Mitochondrial Calcium Uniporter in Signaling and Dynamics

线粒体钙摄取控制许多细胞功能，包括能量代谢、信号和动力学。线粒体内膜电位高度负的强大驱动力支持线粒体钙的积累，但只有在胞浆[钙]升高的情况下，线粒体钙的积累才被激活。CA2信号通过钙单转运体(MTCU)通道传递到线粒体基质，MTCU由成孔的MCU、支架EmRE和MICU1的钙敏感调节二聚体MICU2或MICU3组成。MICU1缺失导致MTCU永久开放，而MICU2缺失增加，MICU3缺失降低MTCU门控的钙敏感性。我们和其他人已经证明，MICU1缺失会导致小鼠的围产期死亡，MICU1和MICU2突变都与人类疾病有关。也开始积累证据支持MICU1在缺血再灌注和癌症等常见疾病中的减少。然而，尽管小鼠具有广泛的疾病相关性，但它们在钙信号和细胞器、细胞和组织结构和功能的组织中的作用仍不确定。在这里，我们提供了初步的数据，表明在小鼠体内细胞间和细胞内的异质性，这可能与复杂器官中细胞的特化有关。MICU1缺失之后是继发性MTCU成分改变，可能是适应性的，也可能是非适应性的，但这些变化和MTCU以外的其他变化的时间顺序尚不清楚。虽然MICU1丢失诱导的细胞损伤归因于线粒体钙超载，但我们的初步发现指出了其他因素的重要性，即线粒体活性氧物种和结构变化。因此，阐明MICUS对细胞内和细胞内钙信号的组织以及线粒体结构和功能的稳定具有重要意义。在这里，我们提出的假设是，MICUS对于单个细胞的钙信号指纹、氧化还原动态平衡以及线粒体的融合-裂变和嵴动态都是重要的。为了测试这些想法，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对MTCU的门控是否在细胞内造成钙信号的异质性；(2)MICU对MTCU门控的控制是否与线粒体氧化还原动态平衡有关；(3)MICU1、MICU2和MICU3是否有助于控制线粒体的融合-裂变动力学和脊的形成，这些贡献取决于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递的机制提供线索，并为干扰MTCU结构和功能启动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.