GEORG SCHMORL PRIZE OF THE GERMAN SPINE SOCIETY (DWG) 2018: combined inflammatory and mechanical stress weakens the annulus fibrosus: evidences from a loaded bovine AF organ culture

Abstract

Purpose: The pathomechanism of annulus fibrosus (AF) failure is still unknown. We hypothesise that mechanical overload and an inflammatory microenvironment contribute to AF structural weakening. Therefore, the objective of this study was to investigate the influence of these factors on the AF, particularly the translamellar bridging network (TLBN) which connects the AF lamellae. Methods: A bovine AF organ culture (AF-OC) model of standardised AF rings was used to study the individual and combined effects of cyclic tensile strain (CTS) and IL-1β (1 ng/mL) culture medium supplementation. AF-OCs were analysed for PGE2 production (ELISA) and deposition of IL-6, COX-2, fibrillin, and MMP3 in the tissue (immunohistochemistry, IHC). The mechanical strength of the TLBN was evaluated using a peel test to measure the strength required to separate an AF segment along a lamellar bound. Results: The combination of CTS + IL-1β led to a significant increase in PGE2 production compared to Control (p < 0.01). IHC evaluations showed that the CTS + IL-1β group exhibited higher production of COX-2 and MMP3 within the TLBN regions compared to the adjacent lamellae and a significant increase in IL-6 ratio compared to Control (p < 0.05). A significant decrease in the annular peel strength was observed in the CTS + IL1β group compared to Control (p < 0.05). Conclusion: Our findings suggest that CTS and IL-1β act synergistically to increase pro-inflammatory and catabolic molecules within the AF, particularly the TLBN, leading to a weakening of the tissue. This standardised model enables the investigation of AF/TLBN structure–function relationship and is a platform to test AF-focused therapeutics. Graphical abstract: These slides can be retrieved under Electronic Supplementary Material.[Figure not available: see fulltext.].