Chemokine CXCL13 mediates orofacial neuropathic pain via CXCR5/ERK pathway in the trigeminal ganglion of mice

Dynamics of Cellular Regulation of Fractalkine/CX3CL1 and Its Receptor CX3CR1 in the Rat Trigeminal Subnucleus Caudalis after Unilateral Infraorbital Nerve Lesion-Extended Cellular Signaling of the CX3CL1/CX3CR1 Axis in the Development of Trigeminal Neuropathic Pain

The cellular distribution and changes in CX3CL1/fractalkine and its receptor CX3CR1 protein levels in the trigeminal subnucleus caudalis (TSC) of rats with unilateral infraorbital nerve ligation (IONL) were investigated on postoperation days 1, 3, 7, and 14 (POD1, POD3, POD7, and POD14, respectively) and compared with those of sham-operated and naïve controls. Behavioral tests revealed a significant increase in tactile hypersensitivity bilaterally in the vibrissal pads of both sham- and IONL-operated animals from POD1 to POD7, with a trend towards normalization in sham controls at POD14. Image analysis revealed increased CX3CL1 immunofluorescence (IF) intensities bilaterally in the TSC neurons of both sham- and IONL-operated rats at all survival periods. Reactive astrocytes in the ipsilateral TSC also displayed CX3CL1-IF from POD3 to POD14. At POD1 and POD3, microglial cells showed high levels of CX3CR1-IF, which decreased by POD7 and POD14. Conversely, CX3CR1 was increased in TSC neurons and reactive astrocytes at POD7 and POD14, which coincided with high levels of CX3CL1-IF and ADAM17-IF. This indicates that CX3CL1/CX3CR1 may be involved in reciprocal signaling between TSC neurons and reactive astrocytes. The level of CatS-IF in microglial cells suggests that soluble CX3CL1 may be involved in neuron-microglial cell signaling at POD3 and POD7, while ADAM17 allows this release at all studied time points. These results indicate an extended CX3CL1/CX3CR1 signaling axis and its role in the crosstalk between TSC neurons and glial cells during the development of trigeminal neuropathic pain.

CXCL13 promotes TNF-α synthesis in rheumatoid arthritis through activating ERK/p38 pathway and inhibiting miR-330-3p generation

Rheumatoid arthritis (RA) is a well-known autoimmune disorder associated with joint pain, joint swelling, cartilage and bone degradation as well as deformity. The chemokine (C-X-C motif) ligand 13 (CXCL13) plays a crucial role in multiple cellular pathogenesis processes, including RA. TNF-α is a vital proinflammatory factor in the progression of RA. However, the role of CXCL13 in TNF-α production in RA has not been fully explored. Our analysis of both database and clinical samples revealed higher levels of CXCL13 and TNF-α in RA samples compared to healthy controls. CXCL13 concentration-dependently induces TNF-α synthesis in RA synovial fibroblasts. CXCL13 enhances TNF-α expression by interacting with the CXCR5 receptor, activating the ERK/p38 pathways, and inhibiting miR-330-3p generation. Importantly, treatment with CXCL13 shRNA counteracted the upregulation of TNF-α production induced by collagen-induced arthritis. Our findings support the notion that CXCL13 is a promising target in the treatment of RA.

Photic sensitization is mediated by cortico-accumbens pathway in rats with trigeminal neuropathic pain

Exposure to light stimuli may trigger or exacerbate perception of pain, also known as a common yet debilitating symptom of photophobia in patient with chronic orofacial pain. Mechanism underlying this phenomenon of photic sensitization in neuropathic condition remains elusive. Here, we found that rats developed hypersensitivity to normal light illumination after establishment of chronic constriction injury of infraorbital nerve (ION-CCI) model, which can be attenuated by blocking the exposure of photic stimulation. Additionally, this behavioral phenotype of light-sensitivity impairment was associated with overexpression of anterior cingulate cortex (ACC) c-fos positive neurons, enhancement of neural excitability in the ACC neurons and its excitatory synaptic transmission between nucleus accumbens (NAc). Optogenetic and chemogenic silencing of ACC-NAc pathway improved trigeminal sensitization in responses to light stimuli by decreasing spontaneous pain-like episodes in ION-CCI animals. In contrast, selective activation of ACC-to-NAc circuits enhanced photic hypersensitivity in dark environment. Thus, our data provided novel role of ACC and its projection to NAc in bidirectional modulation of photic sensation, which may contribute to the understanding of photic allodynia in trigeminal neuropathic pain status.

PACAP/PAC1-R activation contributes to hyperalgesia in 6-OHDA-induced Parkinson's disease model rats via promoting excitatory synaptic transmission of spinal dorsal horn neurons

Pain is a common annoying non-motor symptom in Parkinson's disease (PD) that causes distress to patients. Treatment for PD pain remains a big challenge, as its underlying mechanisms are elusive. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1-R play important roles in regulating a variety of pathophysiological processes. In this study, we investigated whether PACAP/PAC1-R signaling was involved in the mechanisms of PD pain. 6-hydroxydopamine (6-OHDA)-induced PD model was established in rats. Behavioral tests, electrophysiological and Western blotting analysis were conducted 3 weeks later. We found that 6-OHDA rats had significantly lower mechanical paw withdrawal 50% threshold in von Frey filament test and shorter tail flick latency, while mRNA levels of Pacap and Adcyap1r1 (gene encoding PAC1-R) in the spinal dorsal horn were significantly upregulated. Whole-cell recordings from coronal spinal cord slices at L4-L6 revealed that the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) in dorsal horn neurons was significantly increased, which was reversed by application of a PAC1-R antagonist PACAP 6-38 (250 nM). Furthermore, we demonstrated that intrathecal microinjection of PACAP 6-38 (0.125, 0.5, 2 μg) dose-dependently ameliorated the mechanical and thermal hyperalgesia in 6-OHDA rats. Inhibition of PACAP/PAC1-R signaling significantly suppressed the activation of Ca2+/calmodulin-dependent protein kinase II and extracellular signal-regulated kinase (ERK) in spinal dorsal horn of 6-OHDA rats. Microinjection of pAAV-Adcyap1r1 into L4-L6 spinal dorsal horn alleviated hyperalgesia in 6-OHDA rats. Intrathecal microinjection of ERK antagonist PD98059 (10 μg) significantly alleviated hyperalgesia in 6-OHDA rats associated with the inhibition of sEPSCs in dorsal horn neurons. In addition, we found that serum PACAP-38 concentration was significantly increased in PD patients with pain, and positively correlated with numerical rating scale score. In conclusion, activation of PACAP/PAC1-R induces the development of PD pain and targeting PACAP/PAC1-R is an alternative strategy for treating PD pain.

Peripheral CCL2-CCR2 signalling contributes to chronic headache-related sensitization

Migraine, especially chronic migraine, is highly debilitating and still lacks effective treatment. The persistent headache arises from activation and sensitization of primary afferent neurons in the trigeminovascular pathway, but the underlying mechanisms remain incompletely understood. Animal studies indicate that signalling through chemokine C-C motif ligand 2 (CCL2) and C-C motif chemokine receptor 2 (CCR2) mediates the development of chronic pain after tissue or nerve injury. Some migraine patients had elevated CCL2 levels in CSF or cranial periosteum. However, whether the CCL2-CCR2 signalling pathway contributes to chronic migraine is not clear. Here, we modelled chronic headache with repeated administration of nitroglycerin (NTG, a reliable migraine trigger in migraineurs) and found that both Ccl2 and Ccr2 mRNA were upregulated in dura and trigeminal ganglion (TG) tissues that are implicated in migraine pathophysiology. In Ccl2 and Ccr2 global knockout mice, repeated NTG administration did not evoke acute or persistent facial skin hypersensitivity as in wild-type mice. Intraperitoneal injection of CCL2 neutralizing antibodies inhibited chronic headache-related behaviours induced by repeated NTG administration and repetitive restraint stress, suggesting that the peripheral CCL2-CCR2 signalling mediates headache chronification. We found that CCL2 was mainly expressed in TG neurons and cells associated with dura blood vessels, whereas CCR2 was expressed in subsets of macrophages and T cells in TG and dura but not in TG neurons under both control and disease states. Deletion of Ccr2 gene in primary afferent neurons did not alter NTG-induced sensitization, but eliminating CCR2 expression in either T cells or myeloid cells abolished NTG-induced behaviours, indicating that both CCL2-CCR2 signalling in T cells and macrophages are required to establish chronic headache-related sensitization. At cellular level, repeated NTG administration increased the number of TG neurons that responded to calcitonin-gene-related peptide (CGRP) and pituitary adenylate cyclase activating polypeptide (PACAP) as well as the production of CGRP in wild-type but not Ccr2 global knockout mice. Lastly, co-administration of CCL2 and CGRP neutralizing antibodies was more effective in reversing NTG-induced behaviours than individual antibodies. Taken together, these results suggest that migraine triggers activate CCL2-CCR2 signalling in macrophages and T cells. This consequently enhances both CGRP and PACAP signalling in TG neurons, ultimately leading to persistent neuronal sensitization underlying chronic headache. Our work not only identifies the peripheral CCL2 and CCR2 as potential targets for chronic migraine therapy, but also provides proof-of-concept that inhibition of both peripheral CGRP and CCL2-CCR2 signalling is more effective than targeting either pathway alone.

TSLP in DRG neurons causes the development of neuropathic pain through T cells

BACKGROUND

Peripheral nerve injury to dorsal root ganglion (DRG) neurons develops intractable neuropathic pain via induction of neuroinflammation. However, neuropathic pain is rare in the early life of rodents. Here, we aimed to identify a novel therapeutic target for neuropathic pain in adults by comprehensively analyzing the difference of gene expression changes between infant and adult rats after nerve injury.

METHODS

A neuropathic pain model was produced in neonatal and young adult rats by spared nerve injury. Nerve injury-induced gene expression changes in the dorsal root ganglion (DRG) were examined using RNA sequencing. Thymic stromal lymphopoietin (TSLP) and its siRNA were intrathecally injected. T cells were examined using immunofluorescence and were reduced by systemic administration of FTY720.

RESULTS

Differences in changes in the transcriptome in injured DRG between infant and adult rats were most associated with immunological functions. Notably, TSLP was markedly upregulated in DRG neurons in adult rats, but not in infant rats. TSLP caused mechanical allodynia in adult rats, whereas TSLP knockdown suppressed the development of neuropathic pain. TSLP promoted the infiltration of T cells into the injured DRG and organized the expressions of multiple factors that regulate T cells. Accordingly, TSLP caused mechanical allodynia through T cells in the DRG.

CONCLUSION

This study demonstrated that TSLP is causally involved in the development of neuropathic pain through T cell recruitment.

Spinal CBX2 contributes to neuropathic pain by activating ERK signaling pathway in male mice

The deregulated spinal cord proteins induced by nerve injury are the key to neuropathic pain. Integrated transcriptome and translatome analyses can screen out deregulated proteins controlled by only post-transcriptional regulation. By comparing RNA sequencing (RNA-seq) and ribosome profiling sequencing (Ribo-seq) data, we identified an upregulated protein, chromobox 2 (CBX2), with its mRNA level unchanged in the spinal cord after peripheral nerve injury. CBX2 was mainly distributed in the spinal cord neurons. Blocking the SNL-induced increase of spinal CBX2 attenuated the neuronal and astrocytes hyperactivities and pain hypersensitivities in both the development and maintenance phases. Conversely, mimicking the upregulation of CBX2 in the spinal cord facilitated the activities of neurons and astrocytes and produced evoked nociceptive hypersensitivity and spontaneous pain. Our results also revealed that activating the ERK pathway, upregulating CXCL13 in neurons, and CXCL13 further inducing astrocyte activation were possible downstream signaling mechanisms of CBX2 in pain processing. In conclusion, upregulation of CBX2 after nerve injury leads to nociceptive hyperalgesia by promoting neuronal and astrocyte hyperactivities through the ERK pathway. Inhibiting CBX2 upregulation may be therapeutically beneficial.

Targeting Members of the Chemokine Family as a Novel Approach to Treating Neuropathic Pain

Neuropathic pain is a debilitating condition that affects millions of people worldwide. Numerous studies indicate that this type of pain is a chronic condition with a complex mechanism that tends to worsen over time, leading to a significant deterioration in patients' quality of life and issues like depression, disability, and disturbed sleep. Presently used analgesics are not effective enough in neuropathy treatment and may cause many side effects due to the high doses needed. In recent years, many researchers have pointed to the important role of chemokines not only in the development and maintenance of neuropathy but also in the effectiveness of analgesic drugs. Currently, approximately 50 chemokines are known to act through 20 different seven-transmembrane G-protein-coupled receptors located on the surface of neuronal, glial, and immune cells. Data from recent years clearly indicate that more chemokines than initially thought (CCL1/2/3/5/7/8/9/11, CXCL3/9/10/12/13/14/17; XCL1, CX3CL1) have pronociceptive properties; therefore, blocking their action by using neutralizing antibodies, inhibiting their synthesis, or blocking their receptors brings neuropathic pain relief. Several of them (CCL1/2/3/7/9/XCL1) have been shown to be able to reduce opioid drug effectiveness in neuropathy, and neutralizing antibodies against them can restore morphine and/or buprenorphine analgesia. The latest research provides irrefutable evidence that chemokine receptors are promising targets for pharmacotherapy; chemokine receptor antagonists can relieve pain of different etiologies, and most of them are able to enhance opioid analgesia, for example, the blockade of CCR1 (J113863), CCR2 (RS504393), CCR3 (SB328437), CCR4 (C021), CCR5 (maraviroc/AZD5672/TAK-220), CXCR2 (NVPCXCR220/SB225002), CXCR3 (NBI-74330/AMG487), CXCR4 (AMD3100/AMD3465), and XCR1 (vMIP-II). Recent research has shown that multitarget antagonists of chemokine receptors, such as CCR2/5 (cenicriviroc), CXCR1/2 (reparixin), and CCR2/CCR5/CCR8 (RAP-103), are also very effective painkillers. A multidirectional strategy based on the modulation of neuronal-glial-immune interactions by changing the activity of the chemokine family can significantly improve the quality of life of patients suffering from neuropathic pain. However, members of the chemokine family are still underestimated pharmacological targets for pain treatment. In this article, we review the literature and provide new insights into the role of chemokines and their receptors in neuropathic pain.

CXCL13 contributes to chronic pain of a mouse model of CRPS-I via CXCR5-mediated NF-κB activation and pro-inflammatory cytokine production in spinal cord dorsal horn

BACKGROUND

Complex regional pain syndrome type-I (CRPS-I) causes excruciating pain that affect patients' life quality. However, the mechanisms underlying CRPS-I are incompletely understood, which hampers the development of target specific therapeutics.

METHODS

The mouse chronic post-ischemic pain (CPIP) model was established to mimic CRPS-I. qPCR, Western blot, immunostaining, behavioral assay and pharmacological methods were used to study mechanisms underlying neuroinflammation and chronic pain in spinal cord dorsal horn (SCDH) of CPIP mice.

RESULTS

CPIP mice developed robust and long-lasting mechanical allodynia in bilateral hindpaws. The expression of inflammatory chemokine CXCL13 and its receptor CXCR5 was significantly upregulated in ipsilateral SCDH of CPIP mice. Immunostaining revealed CXCL13 and CXCR5 was predominantly expressed in spinal neurons. Neutralization of spinal CXCL13 or genetic deletion of Cxcr5 (Cxcr5^-/-) significantly reduced mechanical allodynia, as well as spinal glial cell overactivation and c-Fos activation in SCDH of CPIP mice. Mechanical pain causes affective disorder in CPIP mice, which was attenuated in Cxcr5^-/- mice. Phosphorylated STAT3 co-expressed with CXCL13 in SCDH neurons and contributed to CXCL13 upregulation and mechanical allodynia in CPIP mice. CXCR5 coupled with NF-κB signaling in SCDH neurons to trigger pro-inflammatory cytokine gene Il6 upregulation, contributing to mechanical allodynia. Intrathecal CXCL13 injection produced mechanical allodynia via CXCR5-dependent NF-κB activation. Specific overexpression of CXCL13 in SCDH neurons is sufficient to induce persistent mechanical allodynia in naïve mice.

CONCLUSIONS

These results demonstrated a previously unidentified role of CXCL13/CXCR5 signaling in mediating spinal neuroinflammation and mechanical pain in an animal model of CRPS-I. Our work suggests that targeting CXCL13/CXCR5 pathway may lead to novel therapeutic approaches for CRPS-I.

Trace amine-associated receptor 1 regulation of Kv1.4 channels in trigeminal ganglion neurons contributes to nociceptive behaviors

BACKGROUND

Trace amines, such as tyramine, are endogenous amino acid metabolites that have been hypothesized to promote headache. However, the underlying cellular and molecular mechanisms remain unknown.

METHODS

Using patch-clamp recording, immunostaining, molecular biological approaches and behaviour tests, we elucidated a critically functional role of tyramine in regulating membrane excitability and pain sensitivity by manipulating Kv1.4 channels in trigeminal ganglion (TG) neurons.

RESULTS

Application of tyramine to TG neurons decreased the A-type K⁺ current (I_A) in a manner dependent on trace amine-associated receptor 1 (TAAR1). Either siRNA knockdown of Gαo or chemical inhibition of βγ subunit (G_βγ) signaling abrogated the response to tyramine. Antagonism of protein kinase C (PKC) prevented the tyramine-induced I_A response, while inhibition of conventional PKC isoforms or protein kinase A elicited no such effect. Tyramine increased the membrane abundance of PKC_θ in TG neurons, and either pharmacological or genetic inhibition of PKC_θ blocked the TAAR1-mediated I_A decrease. Furthermore, PKC_θ-dependent I_A suppression was mediated by Kv1.4 channels. Knockdown of Kv1.4 abrogated the TAAR1-induced I_A decrease, neuronal hyperexcitability, and pain hypersensitivity. In a mouse model of migraine induced by electrical stimulation of the dura mater surrounding the superior sagittal sinus, blockade of TAAR1 signaling attenuated mechanical allodynia; this effect was occluded by lentiviral overexpression of Kv1.4 in TG neurons.

CONCLUSION

These results suggest that tyramine induces Kv1.4-mediated I_A suppression through stimulation of TAAR1 coupled to the G_βγ-dependent PKC_θ signaling cascade, thereby enhancing TG neuronal excitability and mechanical pain sensitivity. Insight into TAAR1 signaling in sensory neurons provides attractive targets for the treatment of headache disorders such as migraine.

Loss of forebrain BIN1 attenuates hippocampal pathology and neuroinflammation in a tauopathy model

Bridging integrator 1 (BIN1) is the second most prevalent genetic risk factor identified by genome-wide association studies (GWAS) for late-onset Alzheimer's disease. BIN1 encodes an adaptor protein that regulates membrane dynamics in the context of endocytosis and neurotransmitter vesicle release. In vitro evidence suggests that BIN1 can directly bind to tau in the cytosol. In addition, BIN1's function limits extracellular tau seed uptake by endocytosis and subsequent propagation as well as influences tau release through exosomes. However, the in vivo roles of BIN1 in tau pathogenesis and tauopathy-mediated neurodegeneration remain uncharacterized. We generated conditional knockout mice with a selective loss of Bin1 expression in the forebrain excitatory neurons and oligodendrocytes in P301S human tau transgenic background (line PS19). PS19 mice develop age-dependent tau neuropathology and motor deficits and are commonly used to study Alzheimer's disease tau pathophysiology. The severity of motor deficits and neuropathology was compared between experimental and control mice that differ with respect to forebrain BIN1 expression. BIN1's involvement in tau pathology and neuroinflammation was quantified by biochemical methods and immunostaining. Transcriptome changes were profiled by RNA-sequencing analysis to gain molecular insights. The loss of forebrain BIN1 expression in PS19 mice exacerbated tau pathology in the somatosensory cortex, thalamus, spinal cord and sciatic nerve, accelerated disease progression and caused early death. Intriguingly, the loss of BIN1 also mitigated tau neuropathology in select regions, including the hippocampus, entorhinal/piriform cortex, and amygdala, thus attenuating hippocampal synapse loss, neuronal death, neuroinflammation and brain atrophy. At the molecular level, the loss of forebrain BIN1 elicited complex neuronal and non-neuronal transcriptomic changes, including altered neuroinflammatory gene expression, concomitant with an impaired microglial transition towards the disease-associated microglial phenotype. These results provide crucial new information on in vivo BIN1 function in the context of tau pathogenesis. We conclude that forebrain neuronal BIN1 expression promotes hippocampal tau pathogenesis and neuroinflammation. Our findings highlight an exciting region specificity in neuronal BIN1 regulation of tau pathogenesis and reveal cell-autonomous and non-cell-autonomous mechanisms involved in BIN1 modulation of tau neuropathology.

Drug repositioning: diacerein as a new therapeutic approach in a mice model of sciatic nerve injury

BACKGROUND

Peripheral nerve injuries negatively impact the quality of life of patients, with no effective treatment available that accelerates sensorimotor recovery and promotes functional improvement and pain relief. The aim of this study was to evaluate the effects of diacerein (DIA) in an experimental mice model of sciatic nerve crush.

METHOD

In this study, male Swiss mice were used, randomly separated into six groups as follows: FO (false-operated + vehicle); FO + DIA (false-operated + diacerein 30 mg/kg); SNI (sciatic nerve injury + vehicle); SNI + DIA in doses of 3, 10 and 30 mg/kg (sciatic nerve injury + treatment with diacerein in doses of 3-30 mg/kg). DIA or vehicle was administered 24 h after the surgical procedure, intragastrically, twice a day. The lesion of the right sciatic nerve was generated by crush.

RESULTS

We found that the treatment of animals with DIA accelerated sensorimotor recovery of the animal. In addition, animals in the sciatic nerve injury + vehicle (SNI) group showed hopelessness, anhedonia, and lack of well-being, which were significantly inhibited by DIA treatment. The SNI group showed a reduction in the diameters of nerve fibers, axons, and myelin sheaths, while DIA treatment recovered all these parameters. In addition, the treatment of animals with DIA prevented an increase the levels of interleukin (IL)-1β and a reduction in the levels of the brain-derived growth factor (BDNF).

CONCLUSIONS

Treatment with DIA reduces hypersensitivity and depression like behaviors in animals. Furthermore, DIA promotes functional recovery and regulates IL-1β and BDNF concentrations.

Daphnetin Improves Neuropathic Pain by Inhibiting the Expression of Chemokines and Inflammatory Factors in the Spinal Cord and Interfering with Glial Cell Polarization

Neuropathic pain (NP) is a common pain disease that seriously affects the quality of life and physical and mental health of patients. Daphnetin is extracted from the Daphne giraldii Nitsche and has the structure of 7,8-dihydroxy coumarin. As a natural product, daphnetin displays a wide range of pharmacological activities, such as analgesia and anti-inflammatory activities, but whether it is able to improve NP through anti-inflammatory effects is unknown. Therefore, this paper intends to investigate the mechanism of daphnetin in improving NP rats affected by the intrathecal injection of tumor necrosis factor-α (TNF-α) from the perspective of anti-inflammation. Our results showed that daphnetin significantly improved hyperalgesia in NP rats. Daphnetin inhibited the activation and polarization of glial cells and neurons in the spinal cord of NP rats and reduced the expression of mRNA and protein of inflammatory factors and chemokine pairs in the spinal cord. Daphnetin inhibited the polarization of human microglia cell 3 (HMC3) cells and human glioma cells (U251) cells toward M1 microglia and A1 astrocytes, respectively, and induced the conversion of M1 microglia and A1 astrocytes to M2 microglia and A2 astrocytes, respectively. In conclusion, daphnetin ameliorates NP by inhibiting the expression of inflammatory factors and chemokines and the polarization of glial cells in the spinal cord of NP rats. This study provides a theoretical basis for the treatment of NP with daphnetin to expand the clinical application of daphnetin.

Chemokine CCL7 mediates trigeminal neuropathic pain via CCR2/CCR3-ERK pathway in the trigeminal ganglion of mice

BACKGROUND

Chemokine-mediated neuroinflammation plays an important role in the pathogenesis of neuropathic pain. The chemokine CC motif ligand 7 (CCL7) and its receptor CCR2 have been reported to contribute to neuropathic pain via astrocyte-microglial interaction in the spinal cord. Whether CCL7 in the trigeminal ganglion (TG) involves in trigeminal neuropathic pain and the involved mechanism remain largely unknown.

METHODS

The partial infraorbital nerve transection (pIONT) was used to induce trigeminal neuropathic pain in mice. The expression of Ccl7, Ccr1, Ccr2, and Ccr3 was examined by real-time quantitative polymerase chain reaction. The distribution of CCL7, CCR2, and CCR3 was detected by immunofluorescence double-staining. The activation of extracellular signal-regulated kinase (ERK) was examined by Western blot and immunofluorescence. The effect of CCL7 on neuronal excitability was tested by whole-cell patch clamp recording. The effect of selective antagonists for CCR1, CCR2, and CCR3 on pain hypersensitivity was checked by behavioral testing.

RESULTS

Ccl7 was persistently increased in neurons of TG after pIONT, and specific inhibition of CCL7 in the TG effectively relieved pIONT-induced orofacial mechanical allodynia. Intra-TG injection of recombinant CCL7 induced mechanical allodynia and increased the phosphorylation of ERK in the TG. Incubation of CCL7 with TG neurons also dose-dependently enhanced the neuronal excitability. Furthermore, pIONT increased the expression of CCL7 receptors Ccr1, Ccr2, and Ccr3. The intra-TG injection of the specific antagonist of CCR2 or CCR3 but not of CCR1 alleviated pIONT-induced orofacial mechanical allodynia and reduced ERK activation. Immunostaining showed that CCR2 and CCR3 are expressed in TG neurons, and CCL7-induced hyperexcitability of TG neurons was decreased by antagonists of CCR2 or CCR3.

CONCLUSION

CCL7 activates ERK in TG neurons via CCR2 and CCR3 to enhance neuronal excitability, which contributes to the maintenance of trigeminal neuropathic pain. CCL7-CCR2/CCR3-ERK pathway may be potential targets for treating trigeminal neuropathic pain.

Silencing of TRPV4-expressing sensory neurons attenuates temporomandibular disorders pain

Identification of potential therapeutic targets is needed for temporomandibular disorders (TMD) pain, the most common form of orofacial pain, because current treatments lack efficacy. Considering TMD pain is critically mediated by the trigeminal ganglion (TG) sensory neurons, functional blockade of nociceptive neurons in the TG may provide an effective approach for mitigating pain associated with TMD. We have previously shown that TRPV4, a polymodally-activated ion channel, is expressed in TG nociceptive neurons. Yet, it remains unexplored whether functional silencing of TRPV4-expressing TG neurons attenuates TMD pain. In this study, we demonstrated that co-application of a positively charged, membrane-impermeable lidocaine derivative QX-314 with the TRPV4 selective agonist GSK101 suppressed the excitability of TG neurons. Moreover, co-administration of QX-314 and GSK101 into the TG significantly attenuated pain in mouse models of temporomandibular joint (TMJ) inflammation and masseter muscle injury. Collectively, these results suggest TRPV4-expressing TG neurons represent a potential target for TMD pain.

Dexmedetomidine postconditioning alleviates spinal cord ischemia-reperfusion injury in rats via inhibiting neutrophil infiltration, microglia activation, reactive gliosis and CXCL13/CXCR5 axis activation

PURPOSE

Spinal cord ischemia-reperfusion (I/R) injury is an unresolved complication and its mechanisms are still not completely understood. Here, we studied the neuroprotective effects of dexmedetomidine (DEX) postconditioning against spinal cord I/R injury in rats and explored the possible mechanisms.

MATERIALS AND METHODS

In the study, rats were randomly divided into five groups: sham group, I/R group, DEX0.5 group, DEX2.5 group, and DEX5 group. I/R injury was induced in experimental rats; 0.5 μg/kg, 2.5 μg/kg, 5 μg/kg DEX were intravenously injected upon reperfusion respectively. Neurological function, histological assessment, and the disruption of blood-spinal cord barrier (BSCB) were evaluated via the BBB scoring, hematoxylin and eosin staining, Evans Blue (EB) extravasation and spinal cord edema, respectively. Neutrophil infiltration was evaluated via Myeloperoxidase (MPO) activity. Microglia activation and reactive gliosis was evaluated via ionized calcium-binding adapter molecule-1(IBA-1) and glial fibrillary acidic protein (GFAP) immunofluorescence, respectively. The expression of C-X-C motif ligand 13 (CXCL13), C-X-C chemokine receptor type 5(CXCR5), caspase-3 was determined by western blotting. The expression levels of interleukin 6(IL-6), tumor necrosis factor-α(TNF-α), IL-1β were determined by ELISA assay.

RESULTS

DEX postconditioning preserved neurological assessment scores, improved histological assessment scores, attenuated BSCB leakage after spinal cord I/R injury. Neutrophil infiltration, microglia activation and reactive gliosis were also inhibited by DEX postconditioning. The expression of CXCL13, CXCR5, caspase-3, IL-6, TNF-α, IL-1β were reduced by DEX postconditioning.

CONCLUSIONS

DEX postconditioning alleviated spinal cord I/R injury, which might be mediated via inhibition of neutrophil infiltration, microglia activation, reactive gliosis and CXCL13/CXCR5 axis activation.

Pathophysiology of Post-Traumatic Trigeminal Neuropathic Pain

Trigeminal nerve injury is one of the causes of chronic orofacial pain. Patients suffering from this condition have a significantly reduced quality of life. The currently available management modalities are associated with limited success. This article reviews some of the common causes and clinical features associated with post-traumatic trigeminal neuropathic pain (PTNP). A cascade of events in the peripheral and central nervous system function is involved in the pathophysiology of pain following nerve injuries. Central and peripheral processes occur in tandem and may often be co-dependent. Due to the complexity of central mechanisms, only peripheral events contributing to the pathophysiology have been reviewed in this article. Future investigations will hopefully help gain insight into trigeminal-specific events in the pathophysiology of the development and maintenance of neuropathic pain secondary to nerve injury and enable the development of new therapeutic modalities.

CXCL13 and CXCR5 are upregulated in PCOS mice ovaries but downregulated following metformin administration

Polycystic ovary syndrome (PCOS) is becoming a common pathology among women, yet its pathogenesis remains enigmatic. The chemokine C-X-C motif ligand 13 (CXCL13) and its receptor type 5 (CXCR5) regulate inflammatory responses but their roles in PCOS remain unknown. Metformin is commonly administered to PCOS patients but its mechanism of action remains unclear. Thus, we aimed to determine the expression of CXCL13 and CXCR5 in the ovaries of PCOS mice and to evaluate the therapeutic effect of metformin on them. The study comprised four groups of mice: control, PCOS, PCOS plus metformin, and PCOS plus vehicle. CXCL13 and CXCR5 were found to be elevated in the ovarian tissues of the PCOS mice. Metformin reduced ovarian CXCL13 and CXCR5 expressions in the PCOS mice. Hence, CXCL13 and CXCR5 are potentially involved in PCOS pathogenesis; and metformin may help alleviate the symptoms of PCOS by inhibiting CXCL13 expression and actions.

P2Y14 receptor in trigeminal ganglion contributes to neuropathic pain in mice

Trigeminal nerve injury is a common complication of various dental and oral procedures, which could induce trigeminal neuropathic pain but lack effective treatments. P2 purinergic receptors have emerged as novel therapeutic targets for such pain. Recent reports implied that the P2Y₁₄ receptor (P2Y₁₄R) was activated and promoted orofacial inflammatory pain and migraine. However, the role and mechanism of P2Y₁₄R in trigeminal neuropathic pain remain unknown. We induced an orofacial neuropathic pain model by chronic constriction injury of the infraorbital nerve (CCI-ION). Von-Frey tests showed that CCI-ION induced orofacial mechanical hypersensitivity. The increased activating transcription factor 3 (ATF3) expression in the trigeminal ganglion (TG) measured by immunofluorescence confirmed trigeminal nerve injury. Immunofluorescence showed that P2Y₁₄R was expressed in trigeminal ganglion neurons (TGNs) and satellite glial cells (SGCs). RT-qPCR and Western blot identified increased expression of P2Y₁₄R in TG after CCI-ION. CCI-ION also upregulated interleukin-1β (IL-1β), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-α (TNF-α) in TG. Notably, CCI-ION-induced mechanical hypersensitivity and pro-inflammatory cytokines production were decreased by a P2Y₁₄R antagonist (PPTN). Trigeminal administration of P2Y₁₄R agonist (UDP-glucose) evoked orofacial mechanical hypersensitivity and increased pro-inflammatory cytokines above in TG. Furthermore, CCI-ION induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 in TG, which also were reduced by PPTN. The inhibitors of ERK1/2 (U0126) and p38 (SB203580) decreased these upregulated pro-inflammatory cytokines after CCI-ION. Collectively, this study revealed that P2Y₁₄R in TG contributed to trigeminal neuropathic pain via ERK- and p38-dependent neuroinflammation. Thus, P2Y₁₄R may be a potential drug target against trigeminal neuropathic pain.

Decoding gene expression signatures in mice trigeminal ganglion across trigeminal neuropathic pain stages via high-throughput sequencing

Trigeminal neuropathic pain (TNP) arises due to peripheral nerve injury, the mechanisms underlying which are little known. The altered gene expression profile in sensory ganglia is critical for neuropathic pain generation and maintenance. We, therefore, assessed the transcriptome of the trigeminal ganglion (TG) from mice at different periods of pain progression. Trigeminal neuropathic pain was established by partial infraorbital nerve transection (pIONT). High-throughput RNA sequencing was applied to detect the mRNA profiles of TG collected at 3 and 10 days after modeling. Injured TG displayed dramatically altered mRNA expression profiles compared to Sham. Different gene expression profiles were obtained at 3 and 10 days after pIONT. Moreover, 314 genes were significantly upregulated, and 81 were significantly downregulated at both 3 and 10 days post-pIONT. Meanwhile, enrichment analysis of these persistent differentially expressed genes (DEGs) showed that the MAPK pathway was the most significantly enriched pathway for upregulated DEGs, validated by immunostaining. In addition, TG cell populations defined by single-nuclei RNA sequencing displayed cellular localization of DEGs at a single-cell resolution. Protein-protein interaction (PPI) and sub-PPI network analyses constructed networks and identified the top 10 hub genes for DEGs at different time points. The present data provide novel information on the gene expression signatures of TG during the development and maintenance phases of TNP, and the identified hub genes and pathways may serve as potential targets for treatment.

CXCL13 expressed on inflamed cerebral blood vessels recruit IL-21 producing TFH cells to damage neurons following stroke

BACKGROUND

Ischemic stroke is a leading cause of mortality worldwide, largely due to the inflammatory response to brain ischemia during post-stroke reperfusion. Despite ongoing intensive research, there have not been any clinically approved drugs targeting the inflammatory component to stroke. Preclinical studies have identified T cells as pro-inflammatory mediators of ischemic brain damage, yet mechanisms that regulate the infiltration and phenotype of these cells are lacking. Further understanding of how T cells migrate to the ischemic brain and facilitate neuronal death during brain ischemia can reveal novel targets for post-stroke intervention.

METHODS

To identify the population of T cells that produce IL-21 and contribute to stroke, we performed transient middle cerebral artery occlusion (tMCAO) in mice and performed flow cytometry on brain tissue. We also utilized immunohistochemistry in both mouse and human brain sections to identify cell types and inflammatory mediators related to stroke-induced IL-21 signaling. To mechanistically demonstrate our findings, we employed pharmacological inhibitor anti-CXCL13 and performed histological analyses to evaluate its effects on brain infarct damage. Finally, to evaluate cellular mechanisms of stroke, we exposed mouse primary neurons to oxygen glucose deprivation (OGD) conditions with or without IL-21 and measured cell viability, caspase activity and JAK/STAT signaling.

RESULTS

Flow cytometry on brains from mice following tMCAO identified a novel population of cells IL-21 producing CXCR5+ CD4+ ICOS-1+ T follicular helper cells (TFH) in the ischemic brain early after injury. We observed augmented expression of CXCL13 on inflamed brain vascular cells and demonstrated that inhibition of CXCL13 protects mice from tMCAO by restricting the migration and influence of IL-21 producing TFH cells in the ischemic brain. We also illustrate that neurons express IL-21R in the peri-infarct regions of both mice and human stroke tissue in vivo. Lastly, we found that IL-21 acts on mouse primary ischemic neurons to activate the JAK/STAT pathway and induce caspase 3/7-mediated apoptosis in vitro.

CONCLUSION

These findings identify a novel mechanism for how pro-inflammatory T cells are recruited to the ischemic brain to propagate stroke damage and provide a potential new therapeutic target for stroke.

Activation of CXCL13/CXCR5 axis aggravates experimental autoimmune cystitis and interstitial cystitis/bladder pain syndrome

The abnormal CXCL13/CXCR5 axis is involved in many inflammatory diseases and its selective inhibitor, TAK-799 has exhibited strong anti-inflammatory potency. The sequencing of clinical specimens from interstitial cystitis/bladder pain syndrome (IC/BPS) has shown that CXCL13 and CXCR5 are highly expressed, but the role of CXCL13/CXCR5 axis in IC/BPS has not been rarely reported. Therefore, in this study, we analyzed the GSE11783 sequencing data of IC/BPS patients and investigate the role and mechanism of CXCL13/CXCR5 axis and TAK-779 in the mouse model of experimental autoimmune cystitis (EAC). We verified that CXCL13 and CXCR5 were significantly up-regulated in EAC model. EAC mice exhibited increased bladder inflammatory factors (IL-6, TNF-α, IL-1β), apoptosis-related proteins (Bax, Caspase-3, Caspase-8), frequency of voiding. Using TAK779 to block CXCL13/CXCR5 axis significantly attenuated these inflammatory damages and efficiently improved bladder function (significant reduction in micturition frequency, significant prolongation of inter-contraction interval). Further investigation showed that inhibiton of JNK and NF-kappaB activation, the bioinformatics analysis-indicated downstream signaling of CXCL13/CXCR5 axis, is responsible for the protective effect of TAK779. Taken together, we demonstrate that activation of the CXCL13/CXCR5 axis is involved in the pathophysiology of IC/BPS and EAC. Blocking CXCL13/CXCR5 axis activation by TAK-779 reduces bladder inflammation and improves bladder function in EAC mice.

Neuronal FcεRIα directly mediates ocular itch via IgE-immune complex in a mouse model of allergic conjunctivitis

Background

Classical understanding of allergic conjunctivitis (ACJ) suggests that ocular itch results from a mast cell-dependent inflammatory process. However, treatments that target inflammatory mediators or immune cells are often unsatisfying in relieving the stubborn itch symptom. This suggests that additional mechanisms are responsible for ocular itch in ACJ. In this study, we aim to determine the role of neuronal FcεRIa in allergic ocular itch.

Methods

Calcium imaging was applied to observe the effect of IgE-immune complex in trigeminal neurons. Genomic FcεRIa knockout mice and adeno-associated virus (AAV) mediated sensory neuron FcεRIa knockdown mice were used in conjunction with behavioral tests to determine ocular itch. In addition, immunohistochemistry, Western blot and quantitative RT-PCR were used for in vitro experiments.

Results

We found that FcεRIα was expressed in a subpopulation of conjunctiva sensory neurons. IgE-IC directly activated trigeminal neurons and evoked acute ocular itch without detectible conjunctival inflammation. These effects were attenuated in both a global FcεRIa-knockout mice and after sensory neuronal-specific FcεRIa-knockdown in the mouse trigeminal ganglion. In an ovalbumin (OVA) induced murine ACJ model, FcεRIα was found upregulated in conjunctiva-innervating CGRP+ sensory neurons. Sensory neuronal-specific knockdown of FcεRIa significantly alleviated ocular itch in the ACJ mice without affecting the immune cell infiltration and mast cell activation in conjunctiva. Although FcεRIα mRNA expression was not increased by IgE in dissociated trigeminal ganglion neurons, FcεRIα protein level was enhanced by IgE in a cycloheximide-resistance manner, with concordant enhancement of neuronal responses to IgE-IC. In addition, incremental sensitization gradually enhanced the expression of FcεRIα in small-sized trigeminal neurons and aggravated OVA induced ocular itch.

Conclusions

Our study demonstrates that FcεRIα in pruriceptive neurons directly mediates IgE-IC evoked itch and plays an important role in ocular itch in a mouse model of ACJ. These findings reveal another axis of neuroimmune interaction in allergic itch condition independent to the classical IgE-mast cell pathway, and might suggest novel therapeutic strategies for the treatment of pruritus in ACJ and other immune-related disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02417-x.

Overview of First-Line and Second-Line Pharmacotherapies for Osteoarthritis with Special Focus on Intra-Articular Treatment

Osteoarthritis (OA) can be defined as the result of pathological processes of various etiologies leading to damage to the articular structures. Although the mechanism of degenerative changes has become better understood due to the plethora of biochemical and genetic studies, the drug that could stop the degenerative cascade is still unknown. All available forms of OA therapy are based on symptomatic treatment. According to actual guidelines, comprehensive treatment of OA should always include a combination of various therapeutic options aimed at common goals, which are pain relief in the first place, and then the improvement of function. Local treatment has become more common practice, which takes place between rehabilitation and pharmacological treatment in the hierarchy of procedures. Only in the case of no improvement and the presence of advanced lesions visible in imaging tests, should surgery be considered. Currently, an increasing number of studies are being published suggesting that intra-articular injections may be as effective or even more effective than non-steroidal anti-inflammatory drugs (NSAIDs) and result in fewer systemic adverse events. The most commonly used preparations are hyaluronic acid (HA), glucocorticosteroids (GS), and also platelet-rich plasma (PRP) in recent years. This review aims to present the mechanism of action and clinical effectiveness of different pharmacological options in relieving pain and improving functions in OA as well as the emerging approach in intra-articular treatment with PRP.

Delayed inhibition of ERK and p38 attenuates neuropathic pain without affecting motor function recovery after peripheral nerve injury

Peripheral nerve injuries (PNIs) often result in persistent neuropathic pain, seriously affecting quality of life. Existing therapeutic interventions for PNI-induced neuropathic pain are far from satisfactory. Extracellular signal-regulated kinases (ERKs) and p38 have been found to participate in triggering and maintaining PNI-induced neuropathic pain. However, ERK and p38 also contribute to axonal regeneration and motor function recovery after PNI, making it difficult to inhibit ERK and p38 for therapeutic purposes. In this study, we simultaneously characterized neuropathic pain and motor function recovery in a mouse sciatic nerve crush injury model to identify the time window for therapeutic interventions. We further demonstrated that delayed delivery of a combination of ERK and p38 inhibitors at three weeks after PNI could significantly alleviate PNI-induced neuropathic pain without affecting motor function recovery. Additionally, the combined use of these two inhibitors could suppress pain markedly better than either inhibitor alone, possibly reducing the required dose of each inhibitor and alleviating the side effects and risks of the inhibitors when used individually.

ZNF382 controls mouse neuropathic pain via silencer-based epigenetic inhibition of Cxcl13 in DRG neurons

Nerve injury-induced changes of gene expression in dorsal root ganglion (DRG) are critical for neuropathic pain genesis. However, how these changes occur remains elusive. Here we report the down-regulation of zinc finger protein 382 (ZNF382) in injured DRG neurons after nerve injury. Rescuing this down-regulation attenuates nociceptive hypersensitivity. Conversely, mimicking this down-regulation produces neuropathic pain symptoms, which are alleviated by C-X-C motif chemokine 13 (CXCL13) knockdown or its receptor CXCR5 knockout. Mechanistically, an identified cis-acting silencer at distal upstream of the Cxcl13 promoter suppresses Cxcl13 transcription via binding to ZNF382. Blocking this binding or genetically deleting this silencer abolishes the ZNF382 suppression on Cxcl13 transcription and impairs ZNF382-induced antinociception. Moreover, ZNF382 down-regulation disrupts the repressive epigenetic complex containing histone deacetylase 1 and SET domain bifurcated 1 at the silencer-promoter loop, resulting in Cxcl13 transcriptional activation. Thus, ZNF382 down-regulation is required for neuropathic pain likely through silencer-based epigenetic disinhibition of CXCL13, a key neuropathic pain player, in DRG neurons.

Neuromedin B receptor stimulation of Cav3.2 T-type Ca2+ channels in primary sensory neurons mediates peripheral pain hypersensitivity

Background: Neuromedin B (Nmb) is implicated in the regulation of nociception of sensory neurons. However, the underlying cellular and molecular mechanisms remain unknown.

Methods: Using patch clamp recording, western blot analysis, immunofluorescent labelling, enzyme-linked immunosorbent assays, adenovirus-mediated shRNA knockdown and animal behaviour tests, we studied the effects of Nmb on the sensory neuronal excitability and peripheral pain sensitivity mediated by Cav3.2 T-type channels.

Results: Nmb reversibly and concentration-dependently increased T-type channel currents (I_T) in small-sized trigeminal ganglion (TG) neurons through the activation of neuromedin B receptor (NmbR). This NmbR-mediated I_T response was G_q protein-coupled, but independent of protein kinase C activity. Either intracellular application of the QEHA peptide or shRNA-mediated knockdown of G_β abolished the NmbR-induced I_T response. Inhibition of protein kinase A (PKA) or AMP-activated protein kinase (AMPK) completely abolished the Nmb-induced I_T response. Analysis of phospho-AMPK (p-AMPK) revealed that Nmb significantly activated AMPK, while AMPK inhibition prevented the Nmb-induced increase in PKA activity. In a heterologous expression system, activation of NmbR significantly enhanced the Cav3.2 channel currents, while the Cav3.1 and Cav3.3 channel currents remained unaffected. Nmb induced TG neuronal hyperexcitability and concomitantly induced mechanical and thermal hypersensitivity, both of which were attenuated by T-type channel blockade. Moreover, blockade of NmbR signalling prevented mechanical hypersensitivity in a mouse model of complete Freund's adjuvant-induced inflammatory pain, and this effect was attenuated by siRNA knockdown of Cav3.2.

Conclusions: Our study reveals a novel mechanism by which NmbR stimulates Cav3.2 channels through a G_βγ-dependent AMPK/PKA pathway. In mouse models, this mechanism appears to drive the hyperexcitability of TG neurons and induce pain hypersensitivity.

Proteome Profile of Trigeminal Ganglion in Murine Model of Allergic Contact Dermatitis: Complement 3 Pathway Contributes to Itch and Pain Sensation

Allergic contact dermatitis (ACD) is a common inflammatory dermatosis characterized by persistent itch and pain after topical contact with reactive chemicals. Although it has been long recognized as a type-IV hypersensitivity, its complexity of pathophysiology mechanism makes it still a clinical aporia in treatment. In this study, we aimed to identify crucial proteins involved in the nociceptive sensation of ACD. Based on a chemical-induced ACD murine model, we collected trigeminal ganglions of ACD and control mice for quantitative tandem mass tag (TMT)-labeling proteomic analysis. Immunohistochemistry was further practiced to validate the bioinformatic analysis. A total of 7685 proteins were identified and analyzed. Sixty-four proteins were significantly upregulated, and 75 proteins were downregulated in ACD mice. GO analysis demonstrated that the changed proteins were significantly enriched in terms of immune and peptidase activity in ACD mice. Proteins involved in the complement and coagulation cascades were notably changed in the KEGG enrichment analysis. The upregulation of complement component 3 (C3) in trigeminal satellite cells of ACD mice was further confirmed by immunohistochemistry. ACD upregulated C3 in trigeminal satellite cells. The complement system in sensory ganglion might play an essential role in forming pruritic and nociceptive sensations in ACD.

Age-related gene expression changes in lumbar spinal cord: Implications for neuropathic pain

Clinically, pain has an uneven incidence throughout lifespan and impacts more on the elderly. In contrast, preclinical models of pathological pain have typically used juvenile or young adult animals to highlight the involvement of glial populations, proinflammatory cytokines, and chemokines in the onset and maintenance of pathological signalling in the spinal dorsal horn. The potential impact of this mismatch is also complicated by the growing appreciation that the aged central nervous system exists in a state of chronic inflammation because of enhanced proinflammatory cytokine/chemokine signalling and glial activation. To address this issue, we investigated the impact of aging on the expression of genes that have been associated with neuropathic pain, glial signalling, neurotransmission and neuroinflammation. We used qRT-PCR to quantify gene expression and focussed on the dorsal horn of the spinal cord as this is an important perturbation site in neuropathic pain. To control for global vs region-specific age-related changes in gene expression, the ventral half of the spinal cord was examined. Our results show that expression of proinflammatory chemokines, pattern recognition receptors, and neurotransmitter system components was significantly altered in aged (24-32 months) versus young mice (2-4 months). Notably, the magnitude and direction of these changes were spinal-cord region dependent. For example, expression of the chemokine, Cxcl13, increased 119-fold in dorsal spinal cord, but only 2-fold in the ventral spinal cord of old versus young mice. Therefore, we propose the dorsal spinal cord of old animals is subject to region-specific alterations that prime circuits for the development of pathological pain, potentially in the absence of the peripheral triggers normally associated with these conditions.

Chemokines and Pain in the Trigeminal System

Chemotactic cytokines or chemokines are a large family of secreted proteins able to induce chemotaxis. Chemokines are categorized according to their primary amino acid sequence, and in particular their cysteine residues that form disulphide bonds to maintain the structure: CC, CXC, CX3C, and XC, in which X represents variable amino acids. Among their many roles, chemokines are known to be key players in pain modulation in the peripheral and central nervous systems. Thus, they are promising candidates for novel therapeutics that could replace current, often ineffective treatments. The spinal and trigeminal systems are intrinsically different beyond their anatomical location, and it has been suggested that there are also differences in their sensory mechanisms. Hence, understanding the different mechanisms involved in pain modulation for each system could aid in developing appropriate pharmacological alternatives. Here, we aim to describe the current landscape of chemokines that have been studied specifically with regard to trigeminal pain. Searching PubMed and Google Scholar, we identified 30 reports describing chemokines in animal models of trigeminal pain, and 15 reports describing chemokines involved in human pain associated with the trigeminal system. This review highlights the chemokines studied to date at different levels of the trigeminal system, their cellular localization and, where available, their role in a variety of animal pain models.

Potential Molecular Targets for Treating Neuropathic Orofacial Pain Based on Current Findings in Animal Models

This review highlights potential molecular targets for treating neuropathic orofacial pain based on current findings in animal models. Preclinical research is currently elucidating the pathophysiology of the disease and identifying the molecular targets for better therapies using animal models that mimic this category of orofacial pain, especially post-traumatic trigeminal neuropathic pain (PTNP) and primary trigeminal neuralgia (PTN). Animal models of PTNP and PTN simulate their etiologies, that is, trauma to the trigeminal nerve branch and compression of the trigeminal root entry zone, respectively. Investigations in these animal models have suggested that biological processes, including inflammation, enhanced neuropeptide-mediated pain signal transmission, axonal ectopic discharges, and enhancement of interactions between neurons and glial cells in the trigeminal pathway, are underlying orofacial pain phenotypes. The molecules associated with biological processes, whose expressions are substantially altered following trigeminal nerve damage or compression of the trigeminal nerve root, are potentially involved in the generation and/or exacerbation of neuropathic orofacial pain and can be potential molecular targets for the discovery of better therapies. Application of therapeutic candidates, which act on the molecular targets and modulate biological processes, attenuates pain-associated behaviors in animal models. Such therapeutic candidates including calcitonin gene-related peptide receptor antagonists that have a reasonable mechanism for ameliorating neuropathic orofacial pain and meet the requirements for safe administration to humans seem worth to be evaluated in clinical trials. Such prospective translation of the efficacy of therapeutic candidates from animal models to human patients would help develop better therapies for neuropathic orofacial pain.

Downregulating lncRNA PVT1 Relieves Astrocyte Overactivation Induced Neuropathic Pain Through Targeting miR-186-5p/CXCL13/CXCR5 Axis

Spinal cord injury (SCI) is one of the main causes leading to neuropathic pain. Here, we aim to explore the molecular mechanism and function of lncRNA PVT1 in neuropathic pain induced by SCI. The expression of lncRNA PVT1, microRNA (miR) - 186-5p was measured via quantitative reverse transcription PCR (qRT-PCR), and the activation of astrocytes (labeled by GFAP) was detected by immunohistochemistry. Western blot was conducted to detect the expression of chemokine ligand 13 (CXCL13), chemokine receptor 5 (CXCR5), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS) and glial fibrillary acidic protein (GFAP) in spinal cord injury lesions. The levels of inflammatory cytokines (including IL-1β and IL-6) and MDA in tissues were examined via Enzyme-linked immunosorbent assay (ELISA). In vitro experiments were also conducted in primary cultured astrocyte to explore the response of astrocyte to lipopolysaccharide (LPS). What's more, the PVT1-miR-186-5p interaction was verified via the dual luciferase activity assay and RNA immunoprecipitation (RIP) assay. The results demonstrated that the levels of PVT1, CXCL13 and CXCR5 were upregulated, while miR-186-5p were decreased in SCI rats' spinal cord and LPS-mediated astrocytes. In the SCI model, PVT1 depletion significantly alleviated neuropathic pain, astrocytic activation and reduced the expression of neuroinflammatory factors and proteins. The relevant mechanism studies confirmed that PVT1 is a competitive endogenous RNA (ceRNA) of miR-186-5p, targets and inhibits its expression and promotes the expression of CXCL13/CXCR5, while miR-186-5p targets CXCL13. In conclusion, inhibition of lncRNA PVT1 alleviates neuropathic pain in SCI rats by upregulating miR-186-5p and down-regulating CXCL13/CXCR5. The PVT1/miR-186-5p/CXCL13/CXCR5 axis can be used as a new therapeutic target for neuropathic pain.

G protein-coupled receptor GPR151 is involved in trigeminal neuropathic pain through the induction of Gβγ/extracellular signal-regulated kinase-mediated neuroinflammation in the trigeminal ganglion

ABSTRACT

Trigeminal nerve injury-induced neuropathic pain is a debilitating chronic orofacial pain syndrome but lacks effective treatment. G protein-coupled receptors (GPCRs), especially orphan GPCRs (oGPCRs) are important therapeutic targets in pain medicine. Here, we screened upregulated oGPCRs in the trigeminal ganglion (TG) after partial infraorbital nerve transection (pIONT) and found that Gpr151 was the most significantly upregulated oGPCRs. Gpr151 mRNA was increased from pIONT day 3 and maintained for more than 21 days. Furthermore, GPR151 was expressed in the neurons of the TG after pIONT. Global mutation or knockdown of Gpr151 in the TG attenuated pIONT-induced mechanical allodynia. In addition, the excitability of TG neurons was increased after pIONT in wild-type (WT) mice, but not in Gpr151-/- mice. Notably, GPR151 bound to Gαi protein, but not Gαq, Gα12, or Gα13, and activated the extracellular signal-regulated kinase (ERK) through Gβγ. Extracellular signal-regulated kinase was also activated by pIONT in the TG of WT mice, but not in Gpr151-/- mice. Gene microarray showed that Gpr151 mutation reduced the expression of a large number of neuroinflammation-related genes that were upregulated in WT mice after pIONT, including chemokines CCL5, CCL7, CXCL9, and CXCL10. The mitogen-activated protein kinase inhibitor (PD98059) attenuated mechanical allodynia and reduced the upregulation of these chemokines after pIONT. Collectively, this study not only revealed the involvement of GPR151 in the maintenance of trigeminal neuropathic pain but also identified GPR151 as a Gαi-coupled receptor to induce ERK-dependent neuroinflammation. Thus, GPR151 may be a potential drug target for the treatment of trigeminal neuropathic pain.

Assessment of Growth Factors, Cytokines, and Cellular Markers in Saliva of Patients with Trigeminal Neuralgia

We proposed to perform a comparative analysis of growth factors, cytokines, and chemokine receptors on the salivary cells in the saliva obtained from trigeminal neuralgia (TN) and normal subjects. Saliva was collected from TN and healthy subjects. Salivary cells were isolated by centrifugation. The expression of the cell surface marker was analyzed by flow cytometry. A cytometric bead array was done to measure the levels of cytokines and growth factors on the flow cytometer. Saliva from TN subjects showed lower growth factor levels of Angiopoietin-2, bFGF, HGF, SCF, TGF-α, and VEGF and higher cytokine levels of IL-1β, TNF-α, CCL2, IL-17A, IL-6, and CXCL8, as well as higher expression levels of chemokine receptors CCR1 (CD191), CR3 (CD11b), CCR2 (CD192), CXCR5 (CD185), and CCR5 (CD196) in the cells from TN saliva. A certain set of cytokines and growth factors in the saliva, as well as chemokine receptors on salivary cells, could be a useful tool in the diagnostics and prognostics of trigeminal neuralgia. Trigeminal neuralgia is one of the significant pathological conditions in the class of chronic diseases around the world. Many targeted approaches are being tried by various research groups to utilize the information of the inflammatory microenvironment to resolve the pathology of chronic TN.

Evolution of mirror-image pain in temporomandibular joint osteoarthritis mouse model

OBJECTIVE

Mirror-image pain is a kind of pain that occurs on the contralateral side, but its pathogenesis remains unclear. To develop an osteoarthritis mouse model for investigating mirror-image pain through observing nocifensive behaviors, histological changes, and nociceptive activity at days 3, 7, 14, 21, and 28 after the chemical induction of unilateral temporomandibular joint (TMJ) osteoarthritis.

METHODOLOGY

We randomly divided 6-week-old mice into sham and complete Freund adjuvant groups. To induce nocifensive behaviors, we applied 0.04 g of von Frey filament, 10 psi of air puff, and cold acetone on both sides of whisker pads at different days. The histology of TMJ on both sides was observed by hematoxylin/eosin staining and microcomputed tomography scanning. Furthermore, the nociceptive activity was evaluated using the phosphorylated cyclic AMP response element binding protein (pCREB) and a microglia marker at different days in the trigeminal subnucleus caudalis.

RESULTS

Nocifensive behaviors against mechanical and temperature stimuli on the contralateral side became stronger than the baseline on day 28, in agreement with the elevation of the pCREB and the microglia marker in the trigeminal subnucleus caudalis. Thus, hypernociception on the contralateral side occurred at day 28.

CONCLUSIONS

Clearly, the TMJ model with unilateral osteoarthritis exhibited mirror-image pain. Therefore, this model is useful in investigating the pathogenesis of pain and in developing treatments.

CXCL10 and CXCR3 in the Trigeminal Ganglion Contribute to Trigeminal Neuropathic Pain in Mice

Purpose

Trigeminal neuropathic pain is very common clinically, but effective treatments are lacking. Chemokines and their receptors have been implicated in the pathogenesis of chronic pain. This study explored the role of the chemokine CXCL10 and its receptor, CXCR3, in trigeminal neuropathic pain in mice.

Materials and Methods

Trigeminal neuropathic pain was established by partial infraorbital nerve ligation (pIONL) in wild-type and Cxcr3^−/− mice. Facial mechanical allodynia was evaluated by behavioral testing. A lentivirus containing Cxcr3 shRNA (LV-Cxcr3 shRNA) was microinjected into the trigeminal ganglion (TG) to knock down Cxcr3 expression. Quantitative polymerase chain reaction assays and immunofluorescence staining were used to examine Cxcl10/Cxcr3 mRNA expression and protein distribution. Western blotting was performed to examine activation of extracellular signal-regulated kinase (ERK) and AKT in the TG. Intra-TG injection of an AKT inhibitor was performed to examine the role of AKT in trigeminal neuropathic pain.

Results

pIONL induced persistent trigeminal neuropathic pain, which was alleviated in Cxcr3^−/− mice. Intra-TG injection of LV-Cxcr3 shRNA attenuated pIONL-induced mechanical allodynia. Furthermore, pIONL increased the expression of CXCR3 and its major ligand, CXCL10, in TG neurons. Intra-TG injection of CXCL10 induced pain hypersensitivity in wild-type mice but not in Cxcr3^−/− mice. CXCL10 also induced activation of ERK and AKT in the TG of wild-type mice. Finally, pIONL-induced activation of ERK and AKT was reduced in Cxcr3^−/− mice. Intra-TG injection of the AKT inhibitor alleviated pIONL-induced mechanical allodynia in WT mice but not in Cxcr3^−/− mice.

Conclusion

CXCL10 acts on CXCR3 to induce ERK and AKT activation in TG neurons and contributes to the maintenance of trigeminal neuropathic pain.

TLR8 in the Trigeminal Ganglion Contributes to the Maintenance of Trigeminal Neuropathic Pain in Mice

Trigeminal neuropathic pain (TNP) is a significant health problem but the involved mechanism has not been completely elucidated. Toll-like receptors (TLRs) have recently been demonstrated to be expressed in the dorsal root ganglion and involved in chronic pain. Here, we show that TLR8 was persistently increased in the trigeminal ganglion (TG) neurons in model of TNP induced by partial infraorbital nerve ligation (pIONL). In addition, deletion or knockdown of Tlr8 in the TG attenuated pIONL-induced mechanical allodynia, reduced the activation of ERK and p38-MAPK, and decreased the expression of pro-inflammatory cytokines in the TG. Furthermore, intra-TG injection of the TLR8 agonist VTX-2337 induced pain hypersensitivity. VTX-2337 also increased the intracellular Ca²⁺ concentration, induced the activation of ERK and p38, and increased the expression of pro-inflammatory cytokines in the TG. These data indicate that TLR8 contributes to the maintenance of TNP through increasing MAPK-mediated neuroinflammation. Targeting TLR8 signaling may be effective for the treatment of TNP.

An Investigation of the Molecular Mechanisms Underlying the Analgesic Effect of Jakyak-Gamcho Decoction: A Network Pharmacology Study

Herbal drugs have drawn substantial interest as effective analgesic agents; however, their therapeutic mechanisms remain to be fully understood. To address this question, we performed a network pharmacology study to explore the system-level mechanisms that underlie the analgesic activity of Jakyak-Gamcho decoction (JGd; Shaoyao-Gancao-Tang in Chinese and Shakuyaku-Kanzo-To in Japanese), an herbal prescription consisting of Paeonia lactiflora Pallas and Glycyrrhiza uralensis Fischer. Based on comprehensive information regarding the pharmacological and chemical properties of the herbal constituents of JGd, we identified 57 active chemical compounds and their 70 pain-associated targets. The JGd targets were determined to be involved in the regulation of diverse biological activities as follows: calcium- and cytokine-mediated signalings, calcium ion concentration and homeostasis, cellular behaviors of muscle and neuronal cells, inflammatory response, and response to chemical, cytokine, drug, and oxidative stress. The targets were further enriched in various pain-associated signalings, including the PI3K-Akt, estrogen, ErbB, neurotrophin, neuroactive ligand-receptor interaction, HIF-1, serotonergic synapse, JAK-STAT, and cAMP pathways. Thus, these data provide a systematic basis to understand the molecular mechanisms underlying the analgesic activity of herbal drugs.

Macrophagic and microglial complexity after neuronal injury

Central nervous system (CNS) injuries do not heal properly in contrast to normal tissue repair, in which functional recovery typically occurs. The reason for this dichotomy in wound repair is explained in part by macrophage and microglial malfunction, affecting both the extrinsic and intrinsic barriers to appropriate axonal regeneration. In normal healing tissue, macrophages promote the repair of injured tissue by regulating transitions through different phases of the healing response. In contrast, inflammation dominates the outcome of CNS injury, often leading to secondary damage. Therefore, an understanding of the molecular mechanisms underlying this dichotomy is critical to advance in neuronal repair therapies. Recent studies highlight the plasticity and complexity of macrophages and microglia beyond the classical view of the M1/M2 polarization paradigm. This plasticity represents an in vivo continuous spectrum of phenotypes with overlapping functions and markers. Moreover, macrophage and microglial plasticity affect many events essential for neuronal regeneration after injury, such as myelin and cell debris clearance, inflammation, release of cytokines, and trophic factors, affecting both intrinsic neuronal properties and extracellular matrix deposition. Until recently, this complexity was overlooked in the translation of therapies modulating these responses for the treatment of neuronal injuries. However, recent studies have shed important light on the underlying molecular mechanisms of this complexity and its transitions and effects on regenerative events. Here we review the complexity of macrophages and microglia after neuronal injury and their roles in regeneration, as well as the underlying molecular mechanisms, and we discuss current challenges and future opportunities for treatment.

Increased peripheral helper T cells type 17 subset correlates with the severity of psoriasis vulgaris

Recently, a new subgroup of T cells, named peripheral helper T (Tph) cells, has been implicated in autoimmune pathogenesis. An imbalance of Tph cell subsets influences the severity of immune-related diseases. However, the characteristics and roles of Tph cell subsets in psoriasis remain unknown. Programmed cell death 1-positive, chemokine C-X-C receptor (CXCR) 5-negative Tph cells can be divided into 3 subgroups based on differential expression of chemokine CXCR3 and chemokine C-C receptor (CCR) 6. CXCR3⁺CCR6^- Tph cells are classified as Tph1, CXCR3^-CCR6^- Tph cells are classified as Tph2, and CXCR3^-CCR6⁺ Tph cells are classified as Tph17. In this study, conditions of circulating Tph cell subsets and CD4⁺CXCR5⁺ follicular helper T (Tfh) cells in 27 patients with psoriasis and 13 healthy individuals were detected by flow cytometry. The level of plasma chemokine C-X-C ligand (CXCL) 13 was measured by enzyme-linked immunosorbent assay. The correlations between the above indexes and disease severity were explored. In the peripheral blood of patients with psoriasis, Tph17 cells had an activated, proliferative phenotype; the quantity of the cells correlated with disease severity. Plasma CXCL13 levels were elevated in psoriasis and associated with disease severity and the frequency of Tph17 cells. CD4⁺CXCR5⁺ Tfh cells were increased in patients and positively correlated with disease severity, the frequency of Tph17 cells, and plasma CXCL13 levels. Our results suggest that Tph17 cells and the CXCL13/CXCR5 axis may be involved in the pathogenesis of psoriasis and represent new immunotherapeutic targets for treating psoriasis.

Chemokine CXCL13 acts via CXCR5-ERK signaling in hippocampus to induce perioperative neurocognitive disorders in surgically treated mice

Background

Perioperative neurocognitive disorders (PNDs) occur frequently after surgery and worsen patient outcome. How C-X-C motif chemokine (CXCL) 13 and its sole receptor CXCR5 contribute to PNDs remains poorly understood.

Methods

A PND model was created in adult male C57BL/6J and CXCR5^−/− mice by exploratory laparotomy. Mice were pretreated via intracerebroventricular injection with recombinant CXCL13, short hairpin RNA against CXCL13 or a scrambled control RNA, or ERK inhibitor PD98059. Then surgery was performed to induce PNDs, and animals were assessed in the Barnes maze trial followed by a fear-conditioning test. Expression of CXCL13, CXCR5, and ERK in hippocampus was examined using Western blot, quantitative PCR, and immunohistochemistry. Levels of interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in hippocampus were assessed by Western blot.

Results

Surgery impaired learning and memory, and it increased expression of CXCL13 and CXCR5 in the hippocampus. CXCL13 knockdown partially reversed the effects of surgery on CXCR5 and cognitive dysfunction. CXCR5 knockout led to similar cognitive outcomes as CXCL13 knockdown, and it repressed surgery-induced activation of ERK and production of IL-1β and TNF-α in hippocampus. Recombinant CXCL13 induced cognitive deficits and increased the expression of phospho-ERK as well as IL-1β and TNF-α in hippocampus of wild-type mice, but not CXCR5^−/− mice. PD98059 partially blocked CXCL13-induced cognitive dysfunction as well as production of IL-1β and TNF-α.

Conclusions

CXCL13-induced activation of CXCR5 may contribute to PNDs by triggering ERK-mediated production of pro-inflammatory cytokines in hippocampus.

Diacerein: Recent insight into pharmacological activities and molecular pathways

Diacerein is a symptomatic slow-acting drug in osteoarthritis (SYSADOA) and the active metabolite is rhein. It is a non-steroidal anti-inflammatory drug with unique pharmacological properties as anti-oxidant and anti-apoptosis. Diacerein has recently shown to have a potential role by mediating anti-inflammatory as well as anti-oxidant and anti-apoptosis in kidney injury, diabetes mullites, and a beneficial effect on pain relief. It may have a therapeutic role in cancer, ulcerative colitis, testicular injury and cervical hyperkeratosis. Furthermore, diacerein has a valuable addition in combination therapy as a synergetic agent. This review, the first of its kind, highlights the proposed roles of diacerein in osteoarthritis and discusses recent results supporting its emerging roles with a particular focus on how these new insights may facilitate the rational development of diacerein for targeted therapies in the future.

CXCL13 is a differentiation- and hypoxia-induced adipocytokine that exacerbates the inflammatory phenotype of adipocytes through PHLPP1 induction

Hypoxia in adipose tissue is regarded as a trigger that induces dysregulation of the secretory profile in adipocytes. Similarly, local dysregulation of adipocytokine secretion is an initial event in the deleterious effects of obesity on metabolism. We previously reported that CXCL13 is highly produced during adipogenesis, however little is known about the roles of CXCL13 in adipocytes. Here, we found that hypoxia, as modeled by 1% O2 or exposure to the hypoxia-mimetic reagent desferrioxamine (DFO) has strong inductive effects on the expression of CXCL13 and CXCR5, a CXCL13 receptor, in both undifferentiated and differentiated adipocytes and in organ-cultured white adipose tissue (WAT). CXCL13 was also highly expressed in WAT from high fat diet-fed mice. Hypoxic profile, typified by increased expression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) and decreased expression of adiponectin, was significantly induced by CXCL13 treatment during adipogenic differentiation. Conversely, the treatment of adipocytes with a neutralizing-antibody against CXCL13 as well as CXCR5 knockdown by specific siRNA effectively inhibited DFO-induced inflammation. The phosphorylation of Akt2, a protective factor of adipose inflammation, was significantly inhibited by CXCL13 treatment during adipogenic differentiation. Mechanistically, CXCL13 induces the expression of PHLPP1, an Akt2 phosphatase, through focal adhesion kinase (FAK) signaling; and correspondingly we show that CXCL13 and DFO-induced IL-6 and PAI-1 expression was blocked by Phlpp1 knockdown. Furthermore, we revealed the functional binding sites of PPARγ2 and HIF1-α within the Cxcl13 promoter. Taken together, these results indicate that CXCL13 is an adipocytokine that facilitates hypoxia-induced inflammation in adipocytes through FAK-mediated induction of PHLPP1 in autocrine and/or paracrine manner.

Transcriptome-Wide Analysis of CXCR5 Deficient Retinal Pigment Epithelial (RPE) Cells Reveals Molecular Signatures of RPE Homeostasis

Age-related macular degeneration (AMD) is the most common cause of irreversible blindness in the elderly population. In our previous studies, we found that deficiency of CXCR5 causes AMD-like pathological phenotypes in mice, characterized by abnormalities and dysfunction of the retinal pigment epithelium (RPE) cells. The abnormalities included abnormal cellular shape and impaired barrier function. In the present study, primary RPE cells were derived separately from CXCR5 knockout (KO) mice and from C57BL6 wild type (WT). The isolated primary cells were cultured for several days, and then total RNA was isolated and used for library preparation, sequencing, and the resultant raw data analyzed. Relative to the WT, a total of 1392 differentially expressed genes (DEG) were identified. Gene ontology analysis showed various biological processes, cellular components, and molecular functions were enriched. Pathway enrichment analysis revealed several pathways, including the PI3K-Akt signaling, mTOR signaling, FoxO, focal adhesion, endocytosis, ubiquitin-mediated proteolysis, TNFα-NF-kB Signaling, adipogenesis genes, p53 signaling, Ras, autophagy, epithelial–mesenchymal transition (EMT), and mitochondrial pathway. This study explores molecular signatures associated with deficiency of CXCR5 in RPE cells. Many of these signatures are important for homeostasis of this tissue. The identified pathways and genes require further evaluation to better understand the pathophysiology of AMD.

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.

Identification of significant gene biomarkers of low back pain caused by changes in the osmotic pressure of nucleus pulposus cells

The incidence of intervertebral disc (IVD) degeneration disease, caused by changes in the osmotic pressure of nucleus pulposus (NP) cells, increases with age. In general, low back pain is associated with IVD degeneration. However, the mechanism and molecular target of low back pain have not been elucidated, and there are no data suggesting specific biomarkers of low back pain. Therefore, the research aims to identify and verify the significant gene biomarkers of low back pain. The differentially expressed genes (DEGs) were screened in the Gene Expression Omnibus (GEO) database, and the identification and analysis of significant gene biomarkers were also performed with various bioinformatics programs. A total of 120 patients with low back pain were recruited. Before surgery, the degree of pain was measured by the numeric rating scale (NRS), which enables comparison of the pain scores from individuals. After surgery, IVD tissues were obtained, and NP cells were isolated. The NP cells were cultured in two various osmotic media, including iso-osmotic media (293 mOsm/kg H₂O) to account for the morbid environment of NP cells in IVD degeneration disease and hyper-osmotic media (450 mOsm/kg H₂O) to account for the normal condition of NP cells in healthy individuals. The relative mRNA expression levels of CCL5, OPRL1, CXCL13, and SST were measured by quantitative real-time PCR in the in vitro analysis of the osmotic pressure experiments. Finally, correlation analysis and a neural network module were employed to explore the linkage between significant gene biomarkers and pain. A total of 371 DEGs were identified, including 128 downregulated genes and 243 upregulated genes. Furthermore, the four genes (CCL5, OPRL1, SST, and CXCL13) were identified as significant gene biomarkers of low back pain (P < 0.001) based on univariate linear regression, and CCL5 (odds ratio, 34.667; P = 0.003) and OPRL1 (odds ratio, 19.875; P < 0.001) were significantly related to low back pain through multivariate logistic regression. The expression of CCL5 and OPRL1 might be correlated with low back pain in patients with IVD degeneration disease caused by changes in the osmotic pressure of NP cells.

[Characteristics of orofacial operant test for orofacial pain sensitivity caused by occlusal interference in rats]

OBJECTIVE

To compare the orofacial pain sensitivity with operant test and mechanical hyperalgesia with von Frey filaments of two orofacial pain models (EOI: experimental occlusal interference; pIONX: partial infraorbital nerve transection). To investigate the operant and evoked characteristics of EOI-rats.

METHODS

The orofacial operant behaviors were tested by Ugo Basile Orofacial Stimulation Test System. The mechanical thresholds of vibrissal pads were tested by von Frey filaments. Male Sprague-Dawley rats were randomly divided into eight groups: von Frey group: sham-EOI, EOI, sham-pIONX, pIONX (sham: sham-operated group); operant test group: sham-EOI, EOI, sham-pIONX, pIONX (sham: sham-operated group). The mechanical thresholds and orofacial operant behaviors were tested on pre-operation and post-operation days l, 3, 7, 10, 14 and 21.

RESULTS

In pIONX of von Frey group, the mechanical withdrawal threshold decreased from days 1 to 21 (P<0.05), peaking from days 7 to 10, and lasted until the end of the experiment. There was no significant difference between the bilateral sides. In pIONX of operant test group, the total contact time decreased from days 10 to 21 (P<0.05), peaking from days 10 to 14, and lasted until the end of the experiment. In EOI of von Frey group, the mechanical withdrawal threshold decreased from days 3 to 21 (P<0.05), peaking on day 7, and lasted until the end of the experiment. There was no significant difference between the bilateral sides. In EOI of operant test group, the total contact time decreased from days 1 to 21 (P<0.05), peaking from days 7 to 10, and lasting until the end of experiment.

CONCLUSION

Orofacial operant test is a stable method to evaluate orofacial pain behaviors, which could discriminate the feature of neuropathic and EOI orofacial pain. In these two animal models, both of the operant behaviors and the mechanical hyperalgesia exhibited different time courses. Orofacial operant test provides a novel method for evaluating the orofacial pain sensitivity and studying the orofacial pain mechanism thoroughly.

Photobiomodulation and B vitamins administration produces antinociception in an orofacial pain model through the modulation of glial cells and cytokines expression

Chronic constriction injury (CCI) of infraorbital nerve (IoN) results in whisker pad mechanical allodynia in rats and activation glial cells contributing to the development of orofacial pain. Whisker pad mechanical allodynia (von Frey stimuli) was tested pre and postoperatively and conducted during the treatment time. Photobiomodulation (PBM) and vitamins B complex (VBC) has been demonstrated therapeutic efficacy in ameliorate neuropathic pain. The aim of this study was to evaluate the antinociceptive effect of PBM, VBC or the combined treatment VBC ​+ ​PBM on orofacial pain due to CCI-IoN. Behavioral and molecular approaches were used to analyses nociception, cellular and neurochemical alterations. CCI-IoN caused mechanical allodynia and cellular alterations including increased expression of glial fibrillary acid protein (GFAP) and ionized calcium binding adaptor molecule 1 (Iba-1), administration of VBC (B1/B6/B12 at 180/180/1.8 ​mg/kg, s.c., 5 times all long 10 sessions) and PBM therapy (904 ​nm, power of 75Wpico, average power of 0.0434 ​W, pulse frequency of 9500 ​Hz, area of the beam 0.13 ​cm², 18 ​s duration, energy density 6 ​J/cm², with an energy per point of 0.78 ​J for 10 sessions) or their combination presented improvement of the nociceptive behavior and decreased expression of GFAP and Iba-1. Additionally, CCI-IoN rats exhibited an upregulation of IL1β, IL6 and TNF-α expression and all treatments prevented this upregulation and also increased IL10 expression. Overall, the present results highlight the pain reliever effect of VBC or PBM alone or in combination, through the modulation of glial cells and cytokines expression in the spinal trigeminal nucleus of rats.

The roles of chemokine (C-X-C motif) ligand 13 in spinal cord ischemia-reperfusion injury in rats

Spinal cord ischemia-reperfusion injury (SCII) remains an unresolved complication and its underlying mechanism has not been fully elucidated. In this study, we studied the role of chemokine (C-X-C motif) ligand 13 (CXCL13) in a rat model of SCII. We examined the time course and cellular distribution of CXCL13 protein in rats after SCII. The effects of siRNA targeting CXCL13 or C-X-C chemokine receptor type 5 (CXCR5) in SCII were also investigated. Neurological function, histological assessment, and disruption of the blood-spinal cord barrier (BSCB) were evaluated. The expression levels of CXCL13, CXCR5, phosphorylated extracellular signal-regulated kinase (p-ERK), caspase-3, interleukin 6 (IL-6), TNF-α, and IL-1β were determined. We found that SCII resulted in impaired hind limb function and increased the expression of CXCL13. In addition, CXCL13 expression demonstrated the most pronounced effect at 24 h after SCII. We reveal that CXCL13 protein was co-expressed with the mature neuron marker NeuN and the microglial marker IBA-1 in spinal cord tissues of model rats. SCII also increased the expression of CXCR5, p-ERK, caspase-3, IL-6, TNF-α, and IL-1β at 24 h after SCII. Pre-treatment with CXCL13 siRNA protected the rats against SCII and decreased the expression of signalling pathway proteins and proinflammatory cytokines mentioned above. CXCR5 siRNA also showed similar protective effects. These findings indicate that CXCL13 is involved in SCII. The CXCL13/CXCR5 axis promotes the development of SCII, possibly via ERK-mediated pathways. Targeting the mechanism of CXCL13 involved in the development of SCII might be a potential approach for the treatment of this condition.