Roles of Macrophages in Advanced Liver Fibrosis, Identified Using a Newly Established Mouse Model of Diet-Induced Non-Alcoholic Steatohepatitis.

Macrophages play critical roles in the pathogenesis of non-alcoholic steatohepatitis (NASH). However, it is unclear which macrophage subsets are critically involved in the development of inflammation and fibrosis in NASH. In TSNO mice fed a high-fat/cholesterol/cholate-based diet, which exhibit advanced liver fibrosis that mimics human NASH, we found that Kupffer cells (KCs) were less abundant and recruited macrophages were more abundant, forming hepatic crown-like structures (hCLS) in the liver. The recruited macrophages comprised two subsets: CD11c+/Ly6C- and CD11c-/Ly6C+ cells. CD11c+ cells were present in a mesh-like pattern around the lipid droplets, constituting the hCLS. In addition, CD11c+ cells colocalized with collagen fibers, suggesting that this subset of recruited macrophages might promote advanced liver fibrosis. In contrast, Ly6C+ cells were present in doughnut-like inflammatory lesions, with a lipid droplet in the center. Finally, RNA sequence analysis indicates that CD11c+/Ly6C- cells promote liver fibrosis and hepatic stellate cell (HSC) activation, whereas CD11c-/Ly6C+ cells are a macrophage subset that play an anti-inflammatory role and promote tissue repair in NASH. Taken together, our data revealed changes in liver macrophage subsets during the development of NASH and shed light on the roles of the recruited macrophages in the pathogenesis of advanced fibrosis in NASH.

Dynamics of Liver Macrophage Subsets in a Novel Mouse Model of Non-Alcoholic Steatohepatitis Using C57BL/6 Mice.

Macrophages are critical for the development of non-alcoholic steatohepatitis (NASH). Our previous findings in TSNO mouse livers showed that an iHFC (high-fat/cholesterol/cholate) diet induced liver fibrosis similar to human NASH and led to the accumulation of distinct subsets of macrophage: CD11c+/Ly6C- and CD11c-/Ly6C+ cells. CD11c+/Ly6C- cells were associated with the promotion of advanced liver fibrosis in NASH. On the other hand, CD11c-/Ly6C+ cells exhibited an anti-inflammatory effect and were involved in tissue remodeling processes. This study aimed to elucidate whether an iHFC diet with reduced cholic acid (iHFC#2 diet) induces NASH in C57BL/6 mice and examine the macrophage subsets accumulating in the liver. Histological and quantitative real-time PCR analyses revealed that the iHFC#2 diet promoted inflammation and fibrosis indicative of NASH in the livers of C57BL/6 mice. Cell numbers of Kupffer cells decreased and recruited macrophages were accumulated in the livers of iHFC#2 diet-fed C57BL/6 mice. Notably, the iHFC#2 diet resulted in the accumulation of three macrophage subsets in the livers of C57BL/6 mice: CD11c+/Ly6C-, CD11c-/Ly6C+, and CD11c+/Ly6C+ cells. However, CD11c+/Ly6C+ cells were not distinct populations in the iHFC-fed TSNO mice. Thus, differences in cholic acid content and mouse strain affect the macrophage subsets that accumulate in the liver.