Role of estrogen receptors in neuroprotection by estradiol against MPTP toxicity

Sex and Brain: The Role of Sex Chromosomes and Hormones in Brain Development and Parkinson's Disease

Sex hormones and genes on the sex chromosomes are not only key factors in the regulation of sexual differentiation and reproduction but they are also deeply involved in brain homeostasis. Their action is crucial for the development of the brain, which presents different characteristics depending on the sex of individuals. The role of these players in the brain is fundamental in the maintenance of brain function during adulthood as well, thus being important also with respect to age-related neurodegenerative diseases. In this review, we explore the role of biological sex in the development of the brain and analyze its impact on the predisposition toward and the progression of neurodegenerative diseases. In particular, we focus on Parkinson's disease, a neurodegenerative disorder that has a higher incidence in the male population. We report how sex hormones and genes encoded by the sex chromosomes could protect from the disease or alternatively predispose toward its development. We finally underline the importance of considering sex when studying brain physiology and pathology in cellular and animal models in order to better understand disease etiology and develop novel tailored therapeutic strategies.

DIFFERENTIAL CONTRIBUTION OF ESTROGEN RECEPTORS TO THE INTESTINAL THERAPEUTIC EFFECTS OF 17β-ESTRADIOL IN A MURINE MODEL OF PARKINSON'S DISEASE

Beneficial effects of estrogens have been reported in Parkinson's disease (PD) for many years. We previously reported their neuroprotective and anti-inflammatory potentials in the enteric nervous system of the intestine, a region possibly affected during the early stages of the disease according to Braak's hypothesis. Three different estrogen receptors have been characterized to date: the estrogen receptor alpha (ERα), the estrogen receptor beta (ERβ) and the G protein coupled estrogen receptor 1 (GPER1). The aim of the present study was to decipher the individual contribution of each estrogen receptor to the therapeutic properties of 17β-estradiol (E2) in the myenteric plexus of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Different agonists, 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT; ERα), 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; ERβ), G1 (GPER1), and antagonists, ICI 182,780 (ERα and ERβ), G15 (GPER1), were used to analyze the involvement of each receptor. We confirmed that G1 protects dopamine (DA) neurons to a similar extent as E2. An anti-inflammatory effect on proinflammatory macrophages and cultured human monocytes was also demonstrated with E2 and G1. The effects of PPT and DPN were less potent than G1 with only a partial neuroprotection of DA neurons by PPT and a partial reduction of interleukin (IL)-1β production in monocytes by PPT and DPN. Overall, the present results indicate that the positive outcomes of estrogens are mainly through activation of GPER1. Therefore, this suggests that targeting GPER1 could be a promising approach for future estrogen-based hormone therapies during early PD.

An effort toward molecular biology of food deprivation induced food hoarding in gonadectomized NMRI mouse model: focus on neural oxidative status

Background

Environmental uncertainty, such as food deprivation, may alter internal milieu of nervous system through various mechanisms. In combination with circumstances of stress or aging, high consumption of unsaturated fatty acids and oxygen can make neural tissues sensitive to oxidative stress (OS). For adult rats, diminished level of gonadal steroid hormones accelerates OS and may result in special behavioral manifestations. This study was aimed to partially answer the question whether OS mediates trade-off between food hoarding and food intake (fat hoarding) in environmental uncertainty (e.g., fluctuations in food resource) within gonadectomized mouse model in the presence of food deprivation-induced food hoarding behavior.

Results

Hoarding behavior was not uniformly expressed in all male mice that exposed to food deprivation. Extended phenotypes including hoarder and non-hoarder mice stored higher and lower amounts of food respectively as compared to that of low-hoarder mice (normal phenotype) after food deprivation. Results showed that neural oxidative status was not changed in the presence of hoarding behavior in gonadectomized mice regardless of tissue type, however, glutathione levels of brain tissues were increased in the presence of hoarding behavior. Decreased superoxide dismutase activity in brain and spinal cord tissues and increased malondialdehyde in brain tissues of gonadectomized mice were also seen.

Conclusions

Although, food deprivation-induced hoarding behavior is a strategic response to food shortage in mice, it did not induce the same amount of hoarding across all colony mates. Hoarding behavior, in this case, is a response to the environmental uncertainty of food shortage, therefore is not an abnormal behavior. Hoarding behavior induced neural OS with regard to an increase in brain glutathione levels but failed to show other markers of neural OS. Decreased superoxide dismutase activity in brain and spinal cord tissues and increased malondialdehyde levels in brain tissues of gonadectomized mice could be a hallmark of debilitated antioxidative defense and more lipid peroxidation due to reduced amount of gonadal steroid hormones during aging.

Sex: A Significant Risk Factor for Neurodevelopmental and Neurodegenerative Disorders

Males and females sometimes significantly differ in their propensity to develop neurological disorders. Females suffer more from mood disorders such as depression and anxiety, whereas males are more susceptible to deficits in the dopamine system including Parkinson's disease (PD), attention-deficit hyperactivity disorder (ADHD) and autism. Despite this, biological sex is rarely considered when making treatment decisions in neurological disorders. A better understanding of the molecular mechanism(s) underlying sex differences in the healthy and diseased brain will help to devise diagnostic and therapeutic strategies optimal for each sex. Thus, the aim of this review is to discuss the available evidence on sex differences in neuropsychiatric and neurodegenerative disorders regarding prevalence, progression, symptoms and response to therapy. We also discuss the sex-related factors such as gonadal sex hormones and sex chromosome genes and how these might help to explain some of the clinically observed sex differences in these disorders. In particular, we highlight the emerging role of the Y-chromosome gene, SRY, in the male brain and its potential role as a male-specific risk factor for disorders such as PD, autism, and ADHD in many individuals.

Striatal GDNF Production Is Independent to Circulating Estradiol Level Despite Pan-Neuronal Activation in the Female Mouse

Gender difference in Parkinson’s disease (PD) suggests that female sex steroids may promote dopaminergic neuron survival and protect them from degeneration. The glial cell line-derived neurotrophic factor (GDNF) is believed to be dopaminotrophic; thus it is considered as a potential therapeutic target in PD. Additionally, GDNF is endogenously synthetized in the caudate/putamen of humans and striatum in rodents. A neuroprotective role of estrogens on the nigrostriatal pathway via the stimulation of GDNF has been proposed. Since the GDNF-producing parvalbumin (Parv) interneurons express the estrogen receptor alpha in the mouse striatum, we sought to determine whether ectopic estrogenic compound modulates the GDNF synthesis in mice. Using an ovariectomized-estradiol (E₂) replacement regimen, which reliably generates a rise of plasma estradiol, we assessed the effects of different levels of E₂ on the activation of striatal neuronal populations, and GDNF production. A strong correlation was found between plasma E₂ and the expression of the immediate early gene cFos in the striatum, as well as in other cortical regions. However, moderate and high E₂ treatments failed to induce any striatal GDNF mRNA and protein synthesis. High E₂ only stimulates cFos induction in a low percentage of striatal Parv neurons whereas the majority of cFos-positive cells are medium spiny neurons. Activation of these projecting neurons by E₂ suggests a role of circulating sex steroids in the modulation of striatal neural pathways.

G-1 exerts neuroprotective effects through G protein-coupled estrogen receptor 1 following spinal cord injury in mice

Spinal cord injury (SCI) always occurs accidently and leads to motor dysfunction because of biochemical and pathological events. Estrogen has been shown to be neuroprotective against SCI through estrogen receptors (ERs), but the underlying mechanisms have not been fully elucidated. In the present study, we investigated the role of a newly found membrane ER, G protein-coupled estrogen receptor 1 (GPR30 or GPER1), and discussed the feasibility of a GPR30 agonist as an estrogen replacement. Forty adult female C57BL/6J mice (10-12 weeks old) were divided randomly into vehicle, G-1, E2, G-1 + G-15 and E2 + G-15 groups. All mice were subjected to SCI using a crushing injury approach. The specific GPR30 agonist, G-1, mimicked the effects of E2 treatment by preventing SCI-induced apoptotic cell death and enhancing motor functional recovery after injury. GPR30 activation regulated phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK/extracellular signal-regulated kinase (ERK) signalling pathways, increased GPR30 and anti-apoptosis proteins Bcl-2 and brain derived neurotrophic factor (BDNF), but decreased the pro-apoptosis factor Bax and cleaved caspase-3. However, the neuroprotective effects of G-1 and E2 were blocked by the specific GPR30 antagonist, G-15. Thus, GPR30 rather than classic ERs is required to induce estrogenic neuroprotective effects. Given that estrogen replacement therapy may cause unexpected side effects, especially on the reproductive system, GPR30 agonists may represent a potential therapeutic approach for treating SCI.

Estrogen receptors modulate striatal metabotropic receptor type 5 in intact and MPTP male mice model of Parkinson's disease

Glutamate is the most important brain excitatory neurotransmitter and glutamate overactivity is well documented in Parkinson's disease (PD). Metabotropic glutamate (mGlu) receptors are reported to interact with membrane estrogen receptors (ERs) and more specifically the mGlu5 receptor subtype. 17β-estradiol and mGlu5 antagonists have neuroprotective effects in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We previously reported that ERα and ERβ are involved in neuroprotection following MPTP toxicity. The present study investigated the implication of ERs on the mGlu5 receptor adaptive response to MPTP toxicity in the brain of wild type (WT), ER knockout (ERKO)α and ERKOβ male mice. Autoradiography of [(3)H]ABP688 specific binding to striatal mGlu5 receptors showed a dorsal/ventral gradient similar for WT, ERKOα and ERKOβ mice with higher values ventrally. The lateral septum had highest [(3)H]ABP688 specific binding that remained unchanged in all experimental groups. ERKOα and ERKOβ mice had similarly lower striatal [(3)H]ABP688 specific binding than WT mice as measured also by Western blots. MPTP dose-dependently decreased striatal [(3)H]ABP688 specific binding in WT but not in ERKOα and ERKOβ mice; this correlated positively with striatal dopamine concentrations. A 17β-estradiol treatment for 10 days left unchanged striatal [(3)H]ABP688 specific binding of unlesioned mice of the three genotypes. 17β-estradiol treatment for 5 days before MPTP and for 5 days after partially prevented the mGlu5 receptor decrease only in WT MPTP mice and this was associated with higher BDNF striatal contents. These results thus show that in male mice ERs affect striatal mGlu5 receptor levels and their response to MPTP.

Neuroprotective Effect of Progesterone in MPTP-Treated Male Mice

BACKGROUND

Numerous studies have reported on the neuroprotective activity of estradiol, whereas the effect of the other ovarian steroid, progesterone, is much less documented.

METHODS

This study sought to investigate neuroprotection with a low dose of progesterone (1 µg) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated male mice to model Parkinson's disease and compare it to the effect of this steroid in intact mice (experiment 1). We also investigated if high doses of progesterone could protect dopaminergic neurons already exposed to MPTP (experiment 2). We measured progesterone effects on various dopaminergic markers [dopamine and its metabolites, dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2)] and on neuroactive steroids in both plasma and the brain.

RESULTS

For experiment 1, our results showed that progesterone completely prevented the effect of MPTP toxicity on dopamine concentrations, on the increase in the 3-methoxytyramine/dopamine ratio, as well as on VMAT2-specific binding in the striatum and the substantia nigra. Progesterone decreased MPTP effects on 3,4-dihydroxyphenylacetic acid concentrations and DAT-specific binding in the lateral part of the anterior striatum and in the middle striatum (medial and lateral parts). Progesterone treatment of intact mice had no effect on the markers investigated. For experiment 2, measures of dopaminergic markers in the striatum showed that 8 mg/kg of progesterone was the most effective dose to reduce MPTP effects, and more limited effects were observed with 16 mg/kg. We found that progesterone treatment increases the levels of brain progesterone itself as well as of its metabolites.

CONCLUSION

Our result showed that progesterone has neuroprotective effects on dopaminergic neurons in MPTP-treated male mice.

Alteration in Nuclear Factor-KappaB Pathway and Functionality of Estrogen via Receptors Promote Neuroinflammation in Frontal Cortex after 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Treatment

The MPTP mediated neurodegeneration in substantia nigra has been well studied, but not the status of frontal cortex. The novelty of the present study is to explore the sex difference of frontal cortex during MPTP intoxication and to investigate the role of estrogen and its receptors in presence of glial cells in a time chase experiment; to identify which pathway of NF-kappaB exist to proceed the neuroinflammation; to investigate the estrogen binding with its nuclear or cytosolic receptors and whether any direct relation exists between estrogen receptor (ER) -beta and NF-kappaB molecules p65 and RelB. The progression of neurodegeneration occurred with the association of glial cells and functional (via its nuclear and cytosolic receptors) estrogen level. Both the canonical and/or non canonical pathways of NF-kappaB exist in frontal cortex of both the sexes after MPTP treatment. The homodimeric or heterodimeric form of ER-beta binds with NF-kappaB molecules p65 and RelB differently, but the canonical or non canonical pathways of NF-kappaB molecules could not be stopped or may be promoted. The changes in the molecular and cellular pattern in frontal cortex of both sexes during MPTP intoxication depends on the estrogen function via its nuclear or cytosolic estrogen receptors.

Estradiol improves right ventricular function in rats with severe angioproliferative pulmonary hypertension: effects of endogenous and exogenous sex hormones

Estrogens are disease modifiers in PAH. Even though female patients exhibit better right ventricular (RV) function than men, estrogen effects on RV function (a major determinant of survival in PAH) are incompletely characterized. We sought to determine whether sex differences exist in RV function in the SuHx model of PAH, whether hormone depletion in females worsens RV function, and whether E2 repletion improves RV adaptation. Furthermore, we studied the contribution of ERs in mediating E2's RV effects. SuHx-induced pulmonary hypertension (SuHx-PH) was induced in male and female Sprague-Dawley rats as well as OVX females with or without concomitant E2 repletion (75 μg·kg(-1)·day(-1)). Female SuHx rats exhibited superior CI than SuHx males. OVX worsened SuHx-induced decreases in CI and SuHx-induced increases in RVH and inflammation (MCP-1 and IL-6). E2 repletion in OVX rats attenuated SuHx-induced increases in RV systolic pressure (RVSP), RVH, and pulmonary artery remodeling and improved CI and exercise capacity (V̇o2max). Furthermore, E2 repletion ameliorated SuHx-induced alterations in RV glutathione activation, proapoptotic signaling, cytoplasmic glycolysis, and proinflammatory cytokine expression. Expression of ERα in RV was decreased in SuHx-OVX but was restored upon E2 repletion. RV ERα expression was inversely correlated with RVSP and RVH and positively correlated with CO and apelin RNA levels. RV-protective E2 effects observed in females were recapitulated in male SuHx rats treated with E2 or with pharmacological ERα or ERβ agonists. Our data suggest significant RV-protective ER-mediated effects of E2 in a model of severe PH.

Raloxifene activates G protein-coupled estrogen receptor 1/Akt signaling to protect dopamine neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice

Raloxifene, used in the clinic, is reported to protect brain dopaminergic neurons in mice. Raloxifene was shown to mediate an effect through the G protein-coupled estrogen receptor 1 (GPER1). We investigated if raloxifene neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated male mice is mediated through GPER1 by using its antagonist G15. Striatal concentrations of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid to dopamine ratio as well as dopamine transporter and vesicular monoamine transporter 2 showed that raloxifene neuroprotection of dopaminergic neurons was blocked by G15. Protection by raloxifene was accompanied by activation of striatal Akt signaling (but not ERK1/2 signaling) and increased Bcl-2 and brain-derived neurotrophic factor levels; these effects were abolished by coadministration with G15. The effect of raloxifene was not mediated through increased levels of 17β-estradiol. MPTP mice had decreased plasma testosterone, dihydrotestosterone, and 3β-diol levels; this was prevented in raloxifene-treated MPTP mice. Our results suggest that raloxifene acted through GPER1 to mediate Akt activation, increase Bcl-2 and brain-derived neurotrophic factor levels, and protection of dopaminergic neurons and plasma androgens.

Estrogen mediates neuroprotection and anti-inflammatory effects during EAE through ERα signaling on astrocytes but not through ERβ signaling on astrocytes or neurons

Estrogens can signal through either estrogen receptor α (ERα) or β (ERβ) to ameliorate experimental autoimmune encephalomyelitis (EAE), the most widely used mouse model of multiple sclerosis (MS). Cellular targets of estrogen-mediated neuroprotection are still being elucidated. Previously, we demonstrated that ERα on astrocytes, but not neurons, was critical for ERα ligand-mediated neuroprotection in EAE, including decreased T-cell and macrophage inflammation and decreased axonal loss. Here, we determined whether ERβ on astrocytes or neurons could mediate neuroprotection in EAE, by selectively removing ERβ from either of these cell types using Cre-loxP gene deletion. Our results demonstrated that, even though ERβ ligand treatment was neuroprotective in EAE, this neuroprotection was not mediated through ERβ on either astrocytes or neurons and did not involve a reduction in levels of CNS inflammation. Given the differential neuroprotective and anti-inflammatory effects mediated via ERα versus ERβ on astrocytes, we looked for molecules within astrocytes that were affected by signaling through ERα, but not ERβ. We found that ERα ligand treatment, but not ERβ ligand treatment, decreased expression of the chemokines CCL2 and CCL7 by astrocytes in EAE. Together, our data show that neuroprotection in EAE mediated via ERβ signaling does not require ERβ on either astrocytes or neurons, whereas neuroprotection in EAE mediated via ERα signaling requires ERα on astrocytes and reduces astrocyte expression of proinflammatory chemokines. These findings reveal important cellular differences in the neuroprotective mechanisms of estrogen signaling through ERα and ERβ in EAE.

Neurosteroid and neurotransmitter alterations in Parkinson's disease

Parkinson's disease (PD) is associated with a massive loss of dopaminergic cells in the substantia nigra leading to dopamine hypofunction and alteration of the basal ganglia circuitry. These neurons, are under the control, among others, of the excitatory glutamatergic and inhibitory γ-aminobutyric acid (GABA) systems. An imbalance between these systems may contribute to excitotoxicity and dopaminergic cell death. Neurosteroids, a group of steroid hormones synthesized in the brain, modulate the function of several neurotransmitter systems. The substantia nigra of the human brain expresses high concentrations of allopregnanolone (3α, 5αtetrahydroprogesterone), a neurosteroid that positively modulates the action of GABA at GABAA receptors and of 5α-dihydroprogesterone, a neurosteroid acting at the genomic level. This article reviews the roles of NS acting as neuroprotectants and as GABAA receptor agonists in the physiology and pathophysiology of the basal ganglia, their impact on dopaminergic cell activity and survival, and potential therapeutic application in PD.

Estrogen receptors and lesion-induced response of striatal dopamine receptors

Neuroprotection by 17β-estradiol and an estrogen receptor (ER) agonist against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion were shown to implicate protein kinase B (Akt) signaling in mice. In order to evaluate the associated mechanisms, this study compared estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) intact or knockout (KO) and wild-type (WT) C57Bl/6 male mice following MPTP treatment of 7, 9, 11mg/kg and/or 17β-estradiol. Striatal D1 and D2 dopamine (DA) receptors were measured by autoradiography with the specific ligands [(3)H]-SCH 23390 and [(3)H]-raclopride, respectively and signaling by Western blot for Akt, glycogen synthase kinase 3β (GSK3β) and extracellular-regulated signal kinases (ERK1 and ERK2). Control ERKOβ mice had lower striatal [(3)H]-SCH 23390 specific binding than WT and ERKOα mice; both KO mice had lower [(3)H]-raclopride specific binding. Striatal D1 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in ERKOα mice and remained unchanged in WT and ERKOβ mice. Striatal D2 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in WT and ERKOα mice and increased in ERKOβ mice. In MPTP-lesioned mice, 17β-estradiol treatment increased D1 receptors in ERKOα and ERKOβ mice and D2 receptors in WT and ERKOβ mice. MPTP did not affect striatal pAkt/Akt and pGSK3β/GSK3β levels in WT and ERKOα mice, while in vehicle-treated ERKOβ mice these levels were higher and increased with MPTP lesioning. Striatal pERK1/ERK1 and pERK2/ERK2 levels showed to a lesser extent a similar pattern. In conclusion, ERs affected the response of striatal DA receptors to a MPTP lesion and post receptor signaling.

Effect of oestrogen receptors on brain NMDA receptors of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice

Parkinson's disease (PD) is characterised by the loss of nigrostriatal dopamine (DA) neurones and glutamate overactivity. There is substantial evidence to suggest that oestrogens prevent or delay the disease. 17β-oestradiol has neuroprotective effects in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and modulates brain NMDA receptors. In MPTP-lesioned mice, oestrogen receptor (ER)α and ERβ are important in 17β-oestradiol-induced neuroprotection. To evaluate the role of ERs in the response of NMDA receptors to lesion, we compared wild-type (WT) with ER knockout (KO) C57Bl/6 male mice that received 7, 9 or 11 mg/kg of MPTP. These mice were also treated with MPTP (9 mg/kg) and 17β-oestradiol. [(3) H]Ro 25-6981 specific binding autoradiography was used to label NMDA receptors containing NR2B subunits. In the frontal and cingulate cortex and striatum, vehicle-treated WT mice had higher [(3) H]Ro 25-6981 specific binding compared to ERKO mice. Cortical [(3) H]Ro 25-6981 specific binding decreased with increasing doses of MPTP in WT and ERKOα but not ERKOβ mice, whereas a dose-related decrease was only observed in the striatum of WT mice remaining low in ERKOα and ERKOβ mice. No effect of 17β-oestradiol treatment in intact or MPTP-lesioned mice of all three genotypes was observed in the cortex, whereas it increased striatal specific binding of intact ERKOβ and MPTP-lesioned WT mice. Striatal [(3) H]Ro 25-6981 specific binding positively correlated with striatal DA concentrations only in WT mice. MPTP and 17β-oestradiol treatments had more limited effects in the hippocampus. Only in the CA3 and dentate gyrus did vehicle and 17β-oestradiol-treated ERKOα mice have higher [(3) H]Ro 25-6981 specific binding than WT and ERKOβ mice, whereas MPTP decreased this specific binding only in the CA1, CA2 and CA3 of ERKOα mice. Hence, brain NMDA receptors were affected by the deletion of ERs, which affect the response to MPTP and 17β-oestradiol treatments with brain region specificity.

Alterations of gene expression of sodium channels in dorsal root ganglion neurons of estrogen receptor knockout (ERKO) mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Estrogen receptors (ERα and ERβ) mediate the neuroprotection of estrogens against MPTP-induced striatal dopamine (DA) depletion. Pain is an important and distressing symptom in Parkinson's disease (PD). Voltage-gated sodium channels in sensory neurons are involved in the development of neuropathic pain. In this study, MPTP caused changes in nociception and alterations of gene expression of voltage-gated sodium channels in dorsal root ganglion (DRG) neurons in ER knockout (ERKO) mice were investigated. We found that administration of MPTP (11 mg/kg) to WT mice led to an extensive depletion of DA and its two metabolites, αERKO mice were observed to be more susceptible to MPTP toxicity than βERKO or WT mice. In addition, we found that the mRNA levels of TTX-S and TTX-R sodium channel subtypes were differentially affected in MPTP-treated WT animals. The MPTP-induced up-regulation of Nav1.1 and Nav1.9, down-regulation of Nav1.6 in DRG neurons may be through ERβ, up-regulation of Nav1.7 and down-regulation of Nav1.8 are dependent on both ERα and ERβ. Therefore, the MPTP-induced alterations of gene expression of sodium channels in DRG neurons could be an important mechanism to affect excitability and nociceptive thresholds, and the ERs appear to play a role in nociception in PD.

Signaling pathways mediating the neuroprotective effects of sex steroids and SERMs in Parkinson's disease

Studies with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease have shown the ability of 17β-estradiol to protect the nigrostriatal dopaminergic system. This paper reviews the signaling pathways mediating the neuroprotective effect of 17β-estradiol against MPTP-induced toxicity. The mechanisms of 17β-estradiol action implicate activation of signaling pathways such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. 17β-estradiol signaling is complex and integrates multiple interactions with signaling molecules that act to potentiate a protective effect. 17β-estradiol signaling is mediated via estrogen receptors, including GPER1, but others receptors, such as the IGF-1 receptor, are implicated in the neuroprotective effect. Glial and neuronal crosstalk is a critical factor in the maintenance of dopamine neuronal survival and in the neuroprotective action of 17β-estradiol. Compounds that stimulate GPER1 such as selective estrogen receptor modulators and phytoestrogens show neuroprotective activity and are alternatives to 17β-estradiol.

Estradiol protects against hippocampal damage and impairments in fear conditioning resulting from transient global ischemia in mice

Estradiol protects against hippocampal damage and some learning impairments resulting from transient global ischemia in rats. Here, we seek to validate a mouse model of transient global ischemia and evaluate the effects of estradiol on ischemia-induced hippocampal damage and behavioral impairments. Female C57Bl6/J mice were ovariectomized and implanted with estradiol- or oil-secreting capsules. One week later, mice experienced 15-min of 2-vessel occlusion (2-VO) or sham surgical procedures. Five days later, mice were exposed to a fear conditioning protocol in which a specific context and novel tone were paired with mild footshock. Twenty-four hours following conditioning, contextual fear was assessed by measuring freezing behavior in the conditioned context (in the absence of the tone). This was followed by assessment of cue fear by measuring freezing behavior to the conditioned tone presented in a new context. When tested in the conditioned context, oil-treated mice that experienced 2-VO exhibited a significant reduction in freezing behavior whereas estradiol-treated mice that experienced 2-VO showed no disruption in freezing behavior. Freezing behavior when presented with the conditioned tone was unaffected by either surgery or hormone treatment. These findings suggest that global ischemia causes impairments in performance on the hippocampally-dependent contextual fear task but not conditioned cue-based fear. Furthermore, estradiol prevented the ischemia-induced impairment in contextual fear conditioning. Fluoro-Jade (FJ) staining revealed neuronal degeneration throughout the dorsal hippocampus of mice that experienced 2-VO. Estradiol treatment reduced the number of FJ+ cells in CA1 and CA2, but not in CA3 or in the dentate gyrus. Together, these findings suggest that 15 min of global ischemia causes extensive hippocampal neurodegeneration and disrupts contextual fear conditioning processes in mice and that estradiol protects against these adverse effects.

Oestrogen receptors and signalling pathways: implications for neuroprotective effects of sex steroids in Parkinson's disease

Parkinson's disease (PD) is an age-related neurodegenerative disorder with a higher incidence in the male population. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, 17β-oestradiol but not androgens were shown to protect dopamine (DA) neurones. We report that oestrogen receptors (ER)α and β distinctly contribute to neuroprotection against MPTP toxicity, as revealed by examining the membrane DA transporter (DAT), the vesicular monoamine transporter 2 (VMAT2) and tyrosine hyroxylase in ER wild-type (WT) and knockout (ERKO) C57Bl/6 male mice. Intact ERKOβ mice had lower levels of striatal DAT and VMAT2, whereas ERKOα mice were the most sensitive to MPTP toxicity compared to WT and ERKOβ mice and had the highest levels of plasma androgens. In both ERKO mice groups, treatment with 17β-oestradiol did not provide neuroprotection against MPTP, despite elevated plasma 17β-oestradiol levels. Next, the recently described membrane G protein-coupled oestrogen receptor (GPER1) was examined in female Macaca fascicularis monkeys and mice. GPER1 levels were increased in the caudate nucleus and the putamen of MPTP-monkeys and in the male mouse striatum lesioned with methamphetamine or MPTP. Moreover, neuroprotective mechanisms in response to oestrogens transmit via Akt/glycogen synthase kinase-3 (GSK3) signalling. The intact and lesioned striata of 17β-oestradiol treated monkeys, similar to that of mice, had increased levels of pAkt (Ser 473)/βIII-tubulin, pGSK3 (Ser 9)/βIII-tubulin and Akt/βIII-tubulin. Hence, ERα, ERβ and GPER1 activation by oestrogens is imperative in the modulation of ER signalling and serves as a basis for evaluating nigrostriatal neuroprotection.

Androgens exacerbate motor asymmetry in male rats with unilateral 6-hydroxydopamine lesion

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by dopamine neuron loss in the nigrostriatal pathway that shows greater incidence in men than women. The mechanisms underlying this gender bias remain elusive, although one possibility is that androgens may increase dopamine neuronal vulnerability to oxidative stress. Motor impairment can be modeled in rats receiving a unilateral injection of 6-hydroxydopamine (6-OHDA), a neurotoxin producing nigrostriatal degeneration. To investigate the role of androgens in PD, we compared young (2 months) and aged (24 months) male rats receiving gonadectomy (GDX) and their corresponding intact controls. One month after GDX, rats were unilaterally injected with 6-OHDA, and their motor impairment and asymmetry were assessed 2 weeks later using the cylinder test and the amphetamine-induced rotation test. Plasma samples were also collected to assess the concentration of testosterone and advanced oxidation protein products, a product of oxidative stress. GDX decreased lesion-induced asymmetry along with oxidative stress and increased amphetamine-induced rotations. These results show that GDX improves motor behaviors by decreasing motor asymmetry in 6-OHDA-treated rats, an effect that may be ascribed to increased release of striatal dopamine and decreased oxidative stress. Collectively, the data support the hypothesis that androgens may underlie the gender bias observed in PD.

Male/Female differences in neuroprotection and neuromodulation of brain dopamine

The existence of a sex difference in Parkinson's disease (PD) is observed as related to several variables, including susceptibility of the disease, age at onset, and symptoms. These differences between men and women represent a significant characteristic of PD, which suggest that estrogens may exert beneficial effects against the development and the progression of the disease. This paper reviews the neuroprotective and neuromodulator effects of 17β-estradiol and progesterone as compared to androgens in the nigrostriatal dopaminergic (NSDA) system of both female and male rodents. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice model of PD and methamphetamine toxicity faithfully reproduce the sex differences of PD in that endogenous estrogen levels appear to influence the vulnerability to toxins targeting the NSDA system. Exogenous 17β-estradiol and/or progesterone treatments show neuroprotective properties against NSDA toxins while androgens fail to induce any beneficial effect. Sex steroid treatments show male and female differences in their neuroprotective action against methamphetamine toxicity. NSDA structure and function, as well as the distribution of estrogen receptors, show sex differences and may influence the susceptibility to the toxins and the response to sex steroids. Genomic and non-genomic actions of 17β-estradiol converge to promote survival factors and the presence of both estrogen receptors α and β are critical to 17β-estradiol neuroprotective action against MPTP toxicity.

Clinicopathological significance and prognostic value of leukemia-related protein 16 expression in invasive ductal breast carcinoma

To explore the expression of leukemia-related protein 16 (LRP16) in invasive ductal breast carcinoma and analyze its correlation with clinicopathological feature and prognosis, immunohistochemistry was performed on 100 cases of invasive ductal breast carcinoma. Medical records were reviewed and clinicopathological analysis was performed. Leukemia-related protein 16 expression was detected in 33 of 100 cases (33%) of the invasive ductal breast carcinoma. Expression of LRP16 in carcinoma was obviously higher than that in normal breast tissue. LRP16 protein expression was found in 27.6% (21/76) of carcinoma at stage I and II, and 50.0% (12/24) of carcinoma at stage III and IV. LRP16 expression was found correlative with metastasis in the axillary lymph node (P = 0.001), stage (P = 0.042), estrogen receptor (ER) expression (P = 0.001), fragile histidine triad (FHIT) expression (P = 0.015) and CD133 expression (P = 0.038), but not with grade (P = 0.543), tumor size (P = 0.263), age (P = 0.840), menopause (P = 0.701) and HER-2 gene amplification (P = 0.463). The difference of the mean disease free survival (DFS) time between cancer patients with LRP16 expression (43.7 months) and those without (77.7 months) was statistically significant (Log rank = 9.989, P = 0.002). The difference of the mean overall survival (OS) time between cancer patients with LRP16 expression (50.0 months) and those without (120.0 months) was statistically significant (Log rank = 9.977, P = 0.002). Our finding suggests that expression of LRP16 protein is correlated with the stage, metastasis, prognosis and expression of ER, progesterone receptor, Ki-67, CD133 and FHIT in invasive ductal breast carcinoma.

Environmentally relevant exposure to 17alpha-ethinylestradiol affects the telencephalic proteome of male fathead minnows

Estrogens are key mediators of neuronal processes in vertebrates. As such, xenoestrogens present in the environment have the potential to alter normal central nervous system (CNS) function. The objectives of the present study were (1) to identify proteins with altered abundance in the male fathead minnow telencephalon as a result of low-level exposure to 17alpha-ethinylestradiol (EE(2)), and (2) to better understand the underlying mechanisms of 17beta-estradiol (E(2)) feedback in this important neuroendocrine tissue. Male fathead minnows exposed to a measured concentration of 5.4 ng EE(2)/L for 48 h showed decreased plasma E(2) levels of approximately 2-fold. Of 77 proteins that were quantified statistically, 14 proteins were down-regulated after EE(2) exposure, including four histone proteins, ATP synthase, H+ transporting subunits, and metabolic proteins (lactate dehydrogenase B4, malate dehydrogenase 1b). Twelve proteins were significantly induced by EE(2) including microtubule-associated protein tau (Mapt), astrocytic phosphoprotein, ependymin precursor, and calmodulin. Mapt showed an increase in protein abundance but a decrease in mRNA expression after EE(2) exposure(,) suggesting there may be a negative feedback response in the telencephalon to decreased mRNA transcription with increasing Mapt protein abundance. These results demonstrate that a low, environmentally relevant exposure to EE(2) can rapidly alter the abundance of proteins involved in cell differentiation and proliferation, neuron network morphology, and long-term synaptic potentiation. Together, these findings provide a better understanding of the molecular responses underlying E(2) feedback in the brain and demonstrate that quantitative proteomics can be successfully used in ecotoxicology to characterize affected cellular pathways and endocrine physiology.

Clinicopathological significance and prognostic value of LRP16 expression in colorectal carcinoma

AIM: To explore the expression of leukemia related protein 16 (LRP16) in colorectal carcinoma, and analyze its correlation with clinicopathologic features and prognosis.

METHODS: Immunohistochemistry for LRP16 was performed in 201 cases of colorectal carcinoma and 60 cases of distal normal mucosa. Medical records were reviewed and clinicopathological analysis was performed.

RESULTS: LRP16 expression was detected in 117 of 201 cases of the colorectal carcinoma and in 21 cases of 60 distal normal mucosa. The expression of LRP16 in carcinoma was significantly higher than that in normal mucosa (χ² = 9.999, P = 0.002). LRP16 protein expression was found in 43.3% (52/120) of carcinoma at stage I and II, and 80.2% (65/81) of carcinoma at stage III and IV (χ² =27.088, P = 0.001). Correlation between LRP16 expression and clinicopathological factors was significant in differentiation (P = 0.010), tumor size (P = 0.001), infiltrative depth (P = 0.000) and distant metastasis (P = 0.027). The difference of median survival time between cancer patients with LRP16 expression (38.0 mo) and those without was statistically significant (105.0 mo, Log rank = 41.455, P = 0.001). The multivariate survival analysis revealed that LRP16 expression was correlated significantly (Cox’s regression: P = 0.001, relative risk = 2.082) with shortened survival in the patients with colorectal cancer.

CONCLUSION: The expression of LRP16 is related to the degree of differentiation, invasiveness, metastasis and prognosis of colorectal carcinoma.

Oestrogen receptors enhance dopamine neurone survival in rat midbrain

Previous findings in our laboratory and elsewhere have shown that ovariectomy of rats in adulthood attenuates cocaine-stimulated locomotor behaviour. Ovarian hormones enhance both cocaine-stimulated behaviour and increase dopamine overflow after psychomotor stimulants. The present study aimed to determine whether ovarian hormones have these effects in part by maintaining dopamine neurone number in the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA) and to investigate the roles of specific oestrogen receptors (ERs) in the maintenance of mesencephalic dopamine neurones. To accomplish this goal, we used unbiased stereological techniques to estimate the number of tyrosine hydroxylase-immunoreactive (TH-IR) cell bodies in midbrain regions of intact, ovariectomised and hormone-replaced female rats and mice. Animals received active or sham gonadectomy on postnatal day 60 and received vehicle, 17beta-oestradiol (E(2)) or selective ER agonists propyl-pyrazole-triol (PPT, ERalpha) or diarylpropionitrile (DPN, ERbeta) for 1 month post-surgery. In both rats and mice, ovariectomy reduced the number of TH-IR cells in the SNpc and VTA. Replacement with E(2), PPT or DPN prevented or attenuated the loss observed with ovariectomy in both rats and mice. An additional study using ER knockout mice revealed that adult female mice lacking ERalpha had fewer TH-IR cells in midbrain regions than wild-type mice, whereas mice lacking ERbeta had TH-IR cell counts comparable to wild-type. These findings suggest that, although both ER subtypes play a role in the maintenance of TH-IR cell number in the SNpc and VTA, ERalpha may play a more significant role.

Androgens induce dopaminergic neurotoxicity via caspase-3-dependent activation of protein kinase Cdelta

Aged men have a greater incidence of Parkinson's disease (PD) than women. PD is a neurodegenerative condition associated with the loss of dopamine neurons in the nigrostriatal pathway. This study examined the neurotoxic effects of androgens in a dopaminergic cell line (N27 cells) and the downstream signaling pathways activated by androgens. Treatment of N27 cells with testosterone- and dihydrotestosterone-induced mitochondrial dysfunction, protein kinase C (PKC)-delta cleavage, and apoptosis in dopaminergic neuronal cells. Inhibition of caspase-3 prevented the cleavage of PKCdelta from the full-length element to the catalytic fragment and apoptosis in N27 cells, suggesting that androgen-induced apoptosis is mediated by caspase-3-dependent activation of PKCdelta. Androgen-induced apoptosis may be specific to dopamine neurons as evidenced by a lack of testosterone-induced apoptosis in GnRH neurons. These results support a neurotoxic consequence of testosterone on dopaminergic neurons and may provide insight into the gender bias found in PD.

Gender differences on MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in C57BL/6 mice

The aim of this study was to investigate the impact of gender difference in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated animal model of Parkinson's disease (PD). In the present study, we investigated the time-dependent alterations of dopamine and its metabolites, striatal tyrosine hydroxylase (TH) protein, dopamine transporter (DAT) protein, glial fibrillary acidic protein (GFAP) protein and midbrain TH protein and motor function in male and female mice 5h and 1, 3 and 7 days after four administrations of MPTP (20mg/kg) at 2-h intervals. The present study showed that the decrease of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) content in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. Our Western blot analysis study also demonstrated that the decrease of both striatal and midbrain TH protein levels in female mice was more pronounced than that in male animals from 1 to 7 days after MPTP treatment. As compared to male mice, in contrast, the increase of striatal GFAP protein levels in female mice was observed from 5h to 7 days after MPTP treatment. Furthermore, the present study showed that motor deficits were found in both male and female mice 1 and 7 days after MPTP treatment. In the present study, moreover, the decrease of striatal DAT protein levels in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. These results demonstrate that our administrations of MPTP at 2-h intervals can cause more severe damage in female mice as compared with male animals. The gender difference may be due to the decrease of DAT expression caused by MPTP. Thus our findings provide further valuable information for the pathogenesis of PD.

Clinicopathological significance of LRP16 protein in 336 gastric carcinoma patients

AIM: To investigate the expression of leukemia related protein 16 (LRP16), and the possible relationship between LRP16 expression and clinicopathological indices in 336 gastric carcinoma patients.

METHODS: Immunohistochemistry was used to detect LRP16 expression in 336 cases of paraffin-embedded gastric carcinoma tissues and 60 cases of distal normal mucosa. The relationships between LRP16 expression and patients’ age, tumor size, histological grade, clinical stage, metastatic status and prognosis were analysed.

RESULTS: The expression of LRP16 was 58.6% (197/336) in gastric carcinoma and 31.7% (19/60) in distal normal gastric mucosa. The expression of LRP16 in carcinoma was significantly higher than that in normal mucosa tissues (χ² = 14.929, P = 0.001). LRP16 protein expression was found in 44.1% (63/143) carcinomas at stage I and II, and 69.4% (134/193) carcinomas at stage III and IV (χ² = 21.804, P = 0.001), and in 56.9% (182/320) of cancers without metastasis but 93.8% (15/16) of those with metastasis (χ² = 8.543, P = 0.003). The expression of LRP16 was correlated with tumor size, infiltrative depth, clinical stage, lymphatic invasion and distant metastasis (all P < 0.05). Follow-up data showed that there was a significant difference in median survival time between cancer patients with expression of LRP16 (27.0 mo) and those without (48.0 mo, Log rank =31.644, P = 0.001).

CONCLUSION: The expression of LRP16 may be associated with invasion, metastasis and prognosis of gastric cancer.

Neuroprotective actions of sex steroids in Parkinson's disease

The sex difference in Parkinson's disease, with a higher susceptibility in men, suggests a modulatory effect of sex steroids in the brain. Numerous studies highlight that sex steroids have neuroprotective properties against various brain injuries. This paper reviews the protective effects of sex hormones, particularly estradiol, progesterone and androgens, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease as compared to methamphetamine toxicity. The molecular mechanisms underlying beneficial actions of sex steroids on the brain have been investigated showing steroid, dose, timing and duration specificities and presently focus is on the dopamine signaling pathways, the next frontier. Both genomic and non-genomic actions of estrogen converge to promote survival factors and show sex differences. Neuroprotection by estrogen involves activation of signaling molecules such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. Interaction with growth factors, such as insulin-like growth factor 1, also contributes to protective actions of estrogen.

Estradiol activates beta-catenin dependent transcription in neurons

Estradiol may fulfill a plethora of functions in neurons, in which much of its activity is associated with its capacity to directly bind and dimerize estrogen receptors. This hormone-protein complex can either bind directly to estrogen response elements (ERE's) in gene promoters, or it may act as a cofactor at non-ERE sites interacting with other DNA-binding elements such as AP-1 or c-Jun. Many of the neuroprotective effects described for estrogen have been associated with this mode of action. However, recent evidence suggests that in addition to these “genomic effects”, estrogen may also act as a more general “trophic factor” triggering cytoplasmic signals and extending the potential activity of this hormone. We demonstrated that estrogen receptor alpha associates with β-catenin and glycogen synthase kinase 3 in the brain and in neurons, which has since been confirmed by others. Here, we show that the action of estradiol activates β-catenin transcription in neuroblastoma cells and in primary cortical neurons. This activation is time and concentration-dependent, and it may be abolished by the estrogen receptor antagonist ICI 182780. The transcriptional activation of β-catenin is dependent on lymphoid enhancer binding factor-1 (LEF-1) and a truncated-mutant of LEF-1 almost completely blocks estradiol TCF-mediated transcription. Transcription of a TCF-reporter in a transgenic mouse model is enhanced by estradiol in a similar fashion to that produced by Wnt3a. In addition, activation of a luciferase reporter driven by the engrailed promoter with three LEF-1 repeats was mediated by estradiol. We established a cell line that constitutively expresses a dominant-negative LEF-1 and it was used in a gene expression microarray analysis. In this way, genes that respond to estradiol or Wnt3a, sensitive to LEF-1, could be identified and validated. Together, these data demonstrate the existence of a new signaling pathway controlled by estradiol in neurons. This pathway shares some elements of the insulin-like growth factor-1/Insulin and Wnt signaling pathways, however, our data strongly suggest that it is different from that of both these ligands. These findings may reveal a set of new physiological roles for estrogens, at least in the Central Nervous System (CNS).

Neuroprotection against excitotoxic brain injury in mice after ovarian steroid depletion

Ovarian steroid hormones influence not only seizure phenomena, but also the neuronal cell death that follows. In the present study, we applied two models of ovarian steroid loss, ovariectomy and chemically-induced ovarian failure, to evaluate kainate-induced seizure activity and the susceptibility of hippocampal neurons to seizure-induced neurodegeneration. Young adult female FVB/NJ mice were ovariectomized with (OVX+E, n=6) or without (OVX, n=8) estrogen replacement. A separate group of females received the ovotoxin, 4-vinylcyclohexene diepoxide (VCD, n=8) to deplete ovarian follicles. Mice underwent kainate-induced status epilepticus and were evaluated for seizure activity (3 h) and delayed hippocampal neuronal injury (7 days). While there were no differences in latency or duration of severe seizures among control, OVX and VCD-treated mice, OVX+E mice exhibited seizures of a significantly longer duration. However, both VCD-induced ovarian failure and OVX led to a dramatic reduction in the extent of excitotoxic cell death, with slightly greater effects observed in VCD-treated mice. Estradiol administration to OVX mice also exerted a significant neuroprotective effect against kainate-induced cell death. These results support and extend earlier findings suggesting that the hormonal milieu may have differential effects on seizure susceptibility that are separate and distinct from those influencing hippocampal neuronal vulnerability. Collectively, these findings highlight the complex interactions among the loss of ovarian steroid hormones, estrogen replacement, seizures, and seizure-induced cell death.

Sex-dependent regulation of hypoxic ventilation in mice and humans is mediated by erythropoietin

Acclimatization to hypoxic exposure relies on an elevated ventilation and erythropoietic activity. We recently proposed that erythropoietin (Epo) links both responses: apart from red blood cell production, cerebral and plasma Epo interact with the central and peripheral respiratory centers. Knowing that women cope better than men with reduced oxygen supply (as observed at high altitude), we analyzed the hypoxic ventilatory response in Epo-overexpressing transgenic male and female mice with high Epo levels in brain and plasma (Tg6) or in wild-type animals injected with recombinant human Epo (rhEpo). Exposure to moderate and severe hypoxia as well as to hyperoxia and injection of domperidone, a potent peripheral ventilatory stimulant, revealed that the presence of transgenic or rhEpo extensively increased the hypoxic ventilatory response in female mice compared with their corresponding male siblings. Alterations of catecholamines in the brain stem's respiratory centers were also sex dependent. In a proof-of-concept study, human volunteers were intravenously injected with 5,000 units rhEpo and subsequently exposed to 10% oxygen. Compared with men, the hypoxic ventilatory response was significantly increased in women. We conclude that Epo exerts a sex-dependent impact on hypoxic ventilation improving the response in female mice and in women that most probably involves sexual hormones. Our data provides an explanation as to why women are less susceptible to hypoxia-associated syndromes than men.

Soy phytoestrogens are neuroprotective against stroke-like injury in vitro

Diets high in soy are neuroprotective in experimental stroke. This protective effect is hypothesized to be mediated by phytoestrogens contained in soy, because some of these compounds have neuroprotective effects in in vitro models of cell death. We tested the ability of the soy phytoestrogens genistein, daidzein, and the daidzein metabolite equol to protect embryonic rat primary cortical neurons from ischemic-like injury in vitro at doses typical of circulating concentrations in human populations (0.1-1 microM). All three phytoestrogens inhibited lactate dehydrogenase (LDH) release from cells exposed to glutamate toxicity or the calcium-ATPase inhibitor, thapsigargin. In cells exposed to hypoxia or oxygen-glucose deprivation (OGD), pretreatment with the phytoestrogens inhibited cell death in an estrogen receptor (ER) dependent manner. Although OGD results in multiple modes of cell death, examination of alpha-spectrin cleavage and caspase-3 activation revealed that the phytoestrogens were able to inhibit apoptotic cell death in this model. In addition, blockade of phosphoinositide 3-kinase prevented the protective effects of genistein and daidzein, and blockade of mitogen-activated protein kinase prevented genistein-dependent neuroprotection. These results suggest that pretreatment with dietary levels of soy phytoestrogens can mimic neuroprotective effects observed with estrogen and appear to use the same ER-kinase pathways to inhibit apoptotic cell death.

Inflammatory response in Parkinsonism

Inflammatory responses have been proposed as important factors in dopaminergic neuro-degeneration in Parkinsonism. Increasing evidence suggests that the alteration of the glial microenvironment induced by neuronal degeneration could be deleterious to the remaining neurons. The activation of microglia/macrophages and reactive astrocytes may have a negative effect on the surrounding parenchyma, perpetuating the neurodegenerative process. However, this alteration may also go beyond the brain parenchyma and stimulate other inflammatory changes in other systems, inducing the release of proinflammatory cytokines and probably Acute Phase Proteins (APP) and Glucocorticoids (GC). In this work we review the latest advances in the field to provide a picture of the state of the art of studies of inflammatory responses and Parkinsonism, hopefully opening up new therapeutic perspectives for patients with Parkinson's disease.

Effects of estrogens on striatal damage after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in male and female mice

Emerging evidence shows a beneficial effect of estrogens for Parkinson's disease, yet the exact potency of these compounds implicated remain obscured. In this study, we investigated the neuroprotective effect of 17beta-estradiol and estrone against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced striatal toxicity in mice. The neuroprotective effects of both compounds were evaluated by HPLC and Western blot analyses 5 days after the last of 4 consecutive injections of MPTP at 1-h intervals to mice. Subacute treatment (10 days) with estrone or 17beta-estradiol at low doses (0.05 and 0.2mg/kg) showed no significant changes against MPTP-induced damage of striatal dopamine terminals in mice. Furthermore, acute treatment with estrone at high doses (0.5 and 2.0mg/kg) showed no significant alterations against MPTP-induced damage of striatal dopamine terminals in mice. In contrast, acute treatment with 17beta-estradiol at high doses exhibited a neuroprotective effect against the damage of striatal dopamine terminals in both male and female mice after MPTP treatments. The results demonstrate that estrogen therapy with high doses may have a neuroprotective effect on the damage of striatal dopamine terminals in the MPTP-induced mice. These findings may lead to be development of estrogen therapy for the prevention and treatment of Parkinson's disease.

Estrogen and SERM neuroprotection in animal models of Parkinson's disease

A higher prevalence and incidence of Parkinson disease (PD) is observed in men and beneficial motor effects of estrogens are observed in parkinsonian women. Lesion of the dopamine (DA) nigrostriatal pathway in animals with 1-methyl 4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) provides a model of PD and this is based on its use in humans as side-product of a drug abuse. Presently treatment of PD is mainly symptomatic. The MPTP mouse is used to study the neuroprotective roles of estrogenic drugs on the DA system. Estrogens, but not androgens, are active neuroprotectants as well as progesterone and dehydroepiandrosterone. An estrogen receptor agonist PPT and the selective estrogen receptor modulator raloxifene are also neuroprotective. Striatal DA neurons of estrogen receptor alpha knockout mice are more susceptible to MPTP toxicity than wild-type mice and neuroprotection by estradiol is associated with the activation of the PI3-K pathway involving Akt, GSK3beta, Bcl2 and BAD.

Resveratrol, a red wine polyphenol, protects dopaminergic neurons in MPTP-treated mice

Phytoestrogens, and particularly resveratrol, a red wine polyphenol, are currently under study for their therapeutic antioxidant properties. Administration of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to C57BL/6 mice targets nigrostriatal dopaminergic neurons, leading to cell death and striatal dopamine (DA) depletion. The aim of the present study was to analyze the protective effect of a diet rich in resveratrol against MPTP-induced neuronal death. Male mice were kept on a phytoestrogen-free diet, supplemented or not with 50 or 100 mg/kg/day of resveratrol for 1 or 2 weeks, after which MPTP was injected intraperitoneally. We observed that daily administration of resveratrol prevented MPTP-induced depletion of striatal DA, and maintained striatal tyrosine hydroxylase (TH) protein levels. Our results also demonstrated that mice treated with resveratrol prior to MPTP administration showed more abundant TH-immunopositive neurons than mice given only MPTP, indicating that resveratrol protects nigral neurons from MPTP insults. Altogether, these data revealed that resveratrol can counteract the toxic effects of the neurotoxin MPTP and, as such, it may be regarded as a powerful molecule for complementary neuroprotective therapy.

Contribution of estrogen receptors alpha and beta to the effects of estradiol in the brain

Clinical and experimental studies show a modulatory role of estrogens in the brain and suggest their beneficial action in mental and neurodegenerative diseases. The estrogen receptors ERalpha and ERbeta are present in the brain and their targeting could bring selectivity and reduced risk of cancer. Implication of ERs in the effect of estradiol on dopamine, opiate and glutamate neurotransmission is reviewed. The ERalpha agonist, PPT, is shown as estradiol to modulate hippocampal NMDA receptors and AMPA receptors in cortex and striatum of ovariectomized rats whereas the ERbeta agonist DPN is inactive. Striatal DPN activity suggests implication of ERbeta in estradiol modulation of D2 receptors and transporters in ovariectomized rats and is supported by the lack of effect of estradiol in ERbeta knockout (ERKObeta) mice. Both ERalpha and ERbeta agonists modulate striatal preproenkephalin (PPE) gene expression in ovariectomized rats. In male mice PPT protects against MPTP toxicity to striatal dopamine; this implicates Akt/GSK3beta signaling and the apoptotic regulators Bcl2 and Bad. This suggests a role for ERalpha in striatal dopamine neuroprotection. ERKOalpha mice are more susceptible to MPTP toxicity and not protected by estradiol; differences in ERKObeta mice are subtler. These results suggest therapeutic potential for the brain of ER specific agonists.