Alcoholic liver disease is a major health problem in the UnIted States. Chronic ethanol ingestion produces a spectrum of liver injury ranging from fatty infiltration to alcoholic hepatitis to cirrhosis. The mechanisms by which ethanol produces its harmful effect have not yet been clearly defined. There is evidence implicating both direct toxicity of ethanol and its metabolites as well as an immune-mediated toxicity. Much of the current work suggests that non-parenchymal cells of the liver play a role in the pathogenesis of liver fibrosis. While Kupffer cells and Ito cells have been studied fairly extensively, little is known about the role of LEC in alcohol liver disease. This grant proposes work which will begin to address the role of liver endothelial cells in activating the immune system and exacerbating alcohol liver disease. Liver endothelial cells play a major role in host defense and homeostasis via their so-called 'scavenger' function whereby they recognize, internalize and degrade a variety of modified proteins and extracellular matrix components. Preliminary data demonstrates that chronic ethanol administration alters receptor mediated endocytosis of a variety of macromolecules, thereby diminishing their important function as scavengers in the hepatic reticuloendothelial system. Additionally, liver endothelial cells play a role in the clearance of acetaldehyde modified proteins and that the ability to metabolize these abnormal substances may become progressively impaired with longstanding ethanol exposure resulting in the development of an immune response to these modified proteins. The principal objective of the current research project is to define and characterize the effects of ethanol administration on the process of receptor mediated endocytosis (RME) in liver endothelial cells (LEC) that may result in the development of an immune response to modified self-proteins.
The specific aims are: 1) To determine the effect of ethanol administration on RME by various scavenger receptors for; formaldehyde treated bovine serum albumin (f- Alb), nonenzymatically glycosylated bovine serum albumin (AGE-Alb), acetylated low density lipoproteins (A-LDL), hyaluronic acid (HA), oxidized low density lipoproteins (Ox-LDL), ovalbumin (OVA) and soluble immune complexes (FcR) which are taken up and metabolized by liver endothelial cells; 2) To determine whether liver endothelial cells play a role in clearance of acetaldehyde modified proteins, and if so whether this function is altered with long-term ethanol use. Additionally, the level of acetaldehyde modification necessary to induce this clearance will be investigated; 3) Determine whether antibodies to specific acetaldehyde modified protein adducts can inhibit the binding and/or endocytosis of the physiologically relevant acetaldehyde modified BSA in an effort to better characterize the site for binding; and, 4) Determine whether ethanol induced decreases in endocytosis results in an extended presence of acetaldehyde modified proteins on the liver endothelial cell surface following binding to their appropriate receptor. The ability of modified self-proteins expressed on LEC membranes to Induce humoral and/or cellular immune responses will be determined. These studies should contribute to the clarification of the role of ethanol modified LEC function and subsequent immune responses in the pathogenesis of alcohol liver injury.
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