Epigenetic regulation of the estrogen receptor alpha promoter in the cerebral cortex following ischemia in male and female rats

Estrogen's sex-specific effects on ischemic cell death and estrogen receptor mRNA expression in rat cortical organotypic explants

Estrogens, such as the biologically active 17-β estradiol (E2), regulate not only reproductive behaviors in adults, but also influence neurodevelopment and neuroprotection in both females and males. E2, contingent upon the timing and concentration of the therapy, is neuroprotective in female and male rodent models of stroke. In Vivo studies suggest that E2 may partially mediate this neuroprotection, particularly in the cortex, via ERα. In Vitro studies, utilizing a chemically induced ischemic injury in cortical explants from both sexes, suggest that ERα or ERβ signaling is needed to mediate the E2 protection. Since we know that the timing and concentration of E2 therapy may be sex-specific, we examined if E2 (1 nM) mediates neuroprotection when female and male cortical explants are separately isolated from postnatal day (PND) 3-4 rat. Changes in basal levels ERα, ERβ, and AR mRNA expression are compared across early post-natal development in the intact cortex and the corresponding days in vitro (DIV) for cortical explants. Following ischemic injury at 7 DIV, cell death and ERα, ERβ and AR mRNA expression was compared in female and male cortical explants. We provide evidence that E2-mediated protection is maintained in isolated cortical explants from females, but not male rats. In female cortical explants, the E2-mediated protection at 24 h occurs secondarily to a blunted transient increase in ERα mRNA at 12 h. These results suggest that cortical E2-mediated protection is influenced by sex and supports data to differentially treat females and males following ischemic injury.

TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype.

METHODS

We cultured sexed hippocampal neurons from ERα+/+ and ERα-/- mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions.

RESULTS

Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα+/+ neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX.

CONCLUSIONS

OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cell survival preferentially in female hippocampal neurons. The sex-dependent neuroprotective actions of 7,8-DHF were blocked by either ANA-12 or by T pre-treatment. These results are consistent with a model for a female-specific neuroprotective pathway in hippocampal neurons in response to hypoxia. The pathway is activated by 7,8-DHF, mediated by TrkB phosphorylation, dependent on ERα and blocked by pre-exposure to T.

The Role of DNA Methylation in Stroke Recovery

Epigenetic alterations affect the onset of ischemic stroke, brain injury after stroke, and mechanisms of poststroke recovery. In particular, DNA methylation can be dynamically altered by maintaining normal brain function or inducing abnormal brain damage. DNA methylation is regulated by DNA methyltransferase (DNMT), which promotes methylation, DNA demethylase, which removes methyl groups, and methyl-cytosine–phosphate–guanine-binding domain (MBD) protein, which binds methylated DNA and inhibits gene expression. Investigating the effects of modulating DNMT, TET, and MBD protein expression on neuronal cell death and neurorepair in ischemic stroke and elucidating the underlying mechanisms can facilitate the formulation of therapeutic strategies for neuroprotection and promotion of neuronal recovery after stroke. In this review, we summarize the role of DNA methylation in neuroprotection and neuronal recovery after stroke according to the current knowledge regarding the effects of DNA methylation on excitotoxicity, oxidative stress, apoptosis, neuroinflammation, and recovery after ischemic stroke. This review of the literature regarding the role of DNA methylation in neuroprotection and functional recovery after stroke may contribute to the development and application of novel therapeutic strategies for stroke.

DNMT3a negatively regulates PTEN to activate the PI3K/AKT pathway to aggravate renal fibrosis

BACKGROUND

Renal fibrosis has become one of the major diseases threatening global public health and harming human life and health. PTEN methylation plays an important role in fibrotic diseases of many organs. However, the relationship between PTEN methylation and renal fibrosis is still elusive.

METHODS

In the present study, we established a unilateral ureteral obstruction (UUO) mouse model in vivo and a transforming growth factor β1 (TGF-β1)-stimulated renal tubular epithelial cell (HK-2) model in vitro. The degree of renal interstitial fibrosis was detected by haematoxylin-eosin (HE) staining and Masson's trichrome staining. Western blot (WB), qRT-PCR, immunohistochemistry (IHC) and methylation-specific PCR (MSP) analyses were used to determine the mechanism by which PTEN methylation regulates renal fibrosis. The α-SMA fibrosis marker was detected by immunofluorescence (IF). Additionally, the relationship of PTEN and DNMT3a in UUO was determined by ChIP-qRT-PCR.

RESULTS

Our results showed that the promoter region of PTEN was methylated in UUO. Compared to the sham group, the expression of PTEN was significantly reduced in the UUO group. However, the demethylation reagent significantly inhibited epithelial-mesenchymal transition (EMT), which showed increased expression of E-cadherin and decreased expression of α-SMA and fibronectin. Moreover, treatment of HK-2 cells with 5-aza-dc reversed the activation of the TGF-β1-induced PI3K/AKT signalling pathway, which inhibited renal fibrosis. WB analysis demonstrated that TGF-β1 inhibited the PTEN protein expression level and DNMT3a knockdown reversed the inhibitory effect of TGF-β1 on PTEN expression. Furthermore, ChIP-qRT-PCR showed that DNMT3a interacted with PTEN. Finally, we found that DNMT3a negatively regulated PTEN to activate the PI3K/AKT signalling pathway and aggravate renal fibrosis in vitro and in vivo.

CONCLUSION

In summary, these results indicated that renal fibrosis is related to the downregulation of PTEN. Additionally, DNMT3a negatively regulates PTEN to activate the PI3K/AKT signalling pathway and induce EMT in renal tubular epithelial cells, thereby aggravating renal fibrosis.

Tet Enzymes-Mediated DNA 5hmC Modification in Cerebral Ischemic and Hemorrhagic Injury

5-Hydroxymethylcytosine (5hmC) has recently been found that plays an important role in many diseases; however, there are still few studies in the field of stroke. The purpose of this review is to introduce the influence and function of 5hmC in stroke, in order for more people can study it. In this review, we introduced the role of 5hmC in ischemia and hemorrhage stroke, and summarized the possible therapeutic prospects of 5hmC in stroke. In conclusion, we suggest that 5hmC may serve as a biomarker or therapeutic target for the treatment of stroke.

Effects of Dietary Soy Protein Isolate Versus Isoflavones Alone on Poststroke Skilled Ladder Rung Walking and Cortical mRNA Expression Differ in Adult Male Rats

Dietary soy protein isolate (SPI) and the isoflavones daidzein and genistein have been shown to provide neuroprotection from stroke. However, the mechanisms remain uncertain. We sought to determine whether the addition of isoflavones to a diet containing caseinate (CAS) as the protein source would induce behavioral neuroprotection similar to that seen previously in rats fed SPI. Furthermore, we aimed to characterize the baseline and poststroke expression of mRNAs involved in pathways previously published as perhaps mediating soy-based neuroprotection from stroke and other markers of neuronal plasticity, oxidative stress, and inflammation. Adult male rats were fed a semipurified diet containing (1) sodium caseinate (CAS), (2) CAS plus daidzein and genistein (CAS+ISO), or (3) SPI for 2 weeks. A subset of rats was euthanized, and tissue was collected for quantitative real-time PCR (qPCR). Remaining rats underwent a middle cerebral artery occlusion to induce a stroke. Samples for qPCR were collected on day 3 poststroke. Rats fed SPI made fewer errors on the skilled ladder rung walking task after stroke compared to rats fed CAS (P < .05). Rats fed CAS+ISO were not different from rats fed CAS or SPI. Significant effects of diet were found at day 0 for Syp, Pparg, and Ywhae and at day 3 for Rtn4 expression. We concluded that the benefits of SPI are not solely attributable to daidzein and genistein.

Nuclear Receptors in Myocardial and Cerebral Ischemia-Mechanisms of Action and Therapeutic Strategies

Nearly 18 million people died from cardiovascular diseases in 2019, of these 85% were due to heart attack and stroke. The available therapies although efficacious, have narrow therapeutic window and long list of contraindications. Therefore, there is still an urgent need to find novel molecular targets that could protect the brain and heart against ischemia without evoking major side effects. Nuclear receptors are one of the promising targets for anti-ischemic drugs. Modulation of estrogen receptors (ERs) and peroxisome proliferator-activated receptors (PPARs) by their ligands is known to exert neuro-, and cardioprotective effects through anti-apoptotic, anti-inflammatory or anti-oxidant action. Recently, it has been shown that the expression of aryl hydrocarbon receptor (AhR) is strongly increased after brain or heart ischemia and evokes an activation of apoptosis or inflammation in injury site. We hypothesize that activation of ERs and PPARs and inhibition of AhR signaling pathways could be a promising strategy to protect the heart and the brain against ischemia. In this Review, we will discuss currently available knowledge on the mechanisms of action of ERs, PPARs and AhR in experimental models of stroke and myocardial infarction and future perspectives to use them as novel targets in cardiovascular diseases.

Estrogen receptor agonists induce anti‑edema effects by altering α and β estrogen receptor gene expression

The present study aimed to examine whether the attenuation of estrogen receptor expression is prevented by propyl pyrazole triol (PPT), an agonist for estrogen receptor α (ERα) or and diarypropiolnitrile (DPN), an agonist for estrogen receptor β (ERβ) after traumatic brain injury (TBI). The tests performed on ovariectomized female Wistar rats included sham group, vehicle group, and treated groups: PPT, DPN, and PPT+DPN 30 minutes after TBI. Blood‑brain barrier (BBB) disruption and brain water content were estimated. RT‑PCR and\r\nwestern blotting were utilized to evaluate ESR1 and ESR2 gene and protein expression. The data indicated that PPT, DPN, and PPT+DPN attenuated TBI‑induced brain edema. Also, BBB disruption after TBI was prevented in PPT, DPN, and PPT+DPN‑treated TBI animals. Estrogen agonist‑treated animals showed a significant elevation in Esr1 mRNA and protein expression levels in the brain tissue of TBI rats. In addition, the data indicated a significant elevation of Esr2 mRNA and protein expression levels in the brain tissue of estrogen agonist‑treated TBI rats. The data shows that both ESR1 and ESR2 agonists can enhance ER mRNA and protein levels in TBI animals' brain. It appears that this effect contributes to the neuroprotective function of ER agonists.

Activation of Glutamate Transporter-1 (GLT-1) Confers Sex-Dependent Neuroprotection in Brain Ischemia

Stroke is one of the leading causes of long-term disability. During ischemic stroke, glutamate is released, reuptake processes are impaired, and glutamate promotes excitotoxic neuronal death. Astrocytic glutamate transporter 1 (GLT-1) is the major transporter responsible for removing excess glutamate from the extracellular space. A translational activator of GLT-1, LDN/OSU 0212320 (LDN) has been previously developed with beneficial outcomes in epileptic animal models but has never been tested as a potential therapeutic for ischemic strokes. The present study evaluated the effects of LDN on stroke-associated brain injury. Male and female mice received LDN or vehicle 24 h before or 2 h after focal ischemia was induced in the sensorimotor cortex. Sensorimotor performance was determined using the Rung Ladder Walk and infarct area was assessed using triphenyltetrazolium chloride staining. Males treated with LDN exhibited upregulated GLT-1 protein levels, significantly smaller infarct size, and displayed better sensorimotor performance in comparison to those treated with vehicle only. In contrast, there was no upregulation of GLT-1 protein levels and no difference in infarct size or sensorimotor performance between vehicle- and LDN-treated females. Taken together, our results indicate that the GLT-1 translational activator LDN improved stroke outcomes in young adult male, but not female mice.

Sex-dependent effects of GPER activation on neuroinflammation in a rat model of traumatic brain injury

The G protein-coupled estrogen receptor (GPER) plays a role in estrogen-mediated neuroprotection and has been considered a potential therapeutic target for treating various neurological diseases. It is increasingly recognized that sex is a biological variable affecting treatment outcomes and efficacy, and that neuroinflammation is a key secondary injury mechanism following brain injury, though it is unknown whether the neuroprotective effects exerted by GPER involve modulation of inflammatory processes. The aim of this study was to investigate whether activation of GPER has a sex-dependent effect on neuroinflammation following traumatic brain injury (TBI), a sexually dimorphic disease. In male and ovariectomized (OVX) female rats, the GPER agonist, G1, inhibited the upregulated expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), increased the expression of the anti-inflammatory cytokine IL-4, and shifted microglia/macrophage polarization toward the M2 phenotype. In gonadally-intact females, G1 caused more pro-inflammatory (IL-6 and TNF-α) and less anti-inflammatory cytokine (IL-4) production, without altering microglia/macrophage polarization. Estradiol supplementation blocked the effects of G1 in OVX females. We also found that post-injury GPER expression was increased in males and OVX females but not in intact females. G1 administration increased Akt phosphorylation in males and OVX females, but had no significant effect in intact females, while Akt inhibition blocked the effects of G1 in males and OVX females. These results indicate that G1 exerts anti-inflammatory effects in males and OVX females but not in intact females; these sex-specific effects are dependent on circulating estrogen levels and are partially mediated through Akt signaling. Future studies are needed to elucidate the relevant molecular mechanisms, especially in females. A better understanding of the sex differences in treatment efficacy with GPER agonists may help improve personalized therapeutic strategies for males and pre- and postmenopausal females with TBI.

The selective oestrogen receptor modulator, bazedoxifene, mimics the neuroprotective effect of 17β-oestradiol in diabetic ischaemic stroke by modulating oestrogen receptor expression and the MAPK/ERK1/2 signalling pathway

Because neuroprotection in stroke should be revisited in the era of recanalisation, the present study analysed the potential neuroprotective effect of the selective oestrogen receptor modulator, bazedoxifene acetate (BZA), in an animal model of diabetic ischaemic stroke that mimics thrombectomy combined with adjuvant administration of a putative neuroprotectant. Four weeks after induction of diabetes (40 mg kg^-1 streptozotocin, i.p.), male Wistar rats were subjected to transient middle cerebral artery occlusion (intraluminal thread technique, 60 minutes) and assigned to one of three groups treated with either: vehicle, BZA (3 mg kg^-1  day^-1 , i.p.) or 17β-oestradiol (E₂ ) (100 μg kg^-1  day^-1 , i.p.). At 24 hours post-ischaemia-reperfusion, brain damage (neurofunctional score, infarct size and apoptosis), expression of oestrogen receptors (ER)α, ERβ and G protein-coupled oestrogen receptor), and activity of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK)1/2 and phosphoinositide 3-kinase/Akt pathways were analysed. At 24 hours after the ischaemic insult, both BZA- and E₂ -treated animals showed lower brain damage in terms of improved neurofunctional condition, decreased infarct size and decreased apoptotic cell death. Ischaemia-reperfusion induced a significant decrease in ERα and ERβ expression without affecting that of G protein-coupled oestrogen receptor, whereas BZA and E₂ reversed such a decrease. The ischaemic insult up-regulated the activity of both the MAPK/ERK1/2 and phosphoinositide 3-kinase/Akt pathways; BZA and E₂ attenuated the increased activity of the ERK1/2 pathway, without affecting that of the Akt pathway. The results of the present study lend further support to the consideration of BZA as an effective and safer alternative overcoming the drawbacks of E₂ with respect to improving diabetic ischaemic stroke outcome after successful reperfusion.

ERα Gene Promoter Methylation in Cognitive Function and Quality of Life of Patients With Alzheimer Disease

OBJECTIVE

Alzheimer disease (AD) has been recognized as a progressive neurodegenerative disorder. This study aims to investigate the effects of estrogen receptor α (ERα) gene promoter methylation on the cognitive function and quality of life (QOL) of patients with AD.

METHODS

A total of 132 patients with AD and 135 healthy individuals were recruited for this study. The DNA in the peripheral blood was extracted and treated with bisulfite; then methylation-specific polymerase chain reaction and reverse transcription quantitative polymerase chain reaction were performed to determine the methylation status of ERα and ERα messenger RNA (mRNA) expression, respectively. Mini-Mental State Examination (MMSE), activities of daily living (ADL), and Quality of Life-Alzheimer Disease scale were employed to evaluate the cognitive functions, ADL, and QOL of the participants.

RESULTS

The methylation group showed a decrease in ERα mRNA expression. The MMSE and ADL scores were indicative of a worse cognitive function in the methylation group. The ERα promoter methylated patients showed a higher rate of abnormal ADL score, while patients in the nonmethylation group enjoyed a better QOL.

CONCLUSIONS

The ERα promoter methylation is related to impaired cognitive function and QOL of patients with AD by inhibiting ERα mRNA expression and transcription.

Sex Differences in the Epigenome: A Cause or Consequence of Sexual Differentiation of the Brain?

Females and males display differences in neural activity patterns, behavioral responses, and incidence of psychiatric and neurological diseases. Sex differences in the brain appear throughout the animal kingdom and are largely a consequence of the physiological requirements necessary for the distinct roles of the two sexes in reproduction. As with the rest of the body, gonadal steroid hormones act to specify and regulate many of these differences. It is thought that transient hormonal signaling during brain development gives rise to persistent sex differences in gene expression via an epigenetic mechanism, leading to divergent neurodevelopmental trajectories that may underlie sex differences in disease susceptibility. However, few genes with a persistent sex difference in expression have been identified, and only a handful of studies have employed genome-wide approaches to assess sex differences in epigenomic modifications. To date, there are no confirmed examples of gene regulatory elements that direct sex differences in gene expression in the brain. Here, we review foundational studies in this field, describe transcriptional mechanisms that could act downstream of hormone receptors in the brain, and suggest future approaches for identification and validation of sex-typical gene programs. We propose that sexual differentiation of the brain involves self-perpetuating transcriptional states that canalize sex-specific development.

Hypermethylation of ERа-A gene and high serum homocysteine level are correlated with cognitive impairment in white matter hyperintensity patients

OBJECTIVE

To investigate the methylation status in promoter region of estrogen receptor alpha (ERа)-A gene and its relation with plasma homocysteine (Hcy) level and cognitive impairment in white matter hyperintensity (WMH) patients.

PATIENTS AND METHODS

210 patients aged 65 and older were selected. The methylation status of CpG islands in ERа-A gene promoter was analyzed by nested methylation-specific PCR. Serum Hcy and estradiol levels were measured by enzyme-linked immunosorbent assay. Cognitive function were evaluated using minimum mental state examination, the montreal cognitive assessment, Stroop color-word test, symbol digit modalities, trail making test B and instrumental activities of daily living (IADL). The severity of WMH was evaluated with the Fazekas scale by brain magnetic resonance imaging.

RESULTS

We found a significant association between the severity of WMH and CpG island methylation of ERа-A gene (P < 0.05). Multiple regression analysis showed that serum Hcy level, methylation of ERа-A gene and WMH severity were significant determining factors for cognitive impairment (P < 0.05). The spearman rank correlation analysis showed a significant correlation of methylation of ERа-A gene with serum Hcy level, WMH severity, cognitive function and IADL status (P < 0.05).

CONCLUSION

Methylation of ERа-A gene promoter has a high frequency in WMH patients with cognitive impairment and is correlated with high plasma Hcy level.

Steroids in Stroke with Special Reference to Progesterone

Both sex and steroid hormones are important to consider in human ischemic stroke and its experimental models. Stroke initiates a cascade of changes that lead to neural cell death, but also activates endogenous protective processes that counter the deleterious consequences of ischemia. Steroids may be part of these cerebroprotective processes. One option to provide cerebroprotection is to reinforce these intrinsic protective mechanisms. In the current review, we first summarize studies describing sex differences and the influence of steroid hormones in stroke. We then present and discuss our recent results concerning differential changes in endogenous steroid levels in the brains of male and female mice and the importance of progesterone receptors (PR) during the early phase after stroke. In the third part, we give an overview of experimental studies, including ours, that provide evidence for the pleiotropic beneficial effects of progesterone and its promising cerebroprotective potential in stroke. We also highlight the key role of PR signaling as well as potential additional mechanisms by which progesterone may provide cerebroprotection.

Sex differences in Hippocampal Memory and Learning following Neonatal Brain Injury: Is There a Role for Estrogen Receptor-α?

Neonatal encephalopathy due to hypoxia-ischemia (HI) leads to severe, life-long morbidities in thousands of neonates born in the USA and worldwide each year. Varying capacities of long-term episodic memory, verbal working memory, and learning can present without cerebral palsy and have been associated with the severity of neonatal encephalopathy sustained at birth. Among children who sustain a moderate degree of HI at birth, girls have larger hippocampal volumes compared to boys. Clinical studies indicate that female neonatal brains are more resistant to the effects of neonatal HI, resulting in better long-term cognitive outcomes compared to males with comparable brain injury. Our most recent mechanistic studies have addressed the origins and cellular basis of sex differences in hippocampal neuroprotection following neonatal HI-related brain injury and implicate estrogen receptor-α (ERα) in the neurotrophin receptor-mediated hippocampal neuroprotection in female mice. This review summarizes the recent findings on ERα-dependent, neurotrophin-mediated hippocampal neuroprotection and weighs the evidence that this mechanism plays an important role in preservation of long-term memory and learning following HI in females.

Estrogen in vascular smooth muscle cells: A friend or a foe?

Cardiovascular disease (CVD) continues to be the leading cause of death worldwide. The effect of estrogen on these diseases has been assessed in in vitro and in vivo models, as well as in observational studies. Collectively, these studies alluded to a cardiovasculo-protective effect of estrogen. However, comprehensive clinical investigation failed to produce concrete proof of a cardiovascular protective effect for hormone replacement therapy (HRT), let alone rule out potential harm. These seemingly paradoxical effects of estrogen were explained by the 'theory of timing and opportunity'. This theory states that the effect of estrogen, whether cardiovasculo-protective or pathological, significantly depends on the age of the individual when estrogen administration takes place. Here, we review the conflicting effects of estrogen on vascular smooth muscle cells, mainly proliferation and migration as two cellular capacities intimately related to physiology and pathophysiology of the cardiovascular system. Furthermore, we critically discuss the major parameters and signaling pathways that may account for the aforementioned paradoxical observations, as well as the key molecular players involved.

Ischemic stroke across sexes: What is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Ischemic stroke across sexes: what is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Regulation of gene expression in ischemic preconditioning in the brain

Stroke is the third leading cause of death and the leading cause of long-term disability, with very few effective treatments and limited progress in the effort to search for novel therapeutic approaches. The phenomenon that a sublethal ischemic insult induces protection against a subsequent severe ischemia, termed ischemic preconditioning (IPC), represents an endogenous protective approach against ischemic brain injury, and may direct a breakthrough to future therapeutic strategies. It is broadly accepted that new protein synthesis is required for IPC-mediated long-term neuroprotection; however, their relative regulatory mechanisms are poorly understood. In the present review, we summarize genomic-based studies on alterations in gene expression and protein synthesis, particularly categorizing potential pathways regulated by IPC. We also review the role of epigenetics, an inheritable genetic regulatory mechanism without changes in DNA sequence, in IPC-mediated neuroprotection.

A Role of Endogenous Progesterone in Stroke Cerebroprotection Revealed by the Neural-Specific Deletion of Its Intracellular Receptors

Treatment with progesterone protects the male and female brain against damage after middle cerebral artery occlusion (MCAO). However, in both sexes, the brain contains significant amounts of endogenous progesterone. It is not known whether endogenously produced progesterone enhances the resistance of the brain to ischemic insult. Here, we used steroid profiling by gas chromatography-tandem mass spectrometry (GC-MS/MS) for exploring adaptive and sex-specific changes in brain levels of progesterone and its metabolites after MCAO. We show that, in the male mouse brain, progesterone is mainly metabolized via 5α-reduction leading to 5α-dihydroprogesterone (5α-DHP), also a progesterone receptor (PR) agonist ligand in neural cells, then to 3α,5α-tetrahydroprogesterone (3α,5α-THP). In the female mouse brain, levels of 5α-DHP and 3α,5α-THP are lower and levels of 20α-DHP are higher than in males. After MCAO, levels of progesterone and 5α-DHP are upregulated rapidly to pregnancy-like levels in the male but not in the female brain. To assess whether endogenous progesterone and 5α-DHP contribute to the resistance of neural cells to ischemic damage, we inactivated PR selectively in the CNS. Deletion of PR in the brain reduced its resistance to MCAO, resulting in increased infarct volumes and neurological deficits in both sexes. Importantly, endogenous PR ligands continue to protect the brain of aging mice. These results uncover the unexpected importance of endogenous progesterone and its metabolites in cerebroprotection. They also reveal that the female reproductive hormone progesterone is an endogenous cerebroprotective neurosteroid in both sexes.SIGNIFICANCE STATEMENT The brain responds to injury with protective signaling and has a remarkable capacity to protect itself. We show here that, in response to ischemic stroke, levels of progesterone and its neuroactive metabolite 5α-dihydroprogesterone are upregulated rapidly in the male mouse brain but not in the female brain. An important role of endogenous progesterone in cerebroprotection was demonstrated by the conditional inactivation of its receptor in neural cells. These results show the importance of endogenous progesterone, its metabolites, and neural progesterone receptors in acute cerebroprotection after stroke. This new concept could be exploited therapeutically by taking into account the progesterone status of patients and by supplementing and reinforcing endogenous progesterone signaling for attaining its full cerebroprotective potential.

Genistein: mechanisms of action for a pleiotropic neuroprotective agent in stroke

Genistein is a plant estrogen promoted as an alternative to post-menopausal hormone therapy because of a good safety profile and its promotion as a natural product. Several preclinical studies of cerebral ischemia and other models of brain injury support a beneficial role for genistein in protecting the brain from injury whether administered chronically or acutely. Like estrogen, genistein is a pleiotropic molecule that engages several different mechanisms to enhance brain health, including reduction of oxidative stress, promotion of growth factor signaling, and immune suppression. These actions occur in endothelial, glial, and neuronal cells to provide a coordinated beneficial action to ischemic challenge. Though many of these protective actions are associated with estrogen-like actions of genistein, additional activities on other receptors and intracellular targets suggest that genistein is more than a mere estrogen-mimic. Importantly, genistein lacks some of the detrimental effects associated with post-menopausal estrogen treatment and may provide an alternative to hormone therapy in those patients at risk for ischemic events.

Differential Effects of E2 on MAPK Activity in the Brain and Heart of Aged Female Rats

Aging and the coincident loss of circulating estrogens at menopause lead to increased risks for neurological and cardiovascular pathologies. Clinical studies show that estrogen therapy (ET) can be beneficial in mitigating these negative effects, in both the brain and heart, when it is initiated shortly after the perimenopausal transition. However, this same therapy is detrimental when initiated >10 years postmenopause. Importantly, the molecular mechanisms underlying this age-related switch in ET efficacy are unknown. Estrogen receptors (ERs) mediate the neuroprotective and cardioprotective functions of estrogens by modulating gene transcription or, non-genomically, by activating second messenger signaling pathways, such as mitogen activated protein kinases (MAPK). These kinases are critical regulators of cell signaling pathways and have widespread downstream effects. Our hypothesis is that age and estrogen deprivation following menopause alters the expression and activation of the MAPK family members p38 and ERK in the brain and heart. To test this hypothesis, we used a surgically induced model of menopause in 18 month old rats through bilateral ovariectomy (OVX) followed by an acute dose of 17β-estradiol (E2) administered at varying time points post-OVX (1 week, 4 weeks, 8 weeks, or 12 weeks). Age and E2 treatment differentially regulated kinase activity in both the brain and heart, and the effects were also brain region specific. MAPK signaling plays an integral role in aging, and the aberrant regulation of those signaling pathways might be involved in age-related disorders. Clinical studies show benefits of ET during early menopause but detrimental effects later, which might be reflective of changes in kinase expression and activation status.

The Emerging Role of Epigenetics in Cerebral Ischemia

Despite great progresses in the treatment and prevention of ischemic stroke, it is still among the leading causes of death and serious long-term disability all over the world, indicating that innovative neural regenerative and neuroprotective agents are urgently needed for the development of therapeutic approaches with greater efficacy for ischemic stroke. More and more evidence suggests that a spectrum of epigenetic processes play an important role in the pathophysiology of cerebral ischemia. In the present review, we first discuss recent developments in epigenetic mechanisms, especially their roles in the pathophysiology of cerebral ischemia. Specifically, we focus on DNA methylation, histone deacetylase, histone methylation, and microRNAs (miRNAs) in the regulation of vascular and neuronal regeneration after cerebral ischemia. Additionally, we highlight epigenetic strategies for ischemic stroke treatments, including the inhibition of histone deacetylase enzyme and DNA methyltransferase activities, and miRNAs. These therapeutic strategies are far from clinic use, but preliminary data indicate that neuroprotective agents targeting these pathways can modulate neural cell regeneration and promote brain repair and functional recovery after cerebral ischemia. A better understanding of how epigenetics influences the process and progress of cerebral ischemia will pave the way for discovering more sensitive and specific biomarkers and new targets and therapeutics for ischemic stroke.

ERα Signaling Is Required for TrkB-Mediated Hippocampal Neuroprotection in Female Neonatal Mice after Hypoxic Ischemic Encephalopathy(1,2,3)

Male neonate brains are more susceptible to the effects of perinatal asphyxia resulting in hypoxia and ischemia (HI)-related brain injury. The relative resistance of female neonatal brains to adverse consequences of HI suggests that there are sex-specific mechanisms that afford females greater neuroprotection and/or facilitates recovery post-HI. We hypothesized that HI preferentially induces estrogen receptor α (ERα) expression in female neonatal hippocampi and that ERα is coupled to Src family kinase (SFK) activation that in turn augments phosphorylation of the TrkB and thereby results in decreased apoptosis. After inducing the Vannucci’s HI model on P9 (C57BL/6J) mice, female and male ERα wild-type (ERα^+/+) or ERα null mutant (ERα^−/−) mice received vehicle control or the selective TrkB agonist 7,8-dihydroxyflavone (7,8-DHF). Hippocampi were collected for analysis of mRNA of ERα and BDNF, protein levels of ERα, p-TrkB, p-src, and cleaved caspase 3 (c-caspase-3) post-HI. Our results demonstrate that: (1) HI differentially induces ERα expression in the hippocampus of the female versus male neonate, (2) src and TrkB phosphorylation post-HI is greater in females than in males after 7,8-DHF therapy, (3) src and TrkB phosphorylation post-HI depend on the presence of ERα, and (4) TrkB agonist therapy decreases the c-caspase-3 only in ERα^+/+ female mice hippocampus. Together, these observations provide evidence that female-specific induction of ERα expression confers neuroprotection with TrkB agonist therapy via SFK activation and account for improved functional outcomes in female neonates post-HI.

Neonatal hyperoxia induces alterations in neurotrophin gene expression

Each year in the United States, nearly 500,000 infants a year are born prematurely. Babies born before 35 weeks gestation are often placed on ventilators and/or given supplemental oxygen. This increase in oxygen, while critical for survival, can cause long-term damage to lungs, retinas and brains. In particular, hyperoxia causes apoptosis in neurons and alters glial activity. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are members of the neurotrophin family of proteins that function to promote the growth, differentiation and development of the nervous system. We hypothesized that hyperoxia can alter the regulation of these genes and by doing so adversely affect the development of the brain. We predicted that mice exposed to hyperoxic conditions would have differences in BDNF and GDNF mRNA expression and relative level of methylated promoter regions coinciding with differences in the relative levels of DNMT1 and DNMT3a mRNA expression. To test this hypothesis, newborn C57Bl/6 mice and their littermates were placed in hyperoxic or normoxic conditions from postnatal day 7 to 12. There were significant decreases in BDNF mRNA expression in the prefrontal cortex following hyperoxia, but a significant increase in the isocortex. GDNF mRNA expression was significantly increased in both the isocortex and prefrontal cortex following hyperoxia. DNMT1 mRNA expression was significantly decreased in the isocortex but significantly increased in the prefrontal following hyperoxia. Together these data suggest that short-term exposure to hyperoxic conditions can affect the regulation and expression of BDNF and GDNF potentially leading to alterations in neural development.

Demethylation of Circulating Estrogen Receptor Alpha Gene in Cerebral Ischemic Stroke

Background

Estrogen is involved in neuron plasticity and can promote neuronal survival in stroke. Its actions are mostly exerted via estrogen receptor alpha (ERα). Previous animal studies have shown that ERα is upregulated by DNA demethylation following ischemic injury. This study investigated the methylation levels in the ERα promoter in the peripheral blood of ischemic stroke patients.

Methods

The study included 201 ischemic stroke patients, and 217 age- and sex-comparable healthy controls. The quantitative methylation level in the 14 CpG sites of the ERα promoter was measured by pyrosequencing in each participant. Multivariate regression model was used to adjust for stroke traditional risk factors. Stroke subtypes and sex-specific analysis were also conducted.

Results

The results demonstrated that the stroke cases had a lower ERα methylation level than controls in all 14 CpG sites, and site13 and site14 had significant adjusted p-values of 0.035 and 0.026, respectively. Stroke subtypes analysis showed that large-artery atherosclerosis and cardio-embolic subtypes had significantly lower methylation levels than the healthy controls at CpG site5, site9, site12, site13 and site14 with adjusted p = 0.039, 0.009, 0.025, 0.046 and 0.027 respectively. However, the methylation level for the patients with small vessel subtype was not significant. We combined the methylation data from the above five sites for further sex-specific analysis. The results showed that the significant association only existed in women (adjusted p = 0.011), but not in men (adjusted p = 0.300).

Conclusions

Female stroke cases have lower ERα methylation levels than those in the controls, especially in large-artery and cardio-embolic stroke subtypes. The study implies that women suffering from ischemic stroke of specific subtype may undergo different protective mechanisms to reduce the brain injury.

Resveratrol neuroprotection in stroke and traumatic CNS injury

Resveratrol, a stilbene formed in many plants in response to various stressors, elicits multiple beneficial effects in vertebrates. Particularly, resveratrol was shown to have therapeutic properties in cancer, atherosclerosis and neurodegeneration. Resveratrol-induced benefits are modulated by multiple synergistic pathways that control oxidative stress, inflammation and cell death. Despite the lack of a definitive mechanism, both in vivo and in vitro studies suggest that resveratrol can induce a neuroprotective state when administered acutely or prior to experimental injury to the CNS. In this review, we discuss the neuroprotective potential of resveratrol in stroke, traumatic brain injury and spinal cord injury, with a focus on the molecular pathways responsible for this protection.

Altering 5-hydroxymethylcytosine modification impacts ischemic brain injury

Epigenetic modifications such as cytosine methylation and histone modification are linked to the pathology of ischemic brain injury. Recent research has implicated 5-hydroxymethylcytosine (5hmC), a DNA base derived from 5-methylcytosine (5mC) via oxidation by ten-eleven translocation (Tet) enzymes, in DNA methylation-related plasticity. Here we show that 5hmC abundance was increased after ischemic injury, and Tet2 was responsible for this increase; furthermore, inhibiting Tet2 expression abolished the increase of 5hmC caused by ischemic injury. The decrease in 5hmC modifications from inhibiting Tet2 activity was accompanied by increased infarct volume after ischemic injury. Genome-wide profiling of 5hmC revealed differentially hydroxymethylated regions (DhMRs) associated with ischemic injury, and DhMRs were enriched among the genes involved in cell junction, neuronal morphogenesis and neurodevelopment. In particular, we found that 5hmC modifications at the promoter region of brain-derived neurotrophic factor (BDNF) increased, which was accompanied by increased BDNF mRNA, whereas the inhibition of Tet2 reduced BDNF mRNA and protein expression. Finally, we show that the abundance of 5hmC in blood samples from patients with acute ischemic stroke was also significantly increased. Together, these data suggest that 5hmC modification could serve as both a potential biomarker and a therapeutic target for the treatment of ischemic stroke.

Changes in the gene expression of estrogen receptors involved in the protective effect of estrogen in rat's trumatic brain injury

It has been demonstrated that estradiol has neuroprotective effects after traumatic brain injury (TBI) in female rats. Since estrogen receptors have an important role in estradiol effects at the cellular level and the exact mechanism(s) of estradiol-induced neuroprotection has not yet been fully clarified, the present study was designed to determine the changes in the levels of estrogen receptors mRNAs and proteins involved in this phenomenon. All experiments were carried out on female Wistar rats. The brain edema and blood-brain-barrier (BBB) disruption were assessed. The TBI method was diffuse type and induced by the Marmarou method. Semiquantitative RT-PCR and immunoblotting were used to assess ERα and ERβ gene expression. The data showed that the level of brain water content was significantly increased in TBI group. The increased water content was significantly attenuated in estradiol-treated (1mg/kg) TBI rats. Disruption of BBB after TBI was significantly inhibited just by estradiol treatment. Estrogen-treated animals showed a significant increase in ERα mRNA (18%) and protein (35%) levels in the brain tissue. Furthermore, in the brain-injured rats the levels of ERβ mRNA were lower than those in control rats. Following estrogen treatment, the protein levels of ERβ were closed to those in control group. In conclusion, the data demonstrate that estrogen treatment can protect brain against traumatic brain injury. Estrogen treatment increases ER mRNA and protein levels which were coincident with its protective effects. It seems that such phenomenon participates in the induction of neuroprotective effects of estrogen. This article is part of a Special Issue entitled 1618.

Effect of sex and age interactions on functional outcome after stroke

Stroke is one of the leading causes of death and disability worldwide. Experimental and clinical studies showed that sex and age play an important role in deciding the outcome after stroke. At younger ages, males were shown to have a higher risk for stroke than females. However, this trend reverses in older ages particularly when females reach menopause. Many preclinical studies indicate that steroid hormones modulate the age-dependent differential stroke outcome. In addition, patterns of cell death pathways activated following cerebral ischemia are distinct between males and females, but independent of steroid hormones. Recent studies also indicate that microRNAs play important roles in mediating sex-specific stroke outcome by regulating stroke-related genes. This review discusses the contribution of sex and age to outcome after stroke with particular emphasis on the experimental studies that examined the effects of steroid hormones, differential cell death pathways, and involvement of sex-specific microRNAs following cerebral ischemia. Current understanding of the role of thrombolytic agents in stroke therapy is also discussed.

Epigenetic regulation of female puberty

Substantial progress has been made in recent years toward deciphering the molecular and genetic underpinnings of the pubertal process. The availability of powerful new methods to interrogate the human genome has led to the identification of genes that are essential for puberty to occur. Evidence has also emerged suggesting that the initiation of puberty requires the coordinated activity of gene sets organized into functional networks. At a cellular level, it is currently thought that loss of transsynaptic inhibition, accompanied by an increase in excitatory inputs, results in the pubertal activation of GnRH release. This concept notwithstanding, a mechanism of epigenetic repression targeting genes required for the pubertal activation of GnRH neurons was recently identified as a core component of the molecular machinery underlying the central restraint of puberty. In this chapter we will discuss the potential contribution of various mechanisms of epigenetic regulation to the hypothalamic control of female puberty.

Sex, epilepsy, and epigenetics

Epilepsy refers to a heterogeneous group of disorders that are associated with a wide range of pathogenic mechanisms, seizure manifestations, comorbidity profiles, and therapeutic responses. These characteristics are all influenced quite significantly by sex. As with other conditions exhibiting such patterns, sex differences in epilepsy are thought to arise-at the most fundamental level-from the "organizational" and "activational" effects of sex hormones as well as from the direct actions of the sex chromosomes. However, our understanding of the specific molecular, cellular, and network level processes responsible for mediating sex differences in epilepsy remains limited. Because increasing evidence suggests that epigenetic mechanisms are involved both in epilepsy and in brain sexual dimorphism, we make the case here that analyzing epigenetic regulation will provide novel insights into the basis for sex differences in epilepsy.

Unilateral lesion increases oestrogen receptor α expression in the intact side of the ventromedial hypothalamic nucleus in ovariectomised rats

To determine the relationship between the right and left sides of the ventrolateral ventromedial hypothalamic nucleus (vlVMN) in regulating the expression of oestrogen receptor (ER)α, the unilateral vlVMN was lesioned and the number of ERα-immunoreactive cells and the ERα mRNA level in the intact side of the vlVMN and arcuate nucleus (ARC) were measured in ovariectomised rats. Twenty-four hours after lesioning, brain samples were collected for analysis of ERα expression by immunohistochemistry and the real-time reverse transcriptase-polymerase chain reaction. The number of ERα-immunoreactive cells in the intact side of the vlVMN but not the ARC in the unilateral lesioned group was significantly higher than that in the control or sham-lesioned group. Expression levels of ERα mRNA in the intact side of the vlVMN but not the ARC in unilateral lesioned rats were significantly higher than those in the sham-lesioned group. Of transcript variants with alternative 5'-untranslated regions (0S, 0N, 0, 0T and E1), the ERα 0 transcript level was significantly increased. These results indicate that unilateral damage of vlVMN induces an increase in ERα in the intact side by increasing ERα transcription in a promoter-specific manner. The findings also suggest the existence of new neuroendocrine control system between the right and left sides for the expression of ERα in the vlVMN.

Sex-Dependent Effects of G Protein–Coupled Estrogen Receptor Activity on Outcome After Ischemic Stroke

Background and Purpose—

Experimental studies indicate that estrogen typically, but not universally, has a neuroprotective effect in stroke. Ischemic stroke increases membrane-bound G protein–coupled estrogen receptor (GPER) distribution and expression in the brain of male but not female mice. We hypothesized that GPER activation may have a greater neuroprotective effect in males than in females after stroke.

Methods—

Vehicle (dimethyl sulfoxide), a GPER agonist (G-1, 30 μg/kg), or a GPER antagonist (G-15, 300 μg/kg) were administered alone or in combination to young or aged male mice, or young intact or ovariectomized female mice, 1 hour before or 3 hours after cerebral ischemia-reperfusion. Some mice were treated with a combination of G-1 and the pan-caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy (Q-V D -OPh), 1 hour before stroke. We evaluated functional and histological end points of stroke outcome up to 72 hours after ischemia-reperfusion. In addition, apoptosis was examined using cleaved caspase-3 immunohistochemistry.

Results—

Surprisingly, G-1 worsened functional outcomes and increased infarct volume in males poststroke, in association with an increased expression of cleaved caspase-3 in peri-infarct neurons. These effects were blocked by G-15 or Q-V D -OPh. Conversely, G-15 improved functional outcomes and reduced infarct volume after stroke in males, whether given before or after stroke. In contrast to findings in males, G-1 reduced neurological deficit, apoptosis, and infarct volume in ovariectomized females, but had no significant effect in intact females.

Conclusions—

Future therapies for acute stroke could exploit the modulation of GPER activity in a sex-specific manner.

Impact of methodology on estrogens' effects on cerebral ischemia in rats: an updated meta-analysis

Background

Although most animal stroke studies have demonstrated potent neuroprotective effects of estrogens, there are a number of articles reporting the opposite. In 2009, we made the case that this dichotomy was related to administered estrogen dose. Several other suggestions for the discordant results have also been propagated, including the age of the experimental animals and the length of hypoestrogenicity prior to estrogen administration. These two suggestions have gained much popularity, probably because of their kinship with the window of opportunity hypothesis, which is commonly used to explain the analogous dichotomy among human studies. We were therefore encouraged to perform an updated meta-analysis, and to improve it by including all relevant variables in a large multiple regression model, where the impact of confounders could be controlled for.

Results

The multiple regression model revealed an indisputable impact of estrogen administration mode on the effects of estrogens in ischemic stroke. Subcutaneous slow-release pellets differed from the injection and silastic capsule treatments in terms of impact of estrogens on ischemic stroke, showing that the first mentioned were more prone to render estrogens damaging. Neither the use of elderly animals nor the adoption of longer wash-out periods influenced estrogens’ effects on experimental ischemic stroke in rats.

Conclusions

We conclude that the discordant results regarding estrogens’ effects in rat models of ischemic stroke are a consequence of differences in estrogen administration modes. These results are not only of importance for the ongoing debate regarding menopausal hormone therapy, but also have an important bearing on experimental stroke methodology and the apparent translational roadblock for suggested stroke interventions.

Epigenetic contributions to hormonally-mediated sexual differentiation of the brain

It has been long established that hormones exert enduring influences on the developing brain that direct the reproductive response in adulthood, although the cellular mechanisms by which organisational effects are maintained have not been determined satisfactorily. Recent interest in epigenetic modifications to the nervous system has highlighted the potential for hormone-induced changes to the genome that could endure for the lifespan but not be transmitted to the next generation. Preliminary evidence suggests that this is indeed possible because sex differences in the histone code and in the methylation of CpGs in the promoters of specific genes have been identified and, at times, functionally correlated with behaviour. The present review provides an overview of epigenetic processes and discusses the current state-of-the-art, and also identifies future directions.

Epigenetic mechanisms in cerebral ischemia

Treatment efficacy for ischemic stroke represents a major challenge. Despite fundamental advances in the understanding of stroke etiology, therapeutic options to improve functional recovery remain limited. However, growing knowledge in the field of epigenetics has dramatically changed our understanding of gene regulation in the last few decades. According to the knowledge gained from animal models, the manipulation of epigenetic players emerges as a highly promising possibility to target diverse neurologic pathologies, including ischemia. By altering transcriptional regulation, epigenetic modifiers can exert influence on all known pathways involved in the complex course of ischemic disease development. Beneficial transcriptional effects range from attenuation of cell death, suppression of inflammatory processes, and enhanced blood flow, to the stimulation of repair mechanisms and increased plasticity. Most striking are the results obtained from pharmacological inhibition of histone deacetylation in animal models of stroke. Multiple studies suggest high remedial qualities even upon late administration of histone deacetylase inhibitors (HDACi). In this review, the role of epigenetic mechanisms, including histone modifications as well as DNA methylation, is discussed in the context of known ischemic pathways of damage, protection, and regeneration.

Visualisation and characterisation of oestrogen receptor α-positive neurons expressing green fluorescent protein under the control of the oestrogen receptor α promoter

Oestrogen receptor (ER)α plays important roles in the development and function of various neuronal systems through activation by its ligands, oestrogens. To visualise ERα-positive neurons, we generated transgenic (tg) mice expressing green fluorescent protein (GFP) under the control of the ERα promoter. In three independent tg lines, GFP-positive neurons were observed in areas previously reported to express ERα mRNA, including the lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus (MPO), hypothalamus, and amygdala. In these areas, GFP signals mostly overlapped with ERα immunoreactivity. GFP fluorescence was seen in neurites and cell bodies of neurons. In addition, the network and detailed structure of neurites were visible in dissociated and slice cultures of hypothalamic neurons. We examined the effect of oestrogen deprivation by ovariectomy on the structure of the GFP-positive neurons. The area of ERα-positive cell bodies in the bed nucleus of the stria terminalis and MPO was measured by capturing the GFP signal and was found to be significantly smaller in ovariectomy mice than in control mice. When neurons in the MPO were infected with an adeno-associated virus that expressed small hairpin RNA targeting the ERα gene, an apparent induction of GFP was observed in this area, suggesting a negative feedback mechanism in which ERα controls expression of the ERα gene itself. Thus, the ERα promoter-GFP tg mice will be useful to analyse the development and plastic changes of the structure of ERα-expressing neurons and oestrogen and its receptor-mediated neuronal responses.

Stroke: understanding the differences between males and females

Stroke is a significant cause of death and long-term disability in the USA. The incidence, mortality, and outcomes of stroke are significantly different between men and women. As with many diseases that affect men and women differently, an understanding on the reasons underlying those differences is critical to effective diagnosis and treatment. This review will examine the sex differences in stroke in both humans and animal models of stroke and review what is known about potential mechanisms underlying these differences. It is clear that there is a complex interaction between hormonal, genetic, and unknown factors at play in generating the sex differences in stroke.

Tolerance to ischemia - an increasingly complex biology

In this review we identify and discuss some of the genomics studies of preconditioning and the ischemic tolerance phenomenon. Such studies have been attempted in multiple species, using different array technologies and with different preconditioning and tolerance models. In addition, studies are starting to reveal epigenetic mechanisms and modifiers of tolerance and preconditioning. Together these studies are starting to reveal some of the immense complexity of the ischemic tolerance phenomenon, yet further studies await to be performed.

Epigenetics and family-centered developmental care for the preterm infant

Adverse experiences early in life have the potential to disrupt normal brain development and create stress response channels in preterm infants that are different from those observed in term infants. Animal models show that epigenetic modifications mediate the effects of maternal separation and environmental stress on susceptibility to disease and psychobehavioral problems later in life. Epigenetic research has the potential to lead to the identification of biological markers, gene expression profiles, and profile changes that occur overtime in response to early-life experiences. Combined with knowledge gained through the use of advanced technologies, epigenetic studies have the promise to refine our understanding about how the brain matures and functions from multiple perspectives including the effect of the environment on brain growth and maturation. Such an understanding will pave the way for care practices that will allow the premature brain to develop to its full capacity and will lead to the best possible outcomes. Neonatal epigenetic research is emerging and rapidly advancing. As scientists overcome biological, technical, and cost-related challenges, such research has a great potential in determining key environmental factors that affect the preterm genome, allowing for targeted interventions. The purpose of this article is to explore existing literature related to epigenetic mechanisms that potentially mediate the effects of the environment on preterm infant brain development.