HIF regulation of Ammonia Processing and Fibrosis in MASLD/MASH

University Of Michigan At Ann Arbor, Ann Arbor MI

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Steatotic liver disease (SLD) prevalence in just the United States is estimated to upwards of a quarter of the population. It ranges in presentation from simple Hepatic Steatosis without evidence of liver injury to development of inflammation and fibrosis (Metabolic Associated Steatohepatitis; MASH). Those individuals that develop MASH have increased risk of progression to advanced fibrosis and ultimately cirrhosis. Understanding the cellular and molecular mechanisms of the transition from simple steatosis to inflammation and fibrosis is needed. Recent work has shown that MASH leads to high level of hepatic and systemic ammonia. Moreover, there is mounting evidence that ammonia can contribute to the progression of MASH. Ammonia levels are detoxified through the urea cycle. The liver is the major site of ammonia detoxification and consistent with the increase in ammonia in MASLD, urea cycle genes are significantly decreased in MASLD. However, the molecular mechanism driving the metabolic reprogramming to alter liver ammonia is unclear. Preliminary studies have implicated the hypoxia-inducible factor (HIF) pathway in the development of liver steatosis and fibrosis. I show that activation of hepatocyte HIF2a (but not HIF1a) signaling decrease urea cycle genes, increases ammonia levels, steatosis, inflammation, and fibrosis. Therefore, I hypothesize that HIF2α exacerbates liver injury and dysfunction by disrupting urea cycle metabolism, resulting in steatosis, and promoting an inflammatory and profibrotic response. To test this hypothesis, I propose two Aims: 1) To understand how dysregulation of HIF signaling drives altered hepatocyte gene expression and metabolism. Hepatic nuclear factor (HNF)4α is the master transcription factor for the regulation of urea cycle genes. I will understand the crosstalk of HIF2α and HNF4α signaling. 2) Define if inhibition of HIF2α is a viable target for clinical intervention in the progression to advanced fibrosis/cirrhosis. Recently a clinically relevant on-target HIF2a, beltifuzan was approved for clear cell renal carcinomas. I will test the role of beltifuzan in preclinical models of MASH. The proposed research seeks to understand the role of HIF signaling in the development of steatosis and fibrosis that if left unabated can progress end stage liver disease and to the sequalae that drive the significant morbidity and mortality of the disease.