IL-33/ST2 signaling contributes to radicular pain by modulating MAPK and NF-κB activation and inflammatory mediator expression in the spinal cord in rat models of noncompressive lumber disk herniation

The intriguing role of IL33/ST2 axis signaling in oral diseases - A systematic review

PURPOSE

Oral diseases act as a silent epidemic, and the pathogenetic role of interleukin-33/ suppression of tumorigenicity-2 axis (IL-33/ST2) remains unclear due to a lack of literature. This review has attempted to highlight the importance of this axis in oral diseases, which may be helpful in developing therapeutic modalities required to halt disease progression.

MATERIALS AND METHODS

A thorough search was conducted using various databases. Original research articles that assessed both IL-33 and ST2 levels in oral diseases using different techniques were included in the review. The risk of bias for each study was analyzed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool and Review Manager 5.4 was used to output the results.

RESULTS

In the qualitative data synthesis we included 13 published articles. The most commonly used method was serum estimation, while methods with optimistic results were saliva, real-time quantitative polymerase chain reaction and immunohistochemistry. The predominant mechanism of action was nuclear factor kappa B signaling and type 2 immune response. However, salivary gland epithelial cell activation, activation of mast cells, type 1 immune response, and upregulated angiogenesis are crucial in mediating IL-33/ST2 signaling in oral diseases.

CONCLUSIONS

Accumulating evidence demonstrates that the IL-33/ST2 axis is a fundamental pathogenetic mechanism of oral diseases of inflammatory, autoimmune, or neoplastic origin.

Acupuncture for radicular pain: a review of analgesic mechanism

Radicular pain, a common and complex form of neuropathic pain, presents significant challenges in treatment. Acupuncture, a therapy originating from ancient traditional Chinese medicine and widely utilized for various pain types, including radicular pain, has shown promising outcomes in the management of lumbar radicular pain, cervical radicular pain, and radicular pain due to spinal stenosis. Despite its efficacy, the exact mechanisms through which acupuncture achieves analgesia are not fully elucidated and are the subject of ongoing research. This review sheds light on the current understanding of the analgesic mechanisms of acupuncture for radicular pain, offering valuable perspectives for both clinical application and basic scientific research. Acupuncture is postulated to relieve radicular pain by several mechanisms: peripherally, it reduces muscle spasms, lessens mechanical pressure on nerve roots, and improves microcirculation; at the molecular level, it inhibits the HMGB1/RAGE and TLR4/NF-κB signaling pathways, thereby decreasing the release of pro-inflammatory cytokines; within the spinal cord, it influences synaptic plasticity; and centrally, it modulates brain function, particularly affecting the medial prefrontal cortex, anterior cingulate cortex, and thalamus within the default mode network. By acting across these diverse biological domains, acupuncture presents an effective treatment modality for radicular pain, and deepening our understanding of the underlying mechanisms regarding analgesia for radicular pain is crucial for enhancing its clinical efficacy and advancement in pain management.

Celecoxib attenuates interleukin 33-induced expression of vascular cell adhesion molecule-1 in human ovarian endometriotic stromal cells

OBJECTIVE

Endometriosis is an estrogen-dependent chronic inflammatory disease in women of reproductive age. A review of the literature revealed that cytokines and inflammatory factors are associated with endometriosis-associated infertility. Interleukin 33 (IL-33) is a strong inducer of other pro-inflammatory cytokines. Vascular cell adhesion molecule-1 (VCAM-1) plays a central role in recruiting inflammatory cells, whose expression facilitates leukocyte adhesion and is rapidly induced by pro-inflammatory cytokines. Many studies have indicated that VCAM-1 expression is high in endometriosis; however, whether the expression of VCAM-1 is related to IL-33 is unclear.

MATERIALS AND METHODS

Human ovarian endometriotic stromal cells (hOVEN-SCs) were treated with IL-33 to enable investigation of cell characterization, gene and protein expression, and signal pathways. Proliferation potential was measured using an MTT assay. Gene expression was analyzed using reverse transcription-polymerase chain reaction. Protein expression assay was performed using western blot analysis.

RESULTS

This study investigated the effects of IL-33 on VCAM-1 and COX-2 expression in hOVEN-SCs. First, the results revealed that the IL-33/ST2/mitogen-activated protein kinase (MAPK) signaling pathway could increase the expression of VCAM-1 and COX-2 in hOVEN-SCs. Second, we discovered that COX-2 expression was essential for IL-33-induced VCAM-1 expression because the effects could be negated through NS398, a selective COX-2 inhibitor. Finally, treatment of IL-33-treated hOVEN-SCs with celecoxib significantly and dose-responsively decreased VCAM-1 expression.

CONCLUSION

Taken together, these results indicate that IL-33 can upregulate VCAM-1 expression in hOVEN-SCs through the IL-33/ST2/MAPK/COX-2 signaling pathway and thereby contribute to endometriosis.

Electroacupuncture prevents the development or establishment of chronic pain via IL-33/ST2 signaling in hyperalgesic priming model rats

BACKGROUND

Chronic pain is acomplexhealth issue. Compared to acute pain, which has a protective value, chronic pain is defined as persistent pain after tissue injury. Few clinical advances have been made to prevent the transition from acute to chronic pain. Electroacupuncture (EA), the most common form of acupuncture, is widely used in clinical practice to relieve pain.

METHODS

The hyperalgesic priming model, established via a carrageenan injection followed by a prostaglandin E2 injection, was used to investigate the development or establishment of chronic pain. We observed the hyperalgesic effect of EA on rats and investigated the expression p38 mitogen-activated protein kinase, interleukin-33 (IL-33), and its receptor ST2 in astrocytes in the L4-L6 spinal cord dorsal horns (SDHs) after EA. The IL-33/ST2 signaling pathway in SDH is associated with the development of chronic pain.

RESULTS

EA can reverse the pain threshold in hyperalgesic priming model rats and regulates the expression of phosphorylated p38, IL-33, and ST2 in astrocytes in the L4-L6 SDHs. We discovered that EA raises the pain threshold. This suggests that EA can prevent the development or establishment of chronic pain by inhibiting IL-33/ST2 signaling in the lower central nervous system.

CONCLUSIONS

EA can alleviate the development or establishment of chronic pain by modulating IL-33/ST2 signaling in SDHs. Our findings will help clinicians understand the mechanisms of EA analgesia.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain

BACKGROUNDS

Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain.

METHODS

Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM).

RESULTS

We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration.

CONCLUSIONS

Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

Glial Cells of the Central Nervous System: A Potential Target in Chronic Prostatitis/Chronic Pelvic Pain Syndrome

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is one of the most common diseases of the male urological system while the etiology and treatment of CP/CPPS remain a thorny issue. Cumulative research suggested a potentially important role of glial cells in CP/CPPS. This narrative review retrospected literature and grasped the research process about glial cells and CP/CPPS. Three types of glial cells showed a crucial connection with general pain and psychosocial symptoms. Microglia might also be involved in lower urinary tract symptoms. Only microglia and astrocytes have been studied in the animal model of CP/CPPS. Activated microglia and reactive astrocytes were found to be involved in both pain and psychosocial symptoms of CP/CPPS. The possible mechanism might be to mediate the production of some inflammatory mediators and their interaction with neurons. Glial cells provide a new insight to understand the cause of complex symptoms of CP/CPPS and might become a novel target to develop new treatment options. However, the activation and action mechanism of glial cells in CP/CPPS needs to be further explored.

Exosomal circRNA-001264 promotes AML immunosuppression through induction of M2-like macrophages and PD-L1 overexpression

Exosomes can help to effectively regulate the crosstalk between cancer cells and normal cells in the tumor microenvironment. They also regulate cancer cell proliferation and apoptosis by virtue of their cargo molecules. Transmission electron microscopy (TEM) together with differential ultracentrifugation served for verifying the presence of exosomes. In vivo and in vitro assays served for determining the role of exosomal circ_001264. RNA pull-down and dual-luciferase reporter assays assisted in the classification of the mechanism of exosomal circ_001264-mediated regulation of the crosstalk between Acute myeloid leukemia (AML) cells and M2 macrophages. Furthermore, we adopted a programmed death ligand 1 antibody (aPD-L1) in combination with exosomal circ_001264 siRNA for antitumor treatment in vitro and in vivo mouse models served for validating the in vivo outcomes. Out study illustrated the aberrant overexpression of circ_001264 in AML patients and its correlation with poor patient prognosis. AML cell-derived exosomal circ_001264 regulated the RAF1 expression and activated the p38-STAT3 signaling pathway, thereby inducing the M2 macrophage polarization. Polarized M2 macrophages can induce PD-L1 overexpression by secreting PD-L1. Here, a programmed death ligand (aPD-L1) was adopted for preventing the immunosuppression, which was able to achieve the desired therapeutic effect at the tumor site. Indeed, in the mouse model, leukemia tumor load decreased remarkably in the exosomal circ_001264 siRNA plus aPD-L1 combination group. Taken together, our study contributed to a theoretical basis for AML treatment. The co-administration of exosomal circ_001264 siRNA and aPD-L1 exhibited an obvious anti-cancer effectiveness in AML.

IL-33/ST2 Signaling in the Pathogenesis of Chronic Pain and Itch

Interleukin-33 (IL-33) is an inflammatory factor with an extensive range of biological effects and pleiotropic roles in diseases. Evidence suggests that IL-33 and its receptor ST2 play a pivotal role in chronic pain and itch at the level of primary sensory neurons, the spinal cord, and the brain. In this review, we outline an evolving understanding of the roles and mechanisms of IL-33 in chronic pathological pain, including inflammatory, neuropathic, and cancer, and chronic pruritus, such as allergic contact dermatitis, atopic dermatitis, and dry skin. Understanding the key roles of IL-33/ST2 signaling may provide exciting insights into the mechanisms of chronic pain and itch and lead to new clues for therapeutic approaches to the resolution of chronic pain and itch.

IL-33/ST2 signaling in pain and itch: Cellular and molecular mechanisms and therapeutic potentials

Pain is a cardinal feature of many diseases. Chronic pain poses heavy burdens to the suffering patients, both physically and mentally. However, current mainstream medications for chronic pain, including opioids, antidepressants and non-steroid anti-inflammatory drugs are sometimes inefficient for chronic pain management and may cause side effects that limit long term usage. IL-33 belongs to IL-1 cytokine family and it exerts biological activities through binding to its specific receptor ST2. IL-33/ST2 signaling is very important in both innate and adaptive immunity. Emerging evidence indicates IL-33/ST2 signaling regulates pain in both immune and somatosensory systems through promoting neuro-immune or neuron-glia crosstalk, neuroinflammation and neuronal hyperexcitability. Some very latest studies indicate a vital part of IL-33/ST2 in mediating chronic itch. This work aims to overview the existing knowledge regarding the mechanisms of IL-33/ST2 involvement in pain and itch conditions, considering their potential similarities. We also summarized some key findings obtained from clinical studies. The targeting of IL-33/ST2 signaling holds promise for the development of novel therapeutic modalities in the management of pain and itch.

IL-33/ST2 axis of human amnion fibroblasts participates in inflammatory reactions at parturition

BACKGROUND

Inflammation of the fetal membranes is an indispensable event of labor onset at both term and preterm birth. Interleukin-33 (IL-33) is known to participate in inflammation via ST2 (suppression of tumorigenicity 2) receptor as an inflammatory cytokine. However, it remains unknown whether IL-33/ST2 axis exists in human fetal membranes to promote inflammatory reactions in parturition.

METHODS

The presence of IL-33 and ST2 and their changes at parturition were examined with transcriptomic sequencing, quantitative real-time polymerase chain reaction, Western blotting or immunohistochemistry in human amnion obtained from term and preterm birth with or without labor. Cultured primary human amnion fibroblasts were utilized to investigate the regulation and the role of IL-33/ST2 axis in the inflammation reactions. A mouse model was used to further study the role of IL-33 in parturition.

RESULTS

Although IL-33 and ST2 expression were detected in both epithelial and fibroblast cells of human amnion, they are more abundant in amnion fibroblasts. Their abundance increased significantly in the amnion at both term and preterm birth with labor. Lipopolysaccharide, serum amyloid A1 and IL-1β, the inflammatory mediators pertinent to labor onset, could all induce IL-33 expression through NF-κB activation in human amnion fibroblasts. In turn, via ST2 receptor, IL-33 induced the production of IL-1β, IL-6 and PGE2 in human amnion fibroblasts via the MAPKs-NF-κB pathway. Moreover, IL-33 administration induced preterm birth in mice.

CONCLUSION

IL-33/ST2 axis is present in human amnion fibroblasts, which is activated in both term and preterm labor. Activation of this axis leads to increased production of inflammatory factors pertinent to parturition, and results in preterm birth. Targeting the IL-33/ST2 axis may have potential value in the treatment of preterm birth.

Identification of novel candidate targets for suppressing ovarian cancer progression through IL-33/ST2 axis components using the system biology approach

Background: Cancer-associated fibroblasts (CAFs) of ovarian cancer (OvC) are the most prevalent element of the tumor microenvironment (TM). By promoting angiogenesis, immunological suppression, and invasion, CAFs speed up the growth of tumors by changing the extracellular matrix's structure and composition and/or initiating the epithelial cells (EPT). IL-33/ST2 signaling has drawn a lot of attention since it acts as a pro-tumor alarmin and encourages spread by altering TM. Methods: Differentially expressed genes (DEGs) of the OvC tumor microenvironment were found in the GEO database, qRT-PCR, western blotting, and immunohistochemistry, and their presence and changes in healthy and tumor tissue content were examined. Primary cultures of healthy fibroblasts and CAFs obtained from healthy and tumor tissues retrieved from OvC samples were used for in vitro and in vivo investigations. Cultured primary human CAFs were utilized to investigate the regulation and the IL-33/ST2 axis role in the inflammation reactions. Results: Although ST2 and IL-33 expression was detected in both epithelial (EPT) and fibroblast cells of ovarian cancer, they are more abundant in CAFs. Lipopolysaccharides, serum amyloid A1, and IL-1β, the inflammatory mediators, could all induce IL-33 expression through NF-κB activation in human CAFs. In turn, via the ST2 receptor, IL-33 affected the production of IL-6, IL-1β, and PTGS2 in human CAFs via the MAPKs-NF-κB pathway. Conclusion: Our findings suggest that IL-33/ST2 is affected by the interaction of CAFs and epithelial cells inside the tumor microenvironment. Activation of this axis leads to increased expression of inflammatory factors in tumor CAFs and EPT cells. Therefore, targeting the IL-33/ST2 axis could have potential value in the prevention of OvC progression.

The role of the neuronal microenvironment in sensory function and pain pathophysiology

The high prevalence of pain and the at times low efficacy of current treatments represent a significant challenge to healthcare systems worldwide. Effective treatment strategies require consideration of the diverse pathophysiologies that underlie various pain conditions. Indeed, our understanding of the mechanisms contributing to aberrant sensory neuron function has advanced considerably. However, sensory neurons operate in a complex dynamic microenvironment that is controlled by multidirectional interactions of neurons with non-neuronal cells, including immune cells, neuronal accessory cells, fibroblasts, adipocytes, and keratinocytes. Each of these cells constitute and control the microenvironment in which neurons operate, inevitably influencing sensory function and the pathology of pain. This review highlights the importance of the neuronal microenvironment for sensory function and pain, focusing on cellular interactions in the skin, nerves, dorsal root ganglia, and spinal cord. We discuss the current understanding of the mechanisms by which neurons and non-neuronal cells communicate to promote or resolve pain, and how this knowledge could be used for the development of mechanism-based treatments.

Eupatilin attenuates the senescence of nucleus pulposus cells and mitigates intervertebral disc degeneration via inhibition of the MAPK/NF-κB signaling pathway

Intervertebral disc degeneration (IDD) is the main cause of low back pain. An increasing number of studies have suggested that inflammatory response or the senescence of nucleus pulposus (NP) cells is strongly associated with the progress of IDD. Eupatilin, the main flavonoid extracted from Artemisia, was reported to be associated with the inhibition of the intracellular inflammatory response and the senescence of cells. However, the relationship between eupatilin and IDD is still unknown. In this study, we explored the role of eupatilin in tumor necrosis factor-α (TNF-α)-induced activation of inflammatory signaling pathways and NP cell senescence, in the anabolism and catabolism of NP cell extracellular matrix (ECM) and in the effect of the puncture-induced model of caudal IDD in the rat. In vitro, eupatilin significantly inhibited TNF-α-induced ECM degradation, downregulated the expression of related markers of NP cells (MMP3, MMP9, and MMP13), and upregulated the expression of SOX9 and COL2A1. Furthermore, eupatilin reduced TNF-α-induced cell senescence by inhibiting the expression of the senescence of NP cell-related markers (p21 and p53). Mechanistically, ECM degradation and cell senescence were reduced by eupatilin, which inhibited the activation of MAPK/NF-κB signaling pathways. Consistent with the in vitro data, eupatilin administration ameliorated the puncture-induced model of caudal IDD in the rat. In conclusion, eupatilin can inhibit the inflammatory response and the senescence of NP cells, which may be a novel treatment strategy for IDD.

Genetic variants of interleukin 1B and 6 are associated with clinical outcome of surgically treated lumbar degenerative disc disease

BACKGROUND

Successfully surgically treating degenerative disc diseases can be challenging to the spine surgeons, the long-term outcome relies on both the physical and mental status of the patient before and after treatment. Numerous studies underlined the role of inflammatory cytokines - like interleukin 1B and 6 - in the development of chronic diseases such as failed back surgery syndrome (FBSS) and major depressive disorder (MDD) which alter the outcome after spinal surgery. Our aim was to evaluate the associations of IL6 and IL1B gene polymorphisms with the long-term outcome of degenerative lumbar spine surgeries.

METHODS

An international genetical database (GENODISC) was combined with our institute's clinical database to create a large pool with long term follow up data. Altogether 431 patient's data were analysed. Patient reported outcome measures and surgical outcome was investigated in association with IL1B and IL6 SNPs with the help of 'SNPassoc' R genome wide association package.

RESULTS

Interleukin 1B variants analysis confirmed association with improvement of pain after surgery on individual SNP level and on haplotype level, moreover relationship with patient reported outcome and preoperative level of depression was found on individual SNP level. IL6 variants were associated with preoperative depression, somatization and with subsequent surgery.

CONCLUSION

Understanding the complexity of spinal surgery patients' long-term well-being is crucial in effectively treating chronic debilitating somatic diseases and the associated mental illnesses. Further studies should investigate more comprehensively the linkage of chronic physical and mental illnesses focusing on their simultaneous treatment.

IL-10 alleviates radicular pain by inhibiting TNF-α/p65 dependent Nav1.7 up-regulation in DRG neurons of rats

BACKGROUND

Lumbar disc herniation (LDH) may induce radicular pain, the upregulation of voltage-gated sodium channels (VGSCs) in dorsal root ganglion (DRG) contributes to radicular pain by generating ectopic discharge of neurons, but the mechanism is unclear. Previously, we reported pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) up-regulated VGSCs in diabetic neuropathy. In this study, we explored the effect of anti-inflammatory cytokine interleukin-10 (IL-10) on radicular pain and the possible mechanisms.

METHODS

Rat model of LDH was induced by implanting autologous nucleus pulposus (NP). Mechanical and thermal pain thresholds were assessed by von Frey filaments and hotplate test respectively. IL-10 and TNF-α level in DRG and cerebrospinal fluid (CSF) were assessed by Enzyme-linked immunosorbent assay (ELISA). IL-10 was intrathecally delivered for 12 days. The expression of IL-10R1 and sodium channel Nav1.7 was displayed by immunofluorescence staining. The protein level of TNF-α and p-p65 was measured by western blotting.

RESULTS

NP implantation increased Nav1.7 expression in DRG neurons, decreased IL-10 level and increased TNF-α level in DRG and CSF. IL-10 significantly alleviated pain behaviors of rats with NP. IL-10R1 was co-localized with neurons but not with satellite cells in DRG. IL-10 decreased Nav1.7 and TNF-α/p-p65 expression in DRG of rats with NP. Co-administration of TNF-α with IL-10 counteracted the effect of IL-10 on pain behaviors, Nav1.7 and TNF-α/p-p65 expression of rats with NP.

CONCLUSIONS

The study revealed that IL-10 alleviated radicular pain by inhibiting TNF-α/p-p65 dependent Nav1.7 up-regulation in DRG neurons.

Curcumenol Mitigates the Inflammation and Ameliorates the Catabolism Status of the Intervertebral Discs In Vivo and In Vitro via Inhibiting the TNFα/NFκB Pathway

Low back pain (LBP) caused by intervertebral disc degeneration (IVDD) is accredited to the release of inflammatory cytokines followed by biomechanical and structural deterioration. In our study, we used a plant-derived medicine, curcumenol, to treat IVDD. A cell viability test was carried out to evaluate the possibility of using curcumenol. RNA-seq was used to determine relative pathways involved with curcumenol addition. Using TNFα as a trigger of inflammation, the activation of the NF-κB signaling pathway and expression of the MMP family were determined by qPCR and western blotting. Nucleus pulposus (NP) cells and the rats’ primary NP cells were cultured. The catabolism status was evaluated by an ex vivo model. A lumbar instability mouse model was carried out to show the effects of curcumenol in vivo. In general, RNA-seq revealed that multiple signaling pathways changed with curcumenol addition, especially the TNFα/NF-κB pathway. So, the NP cells and primary NP cells were induced to suffer inflammation with the activated TNFα/NF-κB signaling pathway and increased expression of the MMP family, such as MMP3, MMP9, and MMP13, which would be mitigated by curcumenol. Owing to the protective effects of curcumenol, the height loss and osteophyte formation of the disc could be prevented in the lumbar instability mouse model in vivo.

Mechanisms and therapeutic targets for neuropathic itch

Neuropathic pruritus conditions arise from structural and/or functional damage of the peripheral or central nervous system. Novel findings of pruritus specific mediators and pathways strengthen the specificity theory of pruritus transmission, however electrophysiological studies suggest that focal activation of nociceptors and distinct discharge patterns of primary afferents also contribute to the development of the sensation of pruritus. A complex interplay between excitatory and inhibitory interneurons at spinal level, non-neuronal cells and descending modulation from upper centers contributes to neuronal sensitization and clinically to the chronicity of pruritus, as well as accompanying phenomena such as alloknesis and hyperknesis. Several topical, systemic and non-pharmacological therapeutic approaches directed at distinct targets are currently available.

Yaobishu Regulates Inflammatory, Metabolic, Autophagic, and Apoptosis Pathways to Attenuate Lumbar Disc Herniation

Objective

Here, we aimed to explore the main mechanism of Yaobishu (YBS) in lumbar disc herniation (LDH).

Methods and Results

Eighteen compounds that might act on LDH were obtained through a combination of network pharmacology prediction and identification by high-performance liquid chromatography-mass spectrometry. The key compounds were palmitic acid and trans-4-hydroxy-3-methoxycinnamate (cinnamate). KEGG analysis demonstrated that palmitic acid target genes mainly regulate the PPAR signaling pathway, Ras signaling pathway, and fatty acid metabolism. Cinnamate target genes were primarily involved in chemical carcinogenesis-receptor activation, lipid and atherosclerosis, the HIF-1 signaling pathway, and nitrogen metabolism. The rat LDH model was constructed using autologous nucleus pulposus tissue implantation. Differential expression gene (DEGs) related to metabolism (CDKN1A and UHRF1), inflammation (S100A9 and SOCS3), autophagy (DCN and LEPR), and apoptosis (CTSW and BCL2A1) in dorsal root ganglion (DRG) tissues of the control and LDH groups was evaluated by RNA-Seq. TNF-α stimulated DRG neuronal cells were used to establish an in vitro LDH model. YBS, palmitic acid, and cinnamate reduced the expression of substance P, CGRP, S100A9, CTSW, and cleaved caspase-3, while enhancing the expression of CDKN1A, UHRF1, PCNA, Ki67, SOCS3, DCN, LEPR, and BCL2A1, as well as telomerase activity. Pearson's correlation analysis confirmed that DCN was positively correlated with BCL2A1, indicating that autophagy might be negatively correlated with apoptosis in LDH. YBS, palmitic acid, and cinnamate reduced the Siegal neurological score and serum IL-1β and IL-18 levels, while increasing changes in the hind paw mechanical withdrawal threshold. The RNA-Seq results further showed that YBS downregulated S100A9 and CTSW expression, while upregulating SOCS3, CDKN1A, UHRF1, DCN, LEPR, and BCL2A1 expression.

Conclusion

YBS and its compounds, palmitic acid, and cinnamate, attenuated LDH by regulating the inflammatory, metabolic, autophagic, and apoptotic pathways. Our results might improve the theoretical and experimental basis for clinical applications of LDH disease treatment.

Protectin DX Attenuates Lumbar Radicular Pain of Non-compressive Disc Herniation by Autophagy Flux Stimulation via Adenosine Monophosphate-Activated Protein Kinase Signaling

Background: Neuroinflammation plays a crucial role in initiating and sustaining lumbar radicular pain (LRP). Protectin DX (PDX) has been experimentally verified to possess pro-resolving properties and anti-inflammatory effects. This study aimed to observe the analgesic effects of PDX and its potential mechanisms in LRP rats with non-compressive lumbar disc herniation (NCLDH). Method: Only male rats were selected to avoid gender-related interferences. Rat models of NCLDH were established, and rats were randomly divided into four groups: the sham group, the vehicle group, the PDX (10 ng PDX) group, and the PDX (100 ng PDX) group. Changes in the mechanical withdrawal threshold and thermal withdrawal latency were observed for 7 days. The mRNAs of pro-inflammatory and anti-inflammatory mediators were evaluated via real-time polymerase chain reaction, whereas western blot and immunohistochemistry were separately conducted to assess the expression levels of autophagy-related proteins and adenosine monophosphate-activated protein kinase (AMPK) signaling. Results: Intrathecal delivery of PDX reduced interleukin (IL)-6 and IL-1β mRNA levels and facilitated mRNA transcription of transforming growth factor-β₁, with attenuation of mechanical and thermal hyperalgesia in LRP rat models. With the application of nucleus pulposus to the dorsal root ganglion, autophagy flux and AMPK signaling were severely disrupted in the spinal dorsal horns, and intrathecal treatment with PDX could dose-dependently restore the dysfunction of autophagy flux and AMPK signaling. Conclusion: These data suggest that PDX possesses pro-resolving properties and exerts potent analgesic effects in LRP by affecting autophagy flux via AMPK signaling.

Inhibition of Spinal Interleukin-33 Attenuates Peripheral Inflammation and Hyperalgesia in Experimental Arthritis

Accumulating evidence indicates that the continuous and intense nociceptive from inflamed tissue may increase the excitability of spinal dorsal horn neurons, which can signal back and modulate peripheral inflammation. Previous studies have demonstrated that spinal interleukin (IL)-33 contributes to the hyperexcitability of spinal dorsal horn neurons. This study was undertaken to investigate whether spinal IL-33 can also influence a peripheral inflammatory response in a rat model of arthritis. Lentivirus-delivered short hairpin RNA targeting IL-33 (LV-shIL-33) was constructed for gene silencing. Rats with adjuvant-induced arthritis (AIA) were injected intrathecally with LV-shIL-33 3 days before the complete Freund's adjuvant (CFA) injection. During an observation period of 21 days, pain-related behavior and inflammation were assessed. In addition, the expression of spinal proinflammatory cytokines and the activation of spinal extracellular signal-regulated kinase (ERK) and nuclear factor-κB (NF-κB) pathways were evaluated on 9 days after CFA treatment. The existence of tissue injury or inflammation in rats with AIA resulted in the upregulation of spinal IL-33, which is predominantly expressed in neurons, astrocytes, and oligodendrocytes. Intrathecal administration of LV-shIL-33 significantly alleviated hyperalgesia, paw swelling, and joint destruction, and attenuated the expression of proinflammatory cytokines [IL-6, IL-1β, and tumor necrosis factor-α (TNF-α)], as well as the activation of ERK and NF-κB/p65 in the spinal cord. Our data suggest that spinal IL-33 contributes to the development of both peripheral inflammation and hyperalgesia. Thus, interference with IL-33 at the spinal level might represent a novel therapeutic target for painful inflammatory disorders.

Decreased intracellular IL-33 impairs endometrial receptivity in women with adenomyosis

Adenomyosis is a common benign uterine lesion that is associated with female infertility, reduced clinical pregnancy rate and high miscarriage risk. While it has been known that the impaired endometrial receptivity is implicated in infertility in patients with adenomyosis, the underlying mechanism remains unclear. In the present study, we showed that intracellular protein level of IL-33 was downregulated in the endometrium of patients with adenomyosis, and IL-33 expression status was shown to be positively correlated with that of HOXA10, an endometrial receptivity marker. The subsequent analysis indicated IL-33 overexpression led to the increase of HOXA10 expression and enhancement of embryo implantation in vitro, which was accompanied with induction of STAT3 phosphorylation. Meanwhile, cryptotanshinone, a potent STAT3 inhibitor, was found to significantly suppress the increase of HOXA10 expression and embryo implantation caused by IL-33 overexpression in vitro, revealing the critical role of STAT3 activity. Consistently, the positive relationship between IL33 and HOXA10 expression in the endometrium was verified in the analysis of adenomyosis mouse model.

Network Pharmacological Dissection of the Mechanisms of Eucommiae Cortex-Achyranthis Radix Combination for Intervertebral Disc Herniation Treatment

Eucommiae cortex (EC) and Achyranthis radix (AR) are herbal medicines widely used in combination for the treatment of intervertebral disc herniation (IDH). The mechanisms of action of the herbal combination have not been understood from integrative and comprehensive points of view. By adopting network pharmacological methodology, we aimed to investigate the pharmacological properties of the EC-AR combination as a therapeutic agent for IDH at a systematic molecular level. Using the pharmacokinetic information for the chemical ingredients of the EC-AR combination obtained from the comprehensive herbal drug-associated databases, we determined its 31 bioactive ingredients and 68 IDH-related therapeutic targets. By analyzing their enrichment for biological functions, we observed that the targets of the EC-AR combination were associated with the regulation of angiogenesis; cytokine and chemokine activity; oxidative and inflammatory stress responses; extracellular matrix organization; immune response; and cellular processes such as proliferation, apoptosis, autophagy, differentiation, migration, and activation. Pathway enrichment investigation revealed that the EC-AR combination may target IDH-pathology-associated signaling pathways, such as those of cellular senescence and chemokine, neurotrophin, TNF, MAPK, toll-like receptor, and VEGF signaling, to exhibit its therapeutic effects. Collectively, these data provide mechanistic insights into the pharmacological activity of herbal medicines for the treatment of musculoskeletal diseases such as IDH.

Interleukin-33 as an early predictor of cetuximab treatment efficacy in patients with colorectal cancer

Background

Cetuximab is used for colorectal cancer (CRC) treatment. However, the early biomarker of treatment efficacy of cetuximab has not been identified.

Methods

After 1 year of cetuximab treatment, patients were divided into an effective group and an ineffective group. The interleukin‐33 (IL‐33) level and the distribution of lymphatic cells in patients were investigated by analyzing the peripheral blood mononuclear cells via flow cytometry analysis and ELISA. The correlation between IL‐33 immunomodulatory effect and cetuximab treatment efficacy was determined through experiments in vivo and in vitro.

Results

The IL‐33 level in the peripheral blood was increased at 4 weeks after cetuximab administration of effective group, meanwhile, the osteopontin (OPN) was reduced. Whereas neither IL‐33 level nor OPN level of ineffective patients changed. In the effective group, the number of natural killer (NK) and CD8⁺ T cells were increased. Moreover, CD137 and CD107a expression on NK cells were higher in the effective group compared to the ineffective group. In vitro cetuximab treatment also increased the number of NK and CD8⁺ T cells as well as CD137 and CD107a expression upon IL‐33 stimulation. Moreover, the secretion of OPN was inhibited by IL‐33 administration in cetuximab‐treated PBMCs from the effective group patients. IL‐33 upregulated the cytotoxicity of NK cells and inhibited tumor cells growth in the effective cetuximab treatment mice.

Conclusion

Effective cetuximab treatment induced a change of IL‐33 and OPN at the early stage and triggered the NK cells antitumor activity. Consequently, significantly increased IL‐33 level and decreased OPN level in the peripheral blood at the early treatment are proposed as potential predictors of cetuximab treatment efficacy.

Electroacupuncture Attenuates Cancer-Induced Bone Pain via NF-κB/CXCL12 Signaling in Midbrain Periaqueductal Gray

Electroacupuncture (EA) is effective in various chronic pains. NF-κB and CXCL12 modulate the formation of chronic pain. Herein, we hypothesized that EA alleviates cancer-induced bone pain (CIBP) through NF-κB/CXCL12 axis in midbrain periaqueductal gray (PAG), which participates in "top-down" pain modulatory circuits. In order to filter the optimum EA frequency for CIBP treatment, 2, 100, or 2/100 Hz EA was set up. In addition, ipsilateral, contralateral, and bilateral EA groups were established to affirm the optimal EA scheme. Bilateral 2/100 Hz EA was considered as the optimal therapeutic scheme and was applied in a subsequent experiment. Western blotting along with immunofluorescence illustrated that CIBP induces a rapid and substantial increase in CXCL12 protein level and NF-κB phosphorylation in vlPAG from day 6 to day 12. Anti-CXCL12 neutralizing antibody and pAAV-U6-shRNA(CXCL12)-CMV-EGFP-WPRE in vlPAG remarkably improved the mechanical pain threshold of the hind paw in CIBP model relative to the control. EA inhibited the upregulation of pNF-κB and CXCL12 in vlPAG of CIBP. The recombinant CXCL12 and pAAV-CMV-CXCL12-EF1a-EGFP-3Xflag-WPRE reversed the abirritation of EA in the CIBP rat model. NF-κB phosphorylation mediated-CXCL12 expression contributed to CIBP allodynia, whereas EA suppressed NF-κB phosphorylation in CIBP. According to the above evidence, we conclude that bilateral 2/100 Hz EA is an optimal therapeutic scheme for CIBP. The abirritation mechanism of EA might reduce the expression of CXCL12 by inhibiting the activation of NF-κB, which might lead to the restraint of descending facilitation of CIBP.

Hyperactivity of Innate Immunity Triggers Pain via TLR2-IL-33-Mediated Neuroimmune Crosstalk

The innate immune system responds to infections that give rise to pain. How the innate immune system interacts with the sensory nervous system and contributes to pain is poorly understood. Here we report that hyperactivity of innate immunity primes and initiates pain states via the TLR2-interleukin-33 (IL-33) axis. Toll-like receptors (TLRs) are upregulated in the complete Freund's adjuvant (CFA) pain model, and knockout of TLR2 abolishes CFA-induced pain. Selective activation of TLR2/6 triggers acute pain via upregulation of IL-33 in the hindpaw, dorsal root ganglia (DRG), and spinal cord in an NLRP3-dependent manner. The IL-33 increase further initiates priming of nociceptive neurons and pain states. Finally, blocking IL-33 receptors at the spinal level mediates analgesia during acute and chronic inflammatory pain, underscoring an important function of IL-33 in pain signaling. Collectively, our data reveal a critical role of the TLR2-IL-33 axis in innate immune activation for pain initiation and maintenance.

The Role of NF-κB/NLRP3 Inflammasome Signaling Pathway in Attenuating Pyroptosis by Melatonin Upon Spinal Nerve Ligation Models

Accumulated evidence has demonstrated causative links between neuropathic pain (NP) and immune-mediated inflammatory disorders. However, the role of inflammasome-induced pyroptosis in NP remains elusive. Melatonin possesses a well-documented analgesic action in various pain models. The current study aimed to test our hypothesis that melatonin regulated pyroptosis to alleviate NP by inhibiting NF-κB/NLRP3-dependent signaling. A rat model of spinal nerve ligation (SNL) was established to explore the potential association between melatonin and pyroptosis. Behavioral experiments revealed that SNL provoked severe allodynia which was suppressed by the administration of melatonin, a caspase-1 inhibitor (VX-765), or an NF-κB inhibitor (BAY 11-7085). SNL significantly up-regulated the inflammatory cytokines associated with the excessive activation of NLRP3 components and NF-κB signaling, as well as a marked pyroptosis activation. These effects were partially inhibited by melatonin, VX-765 or BAY 11-7085, and when melatonin and inhibitors were added together, the effect was enhanced. In conclusion, melatonin has potent analgesic and anti-inflammatory effects in SNL models through preventing pyroptosis via the NF-κB/NLRP3 inflammasome signaling pathway.

Red nucleus IL-33 facilitates the early development of mononeuropathic pain in male rats by inducing TNF-α through activating ERK, p38 MAPK, and JAK2/STAT3

Background

Our recent studies have identified that the red nucleus (RN) dual-directionally modulates the development and maintenance of mononeuropathic pain through secreting proinflammatory and anti-inflammatory cytokines. Here, we further explored the action of red nucleus IL-33 in the early development of mononeuropathic pain.

Methods

In this study, male rats with spared nerve injury (SNI) were used as mononeuropathic pain model. Immunohistochemistry, Western blotting, and behavioral testing were used to assess the expressions, cellular distributions, and actions of red nucleus IL-33 and its related downstream signaling molecules.

Results

IL-33 and its receptor ST2 were constitutively expressed in the RN in naive rats. After SNI, both IL-33 and ST2 were upregulated significantly at 3 days and peaked at 1 week post-injury, especially in RN neurons, oligodendrocytes, and microglia. Blockade of red nucleus IL-33 with anti-IL-33 neutralizing antibody attenuated SNI-induced mononeuropathic pain, while intrarubral administration of exogenous IL-33 evoked mechanical hypersensitivity in naive rats. Red nucleus IL-33 generated an algesic effect in the early development of SNI-induced mononeuropathic pain through activating NF-κB, ERK, p38 MAPK, and JAK2/STAT3, suppression of NF-κB, ERK, p38 MAPK, and JAK2/STAT3 with corresponding inhibitors markedly attenuated SNI-induced mononeuropathic pain or IL-33-evoked mechanical hypersensitivity in naive rats. Red nucleus IL-33 contributed to SNI-induced mononeuropathic pain by stimulating TNF-α expression, which could be abolished by administration of inhibitors against ERK, p38 MAPK, and JAK2/STAT3, but not NF-κB.

Conclusions

These results suggest that red nucleus IL-33 facilitates the early development of mononeuropathic pain through activating NF-κB, ERK, p38 MAPK, and JAK2/STAT3. IL-33 mediates algesic effect partly by inducing TNF-α through activating ERK, p38 MAPK and JAK2/STAT3.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02198-9.

Interleukin-33 promotes invasiveness of human ovarian endometriotic stromal cells through the ST2/MAPK/MMP-9 pathway activated by 17β-estradiol

OBJECTIVE

Endometriosis is an estrogen-dependent, benign, and chronic gynecological disorder occurring in women of reproductive age. Although the pathogenesis of endometriosis is poorly understood, implantation theory indicates that viable endometrial cells shed from the endometrium into the pelvic peritoneum or ovaries, possibly through retrograde menstruation, and then reattach, invade, and damage other tissues. Interleukin (IL)-33, a new member of the IL-1 superfamily, is mainly upregulated by stromal cells following proinflammatory stimulation. Matrix metalloproteinases (MMPs) are involved in the degradation and reconstruction of the extracellular matrix. MMP-9 participates in the pathogenesis of endometriosis by promoting the invasion of endometriotic cells. This study investigated the effect of IL-33 on the cell invasion ability of and MMP-9 expression in human stromal cells derived from ovarian endometrioma (hOVEN-SCs).

MATERIALS AND METHODS

We isolated hOVEN-SCs from human ovarian endometrioma. Gene expression was analyzed using the Illumina Human WG-6 v2 Expression BeadChips microarray platform and through reverse transcription-polymerase chain reaction. Cell migration and invasion were examined by performing the transwell chamber assay.

RESULTS

We found that 17β-estradiol could increase the expression of IL-33 and ST2 through the estrogen receptor pathway in hOVEN-SCs. Moreover, IL-33 upregulated MMP-9 expression in and enhanced the invasion ability of hOVEN-SCs through the ST2/MAPK signaling pathway. Our results showed that MMP-9 expression was essential for IL-33-induced cell invasion.

CONCLUSION

Our main finding is that 17β-estradiol could increase IL-33 expression through the estrogen receptor pathway and activate MMP-9 expression in and invasion ability of hOVEN-SCs through the IL-33/ST2/MAPK signaling pathway. The results of this study and further related studies may provide new strategies for the prevention and treatment of endometriosis.

Effect of IL-33 on pyroptosis of macrophages in mice with sepsis via NF-κB/p38 MAPK signaling pathway

PURPOSE

To demonstrate the effect of IL-33 on the macrophage pyroptosis in mice with sepsis through the NF-kB/p38 MAPK signal pathway.

METHODS

In total, 24 C57BL/6 mice were divided into the sham operation group (sham) and the cecal ligation and puncture group (CLP). After CLP, 24 IL-33-/- mice were divided into the IL-33-/- group and the IL-33-/- intervention group. The latter group was intraperitoneally injected with IL-33. Mouse mortality was observed after CLP. Macrophage apoptosis in peritoneal lavage fluid was detected by flow cytometry. Serum inflammatory factor level was detected by ELISA. Apoptotic protein expression and NF-κB/p38 MAKP signaling pathway protein expression were detected by qRT-PCR and Western blot.

RESULTS

Knocking out IL-33 significantly reduced the mortality of CLP mice, as well as the mRNA expression of IL-33 and the levels of serum inflammatory factors, including IL-33, IL-1β, and IL-18. It also reduced the rate of macrophage apoptosis and the expression of the apoptotic protein caspase-1 p10; increased the expression of IκBα; and reduced the protein expression of NF-κB and p38 MAPK. These effects were reversed after exogenous injection of IL-33.

CONCLUSIONS

IL-33 can increase the level of macrophage pyroptosis in mice with sepsis (by activating the NF-kB/p38MAPK signal pathway) and the mortality of these mice.

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

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

IL-1β promotes disc degeneration and inflammation through direct injection of intervertebral disc in a rat lumbar disc herniation model

BACKGROUND CONTEXT

Lumbar intervertebral disc herniation (LDH) is a common disease that causes low back pain, radiating leg pain, and sensory impairment. Preclinical studies rely heavily upon standardized animal models of human diseases to predict clinical treatment efficacy and to identify and investigate potential adverse events in human subjects. The current method for making the LDH model involves harvesting the nucleus pulposus (NP) from autologous coccygeal discs and applying to the lumbar nerve roots just proximal to the corresponding dorsal root ganglion. However, this surgical method generates a model that exhibits very different characteristics of disc herniation than that observed in human.

PURPOSE

To produce a rat LDH model that better resembles disc herniation in humans and a standardized and uniform LDH model using Interleukin-1 beta (IL-1β).

STUDY DESIGN

Experimental rat LDH model.

METHODS

We exposed the L5-6 disc dorsolaterally on the right side through hemi-laminectomy without nerve compression. Herniation was initiated by puncturing the exposed disc with a 30-gauge needle at a depth of 4 mm. Interleukin-1 beta (IL-1β) was injected simultaneously to heighten the pathological processes of disc degeneration, including inflammatory responses, matrix destruction, and herniation of the NP. We performed histological staining to assess morphological changes, immunohistochemistry to analyze inflammation- and pain-related expression within and around the puncture site of the L5-6 disc, and real-time polymerase chain reaction to examine expression of markers for degenerative processes. In addition, we performed locomotor tests on the rats.

RESULTS

We found that the IL-1β groups showed that the border between the annulus fibrosis and nucleus pulposus was severely interrupted compared to that of the control (puncture only) group. And, the injection of IL-1β leads to accelerated disc degeneration and inflammation in a more consistent manner in LDH model. Functional deficit was consistently induced by puncturing and injection of IL-1β in the exposed disc.

CONCLUSIONS

The method proposed here can be used as an index to control the severity of disc degeneration and inflammation through the injected IL-1β concentration concurrent with surgically induced herniation.

CLINICAL SIGNIFICANCE

Our proposed model may facilitate research in drug development to evaluate the efficacy of potential therapeutic agents for disc herniation and neuropathic pain and may also be used for nonclinical studies to more accurately assess the effectiveness of various treatment strategies according to the severity of disc degeneration.

Interleukin-33 modulates lipopolysaccharide-mediated inflammatory response in rat primary astrocytes

Astrocytes have a crucial role in the modulation of the neuroinflammatory response. However, the underlying mechanisms have yet to be fully defined. Interleukin-33 (IL-33) is constitutively expressed in astrocytes, which has been found to orchestrate inflammatory responses in a large variety of immune-mediated and inflammatory diseases of the nervous system. Thus, the purpose of this study was to elucidate the potential effect of IL-33 in the regulation of inflammatory response in primary cultured astrocytes. We investigated the role of IL-33 in the regulation of inflammatory responses in the lipopolysaccharide-stimulated astrocytes. This study utilized lentiviral short hairpin RNA vectors to target IL-33 (LV-shIL-33) for gene silencing. After lipopolysaccharide stimulation, the expression levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), as well as the activation of nuclear factor-kappa B (NF-κB) and extracellular signal-regulated kinase (ERK) signaling pathways, were evaluated to elucidate the mechanisms related to the contributions of IL-33 to the inflammatory response in astrocytes. We found that the expression IL-33 has increased in rat primary cultured astrocytes after lipopolysaccharide stimulation. Administration of LV-shIL-33 knocked down the expression of IL-33 and markedly reduced the overexpression of spinal IL-1β, IL-6, and TNF-α, and attenuated the activation of ERK and NF-κB/p65. This study shows that IL-33 participates in regulating inflammatory responses in primary cultured astrocytes, which might provide additional targets for controlling inflammatory responses following neurological diseases. See Video abstract, http://links.lww.com/WNR/A627.

Therapeutic Opportunities of Interleukin-33 in the Central Nervous System

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is involved in various diseases. IL-33 exerts its effects via its heterodimeric receptor complex, which comprises suppression of tumorigenicity 2 (ST2) and the IL-1 receptor accessory protein (IL-1RAP). Increasing evidence has demonstrated that IL-33/ST2 signaling plays diverse but crucial roles in the homeostasis of the central nervous system (CNS) and the pathogenesis of CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, infection, trauma, and ischemic stroke. In the current review, we focus on the functional roles and cellular signaling mechanisms of IL-33 in the CNS and evaluate the potential for diagnostic and therapeutic applications.

Therapeutic effects of peripherally administrated neural crest stem cells on pain and spinal cord changes after sciatic nerve transection

BACKGROUND

Severe peripheral nerve injury significantly affects patients' quality of life and induces neuropathic pain. Neural crest stem cells (NCSCs) exhibit several attractive characteristics for cell-based therapies following peripheral nerve injury. Here, we investigate the therapeutic effect of NCSC therapy and associated changes in the spinal cord in a sciatic nerve transection (SNT) model.

METHODS

Complex sciatic nerve gap injuries in rats were repaired with cell-free and cell-laden nerve scaffolds for 12 weeks (scaffold and NCSC groups, respectively). Catwalk gait analysis was used to assess the motor function recovery. The mechanical withdrawal threshold and thermal withdrawal latency were used to assess the development of neuropathic pain. Activation of glial cells was examined by immunofluorescence analyses. Spinal levels of extracellular signal-regulated kinase (ERK), NF-κB P65, brain-derived neurotrophic factor (BDNF), growth-associated protein (GAP)-43, calcitonin gene-related peptide (CGRP), and inflammation factors were calculated by western blot analysis.

RESULTS

Catwalk gait analysis showed that animals in the NCSC group exhibited a higher stand index and Max intensity At (%) relative to those that received the cell-free scaffold (scaffold group) (p < 0.05). The mechanical and thermal allodynia in the medial-plantar surface of the ipsilateral hind paw were significantly relieved in the NCSC group. Sunitinib (SNT)-induced upregulation of glial fibrillary acidic protein (GFAP) (astrocyte) and ionized calcium-binding adaptor molecule 1 (Iba-1) (microglia) in the ipsilateral L4-5 dorsal and ventral horn relative to the contralateral side. Immunofluorescence analyses revealed decreased astrocyte and microglia activation. Activation of ERK and NF-κB signals and expression of transient receptor potential vanilloid 1 (TRPV1) expression were downregulated.

CONCLUSION

NCSC-laden nerve scaffolds mitigated SNT-induced neuropathic pain and improved motor function recovery after sciatic nerve repair. NCSCs also protected the spinal cord from SNT-induced glial activation and central sensitization.

Biomaterial-supported MSC transplantation enhances cell-cell communication for spinal cord injury

The spinal cord is part of the central nervous system (CNS) and serves to connect the brain to the peripheral nervous system and peripheral tissues. The cell types that primarily comprise the spinal cord are neurons and several categories of glia, including astrocytes, oligodendrocytes, and microglia. Ependymal cells and small populations of endogenous stem cells, such as oligodendrocyte progenitor cells, also reside in the spinal cord. Neurons are interconnected in circuits; those that process cutaneous sensory input are mainly located in the dorsal spinal cord, while those involved in proprioception and motor control are predominately located in the ventral spinal cord. Due to the importance of the spinal cord, neurodegenerative disorders and traumatic injuries affecting the spinal cord will lead to motor deficits and loss of sensory inputs.

Spinal cord injury (SCI), resulting in paraplegia and tetraplegia as a result of deleterious interconnected mechanisms encompassed by the primary and secondary injury, represents a heterogeneously behavioral and cognitive deficit that remains incurable. Following SCI, various barriers containing the neuroinflammation, neural tissue defect (neurons, microglia, astrocytes, and oligodendrocytes), cavity formation, loss of neuronal circuitry, and function must be overcame. Notably, the pro-inflammatory and anti-inflammatory effects of cell–cell communication networks play critical roles in homeostatic, driving the pathophysiologic and consequent cognitive outcomes. In the spinal cord, astrocytes, oligodendrocytes, and microglia are involved in not only development but also pathology. Glial cells play dual roles (negative vs. positive effects) in these processes. After SCI, detrimental effects usually dominate and significantly retard functional recovery, and curbing these effects is critical for promoting neurological improvement. Indeed, residential innate immune cells (microglia and astrocytes) and infiltrating leukocytes (macrophages and neutrophils), activated by SCI, give rise to full-blown inflammatory cascades. These inflammatory cells release neurotoxins (proinflammatory cytokines and chemokines, free radicals, excitotoxic amino acids, nitric oxide (NO)), all of which partake in axonal and neuronal deficit.

Given the various multifaceted obstacles in SCI treatment, a combinatorial therapy of cell transplantation and biomaterial implantation may be addressed in detail here. For the sake of preserving damaged tissue integrity and providing physical support and trophic supply for axon regeneration, MSC transplantation has come to the front stage in therapy for SCI with the constant progress of stem cell engineering. MSC transplantation promotes scaffold integration and regenerative growth potential. Integrating into the implanted scaffold, MSCs influence implant integration by improving the healing process. Conversely, biomaterial scaffolds offer MSCs with a sheltered microenvironment from the surrounding pathological changes, in addition to bridging connection spinal cord stump and offering physical and directional support for axonal regeneration. Besides, Biomaterial scaffolds mimic the extracellular matrix to suppress immune responses.

Here, we review the advances in combinatorial biomaterial scaffolds and MSC transplantation approach that targets certain aspects of various intercellular communications in the pathologic process following SCI. Finally, the challenges of biomaterial-supported MSC transplantation and its future direction for neuronal regeneration will be presented.

Systematically characterized mechanism of treatment for lumbar disc herniation based on Yaobitong capsule ingredient analysis in rat plasma and its network pharmacology strategy by UPLC-MS/MS

ETHNOPHARMACOLOGICAL RELEVANCE

Yaobitong capsule (YBTC) was a traditional Chinese medicine (TCM) and it had clinically used to treat lumbar disc degeneration (LDH) for a long time. However, the active ingredients of YBTC absorption into the plasma and its pharmacological mechanism of treatment for LDH still remained unclear.

AIM OF THE STUDY

In this study, our research committed to identify the absorbed active ingredients of YBTC in rat plasma, and it may be a potential mechanism of action on LDH by the biological targets regulating related pathways.

MATERIALS AND METHODS

An ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was established to identify the absorption components and metabolites of YBTC in rat plasma, and the network pharmacology was further investigated to illuminate its potential mechanism of treatment for LDH by the biological targets regulating related pathways.

RESULTS

The network analysis found that 56 components were identified as its main active ingredients including ginsenoside Rg1, ginsenoside Rb1, senkyunolide H, and tetrahydropalmatine, etc. Combining with biological process, cellular component and molecular functions of GO, and kyotoencyclopedia of genes and genomes pathway enrichment analysis to perform network topology analysis on core targets. These active ingredients regulated 29 mainly pathways by 87 direct target genes including MAPK, Ras, PI3K-Akt, and NF-kappa B signaling pathway, etc. CONCLUSION: In this study, the absorption active ingredients of YBTC in rat plasma were firstly combined with the network pharmacology investigation to elucidate its biological mechanism of treatment for LDH in vivo. It inhibited excessive inflammatory reactions, thereby reducing the sensitivity of the nerves to reduce pain and relieve LDH, and potential medicine targets could be identified to clarify the molecular mechanism of YBTCs' regulation of LDH.

The active second-generation proteasome inhibitor oprozomib reverts the oxaliplatin-induced neuropathy symptoms

Oxaliplatin-induced neuropathy (OXAIN) is a major adverse effect of this antineoplastic drug, widely used in the treatment of colorectal cancer. Although its molecular mechanisms remain poorly understood, recent evidence suggest that maladaptive neuroplasticity and oxidative stress may participate to the development of this neuropathy. Given the role played on protein remodeling by ubiquitin-proteasome system (UPS) in response to oxidative stress and in neuropathic pain, we investigated whether oxaliplatin might cause alterations in the UPS-mediated degradation pathway, in order to identify new pharmacological tools useful in OXAIN. In a rat model of OXAIN (2.4 mg kg^-1 i.p., daily for 10 days), a significant increase in chymotrypsin-(β5) like activity of the constitutive proteasome 26S was observed in the thalamus (TH) and somatosensory cortex (SSCx). In addition, the selective up-regulation of β5 and LMP7 (β5i) subunit gene expression was assessed in the SSCx. Furthermore, this study revealed that oprozomib, a selective β5 subunit proteasome inhibitor, is able to normalize the spinal prodynorphin gene expression upregulation induced by oxaliplatin, as well as to revert mechanical allodynia and thermal hyperalgesia observed in oxaliplatin-treated rats. These results underline the relevant role of UPS in the OXAIN and suggest new pharmacological targets to counteract this severe adverse effect. This preclinical study reveals the involvement of the proteasome in the oxaliplatin-induced neuropathy and adds useful information to better understand the molecular mechanism underlying this pain condition. Moreover, although further evidence is required, these findings suggest that oprozomib could be a therapeutic option to counteract chemotherapy-induced neuropathy.

IL-33 enhances macrophage release of IL-1β and promotes pain and inflammation in gouty arthritis

OBJECTIVE

To investigate the role of IL-33 in gouty arthritis.

MATERIAL

174 Balb/c (wild-type) and 54 ST2^-/- mice were used in this study. In vitro experiments were conducted in bone marrow-derived macrophages (BMDMs). Synovial fluid samples from gouty arthritis (n = 7) and osteoarthritis (n = 8) hospital patients were used to measure IL-33 and sST2 levels.

METHODS

Gout was induced by injection of monosodium urate (MSU) crystals in the knee joint of mice. Pain was determined using the electronic von Frey and static weight bearing. Neutrophil recruitment was determined by H&E staining, Rosenfeld staining slides, and MPO activity. ELISA was used for cytokine and sST2 measurement. The priming effect of IL-33 was determined in BMDM.

RESULTS

Synovial fluid of gout patients showed higher IL-33 levels and neutrophil counts than osteoarthritis patients. In mice, the absence of ST2 prevented mechanical pain, knee joint edema, neutrophil recruitment to the knee joint, and lowered IL-1β and superoxide anion levels. In macrophages, IL-33 enhanced the release of IL-1β and TNF-α, and BMDMs from ST2^-/- showed reduced levels of these cytokines after stimulus with MSU crystals.

CONCLUSION

IL-33 mediates gout pain and inflammation by boosting macrophages production of cytokines upon MSU crystals stimulus.

Activation of p38MAPK in spinal microglia contributes to autologous nucleus pulposus-induced mechanical hyperalgesia in a modified rat model of lumbar disk herniation

Recent studies have implicated the activation of p38 mitogen-activated protein kinase (MAPK) and glial cells contribute to hyperalgesia following nerve injury or nerve compression. In our work, we investigated the underlying mechanisms of autologous nucleus pulposus (NP)-induced mechanical hyperalgesia in a modified rat model of lumbar disk herniation (LDH). Firstly, our results showed that 50% mechanical withdrawal threshold (50% MWT) decreased on postoperative day (POD) 1 and significantly minimally reduced on POD 7 and lasted for day 28 after surgery (P < 0.05). Secondly, phosphorylation of p38MAPK (p-p38MAPK) and glial cells were monitored on POD 1, 3, 7, 14 and 28 using immunofluorescence staining. P38MAPK activation, observed in the spinal cord, began to increase on POD 1, peaked on POD 3, and significantly decreased on POD 14 and POD 28 (P < 0.05). Microglia activation was initiated at day 1, maximal at day 3, and maintained until day 14 after surgery (P < 0.05). Astrocytic activation was found in 7 to 14 days after modelling (P < 0.05). Then, double immunostaining method was applied to observe the co-expression of p-p38MAPK and glial cells, and it showed that p-p38MAPK was mainly expressed in activated microglia, rarely in neurons, and none in astrocytes. Lastly, we discovered that both SB203580 (50ug, p38MAPK inhibitor) and minocycline (0.5 mg, microglial inhibitor) would inhibit the p-p38MAPK protein expression tested by western blot analysis and reduce mechanical hyperalgesia. In conclusion, current study suggest that activation or phosphorylation of p38MAPK in spinal microglia contributes to autologous NP-induced mechanical hyperalgesia in our animal model.

IL-33/IL1RL1 axis regulates cell survival through the p38 MAPK pathway in acute myeloid leukemia

Acute myeloid leukemia (AML) is often characterized by the presence of specific and recurrent chromosomal abnormalities. Current treatments have greatly increased remission rate, but relapse still occurs. Therefore, novel therapeutic approaches are required. Previously, using a conditional Cbfb-MYH11 knockin mouse model, we showed that Cbfb-MYH11 induces the expression of a cytokine receptor, IL1RL1. Treatment with IL-33, the only known ligand of IL1RL1, promotes leukemia cell survival in vitro. We further found that IL1RL1⁺ cells survive better with chemotherapy than IL1RL1^- population. However, the mechanism is not clear. Here, we show that IL-33 treatment decreased drug sensitivity in the human inv(16) AML cell line ME-1. By RT-PCR, we found that IL-33 increased the expression of IL-4 and IL-6 and led to the activation of both p38 MAPK and NF-κB. We also showed that IL-33 decreased apoptosis with increased phosphorylation of p38 MAPK. Moreover, pre-treatment with MAPK inhibitor attenuated the phosphorylation of p38 enhanced by IL-33 and reversed the anti-apoptotic effect by IL-33. Taken together, our findings give news insights into the potential mechanism of the anti-apoptotic effect by IL-33/IL1RL1 axis in AML which will help in future drug development.

Red nucleus IL-6 mediates the maintenance of neuropathic pain by inducing the productions of TNF-α and IL-1β through the JAK2/STAT3 and ERK signaling pathways

We previously reported that interleukin (IL)-6 in the red nucleus (RN) is involved in the maintenance of neuropathic pain induced by spared nerve injury (SNI), and exerts a facilitatory effect via Janus-activated kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) and extracellular signal-regulated kinase (ERK) signal transduction pathways. The present study aimed at investigating the roles of tumor necrosis factor-α (TNF-α) and IL-1β in RN IL-6-mediated maintenance of neuropathic pain and related signal transduction pathways. Being similar to the elevation of RN IL-6 three weeks after SNI, increased protein levels of both TNF-α and IL-1β were also observed in the contralateral RN three weeks after the nerve injury. The upregulations of TNF-α and IL-1β were closely correlative with IL-6 and suppressed by intrarubral injection of a neutralizing antibody against IL-6. Administration of either the JAK2 antagonist AG490 or the ERK antagonist PD98059 to the RN of rats with SNI remarkably increased the paw withdrawal threshold (PWT) and inhibited the up-regulations of local TNF-α and IL-1β. Further experiments indicated that intrarubral injection of exogenous IL-6 in naive rats apparently lowered the PWT of the contralateral hindpaw and boosted the local expressions of TNF-α and IL-1β. Pretreatment with AG490 could block IL-6-induced tactile hypersensitivity and suppress the up-regulations of both TNF-α and IL-1β. However, injection of PD98059 in advance only inhibited the upregulation of IL-1β, but not TNF-α. These findings indicate that RN IL-6 mediates the maintenance of neuropathic pain by inducing the productions of TNF-α and IL-1β. IL-6 induces the expression of TNF-α through the JAK2/STAT3 pathway, and the production of IL-1β through the JAK2/STAT3 and ERK pathways.

Oleanolic acid inhibits mouse spinal cord injury through suppressing inflammation and apoptosis via the blockage of p38 and JNK MAPKs

Spinal cord injury (SCI) is reported as a devastating disease, leading to tissue loss and neurologic dysfunction. However, there is no effective therapeutic strategy for SCI treatment. Oleanolic acid (OA), as a triterpenoid, has anti-oxidant, anti-inflammatory, and anti-apoptotic activities. However, its regulatory effects on SCI have little to be elucidated, as well as the underlying molecular mechanisms. In this study, we attempted to explore the role of OA in SCI progression. Behavior tests suggested that OA treatments markedly alleviated motor function in SCI mice. Evans blue contents up-regulated in spinal cords of SCI mice were significantly reduced by OA in a dose-dependent manner, demonstrating the improved blood-spinal cord barrier. Moreover, we found that OA treatments significantly reduced the apoptotic cell death in spinal cord samples of SCI mice through decreasing the expression of cleaved Caspase-3. In addition, pro-inflammatory response in SCI mice was significantly attenuated by OA treatments. Furthermore, SCI mice exhibited higher activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) signaling pathways, but these effects were clearly blocked in SCI mice with OA treatments, as evidenced by the down-regulated phosphorylation of p38, c-Jun-NH 2 terminal kinase (JNK), IκB kinase α (IKKα), inhibitor of nuclear factor κB-α (IκBα) and NF-κB. The protective effects of OA against SCI were confirmed in lipopolysaccharide (LPS)-stimulated mouse neurons mainly through the suppression of apoptosis and inflammatory response, which were tightly associated with the blockage of p38 and JNK activation. Together, our data demonstrated that OA treatments could dose-dependently ameliorate spinal cord damage through impeding p38- and JNK-regulated apoptosis and inflammation, and therefore OA might be served as an effective therapeutic agent for SCI treatment.

Downregulated miR-524-5p Participates in the Tumor Microenvironment of Ameloblastoma by Targeting the Interleukin-33 (IL-33)/Suppression of Tumorigenicity 2 (ST2) Axis

Background

Ameloblastoma (AB) is a common odontogenic epithelial tumor, with locally invasive behavior and high recurrence. In this study, we hypothesized that miR-524-5p could be involved in the tumor microenvironment by targeting interleukin-33 (IL-33)/suppression of tumorigenicity 2 (ST2) in AB.

Material/Methods

The microRNA (miRNA) expression profile of AB tissues and normal oral mucosa tissues (NOM; 6 paired samples) was analyzed. The miRNAs with fold change ≥2 and P<0.05 were considered to be differentially expressed. Among them, downregulated miR-524-5p was verified by real-time qPCR. Potential targets of miR-524-5p were predicted by bioinformatics analysis. The expression levels of target genes were detected using real-time qPCR and Western blot, respectively. Immunohistochemistry analysis of target genes was performed, and we also assessed the correlation between miR-524-5p and its target.

Results

Microarray analysis results first indicated miR-524-5p is a downregulated miRNA in AB tissues. Real-time qPCR results confirmed the expression pattern of miR-524-5p in AB tissues. Moreover, IL-33 and its receptor ST2 were significantly overexpressed. As shown in immunohistochemistry results, IL-33 was positively expressed in lymphocytes and plasma cells, suggesting that IL-33/ST2 participates in tumor immune responses in the tumor microenvironment. Correlation analysis suggested that miR-524-5p expression was negatively correlated with IL-33/ST2.

Conclusions

Our findings reveal that downregulated miR-524-5p can participate in the tumor microenvironment of AB by targeting the IL-33/ST2 axis.

αB crystalline upregulates the expression of matrix metalloproteinases in trabecular meshwork cells through TLR1/2

PURPOSE

Our previous study identified the TLR1/2 complex as the receptor for αB crystalline (CRYAB). Here, we aimed to determine whether CRYAB could influence the expression of matrix metalloproteinases (MMPs) in trabecular meshwork (TM) cells through TLR1/2.

METHODS

The expression of P65, P38, ERK and JNK, which are downstream of TLR1/2, was identified by western blot (WB) with the interference of a TLR1/2 inhibitor or siRNA-TLR1 (siRNA-TLR2). MMP2 and MMP9 were tested by WB analyses using the same interference conditions in TM cells. C57BL/6N mice were used to study the effects in vivo by anterior chamber injection of CRYAB. Finally, immunohistochemistry was performed to evaluate the alterations in MMP2 and MMP9 between the CRYAB injection group and the normal control group.

RESULTS

For the NF-κB pathway, the expression of P65 was increased in TM cells with the addition of exogenous CRYAB (P<0.01), which was dramatically reduced with inhibition of TLR1/2 by its inhibitor (CU-CPT22) or knockdown of TLR1 (or TLR2) with siRNA-TLRs (P<0.01). For the MAPK pathway, P38, ERK and JNK showed no significant difference when CRYAB or CU-CPT22 was added. Subsequently, MMP2 and MMP9 were upregulated, which was consistent with the increased level of p65 (P<0.001). Finally, elevated expression of MMP2 and MMP9 in mice was demonstrated in trabecular meshwork tissue compared to that of the normal control.

CONCLUSION

CRYAB triggers the activation of MMPs in TM cells in vitro and in vivo, possibly following the TLR1/2-mediated proinflammatory effect on TM cells.

Itch Processing in the Skin

Itching can result from activity of specialized primary afferent neurons (“pruriceptors”) that have been shown to express certain molecular markers such as B-type natriuretic peptide and several members of the Mrgpr-family in rodents. On the other hand, neurons involved in pain processing (“nociceptors”) can also provoke itching when the activation site is restricted to an isolated tiny spot within the epidermis. Individuals classified as having sensitive skin report increased itching and pain sensations upon weak external stimuli that are not painful or itchy in the control group. Numerous possible factors could contribute to sensitive skin along the pathway of transduction of the external stimuli into peripheral neuronal signals, followed by neuronal processing, finally resulting in the perception: (a) reduced local protective factors leading to impaired skin barrier function, (b) increased production of excitatory skin mediators, (c) sensitized peripheral neurons, (d) facilitated spinal and central processing, and (e) reduced descending inhibition from the central nervous system. For all of those pathophysiological mechanisms there are clinical examples such as atopic dermatitis (a,b,c), neuropathic itching (c,e), and restless leg syndrome (d,e). However, none of these factors have been directly linked to the occurrence of sensitive skin. Moreover, individuals reporting sensitive skin are heterogeneous and a subpopulation with defined pathophysiology has not yet been identified. Given that the condition is reported in about 50% of women, and thereby includes many healthy individuals, it appears problematic to assign a definitive pathophysiological mechanism to it.

Chitosan Hydrogel Delivery System Containing Herbal Compound Functions as a Potential Antineuroinflammatory Agent

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) is an anthraquinone compound mainly isolated from the herbal medicine rhubarb. It possesses a wide spectrum of pharmacological effects. However, the lack of sustained release properties and the poor bioavailability hinder clinical transformation. Hydrogel-based drug delivery system provides an ideal carrier to improve the release control and the therapeutic efficacy of drugs. Herein, we present a chitosan hydrogel for the delivery of rhein. This rhein-chitosan hydrogel (CS-Rh gel) exhibited superior characteristics including mechanical strength, sustained release, and low toxicity. For medical application, the enzyme-linked immunosorbent assay and Western blot analyses indicated that CS-Rh gel significantly suppressed the production of proinflammatory cytokines including TNF-α and IL-1β in lipopolysaccharide-induced BV2 cells. Additionally, CS-Rh gel blocked the neuroinflammation-related mitogen-activated protein kinase (JNK, ERK, and p38)-signaling pathways. Interestingly, these inhibitory effects at 48 h outperformed the pharmacologic actions at 24 h, showing that the CS-Rh gel exerted optimal sustained antineuroinflammation. This study highlights a novel chitosan hydrogel containing rhein used as a potential antineuroinflammatory agent.

The involvement of spinal annexin A10/NF-κB/MMP-9 pathway in the development of neuropathic pain in rats

Background

Neuropathic pain (NP) is a prevalent disease, which badly impairs the life quality of patients. The underlying mechanism of NP is still not fully understood. It has been reported that spinal Annexin A10 (ANXA10) contributes to NP. This study aims at exploring the underlying mechanisms of spinal ANXA10 in regulating NP in rats.

Methods

Spinal nerve ligation (SNL) was adopted to establish a NP model in rats. After SNL, paw withdrawal threshold and paw withdrawal latency were recorded to measure pain behaviors, RT-PCR was used to check the change of the expression of spinal ANXA10 mRNA, western blot analysis was used to detect the change of the protein level of ANXA10, nuclear factor kappa B (NF-κB), and maisrix metalloproteinase-9 (MMP-9) in the spinal cord. The levels of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukine-1β (IL-1β), and interleukine-6 (IL-6), were explored by ELISA kits. The effects of both knockdown of spinal ANXA10 and inhibition of NF-κB on pain behaviors and the expression of MMP-9 and proinflammatory cytokines were investigated.

Results

Our present findings highlighted that SNL caused pain hypersensitivity and increased the expression of spinal ANXA10/pNF-κB, TNF-α, IL-1β, and IL-6 both in the early and late phase of NP in rats, while spinal MMP-9 was only slightly increased in the early phase of NP. Knockdown of ANXA10 at the spinal cord level suppressed the SNL-induced hyperalgesia and blocked the activation of NF-κB, TNF-α and IL-1β both in the early and late phase of NP. Spinal ANXA10 knockdown could prevent the upregulation of spinal MMP-9 in the early phase and inhibit IL-6 expression in the late phase of SNL-induced NP.

Conclusions

In conclusion, spinal ANXA10/NF-κB/MMP-9 pathway, along with the activation of proinflammatory cytokines, was involved in the SNL-induced NP. MMP-9 may act as the downstream target of ANXA10/NF-κB pathway in the development rather than the maintenance of NP.

Neuropathic itch

Neuropathic itch is clinically important but has received much less attention as compared to neuropathic pain. In the past decade, itch-specific pathways have been characterized on a cellular and molecular level, but their exact role in the pathophysiology of neuropathic itch is still unclear. Traditionally, mutually exclusive theories for itch such as labeled line, temporal/spatial pattern, or intensity theory have been proposed, and experimental studies in mice mainly favor the specificity theory of itch. By contrast, results in humans also suggest a role for spatial and temporal patterns in neuropathic itch. Rarefication of skin innervation in neuropathy could provide a "spatial contrast" discharge pattern, and axotomy could induce de novo expression of the itch-specific spinal neuropeptide, gastrin-releasing peptide, in primary afferent nociceptors, thereby modulating itch processing in the dorsal horn. Thus, clinical neuropathy may generate itch by changes in the spatial and temporal discharge patterns of nociceptors, hijacking the labeled line processing of itch and abandoning the canonical scheme of mutual exclusive itch theories. Moreover, the overlap between itch and pain symptoms in neuropathy patients complicates direct translation from animal experiments and, on a clinical level, necessitates collaboration between medical specialities, such as dermatologists, anesthesiologists, and neurologists.

Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

Crosstalk between NFκB-dependent astrocytic CXCL1 and neuron CXCR2 plays a role in descending pain facilitation

BACKGROUND

Despite accumulating evidence on the role of glial cells and their associated chemicals in mechanisms of pain, few studies have addressed the potential role of chemokines in the descending facilitation of chronic pain. We aimed to study the hypothesis that CXCL1/CXCR2 axis in the periaqueductal gray (PAG), a co-restructure of the descending nociceptive system, is involved in descending pain facilitation.

METHODS

Intramedullary injection of Walker 256 mammary gland carcinoma cells of adult female Sprague Dawley rats was used to establish a bone cancer pain (BCP) model. RT-PCR, Western blot, and immunohistochemistry were performed to detect pNfkb, Cxcl1, and Cxcr2 and their protein expression in the ventrolateral PAG (vlPAG). Immunohistochemical co-staining with NeuN, GFAP, and CD11 were used to examine the cellular location of pNFκB, CXCL1, and CXCR2. The effects of NFκB and CXCR2 antagonists and CXCL1 neutralizing antibody on pain hypersensitivity were evaluated by behavioral testing.

RESULTS

BCP induced cortical bone damage and persistent mechanical allodynia and increased the expression of pNFκB, CXCL1, and CXCR2 in vlPAG. The induced phosphorylation of NFκB was co-localized with GFAP and NeuN, but not with CD11. Micro-injection of BAY11-7082 attenuated BCP and reduced CXCL1 increase in the spinal cord. The expression level of CXCL1 in vlPAG showed co-localization with GFAP, but not with CD11 and NeuN. Micro-administration of CXCL1 neutralizing antibody from 6 to 9 days after inoculation attenuated mechanical allodynia. Furthermore, vlPAG application of CXCL1 elicited pain hypersensitivity in normal rats. Interestingly, CXCR2 was upregulated in vlPAG neurons (not with CD11 and GFAP) after BCP. CXCR2 antagonist SB225002 completely blocked the CXCL1-induced mechanical allodynia and attenuated BCP-induced pain hypersensitivity.

CONCLUSION

The NFκB-dependent CXCL1-CXCR2 signaling cascade played a role in glial-neuron interactions and in descending facilitation of BCP.