Regulation of cardiac gene expression by MEF2-Myocardin transcription complexes

心血管疾病是成年人最常见的死亡原因，先天性心脏病是美国最常见的出生缺陷形式。AMP激活的蛋白激酶(AMPK)是能量平衡和动态平衡的主要调节者，在心肌肥厚和心力衰竭时从脂肪酸到糖酵解的转换中起着核心作用。AMPKa2是心脏中表达的催化亚基的主要亚型，由Prkaa2基因编码。虽然AMPK及其在代谢和心力衰竭中的作用已经被广泛研究，但编码AMPK亚单位的基因的转录控制是完全未知的。MADS盒转录因子MEF2C是心脏发育所必需的转录因子，是一种信号反应型转录因子，可与多种辅因子相互作用，负向或正向调节转录。MEF2C最有效的转录辅助激活因子是SAP结构域转录调节因子Myocardin。MEF2C与心脏中高度丰富的Myocardin-93s特异地相互作用，但Myocardin-MEF2复合体促进协同作用的转录靶点和机制尚未确定。初步研究发现，Prkaa2基因是MEF2C-Myocardin复合体通过一种新的心脏特异性增强子直接转录的靶点。这个增强子包含两个真正的MEF2结合位点，它们以倍增的方式共同作用于Myocardin-93S和MEF2C。尽管转录协同作用在许多背景下经常被观察到，并且是一种描述良好的现象，但顺式作用元件的作用、它们的位置、间距和序列在促进协同作用中的作用还远没有被很好地描述。利用转基因小鼠、细胞培养、生化和质谱学方法，这项工作将确定MEF2-Myocardin转录协同作用的决定因素，将通过交互作用组图确定MEF2C和Myocardin的其他相互作用伙伴，并将在体内确定Myocardin-MEF2复合体的靶点。这项工作还将首次确定Prkaa2的上游调控。这项工作可能为在心力衰竭期间操纵AMPK的表达提供额外的策略。

Cardiovascular disease is the most common cause of mortality in adults, and congenital heart defects are the most common form of birth defects in the US. AMP-activated protein kinase (AMPK) is a master regulator of energy balance and homeostasis and plays a central role in the switch from fatty acids to glycolysis during cardiac hypertrophy and heart failure. AMPKa2 is the predominant isoform ofthe catalytic subunit expressed in the heart and is encoded by the Prkaa2 gene. Although AMPK and its role in metabolism and heart failure have been extensively studied, the transcripfional control ofthe genes encoding AMPK subunits is completely unknown. The MADS box transcription factor MEF2C is required for cardiac development and functions as a signal responsive transcription factor that interacts with a variety of cofactors to either negatively or positively regulate transcription. The most potent transcriptional coactivator for MEF2C is the SAP domain transcripfional regulator Myocardin. MEF2C specifically interacts with Myocardin-93S, which is highly enriched in the heart, yet the transcripfional targets and mechanisms of synergy facilitated by the Myocardin-MEF2 complex have not been identified. Preliminary studies found that the Prkaa2 gene is a direct transcripfional target ofthe MEF2C-Myocardin complex via a novel cardiac- specific enhancer. This enhancer contains two bona fide MEF2 binding sites that function together in a multiplicative fashion in response to Myocardin-93S and MEF2C. Although transcripfional synergy is frequently observed in many contexts and is a well-described phenomenon, the role of cis-acting elements, their position, spacing, and sequence in facilitating synergy have been far less well described. Using transgenic mouse, cell culture, biochemical, and mass spectrometry approaches, this work will define determinants of MEF2-Myocardin transcripfional synergy, will identify additional interaction partners for MEF2C and Myocardin through interactome mapping, and will identify in vivo targets ofthe Myocardin-MEF2 complex. This work will also determine the upstream regulation of Prkaa2 for the first time. This work may provide additional strategies for manipulating AMPK expression during heart failure.