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

 描述（由申请人提供）：心肌细胞在单分子水平上精确调节其含肌动蛋白的细丝组装的机制在很大程度上仍然是未知的。我们已经发现Leiomodin 2（Lmod 2），一种横纹肌特异性肌动蛋白结合蛋白，在哺乳动物中作为第一个描述的肌动蛋白丝尖端延伸因子起作用。然而，关于Lmod 2在心脏中的功能知之甚少。对我们独特的Lmod 2敲除（KO）小鼠的初步分析显示，它们在出生后约3周死亡，心脏显示严重的收缩功能障碍和室腔扩大，与扩张型心肌病（DCM）一致。引人注目的是，Lmod 2 KO心脏具有较短的细丝。当我们分析患有DCM的人类心脏样本和来自DCM的多个小鼠模型的心脏时，我们发现它们也有较短的细丝。值得注意的是，当DCM在一个经过充分研究的DCM小鼠模型（肌肉LIM蛋白（MLP）敲除小鼠）的心脏中被“拯救”时，适当的细丝长度得到了恢复。我们推测，细丝长度的变化是一个复杂的重塑发生在DCM的一般机制。 这项工作的长期目标是发现扩张心脏的常见病理生理学，这些病理生理学可用作治疗DCM的治疗靶点。该提案的直接目标是确定肌动蛋白细丝结构在心肌中调节的机制，Lmod 2在此调节中的作用，以及此调节中的缺陷如何导致DCM。使用新型转基因小鼠（具有异常长或短的细丝）、人肌肉样品和原代心肌细胞，我们将采取多学科方法来实现三个特定目的，集中于确定：1）Lmod 2的缺失对心脏发育和功能的影响; 2）Lmod 2发挥作用以延长细丝的机制;以及3）细纤维长度失调在心肌病中的作用，以及如果在体内扩张的心脏中恢复细纤维调节，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志物（即，细纤维长度失调）的复杂重塑中看到的DCM。这些发现可能有助于DCM的早期检测，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.