Aging is associated with central fat redistribution and insulin resistance. To identify age-related adipose features, we evaluated the senescence and adipogenic potential of adipose-derived stromal ...cells (ASCs) from abdominal subcutaneous fat obtained from healthy normal-weight young (<25 years) or older women (>60 years). Increased cell passages of young-donor ASCs (in vitro aging) resulted in senescence but not oxidative stress. ASC-derived adipocytes presented impaired adipogenesis but no early mitochondrial dysfunction. Conversely, aged-donor ASCs at early passages displayed oxidative stress and mild senescence. ASC-derived adipocytes exhibited oxidative stress, and early mitochondrial dysfunction but adipogenesis was preserved. In vitro aging of aged-donor ASCs resulted in further increased senescence, mitochondrial dysfunction, oxidative stress, and severe adipocyte dysfunction. When in vitro aged young-donor ASCs were treated with metformin, no alteration was alleviated. Conversely, metformin treatment of aged-donor ASCs decreased oxidative stress and mitochondrial dysfunction resulting in decreased senescence. Metformin's prevention of oxidative stress and of the resulting senescence improved the cells' adipogenic capacity and insulin sensitivity. This effect was mediated by the activation of AMP-activated protein kinase as revealed by its specific inhibition and activation. Overall, aging ASC-derived adipocytes presented impaired adipogenesis and insulin sensitivity. Targeting stress-induced senescence of ASCs with metformin may improve age-related adipose tissue dysfunction.
Nonalcoholic fatty liver disease (NAFLD) is associated with all features of the metabolic syndrome. Although deposition of excess triglycerides within liver cells, a hallmark of NAFLD, is associated ...with a loss of insulin sensitivity, it is not clear which cellular abnormality arises first. We have explored this in mice overexpressing carbohydrate responsive element-binding protein (ChREBP). On a standard diet, mice overexpressing ChREBP remained insulin sensitive, despite increased expression of genes involved in lipogenesis/fatty acid esterification and resultant hepatic steatosis (simple fatty liver). Lipidomic analysis revealed that the steatosis was associated with increased accumulation of monounsaturated fatty acids (MUFAs). In primary cultures of mouse hepatocytes, ChREBP overexpression induced expression of stearoyl-CoA desaturase 1 (Scd1), the enzyme responsible for the conversion of saturated fatty acids (SFAs) into MUFAs. SFA impairment of insulin-responsive Akt phosphorylation was therefore rescued by the elevation of Scd1 levels upon ChREBP overexpression, whereas pharmacological or shRNA-mediated reduction of Scd1 activity decreased the beneficial effect of ChREBP on Akt phosphorylation. Importantly, ChREBP-overexpressing mice fed a high-fat diet showed normal insulin levels and improved insulin signaling and glucose tolerance compared with controls, despite having greater hepatic steatosis. Finally, ChREBP expression in liver biopsies from patients with nonalcoholic steatohepatitis was increased when steatosis was greater than 50% and decreased in the presence of severe insulin resistance. Together, these results demonstrate that increased ChREBP can dissociate hepatic steatosis from insulin resistance, with beneficial effects on both glucose and lipid metabolism.
Mutations in the lamin A/C gene encoding nuclear lamins A and C (lamin A/C) cause familial partial lipodystrophy type 2 (FPLD2) and related lipodystrophy syndromes. These are mainly characterized by ...redistribution of adipose tissue associated with insulin resistance. Several reports suggest that alterations in the extracellular matrix of adipose tissue leading to fibrosis play a role in the pathophysiology of lipodystrophy syndromes. However, the extent of extracellular matrix alterations in FPLD2 remains unknown. We show significantly increased fibrosis and altered expression of genes encoding extracellular matrix proteins in cervical subcutaneous adipose tissue from a human subject with FLPD2. Similar extracellular matrix alterations occur in adipose tissue of transgenic mice expressing an FPLD2-causing human lamin A variant and in cultured fibroblasts from human subjects with FPLD2 and related lipodystrophies. These abnormalities are associated with increased transforming growth factor-β signaling and defects in matrix metalloproteinase 9 activity. Our data demonstrate that lamin A/C gene mutations responsible for FPLD2 and related lipodystrophies are associated with transforming growth factor-β activation and an extracellular matrix imbalance in adipose tissue, suggesting that targeting these alterations could be the basis of novel therapies
Summary
To maintain bone mass turnover and bone mineral density (BMD), bone marrow (BM) mesenchymal stem cells (MSCs) are constantly recruited and subsequently differentiated into osteoblasts. ...HIV‐infected patients present lower BMD than non‐HIV infected individuals and a higher prevalence of osteopenia/osteoporosis. In antiretroviral treatment (ART)‐naive patients, encoded HIV proteins represent pathogenic candidates. They are released by infected cells within BM and can impact on neighbouring cells. In this study, we tested whether HIV proteins Tat and/or Nef could induce senescence of human BM‐MSCs and reduce their capacity to differentiate into osteoblasts. When compared to nontreated cells, MSCs chronically treated with Tat and/or Nef up to 30 days reduced their proliferative activity and underwent early senescence, associated with increased oxidative stress and mitochondrial dysfunction. The antioxidant molecule N‐acetyl‐ cysteine had no or minimal effects on Tat‐ or Nef‐induced senescence. Tat but not Nef induced an early increase in NF‐κB activity and cytokine/chemokine secretion. Tat‐induced effects were prevented by the NF‐κB inhibitor parthenolide, indicating that Tat triggered senescence via NF‐κB activation leading to oxidative stress. Otherwise, Nef‐ but not Tat‐treated cells displayed early inhibition of autophagy. Rapamycin, an autophagy inducer, reversed Nef‐induced senescence and oxidative stress. Moreover, Tat+Nef had cumulative effects. Finally, Tat and/or Nef decreased the MSC potential of osteoblastic differentiation. In conclusion, our in vitro data show that Tat and Nef could reduce the number of available precursors by inducing MSC senescence, through either enhanced inflammation or reduced autophagy. These results offer new insights into the pathophysiological mechanisms of decreased BMD in HIV‐infected patients.
Epidemiological data indicate a strong risk for development of insulin resistance (IR), and, ultimately, overt diabetes mellitus (DM) in patients with chronic hepatitis C virus (HCV) infection. ...Steatosis, or fatty liver, is closely linked with IR in persons without HCV, such as those with metabolic syndrome, primarily due to increased visceral fat leading to altered adipokine production and increased free fatty acid (FFA) release. Moreover, there is evidence that liver fat can have an impact on the development of hepatic IR independently of changes in adipose tissue. Multiple mechanisms can account for the development of IR in patients with chronic HCV. In particular, there is evidence for a triangular interaction between steatosis, inflammatory processes and IR. In patients infected by the genotype 1 virus, steatosis is strongly related to IR, leading to a metabolic steatosis, while, in genotype 3 patients, steatosis is related to viral load in the context of a viral steatosis. Chronic inflammatory processes in the liver may be mediated by persistently activated macrophages and other immune cells, with concomitant overproduction of pro‐inflammatory cytokines such as tumour necrosis factor‐α. Activation of inflammatory pathways, together with increased levels of FFAs, can disrupt hepatocyte intracellular pathways and inhibit insulin signalling, leading to IR. Molecular studies have also shown that the HCV core protein can directly inhibit the insulin signalling pathway and increase reactive oxygen species production, both of which can further exacerbate IR. The available data provide an understanding of chronic HCV whereby chronic inflammatory processes, steatosis and IR contribute to each other, leading to an increased risk of DM, and its associated poor outcomes, in persons with chronic HCV.
Early in the HIV epidemic, lipodystrophy, characterized by subcutaneous fat loss (lipoatrophy), with or without central fat accumulation (lipohypertrophy), was recognized as a frequent condition ...among people living with HIV (PLWH) receiving combination antiretroviral therapy. The subsequent identification of thymidine analogue nucleoside reverse transcriptase inhibitors as the cause of lipoatrophy led to the development of newer antiretroviral agents; however, studies have demonstrated continued abnormalities in fat and/or lipid storage in PLWH treated with newer drugs (including integrase inhibitor-based regimens), with fat gain due to restoration to health in antiretroviral therapy-naive PLWH, which is compounded by the rising rates of obesity. The mechanisms of fat alterations in PLWH are complex, multifactorial and not fully understood, although they are known to result in part from the direct effects of HIV proteins and antiretroviral agents on adipocyte health, genetic factors, increased microbial translocation, changes in the adaptive immune milieu after infection, increased tissue inflammation and accelerated fibrosis. Management includes classical lifestyle alterations with a role for pharmacological therapies and surgery in some patients. Continued fat alterations in PLWH will have an important effect on lifespan, healthspan and quality of life as patients age worldwide, highlighting the need to investigate the critical uncertainties regarding pathophysiology, risk factors and management.
Although white AT can contribute to anti-infectious immune responses, it can also be targeted and perturbed by pathogens. The AT's immune involvement is primarily due to strong pro-inflammatory ...responses (with both local and paracrine effects), and the large number of fat-resident macrophages. Adipocytes also exert direct antimicrobial responses. In recent years, it has been found that memory T cells accumulate in AT, where they provide efficient secondary responses against viral pathogens. These observations have prompted researchers to re-evaluate the links between obesity and susceptibility to infections. In contrast, AT serves as a reservoir for several persistence pathogens, such as human adenovirus Ad-36,
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, influenza A virus, and cytomegalovirus (CMV). The presence and persistence of bacterial DNA in AT has led to the concept of a tissue-specific microbiota. The unexpected coexistence of immune cells and pathogens within the specific AT environment is intriguing, and its impact on anti-infectious immune responses requires further evaluation. AT has been recently identified as a site of HIV persistence. In the context of HIV infection, AT is targeted by both the virus and the antiretroviral drugs. AT's intrinsic metabolic features, large overall mass, and wide distribution make it a major tissue reservoir, and one that may contribute to the pathophysiology of chronic HIV infections. Here, we review the immune, metabolic, viral, and pharmacological aspects that contribute to HIV persistence in AT. We also evaluate the respective impacts of both intrinsic and HIV-induced factors on AT's involvement as a viral reservoir. Lastly, we examine the potential consequences of HIV persistence on the metabolic and immune activities of AT.
Adipose tissue is now recognized for its major role in the control of energy metabolism and insulin sensitivity. We review here the human lipodystrophies, that are rare conditions in which total or ...partial fat loss is associated with severe lipid and glucose abnormalities leading to diabetes with early cardiovascular and hepatic complications. The genetic origin of a number of human lipodystrophies has been recently unraveled, emphasizing the importance of proteins of previously unknown or unexpected functions. Major adipose functions were also illuminated when studying acquired forms of lipodystrophies linked to human immunodeficiency virus-antiretrovirals. Overall, most of the proteins or functions affected by mutations or antiretrovirals result in altered adipogenesis and insulin sensitivity, triglyceride storage and formation of the unique adipocyte lipid droplet, oxidative stress and fat remodeling. Some mutations or antiretrovirals could affect directly (peroxisome proliferator-activated receptor-γ, Akt2) or indirectly (lamin A/C, human immunodeficiency virus-protease inhibitors) adipogenesis, through the transcription factors peroxisome proliferator-activated receptor gamma-γ or sterol regulatory element binding protein 1c, and insulin signaling through Akt2 that controls adipocyte lipolysis. A number of proteins mutated in genetic lipodystrophies are involved in the control of triglyceride synthesis towards the lipid droplet (1-acylglycerol-3-phosphate-O-acyltransferase 2), or its functions (seipin, cell death-inducing DFF45-like effector C, perilipin, caveolin-1, cavin-1). Decreased triglyceride storage leads to adipocyte lipotoxicity, mitochondrial dysfunction and increased oxidative stress, which could also be induced by some thymidine analogue antiretrovirals. This results in production of inflammatory mediators and deregulated release of free fatty acids. Thus, the impaired ability of adipose tissue to safely store triglycerides inside the lipid droplet results in impaired insulin sensitivity and adverted liver, muscles and heart functions leading to early complications.
Two of the crucial aspects of human immunodeficiency virus (HIV) infection are (i) viral persistence in reservoirs (precluding viral eradication) and (ii) chronic inflammation (directly associated ...with all-cause morbidities in antiretroviral therapy (ART)-controlled HIV-infected patients). The objective of the present study was to assess the potential involvement of adipose tissue in these two aspects. Adipose tissue is composed of adipocytes and the stromal vascular fraction (SVF); the latter comprises immune cells such as CD4+ T cells and macrophages (both of which are important target cells for HIV). The inflammatory potential of adipose tissue has been extensively described in the context of obesity. During HIV infection, the inflammatory profile of adipose tissue has been revealed by the occurrence of lipodystrophies (primarily related to ART). Data on the impact of HIV on the SVF (especially in individuals not receiving ART) are scarce. We first analyzed the impact of simian immunodeficiency virus (SIV) infection on abdominal subcutaneous and visceral adipose tissues in SIVmac251 infected macaques and found that both adipocytes and adipose tissue immune cells were affected. The adipocyte density was elevated, and adipose tissue immune cells presented enhanced immune activation and/or inflammatory profiles. We detected cell-associated SIV DNA and RNA in the SVF and in sorted CD4+ T cells and macrophages from adipose tissue. We demonstrated that SVF cells (including CD4+ T cells) are infected in ART-controlled HIV-infected patients. Importantly, the production of HIV RNA was detected by in situ hybridization, and after the in vitro reactivation of sorted CD4+ T cells from adipose tissue. We thus identified adipose tissue as a crucial cofactor in both viral persistence and chronic immune activation/inflammation during HIV infection. These observations open up new therapeutic strategies for limiting the size of the viral reservoir and decreasing low-grade chronic inflammation via the modulation of adipose tissue-related pathways.
Aging HIV-infected antiretroviral-treatment (ART)-controlled patients often present cardiovascular and metabolic comorbidities. Thus, it is mandatory that life-long used ART has no cardiometabolic ...toxicity. Protease inhibitors have been associated with cardiometabolic risk, integrase-strand-transfer-inhibitors (INSTI) with weight gain and the CCR5 inhibitor maraviroc with improved vascular function. We have previously reported that the INSTI dolutegravir and maraviroc improved, and ritonavir-boosted atazanavir(atazanavir/r) worsened, inflammation and senescence in human coronary artery endothelial cells (HCAEC)s from adult controls. Here, we analyzed the pathways involved in the drugs' effects on inflammation, senescence and also insulin resistance.
We analyzed the involvement of the anti-inflammatory SIRT-1 pathway in HCAECs. Then, we performed a transcriptomic analysis of the effect of dolutegravir, maraviroc and atazanavir/r and used siRNA-silencing to address ubiquitin-specific-peptidase-18 (USP18) involvement into ART effects.
Dolutegravir reduced inflammation by decreasing NFκB activation and IL-6/IL-8/sICAM-1/sVCAM-1 secretion, as did maraviroc with a milder effect. However, when SIRT-1 was inhibited by splitomicin, the drugs anti-inflammatory effects were maintained, indicating that they were SIRT-1-independant. From the transcriptomic analysis we selected USP18, previously shown to decrease inflammation and insulin-resistance. USP18-silencing enhanced basal inflammation and senescence. Maraviroc still inhibited NFκB activation, cytokine/adhesion molecules secretion and senescence but the effects of dolutegravir and atazanavir/r were lost, suggesting that they involved USP18. Otherwise, in HCAECs, dolutegravir improved and atazanavir/r worsened insulin resistance while maraviroc had no effect. In USP18-silenced cells, basal insulin resistance was increased, but dolutegravir and atazanavir/r kept their effect on insulin sensitivity, indicating that USP18 was dispensable.
USP18 reduced basal inflammation, senescence and insulin resistance in coronary endothelial cells. Dolutegravir and atazanavir/r, but not maraviroc, exerted opposite effects on inflammation and senescence that involved USP18. Otherwise, dolutegravir improved and atazanavir/r worsened insulin resistance independently of USP18. Thus, in endothelial cells, dolutegravir and atazanavir/r oppositely affected pathways leading to inflammation, senescence and insulin resistance.
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