Possible involvement of histone acetylation in the development of emotional resistance to stress stimuli in mice

The epigenetic changes are affected by sex and valproic acid treatment in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) presents distinct sex-specific differences in both symptom expression and treatment outcomes, with the underlying biological mechanisms still remain unclear. Epigenetic modifications, particularly histone acetylation, have been increasingly recognized as critical factors in the pathophysiology of PTSD. Valproic acid (VPA), a potent histone deacetylase (HDAC) inhibitor, has shown promise in modulating epigenetic responses and improving therapeutic outcomes is PTSD, though its effect may differ between sexes. This study aimed to explore the sex-specific epigenetic changes in response to trauma and the impact of VPA treatment in a rat model of PTSD induced by predator scent stress. Sprague-Dawley rats of both sexes were randomly assigned to stressed and non-stressed groups and treated with either VPA (100 mg/kg) or vehicle. Anxiety levels were assessed using the elevated plus maze, followed by analysis of histone H3 and H4 acetylation, HDAC activity, and c-fos expression in the hippocampus. Our findings revealed that traumatic stress led to increased freezing time and anxiety levels, with more pronounced effects observed in females. Additionally, we have identified sex-specific differences in hippocampal epigenetic modifications; stressed females exhibited higher H3 acetylation, and VPA-treated stressed males showed increased H4 acetylation These results highlight the importance of considering sex differences in the epigenetic mechanism underlying PTSD and suggest that personalized therapeutic approaches may be necessary to address these complexities.

Trichostatin A, a histone deacetylase inhibitor, alleviates the emotional abnormality induced by maladaptation to stress in mice

Recent reports have implied that aberrant biochemical processes in the brain are frequently accompanied by subtle shifts in the cellular epigenetic profile that might underlie the pathogenic progression of psychiatric disorders. The aim of the present study was to examine the effect of trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, on the emotional abnormality induced by maladaptation to stress in mice. Mice were exposed to repeated restraint stress for 240 min/day for 14 days. We applied dosing schedules. In one schedule, from the 3rd day of stress exposure, mice were treated with TSA (1650 μM/4 μL, i.c.v.) immediately after the daily exposure to restraint stress. In the other schedule, from the 1st day of stress exposure, mice were treated with TSA 2 h before exposure to restraint stress. After the final exposure to restraint stress, the emotionality of mice was evaluated using the hole-board test. Mice that were exposed to restraint stress for 240 min/day for 14 days showed a decrease in head-dipping behavior. This decreased emotionality observed in stress-maladaptive mice was significantly recovered by chronic treatment with TSA 2 h before daily exposure to restraint stress, which confirmed the development of stress adaptation. On the other hand, no such stress adaptation was observed under chronic treatment with TSA immediately after daily stress exposure. A biochemical study showed that tryptophan hydroxylase, the rate-limiting enzyme in serotonin (5-HT) synthesis, was increased in midbrain containing raphe nuclei obtained from stress-adapted mice that were chronically treated with TSA 2 h before daily stress exposure. These findings suggest that an HDAC inhibitor may have a beneficial effect on stress adaptation by affecting 5-HT neural function in the brain and alleviate the emotional abnormality under conditions of excessive stress.

Activation of 5-HT1A receptor reduces abnormal emotionality in stress-maladaptive mice by alleviating decreased myelin protein in the ventral hippocampus

We previously reported that abnormal emotionality in stress-maladaptive mice was ameliorated by chronic treatment with flesinoxan, a 5-HT_1A receptor agonist. Furthermore, the maintenance of hippocampal myelination appeared to contribute to the development of stress adaptation in mice. However, the effects of 5-HT_1A receptor activation on myelination under the stress-maladaptive situations and the underlying mechanisms remain unknown. In the present study, we examined using flesinoxan whether activation of 5-HT_1A receptor can reduce an abnormal emotional response by acting on oligodendrocytes to preserve myelin proteins in stress-maladaptive mice. Mice were exposed to repeated restraint stress for 4 h/day for 14 days as a stress-maladaptive model. Flesinoxan was given intraperitoneally immediately after the daily exposure to restraint stress. After the final exposure to restraint stress, the emotionality of mice was evaluated by the hole-board test. The expression levels of brain-derived neurotrophic factor (BDNF), phosphorylated-extracellular signal-regulated kinase (p-ERK), phosphorylated-cAMP response element-binding protein (p-CREB), myelin-associated glycoprotein (MAG), myelin basic protein (MBP) and oligodendrocyte transcription factor 2 (olig2) in the hippocampus was assessed by western blotting. Hippocampal oligodendrogenesis were examined by immunohistochemistry. Chronic treatment with flesinoxan suppressed the decrease in head-dipping behaviors in stress-maladaptive mice in the hole-board test. Under this condition, the decreases in MAG and MBP in the hippocampus recovered with increase in BDNF, p-ERK, p-CREB, and olig2. Furthermore, hippocampal oligodendrogenesis in stress-maladaptive mice was promoted by chronic treatment with flesinoxan. These findings suggest that 5-HT_1A receptor activation may promote oligodendrogenesis and myelination via an ERK/CREB/BDNF signaling pathway in the hippocampus and reduces abnormal emotionality due to maladaptation to excessive stress.

EXPRESS: Histone hyperacetylation modulates spinal type II metabotropic glutamate receptor alleviating stress-induced visceral hypersensitivity in female rats

Stress is often a trigger to exacerbate chronic pain including visceral hypersensitivity associated with irritable bowel syndrome, a female predominant functional bowel disorder. Epigenetic mechanisms that mediate stress responses are a potential target to interfere with visceral pain. The purpose of this study was to examine the effect of a histone deacetylase inhibitor, suberoylanilide hydroxamic acid, on visceral hypersensitivity induced by a subchronic stressor in female rats and to investigate the involvement of spinal glutamate receptors. Three daily sessions of forced swim induced visceral hypersensitivity. Intrathecal suberoylanilide hydroxamic acid prevented or reversed the stress-induced visceral hypersensitivity, increased spinal histone 3 acetylation and increased mGluR2 and mGluR3 expression. Chromatin immunoprecipitation (ChIP) analysis revealed enrichment of H3K9Ac and H3K18Ac at several promoter Grm2 and Grm3 regions. The mGluR2/3 antagonist LY341495 reversed the inhibitory effect of suberoylanilide hydroxamic acid on the stress-induced visceral hypersensitivity. In surprising contrast, stress and/or suberoylanilide hydroxamic acid had no effect on spinal NMDA receptor expression or function. These data reveal histone modification modulates mGluR2/3 expression in the spinal cord to attenuate stressinduced visceral hypersensitivity. HDAC inhibitors may provide a potential approach to relieve visceral hypersensitivity associated with irritable bowel syndrome.

Biomarkers of hippocampal gene expression in a mouse restraint chronic stress model

OBJECTIVE

Acute stress provides many beneficial effects whereas chronic stress contributes to a variety of human health issues including anxiety, depression, gastrointestinal problems, cardiac disease, sleep disorders and obesity. The goal of this work was to identify, using a rodent model, hippocampal gene signatures associated with prolonged chronic stress representing candidate biomarkers and therapeutic targets for early diagnosis and pharmacological intervention for stress induced disease.

MATERIALS & METHODS

Mice underwent 'restraint stress' over 7 consecutive days and hippocampal gene-expression changes were analyzed at 3, 12 and 24 h following the final restraint treatment.

RESULTS

Data indicated that mice exposed to chronic restraint stress exhibit a differential gene-expression profile compared with non-stressed controls. The greatest differences were observed 12 and 24 h following the final stress test.

CONCLUSION

Our study indicated that Gpr88, Ttr, Gh and Tac1 mRNAs were modulated in mice exposed to chronic restraint stress. These transcripts represent a panel of biomarkers and druggable targets for further analysis in the context of chronic stress associated disease in humans.

Environmental Enrichment Reduces Anxiety by Differentially Activating Serotonergic and Neuropeptide Y (NPY)-Ergic System in Indian Field Mouse (Mus booduga): An Animal Model of Post-Traumatic Stress Disorder

Exposure to a predator elicits an innate fear response and mimics several behavioral disorders related to post-traumatic stress disorder (PTSD). The protective role of an enriched condition (EC) against psychogenic stressors in various animal models has been well documented. However, this condition has not been tested in field mice in the context of PTSD. In this study, we show that field mice (Mus booduga) housed under EC exhibit predominantly proactive and less reactive behavior compared with mice housed under standard conditions (SC) during exposure to their natural predator (field rat Rattus rattus). Furthermore, we observed that EC mice displayed less anxiety-like behavior in an elevated plus maze (EPM) and light/dark-box after exposure to the predator (7 hrs/7 days). In EC mice, predator exposure elevated the level of serotonin (5-Hydroxytrypamine, [5-HT]) in the amygdala as part of the coping response. Subsequently, the serotonin transporter (SERT) and 5-HT_1A receptor were up-regulated significantly, but the same did not occur in the 5-HT_2C receptor, which is associated with the activation of calmodulin-dependent protein kinase-II (CaMKII) and a transcription factor cAMP response element binding protein (CREB). Our results show that predator exposure induced the activation of CaMKII/CREB, which is accompanied with increased levels of histone acetylation (H3, H4) and decreased histone deacetylases (HDAC1, 2). Subsequently, in the amygdala, the transcription of brain-derived neurotrophic factor (BDNF), neuropeptide Y (NPY) and its Y1 receptor were up-regulated, whereas the Y2 receptor was down-regulated. Therefore, EC facilitated a coping response against a fear associated cue in a PTSD animal model and reduced anxiety by differentially activating serotonergic and NPY-ergic systems.

Epigenetic regulation of resistance to emotional stress: possible involvement of 5-HT1A receptor-mediated histone acetylation

The ability to resist stress is an important defensive function of a living body. Thus, elucidation of the mechanisms by which the brain resists stress could help to pave the way for new therapeutic strategies for stress-related psychiatric disorders including depression. The present review focuses on the roles of brain 5-HT1A receptor-mediated epigenetic mechanisms in the development of resistance to emotional stress. Behavioral pharmacological studies have demonstrated that treatment with a 5-HT1A receptor agonist 24 h before testing suppressed the decrease in emotional behaviors induced by acute restraint stress. Studies with DNA microarray technology have revealed that histone deacetylase genes were decreased in the hippocampus of mice that had been pretreated with a 5-HT1A receptor agonist 24 h beforehand. This preliminary finding was supported by data that hippocampal acetylated histone H3 was increased in mice that had developed emotional resistance to acute restraint stress by 5-HT1A receptor agonist. Furthermore, the histone deacetylase inhibitor trichostatin A also protected against the emotional changes induced by acute restraint stress, accompanied by the induction of histone H3 acetylation. These findings suggest that epigenetic mechanisms that are functionally coupled with 5-HT1A receptors may play a key role in the development of resistance to emotional stress.