Ethanol Effects on Endocytosis in the Liver

Casey, Carol

Abstract

Ethanol abuse with its resulting liver injury is a major health problem in this country and worldwide. Our previous studies have shown that the process of receptor-mediated endocytosis (RME) mediated by the hepatic asialoglycoprotein receptor (ASGP-R) is especially susceptible to the deleterious effects of ethanol. The defects in endocytosis are accompanied by defects in receptor function, in that ligand binding is impaired without a decrease in total receptor protein content. These proposed studies will continue to explore this phenomenon, and in this regard, the following hypothesis has been formulated: """"""""Ethanol-induced inactivation of the ASGP-R leads to altered receptor function and impaired RME. Impaired function of the this receptor could lead to alteration of membrane internalization events after ethanol administration and contribute to aberrations such as increased apoptosis in the liver"""""""". To examine this hypothesis we have proposed 5 specific aims. In the first two aims, we will continue our examination of altered function of the ASGP-R at a biochemical level, by studying post- translational modifications of the receptor (acylation and phosphorylation) as well as examine in detail the effect of ethanol on the two subpopulations which exist for this receptor (Specific Aim 1). The two pathways for these subpopulations are differentially regulated and have different intracellular """"""""itineraries"""""""" post-internalization.
In Specific Aim 2 we will determine whether the ethanol-induced post- translational modifications of the ASGP-R result in impaired intracellular receptor-ligand segregation and routing in hepatocytes.
In Specific Aim 3 we will examine the effect of ethanol on another cell type in the liver, the Kupffer cell. Kupffer cells possess a receptor (the galactosyl receptor) which has similar binding properties to the ASGP-R, except that this receptor on Kupffer cells is responsible for binding and internalizing particles larger than those internalized by the hepatic ASGP-R. We will study the galactosyl receptor on Kuppfer cells to determine if ethanol administration impairs the function of this receptor similarly to the ASGP-R. In the 4th and 5th specific aims, we will examine two potentially important functional consequences of impaired ASGP-R and galactosyl receptor function. We will determine if the ASGP-R and/or the galactosyl receptors are involved in clearing apoptotic bodies in the liver in studies proposed for Specific Aim 4. Our final specific aim is to investigate whether impaired ASGP-R function is associated with increased levels of soluble asialo- glycoconjugates in the plasma. All together, these proposed studies should provide valuable information concerning the basic molecular mechanisms of alcohol-induced hepatotoxicity.