miR-7a alleviates the maintenance of neuropathic pain through regulation of neuronal excitability

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.

MicroRNA-6954-3p Downregulation Contributes to Orofacial Neuropathic Pain in Mice Via Targeting Voltage-Gated Sodium Channel β2 Subunit Protein

The voltage-gated sodium channel β2 subunit protein (SCN2B) plays a crucial role in neuropathic pain. However, the role and mechanisms of SCN2B in orofacial neuropathic pain are still unclear. This study aimed to investigate the upstream regulatory mechanisms of SCN2B in the trigeminal ganglion (TG) underlying orofacial neuropathic pain. Chronic constriction injury of the infraorbital nerve (CCI-ION) of mice was performed to establish the model of orofacial neuropathic pain. Von Frey filament test was performed to detect the head withdrawal threshold (HWT) of mice. Quantitative reverse transcription-polymerase chain, western blotting (WB), fluorescence in situ hybridization, and immunofluorescence (IF) staining were used to detect the expression and distribution of SCN2B and miR-6954-3p in the TG of mice. A luciferase activity assay was carried out to prove the binding between SCN2B messenger ribonucleic acid (mRNA) and miR-6954-3p. After the CCI-ION surgery, the levels of Scn2b mRNA and protein significantly increased and miR-6954-3p decreased in the TG of mice with decreasing HWT. IF staining revealed that SCN2B was expressed specifically in the TG neurons. Silencing SCN2B in the TG of CCI-ION mice significantly increased the HWT. Importantly, the 3'-untranslated region of Scn2b mRNA was proved to bind with miR-6954-3p. Fluorescence in situ hybridization and IF staining demonstrated that miR-6954-3p was expressed in TG neurons and co-expressed with SCN2B. Furthermore, intraganglionic injection of miR-6954-3p agomir into the TG of CCI-ION mice resulted in the downregulation of SCN2B and increased the HWT. These findings suggest that the downregulation of miR-6954-3p in the TG promotes orofacial neuropathic pain by promoting SCN2B expression following trigeminal nerve injury. PERSPECTIVE: This study points to the important role of SCN2B in orofacial neuropathic pain. Furthermore, miR-6954-3p is proven to regulate the expression of SCN2B by binding to the 3'-untranslated region of Scn2b mRNA. These findings indicate that SCN2B and miR-6954-3p are potential therapeutic targets for the treatment of orofacial neuropathic pain.

Predictive and concurrent validity of pain sensitivity phenotype, neuropeptidomics and neuroepigenetics in the MI-RAT osteoarthritic surgical model in rats

Background

Micro-RNAs could provide great insights about the neuropathological mechanisms associated with osteoarthritis (OA) pain processing. Using the validated Montreal Induction of Rat Arthritis Testing (MI-RAT) model, this study aimed to characterize neuroepigenetic markers susceptible to correlate with innovative pain functional phenotype and targeted neuropeptide alterations.

Methods

Functional biomechanical, somatosensory sensitization (peripheral-via tactile paw withdrawal threshold; central-via response to mechanical temporal summation), and diffuse noxious inhibitory control (via conditioned pain modulation) alterations were assessed sequentially in OA (n = 12) and Naïve (n = 12) rats. Joint structural, targeted spinal neuropeptides and differential expression of spinal cord micro-RNAs analyses were conducted at the sacrifice (day (D) 56).

Results

The MI-RAT model caused important structural damages (reaching 35.77% of cartilage surface) compared to the Naïve group (P < 0.001). This was concomitantly associated with nociceptive sensitization: ipsilateral weight shift to the contralateral hind limb (asymmetry index) from -55.61% ± 8.50% (D7) to -26.29% ± 8.50% (D35) (P < 0.0001); mechanical pain hypersensitivity was present as soon as D7 and persisting until D56 (P < 0.008); central sensitization was evident at D21 (P = 0.038); pain endogenous inhibitory control was distinguished with higher conditioned pain modulation rate (P < 0.05) at D7, D21, and D35 as a reflect of filtrated pain perception. Somatosensory profile alterations of OA rats were translated in a persistent elevation of pro-nociceptive neuropeptides substance P and bradykinin, along with an increased expression of spinal miR-181b (P = 0.029) at D56.

Conclusion

The MI-RAT OA model is associated, not only with structural lesions and static weight-bearing alterations, but also with a somatosensory profile that encompasses pain centralized sensitization, associated to active endogenous inhibitory/facilitatory controls, and corresponding neuropeptidomic and neuroepigenetic alterations. This preliminary neuroepigenetic research confirms the crucial role of pain endogenous inhibitory control in the development of OA chronic pain (not only hypersensitivity) and validates the MI-RAT model for its study.

BDNF in Neuropathic Pain; the Culprit that Cannot be Apprehended

In males but not in females, brain derived neurotrophic factor (BDNF) plays an obligatory role in the onset and maintenance of neuropathic pain. Afferent terminals of injured peripheral nerves release colony stimulating factor (CSF-1) and other mediators into the dorsal horn. These transform the phenotype of dorsal horn microglia such that they express P2X4 purinoceptors. Activation of these receptors by neuron-derived ATP promotes BDNF release. This microglial-derived BDNF increases synaptic activation of excitatory dorsal horn neurons and decreases that of inhibitory neurons. It also alters the neuronal chloride gradient such the normal inhibitory effect of GABA is converted to excitation. By as yet undefined processes, this attenuated inhibition increases NMDA receptor function. BDNF also promotes the release of pro-inflammatory cytokines from astrocytes. All of these actions culminate in the increase dorsal horn excitability that underlies many forms of neuropathic pain. Peripheral nerve injury also alters excitability of structures in the thalamus, cortex and mesolimbic system that are responsible for pain perception and for the generation of co-morbidities such as anxiety and depression. The weight of evidence from male rodents suggests that this preferential modulation of excitably of supra-spinal pain processing structures also involves the action of microglial-derived BDNF. Possible mechanisms promoting the preferential release of BDNF in pain signaling structures are discussed. In females, invading T-lymphocytes increase dorsal horn excitability but it remains to be determined whether similar processes operate in supra-spinal structures. Despite its ubiquitous role in pain aetiology neither BDNF nor TrkB receptors represent potential therapeutic targets.

RALY participates in nerve trauma-induced nociceptive hypersensitivity through triggering Eif4g2 gene expression in primary sensory neurons

BACKGROUND AND PURPOSE

Peripheral nerve trauma-induced dysregulation of pain-associated genes in the primary sensory neurons of dorsal root ganglion (DRG) contributes to neuropathic pain genesis. RNA-binding proteins participate in gene transcription. We hypothesized that RALY, an RNA-binding protein, participated in nerve trauma-induced dysregulation of DRG pain-associated genes and nociceptive hypersensitivity.

METHODS AND RESULTS

Immunohistochemistry staining showed that RALY was expressed exclusively in the nuclei of DRG neurons. Peripheral nerve trauma caused by chronic constriction injury (CCI) of unilateral sciatic nerve produced time-dependent increases in the levels of Raly mRNA and RALY protein in injured DRG. Blocking this increase through DRG microinjection of adeno-associated virus 5 (AAV5)-expressing Raly shRNA reduced the CCI-induced elevation in the amount of eukaryotic initiation factor 4 gamma 2 (Eif4g2) mRNA and Eif4g2 protein in injured DRG and mitigated the development and maintenance of CCI-induced nociceptive hypersensitivity, without altering basal (acute) response to noxious stimuli and locomotor activity. Mimicking DRG increased RALY through DRG microinjection of AAV5 expressing Raly mRNA up-regulated the expression of Eif4g2 mRNA and Eif4g2 protein in the DRG and led to hypersensitive responses to noxious stimuli in the absence of nerve trauma. Mechanistically, CCI promoted the binding of RALY to the promoter of Eif4g2 gene and triggered its transcriptional activity.

CONCLUSION AND IMPLICATIONS

Our findings indicate that RALY participates in nerve trauma-induced nociceptive hypersensitivity likely through transcriptionally triggering Eif4g2 expression in the DRG. RALY may be a potential target in neuropathic pain management.

Understanding molecular mechanisms and miRNA-based targets in diabetes foot ulcers

In today's culture, obesity and overweight are serious issues that have an impact on how quickly diabetes develops and how it causes complications. For the development of more effective therapies, it is crucial to understand the molecular mechanisms underlying the chronic problems of diabetes. The most prominent effects of diabetes are microvascular abnormalities such as retinopathy, nephropathy, and neuropathy, especially diabetes foot ulcers, as well as macrovascular abnormalities such as heart disease and atherosclerosis. MicroRNAs (miRNAs), which are highly conserved endogenous short non-coding RNA molecules, have been implicated in several physiological functions recently, including the earliest stages of the disease. By binding to particular messenger RNAs (mRNAs), which cause mRNA degradation, translation inhibition, or even gene activation, it primarily regulates posttranscriptional gene expression. These molecules exhibit considerable potential as diagnostic biomarkers for disease and are interesting treatment targets. This review will provide an overview of the latest findings on the key functions that miRNAs role in diabetes and its complications, with an emphasis on the various stages of diabetic wound healing.

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.

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.

Neuropathic pain; what we know and what we should do about it

Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.

Neat1 lncRNA organizes the inflammatory gene expressions in the dorsal root ganglion in neuropathic pain caused by nerve injury

Primary sensory neurons regulate inflammatory processes in innervated regions through neuro-immune communication. However, how their immune-modulating functions are regulated in concert remains largely unknown. Here, we show that Neat1 long non-coding RNA (lncRNA) organizes the proinflammatory gene expressions in the dorsal root ganglion (DRG) in chronic intractable neuropathic pain in rats. Neat1 was abundantly expressed in the DRG and was upregulated after peripheral nerve injury. Neat1 overexpression in primary sensory neurons caused mechanical and thermal hypersensitivity, whereas its knockdown alleviated neuropathic pain. Bioinformatics analysis of comprehensive transcriptome changes indicated the inflammatory response was the most relevant function of genes upregulated through Neat1. Consistent with this, upregulation of proinflammatory genes in the DRG following nerve injury was suppressed by Neat1 knockdown. Expression changes of these proinflammatory genes were regulated through Neat1-mRNA interaction-dependent and -independent mechanisms. Notably, Neat1 increased proinflammatory genes by stabilizing its interacting mRNAs in neuropathic pain. Finally, Neat1 in primary sensory neurons contributed to spinal inflammatory processes that mediated peripheral neuropathic pain. These findings demonstrate that Neat1 lncRNA is a key regulator of neuro-immune communication in neuropathic pain.

Narrative Review of the Complex Interaction between Pain and Trauma in Children: A Focus on Biological Memory, Preclinical Data, and Epigenetic Processes

The incidence and collective impact of early adverse experiences, trauma, and pain continue to increase. This underscores the urgent need for translational efforts between clinical and preclinical research to better understand the underlying mechanisms and develop effective therapeutic approaches. As our understanding of these issues improves from studies in children and adolescents, we can create more precise preclinical models and ultimately translate our findings back to clinical practice. A multidisciplinary approach is essential for addressing the complex and wide-ranging effects of these experiences on individuals and society. This narrative review aims to (1) define pain and trauma experiences in childhood and adolescents, (2) discuss the relationship between pain and trauma, (3) consider the role of biological memory, (4) decipher the relationship between pain and trauma using preclinical data, and (5) examine the role of the environment by introducing the importance of epigenetic processes. The ultimate scope is to better understand the wide-ranging effects of trauma, abuse, and chronic pain on children and adolescents, how they occur, and how to prevent or mitigate their effects and develop effective treatment strategies that address both the underlying causes and the associated physiological and psychological effects.

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.

FUS Contributes to Nerve Injury-Induced Nociceptive Hypersensitivity by Activating NF-κB Pathway in Primary Sensory Neurons

Dysregulation of pain-associated genes in the dorsal root ganglion (DRG) is considered to be a molecular basis of neuropathic pain genesis. Fused in sarcoma (FUS), a DNA/RNA-binding protein, is a critical regulator of gene expression. However, whether it contributes to neuropathic pain is unknown. This study showed that peripheral nerve injury caused by the fourth lumbar (L4) spinal nerve ligation (SNL) or chronic constriction injury (CCI) of the sciatic nerve produced a marked increase in the expression of FUS protein in injured DRG neurons. Blocking this increase through microinjection of the adeno-associated virus (AAV) 5-expressing Fus shRNA into the ipsilateral L4 DRG mitigated the SNL-induced nociceptive hypersensitivities in both male and female mice. This microinjection also alleviated the SNL-induced increases in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) and glial fibrillary acidic protein (GFAP) in the ipsilateral L4 dorsal horn. Furthermore, mimicking this increase through microinjection of AAV5 expressing full-length Fus mRNA into unilateral L3/4 DRGs produced the elevations in the levels of p-ERK1/2 and GFAP in the dorsal horn, enhanced responses to mechanical, heat and cold stimuli, and induced the spontaneous pain on the ipsilateral side of both male and female mice in the absence of SNL. Mechanistically, the increased FUS activated the NF-κB signaling pathway by promoting the translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Our results indicate that DRG FUS contributes to neuropathic pain likely through the activation of NF-κB in primary sensory neurons.SIGNIFICANCE STATEMENT In the present study, we reported that fused in sarcoma (FUS), a DNA/RNA-binding protein, is upregulated in injured dorsal root ganglion (DRG) following peripheral nerve injury. This upregulation is responsible for nerve injury-induced translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Because blocking this upregulation alleviates nerve injury-induced nociceptive hypersensitivity, DRG FUS participates in neuropathic pain likely through the activation of NF-κB in primary sensory neurons. FUS may be a potential target for neuropathic pain management.

Increased extracellular release of microRNAs from dorsal root ganglion cells in a rat model of neuropathic pain caused by peripheral nerve injury

microRNAs (miRNAs) are extracellularly released by cells for intercellular communication, while intracellularly, they inhibit the expression of specific genes. An increasing number of studies suggest that extracellular miRNAs have great potential as both therapeutic targets and disease-specific biomarkers in a variety of diseases, including pain disorders. However, little is known about miRNA release from dorsal root ganglion (DRG) neurons in neuropathic pain caused by peripheral nerve injury. In this study, we investigated the changes in the extracellular release of miRNAs from DRG neurons in a rat model of neuropathic pain induced by chronic constriction injury of the sciatic nerve. We found increased release of six miRNAs (let-7d, miR-21, miR-142-3p, miR-146b, miR-203-3p and miR-221) from primary cultured DRG neurons prepared from rats 7 days after nerve injury. Among these, miR-221 was also increased in serum from days 7 to 28 after nerve injury. In contrast, serum miR-221 levels and its release from DRG neurons were unchanged in an inflammatory pain model produced by intraplantar injection of complete Freund's adjuvant. These results suggest that the increased release of specific miRNAs by DRG neurons may be involved in the pathophysiology of neuropathic pain through extracellular as well as intracellular mechanisms. Furthermore, serum miR-221 may be useful as a biomarker of neuropathic pain caused by peripheral nerve injury.

Regulation by noncoding RNAs of local translation, injury responses, and pain in the peripheral nervous system

Neuropathic pain is a chronic condition arising from damage to somatosensory pathways that results in pathological hypersensitivity. Persistent pain can be viewed as a consequence of maladaptive plasticity which, like most enduring forms of cellular plasticity, requires altered expression of specific gene programs. Control of gene expression at the level of protein synthesis is broadly utilized to directly modulate changes in activity and responsiveness in nociceptive pathways and provides an effective mechanism for compartmentalized regulation of the proteome in peripheral nerves through local translation. Levels of noncoding RNAs (ncRNAs) are commonly impacted by peripheral nerve injury leading to persistent pain. NcRNAs exert spatiotemporal regulation of local proteomes and affect signaling cascades supporting altered sensory responses that contribute to hyperalgesia. This review discusses ncRNAs found in the peripheral nervous system (PNS) that are dysregulated following nerve injury and the current understanding of their roles in pathophysiological pain-related responses including neuroimmune interactions, neuronal survival and axon regeneration, Schwann cell dedifferentiation and proliferation, intercellular communication, and the generation of ectopic action potentials in primary afferents. We review progress in the field beyond cataloging, with a focus on the relevant target transcripts and mechanisms underlying pain modulation by ncRNAs.

The Role of microRNAs in Regulating Cancer Cell Response to Oxaliplatin-Containing Regimens

Oxaliplatin (cyclohexane-1,2-diamine; oxalate; platinum [2+]) is a third-generation chemotherapeutic drug with anticancer effects. Oxaliplatin has a role in the treatment of several cancers. It is one of the few drugs which can eliminate the neoplastic cells of colorectal cancer. Also, it has an influential role in breast cancer, lung cancer, bladder cancer, prostate cancer, and gastric cancer. Although oxaliplatin has many beneficial effects in cancer treatment, resistance to this drug is in the way to cure neoplastic cells and reduce treatment efficacy. microRNAs are a subtype of small noncoding RNAs with ∼22 nucleotides that exist among species. They have diverse roles in physiological processes, including cellular proliferation and cell death. Moreover, miRNAs have essential roles in resistance to cancer treatment and can strengthen sensitivity to chemotherapeutic drugs and regimens. In colorectal cancer, the co-treatment of oxaliplatin with anti-miR-19a can partially reverse the oxaliplatin resistance through the upregulation of phosphatase and tensin homolog (PTEN). Moreover, by preventing the spread of gastric cancer cells and downregulating glypican-3 (GPC3), MiR-4510 may modify immunosuppressive signals in the tumor microenvironment. Treatment with oxaliplatin may develop into a specialized therapeutic drug for patients with miR-4510 inhibition and glypican-3-expressing gastric cancer. Eventually, miR-122 upregulation or Wnt/β-catenin signaling suppression boosted the death of HCC cells and made them more sensitive to oxaliplatin. Herein, we have reviewed the role of microRNAs in regulating cancer cells' response to oxaliplatin, with particular attention to gastrointestinal cancers. We also discussed the role of these noncoding RNAs in the pathophysiology of oxaliplatin-induced neuropathic pain.

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.

Role of Epigenetic Mechanisms in Chronic Pain

Pain is an unpleasant but essential-to-life sensation, usually resulting from tissue damage. When pain persists long after the injury has resolved, it becomes pathological. The precise molecular and cellular mechanisms causing the transition from acute to chronic pain are not fully understood. A key aspect of pain chronicity is that several plasticity events happen along the neural pathways involved in pain. These long-lasting adaptive changes are enabled by alteration in the expression of relevant genes. Among the different modulators of gene transcription in adaptive processes in the nervous system, epigenetic mechanisms play a pivotal role. In this review, I will first outline the main classes of epigenetic mediators and then discuss their implications in chronic pain.

miR-544-3p mediates arthritis pain through regulation of FcγRI

ABSTRACT

Chronic joint pain is a major symptom in rheumatoid arthritis (RA) and its adequate treatment represents an unmet medical need. Noncoding microRNAs (miRNAs) have been implicated in the pathogenesis of RA as negative regulators of specific target mRNAs. Yet, their significance in RA pain is still not well defined. We and other groups recently identified neuronally expressed FcγRI as a key driver of arthritis pain in mouse RA models. Thus, we tested the hypothesis that miRNAs that target and regulate neuronal FcγRI attenuate RA pain. Here, we show that miR-544-3p was robustly downregulated, whereas FcγRI was significantly upregulated in the dorsal root ganglion (DRG) in mouse RA models. Intrathecal injection of miR-544-3p mimic attenuated established mechanical and heat hyperalgesia partly through the downregulation of FcγRI in the DRG in a mouse model of collagen II-induced arthritis. Moreover, this effect was likely mediated, at least in part, by FcγRI because miR-544-3p mimic downregulated Fcgr1 mRNA expression in the DRG during arthritis and genetic deletion of Fcgr1 produced similar antihyperalgesic effects in the collagen II-induced arthritis model. This notion was further supported by a dual luciferase assay showing that miR-544-3p directly targeted Fcgr1 3'UTR. In naïve mice, miR-544-3p mediated acute joint pain hypersensitivity induced by IgG immune complex through the regulation of FcγRI. These findings suggest that miR-544-3p causally participates in the maintenance of arthritis pain by targeting neuronal FcγRI, and thus define miR-544-3p as a new potential therapeutic target for treating RA pain.

Genetic and epigenetic mechanisms influencing acute to chronic postsurgical pain transitions in pediatrics: Preclinical to clinical evidence

Background

Chronic postsurgical pain (CPSP) in children remains an important problem with no effective preventive or therapeutic strategies. Recently, genomic underpinnings explaining additional interindividual risk beyond psychological factors have been proposed.

Aims

We present a comprehensive review of current preclinical and clinical evidence for genetic and epigenetic mechanisms relevant to pediatric CPSP.

Methods

Narrative review.

Results

Animal models are relevant to translational research for unraveling genomic mechanisms. For example, Cacng2, p2rx7, and bdnf mutant mice show altered mechanical hypersensitivity to injury, and variants of the same genes have been associated with CPSP susceptibility in humans; similarly, differential DNA methylation (H1SP) and miRNAs (miR-96/7a) have shown translational implications. Animal studies also suggest that crosstalk between neurons and immune cells may be involved in nociceptive priming observed in neonates. In children, differential DNA methylation in regulatory genomic regions enriching GABAergic, dopaminergic, and immune pathways, as well as polygenic risk scores for enhanced prediction of CPSP, have been described. Genome-wide studies in pediatric CPSP are scarce, but pathways identified by adult gene association studies point to potential common mechanisms.

Conclusions

Bench-to-bedside genomics research in pediatric CPSP is currently limited. Reverse translational approaches, use of other -omics, and inclusion of pediatric/CPSP endophenotypes in large-scale biobanks may be potential solutions. Time of developmental vulnerability and longitudinal genomic changes after surgery warrant further investigation. Emergence of promising precision pain management strategies based on gene editing and epigenetic programing emphasize need for further research in pediatric CPSP-related genomics.

miR‑223 ameliorates thalamus hemorrhage‑induced central poststroke pain via targeting NLRP3 in a mouse model

Central poststroke pain (CPSP) is a central neuropathic pain syndrome that occurs following a stroke and mainly manifests as pain and paresthesia in the body region corresponding to the brain injury area. At present, due to the lack of clinical attention given to CPSP, patients suffer from long-term pain that seriously affects their quality of life. Current literature indicates that microRNA (miR)-223 can impede inflammation and prevent collateral damage. The NLR family pyrin domain containing 3 (NLRP3) inflammasome induces IL-18 and IL-1β secretion and maturation and participates in the inflammatory response. Previous evidence has confirmed that miR-223 can negatively regulate NLRP3 in the development of inflammatory responses. However, whether the miR-223 targeting of NLRP3 is involved in CPSP remains unclear. In the present study, the expression of miR-223 was detected by reverse transcription-quantitative PCR analysis. The expression levels of NLRP3, caspase-1, ASC, IL-18, IL-1β, ERK1/2, p-ERK1/2 and GFAP were detected by western blot analysis. The results demonstrated that thalamic hemorrhagic stroke triggered by microinjection of collagenase Ⅳ (Coll IV) into the ventral posterior lateral (VPL) nucleus results in pain hypersensitivity. miR-223 expression level were significantly reduced in the CPSP model. The expression levels of NLRP3, caspase-1, ASC, IL-18 and IL-1β were significantly increased in the CPSP model. The expression level of GFAP was detected to determine astrocyte activation. The results demonstrated that astrocyte activation induced by Coll IV produced a CPSP model. The p-ERK1/2 expression level was demonstrated to be significantly increased in the CPSP model. The introduction of an miR-223 agomir significantly attenuated thalamic pain and significantly decreased the levels of NLRP3, caspase-1, ASC and proinflammatory cytokines (IL-18 and IL-1β). Furthermore, introducing a miR-223 antagomir into the VPL nucleus of naïve mice mimicked thalamic pain and significantly increased the levels of NLRP3, caspase-1, ASC and proinflammatory cytokine levels (IL-18 and IL-1β). These results indicated that miR-223 inhibited NLRP3 inflammasome activity (caspase-1, NLRP3 and ASC), which ameliorated thalamus hemorrhage-induced CPSP in mice via NLRP3 downregulation. In conclusion, these results may determine the mechanisms underlying CPSP and facilitate development of targeted therapy for CPSP.

Roles of the Neuron-Restrictive Silencer Factor in the Pathophysiological Process of the Central Nervous System

The neuron-restrictive silencer factor (NRSF), also known as repressor element 1 (RE-1) silencing transcription factor (REST) or X2 box repressor (XBR), is a zinc finger transcription factor that is widely expressed in neuronal and non-neuronal cells. It is a master regulator of the nervous system, and the function of NRSF is the basis of neuronal differentiation, diversity, plasticity, and survival. NRSF can bind to the neuron-restrictive silencer element (NRSE), recruit some co-repressors, and then inhibit transcription of NRSE downstream genes through epigenetic mechanisms. In neurogenesis, NRSF functions not only as a transcriptional silencer that can mediate the transcriptional inhibition of neuron-specific genes in non-neuronal cells and thus give neuron cells specificity, but also as a transcriptional activator to induce neuronal differentiation. Many studies have confirmed the association between NRSF and brain disorders, such as brain injury and neurodegenerative diseases. Overexpression, underexpression, or mutation may lead to neurological disorders. In tumorigenesis, NRSF functions as an oncogene in neuronal tumors, such as neuroblastomas, medulloblastomas, and pheochromocytomas, stimulating their proliferation, which results in poor prognosis. Additionally, NRSF-mediated selective targets gene repression plays an important role in the development and maintenance of neuropathic pain caused by nerve injury, cancer, and diabetes. At present, several compounds that target NRSF or its co-repressors, such as REST-VP16 and X5050, have been shown to be clinically effective against many brain diseases, such as seizures, implying that NRSF and its co-repressors may be potential and promising therapeutic targets for neural disorders. In the present review, we introduced the biological characteristics of NRSF; reviewed the progress to date in understanding the roles of NRSF in the pathophysiological processes of the nervous system, such as neurogenesis, brain disorders, neural tumorigenesis, and neuropathic pain; and suggested new therapeutic approaches to such brain diseases.

New Vistas in microRNA Regulatory Interactome in Neuropathic Pain

Neuropathic pain is a chronic pain condition seen in patients with diabetic neuropathy, cancer chemotherapy-induced neuropathy, idiopathic neuropathy as well as other diseases affecting the nervous system. Only a small percentage of people with neuropathic pain benefit from current medications. The complexity of the disease, poor identification/lack of diagnostic and prognostic markers limit current strategies for the management of neuropathic pain. Multiple genes and pathways involved in human diseases can be regulated by microRNA (miRNA) which are small non-coding RNA. Several miRNAs are found to be dysregulated in neuropathic pain. These miRNAs regulate expression of various genes associated with neuroinflammation and pain, thus, regulating neuropathic pain. Some of these key players include adenylate cyclase (Ac9), toll-like receptor 8 (Tlr8), suppressor of cytokine signaling 3 (Socs3), signal transducer and activator of transcription 3 (Stat3) and RAS p21 protein activator 1 (Rasa1). With advancements in high-throughput technology and better computational power available for research in present-day pharmacology, biomarker discovery has entered a very exciting phase. We dissect the architecture of miRNA biological networks encompassing both human and rodent microRNAs involved in the development of neuropathic pain. We delineate various microRNAs, and their targets, that may likely serve as potential biomarkers for diagnosis, prognosis, and therapeutic intervention in neuropathic pain. miRNAs mediate their effects in neuropathic pain by signal transduction through IRAK/TRAF6, TLR4/NF-κB, TXIP/NLRP3 inflammasome, MAP Kinase, TGFβ and TLR5 signaling pathways. Taken together, the elucidation of the landscape of signature miRNA regulatory networks in neuropathic pain will facilitate the discovery of novel miRNA/target biomarkers for more effective management of neuropathic pain.

GADD45A induces neuropathic pain by activating P53 apoptosis pathway in mice

BACKGROUND

Neuropathic pain is a common condition with current heights of varying etiology. The therapeutic drugs are also poorly work and often limited by side effects such as dizziness.

OBJECTIVE

This study aimed to explore the function mechanism of GADD45A in neuropathic pain.

METHODS

The DEGs in neuropathic pain mouse model chip were screened by bioinformatics analysis. The expression of GADD45A in SNL model was determined by RT-qPCR and Immunofluorescence assay. The protein expression of p53-apoptosis pathway proteins was determined by western blotting.

RESULTS

Combination analysis of bioinformatics methods revealed that the expression of GADD45A was upregulated in SNL. The results of RT-qPCR assay and Immunofluorescence assay revealed that GADD45A was overexpressed in all of time points SNL model. Furthermore, knockdown of GADD45A in SNL remarkably antagonized the malignance phenotype compared with the Ad-GFP treated SNL. In addition, knockdown of GADD45A downregulated the expression of p53 and reduced the apoptosis of spinal cord nerve cells.

CONCLUSIONS

Our study suggests that GADD45A may be a biomarker in the neuropathic pain of mice.

DNA Methylation and Non-Coding RNAs during Tissue-Injury Associated Pain

While about half of the population experience persistent pain associated with tissue damages during their lifetime, current symptom-based approaches often fail to reduce such pain to a satisfactory level. To provide better patient care, mechanism-based analgesic approaches must be developed, which necessitates a comprehensive understanding of the nociceptive mechanism leading to tissue injury-associated persistent pain. Epigenetic events leading the altered transcription in the nervous system are pivotal in the maintenance of pain in tissue injury. However, the mechanisms through which those events contribute to the persistence of pain are not fully understood. This review provides a summary and critical evaluation of two epigenetic mechanisms, DNA methylation and non-coding RNA expression, on transcriptional modulation in nociceptive pathways during the development of tissue injury-associated pain. We assess the pre-clinical data and their translational implication and evaluate the potential of controlling DNA methylation and non-coding RNA expression as novel analgesic approaches and/or biomarkers of persistent pain.

Advances With Non-coding RNAs in Neuropathic Pain

Neuropathic pain (NP) is one of the most common types of clinical pain. The common causes of this syndrome include injury to the central or peripheral nervous systems and pathological changes. NP is characterized by spontaneous pain, hyperalgesia, abnormal pain, and paresthesia. Because of its diverse etiology, the pathogenesis of NP has not been fully elucidated and has become one of the most challenging problems in clinical medicine. This kind of pain is extremely resistant to conventional treatment and is accompanied by serious complications. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), contribute to diverse biological processes by regulating the expression of various mRNAs involved in pain-related pathways, at the posttranscriptional level. Abnormal regulation of ncRNAs is closely related to the occurrence and development of NP. In this review, we summarize the current state of understanding of the roles of different ncRNAs in the development of NP. Understanding these mechanisms can help develop novel therapeutic strategies to prevent or treat chronic pain.

MiR-30d Participates in Vincristine-Induced Neuropathic Pain by Down-Regulating GAD67

Vincristine is a common chemotherapeutic agent in cancer treatment, while it often causes chemotherapy-induced peripheral neuropathy(CIPN), which brings patients a great disease burden and associated economic pressure. The mechanism under CIPN remains mostly unknown. The previous study has shown that cell-type-specific spinal synaptic plasticity in the dorsal horn plays a pivotal role in neuropathic pain. Downregulation of GABA transmission, which mainly acts as an inhibitory pathway, has been reported in the growing number of research. Our present study found that GAD67, responsible for > 90% of basal GABA synthesis, is down-regulated, while its relative mRNA remains unchanged in vincristine-induced neuropathy. Considering microRNAs (miRNAs) as a post-transcription modifier by degrading targeted mRNA or repressing mRNA translation, we performed genome-wide miRNA screening and revealed that miR-30d might contribute to GAD67 down-regulation. Further investigation confirmed that miR-30d could affect the fluorescence activity of GAD67 by binding to the 3 'UTR of the GAD67 gene, and intrathecal injection of miR-30d antagomir increased the expression of GAD67, partially rescued vincristine-induced thermal hyperalgesia and mechanical allodynia. In summary, our study revealed the molecule interactions of GAD67 and miR-30d in CIPN, which has not previously been discussed in the literature. The results give more profound insight into understanding the CIPN mechanism and hopefully helps pain control.

Mediators of Neuropathic Pain; Focus on Spinal Microglia, CSF-1, BDNF, CCL21, TNF-α, Wnt Ligands, and Interleukin 1β

Intractable neuropathic pain is a frequent consequence of nerve injury or disease. When peripheral nerves are injured, damaged axons undergo Wallerian degeneration. Schwann cells, mast cells, fibroblasts, keratinocytes and epithelial cells are activated leading to the generation of an "inflammatory soup" containing cytokines, chemokines and growth factors. These primary mediators sensitize sensory nerve endings, attract macrophages, neutrophils and lymphocytes, alter gene expression, promote post-translational modification of proteins, and alter ion channel function in primary afferent neurons. This leads to increased excitability and spontaneous activity and the generation of secondary mediators including colony stimulating factor 1 (CSF-1), chemokine C-C motif ligand 21 (CCL-21), Wnt3a, and Wnt5a. Release of these mediators from primary afferent neurons alters the properties of spinal microglial cells causing them to release tertiary mediators, in many situations via ATP-dependent mechanisms. Tertiary mediators such as BDNF, tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and other Wnt ligands facilitate the generation and transmission of nociceptive information by increasing excitatory glutamatergic transmission and attenuating inhibitory GABA and glycinergic transmission in the spinal dorsal horn. This review focusses on activation of microglia by secondary mediators, release of tertiary mediators from microglia and a description of their actions in the spinal dorsal horn. Attention is drawn to the substantial differences in the precise roles of various mediators in males compared to females. At least 25 different mediators have been identified but the similarity of their actions at sensory nerve endings, in the dorsal root ganglia and in the spinal cord means there is considerable redundancy in the available mechanisms. Despite this, behavioral studies show that interruption of the actions of any single mediator can relieve signs of pain in experimental animals. We draw attention this paradox. It is difficult to explain how inactivation of one mediator can relieve pain when so many parallel pathways are available.

Differential RNA packaging into small extracellular vesicles by neurons and astrocytes

BACKGROUND

Small extracellular vesicles (sEVs) mediate intercellular communication by transferring RNA, proteins, and lipids to recipient cells. These cargo molecules are selectively loaded into sEVs and mirror the physiological state of the donor cells. Given that sEVs can cross the blood-brain barrier and their composition can change in neurological disorders, the molecular signatures of sEVs in circulation can be potential disease biomarkers. Characterizing the molecular composition of sEVs from different cell types is an important first step in determining which donor cells contribute to the circulating sEVs.

METHODS

Cell culture supernatants from primary mouse cortical neurons and astrocytes were used to purify sEVs by differential ultracentrifugation and sEVs were characterized using nanoparticle tracking analysis, transmission electron microscopy and western blot. RNA sequencing was used to determine differential expression and loading patterns of miRNAs in sEVs released by primary neurons and astrocytes. Motif analysis was conducted on enriched miRNAs in sEVs and their respective donor cells.

RESULTS

Sequencing total cellular RNA, and miRNAs from sEVs isolated from culture media of postnatal mouse cortical neurons and astrocytes revealed a distinct profile between sEVs and their corresponding cells. Though the total number of detected miRNAs in astrocytes was greater than neurons, neurons expressed more sEV-associated miRNAs than astrocytes. Only 20.7% of astrocytic miRNAs were loaded into sEVs, while 41.0% of neuronal miRNAs were loaded into sEVs, suggesting differences in the cellular sorting mechanisms. We identified short RNA sequence motifs, or EXOmotifs, on the miRNAs that were differentially loaded or excluded from sEVs. A sequence motif GUAC was enriched in astrocytic sEVs. miRNAs preferably retained in neurons or astrocytes had a similar RNA motif CACACA, suggesting a cell-type-independent mechanism to maintain cellular miRNAs. mRNAs of five RNA-binding proteins associated with passive or active RNA sorting into sEVs were differentially expressed between neurons and astrocytes, one of which, major vault protein was higher in astrocytes than in neurons and detected in astrocytic sEVs.

CONCLUSIONS

Our studies suggest differences in RNA sorting into sEVs. These differences in miRNA signatures can be used for determining the cellular sources of sEVs altered in neurological disorders. Video abstract.

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

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

Vitamin D Deficiency and Molecular Changes in Circulating MicroRNAs in Older Adults with Lower Back Pain

Background

MicroRNAs play an essential role in regulating pain processing within a wide range of clinical pain disorders.

Objectives

The present study aimed to evaluate the role of circulating miRNAs as biomarkers of lower back pain in older adults. In addition, the correlation between miRNAs and other related cofounders such as muscle function, adiposity, malnutrition, and Ca and vitamin D intake was assessed.

Methods

A total of 110 older subjects with an age range of 40-60 years were included in this study. The participants were classified according to a modified Oswestry lower back pain disability questionnaire (OSW) into subjects with minimal LBP (n = 40; LBP score: 0-20%), moderate LBP (n = 35; LBP score: 20-40%), and severe LBP (n = 35; LBP score: 41-60%). RT-PCR and immunoassays were used to study the circulating miRNA profile, vitamin D status, and CRP, IL-6, TNF-α, s-Ca, s-BAP, s-OC, and s-NTX levels. In addition, malnutrition and muscle performance were estimated in all subjects as other factors related to LBP.

Results

In this study, normal LBP-OSW cutoff values (8.96 ± 3.6) were reported in 36.4% of the total population, whereas 63.6% of the population had higher LBP-OSW scores, classified as follows: 31.8% with moderate LBP (LBP-OSW score: 31.4 ± 9.1) and 31.8% with severe LBP (LBP-OSW score: 54.9 ± 14.6). Four circulating miRNAs, namely, miR-146a, miR-558, miR-155, and miR-124a, as biomarkers of the intensity of back pain were identified in all participants. In subjects with moderate to severe LBP, the expression levels of miR-146a and miR-558 were significantly reduced and those of miR-155 and miR-124a were significantly increased compared to subjects with minimal LBP scores. Subjects with moderate to severe LBP showed a significant increase in adiposity markers, lower PA, muscle performance, malnutrition, and lower Ca and vitamin D intake compared to normal controls. In addition, serum levels of vitamin D and circulated plasma markers of inflammation and bone metabolism such as CRP, IL-6, TNF-α, s-Ca, s-BAP, s-OC, and s-NTX were significantly reduced in severe LBP cases compared to those with minimal LBP scores. The expressed circulating miRNAs were significantly associated with the measured muscle performance, adiposity, PA score, inflammation, and bone metabolism cofounders in subjects with higher LBP-OSW scores. The expressed miRNAs, along with other LBP cofounders, were significantly associated with ∼63.9-86.4% of the incidence of LBP in older adults.

Conclusions

In older adults with vitamin D deficiency, the severity of LBP was significantly associated with the expression of circulating miRNAs, adiposity, bone metabolism, inflammation, and muscle performance. In addition, the expressed miRNAs, along with other LBP cofounders, were significantly associated with ∼63.9-86.4% of the incidence of LBP in older adults. These results suggest the possibility of using microRNAs as therapeutics to alleviate established pain and as biomarkers in old adults with painful conditions.

Electroacupuncture Inhibits Autophagy of Neuron Cells in Postherpetic Neuralgia by Increasing the Expression of miR-223-3p

Postherpetic neuralgia (PHN) is a complication of herpes zoster viral infection. Its main manifestations are continuous or intermittent burning-like and electroshock-like pain in the affected nerves. Electroacupuncture (EA) is widely used in clinical treatment and exerts effects in alleviating neuropathic pain. In this study, we investigated the effect and underlying mechanism of EA on PHN. Sprague-Dawley rats were treated with resiniferatoxin (RTX) to establish a PHN model and subjected to EA and/or miR-223-3p overexpression (OV) or interference. Mechanical withdrawal latency was measured as an indication of pain sensitivity. Hematoxylin-eosin staining and transmission electron microscopy were performed to observe neuron cell morphology and autophagic vacuoles, respectively. ELISA was performed to detect reactive oxygen species (ROS) production and the levels of tumor necrosis factor- (TNF-) α, inducible nitric oxide synthase (iNOS), interleukin- (IL-) 6, and IL-10. Changes in autophagy and apoptosis-related miRNAs were detected by immunofluorescence and qRT-PCR, respectively. In RTX-treated rats, OV and EA reduced pain sensitivity, decreased the number of eosinophils, and increased that of nerve cells. ROS generation and the levels of TNF-α and iNOS were significantly reduced, while those of IL-6 and IL-10 were increased. OV and EA induced fewer autophagic vacuoles than those in the model group. The expression of autophagy-related protein microtubule-associated protein 1 light chain 3-II, ATG9, and Rab1 was decreased by OV and EA, whereas that of P62 was increased. qRT-PCR revealed that miR-223-3p expression in the model group decreased but was increased by EA. EA inhibits neuron cell autophagy in PHN by increasing miR-223-3p expression.

Pharmacology and Mechanism of Action of HSK16149, a Selective Ligand of α2δ Subunit of Voltage-Gated Calcium Channel with Analgesic Activity in Animal Models of Chronic Pain

Chronic pain is a public health problem because current treatments are unsatisfactory with small therapeutic index. Although pregabalin is effective for treating chronic pain, the clinical use is limited because of its side effects. Therefore, improving its therapeutic index is essential. In this study, HSK16149 was found to be a novel ligand of voltage-gated calcium channel (VGCC) α ₂ δ subunit. HSK16149 inhibited [³H]gabapentin binding to the α ₂ δ subunit and was 23 times more potent than pregabalin. In two rat models of neuropathic pain, the minimum effective dose (MED) of HSK16149 was 10 mg/kg, and the efficacy was similar to that of 30 mg/kg pregabalin. Moreover, the efficacy of HSK16149 could persist up to 24 hours postadministration at 30 mg/kg, whereas the efficacy of pregabalin lasted only for 12 hours at 30 mg/kg in streptozotocin-induced diabetic neuropathy model, indicating that HSK16149 might be a longer-acting drug candidate. HSK16149 could also inhibit mechanical allodynia in intermittent cold stress model and decrease phase II pain behaviors in formalin-induced nociception model. In addition, the locomotor activity test showed that the MED of HSK16149 was similar to that of pregabalin, whereas in the Rotarod test, the MEDs of HSK16149 and pregabalin were 100 and 30 mg/kg, respectively. These findings indicated that HSK16149 might have a better safety profile on the central nervous system. In summary, HSK16149 is a potent ligand of VGCC α ₂ δ subunit with a better therapeutic index than pregabalin. Hence, it could be an effective and safe drug candidate for treating chronic pain. SIGNIFICANCE STATEMENT: As a novel potent ligand of voltage-gated calcium channel α ₂ δ subunit, HSK16149 has the potential to be an effective and safe drug candidate for the treatment of chronic pain.

K+ Channels in Primary Afferents and Their Role in Nerve Injury-Induced Pain

Sensory abnormalities generated by nerve injury, peripheral neuropathy or disease are often expressed as neuropathic pain. This type of pain is frequently resistant to therapeutic intervention and may be intractable. Numerous studies have revealed the importance of enduring increases in primary afferent excitability and persistent spontaneous activity in the onset and maintenance of peripherally induced neuropathic pain. Some of this activity results from modulation, increased activity and /or expression of voltage-gated Na+ channels and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. K+ channels expressed in dorsal root ganglia (DRG) include delayed rectifiers (Kv1.1, 1.2), A-channels (Kv1.4, 3.3, 3.4, 4.1, 4.2, and 4.3), KCNQ or M-channels (Kv7.2, 7.3, 7.4, and 7.5), ATP-sensitive channels (KIR6.2), Ca2+-activated K+ channels (KCa1.1, 2.1, 2.2, 2.3, and 3.1), Na+-activated K+ channels (KCa4.1 and 4.2) and two pore domain leak channels (K2p; TWIK related channels). Function of all K+ channel types is reduced via a multiplicity of processes leading to altered expression and/or post-translational modification. This also increases excitability of DRG cell bodies and nociceptive free nerve endings, alters axonal conduction and increases neurotransmitter release from primary afferent terminals in the spinal dorsal horn. Correlation of these cellular changes with behavioral studies provides almost indisputable evidence for K+ channel dysfunction in the onset and maintenance of neuropathic pain. This idea is underlined by the observation that selective impairment of just one subtype of DRG K+ channel can produce signs of pain in vivo. Whilst it is established that various mediators, including cytokines and growth factors bring about injury-induced changes in DRG function and excitability, evidence presently available points to a seminal role for interleukin 1β (IL-1β) in control of K+ channel function. Despite the current state of knowledge, attempts to target K+ channels for therapeutic pain management have met with limited success. This situation may change with the advent of personalized medicine. Identification of specific sensory abnormalities and genetic profiling of individual patients may predict therapeutic benefit of K+ channel activators.

Human genetics and neuropathology suggest a link between miR-218 and amyotrophic lateral sclerosis pathophysiology

Motor neuron-specific microRNA-218 (miR-218) has recently received attention because of its roles in mouse development. However, miR-218 relevance to human motor neuron disease was not yet explored. Here, we demonstrate by neuropathology that miR-218 is abundant in healthy human motor neurons. However, in amyotrophic lateral sclerosis (ALS) motor neurons, miR-218 is down-regulated and its mRNA targets are reciprocally up-regulated (derepressed). We further identify the potassium channel Kv10.1 as a new miR-218 direct target that controls neuronal activity. In addition, we screened thousands of ALS genomes and identified six rare variants in the human miR-218-2 sequence. miR-218 gene variants fail to regulate neuron activity, suggesting the importance of this small endogenous RNA for neuronal robustness. The underlying mechanisms involve inhibition of miR-218 biogenesis and reduced processing by DICER. Therefore, miR-218 activity in motor neurons may be susceptible to failure in human ALS, suggesting that miR-218 may be a potential therapeutic target in motor neuron disease.

MicroRNAs in the Spinal Microglia Serve Critical Roles in Neuropathic Pain

Neuropathic pain (NP) can occur after peripheral nerve injury (PNI), and it can be converted into a maladaptive, detrimental phenotype that causes a long-term state of pain hypersensitivity. In the last decade, the discovery that dysfunctional microglia evoke pain, called "microgliopathic pain," has challenged traditional neuronal views of "pain" and has been extensively explored. Recent studies have shown that microRNAs (miRNAs) can act as activators or inhibitors of spinal microglia in NP conditions. We first briefly review spinal microglial activation in NP. We then comprehensively describe miRNA expression changes and their potential mechanisms in the response of microglia to nerve injury. We summarize the roles of the following two representative miRNAs: miR-124, which reverses NP by keeping microglia quiescent, and miR-155, which promotes NP following microglial activation. Finally, we focused on the therapeutic potential of microglial miRNAs in NP. The findings we summarized may be essential tools for basic research and clinical treatment of NP.

Epigenetic restoration of voltage-gated potassium channel Kv1.2 alleviates nerve injury-induced neuropathic pain

Voltage-gated potassium channels (Kv) are important regulators of neuronal excitability for its role of regulating resting membrane potential and repolarization. Recent studies show that Kv channels participate in neuropathic pain, but the detailed underlying mechanisms are far from being clear. In this study, we used siRNA, miR-137 agomir, and antagomir to regulate the expression of Kv1.2 in spinal cord and dorsal root ganglia (DRG) of naïve and chronic constriction injury (CCI) rats. Kv currents and neuron excitability in DRG neurons were examined by patch-clamp whole-cell recording to verify the change in Kv1.2 function. The results showed that Kv1.2 was down-regulated in DRG and spinal dorsal horn (SDH) by CCI. Knockdown of Kv1.2 by intrathecally injecting Kcna2 siRNA induced significant mechanical and thermal hypersensitivity in naïve rats. Concomitant with the down-regulation of Kv1.2 was an increase in the expression of the miR-137. The targeting and regulating of miR-137 on Kcna2 was verified by dual-luciferase reporter system and intrathecal injecting miR-137 agomir. Furthermore, rescuing the expression of Kv1.2 in CCI rats, achieved through inhibiting miR-137, restored the abnormal Kv currents and excitability in DRG neurons, and alleviated mechanical allodynia and thermal hyperalgesia. These results indicate that the miR-137-mediated Kv1.2 impairment is a crucial etiopathogenesis for the nerve injury-induced neuropathic pain and can be a novel potential therapeutic target for neuropathic pain management.

The role of microRNAs in neurons and neuroimmune communication in the dorsal root ganglia in chronic pain

Despite being a life-restricting condition, chronic pain remains poorly treated. A better understanding of the underlying mechanisms of chronic pain and thence development of innovative targets is therefore essential. Recently we have started to elucidate the importance of the role of microRNAs (miRs) in preclinical chronic pain. miRs are small, non-coding RNAs that regulate genes including those involved in nociceptive signalling. MiRs can exert their effects both intracellularly and extracellularly, the latter of which requires that they are released either as naked species or packaged in exosomes. Here we discuss changes in miR expression that occur in the dorsal root ganglia in murine models of chronic pain. We consider the downstream targets of changes in miR expression, including voltage-gated ion channels, as well as discuss extracellular consequences such as changes in macrophage phenotype that constitute of means by which neuron-immune cell crosstalk occurs. Such miR-mediated intracellular communication could provide a novel target for the treatment of chronic pain, which would be most effective if tailored to the specific cause of pain. Indeed, we conclude by reviewing evidence for the involvement of miRs in clinical cases of chronic pain, supporting the notion that tailored, miR-targeted therapies could prove to be an effective new strategy for the treatment of chronic pain clinically.

Interactions Among lncRNAs/circRNAs, miRNAs, and mRNAs in Neuropathic Pain

Neuropathic pain (NP) is directly caused by an injury or disease of the somatosensory nervous system. It is a serious type of chronic pain that is a burden to the economy and public health. Although recent studies have improved our understanding of NP, its pathogenesis has not been fully elucidated. Noncoding RNAs, including lncRNAs, circRNAs, and miRNAs, are involved in the pathological development of NP through many mechanisms. In addition, extensive evidence suggests that novel regulatory mechanisms among lncRNAs/circRNAs, miRNAs, and mRNAs play a crucial role in the pathophysiological process of NP. In this review, we comprehensively summarize the regulatory relationship among lncRNAs/circRNAs, miRNAs, and mRNAs and emphasize the important role of the lncRNA/circRNA-miRNA-mRNA axis in NP.

Correlation of miRNA expression with intensity of neuropathic pain in man

Background

Peripheral nerve injury causes changes in expression of multiple receptors and mediators that participate in pain processing. We investigated the expression of microRNAs (miRNAs) – a class of post-transcriptional regulators involved in many physiological and pathophysiological processes – and their potential role in the development or maintenance of chronic neuropathic pain following lingual nerve injury in human and rat.

Methods

We profiled miRNA expression in Sprague-Dawley rat and human lingual nerve neuromas using TaqMan® low-density array cards. Expression of miRNAs of interest was validated via specific probes and correlated with nerve injury-related behavioural change in rat (time spent drinking) and clinical pain (visual analogue scale (VAS) score). Target prediction was performed using publicly available algorithms; gene enrichment and pathway analysis were conducted with MetaCore. Networks of miRNAs and putative target genes were created with Cytoscape; interaction of miRNAs and target genomes in rat and human was displayed graphically using CircosPlot.

Results

rno-miR-138 was upregulated in lingual nerve of injured rats versus sham controls. rno-miR-138 and rno-miR-667 expression correlated with behavioural change at day 3 post-injury (with negative (rno-miR-138) and positive (rno-miR-667) correlations between expression and time spent drinking). In human, hsa-miR-29a was downregulated in lingual nerve neuromas of patients with higher pain VAS scores (painful group) versus patients with lower pain VAS scores (non-painful). A statistically significant negative correlation was observed between expression of both hsa-miR-29a and hsa-miR-500a, and pain VAS score.

Conclusions

Our results show that following lingual nerve injury, there are highly significant correlations between abundance of specific miRNAs, altered behaviour and pain scores. This study provides the first demonstration of correlations between human miRNA levels and VAS scores for neuropathic pain and suggests a potential contribution of specific miRNAs to the development of chronic pain following lingual nerve injury. Putative targets for candidate miRNAs include genes related to interleukin and chemokine receptors and potassium channels.

Long Noncoding RNA SNHG5 Knockdown Alleviates Neuropathic Pain by Targeting the miR-154-5p/CXCL13 Axis

Neuropathic pain is an unneglectable pain condition with limited treatment options owing to its enigmatic underlying mechanisms. Long noncoding RNA small nucleolar RNA host gene 5 (SNHG5) is involved in the progression of a spectrum of human cancers. However, its role in neuropathic pain remains undiscovered. In the present study, we established a mouse spinal nerve ligation (SNL) model, and a significant upregulation of SNHG5 was observed. Then we knocked down SNHG5 level in mouse L5 dorsal root ganglion (DRG) by delivering specific short hairpin RNA against SNHG5 with adenovirus vehicle. Mouse paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) in response to mechanical stimuli was increased after SNHG5 knockdown, accompanied with decreased protein levels of glial fibrillary acidic protein (GFAP) and ionized calcium binding adapter molecule 1 (IBA-1). Besides, SNHG5 directly modulated the expression of miR-154-5p, which was downregulated in SNL mice. MiR-154-5p inhibition abolished the effect of SNHG5 knockdown on mouse behavioral tests and GFAP and IBA-1 levels. In addition, we validated that C-X-C motif chemokine 13 (CXCL13) was a novel downstream target of miR-154-5p, and CXCL13 level was positively related to that of SNHG5 in SNL mice. In conclusion, our study demonstrated that SNHG5 knockdown alleviated neuropathic pain and inhibited the activation of astrocytes and microglia by targeting the miR-154-5p/CXCL13 axis, which might be a novel therapeutic target for neuropathic treatment clinically.

MicroRNA Let-7b-5p Induces Electroacupuncture Tolerance by Downregulating the MKP-1 Gene in Rats Subjected to CFA-induced Inflammatory Nociception

Electroacupuncture (EA) treatment has proved to significantly decrease nociception in inflammatory nociception model by suppressing the phosphorylation of p38 mitogen-activated protein kinase (p38MAPK). However, repeated EA treatment results in gradual attenuation of its analgesic effects, which was defined as “EA tolerance.” Recent studies have shown that let-7b-5p microRNA (miRNA) contributes to the EA tolerance. The present study aimed to explore the function of let-7b-5p in p38MAPK pathway and the development of EA tolerance in the inflammatory nociception. Dual luciferase reporter gene experiments were used in cortical neurons to determine the target gene locus of let-7b-5p. The threshold of nociception was assessed by tail flick latency (TFL) and paw withdrawal threshold (PWT). Western blots were used to measure the expression of mitogen-activated protein kinase phosphatase 1 (MKP-1) and phosphorylation level of p38MAPK after intracerebroventricular (ICV) injections of let-7b-5p agomir, antagomir, and controls. In vitro dual luciferase experiments demonstrated that the MKP-1-3′ untranslated region (UTR) is a target of let-7b-5p. In vivo experiment, rat with repeated EA treatment exhibits gradual decrease in TFL and PWT, which showed formation of EA tolerance. This trend was delayed after IVC injection of let-7b-5p antagomir and facilitated after IVC injection of let-7b-5p agomir. The protein levels of MKP-1 in the EA+let-7b-5p antagomir group were significantly higher than in the EA + let-7b-5p agomir group. However, P-p38MAPK in the EA+let-7b-5p antagomir group was significantly lower than in the EA+let-7b-5p agomir group. By upregulating the p38MAPK pathway through the inactivation of the MKP-1 gene, let-7b-5p contributes to EA tolerance in complete Freund’s adjuvant (CFA)-induced inflammatory nociception rats. Our work revealed the mechanism of EA tolerance and indicated that let-7b-5p could be targeted to improve the long-term effects of EA.

Non-coding RNAs in neuropathic pain

Neuro-immune alterations in the peripheral and central nervous system play a role in the pathophysiology of chronic pain in general, and members of the non-coding RNA (ncRNA) family, specifically the short, 22 nucleotide microRNAs (miRNAs) and the long non-coding RNAs (lncRNAs) act as master switches orchestrating both immune as well as neuronal processes. Several chronic disorders reveal unique ncRNA expression signatures, which recently generated big hopes for new perspectives for the development of diagnostic applications. lncRNAs may offer perspectives as candidates indicative of neuropathic pain in liquid biopsies. Numerous studies have provided novel mechanistic insight into the role of miRNAs in the molecular sequelae involved in the pathogenesis of neuropathic pain along the entire pain pathway. Specific processes within neurons, immune cells, and glia as the cellular components of the neuropathic pain triad and the communication paths between them are controlled by specific miRNAs. Therefore, nucleotide sequences mimicking or antagonizing miRNA actions can provide novel therapeutic strategies for pain treatment, provided their human homologues serve the same or similar functions. Increasing evidence also sheds light on the function of lncRNAs, which converge so far mainly on purinergic signalling pathways both in neurons and glia, and possibly even other ncRNA species that have not been explored so far.

[Trichostatin A suppresses up-regulation of histone deacetylase 4 and reverses differential expressions of miRNAs in the spinal cord of rats with chronic constrictive injury]

OBJECTIVE

To explore the analgesic mechanism of intrathecal trichostatin A (TSA) injection in a rat model of neuropathic pain induced by chronic constrictive injury (CCI).

METHODS

Male SD rats were randomized into sham operation+ DMSO group (group S), CCI +DMSO group (group C), CCI +10 μg TSA group (group T), and in the latter two groups, rat models of neuropathic pain were established induced by CCI. The rats were given intrathecal injections of 10 μL 5% DMSO or 10 μg TSA (in 5% DMSO) once a day on days 7 to 9 after CCI or sham operation. The rats were euthanized after behavioral tests on day 10, and the lumbar segment of the spinal cord was sampled to determine the expression of histone deacetylase 4 (HDAC4) protein and mRNA and detect the differentially expressed miRNAs using a miRNA chip. MiR-190b-5p and miR-142-3p were selected for validation of the results using RT-qPCR.

RESULTS

Compared with those in group S, the rats in group C showed significantly decreased paw withdrawal mechanical threshold (PWMT) from day 3 to day 10 after CCI (P < 0.05); intrathecal injection of TSA significantly reversed the reduction of PWMT following CCI (P < 0.05). Positive HDAC4 expression was detected mainly in the cytoplasm of the neurons in the gray matter of the spinal cord, and was obviously up-regulated after CCI (Ρ < 0.05). Intrathecal injection of TSA significantly suppressed CCI-induced up-regulation of HDAC4 at 10 days after the operation (P < 0.05). Compared with the miRNA profile in group S, miRNA profiling identified 83 differentially expressed miRNAs in group C (fold change ≥2 or ≤0.5, P < 0.05); TSA treatment reversed the expressions of 58 of the differentially expressed miRNAs following CCI, including 41 miRNAs that were decreased after CCI but up-regulated following TSA treatment. The results of real-time PCR validated the changes in the expressions of miR-190b-5p and miR-142-3p.

CONCLUSIONS

TSA suppresses CCI-induced up-regulation of HDAC4 and reverses differential expressions of miRNAs in the spinal cord of rats, which may contribute to the analgesic effect of TSA on neuropathic pain.

The role of microRNAs in the healing of diabetic ulcers

MicroRNAs (miRNAs) are small protected molecules with a length of 18 to 25 nucleotides. Many studies have recently been conducted on miRNAs, illustrating their role in regulating many biological, physiological, and pathological activities, such as maintaining cellular signalling and regulating cellular pathways. The main role of miRNAs is to regulate the expression of genes after translation, which can lead to the destruction or suppression of translation by binding to mRNAs. As any change in the regulation of miRNAs is associated with several physiological abnormalities, such as type 2 diabetes and its complications, these molecules can be used for therapeutic purposes or as biomarkers for the diagnosis of diseases such as diabetes and its complications. In this review article, we will discuss important findings about the miRNAs and the role of these molecules in different phases of the wound-healing process of chronic wounds, especially diabetic ulcer.