A peptidomimetic modulator of the CaV2.2 N-type calcium channel for chronic pain.

Transmembrane Cav2.2 (N-type) voltage-gated calcium channels are genetically and pharmacologically validated, clinically relevant pain targets. Clinical block of Cav2.2 (e.g., with Prialt/Ziconotide) or indirect modulation [e.g., with gabapentinoids such as Gabapentin (GBP)] mitigates chronic pain but is encumbered by side effects and abuse liability. The cytosolic auxiliary subunit collapsin response mediator protein 2 (CRMP2) targets Cav2.2 to the sensory neuron membrane and regulates their function via an intrinsically disordered motif. A CRMP2-derived peptide (CBD3) uncouples the Cav2.2-CRMP2 interaction to inhibit calcium influx, transmitter release, and pain. We developed and applied a molecular dynamics approach to identify the A1R2 dipeptide in CBD3 as the anchoring Cav2.2 motif and designed pharmacophore models to screen 27 million compounds on the open-access server ZincPharmer. Of 200 curated hits, 77 compounds were assessed using depolarization-evoked calcium influx in rat dorsal root ganglion neurons. Nine small molecules were tested electrophysiologically, while one (CBD3063) was also evaluated biochemically and behaviorally. CBD3063 uncoupled Cav2.2 from CRMP2, reduced membrane Cav2.2 expression and Ca2+ currents, decreased neurotransmission, reduced fiber photometry-based calcium responses in response to mechanical stimulation, and reversed neuropathic and inflammatory pain across sexes in two different species without changes in sensory, sedative, depressive, and cognitive behaviors. CBD3063 is a selective, first-in-class, CRMP2-based peptidomimetic small molecule, which allosterically regulates Cav2.2 to achieve analgesia and pain relief without negative side effect profiles. In summary, CBD3063 could potentially be a more effective alternative to GBP for pain relief.

Interleukin-10 signaling in somatosensory neurons controls CCL2 release and inflammatory response.

Appropriate regulation of the inflammatory response is essential for survival. Interleukin-10 (IL-10), a well-known anti-inflammatory cytokine, plays a major role in controlling inflammation. In addition to immune cells, we previously demonstrated that the IL-10 receptor (IL-10R1) is expressed in dorsal root ganglion sensory neurons. There is emerging evidence that these sensory neurons contribute to immunoregulation, and we hypothesized that IL-10 signaling in dorsal root ganglion (DRG) neurons facilitates the regulation of the inflammatory response. We showed that mice that lack IL-10R1 specifically on advillin-positive neurons have exaggerated blood nitric oxide levels, spinal microglia activation, and cytokine upregulation in the spinal cord, liver, and gut compared to wild-type (WT) counterparts in response to systemic lipopolysaccharide (LPS) injection. Lack of IL-10R1 in DRG and trigeminal ganglion (TG) neurons also increased circulating and DRG levels of proinflammatory C-C motif chemokine ligand 2 (CCL2). Interestingly, analysis of published scRNA-seq data revealed that Ccl2 and Il10ra are expressed by similar types of DRG neurons; nonpeptidergic P2X purinoceptor (P2X3R + ) neurons. In primary cultures of DRG neurons, we demonstrated that IL-10R1 inhibits the production of CCL2, but not that of the neuropeptides substance P and calcitonin-gene related peptide (CGRP). Furthermore, our data indicate that ablation of Transient receptor potential vanilloid (TRPV)1 + neurons does not impact the regulation of CCL2 production by IL-10. In conclusion, we showed that IL-10 binds to its receptor on sensory neurons to downregulate CCL2 and contribute to immunoregulation by reducing the attraction of immune cells by DRG neuron-derived CCL2. This is the first evidence that anti-inflammatory cytokines limit inflammation through direct binding to receptors on sensory neurons. Our data also add to the growing literature that sensory neurons have immunomodulatory functions.

Hungry for relief: Potential for neurotensin to address comorbid obesity and pain.

Chronic pain and obesity frequently occur together. An ideal therapy would alleviate pain without weight gain, and most optimally, could promote weight loss. The neuropeptide neurotensin (Nts) has been separately implicated in reducing weight and pain but could it be a common actionable target for both pain and obesity? Here we review the current knowledge of Nts signaling via its receptors in modulating body weight and pain processing. Evaluating the mechanism by which Nts impacts ingestive behavior, body weight, and analgesia has potential to identify common physiologic mechanisms underlying weight and pain comorbidities, and whether Nts may be common actionable targets for both.

Effects of placebo administration on immune mechanisms and relationships with central endogenous opioid neurotransmission.

Behavioral conditioning and expectation can have profound impact on animal and human physiology. Placebo, administered under positive expectation in clinical trials, can have potent effects on disease pathology, obscuring active medications. Emerging evidence suggests placebo-responsive neurotransmitter systems (e.g., endogenous opioid) regulate immune function by manipulating inflammatory proteins including IL-18, a potent pro-inflammatory, nociceptive cytokine implicated in pathophysiology of various diseases. Validation that neuroimmune interactions involving brain µ-opioid receptor (MOR) activity and plasma IL-18 underlie placebo analgesic expectation could have widespread clinical applications. Unfortunately, current lack of mechanistic clarity obfuscates clinical translation. To elucidate neuroimmune interactions underlying placebo analgesia, we exposed 37 healthy human volunteers to a standardized pain challenge on each of 2 days within a Positron Emission Tomography (PET) neuroimaging paradigm using the MOR selective radiotracer, 11C-Carfentanil (CFN). Each day volunteers received an intervention (placebo under analgesic expectation or no treatment), completed PET scanning, and rated their pain experience. MOR BPND parametric maps were generated from PET scans using standard methods. Results showed placebo reduced plasma IL-18 during pain (W74 = -3.7, p < 0.001), the extent correlating with reduction in pain scores. Placebo reduction in IL-18 covaried with placebo-induced endogenous opioid release in the left nucleus accumbens (T148 = 3.33; puncorr < 0.001) and left amygdala (T148 = 3.30; puncorr < 0.001). These findings are consistent with a modulating effect of placebo (under analgesic expectation in humans) on a potent nociceptive, pro-inflammatory cytokine (IL-18) and underlying relationships with endogenous opioid activity, a neurotransmitter system critically involved in pain, stress, and mood regulation.

Nasal administration of mesenchymal stem cells reverses chemotherapy-induced peripheral neuropathy in mice.

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most frequently reported adverse effects of cancer treatment. CIPN often persists long after treatment completion and has detrimental effects on patient's quality of life. There are no efficacious FDA-approved drugs for CIPN. We recently demonstrated that nasal administration of mesenchymal stem cells (MSC) reverses the cognitive deficits induced by cisplatin in mice. Here we show that nasal administration of MSC after cisplatin- or paclitaxel treatment- completely reverses signs of established CIPN, including mechanical allodynia, spontaneous pain, and loss of intraepidermal nerve fibers (IENF) in the paw. The resolution of CIPN is associated with normalization of the cisplatin-induced decrease in mitochondrial bioenergetics in DRG neurons. Nasally administered MSC enter rapidly the meninges of the brain, spinal cord and peripheral lymph nodes to promote IL-10 production by macrophages. MSC-mediated resolution of mechanical allodynia, recovery of IENFs and restoration of DRG mitochondrial function critically depends on IL-10 production. MSC from IL-10 knockout animals are not capable of reversing the symptoms of CIPN. Moreover, WT MSC do not reverse CIPN in mice lacking IL-10 receptors on peripheral sensory neurons. In conclusion, only two nasal administrations of MSC fully reverse CIPN and the associated mitochondrial abnormalities via an IL-10 dependent pathway. Since MSC are already applied clinically, we propose that nasal MSC treatment could become a powerful treatment for the large group of patients suffering from neurotoxicities of cancer treatment.

A Novel Syngeneic Immunocompetent Mouse Model of Head and Neck Cancer Pain Independent of Interleukin-1 Signaling.

BACKGROUND: Pain is one of the first presenting symptoms in patients with head and neck cancer, who often develop chronic and debilitating pain as the disease progresses. Pain is also an important prognostic marker for survival. Unfortunately, patients rarely receive effective pain treatment due to our limited knowledge of the mechanisms underlying head and neck cancer pain (HNCP). Pain is often associated with neuroinflammation and particularly interleukin (IL)-1 signaling. The purpose of this study is to develop a novel syngeneic model of HNCP in immunocompetent mice to examine the contribution of IL-1 signaling. METHODS: Male C57BL/6 mice were injected with a murine model of human papillomavirus (HPV+)-induced oropharyngeal squamous cell carcinoma in their right hindlimb to induce tumor growth. Pain sensitivity was measured via von Frey filaments. Spontaneous pain was assessed via the facial grimace scale. IL-1ß was measured by quantifying gene expression via quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA). RESULTS: Pain hypersensitivity and spontaneous pain develop quickly after the implantation of tumor cells, a time when tumor volume is still insignificant. Spinal and circulating IL-1ß levels are significantly elevated in tumor-bearing mice. Blocking IL-1 signaling either by intrathecal administration of interleukin-1 receptor antagonist (IL-1ra) or by genetic deletion (interleukin-1 receptor knockout [Il1r1-/-]) does not alleviate HNCP. CONCLUSIONS: We established the first syngeneic model of HNCP in immunocompetent mice. Unlike inflammatory or nerve-injured pain, HNCP is independent of IL-1 signaling. These findings challenge the common belief that pain results from tissue compression or IL-1 signaling in patients with head and neck cancer.

7ß-(3-Ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z Notonipetranone Attenuates Neuropathic Pain by Suppressing Oxidative Stress, Inflammatory and Pro-Apoptotic Protein Expressions.

7ß-(3-Ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z-notonipetranone (ECN), a sesquiterpenoid obtained from a natural source has proved to be effective in minimizing various side effects associated with opioids and nonsteroidal anti-inflammatory drugs. The current study focused on investigating the effects of ECN on neuropathic pain induced by partial sciatic nerve ligation (PSNL) by mainly focusing on oxidative stress, inflammatory and apoptotic proteins expression in mice. ECN (1 and 10 mg/kg, i.p.), was administered once daily for 11 days, starting from the third day after surgery. ECN post-treatment was found to reduce hyperalgesia and allodynia in a dose-dependent manner. ECN remarkably reversed the histopathological abnormalities associated with oxidative stress, apoptosis and inflammation. Furthermore, ECN prevented the suppression of antioxidants (glutathione, glutathione-S-transferase, catalase, superoxide dismutase, NF-E2-related factor-2 (Nrf2), hemeoxygenase-1 and NAD(P)H: quinone oxidoreductase) by PSNL. Moreover, pro-inflammatory cytokines (tumor necrotic factor-alpha, interleukin 1 beta, interleukin 6, cyclooxygenase-2 and inducible nitric oxide synthase) expression was reduced by ECN administration. Treatment with ECN was successful in reducing the caspase-3 level consistent with the observed modulation of pro-apoptotic proteins. Additionally, ECN showed a protective effect on the lipid content of myelin sheath as evident from FTIR spectroscopy which showed the shift of lipid component bands to higher values. Thus, the anti-neuropathic potential of ECN might be due to the inhibition of oxidative stress, inflammatory mediators and pro-apoptotic proteins.

Nerve Injury-Induced Chronic Pain Is Associated with Persistent DNA Methylation Reprogramming in Dorsal Root Ganglion.

Nerve injury-induced hyperactivity of primary sensory neurons in the dorsal root ganglion (DRG) contributes to chronic pain development, but the underlying epigenetic mechanisms remain poorly understood. Here we determined genome-wide changes in DNA methylation in the nervous system in neuropathic pain. Spinal nerve ligation (SNL), but not paclitaxel treatment, in male Sprague Dawley rats induced a consistent low-level hypomethylation in the CpG sites in the DRG during the acute and chronic phases of neuropathic pain. DNA methylation remodeling in the DRG occurred early after SNL and persisted for at least 3 weeks. SNL caused DNA methylation changes at 8% of CpG sites with prevailing hypomethylation outside of CpG islands, in introns, intergenic regions, and repetitive sequences. In contrast, SNL caused more gains of methylation in the spinal cord and prefrontal cortex. The DNA methylation changes in the injured DRGs recapitulated developmental reprogramming at the neonatal stage. Methylation reprogramming was correlated with increased gene expression variability. A diet deficient in methyl donors induced hypomethylation and pain hypersensitivity. Intrathecal administration of the DNA methyltransferase inhibitor RG108 caused long-lasting pain hypersensitivity. DNA methylation reprogramming in the DRG thus contributes to nerve injury-induced chronic pain. Restoring DNA methylation may represent a new therapeutic approach to treat neuropathic pain.SIGNIFICANCE STATEMENT Epigenetic mechanisms are critically involved in the transition from acute to chronic pain after nerve injury. However, genome-wide changes in DNA methylation in the nervous system and their roles in neuropathic pain development remain unclear. Here we used digital restriction enzyme analysis of methylation to quantitatively determine genome-wide DNA methylation changes caused by nerve injury. We showed that nerve injury caused DNA methylation changes at 8% of CpG sites with prevailing hypomethylation outside of CpG islands in the dorsal root ganglion. Reducing DNA methylation induced pain hypersensitivity, whereas increasing DNA methylation attenuated neuropathic pain. These findings extend our understanding of the epigenetic mechanism of chronic neuropathic pain and suggest new strategies to treat nerve injury-induced chronic pain.

CD8+ T Cells and Endogenous IL-10 Are Required for Resolution of Chemotherapy-Induced Neuropathic Pain.

Chemotherapy-induced peripheral neuropathy (CIPN), characterized by pain and numbness in hands and feet, is a common side effect of cancer treatment. In most patients, symptoms of CIPN subside after treatment completion. However, in a substantial subgroup, CIPN persists long into survivorship. Impairment in pain resolution pathways may explain persistent CIPN. We investigated the contribution of T cells and endogenous interleukin (IL)-10 to resolution of CIPN. Paclitaxel-induced mechanical allodynia was prolonged in T-cell-deficient (Rag1-/-) mice compared with wild-type (WT) mice. There were no differences between WT and Rag1-/- mice in severity of paclitaxel-induced mechanical allodynia. Adoptive transfer of either CD3+ or CD8+, but not CD4+, T cells to Rag1-/- mice normalized resolution of CIPN. Paclitaxel treatment increased the number of T cells in lumbar dorsal root ganglia (DRG), where CD8+ T cells were the major subset. Inhibition of endogenous IL-10 signaling by intrathecal injection of anti-IL-10 to WT mice or Rag1-/- mice reconstituted with CD8+ T cells delayed recovery from paclitaxel-induced mechanical allodynia. Recovery was also delayed in IL-10 knock-out mice. Conversely, administration of exogenous IL-10 attenuated paclitaxel-induced allodynia. In vitro, IL-10 suppressed abnormal paclitaxel-induced spontaneous discharges in DRG neurons. Paclitaxel increased DRG IL-10 receptor expression and this effect requires CD8+ T cells. In conclusion, we identified a novel mechanism for resolution of CIPN that requires CD8+ T cells and endogenous IL-10. We propose that CD8+ T cells increase DRG IL-10 receptor expression and that IL-10 suppresses the abnormal paclitaxel-induced spontaneous discharges by DRG neurons to promote recovery from CIPN. SIGNIFICANCE STATEMENT: Chemotherapy-induced peripheral neuropathy persists after completion of cancer treatment in a significant subset of patients, whereas others recover. Persistent neuropathy after completion of cancer treatment severely affects quality of life. We propose that understanding how neuropathy resolves will identify novel avenues for treatment. We identified a novel and critical role for CD8+ T cells and for endogenous IL-10 in recovery from paclitaxel-induced neuropathy in mice. Enhancing the capacity of CD8+ T cells to promote resolution or increasing IL-10 signaling are promising targets for novel interventions. Clinically, peripheral blood CD8+ T-cell function and/or the capacity of individuals to produce IL-10 may represent biomarkers of risk for developing persistent peripheral neuropathy after completion of cancer treatment.

Nerve Injury Diminishes Opioid Analgesia through Lysine Methyltransferase-mediated Transcriptional Repression of µ-Opioid Receptors in Primary Sensory Neurons.

The µ-opioid receptor (MOR, encoded by Oprm1) agonists are the mainstay analgesics for treating moderate to severe pain. Nerve injury causes down-regulation of MORs in the dorsal root ganglion (DRG) and diminishes the opioid effect on neuropathic pain. However, the epigenetic mechanisms underlying the diminished MOR expression caused by nerve injury are not clear. G9a (encoded by Ehmt2), a histone 3 at lysine 9 methyltransferase, is a key chromatin regulator responsible for gene silencing. In this study, we determined the role of G9a in diminished MOR expression and opioid analgesic effects in animal models of neuropathic pain. We found that nerve injury in rats induced a long-lasting reduction in the expression level of MORs in the DRG but not in the spinal cord. Nerve injury consistently increased the enrichment of the G9a product histone 3 at lysine 9 dimethylation in the promoter of Oprm1 in the DRG. G9a inhibition or siRNA knockdown fully reversed MOR expression in the injured DRG and potentiated the morphine effect on pain hypersensitivity induced by nerve injury. In mice lacking Ehmt2 in DRG neurons, nerve injury failed to reduce the expression level of MORs and the morphine effect. In addition, G9a inhibition or Ehmt2 knockout in DRG neurons normalized nerve injury-induced reduction in the inhibitory effect of the opioid on synaptic glutamate release from primary afferent nerves. Our findings indicate that G9a contributes critically to transcriptional repression of MORs in primary sensory neurons in neuropathic pain. G9a inhibitors may be used to enhance the opioid analgesic effect in the treatment of chronic neuropathic pain.

Upregulation of neuronal kynurenine 3-monooxygenase mediates depression-like behavior in a mouse model of neuropathic pain.

Pain and depression often co-occur, but the underlying mechanisms have not been elucidated. Here, we used the spared nerve injury (SNI) model in mice to induce both neuropathic pain and depression-like behavior. We investigated whether brain interleukin (IL)-1 signaling and activity of kynurenine 3-monoxygenase (KMO), a key enzyme for metabolism of kynurenine into the neurotoxic NMDA receptor agonist quinolinic acid, are necessary for comorbid neuropathic pain and depression-like behavior. SNI mice showed increased expression levels of Il1b and Kmo mRNA in the contralateral side of the brain. The SNI-induced increase of Kmo mRNA was associated with increased KMO protein and elevated quinolinic acid and reduced kynurenic acid in the contralateral hippocampus. The increase in KMO-protein in response to SNI mostly took place in hippocampal NeuN-positive neurons rather than microglia. Inhibition of brain IL-1 signaling by intracerebroventricular administration of IL-1 receptor antagonist after SNI prevented the increase in Kmo mRNA and depression-like behavior measured by forced swim test. However, inhibition of brain IL-1 signaling has no effect on mechanical allodynia. In addition, intracerebroventricular administration of the KMO inhibitor Ro 61-8048 abrogated depression-like behavior without affecting mechanical allodynia after SNI. We show for the first time that the development of depression-like behavior in the SNI model requires brain IL-1 signaling and activation of neuronal KMO, while pain is independent of this pathway. Inhibition of KMO may represent a promising target for treating depression.

Pannexin-1 Up-regulation in the Dorsal Root Ganglion Contributes to Neuropathic Pain Development.

Pannexin-1 (Panx1) is a large-pore membrane channel involved in the release of ATP and other signaling mediators. Little is known about the expression and functional role of Panx1 in the dorsal root ganglion (DRG) in the development of chronic neuropathic pain. In this study, we determined the epigenetic mechanism involved in increased Panx1 expression in the DRG after nerve injury. Spinal nerve ligation in rats significantly increased the mRNA and protein levels of Panx1 in the DRG but not in the spinal cord. Immunocytochemical labeling showed that Panx1 was primarily expressed in a subset of medium and large DRG neurons in control rats and that nerve injury markedly increased the number of Panx1-immunoreactive DRG neurons. Nerve injury significantly increased the enrichment of two activating histone marks (H3K4me2 and H3K9ac) and decreased the occupancy of two repressive histone marks (H3K9me2 and H3K27me3) around the promoter region of Panx1 in the DRG. However, nerve injury had no effect on the DNA methylation level around the Panx1 promoter in the DRG. Furthermore, intrathecal injection of the Panx1 blockers or Panx1-specific siRNA significantly reduced pain hypersensitivity induced by nerve injury. In addition, siRNA knockdown of Panx1 expression in a DRG cell line significantly reduced caspase-1 release induced by neuronal depolarization. Our findings suggest that nerve injury increases Panx1 expression levels in the DRG through altered histone modifications. Panx1 up-regulation contributes to the development of neuropathic pain and stimulation of inflammasome signaling.

Increased spinal cord Na⁺-K⁺-2Cl⁻ cotransporter-1 (NKCC1) activity contributes to impairment of synaptic inhibition in paclitaxel-induced neuropathic pain.

Microtubule-stabilizing agents, such as paclitaxel (Taxol), are effective chemotherapy drugs for treating many cancers, and painful neuropathy is a major dose-limiting adverse effect. Cation-chloride cotransporters, such as Na(+)-K(+)-2Cl(-) cotransporter-1 (NKCC1) and K(+)-Cl(-) cotransporter-2 (KCC2), critically influence spinal synaptic inhibition by regulating intracellular chloride concentrations. Here we show that paclitaxel treatment in rats significantly reduced GABA-induced membrane hyperpolarization and caused a depolarizing shift in GABA reversal potential of dorsal horn neurons. However, paclitaxel had no significant effect on AMPA or NMDA receptor-mediated glutamatergic input from primary afferents to dorsal horn neurons. Paclitaxel treatment significantly increased protein levels, but not mRNA levels, of NKCC1 in spinal cords. Inhibition of NKCC1 with bumetanide reversed the paclitaxel effect on GABA-mediated hyperpolarization and GABA reversal potentials. Also, intrathecal bumetanide significantly attenuated hyperalgesia and allodynia induced by paclitaxel. Co-immunoprecipitation revealed that NKCC1 interacted with ß-tubulin and ß-actin in spinal cords. Remarkably, paclitaxel increased NKCC1 protein levels at the plasma membrane and reduced NKCC1 levels in the cytosol of spinal cords. In contrast, treatment with an actin-stabilizing agent had no significant effect on NKCC1 protein levels in the plasma membrane or cytosolic fractions of spinal cords. In addition, inhibition of the motor protein dynein blocked paclitaxel-induced subcellular redistribution of NKCC1, whereas inhibition of kinesin-5 mimicked the paclitaxel effect. Our findings suggest that increased NKCC1 activity contributes to diminished spinal synaptic inhibition and neuropathic pain caused by paclitaxel. Paclitaxel disrupts intracellular NKCC1 trafficking by interfering with microtubule dynamics and associated motor proteins.

Massage-like stroking produces analgesia in mice.

Chronic pain treatment remains a major challenge and pharmacological interventions are associated with important side effects. Manual medicine treatments such as massage, acupuncture, manipulation of the fascial system (MFS), and osteopathic manipulative treatments produce pain relief in humans, but the underlying mechanism is poorly understood limiting leverage and optimization of manual medicine techniques as safe pain therapy. To decipher the physiological mechanisms of manipulative medicine treatments, we have established a preclinical model. Here, we established a murine model of massage-like stroking (MLS)-induced analgesia. We characterized that the analgesia effects were present in both sexes, and were independent of the experimenters, handling, consciousness, and opioid receptors. MLS alleviates thermal pain in naive mice and postoperative pain hypersensitivity. This novel model will allow discovery of the physiological mechanisms involved in MLS-induced analgesia and identification of new therapeutic strategies.

HPV+ head and neck cancer-derived small extracellular vesicles communicate with TRPV1+ neurons to mediate cancer pain.

ABSTRACT: Severe pain is often experienced by patients with head and neck cancer and is associated with a poor prognosis. Despite its frequency and severity, current treatments fail to adequately control cancer-associated pain because of our lack of mechanistic understanding. Although recent works have shed some light of the biology underlying pain in HPV-negative oral cancers, the mechanisms mediating pain in HPV+ cancers remain unknown. Cancer-derived small extracellular vesicles (cancer-sEVs) are well positioned to function as mediators of communication between cancer cells and neurons. Inhibition of cancer-sEV release attenuated pain in tumor-bearing mice. Injection of purified cancer-sEVs is sufficient to induce pain hypersensitivity in naive mice that is prevented by QX-314 treatment and in Trpv1-/- mice. Cancer-sEVs triggered calcium influx in nociceptors, and inhibition or ablation of nociceptors protects against cancer pain. Interrogation of published sequencing data of human sensory neurons exposed to human cancer-sEVs suggested a stimulation of protein translation in neurons. Induction of translation by cancer-sEVs was validated in our mouse model, and its inhibition alleviated cancer pain in mice. In summary, our work reveals that HPV+ head and neck squamous cell carcinoma-derived sEVs alter TRPV1+ neurons by promoting nascent translation to mediate cancer pain and identified several promising therapeutic targets to interfere with this pathway.

Tonic Meningeal Interleukin-10 Upregulates Delta Opioid Receptor to Prevent Relapse to Pain.

Chronic pain often alternates between transient remission and relapse of severe pain. While most research on chronic pain has focused on mechanisms maintaining pain, there is a critical unmet need to understand what prevents pain from re-emerging in those who recover from acute pain. We found that interleukin (IL)-10, a pain resolving cytokine, is persistently produced by resident macrophages in the spinal meninges during remission from pain. IL-10 upregulated expression and analgesic activity of δ-opioid receptor (δOR) in the dorsal root ganglion. Genetic or pharmacological inhibition of IL-10 signaling or δOR triggered relapse to pain in both sexes. These data challenge the widespread assumption that remission of pain is simply a return to the naïve state before pain was induced. Instead, our findings strongly suggest a novel concept that: remission is a state of lasting pain vulnerability that results from a long-lasting neuroimmune interactions in the nociceptive system.

Interleukin-10-producing monocytes contribute to sex differences in pain resolution in mice and humans.

Pain is closely associated with the immune system, which exhibits sexual dimorphism. For these reasons, neuro-immune interactions are suggested to drive sex differences in pain pathophysiology. However, our understanding of peripheral neuro-immune interactions on sex differences in pain resolution remains limited. Here, we have shown, in both a mouse model of inflammatory pain and in humans following traumatic pain, that males had higher levels of interleukin (IL)-10 than females, which were correlated with faster pain resolution. Following injury, we identified monocytes (CD11b+ Ly6C+ Ly6G-F4/80 mid ) as the primary source of IL-10, with IL-10-producing monocytes being more abundant in males than females. In a mouse model, neutralizing IL-10 signaling through antibodies, genetically ablating IL-10R1 in sensory neurons, or depleting monocytes with clodronate all impaired the resolution of pain hypersensitivity in both sexes. Furthermore, manipulating androgen levels in mice reversed the sexual dimorphism of pain resolution and the levels of IL-10-producing monocytes. These results highlight a novel role for androgen-driven peripheral IL-10-producing monocytes in the sexual dimorphism of pain resolution. These findings add to the growing concept that immune cells play a critical role in resolving pain and preventing the transition into chronic pain.

Infiltration of peripheral immune cells into the olfactory bulb in a mouse model of acute nasal inflammation.

Chronic nasal inflammation induces robust olfactory bulb (OB) atrophy in mice. Here we examined initial events that occur in the OB after bilateral intranasal administration of lipopolysaccharide, focusing on the olfactory nerve fibers and meninges. We analyzed the time course of OB and meninges inflammation using histological and biochemical approaches. Within 12 h, we observed increased chemokine expression and transient infiltration of peripheral immune cells into the OB, resulting in the development of pro-inflammatory status in the OB. Meningeal immunity was activated. Resident microglia produced anti-inflammatory cytokines within 24 h. These could be the initial events that lead to OB atrophy.

CD8+ T cell-derived IL-13 increases macrophage IL-10 to resolve neuropathic pain.

Understanding the endogenous mechanisms regulating resolution of pain may identify novel targets for treatment of chronic pain. Resolution of chemotherapy-induced peripheral neuropathy (CIPN) after treatment completion depends on CD8+ T cells and on IL-10 produced by other cells. Using Rag2-/- mice lacking T and B cells and adoptive transfer of Il13-/- CD8+ T cells, we showed that CD8+ T cells producing IL-13 were required for resolution of CIPN. Intrathecal administration of anti-IL-13 delayed resolution of CIPN and reduced IL-10 production by dorsal root ganglion macrophages. Depleting local CD206+ macrophages also delayed resolution of CIPN. In vitro, TIM3+CD8+ T cells cultured with cisplatin, apoptotic cells, or phosphatidylserine liposomes produced IL-13, which induced IL-10 in macrophages. In vivo, resolution of CIPN was delayed by intrathecal administration of anti-TIM3. Resolution was also delayed in Rag2-/- mice reconstituted with Havcr2 (TIM3)-/- CD8+ T cells. Our data indicated that cell damage induced by cisplatin activated TIM3 on CD8+ T cells, leading to increased IL-13 production, which in turn induced macrophage IL-10 production and resolution of CIPN. Development of exogenous activators of the IL-13/IL-10 pain resolution pathway may provide a way to treat the underlying cause of chronic pain.