Contribution of Norepinephrine and the Ageing Sympathetic Nervous System to Spine Degeneration

Low back pain (LBP) is a leading cause of disability worldwide and this burden increases steadily with age. More than 40% of LBP cases are associated with intervertebral disc (IVD) and facet joint (FJ) degeneration. There is growing evidence that the autonomic nervous system (ANS), especially the sympathetic branch, influences pathologic processes in the musculoskeletal system. In fact, IVD degeneration is accompanied by invasion of sympathetic nerve fibers releasing norepinephrine (NE). Our aim is to explore how NE and the ageing ANS contribute to molecular alterations during IVD and FJ degeneration. Human IVD cells were isolated, cultured in monolayer (2% O 2 ) and treated with low (10 −8 M) or high (10 −6 M) NE concentrations (untreated cells at day 0 served as control). After 14 days, proliferation (cell count) and viability (LDH assay) were determined. Gene expression of matrix components ( COL1A1, COL2A1, COL10A1, ACAN, COMP ), matrix-metalloproteinases ( MMP1, MMP2, MMP12 ), cytokines ( IL1B, IL6, TNF ), and pain-related substance P ( TAC1 ) was investigated using qPCR. Intracellular signaling pathways were analyzed by immunoblotting. In the in vivo part of the project, the autonomic status of ageing male and female C57BL/6 mice at 3, 6, 12, 18, 24 months was determined by analyzing splenic NE concentrations via ELISA. Currently, IVD and FJ degeneration are assessed using histological (DMMB for proteoglycans and picrosirius red for fibrillar collagens) and immunohistochemical (IHC) detection of ECM components. Moreover, β2-adrenergic receptor (β2-AR) expression will be investigated by IHC, since this receptor was shown to be upregulated during IVD degeneration in our earlier study. In addition, the pain-related neurotransmitters substance P and αCGRP will be analyzed via IHC. Our results demonstrate that human IVD cells respond to NE and that 10 −6 M NE might play a role during IVD degeneration by inhibiting chondrocyte hypertrophy (decreased COL10A1 expression, p <0.01) and matrix degradation (decreased MMP2 expression, p <0.05) but increasing pain (increased TAC1 expression, p <0.05) mediated by PKA and ERK1/2 phosphorylation. Furthermore, we assessed a diminished amount of fibrillar collagens in aged individuals. Moreover, splenic NE levels in aged mice, and so the sympathetic activity, were higher only in males. Our present investigations will clarify, whether and how these changes contribute to an altered expression of β2-AR and sensory neurotransmitters as well as degenerative alterations in murine IVD and FJ tissue.