Up-Regulation of TGF-β Promotes Tendon-to-Bone Healing after Anterior Cruciate Ligament Reconstruction using Bone Marrow-Derived Mesenchymal Stem Cells through the TGF-β/MAPK Signaling Pathway in a New Zealand White Rabbit Model

Background/Aims: This study aimed to explore the role of TGF-β in tendon-to-bone healing after anterior cruciate ligament (ACL) reconstruction using bone marrow-derived mesenchymal stem cells (BMSCs) through the TGF-β/MAPK signaling pathway in a New Zealand white rabbit model. Methods: A total of 72 healthy male New Zealand white rabbits were selected for these experiments. Flow cytometry and immunofluorescence were used to detect the expression of BMSC surface markers, and qRT-PCR was performed to detect TGF-β mRNA expression. The ACL reconstruction model was established with autografts. The rabbits were randomly divided into the following groups: inhibition of TGF-β (inhibition), over-expression of TGF-β (over-expression), empty vector and untreated (n = 18 per group). Hematoxylineosin (HE) staining, toluidine blue staining and Masson trichrome staining were conducted to observe any chondrocyte-like cell growth, and biomechanical tests were used to calculate the maximum load and rigidity. Three-dimensional CT imaging and Western blotting were applied to detect changes in bone tunnel size and bone density and the expression levels of TGF-β/MAPK signaling pathway-related proteins, respectively. Results: CD90 and CD44 were positively expressed, while CD11b was not detected. Compared with the empty vector and untreated groups, TGF-β mRNA expression was significantly decreased in the inhibition group but increased in the over-expression group; the latter group had a larger number of fibroblasts, a tighter tendon-bone interface, an increased number of chondrocyte-like cells and fibrochondrocytes, and more collagen fibers than the inhibition, empty vector and untreated groups. Compared with the empty vector and untreated groups, the maximum load and rigidity; the CT values of bone tunnel and bone tunnel margin; and the protein expression levels of TGF-β, p-ERK1/2, p-p38, p-JNK, c-jun and c-myc were significantly down-regulated in the inhibition group but up-regulated in the over-expression group. Conclusion: Our study indicated that up-regulating TGF-β expression in BMSCs from New Zealand white rabbits could promote tendon-to-bone healing after ACL reconstruction by regulating the TGF-β/MAPK signaling pathway