Non-alcoholic fatty liver disease (NAFLD) is characterised by defective lipid metabolism, inflammation, and hepatic fibrosis, and is closely associated with insulin resistance. These effects are partly mediated by the actions of liver-secreted proteins, also termed hepatokines. Given their pleiotropic actions, we hypothesised that unidentified hepatokines may elucidate therapeutic opportunities to resolve NAFLD-associated fibrosis. Herein, we characterise hepatokine secretion in worsening fibrosis in human NAFLD and evaluate the utility of Elastin microfibril interfacer 1 (EMILIN-1) for hepatic fibrosis treatment in murine NAFLD.
Liver was obtained from 118 patients undergoing bariatric surgery. NAFLD severity and fibrosis grade was assessed histologically. Precision-cut liver slices were prepared and proteomic analysis of hepatokines were performed using liquid chromatography tandem mass spectrometry. Gene editing in mice fed a methionine-choline deficient diet or a high fat, high-fructose and high cholesterol diet was performed using liver-target delivery of adeno-associated viruses. Hepatic fibrosis was assessed histologically, and NAFLD-associated co-morbidities were assessed.
We identified 3333 hepatokines, of which 2322 were detected following 80% completeness in all experimental groups. The secretion 15 hepatokines was altered with NAFLD and no fibrosis vs. NAFLD with significant fibrosis (grade F2-3), respectively. This screen identified EMILIN1, a hepatokine whose secretion was increased with worsening fibrosis severity and is previously reported to reduce the profibrotic cytokine, transforming growth factor β (TGFβ) signaling. Hepatocyte-specific overexpression of EMILIN1 in mice with severe NASH and advanced fibrosis reduced TGFβ signaling and hepatic fibrosis by ~50%, while siRNA-mediated reductions in EMILIN1 exacerbated fibrosis in MCD fed mice. EMILIN1 did not impact NAFLD co-morbidities including adiposity, insulin sensitivity and dyslipidemia.
These data provide a novel resource of hepatokine secretion from human livers and the impact of worsening fibrosis in NAFLD elucidating changes in a small subset of proteins. EMILIN1 was identified as a potential therapeutic target for liver fibrosis.