Aging and Lipid Metaboilism

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Background: Lipids play a fundamental role in many of the major diseases (atherosclerosis, cancer, arthritis) in the elderly as well as in aging itself. Specifically, phospholipids and their metabolites play a central role in cell function by modifying membrane structure and inter- and intracellular signaling. Recently, the intracellular lipid binding protein, acyl-CoA binding protein (ACBP), has emerged as an important regulator of lipid metabolism and signaling. Problem: Aging results in significant changes in phospholipid mass and fatty acid composition, however, the biochemical and molecular mechanism(s) causing these alterations is not known. Purpose: 1) Assess the influence of aging on the activities of the major enzymes involved in phosphatidic acid (PA) biosynthesis which is the central biochemical pathway leading to the synthesis of almost all phospholipids; 2) Evaluate the effects of aging on the fatty acid specificities of these enzymes; 3) Determine the influence of age on ACBP levels and the induction of PA biosynthesis. Methods: Young and old (C57BL/6 x DBA/2) mice fed ad libitum or calorie restricted diets will be used. Endoplasmic reticulum (ER) and mitochondria will be isolated from the liver because the ER and mitochondria are the major sites of de novo phospholipid biosynthesis. The work will focus on the sequential acylation of glycerol-3-phosphate to lysophosphatidic acid then to PA by glycerol-3-phosphate acyltransferase and lysophosphatidic acid acyltransferase respectively. Experiments will also be performed on the activation of fatty acids to acyl-CoAs by acyl-CoA synthetase and acyl-CoA hydrolase. The fatty acids have to be in the acyl-CoA form in order to be utilized by the acyltransferases. Kinetic studies will be conducted using oleoyl-CoA with or without albumin or ACBP present which increases acyltransferase activity. Additional studies will be done using saturated, monounsaturated and polyunsaturated acyl-CoAs. Levels of ACBP will be determined by analyzing protein and gene levels by western blotting and RT-PCR, respectively. Outcome: The experiments will reveal if aging influences enzyme activity by altering ER membrane structure or by altering ACBP expression. Secondly, insight will be gained into whether age alters the utilization of specific fatty acids for phospholipid biosynthesis. Benefit: Characterizing the influence of aging and calorie restriction on phospholipid metabolism may ultimately lead to the development of dietary and/or pharmacologic strategies aimed at maintaining optimal cellular function hence improving the quality of life in the elderly.