The methyltransferase Smyd1 regulates cardiac physiology

项目总结 在美国，冠状动脉疾病是主要的死亡原因，也是慢性心力衰竭的主要原因。 对于冠状动脉疾病患者，临床上已经取得了一些进展，以恢复血液流动。 减少因缺血和随后的再灌流而造成的心肌损伤。 然而，即使有了这些进展，四分之一的患者仍将在一年内死亡或发展为心力衰竭。 缺血损伤对心肌的损害包括代谢和能量方面的缺陷。一些人 关键的表观遗传调节因子可以预防或减少小鼠模型的缺血性损伤和病理重塑， 然而，到目前为止，它们无处不在的表达使它们不适合在人类身上进行治疗靶向。在……里面 相反，我们最近确定了线粒体能量学唯一已知的心肌细胞特异性表观遗传调节因子。 和代谢-组蛋白赖氨酸甲基转移酶Smyd1-具有巨大的治疗潜力 它的组织特异性表达。具体地说，我们在成人中进行了第一次Smyd1功能分析 使用可诱导的、心肌细胞特异性的Smyd1基因敲除小鼠的心肌，并显示Smyd1导联的丢失 心脏代谢紊乱，线粒体呼吸受抑，最终导致心力衰竭 (刊载于AJP)。随后我们发现线粒体能量学的下调是一个早期事件。 在这些基因敲除的小鼠中(发生在心脏功能障碍发作之前)，结果至少部分来自 Smyd1‘S对pGC-1α转录的调控(发表于《美国国家科学院院刊》)。进一步理解Smyd1中S的角色 通过调节心脏生理学，我们最近培育了转基因小鼠，允许诱导的、心肌细胞特异性的 过表达Smyd1a亚型(小鼠与人SMYD1同源)，并使这些小鼠 左前降支的永久性闭塞。我们未发表的初步结果表明，Smyd1a功能增益可以 增强线粒体呼吸和保护免受缺血损伤，尽管这是如何实现的 分子上是未知的。此外，我们从这些小鼠身上获得的初步数据显示，线粒体脊增加 冠内呼吸链超复合体的形成和稳定，伴随着增加 OPA1的表达，已知的眉骨形态的驱动因素。这些结果表明，OPA1在功能上是一种新的 Smyd1a的重要下游靶点，心肌细胞由此上调能量效率，保护它们 来自于缺血损伤。我们的主要假设是，Smyd1a通过调节 线粒体能量学与通过调节两者提高心肌细胞呼吸效率： 1)PGC-1α表达(电子传输链基因表达的调节因子)和2)OPA1介导的突起 电子传递链超复合体的重塑和稳定。我们将在我们的 有条件地过表达Smyd1a的转基因小鼠。此外，我们还将研究细胞中的这些途径。 以及人类组织中可能存在的SMYD1功能丧失变体N101S，我们与合作者进行了鉴定 在匹兹堡大学(莉娜·冈萨雷斯博士)对一名肥厚型心肌病和心力衰竭患者的研究。

PROJECT SUMMARY Coronary artery disease is the leading cause of death in the US and is the primary cause of chronic heart failure. For patients with coronary artery disease, some advancements have been made clinically to restore blood flow in diseased arteries and reduce myocardial injury from the resulting ischemia and subsequent reperfusion. However, even with these advancements one quarter of patients will die or develop heart failure within 1 year. Damage to the myocardium during ischemic injury includes deficiencies in metabolism and energetics. Some key epigenetic regulators can prevent or reduce ischemic injury and pathological remodeling in murine models, however, their ubiquitous expression has made them unsuitable for therapeutic targeting in humans, thus far. In contrast, we recently identified the only known myocyte-specific epigenetic regulator of mitochondrial energetics and metabolism – the histone lysine methyltransferase Smyd1 – which holds great therapeutic potential given its tissue-specific expression. Specifically, we performed the first analysis of Smyd1 function in the adult myocardium using inducible, cardiomyocyte-specific Smyd1 knockout mice and showed that loss of Smyd1 leads to dysregulated cardiac metabolism and suppressed mitochondrial respiration, ultimately leading to heart failure (published in AJP). Subsequently we showed that down-regulation of mitochondrial energetics is an early event in these knockout mice (occurring before the onset of cardiac dysfunction) and results, at least in part, from Smyd1’s regulation of PGC-1α transcription (published in PNAS). To further understand Smyd1’s role in regulating cardiac physiology we recently generated transgenic mice allowing inducible, cardiomyocyte-specific overexpression of the Smyd1a isoform (the mouse ortholog to human SMYD1) and subjected these mice to permanent occlusion of the LAD. Our unpublished preliminary results show that Smyd1a gain-of-function can enhance mitochondrial respiration and protect from ischemic injury, although how this is accomplished molecularly is unknown. In addition, our preliminary data from these mice show increased mitochondrial cristae formation and stabilization of respiratory chain supercomplexes within the cristae, concomitant with increased Opa1 expression, a known driver of cristae morphology. These results implicate Opa1 as a novel, functionally important downstream target of Smyd1a whereby cardiomyocytes upregulate energy efficiency, protecting them from ischemic injury. Our overarching hypothesis is that Smyd1a protects from ischemic injury by regulating mitochondrial energetics and enhancing respiration efficiency in the cardiomyocyte through regulation of both: 1) PGC-1α expression (a regulator of electron transport chain gene expression) and 2) OPA1-mediated cristae remodeling and stabilization of electron transport chain supercomplexes. We will test this hypothesis in our transgenic mice which conditionally overexpress Smyd1a. In addition, we will examine these pathways in cells and human tissue with a putative SMYD1 loss-of-function variant, N101S, which we identified with collaborators at the U. of Pittsburgh (Dr Lina Gonzalez) in a patient with hypertrophic cardiomyopathy and heart failure.