INTRODUCTION: Cells from injured tissue release mediators that induce further tissue degeneration or could lead to recruitment of cells for tissue repair. Nitric oxide (NO) is a mediator that has been previously shown to induce tissue damage. Its production may induce the migration of mesenchymal stem cells (MSCs) into a damaged disc alongside chemoattractants released by disc cells. The present study investigated whether there were differences in NO release and MSC recruitment in a whole organ culture system for intervertebral discs (IVD) with or without end‐plate under "normal" or "degenerative" conditions.
METHODS: Bovine caudal discs with or without end‐plates were cultured under either low frequency (0.2Hz) ‐ high glucose (4.5g/L) ("normal") or high frequency (10Hz) loading ‐ low glucose (2g/L) conditions ("degenerative") for 7 days. Under the latter conditions, the discs were stabbed using a 22G needle in the centre of the disc. Media was collected under each condition for analysis of NO production. PKH26 (fluorescent dye) labelled human MSCs were then added to the discs and co‐cultured for an additional 7 days. After culture, engraftment of MSCs into the disc was analysed microscopically.
RESULTS: Discs under "degenerative" conditions resulted in greater MSC migration compared with "normal" conditions for disc with or without end‐plate. The amount of NO produced under degenerating conditions was significantly greater, although no differences were observed either with or without the end‐plate.
DISCUSSION: The present study has shown that in an ex vivo IVD organ culture system, degenerative conditions induce the production of NO that may indicate degeneration within the disc. This mediator alongside chemoattractants in the media promotes the recruitment of MSCs that may aid in tissue repair. The chemoattractants and the fate of the MSCs within the disc need to be established.