Targeting epigenetic mechanisms for chronic visceral pain: A valid approach for the development of novel therapeutics

Activation of EphrinB2/EphB2 signaling in the spine cord alters glia-neuron interactions in mice with visceral hyperalgesia following maternal separation

Background

Sress early in life has been linked to visceral hyperalgesia and associated functional gastrointestinal disorders. In a mouse model of visceral hyperalgesia, we investigated whether the EphB2 receptor and its EphrinB2 ligand in spinal cord contribute to dysregulation of glia-neuron interactions.

Methods

An established mouse model of stress due to maternal separation (MS). Pups were separated from their mothers for 14 days during early development, then analyzed several weeks later in terms of visceral sensitivity based on the abdominal withdrawal reflex score and in terms of expression of c-fos, EphrinB2, EphB2, and phosphorylated MAP kinases (ERK, p38, JNK).

Results

Visceral hyperalgesia due to MS upregulated EphB2, EphrinB2 and c-fos in the spinal cord, and c-fos levels positively correlated with those of EphB2 and EphrinB2. Spinal astrocytes, microglia, and neurons showed upregulation of EphB2, EphrinB2 and phosphorylated MAP kinases. Blocking EphrinB2/EphB2 signaling in MS mice reduced visceral sensitivity, activation of neurons and glia, and phosphorylation of NMDA receptor. Activating EphrinB2/EphB2 signaling in unstressed mice induced visceral hyperalgesia, upregulation of c-fos, and activation of NMDA receptor similar to maternal separation.

Conclusion

The stress of MS during early development may lead to visceral hyperalgesia by upregulating EphrinB2/EphB2 in the spinal cord and thereby altering neuron-glia interactions.

N4-acetylcytidine acetylation of neurexin 2 in the spinal dorsal horn regulates hypersensitivity in a rat model of cancer-induced bone pain

Cancer-induced bone pain (CIBP) significantly impacts the quality of life and survival of patients with advanced cancer. Despite the established role of neurexins in synaptic structure and function, their involvement in sensory processing during injury has not been extensively studied. In this study using a rat model of CIBP, we observed increased neurexin 2 expression in spinal cord neurons. Knockdown of neurexin 2 in the spinal cord reversed CIBP-related behaviors, sensitization of spinal c-Fos neurons, and pain-related negative emotional behaviors. Additionally, increased acetylation of neurexin 2 mRNA was identified in the spinal dorsal horn of CIBP rats. Decreasing the expression of N-acetyltransferase 10 (NAT10) reduced neurexin 2 mRNA acetylation and neurexin 2 expression. In PC12 cells, we confirmed that neurexin 2 mRNA acetylation enhanced its stability, and neurexin 2 expression was regulated by NAT10. Finally, we discovered that the NAT10/ac4C-neurexin 2 axis modulated neuronal synaptogenesis. This study demonstrated that the NAT10/ac4C-mediated posttranscriptional modulation of neurexin 2 expression led to the remodeling of spinal synapses and the development of conscious hypersensitivity in CIBP rats. Therefore, targeting the epigenetic modification of neurexin 2 mRNA ac4C may offer a new therapeutic approach for the treatment of nociceptive hypersensitivity in CIBP.

Research Progress of Central and Peripheral Corticotropin-Releasing Hormone in Irritable Bowel Syndrome with Comorbid Dysthymic Disorders

Irritable bowel syndrome (IBS) is considered a stress disorder characterized by psychological and gastrointestinal dysfunction. IBS patients not only suffer from intestinal symptoms such as abdominal pain, diarrhea, or constipation but also, experience dysthymic disorders such as anxiety and depression. Studies have found that corticotropin-releasing hormone plays a key role in IBS with comorbid dysthymic disorders. Next, we will summarize the effects of corticotropin-releasing hormone from the central nervous system and periphery on IBS with comorbid dysthymic disorders and relevant treatments based on published literatures in recent years.

Mendelian randomization study of gastroesophageal reflux disease and major depression

This study systematically investigated the causal relationship between gastroesophageal reflux disease (GERD) and major depression (MD). Single-nucleotide polymorphisms (SNPs) associated with disorders of interest were screened via the genome-wide association study (GWAS) enrolling individuals of European descent. Summary-level data for GERD and MD were extracted from the UK Biobank. The inverse-variance-weighted (IVW) method was utilized as the primary analysis. Sensitivity analyses were performed using the MR-Egger method, the Maximum likelihood method, the MR-pleiotropy residual sum outlier (MR-PRESSO) method, and MR-robust adjusted profile score (MR-RAPS) method. MR-Egger regression, heterogeneity tests, pleiotropy tests, and leave-one-out tests were also performed to analyze sensitivity. The MR Steiger test was used to verify the directionality of the exposure to the outcome. An available website tool (https://shiny.cnsgenomics.com/mRnd/) was used to calculate the statistical power of MR analysis. Meta-analysis was applied to test MD's average genetically predicted effect on GERD. Our MR study showed a bidirectional causal association between MD and GERD. Regarding MD to GERD, there was a positive association between them; the ORs were 1.500 (95% CI = 1.320-1.704; P = 4.91E-10) and 2.058 (95% CI = 1.868-2.267; P = 2.20E-48) in the IVW method, respectively. In addition, the meta-analysis also showed a strong positive causal association between MD and GERD. When exposure and outcome were reversed, genetic predisposition to GERD was significantly associated with the overall Risk of advanced MD (ieu-a-1187, OR = 1.982, 95% CI = 1.694-2.319, P = 1.41E-17; ieu-b-102, OR = 1.612, 95% CI = 1.530-2.700, P = 1.15E-70). Our study provides 100% power to detect the causal effect of MD on GERD and vice versa. Genetically predicted MD was positively associated with higher GERD risk, and vice versa. Our study reminds clinicians to pay attention to screening for GERD when diagnosing and treating MD and vice versa. Moreover, there may be positive feedback between MD and GERD when treating and preventing one disorder may benefit the treatment and prevention of the other.

Research hotspots and trends in visceral pain research: A global comprehensive bibliometric analysis

Background

Visceral pain is a complex and heterogeneous disorder that is considered more prominent compared to somatic pain, due to its multiple and complex causes and accompanying emotional and mood disorders. Research has become increasingly extensive over the years, but a bibliometric analysis of this field is lacking. The aim of this study was to analyze global research trends in visceral pain over the past 40 years through visual analysis.

Methods

We conducted a comprehensive search of the literature from January 1981 to December 2021 using the Web of Science core database. The medical subject term 'visceral pain' was searched. We used CiteSpace and VOSviewer for bibliometric analysis and network visualization, including top-ranked authors, keywords, research collaborations, and literature co-occurrence network analysis.

Results

A total of 5,047 articles were included in the analysis. The number of articles on visceral pain has continued to grow steadily over the past 40 years. The United States (1,716 articles), University of California (159 articles), and Neurogastroenterology and Motility (276 articles) were the country, institution, and journal with the most publications, respectively. Keyword analysis showed that inflammation, visceral hypersensitivity, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), anxiety, and quality of life were the research trends and priorities in this research field.

Conclusion

Visceral pain-related research has received increasing attention in recent decades. However, there are still many unresolved issues in the field of visceral pain, such as the specific molecular mechanisms and clinical treatments between visceral pain and inflammation, IBD, IBS, anxiety, and quality of life, which may require further exploration based on modern scientific and technological means and more basic research, especially for the therapeutic targets of visceral pain, which may become a hot spot for future research and provide guidance for the treatment of clinical diseases related to visceral pain.

Role of hippocampal circKcnk9 in visceral hypersensitivity and anxiety comorbidity of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterized by recurrent visceral pain and altered bowel habits (diarrhea or constipation). However, the molecular and pathological mechanisms are poorly understood. This study found neonatal colorectal distension to induce visceral hypersensitivity and anxiety. The expression of hippocampal circKcnk9, a novel circRNA, was significantly increased in IBS-like rats. Interestingly, CA1 shcircKcnk9 treatment inhibited long-term potentiation (LTP) and alleviated visceral hypersensitivity and anxiety in IBS-like rats, whereas overexpression of CA1 circKcnk9 induced LTP, visceral hypersensitivity, and anxiety in controls. Several experiments indicated that increased CA1 circKcnk9 acted as a miR-124-3p sponge, which resulted in the inhibitory effect of miR-124-3p on gene silencing. There was a negative correlation between circKcnk9 and miR-124-3p expression. As expected, CA1 administration of agomiR-124-3p decreased CA1 LTP, visceral hypersensitivity, and anxiety in the IBS-like rats. In contrast, CA1 treatment with antagomiR-124-3p induced LTP, visceral hypersensitivity, and anxiety in the controls. Furthermore, bioinformatic analysis and experimental data showed that EZH2 is a circKcnk9/miR-124-3p target gene, and increased EZH2 expression was involved in visceral hypersensitivity and anxiety in IBS-like rats by enhancing hippocampal synaptic plasticity. In conclusion, early life stress induces increased expression of circKcnk9 in the CA1 of IBS-like rats. Increased circKcnk9 expression regulates synaptic transmission and enhances LTP, leading to visceral hypersensitivity and anxiety in IBS-like rats. The underlying circKcnk9 signaling pathway is miR124-3p/EZH2. Increased circKcnk9 reinforces its sponging of miR124-3p and strongly suppresses miR124-3p activity, resulting in increased expression of the target gene EZH2. This study provides a new epigenetic mechanism for visceral hypersensitivity and anxiety in IBS-like rats.

Gallic Acid Alleviates Visceral Pain and Depression via Inhibition of P2X7 Receptor

Chronic visceral pain can occur in many disorders, the most common of which is irritable bowel syndrome (IBS). Moreover, depression is a frequent comorbidity of chronic visceral pain. The P2X7 receptor is crucial in inflammatory processes and is closely connected to developing pain and depression. Gallic acid, a phenolic acid that can be extracted from traditional Chinese medicine, has been demonstrated to be anti-inflammatory and anti-depressive. In this study, we investigated whether gallic acid could alleviate comorbid visceral pain and depression by reducing the expression of the P2X7 receptor. To this end, the pain thresholds of rats with comorbid visceral pain and depression were gauged using the abdominal withdraw reflex score, whereas the depression level of each rat was quantified using the sucrose preference test, the forced swimming test, and the open field test. The expressions of the P2X7 receptor in the hippocampus, spinal cord, and dorsal root ganglion (DRG) were assessed by Western blotting and quantitative real-time PCR. Furthermore, the distributions of the P2X7 receptor and glial fibrillary acidic protein (GFAP) in the hippocampus and DRG were investigated in immunofluorescent experiments. The expressions of p-ERK1/2 and ERK1/2 were determined using Western blotting. The enzyme-linked immunosorbent assay was utilized to measure the concentrations of IL-1β, TNF-α, and IL-10 in the serum. Our results demonstrate that gallic acid was able to alleviate both pain and depression in the rats under study. Gallic acid also reduced the expressions of the P2X7 receptor and p-ERK1/2 in the hippocampi, spinal cords, and DRGs of these rats. Moreover, gallic acid treatment decreased the serum concentrations of IL-1β and TNF-α, while raising IL-10 levels in these rats. Thus, gallic acid may be an effective novel candidate for the treatment of comorbid visceral pain and depression by inhibiting the expressions of the P2X7 receptor in the hippocampus, spinal cord, and DRG.

Association Between Psychosocial Disorders and Gastroesophageal Reflux Disease: A Systematic Review and Meta-analysis

Background/Aims

The incidence of gastroesophageal reflux disease (GERD) is increasing annually. Studies have suggested that psychosocial disorders may be linked to the development of GERD. However, studies evaluating the association between psychosocial disorders and GERD have been inconsistent. Thus, we conducted a systematic review and meta-analysis of observational studies that evaluated the association between psychosocial disorders and GERD.

Methods

We systematically searched the PubMed, Embase, Cochrane, and Web of Science databases until October 17, 2020. Pooled OR with 95% CI and subgroup analyses were calculated using a random-effects model. Subgroup analyses were performed to identify the sources of heterogeneity. Sensitivity analysis by one-study removal was used to test the robustness of our results.

Results

This meta-analysis included 1 485 268 participants from 9 studies. Studies using psychosocial disorders as the outcome showed that patients with GERD had a higher incidence of psychosocial disorders compared to that in patients without GERD (OR, 2.57; 95% CI, 1.87-3.54; I2 = 93.8%; P < 0.001). Studies using GERD as an outcome showed an association between psychosocial disorders and an increased risk of GERD (OR, 2.23; 95% CI, 1.42-3.51; I2 = 97.1%; P < 0.001). The results of the subgroup analysis showed that the non-erosive reflux disease group had a higher increased risk of anxiety than erosive reflux disease group (OR, 9.45; 95% CI, 5.54- 16.13; I2 = 12.6%; P = 0.285).

Conclusion

Results of our meta-analysis showed that psychosocial disorders are associated with GERD; there is an interaction between the two.

Histone deacetylase inhibitor givinostat attenuates nonalcoholic steatohepatitis and liver fibrosis

Nonalcoholic steatohepatitis (NASH) is a common chronic liver disease that is increasingly prevalent worldwide. Liver inflammation is an important contributor to disease progression from nonalcoholic fatty liver (NAFL) to NASH, but there is a lack of efficient therapies. In the current study we evaluated the therapeutic potential of givinostat, a histone deacetylase (HDAC) inhibitor, in the treatment of NASH in vivo and in vitro. Liver inflammation was induced in mice by feeding a methionine- and choline-deficient diet (MCD) or a fructose, palmitate, cholesterol diet (FPC). The mice were treated with givoinostat (10 mg·kg^-1·d^-1, ip) for 8 or 10 weeks. At the end of the experiment, the livers were harvested for analysis. We showed that givoinostat administration significantly alleviated inflammation and attenuated hepatic fibrosis in MCD-induced NASH mice. RNA-seq analysis of liver tissues form MCD-fed mice revealed that givinostat potently blocked expression of inflammation-related genes and regulated a broad set of lipid metabolism-related genes. In human hepatocellular carcinoma cell line HepG2 and human derived fetal hepatocyte cell line L02, givinostat significantly decreased palmitic acid-induced intracellular lipid accumulation. The benefit of givinostat was further confirmed in FPC-induced NASH mice. Givinostat administration significantly attenuated hepatic steatosis, inflammation as well as liver injury in this mouse model. In conclusion, givinostat is efficacious in reversing diet-induced NASH, and may serve as a therapeutic agent for the treatment of human NASH.

The pathological involvement of spinal cord EphB2 in visceral sensitization in male rats

Patients with post-traumatic stress disorder (PTSD) are usually at an increased risk for chronic disorders, such as irritable bowel syndrome (IBS), characterized by hyperalgesia and allodynia, but its subsequent effect on visceral hyperalgesia and the mechanism remain unclear. The present study employed single prolonged stress (SPS), a model of PTSD-pain comorbidity, behavioral evaluation, intrathecal drug delivery, immunohistochemistry, Western blotting, and RT-PCR techniques. When detecting visceral sensitivity, the score of the abdominal withdrawal reflex (AWR) induced by graded colorectal distention (CRD) was used. The AWR score was reduced in the SPS day 1 group but increased in the SPS day 7 and SPS day 14 groups at 40 mmHg and 60 mmHg, and the score was increased significantly with EphrinB1-Fc administration. The EphB2+ cell density and EphB2 protein and mRNA levels were downregulated in the SPS day 1 group and then upregulated significantly in the SPS day 7 group; these changes were more noticeable with EphrinB1-Fc administration compared with the SPS-only group. The C-Fos-positive reaction induced by SPS was mainly localized in neurons of the spinal dorsal horn, in which the C-Fos-positive cell density and its protein and mRNA levels were upregulated on SPS days 7 and 14; these changes were statistically significant in the SPS + EphrinB1-Fc group compared with the SPS alone group. The present study confirmed the time window for the AWR value, EphB2 and C-Fos changes, and the effect of EphrinB1-Fc on these changes, which suggests that spinal cord EphB2 activation exacerbates visceral pain after SPS.

Differential DNA methylation in Black and White individuals with chronic low back pain enrich different genomic pathways

Compared to Non-Hispanic Whites (NHWs), individuals who self-identify as Non-Hispanic Blacks (NHBs) in the United States experience more severe and disabling chronic low back pain (cLBP). We hypothesized that differences in DNA methylation (DNAm) play a role in racial disparities in cLBP.

PURPOSE

To determine the relationship between DNAm levels and racial group differences in adults with cLBP. Our study's secondary purpose was to perform a race-stratified comparison of adults with cLBP and pain-free controls and identify functional genomic pathways enriched by annotated differentially methylated genes.

PATIENTS AND METHODS

We recruited 49 NHBs and 49 NHWs (49 cLBP and 49 pain-free controls, PFCs), analyzed DNAm from whole blood using reduced representation bisulfite sequencing, and identified enriched genomic pathways.

RESULTS

Among participants with cLBP, we identified 2873 differentially methylated loci (DML; methylation differences of at least 10% and p < 0.0001), many of which were annotated to genes of importance to pain pathology. These DMLs significantly enriched pathways to involved in nociception/pain processing (Dopamine-DARPP32 Feedback in cAMP signaling, GABA Receptor Signaling, Opioid Signaling) and neuronal differentiation (e.g., Calcium Signaling, Axon Guidance Signaling, and Endocannabinoid Neuronal Synapse). Our race stratified analyses of individuals with cLBP versus PFCs revealed 2356 DMLs in NHBs and 772 DMLs in NHWs with p < 0.0001 and > 10% methylation difference. Ingenuity Pathway Analysis revealed that many pathways of significance to pain such as Corticotropin Releasing Hormone Signaling, White Adipose Tissue Browning, and GABA Receptor Signaling pathways, were more significant in NHBs than NHWs.

CONCLUSION

Even though an individual's self-identified race is a social construct, not a biological variable, racism associated with that classification affects virtually every aspect of life, including disease risk. DNAm induced alterations in stress signaling pathways may explain worse pain outcomes in NHBs.

Global gene expression and chromatin accessibility of the peripheral nervous system in animal models of persistent pain

BACKGROUND

Efforts to understand genetic variability involved in an individual's susceptibility to chronic pain support a role for upstream regulation by epigenetic mechanisms.

METHODS

To examine the transcriptomic and epigenetic basis of chronic pain that resides in the peripheral nervous system, we used RNA-seq and ATAC-seq of the rat dorsal root ganglion (DRG) to identify novel molecular pathways associated with pain hypersensitivity in two well-studied persistent pain models induced by chronic constriction injury (CCI) of the sciatic nerve and intra-plantar injection of complete Freund's adjuvant (CFA) in rats.

RESULTS

Our RNA-seq studies identify a variety of biological process related to synapse organization, membrane potential, transmembrane transport, and ion binding. Interestingly, genes that encode transcriptional regulators were disproportionately downregulated in both models. Our ATAC-seq data provide a comprehensive map of chromatin accessibility changes in the DRG. A total of 1123 regions showed changes in chromatin accessibility in one or both models when compared to the naïve and 31 shared differentially accessible regions (DAR)s. Functional annotation of the DARs identified disparate molecular functions enriched for each pain model which suggests that chromatin structure may be altered differently following sciatic nerve injury and hind paw inflammation. Motif analysis identified 17 DNA sequences known to bind transcription factors in the CCI DARs and 33 in the CFA DARs. Two motifs were significantly enriched in both models.

CONCLUSIONS

Our improved understanding of the changes in chromatin accessibility that occur in chronic pain states may identify regulatory genomic elements that play essential roles in modulating gene expression in the DRG.

Environmental enrichment prevents stress-induced epigenetic changes in the expression of glucocorticoid receptor and corticotrophin releasing hormone in the central nucleus of the amygdala to inhibit visceral hypersensitivity

INTRODUCTION

Stress is a known trigger for the symptoms of irritable bowel syndrome (IBS), a gastrointestinal (GI) disorder that presents with abnormal bowel habits and abdominal pain due to visceral hypersensitivity. While behavioral therapies have been used to attenuate IBS symptoms, the underlying mechanisms by which these therapies interact with stress-induced pathology remains to be delineated. Here we use a rat model to test the hypothesis that exposure to environmental enrichment (EE) inhibits stress-induced changes within the brain-gut axis to prevent visceral and somatic hypersensitivity and colonic hyperpermeability.

METHODS

Female rats (n = 8/group) were housed in EE one week before and one week during exposure to water avoidance stress (WAS) while controls were housed in standard cages (SH). One day after the final WAS exposure, colonic and somatic sensitivity were assessed by the visceromotor response (VMR) to colorectal distension (CRD) and withdrawal threshold elicited by an electronic von Frey on the hind paw of the rats respectively. All rats were returned to SH for 3 weeks before colonic and somatic sensitivity were reassessed on day 28. The rats were then immediately euthanized and the spinal cord was collected to assess changes in neuronal activation (assessed via ERK phosphorylation) in response to noxious CRD. A separate cohort of animals (n = 8/group) that did not undergo behavioral assessments was euthanized the day after the final WAS exposure and the central nucleus of the amygdala (CeA) was collected to investigate WAS and EE induced epigenetic changes at the glucocorticoid receptor (GR) and corticotrophin releasing hormone (CRH) promoter. The colon from these rats was also collected to assess colonic permeability via changes in transepithelial electrical resistance (TEER) in vitro.

RESULTS

Exposure to stress persistently increased VMR to CRD (P < 0.01) and decreased the hind paw withdrawal threshold (P < 0.001) in female rats. WAS also decreased TEER in the colon tissue of female rats (p = 0.05). In the CeA, WAS induced a decrease in histone acetylation at the GR promoter but increased histone acetylation at the CRH promoter and reduced GR-CRH interactions in the CeA. Analysis of the spinal cord showed that WAS increased CRD-evoked ERK phosphorylation in the dorsal horn. Exposure to EE prevented WAS-induced changes in the CeA, dorsal horn and colon respectively to prevent visceral and somatic hypersensitivity.

CONCLUSION

Our data reveals that behavioral therapies can produce long lasting molecular and epigenetic changes that can prevent stress-induced pathologies even after completion of the therapy. These results highlight the potential mechanisms by which behavioral therapies may ameliorate visceral pain associated stress-related pathologies such as the irritable bowel syndrome.

An evidence-based review of CGRP mechanisms in the propagation of chronic visceral pain

Chronic pain is typically defined as pain that persists after acute tissue damage and inflammation or as pain that follows a chronic disease process and lasts more than three months. Because of its debilitating impact on the quality of life of patients, recent research aims to investigate the mechanisms behind nociception to discover novel therapeutic agents to alleviate pain. One such target is the neuropeptide calcitonin gene-related peptide (CGRP), which has shown to play an integral role in migraine pathophysiology. Effective treatments of migraines with CGRP antagonists have stimulated our efforts toward checking a possible involvement of CGRP in nonheadache pain conditions such as hypertension, congestive heart failure, Alzheimer's disease, and vascular ischemia. Here, we provide a brief overview of chronic pain, with a particular emphasis on the role of CGRP as a fundamental mediator of nociceptive pain as well as a target for novel therapeutic agents.

Altered BDNF Methylation in Patients with Chronic Musculoskeletal Pain and High Biopsychosocial Complexity

Purpose

The INTERMED instrument, which was developed to measure patient's biopsychosocial (BPS) complexity, represents a powerful diagnostic and therapeutic tool. Epigenetic changes are the interface between signals from the environment and genetic modifications, affecting gene expression, in particular, by DNA methylation of CpG dinucleotides in promotor regions of the corresponding genes. The brain-derived neurotrophic factor (BDNF) gene plays a crucial role in the central sensitization (CS) of pain. In this study, we hypothesized that chronic pain modifies the methylation levels of the BDNF gene in a manner that is interconnected with the BPS status.

Patients and Methods

Fifty-eight chronic musculoskeletal pain patients (CMSP) were enrolled in the study. DNA was extracted from blood samples, the methylation levels of 13 CpG sites in the BDNF promoter were measured by pyrosequencing, and association studies with various patient parameters and the INTERMED scores were performed.

Results

Interestingly, a negative correlation (-0.40) was found between the total INTERMED scores and the average CpG methylation values of the BDNF gene, but no correlation was observed with the severity of pain, degree of anxiety, depression, or kinesiophobia and catastrophism. Moreover, the association was independent of age, sex and level of comorbidities.

Conclusion

This result shows that CMSP, in association with its biopsychosocial context, epigenetically decreases the degree of methylation of the BDNF promoter and should therefore increase the level of BDNF transcription. It also suggests a role of the INTERMED tool to detect a relationship between the BPS complexity and the epigenetic control of a target gene. The possible upregulation of BDNF expression might be, at least in part, the signal for chronic pain-induced central sensitization (CS). This could partly explain why patients with a higher level of complexity feel more pain than those with lower complexity.

Upregulation of TRPC6 Mediated by PAX6 Hypomethylation Is Involved in the Mechanical Allodynia Induced by Chemotherapeutics in Dorsal Root Ganglion

BACKGROUND

Although the action mechanism of antineoplastic agents is different, oxaliplatin, paclitaxel, or bortezomib as first-line antineoplastic drugs can induce painful neuropathy. In rodents, mechanical allodynia is a common phenotype of painful neuropathy for 3 chemotherapeutics. However, whether there is a common molecular involved in the different chemotherapeutics-induced painful peripheral neuropathy remains unclear.

METHODS

Mechanical allodynia was tested by von Frey hairs following i.p. injection of vehicle, oxaliplatin, paclitaxel, or bortezomib in Sprague-Dawley rats. Reduced representation bisulfite sequencing and methylated DNA immunoprecipitation were used to detect the change of DNA methylation. Western blot, quantitative polymerase chain reaction, chromatin immunoprecipitation, and immunohistochemistry were employed to explore the molecular mechanisms.

RESULTS

In 3 chemotherapeutic models, oxaliplatin, paclitaxel, or bortezomib accordantly upregulated the expression of transient receptor potential cation channel, subfamily C6 (TRPC6) mRNA and protein without affecting the DNA methylation level of TRPC6 gene in DRG. Inhibition of TRPC6 by using TRPC6 siRNA (i.t., 10 consecutive days) relieved mechanical allodynia significantly following application of chemotherapeutics. Furthermore, the downregulated recruitment of DNA methyltransferase 3 beta (DNMT3b) at paired box protein 6 (PAX6) gene led to the hypomethylation of PAX6 gene and increased PAX6 expression. Finally, the increased PAX6 via binding to the TPRC6 promoter contributes to the TRPC6 increase and mechanical allodynia following chemotherapeutics treatment.

CONCLUSIONS

The TRPC6 upregulation through DNMT3b-mediated PAX6 gene hypomethylation participated in mechanical allodynia following application of different chemotherapeutic drugs.