Mesenchymal stem cells (MSCs) are exciting candidates for cellular repopulation and repair in intervertebral disc degeneration (IDD). Our purpose is to investigate the interaction between MSCs and nucleus polposus cells (NPCs) and to determine viability of MSC in the intervertebral disc (IVD).

Human NPCs and hMSCs were co-cultured in pellet system at different ratios. Proteoglycans were measured and normalized with DNA content. Histological analysis were also performed. Rabbit MSCs from bone marrow were trasduced with LacZ reporter gene and were injected into a rabbit IVD. Rabbits were sacrificed postoperatively at 3, 6, 12 and 24 weeks. Histological analysis was performed.

Co-culturing of hNPCs with hMSCs resulted in increases proteoglycans as compared with hNPCs alone. Histological examination of the injected IVDs revealed presence of MSCs without apparent decrease in numbers or diminishment of protein production at 3, 6, 12 and 24 weeks.

The data from this study show that there is a synergistic effect between MSCs and NPCs resulting in upregulated proteoglycan synthesis in-vitro. MSC remain viable and continue to express an ex-vivo transduced protein for up to 24 weeks. These results suggest that MSCs can survive in the harsh environment of the IVD and may favourably modify ECM production.

Introduction: Current therapies for degenerative disc disease (DDD) are aimed at treating the pathologic and disabling conditions arising from DDD rather than directly treating the underlying problem of disc degeneration. Our group are exploring the potential of Cell Therapy to repopulate the disc and stopping the progressive loss of proteoglycans. Stem cells appear to be excellent candidates for this purpose, based on their ability to differentiate along multiple connective tissue lineages. The purpose of this study is to investigate the in-vitro interaction between muscle-deroved stem cells (MdSC) and nucleus polposus cells (NPCs) and to determine in-vivo viability of mesenchymal stem cell (MSC) in the harsh environment of the IVD

Materials and Methods: (1) Human NPCs were isolated from patients undergoing disc surgery and were co-cultured for 2 weeks with MdSCs from 3-wk-old mdx mice and in monolayer culture system at different ratios of 0:100, 25:75, 50:50, 75:25, 100:0. Proteoglycan synthesis and DNA content were measured. (2) Rabbit mesenchymal stem cells were isolated from bone marrow and tagged with a retrovirus delivered LacZ reporter gene for tracking. MSCs were then injected into a healthy rabbit IVD via 30G needle. Rabbits were sacrificed at postoperatively at 3, 6, 12 and 24 weeks. Histological analysis for MSC viability was performed.

Results: (1) Co-culturing of NPCs with MdSCs in the monolayer culture system resulted in vigorous increases in proteoglycans synthesis as compared with NPCs alone. The increases were on the 200% for an NPC-to-MDSC ratio of 75:25. DNA content also increased with co-culture. (2) Histological examination revealed presence of MSCs expressing LacZ without apparent decrease in numbers or diminishment of protein production.

Conclusion: The data from this study show that there is a synergistic effect between stem cells and nucleus pulposus cells resulting in upregulated proteoglycan synthesis in-vitro. Mesenchymal stem cells remain viable and continue to express an ex vivo transduced protein without appreciable cell loss for up to 24 weeks post transplantation into the rabbit IVD. These results suggest that MSCs can survive in the harsh environment of the IVD and may favourably modify ECM production. These studies support the feasibility of developing a stem cell therapy approach for DDD.

Current therapies for intervertebral disc degeneration are aimed at treating the pathologic and disabling conditions arising from discopathy rather than directly treating the underlying problem of disc degeneration. Our group is exploring the potential of cell therapy to repopulate the disc and stop the progressive loss of proteoglycans. Stem cells appear to be excellent candidates for this purpose, based on their ability to differentiate along multiple connective tissue lineages. The purpose of this study is to investigate the interaction between stem cells and nucleus polposus cells to test the feasibility of stem cell therapy for the treatment of disc degeneration.

Human nucleus polposus cells (NPCs) were isolated from patients undergoing disc surgery and were co-cultured for 2 weeks with muscle-derived stem cells (MdSCs) from 3-week-old mdx mice in monolayer culture system at different ratio with or without added TGF-β1. Each well contained an admixture of cells with NPC-to-SC ratios of 0:100, 25:75, 50:50, 75:25, and 100:0. Proteoglycan synthesis and DNA content were measured.

Co-culturing of NPCs with MdSCs in the monolayer culture system resulted in vigorous increases in proteoglycans synthesis as compared with NPCs alone and MdSCs alone both with and without TGF-β1. The increases were on the 200% for an NPC-to-MDSC ratio of 75:25. Addition of TGF-β1 to the NPC and MDSC co-cultures resulted in further increases up to 400%. DNA content also increased with co-culture.

The data from this study show that there is a synergistic effect between stem cells and nNPC resulting in upregulated proteoglycan synthesis in vitro. The observed benefits of co-culture might be due either to stem cell plasticity, the stem cells trans-differentiation towards chondrocyte-like cells, or the stimulation of NPC by agents synthesised by stem cells or other mechanisms. Elucidation of the precise mechanisms of action may permit development of strategies to optimise the synergistic effects in vivo. These results support the feasibility of developing a stem cell therapy approach to treat and prevent intervertebral disc degeneration.