Analysis of a Novel Homeobox gene in CV Development

描述（由申请人提供）：这是R01的修订（A1）竞争性更新申请，最初专注于我们在胚胎心脏中发现的一种名为Hop的新型同源结构域蛋白的作用。我们发现Hop功能丧失导致发育性心脏缺陷，而过表达导致心脏肥厚。Hop可以在分子水平上通过募集I类hdac发挥转录共抑制因子的作用。这一发现使我们测试了HDAC抑制剂的作用，我们发现这些药物可以阻断由啤酒花过度表达引起的心脏肥厚，也可以阻断由其他压力引起的肥厚，包括β -肾上腺素能激动剂和拉伸。因此，我们已经寻找了能够解释这些影响的特定I类HDAC(s)，并且我们已经在发育和成人心脏中确定了高水平的HDAC2。HDAC2功能丧失导致小鼠对啤酒花诱导的心肌肥厚和β -肾上腺素能激动剂诱导的肥厚产生抗性。我们已经证明，在这些模型中，对肥大的抵抗是由gsk3 - β的组成性激活引起的，因为gsk3 - β的拮抗剂可以恢复HDAC2缺失动物的肥大能力。我们的数据表明，HDAC2通过直接抑制一种名为INPP5F的新型肌醇多磷酸磷酸酶来影响AKT- gsk3 - β途径，INPP5F的功能是降解PIP3，从而影响AKT级联。这些发现具有直接的临床和转化意义，因为磷酸酶是治疗心血管疾病的优秀药物靶点，因为HDAC抑制剂已经在癌症治疗的临床试验中，可以很容易地适应于心脏领域的使用。因此，我们将通过以下方式进行这些观察：1)开发HDAC2的一个固定等位基因，以便进行组织和时间特异性缺失，并确定HDAC2功能丧失对预先建立的肥大回归的影响；2)阐明Hop与HDAC2的遗传和生化相互作用；3)通过细胞和小鼠的功能获得和功能丧失方法检测INPP5F的功能。这些实验为开发治疗心肌肥厚和心力衰竭的新治疗途径和范式提供了强有力的前景，并对细胞和器官生长调节的更广泛领域产生了影响。

DESCRIPTION (provided by applicant): This is a revised (A1) competitive renewal application for an R01 initially focused on the role of a novel homeodomain protein called Hop that we discovered in the embryonic heart. We have found that Hop loss of function results in a developmental cardiac defect and that over-expression results in cardiac hypertrophy. Hop can function at the molecular level as a transcriptional co-repressor by recruiting class I HDACs. This finding led us to test the effects of HDAC inhibitors and we have found that these agents can block cardiac hypertrophy induced by Hop over-expression and also hypertrophy resulting from other stresses including beta-adrenergic agonists and stretch. Therefore, we have sought the specific class I HDAC(s) that account for these effects, and we have identified high levels of HDAC2 in the developing and adult heart. HDAC2 loss of function results in mice that are resistant to Hop- induced cardiac hypertrophy and to hypertrophy induced by beta-adrenergic agonists. We have shown that resistance to hypertrophy in these models is caused by constitutive activation of GSK3-beta, since antagonists of GSK3-beta restore the ability to hypertrophy on HDAC2 null animals. Our data indicates that HDAC2 affects the AKT-GSK3-beta pathway by directly repressing a novel inositol polyphosphate phosphatase called INPP5F, which functions to degrade PIP3 and thus affects the AKT cascade. These findings have direct clinical and translational implications since phosphatases are excellent drugable targets for the treatment of cardiovascular disease and because HDAC inhibitors are already in clinical trials for the treatment of cancer and could be readily adapted for use in the cardiac arena. Therefore, we will pursue these observations by: 1) Developing a floxed allele of HDAC2 in order to perform tissue and temporal specific deletion and to determine the effects of HDAC2 loss of function on regression of pre-established hypertrophy; 2) Elucidation of the genetic and biochemical interaction between Hop and HDAC2, and; 3) Examination of the function of INPP5F through gain and loss of function approaches in cells and in mice. These experiments offer strong prospects for developing new therapeutic avenues and paradigms for the treatment of cardiac hypertrophy and heart failure, with implications for the more general fields of cellular and organ growth regulation. PUBLIC HEALTH RELEVANCE: This project focuses on the causes of congestive heart failure, and on finding new therapeutic targets. Heart failure is a leading cause of death and disability in the United States, and the incidence is rising. We have found that HDAC inhibitors, which are drugs currently in clinical trials for cancer therapy, have beneficial effects in terms of heart failure prevention in animal models. This project explores the possibility that an enzyme called HDAC2, expressed in the heart, is the molecular target for HDAC inhibitors, and that it functions by regulating a novel phosphatase in the heart called INPP5F. We hope to determine if HDAC2 and INPP5F represent new targets for the development of specific therapies for heart disease.