Transcription Regulation in the Aging Heart

描述（由申请人提供）：此修订后的申请寻求支持，以调查心脏衰老的基本机制。 我们以前观察到，在应对压力，代偿性肥大，蛋白质合成，和UNA合成减少老年人相比，年轻的成年人的心脏。老年心脏心肌储备的减少与基因表达程序的改变有关。我们观察到心脏中c-fos血清反应元件（SRE）的基础结合活性随年龄增加而增加，并且与年轻成人心脏相比，老年人的主要SRE结合蛋白血清反应因子（SRF）也略有增加。由于SRF是许多肌肉基因中的关键转录因子，因此SRF有助于改变这些基因的表达是合理的。在心脏特异性、中度过表达野生型SRF基因的转基因小鼠中，存在显著的心肌细胞肥大、心肌病和早期死亡率。SRF无效是胚胎致死的。产生显性阴性突变SRF转基因小鼠，其中突变在DNA结合结构域中，从而严重损害突变SRF与c-fos SRE结合的能力;这些新生显性阴性转基因小鼠具有扩张的心脏和异常小的心肌细胞，出生后生长和发育不良，并且在出生后12天内全部死亡。这些发现表明，SRF是心脏发育，生长和维护所必需的，但心脏SRF活动的适度增加或减少可能会对动物产生潜在的灾难性后果。我们试图确定SRF活性的轻度变化对心脏的影响，并发现在SRF活性轻度增加的转基因小鼠中，在年轻的成年期有轻度的心脏变化，这似乎与老年时通常观察到的相似。这些发现与一个有趣的概念是一致的，即转录因子如SRF可能参与介导，部分，心肌老化的过程。然而，任何基因的活性与心脏衰老之间的联系以前都没有建立。因此，我们建议对这一新概念进行详细调查，这对未来开发新的治疗靶点具有重要潜力。我们的建议的中心主题是，在一个单一的转录因子，如SRF的改变可能是基础，在一定程度上，通常在心脏中观察到的衰老变化。我们建议验证这一假设，并阐明心脏衰老过程的机制。我们的具体目标是：1）验证心脏衰老过程可能部分归因于基因如血清反应因子（SRF）的转录调节改变的假设; 2）验证老年心脏中SRF水平的轻度降低与延迟的心脏衰老相关的假设; 3）验证SRF可能部分介导在正常成人心脏老化期间观察到的钙处理改变的方面的假设。

DESCRIPTION (provided by applicant): This revised application seeks support to investigate the basic mechanisms of aging in the heart. We previously observed that in response to stress, the compensatory hypertrophy, protein synthesis, and UNA synthesis are reduced in old compared to young adult hearts. This decreased myocardial reserve in old hearts is associated with an altered program of gene expression. We observed that the basal binding activity to the c-fos serum response element (SRE) in the heart was increased with age, and that serum response factor (SRF), the major SRE binding protein, was also slightly increased in old compared with young adult hearts. Inasmuch as SRF is a key transcription factor in many muscle genes, it is plausible that SRF contributes to the altered expression of these genes. In a genetically modified mouse that was generated with cardiac-specific, moderate overexpression of the wild type SRF gene, there was significant cardiomyocyte hypertrophy, cardiomyopathy and early mortality. The SRF null is embryonically lethal. A dominant negative, mutant SRF transgenic mouse was generated in which the mutations are in the DNA binding domain, thereby severely compromising the mutant SRF's ability to bind to the c-fos SRE; these newborn dominant negative transgenic mice had dilated hearts with abnormally small cardiomyocytes, poor postnatal growth and development, and all died within 12 days after birth. These findings suggest that SRF is essential for cardiac development, growth and maintenance, but that a moderate increase or decrease in cardiac SRF activity can have potentially disastrous consequences in the animal. We sought to determine the effect of mild changes in SRF activity on the heart, and found that in a transgenic mouse with mildly increased SRF activity, there were mild cardiac changes in young adulthood which appeared to be similar to those usually observed in old age. These findings are compatible with the intriguing notion that a transcription factor such as SRF may be involved in mediating, in part, the process of myocardial aging. However, a link between the activity of any gene and aging in the heart has not been previously established. We therefore propose to conduct a detailed investigation of this novel concept, which holds significant potential for the future development of new targets of therapy. The central theme of our proposal is that alterations in a single transcription factor such as SRF may underlie, in part, the aging changes that are commonly observed in the heart. We propose to test this hypothesis and to elucidate the mechanism(s) underlying the aging process of the heart. Our specific aims are: l) To test the hypothesis that the process of cardiac aging might be partly attributable to altered transcription regulation of genes such as the serum response factor (SRF); 2) To test the hypothesis that a mildly reduced level of SRF in the old heart would be associated with delayed cardiac aging; 3) To test the hypothesis that SRF might mediate, in part, aspects of altered calcium handling that has been observed during normal adult cardiac aging.