TNF-ALPHA REGULATION OF AT1 RECEPTOR & POST-MI FIBROSIS

心肌梗死后重构过程中纤维组织的沉积是心功能的关键决定因素。纤维化最初见于心肌坏死部位，在那里形成替代疤痕是伤口愈合过程的重要组成部分。广泛的间质纤维化也可发生在心脏的非梗死段。尽管瘢痕和非梗死段心肌纤维组织沉积在决定心功能方面具有重要意义，但心肌梗死后心肌纤维化的机制仍然知之甚少。血管紧张素（Ang） II似乎在心肌梗死后纤维化中起重要作用。AT1与I型受体结合，激活心脏成纤维细胞并刺激其产生与纤维组织沉积相关的蛋白质和生长因子。心肌梗死后，心肌成纤维细胞上的AT1受体密度增加。肿瘤坏死因子- α (TNFalpha)出现在心肌梗死后的心脏中，有证据表明它也参与心肌梗死后的重构。最近来自研究者实验室的证据表明，TNFalpha增加培养的心脏成纤维细胞上的AT1受体密度，这表明这些系统之间的相互作用可能参与心肌梗死后重构。本建议中概述的研究将检验这种相互作用的重要性和所涉及的机制。具体的目的是确定：1。TNFalpha的出现、心肌成纤维细胞AT1受体密度的增加与心肌梗死后重构过程中纤维化的发生之间的时空关联；2. TNFalpha诱导的AT1受体上调是否增强心肌梗死后细胞外基质重塑相关的成纤维细胞功能；3. TNFalpha通过激活NF-kappaB和AP-1介导AT1A基因转录的增加；4. 如果TNFalpha的缺失阻止了AT1受体的上调，并导致心肌梗死后瘢痕形成缺陷。这些结果有望表明，AT1受体的TNFalpha上调在心肌梗死后纤维化中起重要作用，并确定心脏成纤维细胞中AT1受体密度增加的信号转导途径和分子机制。这一信息将为心肌梗死后纤维化的发病机制提供重要的见解。

The deposition of fibrous tissue during post-MI remodeling is a critical determinant of cardiac function. Fibrosis is seen initially at the site of myocardial necrosis where development of a replacement scar is an essential component of the wound healing process. Extensive interstitial fibrosis can also develop in non-infarcted segments of the heart. Despite the importance of fibrous tissue deposition in both the scar and in non-infarcted segments of myocardium in determining cardiac function, the mechanisms responsible for post-MI cardiac fibrosis are still poorly understood. Angiotensin (Ang) II appears to play an important role in post-MI fibrosis. Ang II binding with the type I receptor, AT1 activates cardiac fibroblasts and stimulates them to produce proteins and growth factors associated with fibrous tissue deposition. Moreover, AT1 receptor density is increased on cardiac fibroblasts post-MI. Tumor necrosis factor-alpha (TNFalpha) appears in the heart post-MI and there is evidence to suggest that it also is involved in post-MI remodeling. Recent evidence from the investigator's laboratory showing that TNFalpha increases AT1 receptor density on cultured cardiac fibroblasts suggests that an interaction between these systems may be involved in post-MI remodeling. The studies outlined in this proposal will test the significance of this interaction and the mechanisms involved. The specific aims are to determine: 1. the spatial and temporal association between the appearance of TNFalpha, increased AT1 receptor density on cardiac fibroblasts and development of fibrosis throughout post-MI remodeling; 2. if TNFalpha induced AT1 receptor upregulation enhances cardiac fibroblast functions related to post-MI extra cellular matrix remodeling; 3. increased transcription of the AT1A gene by TNFalpha is mediated by activation of NF-kappaB and AP-1, and; 4. if the absence of TNFalpha prevents AT1 receptor upregulation and causes deficient scar formation post-MI. The results are expected to show that TNFalpha upregulation of the AT1 receptor plays an important role in post-MI fibrosis and to identify signal transduction pathways and molecular mechanisms involved in the increase in AT1 receptor density in cardiac fibroblasts. This information will provide important insights into the pathogenesis of post-MI fibrosis.