PPARs and Adipose Cell Plasticity

Cardiovascular computed tomography and HIV: The evolving role of imaging biomarkers in enhanced risk prediction

The treatment of human immunodeficiency virus (HIV) with antiretroviral (ARV) medications has revolutionised the care for these patients. The dramatic increase in life expectancy has brought new challenges in treating diseases of aging in this cohort. Cardiovascular disease (CVD) is now a leading cause of morbidity and mortality with risk matched HIV-positive patients having double the risk of MI compared to HIV-negative patients. This enhanced risk is secondary to the interplay the virus (and accessory proteins), ARV medications and traditional risk factors. The culmination of these factors can lead to a hybrid metabolic syndrome characterised by heightened ectopic fat. Cardiovascular computed tomography (CT) is ideal for quantifying epicardial adipose tissue volumes, hepatosteatosis and cardiovascular disease burden. The CVD risk attributed to disease burden and plaque morphology is well established in general populations but is less clear in HIV populations. The purpose of this review article is to appraise the latest data on CVD development in HIV-positive patients and how the use of cardiovascular CT may be used to enhance risk prediction in this population. This may have important implications on individualised treatment decisions and risk reduction strategies which will improve the care of these patients.

Inflammation and Metabolic Complications in HIV

PURPOSE OF REVIEW

We aim to provide an in-depth review of recent literature highlighting the role of inflammation involving the adipose tissue, liver, skeletal muscles, and gastrointestinal tract in the development of metabolic complications among persons living with HIV (PLWH).

RECENT FINDINGS

Recent studies in PLWH have demonstrated a significant association between circulating inflammatory markers and development of insulin resistance and metabolic complications. In adipose tissue, pro-inflammatory cytokine expression inhibits adipocyte insulin signaling, which alters lipid and glucose homeostasis. Increased lipolysis and lipogenesis elevate levels of circulating free fatty acids and promote ectopic fat deposition in liver and skeletal muscles. This leads to lipotoxicity characterized by a pro-inflammatory response with worsening insulin resistance. Finally, HIV is associated with gastrointestinal tract inflammation and changes in the gut microbiome resulting in reduced diversity, which is an additional risk factor for diabetes. Metabolic complications in PLWH are in part due to chronic, multisite tissue inflammation resulting in dysregulation of glucose and lipid trafficking, utilization, and storage.

Adipose Tissue is Enriched for Activated and Late-Differentiated CD8+ T Cells and Shows Distinct CD8+ Receptor Usage, Compared With Blood in HIV-Infected Persons

BACKGROUND

Adverse viral and medication effects on adipose tissue contribute to the development of metabolic disease in HIV-infected persons, but T cells also have a central role modulating local inflammation and adipocyte function. We sought to characterize potentially proinflammatory T-cell populations in adipose tissue among persons on long-term antiretroviral therapy and assess whether adipose tissue CD8 T cells represent an expanded, oligoclonal population.

METHODS

We recruited 10 HIV-infected, non-diabetic, overweight or obese adults on efavirenz, tenofovir, and emtricitabine for >4 years with consistent viral suppression. We collected fasting blood and subcutaneous abdominal adipose tissue to measure the percentage of CD4 and CD8 T cells expressing activation, exhaustion, late differentiation/senescence, and memory surface markers. We performed T-cell receptor (TCR) sequencing on sorted CD8 cells. We compared the proportion of each T-cell subset and the TCR repertoire diversity, in blood versus adipose tissue.

RESULTS

Adipose tissue had a higher percentage of CD3CD8 T cells compared with blood (61.0% vs. 51.7%, P < 0.01) and was enriched for both activated CD8HLA-DR T cells (5.5% vs. 0.9%, P < 0.01) and late-differentiated CD8CD57 T cells (37.4% vs. 22.7%, P < 0.01). Adipose tissue CD8 T cells displayed distinct TCRβ V and J gene usage, and the Shannon Entropy index, a measure of overall TCRβ repertoire diversity, was lower compared with blood (4.39 vs. 4.46; P = 0.05).

CONCLUSIONS

Adipose tissue is enriched for activated and late-differentiated CD8 T cells with distinct TCR usage. These cells may contribute to tissue inflammation and impaired adipocyte fitness in HIV-infected persons.

Adipose Tissue in HIV Infection

HIV infection and antiretroviral therapy (ART) treatment exert diverse effects on adipocytes and stromal-vascular fraction cells, leading to changes in adipose tissue quantity, distribution, and energy storage. A HIV-associated lipodystrophic condition was recognized early in the epidemic, characterized by clinically apparent changes in subcutaneous, visceral, and dorsocervical adipose depots. Underlying these changes is altered adipose tissue morphology and expression of genes central to adipocyte maturation, regulation, metabolism, and cytokine signaling. HIV viral proteins persist in circulation and locally within adipose tissue despite suppression of plasma viremia on ART, and exposure to these proteins impairs preadipocyte maturation and reduces adipocyte expression of peroxisome proliferator-activated receptor gamma (PPAR-γ) and other genes involved in cell regulation. Several early nucleoside reverse transcriptase inhibitor and protease inhibitor antiretroviral drugs demonstrated substantial adipocyte toxicity, including reduced mitochondrial DNA content and respiratory chain enzymes, reduced PPAR-γ and other regulatory gene expression, and increased proinflammatory cytokine production. Newer-generation agents, such as integrase inhibitors, appear to have fewer adverse effects. HIV infection also alters the balance of CD4+ and CD8+ T cells in adipose tissue, with effects on macrophage activation and local inflammation, while the presence of latently infected CD4+ T cells in adipose tissue may constitute a protected viral reservoir. This review provides a synthesis of the literature on how HIV virus, ART treatment, and host characteristics interact to affect adipose tissue distribution, immunology, and contribution to metabolic health, and adipocyte maturation, cellular regulation, and energy storage. © 2017 American Physiological Society. Compr Physiol 7:1339-1357, 2017.

Increased adipogenesis in cultured embryonic chondrocytes and in adult bone marrow of dominant negative Erg transgenic mice

In monolayer culture, primary articular chondrocytes have an intrinsic tendency to lose their phenotype during expansion. The molecular events underlying this chondrocyte dedifferentiation are still largely unknown. Several transcription factors are important for chondrocyte differentiation. The Ets transcription factor family may be involved in skeletal development. One family member, the Erg gene, is mainly expressed during cartilage formation. To further investigate the potential role of Erg in the maintenance of the chondrocyte phenotype, we isolated and cultured chondrocytes from the rib cartilage of embryos of transgenic mice that express a dominant negative form of Erg (DN-Erg) during cartilage formation. DN-Erg expression in chondrocytes cultured for up to 20 days did not affect the early dedifferentiation usually observed in cultured chondrocytes. However, lipid droplets accumulated in DN-Erg chondrocytes, suggesting adipocyte emergence. Transcriptomic analysis using a DNA microarray, validated by quantitative RT-PCR, revealed strong differential gene expression, with a decrease in chondrogenesis-related markers and an increase in adipogenesis-related gene expression in cultured DN-Erg chondrocytes. These results indicate that Erg is involved in either maintaining the chondrogenic phenotype in vitro or in cell fate orientation. Along with the in vitro studies, we compared adipocyte presence in wild-type and transgenic mice skeletons. Histological investigations revealed an increase in the number of adipocytes in the bone marrow of adult DN-Erg mice even though no adipocytes were detected in embryonic cartilage or bone. These findings suggest that the Ets transcription factor family may contribute to the homeostatic balance in skeleton cell plasticity.

EGF and bFGF pre-treatment enhances neural specification and the response to neuronal commitment of MIAMI cells

AIMS

Multipotent mesenchymal stromal cells raise great interest for regenerative medicine studies. Some MSC subpopulations have the potential to undergo neural differentiation, including marrow isolated adult multilineage inducible (MIAMI) cells, which differentiate into neuron-like cells in a multi-step neurotrophin 3-dependent manner. Epidermal and basic fibroblast growth factors are often used in neuronal differentiation protocols for MSCs, but with a limited understanding of their role. In this study, we thoroughly assessed for the first time the capacity of these factors to enhance the neuronal differentiation of MSCs.

MATERIALS AND METHODS

We have characterized MIAMI cell neuronal differentiation program in terms of stem cell molecule expression, cell cycle modifications, acquisition of a neuronal morphology and expression of neural and neuronal molecules in the absence and presence of an EGF-bFGF pre-treatment.

RESULTS

EGF-bFGF pre-treatment down-regulated the expression of stemness markers Oct4A, Notch1 and Hes5, whereas neural/neuronal molecules Nestin, Pax6, Ngn2 and the neurotrophin receptor tyrosine kinase 1 and 3 were up-regulated. During differentiation, a sustained Erk phosphorylation in response to NT3 was observed, cells began to exit from the cell cycle and exhibit increased neurite-like extensions. In addition, neuronal β3-tubulin and neurofilament expression was increased; an effect mediated via the Erk pathway. A slight pre-oligodendrocyte engagement was noted, and no default neurotransmitter phenotype was observed. Overall, mesodermal markers were unaffected or decreased, while neurogenic/adipogenic PPARγ2 was increased.

CONCLUSION

EGF and bFGF pre-treatment enhances neural specification and the response to neuronal commitment of MIAMI cells, further increasing their potential use in adult cell therapy of the nervous system.

Antiretroviral-related adipocyte dysfunction and lipodystrophy in HIV-infected patients: Alteration of the PPARγ-dependent pathways

Lipodystrophy and metabolic alterations are major complications of antiretroviral therapy in HIV-infected patients. In vitro studies using cultured murine and human adipocytes revealed that some protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs) were implicated to a different extent in adipose cell dysfunction and that a chronic incubation with some PIs decreased mRNA and protein expression of PPARγ. Defective lamin A maturation linked to PI inhibitory activity could impede the nuclear translocation of SREBP1c, therefore, reducing PPARγ expression. Adipose cell function was partially restored by the PPARγ agonists, thiazolidinediones. Adverse effects of PIs and NRTIs have also been reported in macrophages, a cell type that coexists with, and modulates, adipocyte function in fat tissue. In HIV-infected patients under ART, a decreased expression of PPARγ and of PPARγ-related genes was observed in adipose tissue, these anomalies being more severe in patients with ART-induced lipoatrophy. Altered PPARγ expression was reversed in patients stopping PIs. Treatment of patients with agonists of PPARγ could improve, at least partially, the subcutaneous lipoatrophy. These data indicate that decreased PPARγ expression and PPARγ-related function, resulting from ART-induced adipose tissue toxicity, play a central role in HIV-related lipoatrophy and metabolic consequences.