gms | German Medical Science

Objectives: Inflammation is known to contribute to disc degeneration (DD), but there is limited knowledge regarding a possible involvement of the innate immunity. Terminal complement complex (TCC) was previously identified in herniated human intervertebral disc (IVD) tissues [1]. The present work focuses on i) exploring possible correlations of TCC deposition in the different IVD regions with donor age, distinct disc pathology and disc degeneration degree, and ii) characterizing isolated IVD cells from human disc samples.

Methods: Disc tissues were collected from healthy donors (Healthy, n=18, age 12±7), patients with scoliosis but no signs of disc degeneration (Sc, n=10, age 16±5), or with DD (n=36, age 60±13, Pfirrmann grade 3-5), following ethical approval and patients' informed consent. TCC deposition was investigated in different IVD regions: annulus fibrosus (AF), nucleus pulposus (NP) and endplate (EP). Randomly selected Sc and DD cells (passage 2-5) were analyzed for gene expression of complement regulators (CD46, CD55, CD59), apoptosis (BAX1), inflammation markers (interleukin-6 and -8), matrix proteins (type I and type II collagen, aggrecan, elastin, fibrillin) and degrading enzymes (metalloproteinase-1 and -3), and for flow cytometry analysis of TCC and CD59. TCC deposition was induced in vitro by IVD cells culture with 5% human serum (HS, containing the components C5 to C9 necessary for TCC formation), and analyzed by ELISA. Culture in serum-free medium served as control. Statistical analysis was performed with Kruskal-Wallis test.

Results and conclusion: Although TCC immunopositivity was observed with high variability, a significantly higher frequency of TCC+ cells was found in Healthy (young) and DD compared to Sc group (p<0.05), with no significant differences between the different regions for each donor group. After cell expansion, CD46 and aggrecan were significantly down-regulated in NP cells of DD compared to Sc (p<0.05), whereas over 80% of AF, NP and EP cells were positive for both TCC and CD59, with no differences between DD and Sc. An increase in TCC deposition was observed in presence of HS (p<0.05), but again no differences were observed between DD and Sc expanded cells.

The data suggests that TCC is formed in IVD cells both in very young or strongly degenerated discs, which might correlate with vascularization. However, the phenotype of IVD cells isolated from patients with different disc pathologies was similar. TCC deposition could be induced in vitro, confirming that IVD cells are not completely protected. Further studies exploring the functional relevance and mechanistic role of TCC in DD are needed to better understand if this is a suitable target for new therapeutic approaches.

Acknowledgment: funded by the German Research Foundation (DFG).