microRNA and Pain

Fentanyl induces analgesic effect through miR-381-3p/TRPM7 when combined with bupivacaine in subarachnoid injection

Fentanyl combined with bupivacaine in subarachnoid anesthesia exerts a strong synergistic analgesic effect, extending the duration of analgesia. However, the mechanism of enhanced analgesic effect of fentanyl remains elusive. The present study investigated the potential mechanism of the analgesic effect of fentanyl when combined with bupivacaine. The subarachnoid injection (SI) rat model was employed, and SI of fentanyl or/and bupivacaine was used to investigate their analgesic effect. Dorsal root ganglion (DRG)' RNA sequencing (RNA-Seq) and bioinformatics analysis were performed to evaluate the downstream mechanisms of MicroRNAs (miRNAs). Further validation tests included RT-PCR, Western blot, and immunofluorescence. A single SI of fentanyl or bupivacaine decreased the positive responses to stimulation when used alone or in combination. RNA-seq results revealed that miR-381-3p played a role in the fentanyl-driven promotion of analgesia. Bioinformatics analysis and dual-luciferase reporter identified TRPM7 as a direct downstream target gene of miR-381-3p. In vitro, overexpression of miR-381-3p could further block fentanyl-induced expression of TRPM7, p-ERK1/2, CGRP, and SP. In addition, antagomir-381-3p reversed the inhibitory effect of fentanyl on the expression of TRPM7, p-ERK1/2, CGRP, and SP, in vivo; however, TRPM7 siRNA rescued the effect of antagomir-381-3p. In conclusion, fentanyl inhibits p-ERK by targeting TRPM7 via miR-381-3p, lowering the production of CGRP and SP, and ultimately inducing analgesic effects.

Therapeutic Implication of miRNAs as an Active Regulatory Player in the Management of Pain: A Review

Chronic pain is frequently associated with neuropathy, inflammation, or the malfunctioning of nerves. Chronic pain is associated with a significant burden of morbidity due to opioid use, associated with addiction and tolerance, and disability. MicroRNAs (miRs) are emerging therapeutic targets to treat chronic pain through the regulation of genes associated with inflammation, neuronal excitability, survival, or de-differentiation. In this review, we discuss the possible involvement of miRs in pain-related molecular pathways. miRs are known to regulate high-conviction pain genes, supporting their potential as therapeutic targets.

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.

M2 macrophage polarization: a potential target in pain relief

Pain imposes a significant urden on patients, affecting them physically, psychologically, and economically. Despite numerous studies on the pathogenesis of pain, its clinical management remains suboptimal, leading to the under-treatment of many pain patients. Recently, research on the role of macrophages in pain processes has been increasing, offering potential for novel therapeutic approaches. Macrophages, being indispensable immune cells in the innate immune system, exhibit remarkable diversity and plasticity. However, the majority of research has primarily focused on the contributions of M1 macrophages in promoting pain. During the late stage of tissue damage or inflammatory invasion, M1 macrophages typically transition into M2 macrophages. In recent years, growing evidence has highlighted the role of M2 macrophages in pain relief. In this review, we summarize the mechanisms involved in M2 macrophage polarization and discuss their emerging roles in pain relief. Notably, M2 macrophages appear to be key players in multiple endogenous pathways that promote pain relief. We further analyze potential pathways through which M2 macrophages may alleviate pain.

Epigenetic regulation in opioid induced hyperalgesia

About 25 million American adults experience pain daily and one of the most commonly prescribed drugs to treat pain are opioids. Prolonged opioid usage and dose escalations can cause a paradoxical response where patients experience enhanced pain sensitivity. This opioid induced hyperalgesia (OIH) is a major hurdle when treating pain in the clinic because its underlying mechanisms are still not fully understood. OIH is also commonly overlooked and lacks guidelines to prevent its onset. Research on pain disorders and opioid usage have recognized potential epigenetic drivers of disease including DNA methylation, histone modifications, miRNA regulation, but their involvement in OIH has not been well studied. This article discusses epigenetic changes that may contribute to pathogenesis, with an emphasis on miRNA alterations in OIH. There is a crucial gap in knowledge including how multiple epigenetic modulators contribute to OIH. Elucidating the epigenetic changes underlying OIH and the crosstalk among these mechanisms could lead to the development of novel targets for the prevention and treatment of this painful phenomena.

MicroRNA-Related Polymorphism and Their Association with Fibromyalgia

MicroRNAs are tissue-specific expressed short RNAs that serve post-transcriptional gene regulation. A specific microRNA can bind to mRNAs of different genes and thereby suppress their protein production. In the context of the complex phenotype of fibromyalgia, we used the Axiom miRNA Target Site Genotyping Array to search genome-wide for DNA variations in microRNA genes, their regulatory regions, and in the 3'UTR of protein-coding genes. To identify disease-relevant DNA polymorphisms, a cohort of 176 female fibromyalgia patients was studied in comparison to a cohort of 162 healthy women. The association between 48,329 markers and fibromyalgia was investigated using logistic regression adjusted for population stratification. Results show that 29 markers had p-values < 1 × 10^-3, and the strongest association was observed for rs758459 (p-value of 0.0001), located in the Neurogenin 1 gene which is targeted by hsa-miR-130a-3p. Furthermore, variant rs2295963 is predicted to affect binding of hsa-miR-1-3p. Both microRNAs were previously reported to be differentially expressed in fibromyalgia patients. Despite its limited statistical power, this study reports two microRNA-related polymorphisms which may play a functional role in the pathogenesis of fibromyalgia. For a better understanding of the disease pattern, further functional analyses on the biological significance of microRNAs and microRNA-related polymorphisms are required.

The over-expression of miRNA-206 in peripheral blood of patients with burning mouth syndrome and its relationship with anxiety and depression

BACKGROUND

Burning mouth syndrome (BMS) is characterised by persisting burning pain of the oral mucosa, and its etiopathogenesis remains poorly understood.

OBJECTIVES

Our study aimed to detect the expression of miRNA-206 in the blood and clarify the relationship among miRNA-206, pain, anxiety and depression of BMS patients.

METHODS

Thirty patients with BMS and 30 healthy individuals were enrolled in the experimental and control groups, respectively. Data on medical history and clinical oral examination for all participants were collected. Simultaneously, scores of Visual Analogous Scale (VAS), Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS) were administered. The expression level of miRNA-206 in plasma were determined by RT-(q)PCR. Finally, the relationship of miRNA-206 expression with the VAS score, SAS score, and SDS score was analysed. Chi-square test and t-test were used for statistical analysis of the data, and p < .05 was considered statistically significant.

RESULTS

The majority of the patients with BMS identified the tongue as the main pain area, and showed dry mouth and poor sleep quality. The SAS and SDS scores of patients with BMS were higher than those of healthy controls (p < .05) and were positively correlated with VAS pain score. In addition, miRNA-206 expression was higher in patients with BMS than in healthy individuals (p < .05), and was positively correlated with the VAS and SDS scores (p < .05).

CONCLUSIONS

Patients with BMS suffer from pain and tend to be more anxious and depressed than healthy controls. miRNA-206 expression in the peripheral blood of patients with BMS is positively correlated with pain and depression, which may be involved in the pathogenesis of BMS.

MicroRNAs in spinal cord injury: A narrative review

Spinal cord injury (SCI) is a global medical problem with high disability and mortality rates. At present, the diagnosis and treatment of SCI are still lacking. Spinal cord injury has a complex etiology, lack of diagnostic methods, poor treatment effect and other problems, which lead to the difficulty of spinal cord regeneration and repair, and poor functional recovery. Recent studies have shown that gene expression plays an important role in the regulation of SCI repair. MicroRNAs (miRNAs) are non-coding RNA molecules that target mRNA expression in order to silence, translate, or interfere with protein synthesis. Secondary damage, such as oxidative stress, apoptosis, autophagy, and inflammation, occurs after SCI, and differentially expressed miRNAs contribute to these events. This article reviews the pathophysiological mechanism of miRNAs in secondary injury after SCI, focusing on the mechanism of miRNAs in secondary neuroinflammation after SCI, so as to provide new ideas and basis for the clinical diagnosis and treatment of miRNAs in SCI. The mechanisms of miRNAs in neurological diseases may also make them potential biomarkers and therapeutic targets for spinal cord injuries.

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.

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.

Oral Cancer Cells Release Vesicles that Cause Pain

Oral cancer pain is attributed to the release from cancers of mediators that sensitize and activate sensory neurons. Intraplantar injection of conditioned media (CM) from human tongue cancer cell line HSC-3 or OSC-20 evokes nociceptive behavior. By contrast, CM from noncancer cell lines, DOK, and HaCaT are non-nociceptive. Pain mediators are carried by extracellular vesicles (EVs) released from cancer cells. Depletion of EVs from cancer cell line CM reverses mechanical allodynia and thermal hyperalgesia. CM from non-nociceptive cell lines become nociceptive when reconstituted with HSC-3 EVs. Two miRNAs (hsa-miR-21-5p and hsa-miR-221-3p) are identified that are present in increased abundance in EVs from HSC-3 and OSC-20 CM compared to HaCaT CM. The miRNA target genes suggest potential involvement in oral cancer pain of the toll like receptor 7 (TLR7) and 8 (TLR8) pathways, as well as signaling through interleukin 6 cytokine family signal transducer receptor (gp130, encoded by IL6ST) and colony stimulating factor receptor (G-CSFR, encoded by CSF3R), Janus kinase and signal transducer and activator of transcription 3 (JAK/STAT3). These studies confirm the recent discovery of the role of cancer EVs in pain and add to the repertoire of algesic and analgesic cancer pain mediators and pathways that contribute to oral cancer pain.

Circulating MicroRNAs as a New Class of Biomarkers of Physiological Reactions of the Organism to the Intake of Dietary Supplements and Drugs

BACKGROUND

The analysis of individual microRNAs (miRNAs) as a diagnostic and prognostic tool for the effective treatment of various diseases has aroused particular interest in the scientific community. The determination of circulating miRNAs makes it possible to assess biological changes associated with nutritional processes, the intake of dietary supplements and drugs, etc. The profile of circulating miRNAs reflects the individual adaptation of the organism to the effect of specific environmental conditions.

OBJECTIVE

The objective of this study is to systematize the data and show the importance of circulating miRNAs as new potential biomarkers of the organism's response to the intake of various dietary supplements, drugs, and consider the possibility of their use in doping control.

METHODS

A systematic analysis of scientific publications (ncbi.nlm.nih.gov) on the miRNA expression profile in response to the intake of dietary supplements and drugs most often used by athletes, and supposed their role as potential markers in modern doping control was carried out.

RESULTS

The profile of circulating miRNAs is highly dependent on the intake of a particular drug, and, therefore, may be used as a marker of the effects of biologically active supplements and drugs including the substances from the Prohibited List of the World Anti-Doping Agency (WADA).

CONCLUSION

Monitoring of circulating miRNAs can serve as a high-precision marker for detecting doping abuse in elite sports. However, it is necessary to conduct additional studies on the effect of complex drugs on the profile of circulating miRNAs and individual circulating miRNAs on a particular biological process.

Epigenetic modification of BDNF mediates neuropathic pain via miR-30a-3p/EP300 axis in CCI rats

Recent investigation of microRNAs on chronic pain has developed a breakthrough in neuropathic pain management. In the present study, decreased expression of miR-30a-3p was reported using qRT-PCR analysis and loss of miR-30a-3p promoted neuropathic pain progression in sciatic nerve chronic constrictive injury rats through determining the pain threshold. We predicted miR-30a-3p could target E-cadherin transcriptional activator (EP300) via bioinformatics analysis. Meanwhile, we found that brain-derived neurotrophic factor (BDNF) is involved in neuropathic pain. Here, we exhibited that EP300 epigenetically up-regulated BDNF via enhancing acetylated histone H3 and H4 on the promoter. For another, miR-30a-3p was able to modify the level of BDNF and acetylated histone H3 and H4. Loss of miR-30a-3p enhanced EP300 and BDNF colocalization in CCI rats. Subsequently, it was shown that increased EP300 induced neuropathic pain by an enhancement of neuronal BDNF level in vivo. To sum up, it was revealed that epigenetic modification of BDNF promoted neuropathic pain via EP300 induced by miR-30a-3p in CCI rats.

Sensory neuron-associated macrophages as novel modulators of neuropathic pain

The peripheral nervous system comprises an infinity of neural networks that act in the communication between the central nervous system and the most diverse tissues of the body. Along with the extension of the primary sensory neurons (axons and cell bodies), a population of resident macrophages has been described. These newly called sensory neuron-associated macrophages (sNAMs) seem to play an essential role in physiological and pathophysiological processes, including infection, autoimmunity, nerve degeneration/regeneration, and chronic neuropathic pain. After different types of peripheral nerve injury, there is an increase in the number and activation of sNAMs in the sciatic nerve and sensory ganglia. The activation of sNAMs and their participation in neuropathic pain development depends on the stimulation of pattern recognition receptors such as Toll-like receptors and Nod-like receptors, chemokines/cytokines, and microRNAs. On activation, sNAMs trigger the production of critical inflammatory mediators such as proinflammatory cytokines (eg, TNF and IL-1β) and reactive oxygen species that can act in the amplification of primary sensory neurons sensitization. On the other hand, there is evidence that sNAMs can produce antinociceptive mediators (eg, IL-10) that counteract neuropathic pain development. This review will present the cellular and molecular mechanisms behind the participation of sNAMs in peripheral nerve injury-induced neuropathic pain development. Understanding how sNAMs are activated and responding to nerve injury can help set novel targets for the control of neuropathic pain.

Tissue Specific Reference Genes for MicroRNA Expression Analysis in a Mouse Model of Peripheral Nerve Injury

MicroRNAs (miRNAs) have emerged as master switch regulators in many biological processes in health and disease, including neuropathy. miRNAs are commonly quantified by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), usually estimated as relative expression through reference genes normalization. Different non-coding RNAs (ncRNAs) are used for miRNA normalization; however, there is no study identifying the optimal reference genes in animal models for peripheral nerve injury. We evaluated the stability of eleven ncRNAs, commonly used for miRNA normalization, in dorsal root ganglia (DRG), dorsal horn of the spinal cord (dhSC), and medial prefrontal cortex (mPFC) in the mouse spared nerve injury (SNI) model. After RT-qPCR, the stability of each ncRNA was determined by using four different methods: BestKeeper, the comparative delta-Cq method, geNorm, and NormFinder. The candidates were rated according to their performance in each method and an overall ranking list was compiled. The most stable ncRNAs were: sno420, sno429, and sno202 in DRG; sno429, sno202, and U6 in dhSC; sno202, sno420, and sno142 in mPFC. We provide the first reference genes' evaluation for miRNA normalization in different neuronal tissues in an animal model of peripheral nerve injury. Our results underline the need for careful selection of reference genes for miRNA normalization in different tissues and experimental conditions. We further anticipate that our findings can be used in a broad range of nerve injury related studies, to ensure validity and promote reproducibility in miRNA quantification.

miR-101 down-regulates mTOR expression and attenuates neuropathic pain in chronic constriction injury rat models

We aimed to demonstrate the effects of microRNA (miR)-101 on neuropathic pain and explore the underlying mechanisms. Rat spinal microglia cells were isolated and inflammatory condition was stimulated by 24-h incubation with lipopolysaccharide (LPS). Rats were divided into 4 groups: sham, chronic constriction injury (CCI), CCI + miR-negative control (miR-NC) and CCI + miR-101 mimics. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) tests were conducted. The mRNA levels of key genes were determined by quantitative real-time polymerase chain reaction. Mammalian target of rapamycin (mTOR) protein level was detected by Western blot. Concentrations of interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α were examined by ELISA. MiR-101 was downregulated and mTOR was upregulated in lumbar spinal dorsal horns from CCI rats. Targetscan and luciferase reporter assay confirmed that mTOR was direct target of miR101. MiR-101 mimics inhibited LPS-stimulated increase in the levels of IL-6, IL-1β and TNF-α in primary microglial cells in vitro. In the rat CCI model, miR-101 mimics also suppressed CCI-induced decrease in PWT and PWL and inhibited CCI-induced increase in mRNA and protein levels of IL-6, IL-1β and TNF-α. In addition, miR-101 downregulated mTOR mRNA and protein expressions in CCI rats. Besides, CCI operation resulted in miR-101 downregulation and mTOR mRNA upregulation in spinal microglia cells in a time-dependent manner. In conclusion, miR-101 had neuropathic pain-attenuating activity through targeting mTOR.

Effects of miR-150 on neuropathic pain process via targeting AKT3

MicroRNAs (miRNA) are reported to be a vital regulator of neuropathic pain. Even so, the molecular mechanisms of miRNA function on neuropathic pain development are known little. Our research was designed to investigate the role of miRNA in neuropathic pain development in rat modle set up by chronic sciatic nerve injury (CCI). Increasing miR-150 expression could significantly alleviate neuropathic pain in CCI rats. For farther researching the regulation mechanism of miR-150 on neuropathic pain, we screened AKT3 as a possible target of miR-150 by bioinformatic mechods and predicted a possible target of miR-150 in 3'-untranslated region (UTR) of AKT3 who serves as an oncogene. In rat model, the expression both of AKT3 mRNA and protein were significantly upregulated. The overexpressed miR-150 importantly repressed the level of AKT3 and simultaneously alleviate mechanical and thermal hyperalgesia in rat model. These suppressant impacts of miR-150 on neuropathic pain process can be reversed by the overexpression of AKT3. Considering all above results, our research declared that miR-150 can restrain neuropathic pain process though targeting AKT3 in vivo, suggesting that miR-150 could be the therapeutic target for neuropathic pain therapy by regulating AKT3.

Overexpression of miR-98 attenuates neuropathic pain development via targeting STAT3 in CCI rat models

MicroRNA (miRNA) are significant regulators of neuropathic pain development and neuroinflammation can contribute a lot to the progression of neuropathic pain. Recently, miR-98 has been reported to be involved in various diseases. However, little is known about the role of miR-98 in neuropathic pain development and neuroinflammation. Therefore, our study was aimed to investigate the function of miR-98 in neuropathic pain via establishing a rat model using chronic constriction injury (CCI) of the sciatic nerve. Here, we observed that miR-98 was downregulated in CCI rat models. Overexpression of miR-9 was able to inhibit neuropathic pain progression. Recently, STAT3 has been reported to serve a key role in various processes, including inflammation. Interestingly, our study indicated that STAT3 was dramatically upregulated and activated in CCI rats. By using informatics analysis, STAT3 was predicted as a direct target of miR-98 and the direct correlation was confirmed. Then, miR-98 was overexpressed in CCI rats and it was found that miR-98 was able to repress neuropathic pain development via inhibiting the neuroinflammation. As displayed, interleukin 6 (IL-6), IL-1β, and tumor necrosis factor-α (TNF-α) expression was obviously induced in CCI rats, while miR-98 reduced their protein levels. Finally, we found that overexpression of STAT3 reversed the inhibitory effect of miR-98 on neuropathic pain development. Taken these together, we reported that overexpression of miR-98 attenuated neuropathic pain development via targeting STAT3 in CCI rat models.

MicroRNA-7a ameliorates neuropathic pain in a rat model of spinal nerve ligation via the neurofilament light polypeptide-dependent signal transducer and activator of transcription signaling pathway

Neuropathic pain is a type of chronic pain induced by either central or peripheral nerve injury. MicroRNAs have been recently linked to many diseases, including neuropathic pain. However, the role of miR-7a in neuropathic pain still remains elusive. Thus, we aim to investigate the effects of miR-7a on neuropathic pain based on the spinal nerve ligation rat model. After establishment of spinal nerve ligation rat models, rats were infected with adeno-associated virus-neurofilament light polypeptide, adeno-associated virus-miR-7a or treated with metformin. The paw withdrawal threshold and paw withdrawal latency were assessed afterward, and the expression of miR-7a and neurofilament light polypeptide as well as their interaction was determined. Subsequently, miR-7a was overexpressed or silenced in dorsal root ganglion cells to investigate the role of miR-7a in neuropathic pain. Furthermore, the regulatory effect of neurofilament light polypeptide on neuropathic pain was detected using plasmid overexpressing neurofilament light polypeptide. Spinal nerve ligation rat model exhibited upregulation of neurofilament light polypeptide but downregulation of miR-7a. In addition, neurofilament light polypeptide accumulation or miR-7a inhibition decreased paw withdrawal threshold and paw withdrawal latency. Then, neurofilament light polypeptide accumulation or miR-7a inhibition was observed to increase the phosphorylation level of signal transducer and activator of transcription. miR-7a was found to directly target neurofilament light polypeptide and downregulate neurofilament light polypeptide. In addition, inhibiting the signal transducer and activator of transcription signaling pathway was also revealed to increase paw withdrawal threshold and paw withdrawal latency. Collectively, our study demonstrated that miR-7a ameliorated neuropathic pain via blocking the signal transducer and activator of transcription signaling pathway by repressing neurofilament light polypeptide. These findings, if taken further, can be of important clinical significance in treating patients with neuropathic pain.

Inflammation in the pathophysiology of neuropathic pain

Peripheral nerve injuries and diseases often lead to pain persisting beyond the resolution of damage, indicating an active disease-promoting process, which may result in chronic pain. This is regarded as a maladaptive mechanism resulting from neuroinflammation that originally serves to promote regeneration and healing. Knowledge on these physiological and pathophysiological processes has accumulated over the last few decades and has started to yield potential therapeutic targets. Key players are macrophages, T-lymphocytes, cytokines, and chemokines. In the spinal cord and brain, microglia and astrocytes are involved. Recently, data have been emerging on the regulation of these players. MicroRNAs and other noncoding RNAs have been discussed as potential master switches that may link nerve injury, pain, and inflammation. Clinical disorders most intensely studied in the context of neuroinflammation and pain are the complex regional pain syndrome, polyneuropathies, postherpetic neuralgia, and the fibromyalgia syndrome, in which recently a neuropathic component has been described. Research from several groups has shown an important role of both proinflammatory and anti-inflammatory cytokines in neuropathic and other chronic pain states in humans. There is ample evidence of an analgesic action of anti-inflammatory cytokines in animal models. The interplay of anti-inflammatory cytokines and the nociceptive system provides possibilities and challenges concerning treatment strategies based on this concept.

MiR-134-5p attenuates neuropathic pain progression through targeting Twist1

Neuropathic pain is a kind of chronic pain because of dysfunctions of somatosensory nerve system. Recently, many studies have demonstrated that microRNAs (miRs) play crucial roles in neuropathic pain development. This study was designed to investigate the effects of miR-134-5p on the process of neuropathic pain progression in a rat model established by chronic sciatic nerve injury (CCI). First, we observed that miR-134-5p was significantly decreased in CCI rat models. Overexpression of miR-134-5p strongly alleviated neuropathic pain behaviors including mechanical and thermal hyperalgesia. Meanwhile, inflammatory cytokine expression, such as IL-6, IL-1β and TNF-α in CCI rats were greatly repressed by upregulation of miR-134-5p. Twist1 has been widely regarded as a poor prognosis biomarker in diverse diseases. Here, by using bioinformatic analysis, 3'-untranslated region (UTR) of Twist1 was predicted to be a downstream target of miR-134-5p in our study. Here, we found that overexpression of miR-134-5p was able to suppress Twist1 dramatically. Furthermore, it was exhibited that Twist1 was increased in CCI rats time-dependently and Twist1 was inhibited in vivo. Subsequently, downregulation of Twist1 in CCI rats could depress neuropathic pain progression via inhibiting neuroinflammation. In conclusion, our current study indicated that miR-134-5p may inhibit neuropathic pain development through targeting Twist1. Our findings suggested that miR-134-5p might provide a novel therapeutic target for neuropathic pain.

Effects of miR-26a-5p on neuropathic pain development by targeting MAPK6 in in CCI rat models

MicroRNA are emerging as significant regulators of neuropathic pain progression. In addition, neuroinflammation contributes a lot to neuropathic pain. miR-26a-5p has been identified as an inflammation-associated miRNA in multiple pathological processes. However, little is known about the biological role of miR-26a-5p in neuroinflammation and neuropathic pain development. Therefore, we aimed to investigate the function of miR-26a-5p in neuropathic pain by establishing a rat model using chronic sciatic nerve injury (CCI). A significant decrease of miR-26a-5p expression was observed in the spinal cord tissues form the CCI rats compared to the control group. Moreover, overexpression of miR-26a-5p significantly repressed neuropathic pain and neuroinflammation in CCI rats. MAPK6 was identified as a direct downstream target gene of miR-26a-5p and confirmed by dual-luciferase reporter assays. As displayed, overexpression of miR-26a-5p greatly reduced MAPK6 levels in vitro and in vivo. Meanwhile, MAPK6 expression and miR-26a-5p were oppositely correlated in CCI rats. Furthermore, up-regulation of MAPK6 obviously reversed the suppressive effect of miR-26a-5p on neuroinflammation and neuropathic pain progression. Taken these together, our results implied that miR-26a-5p could act as a negative regulator of neuropathic pain development through targeting MAPK6, which indicated that miR-26a-5p might serve as a potential therapeutic target for neuropathic pain.

MiR-150 alleviates neuropathic pain via inhibiting toll-like receptor 5

MicroRNAs (miRNAs) are reported as vital participators in the pathophysiological course of neuropathic pain. However, the underlying mechanisms of the functional roles of miRNAs in neuropathic pain are largely unknown. This study was designed to explore the potential role of miR-150 in regulating the process of neuropathic pain in a rat model established by chronic sciatic nerve injury (CCI). Overexpression of miR-150 greatly alleviated neuropathic pain development and reduced inflammatory cytokine expression, including COX-2, interleukin IL-6, and tumor necrosis factor (TNF)-α in CCI rats. By bioinformatic analysis, 3'-untranslated region (UTR) of Toll-like receptor (TLR5) was predicted to be a target of miR-150. TLR5 commonly serves as an important regulator of inflammation. Overexpression of miR-150 significantly suppressed the expression of TLR5 in vitro and in vivo. Furthermore, upregulation of TLR5 decreased the miR-150 expression and downregulation of TLR5 increased miR-150, respectively. Overexpression of TLR5 significantly reversed the miR-150-induced suppressive effects on neuropathic pain. In conclusion, our current study indicates that miR-150 may inhibit neuropathic pain development of CCI rats through inhibiting TLR5-mediated neuroinflammation. Our findings suggest that miR-150 may provide a novel therapeutic target for neuropathic pain treatment.

Astroglial MicroRNA-219-5p in the Ventral Tegmental Area Regulates Nociception in Rats

BACKGROUND

The authors previously reported that noncoding microRNA miR-219-5p is down-regulated in the spinal cord in a nociceptive state. The ventral tegmental area also plays critical roles in modulating nociception, although the underlying mechanism remains unknown. The authors hypothesized that miR-219-5p in the ventral tegmental area also may modulate nociception.

METHODS

The authors studied the bidirectional regulatory role of ventral tegmental area miR-219-5p in a rat complete Freund's adjuvant model of inflammatory nociception by measuring paw withdrawal latencies. Using molecular biology technologies, the authors measured the effects of astroglial coiled-coil and C2 domain containing 1A/nuclear factor κB cascade and dopamine neuron activity on the down-regulation of ventral tegmental area miR-219-5p-induced nociceptive responses.

RESULTS

MiR-219-5p expression in the ventral tegmental area was reduced in rats with thermal hyperalgesia. Viral overexpression of ventral tegmental area miR-219-5p attenuated complete Freund's adjuvant-induced nociception from 7 days after complete Freund's adjuvant injection (paw withdrawal latencies: 6.09 ± 0.83 s vs. 3.96 ± 0.76 s; n = 6/group). Down-regulation of ventral tegmental area miR-219-5p in naïve rats was sufficient to induce thermal hyperalgesia from 7 days after lentivirus injection (paw withdrawal latencies: 7.09 ± 1.54 s vs. 11.75 ± 2.15 s; n = 8/group), which was accompanied by increased glial fibrillary acidic protein (fold change: 2.81 ± 0.38; n = 3/group) and reversed by intraventral tegmental area injection of the astroglial inhibitor fluorocitrate. The nociceptive responses induced by astroglial miR-219-5p down-regulation were inhibited by interfering with astroglial coiled-coil and C2 domain containing 1A/nuclear factor-κB signaling. Finally, pharmacologic inhibition of ventral tegmental area dopamine neurons alleviated this hyperalgesia.

CONCLUSIONS

Down-regulation of astroglial miR-219-5p in ventral tegmental area induced nociceptive responses are mediated by astroglial coiled-coil and C2 domain containing 1A/nuclear factor-κB signaling and elevated dopamine neuron activity.

Aberrant microRNA expression in patients with painful peripheral neuropathies

Changes in the neuro-immune balance play a major role in the induction and maintenance of neuropathic pain. We recently reported pathophysiologically relevant alterations in skin and sural nerve cytokine expression in peripheral neuropathies of different etiologies. Immune processes and cytokine expression are under tight control of microRNAs (miRNAs). To identify potential master switches in the neuro-immune balance, we aimed at characterizing inflammation-regulating miRNA profiles in patients with peripheral neuropathies. In an unselected patient cohort with polyneuropathies of different etiologies seen at our neuromuscular center between 2014 and 2015, we determined the systemic and local relative expression of miR-21-5p, miR-146a, and miR-155. In white blood cells we found higher miR-21 (p<0.001) and miR-146a (p<0.001) expression and lower miR-155 (p<0.001) expression when compared to healthy controls. In sural nerve, miR-21 (p<0.02) was increased in painful compared to painless neuropathies. In painful neuropathies, skin biopsies from the lower leg had reduced miR-146a (p<0.001) and miR-155 (p<0.001) expression compared to the thigh. Thus, peripheral neuropathies are associated with aberrant miRNA expression in white blood cells, sural nerve, and skin. These miRNA patterns may help to identify factors that determine the painfulness of peripheral neuropathies and lead to druggable targets.

Identification of the Spinal Expression Profile of Non-coding RNAs Involved in Neuropathic Pain Following Spared Nerve Injury by Sequence Analysis

Neuropathic pain (NP) is caused by damage to the nervous system, resulting in aberrant pain, which is associated with gene expression changes in the sensory pathway. However, the molecular mechanisms are not fully understood. A non-coding Ribose Nucleic Acid (ncRNA) is an RNA molecule that is not translated into a protein. NcRNAs are involved in many cellular processes, and mutations or imbalances of the repertoire within the body can cause a variety of diseases. Although ncRNAs have recently been shown to play a role in NP pathogenesis, the specific effects of ncRNAs in NP remain largely unknown. In this study, sequencing analysis was performed to investigated the expression patterns of ncRNAs in the spinal cord following spared nerve injury-induced NP. A total of 134 long non-coding RNAs (lncRNAs), 12 microRNAs (miRNAs), 188 circular RNAs (circRNAs) and 1066 mRNAs were significantly regulated at 14 days after spared nerve injury (SNI) surgery. Next, quantitative real-time polymerase chain reaction (PCR) was performed to validate the expression of selected lncRNAs, miRNAs, circRNAs, and mRNAs. Bioinformatics tools and databases were employed to explore the potential ncRNA functions and relationships. Our data showed that the most significantly involved pathways in SNI pathogenesis were ribosome, PI3K-Akt signaling pathway, focal adhesion, ECM-receptor interaction, amoebiasis and protein digestion and absorption. In addition, the lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA network of NP was constructed. This is the first study to comprehensively identify regulated ncRNAs of the spinal cord and to demonstrate the involvement of different ncRNA expression patterns in the spinal cord of NP pathogenesis by sequence analysis. This information will enable further research on the pathogenesis of NP and facilitate the development of novel NP therapeutics targeting ncRNAs.

MicroRNA-93 alleviates neuropathic pain through targeting signal transducer and activator of transcription 3

Emerging evidence suggests that microRNAs (miRNAs) play a critical role in the pathogenesis of neuropathic pain. However, the exact role of miRNAs in regulating neuropathic pain remains largely unknown. In this study, we aimed to investigate the potential role of miR-93 in a rat model of neuropathic pain induced by chronic constriction sciatic nerve injury (CCI). We found a significant decrease of miR-93 in the spinal cord of CCI rats compared with sham rats. Overexpression of miR-93 significantly alleviated neuropathic pain development and reduced inflammatory cytokine expression, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-6 in CCI rats. By bioinformatic analysis and dual-luciferase reporter assay, we found that miR-93 directly targeted the 3'-untranslated region (UTR) of signal transducer and activator of transcription 3 (STAT3), an important regulator of inflammation. Overexpression of miR-93 markedly suppressed the expression of STAT3 in vitro and in vivo. Furthermore, overexpression of STAT3 significantly reversed the miR-93 overexpression-induced suppressive effects on neuropathic pain development and neuroinflammation. Taken together, our study suggests that miR-93 inhibits neuropathic pain development of CCI rats possibly through inhibiting STAT3-mediated neuroinflammation. Our findings indicate that miR-93 may serve as a novel therapeutic target for neuropathic pain intervention.

‘Omics’: an emerging field in pain research and management

Precision medicine is an emerging approach for prevention and treatment of diseases considering individuals’ uniqueness. Omics provide one step forward toward advanced precision medicine and include technologies such as genomics, proteomics and metabolomics generating valuable data through characterization of entire biological systems. With the aid of omics, a major shift has been started to occur in understanding of diseases followed by potential fundamental changes in medical care strategies. This short review aims at providing some examples of current omics that are applied in the field of pain in terms of new biomarkers for diagnosis of different pain types, stratification of patients and new therapeutic targets. Implementation of omics would most likely offer breakthrough in the future of pain management.

Circulating miRNA as fine regulators of the physiological responses to physical activity: Pre-analytical warnings for a novel class of biomarkers

MicroRNAs are endogenous non-coding RNAs that post-transcriptionally regulate gene expression by specifically binding the target mRNA and by consequently inducing its degradation. miRNAs can be released into the circulation where they remain stable and they can be measured. Their changes reflect individual biologic adaptation to exposures to specific environmental conditions. As such, measurement of circulating microRNAs represents an opportunity to evaluate biologic changes associated with interventions such as exercise and diet. Physical activity is, indeed, a very important modifying factor for circulating miRNAs. Toward their use in clinical settings several issues should be still solved. Their clinical application is hindered by the high heterogeneity of the analytical procedures used for their measurements. Furthermore, several pre-analytical concerns equally reduce the clinical applicability of miRNA. Pre-analytical phase in sports medicine is an important issue both because, often the conditions in which sampling are performed are peculiar (and not always canonical) and because some of the tested parameters, in the case of professional athletes, enters in routine anti-doping testing and, as such, they should be treated according to precise rules in order to avoid any false positive results. Aim of this review is to give an overview of the main available knowledges about the pre-analytical management of the sample for circulating miRNA evaluation along with the importance of miRNA as regulators of the response to physical activity and their possible future use in anti-doping settings.