Mitochondrial DAMPs-driven Mechanisms of Liver Fibrosis in NASH

Non-alcoholic steatohepatitis (NASH) is rapidly becoming the leading cause of liver-related morbidity and mortality in the developed world. The transition from hepatic steatosis to steatohepatitis is thought to involve dysregulation of mitochondrial function and lipotoxicity, however precise molecular mechanism of “second hit” in driving disease remains elusive. Mitochondria, abundant in the liver, share structural similarities with bacteria and their components can be recognized as “danger signals” if released from damaged cell. Mitochondrial DNA (mtDNA) is a major biologically active component of mitochondria that shares structural similarities with bacterial DNA and is well recognized to alert immune system if released from mitochondria of injured cell. The mechanistic role of extracellular mtDNA in liver fibrosis is still obscure. We have developed novel assays for sensitive and reliable mtDNA measurements in biological samples, methodology to generate biologically active mtDNA preparations at large scale for in vivo and in vitro studies, and recently discovered the direct role of mtDNA in driving hepatic fibrosis. Our preliminary data indicate that mtDNA is released from hepatocytes under lipotoxic conditions in apoptosis signal-regulating kinase 1(Ask1)- dependent manner, circulates in serum of NASH patients, and triggers hepatic fibrosis via activation of hepatic stellate cells via STING-dependent pathway. Based on our preliminary data, we propose the original hypothesis that circulating mtDNA species released from injured hepatocytes are a central driver and biomarkers of hepatic fibrosis progression in NAFLD, which we will address by pursuing three independent, but integrated specific aims: Aim 1. Study the role of Ask1 and related signaling pathways in regulating mtDNA release from hepatocytes under lipotoxic conditions. Aim 2. Define intracellular signaling pathways that mediate mtDNA-elicited pro-fibrogenic effects in hepatic stellate cells. Aim 3. Interrogate the relationship between circulating mtDNA levels and progression of NAFLD/NASH. We will use a mechanistic approach to elucidate the role of hepatocyte-derived mtDNA species play in the pathogenesis of NASH progression by eliciting specific pro-fibrogenic responses. Understanding of this novel pathway may lead to a paradigm shift with direct diagnostic and therapeutic implications for NASH. To this end, our long-term goal is to develop non-invasive mtDNA-based diagnostics and discover novel therapeutic targets to prevent or treat NASH.