Oophorectomy, Hysterectomy, and Risk of Alzheimer's Disease: A Nationwide Case-Control Study

Systematic review and meta-analysis of the effects of menopause hormone therapy on cognition

Introduction

Despite evidence from preclinical studies suggesting estrogen's neuroprotective effects, the use of menopausal hormone therapy (MHT) to support cognitive function remains controversial.

Methods

We used random-effect meta-analysis and multi-level meta-regression to derive pooled standardized mean difference (SMD) and 95% confidence intervals (C.I.) from 34 randomized controlled trials, including 14,914 treated and 12,679 placebo participants.

Results

Associations between MHT and cognitive function in some domains and tests of interest varied by formulation and treatment timing. While MHT had no overall effects on cognitive domain scores, treatment for surgical menopause, mostly estrogen-only therapy, improved global cognition (SMD=1.575, 95% CI 0.228, 2.921; P=0.043) compared to placebo. When initiated specifically in midlife or close to menopause onset, estrogen therapy was associated with improved verbal memory (SMD=0.394, 95% CI 0.014, 0.774; P=0.046), while late-life initiation had no effects. Overall, estrogen-progestogen therapy for spontaneous menopause was associated with a decline in Mini Mental State Exam (MMSE) scores as compared to placebo, with most studies administering treatment in a late-life population (SMD=-1.853, 95% CI -2.974, -0.733; P = 0.030). In analysis of timing of initiation, estrogen-progestogen therapy had no significant effects in midlife but was associated with improved verbal memory in late-life (P = 0.049). Duration of treatment >1 year was associated with worsening in visual memory as compared to shorter duration. Analysis of individual cognitive tests yielded more variable results of positive and negative effects associated with MHT.

Discussion

These findings suggest time-dependent effects of MHT on certain aspects of cognition, with variations based on formulation and timing of initiation, underscoring the need for further research with larger samples and more homogeneous study designs.

Systematic review and meta-analysis of the effects of menopause hormone therapy on risk of Alzheimer's disease and dementia

Introduction

Despite a large preclinical literature demonstrating neuroprotective effects of estrogen, use of menopausal hormone therapy (HT) for Alzheimer's disease (AD) risk reduction has been controversial. Herein, we conducted a systematic review and meta-analysis of HT effects on AD and dementia risk.

Methods

Our systematic search yielded 6 RCT reports (21,065 treated and 20,997 placebo participants) and 45 observational reports (768,866 patient cases and 5.5 million controls). We used fixed and random effect meta-analysis to derive pooled relative risk (RR) and 95% confidence intervals (C.I.) from these studies.

Results

Randomized controlled trials conducted in postmenopausal women ages 65 and older show an increased risk of dementia with HT use compared with placebo [RR = 1.38, 95% C.I. 1.16-1.64, p < 0.001], driven by estrogen-plus-progestogen therapy (EPT) [RR = 1.64, 95% C.I. 1.20-2.25, p = 0.002] and no significant effects of estrogen-only therapy (ET) [RR = 1.19, 95% C.I. 0.92-1.54, p = 0.18]. Conversely, observational studies indicate a reduced risk of AD [RR = 0.78, 95% C.I. 0.64-0.95, p = 0.013] and all-cause dementia [RR = .81, 95% C.I. 0.70-0.94, p = 0.007] with HT use, with protective effects noted with ET [RR = 0.86, 95% C.I. 0.77-0.95, p = 0.002] but not with EPT [RR = 0.910, 95% C.I. 0.775-1.069, p = 0.251]. Stratified analysis of pooled estimates indicates a 32% reduced risk of dementia with midlife ET [RR = 0.685, 95% C.I. 0.513-0.915, p = 0.010] and non-significant reductions with midlife EPT [RR = 0.775, 95% C.I. 0.474-1.266, p = 0.309]. Late-life HT use was associated with increased risk, albeit not significant [EPT: RR = 1.323, 95% C.I. 0.979-1.789, p = 0.069; ET: RR = 1.066, 95% C.I. 0.996-1.140, p = 0.066].

Discussion

These findings support renewed research interest in evaluating midlife estrogen therapy for AD risk reduction.

Gynecological surgery in adulthood imparts cognitive and brain changes in rats: A focus on hysterectomy at short-, moderate-, and long-term intervals after surgery

Premenopausal hysterectomy is associated with a greater relative risk of dementia. We previously demonstrated cognitive impairments in adult rats six weeks after hysterectomy with ovarian conservation compared with intact sham-controls and other gynecological surgery variations. Here, we investigated whether hysterectomy-induced cognitive impairments are transient or persistent. Adult rats received sham-control, ovariectomy (Ovx), hysterectomy, or Ovx-hysterectomy surgery. Spatial working memory, reference memory, and anxiety-like behavior were tested either six-weeks post-surgery, in adulthood; seven-months post-surgery, in early middle-age; or twelve-months post-surgery, in late middle-age. Hysterectomy in adulthood yielded spatial working memory deficits at short-, moderate-, and long-term post-surgery intervals. Serum hormone levels did not differ between ovary-intact, but differed from Ovx, groups. Hysterectomy had no significant impact on healthy ovarian follicle or corpora lutea counts for any post-surgery timepoint compared with intact sham-controls. Frontal cortex, dorsal hippocampus, and entorhinal cortex were assessed for activity-dependent markers. In entorhinal cortex, there were alterations in FOSB and ΔFOSB expression during the early middle-age timepoint, and phosphorylated ERK1/2 levels at the adult timepoint. Collectively, results suggest a primary role for the uterus in regulating cognition, and that memory-related neural pathways may be modified following gynecological surgery. This is the first preclinical report of long-term effects of hysterectomy with and without ovarian conservation on cognition, endocrine, ovarian, and brain assessments, initiating a comprehensive framework of gynecological surgery effects. Translationally, findings underscore critical needs to decipher how gynecological surgeries, especially those involving the uterus, impact the brain and its functions, the ovaries, and overall aging from a systems perspective.

Ageing perspective on cognitive outcomes from reproductive hormone adjustments

In addition to primary reproductive functions, gonadal hormones play an important role in an array of neural mechanisms across the human lifespan. The ageing-related decline in their activity has been linked to the deterioration of cognitive functions in otherwise healthy women, associated with menopause transition, contributing to higher incidents of post-menopause dementia. Given the growing utility of gonadal steroids for birth control, as well as for compensatory treatment of menopause and oophorectomy symptoms, and adjuvant transgender therapy, their long-term effects on neural mechanisms warrant comprehensive assessment. In this article, we present an ageing perspective on the cognitive outcomes from contraceptive and replacement therapeutic use of gonadal hormones and discuss their effects on the risk of developing Alzheimer's and Parkinson's dementia. Despite rising data supporting the ameliorative effects of reproductive hormones on cognitive facilities, their impact varies depending on study design and type of intervention, thus, implying dynamic neuro-endocrine interactions with complex compensatory mechanisms. Elucidating differential effects of reproductive hormone adjustments on cognition with underlying mechanisms is expected not only to shed light on important aspects of brain ageing and dementia but to facilitate their use in personalized medicine with improved safety margins and therapeutic outcomes.

Repurposing of Tibolone in Alzheimer's Disease

Alzheimer's disease (AD) is a debilitating neurodegenerative disease characterised by the accumulation of amyloid-beta and tau in the brain, leading to the progressive loss of memory and cognition. The causes of its pathogenesis are still not fully understood, but some risk factors, such as age, genetics, and hormones, may play a crucial role. Studies show that postmenopausal women have a higher risk of developing AD, possibly due to the decrease in hormone levels, especially oestrogen, which may be directly related to a reduction in the activity of oestrogen receptors, especially beta (ERβ), which favours a more hostile cellular environment, leading to mitochondrial dysfunction, mainly affecting key processes related to transport, metabolism, and oxidative phosphorylation. Given the influence of hormones on biological processes at the mitochondrial level, hormone therapies are of clinical interest to reduce the risk or delay the onset of symptoms associated with AD. One drug with such potential is tibolone, which is used in clinics to treat menopause-related symptoms. It can reduce amyloid burden and have benefits on mitochondrial integrity and dynamics. Many of its protective effects are mediated through steroid receptors and may also be related to neuroglobin, whose elevated levels have been shown to protect against neurological diseases. Its importance has increased exponentially due to its implication in the pathogenesis of AD. In this review, we discuss recent advances in tibolone, focusing on its mitochondrial-protective effects, and highlight how valuable this compound could be as a therapeutic alternative to mitigate the molecular pathways characteristic of AD.

Sex and gender differences in Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis: a narrative review

Neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), exhibit high phenotypic variability and they are very common in the general population. These diseases are associated with poor prognosis and a significant burden on patients and their caregivers. Although increasing evidence suggests that biological sex is an important factor for the development and phenotypical expression of some NDs, the role of sex and gender in the diagnosis and prognosis of NDs has been poorly explored. Current knowledge relating to sex- and gender-related differences in the epidemiology, clinical features, biomarkers, and treatment of AD, PD, and ALS will be summarized in this narrative review. The cumulative evidence hitherto collected suggests that sex and gender are factors to be considered in explaining the heterogeneity of these NDs. Clarifying the role of sex and gender in AD, PD, and ALS is a key topic in precision medicine, which will facilitate sex-specific prevention and treatment strategies to be implemented in the near future.

Role of estrogen in women's Alzheimer's disease risk as modified by APOE

Alzheimer's disease (AD) is characterized by numerous sexual dimorphisms that impact the development, progression, and probably the strategies to prevent and treat the most common form of dementia. In this review, we consider this topic from a female perspective with a specific focus on how women's vulnerability to the disease is affected by the individual and interactive effects of estrogens and apolipoprotein E (APOE) genotype. Importantly, APOE appears to modulate systemic and neural outcomes of both menopause and estrogen-based hormone therapy. In the brain, dementia risk is greater in APOE4 carriers, and the impacts of hormone therapy on cognitive decline and dementia risk vary according to both outcome measure and APOE genotype. Beyond the CNS, estrogen and APOE genotype affect vulnerability to menopause-associated bone loss, dyslipidemia and cardiovascular disease risk. An emerging concept that may link these relationships is the possibility that the effects of APOE in women interact with estrogen status by mechanisms that may include modulation of estrogen responsiveness. This review highlights the need to consider the key AD risk factors of advancing age in a sex-specific manner to optimize development of therapeutic approaches for AD, a view aligned with the principle of personalized medicine.

Sex differences in dementia and response to a lifestyle intervention: Evidence from Nordic population-based studies and a prevention trial

INTRODUCTION

Evidence on sex differences in the risk for dementia has been mixed. The goal was to assess sex differences in the development of dementia, and in the effects of a lifestyle intervention.

METHODS

Two strategies were adopted, one using combined data from three large Nordic population-based cohort studies (n = 2289), adopting dementia as outcome, and 2-year multidomain lifestyle intervention (n = 1260), adopting cognitive change as outcome.

RESULTS

There was higher risk for dementia after age 80 years in women. The positive effects of the lifestyle intervention on cognition did not significantly differ between men and women. Sex-specific analyses suggested that different vascular, lifestyle, and psychosocial risk factors are important for women and men in mid- and late-life.

CONCLUSION

Women had higher risk for dementia among the oldest individuals. Lifestyle interventions may be effectively implemented among older men and women.

Intermittent fasting with a high-protein diet mitigated osteoarthritis symptoms by increasing lean body mass and reducing inflammation in osteoarthritic rats with Alzheimer's disease-like dementia

Menopausal women are susceptible to osteoarthritis(OA) and memory impairment. We hypothesised that Alzheimer's-like disease(AD) exacerbates OA and that intermittent fasting(IMF) with a high-protein(H-P) diet would enhance memory function and relieve OA symptoms in oestrogen-deficient animals induced AD and OA. The action mechanism was also explored. Ovariectomised Sprague-Dawley rats were fed high-fat(H-F) or H-P diets for 2 weeks, and then they had a hippocampal infusion of β-amyloid(25-35) for 4 weeks to induce AD and an injection of monoidoacetate(MIA) into the articular cartilage to induce OA. Non-AD groups had non-AD symptoms by hippocampal amyloid-β(35-25) infusion. IMF suppressed memory impairment in AD rats, especially those fed H-P diets. Compared with non-AD, AD exacerbated OA symptoms, including swelling, limping, slowed treadmill running speed, and uneven weight distribution in the left leg. The exacerbations were linked to increased inflammation and pain, but IMF and H-P lessened the exacerbation. Lean body mass(LBM) decreased with AD, but H-P protected against LBM loss. Histological examination of the knee joint revealed the degree of the cellular invasion into the middle zone, and the changes in the tidemark plateau were greatest in the AD-AL with H-F, while non-AD-IMF improved the cellular invasion to as much as non-AD-AL. H-P reduced the infiltration into the middle zone of the knee and promoted collagen production. In conclusion, AD exacerbated the articular cartilage deterioration and memory impairment, and IMF with H-P alleviated the memory impairment and osteoarthritic symptoms by decreasing hippocampal amyloid-β deposition and proinflammatory cytokine expressions and by increasing LBM.

Precision hormone therapy: identification of positive responders

Since the introduction of menopausal hormone therapy (MHT) in the 1940s, randomized clinical trials and observational studies have been performed to determine the benefits and risks of MHT. However, MHT therapeutic impact remains under debate as multiple factors including genetic biomarkers and medical history contribute to inter-individual variations in neurodegenerative diseases. Herein, we review the characteristics of women who participated in clinical studies and methodological approaches for study analyses to assess the critical variables influencing an association between MHT and risk of neurodegenerative diseases. Outcomes of the review indicated that: (1) observational studies assessed outcomes of MHT in symptomatic women whereas MHT clinical trials were conducted in asymptomatic postmenopausal women not treated for menopausal symptoms, (2) in asymptomatic postmenopausal women, late MHT intervention was of no benefit, (3) different MHT treatments and regimens between observational studies and clinical trials may impact outcomes, and (4) observational studies may provide greater predictive validity for long-term neurological health outcomes as MHT was introduced in symptomatic women and administered over a long period of time. Going forward, achieving precision hormone therapy will require a priori identification of symptomatic women appropriate for MHT and the type and dose of MHT appropriate for their genetic profile and health risks.

Sex as a biological variable in the pathology and pharmacology of neurodegenerative and neurovascular diseases

The incidence of dementia, most commonly caused by cerebrovascular and neurodegenerative diseases, continues to grow as our population ages. Alzheimer disease (AD) and vascular cognitive impairment (VCI) are responsible for more than 80% of all cases of dementia. There are few effective, long-term treatments for AD and VCI-related conditions (e.g., stroke and cerebral amyloid angiopathy (CAA)). This review focuses on AD (as the most common "neurodegenerative" cause of dementia), CAA (as an "emerging" cause of dementia), and stroke (as the most common cause of "vascular" dementia). We will discuss the available literature on the pharmacological therapies that demonstrate sex differences, which refer to any combination of structural, chromosomal, gonadal, or hormonal differences between males and females. We will emphasize the importance of considering sex as a biological variable in the design of preclinical and clinical studies that investigate underlying pathologies or response to pharmacological interventions in dementia. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Hysterectomy Uniquely Impacts Spatial Memory in a Rat Model: A Role for the Nonpregnant Uterus in Cognitive Processes

Approximately one-third of women experience hysterectomy, or the surgical removal of the uterus, by 60 years of age, with most surgeries occurring prior to the onset of natural menopause. The ovaries are retained in about half of these surgeries, whereas for the other half hysterectomy occurs concurrently with oophorectomy. The dogma is that the nonpregnant uterus is dormant. There have been no preclinical assessments of surgical variations in menopause, including hysterectomy, with and without ovarian conservation, on potential endocrine and cognitive changes. We present a novel rat model of hysterectomy alongside sham, ovariectomy (Ovx), and Ovx-hysterectomy groups to assess effects of surgical menopause variations. Rats without ovaries learned the working memory domain of a complex cognitive task faster than did those with ovaries. Moreover, uterus removal alone had a unique detrimental impact on the ability to handle a high-demand working memory load. The addition of Ovx, that is, Ovx-hysterectomy, prevented this hysterectomy-induced memory deficit. Performance did not differ amongst groups in reference memory-only tasks, suggesting that the working memory domain is particularly sensitive to variations in surgical menopause. Following uterus removal, ovarian histology and estrous cycle monitoring demonstrated that ovaries continued to function, and serum assays indicated altered ovarian hormone and gonadotropin profiles by 2 months after surgery. These results underscore the critical need to further study the contribution of the uterus to the female phenotype, including effects of hysterectomy with and without ovarian conservation, on the trajectory of brain and endocrine aging to decipher the impact of common variations in gynecological surgery in women. Moreover, findings demonstrate that the nonpregnant uterus is not dormant, and indicate that there is an ovarian-uterus-brain system that becomes interrupted when the reproductive tract has been disrupted, leading to alterations in brain functioning.

Sex differences in risk factors for vascular contributions to cognitive impairment & dementia

Vascular contributions to cognitive impairment and dementia (VCID) is the second most common cause of dementia. While males overall appear to be at a slightly higher risk for VCID throughout most of the lifespan (up to age 85), some risk factors for VCID more adversely affect women. These include female-specific risk factors associated with pregnancy related disorders (e.g. preeclampsia), menopause, and poorly timed hormone replacement. Further, presence of certain co-morbid risk factors, such as diabetes, obesity and hypertension, also may more adversely affect women than men. In contrast, some risk factors more greatly affect men, such as hyperlipidemia, myocardial infarction, and heart disease. Further, stroke, one of the leading risk factors for VCID, has a higher incidence in men than in women throughout much of the lifespan, though this trend is reversed at advanced ages. This review will highlight the need to take biological sex and common co-morbidities for VCID into account in both preclinical and clinical research. Given that there are currently no treatments available for VCID, it is critical that we understand how to mitigate risk factors for this devastating disease in both sexes.

Ovarian conservation vs removal at the time of benign hysterectomy

Over the last 2 decades, the rate of oophorectomy at the time of hysterectomy in the United States has consistently been between 40-50%. A decline in hormone use has been observed since the release of the principal results of the Women's Health Initiative. Oophorectomy appears to be associated with an increased risk of coronary heart disease, as well as deleterious effects on overall mortality, cognitive functioning, and sexual functioning. Estrogen deficiency from surgical menopause is associated with bone mineral density loss and increased fracture risk. While hormone therapy may mitigate these effects, at no age does there appear to be a survival benefit associated with oophorectomy. Reduction of ovarian cancer risk may be accomplished with salpingectomy at the time of hysterectomy.

Reproductive period, endogenous estrogen exposure and dementia incidence among women in Latin America and China; A 10/66 population-based cohort study

BACKGROUND

Exposure to endogenous estrogen may protect against dementia, but evidence remains equivocal. Such effects may be assessed more precisely in settings where exogenous estrogen administration is rare. We aimed to determine whether reproductive period (menarche to menopause), and other indicators of endogenous estrogen exposure are inversely associated with dementia incidence.

METHODS

Population-based cohort studies of women aged 65 years and over in urban sites in Cuba, Dominican Republic, Puerto Rico and Venezuela, and rural and urban sites in Peru, Mexico and China. Sociodemographic and risk factor questionnaires were administered to all participants, including ages at menarche, birth of first child, and menopause, and parity, with ascertainment of incident 10/66 dementia, and mortality, three to five years later.

RESULTS

9,428 women participated at baseline, with 72-98% responding by site. The 'at risk' cohort comprised 8,466 dementia-free women. Mean age varied from 72.0 to 75.4 years, lower in rural than urban sites and in China than in Latin America. Mean parity was 4.1 (2.4-7.2 by site), generally higher in rural than urban sites. 6,854 women with baseline reproductive period data were followed up for 26,463 person years. There were 692 cases of incident dementia, and 895 dementia free deaths. Pooled meta-analysed fixed effects, per year, for reproductive period (Adjusted Sub-Hazard Ratio [ASHR] 1.001, 95% CI 0.988-1.015) did not support any association with dementia incidence, with no evidence for effect modification by APOE genotype. No association was observed between incident dementia and; ages at menarche, birth of first child, and menopause: nulliparity; or index of cumulative endogenous estrogen exposure. Greater parity was positively associated with incident dementia (ASHR 1.030, 95% CI 1.002-1.059, I2 = 0.0%).

CONCLUSIONS

We found no evidence to support the theory that natural variation in cumulative exposure to endogenous oestrogens across the reproductive period influences dementia incidence in late life.

Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer's disease-induced estrogen deficient rats

Intermittent fasting may be an effective intervention to protect against age-related metabolic disturbances, although it is still controversial. Here, we investigated the effect of intermittent fasting on the deterioration of the metabolism and cognitive functions in rats with estrogen deficiency and its mechanism was also explored. Ovariectomized rats were infused with β-amyloid (25-35; Alzheimer's disease) or β-amyloid (35-25, Non-Alzheimer's disease; normal cognitive function) into the hippocampus. Each group was randomly divided into two sub-groups: one with intermittent fasting and the other fed ad libitum: Alzheimer's disease-ad libitum, Alzheimer's disease-intermittent fasting, Non-Alzheimer's disease-ad libitum, and Non-Alzheimer's disease-intermittent fasting. Rats in the intermittent fasting groups had a restriction of food consumption to a 3-h period every day. Each group included 10 rats and all rats fed a high-fat diet for four weeks. Interestingly, Alzheimer's disease increased tail skin temperature more than Non-Alzheimer's disease and intermittent fasting prevented the increase. Alzheimer's disease reduced bone mineral density in the spine and femur compared to the Non-Alzheimer's disease, whereas bone mineral density in the hip and leg was reduced by intermittent fasting. Fat mass only in the abdomen was decreased by intermittent fasting. Intermittent fasting decreased food intake without changing energy expenditure. Alzheimer's disease increased glucose oxidation, whereas intermittent fasting elevated fat oxidation as a fuel source. Alzheimer's disease and intermittent fasting deteriorated insulin resistance in the fasting state but intermittent fasting decreased serum glucose levels after oral glucose challenge by increasing insulin secretion. Alzheimer's disease deteriorated short and spatial memory function compared to the Non-Alzheimer's disease, whereas intermittent fasting prevented memory loss in comparison to ad libitum. Unexpectedly, cortisol levels were increased by Alzheimer's disease but decreased by intermittent fasting. Intermittent fasting improved dyslipidemia and liver damage index compared to ad libitum. Alzheimer's disease lowered low-density lipoprotein cholesterol and serum triglyceride levels compared to Non-Alzheimer's disease. In conclusion, Alzheimer's disease impaired not only cognitive function but also disturbed energy, glucose, lipid, and bone metabolism in ovariectomized rats. Intermittent fasting protected against the deterioration of these metabolic parameters, but it exacerbated bone mineral density loss and insulin resistance at fasting in Alzheimer's disease-induced estrogen-deficient rats. Impact statement Intermittent fasting was evaluated for its effects on cognitive function and metabolic disturbances in a rat model of menopause and Alzheimer's disease. Intermittent fasting decreased skin temperature and fat mass, and improved glucose tolerance with decreasing food intake. Intermittent fasting also prevented memory loss: short-term and special memory loss. Therefore, intermittent fasting may prevent some of the metabolic pathologies associated with menopause and protect against age-related memory decline.

Sex and the development of Alzheimer's disease

Men and women exhibit differences in the development and progression of Alzheimer's disease (AD). The factors underlying the sex differences in AD are not well understood. This Review emphasizes the contributions of sex steroid hormones to the relationship between sex and AD. In women, events that decrease lifetime exposure to estrogens are generally associated with increased AD risk, whereas estrogen-based hormone therapy administered near the time of menopause may reduce AD risk. In men, estrogens do not exhibit age-related reduction and are not significantly associated with AD risk. Rather, normal age-related depletions of testosterone in plasma and brain predict enhanced vulnerability to AD. Both estrogens and androgens exert numerous protective actions in the adult brain that increase neural functioning and resilience as well as specifically attenuating multiple aspects of AD-related neuropathology. Aging diminishes the activational effects of sex hormones in sex-specific manners, which is hypothesized to contribute to the relationship between aging and AD. Sex steroid hormones may also drive sex differences in AD through their organizational effects during developmental sexual differentiation of the brain. Specifically, sex hormone actions during early development may confer inherent vulnerability of the female brain to development of AD in advanced age. The combined effects of organizational and activational effects of sex steroids yield distinct sex differences in AD pathogenesis, a significant variable that must be more rigorously considered in future research. © 2016 Wiley Periodicals, Inc.

How Studies of the Serotonin System in Macaque Models of Menopause Relate to Alzheimer's Disease1

Serotonin plays a key role in mood or affect, and dysfunction of the serotonin system has been linked to depression in humans and animal models. Depression appears prior to or coincident with overt symptoms of Alzheimer's disease (AD) in about 50% of patients, and some experts consider it a risk factor for the development of AD. In addition, AD is more prevalent in women, who also show increased incidence of depression. Indeed, it has been proposed that mechanisms underlying depression overlap the mechanisms thought to hasten AD. Women undergo ovarian failure and cessation of ovarian steroid production in middle age and the postmenopausal period correlates with an increase in the onset of depression and AD. This laboratory has examined the many actions of ovarian steroids in the serotonin system of non-human primates using a rhesus macaque model of surgical menopause with short or long-term estradiol (E) or estradiol plus progesterone (E+P) replacement therapy. In this mini-review, we present a brief synopsis of the relevant literature concerning AD, depression, and serotonin. We also present some of our data on serotonin neuron viability, the involvement of the caspase-independent pathway, and apoptosis-inducing factor in serotonin-neuron viability, as well as gene expression related to neurodegeneration and neuron viability in serotonin neurons from adult and aged surgical menopausal macaques. We show that ovarian steroids, particularly E, are crucial for serotonin neuron function and health. In the absence of E, serotonin neurons are endangered and deteriorating toward apoptosis. The possibility that this scenario may proceed or accompany AD in postmenopausal women seems likely.

Estrogens, inflammation and cognition

The effects of estrogens are pleiotropic, affecting multiple bodily systems. Changes from the body's natural fluctuating levels of estrogens, through surgical removal of the ovaries, natural menopause, or the administration of exogenous estrogens to menopausal women have been independently linked to an altered immune profile, and changes to cognitive processes. Here, we propose that inflammation may mediate the relationship between low levels of estrogens and cognitive decline. In order to determine what is known about this connection, we review the literature on the cognitive effects of decreased estrogens due to oophorectomy or natural menopause, decreased estrogens' role on inflammation--both peripherally and in the brain--and the relationship between inflammation and cognition. While this review demonstrates that much is unknown about the intersection between estrogens, cognition, inflammation, we propose that there is an important interaction between these literatures.

Ovarian steroids regulate gene expression related to DNA repair and neurodegenerative diseases in serotonin neurons of macaques

Depression often accompanies the perimenopausal transition and it often precedes overt symptomology in common neurodegenerative diseases (NDDs, such as Alzheimer's, Parkinson's, Huntington, amyotrophic lateral sclerosis). Serotonin dysfunction is frequently found in the different etiologies of depression. We have shown that ovariectomized (Ovx) monkeys treated with estradiol (E) for 28 days supplemented with placebo or progesterone (P) on days 14-28 had reduced DNA fragmentation in serotonin neurons of the dorsal raphe nucleus, and long-term Ovx monkeys had fewer serotonin neurons than intact controls. We questioned the effect of E alone or E+P (estradiol supplemented with progesterone) on gene expression related to DNA repair, protein folding (chaperones), the ubiquitin-proteosome, axon transport and NDD-specific genes in serotonin neurons. Ovx macaques were treated with placebo, E or E+P (n=3 per group) for 1 month. Serotonin neurons were laser captured and subjected to microarray analysis and quantitative real-time PCR (qRT-PCR). Increases were confirmed with qRT-PCR in five genes that code for proteins involved in repair of strand breaks and nucleotide excision. NBN1, PCNA (proliferating nuclear antigen), GADD45A (DNA damage-inducible), RAD23A (DNA damage recognition) and GTF2H5 (gene transcription factor 2H5) significantly increased with E or E+P treatment (all analysis of variance (ANOVA), P<0.01). Chaperone genes HSP70 (heat-shock protein 70), HSP60 and HSP27 significantly increased with E or E+P treatment (all ANOVA, P<0.05). HSP90 showed a similar trend. Ubiquinase coding genes UBEA5, UBE2D3 and UBE3A (Parkin) increased with E or E+P (all ANOVA, P<0.003). Transport-related genes coding kinesin, dynein and dynactin increased with E or E+P treatment (all ANOVA, P<0.03). SCNA (α-synuclein) and ADAM10 (α-secretase) increased (both ANOVA, P<0.02) but PSEN1 (presenilin1) decreased (ANOVA, P<0.02) with treatment. APP decreased 10-fold with E or E+P administration. Newman-Keuls post hoc comparisons indicated variation in the response to E alone versus E+P across the different genes. In summary, E or E+P increased gene expression for DNA repair mechanisms in serotonin neurons, thereby rendering them less vulnerable to stress-induced DNA fragmentation. In addition, E or E+P regulated four genes encoding proteins that are often misfolded or malfunctioning in neuronal populations subserving overt NDD symptomology. The expression and regulation of these genes in serotonergic neurons invites speculation that they may mediate an underlying disease process in NDDs, which in turn may be ameliorated or delayed with timely hormone therapy in women.

Menopause, obesity and inflammation: interactive risk factors for Alzheimer's disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disorder, the development of which is regulated by several environmental and genetic risk factors. Two factors theorized to contribute to the initiation and/or progression of AD pathogenesis are age-related increases in inflammation and obesity. These factors may be particularly problematic in women. The onset of menopause in mid-life elevates the vulnerability of women to AD, an increased risk that is likely associated with the depletion of estrogens. Menopause is also linked with an abundance of additional changes, including increased central adiposity and inflammation. Here, we review the current literature to explore the interactions between obesity, inflammation, menopause and AD.