Linking cell death and mitochondrial quality control mechanisms in heart disease

 描述（由申请人提供）：线粒体参与多种基本过程，包括生物发生、裂变/融合、线粒体自噬和细胞死亡-除了它们在细胞中作为ATP生成器的作用之外。这些过程是复杂的，因此，在很大程度上被孤立地研究。然而，很明显，它们在分子水平上、功能上以及在疾病中的作用方面基本上重叠。在这个应用中，我们提出的实验，双向连接Bax，心肌细胞死亡的中央介质，与帕金，心肌细胞线粒体自噬的重要激活剂。使用遗传操作，我们意外地发现，健康细胞中Bax的内源性水平抑制线粒体自噬。我们已经在体外成年心肌细胞和体内心脏中观察到了这一点。我们假设这是一种生理机制，抑制线粒体的不适当或过度消除，这种情况对高度依赖ATP的心肌细胞是有害的。我们将阐明其机制，这可能涉及Bax和Parkin之间的相互作用，并测试在体外和体内的功能意义。Bax和帕金相互作用的事实提出了一个相互的问题：帕金在心脏中对Bax做了什么？先前在非心脏系统中的工作表明，Parkin在细胞死亡期间抑制Bax易位到线粒体，但其机制尚未阐明。已知帕金在体外抑制心肌细胞死亡，并且帕金在体内的缺失显著加剧梗死后重构、心力衰竭和死亡率。这些作用被认为是介导的唯一通过帕金森刺激的线粒体自噬。然而，鉴于Bax与心肌细胞凋亡和坏死之间的直接联系，我们质疑这种观点，并假设帕金主要通过抑制Bax来保护心脏。我们将检验这一假设，并阐明帕金抑制Bax的分子机制。因此，该项目的过度假设是Bax和Parkin相互拮抗以利于心肌细胞：Bax可能以其细胞死亡非活性构象与Parkin结合抑制Parkin介导的线粒体自噬以防止线粒体耗竭。相反，Bax-Parkin相互作用可能通过干扰Bax向其活性构象的转变来抑制Bax，从而抑制心肌细胞凋亡和坏死。这是一个MPI应用程序，汇集了Richard Kitsis（心肌细胞死亡）和Gerald多恩（心脏线粒体自噬）的专业知识。这项研究意义重大，因为它将刺激该领域的发展。 考虑和研究单个线粒体过程之间的联系，如细胞死亡和线粒体自噬。此外，它将导致重新考虑帕金保护心脏的主要机制。这项工作也是高度创新的，因为大多数概念和关系以前没有考虑过。通过本研究，我们将更好地了解急性心肌缺血/再灌注损伤和梗死后重构的发病机制。

 DESCRIPTION (provided by applicant): Mitochondria engage in multiple fundamental processes including biogenesis, fission/fusion, mitophagy, and cell death - in addition to their role as ATP generators in the cell. These processes are complex, and for this reason, have been largely studied in isolation. Yet, it is clear that they overlap substantially at the molecula level, functionally, and with respect to their roles in disease. In this application, we propose experiments that bi-directionally connect Bax, a central mediator of cardiomyocyte death, with Parkin, an important activator of mitophagy in cardiomyocytes. Using genetic manipulations, we have found unexpectedly that endogenous levels of Bax in healthy cells suppress mitophagy. We have observed this in adult cardiomyocytes in vitro and in the heart in vivo. We postulate that this is a physiological mechanism that restrains inappropriate or excessive elimination of mitochondria, a situation that would be deleterious to cardiomyocytes, which are highly dependent on ATP. We will elucidate the mechanism, which may involve an interaction between Bax and Parkin, and test the functional significance in vitro and in vivo. The fact that Bax and Parkin interact raises the reciprocal question: What might Parkin be doing to Bax in the heart? Previous work in non-cardiac systems has shown that Parkin inhibits Bax translocation to mitochondria during cell death, but the mechanism has not been elucidated. Parkin is known to inhibit cardiomyocyte death in vitro, and deletion of Parkin in vivo markedly exacerbates post-infarct remodeling, heart failure, and mortality. These effects have been assumed to be mediated solely through Parkin-stimulated mitophagy. Given the directness of the connection between Bax and cardiomyocyte apoptosis and necrosis, however, we challenge that view and hypothesize that Parkin protects the heart primarily through its inhibition of Bax. We will test ths hypothesis and delineate the molecular mechanism by which Parkin inhibits Bax. Accordingly, the over-arching hypothesis of this project is that Bax and Parkin antagonize each other for the benefit of cardiomyocytes: The binding of Bax, likely in its cell death-inactive conformation, to Parkin inhibits Parkin-mediated mitophagy to prevent mitochondrial depletion. Conversely, the Bax-Parkin interaction inhibits Bax, likely through interfering with its transition to its active conformation, thereby inhibiting cardiomyocyte apoptosis and necrosis. This is an MPI application that brings together the expertise of Richard Kitsis (cardiomyocyte death) and Gerald Dorn (cardiac mitophagy). This research is highly significant as it will stimulate the field to consider and investigate connections between individual mitochondrial processes, such as cell death and mitophagy. In addition, it will lead to a reconsideration of the primary mechanism by which Parkin protects the heart. The work is also highly innovative because most of the concepts and relationships have not been previously considered. Through this research, we will achieve a better understanding of the pathogenesis of acute cardiac injury during ischemia/reperfusion and post-infarct remodeling.