Smooth muscle cell lipid metabolism and serum amyloid A

平滑肌细胞脂质代谢与血清淀粉样蛋白A

• 批准号: 7104791
• 负责人: BARBARA M SCHREIBER
• 金额: $ 36.51万
• 依托单位: BOSTON UNIVERSITY MEDICAL CAMPUS
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7104791
• 关键词: acetyl coA carboxylase; amyloid proteins; blood lipoprotein transport; cAMP response element binding protein; cholesterol; clinical research; endoplasmic reticulum; enhancer binding protein; fatty acid metabolism; gene induction /repression; genetic transcription; human tissue; hydrolysis; intracellular transport; laboratory rabbit; laboratory rat; lipid metabolism; lipid transport; microarray technology; muscle metabolism; phospholipase A2; phospholipids; sphingomyelin phosphodiesterase; transcription factor; vascular smooth muscle

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.

描述（由申请人提供）：平滑肌细胞（SMCs）有助于正常的血管功能，但也有助于动脉粥样硬化。目前对SMC胆固醇分布的机制知之甚少。血清淀粉样蛋白A （SAA）通过血浆脂蛋白沉积和/或局部合成在动脉粥样硬化斑块中积累。我们发现SAA 1)由SMCs响应IL-1ct合成，2)诱导胆固醇转运到内质网（ER）， 3)下调胆固醇和脂肪酸的合成，4)减少胆固醇和磷脂的积累。此外，saa介导的胆固醇运输通过减少被称为固醇反应元件结合蛋白-1 （SREBP）的转录因子的核积累来减少脂质合成。此外，SAA还下调了已知的srebp调控基因乙酰辅酶a羧化酶的表达。有趣的是，与其他将胆固醇运输到内质网的药物不同，SAA介导这种作用没有外源性胆固醇来源，这表明了一种重定向内源性胆固醇池的新机制。我们的基因芯片分析显示，SAA诱导分泌型磷脂酶A2 （sPLA2）和钙依赖性胞质磷脂酶A2 （cPLA2）的表达。此外，我们发现SAA显著增加sPLA2蛋白的表达。此外，已知上调sPLA2基因转录的CCAAT/增强子结合蛋白（C/EBP）家族成员被SAA上调。其他数据表明cAMP反应元件结合蛋白（CREB）在C/EBP表达激活中的作用。最后，鞘磷脂，已被证明抑制sPLA2活性，抑制SAA介导的胆固醇到内质网的运动。因此，我们假设SAA激活CREB， CREB上调C/ ebp的表达，进而上调sPLA2基因的表达。我们进一步假设sPLA2活性导致膜磷脂水解，产生激活鞘磷脂酶的脂肪酸，促进内源性胆固醇运输，从而下调由SREBP激活的基因。我们的目标是：1)通过CREB激活和C/EBP表达，确定无脂和脂相关SAA对sPLA2基因表达的作用；2)确定无脂和脂相关SAA对sPLA2与cPLA2表达和活性的影响；b)确定磷脂酶基因激活对鞘磷脂酶活性的作用；3)确定无脂和脂相关SAA介导的磷脂酶激活对胆固醇运输的影响。SREBP的核可用性和功能。心血管疾病仍然是一个主要的公共卫生问题。阐明促进疾病与预防疾病的机制将导致未来的药物开发策略。