Circulating indian hedgehog is a marker of the hepatocyte-TAZ pathway in experimental NASH and is elevated in humans with NASH

Background & aims: Non-alcoholic steatohepatitis (NASH)-induced liver fibrosis is emerging as the most common cause of liver disease. For evaluation of therapies, there is a pressing need to identify non-invasive, mechanism-based biomarkers. A pro-fibrotic process relevant to human NASH involves a pathway in which a transcriptional regulator called TAZ (WWTR1) in hepatocytes induces the secretion of pro-fibrotic Indian hedgehog (IHH). We therefore reasoned that circulating IHH may be a useful mechanism-based marker to assess changes in NASH fibrosis. Methods: Circulating IHH was assessed in wild-type and hepatocyte-TAZ-silenced NASH mice and in three separate cohorts of patients with mild-moderate NASH. Results: Circulating IHH was elevated in mice with diet-induced NASH compared with chow-fed mice or with NASH mice in which hepatocyte TAZ was silenced, which is an effective means to decrease NASH fibrosis. In patients with fatty liver disease with or without NASH, NASH fibrosis was associated with increased concentrations of circulating IHH. Conclusions: The results of these analyses support further investigation to determine whether circulating IHH may be useful as a mechanism-based indicator of target engagement in anticipated future clinical trials testing NASH fibrosis therapies that block the IHH pathway. Impact and implications: Non-alcoholic steatohepatitis (NASH)-induced liver fibrosis is a common cause of liver disease. Circulating biomarkers that reflect liver fibrosis in NASH would be very useful to evaluate therapies. One mechanism of NASH fibrosis with potential as a therapeutic target involves a liver-secreted protein called Indian hedgehog (IHH). We report that circulating levels of IHH in experimental and human NASH associates with NASH and NASH-associated liver fibrosis, providing the premise for further investigation into using circulating IHH to evaluate anticipated future NASH therapies that block the IHH pathway in liver.