Activation of liver resident macrophages and increased pro-inflammatory cytokine production is a hallmark in the pathogenesis of alcoholic liver disease (ALD). Alcohol-induced oxidative stress plays an important part in macrophage activation. Heat shock proteins are induced by oxidative stress and function as molecular chaperones. Heat shock protein 90 (hsp90) and Grp94/gp96 chaperone signaling molecules of the TLR4 pathway to regulate inflammatory cytokines. Thus, hsp90 and gp96 could link stress and inflammatory pathways and play an important role in development of ALD. Our preliminary studies show that chronic alcohol feeding in mice increases hsp90 and gp96 in isolated Kupffer cells (KCs), compared to pair-fed controls. Hsp90 from chronic alcohol-exposed macrophages associates with IKKb kinase, a pivotal kinase in NFkB activation and TNFa production. Chronic alcohol exposure also increases IKKb kinase activity in macrophages. We hypothesize that chronic alcohol exposure modulates hsp90 and gp96 in macrophages and regulates TLR4 induced NFkB activation and TNFa production, contributing to liver injury. Thus, hsp90 and gp96 play an important role in the pathophysiology of ALD.
The specific aims are as follows: 1) To determine the activation and function of hsp90 in alcoholic liver injury by: A) Measuring chaperone activity, dimer formation, and acetylation of hsp90 in whole liver and isolated Kupffer cells from alcohol-fed mice. B) Evaluating the effect of hsp90 inhibitors, 17-AAG and/or 17-DMAG in induction of pro-inflammatory cytokine production, and alleviation of alcoholic liver injury. 2) To examine the role of hsp90 in alcohol-induced sensitization to LPS-induced inflammatory cytokine production by: A) Studying the interactions of MyD88- dependent down-stream signaling molecules, IRAK-1 and IKK with co-chaperone cdc37 and hsp90 in alcoholic Kupffer cells and whole livers. B) Examining whether hsp90 is required in chronic alcohol mediated LPS-induced, MyD88 independent signaling. C) Evaluating the interaction of Gp96, an ER form of hsp90, with TLR4 in alcohol exposed hepatic macrophages/KCs. 3) To assess the mechanisms by which chronic alcohol induces hsp90 in macrophages by: A) Characterization of the binding of HSF-1, NFkB, stimulatory protein-1 (Sp1) and STAT1 by chromatin immunoprecipitation analysis. B) Delineating the effect of HSF-1 deficiency and HSF-1 inhibition using siRNA on induction of hsp90. C) Determining the role of ROS dependent HSF1 activation on induction of hsp90 by evaluating effect of Rac1 and NADPH oxidase in alcohol-exposed macrophages.
Alcoholic liver disease continues to be a major health problem with respect to morbidity and mortality. Oxidative stress and TLR-induced pro-inflammatory cytokines play an important role in pathogenesis of liver injury by alcohol. Heat shock proteins induced by oxidative stress play an important role in inflammatory responses. Particularly hsp90 regulates and maintains stability of key kinases involved in the LPS-signaling pathway. We hypothesize that hsp90 plays a pivotal role in alcoholic liver disease by maintaining function of kinases that induce pro-inflammatory cytokines. Commercially available hsp90 inhibitors could be used to reduce alcoholic liver disease by ablation of inflammatory responses and these inhibitors will be tested. The significance of HSF-1, a transcription factor that induces hsp90, will provide further knowledge of the essential role of HSF-1 in induction of hsp90 in alcoholic liver injury. Understanding these pathways will provide novel mechanisms and thus extend our horizons to identify potential new drug targets for alcoholic liver disease.
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