NKT-associated hedgehog and osteopontin drive fibrogenesis in non-alcoholic fatty liver disease

Abstract

Immune responses are important in dictating nonalcoholic steatohepatitis (NASH) outcome. We previously reported that upregulation of hedgehog (Hh) and osteopontin (OPN) occurs in NASH, that Hh-regulated accumulation of natural killer T (NKT) cells promotes hepatic stellate cell (HSC) activation, and that cirrhotic livers harbor large numbers of NKT cells. Here, we evaluated the hypothesis that activated NKT cells drive fibrogenesis during NASH by assessing if NKT depletion protects against NASH-fibrosis; identifying the NKT associated fibrogenic factors; and correlating plasma levels of the NKT cell-associated factor OPN with fibrosis severity in mice and humans. When fed methionine choline deficient (MCD) diets for 8 weeks, WT mice exhibited Hh pathway activation, enhanced OPN expression, and NASH-fibrosis. Jα18−/− and CD1d−/− mice which lack NKT cells had significantly attenuated Hh and OPN expression and dramatically less fibrosis. Liver mononuclear cells (LMNC) from MCD diet-fed WT mice contained activated NKT cells, generated Hh and OPN, and stimulated hepatic stellate cells (HSC) to become myofibroblasts (MF); neutralizing these factors abrogated the fibrogenic actions of WT LMNC. LMNC from NKT cell deficient mice were deficient in fibrogenic factors, failing to activate collagen gene expression in HSC. Human NASH livers with advanced fibrosis contained more OPN and Hh protein than those with early fibrosis. Plasma levels of OPN mirrored hepatic OPN expression, and correlated with fibrosis severity. In conclusion, hepatic NKT cells drive production of OPN and Hh ligands that promote fibrogenesis during NASH. Associated increases in plasma levels of OPN may provide a biomarker of NASH-fibrosis.

Chemokine Receptor CXCR6-Dependent Hepatic NK T Cell Accumulation Promotes Inflammation and Liver Fibrosis

“…Prior studies have suggested hepatic endothelium as the major source of CXCL16 in the liver in homeostasis (15), and cholangiocyte-derived CXCL16, secreted following Hedgehogpathway-dependent crosstalk with HSC, as a strong stimulus for NKT cell migration in injury (31,32). In our study, we could clearly demonstrate that also monocyte-derived inflammatory macrophages and resident Kupffer cells (defined as reported in Ref.…”

Osteopontin: A non-invasive parameter of portal hypertension and prognostic marker of cirrhosis

“…OPN also delays liver fibrosis resolution due to sustained fibrillar collagen-I deposition in mice after thioacetamide-induced fibrosis [7] . Recently, plasma OPN levels have been found to predict liver fibrosis in various chronic liver diseases, such as NASH [11] , alcoholic liver disease [12] , and chronic viral hepatitis B [13] and C [14] . Pereira et al [21] have also demonstrated that OPN secretion could be stimulated by Schistosoma mansoni and that serum OPN levels correlated with splenic vein pressure and liver fibrosis stage in patients with schistosomiasis.…”

“…In fact, plasma OPN levels have been found to be significantly elevated in patients with liver cirrhosis and HCC compared to those without HCC [10] . Recently, plasma OPN levels were shown to predict liver fibrosis in various chronic liver diseases, such as non-alcoholic steatohepatitis [11] , alcoholic liver disease [12] , and chronic viral hepatitis B [13] and C [14] . As OPN levels correlate significantly with the fibrosis stage in alcohol-induced liver disease [12] , it follows that OPN levels could be related to the degree of portal hypertension and, hence, serve as a surrogate non-invasive marker of portal hypertension.…”

Evolving therapies for liver fibrosis

“…With the exception of infant fibrosis (biliary atresia, Caroli's disease, congenital hepatic fibrosis) and adult primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), and secondary biliary fibrosis, all liver diseases of other etiologies, once advanced, develop into a portal fibrosis with proliferation of biliary progenitors, especially when excessive hepatocyte apoptosis forces the stem cell niche to produce biliary progenitors. These biliary progenitors are more resistant to enhanced oxidative stress and hepatocyte death, such as induced by ASH, NASH, or severe post-transplant hepatitis C (55)(56)(57)(58)(59)(60). Drugs aimed at the biliary fibrogenic progenitors are effective antifibrotic agents in rodent biliary and advanced non-biliary fibrosis.…”