Silencing Smad7 Potentiates BMP2-induced Chondrogenic Differentiation and Inhibits Endochondral Ossification in Human Synovial Derived Mesenchymal Stem Cells

Abstract

Background: Cartilage injuries pose formidable challenges for effective clinical management. Autologous stem cell-based therapies and transgene-enhanced cartilage tissue engineering may open new avenues for the treatment of cartilage injuries. Bone morphogenetic protein 2 (BMP2) is a promising chondrogenic growth factors for transgene-enhanced cartilage tissue engineering. However the BMP2 is failed to maintain a stable chondrogenic phenotype as it also induces robust endochondral ossification. Recently, human synovial derived mesenchymal stem cells (hSMSCs) arouse interested through the poor differentiation potential into osteogenic lineage. Smad7, a protein to antagonizes TGF-β/BMP signaling pathway has been discovered significant in the endochondral ossification. In the present study ,we further explore the effect of downregulate Smad7 in BMP2-induced chondrogenic differentiation of hSMSCs. Methods: hSMSCs were isolated from synovium of human knee joint through adhesion growth. In vitro and in vivo chondrogenic differentiation models of hSMSCs were constructed . Transgenes of BMP2, silencing Smad7 and Smad7 were expressed by adenoviral vectors. The osteogenic differentiation was detected by alkaline phosphatase staining, alizarin red staining. The chondrogenic differentiation was detected by alcian blue staining. Gene expression was determined by reverse transcription and quantitative real-time PCR (RT-qPCR), Immunofluorescence and immunohistochemistry. The subcutaneous stem cell implantation model was established and evaluated by micro-CT , h＆e staining, alcian blue staining and immunohistochemistry assay.Results: Compared to other MSCs, hSMSCs performed less of capability to osteogenic differentiation. But the occurrence of endochondral ossification is still inevasible during BMP2 induced cartilage formation. We found that silencing Smad7 enhanced the BMP2-induced chondrogenic differentiation of hSMSCs in vitro. Also, it leading to much less of hypertrophic differentiation. The subcutaneous stem cells implantation assays demonstrated silencing Smad7 potentiates BMP2-induced cartilage formation and inhibits endochondral ossification. Conclusion: This study strongly suggests that application of hSMSCs , cell scaffolds and silencing Smad7 can potentiate BMP2-induced chondrogenic differentiation and inhibit endochondral ossification. Thus, inhibit the expression of Smad7 in BMP2-induced hSMSCs differentiation may be a new strategy for cartilage tissue engineering.