H. Aslan, D. Gazit

One of the leading causes for low back pain is the age-related degeneration of the intervertebral disc (IVD). Mesenchymal Stem Cells (MSCs) are excellent candidates for skeletal tissue engineering, and therefore we aimed to investigate stem cell-based platforms towards the treatment of IVD disorders. We have engineered MSCs to express the osteogenic gene, rhBMP-6, using a novel electroporation-based system, and injected them into the lumbar region of mice. The cells were able to fuse 2-3 vertebrae within 5 weeks, as indicated by quantitative, in vivo, micro CT analysis. In addition, Osteocalcin-Luciferase transgenic mice were used to non-invasively and quantitatively monitor osteogenesis in the spinal fusion model, using bioluminescence imaging. We were also able to enhance MSC survival and the extent of bone formation by incorporating synthetic oxygen carriers, perfluorcarbons, into the hydrogel in which the MSCs were delivered to the implantation site. Towards replacing an entire disc, we attempted to form a tissue-engineered IVD by combining two types of scaffolds and engineered MSCs. An annulus fibrosus (AF)-shaped scaffold was seeded with MSCs overexpressing Smad8 and BMP-2 genes, while within the center of the scaffold, MSCs overexpressing the Brachyury gene were suspended in Fibrin hydrogel. The engineered IVD was implanted subcutaneously in NOD/SCID mice. Tissue formation was analyzed using quantitative micro magnetic resonance imaging (uMRI) including magnetization transfer contrast and T2 weighted analysis. Results were compared to native rat disc and validated using immunohistochemistry. Our results indicated that an IVD-like tissue was formed in vivo. Smad8/BMP-2 expressing MSCs formed an AF- like tissue in the outer portion of the graft, and MSCs expressing the Brachyury gene gave rise to NP-like tissue in the center of the construct, positively stained for Collagen II and VI. We conclude, that engineered MSCs can serve as a platform for spine tissue engineering either via spinal fusion of by IVD tissue regeneration.

Keywords (Optional): 
Mesenchymal Stem Cells
Skeletal Tissue Engineering
Gene Therapy
Disc Degeneration