Uptake mechanisms and functions of isolated mitochondria in mesenchymal stromal cells

Mitochondrial transplantation holds great promise as a therapeutic strategy; however, the mechanisms by which recipient cells interact with and internalize isolated mitochondria remain unclear. Therefore, in this study, we isolated functional mitochondria from mesenchymal stromal cells (MSCs) and characterized their biological activities and physicochemical properties. Additionally, effects of isolated mitochondria on MSC functions were evaluated. Treatment with isolated mitochondria promoted cell proliferation, improved cellular viability under stress conditions, and increased the oxygen consumption rate, indicating enhanced bioenergetic capacity. Uptake of isolated mitochondria by MSCs was visualized via fluorescence imaging and quantitatively assessed over time, showing progressive internalization within 24 h. To investigate the mechanism of mitochondrial uptake, endocytosis was chemically inhibited, which revealed that endocytic pathways contributed to the internalization of the isolated mitochondria. These findings suggest that MSCs incorporate isolated mitochondria via active uptake mechanisms and that the internalized mitochondria retain their functional activity. Collectively, our results provide critical evidence of mitochondrial internalization in MSCs and offer insights into the potential applications of mitochondrial therapy for various diseases.