MicroRNA and chronic pain: From mechanisms to therapeutic potential

Roles of non-coding RNAs and exosomal non-coding RNAs, particularly microRNAs, long non-coding RNAs, and circular RNAs, in pathogenic mechanisms behind chronic pain: A review

Chronic pain is a significant public health concern that diminishes patients' quality of life and imposes considerable socioeconomic costs. Effective pharmacological treatments for ongoing pain are limited. Recent studies have indicated that various models of chronic pain-such as neuropathic pain, inflammatory pain, and pain associated with cancer-have abnormal levels of long noncoding RNAs (lncRNAs). Research has explored how these abnormal lncRNAs influence the activation of inflammatory cytokines, microRNAs, and other related molecules, which are crucial to the development of chronic pain. These findings suggest that these lncRNAs are vital in chronic pain mechanisms within the spinal cord and dorsal root ganglion following nerve injury. Additionally, exosomes, which can traverse the blood-brain barrier, are considered carriers of noncoding RNAs (ncRNAs) from neurons to systemic circulation. This study aims to summarize the existing knowledge on ncRNAs and exosomal ncRNAs in the context of chronic pain, highlighting potential biomarkers for diagnosis, regulatory roles in disease progression, therapeutic strategies, and clinical implications.

Innovations in acute and chronic pain biomarkers: enhancing diagnosis and personalized therapy

Pain affects millions worldwide, posing significant challenges in diagnosis and treatment. Despite advances in understanding pain mechanisms, there remains a critical need for validated biomarkers to enhance diagnosis, prognostication, and personalized therapy. This review synthesizes recent advancements in identifying and validating acute and chronic pain biomarkers, including imaging, molecular, sensory, and neurophysiological approaches. We emphasize the emergence of composite, multimodal strategies that integrate psychosocial factors to improve the precision and applicability of biomarkers in chronic pain management. Neuroimaging techniques like MRI and positron emission tomography provide insights into structural and functional abnormalities related to pain, while electrophysiological methods like electroencepholography and magnetoencepholography assess dysfunctional processing in the pain neuroaxis. Molecular biomarkers, including cytokines, proteomics, and metabolites, offer diagnostic and prognostic potential, though extensive validation is needed. Integrating these biomarkers with psychosocial factors into clinical practice can revolutionize pain management by enabling personalized treatment strategies, improving patient outcomes, and potentially reducing healthcare costs. Future directions include the development of composite biomarker signatures, advances in artificial intelligence, and biomarker signature integration into clinical decision support systems. Rigorous validation and standardization efforts are also necessary to ensure these biomarkers are clinically useful. Large-scale collaborative research will be vital to driving progress in this field and implementing these biomarkers in clinical practice. This comprehensive review highlights the potential of biomarkers to transform acute and chronic pain management, offering hope for improved diagnosis, treatment personalization, and patient outcomes.

Mapping the research landscape of microRNAs in pain: a comprehensive bibliometric analysis

Background and objectives

MicroRNAs (miRNAs) have demonstrated significant potential in pain medicine research, including mechanisms, diagnosis, and therapy. However, no relative bibliometric analysis has been performed to summarize the progress in this area quantitatively.

Methods

Literature was retrieved from the Web of Science Core Collection online database. A total of 1,295 papers were retrieved between January 1, 2000 and September 21, 2023 and underwent visualization and analysis using R software [Library [bibliometrix] and biblioshiny packages], VOSviewer (version 1.6.18), CiteSpace software (version 6.2.R4), and the bibliometrics website (http://bibliometric.com).

Results

Publications in this field have increased annually since 2000, demonstrating growing research interest. China emerged as the most productive country, followed by the United States and Germany. Keyword analysis identified "expression," "neuropathic pain," and "microRNAs" as the most relevant keywords. Extensive collaboration among countries and institutions was also observed.

Conclusion

The bibliometric analysis revealed a rapid growth of publications related to miRNAs and pain in the past 2 decades. Keywords analysis indicates that "expression," "neuropathic pain," and "microRNA" are the most frequently used words in this research field. However, more robust and globally recognized basic studies and clinical trials from prestigious journals are required.

Increased levels of Escherichia-Shigella and Klebsiella in the gut contribute to the responsivity of placebo analgesia

Placebo analgesia is observed in both humans and animals. Given the complexity of placebo analgesia involving a variety of neurobiological, psychological, and psychosocial processes, further investigation into its underlying mechanisms is essential. Gut microbiota has been implicated in the responsivity of placebo analgesia, but its precise role remains unknown and warrants further investigations. Here, we conducted a conditioning training model with chronic inflammatory pain induced by complete Freund's adjuvant (CFA) in mice, associating parecoxib with different cues. Hierarchical clustering analysis of placebo analgesia behaviors was employed to classify mice into responders and non-responders phenotypes. Approximately 40% of CFA mice undergoing conditioning training exhibited placebo analgesia. Notably, placebo analgesia responders displayed reduced anxiety-like behaviors. 16S rRNA results revealed a distinct composition of gut microbiota composition among the control, placebo analgesia non-responders and responders groups. Notably, levels of Escherichia Shigella and Klebsiella in the gut were increased considerably in the placebo analgesia responders as compared to both control and non-responders groups. In conclusion, placebo analgesia responders demonstrated marked analgesia, reduced anxiety-like behaviors, and increased levels of Escherichia-Shigella and Klebsiella, implying a potential linkage between gut microbiota and placebo analgesia.

Overexpression of miR-133a-3p reduces microglia activation by binding to GCH1, alleviating neuroinflammation and neuropathic pain

Neuropathic pain is a chronic pain condition that is primarily caused by underlying neurological damage and dysfunction. Recent studies have identified microRNAs (miRNAs) as a key factor in the treatment of neuropathic pain. To explore the effects of miR-133a-3p on neuroinflammation and neuropathic pain via GTP cyclohydrolase (GCH1), and its underlying mechanisms. In vitro models were constructed using BV-2 cells that had been treated with lipopolysaccharide, followed by treatment with either miR-133a-3p mimic or GCH1 viral knockdown/overexpression. The expression of miR-133a-3p and GCH1 in BV-2 cells was quantified by RT-qPCR. The degree of neuroinflammation was quantified using an enzyme-linked immunosorbent assay (ELISA). The targeting relationship between miR-133a-3p and GCH1 was confirmed by western blot and dual luciferase reporter assay. A chronic constriction injury model was employed to induce neuropathic pain in rats, and the mechanical withdrawal threshold (MWT) was quantified. Immunofluorescence was used to demonstrate alterations in microglial cells. The expression of miR-133a-3p was found to be decreased in lipopolysaccharide-induced BV-2 cells. The overexpression of miR-133a-3p was observed to inhibit the expression of IL-1β, IL-6, TNF-α and iNOS, which was attributed to a reduction in GCH1.Nevertheless, OE-GCH1 could partially reverse the downregulation by miR-133a-3p of the expression of inflammatory factors. In animal experiments, intrathecal injection of AVV-miR-133a-3p was observed to alleviate mechanical nociceptive abnormalities induced by activated microglia. Furthermore, miR-133a-3p ameliorated neuroinflammation in the spinal cord of chronic constriction injury rats. In summary, miR-133a-3p improves neuroinflammation and neuropathic pain by binding to GCH1. The binding of miR-133a-3p to GCH1 has been demonstrated to improve neuroinflammation and neuropathic pain.This insight will facilitate the development of new methods to effectively treat neuropathic pain.

miR-374 family is a key regulator of chronic primary pain onset

Introduction

Chronic primary pain conditions (CPPCs) are linked to catecholamine activation of peripheral adrenergic receptors. Yet, catecholamine-dependent epigenetic mechanisms, such as microRNA (miRNA) regulation of mRNA transcripts, remain largely unknown.

Objectives

We sought to identify RNA species correlated with case status in 3 pain cohorts, to validate RNAs found to be dysregulated in a mouse model of CPPC onset, and to directly test the role of adrenergic receptors in miRNA regulation. Furthermore, we tested antinociceptive effects of miR-374 overexpression.

Methods

We used RNA-seq and quantitative reverse transcription polymerase chain reaction to measure RNA expression in 3 pain cohorts. Next, we validated identified RNAs with quantitative reverse transcription polymerase chain reaction in a mouse model of CPPC onset, measuring expression in plasma, peripheral (adipose, muscle, dorsal root ganglia [DRG]), and central (spinal cord) tissues. Then, we stimulated adrenergic receptors in primary adipocyte and DRG cultures to directly test regulation of microRNAs by adrenergic signaling. Furthermore, we used in vitro calcium imaging to measure the antinociceptive effects of miR-374 overexpression.

Results

We found that one miRNA family, miR-374, was downregulated in the plasma of individuals with temporomandibular disorder, fibromyalgia syndrome, or widespread pain following a motor vehicle collision. miR-374 was also downregulated in plasma, white adipose tissue, and spinal cord from mice with multisite mechanical sensitivity. miR-374 downregulation in plasma and spinal cord was female specific. Norepinephrine stimulation of primary adipocytes, but not DRG, led to decreased miR-374 expression. Furthermore, we identified tissue-specific and sex-specific changes in the expression of predicted miR-374 mRNA targets, including known (HIF1A, NUMB, TGFBR2) and new (ATXN7, CRK-II) pain targets. Finally, we demonstrated that miR-374 overexpression in DRG neurons reduced capsaicin-induced nociceptor activity.

Conclusions

Downregulation of miR-374 occurs between adrenergic receptor activation and mechanical hypersensitivity, and its adipocyte source implicates adipose signaling in nociception. Further study of miR-374 may inform therapeutic strategies for the millions worldwide who experience CPPCs.

Piperine attenuates cancer-associated pain induced by microglial activation via increasing miR-150-50p

AIM

Severe painful neuropathy often occurs in cancer patients receiving chemotherapy. Emerging evidence has demonstrated that microglia contribute to the occurrence and development of cancer-associated pain. This study aimed to investigate the mechanisms by which piperine influences cancer-associated pain induced by microglia activation.

METHODS

The tumor cell implantation (TCI) model was adopted as the cancer-associated pain model in mice. Behavioral tests were done to confirm that model mice were sensitive to acute mechanical and thermal pain. Western blot (WB) and immunofluorescence (IF) were conducted to quantify expression level of microglia marker protein Iba1 in mice spinal cord tissues. The expression of miR-150-5p and CXCL12 in the mice spinal cord was evaluated by Quantitative real-time Polymerase Chain Reaction (qRT-PCR) and fluorescence in situ hybridization (FISH). Primary microglia from mice were treated with lipopolysaccharide (LPS) to investigate neuroinflammation.

RESULTS

The modeled mice showed high susceptibility to acute mechanical hyperalgesia and thermal hyperalgesia. The expression of microglia marker protein Iba1 in the model group was increased in vitro and in vivo. Treatment with piperine effectively relieved the cancer-associated pain in mice. The results of FISH and qRT-PCR showed that piperine significantly increased the expression of miR-150-5p and reduced the expression of CXCL12 in the spinal cord of mice. Furthermore, it inhibited the microglia-induced cancer-associated pain.

CONCLUSIONS

Piperine upregulates miR-150-50p levels, inhibits CXCL12 expression, and reduces microglia levels at the lesion site. Therefore, piperine may be a potential drug candidate for the treatment of cancer-associated pain.

Endoplasmic reticulum stress: The underlying mechanism of chronic pain

Chronic pain (CP) affects over 30 % of the global population, imposing significant financial burdens on individuals and society. However, existing treatments for CP offer limited efficacy and troublesome side effects, primarily owing to a lack of knowledge of its precise underlying mechanism. Pathological stimuli disrupt the intricate process of protein folding and endoplasmic reticulum (ER) homeostasis. This disruption leads to the accumulation of misfolded or unfolded proteins in the ER, generating a condition termed ER stress. Emerging data have indicated that ER stress, occurring in the peripheral and central nervous systems, contributes to the development and maintenance of CP. This review aimed to comprehensively explore the intersection of ER stress and CP within the lower and upper nervous systems and highlight the cell-specific contributions of the unfolded protein response in different CP types. We provide a comprehensive synthesis of evidence from animal models, examining neuronal and non-neuronal mechanisms and discuss the damaging ER stress-linked inflammation, autophagy, oxidative stress, and apoptosis, which collectively drive disease progression and contribute to a neurotoxic environment. However, the mechanisms through which ER stress influences the most advanced centre-of-pain projections in the brain remain unclear. Further investigation in this area is crucial to elucidate the relationship between ER stress and CP and facilitate the development of novel therapeutic drugs for this intractable dilemma.

MiRNA Expression in Long-Distance Runners with Musculoskeletal Pain: Implications for Pain Pathophysiology

Background: miRNAs are short, non-coding RNAs whose deregulation has been shown in painful processes, including musculoskeletal pain. This condition, which causes disability, impacts quality of life, and contributes to substantial healthcare costs, is also a critical issue in sports. In this case-control study, we evaluated the expression of four miRNAs involved in inflammation in runners with musculoskeletal pain and elucidated their functions and pathophysiological implications. Methods: A total of 17 runners with musculoskeletal pain and 17 age- and sex-matched runners without pain participated in this study. The levels of the miRNAs were evaluated by qRT-PCR. Bioinformatic tools were employed to identify the target genes and biological processes regulated by these miRNAs. Results: Compared to the controls, the runners with musculoskeletal pain exhibited significantly higher plasma levels of miR-133b (p = 0.02), miR-155-5p (p = 0.003) and let-7a-5p (p = 0.02). Multivariable regression analysis indicated that these three miRNAs exhibit a positive correlation (p < 0.05) with the presence of musculoskeletal pain, adjusted for age. Bioinformatic analysis suggested that the miRNAs hub genes are involved in regulatory processes, neuroinflammatory pathways, and human diseases that are associated with pain pathology. Conclusions: These results enhance our understanding of the potential role of miR-133b, miR-155-5p and let-7a-5p in pain-associated biological processes. The miRNA-mediated negative regulation of genes identified could explain the inflammatory and tissue repair processes in this population. Further studies are needed to confirm and validate the role of these miRNAs in painful conditions, especially considering the significant public health implications of managing inflammatory pain in sports.

Critical Windows: Exploring the Association Between Perinatal Trauma, Epigenetics, and Chronic Pain

Chronic pain is highly prevalent and burdensome, affecting millions of people worldwide. Although it emerges at any point in life, it often manifests in adolescence. Given that adolescence is a unique developmental period, additional strains associated with persistent and often idiopathic pain lead to significant long-term consequences. While there is no singular cause for the chronification of pain, epigenetic modifications that lead to neural reorganization may underpin central sensitization and subsequent manifestation of pain hypersensitivity. Epigenetic processes are particularly active during the prenatal and early postnatal years. We demonstrate how exposure to various traumas, such as intimate partner violence while in utero or adverse childhood experiences, can significantly influence epigenetic regulation within the brain and in turn modify pain-related processes. We provide compelling evidence that the burden of chronic pain is likely initiated early in life, often being transmitted from mother to offspring. We also highlight two promising prophylactic strategies, oxytocin administration and probiotic use, that have the potential to attenuate the epigenetic consequences of early adversity. Overall, we advance understanding of the causal relationship between trauma and adolescent chronic pain by highlighting epigenetic mechanisms that underlie this transmission of risk, ultimately informing how to prevent this rising epidemic.

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.

A novel microglia-targeting strategy based on nanoparticle-mediated delivery of miR-26a-5p for long-lasting analgesia in chronic pain

Accumulating evidence supports the notion that microglia play versatile roles in different chronic pain conditions. However, therapeutic strategies of chronic pain by targeting microglia remain largely overlooked. This study seeks to develop a miRNA-loaded nano-delivery system by targeting microglia, which could provide a decent and long-lasting analgesia for chronic pain. Surface aminated mesoporous silica nanoparticles were adopted to load miR-26a-5p, a potent analgesic miRNA, by electrostatic adsorption, which can avoid miR-26a-5p is rapidly released and degraded. Then, targeting peptide MG1 was modified on the surface of aminated mesoporous silica particles for microglia targeting. In peripheral nerve injury induced neuropathic pain model, a satisfactory anti-allodynia effect with about 6 weeks pain-relief duration were achieved through targeting microglia strategy, which decreased microglia activation and inflammation by Wnt5a, a non-canonical Wnt pathway. In inflammatory pain and chemotherapy induced peripheral neuropathic pain, microglia targeting strategy also exhibited more efficient analgesia and longer pain-relief duration than others. Overall, we developed a microglia-targeting nano-delivery system, which facilitates precisely miR-26a-5p delivery to enhance analgesic effect and duration for several chronic pain conditions.

Role of miRNAs in Brain Development

Non-coding RNAs that are small in size, called microRNAs (miRNAs), exert a consequence in neutralizing gene activity after transcription. The nervous system is a massively expressed organ, and an expanding body of research reveals the vital functions that miRNAs play in the brain's growth and neural activity. The significant benefit of miRNAs on the development of the central nervous system is currently shown through new scientific methods that concentrate on targeting and eradicating vital miRNA biogenesis pathways the elements involving Dicer and DGCR8. Modulation of miRNA has been associated with numerous essential cellular processes on neural progenitors, like differentiation, proliferation, and destiny determination. Current research discoveries that emphasize the significance of miRNAs in the complex process of brain development are included in this book. The miRNA pathway plays a major role in brain development, its operational dynamics, and even diseases. Recent studies on miRNA-mediated gene regulation within neural discrepancy, the circadian period and synaptic remodeling are signs of this. We also discussed how these discoveries may affect our comprehension of the fundamental processes behind brain diseases, highlighting the novel therapeutic opportunities miRNAs provide for treating various human illnesses.

miRNA contributes to neuropathic pains

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

The role of micro-RNAs in neuropathic pain-a scoping review

Neuropathic pain can be caused by a lesion or disease of the somatosensory system characterised by pathological neuro-immune alterations. At a molecular level, microRNAs (miRNAs) act as regulators of gene expression orchestrating both immune and neuronal processes. Thus, miRNAs may act as essential modulators of processes for the establishment and maintenance of neuropathic pain. The objective/aims of this scoping review was to explore and chart the literature to identify miRNAs that are dysregulated in neuropathic pain. The following databases were searched from inception to March 2023: PubMed, EBSCO, CINAHL, Cochrane Library, and SCOPUS. Two independent reviewers screened, extracted data, and independently assessed the risk of bias in included studies. The JBI critical appraisal checklist was used for critical appraisal. A narrative synthesis was used to summarise the evidence. Seven studies (total of 384 participants) that met our eligibility criteria were included in this scoping review. Our review has identified different miRNAs that are commonly involved in the chronic neuropathic pain conditions including miR-132, miR-101, and miR-199a. Our review findings further suggest that expression of miRNAs to be significantly associated with increased diabetic disease duration, HbA1C levels, and fibrinogen levels. Our review findings suggest that there is clear association between miRNA expression and chronic neuropathic pain conditions. Therefore, increasing the specificity by selecting a candidate miRNA and identifying its target mRNA is an area of future research.

Role of GABAergic system in the comorbidity of pain and depression

Patients with chronic pain often suffer with depressive symptoms, and these two conditions can be aggravated by each other over time, leading to an increase in symptom intensity and duration. The comorbidity of pain and depression poses a significant challenge to human health and quality of life, as it is often difficult to diagnose early and treat effectively. Therefore, exploring the molecular mechanisms underlying the comorbidity of chronic pain and depression is crucial to identifying new therapeutic targets for treatment. However, understanding the pathogenesis of comorbidity requires examining interactions among multiple factors, which calls for an integrative perspective. While several studies have explored the role of the GABAergic system in pain and depression, fewer have examined its interactions with other systems involved in their comorbidity. Here, we review the evidence that the role of GABAergic system in the comorbidity of chronic pain and depression, as well as the interactions between the GABAergic system and other secondary systems involved in pain and depression comorbidity, providing a comprehensive understanding of their intricate interplay.

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.

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.

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.

microRNA-181a contributes to gastric hypersensitivity in rats with diabetes by regulating TLR4 expression

Aim: The aim of this study is to investigate the mechanism and interaction of microRNA-181a (miR-181a), toll-like receptor 4 (TLR4) and nuclear factor-kappa B (NF-κB) in gastric hypersensitivity in diabetic rats. Methods: Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ; 65 mg/kg) in female SD rats. Gastric balloon distension technique was used to measure diabetic gastric hypersensitivity. Gastric-specific (T7-T10) dorsal root ganglion (DRG) neurons were acutely dissociated to measure excitability with patch-clamp techniques. Western blotting was employed to measure the expressions of TLR4, TRAF6 and NF-κB subunit p65 in T7-T10 DRGs. The expressions of microRNAs in T7-T10 DRGs were measured with quantitative real-time PCR and fluorescence in situ hybridization. Dual-luciferase reporter gene assay was used to detect the targeting regulation of microRNAs on TLR4. Results: (1) Diabetic rats were more sensitive to graded gastric balloon distention at 2 and 4 weeks. (2) The expression of TLR4 was significantly up-regulated in T7-T10 DRGs of diabetic rats. Intrathecal injection of CLI-095 (TLR4-selective inhibitor) attenuated diabetic gastric hypersensitivity, and markedly reversed the hyper-excitability of gastric-specific DRG neurons. (3) The expressions of miR-181a and miR-7a were significantly decreased in diabetic rats. MiR-181a could directly regulate the expression of TLR4, while miR-7a couldn't. (4) Intrathecal injection of miR-181a agomir down-regulated the expression of TLR4, reduced the hyper-excitability of gastric-specific neurons, and alleviated gastric hypersensitivity. (5) p65 and TLR4 were co-expressed in Dil-labeled DRG neurons. (6) Inhibition of p65 attenuated diabetic gastric hypersensitivity and hyper-excitability of gastric-specific DRG neurons. (7) The expression of TRAF6 was significantly up-regulated in diabetic rats. CLI-095 treatment also reduced the expression of TRAF6 and p65. Conclusion: The reduction of microRNA-181a in T7-T10 DRGs might up-regulate TLR4 expression. TLR4 activated NF-κB through MyD88-dependent signaling pathway, increased excitability of gastric-specific DRG neurons, and contributed to diabetic gastric hypersensitivity.

Noncoding RNAs: Novel Targets for Opioid Tolerance

As a global health problem, chronic pain is one of the leading causes of disability, and it imposes a huge economic and public health burden on families and society. Opioids represent the cornerstone of analgesic drugs. However, opioid tolerance caused by long-term application of opioids is a major factor leading to drug withdrawal, serious side effects caused by dose increases, and even the death of patients, placing an increasing burden on individuals, medicine, and society. Despite efforts to develop methods to prevent and treat opioid tolerance, no effective treatment has yet been found. Therefore, understanding the mechanism underlying opioid tolerance is crucial for finding new prevention and treatment strategies. Noncoding RNAs (ncRNAs) are important parts of mammalian gene transcriptomes, and there are thousands of unique noncoding RNA sequences in cells. With the rapid development of high-throughput genome technology, research on ncRNAs has become a hot topic in biomedical research. In recent years, studies have shown that ncRNAs mediate physiological and pathological processes, including chromatin remodeling, transcription, posttranscriptional modification and signal transduction, which are key regulators of physiological processes in developmental and disease environments and have become biomarkers and potential therapeutic targets for various diseases. An increasing number of studies have found that ncRNAs are closely related to the development of opioid tolerance. In this review, we have summarized the evidence that ncRNAs play an important role in opioid tolerance and that ncRNAs may be novel targets for opioid tolerance.

Analysis of clinical characteristics of centrally mediated abdominal pain syndrome, exploration of diagnostic markers and its relationship with the efficacy of duloxetine treatment

INTRODUCTION

Centrally mediated abdominal pain syndrome (CAPS) is characterized by severe abdominal pain. Diagnosis of CAPS is still an exclusionary diagnosis, there remain no effective diagnostic biomarkers so far. Duloxetine is the major pharmacotherapy of CAPS, while some CAPS patients do not respond to duloxetine treatment. However, there is a lack of molecular markers to predict the efficacy of duloxetine. In our pilot study, we have found differential expression profiles of serum miRNAs between CAPS patients and healthy controls. Our study aims to explore the clinical characteristics, specific miRNAs in serum as diagnostic biomarkers of CAPS and predictive biomarkers of the efficacy of duloxetine.

METHODS/DESIGN

In this prospective cohort study, we plan to enroll 430 participants including 215 CAPS patients and 215 healthy controls. The CAPS group takes duloxetine 30 mg per day as an initial dose. Patients will have 24-week medication period and follow up at week 0, 4, 12, 24 and 36. Blood samples will be obtained from patients at every visits and health controls at the initial visit and a series of questionnaires will be completed by the participants. The primary end points are: The differential expression of miRNAs between CAPS groups and healthy control groups at baseline. The changes in abdominal pain scores before and after duloxetine treatment in patients with CAPS and their relationship with the changes in miRNAs. The secondary end point is the changes in scores of depression, anxiety, sleep quality and quality of life before and after duloxetine treatment in patients with CAPS and their relationship with changes in miRNAs.

DISCUSSION

Findings of study will provide the reliable basis for diagnosis and the predictor of duloxetine efficacy of CAPS. Importantly, findings grant patients a chance to benefit from treatment.

Identification of Epigenetic Interactions between MicroRNA-30c-5p and DNA Methyltransferases in Neuropathic Pain

Neuropathic pain is a prevalent and severe chronic syndrome, often refractory to treatment, whose development and maintenance may involve epigenetic mechanisms. We previously demonstrated a causal relationship between miR-30c-5p upregulation in nociception-related neural structures and neuropathic pain in rats subjected to sciatic nerve injury. Furthermore, a short course of an miR-30c-5p inhibitor administered into the cisterna magna exerts long-lasting antiallodynic effects via a TGF-β1-mediated mechanism. Herein, we show that miR-30c-5p inhibition leads to global DNA hyper-methylation of neurons in the lumbar dorsal root ganglia and spinal dorsal horn in rats subjected to sciatic nerve injury. Specifically, the inhibition of miR-30-5p significantly increased the expression of the novo DNA methyltransferases DNMT3a and DNMT3b in those structures. Furthermore, we identified the mechanism and found that miR-30c-5p targets the mRNAs of DNMT3a and DNMT3b. Quantitative methylation analysis revealed that the promoter region of the antiallodynic cytokine TGF-β1 was hypomethylated in the spinal dorsal horn of nerve-injured rats treated with the miR-30c-5p inhibitor, while the promoter of Nfyc, the host gene of miR-30c-5p, was hypermethylated. These results are consistent with long-term protection against neuropathic pain development after nerve injury. Altogether, our results highlight the key role of miR-30c-5p in the epigenetic mechanisms' underlying neuropathic pain and provide the basis for miR-30c-5p as a therapeutic target.

The emerging power and promise of non-coding RNAs in chronic pain

Chronic pain (CP) is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage lasting longer than 3 months. CP is the main reason why people seek medical care and exerts an enormous economic burden. Genome-wide expression analysis has revealed that diverse essential genetic elements are altered in CP patients. Although many possible mechanisms of CP have been revealed, we are still unable to meet all the analgesic needs of patients. In recent years, non-coding RNAs (ncRNAs) have been shown to play essential roles in peripheral neuropathy and axon regeneration, which is associated with CP occurrence and development. Multiple key ncRNAs have been identified in animal models of CP, such as microRNA-30c-5p, ciRS-7, and lncRNA MRAK009713. This review highlights different kinds of ncRNAs in the regulation of CP, which provides a more comprehensive understanding of the pathogenesis of the disease. It mainly focuses on the contributions of miRNAs, circRNAs, and lncRNAs to CP, specifically peripheral neuropathic pain (NP), diabetic NP, central NP associated with spinal cord injury, complex regional pain syndrome, inflammatory pain, and cancer-induced pain. In addition, we summarize some potential ncRNAs as novel biomarkers for CP and its complications. With an in-depth understanding of the mechanism of CP, ncRNAs may provide novel insight into CP and could become new therapeutic targets in the future.

Disease- and headache-specific microRNA signatures and their predicted mRNA targets in peripheral blood mononuclear cells in migraineurs: role of inflammatory signalling and oxidative stress

BACKGROUND

Migraine is a primary headache with genetic susceptibility, but the pathophysiological mechanisms are poorly understood, and it remains an unmet medical need. Earlier we demonstrated significant differences in the transcriptome of migraineurs' PBMCs (peripheral blood mononuclear cells), suggesting the role of neuroinflammation and mitochondrial dysfunctions. Post-transcriptional gene expression is regulated by miRNA (microRNA), a group of short non-coding RNAs that are emerging biomarkers, drug targets, or drugs. MiRNAs are emerging biomarkers and therapeutics; however, little is known about the miRNA transcriptome in migraine, and a systematic comparative analysis has not been performed so far in migraine patients.

METHODS

We determined miRNA expression of migraineurs' PBMC during (ictal) and between (interictal) headaches compared to age- and sex-matched healthy volunteers. Small RNA sequencing was performed from the PBMC, and mRNA targets of miRNAs were predicted using a network theoretical approach by miRNAtarget.com™. Predicted miRNA targets were investigated by Gene Ontology enrichment analysis and validated by comparing network metrics to differentially expressed mRNA data.

RESULTS

In the interictal PBMC samples 31 miRNAs were differentially expressed (DE) in comparison to healthy controls, including hsa-miR-5189-3p, hsa-miR-96-5p, hsa-miR-3613-5p, hsa-miR-99a-3p, hsa-miR-542-3p. During headache attacks, the top DE miRNAs as compared to the self-control samples in the interictal phase were hsa-miR-3202, hsa-miR-7855-5p, hsa-miR-6770-3p, hsa-miR-1538, and hsa-miR-409-5p. MiRNA-mRNA target prediction and pathway analysis indicated several mRNAs related to immune and inflammatory responses (toll-like receptor and cytokine receptor signalling), neuroinflammation and oxidative stress, also confirmed by mRNA transcriptomics.

CONCLUSIONS

We provide here the first evidence for disease- and headache-specific miRNA signatures in the PBMC of migraineurs, which might help to identify novel targets for both prophylaxis and attack therapy.

Upregulation of Spinal miR-155-5p Contributes to Mechanical Hyperalgesia by Promoting Inflammatory Activation of Microglia in Bone Cancer Pain Rats

Bone cancer pain (BCP) seriously deteriorates the life quality of patients, but its underlying mechanism is still unclear. Spinal microRNAs might contribute to the development of BCP and the role of microglial activation is controversial. In this study, we established a BCP model by injecting Walker 256 breast carcinoma cells into the tibial intramedullary cavity of rats and significant hyperalgesia was observed in the BCP rats. The lumbar spinal cords were harvested to perform RNA sequencing (RNA-seq), and 31 differentially expressed miRNAs (26 upregulated and 5 downregulated) were identified in the BCP rats. Among them, miR-155-5p was significantly upregulated in the BCP rats. Spinal microglial activation was observed during BCP development. miR-155-5p could be expressed in spinal microglia and was significantly upregulated in microglia treated with lipopolysaccharide (LPS) in vitro. Serum/glucocorticoid regulated kinase family member 3 (Sgk3) was predicted to be the possible downstream target of miR-155-5p and this was confirmed using a dual-luciferase reporter assay in vitro. The inhibition of miR-155-5p restored Sgk3-expression-attenuated microglial activation and alleviated hyperalgesia in the BCP rats. In conclusion, spinal miR-155-5p/Sgk3/microglial activation might play an important role in BCP pathogenesis.

Electroacupuncture Alleviates Neuropathic Pain through Regulating miR-206-3p Targeting BDNF after CCI

Background

Electroacupuncture (EA) has benefits for neuropathic pain. However, the underlying mechanisms are still unknown. The current study explores the underlying mechanisms of EA in neuropathic pain of chronic constriction injury (CCI) rats. Material/Methods. Overall, 126 Sprague-Dawley (200-250 g) rats were divided into nine groups randomly: the sham-operated, CCI, CCI+EA, CCI+sham EA, CCI+NS, CCI+AAV-NC, CCI+AAV-miR-206-3p, CCI+EA+NS, and CCI+EA+AAV-miR-206-3p groups. The animals were sacrificed 14 days postsurgery. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests were used to determine differences in neurobehavioral manifestations. qPCR, western blotting, and immunofluorescence (IF) were carried out to detect the expression levels of miR-206-3p, BDNF, BAX/Bcl-2, TNF-α, and IL-6. Nissl staining was measured to observe morphological changes in neurons. Transmission electron microscopy (TEM) was employed to evaluate microscopic changes in dorsal horn synapses.

Results

Hyperalgesia was reduced markedly by EA in the CCI model. The expression level of miR-206-3p was elevated, whereas the expression levels of BDNF, BAX/Bcl-2, TNF-α, and IL-6 were decreased in EA-treated CCI rats. However, a miR-206-3p inhibitor partially abrogated the analgesic effect of EA and resulted in poor behavioral performance and the BDNF, BAX/Bcl-2, TNF-α, and IL-6 expression was elevated as well.

Conclusions

EA can relieve neuropathic pain by regulating the miR-206-3p/BDNF pathway, thus exerting anti-inflammatory and antiapoptotic effect.

Toward Composite Pain Biomarkers of Neuropathic Pain-Focus on Peripheral Neuropathic Pain

Chronic pain affects ~10-20% of the U.S. population with an estimated annual cost of $600 billion, the most significant economic cost of any disease to-date. Neuropathic pain is a type of chronic pain that is particularly difficult to manage and leads to significant disability and poor quality of life. Pain biomarkers offer the possibility to develop objective pain-related indicators that may help diagnose, treat, and improve the understanding of neuropathic pain pathophysiology. We review neuropathic pain mechanisms related to opiates, inflammation, and endocannabinoids with the objective of identifying composite biomarkers of neuropathic pain. In the literature, pain biomarkers typically are divided into physiological non-imaging pain biomarkers and brain imaging pain biomarkers. We review both types of biomarker types with the goal of identifying composite pain biomarkers that may improve recognition and treatment of neuropathic pain.

P2X7 receptor mediated release of microglial prostanoids and miRNAs correlates with reversal of neuropathic hypersensitivity in rats

BACKGROUND

P2X7 receptor antagonists have potential for treating various CNS diseases, including neuropathic pain, although none have been approved for clinical use. Reasons may include insufficient understanding of P2X7 receptor signaling in pain and the lack of a corresponding preclinical mechanistic biomarker.

METHODS

Lu AF27139 is a highly selective and potent small molecule antagonist at rat, mouse, and human forms of the P2X7 receptor, with excellent pharmacokinetic and CNS permeability properties. In the current experiments, we probed the utility of previously characterized and novel signaling cascades exposed to Lu AF27139 using cultured microglia combined with release assays. Subsequently, we assessed the biomarker potential of identified candidate molecules in the rat chronic constriction injury (CCI) model of neuropathic pain; study design limitations precluded their assessment in spared nerve injury (SNI) rats.

RESULTS

Lu AF27139 blocked several pain-relevant pathways downstream of P2X7 receptors in-vitro. At brain and spinal cord receptor occupancy levels capable of functionally blocking P2X7 receptors, it diminished neuropathic hypersensitivity in SNI rats, and less potently in CCI rats. Although tissue levels of numerous molecules previously linked to neuropathic pain and P2X7 receptor function (e.g. IL-6, IL-1β, cathepsin-S, 2-AG) were unaffected by CCI, Lu AF27139-mediated regulation of spinal PGE2 and miRNA (e.g. rno-miR-93-5p) levels increased by CCI aligned with its ability to diminish neuropathic hypersensitivity.

CONCLUSIONS

We have identified a pain-relevant P2X7 receptor-regulated mechanism in neuropathic rats that could hold promise as a translatable biomarker and by association enhance the clinical progression of P2X7 receptor antagonists in neuropathic pain.

microRNA-Based Network and Pathway Analysis for Neuropathic Pain in Rodent Models

Neuropathic pain (NP) is poorly managed, and in-depth mechanisms of gene transcriptome alterations in NP pathogenesis are not yet fully understood. To determine microRNA-related molecular mechanisms of NP and their transcriptional regulation in NP, PubMed, Embase, Web of Science and CINAHL Complete (EBSCO) were searched from inception to April 2021. Commonly dysregulated miRNAs in NP were assessed. The putative targets of these miRNAs were determined using TargetScan, Funrich, Cytoscape and String database. A total of 133 literatures containing miRNA profiles studies and experimentally verify studies were included. Venn analysis, target gene prediction analysis and functional enrichment analysis indicated several miRNAs (miR-200b-3p, miR-96, miR-182, miR-183, miR-30b, miR-155 and miR-145) and their target genes involved in known relevant pathways for NP. Targets on transient receptor potential channels, voltage-gated sodium channels and voltage-gated calcium channels may be harnessed for pain relief. A further delineation of signal processing and modulation in neuronal ensembles is key to achieving therapeutic success in future studies.

Rostral Anterior Cingulate Cortex–Ventrolateral Periaqueductal Gray Circuit Underlies Electroacupuncture to Alleviate Hyperalgesia but Not Anxiety-Like Behaviors in Mice With Spared Nerve Injury

Neuropathic pain is a common cause of chronic pain and is often accompanied by negative emotions, making it complex and difficult to treat. However, the neural circuit mechanisms underlying these symptoms remain unclear. Herein, we present a novel pathway associated with comorbid chronic pain and anxiety. Using chemogenetic methods, we found that activation of glutamatergic projections from the rostral anterior cingulate cortex (rACC^Glu) to the ventrolateral periaqueductal gray (vlPAG) induced both hyperalgesia and anxiety-like behaviors in sham mice. Inhibition of the rACC^Glu-vlPAG pathway reduced anxiety-like behaviors and hyperalgesia in the spared nerve injury (SNI) mice model; moreover, electroacupuncture (EA) effectively alleviated these symptoms. Investigation of the related mechanisms revealed that the chemogenetic activation of the rACC^Glu-vlPAG circuit effectively blocked the analgesic effect of EA in the SNI mice model but did not affect the chronic pain-induced negative emotions. This study revealed a novel pathway, the rACC^Glu-vlPAG pathway, that mediates neuropathic pain and pain-induced anxiety.

LncRNA H19 modulates neuropathic pain through miR-141/GLI2 axis in chronic constriction injury (CCI) rats

BACKGROUND

The participation of long non-coding RNAs (lncRNAs) in progressions of chronic pain has been evaluated. We explored mechanisms of lncRNA H19 in chronic constriction injury (CCI)-induced neuropathic pain model in vivo.

METHODS

The expressions of lncRNA H19, microRNA-141, and GLI Family Zinc Finger 2 (GLI2) in CCI rats were determined by using RT-qPCR. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were used as neuropathic pain index implying mechanical allodynia and thermal hyperalgesia. The protein concentrations of IL-1β, IL-6 and TNF-α in rats were examined by ELISA assay. RT-qPCR analyzed gene expression changes of lncRNA H19, miR-141 and GLI2. Online bioinformatics predictions supported that the bindings between miR-141 and GLI2 and dual luciferase reporter method, and RNA pull-down assays determined connections within lncRNA H19, miR-141 and GLI2 in HEK 293 cells.

RESULTS

LncRNA H19 was upregulated in the tissues of rats. Also, thermal hyperalgesia and mechanical allodynia were inhibited by lncRNA H19 suppression in rats. Moreover, IL-1β, IL-6 and TNF-α protein concentrations were suppressed by the downregulation of lncRNA H19 in rats. Furthermore, miR-141 was reduced in CCI rats and restored by the lncRNA H19 knockdown, suggesting the potential negative associations of miR-141 with lncRNA H19. GLI2 targeted miR-141 and GLI2 was increased in CCI rats. Additionally, the neuropathic pain was inhibited by the inhibition of GLI2 in rats, which was reversed by the miR-141 inhibitors.

CONCLUSION

LncRNA H19 aggravated the neuropathic pain of CCI rats through miR-141/GLI2 axis, implying that lncRNA H19 might be a biomarker for the inflammation-related neuropathic pain.

Expression of Selected microRNAs in Migraine: A New Class of Possible Biomarkers of Disease?

Preliminary but convergent findings suggest a role for microRNAs (miRNAs) in the generation and maintenance of chronic pain and migraine. Initial observations showed that serum levels of miR-382-5p and miR-34a-5p expression were increased in serum during the migraine attack, with miR-382-5p increasing in the interictal phase as well. By contrast, miR-30a-5p levels were lower in migraine patients compared to healthy controls. Of note, antimigraine treatments proved to be capable of influencing the expression of these miRNAs. Altogether, these observations suggest that miRNAs may represent migraine biomarkers, but several points are yet to be elucidated. A major concern is that these miRNAs are altered in a broad spectrum of painful and non-painful conditions, and thus it is not possible to consider them as truly “migraine-specific” biomarkers. We feel that these miRNAs may represent useful tools to uncover and define different phenotypes across the migraine spectrum with different treatment susceptibilities and clinical features, although further studies are needed to confirm our hypothesis. In this narrative review we provide an update and a critical analysis of available data on miRNAs and migraines in order to propose possible interpretations. Our main objective is to stimulate research in an area that holds promise when it comes to providing reliable biomarkers for theoretical and practical scientific advances.

How Well Do Current Laboratory Biomarkers Inform Clinical Decision-Making in Chronic Pain Management?

OBJECTIVE

Decision-making in chronic pain patients involves a combination of subjective and objective criteria, including patient history, physical examination, imaging, and patient response to prior treatments, clinical experience, probabilities, and recognition of patterns. However, there is a distinct lack of objective laboratory biomarkers in use in routine clinical care. The objective was to review the literature to identify and describe specific biomarkers in chronic pain management.

METHODS

This is a narrative review of the literature regarding the use of laboratory biomarkers in chronic pain. A librarian-assisted literature search of the PubMed, Science Direct, and Google Scholar databases was performed and resulted in 304 possible manuscripts. We included manuscripts assessing laboratory collected biomarkers from urine, serum, cerebrospinal fluid, and saliva. After screening and review of the initial literature search results, a total of 75 manuscripts were included in the narrative review.

CONCLUSION

The studies reviewed suggested that specific biomarkers may help identify those patients at risk of disease development and function as a prognostic indicator for disease progression and treatment response. However, additional research is necessary before specific recommendations can be made, and current clinical decision-making is modified.

Crosstalk Between MicroRNAs and Circular RNAs in Human Diseases: A Bibliographic Study

Background: Crosstalk of circular RNAs (circRNAs) and microRNAs (miRNAs) refers to the communication and co-regulation between them. circRNAs can act as miRNAs sponges, and miRNAs can mediate circRNAs. They interact to regulate gene expression and participate in the occurrence and development of various human diseases.

Methods: Publications on the crosstalk between miRNAs and circRNAs in human diseases were collected from Web of Science. The collected material was limited to English articles and reviews. CiteSpace and Microsoft Excel were used for bibliographic analysis.

Results: A total of 1,013 papers satisfied the inclusion criteria. The publication outputs and types of researched diseases were analyzed, and bibliographic analysis was used to characterize the most active journals, countries, institutions, keywords, and references. The annual number of publications remarkably increased from 2011 to 2020. Neoplasm was the main research hotspot (n = 750 publications), and Biochemical and Biophysical Research Communications published the largest number of papers (n = 64) on this topic. Nanjing Medical University ranked first among institutions actively engaged in this field by publishing 72 papers, and China contributed 96.84% of the 1,013 papers (n = 981 publications) analyzed. Burst keywords in recent years included glioblastoma, miR-7, skeletal muscle, and non-coding RNA.

Conclusion: Crosstalk between miRNAs and circRNAs in human diseases is a popular research topic. This study provides important clues on research trends and frontiers.

MicroRNAs as Potential Orchestrators of Alzheimer's Disease-Related Pathologies: Insights on Current Status and Future Possibilities

Alzheimer's disease (AD) is a progressive and deleterious neurodegenerative disease, strongly affecting the cognitive functions and memory of seniors worldwide. Around 58% of the affected patients live in low and middle-income countries, with estimates of increasing deaths caused by AD in the coming decade. AD is a multifactor pathology. Mitochondrial function declines in AD brain and is currently emerging as a hallmark of this disease. It has been considered as one of the intracellular processes severely compromised in AD. Many mitochondrial parameters decline already during aging; mitochondrial efficiency for energy production, reactive oxygen species (ROS) metabolism and the de novo synthesis of pyrimidines, to reach an extensive functional failure, concomitant with the onset of neurodegenerative conditions. Besides its impact on cognitive functions, AD is characterized by loss of synapses, extracellular amyloid plaques composed of the amyloid-β peptide (Aβ), and intracellular aggregates of hyperphosphorylated Tau protein, accompanied by drastic sleep disorders, sensory function alterations and pain sensitization. Unfortunately, till date, effective management of AD-related disorders and early, non-invasive AD diagnostic markers are yet to be found. MicroRNAs (miRNAs) are small non-coding nucleic acids that regulate key signaling pathway(s) in various disease conditions. About 70% of experimentally detectable miRNAs are expressed in the brain where they regulate neurite outgrowth, dendritic spine morphology, and synaptic plasticity. Increasing studies suggest that miRNAs are intimately involved in synaptic function and specific signals during memory formation. This has been the pivotal key for considering miRNAs crucial molecules to be studied in AD. MicroRNAs dysfunctions are increasingly acknowledged as a pivotal contributor in AD via deregulating genes involved in AD pathogenesis. Moreover, miRNAs have been proved to control pain sensitization processes and regulate circadian clock system that affects the sleep process. Interestingly, the differential expression of miRNA panels implies their emerging potential as diagnostic AD biomarkers. In this review, we will present an updated analysis of miRNAs role in regulating signaling processes that are involved in AD-related pathologies. We will discuss the current challenges against wider use of miRNAs and the future promising capabilities of miRNAs as diagnostic and therapeutic means for better management of AD.

MicroRNA-133b-3p targets purinergic P2X4 receptor to regulate central poststroke pain in rats

Central poststroke pain (CPSP) is a neuropathic pain syndrome that usually occurs after cerebrovascular accidents. Currently, the pathogenesis of CPSP is not fully understood. Purinergic P2X4 receptor (P2X4R) is implicated in neuropathic pain including CPSP. Herein, we demonstrated that the levels of microRNA-133b-3p (miR-133b-3p), which targets P2X4R transcripts, were significantly downregulated in the ventral posterolateral nucleus of the thalamus (VPL), cerebrospinal fluid (CSF), and plasma of CPSP rats. The expression levels of miR-133b-3p negatively correlated with the severity of allodynia. Genetic knockdown of P2X4R in the VPL protected CPSP rats against allodynia. Similarly, genetic overexpression of miR-133b-3p in the VPL reversed the allodynia established in CPSP rats via downregulation of P2X4R expression. Treatment using gabapentin in CPSP rats significantly restored the decreased miR-133b-3p expression in the VPL, CSF, and plasma and blocked allodynia in CPSP rats. The administration of an miR-133b-3p inhibitor into the VPL abolished the antiallodynic activity of gabapentin. This mechanism was associated with P2X4R expression and involved the endogenous opioid system. Human patients with CPSP showed decreased plasma levels of miR-133b-3p compared with those of control participants. Logistic regression analysis of our patient cohort showed that determining plasma levels of miR-133b-3p may be useful for CPSP diagnosis and treatment.

Inhibition of plasminogen/plasmin system retrieves endogenous nerve growth factor and adaptive spinal synaptic plasticity following peripheral nerve injury

Dysfunctions of the neuronal-glial crosstalk and/or impaired signaling of neurotrophic factors represent key features of the maladaptive changes in the central nervous system (CNS) in neuroinflammatory as neurodegenerative disorders. Tissue plasminogen activator (tPA)/plasminogen (PA)/plasmin system has been involved in either process of maturation and degradation of nerve growth factor (NGF), highlighting multiple potential targets for new therapeutic strategies. We here investigated the role of intrathecal (i.t.) delivery of neuroserpin (NS), an endogenous inhibitor of plasminogen activators, on neuropathic behavior and maladaptive synaptic plasticity in the rat spinal cord following spared nerve injury (SNI) of the sciatic nerve. We demonstrated that SNI reduced spinal NGF expression, induced spinal reactive gliosis, altering the expression of glial and neuronal glutamate and GABA transporters, reduced glutathione (GSH) levels and is associated to neuropathic behavior. Beside the increase of NGF expression, i.t. NS administration reduced reactive gliosis, restored synaptic homeostasis, GSH levels and reduced neuropathic behavior. Our results hereby highlight the essential role of tPA/PA system in the synaptic homeostasis and mechanisms of maladaptive plasticity, sustaining the beneficial effects of NGF-based approach in neurological disorders.

Macrophage-derived extracellular vesicles regulates USP5-mediated HDAC2/NRF2 axis to ameliorate inflammatory pain

Emerging research has highlighted the capacity of microRNA-23a-3p (miR-23a-3p) to alleviate inflammatory pain. However, the molecular mechanism by which miR-23a-3p attenuates inflammatory pain is yet to be fully understood. Hence, the current study aimed to elucidate the mechanism by which miR-23a-3p influences inflammatory pain. Bioinformatics was initially performed to predict the inflammatory pain related downstream targets of miR-23a-3p in macrophage-derived extracellular vesicles (EVs). An animal inflammatory pain model was established using Complete Freund's Adjuvant (CFA). The miR-23a-3p expression was downregulated in the microglia of CFA-induced mice, after which the inflammatory factors were determined by ELISA. FISH and immunofluorescence were performed to analyze the co-localization of miR-23a-3p and microglia. Interestingly, miR-23a-3p was transported to the microglia via M2 macrophage-EVs, which elevated the mechanical allodynia and the thermal hyperalgesia thresholds in mice model. The miR-23a-3p downstream target, USP5, was found to stabilize HDAC2 via deubiquitination to promote its expression while inhibiting the expression of NRF2. Taken together, the key findings of the current study demonstrate that macrophage-derived EVs containing miR-23a-3p regulates the HDAC2/NRF2 axis by decreasing USP5 expression to alleviate inflammatory pain, which may provide novel therapeutic targets for the treatment of inflammatory pain.

A comprehensive review on biomarkers associated with painful temporomandibular disorders

Pain of the orofacial region is the primary complaint for which patients seek treatment. Of all the orofacial pain conditions, one condition that possess a significant global health problem is temporomandibular disorder (TMD). Patients with TMD typically frequently complaints of pain as a symptom. TMD can occur due to complex interplay between peripheral and central sensitization, endogenous modulatory pathways, and cortical processing. For diagnosis of TMD pain a descriptive history, clinical assessment, and imaging is needed. However, due to the complex nature of pain an additional step is needed to render a definitive TMD diagnosis. In this review we explicate the role of different biomarkers involved in painful TMD. In painful TMD conditions, the role of biomarkers is still elusive. We believe that the identification of biomarkers associated with painful TMD may stimulate researchers and clinician to understand the mechanism underlying the pathogenesis of TMD and help them in developing newer methods for the diagnosis and management of TMD. Therefore, to understand the potential relationship of biomarkers, and painful TMD we categorize the biomarkers as molecular biomarkers, neuroimaging biomarkers and sensory biomarkers. In addition, we will briefly discuss pain genetics and the role of potential microRNA (miRNA) involved in TMD pain.

Exploring epigenetic and microRNA approaches for γ-globin gene regulation

Therapeutic interventions aimed at inducing fetal hemoglobin and reducing the concentration of sickle hemoglobin is an effective approach to ameliorating acute and chronic complications of sickle cell disease, exemplified by the long-term use of hydroxyurea. However, there remains an unmet need for the development of additional safe and effective drugs for single agent or combination therapy for individuals with β-hemoglobinopathies. Regulation of the γ-globin to β-globin switch is achieved by chromatin remodeling at the HBB locus on chromosome 11 and interactions of major DNA binding proteins, such as KLF1 and BCL11A in the proximal promoters of the globin genes. Experimental evidence also supports a role of epigenetic modifications including DNA methylation, histone acetylation/methylation, and microRNA expression in γ-globin gene silencing during development. In this review, we will critically evaluate the role of epigenetic mechanisms in γ-globin gene regulation and discuss data generated in tissue culture, pre-clinical animal models, and clinical trials to support drug development to date. The question remains whether modulation of epigenetic pathways will produce sufficient efficacy and specificity for fetal hemoglobin induction and to what extent targeting these pathways form the basis of prospects for clinical therapy.

The Interplay between Chronic Pain, Opioids, and the Immune System

Chronic pain represents one of the most serious worldwide medical problems, in terms of both social and economic costs, often causing severe and intractable physical and psychological suffering. The lack of biological markers for pain, which could assist in forming clearer diagnoses and prognoses, makes chronic pain therapy particularly arduous and sometimes harmful. Opioids are used worldwide to treat chronic pain conditions, but there is still an ambiguous and inadequate understanding about their therapeutic use, mostly because of their dual effect in acutely reducing pain and inducing, at the same time, tolerance, dependence, and a risk for opioid use disorder. In addition, clinical studies suggest that opioid treatment can be associated with a high risk of immune suppression and the development of inflammatory events, worsening the chronic pain status itself. While opioid peptides and receptors are expressed in both central and peripheral nervous cells, immune cells, and tissues, the role of opioids and their receptors, when and why they are activated endogenously and what their exact role is in chronic pain pathways is still poorly understood. Thus, in this review we aim to highlight the interplay between pain and immune system, focusing on opioids and their receptors.

MicroRNA-124-3p attenuates the development of nerve injury-induced neuropathic pain by targeting early growth response 1 in the dorsal root ganglia and spinal dorsal horn

Emerging evidence indicates the early growth response 1 (Egr1) plays an important role in the pathogenesis of chronic pain. However, the regulation of Egr1 expression in the DRG and spinal cord in neuropathic pain remains unclear. In the current study, the neuropathic pain was conducted by lumber 5 spinal nerve ligation (SNL) in rats. The role of miR-124-3p in Egr1 expression was examined. Our results showed that the SNL led to a significant increase in the expression of Egr1 mRNA and protein in the DRG and dorsal horn. This increased expression of Egr1 correlated with a reduction of miR-124-3p in the same region. Prior i.t. injection of Egr1 decoy AYX1 inhibited the expression of Egr1 and attenuated the neuropathic pain-like hypersensitivity following SNL. The dual-luciferase reporter assay revealed the luciferase activity of the Egr1 3'-UTR plasmid was inhibited by the miR-124-3p agomir. But this inhibition was completely reversed in the mutant 3'-UTR Egr1 group. In vivo, the SNL-induced behavioral signs of neuropathic pain and the increases in Egr1 mRNA and protein in the DRG and dorsal horn were prevented by prior to i.t. injection of miR-124-3p agomir. While, i.t. injection of miR-124-3p antagomir in naïve rats resulted in mechanical allodynia and thermal hyperalgesia and an overexpression of Egr1 in the DRG and dorsal horn. Together, our results suggest that the miR-124-3p-regulated Egr1 expression in the DRG and dorsal horn contributes to the development of neuropathic pain. Targeting miR-124-3p might be a promising therapeutic strategy in the treatment of chronic pain.

Diabetic neuropathic pain induced by streptozotocin alters the expression profile of non-coding RNAs in the spinal cord of mice as determined by sequencing analysis

Diabetic neuropathic pain (DNP) is one of the most serious complications of diabetes. Patients with DNP always exhibit spontaneous and stimulus-evoked pain. However, the pathogenesis of DNP remains to be fully elucidated. Non-coding RNAs (ncRNAs) serve important roles in several cellular processes and dysregulated expression may result in the development of several diseases, including DNP. Although ncRNAs have been suggested to be involved in the pathogenesis of DNP, their precise roles remain to be determined. In the present study, sequencing analysis was used to investigate the expression patterns of coding genes, microRNAs (miRNAs), long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in the spinal cord of mice with streptozotocin (STZ)-induced DNP. A total of 30 mRNAs, 148 miRNAs, 9 lncRNAs and 135 circRNAs exhibited significantly dysregulated expression 42 days after STZ injection. Functional enrichment analysis indicated that protein digestion and absorption pathways were the most significantly affected pathways of the differentially expressed (DE) mRNAs. The Rap1 signaling pathway, human T-lymphotropic virus-I infection and the MAPK signaling pathway were the three most significant pathways of the DE miRNAs. A total of 2,118 distinct circRNAs were identified and the length of the majority of the circRNAs was <1,000 nucleotides (nt) (1,552 circRNAs were >1,000 nt) with a median length of 620 nt. In the present study, the expression characteristics of coding genes, miRNAs, lncRNAs and circRNAs in DNP mice were determined; it paves the road for further studies on the mechanisms associated with DNP and potentially facilitates the discovery of novel ncRNAs for therapeutic targeting in the management of DNP.

A genome-wide screen reveals microRNAs in peripheral sensory neurons driving painful diabetic neuropathy

ABSTRACT

Diabetes is a leading cause of peripheral neuropathy (diabetic peripheral neuropathy, DPN), and uncontrolled long-lasting hyperglycemia leads to severe complications. A major proportion of diabetics develop excruciating pain with a variable course. Mechanisms leading to painful DPN are not completely understood and treatment options limited. We hypothesized that epigenetic modulation at the level of microRNA (miRNA) expression triggered by metabolic imbalance and nerve damage regulates the course of pain development. We used clinically relevant preclinical models, genome-wide screening, in silico analyses, cellular assays, miRNA fluorescent in situ hybridization, in vivo molecular manipulations, and behavioral analyses in the current study. We identified miRNAs and their targets that critically impact on nociceptive hypersensitivity in painful DPN. Our analyses identify miR-33 and miR-380 expressed in nociceptive neurons as critical denominators of diabetic pain and miR-124-1 as a mediator of physiological nociception. Our comprehensive analyses on the putative mRNA targets for miR-33 or miR-124-1 identified a set of mRNAs that are regulated after miR-33 or miR-124-1 overexpression in dorsal root ganglia in vivo. Our results shed light on the regulation of DPN pathophysiology and implicate specific miRNAs as novel therapeutic targets for treating painful DPN.

Pain Biomarkers in Cancer: An Overview

BACKGROUND

Pain is a common symptom in oncologic patients and its management is generally guided with reference to pain individually perceived by patients and expressed through self-reported scales. However, the utility of these tools is limited as it strongly depends on patients' opinions. For this reason, more objective instruments are desirable.

OBJECTIVE

In this overview, scientific articles indicating potential markers to be used for pain management in cancer were collected and discussed.

METHODS

Research was performed on principal electronic scientific databases by using the words "pain", "cancer", "markers" and "biomarkers" as the main keywords, and findings describing potential biomarkers for the management of cancer pain were reported.

RESULTS

Studies on pain markers not specific for cancer typology (inflammatory, genetic markers predicting response to analgesic drugs, neuroimaging markers) and pain markers for specific types of cancer (bone cancer, breast cancer, lung cancer, head and neck cancer, prostate cancer, cancer in pediatrics) have been presented and commented on.

CONCLUSION

This overview supports the view of the involvement of inflammatory mediators in the mechanisms underlying cancer pain. Only a small amount of data from research up till today is available on markers that can help in the management of pain, except for pro-inflammatory cytokines and other inflammatory indexes such as C-reactive protein (CRP). However, biomarkers are a promising strategy useful to predict pain intensity and to objectively quantify analgesic response in guiding decisions regarding individual-tailored treatments for cancer patients.

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.

Opportunities and challenges for nonaddictive interventions in chronic pain

The worlds of chronic pain and addiction continue to intersect too often in many ways. Chronic pain significantly impairs and disrupts the quality of life of millions of people worldwide. Opioids remain the most prescribed pharmacotherapy offered to patients to alleviate chronic pain. The extensive and often unnecessary prescription of opioids has created a surge in the prevalence of opioid use disorders and opioid overdose-related deaths. In this brief review, we aim to provide a bench-to-bedside overview of promising biomarkers, therapeutic targets, and challenges related to treating patients with chronic pain. We hope this review will inspire new opportunities and insights into the development of novel, nonaddictive treatments for chronic pain that will be available to patients in the near future.