Neuroprotective effects of nonfeminizing estrogens in retinal photoreceptor neurons

A two sample Mendelian randomized study of the association of sex hormones and behavioral and clinical risk factors with macular hole

Macular hole (MH) is a disease of the vitreoretinal interface that develops in relation to age and gender, and is 3.3 times more prevalent in females than in males. However, it remains inconclusive whether gender plays a role in the pathogenesis of MH. We adopted a two-sample Mendelian randomisation (MR) analysis to explore the relationship between free testosterone, bioavailable testosterone, oestradiol, menopause, smoking, alcohol consumption, type 2 diabetes, diastolic blood pressure, and systolic blood pressure and the risk of MH. We found that genetically predicted free testosterone levels in males were significantly associated with an increased risk of MH (IVW model: OR = 1.642; 95% CI, 1.162-2.322; P = 0.005), while genetically predicted oestradiol levels in females were significantly associated with a reduced risk of MH (IVW model: OR = 0.711; 95% CI, 0.517-0.978; P = 0.036). A sensitivity analysis verified the robustness of the causal relationship. MVMR results indicate that oestradiol in females is associated with MH risk using the IVW method (OR = 0.66; 95% CI, 0.47-0.88; P = 0.011). Our study demonstrates that the genetic risk of free testosterone in males and oestradiol in females may be correlated with MH risk.

Evidence-based neuroprotective potential of nonfeminizing estrogens: In vitro and in vivo studies

Menopause weakens the brain's structural integrity and increases its susceptibility to a range of degenerative and mental illnesses. 17β estradiol (17βE2) exhibits potent neuroprotective properties. Exogenous estrogen supplementation provides neuroprotection, but the findings presented by the Million Women Study (MWS) and the Women's Health Initiative (WHI), as well as the increased risk of endometrial cancer, breast cancer and venous thromboembolism associated with estrogen use, have cast doubt on its clinical use for neurological disorders. Thus, the objective of our review article is to compile all in vitro and in vivo studies conducted till date demonstrating the neuroprotective potential of nonfeminizing estrogens. This objective has been achieved by gathering various research and review manuscripts from different records such as PubMed, Embase, Scopus, Google Scholar, Web of Science and OVID, using different terms like 'estrogen deficiency, 17β estradiol, non-feminising estrogens, and brain disorder'. However, recent evidence has revealed the contribution of numerous non-estrogen receptor-dependent pathways in neuroprotective effects of estrogen. In conclusion, synthetic nonfeminizing estrogens that have little or no ER binding but are equally powerful (and in some cases more potent) in delivering neuroprotection are emerging as viable and potential alternatives.

Astragaloside IV attenuates ferroptosis and protects against iron overload-induced retinal injury

Retinal injury may be exacerbated by iron overload. Astragaloside IV (AS-IV) has potential applications in the food and healthcare industry to promote eye health. We sought to determine the mechanisms responsible for the protective effects of AS-IV on photoreceptor and retinal pigment epithelium cell death induced by iron overload. We conducted in vitro and in vivo experiments involving AS-IV pretreatment. We tested AS-IV for its ability to protect iron-overload mice from retinal injury. In particular, we analyzed the effects of AS-IV on iron overload-induced ferroptosis in 661W and ARPE-19 cells. AS-IV not only attenuated iron deposition and retinal injury in iron-overload mice but also effectively reduced iron overload-induced ferroptotic cell death in 661W and ARPE-19 cells. AS-IV effectively prevented ferroptosis by inhibiting iron accumulation and lipid peroxidation. In addition, inhibiting nuclear factor erythroid 2-related factor 2 (Nrf2) eliminated the protective effect of AS-IV against ferroptosis. The results suggest that ferroptosis might be a significant cause of retinal cell death associated with iron overload. AS-IV provides protection from iron overload-induced ferroptosis, partly by activating the Nrf2 signaling pathway.

Etiology of Idiopathic Macular Holes in the Light of Estrogen Hormone

The aim of this review was to identify a new potential explanation for the development of macular holes in relation to the female sex and to explain the possible underlying pathways. This approach was based on the evaluation of anatomical, physiological, and morphological analyses currently available in the literature. The findings showed that estrogen exerts a protective effect on the neuroretina and may influence Müller and cone cells. Both cell types are responsible for the building of the fovea structure. However, this protection may be lost due to the sudden decrease in estrogen levels during menopause. In conclusion, the fovea cones, through its sensitivity to estrogen and high energy consumption, may be very vulnerable to damage caused by a sudden changes in the concentration of estrogen in menopausal females. Such changes may result in cone degeneration, and thus a destroyed structure of the fovea, and may lead to the development of a hole in the fovea, as in the case of macular holes. This review revealed that under the decreasing influence of estrogen may cones play a key role with regard to the etiology of the development of macular holes. This aspect may be of strategic importance in prophylactic therapy for the prevention of the development of macular holes in premenopausal females or after ocular trauma.

Sex-related differences in retinal function in Wistar rats: implications for toxicity and safety studies

Introduction: Wistar Han rats are a preferred strain of rodents for general toxicology and safety pharmacology studies in drug development. In some of these studies, visual functional tests that assess for retinal toxicity are included as an additional endpoint. Although the influence of gender on human retinal function has been documented for more than 6 decades, preclinically it is still uncertain if there are differences in retinal function between naïve male and female Wistar Han rats. Methods: In this study, sex-related differences in the retinal function were quantified by analyzing electroretinography (ERG) in 7-9-week-old (n = 52 males and 51 females) and 21-23-week-old Wistar Han rats (n = 48 males and 51 females). Optokinetic tracking response, brainstem auditory evoked potential, ultrasonic vocalization and histology were tested and evaluated in a subset of animals to investigate the potential compensation mechanisms of spontaneous blindness. Results/Discussion: Absence of scotopic and photopic ERG responses was found in 13% of 7-9-week-old (7/52) and 19% of 21-23-week-old males (9/48), but none of female rats (0/51). The averaged amplitudes of rod- and cone-mediated ERG b-wave responses obtained from males were significantly smaller than the amplitudes of the same responses from age-matched females (-43% and -26%, respectively) at 7-9 weeks of age. There was no difference in the retinal and brain morphology, brainstem auditory responses, or ultrasonic vocalizations between the animals with normal and abnormal ERGs at 21-23 weeks of age. In summary, male Wistar Han rats had altered retinal responses, including a complete lack of responses to test flash stimuli (i.e., blindness), when compared with female rats at 7-9 and 21-23 weeks of age. Therefore, sex differences should be considered when using Wistar Han rats in toxicity and safety pharmacology studies with regards to data interpretation of retinal functional assessments.

Differential distribution of steroid hormone signaling networks in the human choroid-retinal pigment epithelial complex

Background

The retinal pigment epithelium (RPE), a layer of pigmented cells that lies between the neurosensory retina and the underlying choroid, plays a critical role in maintaining the functional integrity of photoreceptor cells and in mediating communication between the neurosensory retina and choroid. Prior studies have demonstrated neurotrophic effects of select steroids that mitigate the development and progression of retinal degenerative diseases via an array of distinct mechanisms of action.

Methods

Here, we identified major steroid hormone signaling pathways and their key functional protein constituents controlling steroid hormone signaling, which are potentially involved in the mitigation or propagation of retinal degenerative processes, from human proteome datasets with respect to their relative abundances in the retinal periphery, macula, and fovea.

Results

Androgen, glucocorticoid, and progesterone signaling networks were identified and displayed differential distribution patterns within these three anatomically distinct regions of the choroid-retinal pigment epithelial complex. Classical and non-classical estrogen and mineralocorticoid receptors were not identified.

Conclusion

Identified differential distribution patterns suggest both selective susceptibility to chronic neurodegenerative disease processes, as well as potential substrates for drug target discovery and novel drug development focused on steroid signaling pathways in the choroid-RPE.

Age and Sex-Related Changes in Retinal Function in the Vervet Monkey

Among the deficits in visual processing that accompany healthy aging, the earliest originate in the retina. Moreover, sex-related differences in retinal function have been increasingly recognized. To better understand the dynamics of the retinal aging trajectory, we used the light-adapted flicker electroretinogram (ERG) to functionally assess the state of the neuroretina in a large cohort of age- and sex-matched vervet monkeys (N = 35), aged 9 to 28 years old, with no signs of obvious ocular pathology. We primarily isolated the cone–bipolar axis by stimulating the retina with a standard intensity light flash (2.57 cd/s/m²) at eight different frequencies, ranging from 5 to 40 Hz. Sex-specific changes in the voltage and temporal characteristics of the flicker waveform were found in older individuals (21–28 years-old, N = 16), when compared to younger monkeys (9–20 years-old, N = 19), across all stimulus frequencies tested. Specifically, significantly prolonged implicit times were observed in older monkeys (p < 0.05), but a significant reduction of the amplitude of the response was only found in old male monkeys (p < 0.05). These changes might reflect ongoing degenerative processes targeting the retinal circuitry and the cone subsystem in particular. Altogether, our findings corroborate the existing literature in humans and other species, where aging detrimentally affects photopic retinal responses, and draw attention to the potential contribution of different hormonal environments.

Girl Power in Glaucoma: The Role of Estrogen in Primary Open Angle Glaucoma

Estrogen is essential in maintaining various physiological features in women, and a decline in estrogen levels are known to give rise to numerous unfortunate symptoms associated with menopause. To alleviate these symptoms hormone replacement therapy with estrogen is often used, and has been shown to be fruitful in improving quality of life in women suffering from postmenopausal discomforts. An often forgotten condition associated with menopause is the optic nerve disorder, glaucoma. Thus, estrogen may also have an impact in maintaining the retinal ganglion cells (RGCs), which make up the optic nerve, thereby preventing glaucomatous neurodegeneration. This review aims to provide an overview of possible associations of estrogen and the glaucoma subtype, primary open-angle glaucoma (POAG), by evaluating the current literature through a PubMed-based literature search. Multiple in vitro and in vivo studies of RGC protection, as well as clinical and epidemiological data concerning the well-defined retinal neurodegenerative disorder POAG have been reviewed. Over all, deficiencies in retinal estrogen may potentially instigate RGC loss, visual disability, and eventual blindness. Estrogen replacement therapy may therefore be a beneficial future treatment. However, more studies are needed to confirm the relevance of estrogen in glaucoma prevention.

Eye Conditions in Women

Changes in vision can have significant impact on health and quality of life. Differences between women and men have been identified in the incidence of several eye conditions. Some of these differences are a result of the greater longevity of women. However, the eye, like other organs, is susceptible to the impacts of inflammation and sex steroids. Conditions, such as thyroid eye disease, optic neuritis, and dry eye disease are related to autoimmune or inflammatory conditions and are, thus, more common among women. Idiopathic intracranial hypertension occurs disproportionately in women of childbearing age; the etiology of this condition appears to be related to both inflammatory and sex hormone fluctuations.

Molecular mechanisms and cellular events involved in the neuroprotective actions of estradiol. Analysis of sex differences

Estradiol, either from peripheral or central origin, activates multiple molecular neuroprotective and neuroreparative responses that, being mediated by estrogen receptors or by estrogen receptor independent mechanisms, are initiated at the membrane, the cytoplasm or the cell nucleus of neural cells. Estrogen-dependent signaling regulates a variety of cellular events, such as intracellular Ca²⁺ levels, mitochondrial respiratory capacity, ATP production, mitochondrial membrane potential, autophagy and apoptosis. In turn, these molecular and cellular actions of estradiol are integrated by neurons and non-neuronal cells to generate different tissue protective responses, decreasing blood-brain barrier permeability, oxidative stress, neuroinflammation and excitotoxicity and promoting synaptic plasticity, axonal growth, neurogenesis, remyelination and neuroregeneration. Recent findings indicate that the neuroprotective and neuroreparative actions of estradiol are different in males and females and further research is necessary to fully elucidate the causes for this sex difference.

Changes in visual function and ocular morphology in women who have undergone ART treatment and children born as a result of ART treatment: a systematic review

As all the structures of the human eye are characterized by sex hormone receptors, this study tested the hypothesis that assisted reproductive technology (ART) treatment influences visual function and ocular morphology in women who have undergone ART treatment and children born as a result of ART treatment. A systematic literature search of all original articles published up to August 2018 was performed using the PubMed database, including all original studies available in the literature. Review articles, studies in which participants underwent mixed interventions (i.e. other than ART treatment), studies reporting data on ocular malformations in ART offspring, and studies written in languages other than English were excluded. All selected articles were analysed to assess the level of evidence according to the Oxford Centre for Evidence-Based Medicine 2011 guidelines, and the quality of evidence according to the Grading of Recommendations Assessment, Development and Evaluation system. Although sparse data suggest that ART treatment can influence visual function and ocular morphology in women who have undergone ART treatment and children born as a result of ART treatment, the available evidence is inconclusive given its low level and quality. More high-quality research is needed to assess the potential interaction between ART treatment and the eye.

Sex Hormones and Optic Nerve Disorders: A Review

Aim: This review article presents a comprehensive overview of the literature on sex hormones (estrogens, androgens, progesterone) and optic nerve disorders, with a discussion of the implications for therapy and prevention.

Methods: Epidemiological, pre-clinical and clinical studies were reviewed.

Results: Analysis of the biological basis for a relationship between eye diseases and sex hormones showed that some types of hormones can exert a protective effect either directly on the retina and optic nerve or indirectly by modulating ocular blood flow. For example, it seems that estrogen exposure has a protective effect against glaucoma, whereas its deficit may lead to early onset of the disease. If further studies confirm the data in the literature, estrogen therapy, because of its antioxidant action, may be effective in the treatment of Leber's hereditary optic neuropathy, whereas, in the light of current studies, there does not seem to be an influence of estrogen on non-arteritic anterior ischemic optic neuritis (NAION).

Conclusions: Although there is some evidence that in some optic nerve pathologies the sex hormones seem to play an important role there are still too few studies providing evidence for its wider use in clinical practice.

Metal-Organic Frameworks as Drug Delivery Platforms for Ocular Therapeutics

Metal-organic frameworks (MOFs) have been evaluated as potential nanocarriers for intraocular incorporation of brimonidine tartrate to treat chronic glaucoma. Experimental results show that UiO-67 and MIL-100 (Fe) exhibit the highest loading capacity with values up to 50-60 wt %, whereas the performance is quite limited for MOFs with narrow cavities (below 0.8 nm, for example, UiO-66 and HKUST-1). The large loading capacity in UiO-67 is accompanied by an irreversible structural amorphization in aqueous and physiological media that promotes extended release kinetics above 12 days. Compared to the traditional drawbacks associated with the sudden release of the commercial drugs (e.g., ALPHAGAN), these results anticipate UiO-67 as a potential nanocarrier for drug delivery in intraocular therapeutics. These promising results are further supported by cytotoxicity tests using retinal photoreceptor cells (661W). Toxicity of these structures (including the metal nodes and organic ligands) for retinal cells is rather low for all samples evaluated, except for HKUST-1.

Impact of aromatase absence on murine intraocular pressure and retinal ganglion cells

We hypothesize that aromatase, an enzyme that regulates estrogen production, plays a significant role in the control of intraocular pressure (IOP) and retinal ganglion cells (RGCs). To begin to test our hypothesis, we examined the impact of aromatase absence, which completely eliminates estrogen synthesis, in male and female mice. Studies were performed with adult, age-matched wild type (WT) and aromatase knockout (ArKO) mice. IOP was measured in a masked fashion in both eyes of conscious mice at 12 and 24 weeks of age. Retinas were obtained and processed for RGC counting with a confocal microscope. IOP levels in both 12- and 24-week old female ArKO mice were significantly higher than those of age- and sex-matched WT controls. The mean increase in IOP was 7.9% in the 12-week-, and 19.7% in the 24-week-old mice, respectively. These changes were accompanied by significant 9% and 7% decreases in RGC numbers in the ArKO female mice, relative to controls, at 12- and 24-weeks, respectively. In contrast, aromatase deficiency did not lead to an increased IOP in male mice. There was a significant reduction in RGC counts in the 12-, but not 24-, week-old male ArKO mice, as compared to their age- and sex-matched WT controls. Overall, our findings show that aromatase inhibition in females is associated with elevated IOP and reduced RGC counts.

Gonadal Hormones and Retinal Disorders: A Review

AIM

Gonadal hormones are essential for reproductive function, but can act on neural and other organ systems, and are probably the cause of the large majority of known sex differences in function and disease. The aim of this review is to provide evidence for this hypothesis in relation to eye disorders and to retinopathies in particular.

METHODS

Epidemiological studies and research articles were reviewed.

RESULTS

Analysis of the biological basis for a relationship between eye diseases and hormones showed that estrogen, androgen, and progesterone receptors are present throughout the eye and that these steroids are locally produced in ocular tissues. Sex hormones can have a neuroprotective action on the retina and modulate ocular blood flow. There are differences between the male and the female retina; moreover, sex hormones can influence the development (or not) of certain disorders. For example, exposure to endogenous estrogens, depending on age at menarche and menopause and number of pregnancies, and exposure to exogenous estrogens, as in hormone replacement therapy and use of oral contraceptives, appear to protect against age-related macular degeneration (both drusenoid and neurovascular types), whereas exogenous testosterone therapy is a risk factor for central serous chorioretinopathy. Macular hole is more common among women than men, particularly in postmenopausal women probably owing to the sudden drop in estrogen production in later middle age. Progestin therapy appears to ameliorate the course of retinitis pigmentosa. Diabetic retinopathy, a complication of diabetes, may be more common among men than women.

CONCLUSION

We observed a correlation between many retinopathies and sex, probably as a result of the protective effect some gonadal hormones may exert against the development of certain disorders. This may have ramifications for the use of hormone therapy in the treatment of eye disease and of retinal disorders in particular.

The impact of combined oral contraceptives on ocular tissues: a review of ocular effects

The aim of this manuscript is to review the action and adverse effects of combined oral contraceptives (COCs) on ocular tissues. The percentage of unwanted pregnancies and the subsequent abortions make contraception crucial worldwide. Over 100 million women around the world use common contraceptive methods, including intrauterine devices, combined estrogen and progestin oral contraceptives, as well as progestin only preparations (oral contraceptives, implants or injections). COCs are widely used for contraception, but they are also indicated in menorrhagia, endometriosis, acne and hirsutism, fibroid uterus and premenstrual syndrome. However, they have been associated with high rates of cardiovascular events, venous thromboembolic disease, ischemic strokes and breast cancer. The incidence of COCs-related ocular complications is estimated to be 1 in 230 000, including dry eye symptoms, corneal edema, lens opacities and retinal neuro-ophthalmologic or vascular complications. We may infer that the serious ocular complications of COCs can be prevented by eliminating the estrogen dosage and choosing third-generation progestins. In any case, doctors should take into consideration the systemic and ocular history of the patients before selecting any method of contraception.

Oral Contraceptive Use and Prevalence of Self-Reported Glaucoma or Ocular Hypertension in the United States

PURPOSE

To investigate the association between oral contraceptive (OC) use and glaucoma prevalence in the United States.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 3406 female participants, aged 40 years or older, from the 2005 to 2008 National Health and Nutrition Examination Survey, who reported a presence or absence of glaucoma or ocular hypertension completed both the vision and the reproductive health questionnaires and underwent eye examinations.

METHODS

Multivariate regression analysis was used to assess the correlation between OC use and self-reported glaucoma or ocular hypertension (n = 231 cases), controlling for potential confounders, including age, ethnicity, systemic comorbidities such as hypertension and stroke, ocular diseases such as cataract and diabetic retinopathy, and reproductive health factors, including age at menopause, age at menarche, history of hormone replacement therapy, and gynecological surgical history.

MAIN OUTCOME MEASURES

The outcome variable was self-reported glaucoma or ocular hypertension.

RESULTS

After adjusting for confounders, those with ≥3 years of OC use had greater odds (odds ratio, 1.94; 95% confidence interval, 1.22-3.07) of self-reported glaucoma or ocular hypertension. Other factors associated with higher glaucoma or ocular hypertension prevalence included older age, African American race, and later age at menarche.

CONCLUSIONS

Oral contraceptive use may be associated with increased risk of self-reported glaucoma or ocular hypertension.

Neuroactive gonadal drugs for neuroprotection in male and female models of Parkinson's disease

The existence of sex differences in Parkinson's disease (PD) incidence is well documented with greater prevalence and earlier age at onset in men than in women. These reported sex differences could be related to estrogen exposure. In PD animal models, estrogen is well documented to be neuroprotective against dopaminergic neuron loss induced by neurotoxins. Using the 1-methyl 4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) mouse model, we showed that several compounds are neuroprotective on dopaminergic neurons including estrogen, the selective estrogen receptor modulator raloxifene, progesterone, dehydroepiandrosterone, the estrogen receptor alpha (ERα) agonist PPT as well as the G protein-coupled membrane estrogen receptor (GPER1) specific agonist G1. Accumulating evidence suggests that GPER1 could be implicated in the neuroprotective effects of estrogen, raloxifene and G1 in collaboration with ERα. We recently reported that the 5α-reductase inhibitor Dutasteride is also neuroprotective and could bring an alternative to estrogens for therapy in male. Additional studies are needed to optimize therapies with these gonadal drugs into safe personalized treatments according to sex for treatment of PD.

Selective Aryl Hydrocarbon Receptor Modulator 3,3'-Diindolylmethane Impairs AhR and ARNT Signaling and Protects Mouse Neuronal Cells Against Hypoxia

The neuroprotective potential of 3,3'-diindolylmethane (DIM), which is a selective aryl hydrocarbon receptor modulator, has recently been shown in cellular and animal models of Parkinson's disease and lipopolysaccharide-induced inflammation. However, there are no data concerning the protective capacity and mechanisms of DIM action in neuronal cells exposed to hypoxia. The aim of the present study was to investigate the neuroprotective potential of DIM against the hypoxia-induced damage in mouse hippocampal cells in primary cultures, with a particular focus on DIM interactions with the aryl hydrocarbon receptor (AhR), its nuclear translocator ARNT, and estrogen receptor β (ERβ). In the present study, 18 h of hypoxia induced apoptotic processes, in terms of the mitochondrial membrane potential, activation of caspase-3, and fragmentation of cell nuclei. These effects were accompanied by substantial lactate dehydrogenase release and neuronal cell death. The results of the present study demonstrated strong neuroprotective and anti-apoptotic actions of DIM in hippocampal cells exposed to hypoxia. In addition, DIM decreased the Ahr and Arnt mRNA expression and stimulated Erβ mRNA expression level. DIM-induced mRNA alterations were mirrored by changes in protein levels, except for ERβ, as detected by ELISA, Western blotting, and immunofluorescence labeling. We also demonstrated that DIM decreased the expression of AhR-regulated CYP1A1. Using specific siRNAs, we provided evidence that impairment of AhR and ARNT, but not ERβ plays a key role in the neuroprotective action of DIM against hypoxia-induced cell damage. This study may have implication for identifying new agents that could protect neurons against hypoxia by targeting AhR/ARNT signaling.

Estrogen receptor variant ER-α36 is involved in estrogen neuroprotection against oxidative toxicity

It is well known that estrogen exerts neuroprotective effect against various neuronal damages. However, the estrogen receptor (ER) that mediates estrogen neuroprotection has not been well established. In this study, we investigated the potential receptor that mediates estrogen neuroprotection and the underlying molecular mechanisms. Hydrogen peroxide (H2O2) was chosen as an agent in our study to mimic free radicals that are often involved in the pathogenesis of many degenerative diseases. We found that in human SY5Y and IMR-32 cells, the estrogen neuroprotection against H2O2 toxicity was abrogated by knockdown of a variant of estrogen receptor-α, ER-α36. We also studied the rapid estrogen signaling mediated by ER-α36 in neuroprotective effect and found the PI3K/AKT and MAPK/ERK1/2 signaling mediated by ER-α36 is involved in estrogen neuroprotection. We also found that GPER, an orphan G protein-coupled receptor, is not involved in ER-α36-mediated rapid estrogen response. Our study thus demonstrates that ER-α36-mediated rapid estrogen signaling is involved in the neuroprotection activity of estrogen against oxidative toxicity.

Neuroprotective actions of progesterone in an in vivo model of retinitis pigmentosa

Progesterone has been shown to have neuroprotective effects in experimental acute brain injury models, but little is known about the effects of steroid sex hormones in models of retinitis pigmentosa (RP). The aim of this study was to asses whether progesterone had a protective effect in one animal model of RP (the rd1 mice), and whether its action was due at least in part, to its ability to reduce free radical damage or to increase antioxidant defences. Rd1 and wild type (wt) mice received an oral administration of 100 mg/kg body/weight of progesterone on alternate days starting at postnatal day 7 (PN7) and were sacrificed at different postnatal days. Our results show that progesterone decreases cell death, as the number of TUNEL-positive cells were decreased in the ONL of the retina from treated rd1 mice. At PN15, treatment with progesterone increased values of ERG b-wave amplitude (p<0,5) when compared with untreated mice. Progesterone also decreased the observed gliosis in RP, though this effect was transient. Treatment with progesterone significantly reduced retinal glutamate concentrations at PN15 and PN17. To clarify the mechanism by which progesterone is able to decrease retinal glutamate concentration, we examined expression levels of glutamine synthase (GS). Our results showed a significant increase in GS in rd1 treated retinas at PN13. Treatment with progesterone, significantly increase not only GSH but also oxidized glutathione retinal concentrations, probably because progesterone is able to partially increase glutamate cysteine ligase c subunit (GCLC) at PN15 and PN17 (p<0,05). In summary, our results demonstrate that oral administration of progesterone appears to act on multiple levels to delay photoreceptor death in this model of RP.

Oestrogen, ocular function and low-level vision: a review

Over the past 10 years, a literature has emerged concerning the sex steroid hormone oestrogen and its role in human vision. Herein, we review evidence that oestrogen (oestradiol) levels may significantly affect ocular function and low-level vision, particularly in older females. In doing so, we have examined a number of vision-related disorders including dry eye, cataract, increased intraocular pressure, glaucoma, age-related macular degeneration and Leber's hereditary optic neuropathy. In each case, we have found oestrogen, or lack thereof, to have a role. We have also included discussion of how oestrogen-related pharmacological treatments for menopause and breast cancer can impact the pathology of the eye and a number of psychophysical aspects of vision. Finally, we have reviewed oestrogen's pharmacology and suggest potential mechanisms underlying its beneficial effects, with particular emphasis on anti-apoptotic and vascular effects.

Differences in neuroretinal function between adult males and females

PURPOSE

To determine whether neuroretinal function differs in healthy adult males and females younger and older than 50 years.

METHODS

This study included one eye from each of 50 normal subjects (29 females and 21 males). Neuroretinal function was assessed using first-order P1 implicit times (ITs) and N1-P1 amplitudes (AMPs) obtained from photopic multifocal electroretinograms. To assess local differences, retinal maps of local IT and (separately) AMP averages were constructed for each subject group. To examine global differences, each subject's 103 ITs and (separately) AMPs were also averaged to create whole-eye averages. Subsequently, retinal maps and whole-eye averages of one subject group were compared with those of another.

RESULTS

In subjects younger than 50 years, neuroretinal function differed significantly between the males and females: local ITs were significantly shorter at 83 of 103 tested retinal locations, and whole-eye IT averages were shorter (p = 0.015) in the males compared with the females. In contrast, no analysis indicated that the males and females older than 50 years were significantly different. A subanalysis showed that the females who reported a hysterectomy (n = 5) had the longest whole-eye ITs of all subject groups (p ≤ 0.0013). In the females who did not report a hysterectomy, neuroretinal function was worse in the females older than 50 years compared with the females younger than 50 years: local ITs were significantly longer at 62 of 103 retinal locations tested, and whole-eye IT averages tended to be greater (p = 0.04). Conversely, ITs were not statistically different between the younger and older males. N1-P1 amplitudes did not differ between the sexes.

CONCLUSIONS

Multifocal electroretinogram IT differs between males and females, depending on the age group and hysterectomy status.

Estrogen signalling in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is a multifactorial eye disease that is associated with aging, family history, smoking, obesity, cataract surgery, arteriosclerosis, hypertension, hypercholesterolemia and unhealthy diet. Gender has commonly been classified as a weak or inconsistent risk factor for AMD. This disease is characterized by degeneration of retinal pigment epithelial (RPE) cells, Bruch's membrane, and choriocapillaris, which secondarily lead to damage and death of photoreceptor cells and central visual loss. Pathogenesis of AMD involves constant oxidative stress, chronic inflammation, and increased accumulation of lipofuscin and drusen. Estrogen has both anti-oxidative and anti-inflammatory capacity and it regulates signaling pathways that are involved in the pathogenesis of AMD. In this review, we discuss potential cellular signaling targets of estrogen in retinal cells and AMD pathology.

Cell surface translocation of annexin A2 facilitates glutamate-induced extracellular proteolysis

Glutamate-induced elevation in intracellular Ca(2+) has been implicated in excitotoxic cell death. Neurons respond to increased glutamate levels by activating an extracellular proteolytic cascade involving the components of the plasmin-plasminogen system. AnxA2 is a Ca(2+)-dependent phospholipid binding protein and serves as an extracellular proteolytic center by recruiting the tissue plasminogen activator and plasminogen and mediating the localized generation of plasmin. Ratiometric Ca(2+) imaging and time-lapse confocal microscopy demonstrated glutamate-induced Ca(2+) influx. We showed that glutamate translocated both endogenous and AnxA2-GFP to the cell surface in a process dependent on the activity of the NMDA receptor. Glutamate-induced translocation of AnxA2 is dependent on the phosphorylation of tyrosine 23 at the N terminus, and mutation of tyrosine 23 to a non-phosphomimetic variant inhibits the translocation process. The cell surface-translocated AnxA2 forms an active plasmin-generating complex, and this activity can be neutralized by a hexapeptide directed against the N terminus. These results suggest an involvement of AnxA2 in potentiating glutamate-induced cell death processes.

Neuroprotective effect of estrogen: role of nonsynaptic NR2B-containing NMDA receptors

Excessive activation of N-methyl-D-aspartate receptors (NMDARs) has been implicated in the pathophysiology of chronic neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. Some studies reported that NR2A and NR2B play different roles in the central nervous system (CNS). The NR2A subunit is primarily found in the synapses and is required for glutamate-mediated neuronal survival. On the other hand, the NR2B subunit is primarily found in the extrasynaptic sites and is required for glutamate-mediated neuronal death in both in vitro and in vivo experiments. Estrogen is a steroid hormone well known for its widespread effects such as neuroprotection in the brain. Classically, estrogen can bind to two kinds of nuclear receptors, namely, estrogen receptor α (ERα) and estrogen receptor β (ERβ), and produce physiological and neuroprotective effects. Aside from nuclear receptors, estrogen has one membrane receptor, which can either be G-protein-coupled receptor 30 (GPR30), Gq-mER, or ER-X. NMDA exposure clearly promotes NR2B subunit phosphorylation at Ser-1303 and causes neuronal cell death. GPR30 mediates rapid non-genomic effects to protect neurons against injury by inhibiting p-DAPK1 dephosphorylation, which inhibits NR2B subunit phosphorylation at Ser-1303. In addition, NMDA exposure and global ischemia activate the autophagy pathway and induce cell death, which are markedly blocked by the NR2B antagonist Ro 25-6981. Thus, NR2B signaling, autophagy induction and cell death may be closely related. Ro 25-6981 inhibits the dissociation of the NR2B-Beclin-1 signaling complex and delays autophagy in vivo, thus confirming the link between NR2B signaling and autophagy. In short, ERα, ERβ, and GPR30 are involved in the neuroprotection of estrogen in the CNS. Additional research must be conducted to reveal the mechanism of estrogen action fully and to identify better targets for the development of more effective drugs. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.