miR-34c-5p functions as pronociceptive microRNA in cancer pain by targeting Cav2.3 containing calcium channels

Epigenetic mechanisms of bone cancer pain

The management and treatment of bone cancer pain (BCP) remain significant clinical challenges, imposing substantial economic burdens on patients and society. Extensive research has demonstrated that BCP induces changes in the gene expression of peripheral sensory nerves and neurons, which play crucial roles in the onset and maintenance of BCP. However, our understanding of the epigenetic mechanisms of BCP underlying the transcriptional regulation of pro-nociceptive (such as inflammatory factors and the transient receptor potential family) and anti-nociceptive (such as potassium channels and opioid receptors) genes remains limited. This article reviews the epigenetic regulatory mechanisms in BCP, analyzing the roles of histone modifications, DNA methylation, and noncoding RNAs (ncRNAs) in the expression of pro-nociceptive and anti-nociceptive genes. Finally, we provide a comprehensive view of the functional mechanisms of epigenetic regulation in BCP and explore the potential of these epigenetic molecules as therapeutic targets for BCP.

Pathology of pain and its implications for therapeutic interventions

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

Role of Cav2.3 (R-type) Calcium Channel in Pain and Analgesia: A Scoping Review

BACKGROUND

Voltage-gated calcium channels (VGCCs) play an important role in pain development and maintenance. As Cav2.2 and Cav3.2 channels have been identified as potential drug targets for analgesics, the participation of Cav2.3 (that gives rise to R-type calcium currents) in pain and analgesia remains incompletely understood.

OBJECTIVE

Identify the participation of Cav2.3 in pain and analgesia.

METHODS

To map research in this area as well as to identify any existing gaps in knowledge on the potential role of Cav2.3 in pain signalling, we conducted this scoping review. We searched PubMed and SCOPUS databases, and 40 articles were included in this study. Besides, we organized the studies into 5 types of categories within the broader context of the role of Cav2.3 in pain and analgesia.

RESULTS

Some studies revealed the expression of Cav2.3 in pain pathways, especially in nociceptive neurons at the sensory ganglia. Other studies demonstrated that Cav2.3-mediated currents could be inhibited by analgesic/antinociceptive drugs either indirectly or directly. Some articles indicated that Cav2.3 modulates nociceptive transmission, especially at the pre-synaptic level at spinal sites. There are studies using different rodent pain models and approaches to reduce Cav2.3 activity or expression and mostly demonstrated a pro-nociceptive role of Cav2.3, despite some contradictory findings and deficiencies in the description of study design quality. There are three studies that reported the association of single-nucleotide polymorphisms in the Cav2.3 gene (CACNA1E) with postoperative pain and opioid consumption as well as with the prevalence of migraine in patients.

CONCLUSION

Cav2.3 is a target for some analgesic drugs and has a pro-nociceptive role in pain.

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.

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

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

The 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.

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.

Increased BMSC exosomal miR-140-3p alleviates bone degradation and promotes bone restoration by targeting Plxnb1 in diabetic rats

Background

Diabetes mellitus (DM) is considered to be an important factor for bone degeneration disorders such as bone defect nonunion, which is characterized by physical disability and tremendous economy cost to families and society. Exosomal miRNAs of BMSCs have been reported to participate in osteoblastogenesis and modulating bone formation. However, their impacts on the development of bone degeneration in DM are not yet known. The role of miRNAs in BMSCs exosomes on regulating hyperglycemia bone degeneration was investigated in the present study.

Results

The osteogenic potential in bone defect repair of exosomes derived from diabetes mellitus BMSCs derived exosomes (DM-Exos) were revealed to be lower than that in normal BMSCs derived exosomes (N-Exos) in vitro and in vivo. Here, we demonstrate that miR-140-3p level was significantly altered in exosomes derived from BMSCs, ADSCs and serum from DM rats. In in vitro experiments, upregulated miR-140-3p exosomes promoted DM BMSCs differentiation into osteoblasts. The effects were exerted by miR-140-3p targeting plxnb1, plexin B1 is the receptor of semaphoring 4D(Sema4D) that inhibited osteocytes differentiation, thereby promoting bone formation. In DM rats with bone defect, miR-140-3p upregulated exosomes were transplanted into injured bone and accelerated bone regeneration. Besides, miR-140-3p in the exosomes was transferred into BMSCs and osteoblasts and promoted bone regeneration by targeting the plexin B1/RohA/ROCK signaling pathway.

Conclusions

Normal-Exos and miR-140-3p overexpressed-Exos accelerated diabetic wound healing by promoting the osteoblastogenesis function of BMSCs through inhibition plexin B1 expression which is the receptor of Sema4D and the plexin B1/RhoA/ROCK pathway compared with diabetes mellitus-Exos. This offers a new insight and a new therapy for treating diabetic bone unhealing.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01267-2.

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.

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

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

MiR-135-5p Alleviates Bone Cancer Pain by Regulating Astrocyte-Mediated Neuroinflammation in Spinal Cord through JAK2/STAT3 Signaling Pathway

Bone cancer pain (BCP) was associated with microRNA dysregulation. In this study, we intended to clarify the potential role of miR-135-5p in a BCP mouse model, which was established by tumor cell implantation (TCI) in the medullary cavity of the mouse femur. The BCP-related behaviors were tested, including the paw withdrawal mechanical threshold (PWMT) and number of spontaneous flinches (NSF). The miRNA expression profiles in astrocytes of the sham and tumor groups were compared, and miRNA microarray and quantitative real-time PCR (qRT-PCR) assays confirmed that the amount of expression of miR-135-5p was significantly decreased in astrocytes of the tumor group. Gain- and loss-of-function studies showed that miR-135-5p could inhibit astrocyte activation and inflammation cytokine (TNF-α and IL-1β) expression. The relation between miR-135-5p and JAK2 was detected by bioinformatic analysis and dual luciferase reporter gene assay. By conducting in vitro experiments, it was shown that the miR-135-5P mimics lowered the level of JAK2/STAT3 proteins and inflammatory factors in astrocytes. Moreover, in vivo analysis on BCP mice model indicated that the miR-135-5p agonist could sufficiently increase PWMT and decrease NSF. Meanwhile, reduced activation of astrocytes in the spinal cord, as well as decreased expression of JAK2/STAT3 and inflammatory mediators, were found after miR-135-5p agonist treatment. Collectively, the results showed that miR-135-5p could potentially reduce BCP in mice through inhibiting astrocyte-mediated neuroinflammation and blocking of the JAK2/STAT3 signaling pathway, indicating that the upregulation of miR-135-5P could be a therapeutic focus in BCP treatment.

Nociception and Pain: New Roles for Exosomes

The interchange of information from one cell to another relies on the release of hundreds of different molecules including small peptides, amino acids, nucleotides, RNA, steroids, retinoids, or fatty acid metabolites. Many of them are released to the extracellular matrix as free molecules and others can be part of the cargo of cellular vesicles. Small extracellular vesicles (30-150 nm), also known as exosomes, are a known mechanism of cell-to-cell communication in the nervous system. Exosomes participate in the pathogenesis of several neurological conditions including Alzheimer's and Parkinson's disease. However, exciting emerging evidence demonstrates that exosomes also regulate mechanisms of the sensory process including nociception. The goal of this review is to summarize the literature on exosome biogenesis, methods of small vesicle isolation and purification, and their role in nociception. We also provide insights on the potential applications of exosomes as pain biomarkers or as novel therapeutics.

Calcium channelopathies and intellectual disability: a systematic review

BACKGROUND

Calcium ions are involved in several human cellular processes including corticogenesis, transcription, and synaptogenesis. Nevertheless, the relationship between calcium channelopathies (CCs) and intellectual disability (ID)/global developmental delay (GDD) has been poorly investigated. We hypothesised that CCs play a major role in the development of ID/GDD and that both gain- and loss-of-function variants of calcium channel genes can induce ID/GDD. As a result, we performed a systematic review to investigate the contribution of CCs, potential mechanisms underlying their involvement in ID/GDD, advancements in cell and animal models, treatments, brain anomalies in patients with CCs, and the existing gaps in the knowledge. We performed a systematic search in PubMed, Embase, ClinVar, OMIM, ClinGen, Gene Reviews, DECIPHER and LOVD databases to search for articles/records published before March 2021. The following search strategies were employed: ID and calcium channel, mental retardation and calcium channel, GDD and calcium channel, developmental delay and calcium channel.

MAIN BODY

A total of 59 reports describing 159 cases were found in PubMed, Embase, ClinVar, and LOVD databases. Variations in ten calcium channel genes including CACNA1A, CACNA1C, CACNA1I, CACNA1H, CACNA1D, CACNA2D1, CACNA2D2, CACNA1E, CACNA1F, and CACNA1G were found to be associated with ID/GDD. Most variants exhibited gain-of-function effect. Severe to profound ID/GDD was observed more for the cases with gain-of-function variants as compared to those with loss-of-function. CACNA1E, CACNA1G, CACNA1F, CACNA2D2 and CACNA1A associated with more severe phenotype. Furthermore, 157 copy number variations (CNVs) spanning calcium genes were identified in DECIPHER database. The leading genes included CACNA1C, CACNA1A, and CACNA1E. Overall, the underlying mechanisms included gain- and/ or loss-of-function, alteration in kinetics (activation, inactivation) and dominant-negative effects of truncated forms of alpha1 subunits. Forty of the identified cases featured cerebellar atrophy. We identified only a few cell and animal studies that focused on the mechanisms of ID/GDD in relation to CCs. There is a scarcity of studies on treatment options for ID/GDD both in vivo and in vitro.

CONCLUSION

Our results suggest that CCs play a major role in ID/GDD. While both gain- and loss-of-function variants are associated with ID/GDD, the mechanisms underlying their involvement need further scrutiny.

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.

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

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

High-Voltage-Activated Calcium Channel in the Afferent Pain Pathway: An Important Target of Pain Therapies

High-voltage-activated (HVA) Ca2+ channels are widely expressed in the nervous system. They play an important role in pain conduction by participating in various physiological processes such as synaptic transmission, changes in synaptic plasticity, and neuronal excitability. Available evidence suggests that the HVA channel is an important therapeutic target for pain management. In this review, we summarize the changes in different subtypes of HVA channel during pain and present the currently available evidence from the clinical application of HVA channel blockers. We also review novel drugs in various phases of development. Moreover, we discuss the future prospects of HVA channel blockers in order to promote "bench-to-bedside" translation.

High-throughput sequencing reveals biofluid exosomal miRNAs associated with immunity in pigs

Large numbers of miRNAs are found in biofluid exosomes. We isolated ~50-200 nm diameter exosomes from four types of porcine biofluid (urine, plasma, semen, and bile) using serial centrifugation and ultracentrifugation procedures. A total of 42.15 M raw data were generated from four small RNA libraries. This produced 40.17 M map-able sequences, of which we identified 204 conserved miRNAs, and 190 novel candidate miRNAs. Furthermore, we identified 34 miRNAs specifically expressed in only one library, all with well-characterized immune-related functions. A set of five universally abundant miRNAs (miR-148a-3p, miR-21-5p, let-7f-5p, let-7i-5p, and miR-99a-5p) across all four biofluids was also found. Function enrichment analysis revealed that the target genes of the five ubiquitous miRNAs are primarily involved in immune and RNA metabolic processes. In summary, our findings suggest that porcine biofluid exosomes contain a large number of miRNAs, many of which may be crucial regulators of the immune system.

lnc-3215 Suppression Leads to Calcium Overload in Selenium Deficiency-Induced Chicken Heart Lesion via the lnc-3215-miR-1594-TNN2 Pathway

Selenium deficiency has been proven to induce calcium disorders in the chicken heart. However, detailed regulatory mechanisms, e.g., the long noncoding RNA (lncRNA)-microRNA (miRNA)-mRNA regulatory axis, have not yet been described. Here, we point out lnc-2315, miR-1594, and Troponin T (TNNT2) based on the results of lncRNA and miRNA comparative genomics group analysis of Se-deficient chicken hearts compared with control hearts. We employed lnc-3215 and TNNT2 knockdown, miR-1594 knockdown, and overexpression models in the chicken embryos in vivo, and lnc-3215, miR-1594, and TNNT2 knockdown and overexpression models in cardiomyocytes in vitro. The dual-luciferase reporter assay and quantitative real-time PCR were used to confirm the relationships between miR-1594 and TNNT2, lnc-3215, and miR-1594 in cardiomyocytes. Our results revealed that TNNT2 suppression induced cardiac calcium overload in vivo and in vitro. miR-1594 activates cardiac calcium overload by targeting TNNT2. Moreover, we found that lnc-3215 regulates miR-1594, and thus influences the TNNT2 expression in vivo and in vitro; these conclusions were verified by gene knockdown in chicken embryos. Our present study revealed a novel regulatory model of a calcium program, which comprises lnc-3215, miR-1594, and TNNT2 in the chicken heart. Our conclusions may provide a feasible diagnostic tool for Se-deficient cardiomyocytes injury.

Spinal circRNA-9119 Suppresses Nociception by Mediating the miR-26a-TLR3 Axis in a Bone Cancer Pain Mouse Model

Altered expression of circular RNA (circRNA) is recognized as a contributor to malignant pain where microRNA (miRNA) exerts an essential effect. We generated a murine model for bone malignancy pain in which 2472 osteolytic sarcoma cells were injected into the femurs of mice. CircRNA microarray and quantitative PCR (qPCR) and revealed that circ9119 expression was repressed in the spinal cord of bone malignancy pain model mice, which is the first relay site involved in the transmission of nociceptive information to the cerebrum of mice that receive spinal analgesics for malignancy pain. Overexpression of circ9119 by plasmid injection in the model mice reduced progressive thermal hyperalgesia and mechanical hyperalgesia. Bioinformatics prediction and dual-luciferase reporter assay showed that circ9119 functions as a sponge of miR-26a, which targets the TLR3 3'-untranslated region. Furthermore, expression of miR-26a was elevated and TLR3 level was repressed in bone malignancy pain model mice, which were counteracted by circ9119 in the spinal cord of tumor-bearing mice. Moreover, excessive expression of miR-26a was involved in the recovery of mice from progressive thermal hyperalgesia and mechanical hyperalgesia triggered via circ9119. TLR3 knockdown in bone malignancy pain model mice thoroughly impaired pain in the initial stages and reduced the effects of circ9119 on hyperalgesia. Our research findings indicate that targeting the circ9119-miR-26a-TLR3 axis may be a promising analgesic strategy to manage malignancy pain.

MicroRNA-1224 Splicing CircularRNA-Filip1l in an Ago2-Dependent Manner Regulates Chronic Inflammatory Pain via Targeting Ubr5

Dysfunctions of gene transcription and translation in the nociceptive pathways play the critical role in development and maintenance of chronic pain. Circular RNAs (circRNAs) are emerging as new players in regulation of gene expression, but whether and how circRNAs are involved in chronic pain remain elusive. We showed here that complete Freund's adjuvant-induced chronic inflammation pain significantly increased circRNA-Filip1l (filamin A interacting protein 1-like) expression in spinal neurons of mice. Blockage of this increase attenuated complete Freund's adjuvant-induced nociceptive behaviors, and overexpression of spinal circRNA-Filip1l in naive mice mimicked the nociceptive behaviors as evidenced by decreased thermal and mechanical nociceptive threshold. Furthermore, we found that mature circRNA-Filip1l expression was negatively regulated by miRNA-1224 via binding and splicing of precursor of circRNA-Filip1l (pre-circRNA-Filip1l) in the Argonaute-2 (Ago2)-dependent manner. Increase of spinal circRNA-Filip1l expression resulted from the decrease of miRNA-1224 expression under chronic inflammation pain state. miRNA-1224 knockdown or Ago2 overexpression induced nociceptive behaviors in naive mice, which was prevented by the knockdown of spinal circRNA-Filip1l. Finally, we demonstrated that a ubiquitin protein ligase E3 component n-recognin 5 (Ubr5), validated as a target of circRNA-Filip1l, plays a pivotal role in regulation of nociception by spinal circRNA-Filip1l. These data suggest that miRNA-1224-mediated and Ago2-dependent modulation of spinal circRNA-Filip1l expression regulates nociception via targeting Ubr5, revealing a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.SIGNIFICANCE STATEMENT circRNAs are emerging as new players in regulation of gene expression. Here, we found that the increase of circRNA-Filip1l mediated by miRNA-1224 in an Ago2-dependent way in the spinal cord is involved in regulation of nociception via targeting Ubr5 Our study reveals a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.

The Regulatory Mechanisms and Therapeutic Potential of MicroRNAs: From Chronic Pain to Morphine Tolerance

Chronic pain, including cancer-related pain, is a pain condition often caused by inflammation or dysfunctional nerves. Chronic pain treatment poses a significant health care challenge, where opioids especially morphine are widely used and patients often develop tolerance over time with aggravated pain. microRNA (miRNA) is known to play important roles in regulating gene expressions in the nervous system to affect neuronal network plasticity related to algogenesis and the developing of morphine tolerance. In this article, we reviewed studies conducted in rodent animal models investigating the mechanisms of miRNAs regulation in chronic pain with different phenotypes and morphine tolerance. In addition, the potential of targeting miRNAs for chronic pain and morphine tolerance treatment is also reviewed. Finally, we point out the directions of the future research in chronic pain and morphine tolerance.

miRNAs: Important Targets for Oral Cancer Pain Research

Pain is a symptom shared by an incredible number of diseases. It is also one of the primary conditions that prompt individuals to seek medical treatment. Head and neck squamous cell carcinoma (HNSCC) corresponds to a heterogeneous disease that may arise from many distinct structures of a large, highly complex, and intricate region. HNSCC affects a great number of patients worldwide and is directly associated with chronic pain, which is especially prominent during the advanced stages of oral squamous cell carcinoma (OSCC), an anatomical and clinical subtype that corresponds to the great majority oral cancers. Although the cellular and molecular bases of oral cancer pain have not been fully established yet, the results of recent studies suggest that different epigenetic mechanisms may contribute to this process. For instance, there is strong scientific evidence that microRNAs (miRNAs), small RNA molecules that do not encode proteins, might act by regulating the mechanisms underlying cancer-related pain. Among the miRNAs that could possibly interfere in pain-signaling pathways, miR-125b, miR-181, and miR-339 emerge as some of the most promising candidates. In fact, such molecules apparently contribute to inflammatory pain. Moreover, these molecules possibly influence the activity of endogenous pain control systems (e.g., opioidergic and serotonergic systems), which could ultimately result in peripheral and central sensitization, central nervous system (CNS) phenomena innately associated with chronic pain. This review paper focuses on the current scientific knowledge regarding the involvement of miRNAs in cancer pain, with special attention dedicated to OSCC-related pain.