Alcohol consumption results in damage to multiple organs, especially liver. An early effect of alcohol intoxication is the inhibition of hepatic protein synthesis. However the underlying mechanisms responsible for the inhibition are not known. Liver has 1 of the highest protein synthetic rates in the body and hepatic proteins are critically important for whole body metabolism of drugs, fat, amino acids, and glucose. Therefore, ameliorating the alcohol-induced defect in hepatic protein synthesis could have wide reaching consequences beyond alcoholic liver disease. The long-term goal of these studies is to elucidate the mechanism underlying the alcohol-induced decreases in hepatic protein synthesis in order to devise ways to reverse the defect. Preliminary data indicates that alcohol causes a defect in the formation of the 43S preinitiation complex [controlled by eukaryotic initiation factor 2 (elF2) and elF2B]; through phosphorylation of the a-subunit of elF2 at Ser51. Ethanol or its metabolites may cause a selective activation of 1 of the known elF2 kinases (PERK, GCN2, PKR or HRI) or inhibit elF2a phosphatase activity. Our hypothesis is that ethanol or its metabolites cause selective activation of 1 or more of the 4 kinases responsible for phosphorylation of elF2a and/or inhibition of phosphatase, and that augmented phosphorylation of elF2a affects the translation of mRNA into protein following acute ethanol intoxication. Using mice as a model system will allow us to manipulate the genome to genetically oblate the kinases involved in elF2 phosphorylation to determine the effect of alcohol intoxication following knockout of elF2 kinases.
2 specific aims are proposed to test this hypothesis and elucidate the mechanisms underlying this defect in hepatic protein synthesis using pharmacological, biochemical, physiological, and transgenic approaches.
Specific Aim 1 will examine the effects of inhibitors of ethanol metabolism, individual ethanol metabolites or derived components on elF2a phosphorylation to establish if the effects of ethanol to increase phosphorylation of elF2a require its metabolism.
Specific Aim 2 will determine which of the elF2 kinases are responsible for the increased phosphorylation of elF2 following acute alcohol intoxication, using mice strains genetically engineered to be deficient in individual and multiple elF2 kinases. In addition, we will examine the potential role of decreased phosphatase activity as a means to increase phosphorylation of elF2a. This exploratory R21 proposal deals with a new direction in the alcohol field and offers the promise of providing mechanism(s) into ethanol effects on translational control and ethanol-induced cellular damage in liver. ? ? ?
| Karinch, Anne M; Martin, Jonathan H; Vary, Thomas C (2008) Acute and chronic ethanol consumption differentially impact pathways limiting hepatic protein synthesis. Am J Physiol Endocrinol Metab 295:E3-9 |
