Meanwhile, compared with MSC–EV–NC mimic, miR-181a–2–3p expression levels were elevated and those of EGR1, NOX4, and p–p38 were all reduced in PD mice injected with MSC–EV–miR-181a–2–3p mimic (Fig. 9B, C; Supplementary Fig. 3C). The gene discussed is EGR1; the disease is Parkinson disease.