Hepatocyte Hypoxia Inducible Factor-1 Mediates the Development of Liver Fibrosis in a Mouse Model of Nonalcoholic Fatty Liver Disease

Abstract

BackgroundObstructive sleep apnea (OSA) is associated with the progression of non-alcoholic fatty liver disease (NAFLD) to steatohepatitis and fibrosis. This progression correlates with the severity of OSA-associated hypoxia. In mice with diet induced obesity, hepatic steatosis leads to liver tissue hypoxia, which worsens with exposure to intermittent hypoxia. Emerging data has implicated hepatocyte cell signaling as an important factor in hepatic fibrogenesis. We hypothesized that hepatocyte specific knockout of the oxygen sensing α subunit of hypoxia inducible factor-1 (HIF-1), a master regulator of the global response to hypoxia, may be protective against the development of liver fibrosis.MethodsWild-type mice and mice with hepatocyte-specific HIF-1α knockout (Hif1a-/-hep) were fed a high trans-fat diet for six months, as a model of NAFLD. Hepatic fibrosis was evaluated by Sirius red stain and hydroxyproline assay. Liver enzymes, fasting insulin, and hepatic triglyceride content were also assessed. Hepatocytes were isolated from Hif1a-/-hep mice and wild-type controls and were exposed to sustained hypoxia (1% O2) or normoxia (16% O2) for 24 hours. The culture media was used to reconstitute type I collagen and the resulting matrices were examined for collagen cross-linking.ResultsWild-type mice on a high trans-fat diet had 80% more hepatic collagen than Hif1a-/-hep mice (2.21 μg collagen/mg liver tissue, versus 1.23 μg collagen/mg liver tissue, p = 0.03), which was confirmed by Sirius red staining. Body weight, liver weight, mean hepatic triglyceride content, and fasting insulin were similar between groups. Culture media from wild-type mouse hepatocytes exposed to hypoxia allowed for avid collagen cross-linking, but very little cross-linking was seen when hepatocytes were exposed to normoxia, or when hepatocytes from Hif1a-/-hep mice were used in hypoxia or normoxia.ConclusionsHepatocyte HIF-1 mediates an increase in liver fibrosis in a mouse model of NAFLD, perhaps due to liver tissue hypoxia in hepatic steatosis. HIF-1 is necessary for collagen cross-linking in an in vitro model of fibrosis.

Specific Commensal Bacterium Critically Regulates Gut Microbiota Osteoimmunomodulatory Actions During Normal Postpubertal Skeletal Growth and Maturation

“…Cxcl1 , Cxcl11 , Hif1a , Col4a1 , and Fn1 were unexpectedly elevated in the liver of MPF versus EF mice, suggesting that SFB within the complex commensal gut microbiota leads to proinflammatory innate immune response effects in the liver. Astonishingly, these findings are in line with seminal reports demonstrating that CXCL1, CXCL11, HIF1A, COL4A1, and FN1 are implicated in liver fibrosis …”

“…Interestingly, CXCL11 has also been shown to endorse T H 1 cell proinflammatory cytokine production and facilitate T H 17 cell development in an experimental colitis model . Hypoxia inducible factor 1 ( Hif1a ), collagen type IV ( Col4a1 ), and fibronectin ( Fn1 ) are profibrotic factors that promote liver fibrosis . Considering that SFB colonization within a complex gut microbiota increased serum IL17A levels (Fig.…”

Blood-Stage Plasmodium Berghei ANKA Infection Promotes Hepatic Fibrosis by Enhancing Hedgehog Signaling in Mice

“…1F). Under hypoxic conditions, hepatocytes undergo apoptosis, whereas HSCs are activated and proliferate [47][48][49][50]. These apoptotic hepatocytes release various cytokines to stimulate HSCs and inflammation [16,17].…”

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

“…On the other hand, despite the fact that HIF-1a appears to sustain fibrogenesis in the bile duct ligation experimental model of CLD, (20) other studies designed to specifically target hepatocyte HIF-1a in experimental models of alcohol-related or NAFLD-related steatosis and progression have led to conflicting results. (21)(22)(23)(24) In this study, the analysis of liver biopsies from a cohort of NAFLD patients and the induction of experimental NAFLD with two different dietary protocols in mice carrying hepatocyte-specific deletion of HIF-2a provide evidence indicating that HIF-2a plays a critical role in NAFLD progression by up-regulating hepatocyte expression of histidine-rich glycoprotein (HRGP).…”

“…At present, relevant human data about the role of HIF‐2α in fatty liver development and NAFLD progression are lacking. On the other hand, despite the fact that HIF‐1α appears to sustain fibrogenesis in the bile duct ligation experimental model of CLD, other studies designed to specifically target hepatocyte HIF‐1α in experimental models of alcohol‐related or NAFLD‐related steatosis and progression have led to conflicting results …”