Epigenetic regulation of estrogen receptor α contributes to age-related differences in transcription across the hippocampal regions CA1 and CA3

Examination of CA1 Hippocampal DNA Methylation as a Mechanism for Closing of Estrogen's Critical Window

There is a critical window for estrogen replacement therapy, beyond which estradiol (E2) fails to enhance cognition and N-methyl-D-aspartate (NMDA) receptor function, and E2-responsive transcription decreases. Much less attention has been given to the mechanism for closing of the critical window, which is thought to involve the decline in estrogen signaling cascades, possibly involving epigenetic mechanisms, including DNA methylation. This study investigated changes in DNA methylation in region CA1 of the hippocampus of ovariectomized female rats over the course of brain aging and in response to E2-treatment, using whole genome bisulfite sequencing. Differential methylation of CpG and non-CpG (CHG and CHH) sites and associated genes were characterized in aged controls (AC), middle-age controls (MC), and young controls (YC) and differential methylation in response to E2-treatment (T) was examined in each age group (AT-AC, MT-MC, and YT-YC). Possible candidate genes for the closing of the critical window were defined as those that were hypomethylated by E2-treatment in younger animals, but were unresponsive in aged animals. Gene ontology categories for possible critical window genes were linked to response to hormones (Adcyap1, Agtr2, Apob, Ahr, Andpro, Calm2, Cyp4a2, Htr1b, Nr3c2, Pitx2, Pth, Pdk4, Slc2a2, Tnc, and Wnt5a), including G-protein receptor signaling (Gpr22 and Rgs4). Other possible critical window genes were linked to glutamate synapses (Nedd4, Grm1, Grm7, and Grin3a). These results suggest that decreased E2 signaling with advanced age, and/or prolonged E2 deprivation, results in methylation of E2-responsive genes, including those involved in rapid E2 signaling, which may limit subsequent transcription.

Differential ESR1 Promoter Methylation in the Peripheral Blood-Findings from the Women 40+ Healthy Aging Study

Background Estrogen receptor α (ERα) contributes to maintaining biological processes preserving health during aging. DNA methylation changes of ERα gene (ESR1) were established as playing a direct role in the regulation of ERα levels. In this study, we hypothesized decreased DNA methylation of ESR1 associated with postmenopause, lower estradiol (E2) levels, and increased age among healthy middle-aged and older women. Methods We assessed DNA methylation of ESR1 promoter region from dried blood spots (DBSs) and E2 from saliva samples in 130 healthy women aged 40-73 years. Results We found that postmenopause and lower E2 levels were associated with lower DNA methylation of a distal regulatory region, but not with DNA methylation of proximal promoters. Conclusion Our results indicate that decreased methylation of ESR1 cytosine-phosphate-guanine island (CpGI) shore may be associated with conditions of lower E2 in older healthy women.

Sleep and Methylation of Estrogen Receptor Genes, ESR1 and GPER, in Healthy Middle-Aged and Older Women: Findings from the Women 40+ Healthy Aging Study

PURPOSE

Sleep problems in middle-aged and older women are very common and have been associated with menopause-related changes in estrogen levels. However, not all women experience sleep problems as they enter perimenopause, and epigenetic mechanisms might contribute to the differences in sleep quality within this population. In this study, we hypothesized that increased methylation of two estrogen receptor (ER) genes (ESR1 and GPER) would be associated with increased sleep problems in healthy pre-, peri-, and postmenopausal women, either directly or indirectly through the experience of vasomotor symptoms (VMS).

MATERIALS AND METHODS

In 130 healthy women aged 40-73 years, we assessed DNA methylation from dried blood spots (DBS). Women rated their sleep quality using the Pittsburgh Sleep Quality Index (PSQI), and VMS using the Menopause Rating Scale (MRS).

RESULTS

Higher percentage methylation of ESR1 was associated with increased sleep problems, mediated by VMS, even after controlling for age, menopausal status, body mass index, estradiol levels, depressive symptoms, and caffeine consumption. There was no significant association between GPER methylation and either sleep problems or VMS.

CONCLUSION

The study findings support an association between increased ESR1 methylation and sleep problems through increased VMS among healthy women aged 40-73 years.

Network analysis of canine brain morphometry links tumour risk to oestrogen deficiency and accelerated brain ageing

Structural ‘brain age’ is a valuable but complex biomarker for several brain disorders. The dog is an unrivalled comparator for neurological disease modeling, however canine brain morphometric diversity creates computational and statistical challenges. Using a data-driven approach, we explored complex interactions between patient metadata, brain morphometry, and neurological disease. Twenty-four morphometric parameters measured from 286 canine brain magnetic resonance imaging scans were combined with clinical parameters to generate 9,438 data points. Network analysis was used to cluster patients according to their brain morphometry profiles. An ‘aged-brain’ profile, defined by a small brain width and volume combined with ventriculomegaly, was revealed in the Boxer breed. Key features of this profile were paralleled in neutered female dogs which, relative to un-neutered females, had an 11-fold greater risk of developing brain tumours. Boxer dog and geriatric dog groups were both enriched for brain tumour diagnoses, despite a lack of geriatric Boxers within the cohort. Our findings suggest that advanced brain ageing enhances brain tumour risk in dogs and may be influenced by oestrogen deficiency—a risk factor for dementia and brain tumours in humans. Morphometric features of brain ageing in dogs, like humans, might better predict neurological disease risk than patient chronological age.

Saikosaponin‑D improves fear memory deficits in ovariectomized rats via the action of estrogen receptor‑α in the hippocampus

Saikosaponin‑D (SSD), which is the main bioactive component in the traditional Chinese medicine Chai Hu (Bupleurum falcatum L), possesses estrogen‑like properties and is widely used in treating estrogen‑related neurological disorders. The current study aimed to investigate the protective effects of SSD on the fear memory deficit in ovariectomized (OVX) rats and the potential underlying mechanism. SSD treatment significantly prolonged freezing time in OVX rats in a manner similar to that of estradiol (E2), whereas this effect was markedly suppressed by co‑administration of ICI182780, a non‑selective estrogen receptor (ER) inhibitor. The expression of ERα in the hippocampus of OVX rats was significantly elevated by SSD; however, Erβ expression and E2 synthesis were not markedly affected by SSD treatment. Collectively, this study demonstrated that SSD‑mediated fear memory improvement in OVX rats may be attributed not to E2 levels or ERβ activity, but to ERα activation in the hippocampus.

Epigenetic mechanisms related to cognitive decline during aging

Cognitive decline is a hallmark of the aging nervous system, characterized by increasing memory loss and a deterioration of mental capacity, which in turn creates a favorable context for the development of neurodegenerative diseases. One of the most detrimental alterations that occur at the molecular level in the brain during aging is the modification of the epigenetic mechanisms that control gene expression. As a result of these epigenetic-driven changes in the transcriptome most of the functions of the brain including synaptic plasticity, learning, and memory decline with aging. The epigenetic mechanisms altered during aging include DNA methylation, histone modifications, nucleosome remodeling, and microRNA-mediated gene regulation. In this review, we examine the current evidence concerning the changes of epigenetic modifications together with the molecular mechanisms underlying impaired neuronal gene transcription during aging. Herein, we discuss the alterations of DNA methylation pattern that occur in old neurons. We will also describe the most prominent age-related histone posttranslational modifications in the brain since changes in acetylation and methylation of specific lysine residues on H3 and H4 are associated to functional decline in the old. In addition, we discuss the role that changes in the levels of certain miRNAs would play in cognitive decline with aging. Finally, we provide an overview about the mechanisms either extrinsic or intrinsic that would trigger epigenetic changes in the aging brain, and the consequences of these changes, i.e., altered transcriptional profile and reactivation of transposable elements in old brain.

Loss of the interaction between estradiol and insulin-like growth factor I in brain endothelial cells associates to changes in mood homeostasis during peri-menopause in mice

We recently reported that exercise increases resilience to stress in young female mice. Underlying mechanisms include an interaction of the ovarian hormone estradiol (E2) with insulin-like growth factor I (IGF-I), and an increase in the hippocampal levels of the latter. Since changes in mood regulation during aging may contribute to increasing incidence of affective disorders at older age, we determined whether the protective actions of exercise are maintained at later ages. We found that during peri-menopause, exercise no longer improves resilience to stress and even becomes anxiogenic. Furthermore, the interaction seen in young females between the E2 α receptor (ERα) and the IGF-I receptor (IGF-IR) is lost at middle-age. In addition, E2 no longer induces IGF-I uptake by brain endothelial cells, and consequently, hippocampal IGF-I levels do not increase. Treatment of middle-aged females with an ERα agonist did not recover the positive actions of exercise. Collectively, these data indicate that the loss of action of exercise during peri-menopause may be related to a loss of the interaction of IGF-IR with ERα in brain endothelial cells that cannot be ameliorated by estrogen therapy. Changes in regulation of mood by physical activity may contribute to increased appearance of affective disorders along age.

Estrogen-related receptors alpha, beta and gamma expression and function is associated with transcriptional repressor EZH2 in breast carcinoma

BACKGROUND

Orphan nuclear receptors ERRα, ERRβ and ERRγ that belong to NR3B or type IV nuclear receptor family are well studied for their role in breast cancer pathophysiology. Their homology with the canonical estrogen receptor dictates their possible contributing role in mammary gland development and disease. Although function and regulation of ERRα, ERRγ and less about ERRβ is reported, role of histone methylation in their altered expression in cancer cells is not studied. Transcriptional activity of nuclear receptors depends on co-regulatory proteins. The present study for the first time gives an insight into regulation of estrogen-related receptors by histone methylation specifically through methyltransferase EZH2 in breast cancer.

METHODS

Expression of ERRα, ERRβ, ERRγ and EZH2 was assessed by immunohistochemistry in four identical tissue array slides that were prepared as per the protocol. The array slides were stained with ERRα, ERRβ, ERRγ and EZH2 simultaneously. Array data was correlated with expression in MERAV expression dataset. Pearson correlation coeficient r was calculated from the partial matrix expression values available at MERAV database to study the strength of association between EZH2 and three orphan nuclear receptors under study. By western blot and real time PCR, their correlated expression was studied in breast cancer cell lines MCF-7, MDA-MB-231, T47D and MDA-MB-453 including normal breast epithelial MCF-10A cells at both protein and RNA level. Regulation of ERRα, ERRβ, ERRγ by EZH2 was further investigated upon overexpression and silencing of EZH2. The interaction between ERRs and EZH2 was validated in vivo by CHIP-qPCR.

RESULTS

We found a negative correlation between estrogen-related receptors and Enhancer of Zeste Homolog 2, a global repressor gene. Immunohistochemistry in primary breast tumors of different grades showed a correlated expression of estrogen-related receptors and EZH2. Their correlated expression was further validated using online MERAV expression dataset where a negative correlation of variable strengths was observed in breast cancer. Ectopic expression of EZH2 in low EZH2-expressing normal breast epithelial cells abrogated their expression and at the same time, its silencing enhanced the expression of estrogen-related receptors in cancerous cells. Global occupancy of EZH2 on ERRα and ERRβ was observed in-vivo.

CONCLUSION

Our findings identify EZH2 as a relevant coregulator for estrogen-related receptors in breast carcinoma.

Aging in the Brain: New Roles of Epigenetics in Cognitive Decline

Gene expression in the aging brain depends on transcription signals generated by senescent physiology, interacting with genetic and epigenetic programs. In turn, environmental factors influence epigenetic mechanisms, such that an epigenetic-environmental link may contribute to the accumulation of cellular damage, susceptibility or resilience to stressors, and variability in the trajectory of age-related cognitive decline. Epigenetic mechanisms, DNA methylation and histone modifications, alter chromatin structure and the accessibility of DNA. Furthermore, small non-coding RNA, termed microRNA (miRNA) bind to messenger RNA (mRNA) to regulate translation. In this review, we examine key questions concerning epigenetic mechanisms in regulating the expression of genes associated with brain aging and age-related cognitive decline. In addition, we highlight the interaction of epigenetics with senescent physiology and environmental factors in regulating transcription.

Sexually divergent DNA methylation patterns with hippocampal aging

DNA methylation is a central regulator of genome function, and altered methylation patterns are indicative of biological aging and mortality. Age‐related cellular, biochemical, and molecular changes in the hippocampus lead to cognitive impairments and greater vulnerability to neurodegenerative disease that varies between the sexes. The role of hippocampal epigenomic changes with aging in these processes is unknown as no genome‐wide analyses of age‐related methylation changes have considered the factor of sex in a controlled animal model. High‐depth, genome‐wide bisulfite sequencing of young (3 month) and old (24 month) male and female mouse hippocampus revealed that while total genomic methylation amounts did not change with aging, specific sites in CG and non‐CG (CH) contexts demonstrated age‐related increases or decreases in methylation that were predominantly sexually divergent. Differential methylation with age for both CG and CH sites was enriched in intergenic and intronic regions and under‐represented in promoters, CG islands, and specific enhancer regions in both sexes, suggesting that certain genomic elements are especially labile with aging, even if the exact genomic loci altered are predominantly sex‐specific. Lifelong sex differences in autosomal methylation at CG and CH sites were also observed. The lack of genome‐wide hypomethylation, sexually divergent aging response, and autosomal sex differences at CG sites was confirmed in human data. These data reveal sex as a previously unappreciated central factor of hippocampal epigenomic changes with aging. In total, these data demonstrate an intricate regulation of DNA methylation with aging by sex, cytosine context, genomic location, and methylation level.

DNA Methylation of Synaptic Genes in the Prefrontal Cortex Is Associated with Aging and Age-Related Cognitive Impairment

The current study investigates DNA methylation as a possible epigenetic regulator of transcription associated with aging and cognitive function. Young and aged male Fischer 344 rats were behaviorally characterized on a set shifting task, and whole genome bisulfite sequencing was employed to profile the DNA methylome of the medial prefrontal cortex (mPFC). DNA methylation was also compared to RNA expression in the mPFC from the same animals. Variability in methylation was mainly observed for CpG sites as opposed to CHG and CHH sites. Gene bodies, specifically introns, contain the highest levels of methylation. During aging, hypermethylation was observed for genes linked to synaptic function and GTPase activity. Furthermore, impaired cognitive flexibility during aging was associated with hypermethylation of genes linked to postsynaptic density, dendrites, the axon terminus, and Ca²⁺ channels. Finally, comparison with RNA expression confirmed that hypermethylation was correlated with decreased expression of synaptic genes. The results indicate that DNA methylation over the lifespan contributes to synaptic modification observed in brain aging and age-related cognitive impairment.

Histone Deacetylase 2 Inhibition Attenuates Downregulation of Hippocampal Plasticity Gene Expression during Aging

The brain undergoes several anatomical, biochemical, and molecular changes during aging, which subsequently result in downregulation of synaptic plasticity genes and decline of memory. However, the regulation of these genes during aging is not clearly understood. Previously, we reported that the expression of histone deacetylase (HDAC)2 was upregulated in the hippocampus of old mice and negatively correlated with the decline in recognition memory. As HDAC2 regulates key synaptic plasticity neuronal immediate early genes (IEGs), we have examined their expression and epigenetic regulation. We noted that the expression of neuronal IEGs decreased both at mRNA and protein level in the hippocampus of old mice. To explore the underlying regulation, we analyzed the binding of HDAC2 and level of histone acetylation at the promoter of neuronal IEGs. While the binding of HDAC2 was higher, H3K9 and H3K14 acetylation level was lower at the promoter of these genes in old as compared to young and adult mice. Further, we inhibited HDAC2 non-specifically by sodium butyrate and specifically by antisense oligonucleotide to recover epigenetic modification, expression of neuronal IEGs, and memory in old mice. Inhibition of HDAC2 increased histone H3K9 and H3K14 acetylation level at the promoter of neuronal IEGs, their expression, and recognition memory in old mice as compared to control. Thus, inhibition of HDAC2 can be used as a therapeutic target to recover decline in memory due to aging and associated neurological disorders.