Microbiota-driven gut vascular barrier disruption is a prerequisite for non-alcoholic steatohepatitis development

Abstract Background and Aims Fatty liverdisease, including nonalcoholic fatty liver(NAFLD) and steatohepatitis(NASH), has been associated with increased intestinal barrier permeability and translocation of bacteria or bacterial products into the blood circulation. In this study we aim to unravel the role of both intestinal barriers integrity and microbiota in NAFDL/NASH development. Methods C57BL/6J mice were fed with High Fat Diet (HFD) or Methionine Choline Deficient Diet for one week or longer to recapitulate NASH disease aspects (steatosis, inflammation, insulin resistance). Genetic and pharmacological strategies have been used to modulate the intestinal barriers integrity. Results We show that disruption of intestinal epithelial barrier and gut vascular barrier (GVB) are early events in NASH pathogenesis. Mice fed a HFD for only one week undergo a diet-induced dysbiosisthat drives GVB damage and bacteria translocation into the liver. Fecal microbiota transplantation from HFD-fed mice into specific pathogen-freerecipients induces GVB damage and epidydimal adipose tissue enlargement. GVB disruption depends on interference with the WNT/β-catenin signaling pathway, as shown by genetic intervention driving β-catenin activation only in endothelial cells, preventing GVB disruption and NASH development. The bile acid analogue and farnesoid X receptoragonist obeticholic aciddrives β-catenin activation in endothelial cells. Accordingly, pharmacologic intervention with OCA protects against GVB disruption, both as preventive and therapeutic agent. Importantly, we found upregulation of the GVB leakage marker in the colon of NASH patients. Conclusions We have identified a new player in NASH development, the GVB, whose damage leads to bacteria or bacterial product translocation into the blood circulation. Treatment aimed at restoring β-catenin activation in endothelial cells, such as administration of OCA, protects against GVB damage and NASH development. Lay summary Fatty liverdisease incidence is reaching epidemic in USA, with more than 30% of adults having NAFLD ( nonalcoholic fatty liver disease). NAFLD can develop into NASH ( steatohepatitis), a more severe stage, that can ultimately turn into cirrhosis and hepatocellularcarcinoma. There is a known link between increased intestinal permeabilityand the development of the disease, however there is no clear description of the initiation of NASH, i.e. if it is a cause or a consequence of NASH. Here, we demonstrate for the first time that high fat diet induces changes in the microbiota, that will in turn disrupt the intestinal barrier. Indeed, there exist two layers of barrier that are sequentially disrupted when microbiota changes following high fat diet consumption. This disruption allows bacteria from the intestine to reach the blood stream and disseminate to the liver fostering the development of a fatty liver. When using a genetically modified mousemodel, or a drug (OCA) that protects against barrier disruption, there is no development of the disease. This clearly shows that barrier disruption is a prerequisite for the disease to develop. Finally, we also found indication of barrier disruption in human samples from NASH patients, supporting the idea of a general mechanism. Altogether, these data clearly decipher the very first steps of fatty liverdisease onset, and lead the way for a treatment using OCA to block barrier disruption.