Genetic Regulation of Metabolic and Fibrotic Programs in Hypertrophic Heart

描述（由申请人提供）： 心脏对压力和增加的需求作出反应，通过建立适应性或代偿性肥大反应来使心输出量正常化。随着长期的压力，这种适应性阶段发展为适应不良或失代偿性肥大，其特征是代谢耗尽的心肌细胞死亡，并被产生胶原的肌成纤维细胞取代，从而产生瘢痕性纤维化。在失代偿性肥大进展的基础过程中，代谢衰竭和瘢痕性纤维化是最重要的，使其成为治疗干预的关键靶点。这些过程本质上是遗传的，具有明确定义的基因和控制其表达的调控机制。但是，肥厚性应激信号如何与这些调节机制相互作用以控制代谢或纤维化基因表达，以及这如何使心脏适应（或不适应）应激，还没有得到充分的定义。如果没有这些知识，试图设计通过维持适应性反应或预防适应不良反应来治疗心脏肥大的疗法可能是徒劳的。我们研究的长期目标是了解心脏将肥大应激信号转化为基因组应激反应的分子机制。我们的实验室一直在研究一种名为CLP-1（心脏谱系蛋白-1）的分子，我们已经证明它对于将肥大应激信号整合到基因组应激反应中至关重要。CLP-1是一种抑制性转录调节因子，可控制P-TEF B（P-转录延伸因子B）的活性，后者是一种激活RNA聚合酶II以转录基因的转录调节因子。CLP-1作为基因转录的重要调控因子，在多种生理和病理过程中发挥重要作用，这些过程涉及细胞外信号整合到协调的基因组反应中。本申请的目的是确定响应于肥大刺激，CLP-1如何控制调节能量底物使用的代谢程序和调节肥大心室肌重构的纤维化程序中的基因转录。 我们的假设是，CLP-1转录抑制因子水平的降低可能会增加代偿性应激反应基因（包括代谢基因）的转录能力和反应性，以维持心肌细胞活力，从而减轻更具破坏性的纤维化、修复性或瘢痕性纤维化的形成。我们检验这一假设的实验模型是CLP-1基因剂量减少的小鼠，CLP-1 +/-杂合小鼠，通过身体肥大或与已建立的肥大小鼠模型杂交而变得肥大。为了验证我们的假设，我们提出了三个具体目标。在目标#1中，我们将确定指导能量底物使用的基因是否被上调以维持肥大心肌细胞的代谢输出和活力。在目标#2中，我们将检查在从代偿性肥大到失代偿性肥大的进展期间在CLP-1 +/-肥大心脏中发展的纤维化类型，以确定降低的CLP-1水平和肥大心肌细胞的持续代谢活力是否减轻更严重形式的修复性或瘢痕性纤维化的形成。在目标#3中，我们将确定CLP-1-P-TEFb调节机制是否可以通过增强控制其表达的信号转导途径来直接上调特定的应激反应基因。 这种方法是创新的，因为它将重点从研究心脏病的原因转移到那些专注于如何防止患病心脏发展到衰竭的研究上。由于大多数心脏病患者属于后一类，他们将从我们的研究中受益。总之，我们的研究表明，CLP-1通过控制应激反应基因在控制心肌细胞对肥大刺激的反应中占据关键地位。这些研究是重要的，因为它们将提供更深入的了解适应性肥大反应的分子事件，以及如何控制它们以减轻肥大心脏收缩功能障碍和衰竭的进展。

DESCRIPTION (provided by applicant): The heart responds to stress and increased demand by mounting an adaptive or compensatory hypertrophic response to normalize cardiac output. With prolonged stress, this adaptive phase devolves to a maladaptive or decompensatory hypertrophy marked by the death of metabolically depleted cardiomyocytes and replacement by collagen-producing myofibroblasts that produce a scarring fibrosis. Of the processes underlying the progression to decompensatory hypertrophy, metabolic failure and scarring fibrosis are the most consequential making them key targets for therapeutic intervention. These processes are genetic in nature with well-defined genes and regulatory mechanisms controlling their expression. But exactly how hypertrophic stress signals interact with these regulatory mechanisms to control metabolic or fibrotic gene expression and how this allows the heart to adapt (or not) to stress has yet to be adequately defined. Without this knowledge, attempts to devise therapies to treat cardiac hypertrophy by either maintaining the adaptive or preventing the maladaptive response are likely to be unproductive. The long-term goal of our research is to understand the molecular mechanisms with which the heart translates hypertrophic stress signals into a genomic stress response. Our laboratory has been studying a molecule called CLP-1 (Cardiac Lineage Protein-1) that we have shown to be critical for integrating hypertrophic stress signals into a genomic stress response. CLP-1 is an inhibitory transcriptional modulator that controls the activity of P-TEFb (P-Transcriptional Elongation Factor b), a transcriptional regulator that activates RNA polymerase II to transcribe genes. As a critical regulator of gene transcription, CLP-1 plays an important role in a variety of physiologicl and pathological processes that involve integration of extracellular signals into a coordinated genomic response. The objective of this application is to determine how in response to hypertrophic stimuli CLP-1 controls the transcription of genes in the metabolic program regulating energy substrate usage and in the fibrotic program regulating remodeling of the hypertrophic ventricular myocardium. Our hypothesis is that reduced levels of the CLP-1 transcriptional inhibitor could be increasing the transcriptional competency and responsiveness of compensatory stress response genes, including metabolic genes, in order to maintain cardiomyocyte viability at levels that mitigate formation of the more damaging form of fibrosis, reparative or scarring fibrosis. Our experimental model for examining this hypothesis are mice with reduced CLP-1 gene dosage, CLP-1+/- heterozygous mice, rendered hypertrophic physically or by crossing with established mouse models of hypertrophy. To test our hypothesis, we propose three specific aims. In aim #1, we will determine if the genes directing energy substrate usage are up-regulated to maintain the metabolic output and viability of hypertrophic cardiomyocytes. In aim #2, we will examine the type of fibrosis that develops in CLP-1+/- hypertrophic hearts during the progression from compensatory to decompensatory hypertrophy to determine if reduced CLP-1 levels and sustained metabolic viability of hypertrophic cardiomyocytes mitigates formation of the more severe form of reparative or scarring fibrosis. And in aim #3, we will determine if the CLP-1-P-TEFb regulatory mechanism can directly up-regulate specific stress response genes by potentiating the signal transduction pathway controlling their expression. This approach is innovative in that it shifts the focus away from studies on the causes of heart disease to those focusing on how to prevent the diseased heart from progressing to failure. Since most people with heart disease fall into this latter category, they stand to benefit from the insights our research can provide. In all, our studies should demonstrate that CLP-1 occupies a critical position for controlling the response of cardiac cells to hypertrophic stimuli via its control of stress response genes. These studies are significant since they will provide greater insight into the molecular events underlying the adaptive hypertrophic response and how they can be controlled to mitigate the progression of hypertrophic hearts to contractile dysfunction and failure.