Early initiation of hormone therapy in menopausal women is associated with increased hippocampal and posterior cingulate cholinergic activity

Choline kinase alpha genotype is related to hippocampal brain volume and cognition in postmenopausal women

This study examined how single nucleotide polymorphisms (SNPs) related to choline synthesis and metabolism, processes largely regulated by estrogen, influenced hippocampal volume and neuropsychological function following menopause. We investigated the effect of choline kinase alpha (CHKA) genotype on brain volume and neuropsychological performance in postmenopausal women. The effect alleles of certain CHKA SNPs (rs6591331 T, rs10791957 A) are associated with varied responses to choline deficiency and delegation of choline to physiological pathways. The presence of these alleles was hypothesized to correlate with worse cognitive performance in women after menopause. Results from structural MRI scans revealed larger right hippocampal volumes in subjects with a T/T CHKA rs6591331 genotype compared to A/A subjects. Delayed memory scores from the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) were lower in subjects with T/T genotypes compared to those with the A/T genotype and the A/A genotype. Based on these findings, we proposed a CHKA-dependent mechanism present within the brain to compensate for the decreased estrogen and biosynthesized choline associated with menopause.

The historical progression of positron emission tomography research in neuroendocrinology

The rapid and continual development of a number of radiopharmaceuticals targeting different receptor, enzyme and small molecule systems has fostered Positron Emission Tomography (PET) imaging of endocrine system actions in vivo in the human brain for several decades. PET radioligands have been developed to measure changes that are regulated by hormone action (e.g., glucose metabolism, cerebral blood flow, dopamine receptors) and actions within endocrine organs or glands such as steroids (e.g., glucocorticoids receptors), hormones (e.g., estrogen, insulin), and enzymes (e.g., aromatase). This systematic review is targeted to the neuroendocrinology community that may be interested in learning about positron emission tomography (PET) imaging for use in their research. Covering neuroendocrine PET research over the past half century, researchers and clinicians will be able to answer the question of where future research may benefit from the strengths of PET imaging.

The Role of Hormonal Replacement Therapy in BRCA Mutated Patients: Lights and Shadows

All cancers develop as a result of mutations in genes. DNA damage induces genomic instability and subsequently increases susceptibility to tumorigenesis. Women who carry mutations of BRCA 1 and BRCA2 genes have an augmented risk of breast and ovarian cancer and a markedly augmented probability of dying because of cancer compared to the general population. As a result, international guidelines recommend that all BRCA1\2 mutation carriers be offered risk-reducing bilateral salpingo-oophorectomy at an early age to reduce the risk of cancer and decrease the mortality rate of this high-risk population. NCCN guidelines recommend risk-reducing bilateral salpingo-oophorectomy in pre-menopausal women, between 35-40 years in BRCA1 mutation carriers and between 40-45 years in BRCA2 mutation carriers. Unfortunately, the well-documented reduction of cancer risk is counterbalanced by early sterility and premature ovarian failure with an early onset of secondary menopausal syndromes such as neuromotor, cardiovascular, cognitive and urogenital deficiency. Hormonal replacement therapy significantly compensates for hormonal deprivation and counteracts menopausal syndrome morbidity and mortality; however, some data suggest a possible correlation between hormonal medications and cancer risk, especially in BRCA1\2 carriers who undergo long-term regimens. Conversely, short-term treatment before the age of natural menopause does not appear to increase the cancer risk in BRCA1 mutation carriers without a personal history of breast cancer after prophylactic surgery. Few data are available on BRCA2 mutation carriers and more well-designed studies are needed. In conclusion, clinicians should propose short-term hormone replacement therapy to BRCA 1 carriers to counteract hormonal deprivation; personalized counselling should be offered to BRCA2 mutation carriers for a balance between the risks and benefits of the treatment.

Memory-Enhancing Effect of 8-Week Consumption of the Quercetin-Enriched Culinary Herbs-Derived Functional Ingredients: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Due to great demand for memory enhancers, the memory-enhancing effects and the possible underlying mechanisms of the functional ingredients derived from the combined extract of Polygonum odoratum and Morus alba were investigated. A total of 45 participants randomly received either a placebo or the developed herbal supplement at a dose of 50 or 1500 mg/day. The consumption was done once daily for 8 weeks. Working memory was assessed via both an event-related potential and computerized battery tests at baseline and at the end of the 8-week study period. Acetylcholinesterase (AChE) and monoamine oxidase type A and type B (MAO-A, MAO-B) levels were also measured at the end of the study. The subjects who consumed the supplement containing a developed functional ingredient at a dose of 1500 mg/day showed reduced latencies but increased amplitudes of N100 and P300. An improvement in working memory and the suppression of AChE, MAO-A, and MAO-B activities were also observed. Therefore, this study clearly demonstrates the cognitive enhancing effect of the developed herbal congee, which may be associated with the suppressions of AChE and both types of MAO.

Estradiol treatment in young postmenopausal women with self-reported cognitive complaints: Effects on cholinergic-mediated cognitive performance

OBJECTIVE

Older women are at increased risk of developing Alzheimer's disease compared to men. One proposed reason is that following menopause there is a decline in estrogens. Estrogens are important for cholinergic functioning and attenuate the impact of cholinergic antagonists on cognitive performance in postmenopausal women. Self-reported or subjective cognitive complaints in middle or older age may represent a harbinger of cognitive decline and those who endorse cognitive complaints appear more likely to develop future cognitive impairment. However, the response of individuals with cognitive complaints after menopause to estrogen and the relationship to cholinergic functioning has not been investigated. This study investigated the effect of estrogen treatment using 17β-estradiol on cognitive performance following anticholinergic blockade in postmenopausal women and the relationship of this interaction with the level of self-reported (subjective) postmenopausal cognitive complaints.

METHODS

Forty postmenopausal women (aged 50-60 years) completed a 3-month treatment regimen of either 1 mg oral estradiol or placebo. Participants then completed four challenge days in which they completed cognitive and behavioral tasks after one of four cholinergic antagonist drug conditions (oral mecamylamine (MECA), intravenous scopolamine, combined MECA and scopolamine, or PLC).

RESULTS

Compared to PLC, the estradiol treated group performed worse on attention tasks under cholinergic challenge including the choice reaction time task and the critical flicker fusion task. In addition, participants who endorsed greater cognitive complaints showed reduced performance on the N-back working memory task, regardless of whether they received estradiol treatment.

CONCLUSIONS

The findings of this study indicate that estradiol treatment was unable to mitigate anticholinergic blockade in postmenopausal women with subjective cognitive complaints, and worsened performance on attention tasks. Moreover, the present study suggests that greater levels of cognitive complaints following menopause may be associated with an underlying decline in cholinergic function that may manifest as an inability to compensate during working memory tasks.

Postmenopausal hormone treatment alters neural pathways but does not improve verbal cognitive function

OBJECTIVE

Cognitive outcomes in trials of postmenopausal hormone treatment have been inconsistent. Differing outcomes may be attributed to hormone formulation, treatment duration and timing, and differential cognitive domain effects. We previously demonstrated treatment benefits on visual cognitive function. In the present study, we describe the effects of hormone treatment on verbal outcomes in the same women, seeking to understand the effects of prior versus current hormone treatment on verbal function.

METHODS

This is a cross-sectional evaluation of 57 women (38 hormone users [25 prior long-term users and 13 current users] and 19 never-users). Hormone users took identical formulations of estrogen or estrogen + progestin (0.625 mg/d conjugated equine estrogens with or without medroxyprogesterone acetate) for at least 10 years, beginning within 2 years of menopause. Women were evaluated with tests of verbal function and functional magnetic resonance imaging (fMRI) of a verbal discrimination task.

RESULTS

All women scored similarly on assessments of verbal function (Hopkins Verbal Learning Test and a verbal discrimination task performed during the fMRI scanning session); however, women ever treated with hormones had more left inferior frontal (T = 3.72; P < 0.001) and right prefrontal cortex (T = 3.53; P < 0.001) activation during the verbal task. Hormone-treated women performed slightly worse on the verbal discrimination task (mean accuracy 81.72 ± 11.57 ever-treated, 85.30 ± 5.87 never-treated, P = 0.14), took longer to respond (mean reaction time 1.10 ± 0.17 s ever-treated, 1.02 ± 0.11 never-treated, P = 0.03), and remembered fewer previously viewed words (mean accuracy 62.21 ± 8.73 ever-treated, 65.45 ± 7.49 never-treated, P = 0.18). Increased posterior cingulate activity was associated with longer response times (R = 0.323, P = 0.015) and worse delayed verbal recall (R = -0.328, P = 0.048), suggesting that increased activation was associated with less efficient cognitive processing. We did not detect between group differences in activation in the left prefrontal cortex, superior frontal cortex, thalamus, or occipital/parietal junction.

CONCLUSIONS

Although current and past hormone treatment was associated with differences in neural pathways used during verbal discrimination, verbal function was not higher than never-users.

The Role of Estrogen in Brain and Cognitive Aging

There are 3 common physiological estrogens, of which estradiol (E2) is seen to decline rapidly over the menopausal transition. This decline in E2 has been associated with a number of changes in the brain, including cognitive changes, effects on sleep, and effects on mood. These effects have been demonstrated in both rodent and non-human preclinical models. Furthermore, E2 interactions have been indicated in a number of neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, and depression. In normal brain aging, there are a number of systems that undergo changes and a number of these show interactions with E2, particularly the cholinergic system, the dopaminergic system, and mitochondrial function. E2 treatment has been shown to ameliorate some of the behavioral and morphological changes seen in preclinical models of menopause; however, in clinical populations, the effects of E2 treatment on cognitive changes after menopause are mixed. The future use of sex hormone treatment will likely focus on personalized or precision medicine for the prevention or treatment of cognitive disturbances during aging, with a better understanding of who may benefit from such treatment.

Age-specific associations between oestradiol, cortico-amygdalar structural covariance, and verbal and spatial skills

Oestradiol is known to play an important role in the developing human brain, although little is known about the entire network of potential regions that might be affected and how these effects may vary from childhood to early adulthood, which in turn can explain sexually differentiated behaviours. In the present study, we examined the relationships between oestradiol, cortico-amygdalar structural covariance, and cognitive or behavioural measures typically showing sex differences (verbal/spatial skills, anxious-depressed symptomatology) in 152 children and adolescents (aged 6-22 years). Cortico-amygdalar structural covariance shifted from positive to negative across the age range. Oestradiol was found to diminish the impact of age on cortico-amygdalar covariance for the pre-supplementary motor area/frontal eye field and retrosplenial cortex (across the age range), as well as for the posterior cingulate cortex (in older children). Moreover, the influence of oestradiol on age-related cortico-amygdalar networks was associated with higher word identification and spatial working memory (across the age range), as well as higher reading comprehension (in older children), although it did not impact anxious-depressed symptoms. There were no significant sex effects on any of the above relationships. These findings confirm the importance of developmental timing on oestradiol-related effects and hint at the non-sexually dimorphic role of oestradiol-related cortico-amygdalar structural networks in aspects of cognition distinct from emotional processes.

Effects of the experimental administration of oral estrogen on prefrontal functions in healthy young women

17-Beta-estradiol (E2) stimulates neural plasticity and dopaminergic transmission in the prefrontal cortex, which is critically involved in attentional control, working memory, and other executive functions. Studies investigating E2's actions on prefrontally mediated behavior in the course of the menstrual cycle or during hormone replacement therapy are inconclusive, with numerous null findings as well as beneficial and detrimental effects. The current study focused on the effect of E2 on attentional performance, as animal studies indicate that supraphysiological doses (i.e., above estrous cycle levels) of E2 have beneficial effects on measures of attention in female rodents. To translate these findings to humans, we administered 12 mg E2-valerate or placebo orally to 34 naturally cycling women in the low-hormone early follicular phase using a randomized, double-blinded, pre-post design. Behavioral performance was tested twice during baseline and E2 peak, where E2 levels reached mildly supraphysiological levels in the E2 group. Aside from mainly prefrontally mediated tasks of attention, working memory, and other executive functions, we employed tasks of affectively modulated attention, emotion recognition, and verbal memory. E2 administration had a significant, but subtle negative impact on general processing speed and working memory performance. These effects could be related to an overstimulation of dopaminergic transmission. The negative effect of supraphysiological E2 on working memory connects well to animal literature. There were no effects on attentional performance or any other measure. This could be explained by different E2 levels being optimal for changing behavioral performance in specific tasks, which likely depends on the brain regions involved.

Luteinizing hormone acts at the hippocampus to dampen spatial memory

Luteinizing hormone (LH) rises dramatically during and after menopause, and has been correlated with an increased incidence of Alzheimer's disease and decreased memory performance in humans and animal models. To test whether LH acts directly on the dorsal hippocampus to affect memory, ovariectomized female rats were infused with either the LH-homologue human chorionic gonadotropin (hCG) or the LH receptor antagonist deglycosylated-hCG (dg-hCG). Infusion of hCG into either the lateral ventricle or the dorsal hippocampus caused significant memory impairments in ovariectomized estradiol-treated females. Consistent with this, infusion of the LH antagonist dg-hCG into the dorsal hippocampus caused an amelioration of memory deficits in ovariectomized females. Furthermore, the gonadotropin-releasing hormone antagonist Antide, failed to act in the hippocampus to affect memory. These findings demonstrate a significant role for LH action in the dorsal hippocampus in spatial memory dysfunction.

Luteinizing hormone as a key player in the cognitive decline of Alzheimer's disease

This article is part of a Special Issue "SBN 2014". Alzheimer's disease is one of the most prevalent and costly neurological diseases in the world. Although decades of research have focused on understanding Alzheimer's disease pathology and progression, there is still a great lack of clinical treatments for those who suffer from it. One of the factors most commonly associated with the onset of Alzheimer's disease is a decrease in levels of gonadal hormones, such as estrogens and androgens. Despite the correlational and experimental data which support the role of these hormones in the etiology of Alzheimer's disease, clinical trials involving their reintroduction through hormone therapy have had varied results and these gonadal hormones often have accompanying health risks. More recently, investigation has turned toward other hormones in the hypothalamic-pituitary-gonadal axis that are disrupted by age-related decreases in gonadal hormones. Specifically, luteinizing hormone, which is increased with age in both men and women (in response to removal of negative feedback), has surfaced as a potentially powerful player in the risk and onset of Alzheimer's disease. Mounting evidence in basic research and epidemiological studies supports the role of elevated luteinizing hormone in exacerbating age-related cognitive decline in both males and females. This review summarizes the recent developments involving luteinizing hormone in increasing the cognitive deficits and molecular pathology characteristic of Alzheimer's disease.

Estrogen-cholinergic interactions: Implications for cognitive aging

This article is part of a Special Issue "Estradiol and Cognition". While many studies in humans have investigated the effects of estrogen and hormone therapy on cognition, potential neurobiological correlates of these effects have been less well studied. An important site of action for estrogen in the brain is the cholinergic system. Several decades of research support the critical role of CNS cholinergic systems in cognition in humans, particularly in learning and memory formation and attention. In humans, the cholinergic system has been implicated in many aspects of cognition including the partitioning of attentional resources, working memory, inhibition of irrelevant information, and improved performance on effort-demanding tasks. Studies support the hypothesis that estradiol helps to maintain aspects of attention and verbal and visual memory. Such cognitive domains are exactly those modulated by cholinergic systems and extensive basic and preclinical work over the past several decades has clearly shown that basal forebrain cholinergic systems are dependent on estradiol support for adequate functioning. This paper will review recent human studies from our laboratories and others that have extended preclinical research examining estrogen-cholinergic interactions to humans. Studies examined include estradiol and cholinergic antagonist reversal studies in normal older women, examinations of the neural representations of estrogen-cholinergic interactions using functional brain imaging, and studies of the ability of selective estrogen receptor modulators such as tamoxifen to interact with cholinergic-mediated cognitive performance. We also discuss the implications of these studies for the underlying hypotheses of cholinergic-estrogen interactions and cognitive aging, and indications for prophylactic and therapeutic potential that may exploit these effects.

Actions and interactions of estradiol and glucocorticoids in cognition and the brain: Implications for aging women

Menopause involves dramatic declines in estradiol production and levels. Importantly, estradiol and the class of stress hormones known as glucocorticoids exert countervailing effects throughout the body, with estradiol exerting positive effects on the brain and cognition, glucocorticoids exerting negative effects on the brain and cognition, and estradiol able to mitigate negative effects of glucocorticoids. Although the effects of these hormones in isolation have been extensively studied, the effects of estradiol on the stress response and the neuroprotection offered against glucocorticoid exposure in humans are less well known. Here we review evidence suggesting that estradiol-related protection against glucocorticoids mitigates stress-induced interference with cognitive processes. Animal and human research indicates that estradiol-related mitigation of glucocorticoid damage and interference is one benefit of estradiol supplementation during peri-menopause or soon after menopause. The evidence for estradiol-related protection against glucocorticoids suggests that maintaining estradiol levels in post-menopausal women could protect them from stress-induced declines in neural and cognitive integrity.

Functional and molecular neuroimaging of menopause and hormone replacement therapy

The level of gonadal hormones to which the female brain is exposed considerably changes across the menopausal transition, which in turn, is likely to be of great relevance for neurodegenerative diseases and psychiatric disorders. However, the neurobiological consequences of these hormone fluctuations and of hormone replacement therapy in the menopause have only begun to be understood. The present review summarizes the findings of thirty-five studies of human brain function, including functional magnetic resonance imaging, positron and single-photon computed emission tomography studies, in peri- and postmenopausal women treated with estrogen, or estrogen-progestagen replacement therapy. Seven studies using gonadotropin-releasing hormone agonist intervention as a model of hormonal withdrawal are also included. Cognitive paradigms are employed by the majority of studies evaluating the effect of unopposed estrogen or estrogen-progestagen treatment on peri- and postmenopausal women's brain. In randomized-controlled trials, estrogen treatment enhances activation of fronto-cingulate regions during cognitive functioning, though in many cases no difference in cognitive performance was present. Progestagens seems to counteract the effects of estrogens. Findings on cognitive functioning during acute ovarian hormone withdrawal suggest a decrease in activation of the left inferior frontal gyrus, thus essentially corroborating the findings in postmenopausal women. Studies of the cholinergic and serotonergic systems indicate these systems as biological mediators of hormonal influences on the brain. More, hormonal replacement appears to increase cerebral blood flow in several cortical regions. On the other hand, studies on emotion processing in postmenopausal women are lacking. These results call for well-powered randomized-controlled multi-modal prospective neuroimaging studies as well as investigation on the related molecular mechanisms of effects of menopausal hormonal variations on the brain.

Effects of estrogen and testosterone treatment on serotonin transporter binding in the brain of surgically postmenopausal women--a PET study

Sex hormones and the serotonergic system interact in the regulation of mood, learning, memory and sexual behaviour. However, the mechanisms have not been fully explored. The serotonin transporter protein (5-HTT) regulates synaptic concentrations of serotonin and is a primary target for selective serotonin reuptake inhibitors. The aim of this study was to explore how estrogen treatment alone or in combination with testosterone affects 5-HTT binding potentials measured by positron emission tomography (PET) in specific brain regions of postmenopausal women. Ten healthy surgically postmenopausal women (years since oophorectomy 7.5 ± 4.0, mean ± SD) underwent PET examinations at baseline, after three months of estrogen treatment (transdermal estradiol 100 μg/24 hours) and after another three months of combined estrogen and testosterone (testosterone undecanoate 40 mg daily) treatment using the radioligand [(11)C] MADAM developed for examination of the serotonin transporter. The 5-HTT binding potentials decreased significantly in several cortical regions, as well as in limbic and striatal regions after both estrogen treatment alone and combined estrogen/testosterone treatment in comparison to baseline. The observed decrease in 5-HTT could either be due to direct effects on serotonin transporter expression or be the result of indirect adaptation to estrogen and /or testosterone effects on synaptic serotonin levels. Although the mechanism still needs further exploration, the study supports the view that gonadal hormones play a role in serotonin regulated mood disorders.

Insulin resistance and medial prefrontal gyrus metabolism in women receiving hormone therapy

Insulin resistance (IR) is a putative risk factor for cognitive decline and dementia, and has been shown to impede neuronal glucose metabolism in animal models. This post hoc study focused on metabolic changes in the medial prefrontal region, a brain region exhibiting decline years before documented cognitive changes, relative to high or low IR status in a cohort of postmenopausal women at risk for dementia who were randomized to continue or discontinue existing stable hormone therapy (HT) for 2 years. Subjects were dichotomized into high and low IR groups based on the homeostatic model assessment of insulin resistance, which was within clinically normal limits for the group as a whole at both baseline and 2-year follow-up. Results showed that high and low IR groups showed significant differences in metabolic decline of the medial prefrontal gyrus, regardless of HT randomization group. However, HT randomization was predictive of metabolic decline only in women with low HOMA (homeostatic assessment of insulin resistance). Performance in working memory was consistent with observed metabolic changes. These results suggest IR may be an independent moderator of regional metabolic changes, while protective metabolic effects of HT are most apparent in those at low-end range of IR. If replicated in future studies, these findings will help to better understand the interaction between putative risk and protective factors, and further delineate cohort postmenopausal women who may benefit from HT.

The Women's Health Initiative trial and related studies: 10 years later: a clinician's view

The Women's Health Initiative (WHI) assessed the long-term effects of hormone therapy (HT) in postmenopausal women. The WHI started HT treatment on women aged 50-79 years in order to ascertain these effects. The study was ended early, due to findings of increased risk of coronary heart disease, breast cancer, stroke, and thromboembolic complications in women receiving estrogen plus progestin, compared to placebo. An increased risk of thromboembolic complications was also demonstrated in the estrogen only component of the WHI. The WHI results were initially reported for all subjects, and showed little difference when data were not analyzed by age. New WHI sub-analyses stratifying results by age, and an extended follow-up of the WHI offer a more complete picture of the effects of HT, revealing that starting HT in postmenopausal women less than ten years from last menstrual period appears to have less risk. In addition, hysterectomized women treated with estrogen only in the WHI have showed less risk of adverse outcomes than women in the estrogen plus progestin group. In this paper, we review data supporting the use of HT administered to postmenopausal women, showing it to have more benefit than risk for symptom control, prevention of bone mineral loss and fracture, and improvement of the metabolic profile in women who began HT when they were less than 60 years of age and had their last menstrual period less than ten years previous. In hysterectomized women treated with estrogen only, a reduction in breast cancer risk was noted in all age groups. The WHI raised many important questions. Ten years later, some have been answered, including confirmation that HT for most newly menopausal women is safe and effective. The treatment of the aging woman, including hormone treatment after menopause, should remain one of our highest research priorities. This article is part of a Special Issue entitled 'Menopause'.

Hormonal environment affects cognition independent of age during the menopause transition

CONTEXT

Cognitive decline is prevalent in aging populations, and cognitive complaints are common during menopause. However, the extent of hormonal influence is unclear, particularly when considered independent of the aging process.

OBJECTIVE

We sought to determine differences in cognitive function attributable to menopause, hypothesizing that differences would be associated with reproductive rather than chronological age.

DESIGN AND SETTING

In this cross-sectional study at a university hospital, we combined neuropsychological measures with functional magnetic resonance imaging to comprehensively assess cognitive function.

PARTICIPANTS

Sixty-seven menopausal women, aged 42-61 yr, recruited from a population-based menopause study, grouped into menopause stages based on hormonal and cycle criteria (premenopause, perimenopause, and postmenopause), participated in the study.

MAIN OUTCOME MEASURES

Neuropsychological and functional magnetic resonance imaging measures of verbal, visual, and executive cognitive function.

RESULTS

We found age-independent menopause effects on verbal function. Menopause groups differed in phonemic verbal fluency (F = 3.58, P < 0.019) and regional brain activation (inferior frontal cortex: corrected P < 0.000 right, P < 0.036 left; left prefrontal cortex: P < 0.012); left temporal pole: P < 0.001). Verbal measures correlated with estradiol and FSH (phonemic fluency: R = 0.249, P < 0.047 estradiol, R = -0.275, P < 0.029 FSH; semantic fluency: R = 0.318, P < 0.011 estradiol, R = -0.321, P < 0.010 FSH; right inferior frontal cortex: R = 0.364, P < 0.008 FSH; left inferior frontal cortex: R = -0.431, P < 0.001 estradiol, left prefrontal cortex: R = 0.279, P < 0.045 FSH; left temporal pole: R = -0.310, P < 0.024 estradiol, R = 0.451, P < 0.001 FSH; left parahippocampal gyrus: R = -0.278, P < 0.044 estradiol; left parietal cortex: R = -0.326, P < 0.017 estradiol).

CONCLUSIONS

Results suggest that verbal fluency mechanisms are vulnerable during the menopausal transition. Targeted intervention may preserve function of this critical cognitive domain.

Estrogen regulation of mitochondrial bioenergetics: implications for prevention of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. Increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. Compromised aerobic glycolysis pathway coupled with oxidative stress is first accompanied by a shift toward a ketogenic pathway that eventually progresses into fatty acid oxidation (FAO) pathways and leads to white matter degeneration and overproduction and mitochondrial accumulation of β-amyloid. Estrogen-induced signaling pathways converge upon the mitochondria to enhance mitochondrial function and to sustain aerobic glycolysis coupled with citric acid cycle-driven oxidative phosphorylation to potentiate ATP (Adenosine triphosphate) generation. In addition to potentiated mitochondrial bioenergetics, estrogen also enhances neural survival and health through maintenance of calcium homeostasis, promotion of antioxidant defense against free radicals, efficient cholesterol trafficking, and beta amyloid clearance. Significantly, the convergence of E2 mechanisms of action onto mitochondria is also a potential point of vulnerability when activated in diseased neurons that exacerbates degeneration through increased load on dysregulated calcium homeostasis. The "healthy cell bias of estrogen action" hypothesis examines the role that regulating mitochondrial function and bioenergetics play in promoting neural health and the mechanistic crossroads that lead to divergent outcomes following estrogen exposure. As the continuum of neurological health progresses from healthy to unhealthy, so too do the benefits of estrogen or hormone therapy.