Intestinal fungi in fatty liver disease and atherosclerosis

Non-alcoholic steatohepatitis (NASH) is a liver disease characterized by lipid accumulation in combination with the presence of inflammation in the liver. Whereas accumulation of lipids is still reversible, NASH could progress to advanced stages including hepatic fibrosis and cirrhosis. Importantly, cardiovascular disease such as atherosclerosis is the leading cause of death in these patients. Although the rising prevalence of NASH increases the demand for effective treatment, underlying mechanisms driving NASH are not fully elucidated, leaving a liver transplantation as the only solution for advanced stages. Insights into causes of hepatic inflammation is of great importance in order to identify new treatment options against NASH and related atherosclerosis. An important role has been proposed for the gut microbiome in developing fatty liver disease. The gut is colonized by trillions of microbes and a noble interaction between host and microbiota is necessary to preserve normal physiology. A disruption of this balance in the gut is known as dysbiosis which has been associated with chronic liver disease. Notably, research has largely focused specifically on intestinal bacteria. However, the gut microbiota also contains fungi; its role for NASH and atherosclerosis has not been addressed. I hypothesize that fungal dysbiosis contributes to the development of hepatic inflammation in NASH. In line, I expect that targeted manipulation of intestinal fungi can ameliorate experimental NASH and atherosclerosis. Through the proposed study, I will characterize the intestinal fungi in murine models of NASH and atherosclerosis using cutting-edge microbiomic approaches. Further, an anti-fungal based interventions will be tested in human-like preclinical mouse models. The mapping of fungal dysbiosis in our murine models is highly innovative and will give critical novel insights in the underlying pathology of diet-induced steatohepatitis and related cardiovascular complications and potentially lead to novel treatment strategies.

Engineering bacteria to protect against fatty liver disease. Unhealthy nutrition and alcohol abuse causes fat accumulation in the liver (steatosis), which may progress to fibrosis and end-stage organ disease (cirrhosis), the 12th leading cause of mortality worldwide. In fact, approximately half of all cirrhotic deaths are alcohol-related. Currently, the underlying mechanisms by which alcohol contributes to liver injury are largely unknown. Hence, therapeutic options and non-invasive markers to detect alcoholic fatty liver disease are poor. An important role has been proposed for intestinal bacteria in developing fatty liver disease. Trillions of microbes colonize the human gut and a noble interaction between host and bacteria is necessary to preserve normal physiology. A disruption of this balance in the gut is known as dysbiosis, which has been associated with chronic liver disease. Yet, how dysbiosis contributes to alcohol-related liver disease is not entirely known. In this project, using a mouse model of alcohol-induced liver disease, we found that the production of interleukin-22 (IL-22), an important regulator of antimicrobial defense in the gut, is impaired. We engineered specific bacteria to produce high-amounts of IL-22 and fed these bacteria to mice along with the alcohol diet. This highly innovative approach protected mice from developing liver damage and inflammation compared to control mice. Mechanistically, we found that impaired IL-22 was due to lower intestinal levels of indole-3-acetic acid (IAA), a bacteria-derived metabolite. Importantly, we also found that intestinal levels of IAA are lower in patients with alcoholic hepatitis compared with healthy controls. Supplementation with IAA to restore intestinal levels protected mice from alcohol-induced fatty liver by inducing intestinal expression of IL-22. In summary, using experimental mouse models and alcoholic hepatitis patient material, we discovered that diminished IL-22 dependent defense in the gut due to lower levels of indole derivatives is a novel mechanism by which alcohol consumption drives liver injury. Further, our data show that engineered bacteria are a promising tool for enhanced therapeutics for alcohol-induced liver disease.