Lipid Metabolism in the Aging Immune System

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DESCRIPTION (provided by applicant): Lipids play a fundamental role in many of the major diseases (atherosclerosis, cancer, arthritis) in the elderly as well as in aging itself. Specifically, phosphatidic acid (PA) plays a central role in cell function by modifying membrane structure via synthesis into phospholipids and serving as a potent intracellular signaling molecule. Recently, the intracellular lipid binding protein, acyl-CoA binding protein (ACBP), has emerged as an important regulator of PA synthesis and intracellular signaling. Phospholipid alterations in T-cells are associated with reduced immune function in the elderly. Problem: Aging results in significant changes in phospholipid mass and fatty acid composition in T-cells, however, the biochemical and molecular mechanism(s) causing these alterations is not known. Purpose: 1) Determine if reduced PA biosynthesis via glycerol-3-phosphate acyltransferase (GPAT) accounts, at least in part, for reduced T-cell proliferation; 2) Determine the role of ACBP in PA biosynthesis in aged T-cell dysfunction; 3) Assess the role of ACBP in aged T-cell subset dysfunction. Methods: Young and old rats fed ad libitum diets will bell used. Endoplasmic reticulum (ER) (microsomes) and mitochondria will be isolated from the splenic T-cells because the ER and mitochondria are the major sites of de novo PA biosynthesis. The work will focus on the acylation of glycerol-3-phosphate to lysophosphatidic acid then to PA by (GPAT) and lysophosphatidic acid acyltransfcrase respectively. Experiments will be designed to determine if the aging effects on GPAT are pre- (gene expression) or posttranscriptional (phosphorylation, protein levels) in nature. This is significant because GPAT is the rate-limiting enzyme in PA biosynthesis. The influence of ACBP in mediating reduced T-cell function with age will be assessed by examining whether over-expressed ACBP alters T-cell oroliferation and what impact aging has on ACBP levels by analyzing protein and gene expression by western immunoblotting_and RT-PCR, respectively. ACBP's influence on CD4+ and CD8+ T-cell sub sets and memory/naive-T-cell function with age will be determined by transfecting ACBP into those aged T-cell populations which exhibit altered ACBP expression with age and examining cytokine production by flow cytometry. Outcome: The experiments will give insight into whether alterations in PA synthesis and ACBP expression or function are an important mechanistic explanation for the age-dependent loss of T-cell proliferation. Secondly, insight will be gained into whether ACBP plays a role in the age-dependent dysfunction of specific T-cell subsets. Benefit: Characterizing the influence of aging on ACBP and PA synthesis may ultimately lead to the development of dietary and/or pharmacologic strategies aimed at maintaining optimal immune function hence improving the quality of life in the elderly.