Table 1 The biological effects and main related mechanisms of miR-21

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)