Inhibition of the regulator of G protein signalling RGS4 in the spinal cord decreases neuropathic hyperalgesia and restores cannabinoid CB₁ receptor signalling

Abstract

BACKGROUND AND PURPOSERegulators of G protein signalling (RGS) are major determinants of metabotropic receptor activity, reducing the lifespan of the GTP-bound state of G proteins. Because the reduced potency of analgesic agents in neuropathic pain may reflect alterations in RGS, we assessed the effects of CCG 63802, a specific RGS4 inhibitor, on pain hypersensitivity and signalling through cannabinoid receptors, in a model of neuropathic pain. EXPERIMENTAL APPROACHThe partial sciatic nerve ligation (PSNL) model in male Sprague Dawley rats was used to measure paw withdrawal thresholds to mechanical (von Frey hairs) or thermal (Hargreaves method) stimuli, during and after intrathecal injection of CCG 63802. HEK293 cells expressing CB 1 receptors and conditional expression of RGS4 were used to correlate cAMP production and ERK phosphorylation with receptor activation and RGS4 action. KEY RESULTSTreatment of PSNL rats with CCG 63802, twice daily for 7 days after nerve injury, attenuated thermal hyperalgesia during treatment. Spinal levels of anandamide were higher in PSNL animals, irrespective of the treatment. Although expression of CB 1 receptors was unaffected, HU210-induced CB 1 receptor signalling was inhibited in PSNL rats and restored after intrathecal CCG 63802. In transfected HEK cells expressing CB 1 receptors and RGS4, inhibition of cAMP production, a downstream effect of CB 1 receptor signalling, was blunted after RGS4 overexpression. RGS4 expression also attenuated the CB 1 receptor-controlled activation of ERK1/2. CONCLUSIONS AND IMPLICATIONSInhibition of spinal RGS4 restored endogenous analgesic signalling pathways and mitigated neuropathic pain. Signalling through CB 1 receptors may be involved in this beneficial effect

Regulator of G-Protein Signaling (RGS) Protein Modulation of Opioid Receptor Signaling as a Potential Target for Pain Management

“…A more important role for RGS4 might be in chronic pain states, where RGS4 expression is dynamically regulated. For example, following sciatic nerve injury in the rat there is an upregulation of RGS4 mRNA expression in the dorsal horn of the spinal cord, with no change in the mRNA of other RGS proteins measured (RGS6, 7, 8, 9, 11, 12, 14, 17, 19;Garnier et al, 2003;Bosier et al, 2015;Taccola et al, 2016). At the same time rats become hypersensitive to noxious stimuli and the potency of MOR agonists decreases.…”

“…In support of a role for up-regulated RGS4 (and RGS3) in reducing the effectiveness of morphine, use of the inhibitor CCG-63802 (Figure 2; Blazer et al, 2010) to prevent RGS4 action attenuates hyperalgesia following nerve injury (Bosier et al, 2015;Taccola et al, 2016). This attenuation can be attributed to the rescue of tonically active endogenous antinociception systems, such as the enkephalins, although in one study using this inhibitor (Bosier et al, 2015) endogenous cannabinoids rather than opioid endogenous opioids were implicated.…”

Development of a bimolecular luminescence complementation assay for RGS: G protein interactions in cells

“…These efforts ultimately led to the discovery of CCG-50014, an RGS4 selective inhibitor with nanomolar potency that acts by covalently modifying cysteine residues (Roman, Ota et al 2009, Blazer, Zhang et al 2011). Recent reports have shown CCG-50014’s ability to reduce neuropathic hyperalgesia in vivo (Bosier, Doyen et al 2015) and enhance opioid-mediated analgesia in vivo (Yoon, Woo et al 2015). Furthermore, treatment of mice with CCG-50014 analog CCG-203769 caused a reversion of raclopride induced akinesia and bradykinesia, demonstrating reduction of Parkinsonian behaviors (Blazer, Storaska et al 2015).…”

Identification of small molecule inhibitors of regulator of G protein signaling proteins for pretherapeutic development for treatment of multiple pathologies

“…Despite RGS17's proTile as primarily a neuronal RGS, it has been implicated in several carcinomas outside of the central nervous system ( Figure 5). RGS17 mRNA expression has been found to be increased in lung, prostate, and breast cancer as was tested in a mouse model of neuropathic pain with promising results [45]. The importance of this study cannot be understated, as the targeting of RGS proteins for therapeutic intervention has been somewhat controversial given their generally ubiquitous expression, high degree of overlapping activities, and high degree of similarity with respect to the RH domain.…”

“…Given the role of the RGS superfamily in regulating G protein signaling, and the wide array of tissue distribution, it is not surprising that RGS proteins have been implicated in a an assortment of disease states (Table 1) (Citations are as follows, RGS1 [35][36][37], RGS2 [38][39][40][41], RGS4 [42][43][44][45][46], RGS5 [47,48], RGS6 [39,[49][50][51], RGS10 [52], RGS16 [53,54], RGS17 [52,[55][56][57]). The focus of this work is on R7 family member RGS6, and on RZ family member RGS17.…”