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

线粒体损伤是肝硬化的主要原因和潜在的治疗靶点。 心力衰竭（HF）的发展。在兴奋-收缩偶联过程中，Ca2+从 肌浆网的二进连接（jSR）启动肌肉收缩。JSR通常 与线粒体相连，在那里产生高[Ca2 +]纳米结构域以促进Ca2 + 传播到线粒体基质以刺激ATP产生（兴奋-能量学 耦合）。跳动的心脏消耗大量能量;因此，心肌细胞必须有效地 动态平衡能量需求和供应，同时避免潜在的Ca2+介导 毒性我们发现，线粒体Ca 2+单向转运体（mtCU），负责Ca 2+摄取， 集中在与jSR的界面处的热点，而强Na+依赖性Ca2 + 挤出（线粒体Na +/Ca2+交换器，NCLX）大多被排除在这些片段之外。 在这个提议中，我们提出了一个总体主题，即线粒体， 与jSR，重塑他们的膜结构和蛋白质分布不对称成两个 区域近端和远端从jSR，以保护其长期的完整性，同时服务于 激发-能量耦合这种适应的不平衡导致HF。基于我们 初步数据和已发表的文献;我们假设线粒体Ca2+内流和 流出物是唯一的距离，因此在基质中创建[Ca2 +]梯度，以确保 通过最小化Ca2+的量，有效的Ca2+介导的能量产生而没有毒性 所需的循环通过矩阵为一个给定的[Ca2 +]上升。线粒体近端区 jSR形成了一个Ca2+容器，具有增强的Ca2+进入，但有限的退出和较少的膜 扩散的屏障，而线粒体区远端jSR有致密的嵴膜， ATP生成旺盛而不受Ca2+毒性的影响。最后，恒定的高Ca 2 + Ca2+受体区使其更容易通过线粒体进行生理性线粒体自噬 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 Ca2+输入的情况下（没有兴奋-能量学），具有过量的片段化线粒体 偶联），因此导致HF病因学。三个具体目标是： 1)研究不同的亚线粒体分布的生理意义， 线粒体Ca~（2+）的摄取和排出机制。2.到 建立与带状Ca2+运输相关的亚线粒体结构分区。3.到 评估分区对线粒体维持/质量控制的影响，以及如何过度 与应力有关的破碎化可能使分带不适应并导致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.