Advanced Center for Chronic Diseases (ACCDiS), Facultad de Ciencias Químicas y Farmaceuticas & Facultad de Medicina, Universidad de Chile, Santiago, Chile.
Advanced Center for Chronic Diseases (ACCDiS), Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Cell Death Dis. 2021 Jun 28;12(7):657. doi: 10.1038/s41419-021-03945-9.
Subcellular organelles communicate with each other to regulate function and coordinate responses to changing cellular conditions. The physical-functional coupling of the endoplasmic reticulum (ER) with mitochondria allows for the direct transfer of Ca between organelles and is an important avenue for rapidly increasing mitochondrial metabolic activity. As such, increasing ER-mitochondrial coupling can boost the generation of ATP that is needed to restore homeostasis in the face of cellular stress. The mitochondrial unfolded protein response (mtUPR) is activated by the accumulation of unfolded proteins in mitochondria. Retrograde signaling from mitochondria to the nucleus promotes mtUPR transcriptional responses aimed at restoring protein homeostasis. It is currently unknown whether the changes in mitochondrial-ER coupling also play a role during mtUPR stress. We hypothesized that mitochondrial stress favors an expansion of functional contacts between mitochondria and ER, thereby increasing mitochondrial metabolism as part of a protective response. Hela cells were treated with doxycycline, an antibiotic that inhibits the translation of mitochondrial-encoded proteins to create protein disequilibrium. Treatment with doxycycline decreased the abundance of mitochondrial encoded proteins while increasing expression of CHOP, C/EBPβ, ClpP, and mtHsp60, markers of the mtUPR. There was no change in either mitophagic activity or cell viability. Furthermore, ER UPR was not activated, suggesting focused activation of the mtUPR. Within 2 h of doxycycline treatment, there was a significant increase in physical contacts between mitochondria and ER that was distributed throughout the cell, along with an increase in the kinetics of mitochondrial Ca uptake. This was followed by the rise in the rate of oxygen consumption at 4 h, indicating a boost in mitochondrial metabolic activity. In conclusion, an early phase of the response to doxycycline-induced mitochondrial stress is an increase in mitochondrial-ER coupling that potentiates mitochondrial metabolic activity as a means to support subsequent steps in the mtUPR pathway and sustain cellular adaptation.
细胞内细胞器通过相互通讯来调节功能，并协调对细胞内环境变化的反应。内质网（ER）与线粒体之间的物理功能连接允许 Ca 直接在细胞器之间传递，这是快速增加线粒体代谢活性的重要途径。因此，增加 ER-线粒体的偶联可以增加生成 ATP 的能力，从而在面对细胞应激时恢复细胞内环境的稳定。线粒体未折叠蛋白反应（mtUPR）是由线粒体中未折叠蛋白的积累激活的。线粒体到细胞核的逆行信号转导促进了 mtUPR 转录反应，旨在恢复蛋白质的内环境稳定。目前尚不清楚线粒体-ER 偶联的变化是否也在 mtUPR 应激中发挥作用。我们假设线粒体应激有利于线粒体和 ER 之间功能性接触的扩大，从而增加线粒体代谢作为保护性反应的一部分。我们用强力霉素（一种抑制线粒体编码蛋白翻译的抗生素）处理 HeLa 细胞，以产生蛋白失衡。强力霉素处理降低了线粒体编码蛋白的丰度，同时增加了 CHOP、C/EBPβ、ClpP 和 mtHsp60 的表达，这些都是 mtUPR 的标志物。线粒体吞噬活性或细胞活力没有变化。此外，未激活内质网 UPR，这表明 mtUPR 被选择性激活。在强力霉素处理后的 2 小时内，线粒体和 ER 之间的物理接触显著增加，并且分布在整个细胞中，同时线粒体 Ca 摄取动力学增加。这之后在 4 小时时耗氧量增加，表明线粒体代谢活性增强。总之，强力霉素诱导的线粒体应激反应的早期阶段是线粒体-ER 偶联的增加，这增强了线粒体代谢活性，作为支持 mtUPR 途径中后续步骤和维持细胞适应的一种手段。
