Evidence of oxidative injury during aging of the liver in a mouse model.
Colantoni A,Idilman R,de Maria N,Duffner L A,Van Thiel D H,Witte P L,Kovacs E J
Journal of the American Aging Association
The aim of the present study was to determine whether oxidative stress contributes to aging of the liver in a mouse model. Liver was obtained from young (3-5 months old) and aged (18-24 months old) mice. No age-induced gross changes in liver morphology were detected by light microscopy. Apoptosis was measured using the fragment end labeling of DNA for the immunohistochemical identification of the apoptotic nuclei. The total apoptotic cells represented 1% of the total cells in livers of young mice and 8% in those of aged mice. Among the total apoptotic cells in livers of aged animals, 15% were hepatocytes, 40% sinusoidal endothelial cells, and 45% bile duct cells. Hepatic lipid peroxidation, expressed as malonaldehyde levels, protein oxidation, measured by protein carbonyl content, and DNA oxidation, measured as 8-hydroxy-2'-deoxyguanosine (oxo(8)dG), were significantly increased in the livers of aged animals as compared to younger mice. The apoptotic cells presented elevated levels of oxidized DNA, detected by immunohistochemistry using an antibody directed against oxo(8)dG in serial sections. These results suggest that livers of aged animals presents evidence of increased oxidative injury and apoptosis. Because the apoptotic cells in the aged livers are mostly bile duct cells and sinusoidal endothelial cells, the cells most sensitive to oxidative stress injury, it can be hypothesized that reactive oxygen species-induced apoptosis in these cells contributes to the aging of the liver.
Caloric restriction reduces age-related pseudocapillarization of the hepatic sinusoid.
Jamieson Hamish A,Hilmer Sarah N,Cogger Victoria C,Warren Alessandra,Cheluvappa Rajkumar,Abernethy Darrell R,Everitt Arthur V,Fraser Robin,de Cabo Rafael,Le Couteur David G
Age-related changes in the hepatic sinusoid, called pseudocapillarization, may contribute to the pathogenesis of dyslipidemia. Caloric restriction (CR) is a powerful model for the study of aging because it extends lifespan. We assessed the effects of CR on the hepatic sinusoid to determine whether pseudocapillarization is preventable and hence a target for the prevention of age-related dyslipidemia. Livers from young (6 months) and old (24 months) CR and ad libitum fed (AL) F344 rats were examined using electron microscopy and immunohistochemistry. In old age, there was increased thickness of the liver sinusoidal endothelium and reduced endothelial fenestration porosity. In old CR rats, endothelial thickness was less and fenestration porosity was greater than in old AL rats. Immunohistochemistry showed that CR prevented age-related decrease in caveolin-1 expression and increase in peri-sinusoidal collagen IV staining, but did not alter the age-related increase of von Willebrand's factor. CR reduces age-related pseudocapillarization of the hepatic sinusoid and correlates with changes in caveolin-1 expression.
Antigen handling in aging. II. The role of Kupffer and endothelial cells in antigen processing in Fischer 344 rats.
Caperna T J,Garvey J S
Mechanisms of ageing and development
A method has been developed for the purification of Kupffer and endothelial cells from rat liver by collagenase enzyme perfusion followed by centrifugal elutriation. After intravenous injection of a soluble antigen, [3H]azoaniline bovine serum albumin ( [3H]BSA), its distribution was studied in isolated cell populations from liver and spleen tissue of two aged groups of male F-344 rats. In young adult rats (6-8 months) both sinusoidal cell types contained the same amount of [3H]BSA; however, in older rats (22-24 months) the amount of antigen in the endothelial cells was significantly decreased. In comparison to the liver, the spleen retained only a small fraction of the injected dose. In order to assess the catabolic properties of both Kupffer and endothelial cells, supernatants obtained from in vitro cell culture were evaluated for both biological and physiochemical properties. Antigen was almost completely degraded by both cell types as determined by gel filtration and did not directly stimulate BSA-primed lymphocytes in vitro; however, these supernatants were shown to enhance the lymphoproliferative response of primed lymphocytes to additional antigen exposure. Kupffer cell receptors, Fc and C3, assayed by direct rosetting, did not vary with age; endothelial cells also possessed Fc receptors that were found to be unchanged with age. These studies are an initial attempt to better define our previous finding of defective antigen handling with aging by use of isolated pure cell populations.
Hepatic sinusoidal pseudocapillarization with aging in the non-human primate.
Cogger Victoria C,Warren Alessandra,Fraser Robin,Ngu Meng,McLean Allan J,Le Couteur David G
BACKGROUND/AIMS:Age-related changes in the hepatic sinusoid termed pseudocapillarization have been reported in the rat and human and have implications for disease susceptibility in old age. In this study, we investigated whether similar changes occur in the livers of old baboons and thus represent a widespread aging change. METHODS:Liver tissue from five young baboons (5.4+/-0.5yrs) and five old baboons (21.8+/-0.7yrs) was compared by transmission electron microscopy, scanning electron microscopy and immunohistochemistry. RESULTS:The thickness of the sinusoidal endothelium was increased in old baboons (130+/-8 nm versus 186+/-9 nm, P<0.001) and the frequency of endothelial fenestrae decreased, with the porosity declining from 4.2+/-0.5% to 2.4+/-0.4% (P=0.006). The expression of laminin and von Willebrands factor was more extensive in old baboons. Novel perisinusoidal ring-shaped cells, probably fat-engorged stellate cells, were prominent in the old baboons. CONCLUSIONS:Pseudocapillarization is a significant age-related change in the baboon liver. Aging in baboons is associated with a novel aging change in the stellate cell not reported in other species. Hepatic pseudocapillarization is a widespread aging liver change found in several species including humans and other non-human primates.
Impaired integrin α /β -mediated hepatocyte growth factor release by stellate cells of the aged liver.
Rohn Friederike,Kordes Claus,Buschmann Tobias,Reichert Doreen,Wammers Marianne,Poschmann Gereon,Stühler Kai,Benk Amelie S,Geiger Fania,Spatz Joachim P,Häussinger Dieter
Hepatic blood flow and sinusoidal endothelial fenestration decrease during aging. Consequently, fluid mechanical forces are reduced in the space of Disse where hepatic stellate cells (HSC) have their niche. We provide evidence that integrin α /β is an important mechanosensor in HSC involved in shear stress-induced release of hepatocyte growth factor (HGF), an essential inductor of liver regeneration which is impaired during aging. The expression of the integrin subunits α and β decreases in liver and HSC from aged rats. CRISPR/Cas9-mediated integrin α and β knockouts in isolated HSC lead to lowered HGF release and impaired cellular adhesion. Fluid mechanical forces increase integrin α and laminin gene expression whereas integrin β remains unaffected. In the aged liver, laminin β2 and γ1 protein chains as components of laminin-521 are lowered. The integrin α knockout in HSC reduces laminin expression via mechanosensory mechanisms. Culture of HSC on nanostructured surfaces functionalized with laminin-521 enhances Hgf expression in HSC, demonstrating that these ECM proteins are critically involved in HSC function. During aging, HSC acquire a senescence-associated secretory phenotype and lower their growth factor expression essential for tissue repair. Our findings suggest that impaired mechanosensing via integrin α /β in HSC contributes to age-related reduction of ECM and HGF release that could affect liver regeneration.
Factor VIII-Related Antigen Detects Phenotypic Change of Sinusoidal to Vascular Endothelium in Hepatic Fibrosis of Elderly Cadavers.
Mak Ki M,Sehgal Priya,Harris Cynthia K
International scholarly research notices
In advanced stages of hepatic fibrosis, the liver sinusoidal endothelium transforms to vascular endothelium with accompanying expression of factor VIII-related antigen (FVIIIRAg), a phenotypic marker of vascular endothelial cells. Liver fibrosis has been shown to be associated with aging and was found to be prevalent in elderly cadavers. Using immunohistochemistry, we studied FVIIIRAg expression in the livers of elderly cadavers with progressive stages of fibrosis. The vascular endothelium of portal tracts and central veins was stained for FVIIIRAg, providing an internal positive control. The incidence of FVIIIRAg expression was low in the sinusoids of livers that showed minimal fibrosis or perisinusoidal fibrosis but was increased in livers with advanced fibrosis (i.e., septa formation, bridging fibrosis, and cirrhosis). FVIIIRAg positive sinusoidal endothelial cells were distributed in loose aggregates in the periportal, periseptal, and midlobular parenchyma and were found less frequently in the centrilobular area. FVIIIRAg immune deposits appeared patchy and discontinuous along the sinusoidal lining, likely representing focalized transformation of sinusoidal to vascular endothelium. There was a discrete localization of FVIIIRAg immunoreactivity in the foci of severe parenchymal fibrosis. Conclusion. FVIIIRAg is a reliable marker for detecting the transformation of sinusoidal to vascular endothelium in advanced liver fibrosis in elderly cadavers.
The effect of old age on liver oxygenation and the hepatic expression of VEGF and VEGFR2.
Cheluvappa Rajkumar,Hilmer Sarah N,Kwun Sun Young,Jamieson Hamish A,O'Reilly Jennifer N,Muller Michael,Cogger Victoria C,Le Couteur David G
In old age, the liver contains less ATP and hypoxia-responsive genes are upregulated. Age-related changes in hepatic perfusion and the liver sinusoidal endothelial cell (LSEC) could contribute to this altered hepatic oxygen-dependent metabolism by causing intrahepatocytic hypoxia. Furthermore, age-related changes in the LSEC ('pseudocapillarization') have been partially induced by ATP depletion. To investigate whether there is intracellular hypoxia in the old rat liver, pimonidazole immunohistochemistry in intact livers and ATP levels in isolated LSECs were studied from young and old rats. There were no age-related changes. To determine whether defenestration of the LSEC could impair oxygen diffusion, pimonidazole immunohistochemistry was performed in rats treated with poloxamer 407. Despite defenestration, there was no change in pimonidazole staining. Immunohistochemistry was then performed to determine whether there are age-related changes in VEGF and VEGFR2. VEGF staining was not associated with age. However, there was an increase in perisinusoidal VEGFR2 expression with increasing age. In conclusion, liver hypoxia does not occur in old age and LSEC pseudocapillarization does not constitute an oxygen-diffusion barrier. There are no age-related changes in VEGF expression but an increase in perisinusoidal VEGFR2 expression, which has implications for the effects of aging on the hepatic sinusoid.
The influence of old age and poloxamer-407 on the hepatic disposition of diazepam in the isolated perfused rat liver.
Mitchell Sarah J,Huizer-Pajkos Aniko,Cogger Victoria C,McLachlan Andrew J,Le Couteur David G,Jones Brett,de Cabo Rafael,Hilmer Sarah N
BACKGROUND AND PURPOSE:The normal liver sinusoidal endothelium is thin and punctuated with fenestrations 50-200 nm in diameter that filter endobiotics and xenobiotics. Defenestration of the liver sinusoidal endothelium in old age and after pre-treatment with poloxamer-407 (P407) has been shown to prevent the transfer of small chylomicrons across the liver sinusoidal endothelium. The aim of this study was to investigate the impact of liver sinusoidal endothelium fenestrations on the hepatic uptake of the highly protein-bound drug diazepam. We hypothesized that defenestration will reduce the hepatic extraction of drugs which are highly bound to albumin. METHODOLOGY:The isolated perfused rat liver (IPRL) model and multiple indicator dilution technique were used to investigate the effect of fenestrations in the liver sinusoidal endothelium on the hepatic disposition of diazepam in old and young rats, and in young rats treated with P407 or vehicle. A bolus dose of (14)C-diazpeam and non-extracted tracers ((3)H-sucrose and Evans blue) was injected into the portal vein. The single-pass recovery of diazepam and markers and the apparent volume of distribution were determined. RESULTS:Scanning electron microscopy confirmed reduced porosity of the liver sinusoidal endothelial cells in P407-treated rats and old rats compared to young and control rats. The fractional recovery of diazepam was significantly increased in P407-treated rats compared to controls (0.20 ± 0.16, n = 12, P407; 0.08 ± 0.05, n = 8, controls; p = 0.0029), and in old rats compared to young rats (0.15 ± 0.03, n = 11, old; 0.10 ± 0.02, n = 11, young; p = 0.0004) following a single pass. CONCLUSION:Defenestration due to age-related pseudocapillarization and treatment with P407 resulted in reduced hepatic extraction of diazepam after a single pass through the IPRL. These results highlight the importance of the liver sinusoidal endothelium in the ultrafiltration of highly protein-bound drugs, and may also provide an additional mechanism for reduced hepatic clearance of diazepam in conditions associated with defenestration.
Age-related changes in the liver sinusoidal endothelium: a mechanism for dyslipidemia.
LE Couteur David G,Cogger Victoria C,McCuskey Robert S,DE Cabo Rafael,Smedsrød Bârd,Sorensen Karen K,Warren Alessandra,Fraser Robin
Annals of the New York Academy of Sciences
The liver sinusoidal endothelial cell (LSEC) influences the transfer of substrates between the sinusoidal blood and hepatocytes and has a major role in endocytosis; therefore, changes in the LSEC have significant implications for hepatic function. There are major morphological changes in the LSEC in old age called pseudocapillarization. These changes include increased LSEC thickness and reduced numbers of pores in the LSEC, which are called fenestrations. Pseudocapillarization has been found in old humans, rats, mice, and nonhuman primates. In addition, old age is associated with impaired LSEC endocytosis and increased leukocyte adhesion, which contributes to reduced hepatic perfusion. Given that fenestrations in the endothelium allow passage of some lipoproteins, including chylomicron remnants, age-related reduction in fenestrations impairs hepatic lipoprotein metabolism. In old rats, caloric restriction was associated with complete preservation of LSEC morphology and fenestrations. In conclusion, pseudocapillarization of the LSEC is a newly discovered aging change that, through its effects on lipoproteins, contributes to the association between old age, dyslipidemia, and vascular disease.
Sinusoidal endothelial cells of the liver: fine structure and function in relation to age.
De Leeuw A M,Brouwer A,Knook D L
Journal of electron microscopy technique
Liver endothelial cells form a continuous lining of the liver capillaries, or sinusoids, separating parenchymal cells and fat-storing cells from sinusoidal blood. Liver sinusoidal endothelial cells differ in fine structure from endothelial cells lining larger blood vessels and from other capillary endothelia in that they lack a distinct basement membrane and also contain open pores, or fenestrae, in the thin cytoplasmic projections which constitute the sinusoidal wall. This distinctive morphology supports the protective role played by liver endothelium, the cells forming a general barrier against pathogenic agents and serving as a selective sieve for substances passing from the blood to parenchymal and fat-storing cells, and vice versa. Sinusoidal endothelial cells, furthermore, significantly participate in the metabolic and clearance functions of the liver. They have been shown to be involved in the endocytosis and metabolism of a wide range of macromolecules, including glycoproteins, lipoproteins, extracellular matrix components, and inert colloids, establishing endothelial cells as a vital link in the complex network of cellular interactions and cooperation in the liver. Fine structural studies in combination with the development of cell isolation and culture techniques from both experimental animal and human liver have greatly contributed to the elucidation of these endothelial cell functions. Morphological and biochemical investigations have both revealed little changes with age except for an accumulation of iron ferritin and a decrease in the activities of glucose-6-phosphatase, Mg-ATPase, and in glucagon-stimulated adenylcyclase. Future studies are likely to disclose more fully the role of sinusoidal endothelial cells in the regulation of liver hemodynamics, in liver metabolism and blood clearance, in the maintenance of hepatic structure, in the pathogenesis of various liver diseases, and in the aging process in the liver.
Effects of old age on vascular complexity and dispersion of the hepatic sinusoidal network.
Warren Alessandra,Chaberek Slawomir,Ostrowski Kazimierz,Cogger Victoria C,Hilmer Sarah N,McCuskey Robert S,Fraser Robin,Le Couteur David G
Microcirculation (New York, N.Y. : 1994)
OBJECTIVES:In old age, there are marked changes in both the structure of the liver sinusoidal endothelial cell and liver perfusion. The objective of this study was to determine whether there are also aging changes in the microvascular architecture and vascular dispersion of the liver that might influence liver function. METHODS:Vascular corrosion casts and light micrographs of young (4 months) and old (24 months) rat livers were compared. Fractal and Fourier analyses and micro-computed tomography were used. Vascular dispersion was determined from the dispersion number for sucrose and 100-nm microspheres in impulse response experiments. RESULTS:Age did not affect sinusoidal dimensions, sinusoidal density, or dispersion number. There were changes in the geometry and complexity of the sinusoidal network as determined by fractal dimension and degree of anisotropy. CONCLUSIONS:There are small, age-related changes in the architecture of the liver sinusoidal network, which may influence hepatic function and reflect broader aging changes in the microcirculation. However, sinusoidal dimensions and hepatic vascular dispersion are not markedly influenced by old age.
Hepatic disposal of advanced glycation end products during maturation and aging.
Svistounov Dmitri,Oteiza Ana,Zykova Svetlana N,Sørensen Karen Kristine,McCourt Peter,McLachlan Andrew J,McCuskey Robert S,Smedsrød Bård
UNLABELLED:Aging is characterized by progressive loss of metabolic and biochemical functions and accumulation of metabolic by-products, including advanced glycation end products (AGEs), which are observed in several pathological conditions. A number of waste macromolecules, including AGEs are taken up from the circulation by endocytosis mainly into liver sinusoidal endothelial cells (LSECs) and Kupffer cells (KCs). However, AGEs still accumulate in different tissues with aging, despite the presence of this clearance mechanism. The aim of the present study was to determine whether the efficiency of LSECs and KCs for disposal of AGEs changes through aging. RESULTS:After intravenous administration of (14)C-AGE-albumin in pre-pubertal, young adult, middle aged and old mice, more than 90% of total recovered (14)C-AGE was liver associated, irrespective of age. LSECs and KCs represented the main site of uptake. A fraction of the (14)C-AGE degradation products ((14)C-AGE-DPs) was stored for months in the lysosomes of these cells after uptake. The overall rate of elimination of (14)C-AGE-DPs from the liver was markedly faster in pre-pubertal than in all post-pubertal age groups. The ability to eliminate (14)C-AGE-DPs decreased to similar extents after puberty in LSECs and KCs. A rapid early removal phase was characteristic for all age groups except the old group, where this phase was absent. CONCLUSIONS:Removal of AGE-DPs from the liver scavenger cells is a very slow process that changes with age. The ability of these cells to dispose of AGEs declines after puberty. Decreased AGE removal efficiency early in life may lead to AGE accumulation.
Age-related changes in the hepatic microcirculation in mice.
Ito Yoshiya,Sørensen Karen K,Bethea Nancy W,Svistounov Dmitri,McCuskey Margaret K,Smedsrød Bård H,McCuskey Robert S
Aging of the liver is associated with impaired metabolism of drugs, adverse drug interactions, and susceptibility to toxins. Since reduced hepatic blood flow is suspected to contribute this impairment, we examined age-related alterations in hepatic microcirculation. Livers of C57Bl/6 mice were examined at 0.8 (pre-pubertal), 3 (young adult), 14 (middle-aged), and 27 (senescent) months of age using in vivo and electron microscopic methods. The results demonstrated a 14% reduction in the numbers of perfused sinusoids between 0.8 and 27 month mice associated with 35% reduction in sinusoidal blood flow. This was accompanied by an inflammatory response evidenced by a fivefold increase in leukocyte adhesion in 27 month mice, up-regulated expression of ICAM-1, and increases in intrahepatic macrophages. Sinusoidal diameter decreased 6-10%. Liver sinusoidal endothelial cell (LSEC) dysfunction was seen as early as 14 months when there was a threefold increase in the numbers of swollen LSEC. The endocytotic capacity of LSEC also was found to be reduced in older animals. The sinusoidal endothelium in 27 month old mice exhibited pseudocapillarization. In conclusion, the results suggest that leukocyte accumulation in the sinusoids and narrowing of sinusoidal lumens due to pseudocapillarization and dysfunction of LSEC reduce sinusoidal blood flow in aged livers.
Expression pattern of CYP24 in liver during ageing in long-term diabetes.
Vuica Ana,Vukojević Katarina,Ferhatović Hamzić Lejla,Jerić Milka,Puljak Livia,Grković Ivica,Filipović Natalija
Association of liver calcitriol (active vitamin D metabolite) catabolism with osteomalacia during prolonged use of certain drugs was reported in several recent studies. To examine whether the increased calcitriol catabolism could be a potential link between ageing/diabetes mellitus (DM) and bone loss, we studied the dynamic of expression of CYP24, the main calcitriol catabolising enzyme in the liver of rats during ageing and a long-term experimental DM1. DM1 model was induced with intraperitoneally injected streptozotocin (STZ) (55mg/kg). Sprague-Dawley rats were sacrificed 6 and 12 months after the DM1 induction. The immunohistochemical analyses of CYP24 and transforming growth factor β 1 (TGF-β1) expression in the liver were performed. We found that ageing and long-term DM1 resulted in a significantly increased expression of CYP24 in hepatocytes, as well as in non-hepatocyte liver cells (Kupffer cells, hepatic stellate cells and sinusoidal endothelial cells). Ageing and long-term DM1 resulted in an increased expression of TGF-β1 as well. Expression of CYP24 coexisted with the expression of TGF-β1 in all types of hepatic cells. We concluded that liver has the capacity for an active vitamin D catabolism in different populations of liver cells, especially in sinusoidal endothelial cells, through an expression of CYP24. That capacity is substantially increased during ageing and long-term diabetes mellitus. Increased liver calcitriol catabolism could be one of the mechanisms of the bone metabolism impairment related to ageing and diabetes.
The liver sieve and atherosclerosis.
Fraser Robin,Cogger Victoria C,Dobbs Bruce,Jamieson Hamish,Warren Alessandra,Hilmer Sarah N,Le Couteur David G
SUMMARY:The 'liver sieve' is a term developed to describe the appearance and the role of fenestrations in the liver sinusoidal endothelial cell (LSEC). LSECs are gossamer-thin cells that line the hepatic sinusoid and they are perforated with pores called fenestrations clustered in sieve plates. There is growing evidence that fenestrations act like a permselective ultrafiltration system which is important for the hepatic uptake of many substrates, particularly chylomicron remnant lipoproteins. The liver sieve is a very efficient exchange system, however in conditions such as hepatic cirrhosis and fibrosis, diabetes mellitus and old age, there is defenestration of the liver sieve. Such defenestration has been shown to influence the hepatic uptake of various substrates including lipoproteins. In the future, pharmacological manipulation of the liver sieve may play a number of therapeutic roles including the management of dyslipidaemia; increasing the efficiency of liver-targeted gene therapy; and improving regeneration of old livers.
Novel targets for delaying aging: The importance of the liver and advances in drug delivery.
Hunt Nicholas J,McCourt Peter A G,Le Couteur David G,Cogger Victoria C
Advanced drug delivery reviews
Age-related changes in liver function have a significant impact on systemic aging and susceptibility to age-related diseases. Nutrient sensing pathways have emerged as important targets for the development of drugs that delay aging and the onset age-related diseases. This supports a central role for the hepatic regulation of metabolism in the association between nutrition and aging. Recently, a role for liver sinusoidal endothelial cells (LSECs) in the relationship between aging and metabolism has also been proposed. Age-related loss of fenestrations within LSECs impairs the transfer of substrates (such as lipoproteins and insulin) between sinusoidal blood and hepatocytes, resulting in post-prandial hyperlipidemia and insulin resistance. Targeted drug delivery methods such as nanoparticles and quantum dots will facilitate the direct delivery of drugs that regulate fenestrations in LSECs, providing an innovative approach to ameliorating age-related diseases and increasing healthspan.
Old age and the hepatic sinusoid.
Le Couteur David G,Warren Alessandra,Cogger Victoria C,Smedsrød Bård,Sørensen Karen K,De Cabo Rafael,Fraser Robin,McCuskey Robert S
Anatomical record (Hoboken, N.J. : 2007)
Morphological changes in the hepatic sinusoid with old age are increasingly recognized. These include thickening and defenestration of the liver sinusoidal endothelial cell, sporadic deposition of collagen and basal lamina in the extracellular space of Disse, and increased numbers of fat engorged, nonactivated stellate cells. In addition, there is endothelial up-regulation of von Willebrand factor and ICAM-1 with reduced expression of caveolin-1. These changes have been termed age-related pseudocapillarization. The effects of old age on Kupffer cells are inconsistent, but impaired responsiveness is likely. There are functional implications of these aging changes in the hepatic sinusoid. There is reduced sinusoidal perfusion, which will impair the hepatic clearance of highly extracted substrates. Blood clearance of a variety of waste macromolecules takes place in liver sinusoidal endothelial cells (LSECs). Previous studies indicated either that aging had no effect, or reduced the endocytic capacity of LSECs. However, a recent study in mice showed reduced endocytosis in pericentral regions of the liver lobules. Reduced endocytosis may increase systemic exposure to potential harmful waste macromolecules such as advanced glycation end products Loss of fenestrations leads to impaired transfer of lipoproteins from blood to hepatocytes. This provides a mechanism for impaired chylomicron remnant clearance and postprandial hyperlipidemia associated with old age. Given the extensive range of substrates metabolized by the liver, age-related changes in the hepatic sinusoid and microcirculation have important systemic implications for aging and age-related diseases.
CTRP13 attenuates the expression of LN and CAV-1 Induced by high glucose via CaMKKβ/AMPK pathway in rLSECs.
Zhang Qi,Niu Xiang'e,Tian Limin,Liu Jing,Niu Ruilan,Quan Jinxing,Yu Jing,Lin Wenyan,Qian Zibing,Zeng Peiyun
OBJECTIVE:To investigate the effect and mechanism of CTRP13 on hepatic sinusoidal capillarization induced by high glucose in rat liver sinusoidal endothelial cells (rLSECs). RESULTS:CTRP13 was reduced in high glucose-treated rLSECs. High glucose increased LN and CAV-1 expression and inhibited CaMKKβ and AMPK phosphorylation. CTRP13 overexpression protected rLSECs against high glucose-induced increase of LN and CAV-1 expression. Moreover, CTRP13 overexpression increased high glucose-induced inhibition of CaMKKβ and AMPK activation in CTRP13-overexpressing rLSECs. Inhibition of CaMKKβ and AMPK disturbed the protective effects of CTRP13 in high glucose-induced increase of LN and CAV-1. Hepatic steatosis was enhanced and basement membrane was thickened in liver of diabetic fatty liver rats. CONCLUSIONS:Our data identified the protective role of CTRP13 in hepatic sinusoidal capillarization induced by high glucose via activating CAMKKβ/AMPK pathway. CTRP13 may be a potential target for screening and treating diabetic fatty liver. METHODS:Construct lentiviral CTRP13 overexpression vector and transfect rLSECs. Use STO-609 (a CaMKKβ inhibitor) or Compound C (an AMPK inhibitor) to treat rLSECs. CTRP13, CaMKKβ, AMPK, laminin (LN) and caveolin-1 (CAV-1) were detected by qRT-PCR and Western blotting. Establish rat model of diabetic fatty liver. Use immunohistochemistry, hematoxylin-eosin and silver staining to observe the histopathological features of liver.
Ultrastructure of the liver microcirculation influences hepatic and systemic insulin activity and provides a mechanism for age-related insulin resistance.
Mohamad Mashani,Mitchell Sarah Jayne,Wu Lindsay Edward,White Melanie Yvonne,Cordwell Stuart James,Mach John,Solon-Biet Samantha Marie,Boyer Dawn,Nines Dawn,Das Abhirup,Catherine Li Shi-Yun,Warren Alessandra,Hilmer Sarah Nicole,Fraser Robin,Sinclair David Andrew,Simpson Stephen James,de Cabo Rafael,Le Couteur David George,Cogger Victoria Carroll
While age-related insulin resistance and hyperinsulinemia are usually considered to be secondary to changes in muscle, the liver also plays a key role in whole-body insulin handling and its role in age-related changes in insulin homeostasis is largely unknown. Here, we show that patent pores called 'fenestrations' are essential for insulin transfer across the liver sinusoidal endothelium and that age-related loss of fenestrations causes an impaired insulin clearance and hyperinsulinemia, induces hepatic insulin resistance, impairs hepatic insulin signaling, and deranges glucose homeostasis. To further define the role of fenestrations in hepatic insulin signaling without any of the long-term adaptive responses that occur with aging, we induced acute defenestration using poloxamer 407 (P407), and this replicated many of the age-related changes in hepatic glucose and insulin handling. Loss of fenestrations in the liver sinusoidal endothelium is a hallmark of aging that has previously been shown to cause deficits in hepatic drug and lipoprotein metabolism and now insulin. Liver defenestration thus provides a new mechanism that potentially contributes to age-related insulin resistance.
Liver aging and pseudocapillarization in a Werner syndrome mouse model.
Cogger Victoria C,Svistounov Dmitri,Warren Alessandra,Zykova Svetlana,Melvin Richard G,Solon-Biet Samantha M,O'Reilly Jennifer N,McMahon Aisling C,Ballard J William O,De Cabo Rafa,Le Couteur David G,Lebel Michel
The journals of gerontology. Series A, Biological sciences and medical sciences
Werner syndrome is a progeric syndrome characterized by premature atherosclerosis, diabetes, cancer, and death in humans. The knockout mouse model created by deletion of the RecQ helicase domain of the mouse Wrn homologue gene (Wrn(∆hel/∆hel)) is of great interest because it develops atherosclerosis and hypertriglyceridemia, conditions associated with aging liver and sinusoidal changes. Here, we show that Wrn(∆hel/∆hel) mice exhibit increased extracellular matrix, defenestration, decreased fenestration diameter, and changes in markers of liver sinusoidal endothelial cell inflammation, consistent with age-related pseudocapilliarization. In addition, hepatocytes are larger, have increased lipofuscin deposition, more frequent nuclear morphological anomalies, decreased mitochondria number, and increased mitochondrial diameter compared to wild-type mice. The Wrn(∆hel/∆hel) mice also have altered mitochondrial function and altered nuclei. Microarray data revealed that the Wrn(∆hel/∆hel) genotype does not affect the expression of many genes within the isolated hepatocytes or liver sinusoidal endothelial cells. This study reveals that Wrn(∆hel/∆hel) mice have accelerated typical age-related liver changes including pseudocapillarization. This confirms that pseudocapillarization of the liver sinusoid is a consistent feature of various aging models. Moreover, it implies that DNA repair may be implicated in normal aging changes in the liver.
Arsenic requires sphingosine-1-phosphate type 1 receptors to induce angiogenic genes and endothelial cell remodeling.
Straub Adam C,Klei Linda R,Stolz Donna B,Barchowsky Aaron
The American journal of pathology
Arsenic in drinking water is a major public health concern as it increases risk and incidence of cardiovascular disease and cancer. Arsenic exposure affects multiple vascular beds, promoting liver sinusoidal capillarization and portal hypertension, ischemic heart disease, peripheral vascular disease, and tumor angiogenesis. While Rac1-GTPase and NADPH oxidase activities are essential for arsenic-stimulated endothelial cell signaling for angiogenesis or liver sinusoid capillarization, the mechanism for initiating these effects is unknown. We found that arsenic-stimulated cell signaling and angiogenic gene expression in human microvascular endothelial cells were Pertussis toxin sensitive, indicating a G-protein coupled signaling pathway. Incubating human microvascular endothelial cells with the sphingosine-1-phosphate type 1 receptor (S1P(1)) inhibitor VPC23019 or performing small interfering RNA knockdown of S1P(1) blocked arsenic-stimulated HMVEC angiogenic gene expression and tube formation, but did not affect induction of either HMOX1 or IL8. Liver sinusoidal endothelial cells (LSECs) defenestrate and capillarize in response to aging and environmental oxidant stresses. We found that S1P(1) was enriched on LSECs in vivo and in primary cell culture and that VPC23019 inhibited both sphingosine-1-phosphate-stimulated and arsenic-stimulated LSEC oxidant generation and defenestration. These studies identified novel roles for S1P(1) in mediating arsenic stimulation of both angiogenesis and pathogenic LSEC capillarization, as well as demonstrating a role for S1P(1) in mediating environmental responses in the liver vasculature, providing possible mechanistic insight into arsenic-induced vascular pathogenesis and disease.
Hallmarks of Aging in the Liver.
Hunt Nicholas J,Kang Sun Woo Sophie,Lockwood Glen P,Le Couteur David G,Cogger Victoria C
Computational and structural biotechnology journal
While the liver demonstrates remarkable resilience during aging, there is growing evidence that it undergoes all the cellular hallmarks of aging, which increases the risk of liver and systemic disease. The aging process in the liver is driven by alterations of the genome and epigenome that contribute to dysregulation of mitochondrial function and nutrient sensing pathways, leading to cellular senescence and low-grade inflammation. These changes promote multiple phenotypic changes in all liver cells (hepatocytes, liver sinusoidal endothelial, hepatic stellate and Küpffer cells) and impairment of hepatic function. In particular, age-related changes in the liver sinusoidal endothelial cells are a significant but under-recognized risk factor for the development of age-related cardiometabolic disease.
Ischemia/Reperfusion Injury in the Aged Liver: The Importance of the Sinusoidal Endothelium in Developing Therapeutic Strategies for the Elderly.
Hide Diana,Warren Alessandra,Fernández-Iglesias Anabel,Maeso-Díaz Raquel,Peralta Carmen,Le Couteur David G,Bosch Jaime,Cogger Victoria C,Gracia-Sancho Jordi
The journals of gerontology. Series A, Biological sciences and medical sciences
The liver endothelium plays a key role in the progression and resolution of liver diseases in young and adult individuals. However, its role in older people remains unknown. We have herein evaluated the importance of the sinusoidal endothelium in the pathophysiology of acute liver injury, and investigated the applicability of simvastatin, in aged animals. Eighteen-months-old male Wistar rats underwent 60 minutes of partial warm ischemia followed by 2 hours of reperfusion (WIR). A group of aged rats received simvastatin for 3 days before WIR. Endothelial phenotype, parenchymal injury, oxidative and nitrosative stress, and fenestrae dynamics were analyzed. The effects of WIR and simvastatin were investigated in primary LSEC from aged animals. The results of this study demonstrated that WIR significantly damages the liver endothelium and its effects are markedly worse in old animals. WIR-aged livers exhibited reduced vasodilation and sinusoidal capillarization, associated with liver damage and cellular stress. Simvastatin prevented the detrimental effects of WIR in aged livers. In conclusion, the liver sinusoidal endothelium of old animals is highly vulnerable to acute insult, thus targeted protection is especially relevant in preventing liver damage. Simvastatin represents a useful therapeutic strategy in aging.
Age-related loss of responsiveness to 2,5-dimethoxy-4-iodoamphetamine in liver sinusoidal endothelial cells.
Cogger Victoria C,Mitchell Sarah J,Warren Alessandra,de Cabo Rafael,Le Couteur David G
The journals of gerontology. Series A, Biological sciences and medical sciences
Age-related pseudocapillarization of the liver sinusoidal endothelium is associated with impaired lipid and drug metabolism and the development of disease. 2,5-Dimethoxy-4-iodoamphetamine is a serotonin receptor 2 agonist that has been shown to have beneficial effects on the liver sinusoidal endothelium in the setting of partial hepatectomy. Here, we have assessed whether 2,5-dimethoxy-4-iodoamphetamine influences ultrastructure of the sinusoidal endothelium in normal 7- and 24-month-old C57Bl6 mice. Following 48 hours of 2,5-dimethoxy-4-iodoamphetamine administration, we found that the liver endothelium in the young, but not in the old, mice had increased porosity compared with controls. This effect appeared to be modulated by increased fenestration size rather than a change in fenestration number. 2,5-Dimethoxy-4-iodoamphetamine is a useful manipulator of fenestration size in the young liver and could be harnessed in the search for therapeutic interventions for pseudocapillarization.
Age-related changes in scavenger receptor-mediated endocytosis in rat liver sinusoidal endothelial cells.
Simon-Santamaria Jaione,Malovic Ivana,Warren Alessandra,Oteiza Ana,Le Couteur David,Smedsrød Bård,McCourt Peter,Sørensen Karen Kristine
The journals of gerontology. Series A, Biological sciences and medical sciences
Liver sinusoidal endothelial cells (LSECs) play an essential role in systemic waste clearance by effective endocytosis of blood-borne waste macromolecules. We aimed to study LSECs' scavenger function during aging, and whether age-related morphological changes (eg, defenestration) affect this function, in F344/BN F1 rats. Endocytosis of the scavenger receptor ligand formaldehyde-treated serum albumin was significantly reduced in LSECs from old rats. Ligand degradation, LSEC protein expression of the major scavenger receptors for formaldehyde-treated serum albumin endocytosis, stabilin-1 and stabilin-2, and their staining patterns along liver sinusoids, was similar at young and old age, suggesting that other parts of the endocytic machinery are affected by aging. Formaldehyde-treated serum albumin uptake per cell, and cell porosity evaluated by electron microscopy, was not correlated, indicating that LSEC defenestration is not linked to impaired endocytosis. We report a significantly reduced LSEC endocytic capacity at old age, which may be especially important in situations with increased circulatory waste loads.
Old age is associated with ultrastructural changes in isolated rat liver sinusoidal endothelial cells.
O'Reilly Jennifer N,Cogger Victoria C,Le Couteur David G
Journal of electron microscopy
Old age is associated with ultrastructural changes in the hepatic sinusoid called pseudocapillarization, which include defenestration and thickening of the sinusoidal endothelium. We investigated whether such changes also occur in isolated and cultured liver sinusoidal endothelial cells. Liver sinusoidal endothelial cells were isolated from young (6-10 months, n = 4) and old (24-26 months, n = 4) F344 rats and fenestrations evaluated using scanning electron microscopy. Fenestration diameter was reduced in old age from 194 +/- 1 nm to 185 +/- 1 nm (P < 0.001) and there was an age-related increase in the number fused fenestrations and large gaps. Age-related changes in the diameter of fenestrations in the liver sinusoidal endothelial cell are maintained following isolation and culture. This suggests that this age-related change may be intrinsic to the liver endothelial cell and/or irreversible.
Effects of aging on liver microcirculatory function and sinusoidal phenotype.
Maeso-Díaz Raquel,Ortega-Ribera Martí,Fernández-Iglesias Anabel,Hide Diana,Muñoz Leticia,Hessheimer Amelia J,Vila Sergi,Francés Rubén,Fondevila Constantino,Albillos Agustín,Peralta Carmen,Bosch Jaime,Tacke Frank,Cogger Victoria C,Gracia-Sancho Jordi
The socioeconomic and medical improvements of the last decades have led to a relevant increase in the median age of worldwide population. Although numerous studies described the impact of aging in different organs and the systemic vasculature, relatively little is known about liver function and hepatic microcirculatory status in the elderly. In this study, we aimed at characterizing the phenotype of the aged liver in a rat model of healthy aging, particularly focusing on the microcirculatory function and the molecular status of each hepatic cell type in the sinusoid. Moreover, major findings of the study were validated in young and aged human livers. Our results demonstrate that healthy aging is associated with hepatic and sinusoidal dysfunction, with elevated hepatic vascular resistance and increased portal pressure. Underlying mechanisms of such hemodynamic disturbances included typical molecular changes in the cells of the hepatic sinusoid and deterioration in hepatocyte function. In a specific manner, liver sinusoidal endothelial cells presented a dysfunctional phenotype with diminished vasodilators synthesis, hepatic macrophages exhibited a proinflammatory state, while hepatic stellate cells spontaneously displayed an activated profile. In an important way, major changes in sinusoidal markers were confirmed in livers from aged humans. In conclusion, our study demonstrates for the first time that aging is accompanied by significant liver sinusoidal deregulation suggesting enhanced sinusoidal vulnerability to chronic or acute injuries.
Long live the liver: immunohistochemical and stereological study of hepatocytes, liver sinusoidal endothelial cells, Kupffer cells and hepatic stellate cells of male and female rats throughout ageing.
Marcos Ricardo,Correia-Gomes Carla
Cell and tissue research
Male/female differences in enzyme activity and gene expression in the liver are known to be attenuated with ageing. Nevertheless, the effect of ageing on liver structure and quantitative cell morphology remains unknown. Male and female Wistar rats aged 2, 6, 12 and 18 months were examined by means of stereological techniques and immunohistochemical tagging of hepatocytes (HEP), liver sinusoidal endothelial cells (LSEC), Kupffer cells (KC) and hepatic stellate cells (HSC) in order to assess the total number and number per gram of these cells throughout life. The mean cell volume of HEP and HSC, the lobular position and the collagen content of the liver were also evaluated with stereological techniques. The number per gram of HSC was similar for both genders and was maintained throughout ageing. The mean volume of HSC was also conserved but differences in the cell body and lobular location were observed. Statistically significant gender differences in HEP were noted in young rats (females had smaller and more binucleated HEP) but were attenuated with ageing. The same occurred for KC and LSEC, since the higher number per gram in young females disappeared in older animals. Liver collagen increased with ageing but only in males. Thus, the numbers of these four cell types are related throughout ageing, with well-defined cell ratios. The shape and lobular position of HSC change with ageing in both males and females. Gender dimorphism in HEP, KC and LSEC of young rat liver disappears with ageing.
Manipulating fenestrations in young and old liver sinusoidal endothelial cells.
Hunt Nicholas J,Lockwood Glen P,Warren Alessandra,Mao Hong,McCourt Peter A G,Le Couteur David G,Cogger Victoria C
American journal of physiology. Gastrointestinal and liver physiology
Fenestrations are pores within liver sinusoidal endothelial cells (LSECs) that enable the transfer of substrates (particularly insulin and lipoproteins) between blood and hepatocytes. With increasing age, there are marked reductions in fenestrations, referred to as pseudocapillarization. Currently, fenestrations are thought to be regulated by vascular endothelial growth factor and nitric oxide (NO) pathways promoting remodeling of the actin cytoskeleton and cell membrane lipid rafts. We investigated the effects of drugs that act on these pathways on fenestrations in old (18-24 mo) and young mice (3-4 mo). Isolated LSECs were incubated with either cytochalasin 7-ketocholesterol, sildenafil, amlodipine, simvastatin, 2, 5-dimethoxy-4-iodoamphetamine (DOI), bosentan, TNF-related apoptosis-inducing ligand (TRAIL) or nicotinamide mononucleotide (NMN). LSECs were visualized under scanning electron microscopy to quantify fenestration porosity, diameter, and frequency, as well as direct stochastic optical reconstruction microscopy to examine actin and NO synthase. In young and old LSECs, fenestration porosity, diameter and frequency were increased by 7-ketocholesterol, while porosity and/or frequency were increased with NMN, sildenafil, amlodipine, TRAIL, and cytochalasin D. In old mice only, bosentan and DOI increased fenestration porosity and/or frequency. Modification of the actin cytoskeleton was observed with all agents that increased fenestrations, while NO synthase was only increased by sildenafil, amlodipine, and TRAIL. In conclusion, agents that target NO, actin, or lipid rafts promote changes in fenestrations in mice LSECs. Regulation of fenestrations occurs via both NO-dependent and independent pathways. This work indicates that age-related defenestration can be reversed pharmacologically, which has potential translational relevance for dyslipidemia and insulin resistance. NEW & NOTEWORTHY We demonstrate the effects of multiple nitric oxide-dependent and -independent pharmaceutical agents on fenestrations of the liver sinusoidal endothelium. Fenestrations are reorganized in response to nicotinamide mononucleotide, sildenafil, amlodipine, and TNF-related apoptosis-inducing ligand. This work indicates that age-related defenestration can be reversed pharmacologically, which has potential translational relevance for dyslipidemia and insulin resistance in old age.
The effect of aging on VEGF/VEGFR2 signal pathway genes expression in rat liver sinusoidal endothelial cell.
Wang Wan-Li,Zheng Xing-Long,Li Qing-Shan,Liu Wen-Yan,Hu Liang-Shuo,Sha Huan-Chen,Guo Kun,Lv Yi,Wang Bo
Molecular and cellular biochemistry
Liver sinusoidal endothelial cells (LSECs) play a key role in the initiation and neoangiogenesis of liver regeneration. We presume that the abnormity of the VEGF/VEGFR2 and its pathway gene Id1, Wnt2 and HGF expression in aged LSECs may be an important mechanism to affect liver regeneration of the elderly. LSECs from two different groups (adult and old) were isolated in a rodent model, and observed by SEM and TEM. The adult and old rats were underwent 70% partial hepatectomy. The proliferation of hepatocytes and LSECs were analyzed by Immunofluorescence staining. The expression of VEGF/VEGFR2 and its pathway gene in isolated LSECs and liver tissue after hepatectomy were detected by qRT-PCR and Western blot. There is a decreased number of endothelial fenestrae in the LSECs of the old group, compared to the adult group. The old group had a lower expression of VEGF/VEGFR2 and its pathway gene than the adult groups (p < 0.01). The results of western blot were consistent with those of qRT-PCR. The hepatocytes had a high proliferation rate at first 4 days after hepatectomy, and a significantly higher proliferation rate in the adult group. The LSECs began to proliferate after 4 days of hepatectomy, and showed a quantity advantage in the adult group. The adult group had a significantly higher expression of VEGF/VEGFR2 and its pathway gene after hepatectomy than the old group (p < 0.01). LSCEs turn to be defenestration in structure and have a low expression of VEGF/VEGFR2 and its pathway gene with aging.
The Effects of Metformin on Age-Related Changes in the Liver Sinusoidal Endothelial Cell.
Hunt Nicholas J,Lockwood Glen P,Kang Sun Woo Sophie,Pulpitel Tamara,Clark Ximonie,Mao Hong,McCourt Peter A G,Cooney Gregory J,Wali Jibran A,Le Couteur Frank H,Le Couteur David G,Cogger Victoria C
The journals of gerontology. Series A, Biological sciences and medical sciences
Age-related changes in the liver sinusoidal endothelium, particularly the reduction in fenestrations, contribute to insulin resistance in old age. Metformin impacts on the aging process and improves insulin resistance. Therefore, the effects of metformin on the liver sinusoidal endothelium were studied. Metformin increased fenestrations in liver sinusoidal endothelial cells isolated from both young and old mice. Mice administered metformin in the diet for 12 months had increased fenestrations and this was associated with lower insulin levels. The effect of metformin on fenestrations was blocked by inhibitors of AMP-activated protein kinase (AMPK), endothelial nitric oxide synthase, and myosin light chain kinase phosphorylation. Metformin led to increased transgelin expression and structural changes in the actin cytoskeleton but had no effect on lactate production. Metformin also generated fenestration-like structures in SK-Hep1 cells, a liver endothelial cell line, and this was associated with increased ATP, cGMP, and mitochondrial activity. In conclusion, metformin ameliorates age-related changes in the liver sinusoidal endothelial cell via AMPK and endothelial nitric oxide pathways, which might promote insulin sensitivity in the liver, particularly in old age.