Src activation in the hypothalamic arcuate nucleus may play an important role in pain hypersensitivity

Network Pharmacology and In vitro Experimental Verification to Explore the Mechanism of Chaiqin Qingning Capsule in the Treatment of Pain

BACKGROUND

Chaiqin Qingning capsule (CQQNC) has been used to relieve pain in practice. However, the active components, pain targets, and molecular mechanisms for pain control are unclear.

OBJECTIVE

To explore the active components and potential mechanisms of the analgesic effect of CQQNC through network pharmacology and in vitro experiments.

METHODS

The main active components and the corresponding targets of CQQNC were screened from the TCMSP and the SwissTargetPrediction databases. Pain-related targets were selected in the OMIM, Gene- Cards, and DrugBank databases. These targets were intersected to obtain potential analgesic targets. The analgesic targets were imported into the STRING and DAVID databases for protein-protein interaction (PPI), gene ontology (GO) function enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Cytoscape software (V3.7.1) was used to construct an active component-intersection network. Finally, the key components were docked with the core targets. The analgesic mechanism of CQQNC was verified by RAW264.7 cell experiment.

RESULTS

30 active CQQNC components, 617 corresponding targets, and 3,214 pain-related target genes were found. The main active components were quercetin, kaempferol, and chenodeoxycholic acid etc. The key targets were ALB, AKT1, TNF, IL6, TP53, IL1B, and SRC. CQQNC can exert an analgesic effect through PI3K-Akt, MAPK signaling pathways, etc. Molecular docking showed that these active components had good binding activities with key targets. The results of in vitro experiments showed that CQQNC could exert antiinflammatory and analgesic effects through MAPK/AKT/NF-kB signaling pathways.

CONCLUSION

CQQNC exerts pain control through inhibiting MAPK/AKT/NF-kB signaling pathways.

Epigenetic regulation of beta-endorphin synthesis in hypothalamic arcuate nucleus neurons modulates neuropathic pain in a rodent pain model

Although beta-endorphinergic neurons in the hypothalamic arcuate nucleus (ARC) synthesize beta-endorphin (β-EP) to alleviate nociceptive behaviors, the underlying regulatory mechanisms remain unknown. Here, we elucidated an epigenetic pathway driven by microRNA regulation of β-EP synthesis in ARC neurons to control neuropathic pain. In pain-injured rats miR-203a-3p was the most highly upregulated miRNA in the ARC. A similar increase was identified in the cerebrospinal fluid of trigeminal neuralgia patients. Mechanistically, we found histone deacetylase 9 was downregulated following nerve injury, which decreased deacetylation of histone H3 lysine-18, facilitating the binding of NR4A2 transcription factor to the miR-203a-3p gene promoter, thereby upregulating miR-203a-3p expression. Further, increased miR-203a-3p was found to maintain neuropathic pain by targeting proprotein convertase 1, an endopeptidase necessary for the cleavage of proopiomelanocortin, the precursor of β-EP. The identified mechanism may provide an avenue for the development of new therapeutic targets for neuropathic pain treatment.

Role of the blood-spinal cord barrier: An adheren junction regulation mechanism that promotes chronic postsurgical pain

Chronic postsurgical pain (CPSP) is a serious postoperative complication with high incidence, and its pathogenesis involves neuroimmune interactions and the breakdown of the blood-spinal cord barrier (BSCB), the decreased level of adheren junction (AJ)-related proteins is an important cause of BSCB injury. Vascular endothelial-cadherin (VE-cadherin) and p120 catenin (p120) constitute the endothelial barrier adheren junction. The Src/p120/VE-cadherin pathway is involved in the regulation of the endothelial barrier function. However, the role of the BSCB-AJ regulatory mechanism in CPSP has not been reported. In this study, we established a skin/muscle incision and retraction (SMIR) model and evaluated the paw withdrawal threshold (PWT), the effects of an Src inhibitor and p120 knockdown on p-Src, p120 and VE-cadherin expression, as well as BSCB-AJ function in rat spinal cord were observed to explore the regulation of BSCB-AJ function by the p-Src/p120/VE-cadherin pathway in promoting SMIR-induced CPSP. The levels of p-Src, p120 and VE-cadherin in the spinal cord were detected by Western blot. Meanwhile, BSCB permeability test was used to detect the changes in BCSB function. Finally, the spatial and temporal localization of p120 in spinal cord was detected by immunofluorescence. Our findings indicated that p-Src/p120/VE-cadherin could induce BSCB-AJ dysfunction and promote the development of CPSP.

The nonreceptor protein tyrosine kinase Src participates in every step of cancer-induced bone pain

Cancer-induced bone pain (CIBP) is a refractory form of pain that has a high incidence in advanced tumors. Src protein tyrosine kinase is mainly composed of six domains, with two states of automatic inhibition and activation. The modular domain allows Src to conveniently regulate by and communicate with a variety of proteins, directly or indirectly participate in each step of the CIBP process. Src is beneficial to the growth and proliferation of tumor cells, and it can promote the metastases of primary tumors to bone. In the microenvironment of bone metastasis, it mainly mediates bone resorption, activates related peripheral receptors to participate in the formation of pain signals, and may promote the generation of pathological sensory nerve fibers. In the process of pain signal transmission, it mainly mediates NMDAR and central glial cells to regulate pain signal intensity and central sensitization, but it is not limited to these two aspects. Both basic experimentation and clinical research have shown encouraging potential, providing new ideas and inspiration for the prevention and treatment of CIBP.

MicroRNA-547-5p-mediated interleukin-33/suppressor of tumorigenicity 2 signaling underlies the genesis and maintenance of neuropathic pain and is targeted by the therapy with bone marrow stromal cells

Interleukin-33 (IL-33)/suppressor of tumorigenicity 2 (ST2) signaling is known to promote inflammation and the genesis and maintenance of neuropathic pain. However, it remained mostly unknown how IL-33/ST2 signaling can be enhanced by neuropathic stimulations. Here, we report that the chronic constriction nerve injury (CCI)-induced increases in the expression of IL-33 and ST2 and a decrease in microRNA (miRNA)-547-5p not only in the dorsal root ganglia (DRG) but also in spinal dorsal horn (SDH) ipsilateral to the CCI. We found that increasing endogenous miRNA-547-5p by the intrathecal (i.t.) infusion of agomir-miR-547-5p did not produce any effect in naive rats but blocked the CCI-induced increases in the IL-33 and ST2, and pain sensitivity. The reducing endogenous miRNA-547-5p by the i.t. delivering antagomir-miR-547-5p into naive rats caused significant changes in IL-33 and ST2 expressions in both the DRG and SDH, and pain sensitivity, which were similar to those induced by the CCI. Since increasing IL-33 by the i.t. infusion of recombinant IL-33 produced no change in the expression of miR-547-5p, and the CCI still reduced miR-547-5p expression in rats with the IL-33 knockdown, we conclude that the reduction of miR-547-5p can be an upstream event leading to the enhancement of IL-33/ST2 signaling induced by the CCI. The intravenous application of bone marrow stromal cells (BMSCs) reduced the depression of miR-547-5p in both the DRG and SDH, and pain hypersensitivity produced by the CCI or antagomir-miR547-5p application. However, the BMSC effect was significantly occluded by the pretreatment with miR-547-5p agomir or the IL-33 knockdown, demonstrating a novel mechanism underlying the BMSC therapy.

Downregulation of GRK6 in arcuate nucleus promotes chronic visceral hypersensitivity via NF-κB upregulation in adult rats with neonatal maternal deprivation

AIMS

The arcuate nucleus is a vital brain region for coursing of pain command. G protein-coupled kinase 6 (GRK6) accommodates signaling through G protein-coupled receptors. Studies have demonstrated that GRK6 is involved in inflammatory pain and neuropathic pain. The present study was designed to explore the role and the underlying mechanism of GRK6 in arcuate nucleus of chronic visceral pain.

METHODS

Chronic visceral pain of rats was induced by neonatal maternal deprivation and evaluated by monitoring the threshold of colorectal distension. Western blotting, immunofluorescence, real-time quantitative polymerase chain reaction techniques, and Nissl staining were employed to determine the expression and mutual effect of GRK6 with nuclear factor κB (NF-κB).

RESULTS

Expression of GRK6 in arcuate nucleus was significantly reduced in neonatal maternal deprivation rats when compared with control rats. GRK6 was mainly expressed in arcuate nucleus neurons, but not in astrocytes, and a little in microglial cells. Neonatal maternal deprivation reduced the percentage of GRK6-positive neurons of arcuate nucleus. Overexpression of GRK6 by Lentiviral injection into arcuate nucleus reversed chronic visceral pain in neonatal maternal deprivation rats. Furthermore, the expression of NF-κB in arcuate nucleus was markedly upregulated in neonatal maternal deprivation rats. NF-κB selective inhibitor pyrrolidine dithiocarbamate suppressed chronic visceral pain in neonatal maternal deprivation rats. GRK6 and NF-κB were expressed in the arcuate nucleus neurons. Importantly, overexpression of GRK6 reversed NF-κB expression at the protein level. In contrast, injection of pyrrolidine dithiocarbamate once daily for seven consecutive days did not alter GRK6 expression in arcuate nucleus of neonatal maternal deprivation rats.

CONCLUSIONS

Present data suggest that GRK6 might be a pivotal molecule participated in the central mechanisms of chronic visceral pain, which might be mediated by inhibiting NF-κB signal pathway. Overexpression of GRK6 possibly represents a potential strategy for therapy of chronic visceral pain.

Suppression of Superficial Microglial Activation by Spinal Cord Stimulation Attenuates Neuropathic Pain Following Sciatic Nerve Injury in Rats

We evaluated the mechanisms underlying the spinal cord stimulation (SCS)-induced analgesic effect on neuropathic pain following spared nerve injury (SNI). On day 3 after SNI, SCS was performed for 6 h by using electrodes paraspinally placed on the L4-S1 spinal cord. The effects of SCS and intraperitoneal minocycline administration on plantar mechanical sensitivity, microglial activation, and neuronal excitability in the L4 dorsal horn were assessed on day 3 after SNI. The somatosensory cortical responses to electrical stimulation of the hind paw on day 3 following SNI were examined by using in vivo optical imaging with a voltage-sensitive dye. On day 3 after SNI, plantar mechanical hypersensitivity and enhanced microglial activation were suppressed by minocycline or SCS, and L4 dorsal horn nociceptive neuronal hyperexcitability was suppressed by SCS. In vivo optical imaging also revealed that electrical stimulation of the hind paw-activated areas in the somatosensory cortex was decreased by SCS. The present findings suggest that SCS could suppress plantar SNI-induced neuropathic pain via inhibition of microglial activation in the L4 dorsal horn, which is involved in spinal neuronal hyperexcitability. SCS is likely to be a potential alternative and complementary medicine therapy to alleviate neuropathic pain following nerve injury.

Regulation of the firing activity by PKA-PKC-Src family kinases in cultured neurons of hypothalamic arcuate nucleus

The cAMP‐dependent protein kinase A family (PKAs), protein kinase C family (PKCs), and Src family kinases (SFKs) are found to play important roles in pain hypersensitivity. However, more detailed investigations are still needed in order to understand the mechanisms underlying the actions of PKAs, PKCs, and SFKs. Neurons in the hypothalamic arcuate nucleus (ARC) are found to be involved in the regulation of pain hypersensitivity. Here we report that the action potential (AP) firing activity of ARC neurons in culture was up‐regulated by application of the adenylate cyclase activator forskolin or the PKC activator PMA, and that the forskolin or PMA application‐induced up‐regulation of AP firing activity could be blocked by pre‐application of the SFK inhibitor PP2. SFK activation also up‐regulated the AP firing activity and this effect could be prevented by pre‐application of the inhibitors of PKCs, but not of PKAs. Furthermore, we identified that forskolin or PMA application caused increases in the phosphorylation not only in PKAs at T197 or PKCs at S660 and PKCα/βII at T638/641, but also in SFKs at Y416. The forskolin or PMA application‐induced increase in the phosphorylation of PKAs or PKCs was not affected by pre‐treatment with PP2. The regulations of the SFK and AP firing activities by PKCs were independent upon the translocation of either PKCα or PKCβII. Thus, it is demonstrated that PKAs may act as an upstream factor(s) to enhance SFKs while PKCs and SFKs interact reciprocally, and thereby up‐regulate the AP firing activity in hypothalamic ARC neurons.