Department of Brain Sciences, The Weizmann Institute of Science, Rehovot 7610001, Israel.
Computational Biology and Applied Mathematics (IBENS), Ecole Normale Supérieure-PSL, 75005 Paris, France.
Int J Mol Sci. 2022 Oct 14;23(20):12321. doi: 10.3390/ijms232012321.
While neuronal mitochondria have been studied extensively in their role in health and disease, the rules that govern calcium regulation in mitochondria remain somewhat vague. In the present study using cultured rat hippocampal neurons transfected with the mtRCaMP mitochondrial calcium sensor, we investigated the effects of cytosolic calcium surges on the dynamics of mitochondrial calcium ([Ca]m). Cytosolic calcium ([Ca]c) was measured using the high affinity sensor Fluo-2. We recorded two types of calcium events: local and global ones. Local events were limited to a small, 2-5 µm section of the dendrite, presumably caused by local synaptic activity, while global events were associated with network bursts and extended throughout the imaged dendrite. In both cases, cytosolic surges were followed by a delayed rise in [Ca]m. In global events, the rise lasted longer and was observed in all mitochondrial clusters. At the end of the descending part of the global event, [Ca]m was still high. Global events were accompanied by short and rather high [Ca]m surges which we called spikelets, and were present until the complete decay of the cytosolic event. In the case of local events, selective short-term responses were limited to the part of the mitochondrial cluster that was located directly in the center of [Ca]c activity, and faded quickly, while responses in the neighboring regions were rarely observed. Caffeine (which recruits ryanodine receptors to supply calcium to the mitochondria), and carbonyl cyanide m-chlorophenyl hydrazine (CCCP, a mitochondrial uncoupler) could affect [Ca]m in both global and local events. We constructed a computational model to simulate the fundamental role of mitochondria in restricting calcium signals within a narrow range under synapses, preventing diffusion into adjacent regions of the dendrite. Our results indicate that local cytoplasmic and mitochondrial calcium concentrations are highly correlated. This reflects a key role of signaling pathways that connect the postsynaptic membrane to local mitochondrial clusters.
尽管神经元线粒体在健康和疾病中的作用已经得到了广泛的研究，但调节线粒体钙的规则仍然有些模糊。在本研究中，我们使用转染了 mtRCaMP 线粒体钙传感器的培养大鼠海马神经元，研究了细胞质钙激增对线粒体钙动态([Ca]m)的影响。细胞质钙([Ca]c)使用高亲和力传感器 Fluo-2 进行测量。我们记录了两种钙事件：局部和全局事件。局部事件仅限于树突的一小段 2-5 µm 区域，推测是由局部突触活动引起的，而全局事件与网络爆发有关，并扩展到整个成像树突。在这两种情况下，细胞质激增后都会出现线粒体钙的延迟上升。在全局事件中，上升持续时间更长，并且在所有线粒体簇中都观察到。在全局事件下降部分结束时，[Ca]m 仍然很高。全局事件伴随着短暂而相当高的[Ca]m 激增，我们称之为刺突，并且在细胞质事件完全衰减之前一直存在。在局部事件的情况下，选择性的短期反应仅限于位于细胞质活动中心直接的线粒体簇部分，并且很快消失，而在相邻区域几乎观察不到反应。咖啡因（招募肌浆网受体将钙供应给线粒体）和羰基氰化物 m-氯苯腙（CCCP，线粒体解偶联剂）可以影响全局和局部事件中的[Ca]m。我们构建了一个计算模型来模拟线粒体在突触内将钙信号限制在狭窄范围内的基本作用，防止钙扩散到树突的相邻区域。我们的结果表明，局部细胞质和线粒体钙浓度高度相关。这反映了连接突触后膜和局部线粒体簇的信号通路的关键作用。
