Structural-functional zoning of the mitochondrion in cardiac Ca2+, ROS, and energetics regulation

线粒体损伤是高血压的主要因素和潜在的治疗靶点。 心力衰竭(HF)的发展。在兴奋-收缩耦合过程中，钙离子从 肌浆网的二分连接(JSR)，启动肌肉收缩。JSR经常 拴在线粒体上，在那里产生一个高[钙]纳米结构域来促进钙离子 传播到线粒体基质以刺激ATP的产生(激发能量学 耦合)。心脏跳动消耗大量能量；因此，心肌细胞必须高效地 动态平衡能源供需，避免潜在的钙离子中介 毒性。我们发现线粒体钙离子单一转运体(MTCU)负责钙的摄取， 集中在JSR界面的热点，而强健的依赖Na+的钙 挤出(线粒体Na+/Ca~(2+)交换器，NCLX)大多被排除在这些片段之外。 在这个提案中，我们提出了一个总体主题，即线粒体，它与 利用JSR，将它们的膜结构和蛋白质分布不对称地重塑为两个 JSR近端和远端的区域，以保护其长期完整性，同时为 激发-能量耦合。这种适应的不平衡导致了心衰。基于我们的 初步数据和已发表的文献；我们假设线粒体钙离子内流和 外流的距离是唯一的，因此在基质中创建了[Ca2+]梯度，以确保 有效钙离子通过最大限度地减少钙离子的量而无毒性地介导能量生产 对于给定的[Ca~(2+)]升高，需要在基质中循环。近端的线粒体带 JSR形成钙离子受体，钙离子内流增强，但外流受限，膜较少 扩散障碍，而JSR远端的线粒体带有致密的脊膜 活力旺盛的ATP生成，不受钙离子毒害。最后，恒定的高钙离子在 Ca~(2+)受体带使其更容易通过线粒体发生生理性吞噬 裂变。然而，长期的压力会使这种生理防御机制变得不适应， 在没有JSR钙离子输入的情况下，线粒体碎片过多(无激发能量学 偶联)，由于失去并列，从而导致心力衰竭的病因。三个具体目标是： 1)研究不同亚线粒体内分布的生理学意义 激发-能量耦合中线粒体钙摄取和排泄机制的研究。2.至 建立与钙离子区带运输相关的线粒体亚区结构区划。3.至 评估分区对线粒体维护/质量控制的影响以及影响程度 与压力相关的碎片化可能会使分区不适应，并导致HF。

Mitochondrial impairment is a main contributor and potential therapeutic target in the development of heart failure (HF). During excitation-contraction coupling, Ca2+ is released from the sarcoplasmic reticulum of dyadic junction (jSR) to initiate muscle contraction. jSR is often tethered to mitochondria, where a high [Ca2+] nanodomain is created to facilitate Ca2+ propagation to the mitochondrial matrix to stimulate ATP production (excitation-energetics coupling). The beating heart consumes much energy; thus, cardiomyocytes must be efficient in dynamically balancing energy demands and supplies while avoiding potential Ca2+ mediated toxicity. We find that mitochondrial Ca2+ uniporter (mtCU), responsible for Ca2+ uptake, concentrate to hotspots at the interface with jSR whereas the robust Na+-dependent Ca2+ extrusion (mitochondrial Na+/Ca2+ exchanger, NCLX) is mostly excluded from these segments. In this proposal, we put forward the overarching theme that the mitochondria, which associate with jSR, remodel their membrane structure and protein distribution asymmetrically into two zones proximal and distal from jSR, to protect their long-term integrity while serving the excitation-energetics coupling. Imbalance in this adaptation leads to HF. Based on our preliminary data and published literature; we hypothesize that mitochondrial Ca2+ influx and efflux are uniquely distanced, and so a [Ca2+] gradient is created in the matrix to ensure an effective Ca2+ mediated energy production without toxicity by minimizing the amount of Ca2+ required to cycle through the matrix for a given [Ca2+] rise. The mitochondrial zone proximal to the jSR forms a Ca2+ receptacle with enhanced Ca2+ entry but limited exit and less membrane barriers for diffusion, while the mitochondrial zone distal to jSR has dense cristae membrane for vigorous ATP generation without subjecting to Ca2+ toxicity. Finally, the constant high Ca2+ in Ca2+ receptacle zone renders it more susceptible for physiological mitophagy via mitochondrial fission. However, prolonged stress turns this physiological defense mechanism maladaptive, with excess of fragmented mitochondria without jSR Ca2+ input (no excitation-energetics coupling) due to the loss of juxtaposition, as such leads to HF etiology. Three specific aims are: 1) Investigate the physiological implications of differential submitochondrial distribution of mitochondrial Ca2+ uptake and extrusion mechanisms in excitation-energetics coupling. 2. To establish submitochondrial structural zoning associated with the zonal Ca2+ transport. 3. To assess the impact of zoning on mitochondrial maintenance/quality control and how excessive fragmentations associated with stresses could turn zoning maladaptive and lead to HF.