Innate immune signaling in alcoholic liver disease

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Abstract Alcoholic liver disease (ALD) and its clinically most devastating presentation, alcoholic hepatitis, is a result of cumulative biological events such as leaky gut, hepatocyte damage and inflammation that collectively contribute to the severity of liver damage. Our studies delineated a unique role for interferon regulatory factor 3 (IRF3) in alcohol-related inflammation and hepatocyte damage. We reported that the endoplasmic reticulum (ER) adapter, stimulator of interferon genes (STING), is required for IRF3 phosphorylation and that IRF3 induces mitochondrial apoptosis in hepatocytes. Preliminary data shows that both alcohol binge or chronic alcohol increase circulating bacterial 16S DNA and mitochondrial DNA levels in mice and humans. These double stranded DNAs are ligands for the cyclic GMP-AMP kinase (cGAS) that produces 2′3′-cGAMP (cGAMP) that can activate STING to trigger IRF3 activation and Type I IFN production. We postulate that STING activation is at the crossroads of alcohol-induced liver pathology and in addition to ER stress, STING is also activated via cGAS-cGAMP in ALD. We further hypothesize that cGAS-mediated signals and STING activation represent a trigger for an acute-on-chronic alcohol-induced liver injury often seen in acute alcoholic hepatitis. We proposee that the cGAS-cGAMP-STING activation axis plays a role both in hepatocytes and immune cells in alcoholic hepatitis. We also discovered that sterile danger signals released by damaged hepatocytes activate the NLRP3 inflammasome in immune cells and that disruption of inflammasome activation pathways can ameliorate ALD in mice. We propose that inflammasome activation and ER stress are bi-directionally regulated in ALD. Our Aims are: 1. To investigate the role of the DNA sensor, cGAS, and dsDNA in STING-IRF3 activation in ALD; 2. To delineate the cell-specificity of cGAS and STING activation in ALD in hepatocytes and innate immune cells; 3. To investigate interactions between ER stress, inflammasome activation and STING-IRF3 activation in ALD; 4. To investigate the biological effect and therapeutic benefit of cGAS and STING inhibition on liver damage, steatosis and inflammation in ALD. These experiments will test novel roles of the cGAS-STING innate immune signaling pathways in ALD and identify key signaling molecules, for designing new therapies for ALD.