Epigenetic Modifications Associated to Neuroinflammation and Neuropathic Pain After Neural Trauma

The Role of PKM2 in Multiple Signaling Pathways Related to Neurological Diseases

Pyruvate kinase M2 (PKM2) is a key rate-limiting enzyme in glycolysis. It is well known that PKM2 plays a vital role in the proliferation of tumor cells. However, PKM2 can also exert its biological functions by mediating multiple signaling pathways in neurological diseases, such as Alzheimer's disease (AD), cognitive dysfunction, ischemic stroke, post-stroke depression, cerebral small-vessel disease, hypoxic-ischemic encephalopathy, traumatic brain injury, spinal cord injury, Parkinson's disease (PD), epilepsy, neuropathic pain, and autoimmune diseases. In these diseases, PKM2 can exert various biological functions, including regulation of glycolysis, inflammatory responses, apoptosis, proliferation of cells, oxidative stress, mitochondrial dysfunction, or pathological autoimmune responses. Moreover, the complexity of PKM2's biological characteristics determines the diversity of its biological functions. However, the role of PKM2 is not entirely the same in different diseases or cells, which is related to its oligomerization, subcellular localization, and post-translational modifications. This article will focus on the biological characteristics of PKM2, the regulation of PKM2 expression, and the biological role of PKM2 in neurological diseases. With this review, we hope to have a better understanding of the molecular mechanisms of PKM2, which may help researchers develop therapeutic strategies in clinic.

The Brain-Gut Axis, an Important Player in Alzheimer and Parkinson Disease: A Narrative Review

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are severe age-related disorders with complex and multifactorial causes. Recent research suggests a critical link between neurodegeneration and the gut microbiome, via the gut-brain communication pathway. This review examines the role of trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, in the development of AD and PD, and investigates its interaction with microRNAs (miRNAs) along this bidirectional pathway. TMAO, which is produced from dietary metabolites like choline and carnitine, has been linked to increased neuroinflammation, protein misfolding, and cognitive decline. In AD, elevated TMAO levels are associated with amyloid-beta and tau pathologies, blood-brain barrier disruption, and neuronal death. TMAO can cross the blood-brain barrier and promote the aggregation of amyloid and tau proteins. Similarly, TMAO affects alpha-synuclein conformation and aggregation, a hallmark of PD. TMAO also activates pro-inflammatory pathways such as NF-kB signaling, exacerbating neuroinflammation further. Moreover, TMAO modulates the expression of various miRNAs that are involved in neurodegenerative processes. Thus, the gut microbiome-miRNA-brain axis represents a newly discovered mechanistic link between gut dysbiosis and neurodegeneration. MiRNAs regulate the key pathways involved in neuroinflammation, oxidative stress, and neuronal death, contributing to disease progression. As a direct consequence, specific miRNA signatures may serve as potential biomarkers for the early detection and monitoring of AD and PD progression. This review aims to elucidate the complex interrelationships between the gut microbiota, trimethylamine-N-oxide (TMAO), microRNAs (miRNAs), and the central nervous system, and the implications of these connections in neurodegenerative diseases. In this context, an overview of the current neuroradiology techniques available for studying neuroinflammation and of the animal models used to investigate these intricate pathologies will also be provided. In summary, a bulk of evidence supports the concept that modulating the gut-brain communication pathway through dietary changes, the manipulation of the microbiome, and/or miRNA-based therapies may offer novel approaches for implementing the treatment of debilitating neurological disorders.

Communicating pain: emerging axonal signaling in peripheral neuropathic pain

Peripheral nerve damage often leads to the onset of neuropathic pain (NeuP). This condition afflicts millions of people, significantly burdening healthcare systems and putting strain on families' financial well-being. Here, we will focus on the role of peripheral sensory neurons, specifically the Dorsal Root Ganglia neurons (DRG neurons) in the development of NeuP. After axotomy, DRG neurons activate regenerative signals of axons-soma communication to promote a gene program that activates an axonal branching and elongation processes. The results of a neuronal morphological cytoskeleton change are not always associated with functional recovery. Moreover, any axonal miss-targeting may contribute to NeuP development. In this review, we will explore the epidemiology of NeuP and its molecular causes at the level of the peripheral nervous system and the target organs, with major focus on the neuronal cross-talk between intrinsic and extrinsic factors. Specifically, we will describe how failures in the neuronal regenerative program can exacerbate NeuP.

CBP Expression Contributes to Neuropathic Pain via CREB and MeCP2 Regulation in the Spared Nerve Injury Rat Model

Background and Objectives: This study aimed to investigate the relationship between neuropathic pain and CREB-binding protein (CBP) and methyl-CpG-binding protein 2 (MeCP2) expression levels in a rat model with spared nerve injury (SNI). Materials and Methods: Rat (male Sprague-Dawley white rats) models with surgical SNI (n = 6) were prepared, and naive rats (n = 5) were used as controls. The expression levels of CBP and MeCP2 in the spinal cord and dorsal root ganglion (DRG) were compared through immunohistochemistry at 7 and 14 days after surgery. The relationship between neuropathic pain and CBP/MeCP2 was also analyzed through intrathecal siRNA administration. Results: SNI induced a significant increase in the number of CBPs in L4 compared with contralateral DRG as well as with naive rats. The number of MeCP2 cells in the dorsal horn on the ipsilateral side decreased significantly compared with the contralateral dorsal horn and the control group. SNI induced a significant decrease in the number of MeCP2 neurons in the L4 ipsilateral DRG compared with the contralateral DRG and naive rats. The intrathecal injection of CBP siRNA significantly inhibited mechanical allodynia induced by SNI compared with non-targeting siRNA treatment. MeCP2 siRNA injection showed no significant effect on mechanical allodynia. Conclusions: The results suggest that CBP and MeCP2 may play an important role in the generation of neuropathic pain following peripheral nerve injury.

Research trends on acupuncture for neuropathic pain: A bibliometric analysis from 1979 to 2023

BACKGROUND

Acupuncture has drawn increasing attention as a complementary and alternative therapy for neuropathic pain (NP). The present study aimed to summarize the current status and research trends on acupuncture for NP over the past several decades.

METHODS

The publications on acupuncture for NP in the database of Web of Science Core Collection from 1979 to 2023 were searched. VOSviewer (1.6.15) and CiteSpace software (5.5.R2) were applied to identify active authors, journals, countries and institutions, co-cited references and hot keywords.

RESULTS

A total of 642 publications were finally included, and the quantitative trend of annual publications on acupuncture for NP have shown overall upward from 1979 to 2023. Peoples R China was the most productive and influential country, while Kyung Hee University from South Korea was both the first in publications and citations. Fang JQ ranked the first productive author and Han JS was the first 1 among the co-cited authors. The first productive journal was Evidence-based Complementary and Alternative Medicine, while the first co-cited journal was Pain. The high-frequency keywords were divided into 9 clusters, and the frontier topic focused on "Chronic pain".

CONCLUSION

This present study visually showed the research status and trends of acupuncture for NP from 1979 to 2023 on the basis of bibliometric analysis, which may in some way help researcher discovery and explore some new research directions and ideas in the future.

Epigenetic mechanism of miR-26b-5p-enriched MSCs-EVs attenuates spinal cord injury

Mesenchymal stem cells (MSCs) and extracellular vesicles (EVs) are promising therapies for the treatment of spinal cord injury (SCI). This study sought to explore the epigenetic mechanism of miR-26b-5p-enriched MSCs-EVs in SCI. MSCs and MSCs-EVs were isolated and characterized. The SCI rat model was established, followed by Basso-Beattie-Bresnahan scoring and H&E staining. In vitro cell models were established in PC12 cells with lipopolysaccharide (LPS) treatment, followed by cell viability evaluation using CCK-8 assay. The levels of miR-26b-5p, lysine demethylase 6A (KDM6A), NADPH oxidase 4 (NOX4), reactive oxygen species (ROS), and inflammatory factors (TNF-α/IL-1β/IL-6) in tissues and cells were detected. The levels of cy3-lablled miR-26b-5p in tissues and cells were observed by confocal microscopy. The binding of miR-26b-5p to KDM6A 3'UTR and the enrichments of KDM6A and H3K27me3 at the NOX4 promoter were analyzed. MSCs-EVs attenuated motor dysfunction, inflammation, and oxidative stress in SCI rats. MSCs-EVs delivered miR-26b-5p into PC12 cells to reduce LPS-induced inflammation and ROS production and enhance cell viability. miR-26b-5p inhibited KDM6A, and KDM6A reduced H3K27me3 at the NOX4 promoter to promote NOX4. Overexpression of KDM6A or NOX4 reversed the alleviative role of MSCs-EVs in SCI or LPS-induced cell injury. Overall, MSCs-EVs delivered miR-26b-5p into cells to target the KDM6A/NOX4 axis and facilitate the recovery from SCI.

Curcumin can improve spinal cord injury by inhibiting DNA methylation

Spinal cord injury (SCI) is a serious central nervous system disease. Traumatic SCI often causes persistent neurological deficits below the injury level. Epigenetic changes occur after SCI. Studies have shown DNA methylation to be a key player in nerve regeneration and remodeling, and in regulating some pathophysiological characteristics of SCI. Curcumin is a natural polyphenol from turmeric. It has anti-inflammatory, antioxidant, and neuroprotective effects, and can mitigate the cell and tissue damage caused by SCI. This report analyzed the specific functions of DNA methylation in central nervous system diseases, especially traumatic brain injury and SCI. DNA methylation can regulate the level of gene expressions in the central nervous system. Therefore, pharmacological interventions regulating DNA methylation may be promising for SCI.

Evaluation of epigenetic (HDAC, DNMT) and pain (Gad65, TGF) factors following photobiomodulation therapy in a neuropathic pain model

Photobiomodulation therapy (PBMT) is converted to the most common analgesic treatment before the whole mechanism is yet to be discovered. This study for the first time was designed to investigate alternations of epigenetic factors after pain and PBMT. The CCI model was chosen to induce pain. Pain evaluation tests including plantar, acetone, von Frey, and pinch were done weekly. Then spinal cord tissue was isolated for evaluating mRNA expression of DNMT3a, HDAC1, and NRSF using RT-qPCR method, and protein expression factors of HDAC2 and DNMT3a using western blotting. GAD65 and TGF-β proteins were assessed by the IHC method. PBMT increased the pain threshold up to the point where it roughly met the pain threshold of the control group. After three weeks of treatment, both PBMT protocols demonstrated a reduction in allodynia and hyperalgesia. While some molecules, such as TGF-β and Gad65, increased following PBMT, we observed no inhibition of NRSF, HDAC1, and DNMT3a expression despite implementing two different protocols.

Potential Therapeutic Effects of Short-Chain Fatty Acids on Chronic Pain

The intestinal homeostasis maintained by the gut microbiome and relevant metabolites is essential for health, and its disturbance leads to various intestinal or extraintestinal diseases. Recent studies suggest that gut microbiome-derived metabolites short-chain fatty acids (SCFAs) are involved in different neurological disorders (such as chronic pain). SCFAs are produced by bacterial fermentation of dietary fibers in the gut and contribute to multiple host processes, including gastrointestinal regulation, cardiovascular modulation, and neuroendocrine-immune homeostasis. Although SCFAs have been implicated in the modulation of chronic pain, the detailed mechanisms that underlie such roles of SCFAs remain to be further investigated. In this review, we summarize currently available research data regarding SCFAs as a potential therapeutic target for chronic pain treatment and discuss several possible mechanisms by which SCFAs modulate chronic pain.

Peripheral neuropathy associated with monomethyl auristatin E-based antibody-drug conjugates

Since the successful approval of gemtuzumab ozogamicin, antibody-drug conjugates (ADCs) have emerged as a pivotal category of targeted therapies for cancer. Among these ADCs, the use of monomethyl auristatin E (MMAE) as a payload is prevalent in the development of ADC drugs, which has significantly improved overall therapeutic efficacy against various malignancies. However, increasing clinical observations have raised concerns regarding the potential nervous system toxicity associated with MMAE-based ADCs. Specifically, a higher incidence of peripheral neuropathy has been reported in ADCs incorporating MMAE as payloads. Considering the increasing global use of MMAE-based ADCs, it is imperative to provide an inclusive overview of diagnostic and management strategies for this adverse event. In this review, we examine current information and what future research directions are required to better understand and manage this type of clinical challenge.

Perspectives on pain in Down syndrome

Down syndrome (DS) or trisomy 21 is a genetic condition often accompanied by chronic pain caused by congenital abnormalities and/or conditions, such as osteoarthritis, recurrent infections, and leukemia. Although DS patients are more susceptible to chronic pain as compared to the general population, the pain experience in these individuals may vary, attributed to the heterogenous structural and functional differences in the central nervous system, which might result in abnormal pain sensory information transduction, transmission, modulation, and perception. We tried to elaborate on some key questions and possible explanations in this review. Further clarification of the mechanisms underlying such abnormal conditions induced by the structural and functional differences is needed to help pain management in DS patients.

Neuroprotective effects of GSK-343 in an in vivo model of MPTP-induced nigrostriatal degeneration

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic nigrostriatal neurons, which causes disabling motor disorders. Scientific findings support the role of epigenetics mechanism in the development and progression of many neurodegenerative diseases, including PD. In this field, some studies highlighted an upregulation of Enhancer of zeste homolog 2 (EZH2) in the brains of PD patients, indicating the possible pathogenic role of this methyltransferase in PD. The aim of this study was to evaluate the neuroprotective effects of GSK-343, an EZH2 inhibitor, in an in vivo model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic degeneration. Specifically, nigrostriatal degeneration was induced by MPTP intraperitoneal injection. GSK-343 was administered intraperitoneally daily at doses of 1 mg/kg, 5 mg/kg and 10 mg/kg, mice were killed 7 days after MPTP injection. Our results demonstrated that GSK-343 treatment significantly improved behavioral deficits and reduced the alteration of PD hallmarks. Furthermore, GSK-343 administration significantly attenuated the neuroinflammatory state through the modulation of canonical and non-canonical NF-κB/IκBα pathway as well as the cytokines expression and glia activation, also reducing the apoptosis process. In conclusion, the obtained results provide further evidence that epigenetic mechanisms play a pathogenic role in PD demonstrating that the inhibition of EZH2, mediated by GSK-343, could be considered a valuable pharmacological strategy for PD.

Mesenchymal stem cell-derived exosomes: a possible therapeutic strategy for repairing heart injuries

Mesenchymal stem cells (MSCs) are one of the most potent therapeutic strategies for repairing cardiac injury. It has been shown in the latest studies that MSCs cannot survive in the heart for a long time. Consequently, the exosomes secreted by MSCs may dominate the repair of heart injury and promote the restoration of cardiac cells, vascular proliferation, immune regulation, etc. Based on the current research, the progress of the acting mechanism, application prospects and challenges of exosomes, including non-coding RNA, in repairing cardiac injuries are summarised in this article.

Autism Spectrum Disorder: A Neuro-Immunometabolic Hypothesis of the Developmental Origins

Fetal neuroinflammation and prenatal stress (PS) may contribute to lifelong neurological disabilities. Astrocytes and microglia, among the brain's non-neuronal "glia" cell populations, play a pivotal role in neurodevelopment and predisposition to and initiation of disease throughout lifespan. One of the most common neurodevelopmental disorders manifesting between 1-4 years of age is the autism spectrum disorder (ASD). A pathological glial-neuronal interplay is thought to increase the risk for clinical manifestation of ASD in at-risk children, but the mechanisms remain poorly understood, and integrative, multi-scale models are needed. We propose a model that integrates the data across the scales of physiological organization, from genome to phenotype, and provides a foundation to explain the disparate findings on the genomic level. We hypothesize that via gene-environment interactions, fetal neuroinflammation and PS may reprogram glial immunometabolic phenotypes that impact neurodevelopment and neurobehavior. Drawing on genomic data from the recently published series of ovine and rodent glial transcriptome analyses with fetuses exposed to neuroinflammation or PS, we conducted an analysis on the Simons Foundation Autism Research Initiative (SFARI) Gene database. We confirmed 21 gene hits. Using unsupervised statistical network analysis, we then identified six clusters of probable protein-protein interactions mapping onto the immunometabolic and stress response networks and epigenetic memory. These findings support our hypothesis. We discuss the implications for ASD etiology, early detection, and novel therapeutic approaches. We conclude with delineation of the next steps to verify our model on the individual gene level in an assumption-free manner. The proposed model is of interest for the multidisciplinary community of stakeholders engaged in ASD research, the development of novel pharmacological and non-pharmacological treatments, early prevention, and detection as well as for policy makers.

DNA Methylation in Alcohol Use Disorder

Excessive drinking damages the central nervous system of individuals and can even cause alcohol use disorder (AUD). AUD is regulated by both genetic and environmental factors. Genes determine susceptibility to alcohol, and the dysregulation of epigenome drives the abnormal transcription program and promotes the occurrence and development of AUD. DNA methylation is one of the earliest and most widely studied epigenetic mechanisms that can be inherited stably. In ontogeny, DNA methylation pattern is a dynamic process, showing differences and characteristics at different stages. DNA dysmethylation is prevalent in human cancer and alcohol-related psychiatric disorders, resulting in local hypermethylation and transcriptional silencing of related genes. Here, we summarize recent findings on the roles and regulatory mechanisms of DNA methylation, the development of methyltransferase inhibitors, methylation alteration during alcohol exposure at different stages of life, and possible therapeutic options for targeting methylation in human and animal studies.

REAC Antalgic Neuro Modulation in Chronic Post Herpetic Neuralgia

BACKGROUND

Chronic post-herpetic neuralgia (CPHN) is a symptomatic condition that afflicts adults and elderly individuals. The chronicity of this symptomatology can be conditioned by the epigenetic modifications induced by the virus on the processes of neurotransmission and sensitivity to pain. The aim of this study is to investigate whether manipulating endogenous bioelectrical activity (EBA), responsible for neurotransmission processes and contributing to the induction of epigenetic modifications, can alleviate pain symptoms.

METHODS

This manipulation was carried out with the antalgic neuromodulation (ANM) treatment of radioelectric asymmetric conveyer (REAC) technology. Pain assessment before and after treatment was performed using a numerical analog scale (NAS) and a simple descriptive scale (SDS).

RESULTS

The results of the analysis showed an over four-point decrease in NAS scale score and over one point decrease in SDS scale score, with a statistical significance for both tests of p < 0.005.

CONCLUSIONS

The results obtained in this study demonstrate how REAC ANM manipulation of EBA can lead to improvement in epigenetically conditioned symptoms such as CPHN. These results should prompt further research to expand knowledge and ensure optimized therapeutic outcomes.

EZH2 Methyltransferase Regulates Neuroinflammation and Neuropathic Pain

Recent studies by us and others have shown that enhancer of zeste homolog-2 (EZH2), a histone methyltransferase, in glial cells regulates the genesis of neuropathic pain by modulating the production of proinflammatory cytokines and chemokines. In this review, we summarize recent advances in this research area. EZH2 is a subunit of polycomb repressive complex 2 (PRC2), which primarily serves as a histone methyltransferase to catalyze methylation of histone 3 on lysine 27 (H3K27), ultimately resulting in transcriptional repression. Animals with neuropathic pain exhibit increased EZH2 activity and neuroinflammation of the injured nerve, spinal cord, and anterior cingulate cortex. Inhibition of EZH2 with DZNep or GSK-126 ameliorates neuroinflammation and neuropathic pain. EZH2 protein expression increases upon activation of Toll-like receptor 4 and calcitonin gene-related peptide receptors, downregulation of miR-124-3p and miR-378 microRNAs, or upregulation of Lncenc1 and MALAT1 long noncoding RNAs. Genes suppressed by EZH2 include suppressor of cytokine signaling 3 (SOCS3), nuclear factor (erythroid-derived 2)-like-2 factor (NrF2), miR-29b-3p, miR-146a-5p, and brain-specific angiogenesis inhibitor 1 (BAI1). Pro-inflammatory mediators facilitate neuronal activation along pain-signaling pathways by sensitizing nociceptors in the periphery, as well as enhancing excitatory synaptic activities and suppressing inhibitory synaptic activities in the CNS. These studies collectively reveal that EZH2 is implicated in signaling pathways known to be key players in the process of neuroinflammation and genesis of neuropathic pain. Therefore, targeting the EZH2 signaling pathway may open a new avenue to mitigate neuroinflammation and neuropathic pain.

Systematic identification of potential key microRNAs and circRNAs in the dorsal root ganglia of mice with sciatic nerve injury

Background

Neuropathic pain (NeP) is a pathological condition arising from a lesion or disease affecting the somatosensory system. Accumulating evidence has shown that circular RNAs (circRNAs) exert critical functions in neurodegenerative diseases by sponging microRNAs (miRNAs). However, the functions and regulatory mechanisms of circRNAs as competitive endogenous RNAs (ceRNAs) in NeP remain to be determined.

Methods

The sequencing dataset GSE96051 was obtained from the public Gene Expression Omnibus (GEO) database. First, we conducted a comparison of gene expression profiles in the L3/L4 dorsal root ganglion (DRG) of sciatic nerve transection (SNT) mice (n = 5) and uninjured mice (Control) (n = 4) to define the differentially expressed genes (DEGs). Then, critical hub genes were screened by exploring protein–protein interaction (PPI) networks with Cytoscape software, and the miRNAs bound to them were predicted and selected and then validated by qRT-PCR. Furthermore, key circRNAs were predicted and filtered, and the network of circRNA-miRNA-mRNA in NeP was constructed.

Results

A total of 421 DEGs were identified, including 332 upregulated genes and 89 downregulated genes. Ten hub genes, including IL6, Jun, Cd44, Timp1, and Csf1, were identified. Two miRNAs, mmu-miR-181a-5p and mmu-miR-223-3p, were preliminarily verified as key regulators of NeP development. In addition, circARHGAP5 and circLPHN3 were identified as key circRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that these differentially expressed mRNAs and targeting miRNAs were involved in signal transduction, positive regulation of receptor-mediated endocytosis and regulation of neuronal synaptic plasticity. These findings have useful implications for the exploration of new mechanisms and therapeutic targets for NeP.

Conclusion

These newly identified miRNAs and circRNAs in networks reveal potential diagnostic or therapeutic targets for NeP.

Design, Synthesis, and Biological Evaluation of a Potent Dual EZH2-BRD4 Inhibitor for the Treatment of Some Solid Tumors

Enhancer of zeste homolog 2 (EZH2) mediates the trimethylation of histone 3 lysine 27 (H3K27) to promote gene silencing. Inhibition of EZH2 is a viable strategy for cancer treatment; however, only a small subset of hematological malignancies are sensitive to small-molecule EZH2 inhibitors. EZH2 inhibitors cause H3K27 acetylation in most solid tumors, leading to drug resistance. Bromodomain-containing protein 4 (BRD4) inhibitors were reported to enhance the sensitivity of solid tumors to EZH2 inhibitors. Thus, we designed and evaluated a series of dual EZH2-BRD4 inhibitors. ZLD-2, the most promising compound, exhibited potent inhibitory activity against EZH2 and BRD4. Compared to the EZH2 inhibitor GSK126, ZLD-2 displayed potent antiproliferation activity against breast, lung, bladder, and pancreatic cancer cells. In vivo, ZLD-2 exhibited antitumor activity in a BxPC-3 mouse xenograft model, whereas GSK126 promoted tumor growth. Thus, ZLD-2 may be a lead compound for treating solid tumors.

Inflammation and histone modification in chronic pain

Increasing evidence suggests that epigenetic mechanisms have great potential in the field of pain. The changes and roles of epigenetics of the spinal cord and dorsal root ganglia in the chronic pain process may provide broad insights for future pain management. Pro-inflammatory cytokines and chemokines released by microglia and astrocytes, as well as blood-derived macrophages, play critical roles in inducing and maintaining chronic pain, while histone modifications may play an important role in inflammatory metabolism. This review provides an overview of neuroinflammation and chronic pain, and we systematically discuss the regulation of neuroinflammation and histone modifications in the context of chronic pain. Specifically, we analyzed the role of epigenetics in alleviating or exacerbating chronic pain by modulating microglia, astrocytes, and the proinflammatory mediators they release. This review aimed to contribute to the discovery of new therapeutic targets for chronic pain.

Global research trends on epigenetics and neuropathic pain: A bibliometric analysis

Objective

Neuropathic pain (NP) is a common disease that manifests with pathological changes in the somatosensory system. In recent years, the interactions of NP with the epigenetic mechanism have been increasingly elucidated. However, only a few studies have used bibliometric tools to systematically analyze knowledge in this field. The objective of this study is to visually analyze the trends, hotspots, and frontiers in epigenetics and NP research by using a bibliometric method.

Methods

Studies related to epigenetics and NP were searched from the Science Citation Index-Expanded of the Web of Science Core Collection database. Search time is from inception to November 30, 2022. No restrictions were placed on language. Only articles and reviews were included as document types. Data on institutions, countries, authors, journal distribution, and keywords were imported into CiteSpace software for visual analysis.

Results

A total of 867 publications met the inclusion criteria, which spanned the period from 2000 to 2022. Over the years, the number of publications and the frequency of citations exhibited a clear upward trend in general, reaching a peak in 2021. The major contributing countries in terms of the number of publications were China, the United States, and Japan. The top three institutions were Rutgers State University, Xuzhou Medical University, and Nanjing Medical University. Molecular Pain, Pain, and Journal of Neuroinflammation contributed significantly to the volume of issues. Among the top 10 authors in terms of the number of publications, Tao Yuan-Xiang contributed 30 entries, followed by Zhang Yi with 24 and Wu Shao-Gen with 20. On the basis of the burst and clusters of keywords, "DNA methylation," "Circular RNA," "acetylation," "long non-coding RNA," and "microglia" are global hotspots in the field.

Conclusion

The bibliometric analysis indicates that the number of publications related to epigenetics and NP is exhibiting a rapid increase. Keyword analysis shows that "DNA methylation," "Circular RNA," "acetylation," "long non-coding RNA" and "microglia" are the most interesting terms for researchers in the field. More rigorous clinical trials and additional studies that explore relevant mechanisms are required in the future.

Overview of Anti-Inflammatory and Anti-Nociceptive Effects of Polyphenols to Halt Osteoarthritis: From Preclinical Studies to New Clinical Insights

Knee osteoarthritis (OA) is one of the most multifactorial joint disorders in adults. It is characterized by degenerative and inflammatory processes that are responsible for joint destruction, pain and stiffness. Despite therapeutic advances, the search for alternative strategies to target inflammation and pain is still very challenging. In this regard, there is a growing body of evidence for the role of several bioactive dietary molecules (BDMs) in targeting inflammation and pain, with promising clinical results. BDMs may be valuable non-pharmaceutical solutions to treat and prevent the evolution of early OA to more severe phenotypes, overcoming the side effects of anti-inflammatory drugs. Among BDMs, polyphenols (PPs) are widely studied due to their abundance in several plants, together with their benefits in halting inflammation and pain. Despite their biological relevance, there are still many questionable aspects (biosafety, bioavailability, etc.) that hinder their clinical application. This review highlights the mechanisms of action and biological targets modulated by PPs, summarizes the data on their anti-inflammatory and anti-nociceptive effects in different preclinical in vitro and in vivo models of OA and underlines the gaps in the knowledge. Furthermore, this work reports the preliminary promising results of clinical studies on OA patients treated with PPs and discusses new perspectives to accelerate the translation of PPs treatment into the clinics.

Increased ten-eleven translocation methylcytosine dioxygenase one in dorsal root ganglion contributes to inflammatory pain in CFA rats

DNA hydroxylation catalyzed by Tet dioxygenases occurs abundantly in neurons in mammals. However, effects of ten-eleven translocation methylcytosine dioxygenase 1 (TET1) expression and hydroxymethylation status on neuron injury remain unclear. This study was designed to explore the effects of TET1 and TET2 expression in the inflammatory pain of rats induced by complete Freund's adjuvant (CFA). Mechanical paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL) were detected to assess pain behavior. The expression of TET1 and TET2 were measured in the dorsal root ganglion (DRG) with western blotting analysis. Immunofluorescence staining is employed to detect the expression and co-location of TRPV1 with TET1. Intrathecal administration of Bobcat339 was used to inhibit TET1 function in dorsal root ganglion. The paw withdrawal threshold and thermal withdrawal latency of rats were significantly reduced after CFA Injection. Western blot results showed that the expression of TET1 was significantly increased at 3 days after CFA injection, but TET2 had no statistical difference. Immunofluorescence results showed that TET1 was co-localized with TRPV1. Intrathecal administration of Bobcat339 improved mechanical and thermal pain threshold in CFA rats. Our findings highlight the role of TET1 in chronic inflammatory pain model. The expression of TET1 was increased in CFA rats, and suppression of TET1 will ameliorate inflammatory pain.

Genome-wide DNA methylation study identifies significant epigenomic changes associated with internalized stigma in adults with non-specific chronic low back pain

Non-specific chronic low back pain (cLBP) represents a common musculoskeletal condition with no identifiable cause. It cannot be diagnosed with conventional neuroimaging techniques such as computerized tomography (CT). The diagnostic uncertainty that characterizes non-specific cLBP can lead to stigmatizing responses from others that can become internalized Among individuals with non-specific cLBP, internalized stigma is associated with greater pain intensity and disability. Yet, no study has examined the biological mechanism linking high internalized stigma to worse outcomes in individuals with non-specific cLBP. We aimed to identify differentially methylated loci (DML), enrichment pathways, and associated network interactions among individuals with non-specific cLBP experiencing low vs. high internalized stigma. We examined DNA methylation in whole blood samples from 48 adults, ages 19-85, using reduced representation bisulfite sequencing (RRBS). After controlling for age, sex, race, and multiple testing, differentially methylated loci (DML) differed in adults with low vs. high internalized stigma by at least 10% and q < 0.01 in 3,665 CpG sites: 2,280 hypomethylated and 1,385 hypermethylated. Gene ontology (GO) analyses of the annotated genes from these sites revealed significant enrichment of 274 biological processes, 29 cellular components, and 24 molecular functions (adjusted p < 0.05). The top enriched molecular functions regulate protein binding and DNA binding of transcription factor activity. Pathway analyses indicated that many functional genomic pathways, including Hippo Signaling, Melanogenesis, and Pathways in Cancer, were enriched with differentially methylated genes. Also, there was a significant interaction between relevance pathways such as P53, mTOR, PI3K-Akt, and Wnt signaling pathways. These pathways have previously been associated with neuroinflammation, neurodegeneration, and stress-related conditions. Thus, findings point to possible stress-induced DNAm changes as the link between high levels of internalized stigma and worse outcomes in adults with non-specific cLBP.

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.

Paeonol inhibits chronic constriction injury-induced astrocytic activation and neuroinflammation in rats via the HDAC/miR-15a pathway

Neuropathic pain affects millions of people in the worldwide, but the major therapeutics perform limited effectiveness. Paeonol (PAE) is widely distributed in Paeonis albiflora, and has manifested anti-inflammatory and antioxidative effects in multiple diseases. The present study aims to elucidate the effect of Paeonol (PAE) on neuropathic pain (NP) and the potential targets. Chronic constriction injury model was established to mimic NP in vivo in rats. The expression of GFAP, HDAC2, AHDAC3, Ac-H3K9, Histone-H3, Ac-H4K12, Histone-H4, TNF-α, IL-1β, and IL-6 was assessed by real-time polymerase chain reaction, western blot, and/or enzyme-linked immunosorbent assay kits. Ultimately, results indicated that intervention of PAE significantly blocked neuroinflammation and astrocytic activation via blocking HDAC/miR-15a signaling in CCI rats. These data revealed PAE is a novel therapeutic target for the treatment of neuropathic pain.

Cellular and Molecular Machinery of Neuropathic Pain: an Emerging Insight

Purpose of Review

Neuropathic pain (NP) has been ubiquitously characterized by lesion and its linked somatosensory system either the central nervous system (CNS) or peripheral nervous system (PNS) This PNS episode is the most prevalent site of NP origin and is found to be associated with afferent nerve fibers carrying pain signals from injured/trauma site to the CNS including the brain. Several kinds of pharmacotherapeutic drugs shuch as analgesics, anti-convulsants, and anti-depressants are being employed for the its possible interventions. The NP has been a great interest to follow different pathophysiological mechanisms which are often considered to correlate with the metabolic pathways and its mediated disease. There is paucity of knowledge to make such mechanism via NP.

Recent Finding

Most notably, recent pandemic outbreak of COVID-19 has also been reported in chronic pain mediated diabetes, inflammatory disorders, and cancers. There is an increasing incidence of NP and its complex mechanism has now led to identify the possible investigations of responsible genes and proteins via bioinformatics tools. The analysis might be more instrumental as collecting the genes from pain genetic database, analyzing the variants through differential gene expression (DEG) and constructing the protein–protein interaction (PPI) networks and thereby determining their upregulating and downregulating pathways.

Summary

This review sheds a bright light towards several mechanisms at both cellular and molecular level, correlation of NP-mediated disease mechanism and possible cell surface biomarkers (receptors), and identified genes could be more promising for their pharmacological targets.

Intermittent Fasting: Potential Utility in the Treatment of Chronic Pain across the Clinical Spectrum

Dietary behavior can have a consequential and wide-ranging influence on human health. Intermittent fasting, which involves intermittent restriction in energy intake, has been shown to have beneficial cellular, physiological, and system-wide effects in animal and human studies. Despite the potential utility in preventing, slowing, and reversing disease processes, the clinical application of intermittent fasting remains limited. The health benefits associated with the simple implementation of a 12 to 16 h fast suggest a promising role in the treatment of chronic pain. A literature review was completed to characterize the physiologic benefits of intermittent fasting and to relate the evidence to the mechanisms underlying chronic pain. Research on different fasting regimens is outlined and an overview of research demonstrating the benefits of intermittent fasting across diverse health conditions is provided. Data on the physiologic effects of intermittent fasting are summarized. The physiology of different pain states is reviewed and the possible implications for intermittent fasting in the treatment of chronic pain through non-invasive management, prehabilitation, and rehabilitation following injury and invasive procedures are presented. Evidence indicates the potential utility of intermittent fasting in the comprehensive management of chronic pain and warrants further investigation.

Epigenetic Connection of the Calcitonin Gene-Related Peptide and Its Potential in Migraine

The calcitonin gene-related peptide (CGRP) is implicated in the pathogenesis of several pain-related syndromes, including migraine. Targeting CGRP and its receptor by their antagonists and antibodies was a breakthrough in migraine therapy, but the need to improve efficacy and limit the side effects of these drugs justify further studies on the regulation of CGRP in migraine. The expression of the CGRP encoding gene, CALCA, is modulated by epigenetic modifications, including the DNA methylation, histone modification, and effects of micro RNAs (miRNAs), circular RNAs, and long-coding RNAs (lncRNAs). On the other hand, CGRP can change the epigenetic profile of neuronal and glial cells. The promoter of the CALCA gene has two CpG islands that may be specifically methylated in migraine patients. DNA methylation and lncRNAs were shown to play a role in the cell-specific alternative splicing of the CALCA primary transcript. CGRP may be involved in changes in neural cytoarchitecture that are controlled by histone deacetylase 6 (HDAC6) and can be related to migraine. Inhibition of HDAC6 results in reduced cortical-spreading depression and a blockade of the CGRP receptor. CGRP levels are associated with the expression of several miRNAs in plasma, making them useful peripheral markers of migraine. The fundamental role of CGRP in inflammatory pain transmission may be epigenetically regulated. In conclusion, epigenetic connections of CGRP should be further explored for efficient and safe antimigraine therapy.

Functional and transcriptional profiling of microglial activation during the chronic phase of TBI identifies an age-related driver of poor outcome in old mice

Elderly patients with traumatic brain injury (TBI) have greater mortality and poorer outcomes than younger individuals. The extent to which old age alters long-term recovery and chronic microglial activation after TBI is unknown, and evidence for therapeutic efficacy in aged mice is sorely lacking. The present study sought to identify potential inflammatory mechanisms underlying age-related outcomes late after TBI. Controlled cortical impact was used to induce moderate TBI in young and old male C57BL/6 mice. At 12 weeks post-injury, aged mice exhibited higher mortality, poorer functional outcomes, larger lesion volumes, and increased microglial activation. Transcriptomic analysis identified age- and TBI-specific gene changes consistent with a disease-associated microglial signature in the chronically injured brain, including those involved with complement, phagocytosis, and autophagy pathways. Dysregulation of phagocytic and autophagic function in microglia was accompanied by increased neuroinflammation in old mice. As proof-of-principle that these pathways have functional importance, we administered an autophagic enhancer, trehalose, in drinking water continuously for 8 weeks after TBI. Old mice treated with trehalose showed enhanced functional recovery and reduced microglial activation late after TBI compared to the sucrose control group. Our data indicate that microglia undergo chronic changes in autophagic regulation with both normal aging and TBI that are associated with poorer functional outcome. Enhancing autophagy may therefore be a promising clinical therapeutic strategy for TBI, especially in older patients.

Protein Tyrosine Phosphatase Receptor Type D Regulates Neuropathic Pain After Nerve Injury via the STING-IFN-I Pathway

Neuropathic pain is usually caused by injury or dysfunction of the somatosensory system, and medicine is a common way of treatment. Currently, there are still no satisfactory drugs, like opioids and lidocaine, which carry a high risk of addiction. Protein tyrosine phosphatase receptor type D (PTPRD) is a known therapeutic target in addiction pathways and small molecule inhibitors targeting it, such as 7-butoxy illudalic acid analog (7-BIA), have recently been developed to tackle addition. PTPRD is also upregulated in the dorsal root ganglion (DRG) in a rat model of neuropathic pain, but is not yet clear whether PTPRD contributes to the development of neuropathic pain. Here, we established a chronic constriction injury (CCI) and evaluated PTPRD expression and its association with neuropathic pain. PTPRD expression was found to gradually increase after CCI in DRGs, and its expression was concomitant with the progressive development of hypersensitivity as assessed by both mechanical and thermal stimuli. Both PTPRD knockdown and administration of PTPRD inhibitor 7-BIA alleviated CCI-induced neuropathic pain while upregulating STING and IFN-α in the DRG. Treatment with H-151, a STING inhibitor, abolished the analgesic effects of PTPRD knockdown. Taken together, our study suggests that increased levels of PTPRD in the DRG following CCI are involved in the development of neuropathic pain via the STING-IFN-I pathway. 7-BIA, a small molecule inhibitor of PTPRD with anti-addiction effects, may represent a novel and safe therapeutic strategy for the clinical management of neuropathic pain without the risk of addiction.

Modulation of Neuropathic Pain by Glial Regulation in the Insular Cortex of Rats

The insular cortex (IC) is known to process pain information. However, analgesic effects of glial inhibition in the IC have not yet been explored. The aim of this study was to investigate pain alleviation effects after neuroglia inhibition in the IC during the early or late phase of pain development. The effects of glial inhibitors in early or late phase inhibition in neuropathic pain were characterized in astrocytes and microglia expressions in the IC of an animal model of neuropathic pain. Changes in withdrawal responses during different stages of inhibition were compared, and morphological changes in glial cells with purinergic receptor expressions were analyzed. Inhibition of glial cells had an analgesic effect that persisted even after drug withdrawal. Both GFAP and CD11b/c expressions were decreased after injection of glial inhibitors. Morphological alterations of astrocytes and microglia were observed with expression changes of purinergic receptors. These findings indicate that inhibition of neuroglia activity in the IC alleviates chronic pain, and that purinergic receptors in glial cells are closely related to chronic pain development.

When left does not seem right: epigenetic and bioelectric differences between left- and right-sided breast cancer

Background

During embryogenesis lateral symmetry is broken, giving rise to Left/Right (L/R) breast tissues with distinct identity. L/R-sided breast tumors exhibit consistently-biased incidence, gene expression, and DNA methylation. We postulate that a differential L/R tumor-microenvironment crosstalk generates different tumorigenesis mechanisms.

Methods

We performed in-silico analyses on breast tumors of public datasets, developed xenografted tumors, and conditioned MDA-MB-231 cells with L/R mammary extracts.

Results

We found L/R differential DNA methylation involved in embryogenic and neuron-like functions. Focusing on ion-channels, we discovered significant L/R epigenetic and bioelectric differences. Specifically, L-sided cells presented increased methylation of hyperpolarizing ion channel genes and increased Ca²⁺ concentration and depolarized membrane potential, compared to R-ones. Functional consequences were associated with increased proliferation in left tumors, assessed by KI67 expression and mitotic count.

Conclusions

Our findings reveal considerable L/R asymmetry in cancer processes, and suggest specific L/R epigenetic and bioelectric differences as future targets for cancer therapeutic approaches in the breast and many other paired organs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00440-5.

Genome-Wide Epigenomic Analyses in Patients With Nociceptive and Neuropathic Chronic Pain Subtypes Reveals Alterations in Methylation of Genes Involved in the Neuro-Musculoskeletal System

Nociceptive pain involves the activation of nociceptors without damage to the nervous system, whereas neuropathic pain is related to an alteration in the central or peripheral nervous system. Chronic pain itself and the transition from acute to chronic pain may be epigenetically controlled. In this cross-sectional study, a genome-wide DNA methylation analysis was performed using the blood DNA reduced representation bisulfite sequencing (RRBS) technique. Three prospective cohorts including 20 healthy controls (CTL), 18 patients with chronic nociceptive pain (NOCI), and 19 patients with chronic neuropathic pain (NEURO) were compared at both the single CpG and differentially methylated region (DMR) levels. Genes with DMRs were seen in the NOCI and NEURO groups belonged to the neuro-musculoskeletal system and differed between NOCI and NEURO patients. Our results demonstrate that the epigenetic disturbances accompanying nociceptive pain are very different from those accompanying neuropathic pain. In the former, among others, the epigenetic disturbance observed would affect the function of the opioid analgesic system, whereas in the latter it would affect that of the GABAergic reward system. This study presents biological findings that help to characterize NOCI- and NEURO-affected pathways and opens the possibility of developing epigenetic diagnostic assays. PERSPECTIVE: Our results help to explain the various biological pathways modifications underlying the different clinical manifestations of nociceptive and neuropathic pains. Furthermore, the new targets identified in our study might help to discover more specific treatments for nociceptive or neuropathic pains.

Novel Histone Modifications in Microglia Derived from a Mouse Model of Chronic Pain

As the resident immune cells in the central nervous system, microglia play an important role in the maintenance of its homeostasis. Dysregulation of microglia has been associated with the development and maintenance of chronic pain. However, the relevant molecular pathways remain poorly defined. In this study, we used a mass spectrometry-based proteomic approach to screen potential changes of histone protein modifications in microglia isolated from the brain of control and cisplatin-induced neuropathic pain adult C57BL/6J male mice. We identified several novel microglial histone modifications associated with pain including statistically significantly decreased histone H3.1 lysine 27 mono-methylation (H3.1K27me1, 54.8% of control) and lysine 56 tri-methylation (7.5% of control), as well as a trend suggesting increased histone 3 tyrosine 41 nitration. We further investigated the functional role of H3.1K27me1 and found that treatment of cultured microglial cells for 4 consecutive days with 1-10 μM of NCDM-64, a potent and selective inhibitor of lysine demethylase 7A, an enzyme responsible for the demethylation of H3K27me1, dose-dependently elevated its levels with a greater than a 2-fold increase observed at 10 μM compared to vehicle-treated control cells. Moreover, pre-treatment of mice with NCDM-64 (10 or 25 mg/kg/day, i.p.) prior to cisplatin treatment prevented the development of neuropathic pain in mice. The identification of specific chromatin marks in microglia associated with chronic pain may yield critical insight into the contribution of microglia to the development and maintenance of pain, and opens new avenues for the development of novel non-opioid therapeutics for the effective management of chronic pain. This article is protected by copyright. All rights reserved.

Mice lacking perforin have improved regeneration of the injured femoral nerve

The role that the immune system plays after injury of the peripheral nervous system is still not completely understood. Perforin, a natural killer cell- and T-lymphocyte-derived enzyme that mediates cytotoxicity, plays important roles in autoimmune diseases, infections and central nervous system trauma, such as spinal cord injury. To dissect the roles of this single component of the immune response to injury, we tested regeneration after femoral nerve injury in perforin-deficient (Pfp^–/–) and wild-type control mice. Single frame motion analysis showed better motor recovery in Pfp^–/– mice compared with control mice at 4 and 8 weeks after injury. Retrograde tracing of the motoneuron axons regrown into the motor nerve branch demonstrated more correctly projecting motoneurons in the spinal cord of Pfp^–/– mice compared with wild-types. Myelination of regrown axons measured by g-ratio was more extensive in Pfp^–/– than in wild-type mice in the motor branch of the femoral nerve. Pfp^–/– mice displayed more cholinergic synaptic terminals around cell bodies of spinal motoneurons after injury than the injured wild-types. We histologically analyzed lymphocyte infiltration 10 days after surgery and found that in Pfp^–/– mice the number of lymphocytes in the regenerating nerves was lower than in wild-types, suggesting a closed blood-nerve barrier in Pfp^–/– mice. We conclude that perforin restricts motor recovery after femoral nerve injury owing to decreased survival of motoneurons and reduced myelination.

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.

Intrathecal IGF2 siRNA injection provides long-lasting anti-allodynic effect in a spared nerve injury rat model of neuropathic pain

Previous studies have shown an increase of insulin-like growth factor-2 (IGF2) in animal models of neuropathic pain. We aimed to examine the hypothesis that reducing the expression of IGF2 using intrathecal IGF2 small-interfering RNA (siRNA) would attenuate the development of neuropathic pain in rats after spared nerve injury (SNI). Male Wistar rats were divided into three groups: sham-operated group, in which surgery was performed to cut the muscles without injuring the nerves; SNI group, in which SNI surgery was performed to sever the nerves; and SNI + siRNA IGF2 group, in which SNI surgery was performed, and IGF2-siRNA was administered intrathecally 1 day after SNI. The rats were assessed for mechanical allodynia and cold allodynia 1 day before surgery (baseline), and at 2, 4, 6, 8, and 10 days after siRNA treatment. The rat spinal cord was collected for quantitative polymerase chain reaction and western blot analysis. Compared with the SNI group, rats that received IGF2 siRNA showed a significantly increased SNI-induced paw-withdrawal threshold to metal filament stimulation from Day 4 to Day 10 after SNI surgery. IGF2 siRNA significantly decreased the response duration from the acetone test from Day 2 to Day 10 following SNI surgery. SNI increased IGF2 mRNA expression on Day 2 and increased IGF2 protein expression on Day 8 and Day 10 in the spinal cord of the SNI rats. However, the above-mentioned effects of IGF2 mRNA and protein expression were significantly inhibited in the SNI + IGF2 siRNA group. We demonstrated that intrathecal administration of IGF2 siRNA provided significant inhibition of SNI-induced neuropathic pain via inhibition of IGF2 expression in the spinal cord. The analgesic effect lasted for 10 days. Further exploration of intrathecal IGF2 siRNA administration as a potential therapeutic strategy for neuropathic pain is warranted.

Epigenetic modifications in neuropathic pain

Neuropathic pain (NP) is a common symptom in many diseases of the somatosensory nervous system, which severely affects the patient’s quality of life. Epigenetics are heritable alterations in gene expression that do not cause permanent changes in the DNA sequence. Epigenetic modifications can affect gene expression and function and can also mediate crosstalk between genes and the environment. Increasing evidence shows that epigenetic modifications, including DNA methylation, histone modification, non-coding RNA, and RNA modification, are involved in the development and maintenance of NP. In this review, we focus on the current knowledge of epigenetic modifications in the development and maintenance of NP. Then, we illustrate different facets of epigenetic modifications that regulate gene expression and their crosstalk. Finally, we discuss the burgeoning evidence supporting the potential of emerging epigenetic therapies, which has been valuable in understanding mechanisms and offers novel and potent targets for NP therapy.

Elevated Serum Neuropeptide FF Levels Are Associated with Cognitive Decline in Patients with Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) has high incidence globally and is frequently accompanied by subsequent cognitive decline. Accurate early risk-categorization of SCI patients for cognitive decline using biomarkers can enable the timely application of appropriate neuroprotective measures and the development of new agents for the management of SCI-associated cognitive decline. Neuropeptide FF is an endogenous neuropeptide with a multitude of functions and is associated with neuroinflammatory processes. This prospective study investigated the predictive value of serum neuropeptide FF levels measured after acute SCI for subsequent cognitive decline.

METHODS

88 patients presenting with acute SCI without preexisting neurological injury, brain trauma, or severe systemic illness and 60 healthy controls were recruited. Serum neuropeptide FF levels, clinical, and routine laboratory variables including low-density lipoprotein, high-density lipoprotein, fasting blood glucose, total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH) levels collected from all subjects were assessed. Montreal cognitive assessment (MoCA) was performed 3 months after enrollment. SCI patients were grouped according to quartile of serum neuropeptide FF level and MoCA scores were compared using ANOVA. Additionally, multivariate linear regression with clinical and laboratory variables was performed to predict MoCA scores.

RESULTS

SCI patients displayed significantly higher baseline serum neuropeptide FF levels than healthy controls (38.5 ± 4.1 versus 23.4 ± 2.0 pg/ml, p < 0.001∗∗). SCI patients in higher quartiles of baseline serum neuropeptide FF displayed significantly lower MoCA scores at 3 months. Linear regression analysis indicated serum neuropeptide FF levels as a significant independent predictor of worse MoCA scores after SCI (r = 0.331, p = 0.034∗).

CONCLUSION

Early serum neuropeptide FF levels significantly and independently predicted cognitive decline after acute SCI among patients without preexisting neurological disorders.

Propofol Alleviates Neuropathic Pain Induced by Chronic Contractile Injury by Regulating the Spinal glun2b-p38mapkepac1 Pathway

BACKGROUND

Propofol acts as an intravenous anesthetic cure which is widely used as a therapy for the craniocerebral injury that comprised surgical anesthesia as well as the sedation done in the intensive care units. Propofol is one of the most commonly used and efficient anesthetics where the painful effects are followed by an injection of propofol. In many cases, patients experience pain followed by anxiety, boredom, fear, and even myocardial ischemia.

OBJECTIVE

This study was performed to investigate the underlying mechanism of propofol and its effect on regulating spinal glun2b-p38mapkepac1 pathways in chronic contractile injury. Material and Methods. Contractile injury was performed by ligation around the nerve of the thigh region postanesthesia. Rats were divided into three groups to analyze the changes like mechanical allodynia by the paw withdrawal threshold and histopathological analysis for assessing cellular degradation. L4-L6 from the spinal dorsal horns were isolated and harvested for studying protein expression, by the method of western blotting and immunofluorescence analysis.

RESULTS

The pain caused due to mechanical allodynia in the paw region was highest at 1 hour postinduction and lasted for three days postinjury. Pain was significantly less in the group receiving propofol when compared with the isoflurane group for the first two hours of injury. In the propofol group, EPAC1, GluN2B, and p38 MAP K were significantly lower.

CONCLUSION

In the rat model of induced chronic contractile injury, postsurgery there was a suppression of the GluN2B-p38MAPK/EPAC1 signaling pathway in the propofol group. As the p38MAPK/EPAC pathway has a significant role in the postoperative hyperalgesia, thus our experiment suggests that propofol has analgesic effects.

Interplay between Prokineticins and Histone Demethylase KDM6A in a Murine Model of Bortezomib-Induced Neuropathy

Chemotherapy-induced neuropathy (CIN) is a major adverse effect associated with many chemotherapeutics, including bortezomib (BTZ). Several mechanisms are involved in CIN, and recently a role has been proposed for prokineticins (PKs), a chemokine family that induces proinflammatory/pro-algogen mediator release and drives the epigenetic control of genes involved in cellular differentiation. The present study evaluated the relationships between epigenetic mechanisms and PKs in a mice model of BTZ-induced painful neuropathy. To this end, spinal cord alterations of histone demethylase KDM6A, nuclear receptors PPARα/PPARγ, PK2, and pro-inflammatory cytokines IL-6 and IL-1β were assessed in neuropathic mice treated with the PK receptors (PKRs) antagonist PC1. BTZ treatment promoted a precocious upregulation of KDM6A, PPARs, and IL-6, and a delayed increase of PK2 and IL-1β. PC1 counteracted allodynia and prevented the increase of PK2 and of IL-1β in BTZ neuropathic mice. The blockade of PKRs signaling also opposed to KDM6A increase and induced an upregulation of PPAR gene transcription. These data showed the involvement of epigenetic modulatory enzymes in spinal tissue phenomena associated with BTZ painful neuropathy and underline a role of PKs in sustaining the increase of proinflammatory cytokines and in exerting an inhibitory control on the expression of PPARs through the regulation of KDM6A gene expression in the spinal cord.

KDM6B epigenetically regulated-interleukin-6 expression in the dorsal root ganglia and spinal dorsal horn contributes to the development and maintenance of neuropathic pain following peripheral nerve injury in male rats

The lysine specific demethylase 6B (KDM6B) has been implicated as a coregulator in the expression of proinflammatory mediators, and in the pathogenesis of inflammatory and arthritic pain. However, the role of KDM6B in neuropathic pain has yet to be studied. In the current study, the neuropathic pain was determined by assessing the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) following lumbar 5 spinal nerve ligation (SNL) in male rats. Immunohistochemistry, Western blotting, qRT-PCR, and chromatin immunoprecipitation (ChIP)-PCR assays were performed to investigate the underlying mechanisms. Our results showed that SNL led to a significant increase in KDM6B mRNA and protein in the ipsilateral L4/5 dorsal root ganglia (DRG) and spinal dorsal horn; and this increase correlated a markedly reduction in the level of H3K27me3 methylation in the same tissue. Double immunofluorescence staining revealed that the KDM6B expressed in myelinated A- and unmyelinated C-fibers in the DRG; and located in neuronal cells, astrocytes, and microglia in the dorsal horn. Behavioral data showed that SNL-induced mechanical allodynia and thermal hyperalgesia were impaired by the treatment of prior to i.t. injection of GSK-J4, a specific inhibitor of KDM6B, or KDM6B siRNA. Both microinjection of AAV2-EGFP-KDM6B shRNA in the lumbar 5 dorsal horn and sciatic nerve, separately, alleviated the neuropathic pain following SNL. The established neuropathic pain was also partially attenuated by repeat i.t. injections of GSK-J4 or KDM6B siRNA, started on day 7 after SNL. SNL also resulted in a remarkable increased expression of interleukin-6 (IL-6) in the DRG and dorsal horn. But this increase was dramatically inhibited by i.t. injection of GSK-J4 and KDM6B siRNA; and suppressed by prior to microinjection of AAV2-EGFP-KDM6B shRNA in the dorsal horn and sciatic nerve. Results of ChIP-PCR assay showed that SNL-induced enhanced binding of STAT3 with IL-6 promoter was inhibited by prior to i.t. injection of GSK-J4. Meanwhile, the level of H3K27me3 methylation was also decreased by the treatment. Together, our results indicate that SNL-induced upregulation of KDM6B via demethylating H3K27me3 facilitates the binding of STAT3 with IL-6 promoter, and subsequently mediated-increase in the expression of IL-6 in the DRG and dorsal horn contributes to the development and maintenance of neuropathic pain. Targeting KDM6B might a promising therapeutic strategy to treatment of chronic pain.

Dual BET/HDAC inhibition to relieve neuropathic pain: Recent advances, perspectives, and future opportunities

Despite the intense research on developing new therapies for neuropathic pain states, available treatments have limited efficacy and unfavorable safety profiles. Epigenetic alterations have a great influence on the development of cancer and neurological diseases, as well as neuropathic pain. Histone acetylation has prevailed as one of the well investigated epigenetic modifications in these diseases. Altered spinal activity of histone deacetylase (HDAC) and Bromo and Extra terminal domain (BET) have been described in neuropathic pain models and restoration of these aberrant epigenetic modifications showed pain-relieving activity. Over the last decades HDACs and BETs have been the focus of drug discovery studies, leading to the development of numerous small-molecule inhibitors. Clinical trials to evaluate their anticancer activity showed good efficacy but raised toxicity concerns that limited translation to the clinic. To maximize activity and minimize toxicity, these compounds can be applied in combination of sub-maximal doses to produce additive or synergistic interactions (combination therapy). Recently, of particular interest, dual BET/HDAC inhibitors (multi-target drugs) have been developed to assure simultaneous modulation of BET and HDAC activity by a single molecule. This review will summarize the most recent advances with these strategies, describing advantages and limitations of single drug treatment vs combination regimens. This review will also provide a focus on dual BET/HDAC drug discovery investigations as future therapeutic opportunity for human therapy of neuropathic pain.

Calcitonin gene-related peptide induces the histone H3 lysine 9 acetylation in astrocytes associated with neuroinflammation in rats with neuropathic pain

Aims

Calcitonin gene‐related peptide (CGRP) as a regulator of astrocyte activation may facilitate spinal nociceptive processing. Histone H3 lysine 9 acetylation (H3K9ac) is considered an important regulator of cytokine and chemokine gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K9ac in the activation of astrocytes, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain.

Methods

Astroglial cells (C6) were treated with CGRP and differentially enrichments of H3K9ac on gene promoters were examined using ChIP‐seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on astrocyte activation and H3K9ac signaling in CCI‐induced neuropathic pain. Specific inhibitors were employed to delineate the involved signaling.

Results

Intrathecal injection of CGRP and CCI increased the number of astrocytes displaying H3K9ac in the spinal dorsal horn of rats. Treatment of CGRP was able to up‐regulate H3K9ac and glial fibrillary acidic protein (GFAP) expression in astroglial cells. ChIP‐seq data indicated that CGRP significantly altered H3K9ac enrichments on gene promoters in astroglial cells following CGRP treatment, including 151 gaining H3K9ac and 111 losing this mark, which mostly enriched in proliferation, autophagy, and macrophage chemotaxis processes. qRT‐PCR verified expressions of representative candidate genes (ATG12, ATG4C, CX3CR1, MMP28, MTMR14, HMOX1, RET) and RTCA verified astrocyte proliferation. Additionally, CGRP treatment increased the expression of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn. CGRP antagonist and HAT inhibitor attenuated mechanical and thermal hyperalgesia in CCI rats. Such analgesic effects were concurrently associated with the reduced levels of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn of CCI rats.

Conclusion

Our findings highly indicate that CGRP is associated with the development of neuropathic pain through astrocytes‐mediated neuroinflammatory responses via H3K9ac in spinal dorsa horn following nerve injury.

This study found that CGRP act on their astrocytic receptors and lead to H3K9 acetylation (H3K9ac), which are mainly associated with proliferation‐, autophagy‐, and inflammation‐related gene expression. The number of astrocytes with H3K9ac expression is increased after nerve injury. Inhibition of CGRP attenuates the development of neuropathic pain, which was accompanied by the suppression of H3K9ac, CX3CR1, and IL‐1β expression in CCI rats.

Mechanistic Insight into the Effects of Curcumin on Neuroinflammation-Driven Chronic Pain

Chronic pain is a persistent and unremitting condition that has immense effects on patients' quality of life. Studies have shown that neuroinflammation is associated with the induction and progression of chronic pain. The activation of microglia and astrocytes is the major hallmark of spinal neuroinflammation leading to neuronal excitability in the projection neurons. Excessive activation of microglia and astrocytes is one of the major contributing factors to the exacerbation of pain. However, the current chronic pain treatments, mainly by targeting the neuronal cells, remain ineffective and unable to meet the patients' needs. Curcumin, a natural plant product found in the Curcuma genus, improves chronic pain by diminishing the release of inflammatory mediators from the spinal glia. This review details the role of curcumin in microglia and astrocytes both in vitro and in vivo and how it improves pain. We also describe the mechanism of curcumin by highlighting the major glia-mediated cascades in pain. Moreover, the role of curcumin on inflammasome and epigenetic regulation is discussed. Furthermore, we discuss the strategies used to improve the efficacy of curcumin. This review illustrates that curcumin modulating microglia and astrocytes could assure the treatment of chronic pain by suppressing spinal neuroinflammation.

Paternal exposure to excessive methionine altered behavior and neurochemical activities in zebrafish offspring

An increase in plasma L-methionine (Met) levels, even if transitory, can cause important toxicological alterations in the affected individuals. Met is essential in the regulation of epigenetic mechanisms and its influence on the subsequent generation has been investigated. However, few studies have explored the influence of a temporary increase in Met levels in parents on their offspring. This study evaluated the behavioral and neurochemical effects of parental exposure to high Met concentration (3 mM) in zebrafish offspring. Adult zebrafish were exposed to Met for 7 days, maintained for additional 7 days in tanks that contained only water, and then used for breeding. The offspring obtained from these fish (F1) were tested in this study. During the early stages of offspring development, morphology, heart rate, survival, locomotion, and anxiety-like behavior were assessed. When these animals reached the adult stage, locomotion, anxiety, aggression, social interaction, memory, oxidative stress, and levels of amino acids and neurotransmitters were analyzed. F1 larvae Met group presented an increase in the distance and mean speed when compared to the control group. F1 adult Met group showed decreased anxiety-like behavior and locomotion. An increase in reactive oxygen species was also observed in the F1 adult Met group whereas lipid peroxidation and antioxidant enzymes did not change when compared to the control group. Dopamine, serotonin, glutamate, and glutathione levels were increased in the F1 adult Met group. Taken together, our data show that even a transient increase in Met in parents can cause behavioral and neurochemical changes in the offspring, promoting transgenerational effects.

Spinal Cord Injury Causes Reduction of Galanin and Gastrin Releasing Peptide mRNA Expression in the Spinal Ejaculation Generator of Male Rats

Spinal cord injury (SCI) in men is commonly associated with sexual dysfunction, including anejaculation, and chronic mid-thoracic contusion injury in male rats also impairs ejaculatory reflexes. Ejaculation is controlled by a spinal ejaculation generator consisting of a population of lumbar spinothalamic (LSt) neurons that control ejaculation through release of four neuropeptides including galanin and gastrin releasing peptide (GRP) onto lumbar and sacral autonomic and motor nuclei. It was recently demonstrated that spinal contusion injury in male rats caused reduction of GRP-immunoreactivity, but not galanin-immunoreactivity in LSt cells, indicative of reduced GRP peptide levels, but inconclusive results for galanin. The current study further tests the hypothesis that contusion injury causes a disruption of GRP and galanin mRNA in LSt cells. Male rats received mid-thoracic contusion injury and galanin and GRP mRNA were visualized 8 weeks later in the lumbar spinal cord using fluorescent in situ hybridization. Spinal cord injury significantly reduced GRP and galanin mRNA in LSt cells. Galanin expression was higher in LSt cells compared to GRP. However, expression of the two transcripts were positively correlated in LSt cells in both sham and SCI animals, suggesting that expression for the two neuropeptides may be co-regulated. Immunofluorescent visualization of galanin and GRP peptides demonstrated a significant reduction in GRP-immunoreactivity, but not galanin in LSt cells, confirming the previous observations. In conclusion, SCI reduced GRP and galanin expression in LSt cells with an apparent greater impact on GRP peptide levels. GRP and galanin are both essential for triggering ejaculation and thus such reduction may contribute to ejaculatory dysfunction following SCI in rats.

Nerve Excitability and Neuropathic Pain is Reduced by BET Protein Inhibition After Spared Nerve Injury

Neuropathic pain is a common disability produced by enhanced neuronal excitability after nervous system injury. The pathophysiological changes that underlie the generation and maintenance of neuropathic pain require modifications of transcriptional programs. In particular, there is an induction of pro-inflammatory neuromodulators levels, and changes in the expression of ion channels and other factors intervening in the determination of the membrane potential in neuronal cells. We have previously found that inhibition of the BET proteins epigenetic readers reduced neuroinflammation after spinal cord injury. Within the present study we aimed to determine if BET protein inhibition may also affect neuroinflammation after a peripheral nerve injury, and if this would beneficially alter neuronal excitability and neuropathic pain. For this purpose, C57BL/6 female mice underwent spared nerve injury (SNI), and were treated with the BET inhibitor JQ1, or vehicle. Electrophysiological and algesimetry tests were performed on these mice. We also determined the effects of JQ1 treatment after injury on neuroinflammation, and the expression of neuronal components important for the maintenance of axon membrane potential. We found that treatment with JQ1 affected neuronal excitability and mechanical hyperalgesia after SNI in mice. BET protein inhibition regulated cytokine expression and reduced microglial reactivity after injury. In addition, JQ1 treatment altered the expression of SCN3A, SCN9A, KCNA1, KCNQ2, KCNQ3, HCN1 and HCN2 ion channels, as well as the expression of the Na⁺/K⁺ ATPase pump subunits. In conclusion, both, alteration of inflammation, and neuronal transcription, could be the responsible epigenetic mechanisms for the reduction of excitability and hyperalgesia observed after BET inhibition. Inhibition of BET proteins is a promising therapy for reducing neuropathic pain after neural injury.

Calcitonin gene-related peptide regulates spinal microglial activation through the histone H3 lysine 27 trimethylation via enhancer of zeste homolog-2 in rats with neuropathic pain

BACKGROUND

Calcitonin gene-related peptide (CGRP) as a mediator of microglial activation at the transcriptional level may facilitate nociceptive signaling. Trimethylation of H3 lysine 27 (H3K27me3) by enhancer of zeste homolog 2 (EZH2) is an epigenetic mark that regulates inflammatory-related gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K27me3 in microglial activation after nerve injury, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain.

METHODS

Microglial cells (BV2) were treated with CGRP and differentially enrichments of H3K27me3 on gene promoters were examined using ChIP-seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on microglial activation and EZH2/H3K27me3 signaling in CCI-induced neuropathic pain.

RESULTS

Overexpressions of EZH2 and H3K27me3 were confirmed in spinal microglia of CCI rats by immunofluorescence. CGRP treatment induced the increased of H3K27me3 expression in the spinal dorsal horn and cultured microglial cells (BV2) through EZH2. ChIP-seq data indicated that CGRP significantly altered H3K27me3 enrichments on gene promoters in microglia following CGRP treatment, including 173 gaining H3K27me3 and 75 losing this mark, which mostly enriched in regulation of cell growth, phagosome, and inflammation. qRT-PCR verified expressions of representative candidate genes (TRAF3IP2, BCL2L11, ITGAM, DAB2, NLRP12, WNT3, ADAM10) and real-time cell analysis (RTCA) verified microglial proliferation. Additionally, CGRP treatment and CCI increased expressions of ITGAM, ADAM10, MCP-1, and CX3CR1, key mediators of microglial activation in spinal dorsal horn and cultured microglial cells. Such increased effects induced by CCI were suppressed by CGRP antagonist and EZH2 inhibitor, which were concurrently associated with the attenuated mechanical and thermal hyperalgesia in CCI rats.

CONCLUSION

Our findings highly indicate that CGRP is implicated in the genesis of neuropathic pain through regulating microglial activation via EZH2-mediated H3K27me3 in the spinal dorsal horn.