Postoperative pain develops after surgical operation. Inadequately managed postoperative pain is oftentimes associated with deterioration in life quality and delayed rehabilitation. Clinical studies confirmed analgesic effects of acupuncture on patients with postoperative pain. We hereby explored mechanisms underlying how acupuncture alleviates postoperative pain. A mouse model of skin incision-induced pain was established to mimic postoperative pain condition. Electroacupuncture (EA) or sham EA was administered at ST36 and BL60 acupoints in model mice. A combination of RNA-Sequencing (RNA-Seq), immunostaining, biochemical assay, in vivo imaging and behavioral test were applied for mechanism investigations. 2/100 Hz EA intervention ameliorated mechanical allodynia and improved cumulative pain of incisional pain model mice. Sham EA exerted no obvious analgesic effect. Incisional pain model mice develop gait impairment, which was improved by EA intervention. RNA-Seq identified EA significantly reduced Il33 gene overexpression in the incised skin tissues of model mice. IL-33 was produced from keratinocytes upon skin incision. EA reduced IL-33 overproduction from keratinocytes, resulting in less macrophage infiltration and less ROS accumulation in the incised skin. Adoptive transfer of macrophages into the incised tissue abrogated the ameliorative effects of EA on macrophage infiltration as well as ROS accumulation in incised skin and further reversed EA-induced analgesia on incisional pain model mice. Additionally, EA intervention did not affect skin wound healing process. These results demonstrate that EA ameliorates incisional pain via suppressing IL-33 overproduction in incised skin tissue. EA-induced suppression of IL-33 overproduction results in less macrophage infiltration and ROS accumulation that contribute to analgesia. Our work helps to support EA as an alternative and green therapy for postoperative pain management.

Postoperative pain impairs patients' quality of life. Mechanisms underlying postoperative pain remain incompletely understood. We investigated postoperative pain in a mouse model of skin plus deep tissue incision (INC). We found Cxcl5 was among the top upregulated genes in incision site, which was produced from both incised skin and muscle. Single-cell RNA-sequencing reveals elevated human CXCL5 gene expression in human skin wounds. Neutralizing CXCL5 abrogated INC pain. Global knockout of CXCL5 receptor CXCR2 improved INC pain, but markedly delayed wound healing. Cxcr2 conditional knockout in nociceptive sensory neurons improved INC pain without affecting wound healing and local inflammation. CXCR2 expression and its coupling with TRPA1 were enhanced in DRG neurons innervating the incised site, resulting in neuron hyperexcitability upon CXCL5 stimulation. CXCL5 further enhances TRPV1 activity via neuronal CXCR2-mediated signaling in DRG neurons innervating the incised site. Neuronal CXCR2-mediated TRPV1/TRPA1 modulation synergistically contributes to heat and mechanical hypersensitivities of INC pain. Targeted Cxcr2 knockdown in incision site-innervating DRG neurons ameliorates INC pain. Our work reveals a critical role of neuronal CXCR2 signaling in nociceptive sensory neurons that mediates INC pain via concurrently activating TRPA1 and sensitizing TRPV1. Targeting sensory neuronal CXCR2 represents a promising strategy for INC pain without affecting wound healing.

BACKGROUND:Electroacupuncture (EA) relieves acute gouty arthritis (AGA), but its mechanisms are poorly understood. Our recent work reveals that CXCR2-TRPA1 coupling in dorsal root ganglion (DRG) neurons mediates joint pain and facilitates inflammation in AGA model animals via promoting sensory neuron excitability and neutrophil infiltration. We hereby explored whether EA alleviates AGA via modulating CXCR2-TRPA1 signaling in DRG neurons. METHODS:AGA model was established in mice by injecting monosodium urate to ankle joints. EA was applied on bilateral ST36 acupoints. Biochemical assays, RNA-Sequencing, behavioral tests and Ca2+ imaging, etc. were used for mechanism exploration. RESULTS:EA improves AGA in model mice. EA reduced CXCR2 overexpression in joint innervating DRG neurons of model mice by reducing STAT3 overactivation. Neuronal CXCR2-TRPA1 coupling underwent enhancement during AGA, which was weakened by EA. Targeted knockdown of CXCR2 expression via AAV-PHP.S capsid in joint innervating DRG neurons ameliorated AGA in model mice, an effect mimicking EA. EA further reduced downstream effects conveyed through neuronal CXCR2-TRPA1 signaling, including CGRP/substance P release and neutrophil infiltration, in ankle joints of model mice. Conversely, targeted overexpression of CXCR2 in DRG neurons abrogated the ameliorative effects of EA. CONCLUSIONS:Our study demonstrates that EA reduces STAT3 activation to restrain CXCR2 overexpression in DRG during AGA. This effect further attenuates the enhanced neuronal CXCR2-TRPA1 coupling in DRG neurons, resulting in less sensory neuron activation, neuropeptide release and neurogenic inflammation. Collectively, this work provides novel insights into how EA ameliorates AGA, thereby further supporting EA as a viable treatment option for AGA.

Myocardial ischemia-reperfusion injury (MIRI) is a life-threatening complication of myocardial infarcts, with inner mitochondrial membrane protein dysfunction involved in MIRI-induced heart injury. The role of outer mitochondrial membrane protein mitochondrial antiviral signaling protein (MAVS) is unknown. Here, we show that MAVS expression increases in infarcted myocardium of male wild-type mice. Global MAVS-knock-out or myocardial-specific MAVS knockdown protects male mice from acute and chronic MIRI. MIRI induces double-stranded RNA in affected myocardium, activating intracellular retinoic acid-inducible gene I (RIG-I) signaling, which leads to MAVS aggregation and subsequent non-canonical downstream signaling. MAVS aggregates recruit tumor necrosis factor-associated factor family 6 (TRAF6) and transforming growth factor-β-activated kinase 1 (TAK1), the activating mitogen-activated protein kinase (MAPK) pathway and apoptosis. MAVS-knock-out reduces c-jun-NH2 terminal kinase (JNK) phosphorylation and apoptosis. JNK inhibition protects against MIRI in wild-type male mice, whereas JNK agonist impairs protection in MAVS-knock-out male mice. MIRI activates RIG-I/MAVS pathway and subsequently triggers the TAK1/TRAF6 complex, leading to the activation of the MAPK/JNK signaling cascade. This sequential activation cascade may serve as a potential therapeutic target for MIRI.

The TRP superfamily of channels (nomenclature as agreed by NC-IUPHAR [177, 1080]), whose founder member is the Drosophila Trp channel, exists in mammals as six families; TRPC, TRPM, TRPV, TRPA, TRPP and TRPML based on amino acid homologies. TRP subunits contain six putative TM domains and assemble as homo- or hetero-tetramers to form cation selective channels with diverse modes of activation and varied permeation properties (reviewed by [734]). Established, or potential, physiological functions of the individual members of the TRP families are discussed in detail in the recommended reviews and in a number of books [404, 690, 1163, 258]. The established, or potential, involvement of TRP channels in disease [1134] is reviewed in [452, 689], [692] and [468], together with a special edition of Biochemica et Biophysica Acta on the subject [689]. Additional disease related reviews, for pain [637], stroke [1143], sensation and inflammation [994], itch [130], and airway disease [313, 1058], are available. The pharmacology of most TRP channels has been advanced in recent years. Broad spectrum agents are listed in the tables along with more selective, or recently recognised, ligands that are flagged by the inclusion of a primary reference. See Rubaiy (2019) for a review of pharmacological tools for TRPC1/C4/C5 channels [810]. Most TRP channels are regulated by phosphoinostides such as PtIns(4,5)P2 although the effects reported are often complex, occasionally contradictory, and likely to be dependent upon experimental conditions, such as intracellular ATP levels (reviewed by [1015, 693, 806]). Such regulation is generally not included in the tables.When thermosensitivity is mentioned, it refers specifically to a high Q10 of gating, often in the range of 10-30, but does not necessarily imply that the channel's function is to act as a 'hot' or 'cold' sensor. In general, the search for TRP activators has led to many claims for temperature sensing, mechanosensation, and lipid sensing. All proteins are of course sensitive to energies of binding, mechanical force, and temperature, but the issue is whether the proposed input is within a physiologically relevant range resulting in a response. TRPA (ankyrin) familyTRPA1 is the sole mammalian member of this group (reviewed by [295]). TRPA1 activation of sensory neurons contribute to nociception [417, 895, 606]. Pungent chemicals such as mustard oil (AITC), allicin, and cinnamaldehyde activate TRPA1 by modification of free thiol groups of cysteine side chains, especially those located in its amino terminus [579, 60, 368, 581]. Alkenals with α, β-unsaturated bonds, such as propenal (acrolein), butenal (crotylaldehyde), and 2-pentenal can react with free thiols via Michael addition and can activate TRPA1. However, potency appears to weaken as carbon chain length increases [26, 60]. Covalent modification leads to sustained activation of TRPA1. Chemicals including carvacrol, menthol, and local anesthetics reversibly activate TRPA1 by non-covalent binding [428, 515, 1089, 1088]. TRPA1 is not mechanosensitive under physiological conditions, but can be activated by cold temperatures [429, 213]. The electron cryo-EM structure of TRPA1 [745] indicates that it is a 6-TM homotetramer. Each subunit of the channel contains two short ‘pore helices’ pointing into the ion selectivity filter, which is big enough to allow permeation of partially hydrated Ca2+ ions. TRPC (canonical) familyMembers of the TRPC subfamily (reviewed by [286, 783, 18, 4, 94, 450, 744, 70]) fall into the subgroups outlined below. TRPC2 is a pseudogene in humans. It is generally accepted that all TRPC channels are activated downstream of Gq/11-coupled receptors, or receptor tyrosine kinases (reviewed by [770, 959, 1080]). A comprehensive listing of G-protein coupled receptors that activate TRPC channels is given in [4]. Hetero-oligomeric complexes of TRPC channels and their association with proteins to form signalling complexes are detailed in [18] and [451]. TRPC channels have frequently been proposed to act as store-operated channels (SOCs) (or compenents of mulimeric complexes that form SOCs), activated by depletion of intracellular calcium stores (reviewed by [746, 18, 775, 825, 1129, 157, 730, 64, 158]). However, the weight of the evidence is that they are not directly gated by conventional store-operated mechanisms, as established for Stim-gated Orai channels. TRPC channels are not mechanically gated in physiologically relevant ranges of force. All members of the TRPC family are blocked by 2-APB and SKF96365 [350, 349]. Activation of TRPC channels by lipids is discussed by [70]. Important progress has been recently made in TRPC pharmacology [810, 623, 440, 102, 856, 192, 293]. TRPC channels regulate a variety of physiological functions and are implicated in many human diseases [298, 71, 890, 1038, 1032, 154, 103, 565, 918, 412]. TRPC1/C4/C5 subgroup TRPC1 alone may not form a functional ion channel [230]. The structures of the apo and antagonist-bound states of TRPC1/TRPC4 heteromeric channels have been resolved by cryo-EM [1070]. TRPC4/C5 may be distinguished from other TRP channels by their potentiation by micromolar concentrations of La3+. TRPC2 is a pseudogene in humans, but in other mammals appears to be an ion channel localized to microvilli of the vomeronasal organ. It is required for normal sexual behavior in response to pheromones in mice. It may also function in the main olfactory epithelia in mice [1122, 727, 728, 1123, 543, 1176, 1117].TRPC3/C6/C7 subgroup All members are activated by diacylglycerol independent of protein kinase C stimulation [350].TRPM (melastatin) familyMembers of the TRPM subfamily (reviewed by [277, 349, 746, 1159]) fall into the five subgroups outlined below. TRPM1/M3 subgroupIn darkness, glutamate released by the photoreceptors and ON-bipolar cells binds to the metabotropic glutamate receptor 6 , leading to activation of Go . This results in the closure of TRPM1. When the photoreceptors are stimulated by light, glutamate release is reduced, and TRPM1 channels are more active, resulting in cell membrane depolarization. Human TRPM1 mutations are associated with congenital stationary night blindness (CSNB), whose patients lack rod function. TRPM1 is also found melanocytes. Isoforms of TRPM1 may present in melanocytes, melanoma, brain, and retina. In melanoma cells, TRPM1 is prevalent in highly dynamic intracellular vesicular structures [401, 712]. TRPM3 (reviewed by [718]) exists as multiple splice variants which differ significantly in their biophysical properties. TRPM3 is expressed in somatosensory neurons and may be important in development of heat hyperalgesia during inflammation (see review [947]). TRPM3 is frequently coexpressed with TRPA1 and TRPV1 in these neurons. TRPM3 is expressed in pancreatic beta cells as well as brain, pituitary gland, eye, kidney, and adipose tissue [717, 946]. TRPM3 may contribute to the detection of noxious heat [1024]. TRPM2TRPM2 is activated under conditions of oxidative stress (respiratory burst of phagocytic cells). The direct activators are calcium, adenosine diphosphate ribose (ADPR) [976] and cyclic ADPR (cADPR) [1126]. As for many ion channels, PI(4,5)P2 must also be present [1117]. Numerous splice variants of TRPM2 exist which differ in their activation mechanisms [240]. Recent studies have reported structures of human (hs) TRPM2, which demonstrate two ADPR binding sites in hsTRPM2, one in the N-terminal MHR1/2 domain and the other in the C-terminal NUDT9-H domain. In addition, one Ca2+ binding site in the intracellular S2-S3 loop is revealed and proposed to mediate Ca2+ binding that induces conformational changes leading the ADPR-bound closed channel to open [390, 1034]. Meanwhile, a quadruple-residue motif (979FGQI982) was identified as the ion selectivity filter and a gate to control ion permeation in hsTRPM2 [1128]. TRPM2 is involved in warmth sensation [853], and contributes to several diseases [76]. TRPM2 interacts with extra synaptic NMDA receptors (NMDAR) and enhances NMDAR activity in ischemic stroke [1172]. Activation of TRPM2 in macrophages promotes atherosclerosis [1173, 1155]. Moreover, silica nanoparticles induce lung inflammation in mice via ROS/PARP/TRPM2 signaling-mediated lysosome impairment and autophagy dysfunction [1035]. Recent studies have designed various compounds for their potential to selectively inhibit the TRPM2 channel, including ACA derivatives A23, and 2,3-dihydroquinazolin-4(1H)-one derivatives [1145, 1147]. TRPM4/5 subgroupTRPM4 and TRPM5 have the distinction within all TRP channels of being impermeable to Ca2+ [1080]. A splice variant of TRPM4 (i.e.TRPM4b) and TRPM5 are molecular candidates for endogenous calcium-activated cation (CAN) channels [330]. TRPM4 is active in the late phase of repolarization of the cardiac ventricular action potential. TRPM4 deletion or knockout enhances beta adrenergic-mediated inotropy [597]. Mutations are associated with conduction defects [407, 597, 884]. TRPM4 has been shown to be an important regulator of Ca2+ entry in to mast cells [999] and dendritic cell migration [52]. TRPM5 in taste receptor cells of the tongue appears essential for the transduction of sweet, amino acid and bitter stimuli [541] TRPM5 contributes to the slow afterdepolarization of layer 5 neurons in mouse prefrontal cortex [517]. Both TRPM4 and TRPM5 are required transduction of taste stimuli [247]. TRPM6/7 subgroupTRPM6 and 7 combine channel and enzymatic activities (‘chanzymes’) [173]. These channels have the unusual property of permeation by divalent (Ca2+, Mg2+, Zn2+) and monovalent cations, high single channel conductances, but overall extremely small inward conductance when expressed to the plasma membrane. They are inhibited by internal Mg2+ at ~0.6 mM, around the free level of Mg2+ in cells. Whether they contribute to Mg2+ homeostasis is a contentious issue. PIP2 is required for TRPM6 and TRPM7 activation [815, 1085]. When either gene is deleted in mice, the result is embryonic lethality [416, 1073]. The C-terminal kinase region of TRPM6 and TRPM7 is cleaved under unknown stimuli, and the kinase phosphorylates nuclear histones [483, 484]. TRPM7 is responsible for oxidant- induced Zn2+ release from intracellular vesicles [3] and contributes to intestinal mineral absorption essential for postnatal survival [626]. The putative metal transporter proteins CNNM1-4 interact with TRPM7 and regulate TRPM7 channel activity [40, 471]. TRPM8Is a channel activated by cooling and pharmacological agents evoking a ‘cool’ sensation and participates in the thermosensation of cold temperatures [63, 179, 225] reviewed by [1017, 566, 461, 653]. Direct chemical agonists include menthol and icilin[1094]. Besides, linalool can promote ERK phosphorylation in human dermal microvascular endothelial cells, down-regulate intracellular ATP levels, and activate TRPM8 [68]. Recent studies have found that TRPM8 has typical S4-S5 connectomes with clear selective filters and exowell rings [516], and have identified cryo-electron microscopy structures of mouse TRPM8 in closed, intermediate, and open states along the ligand- and PIP2-dependent gated pathways [1119]. Moreover, the last 36 amino acids at the carboxyl terminal of TRPM8 are key protein sequences for TRPM8's temperature-sensitive function [195]. TRPM8 deficiency reduced the expression of S100A9 and increased the expression of HNF4α in the liver of mice, which reduced inflammation and fibrosis progression in mice with liver fibrosis, and helped to alleviate the symptoms of bile duct disease [560]. Channel deficiency also shortens the time of hypersensitivity reactions in migraine mouse models by promoting the recovery of normal sensitivity [12]. A cyclic peptide DeC‐1.2 was designed to inhibit ligand activation of TRPM8 but not cold activation, which can eliminate the side effects of cold dysalgesia in oxaliplatin-treated mice without changing body temperature [9]. Analysis of clinical data shows that TRPM8-specific blockers WS12 can reduce tumor growth in colorectal cancer xenografted mice by reducing transcription and activation of Wnt signaling regulators and β-catenin and its target oncogenes, such as C-Myc and Cyclin D1 [736]. TRPML (mucolipin) familyThe TRPML family [787, 1140, 780, 1092, 191] consists of three mammalian members (TRPML1-3). TRPML channels are probably restricted to intracellular vesicles and mutations in the gene (MCOLN1) encoding TRPML1 (mucolipin-1) cause the neurodegenerative disorder mucolipidosis type IV (MLIV) in man. TRPML1 is a cation selective ion channel that is important for sorting/transport of endosomes in the late endocytotic pathway and specifically, fission from late endosome-lysosome hybrid vesicles and lysosomal exocytosis [827]. TRPML2 and TRPML3 show increased channel activity in low luminal sodium and/or increased luminal pH, and are activated by similar small molecules [322, 147, 882]. A naturally occurring gain of function mutation in TRPML3 (i.e. A419P) results in the varitint waddler (Va) mouse phenotype (reviewed by [787, 694]). TRPP (polycystin) familyThe TRPP family (reviewed by [217, 215, 303, 1068, 377]) or PKD2 family is comprised of PKD2 (PC2), PKD2L1 (PC2L1), PKD2L2 (PC2L2), which have been renamed TRPP1, TRPP2 and TRPP3, respectively [1080]. It should also be noted that the nomenclature of PC2 was TRPP2 in old literature. However, PC2 has been uniformed to be called TRPP2 [348]. PKD2 family channels are clearly distinct from the PKD1 family, whose function is unknown. PKD1 and PKD2 form a hetero-oligomeric complex with a 1:3 ratio. [910]. Although still being sorted out, TRPP family members appear to be 6TM spanning nonselective cation channels. TRPV (vanilloid) familyMembers of the TRPV family (reviewed by [1001]) can broadly be divided into the non-selective cation channels, TRPV1-4 and the more calcium selective channels TRPV5 and TRPV6. TRPV1-V4 subfamilyTRPV1 is involved in the development of thermal hyperalgesia following inflammation and may contribute to the detection of noxius heat (reviewed by [767, 887, 927]). Numerous splice variants of TRPV1 have been described, some of which modulate the activity of TRPV1, or act in a dominant negative manner when co-expressed with TRPV1 [849]. The pharmacology of TRPV1 channels is discussed in detail in [332] and [1022]. TRPV2 is probably not a thermosensor in man [740], but has recently been implicated in innate immunity [551]. Functional TRPV2 expression is described in placental trophoblast cells of mouse [205]. TRPV3 and TRPV4 are both thermosensitive. There are claims that TRPV4 is also mechanosensitive, but this has not been established to be within a physiological range in a native environment [127, 534]. TRPV5/V6 subfamily TRPV5 and TRPV6 are highly expressed in placenta, bone, and kidney. Under physiological conditions, TRPV5 and TRPV6 are calcium selective channels involved in the absorption and reabsorption of calcium across intestinal and kidney tubule epithelia (reviewed by [1064, 206, 655, 272]).TRPV6 is reported to play a key role in calcium transport in the mouse placenta [1063].

This study analyzed adverse events (AEs) of GLP-1RA and metformin combination therapy using FAERS data (2004-2024). A retrospective disproportionality analysis was conducted using the reporting odds ratio (ROR) on FAERS data (2004-2024), with Bayesian confidence propagation neural network (BCPNN) employed for sensitivity analysis. Adverse reactions were compared between combination therapy and monotherapy (GLP-1 RAs or metformin alone), followed by stratified analyses by gender, age, and body weight. Among 48,214 reports (57.5% female), common AEs included nausea and weight loss. Unexpected signals included kidney injury and pancreatic cancer. Monotherapy showed higher AE rates. Males reported more renal calculi and early-onset AEs (≤ 30 days), while females had delayed AEs (> 360 days). Weight loss was consistent across all demographics. The combination therapy of GLP-1 receptor agonists and metformin demonstrates superior safety over monotherapy, while revealing novel adverse events and demographic-specific risk patterns, thereby offering reliable evidence to inform clinical practice.

Complex regional pain syndrome type I (CRPS-I) develops after an initial injury. It causes prolonged pain that persists beyond the usual expected time for tissue healing. Mechanisms underlying pain chronicity of CRPS-I remain unknown. Here, we identified the presence of long-lasting infiltration of macrophages in local dorsal root ganglia (DRG) of a rat model of CRPS-I. We demonstrate that regenerating islet-derived 3β (Reg3β) is specifically produced by DRG neurons upon model establishment and functions as an important signaling molecule to drive proinflammatory macrophage infiltration in local DRG. Infiltrated macrophages produce TNF-α, which causes hyperexcitability of nociceptive DRG neurons and reciprocally promotes Reg3β overexpression and secretion from DRG neurons to recruit more macrophages. Our work reveals a positive feedback signaling conveyed by neuronal Reg3β/macrophage TNF-α that contributes to neuroinflammation in DRG, resulting in persistent pain in a rat model of CRPS-I. This finding provides insights into the neuroimmune interaction in local DRG that contributes to pain chronicity of CRPS-I.

Background and purpose ST2, a member of the interleukin-1 (IL-1) receptor family, along with its ligand IL-33, plays critical roles in immune regulation and inflammatory responses. This study investigates the roles of endogenous IL-33/ST2 signaling in subarachnoid hemorrhage (SAH) and elucidates the underlying mechanisms. Methods Dynamic changes in endogenous IL-33 levels were examined following SAH induction in vivo. Rats underwent the endovascular perforation model of SAH and were randomly assigned to receive either recombinant IL-33 (rIL-33) or a vehicle, administered intranasally 1 h post-SAH. ST2 siRNA or an AKT selective inhibitor was administered intraperitoneally (i.p.) 48 h prior to SAH induction to explore the potential mechanisms of IL-33-mediated neuroprotection. Results Endogenous IL-33 and ST2 levels were elevated in in vitro models of SAH. Exogenous IL-33 significantly alleviated neuronal apoptosis, reduced brain edema, and enhanced short-term neurofunction in a dose-dependent manner following SAH in rats. Conclusion Exogenous rIL-33 alleviates SAH-induced neurological deficits by promoting M2-like polarization of microglia post-SAH. These findings suggest a potential role of the microglial ST2/AKT axis in IL-33-related neuroprotection, which warrants further investigation.

Pain memory, which includes sensory and emotional memory, is one of the main causes of pain complications and prolongation. Recent research has identified the insular cortex (IC) as a critical brain region involved in the integration of information pertaining to pain, emotion, reward, cognition and memory. GABAergic neuronal activity in the IC has been demonstrated to be strongly correlated with the manifestation of pain-related aversive behavior. Electroacupuncture (EA) relieves pain-related aversive memory by activating μ opioid receptors (MORs) in the IC. The results of this study demonstrate that activating MORs in the IC may inhibit GABAergic neuron activity and thus alleviate the relapse of behaviors associated with pain sensory memory and pain-related aversive memory. The relapse of such behaviors was found to be alleviated by EA in model mice; however, antagonism of MORs in the IC reversed the therapeutic effect of EA. In consideration of these findings, we suggest that EA may affect GABAergic neuron activity through activation of MORs in the IC thereby alleviating the relapse of behaviors associated with pain sensory memory and pain-related aversive memory. The study provides novel insights into the mechanisms by which EA chronic pain and behaviors associated with chronic pain-related aversive memory.

Accumulating evidence highlights the anti-inflammatory and analgesic effects of electroacupuncture (EA), yet the underlying mechanisms remain poorly understood. The P2X7 purinergic receptor (P2X7R), located in the peripheral and central nervous systems, has been implicated in the development of chronic inflammatory pain. Inhibition of P2X7R expression has been associated with the analgesic effects of EA. Within the dorsal root ganglia, P2X7R is exclusively expressed in satellite glial cells (SGCs), but its role in the anti-inflammatory effects of EA remains to be elucidated. A chronic inflammatory pain model was established in rats via intraplantar injection of Complete Freund’s Adjuvant (CFA). Western blotting, immunostaining, behavioral assay, pharmacological interventions, AAV-mediated knockdown assays, SGCs culture and real-time cell proliferation analysis were utilized to investigate the cellular mechanisms underlying the effects of EA at the ST36 and BL60 acupuncture points in mitigating inflammatory pain. Rats injected with CFA exhibited long-lasting pain hypersensitivity in the ipsilateral hind paw, accompanied by upregulated expression of P2X7R and TNF-α in the L4-6 DRGs. Pharmacological inhibition or shRNA-mediated knockdown of P2X7R in SGCs significantly attenuated inflammatory pain hypersensitivity, reduced P38 MAPK phosphorylation, and decreased TNF-α levels. EA treatment significantly alleviated CFA-induced pain hypersensitivity and suppressed P2X7R expression alongside its downstream P38 MAPK/TNF-α signaling. The analgesic effects of EA were reversed by the P2X7R agonist BzATP. In vitro findings confirmed that TNF-α secretion by SGCs was markedly elevated in the CFA model but reduced by EA treatment, mimicking the effects of P2X7R antagonism. These findings demonstrate that the inhibition of P2X7R in SGCs and its downstream P38 MAPK/TNF-α signaling pathway contributes to the analgesic effects of EA in chronic inflammatory pain. Targeting peripheral P2X7R in SGCs may provide new insights into the cellular mechanisms of EA’s anti-inflammatory effects.

The TRP superfamily of channels (nomenclature as agreed by NC-IUPHAR [177, 1080]), whose founder member is the Drosophila Trp channel, exists in mammals as six families; TRPC, TRPM, TRPV, TRPA, TRPP and TRPML based on amino acid homologies. TRP subunits contain six putative TM domains and assemble as homo- or hetero-tetramers to form cation selective channels with diverse modes of activation and varied permeation properties (reviewed by [734]). Established, or potential, physiological functions of the individual members of the TRP families are discussed in detail in the recommended reviews and in a number of books [404, 690, 1163, 258]. The established, or potential, involvement of TRP channels in disease [1134] is reviewed in [452, 689], [692] and [468], together with a special edition of Biochemica et Biophysica Acta on the subject [689]. Additional disease related reviews, for pain [637], stroke [1143], sensation and inflammation [994], itch [130], and airway disease [313, 1058], are available. The pharmacology of most TRP channels has been advanced in recent years. Broad spectrum agents are listed in the tables along with more selective, or recently recognised, ligands that are flagged by the inclusion of a primary reference. See Rubaiy (2019) for a review of pharmacological tools for TRPC1/C4/C5 channels [810]. Most TRP channels are regulated by phosphoinositides such as PtIns(4,5)P2 although the effects reported are often complex, occasionally contradictory, and likely to be dependent upon experimental conditions, such as intracellular ATP levels (reviewed by [1015, 693, 806]). Such regulation is generally not included in the tables.When thermosensitivity is mentioned, it refers specifically to a high Q10 of gating, often in the range of 10-30, but does not necessarily imply that the channel's function is to act as a 'hot' or 'cold' sensor. In general, the search for TRP activators has led to many claims for temperature sensing, mechanosensation, and lipid sensing. All proteins are of course sensitive to energies of binding, mechanical force, and temperature, but the issue is whether the proposed input is within a physiologically relevant range resulting in a response. TRPA (ankyrin) familyTRPA1 is the sole mammalian member of this group (reviewed by [295]). TRPA1 activation of sensory neurons contribute to nociception [417, 895, 606]. Pungent chemicals such as mustard oil (AITC), allicin, and cinnamaldehyde activate TRPA1 by modification of free thiol groups of cysteine side chains, especially those located in its amino terminus [579, 60, 368, 581]. Alkenals with α, β-unsaturated bonds, such as propenal (acrolein), butenal (crotylaldehyde), and 2-pentenal can react with free thiols via Michael addition and can activate TRPA1. However, potency appears to weaken as carbon chain length increases [26, 60]. Covalent modification leads to sustained activation of TRPA1. Chemicals including carvacrol, menthol, and local anesthetics reversibly activate TRPA1 by non-covalent binding [428, 515, 1089, 1088]. TRPA1 is not mechanosensitive under physiological conditions, but can be activated by cold temperatures [429, 213]. The electron cryo-EM structure of TRPA1 [745] indicates that it is a 6-TM homotetramer. Each subunit of the channel contains two short ‘pore helices’ pointing into the ion selectivity filter, which is big enough to allow permeation of partially hydrated Ca2+ ions. TRPC (canonical) familyMembers of the TRPC subfamily (reviewed by [286, 783, 18, 4, 94, 450, 744, 70]) fall into the subgroups outlined below. TRPC2 is a pseudogene in humans. It is generally accepted that all TRPC channels are activated downstream of Gq/11-coupled receptors, or receptor tyrosine kinases (reviewed by [770, 959, 1080]). A comprehensive listing of G protein coupled receptors that activate TRPC channels is given in [4]. Hetero-oligomeric complexes of TRPC channels and their association with proteins to form signalling complexes are detailed in [18] and [451]. TRPC channels have frequently been proposed to act as store-operated channels (SOCs) (or components of multimeric complexes that form SOCs), activated by depletion of intracellular calcium stores (reviewed by [746, 18, 775, 825, 1129, 157, 730, 64, 158]). However, the weight of the evidence is that they are not directly gated by conventional store-operated mechanisms, as established for STIM-gated Orai channels. TRPC channels are not mechanically gated in physiologically relevant ranges of force. All members of the TRPC family are blocked by 2-APB and SKF96365 [350, 349]. Activation of TRPC channels by lipids is discussed by [70]. Important progress has been recently made in TRPC pharmacology [810, 623, 440, 102, 856, 192, 293]. TRPC channels regulate a variety of physiological functions and are implicated in many human diseases [298, 71, 890, 1038, 1032, 154, 103, 565, 918, 412]. TRPC1/C4/C5 subgroup TRPC1 alone may not form a functional ion channel [230]. The structures of the apo and antagonist-bound states of TRPC1/TRPC4 heteromeric channels have been resolved by cryo-EM [1070]. TRPC4/C5 may be distinguished from other TRP channels by their potentiation by micromolar concentrations of La3+. TRPC2 is a pseudogene in humans, but in other mammals appears to be an ion channel localized to microvilli of the vomeronasal organ. It is required for normal sexual behavior in response to pheromones in mice. It may also function in the main olfactory epithelia in mice [1122, 727, 728, 1123, 543, 1176, 1117].TRPC3/C6/C7 subgroup All members are activated by diacylglycerol independent of protein kinase C stimulation [350].TRPM (melastatin) familyMembers of the TRPM subfamily (reviewed by [277, 349, 746, 1159]) fall into the five subgroups outlined below. TRPM1/M3 subgroupIn darkness, glutamate released by the photoreceptors and ON-bipolar cells binds to the metabotropic glutamate receptor 6 , leading to activation of Go . This results in the closure of TRPM1. When the photoreceptors are stimulated by light, glutamate release is reduced, and TRPM1 channels are more active, resulting in cell membrane depolarization. Human TRPM1 mutations are associated with congenital stationary night blindness (CSNB), whose patients lack rod function. TRPM1 is also found melanocytes. Isoforms of TRPM1 may present in melanocytes, melanoma, brain, and retina. In melanoma cells, TRPM1 is prevalent in highly dynamic intracellular vesicular structures [401, 712]. TRPM3 (reviewed by [718]) exists as multiple splice variants which differ significantly in their biophysical properties. TRPM3 is expressed in somatosensory neurons and may be important in development of heat hyperalgesia during inflammation (see review [947]). TRPM3 is frequently coexpressed with TRPA1 and TRPV1 in these neurons. TRPM3 is expressed in pancreatic beta cells as well as brain, pituitary gland, eye, kidney, and adipose tissue [717, 946]. TRPM3 may contribute to the detection of noxious heat [1024]. TRPM2TRPM2 is activated under conditions of oxidative stress (respiratory burst of phagocytic cells). The direct activators are calcium, adenosine diphosphate ribose (ADPR) [976] and cyclic ADPR (cADPR) [1126]. As for many ion channels, PI(4,5)P2 must also be present [1117]. Numerous splice variants of TRPM2 exist which differ in their activation mechanisms [240]. Recent studies have reported structures of human (hs) TRPM2, which demonstrate two ADPR binding sites in hsTRPM2, one in the N-terminal MHR1/2 domain and the other in the C-terminal NUDT9-H domain. In addition, one Ca2+ binding site in the intracellular S2-S3 loop is revealed and proposed to mediate Ca2+ binding that induces conformational changes leading the ADPR-bound closed channel to open [390, 1034]. Meanwhile, a quadruple-residue motif (979FGQI982) was identified as the ion selectivity filter and a gate to control ion permeation in hsTRPM2 [1128]. TRPM2 is involved in warmth sensation [853], and contributes to several diseases [76]. TRPM2 interacts with extra synaptic NMDA receptors (NMDAR) and enhances NMDAR activity in ischemic stroke [1172]. Activation of TRPM2 in macrophages promotes atherosclerosis [1173, 1155]. Moreover, silica nanoparticles induce lung inflammation in mice via ROS/PARP/TRPM2 signaling-mediated lysosome impairment and autophagy dysfunction [1035]. Recent studies have designed various compounds for their potential to selectively inhibit the TRPM2 channel, including ACA derivatives A23, and 2,3-dihydroquinazolin-4(1H)-one derivatives [1145, 1147]. TRPM4/5 subgroupTRPM4 and TRPM5 have the distinction within all TRP channels of being impermeable to Ca2+ [1080]. A splice variant of TRPM4 (i.e.TRPM4b) and TRPM5 are molecular candidates for endogenous calcium-activated cation (CAN) channels [330]. TRPM4 is active in the late phase of repolarization of the cardiac ventricular action potential. TRPM4 deletion or knockout enhances beta adrenergic-mediated inotropy [597]. Mutations are associated with conduction defects [407, 597, 884]. TRPM4 has been shown to be an important regulator of Ca2+ entry in to mast cells [999] and dendritic cell migration [52]. TRPM5 in taste receptor cells of the tongue appears essential for the transduction of sweet, amino acid and bitter stimuli [541] TRPM5 contributes to the slow afterdepolarization of layer 5 neurons in mouse prefrontal cortex [517]. Both TRPM4 and TRPM5 are required transduction of taste stimuli [247]. TRPM6/7 subgroupTRPM6 and 7 combine channel and enzymatic activities (‘chanzymes’) [173]. These channels have the unusual property of permeation by divalent (Ca2+, Mg2+, Zn2+) and monovalent cations, high single channel conductances, but overall extremely small inward conductance when expressed to the plasma membrane. They are inhibited by internal Mg2+ at ~0.6 mM, around the free level of Mg2+ in cells. Whether they contribute to Mg2+ homeostasis is a contentious issue. PIP2 is required for TRPM6 and TRPM7 activation [815, 1085]. When either gene is deleted in mice, the result is embryonic lethality [416, 1073]. The C-terminal kinase region of TRPM6 and TRPM7 is cleaved under unknown stimuli, and the kinase phosphorylates nuclear histones [483, 484]. TRPM7 is responsible for oxidant- induced Zn2+ release from intracellular vesicles [3] and contributes to intestinal mineral absorption essential for postnatal survival [626]. The putative metal transporter proteins CNNM1-4 interact with TRPM7 and regulate TRPM7 channel activity [40, 471]. TRPM8Is a channel activated by cooling and pharmacological agents evoking a ‘cool’ sensation and participates in the thermosensation of cold temperatures [63, 179, 225] reviewed by [1017, 566, 461, 653]. Direct chemical agonists include menthol and icilin[1094]. Besides, linalool can promote ERK phosphorylation in human dermal microvascular endothelial cells, down-regulate intracellular ATP levels, and activate TRPM8 [68]. Recent studies have found that TRPM8 has typical S4-S5 connectomes with clear selective filters and exowell rings [516], and have identified cryo-electron microscopy structures of mouse TRPM8 in closed, intermediate, and open states along the ligand- and PIP2-dependent gated pathways [1119]. Moreover, the last 36 amino acids at the carboxyl terminal of TRPM8 are key protein sequences for TRPM8's temperature-sensitive function [195]. TRPM8 deficiency reduced the expression of S100A9 and increased the expression of HNF4α in the liver of mice, which reduced inflammation and fibrosis progression in mice with liver fibrosis, and helped to alleviate the symptoms of bile duct disease [560]. Channel deficiency also shortens the time of hypersensitivity reactions in migraine mouse models by promoting the recovery of normal sensitivity [12]. A cyclic peptide DeC‐1.2 was designed to inhibit ligand activation of TRPM8 but not cold activation, which can eliminate the side effects of cold dysalgesia in oxaliplatin-treated mice without changing body temperature [9]. Analysis of clinical data shows that TRPM8-specific blockers WS12 can reduce tumor growth in colorectal cancer xenografted mice by reducing transcription and activation of Wnt signaling regulators and β-catenin and its target oncogenes, such as C-Myc and Cyclin D1 [736]. TRPML (mucolipin) familyThe TRPML family [787, 1140, 780, 1092, 191] consists of three mammalian members (TRPML1-3). TRPML channels are probably restricted to intracellular vesicles and mutations in the gene (MCOLN1) encoding TRPML1 (mucolipin-1) cause the neurodegenerative disorder mucolipidosis type IV (MLIV) in man. TRPML1 is a cation selective ion channel that is important for sorting/transport of endosomes in the late endocytotic pathway and specifically, fission from late endosome-lysosome hybrid vesicles and lysosomal exocytosis [827]. TRPML2 and TRPML3 show increased channel activity in low luminal sodium and/or increased luminal pH, and are activated by similar small molecules [322, 147, 882]. A naturally occurring gain of function mutation in TRPML3 (i.e. A419P) results in the varitint waddler (Va) mouse phenotype (reviewed by [787, 694]). TRPP (polycystin) familyThe TRPP family (reviewed by [217, 215, 303, 1068, 377]) or PKD2 family is comprised of PKD2 (PC2), PKD2L1 (PC2L1), PKD2L2 (PC2L2), which have been renamed TRPP1, TRPP2 and TRPP3, respectively [1080]. It should also be noted that the nomenclature of PC2 was TRPP2 in old literature. However, PC2 has been uniformed to be called TRPP2 [348]. PKD2 family channels are clearly distinct from the PKD1 family, whose function is unknown. PKD1 and PKD2 form a hetero-oligomeric complex with a 1:3 ratio. [910]. Although still being sorted out, TRPP family members appear to be 6TM spanning nonselective cation channels. TRPV (vanilloid) familyMembers of the TRPV family (reviewed by [1001]) can broadly be divided into the non-selective cation channels, TRPV1-4 and the more calcium selective channels TRPV5 and TRPV6. TRPV1-V4 subfamilyTRPV1 is involved in the development of thermal hyperalgesia following inflammation and may contribute to the detection of noxious heat (reviewed by [767, 887, 927]). Numerous splice variants of TRPV1 have been described, some of which modulate the activity of TRPV1, or act in a dominant-negative manner when co-expressed with TRPV1 [849]. The pharmacology of TRPV1 channels is discussed in detail in [332] and [1022]. TRPV2 is probably not a thermosensor in man [740], but has recently been implicated in innate immunity [551]. Functional TRPV2 expression is described in placental trophoblast cells of mouse [205]. TRPV3 and TRPV4 are both thermosensitive. There are claims that TRPV4 is also mechanosensitive, but this has not been established to be within a physiological range in a native environment [127, 534]. TRPV5/V6 subfamily TRPV5 and TRPV6 are highly expressed in placenta, bone, and kidney. Under physiological conditions, TRPV5 and TRPV6 are calcium selective channels involved in the absorption and reabsorption of calcium across intestinal and kidney tubule epithelia (reviewed by [1064, 206, 655, 272]).TRPV6 is reported to play a key role in calcium transport in the mouse placenta [1063].

BackgroundPaclitaxel-induced peripheral neuropathy (PIPN) is prevalent among patients receiving paclitaxel chemotherapy, which results in sensory abnormality as well as neuropathic pain. Conventional medications lack effectiveness on PIPN. Clinical trials identified beneficial effects of acupuncture on PIPN among patients receiving chemotherapy. Here we explored the mechanisms underlying how acupuncture might alleviate PIPN.MethodsA mouse model of PIPN was established by repeated paclitaxel application. Electroacupuncture (EA) was applied at ST36 and BL60 acupoints of model mice. Immunostaining, flow cytometry, behavioral assay, in vivo imaging were utilized for effects determination and mechanism exploration.ResultsEA ameliorated mechanical and cold pain hypersensitivities, reduced sensory neuron damage and improved loss in intra-epidermal nerve fibers (IENFs) in model mice. Macrophages infiltration were detected in DRG and sciatic nerve of model mice, which was reduced by EA. EA affected M1-like pro-inflammatory macrophage infiltration in DRG, whereas it did not affect M2-like macrophages. DRG neurons released chemoattractant CCL2 that recruited macrophages via CCR2 to DRG. EA reduced CCL2 overproduction by DRG neurons and reduced macrophage infiltration. Blocking CCR2 mimicked EA's anti-allodynic effect, whereas exogenously applying recombinant CCL2 reversed the ameliorative effect of EA on macrophage infiltration and abolished EA's anti-allodynia on model mice. EA ameliorated other signs of PIPN, including sensory neuron damage, sciatic nerve morphology impairment and IENFs loss. In mice inoculated with breast cancer cells, EA didn't affect paclitaxel-induced antitumor effect.ConclusionsThese findings suggest EA alleviates PIPN by reducing CCL2/CCR2 mediated-pro-inflammatory macrophage infiltration into sensory ganglia as well as the sciatic nerve. Our study supports EA could be used as a potential non-pharmacological therapy for PIPN.

Chronic pain greatly affects patients' quality of life and poses significant challenges for the healthcare system. Conventional medication is generally inadequate for managing chronic pain and frequently leads to numerous adverse effects. The chemokine C-X-C motif ligand 12 (CXCL12) and its receptor, the chemokine C-X-C motif receptor 4 (CXCR4), are emerging as significant neuromodulators within the nervous system. A growing body of evidence has underscored the critical roles of this chemokine axis in the development and persistence of pathological pain. In this review, we aim to synthesize recent findings that highlight the role and mechanisms of the CXCL12/CXCR4 axis in the etiology of chronic pain conditions. We focus on chronic pain stemming from sciatic nerve injury, diabetic neuropathy, spinal cord injury, bone cancer, opioid tolerance, and opioid-induced hyperalgesia. These conditions represent a diverse range of pathologies that underscore the broad impact of the CXCL12/CXCR4 axis in pain management. Furthermore, we discuss the potential for targeting the CXCL12/CXCR4 axis as a comprehensive therapeutic strategy for chronic pain. In this review, we aim to summarize emerging evidence on the critical role of the CXCL12/CXCR4 signaling in mediating chronic pain pathogenesis and its potential contributions to neurological disorders.

Comorbid chronic neuropathic pain and anxiety is a common disease that represents a major clinical challenge. The underlying mechanisms of chronic neuropathic pain and anxiety are not entirely understood, which limits the exploration of effective treatment methods. Glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) have been implicated in regulating pain, but the potential roles of the vlPAG in neuropathic pain-induced anxiety have not been investigated. Herein, whole-cell recording and immunofluorescence showed that the excitability of CamkIIα neurons in the vlPAG (vlPAG CamkIIα+ neurons) was decreased in mice with spared nerve injury (SNI), while electroacupuncture (EA) activated these neurons. We also showed that chemogenetic inhibition of vlPAG CamkIIα+ neurons resulted in allodynia and anxiety-like behaviors in naive mice. Furthermore, chemogenetic activation of vlPAG CamkIIα+ neurons reduced anxiety-like behaviors and allodynia in mice with SNI, and EA had a similar effect in alleviating these symptoms. Nevertheless, EA combined with chemogenetic activation failed to further relieve allodynia and anxiety-like behaviors. Artificial inhibition of vlPAG CamkIIα+ neurons abolished the analgesic and anxiolytic effects of EA. Overall, our study reveals a novel mechanism of neuropathic pain-induced anxiety and shows that EA may relieve comorbid chronic neuropathic pain and anxiety by activating vlPAG CamkIIα+ neurons. Significance Statement Neuropathic pain is clinically accompanied by anxiety. Both glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) and electroacupuncture (EA) have demonstrated analgesic properties. However, the efficacy of these interventions in addressing neuropathic pain and its concomitant anxiety has yet to be fully elucidated. In a mice model of spared nerve injury (SNI), we observed a decreased excitability of vlPAG CamkIIα neurons. Remarkably, EA treatment significantly enhanced the excitability of these neurons. Further, chemogenetic activation of vlPAG CamkIIα+ neurons not only resulted in analgesia but also mitigated anxiety-like behaviors in SNI mice, mirroring the effects observed with EA treatment. Conversely, inhibition of vlPAG CamkIIα+ neurons activity in naive mice reduced pain thresholds and induced anxiety-like behavior, while also negating the beneficial effects of EA. These findings provide novel insights into the mechanistic interplay between chronic neuropathic pain and anxiety, highlighting the therapeutic potential of targeting vlPAG glutamatergic neurons in these conditions.

Allergic contact dermatitis (ACD) is a common skin disease featured with skin inflammation and a mixed itch/pain sensation. The itch/pain causes the desire to scratch, affecting both physical and psychological aspects of patients. Nevertheless, the mechanisms underlying itch/pain sensation of ACD still remain elusive. Here, we found that oxidative stress and oxidation-related injury were remarkably increased in the inflamed skin of a mouse model of ACD. Reducing oxidative stress significantly attenuated itch/pain-related scratching, allokonesis and skin inflammation. RNA-Sequencing reveals oxidative stress contributes to a series of skin biological processes, including inflammation and immune response. Attenuating oxidative stress reduces overproduction of IL-1β and IL-33, two critical cytokines involved in inflammation and pain/itch, in the inflamed skin of model mice. Exogenously injecting H2O2 into the neck skin of naïve mice triggered IL-33 overproduction in skin keratinocytes and induced scratching, which was reduced in mice deficient in IL-33 receptor ST2. ACD model mice showed remarkable neutrophil infiltration in the inflamed skin. Blocking neutrophil infiltration reduced oxidative stress and attenuated scratching and skin inflammation. Therefore, our study reveals a critical contribution of neutrophil-derived oxidative stress to skin inflammation and itch/pain-related scratching of ACD model mice via mechanisms involving the triggering of IL-33 overproduction in skin keratinocytes. Targeting skin oxidative stress may represent an effective therapy for ameliorating ACD.

Pain aversion is an avoidance response to painful stimuli. Previous research has indicated that the anterior cingulate cortex (ACC) is involved in pain aversion processing. However, as interneurons, the role of GABAergic neurons in the ACC (GABAACC neurons) in pain aversion is still unclear. Electroacupuncture (EA) has been shown to ameliorate pain aversion, but the mechanism is not clarified. The present study provided evidence that inhibition of GABAACC neurons contributed to pain aversion. EA alleviated pain aversion by activating GABAACC neurons in an intensity-dependent manner. Specifically, 0.3 mA EA stimulation showed better effects on pain aversion than 0.1 mA stimulation, which could be reversed by chemical genetic inhibition of GABAACC neurons. These results provide a novel mechanism by which EA alleviates pain aversion by reversing GABAACC neurons.

Excessive deposition of monosodium urate (MSU) crystal in the joint results in gout arthritis, which triggers severe pain and affects life quality. Oxidative stress is a pivotal mechanism that contributes to etiology of gout pain and inflammation. Here we investigated whether activating Nrf2, which plays important roles in regulating endogenous antioxidant response, would attenuate gout arthritis via promoting antioxidant signaling in joint tissues. Gout arthritis model was established by intra-articular injection of MSU (500 μg/ankle) into the right ankle joint of mouse. Pharmacologically activating Nrf2 by activator oltipraz (50, 100 or 150 mg/kg, intraperitoneal) at 1 h before and 5, 23, 47 h after model establishment dose-dependently inhibited joint inflammation, mechanical and heat hypersensitivities in model mice. Oltipraz (100 mg/kg) reversed gait impairments without altering locomotor activity and reduced neutrophil infiltrations in ankle joints. In vitro studies revealed oltipraz (25 μM) inhibited MSU-induced ROS production in mouse macrophages and improved mitochondrial bioenergetics impairments caused by MSU. In vivo ROS imaging combined with biochemical assays confirmed the antioxidant effects of oltipraz on model mice. Nrf2 activation inhibited pro-inflammatory cytokine overproduction in ankle joint and attenuated the overexpression and enhancement in TRPV1 channel in DRG neurons innervating hind limb. Therapeutic effects of oltipraz were abolished by inhibiting Nrf2 or in Nrf2 knockout mice. These results suggest pharmacologically activating Nrf2 alleviates gout pain, gait impairments, inflammation and peripheral sensitization via Nrf2-dependent antioxidant mechanism. Targeting Nrf2 may represent a novel treatment option for gout arthritis.

Itching is an aversive somatosensation that triggers the desire to scratch. Transient receptor potential (TRP) channel proteins are key players in acute and chronic itch. However, whether the modulatory effect of fibroblast growth factor 13 (FGF13) on acute and chronic itch is associated with TRP channel proteins is unclear. Here, we demonstrated that conditional knockout of Fgf13 in dorsal root ganglion neurons induced significant impairment in scratching behaviors in response to acute histamine-dependent and chronic dry skin itch models. Furthermore, FGF13 selectively regulated the function of the TRPV1, but not the TRPA1 channel on Ca2+ imaging and electrophysiological recordings, as demonstrated by a significant reduction in neuronal excitability and current density induced by TRPV1 channel activation, whereas TRPA1 channel activation had no effect. Changes in channel currents were also verified in HEK cell lines. Subsequently, we observed that selective modulation of TRPV1 by FGF13 required its microtubule-stabilizing effect. Furthermore, in FGF13 knockout mice, only the overexpression of FGF13 with a tubulin-binding domain could rescue TRP channel function and the impaired itch behavior. Our findings reveal a novel mechanism by which FGF13 is involved in TRPV1-dependent itch transduction and provide valuable clues for alleviating pathological itch syndrome.