心肌细胞极化和心脏致密化不全的分子机制研究

Ventricular trabeculation and compaction are two interconnected morphogenetic events critical for ventricular wall formation. Altered genetic control of these events can lead to the Left Ventricular Noncompaction (LVNC), a recently classified inherited cardiomyopathy with marked thickening of trabeculae and increased intertrabecular recesses. The etiology and pathogenesis of LVNC are elusive largely due to the heterogeneity of the patients and the overall lack of understanding of the molecular mechanisms orchestrating ventricular trabeculation and compaction. In the past decade, by systematically analyzing the ventricular trabeculation and compaction in several genetically manipulated mice, we were able to identify several critical intercellular and intracellular signaling pathways contributing to normal ventricular wall development, which when disrupted give rise to ventricular hypertrabeculation and noncompaction. Recently, we have demonstrated that endocardial-endothelial Notch1 has an important role in regulating Neuregulin1 (NRG1)-ErbB2/4 signaling pathways and Bone Morphogenetic Protein 10 (BMP10)-mediated signaling pathway. The BMP10 pathway is critical to promote cardiomyocyte proliferation and regulate ventricular wall growth. Elevated level of BMP10 contributes to the ventricular hypertrabeculation. NRG1-ErbB2/4 signaling, however, is potentially a negative regulator of a non-canonical Wnt planner cell polarity (PCP), which is critical to establish cardiomyocyte polarity and myofibrillogenesis and regulate ventricular wall compaction. Enhanced NRG1-ErbB2/4 signaling likely contributes primarily to ventricular noncompaction. Recently, we have identified Dishevelled-associated activator of morphogenesis 1 (Daam1), an effector of Wnt/PCP signaling is down-regulated by NRG1 treatment. Genetic ablation of Daam1 leads to ventricular noncompaction. More importantly, the over-activation of one of the NRG1 down-stream signaling components p21-activated kinase 1 (Pak1) can negatively regulate Daam1 protein expression and function. We hypothesize that there are two independent, yet potentially interrelated, signaling pathways involved in the regulation of ventricular trabeculation and compaction: one primarily regulates cardiomyocyte proliferation and the other regulates cardiomyocyte polarization/myofibrillogenesis. This proposal builds upon these findings and will address the following questions: 1) if Daam1 is a down-stream effector of non-canonical Wnt signaling pathway in developing ventricular cardiomyocytes; 2) if the protein kinase Pak1 is a key negative regulator of Daam1; 3) if over-activation of Pak1 and down-regulation of Daam1 contributes to ventricular noncompaction. These studies will further validate and refine our novel working model for ventricular wall development, and will provide new insights into the molecular pathogenesis of ventricular noncompaction.

心室壁发育中的室壁小梁和致密层的形态缺陷可以导致左室致密化不全（LVNC），进而导致心力衰竭。但LVNC的病因却缺乏深入的分子机制研究。在过去十年的工作中，我们确认了BMP10信号通路是调节心室壁发育的重要信号途径。我们最近的工作发现，非经典Wnt/PCP通路是建立心肌细胞极性、肌丝发生和调节致密层形成的调节因素，敲除Wnt / PCP信号通路中的Daam1基因可以导致心脏致密化不全。据此我们推测，心室小梁和致密层的形成可能由两个相互独立的信号途径参与：一种途径主要调节心肌细胞增殖，而另外一条途径则调节心肌细胞极化与肌丝发生。对此，我们的课题拟解决以下问题:1)确认Daam1是非经典Wnt信号通路中参与心室发育的调节因素 2)确认Pak1激酶是Daam1的负调控因子; 3)确认过度激活的Pak1蛋白和下调表达的Daam1蛋白导致心室致密化不全。该研究将有望阐明LVNC心肌病的分子发病机制。

室壁小梁化和室壁致密化是心室发育过程中中相对独立但又综合协调的两个关键发育过程，与之相关的遗传基因突变将导致特殊的心肌病表型-心肌致密化不全（LVNC）。由于LVNC在临床表型上和基因型上具有高度的异质性，对其病因和病理学、临床分型和诊断、以及发病机理的研究仍非常有限，而且在过去的十多年中存在着许多的争议，其中的关键争议就在于是否存在特异的遗传或信号调控机制。另外，由于LVNC病人的增加，LVNC心衰的病理生理过程也是目前国际关注的研究热点。我们的课题就是围绕着LVNC的发病机理和于此相关的心衰病理过程展开研究。.在过去十年的工作，我们确认了BMP10信号通路是调节心室壁发育的重要信号途径。通过本项目的进一步研究工作发现，非经典Wnt/PCP通路是建立心肌细胞极性、肌丝发生和调节致密层形成的调节因素，敲除Wnt / PCP信号通路中的Daam1基因可以导致心脏致密化不全。我们研究发现Notch1在调控心内膜-心脏内皮细胞之间的Neuregulin1 (NRG1)-ErbB2/4信号通路和BMP10信号通路中起关键作用。其中BMP10信号通路以被证实能够促进心肌细胞增殖和心室壁生长，BMP10异常上调表达导致心室壁小梁增生；而NRG1-ErbB2/4信号通路是非经典Wnt/PCP（Planer Cell Polarity， PCP）信号通路负调节系统，对建立心肌细胞极性、肌丝发生和心室壁正常致密化过程起关键作用，上调NRG1-ErbB2/4信号通路会导致心室致密化不全。最近我们还发现NRG1能够下调Wnt/PCP 信号通路的下游效应分子 Daam1基因，而敲除Daam1基因则会导致心室致密化不全，我们进一步还确认了通过激活NRG1下游信号分子Pak1 同样可以负调控Daam1 基因的表达和功能。基于上述发现，我们推断在心室发育的室壁小梁化和室壁致密化过程中存在两个相互独立又有交互作用的信号调控通路：一个信号途径主要调控心肌细胞的增殖，另一个主要通过调节心肌细胞的极化和肌丝发生过程来调控心肌细胞的功能成熟。这些研究结果不仅能够进一步深入证实我们提出的心室壁发育调控模型，同时也为心肌致密化不全提供了新的分子病理机制和诊断依据。