ETHANOL EFFECTS ON PROTEOLYTIC SYSTEMS IN THE LIVER

The central hypothesis of the proposed investigation is that ethanol
consumption inhibits hepatic proteolysis by affecting the lysosomal and
extralysosomal proteolytic pathways in the liver. An ethanol-elicited
inhibition of protein degradation is one of the principal factors
responsible for ethanol-induced protein accumulation in the liver, a
phenomenon which contributes to hepatomegaly resulting from chronic
drinking. Our aim in these investigations is to examine two key hepatic
proteolytic systems in rat liver and to determine to what degree they are
affected by acute and,/or chronic ethanol administration. The systems to
be analyzed are the hepatic autophagic/lysosomal system and the ubiquitin
proteolytic pathway. These pathways are responsible for the complete
degradation of most intracellular proteins. Disruption of their
intracellular function(s) may lead to other disturbances in liver cell
function. The specific objectives of this proposal are to examine the effects of
acute and/or chronic ethanol consumption on 1) The formation and maturation
of hepatic autophagic vacuoles, 2) endogenous proteolytic activities as
well as HSP-70-mediated proteolytic activities of liver lysosomes 3) the
content of hepatic ubiquitin as well as ubiquitin dependent conjugation and
proteolytic activities in rat liver extracts, and 4) the activities of
these proteolytic systems in different zones of the hepatic lobule. The
latter objective will be important in determining whether any relationship
exists between the ethanol-induced reduction in hepatic proteolysis and
ethanol-elicited specific cell injury. Our investigation will utilize recently updated techniques for the
enrichment and isolation of autophagic vacuoles from the livers of control
and ethanol-fed rats. We will analyze these vacuoles morphologically and
biochemically in order to determine whether ethanol ingestion affects the
formation, maturation and proteolytic capacities of these organelles. We
will then assess the effects of ethanol consumption, as well as that of
ethanol's initial oxidation product acetaldehyde, on the formation and the
degradation of ubiquitin-protein conjugates. Finally, we will analyze the
protein content, the rates of protein catabolism, as well as the
aforementioned proteolytic systems in isolated perivenous and periportal
hepatocytes from control and ethanol-fed rats. Since the liver is responsible for the regulation of serum protein, amino
acid, lipid and glucose levels, it is important to understand the effects
of ethanol toxicity or hepatic protein metabolism.