Role of Type II Collagen Cleavage and Immune Responses in Intervertebral Disc Degeneration in-Vivo

Abstract

Introduction Intervertebral disc (IVD) degeneration (IDD) is a leading etiologic factor of low back pain. Recent studies have shown the role of host immune responses in the initiation of matrix degradation in degenerative IVD disease. To date, although the cascade of production of the proinflammatory cytokines are initiated by the engagement of innate immune receptors such as toll-like receptors (TLR), data regarding the roles of these receptors in the production of the mediators at the site of IVD degeneration are scarce. Bailey is a type II collagen knock-in osteoarthritis mouse model which is resistant to collagenolysis. When the mutant mice are challenged with antigen-induced osteoarthritis, cartilage erosion and inflammation at the site of challenge are significantly reduced. Given that type II collagen is one of the major extracellular matrix molecules in IVD, and both articular joints and IVD share structural as well as functional similarities, we hypothesize that a reduction in collagenolysis in IVD may result in decreased amount of matrix degradation product available for sensitizing the subsequent immune responses, which in turn reduces the extent of disc degeneration. Materials and Methods Type II collagen knock-in mice (with C57BL/6 background) is a gift from Prof. A. J. Fosang (Department of Pediatrics, The University of Melbourne, Melbourne, Australia) and were bred in minimum disease area in the Laboratory Animal Unit, The University of Hong Kong. All experiments involving animal work were authorized by licences from the Hong Kong Government Department of Health and The University of Hong Kong Committee on the Use of Live Animals in Teaching and Research (CULATRs number 2046-09 and 2938-13). Briefly disc degeneration was introduced in 6 to 8-week-old homozygous mice (Col2a1cr/cr) and wildtype (Col2a1+/+) littermates by tail looping surgery. The looped tails were harvested at selected time points postoperation, processed and sectioned for evaluating the morphology of IVD by multichromatic FAST staining and production pattern of inflammatory mediators by immunostaining. Results Our preliminary data have shown that upon compression by prolonged looping, degeneration was noted in the tail intervertebral discs of both Bailey and wildtype littermates. Further, an aberrant production pattern of extracellular matrix was noted in the intervertebral disc in the homozygous mutant. Interestingly, a downregulated expression of TNF-a and MCP-1, which are proinflammatory cytokines, was found in the nucleus pulposus of intervertebral disc of Bailey compared with wildtype littermates upon tail looping. Regardless of the genotype, however, production of both toll-like receptors-2 and -4 was downregulated in nucleus pulposus in compressed disc compared with neighboring uncompressed discs. Conclusion Our finding suggests that an alteration of matrix environment may play an important role in modulating immune responses upon IVD degeneration. Detailed studies of the immunomodulatory effects of extracellular matrix would provide further insights into molecular mechanism and the complex etiology of IDD. Disclosure of Interest None declared