Role of MicroRNA mi R-33 in Controlling Cholesterol/Lipid Homeostasis

描述（由申请人提供）：固醇反应元件结合蛋白（SREBP）转录因子已被鉴定为参与胆固醇和脂质稳态的基因的关键调节因子。由于异常胆固醇和脂质稳态在支持心血管疾病和糖尿病的代谢失调中的突出性，胆固醇/脂质的转录调节因子如SREBP可能代表改善这些疾病的重要治疗靶点。有趣的是，最近也发现称为microRNA（miRNAs）的小调控RNA代表真核基因表达的重要调控因子。最近的研究表明，一种名为miR-122的miRNA可以调节小鼠和非人类灵长类动物的胆固醇水平。这些研究强调了miRNAs在哺乳动物生理学中与人类健康相关的关键作用。有趣的是，我们已经获得了初步数据，表明miR-33 a/B，即嵌入人类SREBP-1和SREBP-2基因内含子序列中的miRNA，与SREBP宿主基因产物协调调节哺乳动物的胆固醇稳态。我们的研究结果表明，miR-33 miRNA靶向ABCA 1胆固醇转运蛋白的翻译抑制，导致ABCA 1蛋白水平降低和胆固醇流出减少。由于SREBP通过LDL受体基因和胆固醇生物合成基因的反式激活来促进胆固醇摄取和合成，因此通过miR-33依赖性下调ABCA 1来抑制胆固醇流出与SREBP协同作用，以有效地提高细胞内胆固醇水平。我们提出了一系列体外和体内研究，以进一步确定miR-33在控制胆固醇和脂质稳态与SREBP合作的功能作用。这些研究可能对我们理解miRNA和转录因子基因调控的整合和协调产生重要影响，并将促进心血管疾病患者增加HDL合成和逆转胆固醇转运的新治疗策略。具体目标是：1。检测miR-33及其宿主基因SREBP在细胞和组织中的共表达。2.确定miR-33在调节胆固醇运输中的作用。公共卫生相关性：胆固醇和脂肪酸在后生动物的许多生理过程中起着关键的功能作用，例如调节膜流动性，充当信号分子，并以甘油三酯的形式提供能量储存。异常的胆固醇和脂质水平与越来越普遍的疾病有关，包括动脉粥样硬化、肥胖、II型糖尿病和高血压（均与代谢综合征相关），以及脂肪代谢障碍、阿尔茨海默病和某些癌症，这强调了充分了解胆固醇和脂质稳态如何调节和维持的重要性。我们和其他人已经研究了胆固醇和脂质是由称为固醇调节元件结合蛋白（SREBP）的基因开关控制的。有趣的是，我们已经注意到在人SREBP-2和-1基因的内含子序列中分别存在microRNA（miR-33 a/B）。初步研究得出了令人惊讶的发现，即miR-33 a/B似乎抑制胆固醇转运蛋白ABCA 1，ABCA 1是HDL合成的关键调节因子，参与预防动脉粥样硬化。由于SREBP促进胆固醇的摄取和合成，我们预测miR-33介导的ABCA 1和胆固醇流出的抑制作用与SREBP合作，以提高细胞内胆固醇水平。我们提出了一系列的体外和体内研究，将描绘的作用，miR-33在控制胆固醇/脂质稳态与SREBP合作。这些研究应该提供新的治疗策略，旨在增加高密度脂蛋白合成和胆固醇清除心血管疾病患者。

DESCRIPTION (provided by applicant): The sterol response element binding protein (SREBP) transcription factors have been identified as key regulators of genes involved in both cholesterol and lipid homeostasis. Because of the prominence of aberrant cholesterol and lipid homeostasis in the metabolic dysregulation underpinning cardiovascular disease and diabetes, transcriptional regulators of cholesterol/lipids such as SREBPs could potentially represent important therapeutic targets to ameliorate these diseases. Interestingly, small regulatory RNAs termed microRNAs (miRNAs) have recently also been found to represent important regulators of eukaryotic gene expression. One miRNA, miR-122, was shown in recent studies to modulate cholesterol levels in mice and non-human primates. These studies have highlighted the critical role played by miRNAs in mammalian physiology with relevance to human health. Intriguingly, we have obtained preliminary data suggesting that miR-33a/b, miRNAs that are embedded within intronic sequences in both SREBP-1 and -2 genes in humans, regulate cholesterol homeostasis in mammals in coordination with the SREBP host gene products. Our results show that miR-33 miRNAs target the ABCA1 cholesterol transporter for translational repression, resulting in lowered ABCA1 protein levels and decreased cholesterol efflux. As SREBPs promote cholesterol uptake and synthesis through the transactivation of the LDL receptor gene and cholesterol biosynthesis genes, inhibition of cholesterol efflux by miR-33-dependent down-regulation of ABCA1 acts in cooperation with SREBPs to effectively boost intracellular cholesterol levels. We propose a series of in vitro and in vivo studies to further determine the functional role of miR-33 in controlling cholesterol and lipid homeostasis in cooperation with SREBPs. These studies could have important ramifications for our understanding of the integration and coordination of miRNA and transcription factor gene regulation and will facilitate novel therapeutic strategies to increase HDL synthesis and reverse cholesterol transport in patients with cardiovascular disease. The Specific Aims are: 1. To examine the co-expression of miR-33 and its host gene SREBP in cells and tissues. 2. To determine the role of miR-33 in regulation of cholesterol trafficking. PUBLIC HEALTH RELEVANCE: Cholesterol and fatty acids play critical functional roles in many physiological processes in metazoans, such as modulating membrane fluidity, serving as signaling molecules, and providing energy storage in the form of triglycerides. Abnormal cholesterol and lipid levels have been linked to increasingly prevalent diseases, including atherosclerosis, obesity, type II diabetes, and hypertension (all associated with metabolic syndrome), as well as lipodystrophy, Alzheimers Disease, and certain cancers, underscoring the importance of understanding fully how cholesterol and lipid homeostasis are regulated and maintained. We and others have investigated cholesterol and lipids are controlled by gene switches termed sterol regulatory element binding protein (SREBP). Intriguingly, we have noted the presence of microRNAs (miR- 33a/b) within intronic sequences in the human SREBP-2 and -1 genes, respectively. Preliminary studies yielded the surprising finding that miR-33a/b appear to repress the cholesterol transporter ABCA1, a key regulator of HDL synthesis that is involved in preventing atherosclerosis. As SREBPs promote cholesterol uptake and synthesis, we predict that miR-33-mediated inhibition of ABCA1 and cholesterol efflux acts in cooperation with SREBPs to boost intracellular cholesterol levels. We propose a series of in vitro and in vivo studies that will delineate the role of miR-33 in controlling cholesterol/lipid homeostasis in cooperation with SREBPs. These studies should provide novel therapeutic strategies aimed at increasing HDL synthesis and cholesterol clearance in patients with cardiovascular disease.