CC chemokine ligand 2 upregulates the current density and expression of TRPV1 channels and Nav1.8 sodium channels in dorsal root ganglion neurons

Abstract

BackgroundInflammation or nerve injury-induced upregulation and release of chemokine CC chemokine ligand 2 (CCL2) within the dorsal root ganglion (DRG) is believed to enhance the activity of DRG nociceptive neurons and cause hyperalgesia. Transient receptor potential vanilloid receptor 1 (TRPV1) and tetrodotoxin (TTX)-resistant Nav1.8 sodium channels play an essential role in regulating the excitability and pain transmission of DRG nociceptive neurons. We therefore tested the hypothesis that CCL2 causes peripheral sensitization of nociceptive DRG neurons by upregulating the function and expression of TRPV1 and Nav1.8 channels.MethodsDRG neuronal culture was prepared from 3-week-old Sprague–Dawley rats and incubated with various concentrations of CCL2 for 24 to 36 hours. Whole-cell voltage-clamp recordings were performed to record TRPV1 agonist capsaicin-evoked inward currents or TTX-insensitive Na+ currents from control or CCL2-treated small DRG sensory neurons. The CCL2 effect on the mRNA expression of TRPV1 or Nav1.8 was measured by real-time quantitative RT-PCR assay.ResultsPretreatment of CCL2 for 24 to 36 hours dose-dependently (EC50 value = 0.6 ± 0.05 nM) increased the density of capsaicin-induced currents in small putative DRG nociceptive neurons. TRPV1 mRNA expression was greatly upregulated in DRG neurons preincubated with 5 nM CCL2. Pretreating small DRG sensory neurons with CCL2 also increased the density of TTX-resistant Na+ currents with a concentration-dependent manner (EC50 value = 0.7 ± 0.06 nM). The Nav1.8 mRNA level was significantly increased in DRG neurons pretreated with CCL2. In contrast, CCL2 preincubation failed to affect the mRNA level of TTX-resistant Nav1.9. In the presence of the specific phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002 or Akt inhibitor IV, CCL2 pretreatment failed to increase the current density of capsaicin-evoked inward currents or TTX-insensitive Na+ currents and the mRNA level of TRPV1 or Nav1.8.ConclusionsOur results showed that CCL2 increased the function and mRNA level of TRPV1 channels and Nav1.8 sodium channels in small DRG sensory neurons via activating the PI3K/Akt signaling pathway. These findings suggest that following tissue inflammation or peripheral nerve injury, upregulation and release of CCL2 within the DRG could facilitate pain transmission mediated by nociceptive DRG neurons and could induce hyperalgesia by upregulating the expression and function of TRPV1 and Nav1.8 channels in DRG nociceptive neurons.

Upregulation of Nuclear Factor of Activated T-Cells by Nerve Injury Contributes to Development of Neuropathic Pain

“…Increased cytokine levels have been shown to influence neuronal activity through several mechanisms, including increases in the neurotransmitter release through Ca 21 -dependent mechanisms and upregulation of transient receptor potential cation channel, subfamily V, member 1 and Nav1.8 sodium channels in DRG neurons (White et al, 2007;Kao et al, 2012). Many cytokines and their receptors, such as the C-C chemokine ligand (CCL2, also known as monocyte chemotactic protein 1) and its receptor CCR2, are critically involved in neuropathic pain induction.…”

Inflammation and nerve fiber interaction in endometriotic pain

“…In DRG from Sprague-Dawley rats, TNFa induces Na v 1.3 (SCNA3) and Na v 1.8 (SCN10A) sodium channel expression [66] and enhances the currents of Na v 1.8 [67]. MCP1 increases Na v 1.8 activity in primary sensory neurons through a CCR2/Gbg-dependent mechanism [68] and upregulates the current density and expression of TRPV1 channels and Na v 1.8 sodium channels in DRG neurons, via activation of the PI3K/Akt signaling pathway [69] (Figure 1).…”

Impaired excitability of renal afferent innervation after exposure to the inflammatory chemokine CXCL1

“…In addition, an influence on the expression of the TRPV1 receptor, which is stimulated by proinflammatory mediators and found in large quantities on sensory afferent nerve units, has been described (22). Therefore, we used CXCL1 to assess its influence on the response pattern of neurons with renal afferents based on our previous work (10) and ongoing interest in the physiology and pathophysiology of renal innervation.…”