Fig. 6. The mechanism by which mesenchymal stem cells-derived exosomes (MSCs-Exos) promotes axonal growth and neuronal regeneration. MSCs-Exos can promote axonal growth by promoting M2 macrophage polarization by inhibiting the NF-κb/NLRP3 signaling pathway. MSCs-Exos with miR-199a-3p/145-5p can target Cblb/Cbl mRNAs to inhibit the NGF/TrkA pathway to promote axonal growth. Human placenta (HP)-MSCs-Exos can promote neuronal regeneration by activating the MEK/ERK/CREB signaling pathway. MSCs-Exos could attenuate R-Smad 6 expression to promote neuronal regeneration by carrying TGFβ. MSCs-Exos with miR-let-7a-5p downregulated SMAD2 expression by inhibiting HMGA2 to promote neuronal regeneration.