Imbalanced spinal infiltration of Th17/Treg cells contributes to bone cancer pain via promoting microglial activation

T cell interactions with microglia in immune-inflammatory processes of ischemic stroke

The primary mechanism of secondary injury after cerebral ischemia may be the brain inflammation that emerges after an ischemic stroke, which promotes neuronal death and inhibits nerve tissue regeneration. As the first immune cells to be activated after an ischemic stroke, microglia play an important immunomodulatory role in the progression of the condition. After an ischemic stroke, peripheral blood immune cells (mainly T cells) are recruited to the central nervous system by chemokines secreted by immune cells in the brain, where they interact with central nervous system cells (mainly microglia) to trigger a secondary neuroimmune response. This review summarizes the interactions between T cells and microglia in the immune-inflammatory processes of ischemic stroke. We found that, during ischemic stroke, T cells and microglia demonstrate a more pronounced synergistic effect. Th1, Th17, and M1 microglia can co-secrete pro-inflammatory factors, such as interferon-γ, tumor necrosis factor-α, and interleukin-1β, to promote neuroinflammation and exacerbate brain injury. Th2, Treg, and M2 microglia jointly secrete anti-inflammatory factors, such as interleukin-4, interleukin-10, and transforming growth factor-β, to inhibit the progression of neuroinflammation, as well as growth factors such as brain-derived neurotrophic factor to promote nerve regeneration and repair brain injury. Immune interactions between microglia and T cells influence the direction of the subsequent neuroinflammation, which in turn determines the prognosis of ischemic stroke patients. Clinical trials have been conducted on the ways to modulate the interactions between T cells and microglia toward anti-inflammatory communication using the immunosuppressant fingolimod or overdosing with Treg cells to promote neural tissue repair and reduce the damage caused by ischemic stroke. However, such studies have been relatively infrequent, and clinical experience is still insufficient. In summary, in ischemic stroke, T cell subsets and activated microglia act synergistically to regulate inflammatory progression, mainly by secreting inflammatory factors. In the future, a key research direction for ischemic stroke treatment could be rooted in the enhancement of anti-inflammatory factor secretion by promoting the generation of Th2 and Treg cells, along with the activation of M2-type microglia. These approaches may alleviate neuroinflammation and facilitate the repair of neural tissues.

Molecular targets in bone cancer pain: a systematic review of inflammatory cytokines

Bone cancer pain (BCP) profoundly impacts patient's quality of life, demanding more effective pain management strategies. The aim of this systematic review was to investigate the role of inflammatory cytokines as potential molecular targets in BCP. A systematic search for animal rodent models of bone cancer pain studies was conducted in PubMed, Scopus, and Web of Science. Methodological quality and risk of bias were assessed using the SYRCLE RoB tool. Twenty-five articles met the inclusion criteria, comprising animal studies investigating molecular targets related to inflammatory cytokines in BCP. A low to moderate risk of bias was reported. Key findings in 23 manuscripts revealed upregulated classic pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-17, IL-18, IL-33) and chemokines in the spinal cord, periaqueductal gray, and dorsal root ganglia. Interventions targeting these cytokines consistently mitigated pain behaviors. Additionally, it was demonstrated that glial cells, due to their involvement in the release of inflammatory cytokines, emerged as significant contributors to BCP. This systematic review underscores the significance of inflammatory cytokines as potential molecular targets for alleviating BCP. It emphasizes the promise of targeted interventions and advocates for further research to translate these findings into effective therapeutic strategies. Ultimately, this approach holds the potential to enhance the patient's quality of life.

Discovery of a CCR2-targeting pepducin therapy for chronic pain

Targeting the CCL2/CCR2 chemokine axis has been shown to be effective at relieving pain in rodent models of inflammatory and neuropathic pain, therefore representing a promising avenue for the development of non-opioid analgesics. However, clinical trials targeting this receptor for inflammatory conditions and painful neuropathies have failed to meet expectations and have all been discontinued due to lack of efficacy. To overcome the poor selectivity of CCR2 chemokine receptor antagonists, we generated and characterized the function of intracellular cell-penetrating allosteric modulators targeting CCR2, namely pepducins. In vivo, chronic intrathecal administration of the CCR2-selective pepducin PP101 was effective in alleviating neuropathic and bone cancer pain. In the setting of bone metastases, we found that T cells infiltrate dorsal root ganglia (DRG) and induce long-lasting pain hypersensitivity. By acting on CCR2-expressing DRG neurons, PP101 attenuated the altered phenotype of sensory neurons as well as the neuroinflammatory milieu of DRGs, and reduced bone cancer pain by blocking CD4+ and CD8+ T cell infiltration. Notably, PP101 demonstrated its efficacy in targeting the neuropathic component of bone cancer pain, as evidenced by its anti-nociceptive effects in a model of chronic constriction injury of the sciatic nerve. Importantly, PP101-induced reduction of CCR2 signaling in DRGs did not result in deleterious tumor progression or adverse behavioral effects. Thus, targeting neuroimmune crosstalk through allosteric inhibition of CCR2 could represent an effective and safe avenue for the management of chronic pain.

Glucose competition between endothelial cells in the blood-spinal cord barrier and infiltrating regulatory T cells is linked to sleep restriction-induced hyperalgesia

BACKGROUND

Sleep loss is a common public health problem that causes hyperalgesia, especially that after surgery, which reduces the quality of life seriously.

METHODS

The 48-h sleep restriction (SR) mouse model was created using restriction chambers. In vivo imaging, transmission electron microscopy (TEM), immunofluorescence staining and Western blot were performed to detect the status of the blood-spinal cord barrier (BSCB). Paw withdrawal mechanical threshold (PWMT) was measured to track mouse pain behavior. The role of infiltrating regulatory T cells (Tregs) and endothelial cells (ECs) in mouse glycolysis and BSCB damage were analyzed using flow cytometry, Western blot, CCK-8 assay, colorimetric method and lactate administration.

RESULTS

The 48-h SR made mice in sleep disruption status and caused an acute damage to the BSCB, resulting in hyperalgesia and neuroinflammation in the spinal cord. In SR mice, the levels of glycolysis and glycolysis enzymes of ECs in the BSCB were found significantly decreased [CON group vs. SR group: CD31+Glut1+ cells: p < 0.001], which could cause dysfunction of ECs and this was confirmed in vitro. Increased numbers of infiltrating T cells [p < 0.0001] and Treg population [p < 0.05] were detected in the mouse spinal cord after 48-h SR. In the co-cultured system of ECs and Tregs in vitro, the competition of Tregs for glucose resulted in the glycolysis disorder of ECs [Glut1: p < 0.01, ENO1: p < 0.05, LDHα: p < 0.05; complete tubular structures formed: p < 0.0001; CCK8 assay: p < 0.001 on 24h, p < 0.0001 on 48h; glycolysis level: p < 0.0001]. An administration of sodium lactate partially rescued the function of ECs and relieved SR-induced hyperalgesia. Furthermore, the mTOR signaling pathway was excessively activated in ECs after SR in vivo and those under the inhibition of glycolysis or co-cultured with Tregs in vitro.

CONCLUSIONS

Affected by glycolysis disorders of ECs due to glucose competition with infiltrating Tregs through regulating the mTOR signaling pathway, hyperalgesia induced by 48-h SR is attributed to neuroinflammation and damages to the barriers, which can be relieved by lactate supplementation.

Blocking brown adipocyte β3-adrenoceptor attenuates blood-spinal cord barrier impairment and chronic postsurgical pain in a rat model of preoperative stress

Preoperative stress has been recognized as an independent risk factor for chronic postsurgical pain (CPSP). However, the underlying mechanisms of CPSP influenced by preoperative stress remain elusive. Previous studies indicated that excessive stress could induce disruption of the blood-spinal cord barrier (BSCB). We wondered whether and how BSCB involves in CPSP by using a single prolonged stress (SPS) combining plantar incision model in male rats to mimic preoperative stress-related postsurgical pain. Here, we observed that preoperative SPS-exposed rats exhibited relentless incisional pain, which was accompanied by impairment of BSCB and persistent elevation of serum IL-6. Intraperitoneal injections of Tocilizumab (an IL-6 receptor monoclonal antibody) not only mitigated BSCB breakdown but also alleviated pain behaviors. In addition, intervening β3-adrenoceptor (ADRB3) signaling in brown adipocytes by SR59230a (a specific ADRB3 antagonist) treatment or removal of brown adipose tissues could effectively decrease serum IL-6 levels, ameliorate BSCB disruption, and alleviate incisional pain. Further results displayed that SI-exposed rats also showed markedly spinal microglia activation. And exogenous His-tagged IL-6 could pass through the disrupted BSCB, which might contribute to microglia activation. Injection of SR59230a or ablation of brown adipose tissues could effectively reduce the activation of spinal microglia. Thus, our findings suggest that serum IL-6 induced by brown adipocyte ADRB3 signaling contributed to BSCB disruption and spinal microglia activation, which might be involved in preoperative stress mediated CPSP. This work indicates a promising treatment strategy for preoperative stress induced CPSP by blocking ADRB3.

Spinal interleukin-16 mediates inflammatory pain via promoting glial activation

Proinflammatory cytokines are crucial contributors to neuroinflammation in the development of chronic pain. Here, we identified il16, which encodes interleukin-16 (IL-16), as a differentially expressed gene in spinal dorsal horn of a complete Freund's Adjuvant (CFA) inflammatory pain model in mice by RNA sequencing. We further investigated whether and how IL-16 regulates pain transmission in the spinal cord and contributes to the development of inflammatory pain hypersensitivity. RNA sequencing and bioinformatics analysis revealed elevated IL-16 transcript levels in the spinal dorsal horn after CFA injection. This increase was further confirmed by qPCR, immunofluorescence, and western blotting. Knockdown of IL-16 by intrathecal injection of IL-16 siRNA not only attenuated CFA-induced mechanical and thermal pain hypersensitivity, but also inhibited enhanced c-fos expression and glial activation in the spinal dorsal horn in male mice injected with CFA. Moreover, exogenous IL-16 induced nociceptive responses and increased c-fos expression and glial activation in spinal dorsal horn. This effect was largely impaired when CD4, the binding receptor for IL-16, was inhibited. In addition, CD4 expression was upregulated in the spinal dorsal horn after CFA injection and CD4 was present in microglia and in contact with astrocytes and activated spinal neurons. Taken together, these results suggest that enhanced IL-16-CD4 signaling triggers pain and activates microglia and astrocytes in the spinal dorsal horn, thus contributing to inflammatory pain. IL-16 may serve as a promising target for the treatment of inflammatory pain.

Neck and shoulder pain and inflammatory biomarkers in plasma among forklift truck operators - A case-control study

OBJECTIVES

The aim of this study was to investigate a panel of inflammatory biomarkers in plasma from forklift truck operators (FLTOs) and healthy controls, and their relation to neck pain characteristics.

METHODS

From employees in a warehouse, 26 FLTOs were recruited and 24 healthy age- and sex-matched controls (CONs) were recruited via advertisement. The inclusion criterion for FLTOs was that they should operate reach decker and/or counterbalanced tilting mast forklift trucks. All participants were asked to answer a questionnaire covering demographic data, pain intensity numeric rating scale (NRS), anatomical spread, psychological distress, and health aspects. Pain sensitivity was measured using a pressure algometer. Blood samples were collected and analyzed for inflammatory proteins in plasma using a panel of 71 cytokines and chemokines. Multivariate data analysis including orthogonal partial least square-discriminant analysis (OPLS-DA) was performed to identify significant biomarkers.

RESULTS

Thirty percent of FLTOs reported NRS > 3 in the neck. Shoulder pain was common in 26% of the FLTOs. Pain and discomfort that most often prevented completion of activities were in the neck (20%), lower back (32%), and hips (27%). The FLTOs reported significantly (p = 0.04) higher levels of anxiety than the CON group and they had significantly lower pressure pain thresholds in the trapezius muscle on both right (p < 0.001) and left sides (p = 0.003). A significant OPLS-DA model could discriminate FLTOs from CON based on nine inflammatory proteins where the expression levels of four proteins were upregulated and five proteins were downregulated in FLTOs compared to CONs. Twenty-nine proteins correlated multivariately with pain intensity.

CONCLUSIONS

The profile of self-reported health, pain intensity, sensitivity, and plasma biomarkers can discriminate FLTOs with pain from healthy subjects. A combination of both self-reported and objective biomarker measurements can be useful for better understanding the pathophysiological mechanisms underlying work-related neck and shoulder pain.

Interleukin-17: A Putative Novel Pharmacological Target for Pathological Pain

Pathological pain imposes a huge burden on the economy and the lives of patients. At present, drugs used for the treatment of pathological pain have only modest efficacy and are also plagued by adverse effects and risk for misuse and abuse. Therefore, understanding the mechanisms of pathological pain is essential for the development of novel analgesics. Several lines of evidence indicate that interleukin-17 (IL-17) is upregulated in rodent models of pathological pain in the periphery and central nervous system. Besides, the administration of IL-17 antibody alleviated pathological pain. Moreover, IL-17 administration led to mechanical allodynia which was alleviated by the IL-17 antibody. In this review, we summarized and discussed the therapeutic potential of targeting IL-17 for pathological pain. The upregulation of IL-17 promoted the development of pathological pain by promoting neuroinflammation, enhancing the excitability of dorsal root ganglion neurons, and promoting the communication of glial cells and neurons in the spinal cord. In general, the existing research shows that IL-17 is an attractive therapeutic target for pathologic pain, but the underlying mechanisms still need to be investigated.

Transcriptome Profiling of miRNA-mRNA Interactions and Associated Mechanisms in Chemotherapy-Induced Neuropathic Pain

Chemotherapy-induced neuropathic pain (CINP) is a dose-limiting adverse event affecting 40% of chemotherapy patients. MiRNA-mRNA interaction plays an important role in various processes. However, detailed profiling of miRNA-mRNA interactions in CINP remains unclear. Here, a rat-based CINP model was established using paclitaxel, followed by nociceptive behavioral tests related to mechanical allodynia, thermal hyperalgesia, and cold allodynia. The landscape of miRNA-mRNA interaction in the spinal dorsal horn was investigated through mRNA transcriptomics and small RNA sequencing. Under CINP condition, 86 differentially expressed mRNAs and 56 miRNAs were identified. Gene Set Enrichment Analysis (GSEA), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated the activity of Odorant binding, postsynaptic specialization and synaptic density, extracellular matrix, mitochondrial matrix, retrograde endocannabinoid signaling, and GTPase activity. Protein-protein interaction (PPI), networks of circRNA-miRNA-mRNA, lncRNA-miRNA-mRNA, and TF-genes were demonstrated. We next explored the immune infiltration microenvironment and found a higher infiltration abundance of Th17 and a lower abundance of MDSC in CINP. RT-qPCR and dual-luciferase assays were used to verify the sequencing results, and single-cell analysis based on the SekSeeq database was conducted. Combined with bioinformatics analyses and experimental validations, Mpz, a protein-coding gene specifically expressed in Schwann cells, was found critical in maintaining CINP under miRNA regulation. Therefore, these data highlight the expression patterns of miRNA-mRNA, and the underlying mechanism in the spinal dorsal horn under CINP condition, and Mpz may serve as a promising therapeutic target for patients with CINP.

Experimental traumatic occlusion drives immune changes in trigeminal ganglion

We previously demonstrated that experimental traumatic occlusion (ETO) induces a long-lasting nociceptive response. These findings were associated with altered neuronal patterns and suggestive satellite glial cell activation. This study aimed to elucidate the activation of satellite glial cells following ETO in the trigeminal ganglion. Moreover, we explored the involvement of resident and infiltrating cells in trigeminal ganglion in ETO. Finally, we investigated the overexpression of purinergic signaling and the CX3CL1/CX3CR1 axis. RT-qPCR and electrophoresis showed overexpression of GFAP in the trigeminal ganglion (TG), and immunohistochemistry corroborated these findings, demonstrating SGCs activation. ELISA reveals enhanced levels of TNF-α and IL-1β in TG after 28 d of ETO. In trigeminal ganglia, ETO groups improved the release of CX3CL1, and immunohistochemistry showed higher CX3CR1+ -immunoreactive cells in ETO groups. Immunohistochemistry and electrophoresis of the P2X7 receptor were found in ETO groups. The mRNA levels of IBA1 are upregulated in the 0.7-mm ETO group, while immunohistochemistry showed higher IBA1+ -immunoreactive cells in both ETO groups. The expression of CD68 by electrophoresis and immunohistochemistry was observed in the ETO groups. For last, ELISA revealed increased levels of IL-6, IL-12, and CCL2 in the TG of ETO groups. Furthermore, the mRNA expression revealed augmented transcription factors and cytokines associated with lymphocyte activation, such as RORγt, IL-17, Tbet, IFNγ, FOXP3, and IL-10. The findings of this study suggested that ETO activates SGCs in TG, and purinergic signaling and CX3CL1/CX3CR1 axis were upregulated. We uncovered the involvement of a distinct subtype of macrophages, named sensory neuron-associated macrophage activation (sNMAs), and detected an expanded number of infiltrated macrophages onto TG. These findings indicate that ETO induces chronic/persistent immune response.

Inhibition of Nuclear Receptor Related Orphan Receptor γ Ameliorates Mechanical Hypersensitivity Through the Suppression of Spinal Microglial Activation

Microglia are crucial in induction of central sensitization under a chronic pain state. Therefore, control of microglial activity is important to ameliorate nociceptive hypersensitivity. The nuclear receptor retinoic acid related orphan receptor γ (RORγ) contributes to the regulation of inflammation-related gene transcription in some immune cells, including T cells and macrophages. Their role and function in regulation of microglial activity and nociceptive transduction have yet to be elaborated. Treatment of cultured microglia with specific RORγ inverse agonists, SR2211 or GSK2981278, significantly suppressed lipopolysaccharide (LPS)-induced mRNA expression of pronociceptive molecules interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor (TNF). Intrathecal treatment of naïve male mice with LPS markedly induced mechanical hypersensitivity and upregulation of ionized calcium-biding adaptor molecule (Iba1) in the spinal dorsal horn, indicating microglial activation. In addition, intrathecal treatment with LPS significantly induced mRNA upregulation of IL-1β and IL-6 in the spinal dorsal horn. These responses were prevented by intrathecal pretreatment with SR2211. In addition, intrathecal administration of SR2211 significantly ameliorated established mechanical hypersensitivity and upregulation of Iba1 immunoreactivity in the spinal dorsal horn of male mice following peripheral sciatic nerve injury. The current findings demonstrate that blockade of RORγ in spinal microglia exerts anti-inflammatory effects, and that RORγ may be an appropriate target for the treatment of chronic pain.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

Interleukin-17 is involved in neuropathic pain and spinal synapse plasticity on mice

Neuropathic pain seriously affects people's life, but its mechanism is not clear. Interleukin-17 (IL-17) is a proinflammation cytokine and involved in pain regulation. Our previous study found that IL-17 markedly enhanced the excitatory activity of spinal dorsal neurons in mice spinal slices. The present study attempts to explore if IL-17 contributes to neuropathic pain and spinal synapse plasticity. A model of spared nerve injury (SNI) was established in C57BL/6 J mice and IL-17a mutant mice. The pain-like behaviors was tested by von Frey test and dynamic mechanical stimuli, and the expression of IL-17 and its receptor, IL-17RA, was detected by immunohistochemical staining. C-fiber evoked field potentials were recorded in vivo. In the spinal dorsal horn, IL-17 predominantly expressed in the superficial spinal astrocytes and IL-17RA expressed mostly in neurons and slightly in astrocytes. The SNI-induced static and dynamic allodynia was significantly prevented by pretreatment of neutralizing IL-17 antibody (intrathecal injection, 2 μg/10 μL) and attenuated in IL-17a mutant mice. Post-treatment of IL-17 neutralizing antibody also partially relieved the established mechanical allodynia. Moreover, spinal long-term potentiation (LTP) of C-fiber evoked field potentials, a substrate for central sensitization, was suppressed by IL-17 neutralizing antibody. Intrathecal injection of IL-17 recombinant protein (0.2 μg/10 μL) mimicked the mechanical allodynia and facilitated the spinal LTP. These data implied that IL-17 in the spinal cord played a crucial role in neuropathic pain and central sensitization.

PbO nanoparticles increase the expression of ICAM-1 and VCAM-1 by increasing reactive oxygen species production in choroid plexus

PbO nanoparticles (nano-PbO) are widely used in the production of electrode materials, but exposure to them can cause brain damage. The first barrier preventing nano-PbO from entering the brain is the choroid plexus. However, the effect of nano-PbO on the choroid plexus remains unclear. Thus, the purpose of this study was to investigate the effect of nano-PbO exposure on lymphocyte cells infiltration, the adhesion protein of the choroid plexus as well as the role of reactive oxygen species (ROS) during the process. Results showed that nano-PbO exposure increased the percentage of lymphocyte cells in the brain and upregulated the expression of surface adhesion proteins, including intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in choroid plexus. Meanwhile, nano-PbO treatment also resulted in the increase of intercellular ROS production, and significantly decrease glutathione (GSH) content, glutathione peroxidase (GSH-PX) activity, and superoxide dismutase (SOD) activity in Z310 cells beside the increase of ICAM and VCAM-1 expression. Treatment with ROS inhibitor N-acetylcysteine (NAC) significantly downregulated the expression of ICAM-1 and VCAM-1expression. In conclusion, exposure to nano-PbO increases the expression of ICAM-1 and VCAM-1 through oxidative stress, which may contribute to peripheral lymphocyte cells infiltration into the brain.

STING Contributes to Cancer-Induced Bone Pain by Promoting M1 Polarization of Microglia in the Medial Prefrontal Cortex

The medial prefrontal cortex (mPFC) is the main cortical area for processing both sensory and affective aspects of pain. Recently, mPFC was reported to participate in cancer-induced bone pain (CIBP) via the mechanism of central inflammation. STING is a key component of neuroinflammation in the central neuron system by activating downstream TBK1 and NF-κB signaling pathways. We aimed to investigate whether STING regulated neuroinflammation in the mPFC in rat models of CIBP. It is worth noting that we found a significant upregulation of STING in the mPFC after CIBP, accompanied by activation of TBK1 and NF-κB signaling pathways. In addition, pain and anxiety-like behaviors were alleviated by intraperitoneal injection of the STING inhibitor C-176. Furthermore, in microglia GMI-R1 cells, C-176 reversed LPS-induced M1 polarization. Collectively, this evidence indicated that STING may contribute to cancer-induced bone pain by activating TBK1 and NF-κB, and by promoting M1 polarization of microglia in the mPFC.

Interleukin-17 as a potential therapeutic target for chronic pain

Chronic pain remains to be a clinical challenge and is recognized as a major health problem with varying impacts on quality of life. Currently, the first-line therapy for chronic pain is opioids, which are often accompanied by unwanted psychoactive side effects. Thus, new and effective treatments for chronic pain are urgently needed and eagerly pursued. Inflammatory cytokines, especially interleukin-17 (IL-17), are reportedly potential therapeutic targets owing to their pivotal role in chronic pain from the neuroinflammation perspective. Recently, substantial evidence confirmed that IL-17 and IL-17 receptors (IL-17Rs) were increased in neuropathic, inflammatory, and cancer pain models. Notably, IL-17/IL-17R antibodies also reportedly relieve or cure inflammatory- and pain-related diseases. However, existing studies have reported controversial results regarding IL-17/IL-17Rs as potential therapeutic targets in diverse animal models of chronic pain. In this review, we present a summary of published studies and discuss the evidence, from basic to clinical to research, regarding the role and mechanism of action between IL-17 and diverse kinds of chronic pain in animal models and clinical patients. Furthermore, we evaluated IL-17-based therapy as a potential therapeutic strategy for inflammatory- and pain-related disease. Importantly, we also discussed clinical trials of IL-17/IL-17R targeting monoclonal antibodies. Overall, we found that IL-17 is a potential therapeutic target for chronic pain from the perspective of neuroinflammation.

The Clinical Effect and Mechanism of Prostant on Urinary Retention and Anal Pain

Anal pain and urinary retention are the two most outstanding complications of the procedure for prolapse and hemorrhoids (PPH) surgery. This study intended to assess the clinical effect and mechanism of Prostant on urinary retention and anal pain after the PPH. Here, 30 patients received PPH surgery. The role and mechanism of Prostant in patients and mice with urinary retention and anal pain were evaluated. ANOVA tests were executed and differences between groups were regarded as statistically significant when p < 0.05. Prostant effectively improved the urination status, lower abdomen symptoms, time to urinate and score of VAS, and the reduction of TNF-α and IL-6. Similarly, Prostant can ameliorate the outcome of urodynamics in urinary retention mice. Mechanically, Prostant reversed the urinary retention-elevated the serum level of hs-CRP and TNF-α, reduction of IL-2, imbalance of Treg/Th17, and level of JAK2 and phosphorylated STAT3. Besides, Prostant ameliorated the pain as shown by the reduction of writhing response, and the elevation of threshold of pain and degree of swelling. Moreover, Prostant antagonized the pain-induced dysregulation of Treg/Th17. Therefore, Prostant can treat patients and mice with anal pain and urinary retention by modulating the balance of Th17/Treg to regulate the secretion and production of inflammatory factors. We hope our results can establish a scientific treatment approach for solving anal pain and urinary retention after PPH surgery of mixed hemorrhoids.

Upregulation of Spinal miR-155-5p Contributes to Mechanical Hyperalgesia by Promoting Inflammatory Activation of Microglia in Bone Cancer Pain Rats

Bone cancer pain (BCP) seriously deteriorates the life quality of patients, but its underlying mechanism is still unclear. Spinal microRNAs might contribute to the development of BCP and the role of microglial activation is controversial. In this study, we established a BCP model by injecting Walker 256 breast carcinoma cells into the tibial intramedullary cavity of rats and significant hyperalgesia was observed in the BCP rats. The lumbar spinal cords were harvested to perform RNA sequencing (RNA-seq), and 31 differentially expressed miRNAs (26 upregulated and 5 downregulated) were identified in the BCP rats. Among them, miR-155-5p was significantly upregulated in the BCP rats. Spinal microglial activation was observed during BCP development. miR-155-5p could be expressed in spinal microglia and was significantly upregulated in microglia treated with lipopolysaccharide (LPS) in vitro. Serum/glucocorticoid regulated kinase family member 3 (Sgk3) was predicted to be the possible downstream target of miR-155-5p and this was confirmed using a dual-luciferase reporter assay in vitro. The inhibition of miR-155-5p restored Sgk3-expression-attenuated microglial activation and alleviated hyperalgesia in the BCP rats. In conclusion, spinal miR-155-5p/Sgk3/microglial activation might play an important role in BCP pathogenesis.

Luteolin relieves lung cancer-induced bone pain by inhibiting NLRP3 inflammasomes and glial activation in the spinal dorsal horn in mice

BACKGROUND

Bone cancer pain (BCP) is one of the most severe complications in cancer patients. However, the pharmacological therapeutic approaches are limited. Luteolin, a major component of flavones, is widely distributed in plants and plays a critical role in the antinociceptive effects, but whether luteolin could alleviate cancer pain and its underlying mechanisms are not known.

HYPOTHESIS/PURPOSE

This study investigated the molecular mechanisms by which luteolin reduced BCP.

METHODS

Behavioral, pharmacological, immunohistochemical, and biochemical approaches were used to investigate the effect of luteolin on BCP.

RESULTS

Luteolin treatment ameliorated Lewis lung cancer (LLC)-induced bone pain in mice in a dose-dependent manner. Luteolin treatment could inhibit the activation of neurons, glial cells, and NOD-like receptor protein 3 (NLRP3) inflammasomes in the dorsal spinal cord in the BCP mouse model. Furthermore, phosphorylated p-38 mitogen-activated protein kinase (MAPK) in the spinal dorsal horn (SDH) was suppressed by luteolin treatment that could influence the analgesic and glial inhibition effects of luteolin.

CONCLUSION

Our results demonstrated that luteolin inhibited neuroinflammation by obstructing glial cell and NLRP3 inflammasome activation via modulating p38 MAPK activity in SDH, ultimately improving LLC-induced BCP.

Remote Limb Ischemic Postconditioning Protects Against Ischemic Stroke by Promoting Regulatory T Cells Thriving

Background Remote limb ischemic postconditioning (RLIPoC) has been demonstrated to protect against ischemic stroke. However, the underlying mechanisms of RLIPoC mediating cross-organ protection remain to be fully elucidated. Methods and Results Ischemic stroke was induced by middle cerebral artery occlusion for 60 minutes. RLIPoC was performed with 3 cycles of 10-minute ischemia followed by 10-minute reperfusion of the bilateral femoral arteries immediately after middle cerebral artery reperfusion. The percentage of regulatory T cells (Tregs) in the spleen, blood, and brain was detected using flow cytometry, and the number of Tregs in the ischemic hemisphere was counted using transgenic mice with an enhanced green fluorescent protein-tagged Foxp3. Furthermore, the metabolic status was monitored dynamically using a multispectral optical imaging system. The Tregs were conditionally depleted in the depletion of Treg transgenic mice after the injection of the diphtheria toxin. The inflammatory response and neuronal apoptosis were investigated using immunofluorescent staining. Infarct volume and neurological deficits were evaluated using magnetic resonance imaging and the modified neurological severity score, respectively. The results showed that RLIPoC substantially reduced infarct volume, improved neurological function, and significantly increased Tregs in the spleen, blood, and ischemic hemisphere after middle cerebral artery occlusion. RLIPoC was followed by subsequent alteration in metabolites, such as flavin adenine dinucleotide and nicotinamide adenine dinucleotide hydrate, both in RLIPoC-conducted local tissues and circulating blood. Furthermore, nicotinamide adenine dinucleotide hydrate can mimic RLIPoC in increasing Tregs. Conversely, the depletion of Tregs using depletion of Treg mice compromised the neuroprotective effects conferred by RLIPoC. Conclusions RLIPoC protects against ischemic brain injury, at least in part by activating and maintaining the Tregs through the nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide hydrate pathway.

Transcriptomic Analysis of Long Noncoding RNA and mRNA Expression Profiles in the Amygdala of Rats with Bone Cancer Pain-Depression Comorbidity

Bone cancer pain (BCP)–depression comorbidity has become a complex clinical problem during cancer treatment; however, its underlying molecular mechanisms have not been clarified. Several long noncoding RNAs (lncRNAs) have been demonstrated to be promising therapeutic targets in depression, but research on the role of lncRNAs in BCP–depression comorbidity has been limited. Therefore, high-throughput RNA sequencing was performed to detect differentially expressed profiles in the amygdala of a BCP–depression rat model in this study. We detected 330 differentially expressed mRNAs (DEmRNAs) and 78 differentially expressed lncRNAs (DElncRNAs) in the BCP–depression comorbidity model and then verified the expression of six DEmRNAs and six DElncRNAs with the greatest degrees of difference by RT-qPCR. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that differentially expressed genes were strongly enriched in inflammatory and immunologic systemic responses. Then the nuclear factor kappa B (NF-κB) signaling pathway and the Th17 differentiation pathway showed significant differences, as determined by Western blot analysis. Finally, we constructed a protein–protein interaction (PPI) network to explore the potential regulatory mechanism of DEmRNAs. In conclusion, our study reveals a new resource for the understanding of dysregulated lncRNAs and mRNAs in BCP–depression comorbidity and provides novel potential therapeutic targets for further approaches.

Recent advances in the role of Th17/Treg cells in tumor immunity and tumor therapy

Th17 and Treg cells play an important role in regulating tissue inflammation and maintaining the stability of the immune system. They regulate inflammatory responses, participate in the occurrence and development of autoimmune diseases and tumors, and determine the disease progress. Malignant tumor is one of the diseases with the highest mortality rate in the world. However, the efficacy of traditional treatment is limited, so it is necessary to find safe and efficient treatment methods. Studies have shown that the balance of Th17/Treg cells plays a critical role in tumor progression. In this paper, we review the antitumor and tumor-suppressing effects of Th17/Treg cells, and new strategies for tumor therapy, combined with new research hotspots such as immune checkpoint therapy, miRNA-related gene therapy, and metabolic pathway regulation of Th17/Treg cell differentiation and tumor generation. The synergistic therapy is expected to be widely used in the future clinical practice, providing a new choice for the prevention and treatment of malignant tumors.

Glial and neuroimmune cell choreography in sexually dimorphic pain signaling

Chronic pain is a major global health issue that affects all populations regardless of sex, age, ethnicity/race, or country of origin, leading to persistent physical and emotional distress and to the loss of patients' autonomy and quality of life. Despite tremendous efforts in the elucidation of the mechanisms contributing to the pathogenesis of chronic pain, the identification of new potential pain targets, and the development of novel analgesics, the pharmacological treatment options available for pain management remain limited, and most novel pain medications have failed to achieve advanced clinical development, leaving many patients with unbearable and undermanaged pain. Sex-specific susceptibility to chronic pain conditions as well as sex differences in pain sensitivity, pain tolerance and analgesic efficacy are increasingly recognized in the literature and have thus prompted scientists to seek mechanistic explanations. Hence, recent findings have highlighted that the signaling mechanisms underlying pain hypersensitivity are sexually dimorphic, which sheds light on the importance of conducting preclinical and clinical pain research on both sexes and of developing sex-specific pain medications. This review thus focuses on the clinical and preclinical evidence supporting the existence of sex differences in pain neurobiology. Attention is drawn to the sexually dimorphic role of glial and immune cells, which are both recognized as key players in neuroglial maladaptive plasticity at the origin of the transition from acute pain to chronic pathological pain. Growing evidence notably attributes to microglial cells a pivotal role in the sexually dimorphic pain phenotype and in the sexually dimorphic analgesic efficacy of opioids. This review also summarizes the recent advances in understanding the pathobiology underpinning the development of pain hypersensitivity in both males and females in different types of pain conditions, with particular emphasis on the mechanistic signaling pathways driving sexually dimorphic pain responses.

Spinal cannabinoid receptor 2 activation reduces hypersensitivity associated with bone cancer pain and improves the integrity of the blood-spinal cord barrier

Background

Disruption of the blood–spinal cord barrier (BSCB) can facilitate inflammation that results in pain hypersensitivity. Proinflammatory cytokines produced by activated microglia and astrocytes damage the BSCB. This study aims to explore whether the BSCB is damaged in the bone cancer pain (BCP) model and to investigate a potential role and mechanism of JWH015 ((2-methyl-1-propyl-1H-indol-3-yl)−1-naphthalenylmethanone), a selective cannabinoid receptor 2 (CB2R) agonist, in preserving the BSCB integrity in the BCP model.

Methods

We used a male mouse model of BCP. Pain hypersensitivity was measured over time. Evans blue dye extravasation, transmission electron microscopy and Western blotting were performed to investigate the permeability and structural integrity of the BSCB. Immunofluorescence staining and western blotting were used to investigate the effect of JWH015 on the activation of glial cells and the levels of proinflammatory cytokines.

Results

A single intrathecal injection of JWH015 ameliorated pain hypersensitivity, the BSCB disruption and microglia and astrocyte activation. Decreases in the expression of ZO-1 and claudin-5 were partially restored by JWH015. The levels of the proinflammatory cytokines interleukin-1β and tumor necrosis factor-α and the enzyme MMP9 were reduced by JWH015. However, all effects were prevented by pretreatment with a CB2R-selective antagonist, AM630 ((6-iodo-2-methyl-1-(2-morpholinoethyl)−1H-indol-3-yl)(4-methoxyphenyl)methanone).

Conclusions

JWH015 alleviates neuroinflammation and maintains the BSCB integrity and permeability in a mouse model of BCP, which is probably mediated by inhibiting glial cells activation. This study reveals the new analgesic mechanism of JWH015 on BCP and provides a perspective to explore novel drugs that target the BSCB to control BCP.

Psychoneuroimmunology goes East: Development of the PNIRSChina affiliate and its expansion into PNIRSAsia-Pacific

The Psychoneuroimmunology Research Society (PNIRS) created an official Chinese regional affiliate in 2012, designated PNIRS_China. Now, just eight years later, the program has been so successful in advancing the science of psychoneuroimmunology that it has expanded to the whole of Asia-Oceania. In 2017, PNIRS_China became PNIRS_Asia-Pacific. Between 2012 and 2019, this outreach affiliate of PNIRS organized seven symposia at major scientific meetings in China as well as nine others in Taiwan, Japan, South Korea, Australia and New Zealand. This paper summarizes the remarkable growth of PNIRS_Asia-Pacific. Here, regional experts who have been instrumental in organizing these PNIRS_Asia-Pacific symposia briefly review and share their views about the past, present and future state of psychoneuroimmunology research in China, Taiwan, Australia and Japan. The newest initiative of PNIRS_Asia-Pacific is connecting Asia-Pacific laboratories with those in Western countries through a simple web-based registration system. These efforts not only contribute to the efforts of PNIRS to serve a truly global scientific society but also to answer the imperative call of increasing diversity in our science.

B14 ameliorates bone cancer pain through downregulating spinal interleukin-1β via suppressing neuron JAK2/STAT3 pathway

Curcumin has several pharmacological properties such as anti-inflammatory, antioxidant, and neuroprotective activities. B14 is a curcumin analogue and is considered to be a more potent compound with preserved pharmacodynamic activities. Based on the previous research studies, janus-activated kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway plays a remarkable role in inflammation, chronic pain, and even contributes to the pathogenesis of neuropathic pain. Pro-inflammatory cytokines interleukin-1β is a downstream factor of JAK2/STAT3 signal transition pathway, which participates in neuron injury and inflammation. We hypothesized that this signal transition pathway played an indispensable role in bone cancer pain. We herein established a bone cancer pain model to monitor the variation of JAK2/STAT3 signal transduction pathway and measured the effect of B14. The results in bone cancer pain model showed that (i) the levels of interleukin-1β were elevated, and the ratios of p-JAK2/JAK2 and p-STAT3/STAT3 were increased; (ii) double immunostaining showed that p-JAK2, p-STAT3, and interleukin-1β were colocalized primarily with neurons, rather than with astrocytes or microglial cells; (iii) B14 injection (intraperitoneally) markedly eased bone cancer pain; (iv) Western blotting showed that B14 injection lowered p-JAK2, p-STAT3, and interleukin-1β levels, meanwhile the ratios of p-JAK2/JAK2 and p-STAT3/STAT3 was reduced; (v) immunofluorescence results also confirmed decreased levels of p-JAK2, p-STAT3, and interleukin-1β in B14 treatment group. These findings suggested that B14 injection attenuated bone cancer pain in rats. This intervention inhibited JAK2/STAT3 cascade activation, downregulating interleukin-1β expression in spinal dorsal horn.

The endocannabinoid system: Novel targets for treating cancer induced bone pain

Treating Cancer-induced bone pain (CIBP) continues to be a major clinical challenge and underlying mechanisms of CIBP remain unclear. Recently, emerging body of evidence suggested the endocannabinoid system (ECS) may play essential roles in CIBP. Here, we summarized the current understanding of the antinociceptive mechanisms of endocannabinoids in CIBP and discussed the beneficial effects of endocannabinoid for CIBP treatment. Targeting non-selective cannabinoid 1 receptors or selective cannabinoid 2 receptors, and modulation of peripheral AEA and 2-AG, as well as the inhibition the function of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have produced analgesic effects in animal models of CIBP. Management of ECS therefore appears to be a promising way for the treatment of CIBP in terms of efficacy and safety. Further clinical studies are encouraged to confirm the possible translation to humans of the very promising results already obtained in the preclinical studies.

T Cells as an Emerging Target for Chronic Pain Therapy

The immune system is critically involved in the development and maintenance of chronic pain. However, T cells, one of the main regulators of the immune response, have only recently become a focus of investigations on chronic pain pathophysiology. Emerging clinical data suggest that patients with chronic pain have a different phenotypic profile of circulating T cells compared to controls. At the preclinical level, findings on the function of T cells are mixed and differ between nerve injury, chemotherapy, and inflammatory models of persistent pain. Depending on the type of injury, the subset of T cells and the sex of the animal, T cells may contribute to the onset and/or the resolution of pain, underlining T cells as a major player in the transition from acute to chronic pain. Specific T cell subsets release mediators such as cytokines and endogenous opioid peptides that can promote, suppress, or even resolve pain. Inhibiting the pain-promoting functions of T cells and/or enhancing the beneficial effects of pro-resolution T cells may offer new disease-modifying strategies for the treatment of chronic pain, a critical need in view of the current opioid crisis.