In vitro interaction between muscle-derived stem cells and nucleus pulposus cells.

BACKGROUND CONTEXT: Current therapies for intervertebral disc degeneration (IDD) are aimed at treating the clinical symptoms arising from IDD rather than directly treating the underlying problem. Pathophysiology of IDD is characterized by a progressive decrease in proteoglycan content and cell density in the nucleus pulposus (NP). A cell-based therapy is a promising concept that uses various cell types to repopulate the disc in an attempt to slow, stop, or reverse the progressive loss of proteoglycans. Stem cells appear to be an excellent candidate for this purpose, based on their ability to differentiate into various connective tissue lineages. The muscle tissue could serve as a good source of adult stem cells because of its vast abundance through out the human body.

PURPOSE: To examine the interaction between the nucleus pulposus cells (NPCs) and the muscle-derived stem cells (MDSCs) in vitro.

STUDY DESIGN: NPCs and MDSCs were cocultured and proteoglycan production and cell proliferation were evaluated.

METHODS: Various ratios of human NPCs were cocultured for 2 weeks with murine MDSCs (transduced with retro/LacZ) in a monolayer culture. Each well contained an admixture of cells with NPC-to-MDSC ratios of 0:100, 25:75, 50:50, 75:25, 100:0. Glycosaminoglycan (GAG) content (1,9 dimethylmethylene blue [DMMB]), newly synthesized proteoglycan ((35)S incorporation), and DNA content were measured, and cultures were stained with 5-bromo-4-chloro-3-indolyl-beta-D-galactosidase (X-Gal) for cell counting.

RESULTS: The NPC-to-MDSC ratio of 75:25 resulted in a significant increase in GAG content compared with NPCs alone. All coculture ratios showed increase in GAG content in comparison with MDSC culture alone. In addition, cocultures showed a significant increase in (35)S incorporation normalized to DNA content in comparison with MDSC alone.

CONCLUSIONS: The data from this study shows a synergistic effect between MDSCs and NPCs resulting in an upregulated proteoglycan synthesis and NPCs proliferation in vitro.