EVs were isolated based on the protocol described previously (Qin et al., 2019 (link)). Briefly, cells were cultured in medium containing Exosome‐depleted FBS Media Supplement (SBI, USA). At 48 h after the preconditioning stimuli, the cell culture supernatant was collected and differentially centrifuged at 4°C for 10 min at 300 × g, then 15 min at 2000 × g and 45 min at 12,000 × g followed by filtration through a 0.22 μm PVDF filter (Millipore, USA). Finally, EVs were pelleted by ultracentrifugation at 120,000 × g for 70 min. The EVs were resolved in phosphate buffer saline (PBS) for the subsequent detection.