Transcription Regulation in the Aging Heart

描述(申请人提供)：本修订申请寻求支持，以研究心脏衰老的基本机制。我们先前观察到，与年轻成人相比，老年心脏对应激的反应是代偿性肥大、蛋白质合成和UNA合成减少。这种老年心脏心肌储备的减少与基因表达程序的改变有关。我们观察到心脏与c-fos血清反应元件(SRE)的基础结合活性随着年龄的增长而增加，而主要的SRE结合蛋白-血清反应因子(SRF)在老年心脏中也略高于年轻成人心脏。由于SRF是许多肌肉基因中的关键转录因子，因此SRF可能导致这些基因表达的改变。在一只心脏特异的、适度过度表达野生型SRF基因的转基因小鼠中，出现了显著的心肌细胞肥大、心肌病和早期死亡。SRF零基因在胚胎上是致命的。产生了一只突变的显性负性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的结合能力；这些新生的显性负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，并在出生后12天内全部死亡。这些发现表明，SRF对于心脏的发育、生长和维持是必不可少的，但心脏SRF活性的适度增加或减少可能对动物产生潜在的灾难性后果。我们试图确定SRF活性轻微变化对心脏的影响，并发现在SRF活性轻微增加的转基因小鼠中，年轻成年时有轻微的心脏变化，似乎与通常在老年观察到的类似。这些发现与一个耐人寻味的概念相一致，即转录因子，如SRF，可能参与部分调节心肌老化的过程。然而，任何基因的活性与心脏衰老之间的联系此前都没有得到证实。因此，我们建议对这一新的概念进行详细的调查，这对未来新的治疗靶点的开发具有巨大的潜力。我们建议的中心主题是，单一转录因子(如SRF)的变化可能是心脏常见的衰老变化的部分原因。我们建议检验这一假说，并阐明心脏衰老过程的机制(S)。我们的具体目标是：L)检验心脏衰老过程可能部分归因于血清反应因子(SRF)等基因转录调控改变的假说；2)检验老年心脏中SRF水平轻微降低与心脏衰老延迟相关的假说；3)检验SRF可能部分介导正常成年人心脏衰老过程中观察到的钙处理变化的假说。

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.