Estrogen-induced cell signaling in the sexually dimorphic nucleus of the rat preoptic area: potential involvement of cofilin in actin dynamics for cell migration

Preoptic and hypothalamic regulation of multi-tiered, chronologically arranged female rat sexual behavior

As in many mammalian behaviors, sexual behavior exhibits structure. Each modular components of the structure, that are linked together over time, occur in probabilistic manner. Endocrine milieu, in particular sex hormones, define the probability to synchronize the behavior with the production of gametes. Developmental experience and environmental cues affect the hormonal milieu of the brain. This is especially true in female mammals, in which ova mature with certain intervals along with ovarian secretion of sex hormones. Estrogens secreted by mature ovarian follicles support both affiliative and executive components of female sexual behavior. In the absence of the ovarian steroids, females avoid males when possible, or antagonize and reject males when put together. Female sexual behavior is intimately linked with the estrous cycle in many species such that females are only receptive for a brief period at the estrus stage surrounding ovulation. Thus, in the rat, females strongly influence the outcome of mating encounter with a male. Affiliative or solicitatory behavior shown by females in estrus leads to the female adapting the lordosis posture, which is characterized by hindleg postural rigidity and lordotic dorsiflexion of the spine, in response to touch-pressure somatosensory stimuli on the skin of the flanks, rump-tail base, perineum region given by male partner. The posture facilitates intromission and consequently fertilization. Although dependence on estrogens is the most important feature of female rat sexual behavior, cervical probing combined with palpation of the hindquarter skin acts as a supranormal stimulus to elicit lordosis. Thus, lordosis behavior is a hub of multi-tiered, chronologically arranged set of behaviors and estrogen appear to alter excitability of neural network for lordosis.

Differential protein expression profile in the hypothalamic GT1-7 cell line after exposure to anabolic androgenic steroids

The abuse of anabolic androgenic steroids (AAS) has been considered a major public health problem during decades. Supraphysiological doses of AAS may lead to a variety of neuroendocrine problems. Precisely, the hypothalamic-pituitary-gonadal (HPG) axis is one of the body systems that is mainly influenced by steroidal hormones. Fluctuations of the hormonal milieu result in alterations of reproductive function, which are made through changes in hypothalamic neurons expressing gonadotropin-releasing hormone (GnRH). In fact, previous studies have shown that AAS modulate the activity of these neurons through steroid-sensitive afferents. To increase knowledge about the cellular mechanisms induced by AAS in GnRH neurons, we performed proteomic analyses of the murine hypothalamic GT1-7 cell line after exposure to 17α-methyltestosterone (17α-meT; 1 μM). These cells represent a good model for studying regulatory processes because they exhibit the typical characteristics of GnRH neurons, and respond to compounds that modulate GnRH in vivo. Two-dimensional difference in gel electrophoresis (2D-DIGE) and mass spectrometry analyses identified a total of 17 different proteins that were significantly affected by supraphysiological levels of AAS. Furthermore, pathway analyses showed that modulated proteins were mainly associated to glucose metabolism, drug detoxification, stress response and cell cycle. Validation of many of these proteins, such as GSTM1, ERH, GAPDH, PEBP1 and PDIA6, were confirmed by western blotting. We further demonstrated that AAS exposure decreased expression of estrogen receptors and GnRH, while two important signaling pathway proteins p-ERK, and p-p38, were modulated. Our results suggest that steroids have the capacity to directly affect the neuroendocrine system by modulating key cellular processes for the control of reproductive function.

Proteomic analyses of limbic regions in neonatal male, female and androgen receptor knockout mice

Background

It is well-established that organizational effects of sex steroids during early development are fundamental for sex-typical displays of, for example, mating and aggressive behaviors in rodents and other species. Male and female brains are known to differ with respect to neuronal morphology in particular regions of the brain, including the number and size of neurons, and the density and length of dendrites in nuclei of hypothalamus and amygdala. The aim of the present study was to use global proteomics to identify proteins differentially expressed in hypothalamus/amygdala during early development (postnatal day 8) of male, female and conditional androgen receptor knockout (AR^NesDel) male mice, lacking androgen receptors specifically in the brain. Furthermore, verification of selected sexually dimorphic proteins was performed using targeted proteomics.

Results

Our proteomic approach, iTRAQ, allowed us to investigate expression differences in the 2998 most abundantly expressed proteins in our dissected tissues. Approximately 170 proteins differed between the sexes, and 38 proteins between AR^NesDel and control males (p < 0.05). In line with previous explorative studies of sexually dimorphic gene expression we mainly detected subtle protein expression differences (fold changes <1.3). The protein MARCKS (myristoylated alanine rich C kinase substrate), having the largest fold change of the proteins selected from the iTRAQ analyses and of known importance for synaptic transmission and dendritic branching, was confirmed by targeted proteomics as differentially expressed between the sexes.

Conclusions

Overall, our results provide solid evidence that a large number of proteins show sex differences in their brain expression and could potentially be involved in brain sexual differentiation. Furthermore, our finding of a sexually dimorphic expression of MARCKS in the brain during development warrants further investigation on the involvement in sexual differentiation of this protein.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0332-1) contains supplementary material, which is available to authorized users.

DNA microarray-based gene expression profiling of estrogenic chemicals

We summarize updated information about DNA microarray-based gene expression profiling by focusing on its application to estrogenic chemicals. First, estrogenic chemicals, including natural/industrial estrogens and phytoestrogens, and the methods for detection and evaluation of estrogenic chemicals were overviewed along with a comprehensive list of estrogenic chemicals of natural or industrial origin. Second, gene expression profiling of chemicals using a focused microarray containing estrogen-responsive genes is summarized. Third, silent estrogens, a new type of estrogenic chemicals characterized by their estrogenic gene expression profiles without growth stimulative or inhibitory effects, have been identified so far exclusively by DNA microarray assay. Lastly, the prospect of a microarray assay is discussed, including issues such as commercialization, future directions of applications and quality control methods.

Higher level of plasma bioactive molecule sphingosine 1-phosphate in women is associated with estrogen

Both sphingosine 1-phosphate (S1P) and estrogen have been documented to play endothelial protective roles. However, it remains unclear whether estrogen could regulate the anabolism of the bioactive molecule S1P and the underlying mechanisms. In this study, 108 healthy participants were separated into three age groups, and their plasma S1P levels were analyzed by liquid chromatography tandem mass spectrometry. Results showed that the plasma S1P levels were significantly higher in women than those in men within the age of 16-55years old and higher in pre-menopausal than post-menopausal women. The experiment in C57 BL/6 mice confirmed the gender difference of plasma S1P level. In vitro study demonstrated that after the stimulation of 17β-estradiol (E2), S1P levels both in EA.hy926 cells and the culture media were increased about 9 and 3 times, respectively; the mRNA expression, the protein level and the activity of sphingosine kinase (SphK) 1, not SphK2, were markedly increased; the mRNA and protein expression of ATP-binding cassette transporter (ABC) C1, G2 and S1P transporter spinster homolog 2 (Spns2) were significantly elevated; furthermore, the mRNA and protein expressions of S1P receptors (S1PRs) 1-2 were increased in a time-dependent manner. This study suggests that E2 markedly improves S1P synthesis by activating SphK1 and induces S1P export via activating ABCC1, G2 and Spns2 from endothelium system, which may consequently lead to the gender difference of plasma S1P in adult human and mouse. The results of this study suggest that E2 may exert its vasculoprotective function by activation of the SphK1-S1P-S1PR signaling axis.

Estrogen Regulates Protein Synthesis and Actin Polymerization in Hippocampal Neurons through Different Molecular Mechanisms

Estrogen rapidly modulates hippocampal synaptic plasticity by activating selective membrane-associated receptors. Reorganization of the actin cytoskeleton and stimulation of mammalian target of rapamycin (mTOR)-mediated protein synthesis are two major events required for the consolidation of hippocampal long-term potentiation and memory. Estradiol regulates synaptic plasticity by interacting with both processes, but the underlying molecular mechanisms are not yet fully understood. Here, we used acute rat hippocampal slices to analyze the mechanisms underlying rapid changes in mTOR activity and actin polymerization elicited by estradiol. Estradiol-induced mTOR phosphorylation was preceded by rapid and transient activation of both extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) and by phosphatase and tensin homolog (PTEN) degradation. These effects were prevented by calpain and ERK inhibitors. Estradiol-induced mTOR stimulation did not require activation of classical estrogen receptors (ER), as specific ERα and ERβ agonists (PPT and DPN, respectively) failed to mimic this effect, and ER antagonists could not block it. Estradiol rapidly activated both RhoA and p21-activated kinase (PAK). Furthermore, a specific inhibitor of RhoA kinase (ROCK), H1152, and a potent and specific PAK inhibitor, PF-3758309, blocked estradiol-induced cofilin phosphorylation and actin polymerization. ER antagonists also blocked these effects of estrogen. Consistently, both PPT and DPN stimulated PAK and cofilin phosphorylation as well as actin polymerization. Finally, the effects of estradiol on actin polymerization were insensitive to protein synthesis inhibitors, but its stimulation of mTOR activity was impaired by latrunculin A, a drug that disrupts actin filaments. Taken together, our results indicate that estradiol regulates local protein synthesis and cytoskeletal reorganization via different molecular mechanisms and signaling pathways.