gms | German Medical Science

Fragestellung: Biological regeneration of damaged intervertebral discs is an experimental focus of regenerative medicine. Recent publications on animal models, including sheep, gave conflicting results with respect to the regenerative potential after disc damage, ranging from reports of induction of significant progressive degenerative developments to complete healing. Here we present a model of severe damage by inflicting a significantly larger wound in open surgery, removing approximately one quarter of the dorsal portion of lumbar discs in order to obtain information on the degree of spontaneous repair in this animal model.

Methodik: One randomly selected intervertebral disc of the lumbar spine of 18 female white Swiss Alpine Sheep (1.5 to 3 year old female animals) was damaged in lumbar disc segments L1-2 through L4-5. An undamaged neighbored disc served as a control. After 7, 11 and 15 weeks each, the lumbar segments were extracted and analysed by histology, biochemistry, and PCR. The data was compared to four lumbar intervertebral discs of a healthy sheep of the same breed and age which was slaughtered for a reason other than experimental purposes.

Ergebnisse und Schlussfolgerung: The data were very consistent with respect to inter-individual variations despite the animals were not inbred. The DNA, collagen and proteoglycan content increased over time in both the damaged and the control discs, indicating adaptive responses to the injury also in the healthy discs The proteoglycan increase behaved similar in all groups, while the collagen content was highest in the damaged group after 15 weeks. The PCR data from collagens I, II, and X, as well as from aggrecan, IL-1ß, and HAS-2 and-3 revealed no statistically significant differences between the groups. Lubricin expression level was similar in all groups but at a surprisingly high level compared to collagen and aggrecan.

The similarity of DNA, proteoglycan and collagen content in all intervertebral discs indicates a relatively rapid regeneration of damaged discs. DNA content in the damaged discs at 15 weeks was slightly higher than in the controls, potentially indicating mild hypercellularity. Also, collagen content per wet weight was slightly elevated in those discs. The expression levels of collagen 2A1 were highest at 11 and 15 weeks after damage. The time-dependent decrease of IL-1 is explained by the subsiding inflammation caused by the damage. The low expression of alkaline phosphatase (despite the presence of endplate tissue) strengthens the hypothesis that the observed intervertebral disc repair did not lead to mineralization. The changes that occurred in the healthy discs may comprise of the most surprising finding and have not been reported, thus far, by other groups. Taken together, the data from the extended damage model still indicate very efficient and rapid repair.