Ubiquitin-like protein modification in diabetic cardiomyopathy

描述(申请人提供)：流行病学研究强烈表明，糖尿病(DM)是心肌梗死(MI)后死亡率和发病率的独立危险因素，特别是因为MI后DM患者的左心功能显著恶化。然而，缺乏的是糖尿病和任何已知的心肌细胞凋亡调节因子之间可信的关系，这些调节因子在心肌梗死后的心功能障碍中发挥重要作用。我们的研究小组已经证明，磷酸二酯酶3A(PDE3A)的下调与细胞凋亡和诱导型cAMP早期抑制因子(ICER)的诱导有关，这为血管紧张素II(Ang II)如何调控心肌细胞凋亡提供了一个机制框架。我们还发现，在转基因小鼠(TG)中，心脏特异性过表达CA-MEK51(MEK51的组成活性形式)诱导的ERK5激活抑制了DM小鼠心肌梗死后ICER的诱导和心肌细胞的凋亡，但ERK5与ICER降低之间的机制尚不清楚。我们的初步数据表明，细胞外信号调节蛋白激酶5(ERK5)和伴侣依赖的E3泛素连接酶芯片(Hsp70相互作用蛋白的羧基末端)在调节糖尿病心肌梗死后的心脏损害中起重要作用。ERK5的激活通过抑制心肌细胞的凋亡而发挥强大的心脏保护作用。此外，ICER被CHIP和ERK5激活泛素化并被降解，从而增强了CHIP泛素连接酶的活性，随后ICER和FoxO1的降解，并抑制了心肌细胞的凋亡和自噬。由于CHIP基因敲除小鼠(KO)在压力超负荷后表现出更多的心肌细胞凋亡和自噬，我们的工作假设是ERK5介导的Ub连接酶CHIP的激活是糖尿病心肌梗死后ICER和FoxO1蛋白降解的关键调节因子，并保护心肌细胞免受凋亡和自噬的影响。芯片介导的泛素化激活并不是ERK5激活的“唯一”下游靶点，ERK5影响的下游分子可能影响心肌梗死损伤。在这次重新提交的报告中，我们增加了一项关于过氧化物酶体增殖物激活受体(PPAR)4的研究，因为ERK5以一种不依赖于芯片的方式调节PPAR 4的反式激活，为我们提供了一个研究ERK5介导的心脏保护中依赖于芯片的信号与独立信号的平台。了解ERK5芯片介导的ICER和FoxO1降解以及随后的心脏保护的作用和分子机制将有助于深入了解糖尿病心肌梗死后心脏恢复不良的原因，并可能揭示新的治疗靶点。其意义在于关于Ub-连接酶芯片在调节细胞凋亡和自噬中的作用的新假说，以及对一个高度临床相关问题的拟议机制研究。

DESCRIPTION (provided by applicant): Epidemiological studies strongly indicate that diabetes mellitus (DM) is an independent risk factor for both mortality and morbidity following myocardial infarction (MI), especially since post-MI left ventricular function is significantly worse in DM patients. However, what is lacking is a plausible relationship between diabetes and any of the known regulators of cardiomyocyte apoptosis known to play a significant role in the post-MI cardiac dysfunction. Our group has demonstrated that down-regulation of phosphodiesterase 3A (PDE3A) is associated with apoptosis and induction of inducible cAMP early repressor (ICER), a proapoptotic transcriptional repressor, providing a mechanistic framework for how angiotensin II (Ang II) regulates myocyte apoptosis. We also showed that ERK5 activation induced by cardiac specific overexpression of CA- MEK51 (constitutively active form of MEK51) in transgenic mice (Tg) inhibited ICER induction and myocyte apoptosis in DM mice after myocardial infarction (DM + MI), but the mechanism between ERK5 and ICER reduction remains unknown. Our preliminary data show that extracellular signal regulated protein kinase 5 (ERK5) and the chaperone-dependent E3 ubiquitin ligase CHIP (carboxyl terminus of Hsp70-interacting protein) are important in regulating heart damage after myocardial infarction in diabetes. ERK5 activation has a strong cardio-protective effect via inhibition of cardiomyocyte apoptosis. Moreover, ICER is ubiquitinated and degraded by CHIP and ERK5 activation enhances CHIP ubiquitin ligase activity, subsequent ICER and FoxO1 degradation, and inhibits both cardiomyocyte apoptosis and autophagy. Since CHIP knockout mice (KO) showed increased myocyte apoptosis and autophagy after pressure overlaod, our working hypothesis is that ERK5-mediated Ub ligase CHIP activation is a key modulator of ICER and FoxO1 protein degradation and protects cardiomyocytes from both apoptosis and autophagy after MI in DM. Activation of CHIP-mediated ubiquitination is not the "only" downstream target of ERK5 activation, and there are several downstream molecules affected by ERK5 likely to impact MI injury. In this resubmission, we added a study on peroxisome proliferator-activated receptor (PPAR) 4 since ERK5 regulates PPAR4 transactivation in a CHIP-independent manner providing us with a platform to study CHIP-dependent vs. independent signaling in ERK5-mediated cardio-protection. Understanding the role and molecular mechanisms of ERK5-CHIP-mediated ICER and FoxO1 degradation and subsequent cardio-protection should provide insight into the reasons for poor cardiac recovery after MI in DM and possibly reveal a novel therapeutic target. The significance lies in the novel hypothesis on the role of the Ub-ligase CHIP in regulating both apoptosis and autophagy, and the proposed mechanistic study of a highly clinically relevant problem.