<i>In Vivo</i> Tracking of Mesenchymal Stem Cell-Derived Extracellular Vesicles Improving Mitochondrial Function in Renal Ischemia–Reperfusion Injury

Abstract

Extracellular vesicles (EVs) released by mesenchymal stem cells (MSCs) have exhibited regenerative capability in animal models of ischemia-reperfusion (I/R) acute kidney injury (AKI) and are considered as potential alternatives to direct MSC therapy. However, real-time <i>in vivo</i> imaging of MSC-EVs in renal I/R injury has yet to be established. Renal intracellular targets of MSC-EVs responsible for their regenerative effects also remain elusive. Here, we report that we real-time observed MSC-EVs specifically accumulated in the injured kidney and were taken up by renal proximal tubular epithelia cells (TECs) <i>via</i> DPA-SCP with aggregation-induced emission (AIE) characteristics. DPA-SCP precisely tracked the fate of MSC-EVs in a renal I/R injury mouse model for 72 h and exhibited superior spatiotemporal resolution and tracking ability to popular commercially available EV tracker PKH26. Further analysis revealed that the accumulated MSC-EVs stimulated mitochondrial antioxidant defense and ATP production <i>via</i> activating the Keap1-Nrf2 signaling pathway, which protected TECs against oxidative insult by reducing mitochondrial fragmentation, normalizing mitochondrial membrane potential, and increasing mitochondrial DNA copy number. Increased microRNA-200a-3p expression in renal TECs induced by MSC-EVs was identified as a regulatory mechanism contributing to the protective actions on mitochondria as well as stimulating the renal signal transduction pathways. In conclusion, MSC-EVs accumulated in the renal tubules during renal I/R injury and promoted the recovery of kidney function <i>via</i> activating the Keap1-Nrf2 signaling pathway and enhancing mitochondrial function of TECs. DPA-SCP with AIE characteristics allows noninvasive and precise <i>in vivo</i> visualization of MSC-EVs in kidney repair.