Plasma β-amyloid in Alzheimer's disease and vascular disease.
Janelidze Shorena,Stomrud Erik,Palmqvist Sebastian,Zetterberg Henrik,van Westen Danielle,Jeromin Andreas,Song Linan,Hanlon David,Tan Hehir Cristina A,Baker David,Blennow Kaj,Hansson Oskar
Scientific reports
Implementation of amyloid biomarkers in clinical practice would be accelerated if such biomarkers could be measured in blood. We analyzed plasma levels of Aβ42 and Aβ40 in a cohort of 719 individuals (the Swedish BioFINDER study), including patients with subjective cognitive decline (SCD), mild cognitive impairment (MCI), Alzheimer's disease (AD) dementia and cognitively healthy elderly, using a ultrasensitive immunoassay (Simoa platform). There were weak positive correlations between plasma and cerebrospinal fluid (CSF) levels for both Aβ42 and Aβ40, and negative correlations between plasma Aβ42 and neocortical amyloid deposition (measured with PET). Plasma levels of Aβ42 and Aβ40 were reduced in AD dementia compared with all other diagnostic groups. However, during the preclinical or prodromal AD stages (i.e. in amyloid positive controls, SCD and MCI) plasma concentration of Aβ42 was just moderately decreased whereas Aβ40 levels were unchanged. Higher plasma (but not CSF) levels of Aβ were associated with white matter lesions, cerebral microbleeds, hypertension, diabetes and ischemic heart disease. In summary, plasma Aβ is overtly decreased during the dementia stage of AD indicating that prominent changes in Aβ metabolism occur later in the periphery compared to the brain. Further, increased levels of Aβ in plasma are associated with vascular disease.
10.1038/srep26801
Chronic Cerebral Hypoperfusion Promotes Amyloid-Beta Pathogenesis via Activating β/γ-Secretases.
Cai Zhiyou,Liu Zhou,Xiao Ming,Wang Chuanling,Tian Fuming
Neurochemical research
Chronic cerebral hypoperfusion (CCH) contributes to the Alzheimer's-like pathogenesis, but the relationship between CCH and the occurrence of Alzheimer's disease (AD) remains obscure. The aim is to elucidate the potential pathophysiological mechanism in the field of amyloid-beta (Aβ) pathology induced by CCH. A rat model of CCH has been developed with permanent bilateral occlusion of common carotid arteries (BCCAO). The cognitive function of rats was tested by the Morris water maze. The levels of Aβ (Aβ40 and Aβ42) and soluble amyloid precursor protein (sAPP: sAPPα and sAPPβ) were determined by enzyme linked immunosorbent assay. The expression of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), presenilin1 (PS1), nicastrin (NCT), anterior pharynx-defective 1alpha (Aph-1α) and presenilin enhancer 2 (Pen-2), sAPPα and sAPPβ were detected by Western blotting. Morris water maze test showed that CCH induced decline in learning and memory related to Aβ levels in the hippocampus. The levels of sAPPα, ADAM10 and ADAM17 in the hippocampus of CCH rats were higher than the control ones (P < 0.05); the levels of sAPPβ, BACE and BACE1 increased more than the control ones (P < 0.05). CCH intervention (1-week or 4-week) markedly increased the expression of PS1, Aph-1α and Pen-2 in the hippocampus of rats, but had no effect on NCT. CCH contributed to cognitive impairment and altered the amyloidogenic and non-amyloidogenic pathway of APP processing by boosting the activity of β-secretase/γ-secretase and α-secretase respectively. The non-amyloidogenic pathway can't overcome the damage role of the amyloidogenic pathway in the process of chronic cerebral hypoperfusion which promotes amyloid-beta pathogenesis.
10.1007/s11064-017-2391-9
The amyloid precursor protein: a biochemical enigma in brain development, function and disease.
Nalivaeva Natalia N,Turner Anthony J
FEBS letters
For 20 years the amyloid cascade hypothesis of Alzheimer disease (AD) has placed the amyloid-β peptide (Aβ), formed from the amyloid precursor protein (APP), centre stage in the process of neurodegeneration. However, no new therapeutic agents have reached the clinic through exploitation of the hypothesis. The APP metabolites, including Aβ, generated by its proteolytic processing, have distinct physiological functions. In particular, the cleaved intracellular domain of APP (AICD) regulates expression of several genes, including APP itself, the β-secretase BACE-1 and the Aβ-degrading enzyme, neprilysin and this transcriptional regulation involves direct promoter binding of AICD. Of the three major splice isoforms of APP (APP695, APP751, APP770), APP695 is the predominant neuronal form, from which Aβ and transcriptionally-active AICD are preferentially generated by selective processing through the amyloidogenic pathway. Despite intensive research, the normal functions of the APP isoforms remain an enigma. APP plays an important role in brain development, memory and synaptic plasticity and secreted forms of APP are neuroprotective. A fuller understanding of the physiological and pathological actions of APP and its metabolic and gene regulatory network could provide new therapeutic opportunities in neurodegeneration, including AD.
10.1016/j.febslet.2013.05.010
What are the links between hypoxia and Alzheimer's disease?
Lall Rahul,Mohammed Raihan,Ojha Utkarsh
Neuropsychiatric disease and treatment
Alzheimer's disease (AD) is the most common neurodegenerative disease. Histological characterization of amyloid plaques and neurofibrillary tangles in the brains of AD patients, alongside genetic studies in individuals suffering the familial form of the disease, has fueled the accumulation of the amyloid-β protein as the initial pathological trigger of disease. Association studies have recently showed that cerebral hypoxia, via both genetic and epigenetic mechanisms, increase amyloid-β deposition by altering expression levels of enzymes involved in the production/degradation of the protein. Furthermore, hypoxia has also been linked to neuronal and glial-cell calcium dysregulation through formation of calcium-permeable pores, dysregulated glutamate signaling, and intracellular calcium-store dysfunction. Hypoxia has also been strongly linked to neuroinflammation; however, this relationship to AD has not been thoroughly discussed in the literature. Here, we highlight and organize critical research evidence showing that in both hypoxic and AD brains, there are similarities in terms of 1) the substances mediating/modulating the neuroinflammatory environment and 2) the immune cells that drive the formation of these substances.
10.2147/NDT.S203103
Pathogenesis of Alzheimer disease: role of oxidative stress, amyloid-β peptides, systemic ammonia and erythrocyte energy metabolism.
Kosenko Elena A,Solomadin Iliya N,Tikhonova Lyudmila A,Reddy V Prakash,Aliev Gjumrakch,Kaminsky Yury G
CNS & neurological disorders drug targets
Aβ exerts prooxidant or antioxidant effects based on the metal ion concentrations that it sequesters from the cytosol; at low metal ion concentrations, it is an antioxidant, whereas at relatively higher concentration it is a prooxidant. Thus Alzheimer disease (AD) treatment strategies based solely on the amyloid-β clearance should be re-examined in light of the vast accumulating evidence that increased oxidative stress in the human brains is the key causative factor for AD. Accumulating evidence indicates that the reduced brain glucose availability and brain hypoxia, due to the relatively lower concentration of ATP and 2,3-diphosphoglycerate, may be associated with increased concentration of endogenous ammonia, a potential neurotoxin in the AD brains. In this review, we summarize the progress in this area, and present some of our ongoing research activities with regard to brain Amyloid-β, systemic ammonia, erythrocyte energy metabolism and the role of 2,3-diphosphoglycerate in AD pathogenesis.
10.2174/18715273113126660130
Physiological roles for amyloid beta peptides.
Pearson Hugh A,Peers Chris
The Journal of physiology
Alzheimer's disease is recognized post mortem by the presence of extracellular senile plaques, made primarily of aggregation of amyloid beta peptide (Abeta). This peptide has consequently been regarded as the principal toxic factor in the neurodegeneration of Alzheimer's disease. As such, intense research effort has been directed at determining its source, activity and fate, primarily with a view to preventing its formation or its biological activity, or promoting its degradation. Clearly, much progress has been made concerning its formation by proteolytic processing of the amyloid precursor protein, and its degradation by enzymes such as neprilysin and insulin degrading enzyme. The activities of Abeta, however, are numerous and yet to be fully elucidated. What is currently emerging from such studies is a diffuse but steadily growing body of data that suggests Abeta has important physiological functions and, further, that it should only be regarded as toxic when its production and degradation are imbalanced. Here, we review these data and suggest that physiological levels of Abeta have important physiological roles, and may even be crucial for neuronal cell survival. Thus, the view of Abeta being a purely toxic peptide requires re-evaluation.
10.1113/jphysiol.2006.111203
The amyloid-β₄₂ proxy, amyloid-β(25-35), induces normal human cerebral astrocytes to produce amyloid-β₄₂.
Dal Prà Ilaria,Whitfileld James F,Pacchiana Raffaella,Bonafini Clara,Talacchi Andrea,Chakravarthy Balu,Armato Ubaldo,Chiarini Anna
Journal of Alzheimer's disease : JAD
Astrocytes in amyloid-β (Aβ)₄₂-accumulating human brains afflicted with Alzheimer's disease (AD) upregulate vascular endothelial growth factor (VEGF)-A synthesis and also become loaded with Aβ₄₂. We have already shown that Aβ(25-35) (surrogate of Aβ₄₂)-induced VEGF-A production in 'normoxic' cultures of early passage normal human cerebral astrocytes (NAHAs) is mediated by the stabilization of VEGF gene-stimulating hypoxia-inducible factor (HIF)-1α and nuclear translocation of HIF-1α•HIF-1β complexes. We have now found that treating these NAHAs with Aβ(25-35) also stimulates them to make Aβ₄₂ (appearing in immunoblots as several bands with M(r)'s from 8 kDa upwards), whose levels peak at 48 h (2.8-fold versus 0 h, p < 0.001) and then start falling slowly. This rise of Aβ₄₂ peptide production coincides with a transiently increased flow of HIF-1α (therefore HIF-1α•HIF-1β complexes; at 24 h, 1.5-fold versus 0 h, p < 0.001) into the nucleus and transient surges first of β-secretase (BACE-1/β-S) mRNA expression (1.2-fold versus 0 h, p = 0.013) and activity peaking at 24-h (1.4-fold versus 0 h, p = 0.001), and then of γ-secretase (γ-S) activity cresting at 48 h (1.6-fold versus 0 h, p < 0.001) that cleave the Aβ₄₂ peptides from amyloid-β protein precursor. Since the genes encoding components of these two secretases have the same HIF-1α•HIF-1β-responsive elements in their promoters as the VEGF gene, these observations suggest that the Aβ₄₂ released from neurons in the AD brain can recruit associated astrocytes via HIF-1α•HIF-1β signaling into the pool of Aβ₄₂-producing cells. In other words, Aβ₄₂ begets Aβ₄₂ in NAHAs.
10.3233/JAD-2011-101626
Expression of the Tau Protein and Amyloid Protein Precursor Processing Genes in the CA3 Area of the Hippocampus in the Ischemic Model of Alzheimer's Disease in the Rat.
Molecular neurobiology
Understanding the mechanisms underlying the selective susceptibility to ischemia of the CA3 region is very important to explain the neuropathology of memory loss after brain ischemia. We used a rat model to study changes in gene expression of the amyloid protein precursor and its cleaving enzymes and tau protein in the hippocampal CA3 sector, after transient 10-min global brain ischemia with survival times of 2, 7, and 30 days. The expression of the α-secretase gene was below control values at all times studied. But, the expression of the β-secretase gene was below the control values at 2-7 days after ischemia and the maximal increase in its expression was observed on day 30. Expression of the presenilin 1 gene was significantly elevated above the control values at 2-7 days after ischemia and decreased below the control values at day 30. Expression of the presenilin 2 gene showed an opposite trend to the expression of presenilin 1. Expression of the amyloid protein precursor gene after ischemia was at all times above the control values with a huge significant overexpression on day 7. Additionally, the expression of the tau protein gene was below the control values 2 days after ischemia, but the significant increase in its expression was observed on days 7-30. Data show that brain ischemia activates neuronal changes and death in the CA3 region of the hippocampus in a manner dependent on amyloid and tau protein, thus determining a new and important way to regulate the survival and/or death of ischemic neurons.
10.1007/s12035-019-01799-z