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 nonalcoholic steatohepatitis (NASH), HIF-1 alpha is upregulated in hepatocytes, where it induces steatosis; however, the role of HIF-1 alpha in macrophages under metabolic stress has not been explored. In this study, we found increased HIF-1 alpha levels in hepatic macrophages in methionine-choline-deficient (MCD) diet-fed mice and in macrophages of patients with NASH compared with controls. The HIF-1 alpha increase was concomitant with elevated levels of autophagy markers BNIP3, Beclin-1, LC3-II, and p62 in both mouse and human macrophages. LysM(Cre) HIF(dPA)fl/fl mice, which have HIF-1 alpha levels stabilized in macrophages, showed higher steatosis and liver inflammation compared with HIF(dPA)fl/fl mice on MCD diet. In vitro and ex vivo experiments reveal that saturated fatty acid, palmitic acid (PA), both induces HIF-1 alpha and impairs autophagic flux in macrophages. Using small interfering RNA-mediated knock-down and overexpression of HIF-1 alpha in macrophages, we demonstrated that PA impairs autophagy via HIF-1 alpha. We found that HIF-1 alpha mediates NF-kappa B activation and MCP-1 production and that HIF-1 alpha-mediated impairment of macrophage autophagy increases IL-1 beta production, contributing to MCD diet-induced NASH. Conclusion: Palmitic acid impairs autophagy via HIF-1 alpha activation in macrophages. HIF-1 alpha and impaired autophagy are present in NASH in vivo in mouse macrophages and in human blood monocytes. We identified that HIF-1 alpha activation and decreased autophagic flux stimulate inflammation in macrophages through upregulation of NF-kappa B activation. These results suggest that macrophage activation in NASH involves a complex interplay between HIF-1 alpha and autophagy as these pathways promote proinflammatory overactivation in MCD diet-induced NASH.