Lack of physical activity along with a western diet and lifestyle is accompanied by an increased incidence of obesity, diabetes, and fatty liver disease (NAFLD). NAFLD is considered an independent risk factor for cardiovascular disease and encompasses multiple progressive disease conditions beginning with hepatic steatosis, non-alcoholic steatohepatitis (NASH) and hepatic fibrosis, which is also associated with aging and increased risk for cirrhosis and hepatocellular carcinoma. The progression of NAFLD with accompanying hepatic fibrosis poses a significant health problem, culminating in liver transplant as the last resort. Treatment options are limited and there is a tremendous need for novel therapeutic concepts. The mechanisms driving NAFLD progression to fibrosis are largely unknown and may involve multiple insults by cell-derived danger- associated molecular patterns (DAMPs) such as extracellular ATP and its metabolites, which were implied to regulate hepatic inflammation and fibrosis. However, the mechanisms that control the release of ATP from hepatocytes are not known. Our preliminary data demonstrate that hepatocytes express functional pannexin-1 (Panx1) channels that release ATP upon lipotoxicity-induced caspase-dependent cleavage. Pharmacological inhibition or genetic deletion of Panx1 in hepatocytes protected mice against diet- and aging-induced steatosis, steatohepatitis and hepatic fibrosis. Based on these data, we will examine the hypothesis that Panx1- dependent ATP release from hepatocytes promotes fibrosis via activation of stellate cells and we will test if inhibition of Panx1 channel function is a feasible therapeutic approach to combat NASH.
In specific Aim 1 we will investigate the effect of hepatic Panx1 deficiency (Panx1fl/fl/Albcre) and virus (AAV8)- mediated Panx1 ablation during the pathologically defined stages of fatty liver disease - steatosis, NASH, and advanced fibrosis, using mice fed a high fructose, palmitate, cholesterol (FPC) diet for 5, 12 or 16 weeks. Virus-mediated hepatic re-expression of Panx1 in Panx1-deficient mice and transgenic overexpression of Panx1 will be used as gain-of-function approaches. We will develop novel liver-specific antisense oligonucleotide (ASO)-mediated therapeutic approaches directed at Panx1, which will be tested in the FPC diet model, in transgenic APOE3- Leiden/CETP mice, a ?humanized? mouse model of metabolic syndrome, and in aging-induced fibrosis.
In specific Aim 2 we will test the hypotheses that (a) Panx1-dependent ATP release from hepatocytes regulates fibrotic capacity of hepatic stellate cells via paracrine effects, and (b) ATP or its metabolites controls metabolism of hepatocytes via Panx1-dependent autocrine mechanisms. Collectively, these data will provide us new information on diet-induced metabolic complications that are now considered predisposing and accelerating factors, part of the cardiometabolic syndrome; also, our new knowledge on liver fibrosis will also have implications for cardiac fibrosis.
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