Transcription Regulation in the Aging Heart

描述（由申请人提供）：本修订后的申请寻求支持，以研究心脏衰老的基本机制。我们之前观察到，与年轻人相比，老年人的心脏在应激反应中代偿性肥大、蛋白质合成和UNA合成减少。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血清反应因子（SRE）的基础结合活性随着年龄的增长而增加，血清反应因子（SRF）是SRE的主要结合蛋白，与年轻人相比，老年人心脏中c-fos血清反应因子（SRF）也略有增加。由于SRF是许多肌肉基因的关键转录因子，因此SRF有助于改变这些基因的表达是合理的。在野生型SRF基因具有心脏特异性、适度过表达的转基因小鼠中，出现了显著的心肌细胞肥大、心肌病和早期死亡。SRF无效是胚胎致命的。产生了显性阴性突变型SRF转基因小鼠，其中突变位于DNA结合域，从而严重损害了突变型SRF与c-fos SRE结合的能力；这些新生的显性阴性转基因小鼠心脏扩张，心肌细胞异常小，出生后生长发育不良，出生后12天内全部死亡。这些发现表明，SRF对心脏的发育、生长和维持至关重要，但心脏SRF活动的适度增加或减少可能对动物造成潜在的灾难性后果。我们试图确定SRF活性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，在青年成年期出现轻度心脏变化，这似乎与老年期通常观察到的变化相似。这些发现与一个有趣的概念相一致，即转录因子如SRF可能部分参与介导心肌衰老过程。然而，任何基因的活动和心脏衰老之间的联系之前都没有建立起来。因此，我们建议对这个新概念进行详细的研究，这对未来开发新的治疗靶点具有重要的潜力。我们建议的中心主题是，单一转录因子（如SRF）的改变可能是心脏中常见的衰老变化的部分原因。我们建议验证这一假设，并阐明心脏老化过程的机制。我们的具体目标是：1)验证心脏老化过程可能部分归因于血清反应因子（SRF）等基因的转录调节改变的假设；2)验证老年心脏SRF轻度降低与心脏延迟衰老相关的假设；3)为了验证SRF可能在一定程度上介导正常成人心脏衰老过程中观察到的钙处理改变的假设。

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.