Heather A. Bimonte-Nelson - US grants

hormone regulation /control mechanism

DESCRIPTION (provided by applicant) The long-term goal of the proposed research is to characterize factors that influence memory and neural deterioration in aging females. Aged and Alzheimer?s disease (AD) patients exhibit memory decline, which is related to deterioration of forebrain cholinergic neurons and projection areas such as hippocampus and cortex. AD is more prevalent in women, and female rats show an earlier and more-extreme age-related memory decline than males. This exaggerated memory loss may be related to ovarian hormone decline. Indeed, ovariectomy (Ovx) compromises cholinergic neuron integrity and nerve growth factor (NGF) levels. Other research suggests a relationship between estrogen and beta-amyloid, the main constituent of plaques seen in AD. These effects may provide a biological explanation for data showing that Ovx results in memory decline. Such an interactive hypothesis has not been directly tested. We propose to test, in aging female rats, whether Ovx exacerbates age-related changes in cortical, forebrain, and hippocampal cholinergic neurons, NGF, and amyloid precursor protein (APP). Further, although estrogen replacement improves memory and decreases risk of heart disease, stroke, and AD in menopausal women, it is controversial since it also increases cancer risk. Raloxifene is a SERM that acts as an estrogen antagonist in breast and uterus, but an agonist in lipid and bone. Since raloxifene increased neurite growth in a cell line and ChAT activity in the hippocampus in Ovx rats, it may also improve memory. We propose to test whether raloxifene, like estrogen, affects working and reference memory, forebrain cholinergic cell integrity, NGF, and APP in aging female rats. Since there is no known cure for AD, we hope that this type of interdisciplinary research will aid in the discovery of new and more efficacious therapies.

The broad hypothesis of this proposal is that age-related hormone change affects age-related cognitive change. The ultimate goat is to attenuate brain aging and cognitive deterioration via hormonal modulation. There is evidence that hormone loss at menopause exacerbates cognitive decline and contributes to the increased prevalence of Alzheimer's disease (AD) in women, and that hormone therapy attenuates these effects. However, recent studies found that combined estrogen/progesterone therapy increased dementia risk in women. Other research found that combined treatment was detrimental to cognitive performance, while estrogen-only was not. We hypothesize that estrogen alone benefits cognition, and that progesterone alters estrogen's effects resulting in a negative outcome of combined hormone treatment. We recently found that ovariectomy (Ovx) was detrimental to cognition in young rats, but enhanced cognition in aged rats. Since progesterone was elevated in aged rats, we hypothesized that removal of elevated progesterone contributed to enhanced scores. Our next study showed that, indeed, progesterone treatment reversed the cognitive enhancing effect of Ovx in aged rats. These findings, taken with data indicating that progesterone enhanced cognitive profiles in young Ovx rats, leads us to hypothesize that Ovx and progesterone have different effects on the young vs aged brain. Although studies have tested the effects that estrogen alone has on the brain and cognition, few studies have tested the effects of progesterone alone or in conjunction with estradiol. This is the goal of the current grant proposal. Specific Aim I tests the hypothesis that progesterone is detrimental to memory and associated neural parameters, and that such effects depend on age. Experiment 1 will evaluate the effects of Ovx and Ovx plus progesterone treatment at ages ranging from adult to aged. This will better define the age at which Ovx transitions from detrimental to beneficial for spatial memory. Specific Aim 2 tests the hypothesis that progesterone counteracts the effects of estrogen on memory and neural parameters related to age-associated cognitive change. Experiment 2 will compare the effects of estrogen to estrogen/progesterone therapy at an age where estrogen enhances cognition. In both studies, a maze battery will evaluate spatial and non-spatial working and reference memory, yielding a thorough cognitive profile. This will be followed by assessment of amyloid precursor protein (APP) processing and neurotrophin levels, both of which are altered by age and hormones. These studies are the next step in elucidating ovarian hormone influences on cognition during aging and will direct future studies. They may yield insight into why several clinical trials indicate that estrogen alone benefits cognition and AD risk, while estrogen/progesterone does not. The proposed research will also detail the mnemonic and neural functions that are compromised with age, ovarian hormone loss, and therapies of estrogen alone or estrogen/progesterone combinations.

DESCRIPTION (provided by applicant): There is increasing evidence that behavioral and hormonal factors alter progression of aging and Alzheimer's Disease (AD). Such knowledge has great implications for strategies to prevent cognitive decline. The rodent model will be used to evaluate two factors that human research suggests alter age- and disease- related changes: prior cognitive experience and a high fat diet. 1) Prior cognitive experience: Does using it prevent you from losing it? People who stay mentally active show less age-related cognitive decline. Animal work addressing this has only used males, and the limitations of cognitive practice have not been detailed. One male and one female group will receive no maze testing, while another will receive only procedural components of testing. The other male and female rats will receive either working or reference memory cognitive practice throughout life, and then spatial and non-spatial working and reference memory testing when they become aged to evaluate whether memory transfer effects occur. Also, we recently found that both-cognitive testing and aging altered neurotrophins. We hypothesize that these alterations due to cognitive testing protect against age-related memory decline. Specific Aim 1 tests the hypothesis that the mnemonic demands of cognitive practice affect whether cognitive practice procedures attenuate age-related neurotrophin and cognitive changes. 2) High fat/cholesterol (HF/HQ diet: Data suggest that a HF/HC diet is a risk factor for cognitive decline in aging and AD. We found that a HF/HC diet impaired memory in middle-aged male rats, and that testosterone treatment improved memory in aged male rats. Since human work found that testosterone treatment improved cognition and lipid profiles in older men, we question whether testosterone reverses the detrimental effects of a HF/HC diet. All animal studies testing effects of a high fat diet used young or middle-aged males. Since data suggest that males are more sensitive to adverse dietary conditions, we will evaluate the effects of a HF/HC diet in middle-aged males vs. females. In women, data suggest that menopause status affects cardiovascular risk factors such as lipid profiles. Middle-aged female rats can be grouped into state of "menopause" (estropause), which affords us the opportunity to evaluate interactions between reproductive senescence, HF/HC diet, and cognition. We will ovariectomize one group of middle-aged females, and divide intact females into estropause state to determine if ovarian hormone removal or reproductive senescence influences cognitive outcome of a HF/HC diet. Specific Aim 2 tests the hypotheses that middle-aged females, like males, show cognitive impairment due to a HF/HC diet depending on state of estropause, and that testosterone attenuates the detrimental effects of a HF/HC diet in middle-aged males. After the maze battery, rats from both studies will have neurotrophin levels assayed in cognitive brain regions.

DESCRIPTION (provided by applicant): The broad goal of this application is to determine which variables influence whether hormone therapy acts as a protectant or a risk factor for cognitive functioning and brain aging. Ovarian hormone loss due to menopause has been linked with cognitive decline and increased risk of Alzheimer's disease. While there is evidence that hormone replacement decreases such effects, recent clinical trials failed to find positive effects, and some found detrimental effects. However, abundant basic science evidence suggests that estrogens exert beneficial effects on cognition and neurobiological variables related to memory. Hence, despite the null and negative findings in some clinical trials, the numerous animal and clinical studies showing positive effects of hormone treatment begs the question of what factors determine whether hormone therapy acts as a protectant or a risk factor for brain functioning and brain aging. We will use the rat model to systematically evaluate variations in current hormone therapies, testing whether they are beneficial or detrimental to cognition, neurotrophins, and markers of synaptic plasticity. Based on prior research, what factors might influence the outcome of estrogen replacement? 1. Dose and type of estrogen. Specific Aim I compares the dose-specific effects of three estrogen preparations: the most commonly used estrogen in animal studies (estradiol), the most commonly used estrogen therapy in the clinic (Premarin, or conjugated equine estrogens), and a promising estrogen therapy that has positive effects on menopausal symptoms (estriol). Neither Premarin nor estriol have been tested for cognitive effects in the rodent. 2. Unopposed vs. opposed estrogen treatment. We recently found that progesterone, given alone, is detrimental to spatial memory, and that tonic estradiol replacement enhances memory and alters neurotrophins in cognitive brain regions in aged rats. When progesterone was added to estradiol treatment, the cognitive and neurotrophin alterations due to estradiol were completely reversed. Specific Aim 2 tests whether the three most common clinically-used progestins alter cognition and the brain when given alone, and counteract estrogen-induced alterations when given as part of combination hormone therapy. Further, we will also test a mechanism of progesterone's effects on cognition. Some metabolites of progesterone have effects on the GABAA receptor. We hypothesize that progesterone is impairing memory by increasing GABAA stimulation, in turn resulting in greater hippocampal inhibition thereby impairing memory. By using GABAA antagonists and agonists as well as metabolites of progesterone that mediate the actions of GAB A on the GABAA receptor, Specific Aim 3 will test whether progesterone's negative effects on cognition, when given alone and concurrently with estradiol, are due to effects mediated by the GABAA system. In each study, rats will be tested on a battery of spatial and non-spatial working and reference memory tests, followed by evaluations of neurotrophin levels and markers of synaptic plasticity in cognitive brain regions. These studies will help elucidate which variations in hormone therapy attenuate or exacerbate age-related changes in cognition and the brain, as well as the mechanism of progesterone's effects when given alone and with estrogen.

The broad goal of our continued program of research is to decipher the cognitive and brain effects of transitional and surgical variants of menopause, including optimizing cognitive aging by discovering efficacious hormone therapy (HT) options in the context of menopause variations seen in women. This incorporates determining memory and brain changes as transitional menopause ensues when ovaries are undergoing follicular depletion, as well as the optimal parameters for interventions subsequent to transitional and surgical menopause variants. Menopause has been associated with cognitive decline and increased dementia risk. However, factors driving these outcomes, and which HT parameters alter effects, are undetermined. Importance is underscored given that most women are living at least one-third of their lives in a menopausal state encompassed by numerous variations (with or without a uterus, follicular deplete ovaries, or HT). In the current grant period, we had 23 publications; using the rat model, we showed that transitional menopause detrimentally impacted memory, that effects were most pronounced during perimenopause when follicles were undergoing early depletion, that higher androstenedione levels were associated with worse memory outcomes, and that short-term hysterectomy (uterus removal) alone impaired memory. We found that progesterone impaired memory, and that these effects were modulated by the GABAergic system. We also showed that several clinically-used synthetic progestins impaired memory, and identified one that enhanced memory: Levonorgestrel (Levo). When taking oral contraceptives or HT, a woman with a uterus must include a progestin along with estrogens to offset estrogen-induced hyperplasia. Thus, we performed an individual versus combination study, and showed that 17?-estradiol (E2) and Levo each enhanced memory when given alone, but impaired memory when given in combination. We also found that E2- induced cognitive benefits were associated with cholinergic integrity, building on literature showing estrogen- cholinergic interactions. This renewal addresses critical questions stemming from these collective findings. Aim 1 tests whether varied E2 regimens attenuate memory impairments associated with the perimenopausal transition, and assesses novel progestins that are anti-androgenic or have minimal androgenicity, with a goal to find options that do not reverse beneficial E2 effects on cognition and the brain. Aim 2 determines how variations in menopause type, including hysterectomy, impact cognition and the brain, testing effects of a temporal window, age, and follicular depletion state. Aim 3 defines how menopause variants and clinically-used HTs interact with candidate neurotransmitter systems in mechanistic detail, systematically examining GABAergic signaling and cholinergic circuitry. We combine behavioral, physiological, and neurobiological approaches in the framework of a blinded and randomized animal model research program to disentangle the complexity of menopause variants and HT opportunities for neurocognitive enhancement, extrapolating directives explicitly from the clinic.

PROJECT SUMMARY/ABSTRACT The broad objective of the Research Education Component is to enrich and support the training of a diverse group of future research leaders in the study of Alzheimer's Disease (AD)-related disorders and brain aging. We will provide a varied range of experiences and activities so that participants gain an integrated perspective to perform critical and impactful studies of AD, related disorders, and brain aging. Use of an interdisciplinary scientific approach will be emphasized, and key features of sound and effective translational science will be highlighted. This component incorporates continuation of activities that were previously successfully implemented in the Outreach and Recruitment Core (formerly entitled the Education and Information Transfer Core). The plan includes travel awards, ethics training, encouragement of underrepresented minorities, mentoring opportunities, continuing education activities, exposure to scientific and public conferences, and information distribution by referencing the availability of the ADCC's resources and research opportunities. The Research Education Component will train, nurture, and support graduate students, postdoctoral fellows, junior faculty, and research associates by leveraging the interdisciplinary and collaborative nature of faculty in the ADCC and related programs. Opportunities will be provided for maximal career development and growth to lead to research independence. The Specific Aims of the Research Education Component address the overarching goals to train, enrich, and provide opportunities for participants so that they develop into research leaders in the field of AD, related disorders, and brain aging. Specific Aim 1 is to provide personalized mentorship and activities geared toward each participant's prior experience and current interests, leading to maximal career development and research independence. Specific Aim 2 is to ensure exemplary training and exposure to the field of AD, related disorders, and brain research using a collaborative, interdisciplinary, and systems scientific approach that underscores the importance of translating basic science discoveries to impactful and real-world clinical outcomes. Specific Aim 3 is to instruct and require adherence to the responsible conduct of research. The program faculty mentors associated with this component span numerous areas of expertise which, together, encompass an interdisciplinary, multifaceted systems approach to AD and aging. The breadth and depth of foci across laboratories allows a dynamic and systematic approach to mentoring, providing tremendous opportunities to personalize the mentee's research exposure based on their own goals and background. Moreover, the collaborative nature of our already established ADCC yields connectedness across program faculty, providing abundant opportunities for training in multiple dimensions and techniques directly applicable to understanding and intervening with AD and aging processes. Of critical importance to training researchers in the field of AD and aging, the Research Education Component builds on the many existing strengths of the ADCC to formalize training and education opportunities in a common geographical location, Arizona.

DESCRIPTION (provided by applicant): In this renewal, we hypothesize that type of menopause and associated hormone changes relate to cognitive responsiveness to hormone therapy (HT). The initial grant used rats to assess variations in HTs with surgical menopause (Ovx), and transitional menopause using 4-vinylcyclohexene diepoxide (VCD). VCD-treated rats undergo ovarian failure; follicles and estrogens deplete, androgens become unopposed, and gonadotropins increase, a profile resembling transitionally menopausal women. Data from the initial grant lay the foundation for testing new hypotheses regarding transitional versus surgical menopause. In women, both transitional and surgical menopause have been related to memory changes. However, most rodent studies have tested cognitive effects after Ovx. Despite insight rat models yield regarding surgical hormone loss, surgical menopause models <13% of women. Here, we examine how different menopause types impact cognitive and brain aging, and aim to determine optimal parameters for the menopause transition and HT. Four aims are proposed, using rats: Aim 1) We found that androstenedione (Andro) relates to impaired memory. Since Andro is directly converted to estrone, and we have shown estrone-induced memory impairments, we hypothesize that Andro's conversion to estrone impairs memory. Aim 1 tests whether Andro's conversion to estrogens, or androgen receptor stimulation, underlies its cognitive detriments. Aim 2) Clinical studies support a critical window during which HT benefits cognition. Rat studies support this; however, these studies used Ovx rats, and gave only 17?-estradiol (E2). E2 is naturally-occurring in women and rats, but is present only in trace amounts in conjugated equine estrogens (CEE) HT. In rats, we found that CEE enhanced memory after surgical menopause, but impaired memory after transitional menopause when given after follicle depletion. Aim 2 tests cognitive change during and after different types of menopause, and whether giving CEE before or during follicular depletion impairs memory, as compared to E2. Aim 3) We found that the HT progestin medroxyprogesterone acetate (MPA) impaired cognition in Ovx rats, and decreased hippocampal glutamic acid decarboxylase (GAD) protein, possibly compensating for GABAA receptor (GABAAR) stimulation. Another progestin, norethindrone acetate (NETA), enhanced memory in Ovx rats. We hypothesize that NETA antagonizes the GABAAR, reducing GABAAR-mediated inhibition, enhancing memory. Aim 3 will determine whether the GABAergic system underlies MPA- and NETA-induced memory changes. Aim 4). This aim tests whether MPA or NETA impacts the effects of CEE or E2. MPA was chosen for this aim to test the HT Prempro (CEE+MPA); NETA was chosen due to its potential to be part of a novel combination HT, as it is used in contraceptives and it enhanced rat cognition. In each study, we will quantify GAD and cholinergic markers, each previously shown to relate to cognition, in brains of cognitively characterized rats. Multiple regression and growth modeling will test relations between the GABAergic system, cholinergic system, hormone levels, and cognition in both menopause models. This work will yield insight into cognitive effects of the menopause transition, variations in menopause type and HTs, and related mechanisms.