INTRODUCTION: Back pain associated with disc degeneration is a common clinical condition. Human umbilical cord blood‐derived mesenchymal stem cells (hUCB‐MSCs) have been shown to differentiate into cells of the adipogenic, osteogenic, and chondrogenic lineages. Injection of hUCB‐MSCs into the intervertebral disc is an attractive therapy to regenerate the disc and restore function. In this study, we determined the effectiveness of hUCB‐MSC therapy for repair of the intervertebral disc in vitro. HUCB‐MSCs were injected into cultured rabbit intervertebral disc explants. Survival of the injected cells, expression of the human collagen type II (Col2) gene, and expression of rabbit anabolic and catabolic genes were assessed.
METHODS: HUCB‐MSCs labeled with a lipophilic dye (Dil) were injected into rabbit disc explants, and maintained in culture for one month. Live cells were stained green with CellTracker Green and transplanted stem cells were stained red with Dil. Resident disc and transplanted cells were visualized by fluorescent microscopy. Human Col2 expression was assessed by RT‐PCR. Rabbit Col2 and matrix metallopeptidase 13 (MMP13) genes were assessed with real time PCR.
RESULTS: HUCB‐MSCs survived in the cultured disc explants for at least one month, and expressed the human Col2 gene, which indicates that the injected stem cells are differentiating into a chondrocyte‐like lineage. Rabbit disc cells expressed higher levels of Col2 and lower levels of MMP13 genes which indicate resident cells have a positive metabolic response to stem cell treatment.
DISCUSSION: We have shown that hUCB‐MSCs survived, expressed the human Col2 gene, and stimulated resident disc cells to express higher levels of Col2 and lower levels of MMP13 genes when transplanted into rabbit intervertebral discs. These data support the potential of a cell therapy approach for disc repair. Further studies in animal models are indicated as the next step towards achieving disc repair in humans.