FAK Signaling in cardiac growth and hypertrophy

描述(申请人提供)：成年哺乳动物心肌细胞是终末分化的细胞，分裂能力非常有限，因此，心脏损伤通常会导致永久性肌肉质量丧失，导致心功能障碍和心力衰竭。因此，更好地了解心肌细胞周期是如何控制的，应该会增强我们为几种迄今难以治愈的心脏疾病提供有效治疗的能力。一些研究表明，心肌细胞在发育过程中的生长状态与细胞外基质和整合素受体表达的调节变化以及这些基质支持心肌细胞体外生长的能力有关。这些数据强调了整合素信号在调节心脏形态发生和心脏病进展方面的重要性，但这些过程在心脏生长的不同阶段是如何微调的尚不清楚。我们在过去的资金周期内完成的研究清楚地表明，FAK在发育过程中调节心肌细胞的增殖，在压力超负荷后调节心肌细胞肥大，在缺血损伤后调节心肌细胞的存活。我们还发现，FAK的活性在出生后的心脏中受到其内源性抑制物frnk的动态调节。我们的结果表明，FRANK在心脏中瞬时表达，峰值出现在出生后5-7天(恰好在细胞周期退出之前)，并且从E10.5开始的心脏选择性表达会导致严重的心肌致密化缺陷和胚胎死亡，并与心肌细胞增殖和冠状神经丛形成障碍相关。重要的是，心肌细胞特异性表达的超激活FAK变异体(bMHC-SuperFAK)能够挽救这种表型，表明FAK在调节这些关键功能中发挥着细胞自主作用。因此，我们的工作假设是，FAK信号的动态调节对于控制心肌细胞在发育过程中细胞周期的退出以及对心脏应激反应的细胞周期重新进入非常重要。我们已经建立了许多转基因的功能获得/功能丧失的小鼠模型，这将使我们能够检验这一假说，并识别对FAK/frnk对心肌细胞增殖的影响至关重要的下游信号。此外，由于FAK信号受许多调节心脏发育和功能的环境信号的影响，或受许多环境信号的影响所必需，我们强烈认为，拟议研究的结果将对我们理解先天性心脏病和心力衰竭的进展具有广泛的影响。我们将利用转基因小鼠、已建立的心肌细胞培养模型和来自人类心脏储存库的样本来确定FAK依赖的机制，这些机制调控先天性和获得性心脏病的发病机制。 公共卫生相关性：我们努力了解调控心脏细胞分裂能力的分子机制，因为在几种先天性心脏病和心力衰竭的情况下，操纵这一功能的策略可能是有效的。虽然心脏细胞可以在发育过程中进行分裂，但分裂时间或地点的改变可能会导致先天性心脏病。此外，这些细胞在出生后不久就失去了分裂的能力，因此对心脏的任何损害都可能导致不可逆转的功能丧失。

DESCRIPTION (provided by applicant): Adult mammalian cardiomyocytes are terminally differentiated cells with very limited capabilities to divide, thus, injury to the heart typically causes permanent loss of muscle mass leading to ventricular dysfunction and heart failure. Therefore, a better understanding of how the myocyte cell cycle is controlled should enhance our ability to provide effective therapy for several heretofore-intractable cardiac diseases. Several studies indicate that the cardiomyocyte growth state in the developing heart correlates with regulated shifts in the expression of extracellular matrix and integrin receptors and the ability of these matrices to support myocyte growth in vitro. These data underscore the importance of integrin signaling in regulating both cardiac morphogenesis and the progression of cardiac disease, but how these processes are fine-tuned during the different phases of cardiac growth is unknown. It is clear from our studies completed within the past funding cycle that FAK functions to mediate cardiomyocyte proliferation during development, cardiomyocyte hypertrophy following pressure overload, and cardiomyocyte survival following an ischemic insult. We have also made the interesting discovery that FAK activity is dynamically regulated in the post-natal heart by expression of its endogenous inhibitor, FRNK. Our results demonstrate that FRNK is transiently expressed in the heart with peak levels occurring 5-7 days post-natal (just prior to cell cycle withdrawal) and that cardiac-selective expression of FRNK starting at E10.5 leads to a severe ventricular non-compaction defect and embryonic lethality associated with impaired cardiomyocyte proliferation and impaired coronary plexus formation. Importantly, ventricular cardiomyocyte-specific expression of a super-activatable FAK variant (bMHC-SuperFAK) was able to rescue this phenotype, indicating a cell autonomous role for FAK in regulating these critical functions. Thus, our working hypothesis is that dynamic regulation of FAK signaling is important for the control of cardiomyocyte cell cycle withdrawal during development and perhaps to cell-cycle re-entry in response to cardiac stress. We have generated many genetically modified gain-of-function/loss-of-function mouse models that will allow us to test this hypothesis and to identify the downstream signals that are important for the effects of FAK/FRNK on cardiomyocyte proliferation. In addition, since FAK signaling is regulated by, or required for, the effects of many of the environmental cues that regulate cardiac development and function, we strongly feel that the results from the proposed studies will have broad implications on our understanding of congenital cardiac disease and on the progression heart failure. We will utilize genetically modified mice, established cardiac cell culture models, and samples from a human heart repository to identify FAK-dependent mechanisms that regulate the pathogenesis of congenital and acquired heart disease. PUBLIC HEALTH RELEVANCE: We strive to understand the molecular mechanisms that regulate the ability of heart cells to divide, since strategies to manipulate this function could be efficacious in the context of several congenital heart diseases and heart failure. While heart cells can undergo division during development, alterations of the timing or locale of division can lead to congenital heart disease. Furthermore, these cells lose the ability to divide shortly after birth, thus any damage to the heart can cause irreversible loss of function.