Alcoholic liver disease (ALD) is a major cause of liver disease and liver related morbidity/mortality in the United States. One major difficulty in devising specific therapies for ALD has been our limited understanding of the mechanism(s) for the development and progression of this liver injury. Cytokines are low molecular weight mediators of cellular communication that are produced and released by numerous cell types such as monocytes, macrophages, and of particular relevance to liver disease, Kupffer cells. Pro-inflammatory cytokines, such as tumor necrosis factor a (TNF), and chemokines, such as interleukin-8, have been postulated to play a role in modulating many of the systemic manifestations of ALD and certain aspects of the liver injury in ALD. Many factors stimulate cytokine production, including endotoxin (lipopolysaccharide or LPS) and reactive oxygen intermediates (ROIs), both of which are of direct relevance to this proposal. Endotoxin stimulates cytokine production via interaction with LPS binding protein (LBP); membrane bound CD 14, and ultimately the recently described LPS receptor, Toll-like receptor TLR4. TLR4 then causes activation of the redox sensitive transcription factor, NFkB, with subsequent production of cytokines such as TNF. NFKB also has been identified as a survival factor against TNF induced apoptosis in multiple cell types. Thus, NFKB not only serves as a transcription factor for several inflammatory cytokines such as TNF and IL-8, but also for several potentially protective factors such as inhibitors of apoptosis (lAPs). Inhibition of NFkB can initiate fulminant liver injury and hepatocyte apoptosis, at least in part, by allowing unregulated signaling via the TNF """"""""death domain."""""""" We postulate that in ALD there is: 1) increased NFkB activation and TNF production in the major cytokine producing cell in the liver (Kupffer cell); and 2) decreased NFkB activation and decreased """"""""protective signaling"""""""" in conjunction with increased TNF death signaling in the target cell (hepatocyte). In this proposal, we will use in vitro systems, in vivo animal models of ALD and ultimately will perform translational human studies to further define mechanisms of liver injury in ALD and potential pathways for intervention.
The specific aims of this proposal are to: 1) Evaluate mechanisms for increased NFkB activation and TNF production by monocyte/Kupffer cells in ALD (priming), 2) Evaluate mechanisms of increased susceptibility to TNF/cytokine hepatotoxicity in ALD (sensitization).
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