SHH and intervertebral disk degenerative disorder: As mentioned above, activation of PI3K/AKT, Shh, and TGF-β signaling pathways, and inhibition of NF-κB and JNK signaling pathways induce IDD remission with stem cell treatment, and the roles of Wnt/β-catenin, ERK1/2, and p38-MAPK pathways in stem-cell-treated IDD remain two-sided.