Estrogen-induced signaling attenuates soluble Aβ peptide-mediated dysfunction of pathways in synaptic plasticity

Echinacoside exhibits antidepressant-like effects through AMPAR-Akt/ERK-mTOR pathway stimulation and BDNF expression in mice

Background

Several natural products have been demonstrated to be effective in the treatment of depressive disorders. Echinacoside, a naturally occurring phenol extracted from Cistanche tubulosa, Echinacea angustifolia, and Cistanche spp, has a wide range of physiological effects, such as antioxidation, neuroprotection, anti-inflammatory, and immunoregulation, which are closely related to depression. In addition, echinacoside can activate protein kinase B (Akt), extracellular signal–regulated kinase (ERK), and brain-derived neurotrophic factor (BDNF) in the brain. A key downstream event of the Akt, ERK, and BDNF signaling pathways, namely mechanistic target of rapamycin (mTOR) signaling, plays a crucial role in generating an rapid antidepressant effect. Thus, echinacoside is a promising therapeutic agent for depression. However, research regarding the role of echinacoside in antidepressant effect and brain mTOR activation remains lacking.

Materials and methods

The forced swimming test and Western blot analysis in C57BL/6 mice was used to investigate the antidepressant-like activities of echinacoside and the underlying mechanism involved inα-amino3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)–Akt/ERK–mTOR pathway.

Results

We confirmed the suggestions by previous reports that echinacoside activates Akt/ERK signaling and further demonstrated that echinacoside could provide antidepressant-like effects in mice via the activation of AMPAR–Akt/ERK–mTOR pathway in the hippocampus.

Conclusions

To the best of our knowledge, our study is the first to reveal that echinacoside is a potential treatment for depressive disorders. Moreover, the present study suggests a mechanism for the neuroprotective effect of echinacoside.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00549-5.

Activity Dependent Mammalian Target of Rapamycin Pathway and Brain Derived Neurotrophic Factor Release Is Required for the Rapid Antidepressant Effects of Puerarin

Puerarin is a traditional Chinese medicine with beneficial effects of reduced depression-like behaviors in mice with stress. Previous studies also show that puerarin can produce neuroprotective effect via activating the Akt or increased brain-derived neurotrophic factor (BDNF) expression. Interestingly, BDNF and Akt downstream target, mammalian target of rapamycin (mTOR) mediate the fast-acting antidepressant properties of ketamine. Until now, the involvement of the mTOR signaling pathway or BDNF on puerarin-induced antidepressant effect remains unknown. We aimed to investigate whether the antidepressant-like effect induced by puerarin would associate mTOR signaling pathway and BDNF release. The antidepressant-like effects of puerarin were evaluated using the forced swim test. The activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionaic acid receptor (AMPAR)-mTOR signaling pathway and release of BDNF in the prefrontal cortex were determined. We also investigated the effect of puerarin on AMPAR trafficking through measuring the PKA phosphorylation of AMPAR subunit GluR1. Our present results show that puerarin exerted antidepressant-like responses that was mediated by AMPAR-induced mTOR signaling pathway and associated with increased BDNF release. Moreover, a significant increase in the GluR1 phosphorylation at its PKA site was noted following puerarin treatment. Our findings are the first to demonstrate that the antidepressant-like actions of puerarin require AMPAR-mTOR signaling pathway activation, are associated with an increased BDNF level and facilitate AMPAR membrane insertion. These findings provide preclinical evidence that puerarin may possess antidepressant property which is mediated by the glutamatergic system.

Effects of estrogen and aging on synaptic morphology and distribution of phosphorylated Tyr1472 NR2B in the female rat hippocampus

Age and estrogens may impact the mobility of N-methyl-D-aspartate receptors (NMDARs) in hippocampal synapses. Here, we used serial section immunogold electron microscopy to examine whether phosphorylated tyrosine 1472 NR2B (pY1472), which is involved in the surface expression of NMDARs, is altered in the dorsal hippocampus of young (3-4 months old) and aged (∼24 months old) ovariectomized rats treated with 17β-estradiol or vehicle for 2 days. The number of gold particles labeling pY1472 was higher in presynaptic and postsynaptic compartments of aged rats with low estradiol (vehicle-treated) compared to other groups. In terminals, pY1472 levels were elevated in aged rats but reduced by estradiol treatment to levels seen in young rats. Conversely, the mitochondria number was lower in aged females but was restored to young levels by estradiol. In the postsynaptic density and dendritic spines, estradiol reduced pY1472 in young and aged rats. As phosphorylation at Y1472 blocks NR2B endocytosis, reduction of pY1472 by estradiol suggests another mechanism through which estrogen enhances synaptic plasticity by altering localization of NMDAR subunits within synapses.

Sex Differences in Psychiatric Disease: A Focus on the Glutamate System

Alterations in glutamate, the primary excitatory neurotransmitter in the brain, are implicated in several psychiatric diseases. Many of these psychiatric diseases display epidemiological sex differences, with either males or females exhibiting different symptoms or disease prevalence. However, little work has considered the interaction of disrupted glutamatergic transmission and sex on disease states. This review describes the clinical and preclinical evidence for these sex differences with a focus on two conditions that are more prevalent in women: Alzheimer's disease and major depressive disorder, and three conditions that are more prevalent in men: schizophrenia, autism spectrum disorder, and attention deficit hyperactivity disorder. These studies reveal sex differences at multiple levels in the glutamate system including metabolic markers, receptor levels, genetic interactions, and therapeutic responses to glutamatergic drugs. Our survey of the current literature revealed a considerable need for more evaluations of sex differences in future studies examining the role of the glutamate system in psychiatric disease. Gaining a more thorough understanding of how sex differences in the glutamate system contribute to psychiatric disease could provide novel avenues for the development of sex-specific pharmacotherapies.

Neuronal Gene Targets of NF-κB and Their Dysregulation in Alzheimer's Disease

Although, better known for its role in inflammation, the transcription factor nuclear factor kappa B (NF-κB) has more recently been implicated in synaptic plasticity, learning, and memory. This has been, in part, to the discovery of its localization not just in glia, cells that are integral to mediating the inflammatory process in the brain, but also neurons. Several effectors of neuronal NF-κB have been identified, including calcium, inflammatory cytokines (i.e., tumor necrosis factor alpha), and the induction of experimental paradigms thought to reflect learning and memory at the cellular level (i.e., long-term potentiation). NF-κB is also activated after learning and memory formation in vivo. In turn, activation of NF-κB can elicit either suppression or activation of other genes. Studies are only beginning to elucidate the multitude of neuronal gene targets of NF-κB in the normal brain, but research to date has confirmed targets involved in a wide array of cellular processes, including cell signaling and growth, neurotransmission, redox signaling, and gene regulation. Further, several lines of research confirm dysregulation of NF-κB in Alzheimer's disease (AD), a disorder characterized clinically by a profound deficit in the ability to form new memories. AD-related neuropathology includes the characteristic amyloid beta plaque formation and neurofibrillary tangles. Although, such neuropathological findings have been hypothesized to contribute to memory deficits in AD, research has identified perturbations at the cellular and synaptic level that occur even prior to more gross pathologies, including transcriptional dysregulation. Indeed, synaptic disturbances appear to be a significant correlate of cognitive deficits in AD. Given the more recently identified role for NF-κB in memory and synaptic transmission in the normal brain, the expansive network of gene targets of NF-κB, and its dysregulation in AD, a thorough understanding of NF-κB-related signaling in AD is warranted and may have important implications for uncovering treatments for the disease. This review aims to provide a comprehensive view of our current understanding of the gene targets of this transcription factor in neurons in the intact brain and provide an overview of studies investigating NF-κB signaling, including its downstream targets, in the AD brain as a means of uncovering the basic physiological mechanisms by which memory becomes fragile in the disease.

Cooperation of Genomic and Rapid Nongenomic Actions of Estrogens in Synaptic Plasticity

Neuroplasticity refers to the changes in the molecular and cellular processes of neural circuits that occur in response to environmental experiences. Clinical and experimental studies have increasingly shown that estrogens participate in the neuroplasticity involved in cognition, behavior, and memory. It is generally accepted that estrogens exert their effects through genomic actions that occur over a period of hours to days. However, emerging evidence indicates that estrogens also rapidly influence the neural circuitry through nongenomic actions. In this review, we provide an overview of the genomic and nongenomic actions of estrogens and discuss how these actions may cooperate in synaptic plasticity. We then summarize the role of epigenetic modifications, synaptic protein synthesis, and posttranslational modifications, and the splice variants of estrogen receptors in the complicated network of estrogens. The combination of genomic and nongenomic mechanisms endows estrogens with considerable diversity in modulating neural functions including synaptic plasticity.

Re-Opening the Critical Window for Estrogen Therapy

A decline in estradiol (E2)-mediated cognitive benefits denotes a critical window for the therapeutic effects of E2, but the mechanism for closing of the critical window is unknown. We hypothesized that upregulating the expression of estrogen receptor α (ERα) or estrogen receptor β (ERβ) in the hippocampus of aged animals would restore the therapeutic potential of E2 treatments and rejuvenate E2-induced hippocampal plasticity. Female rats (15 months) were ovariectomized, and, 14 weeks later, adeno-associated viral vectors were used to express ERα, ERβ, or green fluorescent protein (GFP) in the CA1 region of the dorsal hippocampus. Animals were subsequently treated for 5 weeks with cyclic injections of 17β-estradiol-3-benzoate (EB, 10 μg) or oil vehicle. Spatial memory was examined 48 h after EB/oil treatment. EB treatment in the GFP (GFP + EB) and ERβ (ERβ + EB) groups failed to improve episodic spatial memory relative to oil-treated animals, indicating closing of the critical window. Expression of ERβ failed to improve cognition and was associated with a modest learning impairment. Cognitive benefits were specific to animals expressing ERα that received EB treatment (ERα + EB), such that memory was improved relative to ERα + oil and GFP + EB. Similarly, ERα + EB animals exhibited enhanced NMDAR-mediated synaptic transmission compared with the ERα + oil and GFP + EB groups. This is the first demonstration that the window for E2-mediated benefits on cognition and hippocampal E2 responsiveness can be reinstated by increased expression of ERα.

SIGNIFICANCE STATEMENT

Estradiol is neuroprotective, promotes synaptic plasticity in the hippocampus, and protects against cognitive decline associated with aging and neurodegenerative diseases. However, animal models and clinical studies indicate a critical window for the therapeutic treatment such that the beneficial effects are lost with advanced age and/or with extended hormone deprivation. We used gene therapy to upregulate expression of the estrogen receptors ERα and ERβ and demonstrate that the window for estradiol's beneficial effects on memory and hippocampal synaptic function can be reinstated by enhancing the expression of ERα. Our findings suggest that the activity of ERα controls the therapeutic window by regulating synaptic plasticity mechanisms involved in memory.

Neurogranin restores amyloid β-mediated synaptic transmission and long-term potentiation deficits

Amyloid β (Aβ) is widely considered one of the early causes of cognitive deficits observed in Alzheimer's disease. Many of the deficits caused by Aβ are attributed to its disruption of synaptic function represented by its blockade of long-term potentiation (LTP) and its induction of synaptic depression. Identifying pathways that reverse these synaptic deficits may open the door to new therapeutic targets. In this study, we explored the possibility that Neurogranin (Ng)-a postsynaptic calmodulin (CaM) targeting protein that enhances synaptic function-may rescue Aβ-mediated deficits in synaptic function. Our results show that Ng is able to reverse synaptic depression and LTP deficits induced by Aβ. Furthermore, Ng's restoration of synaptic transmission is through the insertion of GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPARs). These restorative effects of Ng are dependent on the interaction of Ng and CaM and CaM-dependent activation of CaMKII. Overall, this study identifies a novel mechanism to rescue synaptic deficits induced by Aβ oligomers. It also suggests Ng and CaM signaling as potential therapeutic targets for Alzheimer's disease as well as important tools to further explore the pathophysiology underlying the disease.

Utilizing induced pluripotent stem cells (iPSCs) to understand the actions of estrogens in human neurons

This article is part of a Special Issue "Estradiol and Cognition". Over recent years tremendous progress has been made towards understanding the molecular and cellular mechanism by which estrogens exert enhancing effects on cognition, and how they act as a neuroprotective or neurotrophic agent in disease. Currently, much of this work has been carried out in animal models with only a limited number of studies using native human tissue or cells. Recent advances in stem cell technology now make it possible to reprogram somatic cells from humans into induced pluripotent stem cells (iPSCs), which can subsequently be differentiated into neurons of specific lineages. Importantly, the reprogramming of cells allows for the generation of iPSCs that retain the genetic "makeup" of the donor. Therefore, it is possible to generate iPSC-derived neurons from patients diagnosed with specific diseases, that harbor the complex genetic background associated with the disorder. Here, we review the iPSC technology and how it's currently being used to model neural development and neurological diseases. Furthermore, we explore whether this cellular system could be used to understand the role of estrogens in human neurons, and present preliminary data in support of this. We further suggest that the use of iPSC technology offers a novel system to not only further understand estrogens' effects in human cells, but also to investigate the mechanism by which estrogens are beneficial in disease. Developing a greater understanding of these mechanisms in native human cells will also aid in the development of safer and more effective estrogen-based therapeutics.

The Essential Role of Soluble Aβ Oligomers in Alzheimer's Disease

Alzheimer's disease (AD) is a common neurodegenerative disease characterized by amyloid plaque and neurofibrillary tangles (NFT). With the finding that soluble nonfibrillar Aβ levels actually correlate strongly with the severity of the disease, the initial focus on amyloid plaques shifted to the contemporary concept that AD memory failure is caused by soluble Aβ oligomers. The soluble Aβ are known to be more neurotoxicthan fibrillar Aβ species. In this paper, we summarize the essential role of soluble Aβ oligomers in AD and discuss therapeutic strategies that target soluble Aβ oligomers.

Molecular signature of rapid estrogen regulation of synaptic connectivity and cognition

There is now a growing appreciation that estrogens are capable of rapidly activating a number of signaling cascades within the central nervous system. In addition, there are an increasing number of studies reporting that 17β-estradiol, the major biologically active estrogen, can modulate cognition within a rapid time frame. Here we review recent studies that have begun to uncover the molecular and cellular framework which contributes to estrogens ability to rapidly modulate cognition. We first describe the mechanisms by which estrogen receptors (ERs) can couple to intracellular signaling cascades, either directly, or via the transactivation of other receptors. Subsequently, we review the evidence that estrogen can rapidly modulate both neuronal function and structure in the hippocampus and the cortex. Finally, we will discuss how estrogens may influence cognitive function through the modulation of neuronal structure, and the implications this may have on the treatment of a range of brain disorders.

17β-estradiol attenuates ketamine-induced neuroapoptosis and persistent cognitive deficits in the developing brain

Previous studies have demonstrated that the commonly used anesthetic ketamine can induce widespread neuroapoptosis in the neonatal brain and can cause persistent cognitive impairments as the animal matures. Therefore, searching for adjunctive neuroprotective strategies that inhibit ketamine-induced neuroapoptosis and persistent cognitive impairments is highly warranted. The primary goal of this study was to investigate the protective effect of 17β-estradiol against ketamine-induced neuroapoptosis and persistent cognitive impairments in adult rats. Starting from postnatal day 7, Sprague-Dawley male rat pups were given a daily administration of ketamine (75mg/kg, i.p.) or 17β-estradiol (600μg/kg, s.c.) in combination with ketamine (75mg/kg, i.p.). The animals were treated for three consecutive days. 24h after the last injection, the rats were decapitated, and the prefrontal cortex (PFC) was isolated to detect neuroapoptosis by cleaved caspase-3 immunohistochemistry and by using the TUNEL assay. The neuroactive steroid 17β-estradiol was quantified using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The protein levels of BDNF and pAkt were measured by western blot analysis. At two months of age (60 days), the learning and memory abilities were tested using the Morris water maze. The results showed that ketamine triggered significant neuroapoptosis in the neonatal PFC accompanied by the downregulation of 17β-estradiol, BDNF and pAkt. The co-administration of 17β-estradiol with ketamine attenuated these changes. Moreover, 17β-estradiol significantly reversed the learning and memory deficits observed at 60 days of age. In brief, our present data demonstrate that 17β-estradiol attenuates ketamine-induced neuroapoptosis and reverses long-term cognitive deficits in developing rats and thus may be a potential therapeutic and neuroprotective method for the treatment of neurodevelopmental disorders. This article is part of a Special Issue entitled SI: Brain and Memory.

Estrogen receptor α polymorphisms and the risk of cognitive decline: A 2-year follow-up study

OBJECTIVE

The neuroprotective role of estrogen is supported by biochemical studies, but the results from clinical trials of estrogen replacement therapy on cognitive decline are controversial. One possible missing link might be the interindividual difference in estrogen receptor expression. In this study, the association of estrogen receptor α (ESR1) polymorphisms and cognitive decline was investigated.

METHODS

Chinese older adults (n = 284) were recruited, and the cognitive profile was follow-up over 2-year period. Twenty ESR1 polymorphisms were investigated and correlated with the cognitive decline for the subjects.

RESULTS

Significant association was found between ESR1 polymorphisms (rs9340799 [ESR1+351], rs1801132 [ESR1+975], rs6557171, rs9397456, and rs1884049) and subjects with no dementia (Clinical Dementia Rating, CDR 0) and very mild dementia (CDR 0.5). Several ESR1 polymorphisms were associated with cognitive decline as assessed by Chinese versions of Mini-Mental State Examination and Alzheimer Disease Association Scales-Cognitive Subscale. Different sets of ESR1 polymorphisms were associated with cognitive decline from CDR 0 to 0.5 and CDR 0.5 to 1. ESR1 polymorphisms (rs3853248, rs22334693 [ESR1+397], rs9340799 [ESR1+351], rs9397456, rs1801132 [ESR1+975], rs2179922, rs932477, and rs9341016) were associated with the deterioration of episodic memory among subjects with baseline CDR 0, indicating these polymorphisms might be markers for episodic memory decline at an earlier stage.

CONCLUSION

This study showed association between ESR polymorphisms and cognitive decline or specific areas in cognitive profile. These findings might be useful in identifying individuals at risk for early intervention, and more research is required to elucidate the underlying mechanisms.

Intriguing roles of hippocampus-synthesized 17β-estradiol in the modulation of hippocampal synaptic plasticity

Accumulated studies have shown that 17β-estradiol (E2) can be de novo synthesized in the hippocampus, and its role in the regulation of hippocampal synaptic plasticity, which is the basis of learning and memory, has long been exploring. Steroidogenic enzymes (e.g., aromatase) that are essential to the hippocampus-synthesized synthesis of E2 have been detected in the hippocampus. Inhibition of E2 synthesis by aromatase inhibitors significantly reduces the density of hippocampal spine synapses, levels of some synaptic proteins such as spinopholin and synaptophysin. Moreover, the electrophysiological properties of hippocampal neurons are also changed in response to this inhibition. The influences of gonadal and hippocampal E2 on synaptic plasticity may exist some differences, since some reports showed that gonadal (or circulating) estrogens have no obvious effects in the modulation of hippocampal synaptic proteins as evidenced in some ovariectomized animals and postmenopausal women who suffered from Alzheimer's disease (AD). These evidences leads to a hypothesis that hippocampal E2 may play a more important role in modulation of synaptic plasticity than gonadal E2. The signaling pathways, whereby hippocampal E2 modulates synaptic plasticity, insist of classical chronic genomic pathway and rapid nongenomic pathway, which mediated by nonnuclear estrogen receptor (GPER) and/or nuclear or nonnuclear estrogen receptors, which require coactivators for their transcription activity. Among which steroid receptor coactivator-1 (SRC-1) is the predominant coactivator p160 family members in the brain. Several clues have shown that SRC-1 is expressed in hippocampus and is highly correlated with some key synaptic proteins developmentally or after orchidectomy but not ovariectomy, indicating SRC-1 may be regulated by hippocampus-synthesized E2 and profoundly involved in the mediation of hippocampal E2 regulation of hippocampal synaptic plasticity. Further studies about the exact roles of hippocampus-synthesized E2 and therefore SRC-1 are urgently needed in order to facilitate our understanding of hippocampal E2, which will be very important to the development of novel strategies of estrogen replacement therapy against neurodegenerative deficits such as Alzheimer's disease (AD).

Insights into rapid modulation of neuroplasticity by brain estrogens

Converging evidence from cellular, electrophysiological, anatomic, and behavioral studies suggests that the remodeling of synapse structure and function is a critical component of cognition. This modulation of neuroplasticity can be achieved through the actions of numerous extracellular signals. Moreover, it is thought that it is the integration of different extracellular signals regulation of neuroplasticity that greatly influences cognitive function. One group of signals that exerts powerful effects on multiple neurologic processes is estrogens. Classically, estrogens have been described to exert their effects over a period of hours to days. However, there is now increasing evidence that estrogens can rapidly influence multiple behaviors, including those that require forebrain neural circuitry. Moreover, these effects are found in both sexes. Critically, it is now emerging that the modulation of cognition by rapid estrogenic signaling is achieved by activation of specific signaling cascades and regulation of synapse structure and function, cumulating in the rewiring of neural circuits. The importance of understanding the rapid effects of estrogens on forebrain function and circuitry is further emphasized as investigations continue to consider the potential of estrogenic-based therapies for neuropathologies. This review focuses on how estrogens can rapidly influence cognition and the emerging mechanisms that underlie these effects. We discuss the potential sources and the biosynthesis of estrogens within the brain and the consequences of rapid estrogenic-signaling on the remodeling of neural circuits. Furthermore, we argue that estrogens act via distinct signaling pathways to modulate synapse structure and function in a manner that may vary with cell type, developmental stage, and sex. Finally, we present a model in which the coordination of rapid estrogenic-signaling and activity-dependent stimuli can result in long-lasting changes in neural circuits, contributing to cognition, with potential relevance for the development of novel estrogenic-based therapies for neurodevelopmental or neurodegenerative disorders.

Mechanisms underlying the interactions between rapid estrogenic and BDNF control of synaptic connectivity

The effects of the steroid hormone 17β-estradiol and the neurotrophin brain-derived neurotrophic factor (BDNF) on neuronal physiology have been well investigated. Numerous studies have demonstrated that each signal can exert powerful influences on the structure and function of synapses, and specifically on dendritic spines, both within short and long time frames. Moreover, it has been suggested that BDNF is required for the long-term, or genomic, actions of 17β-estradiol on dendritic spines, via its ability to regulate the expression of neurotrophins. Here we focus on the acute, or rapid effects, of 17β-estradiol and BDNF, and their ability to activate specific signalling cascades, resulting in alterations in dendritic spine morphology. We first review recent literature describing the mechanisms by which 17β-estradiol activates these pathways, and the resulting alterations in dendritic spine number. We then describe the molecular mechanisms underlying acute modulation of dendritic spine morphology by BDNF. Finally, we consider how this new evidence may suggest that the temporal interactions of 17β-estradiol and BDNF can occur more rapidly than previously reported. Building on these new data, we propose a novel model for the interactions of this steroid and neurotrophin, whereby rapid, non-genomic 17β-estradiol and acute BDNF signal in a co-operative manner, resulting in dendritic spine formation and subsequent stabilization in support of synapse and circuit plasticity. This extended hypothesis suggests an additional mechanism by which these two signals may modulate dendritic spines in a time-specific manner.

Neuroprotective effects of new protein kinase C activator TPPB against Aβ₂₅₋₃₅ induced neurotoxicity in PC12 cells

Alzheimer's disease (AD) is pathologically characterized by presence of senile plaques in the hippocampus, which are composed mainly of extracellular deposition of a polypeptide known as the beta amyloid, the Aβ. It has been demonstrated on numerous occasions that it was the deposition and aggregation of this Aβ peptide that cause neuronal dysfunction and even finally, the dementia. Lowering the deposition of Aβ or decreasing its neurotoxicity has long been one of the purposes of AD therapy. In previous study, we reported that protein kinase C (PKC) activator TPPB could regulate APP processing by increasing α-secretase activity. In this study we further investigated the potential neuroprotective effect of TPPB against Aβ(25-35)-induced neurotoxicity in PC12 cells. The results indicated that TPPB at concentration of 1 μM could antagonize Aβ(25-35) induced cell damage as evidenced by MTT assays, LDH release and by morphological changes. Furthermore, the neuroprotection in cell viability can be blocked by inhibitors of PKC, Akt and MAPK. The experiment also indicated that TPPB could increase the phosphorylation of Akt, PKC, MARCKS and MAPK, which were inhibited by Aβ(25-35) treatment. Finally, TPPB inhibited the activation of caspase-3 induced by Aβ(25-35). Taken together, the experiment here implies that TPPB has a role against Aβ(25-35)-induced neurotoxicity in PC12 cells and may suggest its therapeutic potential in AD.

Effects of ginsenoside Rg1 or 17β-estradiol on a cognitively impaired, ovariectomized rat model of Alzheimer's disease

Ginsenoside Rg1, which could improve spatial learning and memory, might be a useful agent for preventing and treating cognitive impairment in Alzheimer's disease (AD). The present study was designed to test the neuroprotective effects of ginsenoside Rg1 on an ovariectomized (OVX) and d-galactose (d-gal)-injected rat model of AD, which is characterized with progressive learning and memory deficits, AD-related molecules alteration and differentiation/apoptosis imbalance in hippocampal neurons. OVX Wistar rats received daily injections of d-gal (100mg/kg) combined with different concentrations of ginsenoside Rg1 (5, 10, 20mg/kg) or 17-β-estradiol (E2, 100 μg/kg), or normal saline (NS, 1.0 ml/kg) for 6 weeks. Ovarian steroid deprivation plus d-gal injection led to spatial learning and memory capacity impairments, as well as increased Aβ(1-42) production. Ginsenoside Rg1 and E2-treatment significantly ameliorated these deteriorations in AD rats. Seven weeks after surgery, α-secretase a disintegrin and metallopeptidase domain 10 (ADAM 10) in hippocampus of AD rats was dramatically decreased, while β-secretase β-site APP-cleaving enzyme 1 (BACE 1) increased compared with those in sham-operated ones (P<0.05). Levels of cleaved caspase 3 were increased in the hippocampus of AD rats. Ginsenoside Rg1 and E2-treatment increased ADAM 10 level while reduced BACE 1 level and apoptosis. Moreover, moderate i.e. 10mg/kg/d and high i.e. 20mg/kg/d ginsenoside Rg1 displayed more effective function than low i.e. 5mg/kg/d ginsenoside Rg1. Our findings demonstrate the neuroprotective effects of ginsenoside Rg1 and E2 on AD rats and support the potential application of ginsenoside Rg1 in the treatment of learning and memory impairments in postmenopausal women.

Rapid estradiol modulation of neuronal connectivity and its implications for disease

Estrogens have multiple actions in the brain including modulating synaptic plasticity, connectivity, and cognitive behaviors. While the classical view of estrogens are as endocrine signals, whose effects manifest via the regulation of gene transcription, mounting evidence has been presented demonstrating that estrogens have rapid effects within specific areas of the brain. The emergence that 17 β-estradiol can be produced locally in the brain which can elicit rapid (within minutes) cellular responses has led to its classification as a neurosteroid. Moreover, recent studies have also begun to detail the molecular and cellular underpinnings of how 17 β-estradiol can rapidly modulate spiny synapses (dendritic spines). Remodeling of dendritic spines is a key step in the rewiring of neuronal circuitry thought to underlie the processing and storage of information in the forebrain. Conversely, abnormal remodeling of dendritic spines is thought to contribute to a number of psychiatric and neurodevelopmental disorders. Here we review recent molecular and cellular work that offers a potential mechanism of how 17 β-estradiol may modulate synapse structure and function of cortical neurons. This mechanism allows cortical neurons to respond to activity-dependent stimuli with greater efficacy. In turn this form of plasticity may provide an insight into how 17 β-estradiol can modulate the rewiring of neuronal circuits, underlying its ability to influencing cortically based behaviors. We will then go on to discuss the potential role of 17 β-estradiol modulation of neural circuits and its potential relevance for the treatment of psychiatric and neurodevelopmental disorders.