Estrogen receptor ␤ (ER␤) and androgen receptor (AR) are found in high levels within populations of neurons in the hypothalamus. To determine whether AR or ER␤ plays a role in regulating hypothalamo-pituitary-adrenal (HPA) axis function by direct action on these neurons, we examined the effects of central implants of 17␤-estradiol (E2), 5␣-dihydrotestosterone (DHT), the DHT metabolite 5␣-androstan-3␤,17␤-diol (3␤-diol), and several ER subtype-selective agonists on the corticosterone and adrenocorticotropin (ACTH) response to immobilization stress. In addition, activation of neurons in the paraventricular nucleus (PVN) was monitored by examining c-fos mRNA expression. Pellets containing these compounds were stereotaxically implanted near the PVN of gonadectomized male rats. Seven days later, animals were killed directly from their home cage (nonstressed) or were restrained for 30 min (stressed) before they were killed. Compared with controls, E2 and the ER␣-selective agonists moxestrol and propyl-pyrazole-triol significantly increased the stress induced release of corticosterone and ACTH. In contrast, central administration of DHT, 3␤-diol, and the ER␤-selective compound diarylpropionitrile significantly decreased the corticosterone and ACTH response to immobilization. Cotreatment with the ER antagonist tamoxifen completely blocked the effects of 3␤-diol and partially blocked the effect of DHT, whereas the AR antagonist flutamide had no effect. Moreover, DHT, 3␤-diol, and diarylpropionitrile treatment significantly decreased restraint-induced c-fos mRNA expression in the PVN. Together, these studies indicate that the inhibitory effects of DHT on HPA axis activity may be in part mediated via its conversion to 3␤-diol and subsequent binding to ER␤.

The complexity of gonadal steroid hormone actions is reflected in their broad and diverse effects on a host of integrated systems including reproductive physiology, sexual behavior, stress responses, immune function, cognition, and neural protection. Understanding the specific contributions of androgens and estrogens in neurons that mediate these important biological processes is central to the study of neuroendocrinology. Of particular interest in recent years has been the biological role of androgen metabolites. The goal of this review is to highlight recent data delineating the specific brain targets for the dihydrotestosterone metabolite, 5α-androstane, 3β, 17β-diol (3β-Diol). Studies using both in vitro and in vivo approaches provide compelling evidence that 3β-Diol is an important modulator of the stress response mediated by the hypothalmo-pituitary-adrenal axis. Further, the actions of 3β-Diol are mediated by estrogen receptors, and not androgen receptors, often through a canonical estrogen response element in the promoter of a given target gene. These novel findings compel us to re-evaluate the interpretation of past studies and the design of future experiments aimed at elucidating the specific effects of androgen receptor signaling pathways.

5α-Androstane-3β, 17β-diol (3βAdiol) is a metabolite of the potent androgen, 5α-dihydrotestosterone. Recent studies showed that 3βAdiol binds to estrogen receptor (ER)-β and regulates growth of the prostate gland through an estrogen, and not androgen, receptor-mediated pathway. These data raise the possibility that 3βAdiol could regulate important physiological processes in other tissues that produce 3βAdiol, such as the brain. Although it is widely accepted that the brain is a target for 5α-dihydrotestosterone action, there is no evidence that 3βAdiol has a direct action in neurons. To explore the molecular mechanisms by which 3βAdiol might act to modulate gene transcription in neuronal cells, we examined whether 3βAdiol activates ER-mediated promoter activity and whether ER transactivation is facilitated by a classical estrogen response element (ERE) or an AP-1 complex. The HT-22 neuronal cell line was cotransfected with an expression vector containing ERα, ER-β1, or the ERβ splice variant, ER-β2 and one of two luciferase-reporter constructs containing either a consensus ERE or an AP-1 enhancer site. Cells were treated with 100 nm 17β-estradiol, 100 nm 3βAdiol, or vehicle for 15 h. We show that 3βAdiol activated ER-β1-induced transcription mediated by an ERE equivalent to that of 17β-estradiol. By contrast, 3βAdiol had no effect on ERα- or ER-β2-mediated promoter activity. Moreover, ER-β1 stimulated transcription mediated by an ERE and inhibited transcription by an AP-1 site in the absence of ligand binding. These data provide evidence for activation of ER signaling pathways by an androgen metabolite in neuronal cells.

The dichotomous anxiogenic and anxiolytic properties of estrogens have been reported to be mediated by two distinct neural estrogen receptors (ER), ERα and ERβ, respectively. Using a combination of pharmacological and genetic approaches, we confirmed that the anxiolytic actions of estradiol are mediated by ERβ and extended and these observations to demonstrate the neuroanatomical targets involved in ERβ activation in these behavioral responses. We examined the effects of the biologically active S-enantiomer of diarylpropionitrile (S-DPN) on anxiety-related behavioral measures, the corresponding stress hormonal response to hypothalamo-pituitary-adrenal axis reactivity, and potential sites of neuronal activation in mutant female mice carrying a null mutation for ERβ gene (βERKO). S-DPN administration significantly reduced anxiety-like behaviors in the open field, light-dark exploration, and the elevated plus maze (EPM) in ovariectomized wild-type (WT) mice, but not in their βERKO littermates. Stress-induced corticosterone (CORT) and ACTH were also attenuated by S-DPN in the WT mice but not in the βERKO mice. Using c-fos induction after elevated plus maze, as a marker of stress-induced neuronal activation, we identified the anterodorsal medial amygdala and bed nucleus of the stria terminalis as the neuronal targets of S-DPN action. Both areas showed elevated c-fos mRNA expression with S-DPN treatment in the WT but not βERKO females. These studies provide compelling evidence for anxiolytic effects mediated by ERβ, and its neuroanatomical targets, that send or receive projections to/from the paraventricular nucleus, providing potential indirect mode of action for the control of hypothalamo-pituitary-adrenal axis function and behaviors.

SummaryMycobacterium tuberculosis ( M. tb ) uses the glyoxalate bypass for intracellular survival in vivo . These studies provide evidence that the M. tb malate synthase (MS) has adapted to function as an adhesin which binds to laminin and fibronectin. This binding is achieved via the unique C-terminal region of the M. tb MS. The ability to function as an adhesin necessitates extracellular localization. We provide evidence that despite the absence of a Sec-translocation signal sequence the M. tb MS is secreted/excreted, and is anchored on the cell wall by an undefined mechanism. The MS of Mycobacterium smegmatis is cytoplasmic but the M. tb MS expressed in M. smegmatis localizes to the cell wall and enhances the adherence of the bacteria to lung epithelial A549 cells. Antibodies to the C-terminal laminin/fibronectin-binding domain interfere with the binding of the M. tb MS to laminin and fibronectin and reduce the adherence of M. tb to A549 cells. Coupled to the earlier evidence of in vivo expression of M. tb MS during active but not latent infection in humans, these studies show that a housekeeping enzyme of M. tb contributes to its armamentarium of virulence promoting factors.