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Background & Aims: Molecular mechanisms by which hypoxia might contribute to hepatosteatosis, the earliest stage in non-alcoholic fatty liver disease (NAFLD) pathogenesis, remain still to be elucidated. We aimed to assess the impact of hypoxia-inducible factor 2α (HIF2α) on the fatty acid translocase CD36 expression and function in vivo and in vitro. Methods: CD36 expression and intracellular lipid content were determined in hypoxic hepatocytes, and in hypoxic CD36- or HIF2α -silenced human liver cells. Histological analysis, and HIF2α and CD36 expression were evaluated in livers from animals in which von Hippel-Lindau (Vhl) gene is inactivated (Vhl -deficient mice), or both Vhl and Hif2a are simultaneously inactivated (Vhl Hif2α -deficient mice), and from 33 biopsy-proven NAFLD patients and 18 subjects with histologically normal liver. Results: In hypoxic hepatocytes, CD36 expression and intracellular lipid content were augmented. Noteworthy, CD36 knockdown significantly reduced lipid accumulation, and HIF2A gene silencing markedly reverted both hypoxia-induced events in hypoxic liver cells. Moreover livers from Vhl -deficient mice showed histologic characteristics of non-alcoholic steatohepatitis (NASH) and increased CD36 mRNA and protein amounts, whereas both significantly decreased and NASH features markedly ameliorated in Vhl Hif2α -deficient mice. In addition, both HIF2α and CD36 were significantly overexpressed within the liver of NAFLD patients and, interestingly, a significant positive correlation between hepatic transcript levels of CD36 and erythropoietin (EPO), a HIF2α -dependent gene target, was observed in NAFLD patients. Conclusions: This study provides evidence that HIF2α drives lipid accumulation in human hepatocytes by upregulating CD36 expression and function, and could contribute to hepatosteatosis setup. f/f f/f /f f/f f/f f/f, This work was supported by PI13/01299, PI17/00535 and CIBEREHD from Instituto de Salud Carlos III (ISCIII/FEDER, Spain) to CGM; CP14/00181, PI16/00823 and PI19/00123 (ISCIII/FEDER, Spain), and Beca Eduardo Gallego 2016 (Fundación Francisco Cobos, Spain) to AGR; SAF2016-76815 (Ministerio de Economía y Competitividad/FEDER, Spain), 534/C/2016 (TV3 Marató, Spain) and CIBERCV (ISCIII/FEDER, Spain) to JA.

Introduction: Pulmonary epithelium is the first contact line with oxygen but the role of hypoxia-inducible factors (HIFs) in the airway’s primary response to oxygen fluctuations as well as cigarette smoke remains largely unknown. The lung exhibits the highest levels of HIF2α, which is the main regulator of renal erythropoietin (Epo) in response to hypoxia. Objectives: Here, we first explored whether HIF2a isoform could also induce Epo in the lung as a compensatory response to hypoxia and second, whether the HIF-dependent program could also be induced in other scenarios different from hypoxia such as cigarrete smoke exposure. Methods: We used mouse models of loss and gain of function of HIF2a pathway as well as mice exposure to atmospheric hypoxia and cigarette smoke. Lung tissues from these mice were subjected to protein and RNA analysis as well as immunohistochemistry analysis. Results: Our novel data shows that lung induces Epo expression in response to hypoxia as well as upon constitutive activation of the HIF pathway. Importantly, this extra-renal source of erythropoietin (Epo) is completely dependent on the HIF2a isoform and mainly confined in the bronchial epithelium. Regarding the relevance of HIF2a in bronchial epithelium, we previously showed that HIF2a-dependent genes such as Resistin-like molecular-alpha (RELM-a) are induced in Club cells in response to hypoxia. Significantly our latest data also shows that RELM-a and other HIF-dependent genes are also remarkably induced in cigarette smoke-exposed mice. Conclusions: Our findings have unveiled that bronchial epithelium acts as an extra-renal source of Epo and suggests the role of airway HIF expression in response to cigarette smoke exposure.

Aging is associated with progressive white adipose tissue (WAT) enlargement initiated early in life, but the molecular mechanisms involved remain unknown. Here we show that mitochondrial complex IV (CIV) activity and assembly are already repressed in white adipocytes of middle-aged mice and involve a HIF1A-dependent decline of essential CIV components such as COX5B. At the molecular level, HIF1A binds to the Cox5b proximal promoter and represses its expression. Silencing of Cox5b decreased fatty acid oxidation and promoted intracellular lipid accumulation. Moreover, local in vivo Cox5b silencing in WAT of young mice increased the size of adipocytes, whereas restoration of COX5B expression in aging mice counteracted adipocyte enlargement. An age-dependent reduction in COX5B gene expression was also found in human visceral adipose tissue. Collectively, our findings establish a pivotal role for CIV dysfunction in progressive white adipocyte enlargement during aging, which can be restored to alleviate age-dependent WAT expansion., Cell Reports, 16 (11), ISSN:2666-3864, ISSN:2211-1247

Aims Hypoxic conditions stimulate pulmonary vasoconstriction and vascular remodelling, both pathognomonic changes in pulmonary arterial hypertension (PAH). The secreted protein thrombospondin-1 (TSP1) is involved in the maintenance of lung homeostasis. New work identified a role for TSP1 in promoting PAH. Nonetheless, it is largely unknown how hypoxia regulates TSP1 in the lung and whether this contributes to pathological events during PAH. Methods and results In cell and animal experiments, we found that hypoxia induces TSP1 in lungs, pulmonary artery smooth muscle cells and endothelial cells, and pulmonary fibroblasts. Using a murine model of constitutive hypoxia, gene silencing, and luciferase reporter experiments, we found that hypoxia-mediated induction of pulmonary TSP1 is a hypoxia-inducible factor (HIF)-2α-dependent process. Additionally, hypoxic tsp1−/− pulmonary fibroblasts and pulmonary artery smooth muscle cell displayed decreased migration compared with wild-type (WT) cells. Furthermore, hypoxia-mediated induction of TSP1 destabilized endothelial cell–cell interactions. This provides genetic evidence that TSP1 contributes to vascular remodelling during PAH. Expanding cell data to whole tissues, we found that, under hypoxia, pulmonary arteries (PAs) from WT mice had significantly decreased sensitivity to acetylcholine (Ach)-stimulated endothelial-dependent vasodilation. In contrast, hypoxic tsp1 −/− PAs retained sensitivity to Ach, mediated in part by TSP1 regulation of pulmonary Kv channels. Translating these preclinical studies, we find in the lungs from individuals with end-stage PAH, both TSP1 and HIF-2α protein expression increased in the pulmonary vasculature compared with non-PAH controls. Conclusions These findings demonstrate that HIF-2α is clearly implicated in the TSP1 pulmonary regulation and provide new insights on its contribution to PAH-driven vascular remodelling and vasoconstriction.