Epigenetic regulation of genes that modulate chronic stress-induced visceral pain in the peripheral nervous system

SGLT2 inhibitor empagliflozin ameliorates tubulointerstitial fibrosis in DKD by downregulating renal tubular PKM2

BACKGROUND AND OBJECTIVE

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have been shown to prevent the progression of diabetic kidney disease (DKD). However, their impact on renal fibrosis remains largely uninvestigated. This study aimed to explore the effect of SGLT2 inhibitor empagliflozin on renal fibrosis in DKD patients and DKD models, and the molecular mechanisms involved.

METHODS

Kidney samples of DKD patients and DKD models were used in this study. DKD mouse models included STZ-treated CD-1 mice and HFD-fed C57BL/6 mice were all treated with empagliflozin for 6 to 12 weeks. Kidney pathological changes were analysed and fibrotic factors were detected. HK-2 cells were treated with normal glucose (NG), high glucose (HG), or HG with empagliflozin. RNA sequencing was employed to identify the differentially expressed genes. Epithelial-mesenchymal transition (EMT) markers were detected. Binding of transcription factor and target gene was determined using a dual-luciferase reporter assay.

RESULTS

Empagliflozin significantly ameliorated kidney fibrosis in DKD patients and DKD models. This was evidenced by tubulointerstitial fibrosis reduction observed through PAS and Masson staining, along with fibrotic factors downregulation. RNA sequencing and the subsequent in vitro and in vivo validation identified PKM2 as the most significantly upregulated glycolytic enzyme in DKD patients and models. Empagliflozin downregulated PKM2 and alleviated EMT and renal fibrosis. Importantly, empagliflozin improves fibrosis by downregulating PKM2. The downregulation of PKM2 by empagliflozin was achieved by inhibiting the binding of estrogen-related receptor α at the promoter.

CONCLUSIONS

Empagliflozin ameliorates kidney fibrosis via downregulating PKM2 in DKD.

Unveiling the Mechanisms of Pain in Endometriosis: Comprehensive Analysis of Inflammatory Sensitization and Therapeutic Potential

Endometriosis is a complicated, estrogen-dependent gynecological condition with a high morbidity rate. Pain, as the most common clinical symptom of endometriosis, severely affects women's physical and mental health and exacerbates socioeconomic burden. However, the specific mechanisms behind the occurrence of endometriosis-related pain remain unclear. It is currently believed that the occurrence of endometriosis pain is related to various factors, such as immune abnormalities, endocrine disorders, the brain-gut axis, angiogenesis, and mechanical stimulation. These factors induce systemic chronic inflammation, which stimulates the nerves and subsequently alters neural plasticity, leading to nociceptive sensitization and thereby causing chronic pain. In this paper, we compile and review the articles published on the study of nociceptive sensitization and endometriosis pain mechanisms. Starting from the factors influencing the chronic pain associated with endometriosis, we explain the relationship between these factors and chronic inflammation and further elaborate on the potential mechanisms by which chronic inflammation induces nociceptive sensitization. We aim to reveal the possible mechanisms of endometriosis pain, as well as nociceptive sensitization, and offer potential new targets for the treatment of endometriosis pain.

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

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

The Transcription Factor Tbx5-Dependent Epigenetic Modification Contributes to Neuropathic Allodynia by Activating TRPV1 Expression in the Dorsal Horn

Nerve injury can induce aberrant changes in the spine; these changes are due to, or at least partly governed by, transcription factors that contribute to the genesis of neuropathic allodynia. Here, we showed that spinal nerve ligation (SNL, a clinical neuropathic allodynia model) increased the expression of the transcription factor Tbx5 in the injured dorsal horn in male Sprague Dawley rats. In contrast, blocking this upregulation alleviated SNL-induced mechanical allodynia, and there was no apparent effect on locomotor function. Moreover, SNL-induced Tbx5 upregulation promoted the recruitment and interaction of GATA4 and Brd4 by enhancing its binding activity to H3K9Ac, which was enriched at the Trpv1 promotor, leading to an increase in TRPV1 transcription and the development of neuropathic allodynia. In addition, nerve injury-induced expression of Fbxo3, which abates Fbxl2-dependent Tbx5 ubiquitination, promoted the subsequent Tbx5-dependent epigenetic modification of TRPV1 expression during SNL-induced neuropathic allodynia. Collectively, our findings indicated that spinal Tbx5-dependent TRPV1 transcription signaling contributes to the development of neuropathic allodynia via Fbxo3-dependent Fbxl2 ubiquitination and degradation. Thus, we propose a potential medical treatment strategy for neuropathic allodynia by targeting Tbx5.

ZO-1 and IL-1RAP Phosphorylation: Potential Role in Mediated Brain-Gut Axis Dysregulation in Irritable Bowel Syndrome-like Stressed Mice

Background and Objectives: Irritable Bowel Syndrome (IBS) is a common gastrointestinal disorder often exacerbated by stress, influencing the brain-gut axis (BGA). BGA dysregulation, disrupted intestinal barrier function, altered visceral sensitivity and immune imbalance defects underlying IBS pathogenesis have been emphasized in recent investigations. Phosphoproteomics reveals unique phosphorylation details resulting from environmental stress. Here, we employ phosphoproteomics to explore the molecular mechanisms underlying IBS-like symptoms, mainly focusing on the role of ZO-1 and IL-1RAP phosphorylation. Materials and Methods: Morris water maze (MWM) was used to evaluate memory function for single prolonged stress (SPS). To assess visceral hypersensitivity of IBS-like symptoms, use the Abdominal withdrawal reflex (AWR). Colonic bead expulsion and defecation were used to determine fecal characteristics of the IBS-like symptoms. Then, we applied a phosphoproteomic approach to BGA research to discover the molecular mechanisms underlying the process of visceral hypersensitivity in IBS-like mice following SPS. ZO-1, p-S179-ZO1, IL-1RAP, p-S566-IL-1RAP and GFAP levels in BGA were measured by western blotting, immunofluorescence staining, and enzyme-linked immunosorbent assay to validate phosphorylation quantification. Fluorescein isothiocyanate-dextran 4000 and electron-microscopy were performed to observe the structure and function of the intestinal epithelial barrier. Results: The SPS group showed changes in learning and memory ability. SPS exposure affects visceral hypersensitivity, increased fecal water content, and significant diarrheal symptoms. Phosphoproteomic analysis displayed that p-S179-ZO1 and p-S566-IL-1RAP were significantly differentially expressed following SPS. In addition, p-S179-ZO1 was reduced in mice's DRG, colon, small intestine, spinal and hippocampus and intestinal epithelial permeability was increased. GFAP, IL-1β and p-S566-IL-1RAP were also increased at the same levels in the BGA. And IL-1β showed no significant difference was observed in serum. Our findings reveal substantial alterations in ZO-1 and IL-1RAP phosphorylation, correlating with increased epithelial permeability and immune imbalance. Conclusions: Overall, decreased p-S179-ZO1 and increased p-S566-IL-1RAP on the BGA result in changes to tight junction structure, compromising the structure and function of the intestinal epithelial barrier and exacerbating immune imbalance in IBS-like stressed mice.

Interrelated involvement of the endocannabinoid/endovanilloid (TRPV1) systems and epigenetic processes in anxiety- and working memory impairment-related behavioural effects of nicotine as a stressor

The addictive use of nicotine contained in tobacco is associated with stressor-like emotional and cognitive effects such as anxiety and working memory impairment, and the involvement of epigenetic mechanisms such as histone acetylation has recently been reported. Although the precise nature of behavioural plasticity remains unclear, both anxiogenic- and working memory impairment-like effects were observed in the present experimental model of mice treated with repeated subcutaneous nicotine and/or immobilization stress, and these effects were commonly attenuated by the histone deacetylase (HDAC) inhibitors that induce histone acetylation. Such HDAC inhibitor-induced resilience was mimicked by ligands for the endocannabinoid (ECB) system, a neurotransmitter system that is closely associated with nicotine-induced addiction-related behaviours: the anxiogenic-like effects were mitigated by the cannabinoid type 1 (CB1) agonist arachidonylcyclopropylamide (ACPA), whereas the working memory impairment-like effects were mitigated by the CB1 antagonist SR 141716A. Moreover, the effects of the HDAC inhibitors were also mimicked by ligands for the endovanilloid (transient receptor potential vanilloid 1 [TRPV1]) system, a system that shares common characteristics with the ECB system: the anxiogenic-like effects were mitigated by the TRPV1 antagonist capsazepine, whereas the working memory impairment-like effects were mitigated by the TRPV1 agonist olvanil. Notably, the HDAC inhibitor-induced anxiolytic-like effects were attenuated by SR 141716A, which were further counteracted by capsazepine, whereas the working memory improvement-like effects were attenuated by capsazepine, which were further counteracted by SR 141716A. These results suggest the contribution of interrelated control of the ECB/TRPV1 systems and epigenetic processes such as histone acetylation to novel therapeutic approaches.

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.

Pathology of pain and its implications for therapeutic interventions

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

Whole-genome methylation profiling reveals regions associated with painful temporomandibular disorders and active recovery processes

ABSTRACT

Temporomandibular disorders (TMDs), collectively representing one of the most common chronic pain conditions, have a substantial genetic component, but genetic variation alone has not fully explained the heritability of TMD risk. Reasoning that the unexplained heritability may be because of DNA methylation, an epigenetic phenomenon, we measured genome-wide DNA methylation using the Illumina MethylationEPIC platform with blood samples from participants in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study. Associations with chronic TMD used methylation data from 496 chronic painful TMD cases and 452 TMD-free controls. Changes in methylation between enrollment and a 6-month follow-up visit were determined for a separate sample of 62 people with recent-onset painful TMD. More than 750,000 individual CpG sites were examined for association with chronic painful TMD. Six differentially methylated regions were significantly ( P < 5 × 10 -8 ) associated with chronic painful TMD, including loci near genes involved in the regulation of inflammatory and neuronal response. A majority of loci were similarly differentially methylated in acute TMD consistent with observed transience or persistence of symptoms at follow-up. Functional characterization of the identified regions found relationships between methylation at these loci and nearby genetic variation contributing to chronic painful TMD and with gene expression of proximal genes. These findings reveal epigenetic contributions to chronic painful TMD through methylation of the genes FMOD , PM20D1 , ZNF718 , ZFP57 , and RNF39 , following the development of acute painful TMD. Epigenetic regulation of these genes likely contributes to the trajectory of transcriptional events in affected tissues leading to resolution or chronicity of pain.

Pharmacogenetics in IBS: update and impact of GWAS studies in drug targets and metabolism

INTRODUCTION

Medications are frequently prescribed for patients with irritable bowel syndrome (IBS) or disorders of gut brain interaction. The level of drug metabolism and modifications in drug targets determine medication efficacy to modify motor or sensory function as well as patient response outcomes.

AREAS COVERED

The literature search included PubMed searches with the terms: pharmacokinetics, pharmacogenomics, epigenetics, clinical trials, irritable bowel syndrome, disorders of gut brain interaction, and genome-wide association studies. The main topics covered in relation to irritable bowel syndrome were precision medicine, pharmacogenomics related to drug metabolism, pharmacogenomics related to mechanistic targets, and epigenetics.

EXPERT OPINION

Pharmacogenomics impacting drug metabolism [CYP 2D6 (cytochrome P450 2D6) or 2C19 (cytochrome P450 2C19)] is the most practical approach to precision medicine in the treatment of IBS. Although there are proof of concept studies that have documented the importance of genetic modification of transmitters or receptors in altering responses to medications in IBS, these principles have rarely been applied in patient response outcomes. Genome-wide association (GWAS) studies have now documented the association of symptoms with genetic variation but not the evaluation of treatment responses. Considerably more research, particularly focused on patient response outcomes and epigenetics, is essential to impact this field in clinical medicine.

ZBTB20 mediates stress-induced visceral hypersensitivity via activating the NF-κB/transient receptor potential channel pathway

BACKGROUND

Psychological stress is a major trigger for visceral hypersensitivity (VH) in irritable bowel syndrome. The zinc finger protein ZBTB20 (ZBTB20) is implicated in somatic nociception via modulating transient receptor potential (TRP) channels, but its role in the development of VH is unclear. This study aimed to investigate the role of ZBTB20/TRP channel axis in stress-induced VH.

METHODS

Rats were subjected to water avoidance stress (WAS) for 10 consecutive days. Small interfering RNA (siRNA) targeting ZBTB20 was intrathecally administered. Inhibitors of TRP channels, stress hormone receptors, and nuclear factor kappa-B (NF-κB) were administered. Visceromotor response to colorectal distension was recorded. Dorsal root ganglia (DRGs) were dissected for Western blot, coimmunoprecipitation, and chromatin immunoprecipitation. The DRG-derived neuron cell line was applied for specific research.

KEY RESULTS

WAS-induced VH was suppressed by the inhibitor of TRPV1, TRPA1, or TRPM8, with enhanced expression of these channels in L6-S2 DRGs. The inhibitor of glucocorticoid receptor or β2-adrenergic receptor counteracted WAS-induced VH and TRP channel expression. Concurrently, WAS-induced stress hormone-dependent ZBTB20 expression and NF-κB activation in DRGs. Intrathecally injected ZBTB20 siRNA or an NF-κB inhibitor repressed WAS-caused effect. In cultured DRG-derived neurons, stress hormones promoted nuclear translocation of ZBTB20, which preceded p65 nuclear translocation. And, ZBTB20 siRNA suppressed stress hormone-caused NF-κB activation. Finally, WAS enhanced p65 binding to the promoter of TRPV1, TRPA1, or TRPM8 in rat DRGs.

CONCLUSIONS AND INFERENCES

ZBTB20 mediates stress-induced VH via activating NF-κB/TRP channel pathway in nociceptive sensory neurons.

Epigenetic Connections of the TRPA1 Ion Channel in Pain Transmission and Neurogenic Inflammation - a Therapeutic Perspective in Migraine?

Persistent reprogramming of epigenetic pattern leads to changes in gene expression observed in many neurological disorders. Transient receptor potential cation channel subfamily A member 1 (TRPA1), a member of the TRP channels superfamily, is activated by many migraine triggers and expressed in trigeminal neurons and brain regions that are important in migraine pathogenesis. TRP channels change noxious stimuli into pain signals with the involvement of epigenetic regulation. The expression of the TRPA1 encoding gene, TRPA1, is modulated in pain-related syndromes by epigenetic alterations, including DNA methylation, histone modifications, and effects of non-coding RNAs: micro RNAs (miRNAs), long non-coding RNAs, and circular RNAs. TRPA1 may change epigenetic profile of many pain-related genes as it may modify enzymes responsible for epigenetic modifications and expression of non-coding RNAs. TRPA1 may induce the release of calcitonin gene related peptide (CGRP), from trigeminal neurons and dural tissue. Therefore, epigenetic regulation of TRPA1 may play a role in efficacy and safety of anti-migraine therapies targeting TRP channels and CGRP. TRPA1 is also involved in neurogenic inflammation, important in migraine pathogenesis. The fundamental role of TRPA1 in inflammatory pain transmission may be epigenetically regulated. In conclusion, epigenetic connections of TRPA1 may play a role in efficacy and safety of anti-migraine therapy targeting TRP channels or CGRP and they should be further explored for efficient and safe antimigraine treatment. This narrative/perspective review presents information on the structure and functions of TRPA1 as well as role of its epigenetic connections in pain transmission and potential in migraine therapy.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

Glucocorticoid receptor-mediated Nr1d1 chromatin circadian misalignment in stress-induced irritable bowel syndrome

Stress-elevated glucocorticoids cause circadian disturbances and gut-brain axis (GBA) disorders, including irritable bowel syndrome (IBS). We hypothesized that the glucocorticoid receptor (GR/NR3C1) might cause chromatin circadian misalignment in the colon epithelium. We observed significantly decreased core circadian gene Nr1d1 in water avoidance stressed (WAS) BALB/c colon epithelium, like in IBS patients. WAS decreased GR binding at the Nr1d1 promoter E-box (enhancer box), and GR could suppress Nr1d1 via this site. Stress also altered GR binding at the E-box sites along the Ikzf3-Nr1d1 chromatin and remodeled circadian chromatin 3D structures, including Ikzf3-Nr1d1 super-enhancer, Dbp, and Npas2. Intestinal deletion of Nr3c1 specifically abolished these stress-induced transcriptional alternations relevant to IBS phenotypes in BALB/c mice. GR mediated Ikzf3-Nr1d1 chromatin disease related circadian misalignment in stress-induced IBS animal model. This animal model dataset suggests that regulatory SNPs of human IKZF3-NR1D1 transcription through conserved chromatin looping have translational potential based on the GR-mediated circadian-stress crosstalk.

Endocannabinoid signaling and epigenetics modifications in the neurobiology of stress-related disorders

Stress exposure is associated with psychiatric conditions, such as depression, anxiety, and post-traumatic stress disorder (PTSD). It is also a vulnerability factor to developing or reinstating substance use disorder. Stress causes several changes in the neuro-immune-endocrine axis, potentially resulting in prolonged dysfunction and diseases. Changes in several transmitters, including serotonin, dopamine, glutamate, gamma-aminobutyric acid (GABA), glucocorticoids, and cytokines, are associated with psychiatric disorders or behavioral alterations in preclinical studies. Complex and interacting mechanisms make it very difficult to understand the physiopathology of psychiatry conditions; therefore, studying regulatory mechanisms that impact these alterations is a good approach. In the last decades, the impact of stress on biology through epigenetic markers, which directly impact gene expression, is under intense investigation; these mechanisms are associated with behavioral alterations in animal models after stress or drug exposure, for example. The endocannabinoid (eCB) system modulates stress response, reward circuits, and other physiological functions, including hypothalamus-pituitary-adrenal axis activation and immune response. eCBs, for example, act retrogradely at presynaptic neurons, limiting the release of neurotransmitters, a mechanism implicated in the antidepressant and anxiolytic effects after stress. Epigenetic mechanisms can impact the expression of eCB system molecules, which in turn can regulate epigenetic mechanisms. This review will present evidence of how the eCB system and epigenetic mechanisms interact and the consequences of this interaction in modulating behavioral changes after stress exposure in preclinical studies or psychiatric conditions. Moreover, evidence that correlates the involvement of the eCB system and epigenetic mechanisms in drug abuse contexts will be discussed.

New insights into irritable bowel syndrome pathophysiological mechanisms: contribution of epigenetics

Irritable bowel syndrome (IBS) is a complex multifactorial condition including alterations of the gut-brain axis, intestinal permeability, mucosal neuro-immune interactions, and microbiota imbalance. Recent advances proposed epigenetic factors as possible regulators of several mechanisms involved in IBS pathophysiology. These epigenetic factors include biomolecular mechanisms inducing chromosome-related and heritable changes in gene expression regardless of DNA coding sequence. Accordingly, altered gut microbiota may increase the production of metabolites such as sodium butyrate, a prominent inhibitor of histone deacetylases. Patients with IBS showed an increased amount of butyrate-producing microbial phila as well as an altered profile of methylated genes and micro-RNAs (miRNAs). Importantly, gene acetylation as well as specific miRNA profiles are involved in different IBS mechanisms and may be applied for future diagnostic purposes, especially to detect increased gut permeability and visceromotor dysfunctions. In this review, we summarize current knowledge of the role of epigenetics in IBS pathophysiology.

Carcinogenesis and Metastasis: Focus on TRPV1-Positive Neurons and Immune Cells

Both sensory neurons and immune cells, albeit at markedly different levels, express the vanilloid (capsaicin) receptor, Transient Receptor Potential, Vanilloid-1 (TRPV1). Activation of TRPV1 channels in sensory afferent nerve fibers induces local effector functions by releasing neuropeptides (most notably, substance P) which, in turn, trigger neurogenic inflammation. There is good evidence that chronic activation or inactivation of this inflammatory pathway can modify tumor growth and metastasis. TRPV1 expression was also demonstrated in a variety of mammalian immune cells, including lymphocytes, dendritic cells, macrophages and neutrophils. Therefore, the effects of TRPV1 agonists and antagonists may vary depending on the prominent cell type(s) activated and/or inhibited. Therefore, a comprehensive understanding of TRPV1 activity on immune cells and nerve endings in distinct locations is necessary to predict the outcome of therapies targeting TRPV1 channels. Here, we review the neuro-immune modulation of cancer growth and metastasis, with focus on the consequences of TRPV1 activation in nerve fibers and immune cells. Lastly, the potential use of TRPV1 modulators in cancer therapy is discussed.

DNMT1 involved in the analgesic effect of folic acid on gastric hypersensitivity through downregulating ASIC1 in adult offspring rats with prenatal maternal stress

AIMS

Gastric hypersensitivity (GHS) is a characteristic pathogenesis of functional dyspepsia (FD). DNA methyltransferase 1 (DNMT1) and acid-sensing ion channel 1 (ASIC1) are associated with GHS induced by prenatal maternal stress (PMS). The aim of this study was to investigate the mechanism of DNMT1 mediating the analgesic effect of folic acid (FA) on PMS-induced GHS.

METHODS

GHS was quantified by electromyogram recordings. The expression of DNMT1, DNMT3a, DNMT3b, and ASIC1 were detected by western blot, RT-PCR, and double-immunofluorescence. Neuronal excitability and proton-elicited currents of dorsal root ganglion (DRG) neurons were determined by whole-cell patch clamp recordings.

RESULTS

The expression of DNMT1, but not DNMT3a or DNMT3b, was decreased in DRGs of PMS rats. FA alleviated PMS-induced GHS and hyperexcitability of DRG neurons. FA also increased DNMT1 and decreased ASIC1 expression and sensitivity. Intrathecal injection of DNMT1 inhibitor DC-517 attenuated the effect of FA on GHS alleviation and ASIC1 downregulation. Overexpression of DNMT1 with lentivirus not only rescued ASIC1 upregulation and hypersensitivity, but also alleviated GHS and hyperexcitability of DRG neurons induced by PMS.

CONCLUSIONS

These results indicate that increased DNMT1 contributes to the analgesic effect of FA on PMS-induced GHS by reducing ASIC1 expression and sensitivity.

Genome-wide multi-trait analysis of irritable bowel syndrome and related mental conditions identifies 38 new independent variants

BACKGROUND

Irritable bowel syndrome (IBS) is a chronic disorder of gut-brain interaction frequently accompanied by mental conditions, including depression and anxiety. Despite showing substantial heritability and being partly determined by a genetic component, the genetic underpinnings explaining the high rates of comorbidity remain largely unclear and there are no conclusive data on the temporal relationship between them. Exploring the overlapping genetic architecture between IBS and mental conditions may help to identify novel genetic loci and biological mechanisms underlying IBS and causal relationships between them.

METHODS

We quantified the genetic overlap between IBS, neuroticism, depression and anxiety, conducted a multi-trait genome-wide association study (GWAS) considering these traits and investigated causal relationships between them by using the largest GWAS to date.

RESULTS

IBS showed to be a highly polygenic disorder with extensive genetic sharing with mental conditions. Multi-trait analysis of IBS and neuroticism, depression and anxiety identified 42 genome-wide significant variants for IBS, of which 38 are novel. Fine-mapping risk loci highlighted 289 genes enriched in genes upregulated during early embryonic brain development and gene-sets related with psychiatric, digestive and autoimmune disorders. IBS-associated genes were enriched for target genes of anti-inflammatory and antirheumatic drugs, anesthetics and opioid dependence pharmacological treatment. Mendelian-randomization analysis accounting for correlated pleiotropy identified bidirectional causal effects between IBS and neuroticism and depression and causal effects of the genetic liability of IBS on anxiety.

CONCLUSIONS

These findings provide evidence of the polygenic architecture of IBS, identify novel genome-wide significant variants for IBS and extend previous knowledge on the genetic overlap and relationship between gastrointestinal and mental disorders.

Epigenetic mechanisms underlying stress-induced visceral pain: Resilience versus vulnerability in a two-hit model of early life stress and chronic adult stress

BACKGROUND

Women with a history of early life stress (ELS) have a higher risk of developing irritable bowel syndrome (IBS). In addition, chronic stress in adulthood can exacerbate IBS symptoms such as abdominal pain due to visceral hypersensitivity. We previously showed that sex and the predictability of ELS determine whether rats develop visceral hypersensitivity in adulthood. In female rats, unpredictable ELS confers vulnerability and results in visceral hypersensitivity, whereas predictable ELS induces resilience and does not induce visceral hypersensitivity in adulthood. However, this resilience is lost after exposure to chronic stress in adulthood leading to an exacerbation of visceral hypersensitivity. Evidence suggests that changes in histone acetylation at the promoter regions of glucocorticoid receptor (GR) and corticotrophin-releasing factor (CRF) in the central nucleus of the amygdala (CeA) underlie stress-induced visceral hypersensitivity. Here, we aimed to investigate the role of histone acetylation in the CeA on visceral hypersensitivity in a two-hit model of ELS followed by chronic stress in adulthood.

METHODS

Male and female neonatal rats were exposed to unpredictable, predictable ELS, or odor only (no stress control) from postnatal days 8 to 12. In adulthood, rats underwent stereotaxic implantation of indwelling cannulas. Rats were exposed to chronic water avoidance stress (WAS, 1 h/day for 7 days) or SHAM stress and received infusions of vehicle, the histone deacetylase inhibitor trichostatin A (TSA) or the histone acetyltransferase inhibitor garcinol (GAR) after each WAS session. 24 h after the final infusion, visceral sensitivity was assessed and the CeA was removed for molecular experiments.

RESULTS

In the two-hit model (ELS + WAS), female rats previously exposed to predictable ELS, showed a significant reduction in histone 3 lysine 9 (H3K9) acetylation at the GR promoter and a significant increase in H3K9 acetylation at the CRF promoter. These epigenetic changes were associated with changes in GR and CRF mRNA expression in the CeA and an exacerbation of stress-induced visceral hypersensitivity in female animals. TSA infusions in the CeA attenuated the exacerbated stress-induced visceral hypersensitivity, whereas GAR infusions only partially ameliorated ELS+WAS induced visceral hypersensitivity.

CONCLUSION

The two-hit model of ELS followed by WAS in adulthood revealed that epigenetic dysregulation occurs after exposure to stress in two important periods of life and contributes to the development of visceral hypersensitivity. These aberrant underlying epigenetic changes may explain the exacerbation of stress-induced abdominal pain in IBS patients.

Electrophysiology as a Tool to Decipher the Network Mechanism of Visceral Pain in Functional Gastrointestinal Disorders

Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient's life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs.

Activation of goblet cell Piezo1 alleviates mucus barrier damage in mice exposed to WAS by inhibiting H3K9me3 modification

BACKGROUND

Our recent studies found that intestinal mechanical signals can regulate mucus synthesis and secretion of intestinal goblet cells through piezo type mechanosensitive ion channel component 1 (Piezo1), but the detailed molecular mechanisms remain to be investigated. Previous studies using a water avoidance stress (WAS) model reported decreased intestinal mucus accompanied by abnormal intestinal motility. It has also been reported that the expression of mucin2 was negatively correlated with histone H3 lysine 9 trimethylation (H3K9me3), a key regulator of histone methylation, and that mechanical stimulation can affect methylation. In this study, we aimed to determine whether and how Piezo1 expressed on goblet cells regulates mucus barrier function through methylation modification.

METHODS

A murine WAS model was established and treated with Yoda1 (Piezo1 agonist), and specific Piezo1 flox-mucin2 Cre mice were also tested. The mucus layer thickness and mucus secretion rate of mouse colonic mucosa were detected by a homemade horizontal Ussing chamber, intestinal peristaltic contraction was detected by the ink propulsion test and organ bath, goblet cells and mucus layer morphology were assessed by HE and Alcian blue staining, mucus permeability was detected by FISH, and the expression levels of Piezo1, H3K9me3 and related molecules were measured by Western blots and immunofluorescence. LS174T cells were cultured on a shaker board in vitro to simulate mechanical stimulation. Piezo1 and H3K9me3 were inhibited, and changes in mucin2 and methylation-related pathways were detected by ELISAs and Western blots. ChIP-PCR assays were used to detect the binding of H3K9me3 and mucin2 promoters under mechanical stimulation.

RESULTS

Compared with those of the controls, the mucus layer thickness and mucus secretion rate of the mice exposed to WAS were significantly decreased, the mucus permeability increased, the number of goblet cells decreased, and the intestinal contraction and peristalsis were also downregulated and disordered. Intraperitoneal injection of Yoda1 improved mucus barrier function and intestinal contraction. In the colonic mucosa of mice exposed to WAS, Piezo1 was decreased, and histone H3 lysine 9 trimethylation (H3K9me3) and methyltransferase suppressor of variegation 3-9 homolog 1 (SUV39h1) were increased, but activating Piezo1 alleviated these effects of WAS. Piezo1 flox-mucin2 Cre mice showed decreased mucus expression and increased methylation compared to wild-type mice. Cell experiments showed that mechanical stimulation induced the activation of Piezo1, decreased H3K9me3 and SUV39h1, and upregulated mucin2 expression. Inhibition of Piezo1 or H3K9me3 blocked the promoting effect of mechanical stimulation on LS174T mucin2 expression. The binding of H3K9me3 to the mucin2 promoter decreased significantly under mechanical stimulation, but this could be blocked by the Piezo1 inhibitor GsMTx4.

CONCLUSION

Piezo1 mediates mechanical stimulation to inhibit SUV39h1, thereby reducing H3K9me3 production and its binding to the mucin2 promoter, ultimately promoting mucin2 expression in goblet cells. This study further confirmed that piezo1 on goblet cells could regulate mucus barrier function through methylation.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

Gpr83 Tunes Nociceptor Function, Controlling Pain

The function of peripheral nociceptors is frequently tuned by the action of G protein-coupled receptors (GPRs) that are expressed in them, which contribute to pain alteration. Expanding new information on such GPRs and predicting their potential outcomes can help to construct new analgesic strategies based on their modulations. In this context, we attempted to present a new GPR not yet acknowledged for its pain association. Gpr83 exhibits relatively high expressions in the peripheral nervous system compared to other tissues when we mined and reconstructed Gene Expression Omnibus (GEO) metadata, which we confirmed using immunohistochemistry on murine dorsal root ganglia (DRG). When Gpr83 expression was silenced in DRG, neuronal and behavioral nociception were all downregulated. Pathologic pain in hind paw inflammation and chemotherapy-induced peripheral neuropathy were also alleviated by this Gpr83 knockdown. Dependent on exposure time, the application of a known endogenous Gpr83 ligand PEN showed differential effects on nociceptor responses in vitro. Localized PEN administration mitigated pain in vivo, probably following Gq/11-involved GPR downregulation caused by the relatively constant exposure. Collectively, this study suggests that Gpr83 action contributes to the tuning of peripheral pain sensitivity and thus indicates that Gpr83 can be among the potential GPR targets for pain modulation.

Mechanisms of acupuncture-electroacupuncture on inflammatory pain

Acupuncture, as a traditional treatment, has been extensively used in China for thousands of years. According to the World Health Organization (WHO), acupuncture is recommended for the treatment of 77 diseases. And 16 of these diseases are related to inflammatory pain. As a combination of traditional acupuncture and modern electrotherapy, electroacupuncture (EA) has satisfactory analgesic effects on various acute and chronic pain. Because of its good analgesic effects and no side effects, acupuncture has been widely accepted all over the world. Despite the increase in the number of studies, the mechanisms via which acupuncture exerts its analgesic effects have not been conclusively established. A literature review of related research is of great significance to elaborate on its mechanisms and to inform on further research directions. We elucidated on its mechanisms of action on inflammatory pain from two levels: peripheral and central. It includes the mechanisms of acupuncture in the periphery (immune cells and neurons, purinergic pathway, nociceptive ion channel, cannabinoid receptor and endogenous opioid peptide system) and central nervous system (TPRV1, glutamate and its receptors, glial cells, GABAergic interneurons and signaling molecules). In this review, we collected relevant recent studies to systematically explain the mechanisms of acupuncture in treating inflammatory pain, with a view to providing direction for future applications of acupuncture in inflammatory pain and promoting clinical development.

Peripheral mRNA Expression and Prognostic Significance of Emotional Stress Biomarkers in Metastatic Breast Cancer Patients

Emotional stress is believed to be associated with increased tumor progression. Stress-induced epigenetic modifications can contribute to the severity of disease and poor prognosis in cancer patients. The current study aimed to investigate the expression profiles along with the prognostic significance of psychological stress-related genes in metastatic breast cancer patients, to rationalize the molecular link between emotional stress and cancer progression. We profiled the expression of selected stress-associated genes (5-HTT, NR3C1, OXTR, and FKBP5) in breast cancer including the stress evaluation of all participants using the Questionnaire on Distress in Cancer Patients-short form (QSC-R10). A survival database, the Kaplan-Meier Plotter, was used to explore the prognostic significance of these genes in breast cancer. Our results showed relatively low expressions of 5-HTT (p = 0.02) and OXTR (p = 0.0387) in metastatic breast cancer patients as compared to the non-metastatic group of patients. The expression of NR3C1 was low in tumor grade III as compared to grade II (p = 0.04). Additionally, the expression of NR3C1 was significantly higher in patients with positive estrogen receptor status. However, no significant difference was found regarding FKBP5 expression in breast cancer. The results suggest a potential implication of these genes in breast cancer pathology and prognosis.

Molecular Insights into Epigenetics and Cannabinoid Receptors

The actions of cannabis are mediated by G protein-coupled receptors that are part of an endogenous cannabinoid system (ECS). ECS consists of the naturally occurring ligands N-arachidonylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), their biosynthetic and degradative enzymes, and the CB1 and CB2 cannabinoid receptors. Epigenetics are heritable changes that affect gene expression without changing the DNA sequence, transducing external stimuli in stable alterations of the DNA or chromatin structure. Cannabinoid receptors are crucial candidates for exploring their functions through epigenetic approaches due to their significant roles in health and diseases. Epigenetic changes usually promote alterations in the expression of genes and proteins that can be evaluated by various transcriptomic and proteomic analyses. Despite the exponential growth of new evidence on the critical functions of cannabinoid receptors, much is still unknown regarding the contribution of various genetic and epigenetic factors that regulate cannabinoid receptor gene expression. Recent studies have identified several immediate and long-lasting epigenetic changes, such as DNA methylation, DNA-associated histone proteins, and RNA regulatory networks, in cannabinoid receptor function. Thus, they can offer solutions to many cellular, molecular, and behavioral impairments found after modulation of cannabinoid receptor activities. In this review, we discuss the significant research advances in different epigenetic factors contributing to the regulation of cannabinoid receptors and their functions under both physiological and pathological conditions. Increasing our understanding of the epigenetics of cannabinoid receptors will significantly advance our knowledge and could lead to the identification of novel therapeutic targets and innovative treatment strategies for diseases associated with altered cannabinoid receptor functions.

Circadian dysregulation induces alterations of visceral sensitivity and the gut microbiota in Light/Dark phase shift mice

BACKGROUND

It is well-established that several features of modern lifestyles, such as shift work, jet lag, and using electronics at night, disturb normal circadian rhythm and increase the risk of suffering from functional gastrointestinal disease. Although substantial evidence demonstrates that shift work is closely correlated with the symptoms of visceral hypersensitivity, few basic studies have revealed the mechanism of visceral hypersensitivity induced by circadian rhythm disturbance, especially light/dark phase shifts. Our study explored the mechanism underlying visceral hypersensitivity caused by light/dark phase shift in mice.

METHODS

A 6-h delay light/dark phase shift mice model was constructed. Visceral hypersensitivity was assessed by abdominal withdrawal reflex (AWR) score induced by colorectal distention (CRD) in vivo and contraction of colonic muscle strips induced by acetylcholine ex vivo. Intestinal permeability was evaluated by transepithelial resistance (TEER) and FD4 permeability. The expression of tight junction proteins was detected by western blotting and immunofluorescence staining. The gut microbiota was examined by 16S rDNA sequencing. Fecal microbiota transplantation (FMT) was performed to confirm the relationship between the light/dark phase shift, gut microbiota, and visceral hypersensitivity.

RESULTS

We found that light/dark phase shift increased visceral sensitivity and disrupted intestinal barrier function, caused low-grade intestinal inflammation. Moreover, we found decreased microbial species richness and diversity and a shift in microbial community with a decreased proportion of Firmicutes and an elevated abundance of Proteobacteria at the phylum level. Besides, after the light/dark phase shift, the microflora was significantly enriched in biosynthesizing tryptophan, steroid hormone, secondary metabolites, lipids, and lipopolysaccharides. Mice that underwent FMT from the light/dark phase shift mice model exhibited higher visceral hypersensitivity and worse barrier function. Dysbiosis induced by light/dark phase shift can be transmitted to the mice pretreated with antibiotics by FMT not only at the aspect of microbiota composition but also at the level of bacterial function.

CONCLUSION

Circadian rhythm disturbance induced by the light/dark phase shift produces visceral hypersensitivity similar to the pathophysiology of IBS through modulating the gut microbiota, which may disrupt intestinal barrier function or induce a low-degree gut inflammation.

Chronic stress increases DNA methylation of the GR promoter in the central nucleus of the amygdala of female rats

The central pathophysiological mechanisms underlying irritable bowel syndrome (IBS), a female-predominant gastrointestinal disorder characterized by abdominal pain and abnormal bowel habits, remain poorly understood. IBS patients often report that chronic stress exacerbates their symptoms. Brain imaging studies have revealed that the amygdala, a stress-responsive brain region, of IBS patients is overactive when compared to healthy controls. Previously, we demonstrated that downregulation of the glucocorticoid receptor (GR) in the central nucleus of the amygdala (CeA) underlies stress-induced visceral hypersensitivity in female rats. In the current study, we aimed to evaluate in the CeA of female rats whether chronic water avoidance stress (WAS) alters DNA methylation of the GR exon 1₇ promoter region, a region homologous to the human GR promoter. As histone deacetylase (HDAC) inhibitors are able to change DNA methylation, we also evaluated whether administration of the HDAC inhibitor trichostatin A (TSA) directly into the CeA prevented WAS-induced increases in DNA methylation of the GR exon 1₇ promoter. We found that WAS increased overall and specific CpG methylation of the GR promoter in the CeA of female rats, which persisted for up to 28 days. Administration of the TSA directly into the CeA prevented these stress-induced changes of DNA methylation at the GR promoter. Our results suggest that, in females, changes in DNA methylation are involved in the regulation of GR expression in the CeA. These changes in DNA methylation may contribute to the central mechanisms responsible for stress-induced visceral hypersensitivity.

Epigenetic modulation of visceral nociception

Epigenetics is a process that alters gene activity or phenotype without any changes in the underlying DNA sequence or genotype. These biological changes may have deleterious effects and can lead to various human diseases. Ongoing research is continuing to illuminate the role of epigenetics in a variety of pathophysiologic processes. Several categories of epigenetic mechanisms have been studied including chromatin remodeling, DNA methylation, histone modification, and non-coding RNA mechanisms. These epigenetic changes can have a long-term effect on gene expression without any underlying changes in the DNA sequences. The underlying pathophysiology of disorders of brain-gut interaction and stress-induced visceral pain are not fully understood and the role of epigenetic mechanisms in these disorders are starting to be better understood. Current work is underway to determine how epigenetics plays a role in the neurobiology of patients with chronic visceral pain and heightened visceral nociception. More recently, both animal models and human studies have shown how epigenetic regulation modulates stress-induced visceral pain. While much more work is needed to fully delineate the mechanistic role of epigenetics in the neurobiology of chronic visceral nociception, the current study by Louwies et al., in Neurogastroenterology and Motility provides additional evidence supporting the involvement of epigenetic alterations in the central nucleus of the amygdala in stress-induced visceral hypersensitivity in rodents.

Role of Epigenetic Mechanisms in Chronic Pain

Pain is an unpleasant but essential-to-life sensation, usually resulting from tissue damage. When pain persists long after the injury has resolved, it becomes pathological. The precise molecular and cellular mechanisms causing the transition from acute to chronic pain are not fully understood. A key aspect of pain chronicity is that several plasticity events happen along the neural pathways involved in pain. These long-lasting adaptive changes are enabled by alteration in the expression of relevant genes. Among the different modulators of gene transcription in adaptive processes in the nervous system, epigenetic mechanisms play a pivotal role. In this review, I will first outline the main classes of epigenetic mediators and then discuss their implications in chronic pain.

Somatosensory Profiles Differentiate Pain and Psychophysiological Symptoms Among Young Adults With Irritable Bowel Syndrome: A Cluster Analysis

OBJECTIVE

The aim of this study was to investigate if somatosensory profiles can differentiate pain and psychophysiological symptoms among young adults with irritable bowel syndrome (IBS).

METHODS

We performed a cluster analysis of data collected from a randomized clinical trial of 80 IBS patients and 21 age-matched healthy controls (HCs) to stratify pain and symptoms among young adults with IBS by their peripheral sensory profiles. Data of quantitative sensory testing and IBS-related pain and symptoms were collected at baseline and 6-week and 12-week follow-ups.

RESULTS

Using the K-means method, IBS patients were classified into 2 clusters, the "IBS normal threshold" (IBS-NT) and the "IBS increased threshold" (IBS-IT). The IBS-NT cluster had a similar pain threshold as the HCs, and the IBS-IT cluster had an increased threshold of somatic pain perception (lower cold pain threshold, higher heat pain threshold, and higher pressure pain threshold, all P<0.001) than HCs. Compared with the IBS-NT cluster, the IBS-IT cluster reported higher levels of IBS-related pain intensity, anxiety, fatigue, and sleep disturbance over the 3 visits (all P<0.05).

DISCUSSION

Young adults with IBS fell into 2 clusters, one with a similar sensory threshold as the HCs and another with an increased pain threshold, who reported higher pain intensity and more severe symptoms. Somatic sensory profiles should be integrated into further personalized self-management intervention among patients with IBS.

The Microbiome and Gut Endocannabinoid System in the Regulation of Stress Responses and Metabolism

The endocannabinoid system, with its receptors and ligands, is present in the gut epithelium and enteroendocrine cells, and is able to modulate brain functions, both indirectly through circulating gut-derived factors and directly through the vagus nerve, finally acting on the brain’s mechanisms regarding metabolism and behavior. The gut endocannabinoid system also regulates gut motility, permeability, and inflammatory responses. Furthermore, microbiota composition has been shown to influence the activity of the endocannabinoid system. This review examines the interaction between microbiota, intestinal endocannabinoid system, metabolism, and stress responses. We hypothesize that the crosstalk between microbiota and intestinal endocannabinoid system has a prominent role in stress-induced changes in the gut-brain axis affecting metabolic and mental health. Inter-individual differences are commonly observed in stress responses, but mechanisms underlying resilience and vulnerability to stress are far from understood. Both gut microbiota and the endocannabinoid system have been implicated in stress resilience. We also discuss interventions targeting the microbiota and the endocannabinoid system to mitigate metabolic and stress-related disorders.

Chronic psychological stress alters gene expression in rat colon epithelial cells promoting chromatin remodeling, barrier dysfunction and inflammation

Chronic stress is commonly associated with enhanced abdominal pain (visceral hypersensitivity), but the cellular mechanisms underlying how chronic stress induces visceral hypersensitivity are poorly understood. In this study, we examined changes in gene expression in colon epithelial cells from a rat model using RNA-sequencing to examine stress-induced changes to the transcriptome. Following chronic stress, the most significantly up-regulated genes included Atg16l1, Coq10b, Dcaf13, Nat2, Ptbp2, Rras2, Spink4 and down-regulated genes including Abat, Cited2, Cnnm2, Dab2ip, Plekhm1, Scd2, and Tab2. The primary altered biological processes revealed by network enrichment analysis were inflammation/immune response, tissue morphogenesis and development, and nucleosome/chromatin assembly. The most significantly down-regulated process was the digestive system development/function, whereas the most significantly up-regulated processes were inflammatory response, organismal injury, and chromatin remodeling mediated by H3K9 methylation. Furthermore, a subpopulation of stressed rats demonstrated very significantly altered gene expression and transcript isoforms, enriched for the differential expression of genes involved in the inflammatory response, including upregulation of cytokine and chemokine receptor gene expression coupled with downregulation of epithelial adherens and tight junction mRNAs. In summary, these findings support that chronic stress is associated with increased levels of cytokines and chemokines, their downstream signaling pathways coupled to dysregulation of intestinal cell development and function. Epigenetic regulation of chromatin remodeling likely plays a prominent role in this process. Results also suggest that super enhancers play a primary role in chronic stress-associated intestinal barrier dysfunction.

Microbiota and Pain: Save Your Gut Feeling

Recently, a growing body of evidence has emerged regarding the interplay between microbiota and the nervous system. This relationship has been associated with several pathological conditions and also with the onset and regulation of pain. Dysregulation of the axis leads to a huge variety of diseases such as visceral hypersensitivity, stress-induced hyperalgesia, allodynia, inflammatory pain and functional disorders. In pain management, probiotics have shown promising results. This narrative review describes the peripheral and central mechanisms underlying pain processing and regulation, highlighting the role of the gut-brain axis in the modulation of pain. We summarized the main findings in regard to the stress impact on microbiota’s composition and its influence on pain perception. We also focused on the relationship between gut microbiota and both visceral and inflammatory pain and we provided a summary of the main evidence regarding the mechanistic effects and probiotics use.

Leptin promoter methylation in female patients with painful multisomatoform disorder and chronic widespread pain

Background

Different functional somatic syndromes (FSS), fibromyalgia (FMS) and other unexplained painful conditions share many common clinical traits and are characterized by troubling and functionally disabling somatic symptoms. Chronic pain is most frequently reported and at the center of patients’ level of disease burden. The construct of multisomatoform disorder (MSD) allows to subsume severely impaired patients suffering from FSS, FMS and other unexplained painful conditions to be examined for common underlying processes. Altered leptin levels and a pathological response of the HPA-axis as a result of chronic stress and childhood trauma have been suggested as one of the driving factors of disease development and severity. Previous studies have demonstrated that methylation of the leptin promoter can play a regulatory role in addiction. In this study, we hypothesized that methylation of the leptin promoter is influenced by the degree of childhood traumatization and differs between patients with MSD and controls. A cohort of 151 patients with MSD and 149 matched healthy volunteers were evaluated using clinical and psychometric assessment while methylation level analysis of the leptin promoter was performed using DNA isolated from whole blood.

Results

In female controls, we found CpG C-167 to be negatively correlated with leptin levels, whereas in female patients CpG C-289, C-255, C-193, C-167 and methylation cluster (C-291 to C-167) at putative bindings sites for transcription factors Sp1 and c/EBPalpha were negatively correlated with leptin levels. Methylation levels were significantly lower in female patients CpG C-289 compared with controls. When looking at female patients with chronic widespread pain methylation levels were significantly lower at CpG C-289, C-255 and methylation cluster (C-291 to C-167).

Conclusion

Our findings support the hypothesis that epigenetic regulation of leptin plays a role in the regulation of leptin levels in patients with MSD. This effect is more pronounced in patients with chronic widespread pain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01235-5.

A history of childhood maltreatment is associated with altered DNA methylation levels of DNA methyltransferase 1 in maternal but not neonatal mononuclear immune cells

Childhood maltreatment (CM) is associated with alterations in DNA methylation (DNAm) especially in stress response genes. Due to the higher risk of overall health complications of individuals with a parental history of CM, intergenerational transmission of CM-associated DNAm changes has been investigated but remains unclear. In this study, we investigated if different severities of CM have any influence on the DNAm of DNA methyltransferase 1 (DNMT1), an important enzyme of the DNAm machinery, in immune and buccal cells of mother-newborn dyads. DNAm was assessed by mass spectrometry using immune cell DNA from mothers (N = 117) and their newborns (N = 113), and buccal cell DNA of mother-newborn dyads (N = 68 each). Mothers with a history of CM had lower mean methylation of DNMT1 in immune cells compared to the mothers without a CM history. CM status only influenced maternal DNMT1 gene expression when at least moderate CM was reported. Buccal cell DNAm was not associated with CM status. Maternal history of CM was not linked to any alterations in DNMT1 mean DNAm in any of the cell types studied in newborns. We conclude that the CM-associated alterations in DNMT1 DNAm might point to allostatic load and can be physiologically relevant, especially in individuals with more severe CM experiences, resulting in an activated DNA methylation machinery that might influence stress response genes. Our lack of significant findings in buccal cells shows the tissue-specific effects of CM on DNAm. In our sample with low to moderate maternal CM history, there was no intergenerational transmission of DNMT1 DNAm in newborns.

Stress-induced visceral pain in female rats is associated with epigenetic remodeling in the central nucleus of the amygdala

Stress and anxiety contribute to the pathophysiology of irritable bowel syndrome (IBS), a female-predominant disorder of the gut-brain axis, characterized by abdominal pain due to heightened visceral sensitivity. In the current study, we aimed to evaluate in female rats whether epigenetic remodeling in the limbic brain, specifically in the central nucleus of the amygdala (CeA), is a contributing factor in stress-induced visceral hypersensitivity. Our results showed that 1 h exposure to water avoidance stress (WAS) for 7 consecutive days decreased histone acetylation at the GR promoter and increased histone acetylation at the CRH promoter in the CeA. Changes in histone acetylation were mediated by the histone deacetylase (HDAC) SIRT-6 and the histone acetyltransferase CBP, respectively. Administration of the HDAC inhibitor trichostatin A (TSA) into the CeA prevented stress-induced visceral hypersensitivity through blockade of SIRT-6 mediated histone acetylation at the GR promoter. In addition, HDAC inhibition within the CeA prevented stress-induced histone acetylation of the CRH promoter. Our results suggest that, in females, epigenetic modifications in the limbic brain regulating GR and CRH expression contribute to stress-induced visceral hypersensitivity and offer a potential explanation of how stress can trigger symptoms in IBS patients.

DNA Methylation Changes in Fibromyalgia Suggest the Role of the Immune-Inflammatory Response and Central Sensitization

Fibromyalgia (FM) has been explained as a result of gene-environment interactions. The present study aims to verify DNA methylation differences in eleven candidate genome regions previously associated to FM, evaluating DNA methylation patterns as potential disease biomarkers. DNA methylation was analyzed through bisulfite sequencing, comparing 42 FM women and their 42 healthy sisters. The associations between the level of methylation in these regions were further explored through a network analysis. Lastly, a logistic regression model investigated the regions potentially associated with FM, when controlling for sociodemographic variables and depressive symptoms. The analysis highlighted significant differences in the GCSAML region methylation between patients and controls. Moreover, seventeen single CpGs, belonging to other genes, were significantly different, however, only one cytosine related to GCSAML survived the correction for multiple comparisons. The network structure of methylation sites was different for each group; GRM2 methylation represented a central node only for FM patients. Logistic regression revealed that depressive symptoms and DNA methylation in the GRM2 region were significantly associated with FM risk. Our study encourages better exploration of GCSAML and GRM2 functions and their possible role in FM affecting immune, inflammatory response, and central sensitization of pain.

Estrogen and serotonin enhance stress-induced visceral hypersensitivity in female rats by up-regulating brain-derived neurotrophic factor in spinal cord

BACKGROUND

We previously reported that female offspring of dams subjected to chronic prenatal stress (CPS) develop enhanced visceral hypersensitivity (VHS) following exposure to chronic stress in adult life that is mediated by up-regulation of spinal cord BDNF. The aims of this study were to examine the roles of estrogen receptor alpha (ERα) and an increase in spinal serotonin signaling in promoting this enhanced VHS in female rats and up-regulation of spinal cord BDNF transcription.

METHODS

Pregnant dams were exposed to chronic stress from E11 until delivery. At 8 weeks, a chronic adult stress (CAS) protocol was applied for nine days.

KEY RESULTS

Ovariectomy before CAS or treatment with letrozole before and during CAS significantly prevented the development of enhanced VHS in female CPS+CAS rats. Intrathecal application of ERα siRNA significantly reduced VHS, decreased lumbar-sacral spinal cord expression of both ERα and BDNF, and reversed pro-transcriptional epigenetic modifications at BDNF promoter lX. Cerebrospinal fluid serotonin levels and 5HT3A receptor expression in the LS spinal cord were both significantly increased in female CPS+CAS rats. During CAS, intrathecal infusion of alosetron significantly decreased VHS, reduced BDNF and ERα expression in the LS spinal cord, and attenuated RNA pol II and ERα binding to the BNDF core promoter IX.

CONCLUSIONS & INFERENCES

Serotonin-mediated activation of 5HT3A receptors in the spinal cord drives the development of enhanced female-specific VHS in our two hit CPS+CAS through up-regulation of spinal cord ERα.

Histone post-translational modifications as potential therapeutic targets for pain management

Effective pharmacological management of pain associated with tissue pathology is an unmet medical need. Transcriptional modifications in nociceptive pathways are pivotal for the development and the maintenance of pain associated with tissue damage. Accumulating evidence has shown the importance of the epigenetic control of transcription in nociceptive pathways via histone post-translational modifications (PTMs). Hence, histone PTMs could be targets for novel effective analgesics. Here, we discuss the current understanding of histone PTMs in the modulation of gene expression affecting nociception and pain phenotypes following tissue injury. We also provide a critical view of the translational implications of preclinical models and discuss opportunities and challenges of targeting histone PTMs to relieve pain in clinically relevant tissue injuries.

A novel strategy for treating cancer: understanding the role of Ca2+ signaling from nociceptive TRP channels in regulating cancer progression

Cancer is an aging-associated disease and caused by genomic instability that is driven by the accumulation of mutations and epimutations in the aging process. Although Ca²⁺ signaling, reactive oxygen species (ROS) accumulation, DNA damage response (DDR) and senescence inflammation response (SIR) are processed during genomic instability, the underlying mechanism for the cause of genomic instability and cancer development is still poorly understood and needs to be investigated. Nociceptive transient receptor potential (TRP) channels, which firstly respond to environmental stimuli, such as microbes, chemicals or physical injuries, potentiate regulation of the aging process by Ca²⁺ signaling. In this review, the authors provide an explanation of the dual role of nociceptive TRP channels in regulating cancer progression, initiating cancer progression by aging-induced genomic instability, and promoting malignancy by epigenetic regulation. Thus, therapeutically targeting nociceptive TRP channels seems to be a novel strategy for treating cancers.

Advances in TRP channel drug discovery: from target validation to clinical studies

Transient receptor potential (TRP) channels are multifunctional signalling molecules with many roles in sensory perception and cellular physiology. Therefore, it is not surprising that TRP channels have been implicated in numerous diseases, including hereditary disorders caused by defects in genes encoding TRP channels (TRP channelopathies). Most TRP channels are located at the cell surface, which makes them generally accessible drug targets. Early drug discovery efforts to target TRP channels focused on pain, but as our knowledge of TRP channels and their role in health and disease has grown, these efforts have expanded into new clinical indications, ranging from respiratory disorders through neurological and psychiatric diseases to diabetes and cancer. In this Review, we discuss recent findings in TRP channel structural biology that can affect both drug development and clinical indications. We also discuss the clinical promise of novel TRP channel modulators, aimed at both established and emerging targets. Last, we address the challenges that these compounds may face in clinical practice, including the need for carefully targeted approaches to minimize potential side-effects due to the multifunctional roles of TRP channels.

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.

The Role of Epigenomic Regulatory Pathways in the Gut-Brain Axis and Visceral Hyperalgesia

The gut-brain axis (GBA) is broadly accepted to describe the bidirectional circuit that links the gastrointestinal tract with the central nervous system (CNS). Interest in the GBA has grown dramatically over past two decades along with advances in our understanding of the importance of the axis in the pathophysiology of numerous common clinical disorders including mood disorders, neurodegenerative disease, diabetes mellitus, non-alcohol fatty liver disease (NAFLD) and enhanced abdominal pain (visceral hyperalgesia). Paralleling the growing interest in the GBA, there have been seminal developments in our understanding of how environmental factors such as psychological stress and other extrinsic factors alter gene expression, primarily via epigenomic regulatory mechanisms. This process has been driven by advances in next-generation multi-omics methods and bioinformatics. Recent reviews address various components of GBA, but the role of epigenomic regulatory pathways in chronic stress-associated visceral hyperalgesia in relevant regions of the GBA including the amygdala, spinal cord, primary afferent (nociceptive) neurons, and the intestinal barrier has not been addressed. Rapidly developing evidence suggests that intestinal epithelial barrier dysfunction and microbial dysbiosis play a potentially significant role in chronic stress-associated visceral hyperalgesia in nociceptive neurons innervating the lower intestine via downregulation in intestinal epithelial cell tight junction protein expression and increase in paracellular permeability. These observations support an important role for the regulatory epigenome in the development of future diagnostics and therapeutic interventions in clinical disorders affecting the GBA.

Chronic restraint stress impairs cognition via modulating HDAC2 expression

Background

To investigate the effects of chronic restraint stress on cognition and the probable molecular mechanism in mice.

Methods

In the current work, a restraining tube was used as a way to induce chronic stress in mice. The protein levels were determined with ELISA and western blot. A series of behavior tests, including the Morris water maze, elevated plus maze, open field test, and novel object recognition test, were also performed to examine the anxiety and the ability of learning and memory. Moreover, murine neuroblastoma N2a cells were used to confirm the findings from mice under chronic stress.

Results

Decreased synaptic functions were impaired in chronic stress with the downregulation of PSD95, GluR-1, the neurotrophic factor BDNF, and immediate-onset genes Arc and Egr. Chronic restraint decreased the histone acetylation level in hippocampal neurons while HDAC2 was increased and was co-localized with glucocorticoid receptors. Moreover, chronic stress inhibited the PI3K/AKT signaling pathway and induced energy metabolism dysfunctions.

Conclusion

This work examining the elevated levels of HDAC2 in the hippocampus may provide new insights and targets for drug development for treating many neurodegenerative diseases.

Epigenetic upregulation of acid-sensing ion channel 1 contributes to gastric hypersensitivity in adult offspring rats with prenatal maternal stress

Functional dyspepsia is a common functional gastrointestinal disorder. Gastric hypersensitivity (GHS) is a hallmark of this disorder, but the cellular mechanisms remain largely unknown. Stressors during gestational period could have effects on the offspring's tissue structure and function, which may predispose to gastrointestinal diseases. The aim of this study was to test whether prenatal maternal stress (PMS) induces GHS and to investigate role of acid-sensing ion channel (ASIC)/nuclear factor-κB (NF-κB) signaling by examining Asic1 methylation status in adult offspring rats. Gastric hypersensitivity in response to gastric distension was examined by electromyography recordings. Changes in neuronal excitability were determined by whole-cell patch-clamp recording techniques. Demethylation of CpG islands of Asic1 was determined by methylation-specific PCR and bisulfite sequencing assay. Prenatal maternal stress produced GHS in adult offspring rats. Treatment with amiloride, an inhibitor of ASICs, significantly attenuated GHS and reversed hyperexcitability of gastric-specific dorsal root ganglion (DRG) neurons labeled by the dye DiI. Expression of ASIC1 and NF-κBp65 was markedly enhanced in T7 to T10 DRGs. Furthermore, PMS led to a significant demethylation of CpG islands in the Asic1 promoter. A chromatin immunoprecipitation assay showed that PMS also enhanced the ability of NF-κBp65 to bind the promoter of Asic1 gene. Blockade of NF-κB using lentiviral-p65shRNA reversed upregulation of ASIC1 expression, GHS, and the hyperexcitability of DRG neurons. These data suggest that upregulation of ASIC1 expression is attributed to Asic1 promoter DNA demethylation and NF-κB activation, and that the enhanced interaction of the Asic1 and NF-κBp65 contributes to GHS induced by PMS.

Sexual dimorphic role of the glucocorticoid receptor in chronic muscle pain produced by early-life stress

Fibromyalgia and other chronic musculoskeletal pain syndromes are associated with stressful early life events, which can produce a persistent dysregulation in the hypothalamic-pituitary adrenal (HPA) stress axis function, associated with elevated plasm levels of corticosterone in adults. To determine the contribution of the HPA axis to persistent muscle hyperalgesia in adult rats that had experienced neonatal limited bedding (NLB), a form of early-life stress, we evaluated the role of glucocorticoid receptors on muscle nociceptors in adult NLB rats. In adult male and female NLB rats, mechanical nociceptive threshold in skeletal muscle was significantly lower than in adult control (neonatal standard bedding) rats. Furthermore, adult males and females that received exogenous corticosterone (via dams’ milk) during postnatal days 2–9, displayed a similar lowered mechanical nociceptive threshold. To test the hypothesis that persistent glucocorticoid receptor signaling in the adult contributes to muscle hyperalgesia in NLB rats, nociceptor expression of glucocorticoid receptor (GR) was attenuated by spinal intrathecal administration of an oligodeoxynucleotide (ODN) antisense to GR mRNA. In adult NLB rats, GR antisense markedly attenuated muscle hyperalgesia in males, but not in females. These findings indicate that increased corticosterone levels during a critical developmental period (postnatal days 2–9) produced by NLB stress induces chronic mechanical hyperalgesia in male and female rats that persists in adulthood, and that this chronic muscle hyperalgesia is mediated, at least in part, by persistent stimulation of glucocorticoid receptors on sensory neurons, in the adult male, but not female rat.