Macrophage‐Specific Hypoxia‐Inducible Factor‐1α Contributes to Impaired Autophagic Flux in Nonalcoholic Steatohepatitis

Inflammatory cell activation drives diverse cellular programming during hepatic diseases. Hypoxia-inducible factors (HIFs) have recently been identified as important regulators of immunity and inflammation. In non-alcoholic steatohepatitis (NASH), HIF-1α is upregulated in hepatocytes where it induces steatosis; however, the role of HIF-1α in macrophages under metabolic stress has not been explored. In this study, we found increased HIF-1α levels in hepatic macrophages in methionine-choline-deficient (MCD) diet-fed mice and in macrophages of NASH patients compared to controls. The HIF-1α increase was concomitant with elevated levels of autophagy markers BNIP3, Beclin-1, LC3-II, and p62 both in mouse and human macrophages. LysMCre-HIFdPAfl/fl mice, which have HIF-1α levels stabilized in macrophages, showed higher steatosis and liver inflammation compared to HIFdPAfl/fl mice on MCD diet. In vitro and ex vivo experiments reveal that saturated fatty acid, palmitic acid (PA), induces both HIF-1α and impairs autophagic flux in macrophages. Using siRNA-mediated knock-down and over-expression of HIF-1α in macrophages, we demonstrated that PA impairs autophagy via HIF-1α. We found that HIF-1α mediates NF-κB activation and MCP-1 production and that HIF-1α mediated impairment of macrophage autophagy increases IL-1β production contributing to MCD diet-induced NASH. Conclusions Palmitic acid impairs autophagy via HIF-1α activation in macrophages. HIF-1α and impaired autophagy are present in NASH in vivo in mouse macrophages and in human blood monocytes. We identified that HIF-1α activation and decreased autophagic flux stimulate inflammation in macrophages through upregulation of NF-κB activation. These results suggest that macrophage activation in NASH involves a complex interplay between HIF-1α and autophagy as these pathways promote proinflammatory overactivation in MCD diet-induced NASH.