Coculture of Synovium-Derived Stem Cells and Nucleus Pulposus Cells in Serum-Free Defined Medium With Supplementation of Transforming Growth Factor-β1 A Potential Application of Tissue-Specific Stem Cells in Disc Regeneration

Study Design. A coculture of synovium-derived stem cells (SDSCs) and nucleus pulposus cells (NPCs) in a serum-free pellet system was treated with varying doses of transforming growth factor beta (TGF-beta). Cultures of either SDSCs or NPCs alone served as controls. Objective. The aim was to assess the feasibility of using SDSCs to supplement and replenish NPC population for disc regeneration. Summary of Background Data. SDSCs have been proven to be a tissue-specific type of mesenchymal stem cell capable of chondrogenesis. NPCs are chondrocyte-like cells with a high ratio of aggrecan. However, the capacity of SDSCs to complement the NPC population is not known. Methods. SDSCs were negatively isolated from porcine knee joint synovial tissue and NPCs were isolated from porcine lumbar spines (L-1-L-5). SDSCs and NPCs were cocultured (50: 50) in a serum-free pellet system with the supplementation of varying doses (0, 3, 10, and 30 ng/mL) of TGF-beta 1 for 14 days. SDSCs or NPCs cultured alone served as controls. Chondrogenic differentiation markers were evaluated by histology, immunohistochemistry, biochemistry, and TaqMan PCR. Results. The coculture of SDSCs and NPCs in a pellet system displayed comparable differentiation properties (high levels of collagen II, aggrecan and Sox 9, a low level of collagen I, and no collagen X detectable) to NPCs alone when treated with high doses of TGF-beta 1. Moreover, the coculture and NPCs alone shared a similar higher ratio of aggrecan to collagen II. Hypoxia-inducible factor 1 alpha (HIF-1 alpha) was also observed to be up-regulated in coculture pellets at day 7 and had decreased at day 14 with the time of pellet tissue maturation. Conclusion. SDSCs may act as a potential mesenchymal stem cell candidate for NP regeneration. Further studies are needed to evaluate the in vivo effect of SDSCs on disc regeneration.