Activation of GPR40 produces mechanical antiallodynia via the spinal glial interleukin-10/β-endorphin pathway

Abstract

Background The G protein-coupled receptor 40 (GPR40), broadly expressed in various tissues such as the spinal cord, exerts multiple physiological functions including pain regulation. This study aimed to elucidate the mechanisms underlying GPR40 activation-induced antinociception in neuropathic pain, particularly related to the spinal glial expression of IL-10 and subsequent β-endorphin. Methods Spinal nerve ligation-induced neuropathic pain model was used in this study. β-Endorphin and IL-10 levels were measured in the spinal cord and cultured primary microglia, astrocytes, and neurons. Double immunofluorescence staining of β-endorphin with glial and neuronal cellular biomarkers was also detected in the spinal cord and cultured primary microglia, astrocytes, and neurons. Results GPR40 was expressed on microglia, astrocytes, and neurons in the spinal cords and upregulated by spinal nerve ligation. Intrathecal injection of the GPR40 agonist GW9508 dose-dependently attenuated mechanical allodynia and thermal hyperalgesia in neuropathic rats, with E max values of 80% and 100% MPE and ED 50 values of 6.7 and 5.4 μg, respectively. Its mechanical antiallodynia was blocked by the selective GPR40 antagonist GW1100 but not GPR120 antagonist AH7614. Intrathecal GW9508 significantly enhanced IL-10 and β-endorphin immunostaining in spinal microglia and astrocytes but not in neurons. GW9508 also markedly stimulated gene and protein expression of IL-10 and β-endorphin in cultured primary spinal microglia and astrocytes but not in neurons, originated from 1-day-old neonatal rats. The IL-10 antibody inhibited GW9508-stimulated gene expression of the β-endorphin precursor proopiomelanocortin (POMC) but not IL-10, whereas the β-endorphin antibody did not affect GW9508-stimulated IL-10 or POMC gene expression. GW9508 increased phosphorylation of mitogen-activated protein kinases (MAPKs) including p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK), and its stimulatory effects on IL-10 and POMC expression were blocked by each MAPK isoform inhibitor. Spinal GW9508-induced mechanical antiallodynia was completely blocked by intrathecal minocycline, IL-10 neutralizing antibody, β-endorphin antiserum, and μ-opioid receptor-preferred antagonist naloxone. Conclusions Our results illustrate that GPR40 activation produces antinociception via the spinal glial IL-10/β-endorphin antinociceptive pathway. Electronic supplementary material The online version of this article (10.1186/s12974-019-1457-9) contains supplementary material, which is available to authorized users.

The spinal microglial IL-10/β-endorphin pathway accounts for cinobufagin-induced mechanical antiallodynia in bone cancer pain following activation of α7-nicotinic acetylcholine receptors

“…The asterisk and number sign denote statistical significance (p < 0.001) compared to the control group and cinobufagin group, respectively, by one-way ANOVA followed by the post hoc Student-Newman-Keuls test IL-10 expression [71,[77][78][79]. Furthermore, pretreatment with the IL-10 antibody prevented the GLP-1 receptor agonist exenatide-and GPR40 agonist GW90851-induced expression of β-endorphin but not IL-10, whereas the βendorphin antiserum did not have any effects on their expression of β-endorphin or IL-10 [52,79]. (2) Intrathecal injection of cinobufagin significantly stimulated the gene and protein expression of IL-10 and β-endorphin but not dynorphin A in the ipsilateral spinal cords.…”

“…Expressed in astrocytes and microglia, IL-10 is a known antiinflammatory and immunosuppressive cytokine and exhibits marked antinociception in neuropathic pain and inflammatory pain [42,54,67,77,78]. We have recently discovered that IL-10 produced antinociception through spinal microglial expression of β-endorphin [77,78], by which activation of the GLP-1 receptor and GPR40 produced mechanical antiallodynia and thermal antihyperalgesia in a variety of rodent models of painful hypersensitivity [52,79]. Our current cinobufagin findings further highlight the broad significance of the recently uncovered spinal microglial IL-10/β-endorphin pathway in the regulation of antinociception in chronic pain.…”

“…The quality of each injection was ensured by the observation of an injection-induced tail-flick [53]. The method was validated by using the lidocaine paralysis method [52] and extensively practiced in house.…”

“…We recently discovered that microgliaderived IL-10 in neuropathic pain produced mechanical antiallodynia and thermal antihyperalgesia via autocrine secretion of β-endorphin which interacted with neuronal μopioid receptors [77,78]. Futhermore, we also uncovered that the glucagon-like peptide-1 (GLP-1) receptor agonist exenatide and GPR40 agonist GW9508 produced mechanical antiallodynia and thermal antihyperalgesia in neuropathic rats through autocrine glial secretion of IL-10 and subsequent β-endorphin [52,79]. Thus, we postulated that cinobufagin may produce antinociception by triggering the microglial IL-10/β-endorphin pathway after activation of α7-nAChRs.…”

Cynandione A alleviates neuropathic pain through spinal microglial interleukin-10/β-endorphin expression following α7 nicotinic acetylcholine receptor activation

“…Intrathecal injection of IL-10 produced mechanical antiallodynia and thermal antihyperalgesia through spinal microglial expression of β-endorphin [9]. Furthermore, the spinal glial IL-10 and β-endorphin pathway has been revealed to be associated with the antinociceptive effects of electroacupuncture and the agonists of the glucagon-like peptide-1 (GLP-1) receptor and G proteincoupled receptor 40 (GPR40) in rodent models of neuropathic pain induced by spinal nerve ligation [10][11][12].…”