Estrogen down-regulates glial activation in male mice following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication

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.

HLDF-6 peptides exhibit neuroprotective effects in the experimental model of preclinical Parkinson's disease

The mechanisms of the neuroprotective action of the hexapeptides HLDF-6 encoded by the amino acid sequence 41-46 of Human Leukemia Differentiation Factor and its homoserine derivative HLDF-6H were studied in an experimental 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced model of Parkinson's disease (PD). C57Bl/6 mice received two intraperitoneal injections of 18 mg/kg MPTP-HCl, with an interval of 2 hours. MPTP-induced motor dysfunction was assessed using horizontal grid test. Our data show that chronic intranasal administration of peptides (3 weeks, 300 μg/kg/day) restored normal levels of dopamine and improved its turnover rates in the striatum. Furthermore, peptide administration increased serum estradiol levels and led to a significant improvement in motor functions in MPTP-treated mice. Additionally, peptide treatment increased the levels of mRNA encoding neurotrophin BDNF, but normalized the levels of mRNA encoding the inflammatory mediators TGFβ1, IL1β and IFNγ in the brain. Collectively, our behavioral and biochemical studies demonstrate that HLDF-6 peptides have a therapeutic potential for treating PD. We propose that HLDF-6 peptides may exert their neuroprotective mechanism, at least in part, by normalizing estradiol levels and modulating the expression of key factors involved in neurotrophic support and neuroinflammation.

Parkinson's disease in women: Mechanisms underlying sex differences

Parkinson's disease is a neurodegenerative disease which is associated with different motor, cognitive and mood-related problems. Though it has been established that Parkinson's disease is less prevalent in women in comparison to men, the differences tend to diminish with the advancing age. Different genetic, hormonal, neuroendocrinal and molecular players contribute towards the differences in the Parkinson's disease pathogenesis. Furthermore, data available with respect to the therapeutic management of Parkinson's disease in females is limited; women often tend to suffer more from the side effects of the currently available drugs. The present review highlights the sex-specific differences which play a role in the manifestation of these symptoms and side effects of the currently available therapeutic strategies. We have also discussed the current and upcoming therapeutic strategies which are in the clinical trials such as adenosine 2A (A2A) receptor antagonists, estrogen replacement therapy, α-synuclein targeting vaccines and antibodies, Botulinum toxin A, Fas-associated factor-1 (FAF-1) inhibitors, thiazolidinediones, 5-HT1_A receptor agonists, dopamine D1/D5 receptor agonists, Glucagon-like peptide 1 (GLP-1) analogues and certain plant based principles for the treatment of Parkinson's disease in women.

Brain Selective Estrogen Treatment Protects Dopaminergic Neurons and Preserves Behavioral Function in MPTP-induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra and loss of both motor and non-motor features. Several clinical and preclinical studies have provided evidence that estrogen therapy reduces the risk of PD but have limitations in terms of adverse peripheral effects. Therefore, we examined the potential beneficial effects of the brain-selective estrogen prodrug, 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) on nigrostriatal dopaminergic neurodegeneration and behavioral abnormalities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Wild-type mice were treated with daily subcutaneous injections of DHED (50 and 100 µg/kg) or vehicle for four weeks. To produce PD-like symptoms, mice were injected with MPTP (18 mg/kg in saline; intraperitoneally) four times at 2-hr intervals for one day. After behavioral examination, mice were sacrificed, and the brains were isolated for neurochemical and morphological examinations. MPTP injected mice exhibited loss of dopaminergic neurons and fibers in substantia nigra and striatum respectively, along with impaired motor function at day 7 post MPTP injection. These phenotypes were associated with significantly increased oxidative stress and inflammatory responses in the striatum regions. DHED treatments significantly mitigated behavioral impairments and dopaminergic neurodegeneration induced by MPTP. We further observed that DHED treatment suppressed oxidative stress and inflammation in the striatum of MPTP treated mice when compared to vehicle treated mice. In conclusions, our findings suggest that DHED protects dopaminergic neurons from MPTP toxicity in mouse model of PD and support a beneficial effect of brain-selective estrogen in attenuating neurodegeneration and motor symptoms in PD-related neurological disorders. Graphical Abstract.

Delayed Dopamine Dysfunction and Motor Deficits in Female Parkinson Model Mice

This study analyzed gender differences in the progressive dopamine (DA) deficiency phenotype in the MitoPark (MP) mouse model of Parkinson’s disease (PD) with progressive loss of DA release and reuptake in midbrain DA pathways. We found that the progressive loss of these DA presynaptic parameters begins significantly earlier in male than female MP mice. This was correlated with behavioral gender differences of both forced and spontaneous motor behavior. The degeneration of the nigrostriatal DA system in MP mice is earlier and more marked than that of the mesolimbic DA system, with male MP mice again being more strongly affected than female MP mice. After ovariectomy, DA presynaptic and behavioral changes in female mice become very similar to those of male animals. Our results suggest that estrogen, either directly or indirectly, is neuroprotective in the midbrain DA system. Our results are compatible with epidemiological data on incidence and symptom progression in PD, showing that men are more strongly affected than women at early ages.

Luteolin-7-O-glucoside protects dopaminergic neurons by activating estrogen-receptor-mediated signaling pathway in MPTP-induced mice

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by the degeneration of dopaminergic neurons in substantia nigra (SN). Accumulating evidences implicate the beneficial role of estrogen in the therapy of PD.

METHODS

In the present study, the protective function of luteolin-7-O-glucoside (LUT-7G), a natural flavonoid, was investigated in 1-methyl-4-phenylpyridinium (MPP⁺) treated SH-SY5Y cells and 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) induced mice.

RESULTS

Pre-treatment of LUT-7G increased the viability and reduced the apoptosis of SH-SY5Y cells treated by MPP⁺. At molecular level, the Bcl-2/Bax ratio was increased, while the expression of cleaved caspase 3 was markedly lessened. Moreover, LUT-7G increased the expression of estrogen receptor (ER), ERα and ERβ, and enhanced the activation of ERK1/2/STAT3/c-Fos that could be abolished by ER antagonists. Furthermore, in vivo experiment indicated that pre-treatment of LUT-7G improved the bradykinesia, and enhanced the muscle strength as well as the balancing capacity of mice treated with MPTP. And LUT-7G prevented the injury of TH positive cells in substantia nigra and increased TH positive nerve fibers in striatum. In addition, pre-treatment of LUT-7G also significantly diminished the MPTP-induced gliosis in substantia nigra.

CONCLUSIONS

LUT-7G effectively protected dopaminergic neurons against MPP⁺ or MPTP-induced toxicity, probably by activating the ER-mediated signaling pathway. Our findings explore the therapeutic potential of LUT-7G for PD therapy.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.

Sex differences in Parkinson's disease: Features on clinical symptoms, treatment outcome, sexual hormones and genetics

Parkinson's disease (PD) is the second most frequent age-related neurodegenerative disorder. Sex is an important factor in the development of PD, as reflected by the fact that it is more common in men than in women by an approximate ratio of 2:1. Our hypothesis is that differences in PD among men and women are highly determined by sex-dependent differences in the nigrostriatal dopaminergic system, which arise from environmental, hormonal and genetic influences. Sex hormones, specifically estrogens, influence PD pathogenesis and might play an important role in PD differences between men and women. The objective of this review was to discuss the PD physiopathology and point out sex differences in nigrostriatal degeneration, symptoms, genetics, responsiveness to treatments and biochemical and molecular mechanisms among patients suffering from this disease. Finally, we discuss the role estrogens may have on PD sex differences.

Estrogens and the cognitive symptoms of schizophrenia: Possible neuroprotective mechanisms

Schizophrenia is a complex neuropsychiatric illness with marked sex differences. Women have later onset and lesser symptoms, which has led to the hypothesis that estrogens are protective in schizophrenia. Cognitive dysfunction is a hallmark of the disease and the symptom most correlated with functional outcome. Here we describe a number of mechanisms by which estrogens may be therapeutic in schizophrenia, with a focus on cognitive symptoms. We review the relationship between estrogens and brain derived neurotrophic factor, neuroinflammation, NMDA receptors, GABA receptors, and luteinizing hormone. Exploring these pathways may enable novel treatments for schizophrenia and a greater understanding of this devastating disease.

β-Estradiol-3-benzoate confers neuroprotection in Parkinson MPP+ rat model through inhibition of lipid peroxidation

Estradiol (E2), in addition to its known hormone function, is a neuroactive steroid that has shown neuroprotective profile in several models of neurological diseases. The present study explores the antioxidant effect of β-estradiol-3-benzoate (EB) on the neurotoxicity elicited by MPP⁺ in rat striatum. Male Wistar rats, that were gonadectomized 30days prior to EB, were given 100µgEB per rat every 48h for 11days and animals were infused with MPP⁺ via intrastriatal at day six after beginning EB treatment. EB treatment completely prevented the fall in dopamine caused by MPP⁺, such result was related with decreased lipid peroxidation, a marker of oxidative stress; diminished number of ipsilateral-to-lesion turns and increased signal of the dopamine-synthesizing enzyme Tyrosin Hydroxylase in substantia nigra. The protection elicited by EB was not related to Mn or Cu-Zn superoxide dismutase enzymatic activities or glutathione modulation since none of these parameters were influenced by EB at the times assayed. Whereas, increased expression of PON2 as a result of EB treatment was observed, this phenomenon could be one of the mechanism by which the steroid conferred protection to dopaminergic cells against MPP⁺ injury.

GPER activation is effective in protecting against inflammation-induced nigral dopaminergic loss and motor function impairment

Increasing evidence suggest that excessive inflammatory responses from overactivated microglia play a critical role in Parkinson's disease (PD), contributing to, or exacerbating, nigral dopaminergic (DA) degeneration. Recent results from our group and others demonstrated that selective activation of G protein-coupled estrogen receptor (GPER) with the agonist G1 can protect DA neurons from 1-methyl-4-phenylpyridinium (MPP⁺) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxins. However, it is not known whether modulation of microglial responses is one of the mechanisms by which G1 exerts its DA neuroprotective effects. We analyzed, in the N9 microglial cell line, the effect of G1 on microglial activation induced by lipopolysaccharide (LPS) exposure. The results revealed that G1 significantly decrease phagocytic activity, expression of inducible nitric oxide synthase (iNOS) and release of nitric oxide (NO) induced by LPS. To determine the relevance of this anti-inflammatory effect to the protection of nigral DA cells, the effect of G1 was analyzed in male mice injected unilaterally in the substantia nigra (SN) with LPS. Although G1 treatment did not decrease LPS-induced increase of ionized calcium binding adaptor molecule 1 (iba-1) positive cells it significantly reduced interleukin-1beta (IL-1β), cluster of differentiation 68 (CD68) and iNOS mRNA levels, and totally inhibited nigral DA cell loss and, as a consequence, protected the motor function. In summary, our findings demonstrated that the G1 agonist is able to modulate microglial responses and to protect DA neurons and motor functions against a lesion induced by an inflammatory insult. Since G1 lacks the feminizing effects associated with agonists of the classical estrogen receptors (ERs), the use of G1 to selectively activate the GPER may be a promising strategy for the development of new therapeutics for the treatment of PD and other neuroinflammatory diseases.

Influence of Estrogen Modulation on Glia Activation in a Murine Model of Parkinson's Disease

Epidemiological data suggest a sexual dimorphism in Parkinson disease (PD), with women showing lower risk of developing PD. Vulnerability of the nigrostriatal pathway may be influenced by exposure to estrogenic stimulation throughout fertile life. To further address this issue, we analyzed the progression of nigrostriatal damage, microglia and astrocyte activation and microglia polarization triggered by intrastriatal injection of dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in male, female and ovariectomized (OVX) mice, as well as in OVX mice supplemented with 17βestradiol (OVX+E). Animals were sacrificed at different time points following 6-OHDA injection and brain sections containing striatum and substantia nigra pars compacta (SNc) underwent immunohistochemistry for tyrosine hydroxylase (TH) (dopaminergic marker), immunofluorescence for IBA1 and GFAP (markers of microglia and astrocyte activation, respectively) and triple immunoflorescent to identify polarization of microglia toward the cytotoxic M1 (DAPI/IBA1/TNFα) or cytoprotective M2 (DAPI/IBA1/CD206) phenotype. SNc damage induced by 6-OHDA was significantly higher in OVX mice, as compared to all other experimental groups, at 7 and 14 days after surgery. Astrocyte activation was higher in OVX mice with respect the other experimental groups, at all time points. Microglial activation in the SNc was detected at earlier time points in male, female and OVX+E, while in OVX mice was detected at all time-points. Microglia polarization toward the M2, but not the M1, phenotype was detected in female and OVX+E mice, while the M1 phenotype was observed only in male and OVX mice. Our results support the protective effects of estrogens against nigrostriatal degeneration, suggesting that such effects may be mediated by an interaction with microglia, which tend to polarize preferentially toward an M2, cytoprotective phenotype in the presence of intense estrogenic stimulation.

Menopause and Parkinson's disease. Interaction between estrogens and brain renin-angiotensin system in dopaminergic degeneration

The neuroprotective effects of menopausal hormonal therapy in Parkinson's disease (PD) have not yet been clarified, and it is controversial whether there is a critical period for neuroprotection. Studies in animal models and clinical and epidemiological studies indicate that estrogens induce dopaminergic neuroprotection. Recent studies suggest that inhibition of the brain renin-angiotensin system (RAS) mediates the effects of estrogens in PD models. In the substantia nigra, ovariectomy induces a decrease in levels of estrogen receptor-α (ER-α) and increases angiotensin activity, NADPH-oxidase activity and expression of neuroinflammatory markers, which are regulated by estrogen replacement therapy. There is a critical period for the neuroprotective effect of estrogen replacement therapy, and local ER-α and RAS play a major role. Astrocytes play a major role in ER-α-induced regulation of local RAS, but neurons and microglia are also involved. Interestingly, treatment with angiotensin receptor antagonists after the critical period induced neuroprotection.

Protective Microglia and Their Regulation in Parkinson's Disease

Microglia-mediated neuroinflammation is a hallmark of Parkinson’s disease (PD). In the brains of patients with PD, microglia have both neurotoxic and neuroprotective effects, depending on their activation state. In this review, we focus on recent research demonstrating the neuroprotective role of microglia in PD. Accumulating evidence indicates that the protective mechanisms of microglia may result from their regulation of transrepression pathways via nuclear receptors, anti-inflammatory responses, neuron–microglia crosstalk, histone modification, and microRNA regulation. All of these mechanisms work together to suppress the production of neurotoxic inflammatory components. However, during the progression of PD, the detrimental effects of inflammation overpower the protective actions of microglia. Therefore, an in-depth exploration of the mechanisms underlying microglial neuroprotection, and a means of promoting the transformation of microglia to the protective phenotype, are urgently needed for the treatment of PD.

The Role of Steroid Hormones in the Modulation of Neuroinflammation by Dietary Interventions

Steroid hormones, such as sex hormones and glucocorticoids, have been demonstrated to play a role in different cellular processes in the central nervous system, ranging from neurodevelopment to neurodegeneration. Environmental factors, such as calorie intake or fasting frequency, may also impact on such processes, indicating the importance of external factors in the development and preservation of a healthy brain. The hypothalamic-pituitary-adrenal axis and glucocorticoid activity play a role in neurodegenerative processes, including in disorders such as in Alzheimer's and Parkinson's diseases. Sex hormones have also been shown to modulate cognitive functioning. Inflammation is a common feature in neurodegenerative disorders, and sex hormones/glucocorticoids can act to regulate inflammatory processes. Intermittent fasting can protect the brain against cognitive decline that is induced by an inflammatory stimulus. On the other hand, obesity increases susceptibility to inflammation, while metabolic syndromes, such as diabetes, are associated with neurodegeneration. Consequently, given that gonadal and/or adrenal steroids may significantly impact the pathophysiology of neurodegeneration, via their effect on inflammatory processes, this review focuses on how environmental factors, such as calorie intake and intermittent fasting, acting through their modulation of steroid hormones, impact on inflammation that contributes to cognitive and neurodegenerative processes.

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.

Dietary curcumin supplementation attenuates 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in C57BL mice

Studies in vivo and in vitro suggest that curcumin is a neuroprotective agent. Experiments were conducted to determine whether dietary supplementation with curcumin has neuroprotective effects in a mouse model of Parkinson’s disease (PD). Treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) significantly induced the loss of dopaminergic cells in the substantia nigra and deletion of dopamine in the striatum, which was attenuated by long-term (7 weeks) dietary supplementation with curcumin at a concentration of 0.5% or 2.0% (w/w). Although curcumin did not prevent the MPTP-induced apoptosis of neuroblasts in the subventricular zone (SVZ), it promoted the regeneration of neuroblasts in the anterior part of the SVZ (SVZa) at 3 days after MPTP treatment. Furthermore, curcumin enhanced the MPTP-induced activation of microglia and astrocytes in the striatum and increased the expression of glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-β1 (TGFβ1) in the striatum and SVZ. GDNF and TGFβ1 are thought to play an important role in protecting neurons from injury in the central and peripheral nervous systems. These results suggest that long-term administration of curcumin blocks the neurotoxicity of MPTP in the nigrostriatal dopaminergic system of the mouse and that the neuroprotective effect might be correlated with the increased expression of GDNF and TGFβ1. Curcumin may be effective in preventing or slowing the progression of PD.

Rho Kinase and Dopaminergic Degeneration

The small GTP-binding protein Rho plays an important role in several cellular functions. RhoA, which is a member of the Rho family, initiates cellular processes that act on its direct downstream effector Rho-associated kinase (ROCK). ROCK inhibition protects against dopaminergic cell death induced by dopaminergic neurotoxins. It has been suggested that ROCK inhibition activates neuroprotective survival cascades in dopaminergic neurons. Axon-stabilizing effects in damaged neurons may represent another mechanism of neuroprotection of dopaminergic neurons by ROCK inhibition. However, it has been shown that microglial cells play a crucial role in neuroprotection by ROCK inhibition and that activation of microglial ROCK mediates major components of the microglial inflammatory response. Additional mechanisms such as interaction with autophagy may also contribute to the neuroprotective effects of ROCK inhibition. Interestingly, ROCK interacts with several brain factors that play a major role in dopaminergic neuron vulnerability such as NADPH-oxidase, angiotensin, and estrogen. ROCK inhibition may provide a new neuroprotective strategy for Parkinson’s disease. This is of particular interest because ROCK inhibitors are currently used against vascular diseases in clinical practice. However, it is necessary to develop more potent and selective ROCK inhibitors to reduce side effects and enhance the efficacy.

Gender differences in autoimmune disease

Autoimmune diseases are a range of diseases in which the immune response to self-antigens results in damage or dysfunction of tissues. Autoimmune diseases can be systemic or can affect specific organs or body systems. For most autoimmune diseases there is a clear sex difference in prevalence, whereby females are generally more frequently affected than males. In this review, we consider gender differences in systemic and organ-specific autoimmune diseases, and we summarize human data that outlines the prevalence of common autoimmune diseases specific to adult males and females in countries commonly surveyed. We discuss possible mechanisms for sex specific differences including gender differences in immune response and organ vulnerability, reproductive capacity including pregnancy, sex hormones, genetic predisposition, parental inheritance, and epigenetics. Evidence demonstrates that gender has a significant influence on the development of autoimmune disease. Thus, considerations of gender should be at the forefront of all studies that attempt to define mechanisms that underpin autoimmune disease.

Sex differences in Parkinson's disease and other movement disorders

Movement disorders including Parkinson's disease (PD), Huntington's disease (HD), chorea, tics, and Tourette's syndrome (TS) display sex differences in disease susceptibility, disease pathogenesis, and clinical presentation. PD is more common in males than in females. Epidemiologic studies suggest that exposure to endogenous and exogenous estrogen contributes to these sex differences. There is extensive evidence that estrogen prevents dopaminergic neuron depletion induced by neurotoxins in PD animal models and therefore is neuroprotective. Estrogen may also decrease the efficacy of other neuroprotective substances such as caffeine in females but not males. Sex chromosomes can exert effects independent of sex steroid hormones on the development and maintenance of the dopamine system. As a result of hormone, chromosome and other unknown effects, there are sexual dimorphisms in the basal ganglia, and at the molecular levels in dopaminergic neurons that may lead to distinct mechanisms of pathogenesis in males and females. In this review, we summarize the evidence that estrogen and selective estrogen receptor modulators are neuroprotective in PD and discuss potential mechanisms of action. We also briefly review how sex differences in basal ganglia function and dopaminergic pathways may impact HD, chorea, and tics/Tourette's syndrome. Further understanding of these sex differences may lead to novel therapeutic strategies for prevention and treatment of these diseases.

Age-related changes in brain support cells: Implications for stroke severity

Stroke is one of the leading causes of adult disability and the fourth leading cause of mortality in the US. Stroke disproportionately occurs among the elderly, where the disease is more likely to be fatal or lead to long-term supportive care. Animal models, where the ischemic insult can be controlled more precisely, also confirm that aged animals sustain more severe strokes as compared to young animals. Furthermore, the neuroprotection usually seen in younger females when compared to young males is not observed in older females. The preclinical literature thus provides a valuable resource for understanding why the aging brain is more susceptible to severe infarction. In this review, we discuss the hypothesis that stroke severity in the aging brain may be associated with reduced functional capacity of critical support cells. Specifically, we focus on astrocytes, that are critical for detoxification of the brain microenvironment and endothelial cells, which play a crucial role in maintaining the blood brain barrier. In view of the sex difference in stroke severity, this review also discusses studies of middle-aged acyclic females as well as the effects of the estrogen on astrocytes and endothelial cells.

Gonadal hormones and the control of reactive gliosis

Astrocytes and microglia respond to central nervous system (CNS) injury with changes in morphology, proliferation, migration and expression of inflammatory regulators. This phenomenon is known as reactive gliosis. Activation of astrocytes and microglia after acute neural insults, such as stroke or traumatic CNS injury, is considered to be an adaptive response that contributes to minimize neuronal damage. However, reactive gliosis may amplify CNS damage under chronic neurodegenerative conditions. Progesterone, estradiol and testosterone have been shown to control reactive gliosis in different models of CNS injury, modifying the number of reactive astrocytes and reactive microglia and the expression of anti-inflammatory and proinflammatory mediators. The actions of gonadal hormones on reactive gliosis involve different mechanisms, including the modulation of the activity of steroid receptors, such as estrogen receptors α and β, the regulation of nuclear factor-κB mediated transcription of inflammatory molecules and the recruitment of the transcriptional corepressor c-terminal binding protein to proinflammatory promoters. In addition, the Parkinson's disease related gene parkin and the endocannabinoid system also participate in the regulation of reactive gliosis by estradiol. The control exerted by gonadal hormones on reactive gliosis may affect the response of neural tissue to trauma and neurodegeneration and may contribute to sex differences in the manifestation of neurodegenerative diseases. However, the precise functional consequences of the regulation of reactive gliosis by gonadal hormones under acute and chronic neurodegenerative conditions are still not fully clarified.

Curcumin protects nigrostriatal dopaminergic neurons and reduces glial activation in 6-hydroxydopamine hemiparkinsonian mice model

This study investigated the effects of curcumin on nigrostriatal dopaminergic (DA) neurons and glial response in 6-hydroxydopamine (6-OHDA) hemiparkinsonian mice. Following unilateral intrastriatal 6-OHDA injection, mice were daily injected with curcumin for seven days, beginning on the day of lesion. Seven days after 6-OHDA lesioning, sections from the striatum and the substantia nigra pars compacta (SNpc) were collected and immunohistochemically stained for DA neurons and reactive glia. Curcumin decreased 6-OHDA-induced loss of nigral tyrosine hydroxylase-immunoreactive (TH-IR) neurons and striatal TH-IR fibers. The neuroprotection was coincided with a significant attenuation of microglial and astroglial reaction in the SNpc and the striatum. These results suggest that the neuroprotective effects of curcumin in 6-OHDA-lesioned mice may be mediated through its anti-inflammatory properties or direct protection on nigral DA neurons, thereby reducing neuronal injury-induced glial activation.

Selective oestrogen receptor modulators decrease the inflammatory response of glial cells

Neuroinflammation comprises a feature of many neurological disorders that is accompanied by the activation of glial cells and the release of pro-inflammatory cytokines and chemokines. Such activation is a normal response oriented to protect neural tissue and it is mainly regulated by microglia and astroglia. However, excessive and chronic activation of glia may lead to neurotoxicity and may be harmful for neural tissue. The ovarian hormone oestradiol exerts protective actions in the central nervous system that, at least in part, are mediated by a reduction of reactive gliosis. Several selective oestrogen receptor modulators may also exert neuroprotective effects by controlling glial inflammatory responses. Thus, tamoxifen and raloxifene decrease the inflammatory response caused by lipopolysaccharide, a bacterial endotoxin, in mouse and rat microglia cells in vitro. Tamoxifen and raloxifene are also able to reduce microglia activation in the brain of male and female rats in vivo after the peripheral administration of lipopolysaccharide. In addition, tamoxifen decreases the microglia inflammatory response induced by irradiation. Furthermore, treatment with tamoxifen and raloxifene resulted in a significant reduction of the number of reactive astrocytes in the hippocampus of young, middle-aged and older female rats after a stab wound injury. Tamoxifen, raloxifene and the new selective oestrogen receptor modulators ospemifene and bazedoxifene decrease the expression and release of interleukine-6 and interferon-γ inducible protein-10 in cultured astrocytes exposed to lipopolysaccharide. Ospemifene and bazedoxifene exert anti-inflammatory effects in astrocytes by a mechanism involving classical oestrogen receptors and the inhibition of nuclear factor-kappa B p65 transactivation. These data suggest that oestrogenic compounds are candidates to counteract brain inflammation under neurodegenerative conditions by targeting the production and release of pro-inflammatory molecules by glial cells.

Dopaminergic neuroprotection of hormonal replacement therapy in young and aged menopausal rats: role of the brain angiotensin system

There is a lack of consensus about the effects of the type of menopause (surgical or natural) and of oestrogen replacement therapy on Parkinson's disease. The effects of the timing of replacement therapy and the female's age may explain the observed differences in such effects. However, the mechanisms involved are poorly understood. The renin-angiotensin system mediates the beneficial effects of oestrogen in several tissues, and we have previously shown that dopaminergic cell loss is enhanced by angiotensin via type 1 receptors, which is activated by ageing. In rats, we compared the effects of oestrogen replacement therapy on 6-hydroxydopamine-induced dopaminergic degeneration, nigral renin-angiotensin system activity, activation of the nicotinamide adenine dinucleotide phosphate oxidase complex and levels of the proinflammatory cytokine interleukin-1β in young (surgical) menopausal rats and aged menopausal rats. In young surgically menopausal rats, the renin-angiotensin system activity was higher (i.e. higher angiotensin converting enzyme activity, higher angiotensin type-1 receptor expression and lower angiotensin type-2 receptor expression) than in surgically menopausal rats treated with oestrogen; the nicotinamide adenine dinucleotide phosphate oxidase activity and interleukin-1β expression were also higher in the first group than in the second group. In aged menopausal rats, the levels of nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity were similar to those observed in surgically menopausal rats. However, oestrogen replacement therapy significantly reduced 6-hydroxydopamine-induced dopaminergic cell loss in young menopausal rats but not in aged rats. Treatment with oestrogen also led to a more marked reduction in nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity in young surgically menopausal rats (treated either immediately or after a period of hypo-oestrogenicity) than in aged menopausal rats. Interestingly, treatment with the angiotensin type-1 receptor antagonist candesartan led to remarkable reduction in renin-angiotensin system activity and dopaminergic neuron loss in both groups of menopausal rats. This suggests that manipulation of the brain renin-angiotensin system may be an efficient approach for the prevention or treatment of Parkinson's disease in oestrogen-deficient females, together with or instead of oestrogen replacement therapy.

Renin angiotensin system and gender differences in dopaminergic degeneration

BACKGROUND

There are sex differences in dopaminergic degeneration. Men are approximately two times as likely as premenopausal women of the same age to develop Parkinson's disease (PD). It has been shown that the local renin angiotensin system (RAS) plays a prominent role in sex differences in the development of chronic renal and cardiovascular diseases, and there is a local RAS in the substantia nigra and dopaminergic cell loss is enhanced by angiotensin via type 1 (AT1) receptors.

RESULTS

In the present study, we observed that intrastriatal injection of 6-hydroxydopamine induced a marked loss of dopaminergic neurons in the substantia nigra of male rats, which was significantly higher than the loss induced in ovariectomized female rats given estrogen implants (i.e. rats with estrogen). However, the loss of dopaminergic neurons was significantly lower in male rats treated with the AT1 antagonist candesartan, and similar to that observed in female rats with estrogen. The involvement of the RAS in gender differences in dopaminergic degeneration was confirmed with AT1a-null mice lesioned with the dopaminergic neurotoxin MPTP. Significantly higher expression of AT1 receptors, angiotensin converting enzyme activity, and NADPH-oxidase complex activity, and much lower levels of AT2 receptors were observed in male rats than in female rats with estrogen.

CONCLUSIONS

The results suggest that brain RAS plays a major role in the increased risk of developing PD in men, and that manipulation of brain RAS may be an efficient approach for neuroprotective treatment of PD in men, without the feminizing effects of estrogen.

Estrogens regulate neuroinflammatory genes via estrogen receptors α and β in the frontal cortex of middle-aged female rats

Background

Estrogens exert anti-inflammatory and neuroprotective effects in the brain mainly via estrogen receptors α (ERα) and β (ERβ). These receptors are members of the nuclear receptor superfamily of ligand-dependent transcription factors. This study was aimed at the elucidation of the effects of ERα and ERβ agonists on the expression of neuroinflammatory genes in the frontal cortex of aging female rats.

Methods

To identify estrogen-responsive immunity/inflammation genes, we treated middle-aged, ovariectomized rats with 17β-estradiol (E2), ERα agonist 16α-lactone-estradiol (16α-LE2) and ERβ agonist diarylpropionitrile (DPN), or vehicle by Alzet minipump delivery for 29 days. Then we compared the transcriptomes of the frontal cortex of estrogen-deprived versus ER agonist-treated animals using Affymetrix Rat230 2.0 expression arrays and TaqMan-based quantitative real-time PCR. Microarray and PCR data were evaluated by using Bioconductor packages and the RealTime StatMiner software, respectively.

Results

Microarray analysis revealed the transcriptional regulation of 21 immunity/inflammation genes by 16α-LE2. The subsequent comparative real-time PCR study analyzed the isotype specific effects of ER agonists on neuroinflammatory genes of primarily glial origin. E2 regulated the expression of sixteen genes, including down-regulation of complement C3 and C4b, Ccl2, Tgfb1, macrophage expressed gene Mpeg1, RT1-Aw2, Cx3cr1, Fcgr2b, Cd11b, Tlr4 and Tlr9, and up-regulation of defensin Np4 and RatNP-3b, IgG-2a, Il6 and ER gene Esr1. Similar to E2, both 16α-LE2 and DPN evoked up-regulation of defensins, IgG-2a and Il6, and down-regulation of C3 and its receptor Cd11b, Ccl2, RT1-Aw2 and Fcgr2b.

Conclusions

These findings provide evidence that E2, 16α-LE2 and DPN modulate the expression of neuroinflammatory genes in the frontal cortex of middle-aged female rats via both ERα and ERβ. We propose that ERβ is a promising target to suppress regulatory functions of glial cells in the E2-deprived female brain and in various neuroinflammatory diseases.

An in vitro experimental model of neuroinflammation: the induction of interleukin-6 in murine astrocytes infected with Theiler's murine encephalomyelitis virus, and its inhibition by oestrogenic receptor modulators

This paper describes an experimental model of neuroinflammation based on the production of interleukin-6 (IL-6) by neural glial cells infected with Theiler's murine encephalomyelitis virus (TMEV). Production of IL-6 mRNA in mock-infected and TMEV-infected SJL/J murine astrocytes was examined using the Affymetrix murine genome U74v2 DNA microarray. The IL-6 mRNA from infected cells showed an eightfold increase in hybridization to a sequence encoding IL-6 located on chromosome number 5. Quantitative real-time reverse transcription PCR (qPCR) was used to study the regulation of IL-6 expression. The presence of IL-6 in the supernatants of TMEV-infected astrocyte cultures was quantified by ELISA and found to be weaker than in cultures of infected macrophages. The IL-6 was induced by whole TMEV virions, but not by Ad.βGal adenovirus, purified TMEV capsid proteins, or UV-inactivated virus. Two recombinant inflammatory cytokines, IL-1α and tumour necrosis factor-α were also found to be potent inducers of IL-6. The secreted IL-6 was biologically active because it fully supported B9 hybridoma proliferation in a [(3) H]thymidine incorporation bioassay. The cerebrospinal fluid of infected mice contained IL-6 during the acute encephalitis phase, peaking at days 2-4 post-infection. Finally, this in vitro neuroinflammation model was fully inhibited, as demonstrated by ELISA and qPCR, by five selective oestrogen receptor modulators.

Manganese-induced NF-kappaB activation and nitrosative stress is decreased by estrogen in juvenile mice

Manganese toxicity can cause a neurodegenerative disorder affecting cortical and basal ganglia structures with a neurological presentation resembling features of Parkinson's disease. Children are more sensitive to Mn-induced neurological dysfunction than adults, and recent studies from our laboratory revealed a marked sensitivity of male juvenile mice to neuroinflammatory injury from Mn, relative to females. To determine the role of estrogen (E2) in mediating sex-dependent vulnerability to Mn-induced neurotoxicity, we exposed transgenic mice expressing an NF-κB-driven enhanced green fluorescent protein (EGFP) reporter construct (NF-κB-EGFP mice) to Mn, postulating that supplementing male mice with E2 during juvenile development would attenuate neuroinflammatory changes associated with glial activation, including expression of inducible nitric oxide synthase (NOS2) and neuronal protein nitration. Juvenile NF-κB-EGFP mice were separated in groups composed of females, males, and males surgically implanted with Silastic capsules containing 25 μg of 17-β-estradiol (E2) or vehicle control. Mice were then treated with 0 or 100 mg/Kg MnCl(2) by intragastric gavage from postnatal days 21-34. Manganese treatment caused alterations in levels of striatal dopamine, as well as increases in NF-κB reporter activity and NOS2 expression in both microglia and astrocytes that were prevented by supplementation with E2. E2 also decreased neuronal protein nitration in Mn-treated mice and inhibited apoptosis in striatal neurons cocultured with Mn-treated astrocytes in vitro. These data indicate that E2 protects against Mn-induced neuroinflammation in developing mice and that NF-κB is an important regulator of neuroinflammatory gene expression in glia associated with nitrosative stress in the basal ganglia during Mn exposure.

Involvement of SRC-suppressed C kinase substrate in neuronal death caused by the lipopolysaccharide-induced reactive astrogliosis

Src-suppressed C kinase substrate (SSeCKS), a protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein, regulating the inflammatory process. In the process of spinal inflammatory diseases by LPS intraspinal injection, expression of SSeCKS in the spinal cord was increased, mainly in active astrocytes and neurons. Induced SSeCKS was colabeled with terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling (an apoptosis maker) in the late inflammation processes. These results indicated that SSeCKS might correlate with the inflammatory reaction and late neurodegeneration after LPS injection. A cell type-specific action for SSeCKS was further studied within C6 cells and PC12 cells. Knockdown of SSeCKS by small-interfering RNAs (siRNAs) blocked the LPS-induced inducible nitric oxide synthase (iNOS) expression in C6 cells, while overexpression SSeCKS enhanced iNOS expression. SSeCKS is also participated in regulation of PC12 cell viability. Loss of SSeCKS rescued PC12 cell viability, and excessive SSeCKS exacerbated the cell death upon conditioned medium and tumor necrosis factor-alpha exposure. This study delineates that SSeCKS may be important for host defenses in spinal inflammation and suggests a valuable molecular mechanism by which astrocytes modify neuronal viability during pathological states.

Estrogen reduces BDNF level, but maintains dopaminergic cell density in the striatum of MPTP mouse model

Degeneration of dopaminergic (DA) axons in the striatum triggers upregulation of striatal trophic activity and striatal DA neuronal number in animal models of Parkinson's disease (PD). The present study investigated the effects of 17beta-estradiol (E2) on brain-derived neurotrophic factor (BDNF) expression and the density of DA neurons in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model in correlation with nigrostriatal DA innervation. Adult male C57Bl/6 mice were treated with E2 or vehicle for 11 days. Following 5 days of E2 or vehicle pretreatment, animals were injected with MPTP on day 6. On day 11, all mice were sacrificed, and the striatum were collected and processed for tyrosine hydroxylase (TH) and BDNF immunohistochemistry. Striatal TH-immunoreactive (IR) neurons were counted. Extent of DA innervation and BDNF expression in the striatum were assessed by measuring optical density of TH and BDNF immunoreactivity, respectively. Pretreatment with E2 partially prevented DA denervation and decreased striatal BDNF upregulation triggered by MPTP, but maintained the density of striatal TH-IR neurons to that observed in MPTP group. These findings suggest that estrogen protection of nigrostriatal DA axons against MPTP as well as preservation of the striatal TH-IR cell density in MPTP/E2 mice may be not mediated by BDNF.

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.

Peripheral vs. Central Sex Steroid Hormones in Experimental Parkinson's Disease

The nigrostriatal dopaminergic (NSDA) pathway degenerates in Parkinson's disease (PD), which occurs with approximately twice the incidence in men than women. Studies of the influence of systemic estrogens in females suggest sex hormones contribute to these differences. In this review we analyze the evidence revealing great complexity in the response of the healthy and injured NSDA system to hormonal influences, and emphasize the importance of centrally generated estrogens. At physiological levels, circulating estrogen (in females) or estrogen precursors (testosterone in males, aromatized to estrogen centrally) have negligible effects on dopaminergic neuron survival in experimental PD, but can modify striatal dopamine levels via actions on the activity or adaptive responses of surviving cells. However, these effects are sexually dimorphic. In females, estradiol promotes adaptive responses in the partially injured NSDA pathway, preserving striatal dopamine, whereas in males gonadal steroids and exogenous estradiol have a negligible or even suppressive effect, effectively exacerbating dopamine loss. On balance, the different effects of gonadal factors in males and females contribute to sex differences in experimental PD. Fundamental sex differences in brain organization, including the sexually dimorphic networks regulating NSDA activity are likely to underpin these responses. In contrast, estrogen generated locally appears to preserve striatal dopamine in both sexes. The available data therefore highlight the need to understand the biological basis of sex-specific responses of the NSDA system to peripheral hormones, so as to realize the potential for sex-specific, hormone-based therapies in PD. Furthermore, they suggest that targeting central steroid generation could be equally effective in preserving striatal dopamine in both sexes. Clarification of the relative roles of peripheral and central sex steroid hormones is thus an important challenge for future studies.

Estrogen or estrogen receptor agonist inhibits lipopolysaccharide induced microglial activation and death

Inflammation is an important pathogenic mechanism in many neurodegenerative disorders. Activated microglia play a pivotal role in releasing pro-inflammatory factors including interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), and cyclooxygenase-2 (COX-2) for inducing inflammation. While microglia mediated inflammation is essential in maintaining CNS homeostasis, chronic inflammation results in activation of proteases for cell death. Here, we examined the effect of PPT (estrogen receptor α agonist), DPN (estrogen receptor β agonist), and estrogen on rat primary microglia following exposure to lipopolysaccharide (LPS). Exposure of microglia to LPS (200 ng/ml) for 24 h induced cell death. After LPS toxicity for 15 min, microglia were treated with 25 nM PPT, 25 nM DPN, or 100 nM estrogen that prevented cell death by attenuating the release of IL-1α, IL-1β, TNF-α, and COX-2. Treatment of cells with 100 nM fulvestrant (estrogen receptor antagonist) prior to addition of PPT, DPN, or estrogen significantly decreased their ability to prevent cell death, indicating involvement of estrogen receptor (ER) in providing PPT, DPN, or estrogen mediated cytoprotection. Reverse transcriptase polymerase chain reaction (RT-PCR) analyses showed alterations in mRNA expression of Bax, Bcl-2, calpain, and calpastatin during apoptosis. We also examined mRNA expression of ERβ and ERα following exposure of microglia to LPS and subsequent treatment with PPT, DPN, or estrogen. We found that estrogen or estrogen receptor agonists upregulated expression of ERs. Overall, results indicate that estrogen receptor agonist or estrogen uses a receptor mediated pathway to protect microglia from LPS toxicity.

Aquaporin-4 knockout enhances astrocyte toxicity induced by 1-methyl-4-phenylpyridinium ion and lipopolysaccharide via increasing the expression of cytochrome P4502E1

The role of aquaporin-4 (AQP4) in the regulation of astrocytes function has been widely investigated. However, there is little information about its contribution to the drug metabolism enzymes such as Cytochrome P4502E1. In the present study, we investigated whether AQP4 is involved in the process of the cell damage caused by MPP(+) and LPS through regulating the expression of CYP2E1 in astrocytes. Compared to the wild-type, in primary astrocytes, AQP4 knockout increased the cell damage and the reactive oxygen species (ROS) production which were induced by MPP(+), LPS and ethanol. Notably, AQP4 knockout enhanced the up-regulation of the expression of CYP2E1 in astrocytes exposed to MPP(+), LPS and ethanol. Furthermore, Diallylsulphide (DAS), a CYP2E1 inhibitor, partially or almost abolished the cell injury and the ROS production of the astrocytes induced by MPP(+) and LPS. These findings indicate AQP4 protects astrocytes from the damage caused by MPP(+) and LPS through reducing the ROS production correlation to the diminished expression of CYP2E1.

Estrogen and angiotensin interaction in the substantia nigra. Relevance to postmenopausal Parkinson's disease

Epidemiological studies have reported that the incidence of Parkinson's disease (PD) is higher in postmenopausal than in premenopausal women of similar age. Several laboratory observations have revealed that estrogen has protective effects against dopaminergic toxins. The mechanism by which estrogen protects dopaminergic neurons has not been clarified, although estrogen-induced attenuation of the neuroinflammatory response plays a major role. We have recently shown that activation of the nigral renin-angiotensin system (RAS), via type 1 (AT1) receptors, leads to NADPH complex and microglial activation and induces dopaminergic neuron death. In the present study we investigated the effect of ovariectomy and estrogen replacement on the nigral RAS and on dopaminergic degeneration induced by intrastriatal injection of 6-OHDA. We observed a marked loss of dopaminergic neurons in ovariectomized rats treated with 6-OHDA, which was significantly reduced by estrogen replacement or treatment with the AT1 receptor antagonist candesartan. We also observed that estrogen replacement induces significant downregulation of the activity of the angiotensin converting enzyme as well as downregulation of AT1 receptors, upregulation of AT2 receptors and downregulation of the NADPH complex activity in the substantia nigra in comparison with ovariectomized rats. The present results suggest that estrogen-induced down-regulation of RAS and NADPH activity may be associated with the reduced risk of PD in premenopausal women, and increased risk in conditions causing early reduction in endogenous estrogen, and that manipulation of brain RAS system may be an efficient approach for the prevention or coadjutant treatment of PD in estrogen-deficient women.

The impact of age and gender on the striatal astrocytes activation in murine model of Parkinson's disease

OBJECTIVE

The aim of the present study was to determine how aging and gender influence the response of astrocytes to 1-methyl-4-phenyl-1,2,3,6-tetrahydropiridine (MPTP) intoxication.

MATERIALS AND METHODS

To asses the MPTP-induced astrocytes activation in nigro-striatal system, we measured the temporal changes in mRNA and protein expression of the specific astrocytic marker, glial fibrillary acidic protein (GFAP; by RT-PCR and Western blot), in the striatum of male and female C57BL/6 mice (2 and 12-month old) after 6 h and 1, 3, 7, 14 and 21 days post-intoxication.

RESULTS

We observed the increases of GFAP mRNA level post-MPTP intoxication in both young and aging males only at early time points, whereas in females (both ages) also at later time points. We noticed maximal increase of GFAP protein content on the 3rd day post-intoxication in young and aged males, whereas in females at the 7-daytime point.

CONCLUSIONS

The present results provide additional information of potential relevance to understand the mechanisms of gender and age-related difference in susceptibility of nigro-striatal system to MPTP insult.

Selective estrogen receptor modulators decrease the production of interleukin-6 and interferon-gamma-inducible protein-10 by astrocytes exposed to inflammatory challenge in vitro

Expression of proinflammatory molecules by glial cells is involved in the pathophysiological changes associated with chronic neurological diseases. Under pathological conditions, astrocytes release a number of proinflammatory molecules, such as interleukin-6 (IL-6) and interferon-gamma-inducible protein-10 (IP-10). The ovarian hormone estradiol exerts protective effects in the central nervous system that, at least in part, may be mediated by a reduction of local inflammation. This study was designed to assess whether estradiol affects the production of IL-6 and IP-10 by primary cultures of newborn mice astrocytes exposed to lipopolysaccharide (LPS), a bacterial endotoxin known to cause neuroinflammation. In addition, the possible anti-inflammatory effect of several selective estrogen receptor modulators (SERMs) was also assessed. LPS induced an increase in the expression of IL-6 and IP-10 mRNA levels in astrocytes and an increase in IL-6 and IP-10 protein levels in the culture medium. These effects of LPS were impaired by estradiol and by the four SERMs tested in our study: tamoxifen, raloxifene, ospemifene, and bazedoxifene. All SERMs tested showed a similar effect on IL-6 and IP-10 mRNA levels, but raloxifene and ospemifene were more effective than tamoxifen and bazedoxifene in reducing protein levels in LPS-treated cultures. Finally, we report that news SERMs, ospemifene and bazedoxifene, exert anti-inflammatory actions by a mechanism involving classical estrogen receptors and by the inhibition of LPS-induced NFkappaB p65 transactivation. The results suggest that estrogenic compounds may be candidates to counteract brain inflammation under neurodegenerative conditions by targeting the production and release of proinflammatory molecules by astrocytes.

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.

Selective estrogen receptor modulators decrease reactive astrogliosis in the injured brain: effects of aging and prolonged depletion of ovarian hormones

After brain injury, astrocytes acquire a reactive phenotype characterized by a series of morphological and molecular modifications, including the expression of the cytoskeletal protein vimentin. Previous studies have shown that estradiol down-regulates reactive astrogliosis. In this study we assessed whether raloxifene and tamoxifen, two selective estrogen receptor modulators, have effects similar to estradiol in astrocytes. We also assessed whether aging and the timing of estrogenic therapy after ovariectomy influence the action of the estrogenic compounds. Four groups of animals were studied: 1) young rats, ovariectomized at 2 months of age; 2) middle-aged rats, ovariectomized at 8 months of age; 3) aged rats, ovariectomized at 18 months of age; and 4) aged rats, ovariectomized at 2 months and sham operated at 18 months of age. Fifteen days after ovariectomy or sham surgery, animals received a stab wound brain injury and the treatment with the estrogenic compounds. The number of vimentin-immunoreactive astrocytes after injury was significantly higher in the hippocampus of aged rats after a long-term ovariectomy compared with aged animals after a short-term ovariectomy and middle-aged rats. In addition, reactive astrocytes were more numerous in the two groups of aged animals than in young animals. Despite these differences, the estrogenic compounds reduced reactive astrogliosis in all animal groups. These findings indicate that estradiol, raloxifene, and tamoxifen are potential candidates for the control of astrogliosis in young and older individuals and after a prolonged depletion of ovarian hormones.

The therapeutic potential of LRRK2 and alpha-synuclein in Parkinson's disease

Current treatments for Parkinson's disease fail to modify disease progression, and the underlying pathogenic mechanisms remain elusive. The identification of specific targets responsible for disease will aid in the development of relevant model systems and the discovery of neuroprotective and neurorestorative therapies. Two promising protein candidates, alpha-synuclein and LRRK2, offer unique insight into the molecular basis of disease and the potential to intervene in pathogenesis. Although multiple lines of evidence support alpha-synuclein and LRRK2 as robust targets for therapy, the connection between protein function and neurodegeneration is unclear. Technology capable of mitigating alpha-synuclein and LRRK2 disease-associated function will ultimately be required before the true value of these proteins as therapeutic targets can be discerned.

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.