Exosomes released from human umbilical cord mesenchymal stem cells (hucMSCs) inhibited cisplatin-induced apoptosis and promoted proliferation in NRK-52E cells. (A) Mitochondrial membrane potentials were analyzed to evaluate cell early apoptosis. The ratio of green to red fluorescence was higher in the cisplatin and human lung fibroblast secreted exosomes (HFL-1-ex) groups than untreated NRK-52E cells, suggesting early apoptosis of cells. The ratio was reversed after treating with hucMSC-ex in cisplatin-induced NRK-52E cells. Original magnification, × 200. (B) Western blot analysis of B cell lymphoma 2 (Bcl-2) protein and Bcl-2-associated X protein (Bax) levels in NRK-52E cells: Bax expression was raised in the phosphate-buffered saline (PBS) and HFL-1-ex groups compared to the control group, and this was reversed in the hucMSC-ex group. The expression pattern for Bcl-2 was also reversed in the hucMSC-ex group. (C) Western blot results indicated increased phosphorylated extracellular-signal-regulated kinase (p-ERK) expression in the hucMSC-ex group compared to the cisplatin and HFL-1-ex groups, correlating with raised proliferating cell nuclear antigen (PCNA) expression. (D) HucMSC-ex and U0126 were added into the medium of cisplatin-treated NRK-52E cells at the same time; p-ERK and PCNA expression were suppressed, as shown by western blot. This indicates that hucMSC-ex promoted injured NRK-52E cell proliferation by activation of the ERK1/2 pathway.