Hypoxia-inducible factor 2α drives nonalcoholic fatty liver progression by triggering hepatocyte release of histidine rich glycoprotein

Mechanisms underlying progression of non-alcoholic fatty liver disease (NAFLD) are still incompletely characterized. Hypoxia and hypoxia inducible factors (HIFs) have been implicated in the pathogenesis of chronic liver diseases but the actual role of HIF-2α in the evolution of NAFLD has never been investigated in detail. In this study, we show that HIF-2α is selectively overexpressed in the cytosol and the nuclei of hepatocytes in a very high percentage (> 90%) of liver biopsies from a cohort of NAFLD patients at different stage of the disease evolution. Similar features were also observed in mice with steatohepatitis induced by feeding a methionine/choline-deficient (MCD) diet. Experiments performed in mice carrying hepatocyte-specific deletion of HIF-2α and related control littermates fed with either choline-deficient L-amino acid-refined (CDAA) or MCD diets showed that HIF-2α deletion ameliorated the evolution of NAFLD by decreasing parenchymal injury, fatty liver, lobular inflammation and the development of liver fibrosis. The improvement in NAFLD progression in HIF-2α deficient mice was related to a selective down-regulation in the hepatocyte production of Histidine-Rich Glycoprotein (HRGP), recently proposed to sustain macrophage M1 polarization. In vitro experiments confirmed that the up-regulation of hepatocyte HRGP expression was hypoxia- and HIF-2α-dependent. Finally, analyses performed on specimens from NAFLD patients indicated that HRGP was overexpressed in all patients showing hepatocyte nuclear staining for HIF-2α and revealed a significant positive correlation between HIF-2α and HRGP liver transcripts levels in these patients

B2-Lymphocyte responses to oxidative stress-derived antigens contribute to the evolution of nonalcoholic fatty liver disease (NAFLD).

Recent evidence implicates adaptive immunity as a key player in the mechanisms supporting hepatic inflammation during the progression of nonalcoholic fatty liver disease (NAFLD). In these settings, patients with NAFLD often show an increase in the circulating levels of antibodies against oxidative stress-derived epitopes (OSE). Nonetheless, the actual role of humoral immunity in NAFLD is still unclear. This study investigates the contribution of B-lymphocytes to NAFLD evolution. B-lymphocyte immunostaining of liver biopsies from NAFLD patients showed that B-cells were evident within cell aggregates rich in T-lymphocytes. In these subjects, B/T-lymphocyte infiltration positively correlated with both circulating IgG targeting oxidative stress-derived epitopes (OSE) and interferon-γ (IFN-γ) levels. Furthermore, high prevalence of lymphocyte aggregates identified patients with more severe lobular inflammation and fibrosis. In mouse models of NAFLD, the onset of steatohepatitis was characterized by hepatic B2-lymphocytes maturation to plasma cells and by an elevation in circulating anti-OSE IgG titers. B-cell responses preceded T-cell activation and were accompanied by the up-regulation in the hepatic expression of B-cell Activating Factor (BAFF). Selective B2-cell depletion in mice over-expressing a soluble form of the BAFF/APRIL receptor Transmembrane Activator and Cyclophilin Ligand Interactor (TACI-Ig) prevented plasma cell maturation and Th-1 activation of liver CD4 <sup>+</sup> T-lymphocytes. Furthermore, TACI-Ig mice showed milder steatohepatitis and a decreased progression to fibrosis. Similarly, mice treatment with the BAFF-neutralizing monoclonal antibody Sandy-2 prevented hepatic B2-cell responses and ameliorated steatohepatitis. From these data we conclude that B2-lymphocyte activation is an early event in NAFLD evolution and contributes to the disease progression through the interaction with T-cells. Furthermore, combined clinical and experimental data suggest that elevated circulating anti-OSE IgG can identify a subset of NAFLD patients in whom adaptive immunity has a relevant role in the disease evolution toward fibrosis

Cancer bio‑immunotherapy XVI annual NIBIT‑(Italian Network for Tumor Biotherapy) meeting, October 11–13 2018, Milan, Italy

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