Inflammatory serine proteases and cardiac repair post myocardial infarction

 描述(申请人提供)：在成人心脏，心肌梗死(MI)后的细胞死亡会引发炎症反应，清除死亡细胞，促进疤痕形成和心脏修复。由于成年哺乳动物心脏的再生能力有限，这种先天免疫反应的诱导可能是不适应的，并损害心脏收缩功能。在新生小鼠中，心肌梗死后心脏可以完全再生，而不会留下疤痕；然而，这种再生能力在出生后很快就会丧失。免疫系统的主动作用及其对损伤的反应被认为是新生儿心脏再生的中心调节因子。然而，新生儿获得性免疫调节心脏再生的确切机制在很大程度上还不清楚。我们发现，出生后第1天(P1)小鼠心肌梗死的诱导导致了一种炎症反应，这种反应未能激活关键的炎性丝氨酸蛋白酶(ISPs)，这种酶是白细胞激活时释放的酶，是炎症部位组织损伤的主要原因。相比之下，当心肌梗死在P7或更晚的时候进行时，可以观察到ISPs的激活，此时心脏的再生能力非常低。由于ISPs的激活发生在心肌损伤后早期，是炎症反应的重要调节因子，并在功能上调节许多调节细胞生长和功能的蛋白质底物，因此我们假设ISPs的激活在调节心脏再生和修复方面发挥积极作用。初步研究表明，在体内使用二肽基肽酶I(DPPI)缺陷的小鼠抑制ISPs，与野生型相比，可促进出生后发育期间和心肌梗死成人心脏的心肌细胞增殖，并改善心脏重构和功能。有趣的是，DPPI缺失也提高了梗死区干细胞的存活率，这表明ISPs不仅通过影响心肌细胞的生长和增殖，而且还通过调节干细胞的存活和生长来调节MI后的修复。这些数据支持这样的假设，即ISPs的激活损害了内源性心脏修复，并导致心肌梗死后的心功能障碍。在这里，我们将确定抑制ISPs是否能增强心肌梗死损伤后新生儿和成人心脏的内源性修复和再生。我们还将确定ISPs调节新生儿和成人心脏再生的机制。长期目标是开发针对DPPI的新策略，以加强MI后的心脏修复，目前还没有单一的药物可用。

 DESCRIPTION (provided by applicant): In the adult heart, cell death following myocardial infarction (MI) initiates an inflammatory reaction that removes dead cells and contributes to scar formation and cardiac repair. Since the regenerative capacity of the adult mammalian heart is limited, induction of this innate immune response could be maladaptive and compromises cardiac contractile function. In neonatal mice, the heart can regenerate fully without scarring following MI; however, this regenerative capacity is largely lost rapidly after birth. A proactive role of the immune system and its response to injury has been proposed to be a central mediator of neonatal heart regeneration. However, the exact mechanisms by which neonatal adaptive immunity modulates heart regeneration are largely unknown. We found that induction of MI in post-natal day 1 (P1) mice induced an inflammatory response that failed to activate key inflammatory serine proteases (ISPs), enzymes released upon leukocyte activation and are the primary reason for tissue damage at the sites of inflammation. In contrast, activation of ISPs was observed when MI was performed at P7 or later, a time when the regenerative capability of the heart is very low. Because activation of ISPs occurs early after myocardial injury, is an important regulator of the inflammatory response and functionally modulates a number of protein substrates that regulate cell growth and function, we hypothesize that activation of ISPs plays an active role in regulating cardiac regeneration and repair. Pilot study shows that inhibition of ISPs in vivo using mice deficient in DiPeptidyl Peptidase I (DPPI), a key enzyme necessary for the cleavage and activation of major ISPs, enhanced cardiomyocyte proliferation during post-natal development and in adult hearts subjected to MI compared to wild-type, along with an improvement in cardiac remodeling and function. Interestingly, DPPI deletion also enhanced the survival of stem cells in the infarcted area, suggesting that ISPs modulate post-MI repair by affecting not only cardiomyocyte growth and proliferation, but also by modulating stem cell survival and growth. These data support the hypothesis that activation of ISPs impairs endogenous cardiac repair and leads to cardiac dysfunction post-MI. Here, we will determine whether inhibition of ISPs enhances endogenous cardiac repair and regeneration in neonatal and adult heart after MI injury. We will also define the mechanisms by which ISPs modulate cardiac regeneration of neonatal and adult hearts. The long term goal is to develop novel strategies targeting DPPI to enhance cardiac repair after MI, for which not a single drug is currently available.