Neurosteroid regulation of central nervous system development

Novel actions of progesterone: what we know today and what will be the scenario in the future?

Objectives

This article is aimed to review the novel actions of progesterone, which otherwise is considered as a female reproductive hormone. The article focuses on its important physiological actions in males too and gives an overview of its novel perspectives in disorders of central and peripheral nervous system.

Key findings

Progesterone may have a potential benefit in treatment of traumatic brain injury, various neurological disorders and male related diseases like benign prostatic hypertrophy (BPH), prostate cancer and osteoporosis. Norethisterone (NETA), a progesterone derivative, decreases bone mineral loss in male castrated mice suggesting its role in osteoporosis. In the future, progesterone may find use as a male contraceptive too, but still needs confirmatory trials for safety, tolerability and acceptability. Megestrol acetate, a progesterone derivative is preferred in prostatic cancer. Further, it may find utility in nicotine addiction, traumatic brain injury (recently entered Phase III trial) and Alzheimer's disease, diabetic neuropathy and crush injuries. Studies also suggest role of progesterone in stroke, for which further clinical trials are needed. The non genomic actions of progesterone may be in part responsible for these novel actions.

Summary

Although progesterone has shown promising role in various non-hormonal benefits, further clinical studies are needed to prove its usefulness in conditions like stroke, traumatic brain injury, neuropathy and crush injury. In male related illnesses like BPH and prostatic Ca, it may prove a boon in near future. New era of hormonal male contraception may be initiated by use of progesterone along with testosterone.

Progesterone synthesis in the nervous system: implications for myelination and myelin repair

Progesterone is well known as a female reproductive hormone and in particular for its role in uterine receptivity, implantation, and the maintenance of pregnancy. However, neuroendocrine research over the past decades has established that progesterone has multiple functions beyond reproduction. Within the nervous system, its neuromodulatory and neuroprotective effects are much studied. Although progesterone has been shown to also promote myelin repair, its influence and that of other steroids on myelination and remyelination is relatively neglected. Reasons for this are that hormonal influences are still not considered as a central problem by most myelin biologists, and that neuroendocrinologists are not sufficiently concerned with the importance of myelin in neuron functions and viability. The effects of progesterone in the nervous system involve a variety of signaling mechanisms. The identification of the classical intracellular progesterone receptors as therapeutic targets for myelin repair suggests new health benefits for synthetic progestins, specifically designed for contraceptive use and hormone replacement therapies. There are also major advantages to use natural progesterone in neuroprotective and myelin repair strategies, because progesterone is converted to biologically active metabolites in nervous tissues and interacts with multiple target proteins. The delivery of progesterone however represents a challenge because of its first-pass metabolism in digestive tract and liver. Recently, the intranasal route of progesterone administration has received attention for easy and efficient targeting of the brain. Progesterone in the brain is derived from the steroidogenic endocrine glands or from local synthesis by neural cells. Stimulating the formation of endogenous progesterone is currently explored as an alternative strategy for neuroprotection, axonal regeneration, and myelin repair.

Allopregnanolone prevents dieldrin-induced NMDA receptor internalization and neurotoxicity by preserving GABA(A) receptor function

Dieldrin is an endocrine disruptor that accumulates in mammalian adipose tissue and brain. It induces convulsions due to its antagonism of the γ-aminobutyric acid A receptor (GABA(A)R). We have previously reported that long-term exposure to dieldrin causes the internalization of the N-methyl-D-aspartate receptor (NMDAR) as a result of persistent GABA(A)R inhibition. Because the neurosteroids 17β-estradiol (E2) and allopregnanolone are known to modulate the function and trafficking of GABA(A)R and NMDAR, we examined the effects of E2 and allopregnanolone on dieldrin-induced GABA(A)R inhibition, NMDAR internalization, and neuronal death in cortical neurons. We found that 1 nM E2 increased the membrane expression of NR1/NR2B receptors and postsynaptic density 95 but did not induce their physical association. In contrast, 10 nM E2 had no effect on these proteins but reduced NR2A membrane expression. We also found that exposure to 60 nM dieldrin for 6 d in vitro caused the internalization of NR1 and NR2B but not NR2A. Treatment with either 1 nM E2 or 10 μM allopregnanolone prevented the dieldrin-induced reduction in membrane levels of the NR1/NR2B receptors. Furthermore, prolonged exposure to 200 nM dieldrin down-regulated the expression of NR2A; this was inhibited only by allopregnanolone. Although both hormones restored NMDAR function, as measured by the NMDA-induced rise in intracellular calcium, allopregnanolone (but not E2) reversed the inhibition of GABA(A)R and neuronal death caused by prolonged exposure to dieldrin. Our results indicate that allopregnanolone protects cortical neurons against the neurotoxicity caused by long-term exposure to dieldrin by maintaining GABA(A)R and NMDAR functionality.

The neurosteroid dehydroepiandrosterone (DHEA) protects the retina from AMPA-induced excitotoxicity: NGF TrkA receptor involvement

The aim of the present study was to investigate the neuroprotective properties of the endogenous neurosteroid dehydroepiandrosterone (DHEA) in an in vivo model of retinal excitotoxicity, and the involvement of Nerve Growth Factor (NGF) in its actions. Adult Sprague-Dawley rats (250-300 g) received intravitreally (RS)-alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide (AMPA; 42 nmol/eye) alone or in combination with DHEA (10(-8), 10(-7), 10(-6) M), or PBS (50 mM, control group). To examine the involvement of NGF and its TrkA receptor in the pharmacological effects of DHEA, animals received AMPA and NGF (60 pg/eye) in the absence or presence of a TrkA receptor inhibitor (Calbiochem 648450, 10(-6) M) or AMPA, DHEA (10(-6) M) and TrkA receptor inhibitor (10(-6), 10(-5) M). Immunohistochemistry studies [choline acetyltransferase (ChAT), brain nitric oxide synthetase (bNOS), calbindin, and TUNEL] and fluorescence-activated cell sorting (FACS) were used to examine retinal cell loss and protection. TrkA receptor immunoreactivity (-IR) and colocalization studies with relevant markers were also performed. AMPA (42 nmol) treatment resulted in a loss of bNOS, ChAT and calbindin immunoreactivities 24 h after its administration. DHEA, administered intravitreally, protected the retina from excitotoxicity in a dose-dependent manner. This effect was mimicked by NGF, and reversed by the NGF TrkA receptor inhibitor. The TrkA receptor is expressed in ganglion cells of rat retina. TUNEL staining and FACS analysis substantiated the neuroprotective actions of DHEA. These results demonstrate for the first time that the neurosteroid DHEA, administered intravitreally, protects the retina from AMPA excitotoxicity. An NGF TrkA receptor mechanism appears to be involved in this neuroprotection.

Serum levels of brain-derived neurotrophic factor and cortisol to sulfate of dehydroepiandrosterone molar ratio associated with clinical response to L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patients

OBJECTIVES

L-Theanine (γ-glutamylethylamide) augmentation to antipsychotic therapy ameliorates positive, activation, and anxiety symptoms in schizophrenia and schizoaffective disorder patients. This study examines the association between circulating levels of neurochemical indicators and the beneficial clinical effects of L-theanine augmentation.

METHODS

Serum levels of neurochemical indicators such as brain-derived neurotrophic factor (BDNF), dehydroepiandrosterone (DHEA), its sulfate (DHEAS), cortisol, cholesterol, and insulin were monitored in 40 schizophrenia and schizoaffective disorder patients during an 8-week, double-blind, randomized, placebo-controlled trial with L-theanine (400 mg/d). Multiple regression analysis was applied for searching association between improvement in symptom scores and changes in circulating levels of neurochemical indicators for an 8-week trial.

RESULTS

Regression models among L-theanine-treated patients indicate that circulating levels of BDNF and cortisol-to-DHEAS*100 molar ratio were significantly associated with the beneficial clinical effects of L-theanine augmentation. Variability of serum BDNF levels accounted for 26.2% of the total variance in reduction of dysphoric mood and 38.2% in anxiety scores. In addition, the changes in cortisol-to-DHEAS*100 molar ratio accounted for 30% to 34% of the variance in activation factor and dysphoric mood scores and for 15.9% in anxiety scores. Regression models among placebo-treated patients did not reach significant level.

CONCLUSIONS

These preliminary results indicate that circulating BDNF and cortisol-to-DHEAS*100 molar ratio may be involved in the beneficial clinical effects of L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patients.

Neurosteroids reduce social isolation-induced behavioral deficits: a proposed link with neurosteroid-mediated upregulation of BDNF expression

The pharmacological action of selective serotonin reuptake inhibitor antidepressants may include a normalization of the decreased brain levels of the brain-derived neurotrophic factor (BDNF) and of neurosteroids such as the progesterone metabolite allopregnanolone, which are decreased in patients with depression and posttraumatic stress disorders (PTSD). The allopregnanolone and BDNF level decrease in PTSD and depressed patients is associated with behavioral symptom severity. Antidepressant treatment upregulates both allopregnanolone levels and the expression of BDNF in a manner that significantly correlates with improved symptomatology, which suggests that neurosteroid biosynthesis and BDNF expression may be interrelated. Preclinical studies using the socially isolated mouse as an animal model of behavioral deficits, which resemble some of the symptoms observed in PTSD patients, have shown that fluoxetine and derivatives improve anxiety-like behavior, fear responses and aggressive behavior by elevating the corticolimbic levels of allopregnanolone and BDNF mRNA expression. These actions appeared to be independent and more selective than the action of these drugs on serotonin reuptake inhibition. Hence, this review addresses the hypothesis that in PTSD or depressed patients, brain allopregnanolone levels, and BDNF expression upregulation may be mechanisms at least partially involved in the beneficial actions of antidepressants or other selective brain steroidogenic stimulant molecules.

Impaired neurosteroid synthesis in multiple sclerosis

High-throughput technologies have led to advances in the recognition of disease pathways and their underlying mechanisms. To investigate the impact of micro-RNAs on the disease process in multiple sclerosis, a prototypic inflammatory neurological disorder, we examined cerebral white matter from patients with or without the disease by micro-RNA profiling, together with confirmatory reverse transcription-polymerase chain reaction analysis, immunoblotting and gas chromatography-mass spectrometry. These observations were verified using the in vivo multiple sclerosis model, experimental autoimmune encephalomyelitis. Brains of patients with or without multiple sclerosis demonstrated differential expression of multiple micro-RNAs, but expression of three neurosteroid synthesis enzyme-specific micro-RNAs (miR-338, miR-155 and miR-491) showed a bias towards induction in patients with multiple sclerosis (P < 0.05). Analysis of the neurosteroidogenic pathways targeted by micro-RNAs revealed suppression of enzyme transcript and protein levels in the white matter of patients with multiple sclerosis (P < 0.05). This was confirmed by firefly/Renilla luciferase micro-RNA target knockdown experiments (P < 0.05) and detection of specific micro-RNAs by in situ hybridization in the brains of patients with or without multiple sclerosis. Levels of important neurosteroids, including allopregnanolone, were suppressed in the white matter of patients with multiple sclerosis (P < 0.05). Induction of the murine micro-RNAs, miR-338 and miR-155, accompanied by diminished expression of neurosteroidogenic enzymes and allopregnanolone, was also observed in the brains of mice with experimental autoimmune encephalomyelitis (P < 0.05). Allopregnanolone treatment of the experimental autoimmune encephalomyelitis mouse model limited the associated neuropathology, including neuroinflammation, myelin and axonal injury and reduced neurobehavioral deficits (P < 0.05). These multi-platform studies point to impaired neurosteroidogenesis in both multiple sclerosis and experimental autoimmune encephalomyelitis. The findings also indicate that allopregnanolone and perhaps other neurosteroid-like compounds might represent potential biomarkers or therapies for multiple sclerosis.

The mislabelling of deoxycorticosterone: making sense of corticosteroid structure and function

Over the 70 or so years since their discovery, there has been continuous interest and activity in the field of corticosteroid functions. However, despite major advances in the characterisation of receptors and coregulators, in some ways we still lack clear insight into the mechanism of receptor activation, and, in particular, the relationship between steroid hormone structure and function remains obscure. Thus, why should deoxycorticosterone (DOC) reportedly be a weak mineralocorticoid, while the addition of an 11β-hydroxyl group produces glucocorticoid activity, yet further hydroxylation at C18 leads to the most potent mineralocorticoid, aldosterone? This review aims to show that the field has been confused by the misreading of the earlier literature and that DOC, far from being relatively inactive, in fact has a wide range of activities not shared by the other corticoids. In contrast to the accepted view, the presence of an 11β-hydroxyl group yields, in corticosterone or cortisol, hormones with more limited functions, and also more readily regulated, by 11β-hydroxysteroid dehydrogenase. This interpretation leads to a more systematic understanding of structure-function relationships in the corticosteroids and may assist more rational drug design.

The biological basis of injury and neuroprotection in the fetal and neonatal brain

A compromised intrauterine environment that delivers low levels of oxygen and/or nutrients, or is infected or inflammatory, can result in fetal brain injury, abnormal brain development and in cases of chronic compromise, intrauterine growth restriction. Preterm birth can also be associated with injury to the developing brain and affect the normal trajectory of brain growth. This review will focus on the effects that episodes of perinatal hypoxia (acute, chronic, associated with inflammation or as an antecedent of preterm birth) can have on the developing brain. In animal models of these conditions we have found that relatively brief (acute) periods of fetal hypoxemia can have significant effects on the fetal brain, for example death of susceptible neuronal populations (cerebellum, hippocampus, cortex) and cerebral white matter damage. Chronic placental insufficiency which includes fetal hypoxemia, nutrient restriction and altered endocrine status can result in fetal growth restriction and long-term deficits in neural connectivity in addition to altered postnatal function, for example in the auditory and visual systems. Maternal/fetal inflammation can result in fetal brain damage, particularly but not exclusively in the white matter; injury is more pronounced when associated with fetal hypoxemia. In the baboon, in which the normal trajectory of growth is affected by preterm birth, there is a direct correlation between a higher flux in oxygen saturation and a greater extent of neuropathological damage. Currently, the only established therapy for neonatal encephalopathy in full term neonates is moderate hypothermia although this only offers some protection to moderately but not severely affected brains. There is no accepted therapy for injured preterm brains. Consequently the search for more efficacious treatments continues; we discuss neuroprotective agents (erythropoietin, N-acetyl cysteine, melatonin, creatine, neurosteroids) which we have trialed in appropriate animal models. The possibility of combining hypothermia with such agents or growth factors is now being considered. A deeper understanding of causal pathways in brain injury is essential for the development of efficacious strategies for neuroprotection.

Palmitoylethanolamide stimulation induces allopregnanolone synthesis in C6 Cells and primary astrocytes: involvement of peroxisome-proliferator activated receptor-α

Palmitoylethanolamide (PEA) regulates many pathophysiological processes in the central nervous system, including pain perception, convulsions and neurotoxicity, and increasing evidence points to its neuroprotective action. In the present study, we report that PEA, acting as a ligand of peroxisome-proliferator activated receptor (PPAR)-α, might regulate neurosteroidogenesis in astrocytes, which, similar to other glial cells and neurones, have the enzymatic machinery for neurosteroid de novo synthesis. Accordingly, we used the C6 glioma cell line and primary murine astrocytes. In the mitochondrial fraction from cells stimulated with PEA, we demonstrated an increase in steroidogenic acute regulatory protein (StAR) and cytochrome P450 enzyme (P450scc) expression, both comprising proteins considered to be involved in crucial steps of neurosteroid formation. The effects of PEA were completely blunted by GW6471, a selective PPAR-α antagonist, or by PPAR-α silencing by RNA interference. Accordingly, allopregnanolone (ALLO) levels were increased in supernatant of PEA-treated astrocytes, as revealed by gas chromatography-mass spectrometry, and this effect was inhibited by GW6471. Moreover, PEA showed a protective effect, reducing malondialdehyde formation in cells treated with l-buthionine-(S,R)-sulfoximine, a glutathione depletor and, interestingly, the effect of PEA was partially inhibited by finasteride, a 5α-reductase inhibitor. A similar profile of activity was demonstrated by ALLO and the lack of an additive effect with PEA suggests that the reduction of oxidative stress by PEA is mediated through ALLO synthesis. The present study provides evidence indicating the involvement of the saturated acylethanolamide PEA in ALLO synthesis through PPAR-α in astrocytes and explores the antioxidative activity of this molecule, confirming its homeostatic and protective role both under physiological and pathological conditions.

Neurosteroid and GABA-A receptor alterations in Alzheimer's disease, Parkinson's disease and multiple sclerosis

Steroid hormones (e.g. estrogens, androgens, progestagens) which are synthesized de novo or metabolized within the CNS are called neurosteroids. There is substantial evidence from animal studies suggesting that these steroids can affect brain function by modulating neurotransmission, and influence neuronal survival, neuronal and glial differentiation and myelination in the CNS by regulating gene expression of neurotrophic factors and anti-inflammatory molecules. Indeed, evidence is emerging that expression of the enzymes responsible for the synthesis of neurosteroids changes in neurodegenerative diseases. Some of these changes may contribute to the pathology, while others, conversely, may represent an attempted rescue program in the diseased brain. Here we review the data on changes in neurosteroid levels and neurosteroid synthesis pathways in the human brain in three neurodegenerative conditions, Alzheimers's (AD) and Parkinson's (PD) diseases and Multiple Sclerosis (MS) and the extent to which these findings may implicate protective or pathological roles for neurosteroids in the course of these diseases.Some neurosteroids can modulate neurotransmitter activity, for example, the pregnane steroids allopregnanolone and 3α5α-tetrahydro-deoxycorticosterone which are potent positive allosteric modulators of ionotropic GABA-A receptors. Therefore, neurosteroid-modulated GABA-A receptor subunit alterations found in AD and PD will also be discussed. These data imply an involvement of neurosteroid changes in the neurodegenerative and neuroinflammatory processes and suggest that they may deserve further investigation as potential therapeutic agents in AD, PD and MS. Finally, suggestions for therapeutic strategies will be included. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Neurosteroids infusion into the CA1 hippocampal region on exploration, anxiety-like behaviour and aversive learning

Neurosteroids (NS) are substances synthesised de novo in the brain that have rapid modulatory effects on ionotropic receptors. Specifically, NS can act as positive allosteric modulators of GABAA receptors as pregnanolone or allopregnanolone (Allop), or GABAA negative modulators and NMDA positive modulators as pregnenolone (PREG) or dehydroepiandrosterone (DHEA) and their sulphate esters (PREGS and DHEAS). Given this, their role in anxiety and emotional disturbances has been suggested. In addition, NS such as PREGS or DHEAS have demonstrated a promnesic role in several learning tests. The aim of the present work is to highlight the role that the dorsal (CA1) hippocampus plays in the behavioural profile of NS such as Allop and PREGS in tests assessing exploration, anxiety and aversive learning in rats. For this purpose, animals were administered intrahippocampally with Allop (0.2μg/0.5μl), PREGS (5ng/0.5μl) or vehicle in each hippocampus, and tested in the Boissier and elevated plus maze (EPM) tests. For learning test we have chosen the passive avoidance paradigm. Results indicate that intrahippocampal administration of Allop enhances exploration, reflected in an increase in the total and the inner number of head-dips. Allop-injected animals also showed an increase in the percentage of entries into the open arms of the EPM, suggesting an anxiolytic-like profile. In addition, post-acquisition PREGS administration enhanced passive avoidance retention, while post-acquisition Allop administration had no effects on aversive learning retention. These results point out the important role of the dorsal (CA1) hippocampus in several NS behavioural effects, such as exploration, anxiety, learning and memory.

Cooperation of sex chromosomal genes and endocrine influences for hypothalamic sexual differentiation

There is little debate that mammalian sexual differentiation starts from the perspective of two primary sexes that correspond to differential sex chromosomes (X versus Y) that lead to individuals with sex typical characteristics. Sex steroid hormones account for most aspects of brain sexual differentiation, however, a growing literature has raised important questions about the role of sex chromosomal genes separate from sex steroid actions. Several important model animals are being used to address these issues and, in particular, they are taking advantage of molecular genetic approaches using different mouse strains. The current review examines the cooperation of genetic and endocrine influences from the perspective of behavioral and morphological hypothalamic sexual differentiation, first in adults and then in development. In the final analysis, there is an ongoing need to account for the influence of hormones in the context of underlying genetic circumstances and null hormone conditions.

Gonadotropin-releasing hormone modulates cholesterol synthesis and steroidogenesis in SH-SY5Y cells

Neurosteroids are involved in Central Nervous System development, brain functionality and neuroprotection but little is known about regulators of their biosynthesis. Recently gonadotropins, Gonadotropin-releasing Hormone (GnRH) and their receptors have been localized in different brain regions, such as hippocampus and cortex. Using human neuronal-like cells we found that GnRH up-regulates the expression of key genes of cholesterol and steroid synthesis when used in a narrow range around 1.0 nM. The expression of Hydroxysterol D24-reductase (seladin-1/DHCR24), that catalyzes the last step of cholesterol biosynthesis, is increased by 50% after 90 min of incubation with GnRH. StAR protein and P450 side chain cleavage (P450scc) are up-regulated by 3.3 times after 90 min and by 3.5 times after 3 h, respectively. GnRH action is mediated by LH and 1.0 nM GnRH enhances the expression of LHβ as well. A two fold increase of cell cholesterol is induced after 90 min of GnRH incubation and 17β-estradiol (E2) production is increased after 24, 48 and 72 h. These data indicate for the first time that GnRH regulates both cholesterol and steroid biosynthesis in human neuronal-like cells and suggest a new physiological role for GnRH in the brain.

The GABAergic deficit hypothesis of major depressive disorder

Increasing evidence points to an association between major depressive disorders (MDDs) and diverse types of GABAergic deficits. In this review, we summarize clinical and preclinical evidence supporting a central and causal role of GABAergic deficits in the etiology of depressive disorders. Studies of depressed patients indicate that MDDs are accompanied by reduced brain concentration of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) and by alterations in the subunit composition of the principal receptors (GABA(A) receptors) mediating GABAergic inhibition. In addition, there is abundant evidence that suggests that GABA has a prominent role in the brain control of stress, the most important vulnerability factor in mood disorders. Furthermore, preclinical evidence suggests that currently used antidepressant drugs (ADs) designed to alter monoaminergic transmission and nonpharmacological therapies may ultimately act to counteract GABAergic deficits. In particular, GABAergic transmission has an important role in the control of hippocampal neurogenesis and neural maturation, which are now established as cellular substrates of most if not all antidepressant therapies. Finally, comparatively modest deficits in GABAergic transmission in GABA(A) receptor-deficient mice are sufficient to cause behavioral, cognitive, neuroanatomical and neuroendocrine phenotypes, as well as AD response characteristics expected of an animal model of MDD. The GABAergic hypothesis of MDD suggests that alterations in GABAergic transmission represent fundamentally important aspects of the etiological sequelae of MDDs that are reversed by monoaminergic AD action.

Light-dependent and circadian clock-regulated activation of sterol regulatory element-binding protein, X-box-binding protein 1, and heat shock factor pathways

The circadian clock is phase-delayed or -advanced by light when given at early or late subjective night, respectively. Despite the importance of the time-of-day-dependent phase responses to light, the underlying molecular mechanism is poorly understood. Here, we performed a comprehensive analysis of light-inducible genes in the chicken pineal gland, which consists of light-sensitive clock cells representing a prototype of the clock system. Light stimulated expression of 62 genes and 40 ESTs by >2.5-fold, among which genes responsive to the heat shock and endoplasmic reticulum stress as well as their regulatory transcription factors heat shock factor (HSF)1, HSF2, and X-box-binding protein 1 (XBP1) were strongly activated when a light pulse was given at late subjective night. In contrast, the light pulse at early subjective night caused prominent induction of E4bp4, a key regulator in the phase-delaying mechanism of the pineal clock, along with activation of a large group of cholesterol biosynthetic genes that are targets of sterol regulatory element-binding protein (SREBP) transcription factor. We found that the light pulse stimulated proteolytic formation of active SREBP-1 that, in turn, transactivated E4bp4 expression, linking SREBP with the light-input pathway of the pineal clock. As an output of light activation of cholesterol biosynthetic genes, we found light-stimulated pineal production of a neurosteroid, 7α-hydroxypregnenolone, demonstrating a unique endocrine function of the pineal gland. Intracerebroventricular injection of 7α-hydroxypregnenolone activated locomotor activities of chicks. Our study on the genome-wide gene expression analysis revealed time-of-day-dependent light activation of signaling pathways and provided molecular connection between gene expression and behavior through neurosteroid release from the pineal gland.

Environmental enrichment alters gene expression of steroidogenic enzymes in the rat hippocampus

Neuroactive steroids are synthesized in the central and peripheral nervous systems. The purpose of this study was to analyze the effects of environmental enrichment on neuroactive steroidogenesis in the rat hippocampus. Environmental enrichment rats were housed in a group of nine in a large cage and three groups of pair-housed rats were housed in a standard cage for 8 weeks. The levels of mRNAs for steroidogenic enzymes and proteins in hippocampus were quantified by real-time RT-PCR. Environmental enrichment increased the mRNA expression levels of 5α-reductase-1 and 3α-hydroxysteroid dehydrogenase, which catalyze synthesis of allopregnanolone from progesterone. Hence, environmental enrichment appears to affect allopregnanolone synthesis.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Neuroregenerative mechanisms of allopregnanolone in Alzheimer's disease

The proliferative pool and regenerative potential of neural stem cells diminishes with age, a phenomenon that may be exacerbated in prodromal and mild Alzheimer's disease (AD) brains. In parallel, the neuroactive progesterone metabolite, allopregnanolone (APα), along with a host of other factors, is decreased in the AD brain. Results of preclinical analyses demonstrate that APα is a potent inducer of neural progenitor proliferation of both rodent and human derived neural progenitor cells in vitro. In vivo, APα significantly increased neurogenesis within the subgranular zone of the dentate gyrus and subventricular zone of the 3xTgAD mouse model. Functionally, APα reversed the learning and memory deficits of 3xTgAD mice prior to and following the onset of AD pathology and was comparably efficacious in aged normal mice. In addition to inducing regenerative responses in mouse models of AD, APα significantly reduced beta-amyloid burden, beta-amyloid binding alcohol dehydrogenase load, and microglial activation. In parallel, APα increased markers of white matter generation and cholesterol homeostasis. Analyses to determine the optimal treatment regimen in the 3xTgAD mouse brain indicated that a treatment regimen of APα once per week was optimal for both inducing neurogenesis and reducing AD pathology. Pharmacokinetic analyses indicated that APα is rapidly increased in both plasma and brain following a single dose. APα is most efficacious when administered once per week which will contribute to its margin of safety. Further, analyses in both animals and humans have provided parameters for safe APα dosage exposure in humans. From a translational perspective, APα is a small molecular weight, blood brain barrier penetrant molecule with substantial preclinical efficacy data as a potential Alzheimer's therapeutic with existing safety data in animals and humans. To our knowledge, APα is the only small molecule that both promotes neural progenitor regeneration in brain and simultaneously reduces AD pathology burden.

Neurosteroids and GABA-A Receptor Function

Neurosteroids represent a class of endogenous steroids that are synthesized in the brain, the adrenals, and the gonads and have potent and selective effects on the GABAA-receptor. 3α-hydroxy A-ring reduced metabolites of progesterone, deoxycorticosterone, and testosterone are positive modulators of GABA(A)-receptor in a non-genomic manner. Allopregnanolone (3α-OH-5α-pregnan-20-one), 5α-androstane-3α, 17α-diol (Adiol), and 3α5α-tetrahydrodeoxycorticosterone (3α5α-THDOC) enhance the GABA-mediated Cl(-) currents acting on a site (or sites) distinct from the GABA, benzodiazepine, barbiturate, and picrotoxin binding sites. 3α5α-P and 3α5α-THDOC potentiate synaptic GABA(A)-receptor function and activate δ-subunit containing extrasynaptic receptors that mediate tonic currents. On the contrary, 3β-OH pregnane steroids and pregnenolone sulfate (PS) are GABA(A)-receptor antagonists and induce activation-dependent inhibition of the receptor. The activities of neurosteroid are dependent on brain regions and types of neurons. In addition to the slow genomic action of the parent steroids, the non-genomic, and rapid actions of neurosteroids play a significant role in the GABA(A)-receptor function and shift in mood and memory function. This review describes molecular mechanisms underlying neurosteroid action on the GABA(A)-receptor, mood changes, and cognitive functions.

Oxidative Stress-Mediated Brain Dehydroepiandrosterone (DHEA) Formation in Alzheimer's Disease Diagnosis

Neurosteroids are steroids made by brain cells independently of peripheral steroidogenic sources. The biosynthesis of most neurosteroids is mediated by proteins and enzymes similar to those identified in the steroidogenic pathway of adrenal and gonadal cells. Dehydroepiandrosterone (DHEA) is a major neurosteroid identified in the brain. Over the years we have reported that, unlike other neurosteroids, DHEA biosynthesis in rat, bovine, and human brain is mediated by an oxidative stress-mediated mechanism, independent of the cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17A1) enzyme activity found in the periphery. This alternative pathway is induced by pro-oxidant agents, such as Fe(2+) and β-amyloid peptide. Neurosteroids are involved in many aspects of brain function, and as such, are involved in various neuropathologies, including Alzheimer's disease (AD). AD is a progressive, yet irreversible neurodegenerative disease for which there are limited means for ante-mortem diagnosis. Using brain tissue specimens from control and AD patients, we provided evidence that DHEA is formed in the AD brain by the oxidative stress-mediated metabolism of an unidentified precursor, thus depleting levels of the precursor in the blood stream. We tested for the presence of this DHEA precursor in human serum using a Fe(2+)-based reaction and determined the amounts of DHEA formed. Fe(2+) treatment of the serum resulted in a dramatic increase in DHEA levels in control patients, whereas only a moderate or no increase was observed in AD patients. The DHEA variation after oxidation correlated with the patients' cognitive and mental status. In this review, we present the cumulative evidence for oxidative stress as a natural regulator of DHEA formation and the use of this concept to develop a blood-based diagnostic tool for neurodegenerative diseases linked to oxidative stress, such as AD.

Pregnenolone sulfate increases glutamate release at neonatal climbing fiber-to-Purkinje cell synapses

Development of cerebellar Purkinje cells (PCs) is modulated by neuroactive steroids. Developing hippocampal pyramidal neurons retrogradely release a pregnenolone sulfate (PregS)-like neurosteroid that may contribute to glutamatergic synapse stabilization. We hypothesized that PregS could exert a similar effect on developing PCs. To test this hypothesis, we performed whole-cell patch-clamp recordings from PCs in acute cerebellar vermis slices from neonatal rats. PregS induced a robust (∼3000%) and reversible increase in AMPA receptor-mediated miniature excitatory postsynaptic current (AMPA-mEPSC) frequency without affecting the amplitude, time-to-rise, or half-width of these events. PregS also increased the frequency of GABA(A) receptor-mediated miniature postsynaptic currents but to a significantly lesser extent (<100%). The PregS-induced increase of AMPA-mEPSC frequency was not significantly decreased by antagonists of receptors (NMDA, glycine, α7 nicotinic acetylcholine and σ1) that have been shown to modulate glutamatergic transmission at PCs and/or mediate the actions of PregS on neurotransmitter release. Ca(2+) chelation experiments suggested that PregS acts by increasing presynaptic terminal [Ca(2+)](i), an effect that is independent of voltage-gated Ca(2+) channels, but is blocked by the antagonist of transient receptor potential (TRP) channels, La(3+). PregS also increased the amplitude of EPSCs evoked by climbing fiber (CF) stimulation and decreased the paired-pulse ratio of these events. Neither CF nor parallel fiber-evoked EPSCs were affected by PregS in slices from juvenile rats. These results suggest that glutamate release at CF-to-PC synapses is an important target of PregS in the neonatal cerebellar cortex, an effect that may play a role in the refinement of these synapses.

Growth in children with clefts: serial hand-wrist x-ray evidence

OBJECTIVE

Serial hand-wrist x-rays were assessed for Tanner-Whitehouse 2 skeletal ages of children with cleft palate, unilateral cleft lip and palate, and bilateral cleft lip and palate. The skeletal ages were compared by cleft type to see whether growth delay might explain the small body size for age and delayed maturation sometimes seen elsewhere in children with clefts.

DESIGN

This is a retrospective study of serial x-rays collected between 1950 and 1968 at the Philadelphia Growth Center. The author was blind to age, sex, and diagnosis while reading these films.

PARTICIPANTS

These x-rays were taken as part of routine auxological evaluation of the normality of growth status.

MAIN OUTCOME MEASURES

Distributions of skeletal age patterns in advance of or delayed from chronological age and frequencies of clinically significant deviant patterns are presented.

CONCLUSIONS

Boys and girls with cleft palate show different maturational patterns, supporting a sex influence on the etiologies of at least some of these anomalies. Boys with unilateral cleft lip and palate and bilateral cleft lip and palate have different maturational patterns, consistent with these anomalies having different sets of etiological factors. Girls with unilateral cleft lip and palate almost always have advanced skeletal ages; whereas, boys sometimes do not. These results support the need for keeping both sex and diagnostic categories separate when conducting etiological searches.

II. Cognitive performance of middle-aged female rats is influenced by capacity to metabolize progesterone in the prefrontal cortex and hippocampus

Cognitive decline can occur with aging; however, some individuals experience less cognitive decline than do others. Secretion of ovarian hormones is reduced post-menopause and may contribute to cognitive function. The extent to which hormonal effects may be parsed out from other age-related factors to influence cognition is of interest. Middle-aged (12-month-old) female rats that were retired breeders were categorized as maintaining or declining reproductive function based upon their estrous cyclicity (regular 4-5 day cycles), fertility (> 60 % successful pregnancy), and fecundity (>10 pups/litter). Performance in object recognition, Y-maze, water maze, inhibitory avoidance, and contextual-cued fear conditioning was evaluated. Estradiol, progesterone (P(4)), dihydroprogesterone, and 5α-pregnan-3α-ol-20-one (3α,5α-THP) were assessed in medial prefrontal cortex (mPFC) and hippocampus; corticosterone was assessed in plasma. Rats maintaining reproductive function performed significantly better on the object recognition, Y-maze, water maze, inhibitory avoidance, and cued fear conditioning tasks than did rats with declining reproductive function. Steroid concentrations varied greatly within groups. Higher levels of P(4) in mPFC and hippocampus were associated with better Y-maze performance. In mPFC, higher levels of P(4) were associated with poorer inhibitory avoidance performance; greater levels of 3α,5α-THP were associated with better object memory. Neither estradiol nor corticosterone levels significantly contributed to cognitive performance. Thus, the capacity for cortico-limbic P(4) utilization may influence cognitive performance in aging.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Dehydroepiandrosterone effects on Akt signaling modulation in central nervous system of young and aged healthy rats

Dehydroepiandrosterone (DHEA) is a steroid synthesized in adrenal cortex as well as in the nervous system. DHEA effects on central nervous system (CNS) have been associated with several brain functions such as marked neurotrophic and neuroprotective activity. DHEA plasma concentration decreases steadily with aging and studies have reported an inverse correlation between levels of DHEA and neurological diseases age-associated. Nonetheless, its mechanisms of action are not yet fully understood. Akt signaling pathway is one protein kinase which has been related to be DHEA modulated. The goal of this study was to investigate whether short-term (6 or 24h) or chronic (5 weeks) DHEA treatment modulates Akt in CNS of adult (3 months) and aged (18 and 24 months) healthy rats. Hypothalamus and hippocampus homogenates were prepared to quantify total-Akt and phosphorylated Akt at Ser(473) (pAkt). The results here presented have shown that acute (50mg/kg) and chronic (10mg/kg) DHEA injections modulate total and pAkt levels. This effect was dose and time-dependent as well as age and tissue-dependent. In addition, the age variable also intervenes on total and pAkt levels expression independently of DHEA treatment.

Neurosteroid transport by the organic solute transporter OSTα-OSTβ

A variety of steroids, including pregnenolone sulfate (PREGS) and dehydroepiandrosterone sulfate (DHEAS) are synthesized by specific brain cells, and are then delivered to their target sites, where they exert potent effects on neuronal excitability. The present results demonstrate that [(3)H]DHEAS and [(3)H]PREGS are relatively high affinity substrates for the organic solute transporter, OSTα-OSTβ, and that the two proteins that constitute this transporter are selectively localized to steroidogenic cells in the cerebellum and hippocampus, namely the Purkinje cells and cells in the cornu ammonis region in both mouse and human brain. Analysis of Ostα and Ostβ mRNA levels in mouse Purkinje and hippocampal cells isolated via laser capture microdissection supported these findings. In addition, Ostα-deficient mice exhibited changes in serum DHEA and DHEAS levels, and in tissue distribution of administered [(3)H]DHEAS. OSTα and OSTβ proteins were also localized to the zona reticularis of human adrenal gland, the major region for DHEAS production in the periphery. These results demonstrate that OSTα-OSTβ is localized to steroidogenic cells of the brain and adrenal gland, and that it modulates DHEA/DHEAS homeostasis, suggesting that it may contribute to neurosteroid action.

Influence of progesterone on GAD65 and GAD67 mRNA expression in the dorsolateral striatum and prefrontal cortex of female rats repeatedly treated with cocaine

Female rats are intensely affected by cocaine, with estrogen probably playing an important role in this effect. Progesterone modulates the GABA system and attenuates the effects of cocaine; however, there is no information about its relevance in changing GABA synthesis pathways after cocaine administration to female rats. Our objective was to investigate the influence of progesterone on the effects of repeated cocaine administration on the isoenzymes of glutamic acid decarboxylase (GAD(65) and GAD(67)) mRNA in brain areas involved in the addiction circuitry. Ovariectomized, intact and progesterone replacement-treated female rats received saline or cocaine (30 mg/kg, ip) acutely or repeatedly. GAD isoenzyme mRNA levels were determined in the dorsolateral striatum (dSTR) and prefrontal cortex (PFC) by RT-PCR, showing that repeated, but not acute, cocaine decreased GADs/beta-actin mRNA ratio in the dSTR irrespective of the hormonal condition (GAD(65): P < 0.001; and GAD(67): P = 0.004). In the PFC, repeated cocaine decreased GAD(65) and increased GAD(67) mRNA ratio (P < 0.05). Progesterone replacement decreased both GAD isoenzymes mRNA ratio after acute cocaine in the PFC (P < 0.001) and repeated cocaine treatment reversed this decrease (P < 0.001). These results suggest that cocaine does not immediately affect GAD mRNA expression, while repeated cocaine decreases both GAD(65) and GAD(67) mRNA in the dSTR of female rats, independently of their hormonal conditions. In the PFC, repeated cocaine increases the expression of GAD isoenzymes, which were decreased due to progesterone replacement.

The interplay between bioactive sphingolipids and steroid hormones

Steroid hormones regulate various physiological processes including development, reproduction, and metabolism. These regulatory molecules are synthesized from cholesterol in endocrine organs - such as the adrenal glands and gonads - via a multi-step enzymatic process that is catalyzed by the cytochrome P450 superfamily of monooxygenases and hydroxysteroid dehydrogenases. Steroidogenesis is induced by trophic peptide hormones primarily via the activation of a cAMP/protein kinase A (PKA)-dependent pathway. However, other signaling molecules, including cytokines and growth factors, control the steroid hormone biosynthetic pathway. More recently, sphingolipids, including ceramide, sphingosine-1-phosphate, and sphingosine, have been found to modulate steroid hormone secretion at multiple levels. In this review, we provide a brief overview of the mechanisms by which sphingolipids regulate steroidogenesis. In addition, we discuss how steroid hormones control sphingolipid metabolism. Finally, we outline evidence supporting the emerging role of bioactive sphingolipids in various nuclear processes and discuss a role for nuclear sphingolipid metabolism in the control of gene transcription.

Alterations in neonatal neurosteroids affect exploration during adolescence and prepulse inhibition in adulthood

Allopregnanolone (AlloP) is a neurosteroid that plays an important role during neural development. Alterations of endogenous neonatal allopregnanolone levels alter the localisation and function of GABA neurons in the adult brain and affect behaviour in adulthood. We have carried out research into the effects of an increase (AlloP administration) or a decrease (administration of finasteride, inhibitor of the AlloP synthesis) of neonatal AlloP levels during the fifth to ninth postnatal days in male Wistar rats on the novelty exploration (Boissier test) at adolescent ages (40 and 60 days old), and on the prepulse inhibition achievement in adulthood (85 days). We also investigated the role of a GABA(A) modulator (midazolam, 1, 1.75 or 2.5mg/kg body weight) in the long-lasting behavioural changes in adulthood (85 days). Results indicate that neonatal finasteride decreases both novelty-exploration (head-dipping and locomotion) and anxiety-relevant scores (the distance travelled in and the number of entries into the central zone) at adolescent age, along with a reduction in body weight and general locomotion. Also, neonatal AlloP administration decreases prepulse inhibition in adulthood. Prepulse inhibition disruption was only partially reproduced decreasing the neonatal AlloP levels by means of finasteride administration. Although there was no interaction between neonatal neurosteroid manipulation and adult benzodiazepine treatments, the effects of midazolam were dose-dependent: the lowest dose of midazolam increased whereas the highest disrupted the expected progressive reduction of the startle response (and the consequent improvement of the PPI percentage) after the gradual increase in prepulse intensity. Reduced prepulse inhibition of startle provides evidence of deficient sensorimotor gating in several disorders, including schizophrenia. Alterations of AlloP levels during maturation could partly explain the inter-individual differences shown by adult subjects in response to novelty (exploration) and in the sensorimotor gating and prepulse inhibition. Also, abrupt changes in neonatal levels of AlloP could be related to a susceptibility to neurodevelopmental disorders.

Pregnenolone, dehydroepiandrosterone, and schizophrenia: alterations and clinical trials

Neurosteroids, such as pregnenolone (PREG), dehydroepiandrosterone (DHEA), and their sulfates (PREGS and DHEAS) are reported to have a modulatory effect on neuronal excitability and synaptic plasticity. They also have many other functions associated with neuroprotection, response to stress, mood regulation, and cognitive performance. Furthermore, these neurosteroids have been linked to, and their levels are altered in, neuropsychiatric disorders. This review highlights what is currently known about the metabolism and mode of action of PREG and DHEA, as well as about alterations of these neurosteroids in schizophrenia. This review also provides substantial information about clinical trials with DHEA and PREG augmentation with of antipsychotic agents in schizophrenia.

Neurosteroids' effects and mechanisms for social, cognitive, emotional, and physical functions

Hormones are trophic factors that integrate central and peripheral nervous system functions, and can influence social, cognitive, emotional and physical (SCEP) processes. Greater understanding of behavioral and neurobiological underpinnings of mental, cognitive, and/or physical changes with maturation is becoming increasingly important as the world's population ages. There are individual differences in how people age, but the factors that influence these differences are not well understood. Social supports are one factor that may influence the trajectory of age-related processes. The loss of close relationships, especially among older persons, is one of the greatest risk factors for mental and physical decline. Progesterone, secreted by the ovaries, or produced de novo in the brain, is readily converted centrally to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), and can influence SCEP, through rapid, non-classical steroid-mediated actions. Our hypothesis is that 3alpha,5alpha-THP is a key trophic factor in SCEP and development. Our research has demonstrated that 3alpha,5alpha-THP facilitates social and sexual behavior of rodents, which evokes further increases in 3alpha,5alpha-THP in midbrain and hippocampus, brain areas involved in SCEP. The role of 3alpha,5alpha-THP to influence social and/or sexual experience, and thereby SCEP, is discussed in this review. Further understanding of these neurobiological and/or behavioral factors may lead to findings that ultimately can promote health and prevent disease.

The effects of DHEA, 3beta-hydroxy-5alpha-androstane-6,17-dione, and 7-amino-DHEA analogues on short term and long term memory in the mouse

Neurosteroids have been reported to modulate memory processes in rodents. Three analogues of dehydroepiandrosterone (DHEA), two of them previously described (7beta-aminoDHEA and 7beta-amino-17-ethylenedioxy-DHEA), and a new one (3beta-hydroxy-5alpha-androstane-6,17-dione) were synthesized, and their effects were evaluated on memory. This study examined their effects on long term and short term memory in male (6 weeks old) NMRI mice in comparison with the reference drug. Long term memory was assessed using the passive avoidance task and short term memory (spatial working memory) using the spontaneous alternation task in a Y maze. Moreover, the effects of DHEA and its analogues on spontaneous locomotion were measured. In all tests, DHEA and analogues were injected at three equimolar doses (0.300-1.350-6.075 microM/kg). DHEA and its three analogues administered immediately post-training at the highest doses (6.075 microM/kg, s.c.) improved retention in passive avoidance test. Without effect per se in the spatial working memory task, the four compounds failed to reverse scopolamine (1mg/kg, i.p.)-induced deficit in spontaneous alternation. These data suggested an action of DHEA and analogues in consolidation of long term memory particularly when emotional components are implied. Moreover, data indicated that pharmacological modulation of DHEA as performed in this study provides derivatives giving the same mnemonic profile than reference molecule.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Expression of ovary-specific acidic protein in steroidogenic tissues: a possible role in steroidogenesis

Ovary-specific acidic protein (OSAP) is a novel molecule discovered from a genomic project designed to identify ovary-selective genes in mice. Whereas public databases suggest extraovarian expression of OSAP, its tissue distribution has not yet been well documented. Thus, the expression profile of mouse and human OSAP was determined by quantitative real-time RT-PCR using RNAs isolated from various tissues. The results demonstrate that the human and mouse OSAP expression profiles are similar; OSAP is prominently expressed in steroidogenic tissues with the highest level of expression observed in the adrenal gland. Placenta served as an exception and possessed minimal level of OSAP mRNA. Immunohistochemical studies show that mouse OSAP localizes almost exclusively to the steroid-producing cells of the ovary, adrenal gland, and testis. Consistent with predictions made by several subcellular localization algorithms, dual labeling studies in Y-1 mouse adrenocortical cells indicate OSAP resides in the mitochondria. Because of its abundant expression in steroidogenic cells and mitochondrial localization, a role for OSAP in steroidogenesis was determined. OSAP silencing by specific small interfering RNAs significantly inhibits 8-bromoadenosine-cAMP-induced progesterone production in Y-1 cells. Reduction in OSAP levels results in mitochondrial fragmentation and a decrease in the cellular content of mitochondrial DNA, indicative of decreased mitochondrial abundance. Lastly, 8-bromoadenosine-cAMP does not regulate OSAP protein expression in Y-1 cells as is the case for other steroidogenic components known to be induced by cAMP. Collectively these results suggest that OSAP is involved in steroidogenesis, potentially through its ability to maintain mitochondrial abundance and morphology.

Pregnanolone sulfate promotes desensitization of activated NMDA receptors

Neurosteroids are potent neuromodulators which act in part by binding to and modifying the activity of neurotransmitter-gated channels. Pregnanolone sulfate (PAS) is an endogenous neurosteroid that inhibits NMDA receptors and is neuroprotective in vivo. To delineate the mechanism of NMDA receptor inhibition by pregnanolone sulfate we used kinetic analyses of equilibrium single-channel currents recorded from individual GluN1/GluN2A receptors. Results show that PAS (0.1 mM) reduces single-channel open probability by 50% solely by increasing approximately 5-fold the mean time spent by receptors in closed conformations. From these data we derive a kinetic scheme that summarizes the effects of PAS on single channel kinetics, accounts for the PAS effects on macroscopic responses and leads us to propose that PAS inhibits NMDA receptor activity by shifting active receptors into desensitized conformations. These findings highlight the neurosteroid inhibitory site on NMDA receptors as a valuable therapeutic target against excitotoxic pathologies including acute and chronic neurodegeneration.

Allopregnanolone treatment delays cholesterol accumulation and reduces autophagic/lysosomal dysfunction and inflammation in Npc1-/- mouse brain

Niemann-Pick Type C (NPC) disease is a devastating developmental disorder with progressive and fatal neurodegeneration. Previous work has shown that a single injection of the neurosteroid allopregnanolone at postnatal day 7 significantly prolonged lifespan of Npc1-/- mice. However, the cellular/molecular basis for this beneficial effect remains undefined. Here, we further characterized the effect of allopregnanolone treatment on cholesterol accumulation, a pathological hallmark of NPC, as well as on autophagic/lysosomal dysfunction, myelination and inflammation in Npc1-/- mouse brains. At 1 month postnatal, accumulation of filipin-labeled unesterified cholesterol was clearly evident not only in neurons but also in microglia in untreated mutant mice, but was mostly absent in allopregnanolone-treated animals. Brain levels of the lysosomal enzymes cathepsins B and D were significantly higher in Npc1-/- than in wild-type mice. Levels of LC3-II, an autophagy marker, were also increased in mutant mouse brain as compared to wild-type mouse brain. Both changes were significantly reduced by allopregnanolone treatment. Injection of the neurosteroid also significantly reduced astrocyte proliferation and microglial activation. Furthermore, allopregnanolone treatment significantly enhanced myelination in mutant mice. Taken together, our results clearly show that allopregnanolone treatment not only reduces cholesterol accumulation and improves autophagic/lysosomal function but also enhances myelination and reduces inflammation. These results provide further support for the potential usefulness of allopregnanolone for treating NPC disease.

N-terminus of MAP2C as a neurosteroid-binding site

The kinetics of neurosteroid binding to recombinant human microtubule-associated protein 2C (rhMAP2C) and neurosteroid regulation of MAP2C-stimulated tubulin assembly were studied. In a quartz crystal microbalance assay, progesterone-BSA at 1-10 nM showed concentration-dependent binding to rhMAP2C, and this binding was competitively inhibited by pregnenolone or progesterone. However, no progesterone-BSA binding to N-terminal 71 amino acid residues rhMAP2C was found. In an rhMAP2C-stimulated tubulin assembly assay, pregnenolone enhanced the assembly of an rhMAP2C-progesterone-BSA complex in a progesterone-reversible manner, progesterone alone had no effect. Although N-terminal 71 amino acid residues rhMAP2C retains an activity to stimulate this assembly, this effect was not affected by pregnenolone or progesterone. These findings suggest that neurosteroids specifically bind to the N-terminus of rhMAP2 and regulate tubulin assembly.

Pregnenolone protects the PC-12 cell line against amyloid beta peptide toxicity but its sulfate ester does not

Pregnenolone (P), the main precursor of the steroids, and its sulfate ester, pregnenolone sulfate (PS), are the major neurosteroids produced in the neural tissue. Many neuroendocrinological studies stressed the neuroprotective role of neurosteroids although it has been suggested that the inhibition of P and PS synthesis can delay neuronal cell death. The potential roles of P and PS in vital neuronal functions and in amyloid beta peptide (Abeta) toxicity are not clearly identified. This work aims to investigate the effects of P and PS on cell viability and Abeta peptide toxicity in a concentration and exposure time-dependent manner in rat PC-12 cells. The cells were treated with 20muM Abeta peptide 25-35 and variable concentrations of P and PS ranging from 0.5muM to 100muM. To examine the effects of steroid treatment on Abeta peptide toxicity, 0.5muM (low) and 50muM (high) neurosteroids were used. The cell viability and lactate dehydrogenase release of cells were evaluated after 24, 48 and 72h. Morphological changes of cells were also examined. The treatment with higher than 1muM concentrations of P and PS significantly decreased the cell viability comparing to untreated cells. At lower concentrations, P and PS had no toxic actions until 72h. The Abeta treatment resulted in a significant decrease in cell viability comparing to untreated cells. P showed a dose-dependent protective effect against Abeta peptide in PC-12 cells. But its sulfate ester did not have the same effect on Abeta peptide toxicity, even it significantly decreased cell viability in Abeta-treated cells. Consequently, the discrepant effects of P and PS on Abeta peptide toxicity may provide insight on the pathogenesis of Alzheimer's disease.

The pathogenesis of Niemann-Pick type C disease: a role for autophagy?

Niemann-Pick type C disease (NPC) is a sphingolipid-storage disorder that results from inherited deficiencies of intracellular lipid-trafficking proteins, and is characterised by an accumulation of cholesterol and glycosphingolipids in late endosomes and lysosomes. Patients with this disorder develop progressive neurological impairment that often begins in childhood, is ultimately fatal and is currently untreatable. How impaired lipid trafficking leads to neurodegeneration is largely unknown. Here we review NPC clinical features and biochemical defects, and discuss model systems used to study this disorder. Recent studies have established that NPC is associated with an induction of autophagy, a regulated and evolutionarily conserved process by which cytoplasmic proteins are sequestered within autophagosomes and targeted for degradation. This pathway enables recycling of limited or damaged macromolecules to promote cell survival. However, in other instances, robust activation of autophagy leads to cell stress and programmed cell death. We summarise evidence showing that autophagy induction and flux are increased in NPC by signalling through a complex of the class III phosphoinositide 3-kinase and beclin-1. We propose that an imbalance between induction and flux through the autophagic pathway contributes to cell stress and neuronal loss in NPC and related sphingolipid-storage disorders, and discuss potential therapeutic strategies for modulating activity of this pathway.

Fast non-genomic effects of progesterone-derived neurosteroids on nociceptive thresholds and pain symptoms

Fast Inhibitory controls mediated by glycine (GlyRs) and GABAA receptors (GABAARs) play an important role to prevent the apparition of pathological pain symptoms of allodynia and hyperalgesia. The use of positive allosteric modulators of these receptors, specifically expressed in the spinal cord, may represent an interesting strategy to limit or block pain expression. In this study, we have used stereoisomers of progesterone metabolites, acting only via non-genomic effects, in order to evaluate the contribution of GlyRs and GABAARs for the reduction of mechanical and thermal heat hypernociception. We show that 3alpha neurosteroids were particularly efficient to elevate nociceptive thresholds in naive animal. It also reduced mechanical allodynia and thermal heat hyperalgesia in the carrageenan model of inflammatory pain. This effect is likely to be mediated by GABAA receptors since 3beta isomer was inefficient. More interestingly, 3alpha5beta neurosteroid was only efficient on mechanical allodynia while having no effect on thermal heat hyperalgesia. We characterized these paradoxical effects of 3alpha5beta neurosteroid using the strychnine and bicuculline models of allodynia. We clearly show that 3alpha5beta neurosteroid exerts an antinociceptive effect via a positive allosteric modulation of GABAARs but, at the same time, is pronociceptive by reducing GlyR function. This illustrates the importance of the inhibitory amino acid receptor channels and their allosteric modulators in spinal pain processing. Moreover, our results indicate that neurosteroids, which are synthesized in the dorsal horn of the spinal cord and have limited side effects, may be of significant interest in order to treat pathological pain symptoms.

Neurosteroids, immunosteroids, and the Balkanization of endocrinology

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic-pituitary-adrenal (HPA) axis for glucocorticoids. However, active steroids can also be synthesized locally in target tissues, either from circulating inactive precursors or de novo from cholesterol. Here, we review recent work demonstrating local steroid synthesis, with an emphasis on steroids synthesized in the brain (neurosteroids) and steroids synthesized in the immune system (immunosteroids). Furthermore, recent evidence suggests that other components of the HPG axis (luteinizing hormone and gonadotropin-releasing hormone) and HPA axis (adrenocorticotropic hormone and corticotropin-releasing hormone) are expressed locally in target tissues, potentially providing a mechanism for local regulation of neurosteroid and immunosteroid synthesis. The balance between systemic and local steroid signals depends critically on life history stage, species adaptations, and the costs of systemic signals. During particular life history stages, there can be a shift from systemic to local steroid signals. We propose that the shift to local synthesis and regulation of steroids within target tissues represents a "Balkanization" of the endocrine system, whereby individual tissues and organs may become capable of autonomously synthesizing and modulating local steroid signals, perhaps independently of the HPG and HPA axes.

Neonatal finasteride induces anxiogenic-like profile and deteriorates passive avoidance in adulthood after intrahippocampal neurosteroid administration

Recent findings indicate that neurosteroids could act as important keys during the brain development. Fluctuations in neonatal allopregnanolone (AlloP) could result in altered pharmacological properties of the GABA(A) receptor system in adulthood. Recent studies demonstrated that neurosteroids play a critical role in regulating normal neurodevelopment in the hippocampus. The aim of the present work is to screen whether developmentally altered neurosteroid levels influence the behavioral response to adult intrahippocampal administration of AlloP, a GABA(A) positive modulating neurosteroid, and pregnenolone sulfate (PregS), a GABA(A) negative modulator in rats. For this purpose, pups received AlloP (10 mg/kg, s.c.), a 5alpha-reductase inhibitor (finasteride, 50 mg/kg, s.c.) or vehicle from the fifth to the ninth postnatal day. At maturity (i.e. 90 days old) a bilateral cannula was implanted into the hippocampus. After recovery from surgery, animals received an administration of AlloP (0.2 microg/0.5 microl), PregS (5 ng/0.5 microl) or vehicle in each hippocampus 5 min before they were tested in the elevated plus maze (EPM) and immediately after the passive avoidance training session, and retention was tested 24 h later. Results indicated that neonatal finasteride treatment deteriorated passive avoidance retention and elicited an anxiogenic-like effect in the EPM test in adulthood, as seen by the reduction of open arm entries and in the time spent in the open arms. Intrahippocampal PregS administration also disrupted passive avoidance, possibly related to its anxiogenic profile. Fluctuations in neonatal AlloP affect the aversive learning and the anxiety-related behavior in adulthood, and this effect could be in part mediated by alterations of the mature functions of the hippocampus, possibly via the GABA(A) receptor. These data point to the role of GABAergic neurosteroids in critical periods of vulnerability that influence normal development of GABAergic pathways in the CNS.

Regulatory role of cytochrome P450scc and pregnenolone in myelination by rat Schwann cells

To investigate the production of steroid hormones by Schwann cells and to examine the regulation of steroid hormone production during myelination, cultures of rat Schwann cells were differentiated into their myelinating phenotype in the absence of neurons with dibutyryl cAMP (db-cAMP). During this process, the expression of P450scc (involved in steroid biosynthesis) was elevated at both the mRNA and protein levels as evident in RT-PCR, Western blots, and immunostaining. Labeling of the cells with [14C] acetate revealed enhanced production of pregnenolone during differentiation into the myelinating phenotype. Disruption of P450scc's activity with an inhibitor diminished the extent of differentiation into the myelinating phenotype as levels of mRNA and protein expression of myelin protein zero (P0) declined. However, the effect was reversed with the addition of pregnenolone. Furthermore, when the differentiating cultures were treated with pregnenolone, mRNA expression of P0 was upregulated, suggesting the stimulation of the differentiation process. Together, these results provide evidence for Schwann cells as a major producer of steroid hormones and pregnenolone production by P450scc as an important regulatory step during myelination.

Multiple roles for sphingolipids in steroid hormone biosynthesis

Steroid hormones are essential regulators of a vast number of physiological processes. The biosynthesis of these chemical messengers occurs in specialized steroidogenic tissues via a multi-step process that is catalyzed by members of the cytochrome P450 superfamily of monooxygenases and hydroxysteroid dehydrogenases. Though numerous signaling mediators, including cytokines and growth factors control steroidogenesis, trophic peptide hormones are the primary regulators of steroid hormone production. These peptide hormones activate a cAMP/cAMP-dependent kinase (PKA) signaling pathway, however, studies have shown that crosstalk between multiple signal transduction pathways and signaling molecules modulates optimal steroidogenic capacity. Sphingolipids such as ceramide, sphingosine, sphingosine-1-phosphate, sphingomyelin, and gangliosides have been shown to control the steroid hormone biosynthetic pathway at multiple levels, including regulating steroidogenic gene expression and activity as well as acting as second messengers in signaling cascades. In this review, we provide an overview of recent studies that have investigated the role of sphingolipids in adrenal, gonadal, and neural steroidogenesis.