Gene and protein expressions of bone marrow mesenchymal stem cells in a bone tunnel for tendon-bone healing

Purpose: Bone marrow mesenchymal stem cells (BMSCs) injected around tendon grafts can enhance tendon-bone healing and promote fibrocartilage formation. To understand gene and protein expressions of cells during tendon-bone healing, auto-BMSCs were implanted into a bone tunnel in anterior cruciate ligament reconstruction in a rabbit model. Methods: BMSCs were harvested from New Zealand white rabbits. By an anterior cruciate ligament reconstruction model, 1×10⁶ BMSCs in 0.35mL of fibrin glue was injected into bone tunnel as Fibrin-BMSC group. Only fibrin glue (Fibrin group) was injected as control. Three chondrogenesis genes and proteins, including Sox 9, collagen Type II (COII), aggrecan, and three osteogenesis genes and proteins, including Runx2, collagen type I (COI), and osteocalcin, between Fibrin-BMSC and Fibrin group were compared by real-time polymerase chain reaction assay and immunohistochemical assay postoperation. Results: In real-time polymerase chain reaction assay, Sox9, COII, aggrecan, COI, and osteocalcin expressions upregulated and Runx2 downregulated were determined in Fibrin-BMSC group at 1 week. COII, aggrecan upregulated, and Runx2 and osteocalcin downregulated were determined at 4 weeks. In immunohistochemical assay, only Sox9, COII, and aggrecan proteins in only Fibrin-BMSC group were observed at 4 weeks. The protein expression as same as gene expression was obtained in a bone tunnel. Conclusion: Auto-BMSCs promoted COII and aggrecan expression and reduced Runx2 and osteocalcin expression in a bone tunnel. It demonstrated that these cells could enhance fibrocartilage formation because of higher chondrogenesis expression during tendon-bone healing.