The goal of this study was to elucidate the mechanisms of 17␤-estradiol (E 2 ) antioxidant and neuroprotective actions in stroke. The results reveal a novel extranuclear receptor-mediated antioxidant mechanism for E 2 during stroke, as well as a hypersensitivity of the CA3/CA4 region to ischemic injury after prolonged hypoestrogenicity. E 2 neuroprotection was shown to involve a profound attenuation of NADPH oxidase activation and superoxide production in hippocampal CA1 pyramidal neurons after stroke, an effect mediated by extranuclear estrogen receptor ␣ (ER␣)-mediated nongenomic signaling, involving Akt activation and subsequent phosphorylation/ inactivation of Rac1, a factor critical for activation of NOX2 NADPH oxidase. Intriguingly, E 2 nongenomic signaling, antioxidant action, and neuroprotection in the CA1 region were lost after long-term E 2 deprivation, and this loss was tissue specific because the uterus remained responsive to E 2 . Correspondingly, a remarkable loss of ER␣, but not ER␤, was observed in the CA1 after long-term E 2 deprivation, with no change observed in the uterus. As a whole, the study reveals a novel, membrane-mediated antioxidant mechanism in neurons by E 2 provides support and mechanistic insights for a "critical period" of E 2 replacement in the hippocampus and demonstrates a heretofore unknown hypersensitivity of the CA3/CA4 to ischemic injury after prolonged hypoestrogenicity.

The retromer complex component VPS35 prevents activation of the BACE1 and Aβ production and thus plays an essential role in limiting Alzheimer’s disease neuropathology.

17␤-Estradiol (E2) has been implicated to be neuroprotective in a variety of neurodegenerative disorders, although the mechanism remains poorly understood. The current study sheds light on this issue by demonstrating that low physiological levels of E2 protects the hippocampus CA1 against global cerebral ischemia by preventing elevation of dickkopf-1 (Dkk1), an antagonist of the Wnt/␤-catenin signaling pathway, which is a principal mediator of neurodegeneration in cerebral ischemia and Alzheimer's disease. E2 inhibition of Dkk1 elevation correlated with a reduction of phospho-␤-catenin and elevation of nuclear ␤-catenin levels, as well as enhancement of Wnt-3, suggesting E2 activation of the Wnt/␤-catenin signaling pathway. In agreement, the ␤-catenin downstream prosurvival factor, survivin, was induced by E2 at 24 and 48 h after cerebral ischemia, an effect observed only in surviving neurons because degenerating neurons lacked survivin expression. E2 suppression of Dkk1 elevation was found to be caused by attenuation of upstream c-Jun N-terminal protein kinase (JNK)/c-Jun signaling, as E2 attenuation of JNK/c-Jun activation and a JNK inhibitor significantly blocked Dkk1 induction. Tau hyperphosphorylation has been implicated to have a prodeath role in Alzheimer's disease and cerebral ischemia, and E2 attenuates tau hyperphosphorylation. Our study demonstrates that tau hyperphosphorylation is strongly induced after global cerebral ischemia, and that E2 inhibits tau hyperphosphorylation by suppressing activation of the JNK/c-Jun/Dkk1 signaling pathway. Finally, exogenous Dkk1 replacement via intracerebroventricular administration completely reversed E2-induced neuroprotection, nuclear ␤-catenin induction, and phospho-tau attenuation, further suggesting that E2 inhibition of Dkk1 is a critical mechanism underlying its neuroprotective and phospho-tau regulatory effects after cerebral ischemia.

Recent work suggests that timing of 17β-estradiol (E2) therapy may be critical for observing a beneficial neural effect. Along these lines, E2 neuroprotection, but not its uterotropic effect, was shown to be lost following long-term E2 deprivation (LTED), and this effect was associated with a significant decrease of estrogen receptor-α (ERα) in the hippocampus but not the uterus. The purpose of the current study was to determine the mechanism underlying the ERα decrease and to determine whether aging leads to a similar loss of hippocampal ERα and E2 sensitivity. The results of the study show that ERα in the rat hippocampal CA1 region but not the uterus undergoes enhanced interaction with the E3 ubiquitin ligase C terminus of heat shock cognate protein 70 (Hsc70)-interacting protein (CHIP) that leads to its ubiquitination/proteasomal degradation following LTED (10-wk ovariectomy). E2 treatment initiated before but not after LTED prevented the enhanced ERα-CHIP interaction and ERα ubiquitination/degradation and was fully neuroprotective against global cerebral ischemia. Administration of a proteasomal inhibitor or CHIP antisense oligonucleotides to knock down CHIP reversed the LTED-induced down-regulation of ERα. Further work showed that these observations extended to natural aging, because aged rats showed enhanced CHIP interaction; ubiquitination and degradation of both hippocampal ERα and ERβ; and, importantly, a correlated loss of E2 neuroprotection against global cerebral ischemia. In contrast, E2 administration to middle-aged rats was still capable of exerting neuroprotection. As a whole, the study provides support for a "critical period" for E2 neuroprotection of the hippocampus and provides important insight into the mechanism underlying the critical period.estradiol | neuroendocrine | steroid | stroke B asic science and clinical observation studies have provided evidence of a beneficial effect of 17β-estradiol (E2) on cardiovascular disease, neuroprotection, and neurodegenerative diseases such as stroke and Alzheimer's disease (1-6). However, the Women's Health Initiative (WHI) surprisingly failed to observe a protective effect of hormone therapy on the cardiovascular system and, in fact, reported a small but significant increase in risk for stroke and dementia (7-9). The average age of subjects in the WHI study was 63 y, far past the onset of menopause. It has been suggested that there may be a "critical period" for the beneficial protective effect of E2 on the brain and that estrogen may need to be administered at perimenopause or earlier to observe a beneficial effect on the cardiovascular and neural system (10-12). In support of a critical period hypothesis for E2 beneficial effects in the brain, work by our laboratory and others has shown that long-term E2 deprivation (LTED) leads to a loss of E2 neuroprotection in animal models of focal and global cerebral ischemia (GCI) (13,14). Intriguingly, recent work by our group showed that the loss of E2 neuroprotection of the hippocampal CA1 region, an area ...

17β-estradiol (estradiol or E2) is implicated as a 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.

17β-estradiol (E2) has been implicated to play a critical role in neuroprotection, synaptic plasticity, and cognitive function. Classically, the role of gonadal-derived E2 in these events is well established, but the role of brain-derived E2 is less clear. To address this issue, we investigated the expression, localization, and modulation of aromatase and local E2 levels in the hippocampus following global cerebral ischemia (GCI) in adult ovariectomized rats. Immunohistochemistry (IHC) revealed that the hippocampal regions CA1, CA3 and dentate gyrus (DG) exhibited high levels of immunoreactive aromatase staining, with aromatase being co-localized primarily in neurons in non-ischemic animals. Following GCI, aromatase became highly expressed in GFAP-positive astrocytes in the hippocampal CA1 region at 2–3 days post GCI reperfusion. An ELISA for E2 and IHC for E2 confirmed the GCI-induced elevation of local E2 in the CA1 region and that the increase in local E2 occurred in astrocytes. Furthermore, central administration of aromatase antisense (AS) oligonucleotides, but not missense (MS) oligonucleotides, blocked the increase in aromatase and local E2 in astrocytes after GCI, and resulted in a significant increase in GCI-induced hippocampal CA1 region neuronal cell death and neuroinflammation. As a whole, these results suggest that brain-derived E2 exerts important neuroprotective and anti-inflammatory actions in the hippocampal CA1 region following GCI.

BackgroundRecent work by our laboratory and others has implicated NADPH oxidase as having an important role in reactive oxygen species (ROS) generation and neuronal damage following cerebral ischemia, although the mechanisms controlling NADPH oxidase in the brain remain poorly understood. The purpose of the current study was to examine the regulatory and functional role of the Rho GTPase, Rac1 in NADPH oxidase activation, ROS generation and neuronal cell death/cognitive dysfunction following global cerebral ischemia in the male rat.Methodology/Principal FindingsOur studies revealed that NADPH oxidase activity and superoxide (O2 −) production in the hippocampal CA1 region increased rapidly after cerebral ischemia to reach a peak at 3 h post-reperfusion, followed by a fall in levels by 24 h post-reperfusion. Administration of a Rac GTPase inhibitor (NSC23766) 15 min before cerebral ischemia significantly attenuated NADPH oxidase activation and O2 − production at 3 h after stroke as compared to vehicle-treated controls. NSC23766 also attenuated “in situ” O2 − production in the hippocampus after ischemia/reperfusion, as determined by fluorescent oxidized hydroethidine staining. Oxidative stress damage in the hippocampal CA1 after ischemia/reperfusion was also significantly attenuated by NSC23766 treatment, as evidenced by a marked attenuation of immunostaining for the oxidative stress damage markers, 4-HNE, 8-OHdG and H2AX at 24 h in the hippocampal CA1 region following cerebral ischemia. In addition, Morris Water maze testing revealed that Rac GTPase inhibition after ischemic injury significantly improved hippocampal-dependent memory and cognitive spatial abilities at 7–9 d post reperfusion as compared to vehicle-treated animals.Conclusions/SignificanceThe results of the study suggest that Rac1 GTPase has a critical role in mediating ischemia/reperfusion injury-induced NADPH oxidase activation, ROS generation and oxidative stress in the hippocampal CA1 region of the rat, and thus contributes significantly to neuronal degeneration and cognitive dysfunction following cerebral ischemia.

Glioma development is a multistep process, involving alterations in genetic and epigenetic mechanisms. Understanding the mechanisms and enzymes that promote epigenetic changes in gliomas are urgently needed to identify novel therapeutic targets. We examined the role of histone demethylase KDM1 in glioma progression. KDM1 was overexpressed in gliomas and its expression positively correlated with histological malignancy. Knockdown of KDM1 expression or its pharmacological inhibition using pargyline or NCL-1 significantly reduced the proliferation of glioma cells. Inhibition of KDM1 promoted up regulation of the p53 target genes p21 and PUMA. Patient-derived primary GBM cells expressed high levels of KDM1 and pharmacological inhibition of KDM1 decreased their proliferation. Further, KDM1 inhibition reduced the expression of stemness markers CD133 and nestin in GBM cells. Mouse xenograft assays revealed that inhibition of KDM1 significantly reduced glioma xenograft tumor growth. Inhibition of KDM1 increased levels of H3K4-me2 and H3K9-Ac histone modifications, reduced H3K9-me2 modification and promoted expression of p53 target genes (p21 and PUMA), leading to apoptosis of glioma xenograft tumors. Our results suggest that KDM1 is overexpressed in gliomas and could be a potential therapeutic target for the treatment of gliomas.