Figure 8. The signaling pathway which miR-21 can regulate multiple functions in astrocytes. TGF-β1 can up-regulate the miR-21 level through binding to TGF-β receptor and SMADs signaling. SMAD2/3 can translocate into nucleus and promote the transcription and maturation of miR-21. After the miR-21 come into the cytoplasm, it can activate the PI3K/Akt/mTOR signaling through inhibiting the PTEN expression. Also TGF-β1 can activate the PI3K/Akt/mTOR signaling, but this can be regulated by miR-21.