Sirtuin 3 Mediated by Spinal cMyc-Enhancer of Zeste Homology 2 Pathway Plays an Important Role in Human Immunodeficiency Virus-Related Neuropathic Pain Model

BACKGROUND

Clinical data demonstrate that chronic use of opioid analgesics increases neuropathic pain in people living with human immunodeficiency virus (HIV). Therefore, it is important to elucidate the molecular mechanisms of HIV-related chronic pain. In this study, we investigated the role of the transcription factor cMyc, epigenetic writer enhancer of zeste homology 2 (EZH2), and sirtuin 3 (Sirt3) pathway in HIV glycoprotein gp120 with morphine (gp120M)-induced neuropathic pain in rats.

METHODS

Neuropathic pain was induced by intrathecal administration of recombinant gp120 with morphine. Mechanical withdrawal threshold was measured using von Frey filaments, and thermal latency using the hotplate test. Spinal expression of cMyc, EZH2, and Sirt3 were measured using Western blots. Antinociceptive effects of intrathecal administration of antisense oligodeoxynucleotide against cMyc, a selective inhibitor of EZH2, or recombinant Sirt3 were tested.

RESULTS

In the spinal dorsal horn, gp120M upregulated expression of cMyc (ratio of gp120M versus control, 1.68 ± 0.08 vs 1.00 ± 0.14, P = .0132) and EZH2 (ratio of gp120M versus control, 1.76 ± 0.05 vs 1.00 ± 0.16, P = .006), and downregulated Sirt3 (ratio of control versus gp120M, 1.00 ± 0.13 vs 0.43 ± 0.10, P = .0069) compared to control. Treatment with intrathecal antisense oligodeoxynucleotide against cMyc, GSK126 (EZH2 selective inhibitor), or recombinant Sirt3 reduced mechanical allodynia and thermal hyperalgesia in this gp120M pain model. Knockdown of cMyc reduced spinal EZH2 expression in gp120M treated rats. Chromatin immunoprecipitation (ChIP) assay showed that enrichment of cMyc binding to the ezh2 gene promoter region was increased in the gp120M-treated rat spinal dorsal horn, and that intrathecal administration of antisense ODN against cMyc (AS-cMyc) reversed the increased enrichment of cMyc. Enrichment of trimethylation of histone 3 on lysine residue 27 (H3K27me3; an epigenetic mark associated with the downregulation of gene expression) binding to the sirt3 gene promoter region was upregulated in the gp120M-treated rat spinal dorsal horn; that intrathecal GSK126 reversed the increased enrichment of H3K27me3 in the sirt3 gene promoter. Luciferase reporter assay demonstrated that cMyc mediated ezh2 gene transcription at the ezh2 gene promoter region, and that H3K27me3 silenced sirt3 gene transcription at the gene promoter region.

CONCLUSION

These results demonstrated that spinal Sirt3 decrease in gp120M-induced neuropathic pain was mediated by cMyc-EZH2/H3K27me3 activity in an epigenetic manner. This study provided new insight into the mechanisms of neuropathic pain in HIV patients with chronic opioids.

Chronic pain recruits hypothalamic dynorphin/kappa opioid receptor signalling to promote wakefulness and vigilance

Increased vigilance in settings of potential threats or in states of vulnerability related to pain is important for survival. Pain disrupts sleep and conversely, sleep disruption enhances pain, but the underlying mechanisms remain unknown. Chronic pain engages brain stress circuits and increases secretion of dynorphin, an endogenous ligand of the kappa opioid receptor (KOR). We therefore hypothesized that hypothalamic dynorphin/KOR signalling may be a previously unknown mechanism that is recruited in pathological conditions requiring increased vigilance. We investigated the role of KOR in wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep in freely moving naïve mice and in mice with neuropathic pain induced by partial sciatic nerve ligation using EEG/EMG recordings. Systemic continuous administration of U69,593, a KOR agonist, over 5 days through an osmotic minipump decreased the amount of NREM and REM sleep and increased sleep fragmentation in naïve mice throughout the light-dark sleep cycle. We used KORcre mice to selectively express a Gi-coupled designer receptor activated by designer drugs (Gi-DREADD) in KORcre neurons of the hypothalamic paraventricular nucleus, a key node of the hypothalamic-pituitary-adrenal stress response. Sustained activation of Gi-DREADD with clozapine-N-oxide delivered in drinking water over 4 days, disrupted sleep in these mice in a similar way as systemic U69,593. Mice with chronic neuropathic pain also showed disrupted NREM and total sleep that was normalized by systemic administration of two structurally different KOR antagonists, norbinaltorphimine and NMRA-140, currently in phase II clinical development, or by CRISPR/Cas9 editing of paraventricular nucleus KOR, consistent with endogenous KOR activation disrupting sleep in chronic pain. Unexpectedly, REM sleep was diminished by either systemic KOR antagonist or by CRISPR/Cas9 editing of paraventricular nucleus KOR in sham-operated mice. Our findings reveal previously unknown physiological and pathophysiological roles of dynorphin/KOR in eliciting arousal. Physiologically, dynorphin/KOR signalling affects transitions between sleep stages that promote REM sleep. Furthermore, while KOR antagonists do not promote somnolence in the absence of pain, they normalized disrupted sleep in chronic pain, revealing a pathophysiological role of KOR signalling that is selectively recruited to promote vigilance, increasing chances of survival. Notably, while this mechanism is likely beneficial in the short-term, disruption of the homeostatic need for sleep over longer periods may become maladaptive resulting in sustained pain chronicity. A novel approach for treatment of chronic pain may thus result from normalization of chronic pain-related sleep disruption by KOR antagonism.

Dysregulation of serum prolactin links the hypothalamus with female nociceptors to promote migraine

Migraine headache results from activation of meningeal nociceptors, however, the hypothalamus is activated many hours before the emergence of pain. How hypothalamic neural mechanisms may influence trigeminal nociceptor function remains unknown. Stress is a common migraine trigger that engages hypothalamic dynorphin/kappa opioid receptor (KOR) signalling and increases circulating prolactin. Prolactin acts at both long and short prolactin receptor isoforms that are expressed in trigeminal afferents. Following downregulation of the prolactin receptor long isoform, prolactin signalling at the prolactin receptor short isoform sensitizes nociceptors selectively in females. We hypothesized that stress may activate the kappa opioid receptor on tuberoinfundibular dopaminergic neurons to increase circulating prolactin leading to female-selective sensitization of trigeminal nociceptors through dysregulation of prolactin receptor isoforms. A mouse two-hit hyperalgesic priming model of migraine was used. Repeated restraint stress promoted vulnerability (i.e. first-hit priming) to a subsequent subthreshold (i.e. second-hit) stimulus from inhalational umbellulone, a TRPA1 agonist. Periorbital cutaneous allodynia served as a surrogate of migraine-like pain. Female and male KORCre; R26lsl-Sun1-GFP mice showed a high percentage of KORCre labelled neurons co-localized in tyrosine hydroxylase-positive cells in the hypothalamic arcuate nucleus. Restraint stress increased circulating prolactin to a greater degree in females. Stress-primed, but not control, mice of both sexes developed periorbital allodynia following inhalational umbellulone. Gi-DREADD activation (i.e. inhibition through Gi-coupled signalling) in KORCre neurons in the arcuate nucleus also increased circulating prolactin and repeated chemogenetic manipulation of these neurons primed mice of both sexes to umbellulone. Clustered regularly interspaced short palindromic repeats-Cas9 deletion of the arcuate nucleus KOR prevented restraint stress-induced prolactin release in female mice and priming from repeated stress episodes in both sexes. Inhibition of circulating prolactin occurred with systemic cabergoline, a dopamine D2 receptor agonist, blocked priming selectively in females. Repeated restraint stress downregulated the prolactin receptor long isoform in the trigeminal ganglia of female mice. Deletion of prolactin receptor in trigeminal ganglia by nasal clustered regularly interspaced short palindromic repeats-Cas9 targeting both prolactin receptor isoforms prevented stress-induced priming in female mice. Stress-induced activation of hypothalamic KOR increases circulating prolactin resulting in trigeminal downregulation of prolactin receptor long and pain responses to a normally innocuous TRPA1 stimulus. These are the first data that provide a mechanistic link between stress-induced hypothalamic activation and the trigeminal nociceptor effectors that produce trigeminal sensitization and migraine-like pain. This sexually dimorphic mechanism may help to explain female prevalence of migraine. KOR antagonists, currently in phase II clinical trials, may be useful as migraine preventives in both sexes, while dopamine agonists and prolactin/ prolactin receptor antibodies may improve therapy for migraine, and other stress-related neurological disorders, in females.

A prolactin-dependent sexually dimorphic mechanism of migraine chronification

OBJECTIVE

Determination of possible sex differences in mechanisms promoting migraine progression and the contribution of prolactin and the prolactin long (PRLR-L) and short (PRLR-S) receptor isoforms.

BACKGROUND

The majority of patients with chronic migraine and medication overuse headache are female. Prolactin is present at higher levels in women and increases migraine. Prolactin signaling at the PRLR-S selectively sensitizes nociceptors in female rodents, while expression of the PRLR-L is protective.

METHODS

Medication overuse headache was modeled by repeated sumatriptan administration in male and female mice. Periorbital and hindpaw cutaneous allodynia served as a surrogate of migraine-like pain. PRLR-L and PRLR-S isoforms were measured in the trigeminal ganglion with western blotting. Possible co-localization of PRLR with serotonin 5HT1B and 5HT1D receptors was determined with RNAscope. Cabergoline, a dopamine receptor agonist that inhibits circulating prolactin, was co-administered with sumatriptan. Nasal administration of CRISPR/Cas9 plasmid was used to edit expression of both PRLR isoforms.

RESULTS

PRLR was co-localized with 5HT1B or 5HT1D receptors in the ophthalmic region of female trigeminal ganglion. A single injection of sumatriptan increased serum PRL levels in female mice. Repeated sumatriptan promoted cutaneous allodynia in both sexes but down-regulated trigeminal ganglion PRLR-L, without altering PRLR-S, only in females. Co-administration of sumatriptan with cabergoline prevented allodynia and down-regulation of PRLR-L only in females. CRISPR/Cas9 editing of both PRLR isoforms in the trigeminal ganglion prevented sumatriptan-induced periorbital allodynia in females.

INTERPRETATION

We identified a sexually dimorphic mechanism of migraine chronification that involves down-regulation of PRLR-L and increased signaling of circulating prolactin at PRLR-S. These studies reveal a previously unrecognized neuroendocrine mechanism linking the hypothalamus to nociceptor sensitization that increases the risk of migraine pain in females and suggest opportunities for novel sex-specific therapies including gene editing through nasal delivery of CRISPR/Cas9 constructs.

Mitochondrial biogenesis factor PGC-1α suppresses spinal morphine tolerance by reducing mitochondrial superoxide

Opioid use disorders (OUDs) have reached an epidemic level in the United States. The opioid epidemic involves illicit opioid use, prescription opioids for analgesia, counterfeit opioids, new psychoactive substances, and diverted opioids. Opioids remain the last option for the treatment of intractable clinical pain, but chronic use of opioids are limited in part due to antinociceptive/analgesic tolerance. Peroxisome proliferator-activated receptor (PPAR)-gamma coactivator-1alpha (PGC-1α), a mitochondrial biogenesis factor can reduce toxic reactive oxygen species (ROS) that play a role in morphine tolerance (MT). Decreased PGC-1α expression has been shown to contribute to various metabolic disorders or neurodegeneration diseases through increasing ROS. We examined the relationship of PGC-1α and ROS in MT. To induce MT, adult Sprague-Dawley rats received intrathecal morphine for 7 days. Mechanical threshold was measured using the von Frey test and thermal latency was examined using the heat plate test. Expression of PGC-1α in the spinal cord dorsal horn (SCDH) was examined using RT-PCR and western blots. Mitochondrial superoxide was detected using MitoSox Red, a mitochondrial superoxide indicator. The antinociceptive effect of recombinant PGC-1α (rPGC-1α) or Mito-Tempol (a mitochondria-targeted superoxide scavenger) was determined using the von Frey test and hot plate test. Furthermore, we examined the effect of rPGC-1α on mitochondrial superoxide using cultured neurons. Our findings include that: (i) spinal MT decreased the expression of spinal PGC-1α in the SCDH neurons; (ii) rPGC-1α increased mechanical threshold and thermal latency in MT animals; (iii) Mito-Tempol reduced MT behavioral response; (iv) rPGC-1α reduced MT-induced mitochondria-targeted superoxide; and (v) cultured neuronal cells treated with TNFα increased mitochondria-targeted superoxide that can be inhibited by rPGC-1α. The present findings suggest that spinal PGC-1α reduce MT through decreasing mitochondria-targeted superoxide in the SCDH.

Activation of ventral tegmental area dopaminergic neurons reverses pathological allodynia resulting from nerve injury or bone cancer

Chronic pain induced by nerve damage due to trauma or invasion of cancer to the bone elicits severe ongoing pain as well as hyperalgesia and allodynia likely reflecting adaptive changes within central circuits that amplify nociceptive signals. The present study explored the possible contribution of the mesolimbic dopaminergic circuit in promoting allodynia related to neuropathic and cancer pain. Mice with ligation of the sciatic nerve or treated with intrafemoral osteosarcoma cells showed allodynia to a thermal stimulus applied to the paw on the injured side. Patch clamp electrophysiology revealed that the intrinsic neuronal excitability of ventral tegmental area (VTA) dopamine neurons projecting to the nucleus accumbens (N.Acc.) was significantly reduced in those mice. We used tyrosine hydroxylase (TH)-cre mice that were microinjected with adeno-associated virus (AAV) to express channelrhodopsin-2 (ChR2) to allow optogenetic stimulation of VTA dopaminergic neurons in the VTA or in their N.Acc. terminals. Optogenetic activation of these cells produced a significant but transient anti-allodynic effect in nerve injured or tumor-bearing mice without increasing response thresholds to thermal stimulation in sham-operated animals. Suppressed activity of mesolimbic dopaminergic neurons is likely to contribute to decreased inhibition of N.Acc. output neurons and to neuropathic or cancer pain-induced allodynia suggesting strategies for modulation of pathological pain states.

MnSOD mediated by HSV vectors in the periaqueductal gray suppresses morphine withdrawal in rats

Morphine appears to be the most active metabolite of heroin; therefore, the effects of morphine are important in understanding the ramifications of heroin abuse. Opioid physical dependence (withdrawal response) may have very long-lasting effects on the motivation for reward, including the incubation of cue-induced drug-seeking behavior. However, the exact mechanisms of morphine withdrawal (MW) are not clear yet, and its treatment remains elusive. Periaqueductal gray (PAG) is one of the important sites in the pathogenesis of MW. Here, we used recombinant herpes simplex virus (HSV) vectors that encode the sod2 gene expressing manganese superoxide dismutase (MnSOD) to evaluate its therapeutic potential in MW. Microinjection of HSV vectors expressing MnSOD into the PAG reduced the MW syndrome. MnSOD vectors suppressed the upregulated mitochondrial superoxide, and endoplasmic reticulum stress markers (glucose-related protein 78 (GRP78) and activating transcription factor 6 alpha (ATF6α)) in the PAG induced by MW. Immunostaining showed that mitochondrial superoxide, GRP78 and ATF6α were colocalized with neuronal nuclei (a neuronal-specific marker), suggesting that they are located in the neurons in the PAG. These results suggest that overexpression of MnSOD by HSV vectors may relieve opioid dependence. This study may provide a novel therapeutic approach to morphine physical withdrawal response.

Molecular Understanding of the Acquisition of Resistance to Anti-cancer Drugs Associated with the Exacerbation of Cancer

Gefitinib and erlotinib target the ATP cleft in the tyrosine kinase EGFR, which is overexpressed in 40-80 percent of non-small-cell lung cancer (NSCLC) and many other epithelial cancers. However, the application of gefitinib is ultimately limited by the emergence of mutations and other molecular mechanisms conferring drug resistance. Furthermore, it has been considered that acquired resistance to gefitinib is associated with a clinically significant risk of accelerated disease progression. We previously established a new gefitinib-resistant NSCLC cell line, HCC827GR, which harbors the T790M mutation. Using HCC827GR, we found that the inhibition of adenosine A2a receptors of NSCLC regulated cancer proliferation and exacerbation, indicating that adenosine A2a receptors may be new targets for a novel strategy in NSCLC therapy. These findings suggest that multilayered crosstalk between G-protein coupled receptors (GPCRs) and EGFR may play an important role in regulating downstream signaling molecules that are implicated in the development of gefitinib-resistant NSCLC.

[Pain and emotional dysregulation: Cellular memory due to pain]

Genetic factors are involved in determinants for the risk of psychiatric disorders, and neurological and neurodegenerative diseases. Chronic pain stimuli and intense pain have effects at a cellular and/or gene expression level, and will eventually induce "cellular memory due to pain", which means that tissue damage, even if only transient, can elicit epigenetically abnormal transcription/translation and post-translational modification in related cells depending on the degree or kind of injury or associated conditions. Such cell memory/transformation due to pain can cause an abnormality in a fundamental intracellular response, such as a change in the three-dimensional structure of DNA, transcription, or translation. On the other hand, pain is a multidimensional experience with sensory-discriminative and motivational-affective components. Recent human brain imaging studies have examined differences in activity in the nucleus accumbens between controls and patients with chronic pain, and have revealed that the nucleus accumbens plays a role in predicting the value of a noxious stimulus and its offset, and in the consequent changes in the motivational state. In this review, we provide a very brief overview of a comprehensive understanding of chronic pain associated with emotional dysregulation due to transcriptional regulation, epigenetic modification and miRNA regulation.

Epigenetic mechanisms of chronic pain

Neuropathic and inflammatory pain promote a large number of persisting adaptations at the cellular and molecular level, allowing even transient tissue or nerve damage to elicit changes in cells that contribute to the development of chronic pain and associated symptoms. There is evidence that injury-induced changes in chromatin structure drive stable changes in gene expression and neural function, which may cause several symptoms, including allodynia, hyperalgesia, anxiety, and depression. Recent findings on epigenetic changes in the spinal cord and brain during chronic pain may guide fundamental advances in new treatments. Here, we provide a brief overview of epigenetic regulation in the nervous system and then discuss the still-limited literature that directly implicates epigenetic modifications in chronic pain syndromes.

Analysis of sleep disorders under pain using an optogenetic tool: possible involvement of the activation of dorsal raphe nucleus-serotonergic neurons

Background

Several etiological reports have shown that chronic pain significantly interferes with sleep. Inadequate sleep due to chronic pain may contribute to the stressful negative consequences of living with pain. However, the neurophysiological mechanism by which chronic pain affects sleep-arousal patterns is as yet unknown. Although serotonin (5-HT) was proposed to be responsible for sleep regulation, whether the activity of 5-HTergic neurons in the dorsal raphe nucleus (DRN) is affected by chronic pain has been studied only infrequently. On the other hand, the recent development of optogenetic tools has provided a valuable opportunity to regulate the activity in genetically targeted neural populations with high spatial and temporal precision. In the present study, we investigated whether chronic pain could induce sleep dysregulation while changing the activity of DRN-5-HTergic neurons. Furthermore, we sought to physiologically activate the DRN with channelrhodopsin-2 (ChR2) to identify a causal role for the DRN-5-HT system in promoting and maintaining wakefulness using optogenetics.

Results

We produced a sciatic nerve ligation model by tying a tight ligature around approximately one-third to one-half the diameter of the sciatic nerve. In mice with nerve ligation, we confirmed an increase in wakefulness and a decrease in non-rapid eye movement (NREM) sleep as monitored by electroencephalogram (EEG). Microinjection of the retrograde tracer fluoro-gold (FG) into the prefrontal cortex (PFC) revealed several retrogradely labeled-cells in the DRN. The key finding of the present study was that the levels of 5-HT released in the PFC by the electrical stimulation of DRN neurons were significantly increased in mice with sciatic nerve ligation. Using optogenetic tools in mice, we found a causal relationship among DRN neuron firing, cortical activity and sleep-to-wake transitions. In particular, the activation of DRN-5-HTergic neurons produced a significant increase in wakefulness and a significant decrease in NREM sleep. The duration of NREM sleep episodes was significantly decreased during photostimulation in these mice.

Conclusions

These results suggest that neuropathic pain accelerates the activity of DRN-5-HTergic neurons. Although further loss-of-function experiments are required, we hypothesize that this activation in DRN neurons may, at least in part, correlate with sleep dysregulation under a neuropathic pain-like state.

[Understanding of the psychiatry in palliative care: dysfunction of the rewarding system under the pain state associated with exacerbating pain]

Recent human brain imaging studies have examined differences in activity in the nucleus accumbens (N.Acc.) in response to heat stimuli between controls and patients with chronic pain, and have revealed that the N.Acc. plays a role in predicting the value of a noxious stimulus and its offset, and in the consequent changes in the motivational state. Nevertheless, the molecular mechanisms of change in the circuitry involved in emotion and motivation in response to chronic pain stimuli were not fully explored. On the other hand, it has been considered that micro RNAs (miRNAs) play important roles as key modulators of post-transcriptional gene expression. We have reported that changes in miRNAs are associated with predicted changes in gene expression of candidate targets in the N.Acc. under neuropathic pain. Therefore, we have introduced a new insight into an epigenetic dysfunction of "mesolimbic motivation/valuation circuitry" under a neuropathic pain-like state. These findings raise intriguing possibilities that miRNA-modulating cellular events along with epigenetic modifications may be associated with neural plasticity and neuronal adaptive responses in mesolimbic motivation/valuation circuitry under which the neuropathic pain may induce negative emotions, exacerbating pain.

Abstract 5349: Aberrant trimethylation of histone H3 lysine 27 is induced by chronic inflammation in mouse colonic epithelial cells, and is involved in the formation of a field for cancerization

A field for cancerization (field defect), where genetic and epigenetic alterations are accumulated in normal-appearing tissues, is involved in human carcinogenesis, especially cancers associated with chronic inflammation. While aberrant DNA methylation is involved in the field defect and induced by chronic inflammation [Ushijima and Hattori, Clin Cancer Res, 2012], it is still unclear for trimethylation of histone H3 lysine 27 (H3K27me3), which is involved in gene repression independent of DNA methylation and functions as a pre-mark for aberrant DNA methylation. In this study, using a mouse colitis model induced by dextran sulfate sodium (DSS), we aimed to clarify whether or not aberrant H3K27me3 is induced by inflammation and involved in a field defect.

Analysis of H3K27me3 levels in colonic epithelial cells by chromatin immunoprecipitation combined with CpG island microarray analysis (ChIP-on-chip analysis) revealed that H3K27me3 levels were increased or decreased for 266 genomic regions by aging, and more extensively (27 increased and 3,782 decreased regions) by colitis. Among the 3,809 regions with alterations by DSS-induced colitis, 212 regions overlapped with those whose alterations were induced by aging. Analysis of the temporal profiles of H3K27me3 levels in the course of DSS treatment revealed that increase or decrease of H3K27me3 was induced as early as two weeks after the initiation of DSS treatment, and persisted at least for 16 weeks, even after the inflammation disappeared. Some of the aberrant H3K27me3 in colonic epithelial cells was carried over into colon tumors. Furthermore, H3K27me3 acquired at Dapk1 by colitis was followed by increased DNA methylation, supporting its function as a pre-mark for aberrant DNA methylation [Takeshima et al., Carcinogenesis, in press]. Regarding mechanisms of aberrant H3K27me3 induction, expression changes of polycomb-related genes including Ezh2, Kdm6a, and Kdm6b, were not involved.

These results demonstrated that aberrant H3K27me3 can be induced by exposure to a specific environment, such as colitis, and suggested that aberrant histone modification, in addition to aberrant DNA methylation, is involved in the formation of a field defect.

Citation Format: Hideyuki Takeshima, Daigo Ikegami, Mika Wakabayashi, Tohru Niwa, Young-Joon Kim, Toshikazu Ushijima. Aberrant trimethylation of histone H3 lysine 27 is induced by chronic inflammation in mouse colonic epithelial cells, and is involved in the formation of a field for cancerization. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5349. doi:10.1158/1538-7445.AM2013-5349

[Role of epigenetic modification in higher brain dysfunction and aging]

Epigenetic mechanisms typically involve heritable alterations in chromatin structure, which, in turn, regulate gene expression. Fundamental insights about epigenetic heritability have come from studies of cell division and development. However, there is increasing evidence that the regulation of chromatin structure through histone modifications and DNA methylation might mediate the expression of key genes involved in acquired chronic disorders. This idea is fascinating because similar mechanisms are used for triggering and storing long-term memories at the cellular level during, for example, higher-brain dysfunction, stress disease, drug dependence, aging, and chronic pain. This review will explore the most current issues in the field of epigenetics, with a focus on next levels of transcriptional mechanisms underlying aging, enriched environment and drug addiction. Epigenetic mechanisms, which are key cellular and molecular processes that integrate diverse environmental stimuli to exert potent and often long-lasting changes in gene expression through the regulation of chromatin structure, contribute to transcriptional and behavioral changes.

Induction of aberrant trimethylation of histone H3 lysine 27 by inflammation in mouse colonic epithelial cells

A field for cancerization (field defect), where genetic and epigenetic alterations are accumulated in normal-appearing tissues, is involved in human carcinogenesis, especially cancers associated with chronic inflammation. Although aberrant DNA methylation is involved in the field defect and induced by chronic inflammation, it is still unclear for trimethylation of histone H3 lysine 27 (H3K27me3), which is involved in gene repression independent of DNA methylation and functions as a pre-mark for aberrant DNA methylation. In this study, using a mouse colitis model induced by dextran sulfate sodium (DSS), we aimed to clarify whether aberrant H3K27me3 is induced by inflammation and involved in a field defect. ChIP-on-chip analysis of colonic epithelial cells revealed that H3K27me3 levels were increased or decreased for 266 genomic regions by aging, and more extensively (23 increased and 3574 decreased regions) by colitis. Such increase or decrease of H3K27me3 was induced as early as 2 weeks after the initiation of DSS treatment, and persisted at least for 16 weeks even after the inflammation disappeared. Some of the aberrant H3K27me3 in colonic epithelial cells was carried over into colon tumors. Furthermore, H3K27me3 acquired at Dapk1 by colitis was followed by increased DNA methylation, supporting its function as a pre-mark for aberrant DNA methylation. These results demonstrated that aberrant H3K27me3 can be induced by exposure to a specific environment, such as colitis, and suggested that aberrant histone modification, in addition to aberrant DNA methylation, is involved in the formation of a field defect.

[Global understanding of pain]

Clinically, it is well-known that chronic pain induces depression, anxiety, and reduced quality of life. Neuropathic pain, which is characterized by spontaneous burning pain, hyperalgesia and allodynia, is the most difficult pain to manage in the pain clinic. However, the complicated pathophysiology of neuropathic pain is not yet understood. A better understanding of its pathophysiology has given us more insight into its various mechanisms and possible treatment options. This review will explore the most current issues in the field of pain, with a focus on transcriptional research, epigenetic research and post-transcriptional research. For a global understanding of the pain, it is necessary to analyze the correlation between these temporal parameters and phenomics.

Hippocampal epigenetic modification at the brain-derived neurotrophic factor gene induced by an enriched environment

Environmental enrichment is an experimental paradigm that increases brain-derived neurotrophic factor (BDNF) gene expression accompanied by neurogenesis in the hippocampus of rodents. In the present study, we investigated whether an enriched environment could cause epigenetic modification at the BDNF gene in the hippocampus of mice. Exposure to an enriched environment for 3-4 weeks caused a dramatic increase in the mRNA expression of BDNF, but not platelet-derived growth factor A (PDGF-A), PDGF-B, vascular endothelial growth factor (VEGF), nerve growth factor (NGF), epidermal growth factor (EGF), or glial fibrillary acidic protein (GFAP), in the hippocampus of mice. Under these conditions, exposure to an enriched environment induced a significant increase in histone H3 lysine 4 (H3K4) trimethylation at the BDNF P3 and P6 promoters, in contrast to significant decreases in histone H3 lysine 9 (H3K9) trimethylation at the BDNF P4 promoter and histone H3 lysine 27 (H3K27) trimethylation at the BDNF P3 and P4 promoters without any changes in the expression of their associated histone methylases and demethylases in the hippocampus. The expression levels of several microRNAs in the hippocampus were not changed by an enriched environment. These results suggest that an enriched environment increases BDNF mRNA expression via sustained epigenetic modification in the mouse hippocampus.

Identification of small molecular compounds and fabrication of its aqueous solution by laser-ablation, expanding primordial cartilage

OBJECTIVE

The discovery of small molecular compounds that expand cartilage is needed. We searched for small molecular compounds that expand cartilage or enhance the actions of bone morphogenetic proteins (BMPs) on cartilage.

DESIGN

Metatarsal primordial cartilage explants prepared from 14.5 days postcoitum (d.p.c.) mouse embryos were organ-cultured in the presence or absence of BMPs and/or 4-(5-Benzol[1,3]dioxol-5-yl-4-pyrldin-2-yl-1H-imidazol-2-yl)-benzamide hydrate (BPIB) and its related molecules. The perichondrium was removed from some of the cartilage explants by partial digestion with collagenase. BPIB aqueous solution was prepared by fragmenting BPIB crystals in water with laser irradiation and then added to cartilage explants in organ culture.

RESULTS

We found that small molecular compounds, BPIB, available as SB431542 from Sigma and its related molecules, expand primordial cartilage explants in organ culture. These molecules are transforming growth factor-β (TGF-β) inhibitors, and the addition of excess TGF-β reduced cartilage expansion induced by these molecules. The co-administration of BPIB and BMPs synergistically expanded cartilage explants. Removal of the perichondrium abolished BIPB-induced cartilage expansion but not BMP-induced cartilage-expansion, suggesting that BPIB, but not BMPs, expands cartilage through the perichondrium. Furthermore, we used the laser-ablation technique to generate BPIB aqueous solution in the presence of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) without the use of hazardous dimethyl sulfoxide (DMSO). The laser-ablation-generated BPIB aqueous solution was more stable, expanded cartilage explants more effectively than BPIB colloidal solution prepared with DMSO, and synergistically enhanced BMP-induced cartilage expansion.

CONCLUSIONS

A small molecular compound, BPIB, expands primordial cartilage explants. A BPIB aqueous solution was created by laser-ablation without using DMSO and proved to be biologically active.

Hippocampal epigenetic modification at the doublecortin gene is involved in the impairment of neurogenesis with aging

Recent research has suggested that epigenetic mechanisms, which exert lasting control over gene expression without altering the genetic code, could mediate stable changes in brain function. A growing body of evidence supports the idea that epigenetic changes play a role in the etiology of aging and its associated brain dysfunction. The present study was undertaken to evaluate the age-related changes in the expression of doublecortin, which is a marker for neuronal precursors, along with epigenetic modification in the hippocampus of aged mice. In the present study, the doublecortin-positive cells were almost completely absent from the dentate gyrus of the hippocampus of 28-month-old mice. Furthermore, the expression level of doublecortin mRNA was significantly decreased in the hippocampus of aged mice. Under these conditions, a significant decrease in H3K4 trimethylation and a significant increase in H3K27 trimethylation at doublecortin promoters were observed with aging without any changes in the expression of their associated histone methylases and demethylases in the hippocampus. These findings suggest that aging produces a dramatic decrease in the expression of doublecortin along with epigenetic modifications in the hippocampus.

Enhanced IL-1beta production in response to the activation of hippocampal glial cells impairs neurogenesis in aged mice

A variety of mechanisms that contribute to the accumulation of age-related damage and the resulting brain dysfunction have been identified. Recently, decreased neurogenesis in the hippocampus has been recognized as one of the mechanisms of age-related brain dysfunction. However, the molecular mechanism of decreased neurogenesis with aging is still unclear. In the present study, we investigated whether aging decreases neurogenesis accompanied by the activation of microglia and astrocytes, which increases the expression of IL-1beta in the hippocampus, and whether in vitro treatment with IL-1beta in neural stem cells directly impairs neurogenesis. Ionized calcium-binding adaptor molecule 1 (Iba1)-positive microglia and glial fibrillary acidic protein (GFAP)-positive astrocytes were increased in the dentate gyrus of the hippocampus of 28-month-old mice. Furthermore, the mRNA level of IL-1beta was significantly increased without related histone modifications. Moreover, a significant increase in lysine 9 on histone H3 (H3K9) trimethylation at the promoter of NeuroD (a neural progenitor cell marker) was observed in the hippocampus of aged mice. In vitro treatment with IL-1beta in neural stem cells prepared from whole brain of E14.5 mice significantly increased H3K9 trimethylation at the NeuroD promoter. These findings suggest that aging may decrease hippocampal neurogenesis via epigenetic modifications accompanied by the activation of microglia and astrocytes with the increased expression of IL-1beta in the hippocampus.

Epigenetic modulation at the CCR2 gene correlates with the maintenance of behavioral sensitization to methamphetamine

The intermittent administration of methamphetamine produces behavioral sensitization to methamphetamine. In the limbic forebrain, mainly including the nucleus accumbens, of mice that had been intermittently treated with methamphetamine, we found a significant increase in mRNA of a chemokine, CCR2. This increase was accompanied by a significant increase in histone H3 lysine 4 (H3K4) trimethylation at its promoter. Interestingly, the maintenance of sensitization to methamphetamine-induced hyperlocomotion was significantly decreased in CCR2 knockout mice. These findings suggest that increased CCR2 associated with epigenetic modification after the intermittent administration of methamphetamine may be associated with the maintenance of sensitization to methamphetamine-induced hyperlocomotion.

Hyperactivity in novel environment with increased dopamine and impaired novelty preference in apoptosis signal-regulating kinase 1 (ASK1)-deficient mice

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein (MAP) kinase kinase kinase family member, which induces apoptosis in various cells through JNK and p38 MAP kinase cascades. In addition to apoptosis signaling, a number of recent in vitro studies have suggested that ASK1 may play roles in neural function. However, the behavioral significance of ASK1 has remained unclear. Here, we subjected ASK1 (-/-) mice to a battery of behavioral tests and found that they displayed temporary hyperactivity in an open-field test. Activities in the familiar field were normal, indicating that the hyperactivity observed was specific to the novel environment. ASK1 (-/-) mice also exhibited impairment of novelty preference 24h after training and superior performance on the rotarod test. Brain tissue contents of dopamine and 4-dihydroxyphenylacetic acid (DOPAC) were elevated in ASK1 (-/-) mice. Our findings thus demonstrate novel behavioral functions of ASK1, including regulation of locomotor activity, novelty preference, and motor coordination with dopaminergic transmission.

Implication of protein kinase C in the orexin-induced elevation of extracellular dopamine levels and its rewarding effect

In the present study, we investigated the role of orexinergic systems in the activation of midbrain dopamine neurons. In an in vitro study, exposure to either orexin A or orexin B under superfusion conditions produced a transient increase in the intracellular Ca(2+) concentration through the phospholipase C (PLC)/protein kinase C (PKC) pathway via G(q11)alpha or Gbetagamma subunits in midbrain cultured neurons, which were shown to be tyrosine hydroxylase (TH)-positive cells, but not in purified midbrain astrocytes. Here we show that in vivo injection with a selective PKC inhibitor chelerythrine chloride or 2-{8-[(dimethylamino)methyl]-6,7,8,9-tetrahydropyrido[1,2-a]indol-3-yl}-3-1-methyl-1H-indol-3-ylmaleimide HCl (Ro-32-0432) into the ventral tegmental area (VTA) significantly suppressed the place preference and increased levels of dopamine in the nucleus accumbens (NAcc) induced by intra-VTA injection of orexins. These results strongly support the idea that activation of the orexin-containing neuron in the VTA leads to the direct activation of mesolimbic dopamine neurons through the activation of the PLC/PKC pathway via G(q11)alpha or Gbetagamma-subunit activation, which could be associated with the development of its rewarding effect.