Vladimir Patchev

Gender differences in the regulation of 3α-hydroxysteroid dehydrogenase in rat brain and sensitivity to neurosteroid-mediated stress protection

The enzyme 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) is involved in the generation of neuroactive steroids through ring-A-reduction of hormonal precursors. We examined the developmental regulation of, gender differences in, and effects of hormonal manipulations on the expression of 3 alpha-HSD in the rat hippocampus. High levels of 3 alpha-HSD mRNA were found on postnatal day 7, coinciding with the stress hyporesponsive period in the rat. Gender differences in 3 alpha-HSD expression were documented during puberty, but not in adulthood. Adrenalectomy and gonadectomy, and supplementation with individual steroid hormones influenced 3 alpha-HSD expression in a gender-specific mode. We also demonstrate that the manifestation of behavioral and endocrine consequences of early life stress depends on the individuals gender and gonadal status. Males are liable to aftereffects of neonatal maternal deprivation, regardless of their adult gonadal status. In females, however, anxiogenic aftereffects of neonatal stress become apparent only after gonadectomy. These data suggest that (i) transient increase of neurosteroid biosynthesis may contribute to stress hyporesponsiveness during early infancy; (ii) gonadal steroids regulate 3 alpha-HSD expression in the hippocampus in a sex-specific mode; (iii) physiological sex steroid secretions in females may mask behavioral consequences of adverse early life events, and (iv) concomitant treatment with the neurosteroid THP counteracts behavioral and endocrine dysregulation induced by neonatal stress in both genders.

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.

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 hypothalamopituitary‐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 3β‐hydroxysteroid dehydrogenase (3(‐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. Patchev, A. V., Fischer, D., Wolf, S. S., Götz, F., Gehin, M., Chambon, P., Patchev, V. K., and Almeida O. F. X. Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF‐2 deficient mice. FASEB J. 21, 231–238 (2007)

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.

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.

Selected aspects of endocrine pharmacology of the aging male

This minireview explores the endocrinology and the clinical consequences of age-related hypogonadism (hypotestosteronemia). In addition, pharmacological and clinical applicability of new androgen formulations is described briefly. Other topics include selective androgen receptor modulators, non-feminizing estrogens, and the possible use of selective aromatase modulators. Finally, a theoretical concept of hormone displacement (i.e. excessive hormone production) is introduced using cortisol as an example.

The Role of ERα and ERβ in theProstate: Insights from Genetic Models and Isoform-Selective Ligands

Androgens are known regulators of the growth and differentiation of the prostate gland and are effective during development and maturity as well as in disease. The role of estrogens is less well characterized, but dual direct and indirect actions on prostate growth and differentiation have been demonstrated, facilitated via both ERα and ERβ. Previous studies using animal models to determine the role of ERβ in the prostate have been problematic due to the centrally mediated responses to estrogen administration via ERα that can lower androgen levels and lead to epithelial regression, thereby masking any direct effects on the prostate mediated by ERβ. Our alternate approach was to use the estrogen-deficient aromatase knockout (ArKO) mouse and the method of tissue recombination to provide new insight into estrogen action on prostate growth and pathology. Firstly, utilizing homo- and heterotypic tissue recombinants, we demonstrate that stromal aromatase deficiency results in the induction of hyperplasia in previously normal prostatic epithelium and that this response is the result of local changes to the paracrine interaction between stroma and epithelium. Secondly, using tissue recombination and an ERβ-specific agonist, we demonstrate that the activation of ERβ results in an anti-proliferative response that is not influenced by alterations to systemic androgen levels or activation of ERα. Finally, using intact ArKO mice this study demonstrates that the administration of an ERβ-specific agonist abrogates existing hyperplastic epithelial pathology specifically in the prostate but an ERβ-specific agonist does not. Therefore, in the absence of stromal aromatase gene expression, epithelial proliferation, leading to prostatic hypertrophy and hyperplasia, may result from a combination of androgenic stimulation of proliferation and failed activation of ERβ by locally synthesized estrogens. These data demonstrate essential and beneficial effects of estrogens that are necessary for normal growth of the prostate and distinguish them from those that adversely alter prostate growth and differentiation. This indicates the potential of antiandrogens and SERMS, as opposed to aromatase inhibitors, for the management of prostate hyperplasia and hypertrophy.

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

ObjectiveEstrogen 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 &ggr;-aminobutyric acid-ergic drugs as a therapeutic alternative, claiming similarity of outcomes to those of estrogen treatment. MethodsUsing 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. ResultsAmong 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. ConclusionsOur 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.