Ubiquitin-like protein modification in diabetic cardiomyopathy

描述（由申请人提供）：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风险因素，尤其是因为MI后DM患者的左心室功能明显恶化。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的合理关系，这些调节因子已知在MI后心功能障碍中起重要作用。我们的小组已经证明，磷酸二酯酶3A（PDE 3A）的下调与细胞凋亡和诱导型cAMP早期阻遏物（ICER），一种促凋亡转录阻遏物的诱导相关，为血管紧张素II（Ang II）如何调节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，由CA-MEK 51（MEK 51的组成性活性形式）的心脏特异性过表达诱导的ERK 5激活抑制了心肌梗死后DM小鼠（DM + MI）中ICER的诱导和心肌细胞凋亡，但ERK 5和ICER减少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（ERK 5）和伴侣依赖性E3泛素连接酶CHIP（热休克蛋白70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是重要的。ERK 5的激活通过抑制心肌细胞凋亡而具有强的心脏保护作用。此外，ICER被CHIP泛素化和降解，ERK 5活化增强CHIP泛素连接酶活性，随后ICER和FoxO 1降解，并抑制心肌细胞凋亡和自噬。由于CHIP基因敲除小鼠（KO）在压力过度负荷后表现出增加的心肌细胞凋亡和自噬，我们的工作假设是ERK 5介导的Ub连接酶CHIP激活是ICER和FoxO 1蛋白降解的关键调节剂，并保护DM中MI后的心肌细胞免于凋亡和自噬。CHIP介导的泛素化的激活不是ERK 5激活的“唯一”下游靶点，并且存在几种受ERK 5影响的下游分子可能影响MI损伤。在这次重新提交中，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ERK 5以非CHIP依赖的方式调节PPAR 4的反式激活，为我们提供了一个研究ERK 5介导的心脏保护中CHIP依赖性与独立性信号传导的平台。了解ERK 5-CHIP介导的ICER和FoxO 1降解的作用和分子机制以及随后的心脏保护作用，将有助于深入了解DM患者MI后心脏恢复不良的原因，并可能揭示一种新的治疗靶点。其意义在于Ub连接酶CHIP在调节细胞凋亡和自噬中的作用的新假设，以及提出的高度临床相关问题的机制研究。

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.