The aims of this study were as follows: (1) to confirm that Substance P (SP) is expressed by nucleus pulposus (NP) and annulus fibrosus (AF) cells; (2) to determine the effect of SP on expression of inflammatory mediators in human disc cells and the effect of inflammatory mediators on the expression of SP; and (3) to characterize the relative expression of SP receptor isoforms in disc tissue and describe whether exposure to SP changes receptor expression.
SP, classically described as a neurotransmitter, acts as an inflammatory regulator in other tissue types, but its role within the intervertebral disc has not been characterized.
Human AF and NP cells from 7 individuals were expanded in monolayer and maintained in alginate bead culture. Cells were treated with SP or interleukin (IL)-1β/tumor necrosis factor-α (TNF-α). After treatment, the cells were recovered and then RNA was isolated and transcribed into cDNA. Quantitative reverse-transcriptase polymerase chain reaction was performed to evaluate expression of inflammatory mediators and SP and its receptors.
Disc cells treated with SP demonstrated significant upregulation of IL-1β, IL-6, and IL-8 in NP and AF cells whereas significant upregulation of RANTES and TNF occurred only in the AF cells. AF and NP cells expressed SP at low levels; expression did not change significantly with SP treatment but was significantly upregulated after treatment with IL-1β/TNF-α. Both SP receptor isoforms were expressed by NP and AF cells.
SP upregulates inflammatory mediators in disc cells. SP and its receptors were expressed in both NP and AF cells, and expression did not change after treatment with SP but increased after treatment with IL-1β/TNF-α. SP likely acts in an autocrine or paracrine manner in intervertebral disc cells and may be involved in “crosstalk” between disc cells and neurons, providing a potential mechanism for transmission of painful discogenic stimuli.
The objective of this study was to examine the role of Substance P (SP) in the intervertebral disc, using cultured human disc cells suspended in alginate beads. We found that human disc cells express SP and its receptors and that treatment of disc cells with SP upregulates inflammatory cytokines.
From the Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, PA.
Address correspondence and reprint requests to Christopher K. Kepler, MD, MBA, Department of Orthopedic Surgery, Thomas Jefferson University, 1015 Walnut St, Room 509, Philadelphia, PA 19107; E-mail: firstname.lastname@example.org
Acknowledgment date: March 21, 2012. First Revision date: March 26, 2013. Second Revision date: June 14, 2013. Acceptance date: June 21, 2013.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Department of Orthopaedics, Thomas Jefferson University, funds were received to support this work.
Relevant financial activities outside the submitted work: board membership, consultancy, royalties, stock/stock options, and grants pending.