RETRACTED: TGFβ3 recruits endogenous mesenchymal stem cells to initiate bone regeneration (Retracted article. See vol. 13, 2022)

Background: The recruitment of a sufficient number of endogenous mesenchymal stem cells (MSCs) is the first stage of in-situ tissue regeneration. Transforming growth factor beta-3 (TGF beta 3) could recruit stem or progenitor cells and endothelial cells to participate in tissue regeneration. However, the mechanism of TGF beta 3 recruiting MSCs toward bone regeneration has remained obscure. Methods: We estimated the promigratory property of TGF beta 3 on human bone marrow MSCs (hBMSCs) cocultured with the vascular cells (human umbilical artery smooth muscle cells or human umbilical vein endothelial cells) or not by Transwell assay. After the addition of the inhibitor (SB431542) or Smad3 siRNA, the levels of MCP1 and SDF1 in coculture medium were tested by ELISA kit, and then the migratory signaling pathway of hBMSCs induced by TGF beta 3 was investigated by western blot analysis. In vivo, a 2-mm FVB/N mouse femur defect model was used to evaluate chemokine secretion, endogenous cell homing, and bone regeneration induced by scaffolds loading 1 mu g TGF beta 3 through qPCR, immunofluorescent staining, immunohistochemical analysis, and Micro-CT, compared to the vehicle group. Results: TGF beta 3 (25 ng/ml) directly showed a nearly 40% increase in migrated hBMSCs via the TGF beta signaling pathway, compared to the vehicle treatment. Then, in the coculture system of hBMSCs and vascular cells, TGF beta 3 further upregulated nearly 3-fold MCP1 secretion from vascular cells in a Smad3-dependent manner, to indirectly enhance nearly more than 50% of migrated hBMSCs. In vivo, TGF beta 3 delivery improved MCP1 expression by nearly 7.9-fold, recruited approximately 2.0-fold CD31(+) vascular cells and 2.0-fold Sca-1(+) PDGFR-alpha(+) MSCs, and achieved 2.5-fold bone volume fraction (BV/TV) and 2.0-fold bone mineral density, relative to TGF beta 3-free delivery. Conclusions: TGF beta 3, as a MSC homing molecule, recruited MSCs to initiate bone formation in the direct-dependent and indirect-dependent mechanisms. This may shed light on the improvement of MSC homing in bone regeneration.