Adipocytes and cardiac remodeling

 描述(申请人提供)：罗格列酮(RSG)是一种核激素过氧化物酶体增殖物激活受体-(PPAR-)的合成激动剂，已作为胰岛素增敏剂成功应用于2型糖尿病的临床。然而，其不良心脏副作用严重阻碍了其临床应用。来自实验模型的现有证据表明，RSG会导致心肌肥厚，这可能导致心力衰竭。目前，RSG诱导心肌肥厚的分子机制尚不清楚。脂肪组织是PPAR-表达和功能的主要部位。我们的初步数据显示，在共培养体系中，RSG激活脂肪细胞中的PPAR-导致心肌细胞肥大。此外，去除脂肪细胞中的PPAR-可减轻RSG诱导的在体心肌肥厚。这些数据表明，脂肪和心脏组织之间存在调节心肌肥厚的功能相互作用。脂肪组织作为内分泌器官起着至关重要的作用，它会分泌细胞因子来调节全身的动态平衡和其他器官的功能。有趣的是，最近的一次筛查以及我们的初步数据显示，脂肪细胞能够释放microRNAs(MiRs)。MIR是一个高度保守的小(~22个核苷酸)非编码RNA家族，它通过降解或抑制靶基因的翻译，在转录后抑制基因的表达。血清中循环细胞外MIR的发现表明，它们可能在调节细胞间通讯方面发挥新的作用。外切体是分泌型miRs的主要运输囊泡，允许miR的转移和细胞间的基因交换。我们的初步研究表明，RSG刺激脂肪细胞中的PPAR-信号导致miR-200a/b/429簇的上调，并导致成熟的miR-200a在外体中的分泌。生物信息学分析和实验研究表明，miR-200A可以靶向调节心肌肥厚的mTOR途径的成分。此外，我们发现miR-200A在饮食诱导的肥胖相关心肌病模型中上调。上述结果提示我们的总体假设是miR-200a/b/429簇的循环成员在两种不同的心肌病模型中调节脂肪和心脏组织之间的通讯，从而对心脏重构产生不利影响。该项目的总体目标是阐明脂肪组织诱导的心脏不良重塑的分子机制，并为脂肪和心脏组织之间一种新的外体miR介导的途径提供见解。因此，我们的具体目标是：1.检测miR-200A/b/429簇的所有成员是否都是从外体的脂肪细胞转运到心肌细胞，并在体外确定这一功能的潜在后果；2.通过脂肪细胞特异性基因敲除小鼠模型，在体内阐明miR-200A和miR-200A/b/429簇在RSG介导的心肌肥大中的作用；3.利用脂肪细胞特异性基因敲除小鼠模型，了解miR-200A和miR-200A/b/429簇对肥胖相关心肌病小鼠的病理生理影响。

 DESCRIPTION (provided by applicant): Rosiglitazone (RSG) is a synthetic agonist of the nuclear hormone Peroxisome Proliferator-Activated Receptor-  (PPAR-) and has been successfully used in the clinic for type 2 diabetes as an insulin-sensitizer. However, adverse cardiac side effects have seriously hindered its clinical application. Existing evidence from experimental models revealed that RSG results in cardiac hypertrophy, which may lead to heart failure. Currently, molecular mechanisms underlying RSG-induced cardiac hypertrophy remain unclear. Adipose tissue is a major site of PPAR- expression and function. Our preliminary dat showed that activation of PPAR- by RSG in adipocytes in a co-culture system resulted in cardiomyocyte hypertrophy. Furthermore, ablation of PPAR- in adipocytes attenuated RSG-induced cardiac hypertrophy in vivo. These data imply a functional interplay between adipose and cardiac tissue that regulates cardiac hypertrophy. Adipose tissue plays a critical role as an endocrine organ, and secretes cytokines that regulate systemic homeostasis and the function of other organs. Interestingly, a recent screen as well as our preliminary data revealed that adipocytes are able to release microRNAs (miRs). miRs are a family of highly conserved, small (~22 nucleotide) noncoding RNAs that post-transcriptionally repress gene expression by degrading or inhibiting translation of their target mRNA. The discovery of circulating extracellula miRs in serum suggests they may play a novel role in mediating cell-cell communication. Exosomes are the major transport vesicle of secretory miRs, allowing miR transfer and genetic exchange between cells. Our preliminary studies demonstrated that RSG stimulation of PPAR- signaling in adipocytes leads to upregulation of the miR-200a/b/429 cluster, and secretion o mature miR-200a in exosomes. Bioinformatics analysis and experimental investigation demonstrated that miR-200a can target components of the mTOR pathway, which regulates cardiac hypertrophy. In addition, we found that miR-200a was upregulated in a diet-induced obesity-associated cardiomyopathy model. The aforementioned suggest our overall hypothesis is that circulating members of the miR-200a/b/429 cluster mediate communication between adipose and cardiac tissue to adversely affect cardiac remodeling in two distinct models of cardiomyopathy. The overall goal of this project is to elucidate molecular mechanisms underlying adverse cardiac remodeling induced by adipose tissue, and provide insights into a novel exosomal miR-mediated pathway between adipose and cardiac tissue. Accordingly, our Specific Aims are: 1. To examine whether all members of the miR-200a/b/429 cluster are transported from adipocytes to cardiomyocytes in exosomes and to determine potential functional consequences of this in vitro; 2. To elucidate the role of miR-200a and the miR-200a/b/429 cluster in RSG-mediated cardiac hypertrophy in vivo by using adipocyte-specific knockout mouse models; and 3. To understand pathophysiological effects of miR-200a and the miR-200a/b/429 cluster in a mouse model of obesity-associated cardiomyopathy using adipocyte-specific knockout mice.