Inflammaging in cervical and lumbar degenerated intervertebral discs: analysis of proinflammatory cytokine and TRP channel expression

To investigate and compare the occurrence of inflammatory processes in the sites of disc degeneration in the lumbar and cervical spine by a gene array and subsequent qPCR and to investigate the mechanistic involvement of transient receptor potential channels TRPC6 and TRPV4. The gene expression of inflammatory cytokines and TRP channels was measured in human disc samples obtained from patients undergoing discectomy at the cervical (n = 24) or lumbar (n = 27) spine for degenerative disc disease (DDD) and disc herniation (DH) and analyzed for differences with regard to spinal level, IVD degeneration grade, Modic grade, age, sex, disc region and surgical extent. Aside from genes with known implication in DDD and DH, four previously unreported genes from the interferon and TRP families (IFNA1, IFNA8, IFNB1, TRPC6) could be detected. A correlation between gene expression and age (IL-15) and IVD degeneration grade (IFNA1, IL-6, IL-15, TRPC6), but not Modic grade, was identified. Significant differences were detected between cervical and lumbar discs (IL-15), nucleus and annulus (IL-6, TNF-alpha, TRPC6), single-level and multi-level surgery (IL-6, IL-8) as well as DDD and DH (IL-8), while sex had no effect. Multiple gene-gene pair correlations, either between different cytokines or between cytokines and TRP channels, exist in the disc. This study supports the relevance of IL-6 and IL-8 in disc diseases, but furthermore points toward a possible pathological role of IL-15 and type I interferons, as well as a mechanistic role of TRPC6. With limited differences in the inflammatory profile of cervical and lumbar discs, novel anti-inflammatory or TRP-modulatory strategies for the treatment of disc pathologies may be applicable independent of the spinal region.