Associate Provost for Research Boston University Medical Campus
NHLBI - National Heart, Lung & Blood	Research Resources

Abstract

Abstract: DESCRIPTION (provided by applicant): Smooth muscle cells (SMCs) contribute to proper vascular function but also to atherosclerosis. Little is known of the mechanisms mediating SMC cholesterol distribution. Serum amyloid A (SAA) accumulates in atherosclerotic plaques by deposition from plasma lipoproteins and/or local synthesis. We showed that SAA 1) is synthesized by SMCs in response to IL-1ct, 2) induces trafficking of cholesterol to the endoplasmic reticulum (ER), 3) down-regulates cholesterol and fatty acid synthesis and 4) decreases accumulation of cholesterol and phospholipid. Furthermore, SAA-mediated cholesterol trafficking decreases lipid synthesis by decreasing nuclear accumulation of the transcription factor known as sterol response element binding protein-1 (SREBP). Moreover, SAA down-regulates expression of the known SREBP-regulated gene acetyl CoA carboxylase. Interestingly, unlike other agents that traffic cholesterol to the ER, SAA mediates this effect without an exogenous cholesterol source, suggesting a novel mechanism of redirecting endogenous cholesterol pools. Our gene microarray analysis showed that SAA induces expression of secretory phospholipase A2 (sPLA2) and calcium-dependent cytosolic phospholipase A2 (cPLA2). Moreover, we show that SAA dramatically increases expression of sPLA2 protein. Additionally, CCAAT/enhancer binding protein (C/EBP) family members, known to up-regulate sPLA2 gene transcription, are up-regulated by SAA. Additional data suggest a role for cAMP response element-binding protein (CREB) in activation of C/EBP expression. Lastly, sphingomyelin, which has been shown to inhibit sPLA2 activity, inhibits the SAA- mediated movement of cholesterol to the ER. Thus, we hypothesize that SAA activates CREB, which up- regulates expression of C/EBPs, which in turn up-regulate expression of the sPLA2 gene. We further hypothesize that sPLA2 activity causes hydrolysis of membrane phospholipids, generating fatty acids that activate sphingomyelinase, contributing to endogenous cholesterol trafficking and hence down-regulation of genes activated by SREBP. Our aims are to 1) determine the role of lipid-free and lipid-associated SAA on sPLA2 gene expression via CREB activation and C/EBP expression 2) establish the effect of lipid-free and lipid-associated SAA on a) sPLA2 vs. cPLA2 expression and activity and b) to determine the role of phospholipase gene activation on sphingomyelinase activity and 3) establish the effect of lipid-free and lipid- associated SAA-mediated phospholipase activation on cholesterol trafficking, nuclear availability and function of SREBP. Cardiovascular disease remains a major public health concern. Elucidation of mechanisms that promote disease vs. protect against it will lead to future strategies for drug development.

Thesaurus Terms:
amyloid protein, cholesterol, fatty acid metabolism, lipid metabolism, muscle metabolism, vascular smooth muscle
acetyl coA carboxylase, blood lipoprotein transport, cAMP response element binding protein, endoplasmic reticulum, enhancer binding protein, gene induction /repression, genetic transcription, hydrolysis, intracellular transport, lipid transport, phospholipase A2, phospholipid, sphingomyelin phosphodiesterase, transcription factor
clinical research, human tissue, laboratory rabbit, laboratory rat, microarray technology

Institution:	BOSTON UNIVERSITY MEDICAL CAMPUS
	715 ALBANY ST, 560
	BOSTON, MA 021182394
Fiscal Year:	2006
Department:	BIOCHEMISTRY
Project Start:	01-APR-2006
Project End:	31-MAR-2011
ICD:	NATIONAL HEART, LUNG, AND BLOOD INSTITUTE
IRG:	AICS