Spatiotemporal CCR1, CCL3(MIP-1α), CXCR4, CXCL12(SDF-1α) expression patterns in a rat spinal cord injury model of posttraumatic neuropathic pain

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Central neuropathic pain is a frequent challenging complication after spinal cord injury (SCI), and specific therapeutic approaches remain elusive. The purpose of the present investigations was to identify potential key mediators of these pain syndromes by analyzing detailed expression profiles of important chemokines in an experimental SCI paradigm of posttraumatic neuropathic pain in rats.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Expression of CCR1, CCL3(MIP-1α), CXCR4, and CXCL12(SDF-1α) was investigated in parallel with behavioral testing for mechanical and thermal nociceptive thresholds after standardized SCI; 100-kdyn (moderate injury) and 200-kdyn (severe injury) force-defined thoracic spinal cord contusion lesions were applied via an Infinite Horizon Impactor at the T-9 level. Sham controls received laminectomies. Hindlimb locomotor function as well as mechanical and thermal sensitivities were monitored weekly by standardized behavioral testing after SCI. Chemokine expression was analyzed by real-time reverse transcriptase polymerase chain reaction in the early (7 days postoperatively) and late (42 days postoperatively) time courses after SCI, and immunohistochemical analysis (anatomical and quantitative) was performed 2, 7, 14, and 42 days after lesioning. Double staining with cellular markers and pain-related peptides (substance P and CGRP) or receptors (TRPV-1, TRPV-2, VRL-1, and TLR-4) was performed. Based on data obtained from behavioral testing, quantified immunohistochemical chemokine expressions in individual animals were correlated with the respective mechanical and thermal sensitivity thresholds 6 weeks after SCI.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>After 200-kdyn lesions, the animals exhibited prolonged reduction in their nociceptive thresholds, while 100-kdyn groups showed pain-related behaviors only in the early time course after SCI. Investigated chemokines were widely induced after SCI, involving cervical, thoracic, and lumbar spinal cord levels far beyond the lesion core. CCR1 and CCL3 were induced significantly in the dorsal horns 2 days after lesioning and remained at high levels after SCI with significantly higher intensities after 200-kdyn than 100-kdyn contusions. CXCR4 and CXCL12 levels continuously increased from 2 to 42 days after moderate and severe lesions. Additionally, chemokines were induced significantly in dorsal columns, with highest density levels 42 days after 200-kdyn lesions. In dorsal horns, CCR1 was coexpressed with TRPV-1 while CXCR4 and CXCL12 were partially coexpressed with substance P and CGRP. In dorsal columns, CCL3/CCR1 colabeled with GFAP, TRPV-2, TRPV-1, TLR-4; CXCR4/CXCL12 coexpressed with GFAP, CD68/ED1, and TLR4. Chemokine immunoreactivity density levels, especially CCL3 and its receptor, correlated in part significantly with nociceptive thresholds.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The authors report lesion grade–dependent upregulation of different chemokines/chemokine receptors after spinal cord contusion lesions in pain-processing spinal cord regions in a clinically relevant model of traumatic SCI in rats. Prolonged chemokine induction further correlated with below-level pain development in the delayed time course after severe SCI and was coexpressed with pain-associated peptides and receptors, suggesting that chemokines play a crucial role in chronic central pain mechanisms after SCI.</jats:p></jats:sec>

Involvement of CC Chemokine Receptor 1 and CCL3 in Acute and Chronic Inflammatory Pain in Mice

“…The enhanced presence of CCL3 can also explain the immediate analgesic effects, independent from an anti-inflammatory action, evoked by the administration of the CCR1 antagonist J113863 in carrageenan-and CFA-inflamed mice. These results add new insights to the previously reported information related to the involvement of CCR1 in neuropathic [7,11,12,35] or neoplastic [10] pain. The possibility of inhibiting inflammatory pain following the acute administration of a CCR1 antagonist seems particularly interesting considering that CCR1 antagonists are already being tested in clinical trials, and that a CCR1 antagonist has been shown to improve rheumatoid arthritis without inducing remarkable adverse reactions [21].…”

“…The stimulation of CCR1 expressed in nociceptors causes Ca 2+ influx and enhances capsaicin responsiveness [6], and the local administration of CCR1 agonists elicits nociceptive behaviours in mice [9,10]. CCR1 is up-regulated in sensory neurons [11] and the spinal cord [7,12] after nerve injury and increased CCR1 mRNA has also been measured in rats 24 hr after receiving carrageenan [13], supporting its involvement in nociceptive processing. Functionally, it has been reported that some types of neuropathic pain can be alleviated by blocking CCR1 expression with siRNA [11], and that the administration of a CCR1 antagonist can prevent some types of murine bone cancer pain [10] and partially reduce writhing responses in mice receiving intraperitoneal acetic acid or mechanical hyperalgesia in inflamed mice [14].…”

“…CCL3 and CCL5 were considered as the more probable candidates to play such a role due to their well-recognized hypernociceptive effects [6,9,29] and to the previous description that both CCL3 [7,11,30] and CCL5 [10,19,31] can be up-regulated under different pathological conditions. In contrast, we have not considered the possible involvement of CCL7 (monocyte chemotactic protein 3, MCP-3) because, although it can also bind to CCR1, its pro-nociceptive effects seem related to CCR2 activation [32].…”

“…Several chemokines activate nociceptive pathways at both peripheral and central level, and this explains their participation in different types of pathological pain [1][2][3][4]. CC chemokine receptor type 1 (CCR1) is expressed in neurons of dorsal root ganglia (DRG) [5,6] as well as in central structures related to pain [7,8]. The stimulation of CCR1 expressed in nociceptors causes Ca 2+ influx and enhances capsaicin responsiveness [6], and the local administration of CCR1 agonists elicits nociceptive behaviours in mice [9,10].…”

Upregulation of Chemokine CXCL12 in the Dorsal Root Ganglia and Spinal Cord Contributes to the Development and Maintenance of Neuropathic Pain Following Spared Nerve Injury in Rats

“…A recent study showed that CXCL12 and its cognate receptor CXCR4 are constitutively expressed in the DRG and spinal cord of naïve rats [15,33]. In the DRG, CXCL12 and CXCR4 are widely distributed in small amounts in small-and medium-sized neurons and glial cells (satellite cells).…”