Table 1.

The biological effects and main related mechanisms of miR-21

Biological effects	Main mechanisms	References
Anti-inflammation	• Reduces IL-1β, IL-6, IL-8, TNF-α, eNOS • Downregulates CCL3	Lv et al. (2020) Liu et al. (2020)
Anti-apoptotic	• Reduces Bax/Bcl-2, and Caspase-3 and Caspase-9, and PTEN protein expressions • Reduces PDCD4	Hu et.al. (2013) Zhang et al. (2019)
Anti-glial scar formation	• Modulates astrocytes’ secretion, proliferation, and apoptosis • Modulates PI3K/Akt/mTOR • Reduces astrocytes hypertrophy in the SCI	Liu et al. (2018) Liu et al. (2018) Bhalala et al. (2012)
Angiogenesis modulation	• Inhibits TIMP3 and promotes MMP2 and MMP9 • Promotes expression of Ang-1, Tie-2, and VEGF •Increases MMP-13 and p-ERK1/2 • Promotes the survival, migration and tube formation of endothelial cells	Hu et al. (2016) Ge et al. (2014) Ma et al. (2020) Hu et al. (2016)
Neuroregeneration modulation	• Promotes neural differentiation of NSPCs • Enhances the expression of cyclin D1 in NSPCs • Activates AKT/GSK-3β signaling Pathway • Modulates Wnt/β-catenin signaling pathway	Gao et al. (2016) Song et al. (2021) Gao et al. (2016) Zhang et al. (2018)