后适应和梗死后的心肌修复

Maladaptive tissue repair after myocardial infarction plays a major role in development of heart failure. Animal studies have demonstrated that postconditioning reduces infarct size. Clinical observations have also yielded encouraging data showing that protection with postconditioning is sustained after a prolonged period of reperfusion in patients, suggesting its role in promoting cardiac repair and function. However, mechanisms underlying postconditioning-mediated beneficial tissue repair are less clear. The current application tests the hypotheses that postconditioning promotes tissue repair and cardiac function through modulating "TGFβ1/Smad/mitochondria" signaling pathways. Three aims are as follows 1) to demonstrate whether the balance between extracellular matrix degradation and deposition, and TGFβ1 activation by postconditioning are associated with TGFβ1/Smad-dependent pathway and myofibroblast accumulation, respectively; 2) to illustrate whether signaling pathways underlying postconditioning-protection is associated with TGFβ1/Smad-independent regulation through stimulation of intracellular MAPKs family; 3) to determine whether the inhibitory effect of postconditioning on mitochondrial transition pore opening is associated with TGFβ1/Smad-dependent pathway using multiple interventions including gene overexpression, gene knockout and pharmacological receptor antagonists. Taken together, it is expected that these results will provide experimental evidence and theoretical basis for pharmacological interventions for treatment in patients with heart failure after myocardial infarction. These studies will also provide a prime example of bench-bedside translational research in development of protective strategy for other organs at risk of maladaptive tissue repair.

心肌梗死后的组织修复异常是心衰发生的关键。动物研究证实后适应可减小心梗面积。临床观察也表明后适应对心梗病人的保护效应在恢复血供后仍然明显,提示其改善心肌异常修复和心功能的作用,但后适应促进修复的机理报道尚少。本研究提出"后适应-TGFβ1/Smad/线粒体-心脏保护"假设,探讨后适应影响心肌修复和心衰的机理，包括:1)阐明后适应保护的分子机制,了解细胞外基质降解和平衡是否通过TGFβ1/Smad依赖性通路?证实TGFβ1活性变化是否和成肌纤维细胞聚集有关?2)证实后适应保护的信号传递是否还受胞浆内蛋白激酶如MAPKs活化的影响:即TGFβ1激活Smad的非依赖性通路是如何调节的?3)利用增强基因表达、基因敲除和受体阻断剂等手段，分析后适应对线粒体膜通透性变化的影响是否也和TGFβ1/Smad的活化过程有关？本研究可为通过药物性干预治疗梗死后心衰及其它脏器损伤的临床研究提供观察数据和依据。

我们和他人的基础研究观察表明，后适应具有减小心梗面积，改善心肌异常修复和促进心功能的作用。本基金资助研究的主要发现是：1）后适应的保护作用，是通过调定血管紧张素II受体及下游的传导来实现，包括对巨噬细胞迁移，成肌纤维细胞的聚集，TGFβ1/Smad的依赖性通路的激活，以及心肌纤维化的生成的抑制；2）在探讨后适应保护机制的同时，我们发现由脾脏释放的巨嗜细胞，参与了由血管紧张素II AT1受体所致的心肌纤维化，这一作用可被切除脾脏所抑制，为后适应心脏保护机理的进一步研究提供了依据；3）证实了血管紧张素II通过活化其AT1受体，抑制ACE2活性和eNOS的表达，增强CD44和透明质酸酶交互作用，进而导致心肌纤维化的信号传导机理；4）利用主动脉狭窄的大鼠，观察了氧自由基活化清除剂Edaravone 和姜黄素curcumin，通过抑制血管紧张素II活化改善心功能的作用，进一步佐证了后适应的保护作用；5）利用敲除细胞表面的透明脂酸酶受体CD44小鼠摸型，发现血管紧张素II引起的巨噬细胞聚集和成纤维细胞增生，和CD44受体-透明脂酸酶受体的交互作用有关；6）证实了免疫抑制剂，cyclosporine在正常个体，不具有调定血管紧张素II和导致高血压以及心肌纤维化的作用，为其在临床心梗治疗的进一步开展，提供了实验证据。上述研究表明，利用后适应作为干预手段，可明显减轻心肌异常修复的程度，这一调定作用是通过抑制血管紧张素II来实现的。因此，在目前临床心梗病人药物治疗不足的前提下，这些结果为后适应在可能用于附助药物治疗，降低心梗病人发病和死亡率，提供了思路和方向。