Pathological arterial muscularization and the role of integrins

描述(申请人提供)：心血管疾病对人类健康造成巨大负担，我们的长期目标是减少血管平滑肌细胞(VSMCs)的过度积累，而VSMCs是许多此类疾病的核心。正常动脉的中膜由交替排列的VSMCs层和弹力层组成。各种动脉疾病，包括动脉粥样硬化、再狭窄、肺动脉高压和主动脉瓣上狭窄(SVAS)，都受到弹性板层缺陷和肌化过度的困扰。SVAS是一种毁灭性的人类疾病，其特征是VSMC负担增加，阻塞大动脉，由弹性蛋白基因ELN杂合零突变引起。类似地，弹性蛋白突变的小鼠会出现大动脉的肌肉化和狭窄，比如主动脉。大血管手术是目前唯一的治疗方法 对于SVAS，由于没有有效的药理选择可用。开发有效的血管疾病治疗方法的一个主要障碍是对过剩VSMC的细胞来源(S)缺乏了解；事实上，先前的研究没有追踪到弹性蛋白突变中的任何细胞群体的谱系。此外，弹性蛋白突变体引起的主动脉高肌化的分子和细胞机制还不是很清楚。我们的初步研究表明，在弹性蛋白突变的主动脉中，整合素�的表达和整合素信号强烈上调，降低�水平或活性可以减弱过度的肌化。此外，编码�ITGB3的基因剂量的减少，延长了ELN(-/-)幼崽的生存能力，这对于任何遗传或药物干预来说都是前所未有的。减轻�表达增加是减少SVAS患者动脉过度肌化的一个有潜力的有吸引力的策略。虽然对�表达的调控知之甚少，但生长停滞特异的同源盒(GAX)转录因子在VSMC中表达，GAX的过度表达降低了�的水平，促进了细胞的增殖和迁移。我们假设，在弹性蛋白突变体中，Gax下调诱导原有的主动脉平滑肌中整合素�的表达，导致血管平滑肌细胞的异常取向、增殖和迁移，从而导致主动脉狭窄。本建议利用转基因突变小鼠以及从小鼠和人VAS主动脉组织和细胞中分离的VSMCs的研究，从三个特定目的来检验这一假说：1)在弹性蛋白突变的主动脉中，确定过量VSMC的细胞来源(S)；2)在弹性蛋白缺陷的小鼠、小鼠VSMC和人SVAS来源的平滑肌细胞中，阐明整合素�诱导主动脉过度肌化的分子和细胞机制；以及3)阐明GAX在调节弹性蛋白突变的整合素样�表达增强和肌化过度中的作用。综上所述，我们建议的研究将勾勒出弹性蛋白缺乏、整合素�和主动脉高肌化之间的潜在联系的机制，从而为开发新的治疗方法来治疗SVAS和其他血管增生性疾病提供具体步骤。

DESCRIPTION (provided by applicant): Cardiovascular diseases exert a massive burden on human health, and our long term objective is to attenuate the excessive accumulation of vascular smooth muscle cells (VSMCs) that is central to many of these diseases. The tunica media of the normal artery is composed of alternating circumferential layers of VSMCs and elastic lamellae. Diverse arterial disorders, including atherosclerosis, restenosis, pulmonary hypertension and supravalvular aortic stenosis (SVAS) are plagued by defective elastic lamellae as well as hypermuscularization. SVAS, a devastating human disease characterized by an increased VSMC burden that occludes large arteries, is caused by heterozygous null mutations in the elastin gene ELN. Similarly, elastin mutant mice develop hypermuscularization and stenosis of large arteries, such as the aorta. Major vascular surgery is the only current treatment for SVAS as no effective pharmacological options are available. A major obstacle to developing effective therapies for vascular disorders is the poor understanding of the cellular source(s) of excess VSMCs; indeed no prior studies have traced the lineage of any cell populations in elastin mutants. In addition, the molecular and cellular mechanisms underlying aortic hypermuscularization in elastin mutants are not well defined. Our initial studies indicate that integrin �expression and integrin signaling is robustly upregulated in the elastin mutant aorta and that reduction of �levels or activity attenuates the excessive muscularization. Furthermore, reduction of the dosage of the gene encoding � Itgb3, extends the viability of Eln(-/-) pups which is unprecedented for any genetic or pharmacological intervention. A potentially attractive strategy for reducing arterial hypermuscularization in SVAS is attenuating the increased �expression. Although little is known regarding regulation of �expression, the growth arrest-specific homeobox (Gax) transcription factor is expressed in VSMCs and Gax overexpression reduces �levels, proliferation and migration. We hypothesize that in elastin mutants, Gax downregulation induces integrin �expression in pre-existing aortic smooth muscle resulting in aberrant VSMC orientation, proliferation and migration and thus aortic stenosis. This proposal utilizes studies of transgenic mutant mice, VSMCs isolated from the murine aorta and human SVAS aortic tissue and cells to test this hypothesis in three specific aims: 1) in the elastin mutant aorta, identify the cellular source(s) of excessive VSMCs; 2) in elastin deficient mice, murine VSMCs and human SVAS-derived smooth muscle cells, elucidate the molecular and cellular mechanisms underlying integrin �induced excess aortic muscularization; and 3) elucidate the role of Gax in mediating enhanced integrin �expression and hypermuscularization in elastin mutants. Taken together, our proposed studies will delineate mechanisms underlying the identified link between elastin deficiency, integrin �and aortic hypermuscularization and thereby provide concrete steps towards developing novel therapeutic strategies for SVAS and other vasculoproliferative diseases.