Deciphering the role of Lmod2 in thin filament length regulation and dilated cardiomyopathy

 描述(申请人提供)：心肌细胞如何在单分子水平上精确地调节其含有肌动蛋白的细丝的组装，其机制在很大程度上仍不清楚。我们发现，Leiomodin 2(Lmod2)是一种横纹肌特异性肌动蛋白结合蛋白，在哺乳动物中是第一个被描述的肌动蛋白细丝点端延长因子。然而，关于Lmod2在心脏中的作用，人们知之甚少。对我们独特的Lmod2基因敲除(KO)小鼠的初步分析显示，它们在出生后约3周死亡，心脏表现出严重的收缩功能障碍和室腔扩大，与扩张型心肌病(DCM)一致。令人惊讶的是，Lmod2 KO心脏有更短的细丝。当我们分析扩张型心肌病人的心脏样本和多种扩张型心肌病小鼠模型的心脏时，我们发现它们也有更短、更细的细丝。值得注意的是，当DCM在经过充分研究的DCM(肌肉LIM蛋白(MLP)基因敲除小鼠)模型小鼠的心脏中被“拯救”时，适当的细丝长度恢复了。我们假设细丝长度变化是扩张型心肌病复杂重塑的一般机制。这项拟议工作的长期目标是发现扩张型心脏的共同病理生理学，可用作治疗扩张型心肌梗死的治疗靶点。这项建议的直接目标是确定肌动蛋白细丝结构在心肌中的调控机制，Lmod2在这一调控中所起的作用，以及这一调控中的缺陷如何导致DCM。利用新型转基因小鼠(具有异常长或短细丝)、人类肌肉样本和原代心肌细胞，我们将采取多学科方法来实现三个特定目标，着重于确定1)Lmod2缺失对心脏发育和功能的影响；2)Lmod2拉长细丝的机制；3)细丝长度失调在心肌疾病中的作用，以及如果在体内扩张的心脏恢复细丝调节是否可以挽救心脏功能和重塑。我们预测，该项目的完成将导致发现一个关键的一般机制和一个新的结构生物标记物(即细丝长度失调)，在DCM中看到的复杂重塑。这些发现将潜在地促进DCM的早期发现，并导致新的治疗选择。

 DESCRIPTION (provided by applicant): The mechanism whereby cardiomyocytes precisely regulate the assembly of their actin-containing thin filaments at the level of single molecules is still largely unknown. We have discovered that Leiomodin 2 (Lmod2), a striated muscle specific actin-binding protein, functions as the first described actin filament pointed- end elongation factor in mammals. Little is known, however, regarding the function of Lmod2 in the heart. Preliminary analysis of our unique Lmod2 knockout (KO) mice reveal that they die ~3 weeks following birth, with hearts displaying severe contractile dysfunction and ventricular chamber enlargement, consistent with dilated cardiomyopathy (DCM). Strikingly, Lmod2 KO hearts have shorter thin filaments. When we analyzed human heart samples with DCM and hearts from multiple mouse models of DCM we discovered that they too have shorter thin filaments. Remarkably, when DCM was "rescued" in the hearts of a well-studied mouse model of DCM (muscle LIM protein (MLP) knockout mice), proper thin filament lengths were restored. We hypothesize that thin filament length changes are a general mechanism of the complex remodeling that occurs in DCM. The long-term goal of the proposed work is to discover common pathophysiologies of dilated hearts that can be used as therapeutic targets for the treatment of DCM. The immediate goals of this proposal are to determine mechanisms by which actin-thin filament architecture is regulated in cardiac muscle, the role Lmod2 plays in this regulation, and how defects in this regulation contribute to DCM. Using novel transgenic mice (with either abnormally long or short thin filaments), human muscle samples and primary cardiomyocytes, we will take a multidisciplinary approach to accomplish three Specific Aims focused on determining: 1) the effect loss of Lmod2 has on cardiac development and function; 2) the mechanism by which Lmod2 functions to elongate thin filaments; and 3) the role thin filament length dysregulation plays in cardiomyopathies, and whether heart function and remodeling can be rescued if thin filament regulation is restored in a dilated heart in vivo. We predict that completion of this project will result in the discovery of one critical general mechanism and a novel structural biomarker (i.e., thin filament length dysregulation) of the complex remodeling seen in DCM. These discoveries will potentially facilitate early detection of DCM and lead to new therapeutic options.