Molecular landscape of the overlap between Alzheimer's disease and somatic insulin-related diseases

Alzheimer's disease (AD) is a multifactorial disease with both genetic and environmental factors contributing to its etiology. Previous evidence has implicated disturbed insulin signaling as a key mechanism that plays a role in both neurodegenerative diseases such as AD and comorbid somatic diseases such as diabetes mellitus type 2 (DM2). In this study, we analysed available genome-wide association studies (GWASs) of AD and somatic insulin-related diseases and conditions (SID), i.e., DM2, metabolic syndrome and obesity, to identify genes associated with both AD and SID that could increase our insights into their molecular underpinnings. We then performed functional enrichment analyses of these genes. Subsequently, using (additional) GWAS data, we conducted shared genetic etiology analyses between AD and SID, on the one hand, and blood and cerebrospinal fluid (CSF) metabolite levels on the other hand. Further, integrating all these analysis results with elaborate literature searches, we built a molecular landscape of the overlap between AD and SID. From the landscape, multiple functional themes emerged, including insulin signaling, estrogen signaling, synaptic transmission, lipid metabolism and tau signaling. We also found shared genetic etiologies between AD/SID and the blood/CSF levels of multiple metabolites, pointing towards "energy metabolism" as a key metabolic pathway that is affected in both AD and SID. Lastly, the landscape provided leads for putative novel drug targets for AD (including MARK4, TMEM219, FKBP5, NDUFS3 and IL34) that could be further developed into new AD treatments.

Regulation of mitochondrial dysfunction by estrogens and estrogen receptors in Alzheimer's disease: A focused review

Alzheimer's disease (AD) is a neurodegenerative disorder that primarily manifests itself by progressive memory loss and cognitive decline, thus significantly affecting memory functions and quality of life. In this review, we proceed from the understanding that the canonical amyloid-β hypothesis, while significant, has faced setbacks, highlighting the need to adopt a broader perspective considering the intricate interplay of diverse pathological pathways for effective AD treatments. Sex differences in AD offer valuable insights into a better understanding of its pathophysiology. Fluctuation of the levels of ovarian sex hormones during perimenopause is associated with changes in glucose metabolism, as a possible window of opportunity to further understand the roles of sex steroid hormones and their associated receptors in the pathophysiology of AD. We review these dimensions, emphasizing the potential of estrogen receptors (ERs) to reveal mitochondrial functions in the search for further research and therapeutic strategies for AD pharmacotherapy. Understanding and addressing the intricate interactions of mitochondrial dysfunction and ERs potentially pave the way for more effective approaches to AD therapy.

Treatment with brain specific estrogen prodrug ameliorates cognitive effects of surgical menopause in mice

Menopause is an endocrine shift leading to increased vulnerability for cognitive impairment and dementia risk factors, in part due to loss of neuroprotective circulating estrogens. Systemic replacement of estrogen post-menopause has limitations, including risk for estrogen-sensitive cancers. A promising therapeutic approach therefore might be to deliver estrogen only to the brain. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in ovariectomized mice (a surgical menopause model). We treated mice with the prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17β-estradiol only in the brain. Young and middle-aged C57BL/6 J mice received ovariectomy and subcutaneous implant containing vehicle or DHED and underwent cognitive testing to assess memory after 1-3.5 months of treatment. Low and medium doses of DHED did not alter metabolic status in middle-aged mice. In both age groups, DHED treatment improved spatial memory in ovariectomized mice. Additional testing in middle-aged mice showed that DHED treatment improved working and recognition memory in ovariectomized mice. These results lay the foundation for future studies determining if this intervention is as efficacious in models of dementia with comorbid risk factors.

Role of estrogen in the regulation of central and peripheral energy homeostasis: from a menopausal perspective

Estrogen plays a prominent role in regulating and coordinating energy homeostasis throughout the growth, development, reproduction, and aging of women. Estrogen receptors (ERs) are widely expressed in the brain and nearly all tissues of the body. Within the brain, central estrogen via ER regulates appetite and energy expenditure and maintains cell glucose metabolism, including glucose transport, aerobic glycolysis, and mitochondrial function. In the whole body, estrogen has shown beneficial effects on weight control, fat distribution, glucose and insulin resistance, and adipokine secretion. As demonstrated by multiple in vitro and in vivo studies, menopause-related decline of circulating estrogen may induce the disturbance of metabolic signals and a significant decrease in bioenergetics, which could trigger an increased incidence of late-onset Alzheimer's disease, type 2 diabetes mellitus, hypertension, and cardiovascular diseases in postmenopausal women. In this article, we have systematically reviewed the role of estrogen and ERs in body composition and lipid/glucose profile variation occurring with menopause, which may provide a better insight into the efficacy of hormone therapy in maintaining energy metabolic homeostasis and hold a clue for development of novel therapeutic approaches for target tissue diseases.

Hormonal Agents for the Treatment of Depression Associated with the Menopause

Perimenopause marks the transition from a woman’s reproductive stage to menopause. Usually occurring between 42 and 52 years of age, it is determined clinically by the onset of irregular menstrual cycles or variable cycle lengths. Women are at an increased risk of depression and anxiety during perimenopause and the menopausal transition. Depressive symptoms experienced in perimenopause are often more severe compared to pre- and post-menopause. During menopausal transition, the impact of fluctuating estrogen in the central nervous system (CNS) can have negative psychological effects for some women. Traditional first-line management of menopausal depression involves antidepressants, with modest outcomes. The positive effects of estrogen treatment in the CNS are becoming increasingly recognised, and hormonal therapy (HT) with estrogen may have a role in the treatment of menopausal depression. In this review we will outline the prevalence, impact and neurochemical basis of menopausal-associated depression, as well as hormone-based approaches that have increasing promise as effective treatments.

Comorbidity of osteoporosis and Alzheimer's disease: Is `AKT `-ing on cellular glucose uptake the missing link?

Osteoporosis and Alzheimer's disease (AD) are both degenerative diseases. Osteoporosis often proceeds cognitive deficits, and multiple studies have revealed common triggers that lead to energy deficits in brain and bone. Risk factors for osteoporosis and AD, such as obesity, type 2 diabetes, aging, chemotherapy, vitamin deficiency, alcohol abuse, and apolipoprotein Eε4 and/or Il-6 gene variants, reduce cellular glucose uptake, and protective factors, such as estrogen, insulin, exercise, mammalian target of rapamycin inhibitors, hydrogen sulfide, and most phytochemicals, increase uptake. Glucose uptake is a fine-tuned process that depends on an abundance of glucose transporters (Gluts) on the cell surface. Gluts are stored in vesicles under the plasma membrane, and protective factors cause these vesicles to fuse with the membrane, resulting in presentation of Gluts on the cell surface. This translocation depends mainly on AKT kinase signaling and can be affected by a range of factors. Reduced AKT kinase signaling results in intracellular glucose deprivation, which causes endoplasmic reticulum stress and iron depletion, leading to activation of HIF-1α, the transcription factor necessary for higher Glut expression. The link between diseases and aging is a topic of growing interest. Here, we show that diseases that affect the same biochemical pathways tend to co-occur, which may explain why osteoporosis and/or diabetes are often associated with AD.

Glucose transporter 3 in neuronal glucose metabolism: Health and diseases

Neurons obtain glucose from extracellular environment for energy production mainly depending on glucose transporter 3 (GLUT3). GLUT3 uptakes glucose with high affinity and great transport capacity, and is important for neuronal energy metabolism. This review summarized the role of neuronal GLUT3 in brain metabolism, function and development under both physiological conditions and in diseases, aiming to provide insights into neuronal glucose metabolism and its effect on brain. GLUT3 stabilizes neuronal glucose uptake and utilization, influences brain development and function, and ameliorates aging-related manifestations. Neuronal GLUT3 is regulated by synaptic activity, hormones, nutrition, insulin and insulin-like growth factor 1 in physiological conditions, and is also upregulated by hypoxia-ischemia. GLUT3-related neuronal glucose and energy metabolism is possibly involved in the pathogenesis, pathophysiological mechanism, progression or prognosis of brain diseases, including Alzheimer's disease, Huntington's disease, attention-deficit/hyperactivity disorder and epilepsy. GLUT3 may be a promising therapeutic target of these diseases. This review also briefly discussed the role of other glucose transporters in neuronal glucose metabolism, which work together with GLUT3 to sustain and stabilize glucose and energy supply for neurons. Deficiency in these glucose transporters may also participate in brain diseases, especially GLUT1 and GLUT4.

A practical nutritional guide for the management of sleep disturbances in menopause

Sleep disturbances (SD) represent one of the main symptoms of menopause and they are caused by several factors. Hormonal changes such as the reduction of oestrogen levels and the consequent vasomotor symptoms (VMS) along with psychiatric disorders such as depression and anxiety could contribute to the onset of SD. Furthermore, obesity per sè or through the obstructive sleep apnoea (OSA) could blunt sleep. Moreover, in menopause is usual a reduction in melatonin, that could contribute to SD. Nutritional strategies are paramount because they could contribute to manage menopause-related SD, in particular tackling obesity and overweight. Furthermore, some foods, such as soy, fish, whole grains, vegetables and fruit could decrease symptoms like depression and VMS, correlated with SD in postmenopausal women. Therefore, the aim of this review is to provide an overview of the current evidence on SD in menopause and to provide nutritional strategies for managing SD in this context.

Impact of estrogen receptor agonists and model of menopause on enzymes involved in brain metabolism, acetyl-CoA production and cholinergic function

Our goal is to understand how loss of circulating estrogens and estrogen replacement affect brain physiology and function, particularly in brain regions involved in cognitive processes. We recently conducted a large metabolomics study characterizing the effects of rodent models of menopause and treatment with estrogen receptor (ER) agonists on neurochemical targets in hippocampus, frontal cortex, and striatum. Here we characterize effects on levels of several key enzymes involved in glucose utilization and energy production, specifically phosphofructokinase, glyceraldehyde 3-phosphate dehydrogenase, and pyruvate dehydrogenase. We also evaluated effects on levels of β-actin and α-tubulin, choline acetyltransferase (ChAT) activity, and levels of ATP citrate lyase. All experiments were conducted in young adult rats. Experiment 1 compared the effects of ovariectomy (OVX), a model of surgical menopause, and 4-vinylcyclohexene diepoxide (VCD)-treatments, a model of transitional menopause, with tissues collected at proestrus and at diestrus. Experiment 2 used a separate cohort of rats to evaluate the same targets in OVX and VCD-treated rats treated with estradiol or with selective ER agonists. Differences in the expression of metabolic enzymes between cycling animals and models of surgical and transitional menopause were detected. These differences were model-, region- and time- dependent, and were modulated by selective ER agonists. Collectively, the findings demonstrate that loss of ovarian function and ER agonist treatments have differing effects in OVX vs. VCD-treated rats. Differences may help to explain differences in the effects of estrogen treatments on brain function and cognition in women who have experienced surgical vs. transitional menopause.

Using a memory systems lens to view the effects of estrogens on cognition: Implications for human health

Understanding the organizing and activating effects of gonadal steroids on adult physiology can guide insight into sex differences in and hormonal influences on health and disease, ranging from diabetes and other metabolic disorders, emotion and stress regulation, substance abuse, pain perception, immune function and inflammation, to cognitive function and dysfunction accompanying neurological disorders. Because the brain is highly sensitive to many forms of estrogens, it is not surprising that many adult behaviors, including cognitive function, are modulated by estrogens. Estrogens are known for their facilitating effects on learning and memory, but it is becoming increasingly clear that they also can impair learning and memory of some classes of tasks and may do so through direct actions on specific neural systems. This review takes a multiple memory systems approach to understanding how estrogens can at the same time enhance hippocampus-sensitive place learning and impair striatum-sensitive response learning by exploring the role estrogen receptor signaling may play in the opposing cognitive effects of estrogens. Accumulating evidence suggests that neither receptor subtype nor the timing of treatment, i.e. rapid vs slow, explain the bidirectional effects of estrogens on different types of learning. New findings pointing to neural metabolism and the provision of energy substrates by astrocytes as a candidate mechanism for cognitive enhancement and impairment are discussed.

A study of the relationship of metabolic MR parameters to estrogen dependence in breast cancer xenografts

(1)H MRS, (31)P MRS and diffusion-weighted MRI (DW-MRI) were applied to study the metabolic changes associated with estrogen dependence in estrogen receptor (ER)-positive BT-474 and triple-negative HCC1806 breast cancer xenografts supplemented with or without 17β-estradiol (E2) at a dose of 0.18 or 0.72 mg/pellet. Furthermore, the effect of estrogen withdrawal on the metabolism of BT-474 and HCC1806 breast cancer xenografts was studied on day 0, day 2 and day 10. Increasing the dose of E2 resulted in a rapid growth and increases in the lactate level and phosphomonoester/β-nucleoside triphosphate (PME/βNTP), phosphocreatine/inorganic phosphate (PCr/Pi) and βNTP/Pi ratios in BT-474 breast cancer xenografts; however, no significant changes were found in HCC1806 breast cancer xenografts. Estrogen withdrawal resulted in a marked decrease in lactate level and PME/βNTP ratio and an observed increase in βNTP/Pi, PCr/Pi and apparent diffusion coefficient (ADC) values of BT-474 breast cancer xenografts on day 10. These data suggest that the lactate level and PME/βNTP, PCr/Pi and βNTP/Pi ratios of ER-positive tumors are closely related to ER dependence.

Quantitative optical imaging of primary tumor organoid metabolism predicts drug response in breast cancer

There is a need for technologies to predict the efficacy of cancer treatment in individual patients. Here, we show that optical metabolic imaging of organoids derived from primary tumors can predict the therapeutic response of xenografts and measure antitumor drug responses in human tumor-derived organoids. Optical metabolic imaging quantifies the fluorescence intensity and lifetime of NADH and FAD, coenzymes of metabolism. As early as 24 hours after treatment with clinically relevant anticancer drugs, the optical metabolic imaging index of responsive organoids decreased (P < 0.001) and was further reduced when effective therapies were combined (P < 5 × 10(-6)), with no change in drug-resistant organoids. Drug response in xenograft-derived organoids was validated with tumor growth measurements in vivo and staining for proliferation and apoptosis. Heterogeneous cellular responses to drug treatment were also resolved in organoids. Optical metabolic imaging shows potential as a high-throughput screen to test the efficacy of a panel of drugs to select optimal drug combinations. Cancer Res; 74(18); 5184-94. ©2014 AACR.

Optical metabolic imaging identifies glycolytic levels, subtypes, and early-treatment response in breast cancer

Abnormal cellular metabolism is a hallmark of cancer, yet there is an absence of quantitative methods to dynamically image this powerful cellular function. Optical metabolic imaging (OMI) is a noninvasive, high-resolution, quantitative tool for monitoring cellular metabolism. OMI probes the fluorescence intensities and lifetimes of the autofluorescent metabolic coenzymes reduced NADH and flavin adenine dinucleotide. We confirm that OMI correlates with cellular glycolytic levels across a panel of human breast cell lines using standard assays of cellular rates of glucose uptake and lactate secretion (P < 0.05, r = 0.89). In addition, OMI resolves differences in the basal metabolic activity of untransformed from malignant breast cells (P < 0.05) and between breast cancer subtypes (P < 0.05), defined by estrogen receptor and/or HER2 expression or absence. In vivo OMI is sensitive to metabolic changes induced by inhibition of HER2 with the antibody trastuzumab (herceptin) in HER2-overexpressing human breast cancer xenografts in mice. This response was confirmed with tumor growth curves and stains for Ki67 and cleaved caspase-3. OMI resolved trastuzumab-induced changes in cellular metabolism in vivo as early as 48 hours posttreatment (P < 0.05), whereas fluorodeoxyglucose-positron emission tomography did not resolve any changes with trastuzumab up to 12 days posttreatment (P > 0.05). In addition, OMI resolved cellular subpopulations of differing response in vivo that are critical for investigating drug resistance mechanisms. Importantly, OMI endpoints remained unchanged with trastuzumab treatment in trastuzumab-resistant xenografts (P > 0.05). OMI has significant implications for rapid cellular-level assessment of metabolic response to molecular expression and drug action, which would greatly accelerate drug development studies.

Ovarian steroids influence cerebral glucose transporter expression in a region- and isoform-specific pattern

Cerebral glucose uptake is mediated by several members of the family of facilitated glucose transporters (protein nomenclature GLUT; gene nomenclature solute carrier family 2 Slc2a). Glucose uptake differs between the sexes and also varies with menstrual status in women and across the rodent oestrous cycle. The present study demonstrates the extent to which hormonal variation across the four stages of the rat oestrous cycle affects the mRNA abundance of four members of the GLUT family, including the most well characterised cerebral transporters Slc2a1 and Slc2a3, as well as the insulin-sensitive transporters Slc2a4 and Slc2a8 in the hypothalamus, hippocampus and prefrontal cortex. Slc2a1 varied significantly across the cycle in the hippocampus and prefrontal cortex, and Slc2a3 and Slc2a4 also showed significant fluctuation in the hippocampus. Transporter expression significantly increased during pro-oestrus in both the hippocampus and prefrontal cortex. Furthermore, ovarian hormones are critical for normal expression of GLUT mRNA, as demonstrated by reduced expression of Slc2a1, Slc2a3 and Sl2a8 in the hippocampus after ovariectomy. Collectively, the data reported in the present study demonstrate that glucose transporters are highly sensitive to hormonal variation and that this sensitivity is regionally distinct; thereby fluctuations likely have specific phenotypic implications.

FDG avidity at PET/CT during adjuvant hormonal therapy in patients with breast cancer

BACKGROUND

We aim to retrospectively evaluate the impact of hormone therapy (HT) on FDG avidity of metastatic lesions in patients with breast cancer (BC) undergoing PET/CT.

PATIENTS AND METHODS

Three hundred eight patients with BC were scanned with PET/CT at 2 Italian institutions (mean time from diagnosis 4 yrs, range: 1-24 yrs). Main indications for PET/CT were elevation of tumor markers (34.4%) and clinical or radiological suspicion of relapse (65.6%). The diagnostic accuracy of FDG PET/CT was computed according to the standard method. Student t test was used to assess the mean differences between the study groups, whereas categorical data were compared with chi-square test. Significance was set at P <0.05.

RESULTS

Two hundred sixty-four patients with positive estrogen receptor and who had received adjuvant HT were included in the analysis. At the time of PET/CT scan, HT was ongoing in 176 patients (66.7%) and 88 (33.3%) had completed adjuvant HT. Ninety-eight (55.7%) patients on HT and 59 (67%) off HT had a positive PET/CT; therefore, the scan resulted negative in the remaining 107 patients, 78 and 29 on and off HT, 44.3% and 33%, respectively (P < 0.001). At a median follow-up of 7 months (range 1-48 mos), disease recurrence was confirmed in either clinical or radiological examinations in 126 (47.7%) patients; 72 (40.9%) versus 54 (61.4%) patients on and off HT, respectively (P < 0.005). True-positive PET/CT results were found in 82% and 91% of patients on and off HT, respectively, whereas it failed to identify disease relapse in 13 (18%) and 5 (9%) patients on and off HT, respectively.

CONCLUSIONS

In our series, FDG PET/CT shows a similar diagnostic accuracy in detecting disease relapse between patients with BC on adjuvant HT versus those who have completed therapy. These preliminary results suggest that the glucose metabolism is not altered by hormonal suppression at the time of the scan.

Potential age-dependent effects of estrogen on neural injury

In 2000, approximately 10 million women were receiving hormone replacement therapy (HRT) for alleviation of menopausal symptoms. A number of prior animal studies suggested that HRT may be neuroprotective and cardioprotective. Then, in 2003, reports from the Women's Health Initiative (WHI) indicated that long-term estrogen/progestin supplementation led to increased incidence of stroke. A second branch of the WHI in women with prior hysterectomy found an even stronger correlation between estrogen supplementation alone and stroke incidence. Follow-up analyses of the data, as well as data from other smaller clinical trials, have also demonstrated increased stroke severity in women receiving HRT or estrogen alone. This review examines the studies indicating that estrogen is neuroprotectant in animal models and explores potential reasons why this may not be true in postmenopausal women. Specifically, age-related differences in estrogen receptors and estrogenic actions in the brain are discussed, with the conclusion that animal models of disease must closely mimic human disease to produce clinically relevant results.

Optical redox ratio differentiates breast cancer cell lines based on estrogen receptor status

Autofluorescence spectroscopy is a powerful imaging technique that exploits endogenous fluorophores. The endogenous fluorophores NADH and flavin adenine dinucleotide (FAD) are two of the principal electron donors and acceptors in cellular metabolism, respectively. The optical oxidation-reduction (redox) ratio is a measure of cellular metabolism and can be determined by the ratio of NADH/FAD. We hypothesized that there would be a significant difference in the optical redox ratio of normal mammary epithelial cells compared with breast tumor cell lines and that estrogen receptor (ER)-positive cells would have a higher redox ratio than ER-negative cells. To test our hypothesis, the optical redox ratio was determined by collecting the fluorescence emission for NADH and FAD via confocal microscopy. We observed a statistically significant increase in the optical redox ratio of cancer compared with normal cell lines (P < 0.05). Additionally, we observed a statistically significant increase in the optical redox ratio of ER(+) breast cancer cell lines. The level of ESR1 expression, determined by real-time PCR, directly correlated with the optical redox ratio (Pearson's correlation coefficient = 0.8122, P = 0.0024). Furthermore, treatment with tamoxifen and ICI 182,870 statistically decreased the optical redox ratio of only ER(+) breast cancer cell lines. The results of this study raise the important possibility that fluorescence spectroscopy can be used to identify subtypes of breast cancer based on receptor status, monitor response to therapy, or potentially predict response to therapy. This source of optical contrast could be a potentially useful tool for drug screening in preclinical models.

Transcriptional interaction of an estrogen receptor splice variant and ErbB4 suggests convergence in gene susceptibility pathways in schizophrenia

Mounting evidence from clinical and basic research suggests that estrogen signaling may be altered in the brains of people with schizophrenia. Previously, we found that DNA sequence variation in the estrogen receptor (ER) alpha gene, lower ERalpha mRNA levels, and/or blunted ERalpha signaling is associated with schizophrenia. In this study, we asked whether the naturally occurring truncated ERalpha isoform, Delta7, which acts as a dominant negative, can attenuate gene expression induced by the wild-type (WT) receptor in an estrogen-dependent manner in neuronal (SHSY5Y) and non-neuronal (CHOK1 and HeLa) cells. In addition, we determined the extent to which ERalpha interacts with NRG1-ErbB4, a leading schizophrenia susceptibility pathway. Reductions in the transcriptionally active form of ErbB4 comprising the intracytoplasmic domain (ErbB4-ICD) have been found in schizophrenia, and we hypothesized that ERalpha and ErbB4 may converge to control gene expression. In the present study, we show that truncated Delta7-ERalpha attenuates WT-ERalpha-driven gene expression across a wide range of estrogen concentrations in cells that express functional ERalpha at base line or upon co-transfection of full-length ERalpha. Furthermore, we find that ErbB4-ICD can potentiate the transcriptional activity of WT-ERalpha at EREs in two cell lines and that this potentiation effect is abolished by the presence of Delta7-ERalpha. Immunofluorescence microscopy revealed nuclear co-localization of WT-ERalpha, Delta7-ERalpha, and ErbB4-ICD, whereas immunoprecipitation assays showed direct interaction. Our findings demonstrate convergence between ERalpha and ErbB4-ICD in the transcriptional control of ERalpha-target gene expression and suggest that this may represent a convergent pathway that may be disrupted in schizophrenia.

Chronic estradiol treatment improves brain homeostasis during aging in female rats

Aging is associated with a reduction in metabolic function, insulin resistance, increased incidence of neurodegenerative diseases, and memory or cognitive dysfunction. In aging females, loss of gonadal function determines the beginning of the period of reduced metabolic function. Estrogens have neuroprotective effects, but the mechanisms by which they exert these effects remain unclear. The effects of estradiol treatment on the activation of the insulin receptor substrate (IRS)-1 signaling pathway, the interactions between estrogen receptor (ER)-alpha and IRS-1 and the p85alpha subunit of phosphatidylinositol-3 kinase, together with the possible effects of estradiol treatment on glucose transporter-3 and -4 levels, were investigated in female rats. The level of expression of each glucose transporter was greater in control and estradiol-treated groups than in the ovariectomized group. Interactions of ERalpha46-IRS-1, ERalpha46-p85alpha, and p85alpha-IRS-1, as well as IRS-1 phosphorylation, appeared to increase with estradiol treatment. The results indicate that estradiol treatment improves some aspects of neuronal homeostasis that are affected by aging; this may indicate that estradiol has neuroprotective effects in female rats. Additional animal studies are required to clarify the neuroprotective role of estradiol in relation to other important molecules involved in the IRS-1-phosphatidylinositol-3 kinase signaling pathway.

Estrogen receptors: new players in diabetes mellitus

Diabetes mellitus type 2 is a systemic disease characterized by imbalance of energy metabolism, which is mainly caused by inadequate insulin action. Recent data have revealed a surprising role for estradiol in regulating energy metabolism and opened new insights into the role of the two estrogen receptors, ERalpha and ERbeta, in this context. New findings on gene modulation by ERalpha and ERbeta of insulin-sensitive tissues indicate that estradiol participates in glucose homeostasis by modulating the expression of genes that are involved in insulin sensitivity and glucose uptake. Drugs that can selectively modulate the activity of either ERalpha or ERbeta in their interactions with target genes represent a promising frontier in diabetes mellitus coadjuvant therapy.

The neurology of menopause

BACKGROUND

Menopause is a normal milestone experienced annually by 2 million American women each year, and many women are concerned about the relation between menopause and health. Associated hormonal changes have the potential to influence neurologic disease, as do hormonal therapies prescribed for menopausal symptoms or other conditions. The objective of this article is to increase neurologists' awareness of the relation between menopause and neurologic illness.

REVIEW SUMMARY

This was a focused review of 4 common neurologic disorders potentially influenced by menopause or by estrogen-containing hormone therapy: stroke, epilepsy, Parkinson disease, and Alzheimer disease. Hormonal effects are germane to each illness, although clinical implications are clearer for stroke and Alzheimer disease than for epilepsy and Parkinson disease. For women with epilepsy, few clinical data directly address the role of menopause or estrogen-containing hormone therapy on seizure frequency. Relevant clinical research findings on Parkinson disease are inconsistent and provide an inadequate basis for practice guidelines. There is clinical trial evidence that hormone therapy does not reduce stroke incidence and may increase risk of ischemic stroke; hormone therapy cannot be recommended for stroke prevention. The natural menopausal transition is not characterized by objective memory loss. There is clinical trial evidence that hormone therapy should not be used for the postmenopausal woman age 65 years or older for the preservation of cognitive skills, prevention of dementia, or treatment of dementia due to Alzheimer disease. Long-term cognitive consequences of short-term hormone therapy used by younger women for menopausal symptoms remains an important area of uncertainty.

CONCLUSIONS

Increased awareness of hormonal influences on neurologic illness is important for the practicing neurologist.

Glucose transporter plasticity during memory processing

Various types of learning, including operant conditioning, induce an increase in cellular activation concomitant with an increase in local cerebral glucose utilization (LCGU). This increase is mediated by increased cerebral blood flow or changes in brain capillary density and diameter. Because glucose transporters are ultimately responsible for glucose uptake, we examined their plastic expression in response to cellular activation. In vitro and in vivo studies have demonstrated that cerebral glucose transporter 1 (GLUT1) expression consistently parallels changes in LCGU. The present study is the first to investigate the effect of memory processing on glucose transporters expression. Changes in GLUT expression produced by training in an operant conditioning task were measured in the brain of CD1 mice. Using semi-quantitative immunohistochemistry, Western blot and real time RT-PCR the cerebral GLUT1 and GLUT3 expression was quantified immediately, 220 min and 24 h following training. Relative to sham-trained and naive controls, operant conditioning training induced an immediate increase in GLUT1 immunoreactivity level in the hippocampus CA1 pyramidal cells as well as in the sensorimotor cortex. At longer post-learning delays, GLUT1 immunoreactivity decreased in the sensorimotor cortex and putamen. Parallel to the changes in protein levels, hippocampus GLUT1 mRNA level also increased immediately following learning. No effect of learning was found on hippocampal GLUT3 protein or mRNA expression. Measures of changes in glucose transporters expression present a link between cellular activation and glucose metabolism. The learning-induced localized increases in GLUT1 protein as well as mRNA levels observed in the present study confirm the previous findings that GLUT1 expression is plastic and respond to changes in cellular metabolic demands.

Gene expression profiles for detecting and distinguishing potential endocrine-disrupting compounds in environmental samples

Industrial and municipal processes may produce and release endocrine-disrupting compounds (EDCs) into the environment, but the exact nature of their effects is difficult to investigate. EDCs typically exert their effect by affecting gene expression aberrantly. To determine if gene expression profiles could be used to detect and distinguish estrogenic EDCs, an estrogen receptor positive human breast cancer cell line (MCF-7) was exposed to known estrogenic compounds, suspected EDCs, and extracts from three effluent samples. A set of specifically estrogen-regulated genes was identified by microarray analysis. Nine estrogen up-regulated genes (IGFBP4, HSPA8, B4GALT1, XBP1, KRT8, GTPBP4, HNRPAB, SLC2A1, and CALM1) and two estrogen down-regulated genes (ID2 and ZNF217) were consistently detectable in response to estrogen and other estrogenic compounds. Gene expression patterns in cells that were exposed to effluent sample extracts were compared to gene expression patterns in cells that were exposed to known endocrines. Using this technique, two of the effluent samples were shown to have estrogenic activity. This approach could easily be extended to screen for other types of receptor-mediated endocrine disruption. For example, cells expressing androgen or aryl hydrocarbon receptors could be used in gene expression profiling assays to detect androgenic effects or for the presence of bioactive aromatic hydrocarbons. Gene expression profiling is emerging as a sensitive and specific method to screen complex samples for endocrine disrupting activity.

A ketogenic diet increases brain insulin-like growth factor receptor and glucose transporter gene expression

A ketogenic diet suppresses seizure activity in children and in juvenile rats. To investigate whether alteration in brain IGF activity could be involved in the beneficial effects of the ketogenic diet, we examined the effects of this diet on IGF system gene expression in the rat brain. Juvenile rats were fed one of three different diets for 7 d: ad libitum standard rat chow (AL-Std), calorie-restricted standard chow (CR-Std), or a calorie-restricted ketogenic diet (CR-Ket). The calorie-restricted diets contained 90% of the rats' calculated energy requirements. The AL-Std diet group increased in weight, whereas the two CR groups merely maintained their weight during the 7-d diet. Glucose levels were significantly reduced in both CR groups compared with the AL-Std group, but only the CR-Ket group developed ketonemia. IGF1 mRNA levels were reduced by 30-50% in most brain regions in both CR groups. IGF1 receptor (IGF1R) mRNA levels were decreased in the CR-Std group but were increased in the CR-Ket diet group. Brain IGF binding protein (IGFBP)-2 and -5 mRNA levels were not altered by diet, but IGFBP-3 mRNA levels were markedly increased by the ketogenic diet while not altered by calorie restriction alone. Brain glucose transporter expression was also investigated in this study. Glucose transporter (GLUT) 4 mRNA levels were quite low and not appreciably altered by the different diets. Parenchymal GLUT1 mRNA levels were increased by the CR-Ket diet, but endothelial GLUT1 mRNA levels were not affected. Neuronal GLUT3 expression was decreased with the CR-Std diet and increased with the CR-Ket diet, in parallel with the IGF1R pattern. These observations reveal divergent effects of dietary caloric content and macronutrient composition on brain IGF system and GLUT expression. In addition, the data may be consistent with a role for enhanced IGF1R and GLUT expression in ketogenic diet-induced seizure suppression.

Increased vulnerability of brain mitochondria in diabetic (Goto-Kakizaki) rats with aging and amyloid-beta exposure

This study evaluated the respiratory indexes (respiratory control ratio [RCR] and ADP/O ratio), mitochondrial transmembrane potential (DeltaPsim), repolarization lag phase, repolarization level, ATP/ADP ratio, and induction of the permeability transition pore of brain mitochondria isolated from normal Wistar and GK diabetic rats of different ages (1.5, 12, and 24 months of age). The effect of amyloid beta-peptides, 50 micromol/l Abeta(25-35) or 2 micromol/l Abeta(1-40), on mitochondrial function was also analyzed. Aging of diabetic mice induced a decrease in brain mitochondrial RCR, ADP/O, and ATP/ADP ratios but induced an increase in the repolarization lag phase. Brain mitochondria from older diabetic rats were more prone to the induction of the permeability transition pore, i.e., mitochondria from 24-month-old diabetic rats accumulated much less Ca(2+) (20 micromol/l) than those isolated from 12-month-old rats (50 micromol/l) or 1.5-month-old rats (100 micromol/l). In the presence of 50 micromol/l Abeta(25-35) or 2 micromol/l Abeta(1-40), age-related mitochondrial effects were potentiated. These results indicate that diabetes-related mitochondrial dysfunction is exacerbated by aging and/or by the presence of neurotoxic agents such as amyloid beta-peptides, supporting the idea that diabetes and aging are risk factors for the neurodegeneration induced by these peptides.