Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide induced mitochondrial elongation. In contrast, oxidatively stressed cells (H₂O₂) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and − 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

线粒体动力学是碎片和拉长形状之间的形态平衡，反映线粒体代谢状态、细胞损伤和线粒体功能障碍。过敏毒素 C5a 源自补体成分 5 裂解，可增强参与病理刺激、先天免疫反应和宿主防御的细胞反应。然而，C5a 及其受体 C5a 受体 (C5aR) 在线粒体中的特异性反应尚不清楚。在这里，我们测试了 C5a/C5aR 信号轴是否影响人源性视网膜色素上皮细胞单层 (ARPE-19) 中的线粒体形态。用 C5a 多肽激活 C5aR 诱导线粒体伸长。相比之下，氧化应激细胞 (H ₂ O ₂ ) 对 C5a 的反应是线粒体碎片增强和固缩核数量增加。 C5a/C5aR 信号传导增加了线粒体融合相关蛋白 mitofusin-1 (MFN1) 和 - 2 (MFN2) 的表达，并增强了视神经萎缩-1 (Opa1) 裂解，这是线粒体融合事件所必需的，而线粒体裂变蛋白、动力相关蛋白 1 (Drp1) 和丝裂原激活蛋白激酶 (MAPK) 依赖性细胞外信号调节蛋白激酶 (Erk1/2) 磷酸化不受影响。此外，C5aR 激活增加了内质网 (ER)-线粒体接触的频率。最后，仅在 C5a 处理的单层中，RPE 单层内的单个细胞中诱导的氧化应激（488 nm 蓝色激光点刺激）仅在相邻周围细胞中诱导线粒体断裂的旁观者效应。 这些结果表明，C5a/C5aR 信号传导产生了一种中间状态，其特征是线粒体融合和 ER-线粒体接触增加，使细胞对氧化应激敏感，导致线粒体断裂和细胞死亡。