High mechanical strain of primary intervertebral disc cells promotes secretion of inflammatory factors associated with disc degeneration and pain
- Equal contributors
1 The Orthopaedics Research Lab, Department of Surgery, McGill University, 1650 Cedar 663 Avenue, Montreal, QC H3G 1A4, Canada
2 McGill Scoliosis & Spine Group, Department of Surgery, McGill University, 1650 Cedar 663 Avenue, Montreal, QC H3G 1A4, Canada
3 Alan Edwards Centre for Research McGill University, 740 Dr. Penfield Avenue, Montreal, QC H3G 0G1, Canada
4 Faculty of Dentistry, McGill University, 3640 University Street, Montreal, QC H3A 0C7, Canada
5 Soft Tissue Biophysics Lab, Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, QC H3A 2B2, Canada
6 McGill University Health Centre, Department of Surgery, Montreal General Hospital, Room C9.173, 1650 Cedar Avenue, Montreal, QC H3G 1A4, Canada
Arthritis Research & Therapy 2014, 16:R21 doi:10.1186/ar4449Published: 23 January 2014
Excessive mechanical loading of intervertebral discs (IVDs) is thought to alter matrix properties and influence disc cell metabolism, contributing to degenerative disc disease and development of discogenic pain. However, little is known about how mechanical strain induces these changes. This study investigated the cellular and molecular changes as well as which inflammatory receptors and cytokines were upregulated in human intervertebral disc cells exposed to high mechanical strain (HMS) at low frequency. The impact of these metabolic changes on neuronal differentiation was also explored to determine a role in the development of disc degeneration and discogenic pain.
Isolated human annulus fibrosus (AF) and nucleus pulposus (NP) cells were exposed to HMS (20% cyclical stretch at 0.001 Hz) on high-extension silicone rubber dishes coupled to a mechanical stretching apparatus and compared to static control cultures. Gene expression of Toll-like receptors (TLRs), neuronal growth factor (NGF) and tumour necrosis factor α (TNFα) was assessed. Collected conditioned media were analysed for cytokine content and applied to rat pheocromocytoma PC12 cells for neuronal differentiation assessment.
HMS caused upregulation of TLR2, TLR4, NGF and TNFα gene expression in IVD cells. Medium from HMS cultures contained elevated levels of growth-related oncogene, interleukin 6 (IL-6), IL-8, IL-15, monocyte chemoattractant protein 1 (MCP-1), MCP-3, monokine induced by γ interferon, transforming growth factor β1, TNFα and NGF. Exposure of PC12 cells to HMS-conditioned media resulted in both increased neurite sprouting and cell death.
HMS culture of IVD cells in vitro drives cytokine and inflammatory responses associated with degenerative disc disease and low-back pain. This study provides evidence for a direct link between cellular strain, secretory factors, neoinnervation and potential degeneration and discogenic pain in vivo.