MIF is an inflammatory cytokine but is hepatoprotective in models of hepatotoxin-induced liver fibrosis. Hepatic fibrosis can also develop from metabolic liver disease, such as nonalcoholic fatty liver disease (NASH). We investigated the role of MIF in high-fat or methionine- and choline-deficient diet mouse models of NASH. Mif(-/-) mice showed elevated liver triglyceride levels (WT, 53±14 mg/g liver; Mif(-/-), 103±7 mg/g liver; P<0.05) and a 2-3-fold increased expression of lipogenic genes. Increased fatty degeneration in the livers of Mif(-/-) mice was associated with increased hepatic inflammatory cells (1.6-fold increase in F4/80(+) macrophages) and proinflammatory cytokines (e.g., 2.3-fold increase in Tnf-α and 2-fold increase in Il-6 expression). However, inflammatory cells and cytokines were decreased by 50-90% in white adipose tissue (WAT) of Mif(-/-) mice. Subset analysis showed that macrophage phenotypes in livers of Mif(-/-) mice were skewed toward M2 (e.g., 1.7-fold and 2.5-fold increase in Arg1 and Il-13, respectively, and 2.5-fold decrease in iNos), whereas macrophages were generally reduced in WAT of these mice (70% reduction in mRNA expression of F4/80(+) macrophages). The protective MIF effect was scrutinized in isolated hepatocytes. MIF reversed inflammation-induced triglyceride accumulation in Hepa1-6 cells and primary hepatocytes and also attenuated oleic acid-elicited triglyceride increase in 3T3-L1 adipocytes. Protection from fatty hepatocyte degeneration was paralleled by a 2- to 3-fold reduction by MIF of hepatocyte proinflammatory cytokine production. Blockade of MIF receptor cluster of differentiation 74 (CD74) but not of CXCR2 or CXCR4 fully reverted the protective effect of MIF, comparable to AMPK inhibition. In summary, we demonstrate that MIF mediates hepatoprotection through the CD74/AMPK pathway in hepatocytes in metabolic models of liver injury.
Keywords: cytokines; fatty liver; hepatic fibrosis; hepatocyte; inflammation.