IL-1β and cathepsin-d modulate cellular terminal complement complex formation in human disc tissue

Introduction:

The complement system activation and terminal complement complex (TCC) formation was previously identified in degenerated disc tissues. However, it is unclear which molecules may play a role in complement activation during disc degeneration (DD). Here, we investigated possible triggers of TCC formation in DD.

Materials and methods:

Disc tissues biopsies were collected from scoliosis (n = 8) and DD (n = 11) patients. Standardized tissue punches from nucleus pulposus (NP), annulus fibrosus (AF) and endplate (EP) were separately cultured. Isolated cells were analyzed by flow cytometry and gene expression. Cells and tissues were stimulated with IL-1β (10 ng/mL), cathepsin-D (0.5ug/mL) or zymosan (100ug/mL). In cell cultures, TCC formation and lytic activity were determined by ELISA and CH50 assay. In tissues cultures, TCC and CD59 formation were analyzed by immunohistochemistry. Statistics: one-way ANOVA.

Results:

Deposition of TCC and lytic activity, as well as expression of CD46, CD55 and CD59 significantly increased with cell culture; however, no differences were found in response to the proinflammatory/degenerative stimuli, neither for scoliosis or DD patients. Compared to non-treated tissues, IL-1β stimulation led to less percentage of TCC+ cells in AF and EP (p < 0.05), whereas the presence of cathepsin-D significantly increased TCC formation in NP (p < 0.01). The percentage of CD59+ cells significantly increased in AF and NP cells stimulated with cathepsin-D and zymosan (p < 0.05).

Discussion:

Interestingly, IL-1β contributed to less TCC formation, which needs to be further investigated. Overall, these results suggest a functional relevance of IL-1β and cathepsin-D in modulating TCC formation, being possible targets for new therapeutic approaches.

Key words:

Human disc, disc degeneration, immune system, complement activation, inflammation