microglia in 5XFAD mice, an AD mouse model. Finally, we showed that metabolic boosting with recombinant interferon-γ treatment reversed the defective glycolytic metabolism and inflammatory functions of microglia, thereby mitigating the AD pathology of 5XFAD mice. Collectively, metabolic reprogramming is crucial for microglial functions in AD, and modulating metabolism might be a new therapeutic strategy for AD.
Interleukin-2 improves amyloid pathology, synaptic failure and memory in Alzheimer's disease mice.
Alves Sandro,Churlaud Guillaume,Audrain Mickael,Michaelsen-Preusse Kristin,Fol Romain,Souchet Benoit,Braudeau Jérôme,Korte Martin,Klatzmann David,Cartier Nathalie
Brain : a journal of neurology
Interleukin-2 (IL-2)-deficient mice have cytoarchitectural hippocampal modifications and impaired learning and memory ability reminiscent of Alzheimer's disease. IL-2 stimulates regulatory T cells whose role is to control inflammation. As neuroinflammation contributes to neurodegeneration, we investigated IL-2 in Alzheimer's disease. Therefore, we investigated IL-2 levels in hippocampal biopsies of patients with Alzheimer's disease relative to age-matched control individuals. We then treated APP/PS1ΔE9 mice having established Alzheimer's disease with IL-2 for 5 months using single administration of an AAV-IL-2 vector. We first found decreased IL-2 levels in hippocampal biopsies of patients with Alzheimer's disease. In mice, IL-2-induced systemic and brain regulatory T cells expansion and activation. In the hippocampus, IL-2 induced astrocytic activation and recruitment of astrocytes around amyloid plaques, decreased amyloid-β42/40 ratio and amyloid plaque load, improved synaptic plasticity and significantly rescued spine density. Of note, this tissue remodelling was associated with recovery of memory deficits, as assessed in the Morris water maze task. Altogether, our data strongly suggest that IL-2 can alleviate Alzheimer's disease hallmarks in APP/PS1ΔE9 mice with established pathology. Therefore, this should prompt the investigation of low-dose IL-2 in Alzheimer's disease and other neuroinflammatory/neurodegenerative disorders.