A novel hepatocyte SHP/CCL2 axis controls liver inflammation in NAFL to NASH transition

Objective Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide, ranging from simple steatosis or non‐alcoholic fatty liver (NAFL) to a more aggressive non‐alcoholic steatohepatitis (NASH) with an increased mortality. Understanding what drives the transition from NAFL to NASH is essential to develop effective prophylactic and therapeutic strategies for NASH. Small heterodimer partner (SHP, Nr0b2) is a unique nuclear receptor important for bile acid, lipid, and glucose metabolism. The aim for this study is to explore a novel mechanism by which hepatocyte SHP regulates liver inflammation during NAFL transition to NASH. Methods Human liver samples from patients with simple steatosis or NASH were used to examine SHP expression. To produce a mouse model of NASH, a diet high in fat, cholesterol, and fructose (HFCF) was given to 2 month‐old male mice. Hepatocyte‐specific overexpression of SHP was achieved by tail vein injection with adeno‐associated virus 8 (AAV8) expressing SHP, driven by the alpha‐1‐antitrypsin (AAT) promoter (AAV8‐AAT‐SHP). On the other hand, hepatocyte‐specific SHP‐deficiency was induced by the administration of AAV8 expressing Cre recombinase driven by the thyroxine‐binding globulin (Tbg) promoter (AAV8‐Tbg‐Cre) on the 2 month‐old male Shp flox/flox mice. The extent of steatosis, inflammation, and fibrosis were evaluated in liver tissues. Mouse primary hepatocytes and macrophage‐like RAW 264.7 cells were included to study mechanisms. Results SHP was decreased in human patients with NASH and in the dietary‐induced mouse model of NASH, suggesting a biological relevance of SHP function in NASH pathogenesis. Increasing hepatic SHP level via AAV8 mediated gene delivery ameliorated diet‐induced NASH progression. In contrast, hepatocyte‐specific deletion of Shp in adult mice ( Shp ‐HKO) resulted in infiltration of macrophages and CD4 + T cells into the liver, which was further supported by the activation of inflammatory signaling pathways in Shp ‐HKO as shown by RNA sequencing. As a result, hepatocyte‐specific Shp ‐deficiency sensitized the liver to diet‐induced inflammation and fibrosis with an attenuation of steatosis. As a proof of concept , in vitro deletion of SHP in mouse primary hepatocytes increased the secretion of chemokine (C‐C motif) ligand 2 (CCL2). Most importantly, the conditioned medium from Shp ‐deficient hepatocytes induced a pro‐inflammatory M1 polarization in RAW264.7 cells and promoted RAW264.7 cell migration. On a molecular level, SHP inhibited CCL2 expression through a direct inhibition of NFκB p65‐induced CCL2 transcription. Conclusions Our study uncovers a novel mechanism by which nuclear receptor SHP regulates hepatocyte and macrophage communication in the NAFL transition to NASH, which is mediated through inhibiting NFκB/CCL2 axis‐initiated macrophage activation. Support or Funding Information Grant support: NCI K22CA184146 and NIH P20 GM103549 to Yuxia Zhang.