In vivo chondrocytic differentiation of the allogenic stem cells in the murine intervertebral disc

Abstract

Various kinds of biological therapeutic methods have been used to treat DDD. Some in vitro studies have shown that bone marrow derived mesenchymal stem cells (BMSC) could differentiate toward a nucleus-pulposus (NP) phenotype. Some in vivo studies also showed that the autograft of BMSC could regenerate the rabbit disc. However, the fate and differentiation status of injected cells are still not very clear. This is partly due to the lack of a stable marker of BMSC; we overcome this by isolating BMSC from green fluorescent protein (GFP) mice. The viable cells can express stable green fluorescent protein. We have also established a mouse model of disc degeneration through annular puncturing method under microscopic guidance. BMSC were injected into the murine discs two weeks after the degeneration was induced by annular puncture. Serials analysis including radiograph, histology, immunostaining and biochemical analysis were performed at 4 and 24 weeks after the transplantation. Radiograph analysis and histological grading confirmed that progressive degeneration of the discs was arrested after the transplantation of the BMSC. Gene expression analysis showed that the proteoglycan genes were upregulated significantly in the regenerated NP. Double staining method suggested the in vivo chondrocytic differentiation of the BMSC in the regeneration process. Our study showed that the allogenic BMSC could arrest the degeneration of the murine discs and increase the extracellular matrix in the NP region. The accumulation of the ECM is caused by the in vivo chondrocytic differentiation of the stem cells.