High mechanical strain of primary intervertebral disc cells promotes secretion of inflammatory factors associated with disc degeneration and pain.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Rahul
R
Gawri
Derek H
DH
Rosenzweig
Emerson
E
Krock
Jean A
JA
Ouellet
Laura S
LS
Stone
Thomas M
TM
Quinn
Lisbet
L
Haglund
D000818:Animals; D017077:Culture Media, Conditioned / Q000494:pharmacology; D006801:Humans; D007249:Inflammation / Q000378:metabolism / Q000503:physiopathology; D007403:Intervertebral Disc / Q000378:metabolism* / Q000503:physiopathology*; D055959:Intervertebral Disc Degeneration / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology*; D016716:PC12 Cells; D010146:Pain / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D013314:Stress, Mechanical; D055815:Young Adult
D017077:Culture Media, Conditioned