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

Neuroinflammatory Pathways Associated with Chronic Post-Thoracotomy Pain: A Review of Current Literature

Chronic post-thoracotomy pain (CPTP) is a major clinical problem that affects up to 35-55% of patients undergoing thoracic incisions. Evidence suggests that multiple cellular signaling pathways and neuro-inflammatory mediators may play an essential role in the pathogenesis of CPTP. In this comprehensive review, we present the current evidence on the cellular signaling pathways and inflammatory changes associated with the initiation and maintenance of CPTP, focusing on the potential application of these findings in the clinical setting. An electronic search of Medline, EMBASE, Cochrane, Google Scholar, and ClinicalTrials.gov was performed, and 3652 abstracts were identified. After an initial abstract screening, 131 studies underwent a full-text review, and nine papers were eventually included in this review. Studies were included if they assessed the cellular signaling pathways or inflammatory processes associated with the induction and/or maintenance of CPTP. All the identified studies were pre-clinical studies conducted on animal models. Our search identified seven cellular pathways (NK-1 receptor (NK-1), Glutaminase 1, Toll-like receptor 4 (TLR4), Resolvins, Ror-2, Sonic hedgehog signaling (Shh), and Wnt5a/Wnts) and six cytokines (IL-1β, IL-6, IL-8, IL-10, IFN-γ, and TNF-α) that were investigated in the context of CPTP. Multiple cellular signaling pathways and inflammatory cytokines may play an important role in the neuroinflammatory changes associated with the induction and maintenance of chronic post-thoracotomy pain in animal models. However, the clinical impact and therapeutic utility of these neuroinflammatory changes in routine clinical practice have yet to be demonstrated.

Spinal nerve transection-induced upregulation of KDM4A in the dorsal root ganglia contributes to the development and maintenance of neuropathic pain via promoting CCL2 expression in rats

Studies indicate that the lysine-specific demethylase 4A (KDM4A), acts as a key player in neuropathic pain, driving the process through its involvement in promoting neuroinflammation. Emerging evidence reveals that C-C Motif Chemokine Ligand 2 (CCL2) participates in neuroinflammation, which plays an important role in the development and maintenance of neuropathic pain. However, it remains unclear if KDM4A plays a role in regulating CCL2 in neuropathic pain. This study found that following spinal nerve transection (SNT) of the lumbar 5 nerve root in rats, the expression of KDM4A and CCL2 increased in the ipsilateral L4/5 dorsal root ganglia (DRG). Injecting KDM4A siRNA into the DRGs of rats post-SNT resulted in a higher paw withdrawal threshold (PWT) and paw-withdrawal latency (PWL) compared to the KDM4A scRNA group. In addition, prior microinjection of AAV-EGFP-KDM4A shRNA also alleviates the decrease in PWT and PWL caused by SNT. Correspondingly, microinjection of AAV-EGFP-KDM4A shRNA subsequent to SNT reduced the established mechanical and thermal hyperalgesia. Furthermore, AAV-EGFP-KDM4A shRNA injection decreased the expression of CCL2 in DRGs. ChIP-PCR analysis revealed that increased binding of p-STAT1 with the CCL2 promoter induced by SNT was inhibited by AAV-EGFP-KDM4A shRNA treatment. These findings suggest that KDM4A potentially influences neuropathic pain by regulating CCL2 expression in DRGs.

Spinal nerve transection-induced upregulation of SAP97 via promoting membrane trafficking of GluA1-containing AMPA receptors in the dorsal horn contributes to the pathogenesis of neuropathic pain

Emerging evidence has implicated an important role of synapse-associated protein-97 (SAP97)-regulated GluA1-containing AMPARs membrane trafficking in cocaine restate and in contextual episodic memory of schizophrenia. Herein, we investigated the role of SAP97 in neuropathic pain following lumbar 5 spinal nerve transection (SNT) in rats. Our results showed that SNT led to upregulation of SAP97, enhanced the interaction between SAP97 and GluA1, and increased GluA1-containing AMPARs membrane trafficking in the dorsal horn. Microinjection of AAV-EGFP-SAP97 shRNA in lumbar 5 spinal dorsal horn inhibited SAP97 production, decreased SAP97-GluA1 interaction, reduced the membrane trafficking of GluA1-containing AMPARs, and partially attenuated neuropathic pain following SNT. Intrathecal injections of SAP97 siRNA or NASPM, an antagonist of GluA1-containing AMPARs, also partially reversed neuropathic pain on day 7, but not on day 14, after SNT. Spinal overexpression of SAP97 by AAV-EGFP-SAP97 enhanced SAP97-GluA1 interaction, increased the membrane insertion of GluA1-containing AMPARs, and induced abnormal pain in naïve rats. In addition, treatment with SAP97 siRNA or NASPM i.t. injection alleviated SNT-induced allodynia and hyperalgesia and exhibited a longer effect in female rats. Together, our results indicate that the SNT-induced upregulation of SAP97 via promoting GluA1-containing AMPARs membrane trafficking in the dorsal horn contributes to the pathogenesis of neuropathic pain. Targeting spinal SAP97 might be a promising therapeutic strategy to treatment of chronic pain.

Spinal Neuronal miR-124 Inhibits Microglial Activation and Contributes to Preventive Effect of Electroacupuncture on Chemotherapy-Induced Peripheral Neuropathy in Mice

Chemotherapy-induced peripheral neuropathy (CIPN) is a persistent and irreversible side effect of antineoplastic agents. Patients with CIPN usually show chronic pain and sensory deficits with glove-and-stocking distribution. However, whether spinal neuronal microRNA (miR)-124 is involved in cisplatin-induced peripheral neuropathy remains to be studied. In this study, miR-124 was significantly reduced in the spinal dorsal horn in CIPN mice. Overexpression of neuronal miR-124 induced by injecting adeno-associated virus with neuron-specific promoter into the spinal cord of mice prevented the development of mechanical allodynia, sensory deficits, and the loss of intraepidermal nerve fibers induced by cisplatin. Meanwhile, cisplatin-induced M1 microglia activation and the release of proinflammatory cytokines were significantly inhibited by overexpression of neuronal miR-124. Furthermore, electroacupuncture (EA) treatment upregulated miR-124 expression in the spinal dorsal horn of CIPN mice. Interestingly, downregulation of spinal neuronal miR-124 significantly inhibited the regulatory effect of EA on CIPN and microglia activity as well as spinal neuroinflammation induced by cisplatin. These results demonstrate that spinal neuronal miR-124 is involved in the prevention and treatment of EA on cisplatin-induced peripheral neuropathy in mice. Our findings suggest that spinal neuronal miR-124 might be a potential target for EA effect, and we provide, to our knowledge, a new experimental basis for EA prevention of CIPN.

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.

Upregulation of lysine-specific demethylase 6B aggravates inflammatory pain through H3K27me3 demethylation-dependent production of TNF-α in the dorsal root ganglia and spinal dorsal horn in rats

AIMS

Lysine-specific demethylase 6B (KDM6B) serves as a key mediator of gene transcription. It regulates expression of proinflammatory cytokines and chemokines in variety of diseases. Herein, the role and the underlying mechanisms of KDM6B in inflammatory pain were studied.

METHODS

The inflammatory pain was conducted by intraplantar injection of complete Freund's adjuvant (CFA) in rats. Immunofluorescence, Western blotting, qRT-PCR, and chromatin immunoprecipitation (ChIP)-PCR were performed to investigate the underlying mechanisms.

RESULTS

CFA injection led to upregulation of KDM6B and decrease in the level of H3K27me3 in the dorsal root ganglia (DRG) and spinal dorsal horn. The mechanical allodynia and thermal hyperalgesia following CFA were alleviated by the treatment of intrathecal injection of GSK-J4, and by microinjection of AAV-EGFP-KDM6B shRNA in the sciatic nerve or in lumbar 5 dorsal horn. The increased production of tumor necrosis factor-α (TNF-α) following CFA in the DRGs and dorsal horn was inhibited by these treatments. ChIP-PCR showed that CFA-induced increased binding of nuclear factor κB with TNF-α promoter was repressed by the treatment of microinjection of AAV-EGFP-KDM6B shRNA.

CONCLUSIONS

These results suggest that upregulated KDM6B via facilitating TNF-α expression in the DRG and spinal dorsal horn aggravates inflammatory pain.

Neuralized1-Mediated CPEB3 Ubiquitination in the Spinal Dorsal Horn Contributes to the Pathogenesis of Neuropathic Pain in Rats

Compelling evidence has shown that Neuralized1 (Neurl1) facilitates hippocampal-dependent memory storage by modulating cytoplasmic polyadenylation element-binding protein 3 (CPEB3)-dependent protein synthesis. In the current study, we investigated the role of Neurl1 in the pathogenesis of neuropathic pain and the underlying mechanisms. The neuropathic pain was evaluated by lumbar 5 spinal nerve ligation (SNL) in rats. Immunofluorescence staining, Western blotting, qRT-PCR, and coimmunoprecipitation (Co-IP) were performed to investigate the underlying mechanisms. Our results showed that SNL led to an increase of Neurl1 in the spinal dorsal horn. Spinal microinjection of AAV-EGFP-Neurl1 shRNA alleviated mechanical allodynia; decreased the level of CPEB3 ubiquitination; inhibited the production of GluA1, GluA2, and PSD95; and reduced GluA1-containing AMPA receptors in the membrane of the dorsal horn following SNL. Knockdown of spinal CPEB3 decreased the production of GluA1, GluA2, and PSD95 in the dorsal horn and attenuated abnormal pain after SNL. Overexpression of Neurl1 in the dorsal horn resulted in pain-related hypersensitivity in naïve rats; raised the level of CPEB3 ubiquitination; increased the production of GluA1, GluA2, and PSD95; and augmented GluA1-containing AMPA receptors in the membrane in the dorsal horn. Moreover, spinal Neurl1 overexpression-induced mechanical allodynia in naïve rats was partially reversed by repeated intrathecal injections of CPEB3 siRNA. Collectively, our results suggest that SNL-induced upregulation of Neurl1 through CPEB3 ubiquitination-dependent production of GluA1, GluA2, and PSD95 in the dorsal horn contributes to the pathogenesis of neuropathic pain in rats. Targeting spinal Neurl1 might be a promising therapeutic strategy for the treatment of neuropathic 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.

Spinal CircKcnk9 Regulates Chronic Visceral Hypersensitivity of Irritable Bowel Syndrome

Dysregulation of circular RNAs (circRNAs) has been reported to be functionally associated with chronic pain, but it is unknown whether and how circRNAs participate in visceral hypersensitivity. The expression of circKcnk9 was increased in spinal neurons of irritable bowel syndrome (IBS)-like rats. ShcircKcnk9 attenuated visceral hypersensitivity and inhibited c-Fos expression in IBS-like rats, whereas overexpression of spinal circKcnk9 induced visceral hypersensitivity and increased c-Fos expression in control rats. Furthermore, circKcnk9 was found to act as a miR-124-3p sponge. MiR-124-3p antagomir restored pain responses downregulated by shcircKcnk9 in IBS-like rats. Finally, the signal transducer and activator of transcription 3 (STAT3), validated as a target of miR-124-3p, could play a critical role in visceral hypersensitivity by regulating NSF/GluR2. PERSPECTIVE: Spinal circKcnk9 functions as a miR-124-3p sponge to promote visceral hypersensitivity by regulating the STAT3/NSF/GluR2 pathway. This pathway might provide a novel epigenetic mechanism of visceral hypersensitivity and a potential circRNA therapeutic target for IBS.

The involvement of EGR1 in neuron apoptosis in the in vitro model of spinal cord injury via BTG2 up-regulation

OBJECTIVE

EGR1 has been implicated in the progression of spinal cord injury (SCI). Nevertheless, its specific mechanism in SCI remains to be investigated. Hence, this study explored the potential mechanism of EGR1 in SCI by focusing on neuron apoptosis.

METHODS

H₂O₂ was utilized to treat rat neurons-dorsal spinal cord (RN-dsc) for the construction of an in vitro model of SCI. Afterwards, cell survival, apoptosis, and LDH leakage were detected to evaluate the injury degree of H₂O₂-treated RN-dsc. The expression of apoptosis-related proteins was also measured. Additionally, EGR1 was silenced and/or BTG2 was overexpressed in RN-dsc before H₂O₂ treatment to assess the impacts of EGR1 and BTG2 on H₂O₂-induced RN-dsc. Jasper online website was utilized to predict binding sites of EGR1 on BTG2, and dual-luciferase reporter gene and chromatin immunoprecipitation (ChIP) assays were utilized to verify the binding between EGR1 and BTG2.

RESULTS

H₂O₂ treatment suppressed survival and promoted apoptosis in RN-dsc, accompanied by upregulated LDH, Bax, and cleaved-caspase-3 and down-regulated Bcl-2. Moreover, EGR1 and BTG2 were up-regulated in H₂O₂-induced RN-dsc. Mechanistically, EGR1 was bound to the promoter of BTG2 to transcriptionally activate BTG2. EGR1 knockdown diminished apoptosis and LDH, Bax, and cleaved-caspase-3 levels while elevating survival and Bcl-2 levels in H₂O₂-induced RN-dsc. These effects of EGR1 knockdown were abrogated by further BTG2 overexpression.

DISCUSSION

Conclusively, EGR1 promotes H₂O₂-induced apoptosis in RN-dsc by activating BTG2 transcription.

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

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

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.

Activation of Double-Stranded RNA-Activated Protein Kinase in the Dorsal Root Ganglia and Spinal Dorsal Horn Regulates Neuropathic Pain Following Peripheral Nerve Injury in Rats

Double-stranded RNA (dsRNA)-activated kinase (PKR) is an important component in inflammation and immune dysfunction. However, the role of PKR in neuropathic pain remains unclear. Here, we showed that lumbar 5 spinal nerve ligation (SNL) led to a significant increase in the level of phosphorylated PKR (p-PKR) in both the dorsal root ganglia (DRG) and spinal dorsal horn. Images of double immunofluorescence staining revealed that p-PKR was expressed in myelinated A-fibers, unmyelinated C-fibers, and satellite glial cells in the DRG. In the dorsal horn, p-PKR was located in neuronal cells, astrocytes, and microglia. Data from behavioral tests showed that intrathecal (i.t.) injection of 2-aminopurine (2-AP), a specific inhibitor of PKR activation, and PKR siRNA prevented the reductions in PWT and PWL following SNL. Established neuropathic pain was also attenuated by i.t. injection of 2-AP and PKR siRNA, which started on day 7 after SNL. Prior repeated i.t. injections of PKR siRNA prevented the SNL-induced degradation of IκBα and IκBβ in the cytosol and the nuclear translocation of nuclear factor κB (NF-κB) p65 in both the DRG and dorsal horn. Moreover, the SNL-induced increase in interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) production was diminished by this treatment. Collectively, these results suggest that peripheral nerve injury-induced PKR activation via NF-κB signaling-regulated expression of proinflammatory cytokines in the DRG and dorsal horn contributes to the pathogenesis of neuropathic pain. Our findings suggest that pharmacologically targeting PKR might be an effective therapeutic strategy for the treatment of neuropathic pain.

microRNA-148a in Exosomes Derived from Bone Marrow Mesenchymal Stem Cells Alleviates Cardiomyocyte Apoptosis in Atrial Fibrillation by Inhibiting SMOC2

Exosomes-related microRNAs (miRNAs) have been considered to be the significant biomarkers contributing to the development of atrial fibrillation (AF). We observed the implicit mechanism of exosomes-miR-148a derived from bone marrow mesenchymal stem cells (BMSCs) in AF. The AF cell and mice models were established firstly. QRT-PCR and Western blot analysis were applied to detect the expression of miR-148a, SPARC-associated modular calcium-binding protein 2 (SMOC2), Bcl-2, Bax, and caspase-3. BMSCs were separated from healthy mice and exosomes were obtained from BMSCs. BMSCs were transfected with mimics and inhibitor, and HL-1 cells were treated with mimics and pcDNA3.1. MTT assay were used to detect cell viability of cells. Flow cytometric analysis and TUNEL analysis were used for detecting cell apoptosis of cells. In our study, exosomes derived from BMSCs inhibited the development of AF, and miR-148a acted a vital role in this segment. SMOC2 was a target gene of miR-148a and promoted apoptosis of HL-1 cells. Additionally, miR-148a mimics decreased cellular apoptosis, eliminated SMOC2 expression, and elevated Bcl-2 expression in AF-treated cells. Collectively, miR-148a overexpressed in BMSC-exosomes restrained cardiomyocytes apoptosis by inhibiting SMOC2.

MiR-199-3p Suppressed Inflammatory Response by Targeting MECP2 to Alleviate TRX-Induced PHN in Mice

Varicella zoster virus–induced postherpetic neuralgia (PHN) can be alleviated by limited medications with serious side effects. This study aims to investigate the underlying molecular mechanism of miR-199-3p in mediating PHN in mice. 293T cells were transfected with miR-199-3p vectors (mimic/inhibitor). The target relationship between miR-199-3p and MECP2 was confirmed using luciferase reporter assay. PHN mouse model was established by TRX injection. Animal behaviors were evaluated using Hargreaves test and Von Frey test. Western blot was used for protein analysis, and quantitative reverse transcription polymerase chain reaction was performed for messenger RNA quantification. Serum levels of inflammatory mediators were determined using ELISA. Paw withdrawal latency (PWL) and mechanical withdrawal threshold (MWT) were decreased in resiniferatoxin-induced PHN mice. Downregulated miR-199-3p and upregulated MECP2 were found in PHN mice. Upregulated miR-199-3p increased PWL and MWT, but inhibited MECP2 in PHN mice. Besides, increased miR-199-3p suppressed proinflammatory indicators and activated anti-inflammatory mediators. It also found that MECP2 was the target of miR-199-3p. Further study showed miR-199-3p enhanced PWL and MWT, and supported inflammatory response via targeting MECP2. miR-199-3p regulated inflammation by targeting MECP2 to alleviate TRX-induced PHN in mice.