Role of Chymase In The Post-Myocardial Infarction Heart

描述（由申请人提供）：糜蛋白酶是一种多功能肥大细胞丝氨酸蛋白酶，在小鼠心脏中体内产生血管紧张素（Ang）II并激活基质金属蛋白酶原（MMP）-2/9。我们表明，联合ACE +糜酶抑制可改善左心室（LV）功能，减少不良心脏重塑，并显著改善MI后的存活率（Wei et al.，《临床投资杂志》120，1229-39，2010）。然而，就其本身而言，糜酶抑制是温和有效的，表明ACE抑制增强糜酶释放。这一点得到以下发现的支持：ACE抑制导致缓激肽/激肽B2受体介导的小鼠肥大细胞蛋白酶（MMCP）-4（人糜酶的功能同系物）在体内LV平滑肌中的释放。虽然这些发现表明，缓激肽增强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糜酶释放所抵消，但糜酶的下游靶点尚不清楚。我们假设MMCP-4的释放限制了心肌梗死后心脏ACE抑制剂治疗的心脏疗效，因为它激活MMP-9前体并产生Ang II。已知MMP-9通过降解间质胶原而促进MI后早期LV扩张，并且Ang II促进心肌细胞肥大和间质纤维化。我们将使用MMCP-4和/或MMP-9靶向缺失的小鼠来探索我们的假设。在具体目标1中，我们将证明，在MI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远端LV心肌中的LV间质纤维化方面的功效。血管紧张素II结合两种受体亚型，AT 1和AT 2。ACE抑制的WT与MMCP-4（-/-）小鼠将用安慰剂与AT 1 + AT 2受体阻断剂的组合治疗，以证实以下假设：尽管ACE抑制，但MMCP-4依赖性Ang II形成涉及MI后心脏中的晚期心肌细胞肥大和LV间质纤维化。在具体目标2中，我们将证明，在ACE通路治疗的MI小鼠中，早期LV间质胶原积聚的衰减、LV扩张和死亡率受到MMCP-4依赖性pro-MMP-9活化的限制。在本目标的第一部分，我们将确定肥大细胞脱粒，MMCP-4依赖性pro-MMP-2/9激活，并在ACE抑制剂治疗的心肌梗死后心脏的LV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的早期LV扩张和功能障碍。在本目标的第二部分中，我们将证明MMCP-4依赖性MMP-9前体激活限制了ACE抑制剂治疗对MI小鼠左室扩张、功能和存活率的疗效。这些发现可以解释为什么在ACE抑制剂中加入AT 1受体阻滞剂并不能改善ACE抑制剂单药治疗的生存结局。这表明，糜酶抑制，而不是进一步中断的肾素-血管紧张素系统，可能是更有效的后心肌梗死患者已经用ACE抑制剂治疗。如果所提出的假设得到证实，我们的研究结果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.