Estrogen receptor β as a therapeutic target for promoting neurogenesis and preventing neurodegeneration

Estrogen receptor β exerts neuroprotective effects by fine-tuning mitochondrial homeostasis through NRF1/PGC-1α

BACKGROUND

Estrogen deficiency causes mitochondrial defects that precede pathological changes related to Alzheimer's disease (AD) in the mouse model of postmenopause. The aim of this study was to investigate in such a mouse model whether and how estrogen receptor β (ERβ) was involved in prevention of mitochondrial damage and protection of neurons in the hippocampus.

METHODS

A mouse model of postmenopausal AD was created by ovariectomizing female 3xTg-AD mice, some of which were subcutaneously injected for six weeks with the non-steroidal ERβ agonist diarylpropionitrile. ERβ expression in female C57BL/6J mice was knocked down using shRNA interference. The different groups of animals were compared in terms of cognitive function using the Y-maze test, new object recognition test, and Morris water maze test, expression of numerous proteins related to mitochondrial biogenesis, mitophagy, apoptosis, and mitochondrial membrane potential, as well as deposition of amyloid β and neurofibrillary tangles. To complement these in vivo studies, we probed the effects of diarylpropionitrile on ERβ expression, apoptosis, and mitochondrial homeostasis in primary rat hippocampal neurons treated with amyloid β.

RESULTS

ERβ knockdown in C57BL/6J mice produced cognitive impairment, reduced mitochondrial biogenesis by downregulating PGC-1α, NRF1, mtTFA, and TOM20, and decreased mitophagy by downregulating Pink1, Parkin, and LC3B while upregulating PARIS and p62. ERβ knockdown promoted neuronal apoptosis by upregulating Cleaved-Caspase 9, Cleaved-Caspase 3, and Bax, while downregulating Bcl2 in hippocampus. Diarylpropionitrile mitigated cognitive decline in ovariectomized 3xTg-AD mice, which was associated with downregulation of BACE1, reduction of Aβ deposition, neurofibrillary tangles, and tau hyperphosphorylation, and upregulation of ERβ, increases in mitochondrial biogenesis and mitophagy, and decreases in apoptosis. The effects of diarylpropionitrile in mice were recapitulated in Aβ-injured primary rat hippocampal neurons.

CONCLUSIONS

ERβ activation can support learning and memory and alleviate AD symptoms in the postmenopausal AD model, which may involve regulation of neuronal mitochondrial biogenesis and mitophagy via NRF1/PGC-1α. This study supports further research on ERβ as a therapeutic target for postmenopausal women with AD.

Retrospective analysis of phytoSERM for management of menopause-associated vasomotor symptoms and cognitive decline: a pilot study on pharmacogenomic effects of mitochondrial haplogroup and APOE genotype on therapeutic efficacy

OBJECTIVE

PhytoSERM is a selective estrogen receptor beta (ERβ) modulator comprised of three phytoestrogens: genistein, daidzein, and S-equol. The PhytoSERM formulation promotes estrogenic action in the brain while largely inactive or inhibitory in reproductive tissue. A phase Ib/IIa clinical trial (ClinicalTrial.gov ID: NCT01723917) of PhytoSERM demonstrated safety and pharmacokinetics profile of PhytoSERM. While this study was not powered for efficacy analysis, we conducted a pilot, retrospective analysis to identify potential responders to PhytoSERM treatment, and to determine the optimal populations to pursue in a phase II clinical trial of efficacy of the PhytoSERM formulation.

METHODS

In this retrospective analysis involving 46 participants (n = 16, placebo; n = 18, 50 mg/d PhytoSERM; and n = 12, 100 mg/d PhytoSERM), the therapeutic effect of PhytoSERM was stratified by 2 genetic risk modulators for Alzheimer's disease: mitochondrial haplogroup and APOE genotype.

RESULTS

Our retrospective responder analysis indicated that participants on 50 mg of daily PhytoSERM (PS50) for 12 weeks significantly reduced hot flash frequency compared with their baseline (mean [95% CI])-1.61, [-2.79, -0.42], P = 0.007). Participants on 50 mg of PhytoSERM also had significantly greater reduction in hot flash frequency at 12 weeks compared with the placebo group (-1.38, -0.17 [median PS50, median placebo], P = 0.04). Fifty milligrams of daily PhytoSERM also preserved cognitive function in certain aspects of verbal learning and executive function. Our analysis further suggests that mitochondrial haplogroup and APOE genotype can modify PhytoSERM response.

CONCLUSION

Our data support a precision medicine approach for further development of PhytoSERM as a safe and effective alternative to hormone therapy for menopause-associated hot flash and cognitive decline. While definitive determination of PhytoSERM efficacy is limited by the small sample size, these data provide a reasonable rationale to extend analyses to a larger study set powered to address statistical significance.

Pharmacokinetics and safety profile of single-dose administration of an estrogen receptor β-selective phytoestrogenic (phytoSERM) formulation in perimenopausal and postmenopausal women

OBJECTIVE

Selected estrogen receptor β-selective phytoestrogen (phytoSERM), a preparation of genistein, daidzein, and S-equol, has an 83-fold selective affinity for estrogen receptor (ER) β, and may promote neuronal survival and estrogenic mechanisms in the brain without exerting feminizing activity in the periphery. The aim of this study was to assess the safety, tolerability, and single-dose pharmacokinetics of the phytoSERM formulation in perimenopausal and postmenopausal women.

METHODS

Eighteen women aged 45 to 60 years from a 12-week clinical trial evaluating cognitive performance and vasomotor symptoms were randomly assigned to placebo, 50 mg, or 100 mg phytoSERM treatment groups. Plasma levels of the three parent phytoestrogens and their metabolites were measured before and at 2, 4, 6, 8, and 24 hours after ingestion by isotope dilution high-performance liquid chromatography (HPLC) electrospray ionization tandem mass spectrometry.

RESULTS

Plasma concentrations of genistein, daidzein, and S-equol peaked at 9, 6, and 4 hours, respectively, for the 50-mg dose, and at 6, 6, and 5 hours, respectively, for the 100-mg dose. The maximum concentration (Cmax) and area under the curve (AUC) for the three parent compounds were greater in the 100-mg dose group, indicating a dose-dependent change in concentration with the phytoSERM treatment. No adverse events were elicited.

CONCLUSIONS

A single-dose oral administration of the phytoSERM formulation was well-tolerated and did not elicit any adverse events. It was rapidly absorbed, reached high plasma concentrations, and showed a linear dose-concentration response in its pharmacokinetics. These findings are consistent with previously reported parameters for each parent compound (Clinicaltrials.gov NCT01723917).

Sex steroids and neurogenesis

The brain has long been known as a dimorphic organ and as a target of sex steroids. It is also a site for their synthesis. Sex steroids in numerous ways can modify cerebral physiology, and along with many processes adult neurogenesis is also modulated by sex steroids. This review will focus on the effects of the main steroids, estrogens, androgens and progestogens, and unveil some aspects of their partly disclosed mechanisms of actions. Gonadal steroids act on different steps of neurogenesis: cell proliferation seems to be increased by estrogens only, while androgens and progestogens favor neuronal renewal by increasing cell survival; differentiation is a common target. Aging is characterized by a cognitive deficiency, paralleled by a decrease in the rate of neuronal renewal and in the levels of circulating gonadal hormones. Therefore, the effects of gonadal hormones on the aging brain are important to consider. The review will also be expanded to related molecules which are agonists to the nuclear receptors. Sex steroids can modify adult neuronal renewal and the extensive knowledge of their actions on neurogenesis is essential, as it can be a leading pathway to therapeutic perspectives.

Aluminum-induced molecular neurodegeneration: The protective role of genistein and chickpea extract

Neurotoxicity of Al is well established and linked to oxidative damage and neurodegeneration. This study investigated the protective role of genistein (Gen) and chickpea extract (CPE) against AlCl₃-induced neurodegeneration. HPLC analysis revealed that biochanin A-7-O-β-D-glucoside and biochanin A are the major components of the CPE. Gene expression of TNF-α, APP, BACE1, PSEN-2 and ER-β were assessed in brain extract using RT-PCR. Also, NF-кB subunit P65 and COX-2 expression were evaluated by western blotting. The cholinergic function, histological examination and oxidative status were also estimated. The AlCl₃ significantly up regulated the expression of the NF-кB subunit P65, COX-2, TNF- α, BACE1and APP while it significantly down regulated PSEN-2 and ER-β expression. The activity of acetyl cholinesterase (AChE) and the oxidative stress parameters as well as the histological examination confirmed the deleterious effect of AlCl₃. The administration of either CPE or Gen attenuated the expression of inflammatory cytokines, inhibited the amyloidogenesis and restored both the AChE activity and ER-β expression. Gen and CPE also inhibited the oxidative stress and ameliorated the histological alterations. Accordingly, the present study provides an insight on the molecular role of Gen and CPE as protective agents against neuronal injury.

Estrogen receptor β in Alzheimer's disease: From mechanisms to therapeutics

Alzheimer's disease (AD) disproportionally affects women and men. The female susceptibility for AD has been largely associated with the loss of ovarian sex hormones during menopause. This review examines the current understanding of the role of estrogen receptor β (ERβ) in the regulation of neurological health and its implication in the development and intervention of AD. Since its discovery in 1996, research conducted over the last 15-20 years has documented a great deal of evidence indicating that ERβ plays a pivotal role in a broad spectrum of brain activities from development to aging. ERβ genetic polymorphisms have been associated with cognitive impairment and increased risk for AD predominantly in women. The role of ERβ in the intervention of AD has been demonstrated by the alteration of AD pathology in response to treatment with ERβ-selective modulators in transgenic models that display pronounced plaque and tangle histopathological presentations as well as learning and memory deficits. Future studies that explore the potential interactions between ERβ signaling and the genetic isoforms of human apolipoprotein E (APOE) in brain aging and development of AD-risk phenotype are critically needed. The current trend of lost-in-translation in AD drug development that has primarily been based on early-onset familial AD (FAD) models underscores the urgent need for novel models that recapitulate the etiology of late-onset sporadic AD (SAD), the most common form of AD representing more than 95% of the current human AD population. Combining the use of FAD-related models that generally have excellent face validity with SAD-related models that hold more reliable construct validity would together increase the predictive validity of preclinical findings for successful translation into humans.

A cell-biased effect of estrogen in prion infection

Prion disorders are associated with the accumulation of a misfolded form (PrP(Sc)) of the normal prion protein, PrP(C). Here, we show that estrogen acts as a regulator of the processes of both prion infection and prion maintenance. Estrogen was found to be cell biased in its effect; it protected cells against prion infection in a prevention mode and enabled prion maintenance in a treatment mode. These processes were regulated by the estrogen receptor subtypes Erα and Erβ. By using specific receptor agonists, Erα was found to be the main receptor active in slowing prion infection, whereas in chronically infected cells, although Erα allowed partial maintenance of PrP(Sc) levels, Erβ was the main receptor involved in maintaining PrP(Sc) in a treatment paradigm. A cell-biased effect of estrogen has been reported for other neurodegenerative disorders, including Alzheimer's disease. Estrogen's effect is dependent on the cell's health status, which impacts the use of estrogen. This work also identified that by targeting the estrogen receptors with the selective estrogen receptor modulators tamoxifen (Tam) and 4-hydroxy-tamoxifen (OHT), PrP(Sc) could be cleared from prion-infected cell culture. Tam and OHT had half-maximal inhibitory concentrations for clearance of PrP(Sc) of 0.47 μM and 0.14 nM, respectively. This work identifies further factors involved in the prion disease process, and through antagonism of the estrogen system, we demonstrate that the estrogen system is a target for controlling PrP(Sc) levels.

Estrogen receptor β-selective phytoestrogenic formulation prevents physical and neurological changes in a preclinical model of human menopause

OBJECTIVE

As an alternative to estrogen therapy, the efficacy of an estrogen receptor β-selective phytoestrogenic (phyto-β-SERM) formulation to regulate climacteric symptoms and decline in brain responses associated with ovarian hormone loss in menopause was assessed.

METHODS

A phyto-β-SERM formulation-containing diet was compared with a commercial soy extract diet and a phytoestrogen-free base/control diet in an ovariectomized (OVX) mouse model of human menopause. Two treatment studies were conducted: (1) a 2-month study assessed the effects of experimental diets on tail skin temperature as a model of menopausal hot flashes, and (2) a 9-month study assessed the long-term impact of the diets on overall health, hair thinning/loss, spatial working memory, and associated protein expression in the hippocampus.

RESULTS

The phyto-β-SERM diet prevented OVX-induced menopause-like changes including the rise in skin temperature, hair thinning/loss, deficit in spatial memory function, and reversed OVX-induced decline in the expression of hippocampal proteins involved in neural plasticity and β-amyloid degradation/clearance. The soy extract diet had no effect or exacerbated OVX-induced changes.

CONCLUSIONS

Overall, the phyto-β-SERM diet induced physical and neurological responses comparable with ovary-intact mice, suggesting the therapeutic potential of the phyto-β-SERM formulation for the prevention/alleviation of climacteric symptoms and decline in brain responses induced by ovarian hormone loss, which provides the basis for further work in postmenopausal women.

17β-Estradiol regulates insulin-degrading enzyme expression via an ERβ/PI3-K pathway in hippocampus: relevance to Alzheimer's prevention

Insulin-degrading enzyme (IDE), an enzyme that primarily degrades insulin, has recently been demonstrated to play a significant role in the catabolism of amyloid β (Aβ) protein in the brain. Reduced IDE expression and/or activity have been associated with the etiology and development of Alzheimer's disease (AD). Using three model systems, the present investigation provides the first documentation indicating that estrogen robustly regulates the expression of IDE in normal, menopausal and early-stage AD brains. In vitro analyses in primary cultures of rat hippocampal neurons revealed that 17β-estradiol (17β-E2) increased IDE in both mRNA and protein levels in a time-dependent manner. Further pharmacological analyses indicated that 17β-E2-induced IDE expression was dependent upon estrogen receptor (ER) β and required activation of phosphatidylinositol 3-kinase (PI3-K). In vivo analyses in adult female rats revealed a brain region-specific responsive profile. Ovariectomy (OVX) induced a significant decline in IDE expression in the hippocampus, which was prevented by 17β-E2. Neither OVX nor 17β-E2 affected IDE expression in the cerebellum. In vivo analyses in triple transgenic AD (3xTg-AD) female mice revealed an inverse correlation between the age-related increase in Aβ load and the decrease in IDE expression in the hippocampal formation. Treatment with 17β-E2 attenuated Aβ accumulation/plaque formation and elevated hippocampal IDE expression in 12-month-old 3xTg-AD OVX mice. Collectively, these findings indicate that 17β-E2 regulates IDE expression in a brain region-specific manner and such a regulatory role in the hippocampus, mediated by an ERβ/PI3-K pathway, could serve as a direct mechanism underlying estrogen-mediated preventative effect against AD when initiated at the onset of menopause.

In silico prediction of estrogen receptor subtype binding affinity and selectivity using statistical methods and molecular docking with 2-arylnaphthalenes and 2-arylquinolines

Over the years development of selective estrogen receptor (ER) ligands has been of great concern to researchers involved in the chemistry and pharmacology of anticancer drugs, resulting in numerous synthesized selective ER subtype inhibitors. In this work, a data set of 82 ER ligands with ERα and ERβ inhibitory activities was built, and quantitative structure-activity relationship (QSAR) methods based on the two linear (multiple linear regression, MLR, partial least squares regression, PLSR) and a nonlinear statistical method (Bayesian regularized neural network, BRNN) were applied to investigate the potential relationship of molecular structural features related to the activity and selectivity of these ligands. For ERα and ERβ, the performances of the MLR and PLSR models are superior to the BRNN model, giving more reasonable statistical properties (ERα: for MLR, R_tr² = 0.72, Q_te² = 0.63; for PLSR, R_tr² = 0.92, Q_te² = 0.84. ERβ: for MLR, R_tr² = 0.75, Q_te² = 0.75; for PLSR, R_tr² = 0.98, Q_te² = 0.80). The MLR method is also more powerful than other two methods for generating the subtype selectivity models, resulting in R_tr² = 0.74 and Q_te² = 0.80. In addition, the molecular docking method was also used to explore the possible binding modes of the ligands and a relationship between the 3D-binding modes and the 2D-molecular structural features of ligands was further explored. The results show that the binding affinity strength for both ERα and ERβ is more correlated with the atom fragment type, polarity, electronegativites and hydrophobicity. The substitutent in position 8 of the naphthalene or the quinoline plane and the space orientation of these two planes contribute the most to the subtype selectivity on the basis of similar hydrogen bond interactions between binding ligands and both ER subtypes. The QSAR models built together with the docking procedure should be of great advantage for screening and designing ER ligands with improved affinity and subtype selectivity property.

Estrogen-induced plasticity from cells to circuits: predictions for cognitive function

Controversy regarding estrogen action in the brain remains at the forefront of basic, translational and clinical science for women's health. Here, I provide an integrative analysis of estrogen-inducible plasticity and posit it as a strategy for predicting cognitive domains affected by estrogen in addition to sources of variability. Estrogen enhancement of plasticity is evidenced by increases in neurogenesis, neural network connectivity and synaptic transmission. In parallel, estrogen increases glucose transport, aerobic glycolysis and mitochondrial function to provide the ATP necessary to sustain increased energetic demand. The pattern of plasticity predicts that estrogen would preferentially affect cognitive tasks of greater complexity, temporal demand and associative challenge. Thus, estrogen deprivation should be associated with decrements in these functions. Estrogen regulation of plasticity and bioenergetics provides a framework for predicting estrogen-dependent cognitive functions while also identifying sources of variability and potential biomarkers for identifying women appropriate for hormone therapy.

A select combination of clinically relevant phytoestrogens enhances estrogen receptor beta-binding selectivity and neuroprotective activities in vitro and in vivo

We have previously shown that a number of naturally occurring phytoestrogens and derivatives were effective to induce some measures of neuroprotective responses but at a much lower magnitude than those induced by the female gonadal estrogen 17beta-estradiol. In the present study, we sought to investigate whether a combination of select phytoestrogens could enhance neural responses without affecting the reproductive system. We performed a range of comparative analyses of the estrogen receptor (ER) alpha/beta binding profile, and in vitro to in vivo estrogenic activities in neural and uterine tissues induced by clinically relevant phytoestrogens: genistein, daidzein, equol, and IBSO03569, when used alone or in combination. Our analyses revealed that both the ERalpha/beta binding profile and neural activities associated with individual phytoestrogens are modifiable when used in combination. Specifically, the combination of genistein plus daidzein plus equol resulted in the greatest binding selectivity for ERbeta and an overall improved efficacy/safety profile when compared with single or other combined formulations, including: 1) an approximate 30% increase in ERbeta-binding selectivity (83-fold over ERalpha); 2) a greater effect on neuronal survival against toxic insults in primary neurons; 3) an enhanced activity in promoting neural proactive defense mechanisms against neurodegeneration, including mitochondrial function and beta-amyloid degradation; and 4) no effect on uterine growth. These observations suggest that select phytoestrogens in combination have the therapeutic potential of an alternative approach to conventional estrogen therapy for long-term safe use to reduce the increased risk of cognitive decline and neurodegenerative disease associated with menopause in women.

WHI and WHIMS follow-up and human studies of soy isoflavones on cognition

Recent follow-up analyses of the previous findings from the Women's Health Initiative and the Women's Health Initiative Memory Study confirmed some health benefits of estrogen-containing hormone therapy (HT) in women within 10 years from the onset of menopause. However, the potential risks associated with long-term administration of HT, such as breast cancer and stroke, remain a concern for therapy recipients, underlying the need for an alternative treatment that is functionally equivalent but with a greater safety profile. Owing to their structural and functional resemblance to mammalian estrogens and lack of evident adverse effects, research interest in plant-derived phytoestrogens has increased in the past decade. While multiple health-promoting benefits of phytoestrogens have been proposed from basic science, the clinical data remain inconclusive. This review provides a comparative analysis of human studies on the effects of soy-based isoflavones on cognition. Of the eight studies published in 2000-2007, seven were conducted in postmenopausal women, four of which revealed a positive impact of isoflavones on cognitive function. Multiple factors could have contributed to the discrepant outcomes across studies, such as variation in the composition of phytoestrogen interventions and the heterogeneous characteristics of the study population. Thus, a well-designed clinical study based on a standardized stable formulation in a well-characterized study population is required in order to reach a clinical consensus. A formulation composed of select estrogen receptor beta-selective phytoestrogens with a rationally designed composition would avoid the potential antagonism present in a mixture and thus enhance therapeutic efficacy. In addition, inclusion of equol in a study formulation offers a potential synergistic effect from equol in both equol-producing and nonproducing individuals, as well as added benefits for men. With respect to the design of study population, a clinically consistent effect could potentially be achieved by stratifying populations based on genotype, age, hormonal history and even diets. Development of an effective phytoestrogen formulation would benefit both women and men to prevent or treat hormone-dependent conditions and, most of all, to improve neurological health and reduce the risk of Alzheimer's disease.

Relationship between estrogen and schizophrenia

There is a wealth of historical and circumstantial evidence to suggest that female patients with schizophrenia may suffer from a deficit in estrogenic function. The prolactin-inducing properties of most antipsychotic drugs, and subsequent negative feedback on estrogen levels, is in keeping with this. The functions of estrogen, its complex receptor organization and its numerous actions are the focus of ongoing research activity. Of particular interest are its neuroprotective properties, particularly with regard to cognitive impairment, and its involvement with neurotransmitter systems, which are the substrate for psychotropic drugs. Estrogen has now been used as an adjunct to standard antipsychotic medication in quite a few studies of female schizophrenia patients. However, most of these are not double-blind, randomized, controlled trials. Only two relatively small double-blind, randomized clinical trials returned positive results: one long-term study that selected for hypoestrogenism reported negative findings. Furthermore, recent evidence of the risks of long-term hormone replacement therapy is of concern. The advent of specific estrogen receptor modulators, which may avoid excess risks of cancer and cardiovascular events, will have little to add to schizophrenia treatment if estrogen is, essentially, devoid of any specific antipsychotic or adjuvant mechanism of action relevant to the pathophysiology of this disorder.