Novel mechanism of smooth muscle phenotypic modulation and vascular remodeling

描述(申请人提供)：血管平滑肌(SMC)表型改变，即血管损伤后从收缩表型到增殖表型的转变，伴随着新生内膜的形成，在几种增殖性心血管疾病的发生和发展中起着关键作用，如动脉粥样硬化、高血压、血管成形术或搭桥术后再狭窄、糖尿病血管并发症和移植动脉病变。然而，SMC表型调节的调控机制却知之甚少。表型调节的一个显著特征是SMC收缩基因下调。血小板衍生生长因子-BB(PDGF-BB)是一种著名的SMC表型调节刺激物，通过转录后调控相关基因下调SMC基因表达，刺激SMC增殖。然而，涉及SMC表型基因表达的转录后机制仍然很大程度上是未知的。我们令人兴奋的初步数据表明，SMC收缩基因的下调是由于其前体mRNAs(Pre-mRNAs)的RNA编辑异常所致。腺苷脱氨酶作用于RNA(ADAR)，将腺苷转化为肌苷(A->I编辑)，促进了这种异常的前mRNA编辑。A-to-I RNA编辑来自内含子或3‘-非翻译区的前mRNA转录本会改变前mRNA的剪接，导致成熟mRNA水平下降和细胞功能异常。PDGF-BB诱导ADAR1，下调SMC肌球蛋白重链(SMMHC)和钙蛋白(CNN)的表达。通过shRNA下调ADAR1，恢复PDGF-BB阻断的SMMHC和CNN的表达，表明ADAR1在SMC表型调控中起重要作用。ADAR1似乎在PDGF-BB诱导的SMC增殖/存活中也起重要作用。体内研究表明，在球囊损伤的大鼠颈动脉中，SMMHC和CNN的成熟mRNA随着其成熟mRNA的减少而积聚。此外，ADAR1最初在中层SMC中高度诱导，随后在损伤后的新生内膜SMC中诱导。重要的是，ADAR1的敲除显著地抑制了损伤诱导的新生内膜的形成，证明了ADAR1在体内血管重塑中的关键作用。这些开创性的发现有力地支持了一种新的假说，即ADAR1/异常RNA编辑介导了PDGF-BB诱导的SMC收缩基因下调和SMC增殖/存活，导致SMC表型改变和血管重构。我们将利用原代培养的SMC、在体大鼠球囊损伤和小鼠金属丝损伤模型，结合分子、细胞和组织学方法，1)确定ADAR1调节SMC表型的作用和机制；2)阐明ADAR1调控SMC增殖/存活的分子机制；3)研究ADAR1在体内SMC表型调节和血管重塑中的作用。这些目标的成功完成将揭开SMC表型调控的新机制，最终将导致确定开发治疗增生性血管疾病的治疗药物的新靶点。

DESCRIPTION (provided by applicant): Vascular smooth muscle (SMC) phenotypic modulation, the transition from a contractile to a proliferative phenotype accompanied by neointima formation following vascular injury, plays a critical role in the development and progression of several proliferative cardiovascular diseases such as atherosclerosis, hypertension, restenosis after angioplasty or bypass, diabetic vascular complications, and transplantation arteriopathy. The regulatory mechanisms underlying SMC phenotypic modulation, however, are poorly understood. A hallmark feature of the phenotypic modulation is the down-regulation of SMC contractile genes. Platelet-derived growth factor-BB (PDGF-BB), a well-known stimulator of SMC phenotypic modulation, down- regulates SMC gene expression and stimulates SMC proliferation via posttranscriptional regulation of the related genes. The post-transcriptional mechanisms involved in SMC phenotype gene expression, however, remain largely unknown. Our exciting preliminary data indicate that the down-regulation of SMC contractile genes is caused by abnormal RNA editing of their precursor mRNAs (pre-mRNAs). This abnormal pre-mRNA editing is facilitated by adenosine deaminase acting on RNA (ADAR), which converts adenosines to inosines (A->I editing). A-to-I RNA editing of the pre-mRNA transcripts from introns or 3'-untranslated regions alters pre- mRNA splicing, leading to decreased mature mRNA levels and abnormal cellular functions. PDGF-BB induces ADAR1 while down-regulating SMC myosin heavy chain (SMMHC) and calponin (CNN). Knockdown of ADAR1 by shRNA restores PDGF-BB-blocked SMMHC and CNN expression, demonstrating that ADAR1 plays an essential role in SMC phenotype modulation. ADAR1 appears to be also important for PDGF-BB-induced SMC proliferation/survival. In vivo studies show that SMMHC and CNN pre-mRNA is accumulated when their mature mRNA is decreased in balloon-injured rat carotid arteries. Moreover, ADAR1 is highly induced in media layer SMCs initially, and neointima SMCs subsequently following the injury. Of importance, knockdown of ADAR1 dramatically inhibits injury-induced neointima formation, demonstrating a critical role of ADAR1 in vascular remodeling in vivo. These seminal findings strongly support a novel hypothesis that ADAR1/abnormal RNA editing mediates PDGF-BB-induced down-regulation of SMC contractile genes and SMC proliferation/survival, leading to SMC phenotypic modulation and vascular remodeling. Using primary culture of SMCs, in vivo rat balloon injury and mouse wire injury models combining with molecular, cellular and histological approaches, we will 1) determine the role and mechanism whereby ADAR1 modulates SMC phenotype; 2) elucidate the molecular mechanisms underlying ADAR1 function in regulating SMC proliferation/survival; and 3) study the role of ADAR1 in SMC phenotypic modulation and vascular remodeling in vivo. Successful completion of these aims will unravel a novel mechanism governing SMC phenotypic modulation, which will ultimately lead to identification of novel targets for developing therapeuti agents to treat proliferative vascular diseases.