As for the mechanism of miR-21 mediates VEGF expression and angiogenesis, recent studies have shown that miR-21 increases VEGF expression via ERK and AKT signal in vascular endothelial cells (Liu et al., 2011); miR-21 promotes angiogenesis by targeting SPRY2 and/or KRIT1 in osteoarthritis and colorectal cancer (Ma et al., 2020; He et al., 2021). The gene discussed is SPRY2; the disease is osteoarthritis.