Role of Chymase In The Post-Myocardial Infarction Heart

描述（由申请人提供）：Chymase是一种多功能肥大细胞丝氨酸蛋白酶，在小鼠心脏体内产生血管紧张素（Ang） II并激活前基质金属蛋白酶(MMP)-2/9。我们发现联合ACE +酶抑制可改善左心室（LV）功能，减少不良的心脏重构，并显著提高心肌梗死后的生存率（Wei等，journal clinical Invest. 120, 1229- 39,2010）。然而，就其本身而言，切酶抑制是轻度有效的，这表明ACE抑制增强了切酶的释放。这一发现支持了ACE抑制导致左室间质中缓激肽/激肽B2受体介导的小鼠肥大细胞蛋白酶(MMCP)-4（人乳糜酶的功能同源物）的释放。尽管这些研究结果表明，缓激肽增强对ace抑制剂治疗的心肌梗死后心脏的有益作用被缓激肽介导的溶酶释放所抵消，但溶酶的下游靶点尚不清楚。我们假设MMCP-4的释放限制了ACE抑制剂治疗在心肌梗死后心脏的疗效，因为它激活了mmp -9前体并产生Ang II。众所周知，MMP-9通过降解间质胶原促进心肌梗死后早期左室扩张，而Ang II促进心肌细胞肥大和间质纤维化。我们将使用靶向缺失MMCP-4和/或MMP-9的小鼠来验证我们的假设。在Specific Aim 1中，我们将证明，心肌梗死后，mmcp -4依赖性Ang II的产生限制了ACE抑制剂在减少晚期心肌细胞肥大和左室远端心肌间质纤维化方面的功效。Ang II结合两种受体亚型AT1和AT2。ACE抑制WT与MMCP-4（-/-）小鼠将分别接受安慰剂和AT1 + AT2受体阻断联合治疗，以证实尽管ACE抑制，MMCP-4依赖性Ang II的形成参与心肌梗死后心脏晚期心肌细胞肥大和左室间质纤维化的假设。在Specific Aim 2中，我们将证明，在ACE抑制剂治疗的心肌梗死小鼠中，早期左室间质胶原积累的衰减、左室扩张和死亡率受到MMCP-4依赖性前mmp -9激活的限制。在本研究的第一部分中，我们将定义肥大细胞脱颗粒、mmcp -4依赖性前mmp -2/9激活和ACE抑制剂治疗的心肌梗死后心脏左室扩张之间的时间关系，并将这些变化与ACE抑制剂治疗的WT小鼠心肌梗死后心脏早期左室扩张和功能障碍联系起来。在本研究的第二部分，我们将证明mmcp -4依赖性的前mmp -9激活限制了ACE抑制剂治疗在心肌梗死小鼠的左室扩张、功能和生存方面的疗效。这些发现可以解释为什么在ACE抑制剂中添加AT1受体阻滞剂并不能改善ACE抑制剂单药治疗的生存结果。这表明，在已经接受ACE抑制剂治疗的心肌梗死后患者中，溶酶抑制可能比进一步中断肾素-血管紧张素系统更有效。如果提出的假设得到证实，我们的发现将为开发针对心血管疾病患者的新型治疗药物提供基础。

DESCRIPTION (provided by applicant): Chymase, a multifunctional mast cell serine protease, generates angiotensin (Ang) II and activates pro-matrix metalloproteinase (MMP)-2/9, in vivo, in the mouse heart. We show that combined ACE + chymase inhibition improves left ventricle (LV) function, decreases adverse cardiac remodeling, and markedly improves survival after MI (Wei et al., J Clin Invest. 120, 1229-39, 2010). However, by itself, chymase inhibition is mildly efficacious, suggesting that ACE inhibition potentiates chymase release. This is supported by the finding that ACE inhibition causes bradykinin/kinin B2 receptor-mediated release of mouse mast cell protease (MMCP)-4 (functional homolog of human chymase) in the LV interstitium in vivo. Although these findings suggest that the beneficial effects of bradykinin potentiation in the ACE-inhibitor-treated post-MI heart are counteracted by bradykinin-mediated chymase release, the downstream targets of chymase are unknown. We hypothesize that MMCP-4 release limits the cardiac efficacy of ACE inhibitor therapy in the post-MI heart because it activates pro-MMP-9 and generates Ang II. It is known that MMP-9 contributes to early post-MI LV dilatation by degrading interstitial collagen, and Ang II promotes cardiomyocyte hypertrophy and interstitial fibrosis. We will explore our hypothesis using mice with targeted deletion of MMCP-4 and/or MMP-9. In Specific Aim 1 we will demonstrate that, after a MI, MMCP-4-dependent Ang II generation limits ACE inhibitor efficacy in reducing late-stage cardiomyocyte hypertrophy and LV interstitial fibrosis in the distal LV myocardium. Ang II binds to two receptor subtypes, AT1 and AT2. ACE-inhibited WT versus MMCP-4(-/-) mice will be treated with placebo versus a combination of AT1 + AT2 receptor blockade to confirm the hypothesis that, despite ACE inhibition, MMCP-4- dependent Ang II formation is involved in late-stage cardiomyocyte hypertrophy and LV interstitial fibrosis in the post-MI heart. In Specific Aim 2 we will demonstrate that, in ACE inhibitor-treated mice with MI, attenuation of early LV interstitial collagen accumulation, LV dilatation and the rate of mortality are limited by MMCP-4- dependent pro-MMP-9 activation. In Part I of this Aim we will define the temporal relationship between mast cell degranulation, MMCP-4-dependent pro-MMP-2/9 activation, and LV dilatation in ACE-inhibitor treated post-MI hearts and relate these changes to early LV dilatation and dysfunction in the post-MI heart of ACE inhibitor-treated WT mice. In Part II of this Aim we will demonstrate that MMCP-4-dependent pro-MMP-9 activation limits the efficacy of ACE inhibitor therapy with respect to LV dilatation, function and survival in mice with MI. Such findings could explain why adding an AT1 receptor blocker to an ACE inhibitor does not improve survival outcomes over ACE inhibitor monotherapy. It suggests that chymase inhibition, rather than further interruption of the renin-angiotensin system, may be more efficacious in post-MI patients already treated with an ACE inhibitor. If the proposed hypotheses are confirmed, our findings would provide a foundation for the development of novel therapeutic agents directed toward patients with cardiovascular disease. PUBLIC HEALTH RELEVANCE: Angiotensin I-converting enzyme inhibitor therapy is particularly efficacious in improving cardiovascular survival following acute MI. We show that its efficacy, with regard to cardiac function and survival, is greatly enhanced by the addition of a chymase inhibitor. The proposed identification of the downstream targets of chymase should provide a foundation for the development of novel therapeutic agents directed toward patients with cardiovascular disease.