Regulation of PAF Acetylhydrolase Expression by Oxidized Phospholipids

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DESCRIPTION (provided by applicant): Platelet-activating factor acetylhydrolase (PAFAH) also known as the lipoprotein-associated phospholipase A2 is a calcium-independent acylhydrolase that catabolizes oxidized phospholipids (oxPL) in the oxidized LDL (oxLDL) particle as well as the lipid mediator platelet-activating factor (PAF). Many recent studies have correlated PAFAH activity with severity of vascular disease and atherosclerosis. Despite the unquestioned importance of this enzyme in the pathogenesis of atherosclerosis and other vascular disease, very little is known about mechanisms regulating its expression and activity. Our preliminary studies indicate that PAFAH expression is induced by oxidized phospholipids (oxPL), derivatives of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine, a component of oxLDL. This provides us with a unique model that we will use to delineate the molecular mechanisms controlling PAFAH expression in the atherosclerotic lesion. We hypothesize that long chain, prostaglandin-like oxPL induce PAFAH by binding to the CD14/ TLR4 complex and the EP2 prostaglandin receptor on dendritic cells in the developing atherosclerotic lesion. These interactions are proposed to induce interleukin 6 (IL6) and the phosphorylation and activation of key transcription factors, events essential for optimal transcription of the PAFAH gene. To test this hypothesis, we propose the following specific aims: 1) Investigate Roles of EP2, IL6, and CD14/ TLR4 in oxPL Induction of PAFAH and 2) Investigate Molecular Mechanisms of oxPL Induction of PAFAH. In Aim 1, we will test the hypothesis that oxPL binding to EP2 and/ or the TLR4-CD14 receptor complex induces IL6 and that this cytokine is essential for optimal PAFAH induction. In Aim 2, we will investigate role of a GC-box, Sp1, and Sp3 in induction of PAFAH by oxPL and determine whether PAFAH induction is dependent on phosphorylation of Sp1/ Sp3 and/ or the association of Sp1 with activated STAT3. We have assembled a unique team of investigators for this purpose, including Dr. Norbert Leitinger (University of Virginia), a pioneer in the study of oxPL, Dr. Zendra Zehner (VCU), and expert in the transcriptional assays, DNAP, and ChIP analyses required for determination of the molecular mechanism of PAFAH induction by oxPL, and the Principal Investigator, Dr. Suzanne Barbour, an expert in the PAFAH enzyme and dendritic cell (DC) biology. Together, the proposed studies should provide insights into the physiological mechanisms that control PAFAH expression in vascular disease. We anticipate that our studies may uncover novel mechanisms to control PAFAH that could eventually result in treatments to prevent initiation or slow progression of atherosclerosis and other vascular diseases. Project Narrative: Platelet-activating Factor Acetylhydrolase (PAFAH) is the lipoprotein-associated phospholipase A2 that has been correlated with the incidence and severity of cardiovascular disease. Preliminary studies from this group of investigators indicate that PAFAH is induced by oxidized phospholipids (oxPL) in the oxidized low density lipoprotein (LDL) particle. The objective of this study is to delineate the molecular mechanisms of PAFAH induction by oxPL in hopes that this will uncover novel mechanisms for regulating the enzyme and thereby controlling cardiovascular disease.