Coculture of synovium-derived stem cells and nucleus pulposus cells in serum-free defined medium with supplementation of transforming growth factor-beta1: 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 (L1-L5). 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-beta1 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-beta1. Moreover, the coculture and NPCs alone shared a similar higher ratio of aggrecan to collagen II. Hypoxia-inducible factor 1alpha (HIF-1alpha) 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.