Signaling Mechanisms Governing Cardiac Hypertrophy

描述（由申请人提供）：鉴定调节病理性心脏生长的细胞内信号转导途径一直是人们非常感兴趣的领域。 这些途径的鉴定将建立新的靶点，调节这些靶点可以改变肥大向心力衰竭的进展。 然而，这是一个难以实现的目标，因为很明显，多个相互作用和/或平行的途径调节心脏的生长。 我们的兴趣集中在糖原合成酶激酶-3途径。 我们已经发现GSK-3是心脏生长的负调节剂。 我们已经建立了一个转基因小鼠表达GSK-3 β在心脏中，这只小鼠的特点是显着受损的心脏生长。 我们还跟踪了GSK-3通路的下游，以确定GSK-3可能在生长中发挥作用的靶点。 我们现在已经确定了一个目标，β-连环蛋白，这是负调控GSK-3。 β-连环蛋白是一种转录因子，一段时间以来，人们已经知道它作为Wnt通路的一部分在胚胎发生过程中调节背腹图案。 此外，在许多癌症中发现了β-连环蛋白的突变，证明了其在肿瘤发生中的作用。 我们提出了三个具体目标，以进一步阐明GSK-3 β和β-连环蛋白在正常和病理性心肌细胞生长中的作用。 具体目标1。 确定β-连环蛋白在心肌肥大发生中的作用。 我们假设β-连环蛋白是体内生理性和病理性肥大的关键调节因子。 我们将使用多种方法，包括病毒介导的基因转移、转基因模型和心脏特异性条件性β-连环蛋白敲除，确定β-连环蛋白是否是体内肥大反应所必需的、足够的或两者兼而有之。 具体目标2。 确定GSK-3 β表达导致心脏生长受损和收缩功能低下的表型的机制。 GSK-3 β有许多靶点，其中任何一个都可能在生长受损中发挥作用。 我们的假设是GSK-3 β主要通过其对β-连环蛋白/c-Myc通路的抑制作用阻断生理性肥大。 我们将再次使用病毒介导的基因转移、转基因和基因敲除来评估这一假设。 具体目标3。 确定调节β-连环蛋白稳定性的机制，以应对肥大性应激。 我们的初步研究已经确定了一种新的机制，通过这种机制，β-连环蛋白被肥大应激稳定，这涉及到GSK-3 β抑制剂PKB/Akt的募集到β-连环蛋白降解复合物中。 我们的假设是，该机制涉及募集Wnt途径的下游组分。 我们将尝试识别所涉及的特定信号因素。 我们相信，本文概述的研究是过去三年来在该资助下进行的工作的逻辑延伸，将使我们能够定义一种新的线性信号通路，包括胞质和核组分，调节心脏的生理和病理性肥大。

DESCRIPTION (provided by applicant): The identification of intracellular signal transduction pathways that regulate pathologic cardiac growth has been an area of intense interest. The identification of these pathways would establish novel targets, modulation of which could alter the progression of hypertrophy to heart failure. This has been a difficult goal to achieve, however, since it is apparent that multiple interacting and/or parallel pathways regulate growth of the heart. Our interests have focused on the glycogen synthase kinase-3 pathway. We have found that GSK-3 is a negative regulator of cardiac growth. We have created a transgenic mouse expressing GSK-3beta in the heart, and this mouse is characterized by markedly impaired cardiac growth. We have also followed the GSK-3 pathway downstream to identify targets of GSK-3 that may play a role in growth. We have now identified one target, beta-catenin, that is negatively regulated by GSK-3. Beta-catenin is a transcription factor that has been known for some time to regulate dorsoventral patterning during embryoganesis as part of the Wnt pathway. In addition, mutations in beta-catenin have been found in a number of cancers, attesting to its role in tumorigenesis. We propose three Specific Aims to further clarify the role of GSK-3beta and beta-catenin in normal and pathologic cardiomyocyte growth. Specific Aim 1. Determine the role of beta-catenin in the development of cardiac hypertrophy. It is our hypothesis that beta-catenin is a critical regulator of physiologic and pathologic hypertrophy in vivo. We will determine whether beta-catenin is necessary, sufficient, or both, for the hypertrophic response in vivo using a variety of approaches including viral mediated gene transfer, transgenic models, and a cardiac-specific conditional knockout of beta-catenin. Specific Aim 2. Determine the mechanisms by which expression of GSK-3beta leads to a phenotype of impaired growth and depressed systolic function of the heart. GSK-3beta has a number of targets, any of which could play a role in impaired growth. It is our hypothesis that GSK-3beta blocks physiologic hypertrophy primarily via its inhibitory effects on the beta-catenin/c-Myc pathway. We will evaluate this hypothesis, again employing viralmediated gene transfer, transgenics, and knockouts. Specific Aim 3. Determine the mechanisms regulating beta-catenin stabilization in response to hypertrophic stress. Our preliminary studies have identified a novel mechanism by which beta-catenin is stabilized by hypertrophic stress, and this involves recruitment of the GSK-3beta inhibitor, PKB/Akt to the beta-catenin degradation complex. It is our hypothesis that the mechanism involves recruitment of downstream components of the Wnt pathway. We will attempt to identify the specific signaling factors involved. We believe that the studies outlined herein, which are a logical extension of the work performed under this grant over the past three years, will allow us to define a novel linear signaling pathway, including cytosolic and nuclear components, regulating physiologic and pathologic hypertrophy of the heart.