Mitochondrial Calcium Uniporter in Signaling and Dynamics

线粒体Ca2+摄取控制许多细胞功能，包括能量代谢，信号传导和动力学。线粒体Ca2+积累由高度负的线粒体内膜电位的强大驱动力支持，但仅在Ca2+信号期间被激活，当细胞质[Ca2+]升高时。Ca2+信号通过一个通道传播到线粒体基质，即钙单转运体（mtCU），由成孔MCU、支架EMRE和MICU1自身、MICU2或MICU3的Ca2+感应调节二聚体组成。MICU1缺失导致mtCU永久打开，而MICU2丢失增加，MICU3丢失降低mtCU门控的Ca2+灵敏度。我们和其他人已经证明MICU1缺失会导致小鼠围产期死亡，MICU1和MICU2突变都与人类疾病有关。支持MICU1在缺血再灌注和癌症等常见疾病中减少的证据也开始积累。然而，尽管micu具有广泛的疾病相关性，但它们对钙信号和细胞器、细胞和组织结构和功能的组织的贡献仍未确定。在这里，我们提供的初步数据表明micu的细胞间和细胞内异质性，这可能与复杂器官中细胞的特化有关。研究表明，MICU1丢失之后会发生二次mtCU组成变化，这种变化可能是自适应的，也可能是不自适应的，但是这些变化和mtCU本身以外的其他变化的时间顺序尚不清楚。虽然MICU1丢失引起的细胞损伤归因于线粒体Ca2+超载，但我们的初步研究结果指出了其他因素的重要性，即线粒体活性氧和结构改变。因此，阐明MICUs参与Ca2+信号胞间和胞内组织以及线粒体结构和功能稳定性的机制具有重要意义。在这里，我们提出了MICUs对单个细胞的Ca2+信号指纹，氧化还原稳态以及线粒体的融合-裂变和嵴动力学很重要的假设。为了验证这些想法，我们开发了新的分析方法，并组装了一系列细胞和小鼠遗传模型。我们的具体目标是确定(1)MICU1门控mtCU是否在Ca2+信号传导中产生细胞内异质性；(2) micu对mtCU门控的控制是否与线粒体氧化还原稳态有关；(3) MICU1、MICU2和MICU3是否参与线粒体融合-裂变动力学和嵴形成的控制，这些作用取决于mtCU的门控。这些目标的完成将为micu支持线粒体膜动力学和信号传导的机制以及mtCU结构和功能紊乱引发的发病机制提供线索。

Mitochondrial Ca2+ uptake controls many cell functions, including energy metabolism, signaling and dynamics. Mitochondrial Ca2+ accumulation is supported by the robust driving force of the highly negative, inner mitochondrial membrane potential, but is activated only during Ca2+ signals, when cytoplasmic [Ca2+] is elevated. Ca2+ signals are propagated to the mitochondrial matrix through a channel, the calcium uniporter (mtCU), comprised of pore-forming MCU, scaffold EMRE, and Ca2+-sensing regulatory dimers of MICU1 with itself, MICU2 or MICU3. MICU1 deletion results in a permanently open mtCU, whereas MICU2 loss increases and MICU3 loss decreases the Ca2+ sensitivity of the mtCU gating. MICU1 deletion has been shown by us and others to cause perinatal death in mouse and both MICU1 and MICU2 mutations have been linked to human diseases. Evidence has also started to accumulate in support of MICU1 decrease in common disorders like ischemia-reperfusion and cancer. However, despite the MICUs broad disease relevance, their contribution to the organization of calcium signaling and organelle, cell and tissue structure and functions remains undetermined. Here we present preliminary data indicating cell-to-cell and intracellular heterogeneity in the MICUs, which might be relevant for specialization of cells in complex organs. MICU1 loss was shown to be followed by secondary mtCU composition changes, which might be either adaptive or maladaptive, however the temporal ordering of these changes and others beyond the mtCU itself are not known. Whereas MICU1 loss-induced cell injury has been attributed to mitochondrial Ca2+ overload, our preliminary findings point to the importance of other contributors, namely mitochondrial reactive oxygen species and structural alterations. Thus, delineating the mechanisms by which MICUs contribute to the inter-and intracellular organization of Ca2+ signaling and the stability of mitochondrial structure and function are of vast significance. Here we pose the hypothesis that MICUs are important for individual cells’ Ca2+ signal fingerprints, for redox homeostasis and for fusion-fission and cristae dynamics of the mitochondria. To test these ideas, we have developed novel assays and assembled an array of cell and mouse genetic models. Our specific aims are to determine (1) if MICU1 gating of the mtCU creates intracellular heterogeneity in Ca2+ signaling; (2) if the control of mtCU gating by MICUs is relevant for mitochondrial redox homeostasis; (3) if MICU1, MICU2 and MICU3 contribute to the control of mitochondrial fusion-fission dynamics and cristae shaping and these contributions depend on the gating of the mtCU. Completion of these aims will provide clues to the mechanisms by which MICUs support mitochondrial membrane dynamics and signaling and to the pathogenesis initiated by perturbing mtCU structure and function.