| Tendon injuries are common and tendon healing outcome is poor, because tendon contains few cells with limited capacities for self-repair/regeneration. The current treatments on tendon injuries including drugs, physiotherapy, and surgery are not ideal and there is a need for the development of novel tissue-engineering strategies for tendon repair.;Previous studies have shown positive effects of bone marrow-derived mesenchymal stem cells (BMSCs), dermal fibroblast, tenocytes, and embryonic stem cells-derived MSCs for tendon repair/regeneration. However, these cells have limitations including insufficient differentiation; risk of teratoma and ectopic bone formation etc. Recently, stem cells have been isolated from tendons of human, mouse, rat and rabbit and considered as a new alternative cell source for tendon tissue engineering (TDSCs). For tenogenic differention of MSCs, connective tissue growth factor (CTGF) and ascorbic acid (one form of vitamin C) are reported to play important roles in promoting collagen and other extracellular matrixes (ECM) production, and regulating the MSCs differentiation towards tenogenic pathway.;The aims of the current study are: (1) To investigate the use of TDSCs in tendon repair in a rat acute patellar tendon injury model; (2) To test the effects of CTGF and ascorbic acid on tenogenic differentiation of TDSCs in vitro; (3) To construct scaffold-free tendon-like tissues in vitro using tenogenically differentiated TDSCs; (4) To promote tendon healing by engineered tendon-like tissues in a rat acute patellar tendon injury model.;In the rat acute patellar tendon injury model, in contract to control group, TDSCs treated group showed better alignment of collagen fibers and the significantly higher ultimate stress and Young's modulus, indicating TDSCs may be an alternative cell source for tendon repair. The effects of CTGF and ascorbic acid on tenogenic differentiation of TDSCs were also confirmed with higher expression of tendon related markers such as Tenomodulin, Scleraxis, Thbs4, Type I Collagen, etc.; with higher production of collagenous proteins. After treatment with CTGF and ascorbic acid for 2 weeks, TDSCs can form cell sheets, which can be harvested, rolled up on a U-shaped spring to form tendon-like tissues in culture, which had loose extracellular matrices and randomly distributed TDSCs and also expressed Tenomodulin, Type I & III collagen. Following transplantation of the engineered tendon-like tissue in nude mice for 8 and 12 weeks, neo-tendon tissues were formed, with thin and parallel collagen fibrils and extracellular matrices of Tenomodulin, Type I & III collagen. Finally in the rat patellar tendon window injury model, data suggested that the engineered tendon-like tissue could promote tendon healing with significantly improved histological features and biomechanical properties comparing to the control group.;In conclusion, our study has indicated that TDSCs can be an alternative cell source in tendon tissue engineering for tendon regeneration. The tenogenic differentiation of TDSCs, induced by CTGF and ascorbic acid in vitro, produces cell sheets, which can be constructed tendon-like tissues in vitro; to form neo-tendon and repair tendon injuries in vivo. The use of engineered scaffold-free tendon tissue for tendon tissue engineering has potentials in clinical application for tendon repair/regeneration. |
