INTRODUCTION: Clusters of cells are frequently seen in degenerate intervertebral discs. These clusters have been shown to be the result of increased proliferation, possibly as an attempt at repair of the degenerate tissue. We hypothesised that cell clusters may contain progenitor or stem cells; if this is so, they could have the potential for use in cell therapy to repair or regenerate the intervertebral disc.
METHODS: Seventeen samples of degenerate disc were obtained from 10 patients undergoing surgery for disc herniation. Both clustered and single cells were isolated by collagenase digestion and sequential filtration through 40μm and 70μm pore cell strainers. These cells were then cultured to passage 5 and growth kinetics and degree of senescence via SA‐β‐Gal examined.
RESULTS: Three cell ‘fractions’, of size >70μm, 40‐70μm and <40μm, were generated from the tissue digests via sequential filtration. Microscopic examination demonstrated that the <40μm fraction contained only single cells with an increasing proportion of clustered cells in the 40‐70 and >70μm fractions. When cultured, the single cells proliferated significantly less at each passage than the cells in the 2 clustered fractions. No significant difference in SA‐β‐Gal expression was seen between sub‐populations.
DISCUSSION: The growth kinetics of the clustered cells showed a greater ability for proliferation than the single cells but no difference in degree of senescence, at least under the culture conditions tested. This supports our hypothesis that there may be a progenitor cell population present within the clusters. If further characterisation shows that these cells have other stem cell properties, then the intervertebral disc will resemble many other musculoskeletal tissues in having its own population of progenitor cells, with potential future uses for tissue repair and regeneration.