AKT Pathway Affects Bone Regeneration in Nonunion Treated with Umbilical Cord-Derived Mesenchymal Stem Cells.

We have previously grafted human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) with blood plasma to treat rat tibia nonunion. To further examine the biological characteristics of this process, we applied an established hUC-MSCs-treated rat nonunion model with the addition of an inhibitor of AKT. SD rats (80) were randomly divided into four groups: a fracture group (positive control); a nonunion group (negative control); a hUC-MSCs grafting with blood plasma group; and a hUC-MSCs grafting with blood plasma & AKT blocker group. The animals were sacrificed under deep anesthesia at 4 and 8 weeks post fracture for analysis. The fracture line became less defined at 4 weeks and disappeared at 8 weeks postoperatively in both the hUC-MSCs grafting with blood plasma and grafting with blood plasma & the AKT blocker, which is similar to the fracture group. Histological immunofluorescence studies showed that the numbers of hUC-MSCs in the calluses were significantly higher in the hUC-MSCs grafting with blood plasma than those in group with the AKT blocker. More bone morphogenetic protein 2 and bone sialoprotein expression and less osteoprotegerin and bone gla protein expression were observed in the AKT blocker group compared to the hUC-MSCs grafting with blood plasma. AKT gene expression in the AKT blocker group was decreased 50% compared to the hUC-MSCs with plasma group and decreased 70% compared to the fracture group, while the elastic modulus was decreased. In summary, our work demonstrates that AKT may play a role in modulating osteogenesis induced by hUC-MSCs.