Estrogen lowers Alzheimer beta-amyloid generation by stimulating trans-Golgi network vesicle biogenesis

Mechanisms of sex differences in Alzheimer's disease

Alzheimer's disease (AD) and the mechanisms underlying its etiology and progression are complex and multifactorial. The higher AD risk in women may serve as a clue to better understand these complicated processes. In this review, we examine aspects of AD that demonstrate sex-dependent effects and delve into the potential biological mechanisms responsible, compiling findings from advanced technologies such as single-cell RNA sequencing, metabolomics, and multi-omics analyses. We review evidence that sex hormones and sex chromosomes interact with various disease mechanisms during aging, encompassing inflammation, metabolism, and autophagy, leading to unique characteristics in disease progression between men and women.

Sex Hormone-Binding Globulin and Risk of Incident Dementia in Middle-Aged to Older Women: Results from the UK Biobank Cohort Study

INTRODUCTION

The association of serum sex hormone-binding globulin (SHBG) concentrations with dementia risk remains uncertain in middle-aged to older women. We examined associations of serum SHBG levels with incidence of all-cause dementia and its subtypes in middle-aged to older women from the large population-based UK Biobank cohort study.

METHODS

Serum total SHBG levels were measured by immunoassay. The incidence of all-cause dementia and its subtypes was recorded. Cox proportional hazards models were used to calculate hazard ratios (HR) for main outcomes.

RESULTS

Among 171,482 community-dwelling women (mean [SD] age was 59.9 [5.4] years, median follow-up of 11.8 years), 2,368 developed dementia, including 1,088 from Alzheimer's disease (AD), 451 from vascular dementia (VAD), and 1,609 from other dementia. After multivariable adjustments, higher serum SHBG levels were significantly associated with higher risks of all-cause dementia, AD, and other dementia (all p < 0.05). Compared to those in the lowest quartile of SHBG levels, participants in the highest quartile of SHBG levels had a higher risk of all-cause dementia (HR: 1.34; 95% confidence interval [CI]: 1.16-1.53), AD (HR: 1.32; 95% CI: 1.07-1.62), and other dementia (HR: 1.44; 95% CI: 1.21-1.70). However, this relationship was not significant for VAD (HR: 1.16; 95% CI: 0.86-1.56).

CONCLUSION

These findings indicated that higher serum SHBG concentrations were independently associated with higher risks of incident all-cause dementia, as well as AD and other dementia among middle-aged to older women. No association was found for VAD.

Rab11 and Its Role in Neurodegenerative Diseases

Vesicles mediate the trafficking of membranes/proteins in the endocytic and secretory pathways. These pathways are regulated by small GTPases of the Rab family. Rab proteins belong to the Ras superfamily of GTPases, which are significantly involved in various intracellular trafficking and signaling processes in the nervous system. Rab11 is known to play a key role especially in recycling many proteins, including receptors important for signal transduction and preservation of functional activities of nerve cells. Rab11 activity is controlled by GEFs (guanine exchange factors) and GAPs (GTPase activating proteins), which regulate its function through modulating GTP/GDP exchange and the intrinsic GTPase activity, respectively. Rab11 is involved in the transport of several growth factor molecules important for the development and repair of neurons. Overexpression of Rab11 has been shown to significantly enhance vesicle trafficking. On the other hand, a reduced expression of Rab11 was observed in several neurodegenerative diseases. Current evidence appears to support the notion that Rab11 and its cognate proteins may be potential targets for therapeutic intervention. In this review, we briefly discuss the function of Rab11 and its related interaction partners in intracellular pathways that may be involved in neurodegenerative processes.

Delineation of Neuroprotective Effects and Possible Benefits of AntioxidantsTherapy for the Treatment of Alzheimer's Diseases by Targeting Mitochondrial-Derived Reactive Oxygen Species: Bench to Bedside

Alzheimer's disease (AD) is considered the sixth leading cause of death in elderly patients and is characterized by progressive neuronal degeneration and impairment in memory, language, etc. AD is characterized by the deposition of senile plaque, accumulation of fibrils, and neurofibrillary tangles (NFTs) which are responsible for neuronal degeneration. Amyloid-β (Aβ) plays a key role in the process of neuronal degeneration in the case of AD. It has been reported that Aβ is responsible for the production of reactive oxygen species (ROS), depletion of endogenous antioxidants, increase in intracellular Ca²⁺ which further increases mitochondria dysfunctions, oxidative stress, release of pro-apoptotic factors, neuronal apoptosis, etc. Thus, oxidative stress plays a key role in the pathogenesis of AD. Antioxidants are compounds that have the ability to counteract the oxidative damage conferred by ROS. Therefore, the antioxidant therapy may provide benefits and halt the progress of AD to advance stages by counteracting neuronal degeneration. However, despite the beneficial effects imposed by the antioxidants, the findings from the clinical studies suggested inconsistent results which might be due to poor study design, selection of the wrong antioxidant, inability of the molecule to cross the blood-brain barrier (BBB), treatment in the advanced state of disease, etc. The present review insights into the neuroprotective effects and limitations of the antioxidant therapy for the treatment of AD by targeting mitochondrial-derived ROS. This particular article will certainly help the researchers to search new avenues for the treatment of AD by utilizing mitochondrial-derived ROS-targeted antioxidant therapies.

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Menopause and cognitive impairment: A narrative review of current knowledge

A severe impairment of cognitive function characterizes dementia. Mild cognitive impairment represents a transition between normal cognition and dementia. The frequency of cognitive changes is higher in women than in men. Based on this fact, hormonal factors likely contribute to cognitive decline. In this sense, cognitive complaints are more common near menopause, a phase marked by a decrease in hormone levels, especially estrogen. Additionally, a tendency toward worsened cognitive performance has been reported in women during menopause. Vasomotor symptoms (hot flashes, sweating, and dizziness), vaginal dryness, irritability and forgetfulness are common and associated with a progressive decrease in ovarian function and a subsequent reduction in the serum estrogen concentration. Hormone therapy (HT), based on estrogen with or without progestogen, is the treatment of choice to relieve menopausal symptoms. The studies conducted to date have reported conflicting results regarding the effects of HT on cognition. This article reviews the main aspects of menopause and cognition, including the neuroprotective role of estrogen and the relationship between menopausal symptoms and cognitive function. We present and discuss the findings of the central observational and interventional studies on HT and cognition.

From Menopause to Neurodegeneration-Molecular Basis and Potential Therapy

The impacts of menopause on neurodegenerative diseases, especially the changes in steroid hormones, have been well described in cell models, animal models, and humans. However, the therapeutic effects of hormone replacement therapy on postmenopausal women with neurodegenerative diseases remain controversial. The steroid hormones, steroid hormone receptors, and downstream signal pathways in the brain change with aging and contribute to disease progression. Estrogen and progesterone are two steroid hormones which decline in circulation and the brain during menopause. Insulin-like growth factor 1 (IGF-1), which plays an import role in neuroprotection, is rapidly decreased in serum after menopause. Here, we summarize the actions of estrogen, progesterone, and IGF-1 and their signaling pathways in the brain. Since the incidence of Alzheimer’s disease (AD) is higher in women than in men, the associations of steroid hormone changes and AD are emphasized. The signaling pathways and cellular mechanisms for how steroid hormones and IGF-1 provide neuroprotection are also addressed. Finally, the molecular mechanisms of potential estrogen modulation on N-methyl-d-aspartic acid receptors (NMDARs) are also addressed. We provide the viewpoint of why hormone therapy has inconclusive results based on signaling pathways considering their complex response to aging and hormone treatments. Nonetheless, while diagnosable AD may not be treatable by hormone therapy, its preceding stage of mild cognitive impairment may very well be treatable by hormone therapy.

The receptor hypothesis and the pathogenesis of depression: Genetic bases and biological correlates

Depression has become one of the most prevalent neuropsychiatric disorders characterized by anhedonia, anxiety, pessimism, or even suicidal thoughts. Receptor theory has been pointed out to explain the pathogenesis of depression, while it is still subject to debate. Additionally, gene abnormality accounts for nearly 40-50% of depression risk, which is a significant factor contributing to the onset of depression. Accordingly, studying on receptors and their gene abnormality are critical parts of the research on internal causes of depression. This review summarizes the pathogenesis of depression from six of the most related receptors and their associated genes, including N-methyl-D-aspartate receptor, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, glucocorticoid receptor, 5-hydroxytryptamine receptor, GABA_A receptor α2, and dopamine receptor; and several "non-classic" receptors, such as metabotropic glutamate receptor, opioid receptor, and insulin receptor. These receptors have received considerable critical attention and are highly implicated in the onset of depression. We begin by providing the biological mechanisms of action of these receptors on the pathogenesis of depression. Then we review the historical and social context about these receptors. Finally, we discuss the limitations of the current state of knowledge and outline insights on future research directions, aiming to provide more novel targets and theoretical basis for the early prevention, accurate diagnosis and prompt treatment of depression.

Differential expression of protein disulfide isomerase (PDI) in regulating endometrial receptivity in humans

Estrogen and progesterone regulate the expression of endometrial proteins that determine endometrial receptivity for embryo implantation. The protein disulfide isomerase (PDI) family of proteins play a diverse role in regulating protein modification and redox function. Although the role of PDIs in cancer progression has been widely studied, their role in endometrial receptivity is largely unknown. We have focused on the expressions of PDIA1, PDIA2, PDIA3, PDIA4, PDIA5, and PDIA6 isoforms in endometrial epithelium under the influence of estrogen and progesterone and investigated their functional role in regulating endometrial receptivity. We found PDIA1-6 transcripts were expressed in endometrial epithelial Ishikawa, RL95-2, AN3CA, and HEC1-B cell lines. The expression of PDIA1 was low and PDIA5 was high in HEC1-B cells, whereas PDIA2 was high in both AN3CA and HEC1-B cells. In Ishikawa cells, estrogen (10 and 100 nM) upregulated PDIA1 and PDIA6, whereas estrogen (100 nM) downregulated PDIA4 and PDIA5; and progesterone (0.1 and 1 μM) downregulated transcript expressions of PDIA1-6. In human endometrial samples, significantly lowered transcript expressions of PDIA2 and PDIA5 were observed in the secretory phase compared with the proliferative phase, whereas no change was observed in the other studied transcripts throughout the cycle. Inhibition of PDI by PDI antibody (5 and 10 μg/mL) and PDI inhibitor bacitracin (1 and 5 mM) significantly increased the attachment of Jeg-3 spheroids onto AN3CA cells. Taken together, our study suggests a role of PDI in regulating endometrial receptivity and the possibility of using PDI inhibitors to enhance endometrial receptivity.

Vps54 regulates Drosophila neuromuscular junction development and interacts genetically with Rab7 to control composition of the postsynaptic density

Vps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). In the wobbler mouse, a model for human motor neuron (MN) disease, reduction in the levels of Vps54 causes neurodegeneration. However, it is unclear how disruption of the GARP complex leads to MN dysfunction. To better understand the role of Vps54 in MNs, we have disrupted expression of the Vps54 ortholog in Drosophila and examined the impact on the larval neuromuscular junction (NMJ). Surprisingly, we show that both null mutants and MN-specific knockdown of Vps54 leads to NMJ overgrowth. Reduction of Vps54 partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no visible impact on endosomal pools. MN-specific knockdown of Vps54 in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses the Vps54 NMJ phenotype. Conversely, knockdown of Vps54 combined with overexpression of dominant negative Rab7 causes NMJ and behavioral abnormalities including a decrease in postsynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest that Vps54 controls larval MN axon development and postsynaptic density composition through a mechanism that requires Rab7.

Upregulation of long noncoding RNA RAB11B-AS1 promotes tumor metastasis and predicts poor prognosis in lung cancer

Background

Lung cancer (LC) is one of the leading causes of cancer-related mortality in China and worldwide. Despite the progress in diagnosis and treatment of LC, the prognosis of LC remains poor. Studies have demonstrated that long non-coding RNAs (lncRNAs) play a critical role in carcinogenesis and cancer development.

Methods

Here we examined the expression and potential function of lnc-RAB11B-AS1 in LC both in vitro and in vivo. All experiments in this study were conducted using A549 and PC-9 cell lines according to protocols described in this paper. The clinic characteristics were analyzed using logistic regression, cox model, log rank test, biochemical analysis using qRT-PCR, transfections, nude mice model, and cell biological analysis using Transwell assay, CCK-8 assay, flow cytometry, and rescue experiments, and immunohistochemistry.

Results

The results showed that lnc-RAB11B-AS1 was significantly overexpressed in LC tissues compared to the corresponding non-tumor tissues. Patients with a higher level of lnc-RAB11B-AS1 expression showed a poorer overall survival rate. Functionally, overexpression of lnc-RAB11B-AS1 promotes cell proliferation, migration and invasion abilities of LC cell lines, which suggests lnc-RAB11B-AS1 may play an oncogenic role in LC. lnc-RAB11B-AS1 was located in physical contiguity with RAB11B gene and found positively regulates the RAB11B expression, and the protein levels of RAB11B in LC tissues also found to positively correlated with the level of lnc-RAB11B-AS1 expression. RAB11B silencing partially abrogated lnc-RAB11B-AS1-induced proliferation of the LC cell lines used in this study.

Conclusions

This study provided a novel evidence into the function of lncRNA-driven carcinogenesis. Our findings highlighted the importance of lnc-RAB11B-AS1 and RAB11B in LC progression and indicated that lnc-RAB11B-AS1 may serve as a novel and valuable prognostic biomarker for LC.

Estrogen Signaling in Alzheimer's Disease: Molecular Insights and Therapeutic Targets for Alzheimer's Dementia

Estrogens play a crucial physiological function in the brain; however, debates exist concerning the role of estrogens in Alzheimer's disease (AD). Women during pre-, peri-, or menopause periods are more susceptible for developing AD, suggesting the connection of sex factors and a decreased estrogen signaling in AD pathogenesis. Yet, the underlying mechanism of estrogen-mediated neuroprotection is unclarified and is complicated by the existence of estrogen-related factors. Consequently, a deeper analysis of estrogen receptor (ER) expression and estrogen-metabolizing enzymes could interpret the importance of estrogen in age-linked cognitive alterations. Previous studies propose that hormone replacement therapy may attenuate AD onset in postmenopausal women, demonstrating that estrogen signaling is important for the development and progression of AD. For example, ERα exerts neuroprotection against AD by maintaining intracellular signaling cascades and study reported reduced expression of ERα in hippocampal neurons of AD patients. Similarly, reduced expression of ERβ in female AD patients has been associated with abnormal function in mitochondria and improved markers of oxidative stress. In this review, we discuss the critical interaction between estrogen signaling and AD. Moreover, we highlight the potential of targeting estrogen-related signaling for therapeutic intervention in AD.

Sex differences in Alzheimer's disease: Understanding the molecular impact

Alzheimer's disease (AD) is a common neurodegenerative disorder that presents with cognitive impairment and behavioral disturbance. Approximately 5.5 million people in the United States live with AD, most of whom are over the age of 65 with two-thirds being woman. There have been major advancements over the last decade or so in the understanding of AD neuropathological changes and genetic involvement. However, studies of sex impact in AD have not been adequately integrated into the investigation of disease development and progression. It becomes indispensable to acknowledge in both basic science and clinical research studies the importance of understanding sex-specific differences in AD pathophysiology and pathogenesis, which could guide future effort in the discovery of novel targets for AD. Here, we review the latest and most relevant literature on this topic, highlighting the importance of understanding sex dimorphism from a molecular perspective and its association to clinical trial design and development in AD research field.

Estrogen deficiency exacerbates Aβ-induced memory impairment through enhancement of neuroinflammation, amyloidogenesis and NF-ĸB activation in ovariectomized mice

Estrogen is well known to have a preventative effect in Alzheimer's disease (AD) pathology. Several studies have demonstrated that nuclear factor kappa-B (NF-ĸB) can contribute to the effects of estrogen on the development of AD. We investigated whether NF-ĸB affects amyloid-beta (Aβ)-induced memory impairment in an estrogen-lacking condition. In the present study, nine-week-old Institute cancer research (ICR) mice were ovariectomized to block estrogen stimulation. Ten weeks after the ovariectomization, mice were administered with Aβ (300 pmol) via intracerebroventricular (ICV) infusion for 2 weeks. Memory impairment, neuroinflammatory protein expression, and amyloidogenic pathways were then measured. Ovariectomized mice demonstrated severe memory impairment, Aβ accumulation, neprilysin downregulation, and activation of NF-ĸB signaling compared to sham-control mice. In vitro experiments demonstrated that β-estradiol (10 μM) inhibited Aβ (1 μM)-induced neuroinflammation in microglial BV-2 cells and prevented Aβ-induced cell death in primary cultured neuronal cells. As in in vivo experiments, NF-ĸB activation was significantly upregulated in in vitro experiments. Furthermore β-estradiol treatment inhibited NF-ĸB activation in both of microglial BV-2 cells and cultured neuronal cells. These findings suggest that estrogen may protect against memory impairment through the regulation of Aβ accumulation and neurogenic inflammation by inhibiting NF-κB activity.

Allosteric binding sites in Rab11 for potential drug candidates

Rab11 is an important protein subfamily in the RabGTPase family. These proteins physiologically function as key regulators of intracellular membrane trafficking processes. Pathologically, Rab11 proteins are implicated in many diseases including cancers, neurodegenerative diseases and type 2 diabetes. Although they are medically important, no previous study has found Rab11 allosteric binding sites where potential drug candidates can bind to. In this study, by employing multiple clustering approaches integrating principal component analysis, independent component analysis and locally linear embedding, we performed structural analyses of Rab11 and identified eight representative structures. Using these representatives to perform binding site mapping and virtual screening, we identified two novel binding sites in Rab11 and small molecules that can preferentially bind to different conformations of these sites with high affinities. After identifying the binding sites and the residue interaction networks in the representatives, we computationally showed that these binding sites may allosterically regulate Rab11, as these sites communicate with switch 2 region that binds to GTP/GDP. These two allosteric binding sites in Rab11 are also similar to two allosteric pockets in Ras that we discovered previously.

An exploratory investigation of brain-selective estrogen treatment in males using a mouse model of Alzheimer's disease

Estrogens are neuroprotective, and studies suggest that they may mitigate the pathology and symptoms of Alzheimer's disease (AD) in female models. However, central estrogen effects have not been examined in males in the context of AD. The purpose of this follow-up study was to assess the benefits of a brain-selective 17β-estradiol estrogen prodrug, 10β,17β-hydroxyestra-1,4-dien-3-one (DHED), also in the male APPswe/PS1dE9 double-transgenic mouse model of the disease. After continuously exposing 6-month old animals to DHED for two months, their brains showed decreased amyloid precursor and amyloid-β protein levels. The DHED-treated APPswe/PS1dE9 double transgenic subjects also exhibited enhanced performance in a cognitive task, while 17β-estradiol treatment did not reach statistical significance. Taken together, data presented here suggest that DHED may also have therapeutic benefit in males and warrant further investigations to fully elucidate the potential of targeted estrogen therapy for a gender-independent treatment of early-stage AD.

Epidemiology of estrogen and dementia in women with Down syndrome

Several lines of investigation have shown a protective role for estrogen in Alzheimer's disease through a number of biological actions. This review examines studies of the role of estrogen-related factors in age at onset and risk for Alzheimer's disease in women with Down syndrome, a population at high risk for early onset of dementia. The studies are consistent in showing that early age at menopause and that low levels of endogenous bioavailable estradiol in postmenopausal women with Down syndrome are associated with earlier age at onset and overall risk for dementia. Polymorphisms in genes associated with estrogen receptor activity and in genes for estrogen biosynthesis affecting endogenous estrogen are related to age at onset and cumulative incidence of dementia, and may serve as biomarkers of risk. To date, no clinical trials of estrogen or hormone replacement therapy (ERT/HRT) have been published for women with Down syndrome. While findings from clinical trials of ERT or HRT for dementia have generally been negative among women in the neurotypical population, the short interval between menopause and onset of cognitive decline, together with a more positive balance between potential benefits and risks, suggests an opportunity to evaluate the efficacy of ERT/HRT for delaying or preventing dementia in this high risk population, although questions concerning the optimal formulation and timing of the hormone therapy are not yet resolved.

Puerarin suppression of Aβ1-42-induced primary cortical neuron death is largely dependent on ERβ

Recent study has suggested that estrogen replacement therapy (ERT) can decrease the risk of the development of Alzheimer's disease (AD), and phytoestrogen has been proposed as a potential alternative to ERT. In this study, we investigated the protective function of puerarin (a phytoestrogen isolated from puerarin lobate) against amyloid beta (Aβ_1-42)-induced toxicity in cortical neurons and established the connection between such a protection and estrogen receptor (ER) activation. Puerarin suppressed Aβ_1-42-induced cortical neuron death in a concentration-dependent manner. Morphological examination showed that puerarin not only suppressed Aβ_1-42-induced decrease in neuron numbers, but also promoted neurite growth. In addition, we found that the neuroprotection of puerarin was dependent on the activation of estrogen receptors (ERs), as demonstrated by activation of ERE-reporter gene. Puerarin preferentially up-regulated the expression of ERβ but not ERα, and ERβ-specific siRNA significantly reduced the neuroprotection of puerarin. Taken together, our results indicated that puerarin is neuroprotective against Aβ_1-42 toxicity via the activation of estrogen receptors, and ERβ plays a key role in the process. Our novel findings provide a potential strategy for the prevention of neurodegeneration and the treatment of AD.

Prolonged day length exposure improves circadian deficits and survival in a transgenic mouse model of Huntington's disease

The circadian disruption seen in patients of Huntington's disease (HD) is recapitulated in the R6/2 mouse model. As the disease progresses, the activity of R6/2 mice increases dramatically during the rest (light) period and decreases during the active (dark) period, eventually leading to a complete disintegration of rest-activity rhythms by the age of ~16 weeks. The suprachiasmatic nucleus controls circadian rhythms by entraining the rest-activity rhythms to the environmental light-dark cycle. Since R6/2 mice can shift their rest-activity rhythms in response to a jet-lag paradigm and also respond positively to bright light therapy (1000 lx), we investigated whether or not a prolonged day length exposure could reduce their daytime activity and improve their behavioural circadian rhythms. We found that a long-day photoperiod (16 h light/8 h dark cycle; 100 lx) significantly improved the survival of R6/2 female mice by 2.4 weeks, compared to mice kept under standard conditions (12 h light/12 h dark cycle). Furthermore, a long-day photoperiod improved the nocturnality of R6/2 female mice. Mice kept under long-day photoperiod also maintained acrophase in activity rhythms (a parameter of rhythmicity strength) in phase with that of WT mice, even if they were symptomatic. By contrast, a short-day photoperiod (8 h light/16 h dark cycle) was deleterious to R6/2 female mice and further reduced the survival by ~1 week. Together, our results support the idea that light therapy may be beneficial for improving circadian dysfunction in HD patients.

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Chronic exposure to a long day (16:8 LD) is beneficial to R6/2 female mice.

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The 16:8 LD cycle slowed body weight loss and improved survival of R6/2 mice.

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Lifespan of R6/2 female mice was extended by ~2.4 weeks under 16:8 LD cycle.

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R6/2 female mice under 16:8 LD had stabilised acrophase in activity rhythms.

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Lifespan of R6/2 female mice was reduced by chronic exposure to a short day (8:16 LD).

Sex Hormone Decline and Amyloid β Synthesis, Transport and Clearance in the Brain

Sex hormones (SH) are essential regulators of the central nervous system. The decline in SH levels along with ageing may contribute to compromised neuroprotection and set the grounds for neurodegeneration and cognitive impairments. In Alzheimer's disease, besides other pathological features, there is an imbalance between amyloid β (Aβ) production and clearance, leading to its accumulation in the brain of older subjects. Aβ accumulation is a primary cause for brain inflammation and degeneration, as well as concomitant cognitive decline. There is mounting evidence that SH modulate Aβ production, transport and clearance. Importantly, SH regulate most of the molecules involved in the amyloidogenic pathway, their transport across brain barriers for elimination, and their degradation in the brain interstitial fluid. This review brings together data on the regulation of Aβ production, metabolism, degradation and clearance by SH.

Traffic jams and the complex role of α-Synuclein aggregation in Parkinson disease

A common pathological event among various neurodegenerative disorders (NDs) is the misfolding and aggregation of different proteins in the brain. This is thought to potentiate aberrant protein-protein interactions that culminate in the disruption of several biological processes and, ultimately, in neuronal cell loss. Although protein aggregates are a common hallmark in several disorders, the molecular pathways leading to their generation remain unclear. The misfolding and aggregation of α-Synuclein (aSyn) is the pathological hallmark of Parkinson disease (PD), the second most common age related ND. It has been postulated that oligomeric species of aSyn, rather than more mature aggregated forms of the protein, are the causative agents of cytotoxicity. In recent years, we have been investigating the molecular mechanisms underlying the initial steps of aSyn accumulation in living cells. Using an unbiased genome-wide lentiviral RNAi screen we identified trafficking and kinase genes as modulators of aSyn oligomerization, aggregation, and toxicity. Among those, Rab8b, Rab11a, Rab13 and Slp5 were found to promote the clearance of aSyn inclusions and reduce aSyn toxicity. Moreover, we found that endocytic recycling and secretion of aSyn was enhanced upon expression of Rab11a or Rab13 in cells accumulating aSyn inclusions. Altogether, our findings suggest specific trafficking steps may prove beneficial as targets for therapeutic intervention in synucleinopathies, and should be further investigated in other models.

shRNA-Based Screen Identifies Endocytic Recycling Pathway Components That Act as Genetic Modifiers of Alpha-Synuclein Aggregation, Secretion and Toxicity

Alpha-Synuclein (aSyn) misfolding and aggregation is common in several neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies, which are known as synucleinopathies. Accumulating evidence suggests that secretion and cell-to-cell trafficking of pathological forms of aSyn may explain the typical patterns of disease progression. However, the molecular mechanisms controlling aSyn aggregation and spreading of pathology are still elusive. In order to obtain unbiased information about the molecular regulators of aSyn oligomerization, we performed a microscopy-based large-scale RNAi screen in living cells. Interestingly, we identified nine Rab GTPase and kinase genes that modulated aSyn aggregation, toxicity and levels. From those, Rab8b, Rab11a, Rab13 and Slp5 were able to promote the clearance of aSyn inclusions and rescue aSyn induced toxicity. Furthermore, we found that endocytic recycling and secretion of aSyn was enhanced upon Rab11a and Rab13 expression in cells accumulating aSyn inclusions. Overall, our study resulted in the identification of new molecular players involved in the aggregation, toxicity, and secretion of aSyn, opening novel avenues for our understanding of the molecular basis of synucleinopathies.

Acceleration of amyloidogenesis and memory impairment by estrogen deficiency through NF-κB dependent beta-secretase activation in presenilin 2 mutant mice

Nearly 7-10 million people are living with Alzheimer's disease (AD) worldwide. Senile plaques composed of β-amyloid (Aβ) are a pathological hallmark of Alzheimer's disease. Presenilin 2 (PS2) mutations increase Aβ generation in the brains of AD patients. The Aβ is generated through the sequential cleavage of amyloid precursor protein by β- and γ-secretases. Additionally, increasing evidences suggest that estrogen can reduce the development of AD via regulation of β-secretases activity and beta-site APP-cleaving enzyme (BACE1) expression. But the underlying correlation mechanism of Aβ generation by PS2 mutations and estrogen remains to be clarified. To investigate the anti-amyloidogenesis effect of estrogen in a PS2 mutative condition, we examined memory impairment in ovariectomized PS2 mutation (N141I) mice in which cognitive function was assessed by the Morris water maze test and passive avoidance test. In addition, Western blot analysis, immunostaining, immunofluorescence staining, ELISA and enzyme activity assays were used to examine the degree of Aβ deposition in the brains. In the present study, Aβ accumulated more in the ovariectomized PS2 mutant mice brain, and greatly worsened memory impairment and glial activation as well as neurogenic inflammation. In parallel with increased memory impairment, activity of β-secretase and expression of the BACE1 increased inovariectomized PS2 mutant mice. Much higher activity of NF-κB was observed by EMSA in ovariectomized PS2 mutant mice. In addition, the Aβ level was decreased by treatment of β-estradiol through inhibiting BACE1 expression in PS2 transfacted PC12 cells. These results suggest that mutation of PS2 can lead to NF-κB mediate amyloidogensis, and this effect can be amplified by the absence of estrogen.

Oxidant/Antioxidant imbalance and the risk of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia characterized by progressive loss of memory and other cognitive functions among older people. Senile plaques and neurofibrillary tangles are the most hallmarks lesions in the brain of AD in addition to neurons loss. Accumulating evidence has shown that oxidative stress-induced damage may play an important role in the initiation and progression of AD pathogenesis. Redox impairment occurs when there is an imbalance between the production and quenching of free radicals from oxygen species. These reactive oxygen species augment the formation and aggregation of amyloid-β and tau protein hyperphosphorylation and vice versa. Currently, there is no available treatments can modify the disease. However, wide varieties of antioxidants show promise to delay or prevent the symptoms of AD and may help in treating the disease. In this review, the role of oxidative stress in AD pathogenesis and the common used antioxidant therapies for AD will summarize.

Rab11 modulates α-synuclein-mediated defects in synaptic transmission and behaviour

A central pathological hallmark of Parkinson's disease (PD) is the presence of proteinaceous depositions known as Lewy bodies, which consist largely of the protein α-synuclein (aSyn). Mutations, multiplications and polymorphisms in the gene encoding aSyn are associated with familial forms of PD and susceptibility to idiopathic PD. Alterations in aSyn impair neuronal vesicle formation/transport, and likely contribute to PD pathogenesis by neuronal dysfunction and degeneration. aSyn is functionally associated with several Rab family GTPases, which perform various roles in vesicle trafficking. Here, we explore the role of the endosomal recycling factor Rab11 in the pathogenesis of PD using Drosophila models of aSyn toxicity. We find that aSyn induces synaptic potentiation at the larval neuromuscular junction by increasing synaptic vesicle (SV) size, and that these alterations are reversed by Rab11 overexpression. Furthermore, Rab11 decreases aSyn aggregation and ameliorates several aSyn-dependent phenotypes in both larvae and adult fruit flies, including locomotor activity, degeneration of dopaminergic neurons and shortened lifespan. This work emphasizes the importance of Rab11 in the modulation of SV size and consequent enhancement of synaptic function. Our results suggest that targeting Rab11 activity could have a therapeutic value in PD.

Mouse embryonic development in a serum-free whole embryo culture system

Mid-gestation stage mouse embryos were cultured utilizing a serum-free culture medium prepared from commercially available stem cell media supplements in an oxygenated rolling bottle culture system. Mouse embryos at E10.5 were carefully isolated from the uterus with intact yolk sac and in a process involving precise surgical maneuver the embryos were gently exteriorized from the yolk sac while maintaining the vascular continuity of the embryo with the yolk sac. Compared to embryos prepared with intact yolk sac or with the yolk sac removed, these embryos exhibited superior survival rate and developmental progression when cultured under similar conditions. We show that these mouse embryos, when cultured in a defined medium in an atmosphere of 95% O2 / 5% CO2 in a rolling bottle culture apparatus at 37 °​C for 16-40 hr, exhibit morphological growth and development comparable to the embryos developing in utero. We believe this method will be useful for investigators needing to utilize whole embryo culture to study signaling interactions important in embryonic organogenesis.

Rab11 as a modulator of synaptic transmission

Many neurodegenerative disorders are characterized by synaptic dysfunction preceding general neuronal loss and subsequent cognitive or behavioral anomalies. Much recent research has been aimed at understanding the early underlying processes leading to dysfunction at the synapse, as this knowledge would likely inform interventions that could potentially slow progression and delay onset of disease. We have recently reported that synaptic dysfunction in a Drosophila melanogaster model of Huntington's disease (HD) can be prevented by enhanced neuronal expression of Rab11, a Rab family GTPase involved in endosomal recycling, which complements studies that have found disrupted Rab11 activity in several models of this disorder. Indeed, inhibition of Rab11 function in fibroblasts of HD patients has been observed to perturb vesicle formation from recycling endosomes. Therefore, our study investigated a potential role of Rab11 in synaptic dysfunction prior to the onset of HD symptoms, with the aim of finding a possible early intervention to disease progression. We found that Rab11 ameliorates synaptic dysfunction due to expression of mutant huntingtin-the causative protein in HD-by normalizing synaptic vesicle size, which consequently ameliorates locomotor deficits in Drosophila larvae. Here we further consider these results and the implications this work has on potential therapeutic intervention in HD and other neurodegenerative disorders.

The Rab family of proteins: 25 years on

Intracellular membrane trafficking requires the complex interplay of several classes of trafficking proteins. Rab proteins, the largest subfamily of the Ras superfamily of small G-proteins, are central regulators of all aspects of intracellular trafficking processes including vesicle budding and uncoating, motility, tethering and fusion. In the present paper, we discuss the discovery, evolution and characterization of the Rab GTPase family. We examine their basic functional roles, their important structural features and the regulatory proteins which mediate Rab function. We speculate on outstanding issues in the field, such as the mechanisms of Rab membrane association and the co-ordinated interplay between distinct Rab proteins. Finally, we summarize the data implicating Rab proteins in an ever increasing number of diseases.

Rab11 proteins in health and disease

Comprising over 60 members, Rab proteins constitute the largest branch of the Ras superfamily of low-molecular-mass G-proteins. This protein family have been primarily implicated in various aspects of intracellular membrane trafficking processes. On the basis of distinct subfamily-specific sequence motifs, many Rabs have been grouped into subfamilies. The Rab11 GTPase subfamily comprises three members: Rab11a, Rab11b and Rab25/Rab11c, which, between them, have been demonstrated to bind more than 30 proteins. In the present paper, we review the function of the Rab11 subfamily. We describe their localization and primary functional roles within the cell and their implication, to date, in disease processes. We also summarize the protein machinery currently known to regulate or mediate their functions and the cargo molecules which they have been shown to transport.

Gender, sex steroid hormones, and Alzheimer's disease

Age-related loss of sex steroid hormones is a established risk factor for the development of Alzheimer's disease (AD) in women and men. While the relationships between the sex steroid hormones and AD are not fully understood, findings from both human and experimental paradigms indicate that depletion of estrogens in women and androgens in men increases vulnerability of the aging brain to AD pathogenesis. We review evidence of a wide range of beneficial neural actions of sex steroid hormones that may contribute to their hypothesized protective roles against AD. Both estrogens and androgens exert general neuroprotective actions relevant to a several neurodegenerative conditions, some in a sex-specific manner, including protection from neuron death and promotion of select aspects of neural plasticity. In addition, estrogens and androgens regulate key processes implicated in AD pathogenesis, in particular the accumulation of β-amyloid protein. We discuss evidence of hormone-specific mechanisms related to the regulation of the production and clearance of β-amyloid as critical protective pathways. Continued elucidation of these pathways promises to yield effective hormone-based strategies to delay development of AD.

A cross-species analysis method to analyze animal models' similarity to human's disease state

Background

Animal models are indispensable tools in studying the cause of human diseases and searching for the treatments. The scientific value of an animal model depends on the accurate mimicry of human diseases. The primary goal of the current study was to develop a cross-species method by using the animal models' expression data to evaluate the similarity to human diseases' and assess drug molecules' efficiency in drug research. Therefore, we hoped to reveal that it is feasible and useful to compare gene expression profiles across species in the studies of pathology, toxicology, drug repositioning, and drug action mechanism.

Results

We developed a cross-species analysis method to analyze animal models' similarity to human diseases and effectiveness in drug research by utilizing the existing animal gene expression data in the public database, and mined some meaningful information to help drug research, such as potential drug candidates, possible drug repositioning, side effects and analysis in pharmacology. New animal models could be evaluated by our method before they are used in drug discovery.

We applied the method to several cases of known animal model expression profiles and obtained some useful information to help drug research. We found that trichostatin A and some other HDACs could have very similar response across cell lines and species at gene expression level. Mouse hypoxia model could accurately mimic the human hypoxia, while mouse diabetes drug model might have some limitation. The transgenic mouse of Alzheimer was a useful model and we deeply analyzed the biological mechanisms of some drugs in this case. In addition, all the cases could provide some ideas for drug discovery and drug repositioning.

Conclusions

We developed a new cross-species gene expression module comparison method to use animal models' expression data to analyse the effectiveness of animal models in drug research. Moreover, through data integration, our method could be applied for drug research, such as potential drug candidates, possible drug repositioning, side effects and information about pharmacology.

Rab11 rescues synaptic dysfunction and behavioural deficits in a Drosophila model of Huntington's disease

Synapse abnormalities in Huntington's disease (HD) patients can precede clinical diagnosis and neuron loss by decades. The polyglutamine expansion in the huntingtin (htt) protein that underlies this disorder leads to perturbations in many cellular pathways, including the disruption of Rab11-dependent endosomal recycling. Impairment of the small GTPase Rab11 leads to the defective formation of vesicles in HD models and may thus contribute to the early stages of the synaptic dysfunction in this disorder. Here, we employ transgenic Drosophila melanogaster models of HD to investigate anomalies at the synapse and the role of Rab11 in this pathology. We find that the expression of mutant htt in the larval neuromuscular junction decreases the presynaptic vesicle size, reduces quantal amplitudes and evoked synaptic transmission and alters larval crawling behaviour. Furthermore, these indicators of early synaptic dysfunction are reversed by the overexpression of Rab11. This work highlights a potential novel HD therapeutic strategy for early intervention, prior to neuronal loss and clinical manifestation of disease.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Protein repertoire impact of Ubiquitin-Proteasome System impairment: insight into the protective role of beta-estradiol

The Ubiquitin-Proteasome System (UPS) and the Autophagy-Lysosome Pathways (ALP) are key mechanisms for cellular homeostasis sustenance and protein clearance. A wide number of Neurodegenerative Diseases (NDs) are tied with UPS impairment and have been also described as proteinopathies caused by aggregate-prone proteins, not efficiently removed by proteasome. Despite the large knowledge on proteasome biological role, molecular mechanisms associated with its impairment are still blur. We have pursued a comprehensive proteomic investigation to evaluate the phenotypic rearrangements in protein repertoires associated with a UPS blockage. Different functional proteomic approaches have been employed to tackle UPS impairment impact on human NeuroBlastoma (NB) cell lines responsive to proteasome inhibition by Epoxomicin. 2-Dimensional Electrophoresis (2-DE) separation combined with Mass Spectrometry and Shotgun Proteomics experiments have been employed to design a thorough picture of protein profile. Unsupervised meta-analysis of the collected proteomic data revealed that all the identified proteins relate each other in a functional network centered on beta-estradiol. Moreover we showed that treatment of cells with beta-estradiol resulted in aggregate removal and increased cell survival due to activation of the autophagic pathway. Our data may provide the molecular basis for the use of beta-estradiol in neurodegenerative disorders by induction of protein aggregate removal.

The potential for estrogens in preventing Alzheimer's disease and vascular dementia

Estrogens are the best-studied class of drugs for potential use in the prevention of Alzheimer's disease (AD). These steroids have been shown to be potent neuroprotectants both in vitro and in vivo, and to exert effects that are consistent with their potential use in prevention of AD. These include the prevention of the processing of amyloid precursor protein (APP) into beta-amyloid (Aß), the reduction in tau hyperphosphorylation, and the elimination of catastrophic attempts at neuronal mitosis. Further, epidemiological data support the efficacy of early postmenopausal use of estrogens for the delay or prevention of AD. Collectively, this evidence supports the further development of estrogen-like compounds for prevention of AD. Several approaches to enhance brain specificity of estrogen action are now underway in an attempt to reduce the side effects of chronic estrogen therapy in AD.

Protein trafficking dysfunctions: Role in the pathogenesis of pulmonary arterial hypertension

Earlier electron microscopic data had shown that a hallmark of the vascular remodeling in pulmonary arterial hypertension (PAH) in man and experimental models includes enlarged vacuolated endothelial and smooth muscle cells with increased endoplasmic reticulum and Golgi stacks in pulmonary arterial lesions. In cell culture and in vivo experiments in the monocrotaline model, we observed disruption of Golgi function and intracellular trafficking with trapping of diverse vesicle tethers, SNAREs and SNAPs in the Golgi membranes of enlarged pulmonary arterial endothelial cells (PAECs) and pulmonary arterial smooth muscle cells (PASMCs). Consequences included the loss of cell surface caveolin-1, hyperactivation of STAT3, mislocalization of eNOS with reduced cell surface/caveolar NO and hypo-S-nitrosylation of trafficking-relevant proteins. Similar Golgi tether, SNARE and SNAP dysfunctions were also observed in hypoxic PAECs in culture and in PAECs subjected to NO scavenging. Strikingly, a hypo-NO state promoted PAEC mitosis and cell proliferation. Golgi dysfunction was also observed in pulmonary vascular cells in idiopathic PAH (IPAH) in terms of a marked cytoplasmic dispersal and increased cellular content of the Golgi tethers, giantin and p115, in cells in the proliferative, obliterative and plexiform lesions in IPAH. The question of whether there might be a causal relationship between trafficking dysfunction and vasculopathies of PAH was approached by genetic means using HIV-nef, a protein that disrupts endocytic and trans-Golgi trafficking. Macaques infected with a chimeric simian immunodeficiency virus (SIV) containing the HIV-nef gene (SHIV-nef), but not the non-chimeric SIV virus containing the endogenous SIV-nef gene, displayed pulmonary arterial vasculopathies similar to those in human IPAH. Only macaques infected with chimeric SHIV-nef showed pulmonary vascular lesions containing cells with dramatic cytoplasmic dispersal and increase in giantin and p115. Specifically, it was the HIV-nef–positive cells that showed increased giantin. Elucidating how each of these changes fits into the multifactorial context of hypoxia, reduced NO bioavailability, mutations in BMPR II, modulation of disease penetrance and gender effects in disease occurrence in the pathogenesis of PAH is part of the road ahead.

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

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

APP processing in Alzheimer's disease

An important pathological feature of Alzheimer's disease (AD) is the presence of extracellular senile plaques in the brain. Senile plaques are composed of aggregations of small peptides called β-amyloid (Aβ). Multiple lines of evidence demonstrate that overproduction/aggregation of Aβ in the brain is a primary cause of AD and inhibition of Aβ generation has become a hot topic in AD research. Aβ is generated from β-amyloid precursor protein (APP) through sequential cleavages first by β-secretase and then by γ-secretase complex. Alternatively, APP can be cleaved by α-secretase within the Aβ domain to release soluble APPα and preclude Aβ generation. Cleavage of APP by caspases may also contribute to AD pathologies. Therefore, understanding the metabolism/processing of APP is crucial for AD therapeutics. Here we review current knowledge of APP processing regulation as well as the patho/physiological functions of APP and its metabolites.

Amyloid beta precursor protein regulates male sexual behavior

Sexual behavior is variable between individuals, ranging from celibacy to sexual addictions. Within normal populations of individual men, ranging from young to middle aged, testosterone levels do not correlate with libido. To study the genetic mechanisms that contribute to individual differences in male sexual behavior, we used hybrid B6D2F1 male mice, which are a cross between two common inbred strains (C57BL/6J and DBA/2J). Unlike most laboratory rodent species in which male sexual behavior is highly dependent upon gonadal steroids, sexual behavior in a large proportion of these hybrid male mice after castration is independent of gonadal steroid hormones and their receptors; thus, we have the ability to discover novel genes involved in this behavior. Gene expression arrays, validation of gene candidates, and transgenic mice that overexpress one of the genes of interest were used to reveal genes involved in maintenance of male sexual behavior. Several genes related to neuroprotection and neurodegeneration were differentially expressed in the hypothalamus of males that continued to mate after castration. Male mice overexpressing the human form of one of these candidate genes, amyloid beta precursor protein (APP), displayed enhanced sexual behavior before castration and maintained sexual activity for a longer duration after castration compared with controls. Our results reveal a novel and unexpected relationship between APP and male sexual behavior. We speculate that declining APP during normal aging in males may contribute to the loss of sexual function.

[Alzheimer disease, memory and estrogen]

Epidemiological studies of Alzheimer disease have shown a higher prevalence of women. Some data argue for a link between Alzheimer disease and the decrease of estrogen in post-menopausal women. Animal studies have shown a beneficial effect of estrogen on memory with a decrease of amyloid deposition in models of AD, whereas estrogen has a positive effect on BDNF. Six studies have shown a positive effect of estrogen therapy on memory and studies on structural and functional imaging have shown a beneficial effect of estrogens but the largest study on prevention of dementia with estrogens (WHI) showed a deleterious effect. To better understand this paradoxical situation, we reviewed the literature on estrogens, memory and Alzheimer disease. We first discuss the promnesic effect of estrogen on mice and rats, second the neuroprotector effect of estrogen on animal models of Alzheimer disease, and third the available human studies. We hypothesize a link with the time of instauration of the estrogen treatment. Nevertheless this hypothesis remains to be demonstrated.

Neuroprotective mechanism conferred by 17beta-estradiol on the biochemical basis of Alzheimer's disease

Estrogen (17beta-estradiol) plays key regulatory roles in a variety of physiological and biological processes. Several lines of evidence also support its role as a protective factor in Alzheimer's disease; however, the basis of this effect is unclear. Here we show that an early-onset Alzheimer's disease transgenic mouse model expressing the double-mutant form of human amyloid precursor protein (APP); Swedish (K670N/M671L) and Indiana (V717F) undergoing treatment with 17beta-estradiol show significantly lower levels of APP processing through beta-secretase and enhanced alpha-secretase processing resulting in marked reductions of APP-CTFbeta, Abeta42 and plaque burden, along with increased levels of the non-amyloidogenic sAPPalpha. Moreover, 17beta-estradiol resulted in elevated brain levels of transthyretin, which inhibits aggregation of Abeta into plaques; though the insulin-degrading enzyme, which breaks down Abeta, was significantly reduced. These results illustrate a multifaceted effect of 17beta-estradiol on the biochemical basis of Alzheimer's disease, through effects on APP processing, Abeta levels and factors that affect its clearance and aggregation. Overall, these results support the need for further long-term longitudinal studies to elucidate consequences of menopause as well as hormone therapy on Alzheimer's disease, and explore its potential as a therapeutic avenue for the disease.

Menopause and mitochondria: windows into estrogen effects on Alzheimer's disease risk and therapy

Metabolic derangements and oxidative stress are early events in Alzheimer's disease pathogenesis. Multi-faceted effects of estrogens include improved cerebral metabolic profile and reduced oxidative stress through actions on mitochondria, suggesting that a woman's endogenous and exogenous estrogen exposures during midlife and in the late post-menopause might favourably influence Alzheimer risk and symptoms. This prediction finds partial support in the clinical literature. As expected, early menopause induced by oophorectomy may increase cognitive vulnerability; however, there is no clear link between age at menopause and Alzheimer risk in other settings, or between natural menopause and memory loss. Further, among older post-menopausal women, initiating estrogen-containing hormone therapy increases dementia risk and probably does not improve Alzheimer's disease symptoms. As suggested by the 'critical window' or 'healthy cell' hypothesis, better outcomes might be expected from earlier estrogen exposures. Some observational results imply that effects of hormone therapy on Alzheimer risk are indeed modified by age at initiation, temporal proximity to menopause, or a woman's health. However, potential methodological biases warrant caution in interpreting observational findings. Anticipated results from large, ongoing clinical trials [Early Versus Late Intervention Trial with Estradiol (ELITE), Kronos Early Estrogen Prevention Study (KEEPS)] will help settle whether midlife estrogen therapy improves midlife cognitive skills but not whether midlife estrogen exposures modify late-life Alzheimer risk. Estrogen effects on mitochondria adumbrate the potential relevance of estrogens to Alzheimer's disease. However, laboratory models are inexact embodiments of Alzheimer pathogenesis and progression, making it difficult to surmise net effects of estrogen exposures. Research needs include better predictors of adverse cognitive outcomes, biomarkers for risks associated with hormone therapy, and tools for monitoring brain function and disease progression.

Action of estrogen on survival of basal forebrain cholinergic neurons: promoting amelioration

Extensive studies during the past two decades provide compelling evidence that the gonadal steroid, estrogen, has the potential to affect the viability of basal forebrain cholinergic neurons. These observations reflect a unique ameliorative feature of estrogen as it restores and protects the cholinergic neurons against noxious stimuli or neurodegenerative processes. Hence, we first address the ameliorative function of estrogen on basal forebrain cholinergic neurons such as the actions of estrogen on neuronal plasticity of cholinergic neurons, estrogen-induced memory enhancement and the ameliorative role of estrogen on cholinergic neuron related neurodegenerative processes such as Alzheimer's disease. Second, we survey recent data as to possible mechanisms underlying the ameliorative actions of estrogen; influencing the amyloid precursor protein processing, enhancement in neurotrophin receptor signaling and estrogen-induced non-classical actions on second messenger systems. In addition, clinical relevance, pitfalls and future aspects of estrogen therapy on basal forebrain cholinergic neurons will be discussed.

Liquiritigenin inhibits Abeta(25-35)-induced neurotoxicity and secretion of Abeta(1-40) in rat hippocampal neurons

AIM

To examine whether liquiritigenin, a newly found agonist of selective estrogen receptor-beta, has neuroprotective activity against beta-amyloid peptide (Abeta) in rat hippocampal neurons.

METHODS

Primary cultures of rat hippocampal neurons were pretreated with liquiritigenin (0.02, 0.2, and 2 micromol/L) prior to Abeta(25-35) exposure. Following treatment, viability of the cells was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis and by a lactate dehydrogenase activity-based cytotoxicity assay. Intracellular Ca(2+) concentration ([Ca(2+)](i)) and levels of reactive oxygen species (ROS), as well as apoptotic rates, were determined. Our studies were extended in tests of whether liquiritigenin treatment could inhibit the secretion of Abeta(1-40) as measured using an ELISA method. In order to analyze which genes may be involved, we used a microarray assay to compare gene expression patterns. Finally, the levels of specific proteins related to neurotrophy and neurodenegeration were detected by Western blotting.

RESULTS

Pretreated neurons with liquiritigenin in the presence of Abeta(25-35) increased cell viability in a concentration-dependent manner. Liquiritigenin treatment also attenuated Abeta(25-35)-induced increases in [Ca(2+)](i) and ROS level and decreased the apoptotic rate of neurons. Some genes, including B-cell lymphoma/leukemia-2 (Bcl-2), neurotrophin 3 (Ntf-3) and amyloid beta (A4) precursor protein-binding, family B, member 1 (Apbb-1) were regulated by liquiritigenin; similar results were shown at the protein level by Western blotting.

CONCLUSION

Our results demonstrate that liquiritigenin exhibits neuroprotective effects against Abeta(25-35)-induced neurotoxicity and that it can decrease the secretion of Abeta(1-40). Therefore, liquiritigenin may be useful for further study as a prodrug for treatment of Alzheimer's disease.Acta Pharmacologica Sinica (2009) 30: 899-906; doi: 10.1038/aps.2009.74.

Protective actions of sex steroid hormones in Alzheimer's disease

Risk for Alzheimer's disease (AD) is associated with age-related loss of sex steroid hormones in both women and men. In post-menopausal women, the precipitous depletion of estrogens and progestogens is hypothesized to increase susceptibility to AD pathogenesis, a concept largely supported by epidemiological evidence but refuted by some clinical findings. Experimental evidence suggests that estrogens have numerous neuroprotective actions relevant to prevention of AD, in particular promotion of neuron viability and reduction of beta-amyloid accumulation, a critical factor in the initiation and progression of AD. Recent findings suggest neural responsiveness to estrogen can diminish with age, reducing neuroprotective actions of estrogen and, consequently, potentially limiting the utility of hormone therapies in aged women. In addition, estrogen neuroprotective actions are also modulated by progestogens. Specifically, continuous progestogen exposure is associated with inhibition of estrogen actions whereas cyclic delivery of progestogens may enhance neural benefits of estrogen. In recent years, emerging literature has begun to elucidate a parallel relationship of sex steroid hormones and AD risk in men. Normal age-related testosterone loss in men is associated with increased risk to several diseases including AD. Like estrogen, testosterone has been established as an endogenous neuroprotective factor that not only increases neuronal resilience against AD-related insults, but also reduces beta-amyloid accumulation. Androgen neuroprotective effects are mediated both directly by activation of androgen pathways and indirectly by aromatization to estradiol and initiation of protective estrogen signaling mechanisms. The successful use of hormone therapies in aging men and women to delay, prevent, and or treat AD will require additional research to optimize key parameters of hormone therapy and may benefit from the continuing development of selective estrogen and androgen receptor modulators.