miRNA-23a/CXCR4 regulates neuropathic pain via directly targeting TXNIP/NLRP3 inflammasome axis

EZH2-dependent myelination following sciatic nerve injury

JOURNAL/nrgr/04.03/01300535-202508000-00028/figure1/v/2024-09-30T120553Z/r/image-tiff Demyelination and remyelination have been major focal points in the study of peripheral nerve regeneration following peripheral nerve injury. Notably, the gene regulatory network of regenerated myelin differs from that of native myelin. Silencing of enhancer of zeste homolog 2 (EZH2) hinders the differentiation, maturation, and myelination of Schwann cells in vitro. To further determine the role of EZH2 in myelination and recovery post-peripheral nerve injury, conditional knockout mice lacking Ezh2 in Schwann cells (Ezh2fl/fl;Dhh-Cre and Ezh2fl/fl;Mpz-Cre) were generated. Our results show that a significant proportion of axons in the sciatic nerve of Ezh2-depleted mice remain unmyelinated. This highlights the crucial role of Ezh2 in initiating Schwann cell myelination. Furthermore, we observed that 21 days after inducing a sciatic nerve crush injury in these mice, most axons had remyelinated at the injury site in the control nerve, while Ezh2fl/fl;Mpz-Cre mice had significantly fewer remyelinated axons compared with their wild-type littermates. This suggests that the absence of Ezh2 in Schwann cells impairs myelin formation and remyelination. In conclusion, EZH2 has emerged as a pivotal regulatory factor in the process of demyelination and myelin regeneration following peripheral nerve injury. Modulating EZH2 activity during these processes may offer a promising therapeutic target for the treatment of peripheral nerve injuries.

Immunomodulation with M2 macrophage-derived extracellular vesicles for enhanced titanium implant osseointegration under diabetic conditions

M2 macrophage-derived extracellular vesicles (M2-EVs) demonstrate the capacity to reduce pro-inflammatory M1 macrophage formation, thereby restoring the M1-M2 macrophage balance and promoting immunoregulation. However, the efficacy of M2-EVs in regulating macrophage polarization and subsequently enhancing osseointegration around titanium (Ti) implants in patients with diabetes mellitus (DM) remains to be elucidated. In this study, Ti implants were coated with polydopamine to facilitate M2-EVs adherence. In vitro experiment results demonstrated that M2-EVs could carry miR-23a-3p, inhibiting NOD-like receptor protein3(NLRP3) inflammasome activation in M1 macrophage and reducing the levels of inflammatory cytokines such as IL-1β by targeting NEK7. This improved the M1-M2 macrophage balance and enhanced mineralization on the Ti implant surfaces. The in vivo experiment results demonstrated that in diabetic conditions, the nanocoated M2-EVs significantly promoted high-quality bone deposition around the Ti implants. The current results provide a novel perspective for simple and effective decoration of M2-EVs on Ti implants; clinically, the method may afford osteoimmunomodulatory effects enhancing implant osseointegration in patients with DM.

Second Generation I-Body AD-214 Attenuates Unilateral Ureteral Obstruction (UUO)-Induced Kidney Fibrosis Through Inhibiting Leukocyte Infiltration and Macrophage Migration

Kidney fibrosis is the common pathological pathway in progressive chronic kidney disease (CKD), and current treatments are largely ineffective. The C-X-C chemokine receptor 4 (CXCR4) is crucial to fibrosis development. By using neural cell adhesion molecules as scaffolds with binding loops that mimic the shape of shark antibodies, fully humanized single-domain i-bodies have been developed. The first-generation i-body, AD-114, demonstrated antifibrotic effects in a mouse model of folic acid (FA)-induced renal fibrosis. The second-generation i-body, AD-214, is an Fc-fusion protein with an extended half-life, enhanced activity, and a mutated Fc domain to prevent immune activation. To investigate the renoprotective mechanisms of AD-214, RPTEC/TERT1 cells (a human proximal tubular cell line) were incubated with TGF-b1 with/without AD-214 and the supernatant was collected to measure collagen levels by Western blot. Mice with unilateral ureteral obstruction (UUO) received AD-214 intraperitoneally (i.p.) every two days for 14 days. Kidney fibrosis markers and kidney function were then analyzed. AD-214 suppressed TGF-b1-induced collagen overexpression in RPTEC/TERT1 cells. In UUO mice, AD-214 reduced extracellular matrix (ECM) deposition, restored kidney function, and limited leukocyte infiltration. In a scratch assay, AD-214 also inhibited macrophage migration. To conclude, i-body AD-214 attenuates UUO-induced kidney fibrosis by inhibiting leukocyte infiltration and macrophage migration.

Bone marrow mesenchymal stem cells-derived exosomes promote spinal cord injury repair through the miR-497-5p/TXNIP/NLRP3 axis

Bone marrow mesenchymal stem cells (BMSCs) indicate a repairing prospect to treat spinal cord injury, a major traumatic disease. This study investigated the repair effect of bone marrow mesenchymal stem cell-derived exosomes (BMSC-Exos) on spinal cord injury. BMSCs were collected to extract BMSC-Exos which were identified by different means. The SCI model of rats was established, the motor behavior was scored by BBB field test, and the spinal cord tissues were separated and stained by HE, Nissl, and Tunel, respectively, as well as analyzed to measure inflammatory and oxidative stress responses. PC12 cells were co-cultured with Exos and analyzed by CCK-8 and flow cytometry to measure cell proliferation and apoptosis. BMSC-Exos improved SCI in rats with the recovery of motor function, alleviation of pathological conditions, and reduction of apoptosis, inflammatory responses, and oxidative stress. BMSC-Exos increased miR-497-5p expression, and miR-497-5p overexpression strengthened the protective effect of BMSC-Exos on SCI. miR-497-5p targeted inactivation of TXNIP/NLRP3 pathway. TXNIP saved the repair effect of miR-497-5p-carrying BMSC-Exos on SCI rats. miR-497-5p-carrying BMSC-Exos alleviated apoptosis and induced proliferation of H2O2-treated PC12 cells. BMSC-Exos promote SCI repair via the miR-497-5p/TXNIP/NLRP3 axis, which may be a target for alleviating SCI-associated nerve damage.

The role of non-coding RNAs in neuropathic pain

Neuropathic pain (NPP) is a refractory pain syndrome, caused by damage or disease of the somatosensory nervous system and characterized by spontaneous pain, hyperalgesia, abnormal pain and sensory abnormality. Non-coding RNAs (ncRNAs), including microRNA (miRNA), long non-coding RNA (lncRNA), circular RNA (circRNA) and Piwi interacting RNA (piRNA), play a notable role in initiation and maintenance of NPP. In this review, we summarize the role of ncRNAs in NPP and their underlaying mechanism. Generally, ncRNAs are interacted with mRNA, protein or DNA to regulate the molecules and signals assciated with neuroinflammation, ion channels, neurotrophic factors and others, and then involved in the occurrence and development of NPP. Therefore, this review not only contributes to deepen our understanding of the pathophysiological mechanism of NPP, but also provides theoretical basis for the development of new therapy strategies for this disorder.

Gynostemma pentaphyllum (Thunb.) Makino Affects Autophagy and Improves Diabetic Peripheral Neuropathy Through TXNIP-Mediated PI3K/AKT/mTOR Signaling Pathway

TXNIP is closely associated with diabetic peripheral neuropathy (DPN). Gynostemma pentaphyllum (Thunb.) Makino (GP), a perennial herb with five leaves, is considered to have medicinal values. However, it is unknown whether GP alleviates DPN by modulating TXNIP-mediated autophagy. The aim of this study was to evaluate the effect of GP on Schwann cell injury during DPN and to investigate the mechanism of GP in DPN for the first time. High-fat diet-fed GK rats and high-glucose-cultured RSC96 cells were used to establish DPN models. The effects of GP on DPN were investigated by blood glucose assay, neurological function assay, pathology assay, and immunohistochemistry. To investigate the effect of GP on autophagy and upstream PI3K/AKT/mTOR signaling pathway in Schwann cells, Western blot and immunofluorescence assay were performed on RSC96 cells to detect the expression of beclin-1 and LC3. Western blot method was used to detect the expression of PI3K, p-Akt/Akt, p-mTOR/mTOR, and RT-qPCR method and was used to detect the expression of PI3K. Apoptosis was detected by flow cytometry. The effects of TXNIP on the above indicators were also detected in RSC96 cells. Finally, the mechanism of GP regulation of autophagy and apoptosis in RSC96 cells was verified. GP reduced blood glucose level, attenuated peripheral nerve myelin damage, and improved nerve function in DPN rats. In addition, GP enhanced autophagy activity and reduced apoptosis in RSC96 cells. GP promoted autophagy by regulating TXNIP-mediated PI3K/AKT/mTOR signaling pathway, and GP reduced apoptosis in RSC96 cells by promoting cellular autophagy. GP attenuates DPN myelin damage in RSC96 cells by enhancing autophagy, and its mechanism may be related to the inhibition of PI3K/AKT/mTOR signaling pathway by up-regulating the expression of TXNIP.

Functional Characterization of an Arylsulfonamide-Based Small-Molecule Inhibitor of the NLRP3 Inflammasome

Considerable evidence indicates that the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome plays key roles in human pathophysiology, suggesting it as a potential drug target. Currently, studies have yet to develop compounds that are promising therapeutics in the clinic by targeting the NLRP3 inflammasome. Herein, we aim to further biologically characterize a previously identified small-molecule inhibitor of the NLRP3 inflammasome from our group, YM-I-26, to confirm its functional activities. We showed that YM-I-26 is highly selective toward the NLRP3 inflammasome and binds to NLRP3 directly. A systemic analysis revealed YM-I-26 with inflammation-related and immunomodulatory activities by the Eurofins BioMAP Diversity PLUS panel. In addition, studies using the mouse microglia BV2 cell model demonstrated that YM-I-26 is not cytotoxic, improved the phagocytotic functions of BV2 cells toward beta-amyloid, and suppressed the production of cytokines of IL-1β and IL-10 upon the activation of the NLRP3 inflammasome. Collectively, our studies support the functional activities of YM-I-26 as a NLRP3 inhibitor in physiologically relevant cell models, and warrant future studies of YM-I-26 and its analogs to advance the drug development as potential therapeutics.

Long non-coding RNA Snhg16 Lessens Ozone Curative Effect on Chronic Constriction Injury mice via microRNA-719/SCN1A axis

We investigated the function and molecular mechanism of long non-coding RNA (lncRNA) small nucleolar RNA host gene 16 (Snhg16) in modifying ozone treatment for neuropathic pain (NP) in a mouse model of chronic constriction injury (CCI). Pain-related behavioral responses were evaluated using paw withdrawal threshold (PWT), paw lifting number (PLN), and paw withdrawal latency (PWL) tests. Interleukin (IL)-1β, IL-10, IL-6, and tumor necrosis factor-alpha (TNF-α) were measured by ELISA and qRT-PCR to evaluate neuroinflammation. qRT-PCR was performed to detect expressions of Snhg16, microRNA (miR)-719, sodium voltage-gated channel alpha subunit 1 (SCN1A), and inflammatory factors. Bioinformatics, dual-luciferase reporter assay, and RNA pull-down verified the underlying molecular mechanisms. Snhg16 expression increased in CCI mice. Snhg16 overexpression retarded the curative effect of ozone and induced NP. miR-719 was sponged by Snhg16. SCN1A was a target of miR-719. Inhibition of miR-719 markedly reversed the effects of Snhg16 on pain-related behavioral responses and neuroinflammation. Upregulation of SCN1A partly abrogated the effects of elevated miR-719 levels on the occurrence of NP. The findings demonstrate that lncRNA Snhg16 promotes NP progression in CCI mice by binding to miR-719 to increase SCN1A expression. The Snhg16/miR-719/SCN1A axis may influence the curative effects of ozone therapy in treating NP.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Comparison of MicroRNA Levels of 18-60-month-old Autistic Children with Those of Their Siblings and Controls

Objective

The present study aims to compare the levels of 7 microRNAs (mi-RNAs) (mi-RNA-125b, mi-RNA-23a-3p, mi-RNA-146a-5p, mi-RNA-106a, mi-RNA-151a-3p, mi-RNA-28, mi-RNA-125a) in the blood of the preschool children with autism and those of their siblings with healthy controls, and to investigate the association between these mi-RNAs and the severity of autism, behavioral problems, and siblings' autistic traits.

Methods

A total of 35 children diagnosed with autism spectrum disorder (ASD) at the ages of 18-60 months (patient group), 35 non-affected siblings of the ASD group (sibling group), and 30 control subjects (control group) were involved in the study. The severity of ASD was measured using the Childhood Autism Rating Scale and the Autism Behavior Checklist (ABC). The behavioral problems of the children with ASD were assessed with the Aberrant Behavior Checklist, and the autistic traits of the siblings were assessed using the Autism spectrum screening scale for children.

Results

mi-RNA-106a-5p, mi-RNA-151a-3p, and mi-RNA-28-3p were found to be expressed significantly lower in the patient group compared to the control group. There was a significant positive correlation between mi-RNA-23a and the sensory subscale of the ABC. mi-RNA-151a was significantly associated with sound sensitivity and mi-RNA-28 with echolalia. After controlling for age and sex, the differences between groups were disappeared.

Conclusion

The present study examined mi-RNAs that have been reported as biomarkers in the literature. Although several symptom clusters are found to be related to certain mi-RNA expression levels, they were not found to be significant in discriminating the patient and healthy groups.

Autophagy in Neuroinflammation: A Focus on Epigenetic Regulation

Neuroinflammation, characterized by the secretion of abundant inflammatory mediators, pro-inflammatory polarization of microglia, and the recruitment of infiltrating myeloid cells to foci of inflammation, drives or exacerbates the pathological processes of central nervous system disorders, especially in neurodegenerative diseases. Autophagy plays an essential role in neuroinflammatory processes, and the underlaying physiological mechanisms are closely correlated with neuroinflammation-related signals. Inhibition of mTOR and activation of AMPK and FOXO1 enhance autophagy and thereby suppress NLRP3 inflammasome activity and apoptosis, leading to the relief of neuroinflammatory response. And autophagy mitigates neuroinflammation mainly manifested by promoting the polarization of microglia from a pro-inflammatory to an anti-inflammatory state, reducing the production of pro-inflammatory mediators, and up-regulating the levels of anti-inflammatory factors. Notably, epigenetic modifications are intimately associated with autophagy and the onset and progression of various brain diseases. Non-coding RNAs, including microRNAs, circular RNAs and long noncoding RNAs, and histone acetylation have been reported to adjust autophagy-related gene and protein expression to alleviate inflammation in neurological diseases. The present review primarily focuses on the role and mechanisms of autophagy in neuroinflammatory responses, as well as epigenetic modifications of autophagy in neuroinflammation to reveal potential therapeutic targets in central nervous system diseases.

Sensory neuron transient receptor potential vanilloid-1 channel regulates angiogenesis through CGRP in vivo

Angiogenesis plays a key role in bone regeneration. The role of neurons of peripheral nerves involved in angiogenesis of bone defects needs to be explored. The transient receptor potential vanilloid 1 (TRPV1), a nociceptor of noxious stimuli, is expressed on sensory neurons. Apart from nociception, little is known about the role of sensory innervation in angiogenesis. Calcitonin gene-related peptide (CGRP), a neuropeptide secreted by sensory nerve terminals, has been associated with vascular regeneration. We characterized the reinnervation of vessels in bone repair and assessed the impact of TRPV1-CGRP signaling on early vascularization. We investigated the pro-angiogenic effect of neuronal TRPV1 in the mouse model of femur defect. Micro-CT analysis with Microfil® reagent perfusion demonstrated neuronal TRPV1 activation enhanced angiogenesis by increasing vessel volume, number, and thickness. Meanwhile, TRPV1 activation upregulated the mRNA and protein expression of vascular endothelial growth factor A (VEGF-A), cell adhesion molecule-1 (CD31), and CGRP. Immunostaining revealed the co-localization of TRPV1 and CGRP in dorsal root ganglia (DRG) sensory neurons. By affecting neuronal TRPV1 channels, the release of neuronal and local CGRP was controlled. We demonstrated that TRPV1 influenced on blood vessel development by promoting CGRP release from sensory nerve terminals. Our results showed that neuronal TRPV1 played a crucial role in regulating angiogenesis during bone repair and provided important clinical implications for the development of novel therapeutic approaches for angiogenesis.

New Insights on NLRP3 Inflammasome: Mechanisms of Activation, Inhibition, and Epigenetic Regulation

Inflammasomes are important modulators of inflammation. Dysregulation of inflammasomes can enhance vulnerability to conditions such as neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Among various inflammasomes, Nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) is the best-characterized inflammasome related to inflammatory and neurodegenerative diseases. NLRP3 is an intracellular sensor that recognizes pathogen-associated molecular patterns and damage-associated patterns resulting in the assembly and activation of NLRP3 inflammasome. The NLRP3 inflammasome includes sensor NLRP3, adaptor apoptosis-associated speck-like protein (ASC), and effector cysteine protease procaspase-1 that plays an imperative role in caspase-1 stimulation which further initiates a secondary inflammatory response. Regulation of NLRP3 inflammasome ameliorates NLRP3-mediated diseases. Much effort has been invested in studying the activation, and exploration of specific inhibitors and epigenetic mechanisms controlling NLRP3 inflammasome. This review gives an overview of the established NLRP3 inflammasome assembly, its brief molecular mechanistic activations as well as a current update on specific and non-specific NLRP3 inhibitors that could be used in NLRP3-mediated diseases. We also focused on the recently discovered epigenetic mechanisms mediated by DNA methylation, histone alterations, and microRNAs in regulating the activation and expression of NLRP3 inflammasome, which has resulted in a novel method of gaining insight into the mechanisms that modulate NLRP3 inflammasome activity and introducing potential therapeutic strategies for CNS disorders.

PD-1 deficiency aggravates spinal cord injury by regulating the reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling pathway

Spinal cord injury (SCI) is a devastating disorder and a leading cause of disability in adults worldwide. Multiple studies have reported the upregulation of programmed cell death 1 (PD-1) following SCI. However, the underlying mechanism of PD-1 deficiency in SCI is not well established. Therefore, we aimed to investigate the role and potential mechanism of PD-1 in SCI pathogenesis. PD-1 Knockout (KO) SCI mouse model was established, and PD-1 expression was evaluated in tissue samples by western blot assay. We then used a series of function gain-and-loss assays to determine the role of PD-1 in SCI pathogenesis. Moreover, mechanistic assays were performed to explore the association between PD-1, neuron-glia antigen-2 (NG2) glia cells, and miR-23b-5p and then investigated the involved signaling pathway. Results illustrated that PD-1 deficiency enhanced the inflammatory response, neuron loss, and functional impairment induced by SCI. We found that NG2 glia depletion aggravated inflammation, reduced neural survival, and suppressed locomotor recovery in murine SCI model. Further analysis indicated that NG2+ cells were increased in the spinal cord of SCI mice, and PD-1 deficiency increased the number of NG2+ cells by activating the Nogo receptor/ras homolog family member A/Rho kinase (NgR/RhoA/ROCK) signaling. Mechanistically, miR-23b-5p was identified as the negative regulator of PD-1 in NG2 glia. MiR-23b-5p deficiency reduced the expression of inflammatory cytokines, enhanced neural survival, and promoted locomotor recovery in SCI mice, which was counteracted by PD-1 deficiency. In conclusion, PD-1 deficiency exacerbates SCI in vivo by regulating reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling.

Newly discovered functions of miRNAs in neuropathic pain: Transitioning from recent discoveries to innovative underlying mechanisms

Neuropathic pain is a widespread clinical issue caused by somatosensory nervous system damage, affecting numerous individuals. It poses considerable economic and public health challenges, and managing it can be challenging due to unclear underlying mechanisms. Nevertheless, emerging evidence suggests that neurogenic inflammation and neuroinflammation play a role in developing pain patterns. Emerging evidence suggests that neurogenic inflammation and neuroinflammation play significant roles in developing neuropathic pain within the nervous system. Increased/decreased miRNA expression patterns could affect the progression of neuropathic and inflammatory pain by controlling nerve regeneration, neuroinflammation, and the expression of abnormal ion channels. However, our limited knowledge of miRNA targets hinders a complete grasp of miRNA's functions. Meanwhile, exploring exosomal miRNA, a recently uncovered role, has significantly advanced our comprehension of neuropathic pain's pathophysiology in recent times. In this review, we present a comprehensive overview of the latest miRNA studies and explore the possible ways miRNAs might play a role in the development of neuropathic pain.

MiR-184-5p represses neuropathic pain by regulating CCL1/CCR8 signaling interplay in the spinal cord in diabetic mice

BACKGROUND

Diabetic neuropathic pain (DNP) is a serious complication for diabetic patients involving nervous system. MicroRNAs (miRNAs) are small-noncoding RNAs which are dysregulated in neuropathic pain, and might be critical molecules for pain treatment. Our previous study has shown miR-184-5p was significantly downregulated in DNP. Therefore, the mechanism of miR-184-5p in DNP was investigated in this study.

METHODS

A DNP model was established through streptozotocin (STZ). The pharmacological tools were injected intrathecally, and pain behavior was evaluated by paw withdrawal mechanical thresholds (PWMTs). Bioinformatics analysis, Dual-luciferase reporter assay and fluorescence-in-situ-hybridization (FISH) were used to seek and confirm the potential target genes of miR-184-5p. The expression of relative genes and proteins was analyzed by quantitative reverse transcriptase real-time PCR (qPCR) and western blotting.

RESULTS

MiR-184-5p expression was down-regulated in spinal dorsal on days 7 and 14 after STZ, while intrathecal administration of miR-184-5p agomir attenuates neuropathic pain induced by DNP and intrathecal miR-184-5p antagomir induces pain behaviors in naïve mice. Chemokine CC motif ligand 1 (CCL1) was found to be a potential target of miR-184-5p and the protein expression of CCL1 and the mRNA expression of CCR8 were up-regulated in spinal dorsal on days 7 and 14 after STZ. The luciferase reporter assay and FISH demonstrated that CCL1 is a direct target of miR-184-5p. MiR-184-5p overexpression attenuated the expression of CCL1/CCR8 in DNP; intrathecal miR-184-5p antagomir increased the expression of CCL1/CCR8 in spinal dorsal of naïve mice.

CONCLUSION

This research illustrates that miR-184-5p alleviates DNP through the inhibition of CCL1/CCR8 signaling expression.

miRNA contributes to neuropathic pains

Neuropathic pain (NP) is a kind of chronic pain caused by direct injury to the peripheral or central nervous system (CNS). microRNAs (miRNAs) are small noncoding RNAs that mostly interact with the 3 untranslated region of messenger RNAs (mRNAs) to regulate the expression of multiple genes. NP is characterized by changes in the expression of receptors and mediators, and there is evidence that miRNAs may contribute to some of these alterations. In this review, we aimed to fully comprehend the connection between NP and miRNA; and also, to establish a link between neurology, biology, and dentistry. Studies have shown that targeting miRNAs may be an effective therapeutic strategy for the treatment of chronic pain and potential target for the prevention of NP.

The CXCL12-CXCR4-NLRP3 axis promotes Schwann cell pyroptosis and sciatic nerve demyelination in rats

Studies have shown that the activation of the NOD-like receptor protein 3 (NLRP3) inflammasome is detrimental to the functional recovery of the sciatic nerve, but the regulatory mechanisms of the NLRP3 inflammasome in peripheral nerves are unclear. C-X-C motif chemokine 12 (CXCL12) can bind to C-X-C chemokine receptor type 4 (CXCR4) and participate in a wide range of nerve inflammation by regulating the NLRP3 inflammasome. Based on these, we explore whether CXCL12-CXCR4 axis regulates the NLRP3 inflammasome in the peripheral nerve. We found that CXCR4/CXCL12, NLRP3 inflammasome-related components, pyroptosis-related proteins and inflammatory factors in the sciatic nerve injured rats were markedly increased compared with the sham-operated group. AMD3100, a CXCR4 antagonist, reverses the activation of NLRP3 inflammasome, Schwann cell pyroptosis and sciatic nerve demyelination. We further treated rat Schwann cells with LPS (lipopolysaccharide) and adenosine triphosphate (ATP) to mimic the cellular inflammation model of sciatic nerve injury, and the results were consistent with those in vivo. In addition, both in vivo and in vitro experiments demonstrated that AMD3100 treatment reduced the phosphorylation of nuclear factor κB (NF-κB) and the expression of thioredoxin interacting protein (TXNIP), which contributes to activating NLRP3 inflammasome. Therefore, our findings suggest that, after sciatic nerve injury, CXCL12-CXCR4 axis may promote Schwann cell pyroptosis and sciatic nerve demyelination through activating NLRP3 inflammasome and slow the recovery process of the sciatic nerve.

The role of TXNIP in cancer: a fine balance between redox, metabolic, and immunological tumor control

Thioredoxin-interacting protein (TXNIP) is commonly considered a master regulator of cellular oxidation, regulating the expression and function of Thioredoxin (Trx). Recent work has identified that TXNIP has a far wider range of additional roles: from regulating glucose and lipid metabolism, to cell cycle arrest and inflammation. Its expression is increased by stressors commonly found in neoplastic cells and the wider tumor microenvironment (TME), and, as such, TXNIP has been extensively studied in cancers. In this review, we evaluate the current literature regarding the regulation and the function of TXNIP, highlighting its emerging role in modulating signaling between different cell types within the TME. We then assess current and future translational opportunities and the associated challenges in this area. An improved understanding of the functions and mechanisms of TXNIP in cancers may enhance its suitability as a therapeutic target.

Quercetin inhibits the NOX2/ROS-mediated NF-κB/TXNIP signaling pathway to ameliorate pyroptosis of cardiomyocytes to relieve sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) has high morbidity and mortality. Quercetin (QUE) has been used to treat many inflammatory diseases related to pyroptosis. However, its effect on SIC has not been reported before. We aimed to explore the therapeutic mechanism of QUE on SIC. We found that the expression levels of NOX2, markers of myocardial injury and inflammatory factors related to pyroptosis were upregulated in the serum of SIC patients. QUE improved the viability and reduced the death rate of LPS-treated H9C2 cells. It could downregulate the expression level of NOX2 and alleviate NOX2-induced mitochondrial damage to inhibit the ROS-mediated NF-κB/TXNIP pathway thus ameliorating cell pyroptosis. Overexpression of NOX2 partially attenuated the anti-pyroptotic effects of QUE on LPS-treated H9C2 cells in vitro. Besides, the results of animal experiments reported that the mitochondrial damage was reduced by QUE treatment, which subsequently inhibited the ROS-mediated NF-κB/TXNIP pathway to ameliorate cell pyroptosis to further alleviate myocardial injury in CLP-induced rats in vivo. To conclude, QUE suppressed the NOX2/ROS-mediated NF-κB/TXNIP signaling pathway to ameliorate pyroptosis of cardiomyocytes to relieve SIC.

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

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

Downregulation of ciRNA-Kat6b in dorsal spinal horn is required for neuropathic pain by regulating Kcnk1 in miRNA-26a-dependent manner

AIMS

Nerve injury-induced maladaptive changes in gene expression in the spinal neurons are essential for neuropathic pain genesis. Circular RNAs (ciRNA) are emerging as key regulators of gene expression. Here, we identified a nervous-system-tissues-specific ciRNA-Kat6 with conservation in humans and mice. We aimed to investigate whether and how spinal dorsal horn ciRNA-Kat6b participates in neuropathic pain.

METHODS

Unilateral sciatic nerve chronic constrictive injury (CCI) surgery was used to prepare the neuropathic pain model. The differentially expressed ciRNAs were obtained by RNA-Sequencing. The identification of nervous-system-tissues specificity of ciRNA-Kat6b and the measurement of ciRNA-Kat6b and microRNA-26a (miRNA-26a) expression level were carried out by quantitative RT-PCR. The ciRNA-Kat6b that targets miRNA-26a and miRNA-26a that targets Kcnk1 were predicted by bioinformatics analysis and verified by in vitro luciferase reports test and in vivo experiments including Western-blot, immunofluorescence, and RNA-RNA immunoprecipitation. The correlation between neuropathic pain and ciRNA-Kat6b, miRNA-26a, or Kcnk1 was examined by the hypersensitivity response to heat and mechanical stimulus.

RESULTS

Peripheral nerve injury downregulated ciRNA-Kat6b in the dorsal spinal horn of male mice. Rescuing this downregulation blocked nerve injury-induced increase of miRNA-26a, reversed the miRNA-26a-triggered decrease of potassium channel Kcnk1, a key neuropathic pain player, in the dorsal horn, and alleviates CCI-induced pain hypersensitivities. On the contrary, mimicking this downregulation increased the miRNA-26a level and decreased Kcnk1 in the spinal cord, resulting in neuropathic pain-like syndrome in naïve mice. Mechanistically, the downregulation of ciRNA-Kat6b reduced the accounts of miRNA-26a binding to ciRNA-Kat6b, and elevated the binding accounts of miRNA-26a to the 3' untranslated region of Kcnk1 mRNA and degeneration of Kcnk1 mRNA, triggering in the reduction of KCNK1 protein in the dorsal horn of neuropathic pain mice.

CONCLUSION

The ciRNA-Kat6b/miRNA-26a/Kcnk1 pathway in dorsal horn neurons regulates the development and maintenance of neuropathic pain, ciRNA-Kat6b may be a potential new target for analgesic and treatment strategies.

Integrated analysis reveals Atf3 promotes neuropathic pain via orchestrating JunB mediated release of inflammatory cytokines in DRG macrophage

The dorsal root ganglion (DRG) is actively involved in the development of neuropathic pain (NP), serving as an intermediate station for pain signals from the peripheral nervous system to the central nervous system. The mechanism by which DRG is involved in NP regulation is not fully understood. The immune system plays a pivotal role in the physiological and pathological states of the human body. In recent years, the immune system has been thought to play an increasingly important role in the pathogenesis of NP. The immune system plays a key role in pain through specific immune cells and their immune-related genes (IRGs). However, the mechanism by which IRGs of DRG regulate NP action has not been fully elucidated. Here, we performed Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of IRGs in DRG bulk-RNA sequencing data from spared nerve injury (SNI) model mice and found that their IRGs were enriched in many pathways, especially in the immune response pathway. Subsequently, we analyzed single-cell RNA sequencing (scRNA-seq) data from DRGs extracted from the SNI model and identified eight cell populations. Among them, the highest IRG activity was presented in macrophages. Next, we analyzed the scRNA and bulk-sequencing data and deduced five common transcription factors (TFs) from differentially expressed genes (DEGs). The protein-protein interaction (PPI) network suggested that Atf3 and JunB are closely related. In vitro experiments, we verified that the protein and mRNA expressions of Atf3 and JunB were up-regulated in macrophages after lipopolysaccharide (LPS) stimulation. Moreover, the down-regulation of Atf3 reduced the release of inflammatory cytokines and decreased the protein and mRNA expression levels of JunB. The down-regulation of JunB also reduced the release of inflammatory cytokines. Furthermore, overexpression of JunB attenuated the effect of Atf3 down-regulation in reducing the release of inflammatory cytokines. Therefore, we speculated that Atf3 might promote NP through JunB-mediated release of inflammatory factors in DRG macrophages.

NLR family pyrin domain containing 3 (NLRP3) inflammasomes and peripheral neuropathic pain - Emphasis on microRNAs (miRNAs) as important regulators

Neuropathic pain is caused by the lesion or disease of the somatosensory system and can be initiated and/or maintained by both central and peripheral mechanisms. Nerve injury leads to neuronal damage and apoptosis associated with the release of an array of pathogen- or damage-associated molecular patterns to activate inflammasomes. The activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome contributes to neuropathic pain and may represent a novel target for pain therapeutic development. In the current review, we provide an up-to-date summary of the recent findings on the involvement of NLRP3 inflammasome in modulating neuropathic pain development and maintenance, focusing on peripheral neuropathic conditions. Here we provide a detailed review of the mechanisms whereby NLRP3 inflammasomes contribute to neuropathic pain via (1) neuroinflammation, (2) apoptosis, (3) pyroptosis, (4) proinflammatory cytokine release, (5) mitochondrial dysfunction, and (6) oxidative stress. We then present the current research literature reporting on the antinociceptive effects of several natural products and pharmacological interventions that target activation, expression, and/or regulation of NLRP3 inflammasome. Furthermore, we emphasize the effects of microRNAs as another regulator of NLRP3 inflammasome. In conclusion, we summarize the possible caveats and future perspectives that might provide successful therapeutic approaches against NLRP3 inflammasome for treating or preventing neuropathic pain conditions.

miR-369-3p Modulates Intestinal Inflammatory Response via BRCC3/NLRP3 Inflammasome Axis

Inflammasomes are multiprotein complexes expressed by immune cells in response to distinct stimuli that trigger inflammatory responses and the release of pro-inflammatory cytokines. Evidence suggests a different role of inflammasome NLRP3 in IBD. NLRP3 inflammasome activation can be controlled by post-translational modifications such as ubiquitination through BRCC3. The aim of this study was to investigate the effect of miR-369-3p on the expression and activation of NLRP3 inflammasomes via BRCC3 regulation. After bioinformatics prediction of Brcc3 as a gene target of miR-369-3p, in vitro, we validated its modulation in bone marrow-derived macrophages (BMDM). The increase in miR-369-3p significantly reduced BRCC3 gene and protein expression. This modulation, in turn, reduced the expression of NLRP3 and blocked the recruitment of ASC adaptor protein by NLRP3. As a result, miR-369-3p reduced the activity of Caspase-1 by the inflammasome, decreasing the cleavage of pro-IL-1β and pro-IL-18. These results support a novel mechanism that seems to act on post-translational modification of NLRP3 inflammasome activation by BRCC3. This may be an interesting new target in the personalized treatment of inflammatory disorders, including IBD.

circACTA2 inhibits NLRP3 inflammasome-mediated inflammation via interacting with NF-κB in vascular smooth muscle cells

circACTA2 derived from the smooth muscle α-actin gene plays an important role in the regulation of vascular smooth muscle cell (VSMC) phenotype. The activation of NLRP3 inflammasome is involved in VSMC phenotypic switching. However, the mechanistic relationship between circACTA2 and NLRP3 inflammasome during vascular remodeling remains poorly understood. Here, we showed that circACTA2 was down-regulated in human intimal hyperplasia. circACTA2 overexpression in circACTA2 transgenic mice significantly decreased the neointimal hyperplasia induced by vascular injury, which is concomitant with a decrease in IL-18, IL-1β, TNF-α, and IL-6 levels. Gain- and loss-of-function studies revealed that circACTA2 alleviated VSMC inflammation by suppressing the activation of NLRP3 inflammasome. Mechanistically, circACTA2 inhibited the expression of NF-κB p65 and p50 subunits and interacted with p50, which impedes the formation of the p50/p65 heterodimer and nuclear translocation induced by TNF-α, thus resulting in the suppression of NLRP3 gene transcription and inflammasome activation. Furthermore, circACTA2 overexpression mitigated inflammation via repressing NLRP3 inflammasome-mediated VSMC pyroptosis. Importantly, employing a decoy oligonucleotide to compete with circACTA2 for binding to p50 could attenuate the expression of NLRP3, ASC, and caspase-1. These findings provide a novel insight into the functional roles of circACTA2 in VSMCs, and targeting the circACTA2-NF-κB-NLRP3 axis represents a promising therapeutic strategy for vascular remodeling.

The emerging role of pyroptosis in neuropathic pain

Neuropathic pain caused by somatosensory system injuries is notoriously difficult to treat. Previous research has shown that neuroinflammation and cell death have been implicated in the pathophysiology of neuropathic pain. Pyroptosis is a form of programmed cell death associated with inflammatory processes, as it can enhance or sustain the inflammatory response by releasing pro-inflammatory cytokines. This review presents the current knowledge on pyroptosis and its underlying mechanisms, including the canonical and noncanonical pathways. Moreover, we discuss recent findings on the role of pyroptosis in neuropathic pain and its potential as a therapeutic target. In conclusion, this review highlights the potential significance of pyroptosis as a promising target for developing innovative therapies to treat neuropathic pain.

The NLRP3 inflammasome: role in the pathobiology of chronic pain

Chronic pain is not only one of the most common health problems, it is often challenging to treat adequately. Chronic pain has a high prevalence globally, affecting approximately 20% of the adult population. Chronic inflammatory pain and neuropathic (nerve) pain conditions are areas of large unmet medical need because analgesic/adjuvant agents recommended for alleviation of these types of chronic pain often lack efficacy and/or they produce dose-limiting side effects. Recent work has implicated the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome in the pathobiology of chronic pain, especially neuropathic and inflammatory pain conditions. NLRP3 is activated by damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). This in turn leads to recruitment and activation of caspase-1 an enzyme that cleaves the inactive IL-1β and IL-18 precursors to their respective mature pro-inflammatory cytokines (IL-1β and IL-18) for release into the cellular milieu. Caspase-1 also cleaves the pyroptosis-inducing factor, gasdermin D, that leads to oligomerization of its N-terminal fragment to form pores in the host cell membrane. This then results in cellular swelling, lysis and release of cytoplasmic contents in an inflammatory form of cell death, termed pyroptosis. The ultimate outcome may lead to the development of neuropathic pain and/or chronic inflammatory pain. In this review, we address a role for NLRP3 inflammasome activation in the pathogenesis of various chronic pain conditions.

GAP-43 targeted indocyanine green-loaded near-infrared fluorescent probe for real-time mapping of perineural invasion lesions in pancreatic cancer in vivo

OBJECTIVE

Perineural invasion (PNI) is associated with local recurrence, distant metastasis, and a poor prognosis in pancreatic cancer. However, rare attempt was made to identified the PNI intraoperative. To facilitate precise R0 excision of the tumor, we planned to develop a fluorescent probe for intraoperative imaging of the PNI using GAP-43 as the target and indocyanine green (ICG) as the carrier.

METHODS

The probe was created by binding peptide antibody and ICG. Its targeting was tested in vitro and in vivo using a co-culture model of PC12 and tumor cells to create an in vitro neural invasion model and a mouse sciatic nerve invasion model. The small animal imaging system and surgical navigation system confirmed the probe's potential clinical applicability. The sciatic nerve damage model was created to confirm the probe's targeting.

RESULTS

We used the pancreatic cancer samples and the public database to confirm that GAP-43 was preferentially overexpressed in pancreatic cancer, particularly in PNI. PC12 cells showed high GAP-43RA-PEG-ICG probe-specific absorption after being co-cultured with tumor cells in vitro. In the sciatic nerve invasion experiment, animals in probe group displayed a significantly stronger fluorescence signal at the PNI compared to ICG-NP and the contralateral normal nerves groups. Although only 60 % of mice appeared to have R0 resections by the naked eye, small animal imaging systems and surgical fluorescence navigation systems could remove the tumor with R0 precision. The injury model used in the probe imaging experimental trials demonstrated that the probe was specifically targeted to the injured nerve, regardless of whether the injury was infiltrated by a tumor or physical.

CONCLUSION

We developed the GAP-43Ra-ICG-PEG, an active-targeting near-infrared fluorescent (NIF) probe, that specifically binds to GAP-43-positive neural cells in an in vitro model of PNI. The probe efficiently visualized PNI lesions in pancreatic cancer in preclinical models, opening up new possibilities for NIRF-guided pancreatic surgery, particularly for PNI patients.

Histone deacetylase 5-induced deficiency of signal transducer and activator of transcription-3 acetylation contributes to spinal astrocytes degeneration in painful diabetic neuropathy

Diabetes patients with painful diabetic neuropathy (PDN) show severe spinal atrophy, suggesting pathological changes of the spinal cord contributes to central sensitization. However, the cellular changes and underlying molecular mechanisms within the diabetic spinal cord are less clear. By using a rat model of type 1 diabetes (T1D), we noted an extensive and irreversible spinal astrocyte degeneration at an early stage of T1D, which is highly associated with the chronification of PDN. Molecularly, acetylation of astrocytic signal transducer and activator of transcription-3 (STAT3) that is essential for maintaining the homeostatic astrocytes population was significantly impaired in the T1D model, resulting in a dramatic loss of spinal astrocytes and consequently promoting pain hypersensitivity. Mechanistically, class IIa histone deacetylase, HDAC5 were aberrantly activated in spinal astrocytes of diabetic rats, which promoted STAT3 deacetylation by direct protein-protein interactions, leading to the PDN phenotypes. Restoration of STAT3 signaling or inhibition of HDAC5 rescued astrocyte deficiency and attenuated PDN in the T1D model. Our work identifies the inhibitory axis of HDAC5-STAT3 induced astrocyte deficiency as a key mechanism underlying the pathogenesis of the diabetic spinal cord that paves the way for potential therapy development for PDN.

The Role of miRNAs in Neuropathic Pain

Neuropathic pain is a debilitating condition affecting around 8% of the adult population in the UK. The pathophysiology is complex and involves a wide range of processes, including alteration of neuronal excitability and synaptic transmission, dysregulated intracellular signalling and activation of pro-inflammatory immune and glial cells. In the past 15 years, multiple miRNAs–small non-coding RNA–have emerged as regulators of neuropathic pain development. They act by binding to target mRNAs and preventing the translation into proteins. Due to their short sequence (around 22 nucleotides in length), they can have hundreds of targets and regulate several pathways. Several studies on animal models have highlighted numerous miRNAs that play a role in neuropathic pain development at various stages of the nociceptive pathways, including neuronal excitability, synaptic transmission, intracellular signalling and communication with non-neuronal cells. Studies on animal models do not always translate in the clinic; fewer studies on miRNAs have been performed involving human subjects with neuropathic pain, with differing results depending on the specific aetiology underlying neuropathic pain. Further studies using human tissue and liquid samples (serum, plasma, saliva) will help highlight miRNAs that are relevant to neuropathic pain diagnosis or treatment, as biomarkers or potential drug targets.

Advances in the role and mechanism of miRNA in inflammatory pain

Pain is a distressing experience associated with tissue damage or potential tissue damage, and its occurrence is related to sensory, emotional, cognitive and social factors. Inflammatory pain is one of the chronic pains where pain hypersensitivity are functional features of inflammation used to protect tissues from further damage. Pain has a serious impact on people's lives and has become a social problem that cannot be ignored. MiRNAs are small non-coding RNA molecules that exert directing effects on RNA silencing by complementary binding to the 3'UTR of target mRNA. MiRNAs can target a number of protein-coding genes and participate in almost all developmental and pathological processes in animals. Growing studies have suggested that miRNAs have significant implications for inflammatory pain via participating in multiple processes during the occurrence and development, such as affecting the activation of glial cells, regulating pro-inflammatory cytokines and inhibiting central and peripheral sensitization. In this review, the advances in the role of miRNAs in inflammatory pain were discussed. miRNAs as a class of micro-mediators are potential biomarkers and therapeutic targets for inflammatory pain, which provides a better diagnostic and treatment approach for inflammatory pain.

Inhibition of microRNA-19a-3p alleviates the neuropathic pain (NP) in rats after chronic constriction injury (CCI) via targeting KLF7

BACKGROUND/PURPOSE

Neuropathic pain(NP) is derived from the dysfunctions of nerve system. The current research is to explore the impact and mechanism of miR-19a-3p in neuropathic pain in rats.

METHODS

The NP was induced through the chronic constriction injury (CCI) surgery in rats. The pro-inflammatory factors (IL-1β, IL-6, TNF-α) in spinal cord tissues from rats were measured using Elisa kits. Moreover, the different levels of thermal hyperalgesia and mechanical allodynia in rats were examined through paw withdrawal latency (PWL) and paw withdrawal threshold (PWT). To investigate into the role of miR-19a-3p and KLF7 in NP of rats, the knockdown of miR-19a-3p alone or along with KLF7 downregulation in rats were achieved through lentivirus injection. The miR-19a-3p and KLF7 expression in spinal cord of rats on Day 3,7,14 after CCI were detected using RT-qPCR. The protein expression of KLF7 were measured by Western blot. Bioinformatics and luciferase assays were used for the prediction and verification of bindings between KLF7 and miR-19a-3p.

RESULTS

CCI surgery caused neuropathic pain in rats with the levels of inflammatory cytokines increased and PWL and PWT decreased. Moreover, miR-19a-3p expression was increased while the protein and mRNA levels were decreased in spinal cord tissues in rats after CCI surgery. In rat microglial cells, miR-19a-3p downregulation could promote the KLF7 in both mRNA and protein expression. In spinal cord tissues of rats, the inhibition of miR-19a-3p enhanced the KLF7 expression. Furthermore, miR-19a-3p downregulation suppressed the IL-1β, IL-6 and TNF-α concentrations, and could decrease the NP but inhibition of KLF7 could partially reverse this in CCI rats.

CONCLUSION

miR-19a-3p inhibition may alleviate NP via KLF7 in CCI rats.

Emerging roles of miRNAs in neuropathic pain: From new findings to novel mechanisms

Neuropathic pain, which results from damage to the somatosensory nervous system, is a global clinical condition that affects many people. Neuropathic pain imposes significant economic and public health burdens and is often difficult to manage because the underlying mechanisms remain unclear. However, mounting evidence indicates a role for neurogenic inflammation and neuroinflammation in pain pattern development. There is increasing evidence that the activation of neurogenic inflammation and neuroinflammation in the nervous system contribute to neuropathic pain. Altered miRNA expression profiles might be involved in the pathogenesis of both inflammatory and neuropathic pain by regulating neuroinflammation, nerve regeneration, and abnormal ion channel expression. However, the lack of knowledge about miRNA target genes prevents a full understanding of the biological functions of miRNAs. At the same time, an extensive study on exosomal miRNA, a newly discovered role, has advanced our understanding of the pathophysiology of neuropathic pain in recent years. This section provides a comprehensive overview of the current understanding of miRNA research and discusses the potential mechanisms of miRNAs in neuropathic pain.

The upregulation of NLRP3 inflammasome in dorsal root ganglion by ten-eleven translocation methylcytosine dioxygenase 2 (TET2) contributed to diabetic neuropathic pain in mice

BACKGROUND

The nucleotide oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) in dorsal root ganglion (DRG) contributes to pain hypersensitivity in multiple neuropathic pain models, but the function of the NLRP3 in diabetic neuropathic pain (DNP) and the regulation mechanism are still largely unknown. Epigenetic regulation plays a vital role in the controlling of gene expression. Ten-eleven translocation methylcytosine dioxygenase 2 (TET2) is a DNA demethylase that contributes to transcriptional activation. TET2 is also involved in high glucose (HG)-induced pathology.

METHODS

DNP was induced in mice via the intraperitoneal injection of streptozotocin (STZ) for five consecutive days and the mechanical threshold was evaluated in STZ-diabetic mice by using von Frey hairs. The expression level of the NLRP3 pathway and TET2 in DRG were determined through molecular biology experiments. The regulation of the NLRP3 pathway by TET2 was examined in in vitro and in vivo conditions.

RESULTS

In the present research, we first established the DNP model and found that NLRP3 pathway was activated in DRG. The treatment of NLRP3 inhibitor MCC950 alleviated the mechanical allodynia of DNP mice. Then we revealed that in STZ-diabetic mice DRG, the genomic DNA was demethylated, and the expression of DNA demethylase TET2 was increased evidently. Using RNA-sequencing analysis, we found that the expression of Txnip, a gene that encodes a thioredoxin-interacting protein (TXNIP) which mediates NLRP3 activation, was elevated in the DRG after STZ treatment. In addition, knocking down of TET2 expression in DRG using TET2-siRNA suppressed the mRNA expression of Txnip and subsequently inhibited the expression/activation of NLRP3 inflammasome in vitro and in vivo as well as relieved the pain sensitivity of DNP animals.

CONCLUSION

The results suggested that the upregulation of the TXNIP/NLRP3 pathway by TET2 in DRG was involved in the pain hypersensitivity of the DNP model.

Ceramide induces pyroptosis through TXNIP/NLRP3/GSDMD pathway in HUVECs

Background

Pyroptosis of endothelial cells is a new cause of endothelial dysfunction in multiple diseases. Ceramide acts as a potential bioactive mediator of inflammation and increases vascular endothelial permeability in many diseases, whether it can aggravate vascular endothelial injury by inducing cell pyroptosis remains unknown. This study was established to explore the effects of C8-ceramide (C8-Cer) on human umbilical vein vascular endothelial cells (HUVECs) and its possible underlying mechanism.

Methods

HUVECs were exposed to various concentrations of C8-Cer for 12 h, 24 h, 48 h. The cell survival rate was measured using the cell counting kit-8 assay. Western blotting and Real-time polymerase chain reaction (RT-PCR) were used to detect the pyroptosis-releated protein and mRNA expressions, respectively. Caspase-1 activity assay was used to detect caspase-1 activity. Hoechst 33342/propidium iodide double staining and flow cytometry were adopted to measure positive staining of cells. Lactate dehydrogenase release assay and enzyme-linked immunosorbent assay were adopted to measure leakage of cellular contents. FITC method was used to detect the permeability of endothelial cells. ROS fluorescence intensity were detected by flow cytometry.

Results

The viability of HUVECs decreased gradually with the increase in ceramide concentration and time. Ceramide upregulated the expression of thioredoxin interacting protein (TXNIP), NLRP3, GSDMD, GSDMD-NT, caspase-1 and Casp1 p20 at the protein and mRNA level in a dose-dependent manner. It also enhanced the PI uptake in HUVECs and upregulated caspase-1 activity. Moreover, it promoted the release of lactate dehydrogenase, interleukin-1β, and interleukin-18. Meanwhile, we found that ceramide led to increased vascular permeability. The inhibitor of NLRP3 inflammasome assembly, MCC950, was able to disrupt the aforementioned positive loop, thus alleviating vascular endothelial cell damage. Interestingly, inhibition of TXNIP either chemically using verapamil or genetically using small interfering RNA (siRNA) can effectively inhibit ceramide-induced pyroptosis and improved cell permeability. In addition, ceramide stimulated reactive oxygen species (ROS) generation. The pretreatment of antioxidant N-acetylcysteine (NAC), ROS scavenger, blocked the expression of pyroptosis markers induced by C8-cer in HUVECs.

Conclusion

The current study demonstrated that C8-Cer could aggravate vascular endothelial cell damage and increased cell permeability by inducing cell pyroptosis. The results documented that the ROS-dependent TXNIP/NLRP3/GSDMD signalling pathway plays an essential role in the ceramide-induced pyroptosis in HUVECs.

Bone marrow mesenchymal stem cell-derived exosomes shuttling miR-150-5p alleviates mechanical allodynia in rats by targeting NOTCH2 in microglia

Background

This study probes into the function and mechanism of bone marrow mesenchymal stem cell (BMSC)-derived exosomes loaded with miR-150-5p in mechanical allodynia.

Methods

BMSCs were infected with miR-150-5p inhibition lentiviruses to obtain exosomes with low miR-150-5p expression. A L5 spinal nerve ligation (SNL) model was established in rats where exosomes, NOTCH2 overexpression/inhibition plasmids, or microglial cells were intrathecally administered. Hind paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of rats were measured. TUNEL staining was used to measure the apoptotic rate in rat spinal dorsal horn (SDH), ELISA to evaluate pro-inflammatory factor levels, and RT-qPCR, western blotting, and immunohistochemistry to detect miR-150-5p and NOTCH2 expression. Immunofluorescence was used for localizing exosomes and NOTCH2 and detecting the expression of OX42, a maker for microglia. Dual luciferase reporter and RNA pull down assays were performed to validate the putative binding between miR-150-5p and NOTCH2.

Results

NOTCH2 expressed at a high level and miR-150-5p was downregulated in SDH of SNL rats. Exosomes injected were localized in rat SDH. BMSC-exosomes or NOTCH2 downregulation increased PWT and PWL of SNL rats and reduced apoptosis and inflammation in SDH. In contrast, NOTCH2 overexpression aggravated mechanical allodynia and SDH injury. Moreover, inhibiting miR-150-5p in BMSC-exosomes offset the therapeutic effects of BMSC-exosomes. Microglia activation induced mechanical allodynia in wild rats, while intrathecal injection of microglial cells incubated with BMSC-exosomes showed alleviated mechanical allodynia in SNL rats. NOTCH2 was targeted by miR-150-5p.

Conclusion

BMSC-derived exosomal miR-150-5p alleviates mechanical allodynia by targeting NOTCH2 in microglial cells.

Non-coding RNA and n6-methyladenosine modification play crucial roles in neuropathic pain

After peripheral nerve injury, pain signals are transmitted from primary sensory neurons in the dorsal root ganglion (DRG) to the central nervous system. Epigenetic modification affects neuropathic pain through alterations in the gene expression in pain-related areas and glial cell activation. Recent studies have shown that non-coding RNA and n6-methyladenosine (m6A) methylation modification play pivotal regulatory roles in the occurrence and maintenance of neuropathic pain. Dysregulation of the RNA m6A level via dynamic changes in methyltransferase and demethylase after central or peripheral nerve injury commonly regulates pain-associated genes, contributing to the induction and maintenance of neuropathic pain. The dynamic process has significant implications for the development and maintenance of neuropathic pain. However, the underlying mechanisms by which non-coding RNA and m6A RNA modification regulate neuropathic pain are not well-characterized. This article elucidates the multiple mechanisms of non-coding RNA and m6A methylation in the context of neuropathic pain, and summarizes its potential functions as well as recent advances.

ISGylation is induced in neurons by demyelination driving ISG15-dependent microglial activation

The causes of grey matter pathology and diffuse neuron injury in MS remain incompletely understood. Axonal stress signals arising from white matter lesions has been suggested to play a role in initiating this diffuse grey matter pathology. Therefore, to identify the most upstream transcriptional responses in neurons arising from demyelinated axons, we analyzed the transcriptome of actively translating neuronal transcripts in mouse models of demyelinating disease. Among the most upregulated genes, we identified transcripts associated with the ISGylation pathway. ISGylation refers to the covalent attachment of the ubiquitin-like molecule interferon stimulated gene (ISG) 15 to lysine residues on substrates targeted by E1 ISG15-activating enzyme, E2 ISG15-conjugating enzymes and E3 ISG15-protein ligases. We further confirmed that ISG15 expression is increased in MS cortical and deep gray matter. Upon investigating the functional impact of neuronal ISG15 upregulation, we noted that ISG15 expression was associated changes in neuronal extracellular vesicle protein and miRNA cargo. Specifically, extracellular vesicle-associated miRNAs were skewed toward increased frequency of proinflammatory and neurotoxic miRNAs and decreased frequency of anti-inflammatory and neuroprotective miRNAs. Furthermore, we found that ISG15 directly activated microglia in a CD11b-dependent manner and that microglial activation was potentiated by treatment with EVs from neurons expressing ISG15. Further study of the role of ISG15 and ISGylation in neurons in MS and neurodegenerative diseases is warranted.

Mitochondria and sensory processing in inflammatory and neuropathic pain

Rheumatic diseases, such as osteoarthritis and rheumatoid arthritis, affect over 750 million people worldwide and contribute to approximately 40% of chronic pain cases. Inflammation and tissue damage contribute to pain in rheumatic diseases, but pain often persists even when inflammation/damage is resolved. Mechanisms that cause this persistent pain are still unclear. Mitochondria are essential for a myriad of cellular processes and regulate neuronal functions. Mitochondrial dysfunction has been implicated in multiple neurological disorders, but its role in sensory processing and pain in rheumatic diseases is relatively unexplored. This review provides a comprehensive understanding of how mitochondrial dysfunction connects inflammation and damage-associated pathways to neuronal sensitization and persistent pain. To provide an overall framework on how mitochondria control pain, we explored recent evidence in inflammatory and neuropathic pain conditions. Mitochondria have intrinsic quality control mechanisms to prevent functional deficits and cellular damage. We will discuss the link between neuronal activity, mitochondrial dysfunction and chronic pain. Lastly, pharmacological strategies aimed at reestablishing mitochondrial functions or boosting mitochondrial dynamics as therapeutic interventions for chronic pain are discussed. The evidence presented in this review shows that mitochondria dysfunction may play a role in rheumatic pain. The dysfunction is not restricted to neuronal cells in the peripheral and central nervous system, but also includes blood cells and cells at the joint level that may affect pain pathways indirectly. Pre-clinical and clinical data suggest that modulation of mitochondrial functions can be used to attenuate or eliminate pain, which could be beneficial for multiple rheumatic diseases.

Human PMSCs-derived small extracellular vesicles alleviate neuropathic pain through miR-26a-5p/Wnt5a in SNI mice model

BACKGROUND

Mesenchymal stem cell (MSCs)-derived small Extracellular Vesicles (sEVs) are considered as a new cell-free therapy for pain caused by nerve injury, but whether human placental mesenchymal stem cell-derived sEVs relieve pain in sciatic nerve injury and its possible mechanism are still unclear. In this study, we investigated the roles of hPMSCs-derived sEVs and related mechanisms in neuropathic pain.

METHODS

The spared nerve injury (SNI) mouse model was employed. Intrathecal injection of sEVs or miR-26a-5p agomir was performed on the seventh day of modeling, to study its anti-nociceptive effect. sEVs' miRNA sequencing (miRNA-Seq) and bioinformatics analysis were performed to study the downstream mechanisms of miRNAs. RT-qPCR, protein assay and immunofluorescence were used for further validation.

RESULTS

A single intrathecal injection of sEVs durably reversed mechanical hypersensitivity in the left hind paw of mice with partial sciatic nerve ligation. Immunofluorescence studies found that PKH26-labeled sEVs were visible in neurons and microglia in the dorsal horn of the ipsilateral L4/5 spinal cord and more enriched in the ipsilateral. According to miRNA-seq results, we found that intrathecal injection of miR-26a-5p agomir, the second high counts microRNA in hPMSCs derived sEVs, significantly suppressed neuropathic pain and neuroinflammation in SNI mice. Bioinformatics analysis and dual-luciferase reporter gene analysis identified Wnt5a as a direct downstream target gene of miR-26a-5p. The results showed that overexpression of miR-26a-5p in vivo could significantly reduce the expression level of Wnt5a. In addition, Foxy5, a mimetic peptide of Wnt5a, can significantly reverse the inhibitory effect of miR-26a-5p on neuroinflammation and neuropathic pain, and at the same time, miR-26a-5p can rescue the effect of Foxy5 by overexpression.

CONCLUSIONS

We reported that hPMSCs derived sEVs as a promising therapy for nerve injury induced neuropathic pain. In addition, we showed that the miR-26a-5p in the sEVs regulated Wnt5a/Ryk/CaMKII/NFAT partly take part in the analgesia through anti-neuroinflammation, which suggests an alleviating pain effect through non-canonical Wnt signaling pathway in neuropathic pain model in vivo.

Inhibition of miR-423-5p Exerts Neuroprotective Effects in an Experimental Rat Model of Cerebral Ischemia/Reperfusion Injury

MicroRNAs (miRNAs) are widely acknowledged to play a unique role in cerebrovascular disease. This research investigates the function of microRNAs in ischemic stroke via a middle cerebral artery occlusion (MCAO) model. Four differentially expressed microRNAs in rat brains were identified by bioinformatics analysis, and qRT-PCR showed that miR-423-5p exhibited the highest expression in cerebral ischemia/reperfusion injury in rats, with peak levels observed at 24 hours. After microRNA inhibitors and mimics were administrated in the rat model of MCAO, the neurological scores and brain water content were detected, and triphenyltetrazolium chloride (TTC), Hematoxylin and Eosin (H&E), and Nissl staining were conducted to explore the influence of miR-423-5p on ischemic stroke. Subsequently, western blot, ELISA, MPO, TUNEL and commercial assay kits were applied to assess the influence of miR-423-5p on NLRP3 inflammasome, apoptosis, and oxidative stress levels in ischemic penumbra tissue. The results showed that miR-423-5p knockdown could effectively improve neurological indicators, such as cerebral infarct volume, brain water content, neurological scores, and nerve tissue damage, and inhibit the NLRP3 inflammasome, apoptosis, and oxidative stress. In contrast, the miR-423-5p mimic yielded opposite results. In conclusion, inhibition of miR-423-5p expression could effectively attenuate ischemic stroke and might be considered a promising target for stroke.

Transcriptome profiling of microRNAs reveals potential mechanisms of manual therapy alleviating neuropathic pain through microRNA-547-3p-mediated Map4k4/NF-κb signaling pathway

BACKGROUND

Local neuroinflammation secondary to spinal nerve compression in lumbar disk herniation (LDH) is a key driver contributing to neuropathic pain. Manual therapy (MT), a widely used nonsurgical therapy, can relieve LDH-mediated pain by reducing inflammation. MT has attracted extensive attention; however, its mechanism remains poorly understood. MicroRNAs (miRNAs) are important regulators of pain signaling transduction, but are rarely reported in the chronic compression of dorsal root ganglia (CCD) model, and further investigation is needed to decipher whether they mediate anti-inflammatory and analgesic effects of MT.

METHODS

We used a combination of in vivo behavioral and molecular techniques to study MT intervention mechanisms. Neuropathic pain was induced in a CCD rat model and MT intervention was performed according to standard procedures. Enzyme-linked immunosorbent assay (ELISA) was used to detect inflammatory cytokine levels in dorsal root ganglia (DRG). Small RNA sequencing, immunofluorescence, Western blot, and qRT-PCR were performed to screen miRNAs and their target genes and determine core factors in the pathway possibly regulated by miRNA-mediated target gene in DRG of MT-treated CCD rats.

RESULTS

Compared with naive rats, small RNA sequencing detected 22 differentially expressed miRNAs in DRG of CCD rats, and compared with CCD rats, MT-treated rats presented 19 differentially expressed miRNAs, which were functionally associated with nerve injury and inflammation. Among these, miR-547-3p was screened as a key miRNA mediating neuroinflammation and participating in neuropathic pain. We confirmed in vitro that its function is achieved by directly regulating its target gene Map4k4. Intrathecal injection of miR-547-3p agomir or MT intervention significantly reduced Map4k4 expression and the expression and phosphorylation of IκBα and p65 in the NF-κB pathway, thus reducing the inflammatory cytokine levels and exerting an analgesic effect, whereas intrathecal injection of miR-547-3p antagomir led to opposite effects.

CONCLUSIONS

In rats, CCD-induced neuropathic pain leads to variation in miRNA expression in DRG, and MT can intervene the transcription and translation of inflammation-related genes through miRNAs to improve neuroinflammation and alleviate neuropathic pain. MiR-547-3p may be a key target of MT for anti-inflammatory and analgesia effects, which is achieved by mediating the Map4k4/NF-κB pathway to regulate downstream inflammatory cytokines.

TXNIP Participated in NLRP3-Mediated Inflammation in a Rat Model of Cervical Spondylotic Myelopathy

Background

Cervical spondylotic myelopathy (CSM) is a spinal cord disease caused by cervical disc degeneration and related pathological changes. Cervical spondylotic myelopathy may result from inflammation responses and neuronal damage. Thioredoxin-interacting protein (TXNIP)/NOD-like receptor protein 3 (NLRP3) signaling promotes inflammation. However, the effects of TXNIP/NLRP3 on the pathogenesis of CSM have not been reported.

Methods

A rat model of chronic cervical cord compression was established to observe changes in the levels of of TNXIP/NeuN and NLRP3/NeuN expression in the damaged anterior horn of the spinal cord following progression of CSM. Rats were injected with TXNIP small interfering RNA (siRNA) and scrambled control to determine the effects of TXNIP inhibition on NLRP3-mediated inflammation in rats with CSM. Behaviors effects and the expression of NLRP3 and pro-caspase-1 in the damaged spinal cord were evaluated.

Results

The expression levels of TXNIP and NLRP3 were significantly increased in the damaged anterior horn of the spinal cord following CSM. Injection of TXNIP siRNA significantly improved behavioral measures and decreased apoptosis in the damaged anterior horn of spinal cord. Furthermore, the levels of NLRP3 and pro-caspase-1 in the lesioned area were reduced by the TXNIP siRNA injection.

Conclusion

Thioredoxin-interacting protein participated in NLRP3 mediated inflammation in a rat model of CSM, which indicated that TXNIP may be a potential therapeutic target in improving CSM.

miR-15b-5p REGULATES THE NLRP3 INFLAMMASOME SIGNAL THROUGH TARGETING SIRT3 TO REGULATE HYPOXIA/REOXYGENATION-INDUCED CARDIOMYOCYTE PYROPTOSIS PROCESS

ABSTRACT

Hypoxia/reoxygenation (H/R) induces pyroptosis in the setting of acute myocardial infarction (AMI). Previous studies have shown that the expression of the miR-15 family is stimulated in myocardial ischemia-reperfusion injury or H/R-induced cardiomyocyte injury, and miR-15 is a promoter of cardiac ischemia-reperfusion or H/R injury. However, whether miR-15b-5p regulates H/R injury and cardiomyocyte pyroptosis and its mechanism still need to be further clarified. Bioinformatics analysis elicited that SIRT3 was the downstream regulatory target gene of miR-15b-5p. SIRT3 has been shown to participate in the regulation of pyroptosis by negatively regulating the NLRP3 inflammasome pathway. Therefore, we hypothesized that miR-15b-5p targets SIRT3 and activated the NLRP3 inflammasome pathway to promote H/R-induced cardiomyocyte pyroptosis. We first show that H/R increases miR-15b-5p in rat cardiomyocytes H9C2. Next, we tested the effects of inhibition of miR-15b-5p or overexpression of SIRT3. We found that miR-15b-5p downregulation or SIRT3 overexpression could reverse the H/R-induced pyroptosis. Furthermore, silencing SIRT3 antagonized the protective effect of miR-15b-5p downregulation on H9C2 cells. NLRP3 inhibitor MCC950 annulled the previously mentioned antagonistic effect of silencing SIRT3 on the protection of miR-15b-5p downregulation against pyroptosis. We then used a rat AMI model to analyze myocardial infarction area by triphenyl tetrazolium chloride staining and assess serum cardiac troponin T level by ELISA and found that miR-15b-5p silencing reduced AMI injury in rats. Collectively, these results suggest that miR-15b-5p increase H/R-induced pyroptosis in cardiomyocytes by targeting SIRT3 and activating the NLRP3 inflammasome.

What role of the cGAS-STING pathway plays in chronic pain?

Chronic pain interferes with daily functioning and is frequently accompanied by depression. Currently, traditional clinic treatments do not produce satisfactory analgesic effects and frequently result in various adverse effects. Pathogen recognition receptors (PRRs) serve as innate cellular sensors of danger signals, sense invading microorganisms, and initiate innate and adaptive immune responses. Among them, cGAS-STING alerts on the presence of both exogenous and endogenous DNA in the cytoplasm, and this pathway has been closely linked to multiple diseases, including auto-inflammation, virus infection, and cancer. An increasing numbers of evidence suggest that cGAS-STING pathway involves in the chronic pain process; however, its role remains controversial. In this narrative review, we summarize the recent findings on the involvement of the cGAS-STING pathway in chronic pain, as well as several possible mechanisms underlying its activation. As a new area of research, this review is unique in considering the cGAS-STING pathway in sensory neurons and glial cells as a part of a broader understanding of pain, including potential mechanisms of inflammation, immunity, apoptosis, and autophagy. It will provide new insight into the treatment of pain in the future.

Reactive Oxygen Species Contributes to Type 2 Diabetic Neuropathic Pain via the Thioredoxin-Interacting Protein-NOD-Like Receptor Protein 3-N-Methyl-D-Aspartic Acid Receptor 2B Pathway

BACKGROUND

The number of patients with diabetic neuropathic pain (DNP) continues to increase, but available treatments are limited. This study aimed to examine the influence of reactive oxygen species (ROS)-thioredoxin-interacting protein (TXNIP)-NOD-like receptor protein 3 (NLRP3)-N-methyl-D-aspartic acid receptor 2B (NR2B) pathway on type 2 DNP.

METHODS

Male Sprague-Dawley rats were fed with a high-fat and high-sugar diet for 8 weeks. Then, rats were intraperitoneally injected with streptozotocin (STZ, 35 mg/kg) to induce type 2 diabetes mellitus in rats. Diabetic rats with <85% of their basic levels in mechanical withdrawal threshold and thermal withdrawal latency were classified as DNP rats on day 14 after STZ injection. DNP rats were treated with ROS scavenger N-tert-Butyl-α-phenylnitrone (PBN, 100 mg·kg-1·d-1) or TXNIP small interfering ribonucleic acid (10 μg/d) once daily for 14 days. The level of ROS, protein levels of NLRP3, TXNIP, cysteinyl aspartate-specific proteinase-1 (caspase-1), interleukin-1β (IL-1β), NR2B phosphorylation at Tyr1472 (p-NR2B), total NR2B (t-NR2B), and distribution of NLRP3 in the spinal cord were examined. In vitro experiments, BV2 cells and PC12 cells were individually cultured and cocultured in a high-glucose environment (35 mmol/L D-glucose). The level of ROS and protein levels of NLRP3, TXNIP, caspase-1, and IL-1β in BV2 cells, and p-NR2B, t-NR2B in PC12 cells were detected. The level of ROS was detected by the flow cytometry approach. The protein levels were detected by the Western blot technique. The location of NLRP3 was observed by immunofluorescent staining. The interaction between TXNIP and NLRP3 was detected by coimmunoprecipitation assay.

RESULTS

The level of spinal ROS increased in DNP rats. The mechanical allodynia and thermal hyperalgesia of DNP rats were alleviated after systemic administration of PBN. This administration decreased protein levels of NLRP3, TXNIP, caspase-1, IL-1β, and p-NR2B and the coupling of TXNIP to NLRP3 in spinal cords of DNP rats. Furthermore, knockdown of spinal TXNIP alleviated nociceptive hypersensitivity and decreased protein levels of NLRP3, TXNIP, caspase-1, IL-1β, and p-NR2B in DNP rats. The level of ROS and protein levels of NLRP3, TXNIP, caspase-1, IL-1β, the coupling of TXNIP to NLRP3, and the IL-1β secretion increased in BV2 cells, and the protein expression of p-NR2B increased in cocultured PC12 cells in a high-glucose environment. All of these in vitro effects were significantly blocked after treatment of PBN.

CONCLUSIONS

Our findings suggest that spinal ROS can contribute to type 2 DNP through TXNIP-NLRP3-NR2B pathway.

The etiological roles of miRNAs, lncRNAs, and circRNAs in neuropathic pain: A narrative review

Background

Non‐coding RNAs (ncRNAs) are involved in neuropathic pain development. Herein, we systematically searched for neuropathic pain‐related ncRNAs expression changes, including microRNAs (miRNAs), long non‐coding RNAs (lncRNAs), and circular non‐coding RNAs (circRNAs).

Methods

We searched two databases, PubMed and GeenMedical, for relevant studies.

Results

Peripheral nerve injury or noxious stimuli can induce extensive changes in the expression of ncRNAs. For example, higher serum miR‐132‐3p, ‐146b‐5p, and ‐384 was observed in neuropathic pain patients. Either sciatic nerve ligation, dorsal root ganglion (DRG) transaction, or ventral root transection (VRT) could upregulate miR‐21 and miR‐31 while downregulating miR‐668 and miR‐672 in the injured DRG. lncRNAs, such as early growth response 2‐antisense‐RNA (Egr2‐AS‐RNA) and Kcna2‐AS‐RNA, were upregulated in Schwann cells and inflicted DRG after nerve injury, respectively. Dysregulated circRNA homeodomain‐interacting protein kinase 3 (circHIPK3) in serum and the DRG, abnormally expressed lncRNAs X‐inactive specific transcript (XIST), nuclear enriched abundant transcript 1 (NEAT1), small nucleolar RNA host gene 1 (SNHG1), as well as ciRS‐7, zinc finger protein 609 (cirZNF609), circ_0005075, and circAnks1a in the spinal cord were suggested to participate in neuropathic pain development. Dysregulated miRNAs contribute to neuropathic pain via neuroinflammation, autophagy, abnormal ion channel expression, regulating pain‐related mediators, protein kinases, structural proteins, neurotransmission excitatory–inhibitory imbalances, or exosome miRNA‐mediated neuron–glia communication. In addition, lncRNAs and circRNAs are essential in neuropathic pain by acting as antisense RNA and miRNA sponges, epigenetically regulating pain‐related molecules expression, or modulating miRNA processing.

Conclusions

Numerous dysregulated ncRNAs have been suggested to participate in neuropathic pain development. However, there is much work to be done before ncRNA‐based analgesics can be clinically used for various reasons such as conservation among species, proper delivery, stability, and off‐target effects.

CXCR4/CX43 Regulate Diabetic Neuropathic Pain via Intercellular Interactions between Activated Neurons and Dysfunctional Astrocytes during Late Phase of Diabetes in Rats and the Effects of Antioxidant N-Acetyl-L-Cysteine

Growing evidence suggests that the interactions between astrocytes and neurons exert important functions in the central sensitization of the spinal cord dorsal horn in rodents with diabetes and neuropathic pain (DNP). However, it still remains unclear how signal transmission occurs in the spinal cord dorsal horn between astrocytes and neurons, especially in subjects with DNP. Chemokine CXC receptor 4 (CXCR4) plays critical roles in DNP, and connexin 43 (CX43), which is also primarily expressed by astrocytes, contributes to the development of neuropathy. We thus postulated that astrocytic and neuronal CXCR4 induces and produces inflammatory factors under persistent peripheral noxious stimulation in DNP, while intercellular CX43 can transmit inflammatory stimulation signals. The results showed that streptozotocin-induced type 1 diabetic rats developed heat hyperalgesia and mechanical allodynia. Diabetes led to persistent neuropathic pain. Diabetic rats developed peripheral sensitization at the early phase (2 weeks) and central sensitization at the late phase (5 weeks) after diabetes induction. Both CXCR4 and CX43, which are localized and coexpressed in neurons and astrocytes, were enhanced significantly in the dorsal horn of spinal cord in rats undergoing DNP during late phase of diabetes, and the CXCR4 antagonist AMD3100 reduced the expression of CX43. The nociceptive behavior was reversed, respectively, by AMD3100 at the early phase and by the antioxidant N-acetyl-L-cysteine (NAC) at the late phase. Furthermore, rats with DNP demonstrated downregulation of glial fibrillary acidic protein (GFAP) as well as upregulation of c-fos in the spinal cord dorsal horn at the late phase compared to the controls, and upregulation of GFAP and downregulation of c-fos were observed upon treatment with NAC. Given that GFAP and c-fos are, respectively, makers of astrocyte and neuronal activation, our findings suggest that CXCR4 as an inflammatory stimulation protein and CX43 as an intercellular signal transmission protein both may induce neurons excitability and astrocytes dysfunction in developing DNP.