Phosphatidylinositol 3-kinase mediates neuroprotection by estrogen in cultured cortical neurons

Sex-dependent phosphorylation of Argonaute 2 reduces the mitochondrial translocation of miR-181c and induces cardioprotection in females

Obesity-induced cardiac dysfunction is growing at an alarming rate, showing a dramatic increase in global prevalence. Mitochondrial translocation of miR-181c in cardiomyocytes results in excessive reactive oxygen species (ROS) production during obesity. ROS causes Sp1, a transcription factor for MICU1, to be degraded via post-translational modification. The subsequent decrease in MICU1 expression causes mitochondrial Ca2+ accumulation, ultimately leading to a propensity for heart failure. Herein, we hypothesized that phosphorylation of Argonaute 2 (AGO2) at Ser 387 (in human) or Ser 388 (in mouse) inhibits the translocation of miR-181c into the mitochondria by increasing the cytoplasmic stability of the RNA-induced silencing complex (RISC). Initially, estrogen offers cardioprotection in pre-menopausal females against the consequences of mitochondrial miR-181c upregulation by driving the phosphorylation of AGO2. Neonatal mouse ventricular myocytes (NMVM) treated with insulin showed an increase in pAGO2 levels and a decrease in mitochondrial miR-181c expression by increasing the binding affinity of AGO2-GW182 in the RISC. Thus, insulin treatment prevented excessive ROS production and mitochondrial Ca2+ accumulation. In human cardiomyocytes, we overexpressed miR-181c to mimic pathological conditions, such as obesity/diabetes. Treatment with estradiol (E2) for 48 h significantly lowered miR-181c entry into the mitochondria through increased pAGO2 levels. E2 treatment also normalized Sp1 degradation and MICU1 transcription that normally occurs in response to miR-181c overexpression. We then investigated these findings using an in vivo model, with age-matched male, female and ovariectomized (OVX) female mice. Consistent with the E2 treatment, we show that female hearts express higher levels of pAGO2 and thus, exhibit higher association of AGO2-GW182 in cytoplasmic RISC. This results in lower expression of mitochondrial miR-181c in female hearts compared to male or OVX groups. Further, female hearts had fewer consequences of mitochondrial miR-181c expression, such as lower Sp1 degradation and significantly decreased MICU1 transcriptional regulation. Taken together, this study highlights a potential therapeutic target for conditions such as obesity and diabetes, where miR-181c is upregulated. NEW AND NOTEWORTHY: In this study, we show that the phosphorylation of Argonaute 2 (AGO2) stabilizes the RNA-induced silencing complex in the cytoplasm, preventing miR-181c entry into the mitochondria. Furthermore, we demonstrate that treatment with estradiol can inhibit the translocation of miR-181c into the mitochondria by phosphorylating AGO2. This ultimately eliminates the downstream consequences of miR-181c overexpression by mitigating excessive reactive oxygen species production and calcium entry into the mitochondria.

The nongenomic neuroprotective effects of estrogen, E2-BSA, and G1 following traumatic brain injury: PI3K/Akt and histopathological study

OBJECTIVES

Studies suggest that both genomic and nongenomic pathways are involved in mediating the salutary effects of steroids following traumatic brain injury (TBI). This study investigated the nongenomic effects of 17β-estradiol (E2) mediated by the PI3K/p-Akt pathway after TBI.

METHODS

Ovariectomized rats were apportioned to E2, E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicles were injected before the induction of TBI and injection of drugs. Diffuse TBI was induced by the Marmarou model. Evans blue (EBC, 5 h), brain water contents (BWC), histopathological changes, and brain PI3K and p-Akt protein expressions were measured 24 h after TBI. The veterinary comma scale (VCS) was assessed before and at different times after TBI.

RESULTS

The results showed a reduction in BWC and EBC and increased VCS in the E2, E2-BSA, and G1 groups. Also, E2, E2-BSA, and G1 reduced brain edema, inflammation, and apoptosis. The ICI and G15 inhibited the beneficial effects of E2, E2-BSA, and G1 on these parameters. All drugs, following TBI, prevented the reduction of brain PI3K/p-Akt expression. The individual or combined use of ICI and G15 eliminated the beneficial effects of E2, E2-BSA, and G1 on PI3K/p-Akt expressions.

CONCLUSIONS

These findings indicated that PI3K/p-Akt pathway plays a critical role in mediating the salutary effects of estradiol on histopathological changes and neurological outcomes following TBI, suggesting that GPER and classic ERs are involved in regulating the expression of PI3K/p-Akt.

Effect of Letrozole on hippocampal Let-7 microRNAs and their correlation with working memory and phosphorylated Tau protein in an Alzheimer's disease-like rat model

Background

Let-7 microRNAs (miRNAs) may contribute to neurodegeneration, including Alzheimer's disease (AD), but, they were not investigated in Streptozotocin (STZ)-induced AD. Letrozole increases the expression of Let-7 in cell lines, with conflicting evidence regarding its effects on memory. This study examined Let-7 miRNAs in STZ-induced AD, their correlation with memory and hyperphosphorylated Tau (p-Tau) and the effects of Letrozole on them.

Methods

Seven groups of adult Sprague Dawley rats were used: Negative control, Letrozole, Letrozole Vehicle, STZ (with AD induced by intracerebroventricular injection of STZ in artificial cerebrospinal fluid (aCSF)), CSF Control, STZ + Letrozole (STZ-L), and CSF + Letrozole Vehicle. Alternation percentage in T-maze was used as a measure of working memory. Let-7a, b and e and p-Tau levels in the hippocampus were estimated using quantitative real-time reverse transcription–polymerase chain reaction (qRT–PCR) and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Significant decreases in alternation percentage and increase in p-Tau concentration were found in the STZ, Letrozole and STZ-L groups. Expression levels of all studied microRNAs were significantly elevated in the Letrozole and the STZ-L groups, with no difference between the two, suggesting that this elevation might be linked to Letrozole administration. Negative correlations were found between alternation percentage and the levels of all studied microRNAs, while positive ones were found between p-Tau concentration and the levels of studied microRNAs.

Conclusions

This study shows changes in the expression of Let-7a, b and e miRNAs in association with Letrozole administration, and correlations between the expression of the studied Let-7 miRNAs and both the status of working memory and the hippocampal p-Tau levels. These findings might support the theory suggesting that Letrozole aggravates pre-existing lesions. They also add to the possibility of Let-7’s neurotoxicity.

Neurosteroids: A novel promise for the treatment of stroke and post-stroke complications

Stroke is the primary reason for death and disability worldwide, with few treatment strategies to date. Neurosteroids, which are natural molecules in the brain, have aroused great interest in the field of stroke. Neurosteroids are a kind of steroid that acts on the nervous system, and are synthesized in the mitochondria of neurons or glial cells using cholesterol or other steroidal precursors. Neurosteroids mainly include estrogen, progesterone (PROG), allopregnanolone, dehydroepiandrosterone (DHEA), and vitamin D (VD). Most of the preclinical studies have confirmed that neurosteroids can decrease the risk of stroke, and improve stroke outcomes. In the meantime, neurosteroids have been shown to have a positive therapeutic significance in some post-stroke complications, such as epilepsy, depression, anxiety, cardiac complications, movement disorders, and post-stroke pain. In this review, we report the historical background, modulatory mechanisms of neurosteroids in stroke and post-stroke complications, and emphasize on the application prospect of neurosteroids in stroke therapy.

Signaling Pathways and Sex Differential Processes in Autism Spectrum Disorder

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders associated with deficits in social communication and restrictive, repetitive patterns of behavior, that affect up to 1 in 54 children. ASDs clearly demonstrate a male bias, occurring ~4 times more frequently in males than females, though the basis for this male predominance is not well-understood. In recent years, ASD risk gene discovery has accelerated, with many whole-exome sequencing studies identifying genes that converge on common pathways, such as neuronal communication and regulation of gene expression. ASD genetics studies have suggested that there may be a "female protective effect," such that females may have a higher threshold for ASD risk, yet its etiology is not well-understood. Here, we review common biological pathways implicated by ASD genetics studies as well as recent analyses of sex differential processes in ASD using imaging genomics, transcriptomics, and animal models. Additionally, we discuss recent investigations of ASD risk genes that have suggested a potential role for estrogens as modulators of biological pathways in ASD, and highlight relevant molecular and cellular pathways downstream of estrogen signaling as potential avenues for further investigation.

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.

Rapamycin blocks the neuroprotective effects of sex steroids in the adult birdsong system

In adult songbirds, the telencephalic song nucleus HVC and its efferent target RA undergo pronounced seasonal changes in morphology. In breeding birds, there are increases in HVC volume and total neuron number, and RA neuronal soma area compared to nonbreeding birds. At the end of breeding, HVC neurons die through caspase-dependent apoptosis and thus, RA neuron size decreases. Changes in HVC and RA are driven by seasonal changes in circulating testosterone (T) levels. Infusing T, or its metabolites 5α-dihydrotestosterone (DHT) and 17 β-estradiol (E2), intracerebrally into HVC (but not RA) protects HVC neurons from death, and RA neuron size, in nonbreeding birds. The phosphoinositide 3-kinase (PI3K)-Akt (a serine/threonine kinase)-mechanistic target of rapamycin (mTOR) signaling pathway is a point of convergence for neuroprotective effects of sex steroids and other trophic factors. We asked if mTOR activation is necessary for the protective effect of hormones in HVC and RA of adult male Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii). We transferred sparrows from breeding to nonbreeding hormonal and photoperiod conditions to induce regression of HVC neurons by cell death and decrease of RA neuron size. We infused either DHT + E2, DHT + E2 plus the mTOR inhibitor rapamycin, or vehicle alone in HVC. Infusion of DHT + E2 protected both HVC and RA neurons. Coinfusion of rapamycin with DHT + E2, however, blocked the protective effect of hormones on HVC volume and neuron number, and RA neuron size. These results suggest that activation of mTOR is an essential downstream step in the neuroprotective cascade initiated by sex steroid hormones in the forebrain.

Activation of Membrane Estrogen Receptors Attenuates NOP-Mediated Tactile Antihypersensitivity in a Rodent Model of Neuropathic Pain

Women manifest a higher prevalence of several chronic pain disorders compared to men. We demonstrated earlier that estrogen rapidly attenuates nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP)-mediated thermal antinociception through the activation of membrane estrogen receptors (mERs). However, the effect of mER activation on NOP-mediated attenuation of tactile hypersensitivity in a neuropathic model of pain and the underlying mechanisms remain unknown. Following spared nerve injury (SNI), male and ovariectomized (OVX) female rats were intrathecally (i.t.) injected with a selective mER agonist and nociceptin/orphanin FQ (N/OFQ), the endogenous ligand for NOP, and their effects on paw withdrawal thresholds (PWTs) were tested. In addition, spinal cord tissue was used to measure changes in phosphorylated extracellular signal regulated kinase (ERK), protein kinase A (PKA), protein kinase C (PKC), and protein kinase B (Akt) levels. SNI significantly reduced PWTs in males and OVX females, indicating tactile hypersensitivity. N/OFQ restored PWTs, indicating an antihypersensitive effect. Selective mER activation attenuated the effect of N/OFQ in an antagonist-reversible manner. SNI led to a robust increase in the phosphorylation of ERK, PKA, PKC, and Akt. However, mER activation did not further affect it. Thus, we conclude that activation of mERs rapidly abolishes NOP-mediated tactile antihypersensitivity following SNI via an ERK-, PKA-, PKC-, and Akt-independent mechanism.

17β‑Estradiol protects against interleukin‑1β‑induced apoptosis in rat nucleus pulposus cells via the mTOR/caspase‑3 pathway

Intervertebral disc degeneration (IVDD) is the main pathological basis of spinal degenerative diseases, and aberrant apoptosis of nucleus pulposus cells (NPCs) is the main cellular process that causes IVDD. In our previous studies, 17β-estradiol (E₂) was demonstrated to protect rat NPCs from interleukin-1β (IL-1β)-induced apoptosis via the PI3K/Akt signaling pathway. However, the downstream signaling pathway of PI3K/Akt is currently unclear. The present study aimed to explore the signaling pathways that are downstream of the PI3K/Akt pathway, including mTOR, NF-κB and glycogen synthase kinase-3β (GSK-3β). Annexin V/propidium iodide double staining was used to determine the incidence of apoptosis. Cell Counting kit-8 and MTS assays were used to determine the proliferation and viability of NPCs, respectively. Cellular binding was evaluated using a cell-collagen binding assay. Western blotting was used to determine the protein expression levels of mTOR, NF-κB and GSK-3β, and their phosphorylation levels, as well as the expression levels of active caspase-3. The results revealed that IL-1β induced NPC apoptosis and increased the early apoptotic rate of NPCs. However, E₂ reduced the early apoptosis of NPCs induced by IL-1β. In addition, E₂ suppressed the decrease in cell viability and binding ability caused by IL-1β cytotoxicity. Western blotting revealed that E₂ also reduced the expression of activated caspase-3, and increased the expression of activated mTOR. As a specific inhibitor of mTOR, rapamycin effectively attenuated the effects of E₂. These findings indicated that E₂ protected NPCs against apoptosis via activation of the mTOR/caspase-3 pathway.

Sex steroid hormones as neuroprotective elements in ischemia models

Among sex steroid hormones, progesterone and estradiol have a wide diversity of physiological activities that target the nervous system. Not only are they carried by the blood stream, but also they are locally synthesized in the brain and for this reason, estradiol and progesterone are considered 'neurosteroids'. The physiological actions of both hormones range from brain development and neurotransmission to aging, illustrating the importance of a deep understanding of their mechanisms of action. In this review, we summarize key roles that estradiol and progesterone play in the brain. As numerous reports have confirmed a substantial neuroprotective role for estradiol in models of neurodegenerative disease, we focus this review on traumatic brain injury and stroke models. We describe updated data from receptor and signaling events triggered by both hormones, with an emphasis on the mechanisms that have been reported as 'rapid' or 'cytoplasmic actions'. Data showing the therapeutic effects of the hormones, used alone or in combination, are also summarized, with a focus on rodent models of middle cerebral artery occlusion (MCAO). Finally, we draw attention to evidence that neuroprotection by both hormones might be due to a combination of 'cytoplasmic' and 'nuclear' signaling.

Role of mTORC1 Controlling Proteostasis after Brain Ischemia

Intense efforts are being undertaken to understand the pathophysiological mechanisms triggered after brain ischemia and to develop effective pharmacological treatments. However, the underlying molecular mechanisms are complex and not completely understood. One of the main problems is the fact that the ischemic damage is time-dependent and ranges from negligible to massive, involving different cell types such as neurons, astrocytes, microglia, endothelial cells, and some blood-derived cells (neutrophils, lymphocytes, etc.). Thus, approaching such a complicated cellular response generates a more complex combination of molecular mechanisms, in which cell death, cellular damage, stress and repair are intermixed. For this reason, animal and cellular model systems are needed in order to dissect and clarify which molecular mechanisms have to be promoted and/or blocked. Brain ischemia may be analyzed from two different perspectives: that of oxygen deprivation (hypoxic damage per se) and that of deprivation of glucose/serum factors. For investigations of ischemic stroke, middle cerebral artery occlusion (MCAO) is the preferred in vivo model, and uses two different approaches: transient (tMCAO), where reperfusion is permitted; or permanent (pMCAO). As a complement to this model, many laboratories expose different primary cortical neuron or neuronal cell lines to oxygen-glucose deprivation (OGD). This ex vivo model permits the analysis of the impact of hypoxic damage and the specific response of different cell types implicated in vivo, such as neurons, glia or endothelial cells. Using in vivo and neuronal OGD models, it was recently established that mTORC1 (mammalian Target of Rapamycin Complex-1), a protein complex downstream of PI3K-Akt pathway, is one of the players deregulated after ischemia and OGD. In addition, neuroprotective intervention either by estradiol or by specific AT2R agonists shows an important regulatory role for the mTORC1 activity, for instance regulating vascular endothelial growth factor (VEGF) levels. This evidence highlights the importance of understanding the role of mTORC1 in neuronal death/survival processes, as it could be a potential therapeutic target. This review summarizes the state-of-the-art of the complex kinase mTORC1 focusing in upstream and downstream pathways, their role in central nervous system and their relationship with autophagy, apoptosis and neuroprotection/neurodegeneration after ischemia/hypoxia.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

17β-Estradiol Protects Rat Annulus Fibrosus Cells Against Apoptosis via α1 Integrin-Mediated Adhesion to Type I Collagen: An In-vitro Study

Background

17β-Estradiol (E2) has been reported to protect annulus fibrosus (AF) cells in vitro against interleukin-1β (IL-1β)-induced apoptosis in a concentration-dependent manner. However, its time-response effect remains unexplored. In addition, integrin α₂/collagen II interaction has been reported to influence the apoptosis of nucleus pulposus cells in vitro. Thus, we hypothesized that integrin α₁/collagen II might play a role in exerting the anti-apoptosis effect by E2. The aim of the current study was to further investigate the anti-apoptotic effect of E2 and determine the role of integrin α₁/collagen II interaction.

Material/Methods

Rat AF cells were primary cultured and used for the following experiments. AF cells were identified by immunocytochemistry of type I collagen. Cell apoptosis was detected by fluorescence-activated cell sorter (FACS) analysis. The activity of active caspase-3 was determined by use of a caspase-3 detection kit. AF cell adhesion to type I collagen was determined by cell adhesion assay. Protein level of integrin subunit α₁ was quantified by Western blot and mRNA expression was determined by real-time qPCR.

Results

The immunocytochemistry of type I collagen revealed that cell purity was eligible for the following experiments with 98% of purity. FACS analysis indicated time-dependent anti-apoptosis effect of E2 at time points of 6 h, 12 h, and 24 h, which was confirmed by Caspase-3 activity. Furthermore, cell adhesion assay showed that E2 significantly increased cell binding to 95% of control, and qPCR and Western blot analysis showed that E2 effectively upregulated integrin α₁. However, estrogen receptor antagonist ICI182780 prohibited the effect of E2.

Conclusions

This study shows that E2 protects against apoptosis in a time-dependent manner, and α₁ integrin-mediated adhesion to collagen II is essential for estrogen-dependent anti-apoptosis in rat annulus fibrosus cells in vitro.

Study of synergistic role of allogenic skin-derived precursor differentiated Schwann cells and heregulin-1β in nerve regeneration with an acellular nerve allograft

Development of tissue structure and three-dimensional microenvironment is crucial for regeneration of axons in the peripheral nerve repair. In this study we aimed to evaluate the efficacy of nerve regeneration by using an acellular nerve allograft (ANA) injected with allogenic skin-derived precursor differentiated Schwann cells (SKP-SCs) and heregulin-1β. Skin-derived precursor cells (SKPs) were generated from dermis of newborn (postnatal day 2) Wistar rats. In a rat model, nerve regeneration was determined across a 15 mm lesion in the sciatic nerve by using an ANA injected with allogenic SKP-SCs and heregulin-1β. The electrophysiological analysis, histological examination and electron microscopy were involved in this study. Cultured SKPs expressed nestin and fibronectin, and differentiated into cells with phenotype of SCs that presented characteristic markers of p75NGFR and S100-β. Implantation of SKP-SCs into the rat models by using ANA and allogenic skin-derived precursor differentiated Schwann cells (SKP-SCs) increases sciatic nerve functional index (SFI), peak amplitudes, nerve conduction velocities, number of myelinated fibers within the graft, while reduces incubation period, sciatic nerve injury-induced weight and contractions loss. Using ANA injected with SKP-SCs combined with heregulin-1β greatly promote peripheral nerve repair in a rat model. Our results suggest that SKP-SCs transplantation with heregulin-1β represents a powerful therapeutic approach, and facilitates the efficacy of acellular nerve allograft in peripheral nerve injury, though the detailed mechanism remains to be elucidated.

Inhibition of p38 pathway-dependent MPTP-induced dopaminergic neurodegeneration in estrogen receptor alpha knockout mice

Approximately, 7-10 million people in the world suffer from Parkinson's disease (PD). Recently, increasing evidence has suggested the protective effect of estrogens against nigrostriatal dopaminergic damage in PD. In this study, we investigated whether estrogen affects 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral impairment in estrogen receptor alpha (ERα)-deficient mice. MPTP (15mg/kg, four times with 1.5-h interval)-induced dopaminergic neurodegeneration was evaluated in ERα wild-type (WT) and knockout (KO) mice. Larger dopamine depletion, behavioral impairments (Rotarod test, Pole test, and Gait test), activation of microglia and astrocytes, and neuroinflammation after MPTP injection were observed in ERα KO mice compared to those in WT mice. Immunostaining for tyrosine hydroxylase (TH) after MPTP injection showed fewer TH-positive neurons in ERα KO mice than WT mice. Levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC, metabolite of dopamine) were also lowered in ERα KO mice after MPTP injection. Interestingly, a higher immunoreactivity for monoamine oxidase (MAO) B was found in the substantia nigra and striatum of ERα KO mice after MPTP injection. We also found an increased activation of p38 kinase (which positively regulates MAO B expression) in ERα KO mice. In vitro estrogen treatment inhibited neuroinflammation in 1-methyl-4-phenyl pyridium (MPP+)-treated cultured astrocyte cells; however, these inhibitory effects were removed by p38 inhibitor. These results indicate that ERα might be important for dopaminergic neuronal survival through inhibition of p38 pathway.

Regulation of cyclooxygenase-2 expression in rat oviductal epithelial cells: Evidence for involvement of GPR30/Src kinase-mediated EGFR signaling

The oviduct plays a crucial role in female reproduction by regulating gamete transport, providing a specific microenvironment for fertilization and early embryonic development. Cyclooxygenase (COX)-derived prostaglandins play essential role in carrying out these oviduct-specific functions. Estrogen upregulates COX-2 expression in rat oviduct; however, the mechanisms responsible for regulation of COX-2 expression in rat oviductal epithelial cells (OECs) remain unclear. In the present study, we proposed that estrogen induces COX-2 expression via G-protein coupled receptor i.e., GPR30 in OECs. To investigate this hypothesis, we examined the effects of E2-BSA, ICI 182,780, GPR30 agonist and GPR30 antagonist on COX-2 expression and explored potential signaling pathway leading to COX-2 expression. Co-localization experiments revealed GPR30 to be primarily located in the peri-nuclear space, which was also the site of E2-BSA-fluorescein isothiocyanate (E2-BSA-FITC) binding. The E2-BSA induced-COX-2 and prostaglandin release were subjected to regulation by both EGFR and PI3K signaling as inhibitors of c-Src kinase (PP2), EGFR (EGFR inhibitor) and PI-3 kinase (LY294002) attenuated E2-BSA mediated effect. These results suggest that EGFR transactivation leading to activation of PI-3K/Akt pathway participates in COX-2 expression in rat OECs. Interestingly, E2-BSA induced COX-2 expression and subsequent prostaglandin release were abolished by NF-κB inhibitor. In addition, E2-BSA induced the nuclear translocation of p65-NF-κB and up-regulated the NF-κB promoter activity in rat OECs. Taken together, results demonstrated that E2-BSA induced the COX-2 expression and consequent PGE2 and PGF2α release in rat OECs. These effects are mediated through GPR30-derived EGFR transactivation and PI-3K/Akt cascade leading to NF-κB activation.

Activation of mTOR: a culprit of Alzheimer's disease?

Alzheimer's disease (AD) is characterized by cognitive impairment in clinical presentation, and by β-amyloid (Aβ) production and the hyper-phosphorylation of tau in basic research. More highlights demonstrate that the activation of the mammalian target of rapamycin (mTOR) enhances Aβ generation and deposition by modulating amyloid precursor protein (APP) metabolism and upregulating β- and γ-secretases. mTOR, an inhibitor of autophagy, decreases Aβ clearance by scissoring autophagy function. mTOR regulates Aβ generation or Aβ clearance by regulating several key signaling pathways, including phosphoinositide 3-kinase (PI3-K)/protein kinase B (Akt), glycogen synthase kinase 3 [GSK-3], AMP-activated protein kinase (AMPK), and insulin/insulin-like growth factor 1 (IGF-1). The activation of mTOR is also a contributor to aberrant hyperphosphorylated tau. Rapamycin, the inhibitor of mTOR, may mitigate cognitive impairment and inhibit the pathologies associated with amyloid plaques and neurofibrillary tangles by promoting autophagy. Furthermore, the upstream and downstream components of mTOR signaling are involved in the pathogenesis and progression of AD. Hence, inhibiting the activation of mTOR may be an important therapeutic target for AD.

17β-estradiol suppresses lipopolysaccharide-induced acute lung injury through PI3K/Akt/SGK1 mediated up-regulation of epithelial sodium channel (ENaC) in vivo and in vitro

Background

17β-estradiol can suppress acute lung injury (ALI) and regulate alveolar epithelial sodium channel (ENaC). However the relationship between these two functions remains unclear. This study is conducted to assess the role of ENaC and the PI3K/Akt/SGK1 signaling pathway in 17β-estradiol therapy in attenuating LPS-induced ALI.

Methods

ALI was induced in C57BL/J male mice by intratracheal administration of lipopolysaccharide (LPS). Concurrent with LPS administration, 17β-estradiol or sterile saline was administered to ALI model with or without the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin. The lung histological changes, inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet/dry weight ratio (W/D) and alveolar fluid clearance (AFC) were measured 4 hours after LPS challenge in vivo. For in vitro studies, LPS-challenged MLE-12 cells were pre-incubated with or without wortmannin for 30 minutes prior to 17β-estradiol treatment. Expression of ENaC subunits was assessed by reverse transcriptase PCR, western blot, cell surface biotinylation, and immunohistochemistry. The levels of phosphorylated Akt and SGK1 in lung tissue and lung cell lines were investigated by western blot.

Results

17β-estradiol suppressed LPS-mediated ALI in mice by diminishing inflammatory mediators and enhancing AFC. 17β-estradiol promoted the expression and surface abundance of α-ENaC, and increased the levels of phosphorylated-Akt and phosphorylated-SGK1 following LPS challenge. This induction was abolished by the PI3K inhibitor wortmannin in vivo and in vitro.

Conclusion

17β-estradiol attenuates LPS-induced ALI not only by repressing inflammation, but also by reducing pulmonary edema via elevation of α-ENaC expression and membrane abundance. These effects were mediated, at least partially, via activation of the PI3K/Akt/SGK1 signaling pathway.

Prolyl hydroxylase inhibitors protect from the bone loss in ovariectomy rats by increasing bone vascularity

The hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF) pathway is involved in skeletal development, bone repair, and postmenopausal osteoporosis. Inhibitors of prolyl hydroxylases (PHD) enhance vascularity, increase callus formation in a stabilized fracture model, and activate the HIF-1α/VEGF pathway. This study examined the effects of estrogen on the HIF-1α/VEGF pathway in osteoblasts and whether PHD inhibitors can protect from bone loss in postmenopausal osteoporosis. Osteoblasts were treated with estrogen, and expressions of HIF-1α and VEGF were measured at mRNA (qPCR) and protein (Western blot) levels. Further, osteoblasts were treated with inhibitors of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, and levels of VEGF mRNA and protein expression were detected. In addition, ovariectomized rats were treated with PHD inhibitors, and bone microarchitecture and bone mechanical strength were assessed using micro-CT and biomechanical analyses (lower ultimate stress, modulus, and stiffness). Blood vessel formation was measured with India Ink Perfusion and immunohistochemistry. Estrogen, in a dose- and time-dependent manner, induced VEGF expression at both mRNA and protein levels and enhanced HIF-1α protein stability. Further, the estrogen-induced VEGF expression in osteoblasts involved the PI3K/Akt pathway. PHD inhibitors increased bone mineral density, bone microarchitecture and bone mechanical strength, and promoted blood vessel formation in ovariectomized rats. In conclusion, estrogen and PHD inhibitors activate the HIF-1α/VEGF pathway in osteoblasts. PHD inhibitors can be utilized to protect bone loss in postmenopausal osteoporosis by improving bone vascularity and angiogenesis in bone marrow.

Sex differences in cognitive impairment and Alzheimer's disease

Studies have shown differences in specific cognitive ability domains and risk of Alzheimer's disease between the men and women at later age. However it is important to know that sex differences in cognitive function during adulthood may have their basis in both organizational effects, i.e., occurring as early as during the neuronal development period, as well as in activational effects, where the influence of the sex steroids influence brain function in adulthood. Further, the rate of cognitive decline with aging is also different between the sexes. Understanding the biology of sex differences in cognitive function will not only provide insight into Alzheimer's disease prevention, but also is integral to the development of personalized, gender-specific medicine. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of sex differences in cognitive function from young to old, and examines the effects of sex hormone treatments on Alzheimer's disease in men and women.

Mechanism of raloxifene-induced upregulation of glutamate transporters in rat primary astrocytes

Raloxifene (RX), a selective estrogen receptor modulator (SERM), exerts neuroprotection in multiple clinical and experimental settings. Astrocytic glutamate transporters GLT-1 (EAAT2) and GLAST (EAAT1) are the main glutamate transporters in the central nervous system, taking up most of excess glutamate from the synaptic cleft to prevent excitotoxic neuronal death. Since drugs targeting astrocytic glutamate transporters to enhance their expression and function represent potential therapeutics for neurodegenerative disorders associated with excitotoxicity, we tested if RX modulates the expression and function of GLT-1 and GLAST in rat primary astrocytes. The results showed that RX significantly increased glutamate uptake and expression of GLT-1 mRNA and protein levels. RX enhanced GLT-1 expression by the activation of multiple signaling pathways including ERK, EGFR, and CREB mediated by estrogen receptors (ERs) ER-α, ER-β, and GPR30. At the transcriptional level, NF-κB played a critical role in RX-induced GLT-1 expression as RX increased NF-κB reporter activity and induced binding of NF-κB p65 and p50 to the GLT-1 promoter. RX attenuated the reduction of GLT-1 expression and glutamate uptake induced by manganese (Mn) whose chronic high levels of exposure cause manganism. RX also upregulated GLAST by increasing its promoter activity and protein levels via the NF-κB pathway and ERs. Our findings provide new insight into the mechanism of RX-induced enhancement of GLT-1 and GLAST expression, as well as the attenuation of Mn-reduced expression of these transporters. These findings will be highly valuable for developing therapeutics of neurodegenerative diseases associated with impaired astrocytic glutamate transporters.

Estrogen is a novel regulator of Tnfaip1 in mouse hippocampus

Tumor necrosis factor‑induced protein 1 (Tnfaip1), also known as B12, has been previously identified as a tumor necrosis factor-α (TNF-α)-inducible protein and is involved in the cytokinesis signaling pathway, DNA synthesis, innate immunity, cell apoptosis, Alzheimer's disease (AD) and type 2 diabetic nephropathy. However, little is known regarding the expression of Tnfaip1 in various tissues or its accurate role in these physiological functions. The focus of this study was on Tnfaip1 expression in different tissues, with a high expression in mouse hippocampus being identified. The age- and gender‑related expression of Tnfaip1 in hippocampus was also investigated. The distribution of Tnfaip1 was mapped using fluorescent immunostaining. Although immunoactivity was found in the CA1, CA3 and DG subregions of the hippocampus in E17.5 and P6 mice, strong staining was only detected in the CA3 subregion in adult mice. These data suggested that Tnfaip1 expression in hippocampus may be regulated by estrogen. Further study showed that the expression of Tnfaip1 in the hippocampus was significantly increased in ovariecto-mized mice compared to Sham mice. In cultured primary hippocampal cells, Tnfaip1 showed different expression levels in different treatments of estrogen or estrogen receptor antagonists. Additional experiments demonstrated the existence of a binding site of ERβ in the Tnfaip1 promoter region, and that ERβ was able to upregulate Tnfaip1 expression. Our study identified a new regulatory factor and a primary regulatory mechanism of Tnfaip1 expression in hippocampus. Since both hippocampus and estrogen are crucial in AD, the results also showed a potential association between Tnfaip1 and hippocampal-related diseases, such as AD, which may be affected by the estrogen level.

Effects of estradiol on high-voltage-activated Ca(2+) channels in cultured rat cortical neurons

OBJECTIVES

Estrogen regulates a wide variety of nonreproductive functions in the central nervous system. Cortical neurons contain a diverse range of voltage-gated ion channels, including calcium (Ca(2+)) channels, and Ca(2+) channels play an important role in the regulation of action potential generation and neuronal excitability. In this study, the effect of estradiol (E2) on high-voltage-activated (HVA) Ca(2+) channels in cultured rat cortical neurons was examined.

METHODS

We used the whole-cell patch-clamp technique to measure the HVA Ca(2+) channels.

RESULTS

We found that HVA Ca(2+) channel currents was inhibited by 17β-E2 in a rapid, reversible and concentration-dependent manner. Moreover, 17β-E2 shifted the steady-state inactivation curve in the hyperpolarizing direction without changing the activation curve. We also found that the inhibitory effects of 17β-E2 on Ca(2+) currents were unaffected by the estrogen receptor (ER) antagonist ICI 182780; however, the protein kinase C (PKC) inhibitor rottlerin and protein kinase A (PKA) inhibitor H-89 blocked the 17β-E2-induced inhibition of Ca(2+) currents.

CONCLUSIONS

E2 inhibited HVA Ca(2+) currents via PKC and PKA-dependent signaling pathway in cortical neurons, and the effects of BPA were independent of classical ER.

Estrogenic endocrine-disrupting chemicals: molecular mechanisms of actions on putative human diseases

Endocrine-disrupting chemicals (EDC), including phthalates, bisphenol A (BPA), phytoestrogens such as genistein and daidzein, dichlorodiphenyltrichloroethane (DDT), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are associated with a variety of adverse health effects in organisms or progeny by altering the endocrine system. Environmental estrogens, including BPA, phthalates, and phytoestrogens, are the most extensively studied and are considered to mimic the actions of endogenous estrogen, 17β-estradiol (E2). Diverse modes of action of estrogen and estrogen receptors (ERα and ERβ) have been described, but the mode of action of estrogenic EDC is postulated to be more complex and needs to be more clearly elucidated. This review examines the adverse effects of estrogenic EDC on male or female reproductive systems and molecular mechanisms underlying EDC effects that modulate ER-mediated signaling. Mechanisms of action for estrogenic EDC may involve both ER-dependent and ER-independent pathways. Recent findings from systems toxicology of examining estrogenic EDC are also discussed.

Oestrogens as modulators of neuronal signalosomes and brain lipid homeostasis related to protection against neurodegeneration

Oestrogens trigger several pathways at the plasma membrane that exert beneficial actions against neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Part of these actions takes place in lipid rafts, which are membrane domains with a singular protein and lipid composition. These microdomains also represent a preferential site for signalling protein complexes, or signalosomes. A plausible hypothesis is that the dynamic interaction of signalosomes with different extracellular ligands may be at the basis of neuronal maintenance against different neuropathologies. Oestrogen receptors are localised in neuronal lipid rafts, taking part of macromolecular complexes together with a voltage-dependent anion channel (VDAC), and other molecules. Oestradiol binding to its receptor at this level enhances neuroprotection against amyloid-β degeneration through the activation of different signal transduction pathways, including VDAC gating modulation. Moreover, part of the stability and functionality of signalling platforms lays on the distribution of lipid hallmarks in these microstructures, which modulate membrane physicochemical properties, thus favouring molecular interactions. Interestingly, recent findings indicate a potential role of oestrogens in the preservation of neuronal membrane physiology related to lipid homeostasis. Thus, oestrogens and docosahexaenoic acid may act synergistically to stabilise brain lipid structure by regulating neuronal lipid biosynthetic pathways, suggesting that part of the neuroprotective effects elicited by oestrogens occur through mechanisms aimed at preserving lipid homeostasis. Overall, oestrogen mechanisms of neuroprotection may occur not only by its interaction with neuronal protein targets through nongenomic and genomic mechanisms, but also through its participation in membrane architecture stabilisation via 'lipostatic' mechanisms.

17β-estradiol confers protection after traumatic brain injury in the rat and involves activation of G protein-coupled estrogen receptor 1

Abstract Traumatic brain injury (TBI) is a significant public health problem in the United States. Despite preclinical success of various drugs, to date all clinical trials investigating potential therapeutics have failed. Recently, sex steroid hormones have sparked interest as possible neuroprotective agents after traumatic injury. One of these is 17β-estradiol (E2), the most abundant and potent endogenous vertebrate estrogen. The goal of our study was to investigate the acute potential protective effects of E2 or the specific G protein-coupled estrogen receptor 1 (GPER) agonist G-1 when administered in an intravenous bolus dose 1 hour post-injury in the lateral fluid percussion (LFP) rodent model of TBI. The results of this study show that, when assessed at 24 hours post-injury, E2 or G-1 confers protection in adult male rats subjected to LFP brain injury. Specifically, we found that an acute bolus dose of E2 or G-1 administered intravenously 1 hour post-TBI significantly increases neuronal survival in the ipsilateral CA 2/3 region of the hippocampus and decreases neuronal degeneration and apoptotic cell death in both the ipsilateral cortex and CA 2/3 region of the hippocampus. We also report a significant reduction in astrogliosis in the ipsilateral cortex, hilus, and CA 2/3 region of the hippocampus. Finally, these effects were observed to be chiefly dose-dependent for E2, with the 5 mg/kg dose generating a more robust level of protection. Our findings further elucidate estrogenic compounds as a clinically relevant pharmacotherapeutic strategy for treatment of secondary injury following TBI, and intriguingly, reveal a novel potential therapeutic target in GPER.

Progesterone-estrogen interactions in synaptic plasticity and neuroprotection

17ß-Estradiol and progesterone exert a number of physiological effects throughout the brain due to interactions with several types of receptors belonging to the traditional family of intracellular hormonal receptors as well as to membrane-bound receptors. In particular, both hormones elicit rapid modifications of neuronal excitability that have been postulated to underlie their effects on synaptic plasticity and learning and memory. Likewise, both hormones have been shown to be neuroprotective under certain conditions, possibly due to the activation of pro-survival pathways and the inhibition of pro-apoptotic cascades. Because of the similarities in their cellular effects, there have been a number of questions raised by numerous observations that progesterone inhibits the effects of estrogen. In this manuscript, we first review the interactions between 17ß-estradiol (E2) and progesterone (P4) in synaptic plasticity, and conclude that, while E2 exerts a clear and important role in long-term potentiation of synaptic transmission in hippocampal neurons, the role of P4 is much less clear, and could be accounted by the direct or indirect regulation of GABAA receptors. We then discuss the neuroprotective roles of both hormones, in particular against excitotoxicity. In this case, the neuroprotective effects of these hormones are very similar to those of the neurotrophic factor BDNF. Interestingly, P4 antagonizes the effects of E2, possibly through the regulation of estrogen receptors or of proteins associated with the receptors or interactions with signaling pathways activated by E2. Overall, this review emphasizes the existence of common molecules and pathways that participate in the regulation of both synaptic plasticity and neurodegeneration.

Gender differences in neurodevelopment and epigenetics

The concept that the brain differs in make-up between males and females is not new. For example, it is well established that anatomists in the nineteenth century found sex differences in human brain weight. The importance of sex differences in the organization of the brain cannot be overstated as they may directly affect cognitive functions, such as verbal skills and visuospatial tasks in a sex-dependent fashion. Moreover, the incidence of neurological and psychiatric diseases is also highly dependent on sex. These clinical observations reiterate the importance that gender must be taken into account as a relevant possible contributing factor in order to understand the pathogenesis of neurological and psychiatric disorders. Gender-dependent differentiation of the brain has been detected at every level of organization--morphological, neurochemical, and functional--and has been shown to be primarily controlled by sex differences in gonadal steroid hormone levels during perinatal development. In this review, we discuss howthe gonadal steroid hormone testosterone and its metabolites affect downstream signaling cascades, including gonadal steroid receptor activation, and epigenetic events in order to differentiate the brain in a gender-dependent fashion.

17β-Estradiol and genistein acute treatments improve some cerebral cortex homeostasis aspects deteriorated by aging in female rats

Aging is associated with decreased insulin sensitivity and impaired cerebral glucose homeostasis. These changes increase neural sensitivity to metabolic damage contributing to cognitive decline, being the decrease in plasma estrogen following menopause one of the main factors involved in aged females. Phytoestrogens as genistein are structurally similar to 17β-estradiol, bind to estrogen receptors, and can evoke both estrogenic and anti-estrogenic effects. Estrogens and phytoestrogens have neuroprotective potential, but the physiological mechanisms are not fully understood. Young and aged female Wistar rats were ovariectomized and treated acutely with 17β-estradiol (1.4μg/kg body weight), genistein (10 or 40 mg/kg body weight), or vehicle. Cortical expression of glucose transporter-3 (GLUT-3) and -4 (GLUT-4), cytochrome c oxidase (CO), estrogen receptor-α (ERα) and -β (ERβ) was measured by Western blotting. There was an age-related decline in GLUT-4, CO and ERβ levels. Both drugs, estradiol and genistein, were able to reverse GLUT-3 downregulation in the cortex following late ovariectomy. However, genistein was the only treatment able to restore completely GLUT-4 levels in aged rats. In contrast, estradiol was more potent than genistein at increasing CO, a marker of cerebral oxidative metabolism. As regards ER levels, estradiol increased the ERα67 quantity diminished by late ovariectomy, while genistein did the same with the other ERα isoform, ERα46, highlighting drug-specific differences in expression changes for both isoforms. On the other hand, no treatment-related differences were found regarding ERβ levels. Therefore, genistein like estradiol could be suitable treatments against cortical metabolic dysfunction caused by aging. These treatments may hold promise as neuroprotective strategies against diabetes and age-related neurodegenerative diseases.

Estrogens need insulin-like growth factor I cooperation to exert their neuroprotective effects in post-menopausal women

BACKGROUND

The abrupt fall in estrogens levels during the menopausal transition may connote an hormonal state predisposing to neurodegenerative disorders, e.g. Alzheimer's disease (AD). Reportedly, the neurotrophic activity of estrogen involves an interaction with IGF-I.

AIM

To evaluate the leukocyte gene expression of progesterone receptor (PR-A/B) and interleukin 6 (IL-6), two parameters under the control of estrogens and involved in the pathogenesis of AD.

SUBJECTS

The study was conducted in non-demented women divided into two groups according to their pre- or post-menopausal state; each group being further divided into two subgroups based on their circulating levels of IGF-I (normal or low). An additional sample of AD-affected women served as a comparison group.

RESULTS

Estrogens maintained their full activity only when IGF-I levels were in the range of normalcy. On the contrary, if the concentrations of one or both hormones were reduced, estrogens were not anymore capable to control the gene expression of PR-A/B or IL-6.

CONCLUSIONS

Before administering hormone-based replacement therapy, characterization of the somatotropic function should be performed in the early phase of the menopause.

The G Protein–Coupled Receptor GPR30 Mediates the Nontranscriptional Effect of Estrogen on the Activation of PI3K/Akt Pathway in Endometrial Cancer Cells

Objective

The goal of this study was to investigate the effect of G protein–coupled receptor 30 (GPR30) on the activation of PI3K/Akt pathway induced by E2 in endometrial cancer cells.

Methods and materials

Immunohistochemistry was performed to determine the location and expression of GPR30, estrogen receptors (ERs), Akt, and phosphorylated Akt. We also investigated the expression of GPR30, ERs, and the level of phosphorylation of Akt induced by E2 in endometrial cancer cells, Ishikawa cells, and HEC-1A cells. We down-regulated the expression of GPR30 in endometrial cancer cell lines by transfection with shGPR30-pGFP-V-RS, a GPR30 antisense expression vector. The cells were then subjected to a proliferation assay. Immunoprecipitation assay was performed to determine whether GPR30 directly bind to PI3K. The stable transfected cells resuspension of 100 μL (5 × 106 cells) was injected subcutaneously into the right flank of athymic mice to perform xenograft tumor formation assays.

Results

E2 stimulated cell proliferation and induced GPR30 expression and PI3K/Akt pathway activation in endometrial cancer cells, Ishikawa cells, and HEC-1A cells, whereas the expression of ERs remained unchangeable. Down-regulation of GPR30 decreased the phosphorylation of Akt and reduced cell proliferation, and GPR30 did not bind to PI3K. Down-regulation of GPR30 significantly inhibited the tumor growth of HEC-1A cells in athymic nude mice.

Conclusions

These findings suggest that GPR30 mediates the nontranscriptional effect of estrogen on the activation of PI3K/Akt pathway in endometrial cancer cells.

Role of Akt/HO-1 pathway in estrogen-mediated attenuation of trauma-hemorrhage-induced lung injury

BACKGROUND

Despite advances in intensive care medicines, hemorrhagic shock leading to multiple organ failure remains the major causes of death in the injured host. Although studies have shown that 17β-estradiol (E2) prevents trauma-hemorrhage-induced lung damage, it remains unknown whether protein kinase B (Akt)/heme oxygenase (HO)-1 plays any role in E2-mediated lung protection after trauma-hemorrhage.

MATERIALS AND METHODS

After a 5-cm midline laparotomy, male rats underwent hemorrhagic shock (mean blood pressure ∼40 mm Hg for 90 min) followed by fluid resuscitation. At the onset of resuscitation, rats were treated with vehicle, E2 (1 kg/mg), E2 plus phosphoinositide 3-kinase inhibitor LY294002 (5 mg/kg), or LY294002. At 2 h after trauma-hemorrhage or sham operation, lung tissue myeloperoxidase activity, wet-to-dry-weight ratio, inflammatory mediators, and apoptosis were measured. Lung Akt, HO-1, and cleaved caspase-3 protein levels were also determined.

RESULTS

E2 attenuated the trauma-hemorrhage-induced increase in lung myeloperoxidase activity, edema formation, inflammatory mediator levels, and apoptosis, which was blocked by co-administration of LY294002. Administration of E2 normalized lung Akt phosphorylation and further increased HO-1 expression and decreased cleaved caspase-3 levels after trauma-hemorrhage. Co-administration of LY294002 prevented the E2-mediated attenuation of shock-induced lung injury.

CONCLUSIONS

Our results collectively suggest that Akt-dependent HO-1 upregulation may play a critical role in E2-meditated lung protection after trauma-hemorrhage.

Neuroprotection and estrogen receptors

This review is intended to assess the state of current knowledge on the role of estrogen receptors (ERs) in the neuroprotective effects of estrogens in models for acute neuronal injury and death. We evaluate the overall evidence that estrogens are neuroprotective in acute injury and critically assess the role of ERα, ERβ, GPR 30, and nonreceptor-mediated mechanisms in these robust neuroprotective effects of this ovarian steroid hormone. We conclude that all three receptors, as well as nonreceptor-mediated mechanisms can be involved in neuroprotection, depending on the model used, the level of estrogen administrated, and the mode of administration of the steroid. Also, the signaling pathways used by both ER-dependent and ER-independent mechanisms to exert neuroprotection are considered. Finally, further studies that are needed to parse out the relative contribution of receptor versus nonreceptor-mediated signaling are discussed.

Effects of 17β-estradiol on adiponectin regulation of the expression of osteoprotegerin and receptor activator of nuclear factor-κB ligand

Adiponectin may exert a negative effect on bone metabolism by regulating osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) expression. However, the action of adiponectin on bone may be influenced by estrogen in women. The present study was undertaken to investigate the effects of 17β-estradiol (E2) on adiponectin-regulated OPG and RANKL expression in human osteoblast. Human osteoblasts were treated with α-MEM containing 10μg/ml adiponectin alone or together with 10(-10) to 10(-8)M E2 for 12-48h. Cells were also treated with α-MEM containing 10μg/ml adiponectin together with 10(-8)M E2 plus p38 agonist-anisomycin or estrogen receptor (ER) antagonist ICI182780 for 48h. The effects of E2 were also investigated by knockdown of ERs or overexpression of p38 MAPK in osteoblasts. Further, we examined the effects of E2 on adiponectin-dependent osteoclastogenesis by the co-culture systems of osteoblast and CD14+ peripheral blood monocytes (PBMCs). Real-time quantitative PCR (RT-PCR) and ELISA were used to detect OPG/RANKL mRNA and their corresponding protein expression, Western Blot was used to analyze the phosphorylated p38 (p-p38) levels. The results showed that E2 blocked adiponectin-induced p38 phosphorylation, decreased adiponectin-regulated OPG/RANKL mRNA and protein expression in a dose- and time-dependent manner. ICI182780 or knockdown of ERs abolished the effects of E2 on adiponectin-dependent p38 phosphorylation and OPG/RANKL expression. Furthermore, anisomycin or overexpression of p38 also reserved the effects of E2 on adiponectin-dependent p38 phosphorylation and OPG/RANKL expression. E2 inhibited adiponectin-dependent osteoclastogenesis in the co-culture systems of osteoblast and CD14+ PBMCs, whereas anisomycin, ICI182780, knockdown of ERs and overexpression of p38 significantly reversed this response. In conclusions, our findings demonstrated, through blocking the activation of adiponectin-induced p38 MAPK, E2 suppressed the adiponectin-regulated OPG/RANKL expression and then inhibited osteoclastogenesis, which suggested that estrogen would suppress the effect of adiponectin on bone metabolism.

17β-Estradiol inhibits apoptotic cell death of oligodendrocytes by inhibiting RhoA-JNK3 activation after spinal cord injury

A delayed oligodendrocyte cell death after spinal cord injury (SCI) contributes to chronic demyelination of spared axons, leading to a permanent neurological deficit. Therefore, therapeutic approaches to prevent oligodendrocyte cell death after SCI should be considered. Estrogens are well known to have a broad neuroprotective effect, but the protective effect of estrogens on oligodendrocytes after injury is largely unknown. Here, we demonstrated that 17β-estradiol attenuates apoptosis of oligodendrocytes by inhibiting RhoA and c-Jun-N-terminal kinase activation after SCI. Estrogen receptor (ER)-α and -β were expressed in oligodendrocytes of the spinal cord, and 17β-estradiol treatment significantly inhibited oligodendrocyte cell death at 7 d after injury as compared with vehicle (cyclodextrin) control. 17β-Estradiol also attenuated caspase-3 and -9 activation at 7 d and reduced the loss of axons from progressive degeneration. In addition, 17β-estradiol inhibited RhoA and JNK3 activation, which were activated and peaked at 3 and/or 5 d after injury. Furthermore, administration of Rho inhibitor, PEP-1-C3 exoenzyme, inhibited RhoA and JNK3 activation, and decreased phosphorylated c-Jun level at 5 d after injury. Additionally, the attenuation of RhoA and JNK3 activation as well as oligodendrocyte cell death by 17β-estradiol was reversed by ER antagonist, ICI182780. Our results thus indicate that 17β-estradiol treatment improves functional recovery after SCI in part by reducing oligodendrocyte cell death via inhibition of RhoA and JNK3 activation, which were ER dependent. Furthermore, improvement of hindlimb motor function by posttreatment of 17β-estradiol suggests its potential as a therapeutic agent for SCI patients.

Post-ischemic estradiol treatment reduced glial response and triggers distinct cortical and hippocampal signaling in a rat model of cerebral ischemia

BACKGROUND

Estradiol has been shown to exert neuroprotective effects in several neurodegenerative conditions, including cerebral ischemia. The presence of this hormone prior to ischemia attenuates the damage associated with such events in a rodent model (middle cerebral artery occlusion (MCAO)), although its therapeutic value when administered post-ischemia has not been assessed. Hence, we evaluated the effects of estradiol treatment after permanent MCAO (pMCAO) was induced in rats, studying the PI3K/AKT/GSK3/β-catenin survival pathway and the activation of SAPK-JNK in two brain areas differently affected by pMCAO: the cortex and hippocampus. In addition, we analyzed the effect of estradiol on the glial response to injury.

METHODS

Male rats were subjected to pMCAO and estradiol (0.04 mg/kg) was administered 6, 24, and 48 h after surgery. The animals were sacrificed 6 h after the last treatment, and brain damage was evaluated by immunohistochemical quantification of 'reactive gliosis' using antibodies against GFAP and Iba1. In addition, Akt, phospho-Akt(Ser473), phospho-Akt(Thr308), GSK3, phospho-GSK3(Ser21/9), β-catenin, SAPK-JNK, and pSAPK-JNK(Thr183/Tyr185) levels were determined in western blots of the ipsilateral cerebral cortex and hippocampus, and regional differences in neuronal phospho-Akt expression were determined by immunohistochemistry.

RESULTS

The increases in the percentage of GFAP- (5.25-fold) and Iba1- (1.8-fold) labeled cells in the cortex and hippocampus indicate that pMCAO induced 'reactive gliosis'. This effect was prevented by post-ischemic estradiol treatment; diminished the number of these cells to those comparable with control animals. pMCAO down-regulated the PI3K/AkT/GSK3/β-catenin survival pathway to different extents in the cortex and hippocampus, the activity of which was restored by estradiol treatment more efficiently in the cerebral cortex (the most affected region) than in the hippocampus. No changes in the phosphorylation of SAPK-JNK were observed 54 h after inducing pMCAO, whereas pMCAO did significantly decrease the phospho-Akt(Ser473) in neurons, an effect that was reversed by estradiol.

CONCLUSION

The present study demonstrates that post-pMCAO estradiol treatment attenuates ischemic injury in both neurons and glia, events in which the PI3K/AKT/GSK3/β-catenin pathway is at least partly involved. These findings indicate that estradiol is a potentially useful treatment to enhance recovery after human ischemic stroke.

Effect of a chronic treatment with 17β-estradiol on striatal dopamine neurotransmission and the Akt/GSK3 signaling pathway in the brain of ovariectomized monkeys

The present experiments sought the effect of chronic treatment with 17β-estradiol on striatal dopaminergic activity and the Akt/GSK3 signaling pathway in the brain of monkeys. Eight female monkeys (Macacca fascicularis) were ovariectomized (OVX) and a month later, half received a month treatment with 17β-estradiol and the other with vehicle. The DA transporter (DAT) was measured by autoradiography with [(125)I]RTI-121 and the vesicular DA transporter (VMAT(2)) with [(3)H]TBZ-OH at three rostro-caudal levels (anterior, middle and posterior) of the caudate nucleus and putamen subdivided in their lateral/medial, ventral/dorsal sub-regions. Specific binding to DAT was increased in all sub-regions of the caudate nucleus and the putamen of 17β-estradiol-treated compared to vehicle-treated monkeys whereas specific binding to VMAT(2) remained unchanged. We measured by Western blot the phosphorylated forms of Akt at serine 473 and threonine 308, GSK3β at serine 9 and tyrosine 216 and GSK3α at serine 21 in anterior, middle and posterior caudate nucleus and putamen. 17β-Estradiol treatment increased in all the caudate nucleus and putamen pAkt (Ser473)/βIII-tubulin, pGSK3β (Ser9)/βIII-tubulin and in putamen Akt/βIII-tubulin compared to vehicle-treated monkeys. In anterior and middle putamen, pAkt (Thr308)/βIII-tubulin was also increased in monkeys treated with 17β-estradiol. pGSK3β (Tyr216)/βIII-tubulin and pGSK3α (Ser21)/βIII-tubulin remained unchanged by the 17β-estradiol treatment. These results suggest that 17β-estradiol activates striatal DA neurotransmission in primates as reflected with increased DAT specific binding and downstream activation of Akt/GSK3 signaling. This supports a beneficial role of a chronic treatment with 17β-estradiol by increasing the activity of signaling pathways implicated in cell survival.

Oestradiol regulates β-catenin-mediated transcription in neurones

Oestradiol acts in the brain by multiple mechanisms, including the regulation of transcriptional activity through classical oestrogen receptors, α and β, and by the activation of membrane/cytoplasm-initiated signalling cascades. In neuroblastoma cells, primary neurones in culture and in the brain in vivo, oestradiol activates the phosphoinositide 3-kinase/Akt/glycogen synthase kinase 3 signalling pathway by a mechanism involving oestrogen receptor α. Through this pathway, oestradiol regulates the stability of β-catenin, induces the translocation of β-catenin to the cell nucleus and regulates β-catenin-mediated transcription through the T cell factor/DNA complex. Genomic analyses in neuroblastoma cells have revealed that the set of genes regulated by oestradiol through β-catenin is not identical to that regulated by the Wnt signalling pathway, revealing a new mechanism for oestradiol signalling in neurones.

Estrogen neuroprotection and the critical period hypothesis

17β-Estradiol (estradiol or E2) is implicated as a neuroprotective factor in a variety of neurodegenerative disorders. This review focuses on the mechanisms underlying E2 neuroprotection in cerebral ischemia, as well as emerging evidence from basic science and clinical studies, which suggests that there is a "critical period" for estradiol's beneficial effect in the brain. Potential mechanisms underlying the critical period are discussed, as are the neurological consequences of long-term E2 deprivation (LTED) in animals and in humans after natural menopause or surgical menopause. We also summarize the major clinical trials concerning postmenopausal hormone therapy (HT), comparing their outcomes with respect to cardiovascular and neurological disease and discussing their relevance to the critical period hypothesis. Finally, potential caveats, controversies and future directions for the field are highlighted and discussed throughout the review.

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.

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.

Estrogen induces neurite outgrowth via Rho family GTPases in neuroblastoma cells

Estrogen (E2) has direct in vivo and in vitro effects, such as inducing neurite outgrowth, on neurons. We investigated the morphological changes and intracellular signaling pathway induced by E2 in neuroblastoma (SH-SY5Y) cells. The effect of medroxyprogesterone acetate (MPA) or progesterone (P4) on the E2-induced neurite outgrowth was also examined using SH-SY5Y cells. Neurite outgrowth was induced by E2 in association with the phosphorylation of Akt, and these effects of E2 were abolished by MPA but not by P4. Progesterone receptor antagonist RU486 blocked the inhibitory effects of MPA. Estrogen receptor antagonist ICI 182,780 and phosphatidylinositol 3-kinase inhibitor LY294002 inhibited the E2-induced neurite outgrowth. Because the Rho family of small GTPases has been shown to be involved in the regulation of neurite outgrowth, we examined the cross-talk among Rac1, Cdc42 and RhoA in the E2-induced neurite outgrowth. E2 immediately increased the Rac1 and Cdc42 activity and decreased the RhoA activity. E2-induced neurite outgrowth was attenuated in cells expressing dominant-negative mutants for Rac1 or Cdc42. These results suggest that regulation of Rho family GTPase activity by E2 is important for the neurite outgrowth in neuroblastoma cells, and that MPA may have an antagonistic effect against E2.