Neurotrophic estrogens: essential profile and endpoints for drug discovery.

Criteria for the early recognition of selective neurotrophic action are crucial for the discovery of estrogens for supplementation therapy. The comparative characterization of 'tool' compounds in different paradigms demonstrates that estrogen-mediated CNS effects are discernible before the manifestation of changes in primary target organs. Agonist activity at, and recruitment of the coactivator SRC-1 by, the estrogen receptor alpha accurately reflect peripheral, but not neurotrophic, efficacy. Interaction with, and SRC-1 recruitment at, the estrogen receptor beta appears to be an essential prerequisite for pronounced CNS effects. Monitoring of the hypothalamo-pituitary-adrenal axis activity and the differential organ-specific induction of estrogen-responsive proteins are helpful for early delineation of CNS efficacy. Behavioral and antioxidant efficacy are useful confirmatory readouts, with limited roles in lead selection. Finally, an algorithm for the identification of estrogens with a neurotrophic profile can be generated by assigning 'performance grades' in a multifarious test array.

Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF-2 deficient mice.

The transcription-intermediary-factor-2 (TIF-2) is a coactivator of the glucocorticoid receptor (GR), and its disruption would be expected to influence glucocorticoid-mediated control of the hypothalamo-pituitary-adrenal (HPA) axis. Here, we show that its targeted deletion in mice is associated with altered expression of several glucocorticoid-dependent components of HPA regulation (e.g., corticotropin-releasing hormone, vasopressin, ACTH, glucocorticoid receptors), suggestive of hyperactivity under basal conditions. At the same time, TIF-2(-/-) mice display significantly lower basal corticosterone levels and a sluggish and blunted initial secretory response to brief emotional and prolonged physical stress. Subsequent analysis revealed this discrepancy to result from pronounced aberrations in the structure and function of the adrenal gland, including the cytoarchitectural organization of the zona fasciculata and basal and stress-induced expression of key elements of steroid hormone synthesis, such as the steroidogenic acute regulatory (StAR) protein and 3beta-hydroxysteroid dehydrogenase (3beta-HSD). In addition, altered expression levels of two nuclear receptors, DAX-1 and steroidogenic factor 1 (SF-1), in the adrenal cortex strengthen the view that TIF-2 deletion disrupts adrenocortical development and steroid biosynthesis. Thus, hyperactivity of the hypothalamo-pituitary unit is ascribed to insidious adrenal insufficiency and impaired glucocorticoid feedback.

FoxG1, a member of the forkhead family, is a corepressor of the androgen receptor.

The androgen receptor (AR) is a ligand-dependent transcriptional regulator which belongs to the nuclear receptor superfamily. The basal transcriptional activity of the androgen receptor is regulated by interaction with coactivator or corepressor proteins. The exact mechanism whereby comodulators influence target gene transcription is only partially understood, especially for corepressors. Whereas several coactivators are described for the AR, only a few corepressors are known. Here, we describe the discovery of a new androgen receptor corepressor, FoxG1, which belongs to the forkhead family. By using a fragment of the AR (aa 325-919) as bait in a yeast two hybrid screen, the C-terminal region (aa 175-489) of FoxG1 (also known as BF1), was identified as AR-interacting protein. Binding of AR to the FoxG1 fragment was verified by one- and two-hybrid assays, and pull-down experiments. In addition, we show that the full-length form of FoxG1 functions as a strong corepressor in the AR-mediated transactivation. The FoxG1 expression profile in adult individuals is restricted to brain and testis in human and decreases during aging in the rodent brain. Both AR and FoxG1 expression are developmentally regulated. Besides its reported role in neurogenesis, the strong expression of FoxG1 in AR-abundant areas of the adult brain suggests possible involvement in neuroendocrine regulation. Taken together, the data presented suggest that, in addition to repression of transcription by direct binding to DNA, FoxG1 may interact with AR in vivo, thereby targeting its repressor function specifically to sex hormone signaling.

Experimental models of stress.

Illustrating the complexity of the stress response and its multifaceted manifestations is the leading idea of this overview of experimental paradigms used for stress induction in laboratory animals. The description of key features of models based on naturalistic stressors, pharmacological challenges, and genomic manipulations is complemented by comprehensive analysis of physiological, behavioral, neurochemical, and endocrine changes and their appropriateness as outcome readouts. Particular attention has been paid to the role of sex and age as determinants of the dynamics of the stress response. Possible translational applications of stress-inducing paradigms as models of disease are briefly sketched.

Developmental expression profiles and distinct regional estrogen responsiveness suggest a novel role for the steroid receptor coactivator SRC-1 as discriminative amplifier of estrogen signaling in the rat brain.

The regional distribution, developmental profiles, and gonadectomy- and estrogen-induced changes in the density of transcripts encoding the steroid receptor coactivator-1 (SRC-1) were examined in the female rat brain by semiquantitative in situ hybridization. The results demonstrate striking differences in the abundance of SRC-1 mRNA in discrete brain regions throughout ontogeny. Whereas transcript densities gradually decreased with age in the cerebral cortex, they peaked prominently during the peripubertal period in the hypothalamic medial preoptic area (MPOA) and ventromedial nucleus (VMN). Gonadectomy and estrogen substitution influenced SRC-1 mRNA levels in sexually mature animals in a region-specific fashion. Ovariectomy resulted in a down-regulation of SRC-1 mRNA levels in the VMN, a brain region richly endowed with estrogen receptors and playing a major role in neuroendocrine control of reproductive functions. In contrast, SRC-1 transcript levels were significantly up-regulated after estradiol treatment. Interestingly, SRC-1 expression in the cortex was refractory to alterations of the estrogen milieu. The obtained SRC-1 mRNA expression profiles during development clearly demonstrate brain region specificity and regulation by estrogen, thus it is proposed that SRC-1 amplifies estrogen receptor-dependent transcription in a temporally and spatially coordinated manner and therefore contributes to the functional specialization of brain areas involved in the regulation of reproduction.

Interactions of sex steroids with mechanisms of inflammation.

Differential sex-specific liability to inflammatory and autoimmune diseases, and changes in symptom severity in association with physiological fluctuations in gonadal secretions are indicative of significant contribution of sex hormones to the regulation of immune responsiveness. Apart from a postulated role in sex-specific organization of the immune system during ontogeny, gonadal steroids may influence the immune response in numerous ways. This review analyzes existing concepts, experimental and clinical data, aiming at the definition of cellular and molecular mechanisms which may serve as suitable targets for discovery of immunomodulatory drugs whose principal feature is specific interaction with sex hormone receptors. Separation of immunomodulatory effects of sex steroids from those which are exerted by glucocorticoids, and subsequent identification of sex-hormone-specific molecular targets appear to be crucial for the justification of drug discovery on the basis of sex steroid receptor ligands.

Neurotropic action of androgens: principles, mechanisms and novel targets.

The importance of androgen signaling is well recognized for numerous aspects of central nervous system (CNS) function, ranging from sex-specific organization of neuroendocrine and behavioral circuits to adaptive capacity, resistance and repair. Nonetheless, concepts for the therapeutic use of androgens in neurological and mental disorders are far from being established. This review outlines some critical issues which interfere with decisions on the suitability of androgens as therapeutic agents for CNS conditions. Among these, sex-specific organization of neural substrates and resulting differential responsiveness to endogenous gonadal steroids, convergence of steroid hormone actions on common molecular targets, co-presence of different sex steroid receptors in target neuronal populations, and in situ biotransformation of natural androgens apparently pose the principal obstacles for the characterization of specific neurotropic effects of androgens. Additional important, albeit less explored aspects consist in insufficient knowledge about molecular targets in the CNS which are under exclusive or predominant androgen control. Own experimental data illustrate the variability of pharmacological effects of natural and synthetic androgens on CNS functions of adaptive relevance, such as sexual behavior, anxiety and endocrine responsiveness to stress. Finally, we present results from an analysis of the consequences of aging for the rat brain transcriptome and examination of the influence of androgens on differentially expressed genes with presumable significance in neuropathology.

Endpoints of drug discovery for menopausal vasomotor symptoms: interpretation of data from a proxy of disease.

OBJECTIVE: Estrogen supplementation is considered a reliable therapeutic approach to symptoms of vasomotor dysregulation (hot flashes) associated with the menopausal transition and sex hormone deprivation. Implication of changes in central neurotransmission in the pathogenesis of hot flashes has prompted the off-label use of serotonergic and γ-aminobutyric acid-ergic drugs as a therapeutic alternative, claiming similarity of outcomes to those of estrogen treatment. METHODS: Using telemetric recordings in a rat model of estrogen deficit-induced vasomotor dysregulation, we compared the long- and short-term effects of estrogen supplementation and treatment with neuropharmaceuticals (venlafaxine, desvenlafaxine, fluoxetine, agomelatine, gabapentin) on endpoints of thermoregulation. RESULTS: Among the tested drugs, only fluoxetine was capable to emulate the restorative action of estradiol on the diurnal oscillations in skin temperature and control of heat dissipation. Unlike estradiol, several of the tested compounds produced marked transient decreases in skin temperature within the first 2 hours of application while being unable to restore physiological diurnal patterns of thermoregulation. CONCLUSIONS: Our findings suggest that in this animal model of impaired thermoregulation, neuropharmaceuticals may simulate therapeutic effects by eliciting immediate but transient hypothermia, which is not associated with the recovery of physiological control of heat dissipation. Therefore, short-term monitoring of drug actions in this disease model may considerably bias readouts of drug discovery for menopausal vasomotor symptoms.

A novel variant of the putative demethylase gene, s-JMJD1C, is a coactivator of the AR.

Evidence is accumulating in support of the view that tissue-specific effects of steroid hormones depend on the recruitment of nuclear receptor comodulator proteins. The latter interact directly with the hormone receptors and modify their transcriptional effects on specific target genes. The mechanisms of comodulator influence on nuclear receptor-controlled gene transcription is only partially understood. Here, we describe the discovery of a new AR coactivator which belongs to the JmjC containing enzyme family as a novel variant of JMJD1C (jumonji domain-containing 1C). By using a fragment of the human AR (aa 325-919) as bait in a yeast two-hybrid screen, a region of the human JMJD1C gene was identified as interacting with AR. A novel splice variant s-JMJD1C was amplified by RACE, and the binding to AR was analysed by GST-pull-down and mammalian one-hybrid experiments. As a nuclear-localized protein, the s-JMJD1C gene is expressed in a variety of human tissues. In the brain, this protein is present in several, but not confined to, AR-expressing neuronal populations and its abundance varies with the hormonal status in a region-specific fashion. Interestingly, the expression of s-JMJD1C is reduced in breast cancer tumors and significantly higher in normal breast tissues indicating a putative role in tumor suppression. As s-JMJD1C has putative demethylase activity, removal of methylation seems to be important for nuclear receptor-based gene regulation.