Study Design. We measured the expression and responses of Toll-Like Receptor 4 (TLR4) activation in the intervertebral disc (IVD) in vitro and in vivo. We hypothesize that stimulation of the IVD with the TLR4 ligand lipopolysaccharide (LPS) results in upregulation of a coordinated set of proinflammatory mediators and inhibition of matrix expression, both consistent with a molecular profile of degeneration.
Objective. To characterize early inflammatory and morphological changes induced by TLR4 activation in the IVD.
Summary of Background Data. TLR4 is a pattern recognition receptor activated in innate immunity that has been implicated in disease mechanisms of inflammatory cartilaginous degeneration. However, no study to date has examined the expression and responses of TLR4 in the IVD.
Methods. IVD cells were stimulated with LPS in a dose-dependent manner, and inflammatory cytokine levels were measured by quantitative reverse transcription-polymerase chain reaction. Histological and inflammatory changes due to in vivo injection of LPS into the rat caudal IVD were measured by enzyme-linked immunosorbent assay and immunoblotting.
Results. Baseline TLR4 expression in IVD tissue varied according to cell type. LPS stimulation resulted in significant increases in tumor necrosis factor α (TNF)-α, interleukin (IL)-1β, IL-6, and nitric oxide levels and significant inhibition in aggrecan and collagen-2. Intradiscal injection of LPS was found to cause moderate degenerative changes in the IVD, with increases in tissue levels of IL-1β, TNF-α, high mobility group box 1 protein (HMGB1), and macrophage migration inhibitory factor (MIF).
Conclusion. This study provides the first evidence that IVD cells express TLR4 and are responsive to TLR4 activation by upregulating a coordinated set of inflammatory cytokines. This study suggests that intradiscal injection of LPS offers a model for triggering inflammation of the IVD, demonstrating that inflammatory insults alone may potentially trigger degenerative changes of the IVD.
We provide first evidence that intervertebral disc (IVD) cells express Toll-Like Receptor 4 (TLR4). TLR4 activation upregulates a coordinated set of proinflammatory mediators. TLR4 activation in vivo offers a model for triggering inflammation and degeneration of the IVD, suggesting that inflammatory insults alone may potentially trigger degenerative disc changes.
*The Feinstein Institute for Medical Research, Manhasset, NY
†Department of Physical Medicine and Rehabilitation
‡Department of Neurosurgery, and
§Department of Medicine, Hofstra North Shore LIJ School of Medicine, Manhasset, NY.
Address correspondence and reprint requests to Nadeen O. Chahine, PhD, Assistant Investigator, The Feinstein Institute for Medical Research, Assistant Professor, Department of Molecular Medicine, Hofstra North Shore-LIJ School of Medicine, 350 Community Dr., Manhasset, NY 11030; E-mail: email@example.com
Acknowledgment date: March 30, 2012. Revision date: June 1, 2012. Acceptance date: July 21, 2012.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Competitive Faculty Award from The Feinstein Institute for Medical Research (NOC) and the Department of Neurosurgery, Hofstra North Shore LIJ School of Medicine funds were received to support this work.
No relevant financial activities outside the submitted work.