Sex differences and synchronous development of steroid receptor coactivator-1 and synaptic proteins in the hippocampus of postnatal female and male C57BL/6 mice

Sex Differences in Organophosphate Model of Benzodiazepine-Refractory Status Epilepticus and Neuronal Damage

Sex differences are common in human epilepsy. Although men are more susceptible to seizure than women, the mechanisms underlying sex-specific vulnerabilities to seizure are unclear. The organophosphate (OP) diisopropylfluorophosphate (DFP) is known to cause neurotoxicity and status epilepticus (SE), a serious neurologic condition that causes prolonged seizures and brain damage. Current therapies for OP poisoning and SE do not consider neuronal variations between male and female brains. Therefore, we investigated sex-dependent differences in electrographic seizure activity and neuronal injury using the DFP model of refractory SE in rats. Electroencephalogram recordings were used to monitor DFP-induced SE, and the extent of brain injury was determined using fluoro-jade-B staining to detect cellular necrosis. After DFP exposure, we observed striking sex-dependent differences in SE and seizure activity patterns as well as protective responses to midazolam treatment. Following acute DFP exposure, male animals displayed more severe SE with intense epileptiform spiking and greater mortality than females. In contrast, we observed significantly more injured cells and cellular necrosis in the hippocampus and other brain regions in females than in males. We also observed extensive neuronal injury in the somatosensory cortex of males. The anticonvulsant effect of midazolam against SE was limited in this model and found to be similar in males and females. However, unlike males, females exhibited substantially more protection against neuronal damage after midazolam treatment. Overall, these results demonstrate significant sex-dependent differences in DFP-induced refractory SE and neuronal damage patterns, suggesting that it may be possible to develop sex-specific neuroprotective strategies for OP intoxication and refractory SE. SIGNIFICANCE STATEMENT: Sex-dependent differences in neurotoxicity and status epilepticus (SE) are key biological variables after organophosphate (OP) exposure. Here, we investigated sex-dependent differences in SE and brain injury after acute diisopropylfluorophosphate exposure. Male rats had more severe SE and less survival than females, while females had more neuronal damage. Females had more neuroprotection to midazolam than males, while both sexes had similar but partial anticonvulsant effects. These findings suggest that a sex-specific therapeutic approach may prevent neurological complications of OP-induced SE.

Sex-specific acute and chronic neurotoxicity of acute diisopropylfluorophosphate (DFP)-intoxication in juvenile Sprague-Dawley rats

Preclinical efforts to improve medical countermeasures against organophosphate (OP) chemical threat agents have largely focused on adult male models. However, age and sex have been shown to influence the neurotoxicity of repeated low-level OP exposure. Therefore, to determine the influence of sex and age on outcomes associated with acute OP intoxication, postnatal day 28 Sprague-Dawley male and female rats were exposed to the OP diisopropylfluorophosphate (DFP; 3.4 mg/kg, s.c.) or an equal volume of vehicle (∼80 µL saline, s.c.) followed by atropine sulfate (0.1 mg/kg, i.m.) and pralidoxime (2-PAM; 25 mg/kg, i.m.). Seizure activity was assessed during the first 4 h post-exposure using behavioral criteria and electroencephalographic (EEG) recordings. At 1 d post-exposure, acetylcholinesterase (AChE) activity was measured in cortical tissue, and at 1, 7, and 28 d post-exposure, brains were collected for neuropathologic analyses. At 1 month post-DFP, animals were analyzed for motor ability, learning and memory, and hippocampal neurogenesis. Acute DFP intoxication triggered more severe seizure behavior in males than females, which was supported by EEG recordings. DFP caused significant neurodegeneration and persistent microglial activation in numerous brain regions of both sexes, but astrogliosis occurred earlier and was more severe in males compared to females. DFP males and females exhibited pronounced memory deficits relative to sex-matched controls. In contrast, acute DFP intoxication altered hippocampal neurogenesis in males, but not females. These findings demonstrate that acute DFP intoxication triggers seizures in juvenile rats of both sexes, but the seizure severity varies by sex. Some, but not all, chronic neurotoxic outcomes also varied by sex. The spatiotemporal patterns of neurological damage suggest that microglial activation may be a more important factor than astrogliosis or altered neurogenesis in the pathogenesis of cognitive deficits in juvenile rats acutely intoxicated with OPs.

Steroid receptor coactivator-1: The central intermediator linking multiple signals and functions in the brain and spinal cord

The effects of steroid hormones are believed to be mediated by their nuclear receptors (NRs). The p160 coactivator family, including steroid receptor coactivator-1 (SRC-1), 2 and 3, has been shown to physically interact with NRs to enhance their transactivational activities. Among which SRC-1 has been predominantly localized in the central nervous system including brain and spinal cord. It is not only localized in neurons but also detectable in neuroglial cells (mainly localized in the nuclei but also detectable in the extra-nuclear components). Although the expression of SRC-1 is regulated by many steroids, it is also regulated by some non-steroidal factors such as injury, sound and light. Functionally, SRC-1 has been implied in normal function such as development and ageing, learning and memory, central regulation on reproductive behaviors, motor and food intake. Pathologically, SRC-1 may play a role in the regulation of neuropsychiatric disorders (including stress, depression, anxiety, and autism spectrum disorder), metabolite homeostasis and obesity as well as tumorigenesis. Under most conditions, the related mechanisms are far from elucidation; although it may regulate spatial memory through Rictor/mTORC2-actin polymerization related synaptic plasticity. Several inhibitors and stimulator of SRC-1 have shown anti-cancer potentials, but whether these small molecules could be used to modulate ageing and central disorder related neuropathology remain unclear. Therefore, to elucidate when and how SRC-1 is turned on and off under different stimuli is very interesting and great challenge for neuroscientists.

S-Palmitoylation of Synaptic Proteins as a Novel Mechanism Underlying Sex-Dependent Differences in Neuronal Plasticity

Although sex differences in the brain are prevalent, the knowledge about mechanisms underlying sex-related effects on normal and pathological brain functioning is rather poor. It is known that female and male brains differ in size and connectivity. Moreover, those differences are related to neuronal morphology, synaptic plasticity, and molecular signaling pathways. Among different processes assuring proper synapse functions are posttranslational modifications, and among them, S-palmitoylation (S-PALM) emerges as a crucial mechanism regulating synaptic integrity. Protein S-PALM is governed by a family of palmitoyl acyltransferases, also known as DHHC proteins. Here we focused on the sex-related functional importance of DHHC7 acyltransferase because of its S-PALM action over different synaptic proteins as well as sex steroid receptors. Using the mass spectrometry-based PANIMoni method, we identified sex-dependent differences in the S-PALM of synaptic proteins potentially involved in the regulation of membrane excitability and synaptic transmission as well as in the signaling of proteins involved in the structural plasticity of dendritic spines. To determine a mechanistic source for obtained sex-dependent changes in protein S-PALM, we analyzed synaptoneurosomes isolated from DHHC7-/- (DHHC7KO) female and male mice. Our data showed sex-dependent action of DHHC7 acyltransferase. Furthermore, we revealed that different S-PALM proteins control the same biological processes in male and female synapses.

Investigation of GluA1 and GluA2 AMPA receptor subtype distribution in the hippocampus and anterior cingulate cortex of Long Evans rats during development

Preadolescent development is characterized by a reorganization of connectivity within and between brain regions that coincides with the emergence of complex behaviors. During the preadolescent period, the rodent hippocampus and regions of the frontal cortex are remodelled as the brain strengthens active connections and eliminates others. In the developing and mature brain, changes in the properties of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAr)-mediated synaptic responses contribute to experience-dependent changes in neural organization and function. AMPAr are made up of 4 subunits, of which GluA1 and GluA2 have been shown to play the most prominent role in functional plasticity. In this study, we sought to determine whether levels of these two subunits changed during the course of pre-adolescent development in the hippocampus and anterior cingulate cortex (ACC). To investigate the developmental changes in GluA1 and GluA2 AMPAr subunits, Western blotting and immunohistochemistry were performed on the ACC and hippocampus from P18 - P30 and compared to adult (P50) levels and distribution. Within the hippocampus, protein levels of GluA1 and GluA2 peaked around P26-30 whereby localized staining in the dentate gyrus reflected this pattern. GluA1 and GluA2 levels within the ACC showed little variation during this developmental period. These results indicate that changes in AMPAr subunits within the hippocampus coincide with developmental modifications that underlie the shift from juvenile- to adult-like capabilities. However, changes in AMPAr distribution in the ACC might not mediate changes that reflect preadolescent developmental shifts.

Inhibition of steroid receptor coactivator-1 in the hippocampus impairs the consolidation and reconsolidation of contextual fear memory in mice

AIMS

Steroid receptor coactivator-1 (SRC-1) is a key coactivator for the efficient transcriptional activity of steroids in the regulation of hippocampal functions. However, the effect of SRC-1 on hippocampal memory processes remains unknown. Our aim was to investigate the roles of hippocampal SRC-1 in the consolidation and reconsolidation of contextual fear memory in mice.

MAIN METHODS

Contextual fear conditioning paradigm was constructed in adult male C57BL/6 mice to examine the fear learning and memory processes. Adeno-associated virus (AAV) vector-mediated RNA interference (RNAi) was infused into hippocampus to block hippocampal SRC-1 level. Immunofluorescent staining was used to detect the efficiency of transfection. High plus maze and open field test were used to determine anxiety and locomotor activity. Western blot analyses were used to detect the expression of SRC-1 and synaptic proteins in the hippocampus.

KEY FINDINGS

We first showed that the expression of SRC-1 was regulated by fear conditioning training in a time-dependent manner, and knockdown of SRC-1 impaired contextual fear memory consolidation without affecting innate anxiety or locomotor activity. In addition, hippocampal SRC-1 was also regulated by the retrieval of contextual fear memory, and downregulation of SRC-1 disrupted fear memory reconsolidation. Moreover, knockdown of SRC-1 reversed the increased GluR1 and PSD-95 levels induced by contextual fear memory retrieval.

SIGNIFICANCE

Our data indicate that hippocampal SRC-1 is required for the consolidation and reconsolidation of contextual fear memory, and SRC-1 may be a potential therapeutic target for mental disorders that are involved in hippocampal memory dysfunction.

Exposure to 1-bromopropane vapors during pregnancy enhances the development of hippocampal neuronal excitability in rat pups during lactation

OBJECTIVES

Although 1-Bromopropane (1-BP) exposure has been reported to cause neurotoxicity in adult humans and animals, its effects on the development of the central nervous system remain unclear. Recently, we reported delayed developmental neurotoxicity (DNT) upon 1-BP exposure in rats. Here we aimed to study the effect of prenatal 1-BP exposure on the hippocampal excitability in the juvenile offspring.

METHODS

Pregnant Wistar rats were exposed to vaporized 1-BP for 20 days (6 h/d) with concentrations of 0 (control), 400, or 700 ppm. Hippocampal slices were prepared from male offspring during postnatal days (PNDs) 13, 14, and 15. Field excitatory postsynaptic potential (fEPSP) and population spike (PS) were recorded simultaneously from the CA1 region.

RESULTS

In the exposed groups, the stimulation/response relationships of fEPSP slope and PS amplitude were enhanced more than in the control group at PND 14. Analysis of fEPSP-spike coupling demonstrated increased values of Top and Eslope50 in the exposed groups. Real-time PCR analysis showed a significant increase in the mRNA levels of the adult type Nav 1.1 Na+ channel subunit and the GluR1 glutamate receptor subunit in the hippocampus of the 700 ppm group at PND 14.

CONCLUSIONS

Our results provide evidence that prenatal exposure to 1-BP accelerates developmental enhancement of hippocampal excitability in the pups before eye-opening. The current study suggests that our evaluation method of DNT is applicable to the industrial chemical 1-BP.

Non-reproductive Functions of Aromatase in the Central Nervous System Under Physiological and Pathological Conditions

The modulation of brain function and behavior by steroid hormones was classically associated with their secretion by peripheral endocrine glands. The discovery that the brain expresses the enzyme aromatase, which produces estradiol from testosterone, expanded this traditional concept. One of the best-studied roles of brain estradiol synthesis is the control of reproductive behavior. In addition, there is increasing evidence that estradiol from neural origin is also involved in a variety of non-reproductive functions. These include the regulation of neurogenesis, neuronal development, synaptic transmission, and plasticity in brain regions not directly related with the control of reproduction. Central aromatase is also involved in the modulation of cognition, mood, and non-reproductive behaviors. Furthermore, under pathological conditions aromatase is upregulated in the central nervous system. This upregulation represents a neuroprotective and likely also a reparative response by increasing local estradiol levels in order to maintain the homeostasis of the neural tissue. In this paper, we review the non-reproductive functions of neural aromatase and neural-derived estradiol under physiological and pathological conditions. We also consider the existence of sex differences in the role of the enzyme in both contexts.

Orchiectomy and letrozole differentially regulate synaptic plasticity and spatial memory in a manner that is mediated by SRC-1 in the hippocampus of male mice

Hippocampal synaptic plasticity is the basis of spatial memory and cognition and is strongly regulated by both testicular androgens (testosterone, T) and hippocampal estrogens (17β-estradiol, E2) converted from T by aromatase, which is inhibited by letrozole (LET), but the contribution of each pathway to spatial memory and the associated mechanisms are unclear. In this study, we first used orchiectomy (ORX) and LET injection to investigate the effects of T and hippocampal E2 on spatial memory and hippocampal synaptic plasticity. Next, we examined the changes in steroid receptors and steroid receptor coactivator-1 (SRC-1) under these treatments. Finally, we constructed an SRC-1 RNA interference lentivirus and an AROM overexpression lentivirus to explore the roles of SRC-1 under T replacement and AROM overexpression. The results revealed spatial memory impairment only after LET. LET induced more actin depolymerization and greater losses of spines, synapses, and postsynaptic proteins compared with ORX. Moreover, although ERα and ERβ were affected by LET and ORX at similar levels, AR, GPR30, and SRC-1 were dramatically decreased by LET compared with ORX. Finally, the T and AROM overexpression-induced changes in synaptic proteins and actin polymerization were blocked by SRC-1 inhibition. These results demonstrate that testicular androgens play a limited role, whereas local E2 is more important for cognition, which may explain why castrated men such as eunuchs usually do not have cognitive disorders. These results also suggest a pivotal role of SRC-1 in the action of steroids; thus, SRC-1 may serve as a novel therapeutic target for cognitive disorders.

Steroid Receptor Coactivator-1 Knockdown Decreases Synaptic Plasticity and Impairs Spatial Memory in the Hippocampus of Mice

Steroids have been demonstrated to play profound roles in the regulation of hippocampal function by acting on their receptors, which need coactivators for their transcriptional activities. Previous studies have shown that steroid receptor coactivator-1 (SRC-1) is the predominant coactivator in the hippocampus, but its exact role and the underlying mechanisms remain unclear. In this study, we constructed SRC-1 RNA interference (RNAi) lentiviruses, injected them into the hippocampus of male mice, and then examined the changes in the expression of selected synaptic proteins, CA1 synapse density, postsynaptic density (PSD) thickness, and in vivo long-term potentiation (LTP). Spatial learning and memory behavior changes were investigated using the Morris water maze. We then transfected the lentiviruses into cultured hippocampal cells and examined the changes in synaptic protein and phospho-cyclic AMP response element-binding protein (pCREB) expression. The in vivo results showed that SRC-1 knockdown significantly decreased the expression of synaptic proteins and CA1 synapse density as well as PSD thickness; SRC-1 knockdown also significantly impaired in vivo LTP and disrupted spatial learning and memory. The in vitro results showed that while the expression of synaptic proteins was significantly decreased by SRC-1 knockdown, pCREB expression was also significantly decreased. The above results suggest a pivotal role of SRC-1 in the regulation of hippocampal synaptic plasticity and spatial learning and memory, strongly indicating SRC-1 may serve as a novel therapeutic target for hippocampus-dependent memory disorders.

Nuclear and membrane estrogen receptor antagonists induce similar mTORC2 activation-reversible changes in synaptic protein expression and actin polymerization in the mouse hippocampus

AIMS

Estrogens play pivotal roles in hippocampal synaptic plasticity through nuclear receptors (nERs; including ERα and ERβ) and the membrane receptor (mER; also called GPR30), but the underlying mechanism and the contributions of nERs and mER remain unclear. Mammalian target of rapamycin complex 2 (mTORC2) is involved in actin cytoskeleton polymerization and long-term memory, but whether mTORC2 is involved in the regulation of hippocampal synaptic plasticity by ERs is unclear.

METHODS

We treated animals with nER antagonists (MPP/PHTPP) or the mER antagonist (G15) alone or in combination with A-443654, an activator of mTORC2. Then, we examined the changes in hippocampal SRC-1 expression, mTORC2 signaling (rictor and phospho-AKTSer473), actin polymerization (phospho-cofilin and profilin-1), synaptic protein expression (GluR1, PSD95, spinophilin, and synaptophysin), CA1 spine density, and synapse density.

RESULTS

All of the examined parameters except synaptophysin expression were significantly decreased by MPP/PHTPP and G15 treatment. MPP/PHTPP and G15 induced a similar decrease in most parameters except p-cofilin, GluR1, and spinophilin expression. The ER antagonist-induced decreases in these parameters were significantly reversed by mTORC2 activation, except for the change in SRC-1, rictor, and synaptophysin expression.

CONCLUSIONS

nERs and mER contribute similarly to the changes in proteins and structures associated with synaptic plasticity, and mTORC2 may be a novel target of hippocampal-dependent dementia such as Alzheimer's disease as proposed by previous studies.

Dose-dependent regulation of steroid receptor coactivator-1 and steroid receptors by testosterone propionate in the hippocampus of adult male mice

Androgens have been proposed to play important roles in the regulation of hippocampus function either directly, through the androgen receptor (AR), or indirectly, through estrogen receptors (ERs), after aromatization into estradiol. Steroid receptor coactivator-1 (SRC-1) is present in the hippocampus of several species, and its expression is regulated by development and aging, as well as by orchidectomy and aromatase inhibitor letrozole administration, while ovariectomy only transiently downregulated hippocampal SRC-1. However, whether the expression of hippocampal SRC-1 can be directly regulated by testosterone, the principal male sex hormone, remains unclear. In the present study, we investigated the expression of hippocampal SRC-1 after orchidectomy and testosterone treatment using immunohistochemistry and Western blot analysis. We found that while hippocampal SRC-1 was significantly downregulated by orchidectomy (ORX), its expression was rescued by treatment with testosterone in a dose-dependent manner. Furthermore, we noticed that the decreased expression of hippocampal AR, ERs and the synaptic proteins GluR-1 and PSD-95 induced by ORX was also rescued by testosterone treatment in a dose-dependent manner. However, we found that hippocampal membrane estrogen receptor GPR30 and dendritic spine marker spinophilin were not altered by ORX or testosterone treatment. Together, the above results provided the first direct evidence for the androgenic regulation on hippocampal SRC-1, indicating that SRC-1 may be a direct target of androgenic regulation on the hippocampus. Furthermore, because AR and ERs can be differentially regulated by testosterone, and the transcriptional activity requires the involvement of local SRC-1, and considering the complicated regulatory pathway of each individual receptor, the converged hub regulator SRC-1 of these nuclear receptor networks is worthy of further investigation.

Steroid receptor coactivator-1 mediates letrozole induced downregulation of postsynaptic protein PSD-95 in the hippocampus of adult female rats

Hippocampus local estrogen which is converted from androgen that catalyzed by aromatase has been shown to play important roles in the regulation of learning and memory as well as cognition through action on synaptic plasticity, but the underlying mechanisms are poorly understood. Steroid receptor coactivator-1 (SRC-1) is one of the coactivators of steroid nuclear receptors; it is widely distributed in brain areas that related to learning and memory, reproductive regulation, sensory and motor information integration. Previous studies have revealed high levels of SRC-1 immunoreactivities in the hippocampus; it is closely related to the levels of synaptic proteins such as PSD-95 under normal development or gonadectomy, but its exact roles in the regulation of these proteins remains unclear. In this study, we used aromatase inhibitor letrozole in vivo and SRC-1 RNA interference in vitro to investigate whether SRC-1 mediated endogenous estrogen regulation of hippocampal PSD-95. The results revealed that letrozole injection synchronously decreased hippocampal SRC-1 and PSD-95 in a dose-dependant manner. Furthermore, when SRC-1 specific shRNA pool was applied to block the expression of SRC-1 in the primary hippocampal neuron culture, both immunocytochemistry and Western blot revealed that levels of PSD-95 were also decreased significantly. Taking together, these results provided the first evidence that SRC-1 mediated endogenous estrogen regulation of hippocampal synaptic plasticity by targeting the expression of synaptic protein PSD-95. Additionally, since letrozole is frequently used to treat estrogen-sensitive breast cancer, the above results also indicate its potential side effects in clinical administration.

Developmental expression of the neuroligins and neurexins in fragile X mice

Neuroligins and neurexins are transsynaptic proteins involved in the maturation of glutamatergic and GABAergic synapses. Research has identified synaptic proteins and function as primary contributors to the development of fragile X syndrome. Fragile X mental retardation protein (FMRP), the protein that is lacking in fragile X syndrome, binds neuroligin-1 and -3 mRNA. Using in situ hybridization, we examined temporal and spatial expression patterns of neuroligin (NLGN) and neurexin (NRXN) mRNAs in the somatosensory (S1) cortex and hippocampus in wild-type (WT) and fragile X knockout (FMR1-KO) mice during the first 5 weeks of postnatal life. Genotype-based differences in expression included increased NLGN1 mRNA in CA1 and S1 cortex, decreased NLGN2 mRNA in CA1 and dentate gyrus (DG) regions of the hippocampus, and increased NRXN3 mRNA in CA1, DG, and S1 cortex between female WT and FMR1-KO mice. In male mice, decreased expression of NRXN3 mRNA was observed in CA1 and DG regions of FMR1-KO mice. Sex differences in hippocampal expression of NLGN2, NRXN1, NRXN2, and NRXN3 mRNAs and in S1 cortex expression of NRXN3 mRNAs were observed WT mice, whereas sex differences in NLGN3, NRXN1, NRXN2, and NRXN3 mRNA expression in the hippocampus and in NLGN1, NRXN2 and NRXN3 mRNA expression in S1 cortex were detected in FMR1-KO mice. These results provide a neuroanatomical map of NLGN and NRXN expression patterns over postnatal development in WT and FMR1-KO mice. The differences in developmental trajectory of these synaptic proteins could contribute to long-term differences in CNS wiring and synaptic function.

Evidence for involvement of steroid receptors and coactivators in neuroepithelial and meningothelial tumors

Steroid receptors such as androgen receptor (AR) and estrogen receptors (ER) ER-α and ER-β, and their receptor coactivators (steroid receptor coactivator, SRC) are widely localized in the brain. Although previous studies have investigated the expression of steroid receptors in brain tumors like astrocytoma, the studies on the expression of steroid receptors and SRCs in other brain tumors are lacking. Here, we investigated the expression of AR, ERs, and SRCs in neuroepithelial (medulloblastoma, ependymoma, oligodendroglioma) and meningothelial meningioma using tissue microarray immunohistochemistry. Compared to normal brain tissue, we found that the expression of SRC-1, SRC-3, and ER-α significantly decreased in meningothelial tumor and neuroepithelial tumor, suggesting that the SRC-1/SRC-3 levels may be regulated by ER-α. Moreover, the levels of AR strongly correlated to the levels of ER-β. Furthermore, correlation was also detected between SRC-3 and AR in neuroepithelial tumor, and between ER-α and ER-β in meningothelial tumor. In addition, the decreased ratio of SRC-1/SRC-3 was associated with an increase of ER-β in neuroepithelial tumor. These results indicate that expressions of different steroid receptors and activators may be tumor type dependent. While AR, ER-α, and ER-β may be involved in the pathogenesis of meningothelial tumor, SRCs/ER-β axis and SRC-3/AR axis may play a role in the pathogenesis of neuroepithelial tumor.

Regional specific regulation of steroid receptor coactivator-1 immunoreactivity by orchidectomy in the brain of adult male mice

Androgens including testosterone and dihydrotestosterone play important roles on brain structure and function, either directly through androgen receptor or indirectly through estrogen receptors, which need coactivators for their transcription activation. Steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but how it is regulated by androgens in the brain remains unclear. In this study, we explored the effect of orchidectomy (ORX) on the expression of SRC-1 in the adult male mice using nickel-intensified immunohistochemistry. The results showed that ORX induced dramatic decrease of SRC-1 immunoreactivity in the olfactory tubercle, piriform cortex, ventral pallidum, most parts of the septal area, hippocampus, substantia nigra (compact part), pontine nuclei and nucleus of the trapezoid body (p<0.01). Significant decrease of SRC-1 was noticed in the dorsal and lateral septal nucleus, medial preoptical area, dorsomedial and ventromedial hypothalamic nucleus and superior paraolivary nucleus (p<0.05). Whereas in other regions examined, levels of SRC-1 immunoreactivity were not obviously changed by ORX (p>0.05). The above results demonstrated ORX downregulation of SRC-1 in specific regions that have been involved in sense of smell, learning and memory, cognition, neuroendocrine, reproduction and motor control, indicating that SRC-1 play pivotal role in the mediating circulating androgenic regulation on these important brain functions. It also indicates that SRC-1 may serve as a novel target for the central disorders caused by the age-related decrease of circulating androgens.

Sex-specific consequences of early life seizures

Seizures are very common in the early periods of life and are often associated with poor neurologic outcome in humans. Animal studies have provided evidence that early life seizures may disrupt neuronal differentiation and connectivity, signaling pathways, and the function of various neuronal networks. There is growing experimental evidence that many signaling pathways, like GABAA receptor signaling, the cellular physiology and differentiation, or the functional maturation of certain brain regions, including those involved in seizure control, mature differently in males and females. However, most experimental studies of early life seizures have not directly investigated the importance of sex on the consequences of early life seizures. The sexual dimorphism of the developing brain raises the question that early seizures could have distinct effects in immature females and males that are subjected to seizures. We will first discuss the evidence for sex-specific features of the developing brain that could be involved in modifying the susceptibility and consequences of early life seizures. We will then review how sex-related biological factors could modify the age-specific consequences of induced seizures in the immature animals. These include signaling pathways (e.g., GABAA receptors), steroid hormones, growth factors. Overall, there are very few studies that have specifically addressed seizure outcomes in developing animals as a function of sex. The available literature indicates that a variety of outcomes (histopathological, behavioral, molecular, epileptogenesis) may be affected in a sex-, age-, region-specific manner after seizures during development. Obtaining a better understanding for the gender-related mechanisms underlying epileptogenesis and seizure comorbidities will be necessary to develop better gender and age appropriate therapies.

Aromatase inhibitor letrozole downregulates steroid receptor coactivator-1 in specific brain regions that primarily related to memory, neuroendocrine and integration

As one of the third generation of aromatase inhibitors, letrozole is a favored drug for the treatment of hormone receptor-positive breast cancer with some adverse effects on the nervous system, but the knowledge is limited and the results are controversial, the mechanism underlying its central action is also unclear. Accumulated evidences have demonstrated that estrogens derived from androgens by aromatase play profound roles in the brain through their receptors, which needs coactivator for the transcription regulation, among which steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but whether it is regulated by letrozole is currently unknown. In this study, we examined letrozole regulation on SRC-1 expression in adult mice brain using immunohistochemistry. The results showed that letrozole induced dramatic decrease of SRC-1 in the medial septal, hippocampus, medial habenular nucleus, arcuate hypothalamic nucleus and superior colliculus (p<0.01). Significant decrease was detected in the dorsal lateral septal nucleus, bed nucleus of stria terminalis, ventral taenia tecta, dorsomedial and ventromedial hypothalamic nuclei, dorsomedial periaqueductal gray, superior paraolivary nucleus and pontine nucleus (p<0.05). In the hippocampus, levels of estradiol content, androgen receptor, estrogen receptor α and β also decreased significantly after letrozole injection. The above results demonstrated letrozole downregulation of SRC-1 in specific regions that are primarily related to learning and memory, cognition and mood, neuroendocrine as well as information integration, indicating that SRC-1 may be one important downstream central target of letrozole. Furthermore, these potential central adverse effects of letrozole should be taken into serious considerations.

Intriguing roles of hippocampus-synthesized 17β-estradiol in the modulation of hippocampal synaptic plasticity

Accumulated studies have shown that 17β-estradiol (E2) can be de novo synthesized in the hippocampus, and its role in the regulation of hippocampal synaptic plasticity, which is the basis of learning and memory, has long been exploring. Steroidogenic enzymes (e.g., aromatase) that are essential to the hippocampus-synthesized synthesis of E2 have been detected in the hippocampus. Inhibition of E2 synthesis by aromatase inhibitors significantly reduces the density of hippocampal spine synapses, levels of some synaptic proteins such as spinopholin and synaptophysin. Moreover, the electrophysiological properties of hippocampal neurons are also changed in response to this inhibition. The influences of gonadal and hippocampal E2 on synaptic plasticity may exist some differences, since some reports showed that gonadal (or circulating) estrogens have no obvious effects in the modulation of hippocampal synaptic proteins as evidenced in some ovariectomized animals and postmenopausal women who suffered from Alzheimer's disease (AD). These evidences leads to a hypothesis that hippocampal E2 may play a more important role in modulation of synaptic plasticity than gonadal E2. The signaling pathways, whereby hippocampal E2 modulates synaptic plasticity, insist of classical chronic genomic pathway and rapid nongenomic pathway, which mediated by nonnuclear estrogen receptor (GPER) and/or nuclear or nonnuclear estrogen receptors, which require coactivators for their transcription activity. Among which steroid receptor coactivator-1 (SRC-1) is the predominant coactivator p160 family members in the brain. Several clues have shown that SRC-1 is expressed in hippocampus and is highly correlated with some key synaptic proteins developmentally or after orchidectomy but not ovariectomy, indicating SRC-1 may be regulated by hippocampus-synthesized E2 and profoundly involved in the mediation of hippocampal E2 regulation of hippocampal synaptic plasticity. Further studies about the exact roles of hippocampus-synthesized E2 and therefore SRC-1 are urgently needed in order to facilitate our understanding of hippocampal E2, which will be very important to the development of novel strategies of estrogen replacement therapy against neurodegenerative deficits such as Alzheimer's disease (AD).

Expression of estrogen receptors, androgen receptor and steroid receptor coactivator-3 is negatively correlated to the differentiation of astrocytic tumors

Astrocytic tumors are the most common primary brain tumors. It has been reported that androgen receptor (AR), estrogen receptors alpha (ERα) and beta (ERβ) and their coactivator SRC-1 and SRC-3 are involved in the regulation of the growth and development of many tumors, but their expression profiles and significances in the astrocytic tumors remain largely unknown. In this study, the expression of AR, ERs, and SRCs, and the possible roles of them in astrocytic neoplasm were evaluated and compared to normal brain tissues by nickel-intensified immunohistochemistry with tissue microarrays. The results showed that there were no age- or gender-differences regarding to the levels of these receptors or coactivators in astrocytic or normal brain tissues. In the high-grade astrocytic tissue, the levels of AR, ERs and SRC-3 were significantly decreased when compared to the low-grade astrocytic tissues, but the levels of SRC-1 remain unchanged. Correlation analysis revealed that the levels of AR, ERs and SRC-3 were negatively correlated to tumor differentiation, and the levels of SRC-3 were positively correlated to that of ERα. Furthermore, the decreased levels of SRC-3 were associated with an increase of ERβ in astrocytic tumors when compared to that of normal brain tissues. These above results indicate a combination of decreased expression of ERs, AR and SRC-3 but not SRC-1 may be involved in the tumorigenesis of gliomas, ERα/SRC-3 axis may play central role in the regulation these tumors.

Synaptic and extrasynaptic location of the receptor tyrosine kinase met during postnatal development in the mouse neocortex and hippocampus

MET, a replicated autism risk gene, encodes a pleiotropic receptor tyrosine kinase implicated in multiple cellular processes during development and following injury. Previous studies suggest that Met modulates excitatory synapse development in the neocortex and hippocampus, although the underlying mechanism is unknown. The peak of Met expression corresponds to the period of process outgrowth and synaptogenesis, with robust expression in hippocampal and neocortical neuropil. Resolving whether neuropil expression represents presynaptic, postsynaptic or glial localization provides insight into potential mechanisms of Met action. The subcellular distribution of Met was characterized using complementary ultrastructural, in situ proximity ligation assay (PLA), and biochemical approaches. At postnatal day (P) 7, immunoelectron microscopy revealed near-equivalent proportions of Met-immunoreactive pre- (axons and terminals) and postsynaptic (dendritic shafts and spines) profiles in the stratum radiatum in the hippocampal CA1 region. Staining was typically in elements in which the corresponding pre- or postsynaptic apposition was unlabeled. By P21, Met-immunoreactive presynaptic profiles predominated and ~20% of Met-expressing profiles were glial. A different distribution of Met-immunoreactive profiles was observed in layer V of somatosensory cortex: Met-labeled spines were rare and a smaller proportion of glial profiles expressed Met. Strikingly, Met-immunoreactive presynaptic profiles predominated over postsynaptic profiles as early as P7. PLA analysis of neurons in vitro and biochemical analysis of tissue subsynaptic fractions confirmed the localization of Met in specific synaptic subcompartments. The study demonstrates that Met is enriched at synapses during development and its activation may modulate synapse formation and stability through both pre- and postsynaptic mechanisms.

Steroid receptor coactivator-1: a versatile regulator and promising therapeutic target for breast cancer

Breast cancer is the leading cause of cancer death for women worldwide. Various therapeutic approaches have been proposed, among which endocrine therapy has recently become popular due to the high sensitivity of breast tissues to steroids such as estrogens and progesterone. The underlying mechanisms of steroid regulation in breast cancer cell proliferation, invasiveness, metastasis and endocrine resistance, however, remain largely unknown. Steroid receptor coactivator-1 (SRC-1) has attracted much attention because it is an important co-regulator and plays a pivotal role in modulating the transcriptional activities of steroid nuclear receptors. Accumulated research has established a strong correlation between SRC-1 and the pathological progression or disease-related features of breast cancer, which supports its potential as a target for specific therapeutic intervention in the clinical management of breast cancer. In addition, a diverse group of downstream molecules have also been shown to participate in various functional pathways related to SRC-1-associated regulation of breast cancer. These downstream molecules are also considered promising therapeutic targets, providing additional options for targeted treatments. In this review, the expression of SRC-1 in breast cancer and the close relationships between SRC-1 and the cell proliferation, invasiveness, metastasis and endocrine resistance of breast cancer will be discussed, followed by a brief summary of its putative functional mechanisms with an emphasis on the potential therapeutic role of SRC-1.

Understanding stress-effects in the brain via transcriptional signal transduction pathways

Glucocorticoid hormones exert crucial effects on the brain in relation to physiology, endocrine regulation, mood and cognition. Their two receptor types, glucocorticoid and mineralocorticoid receptors (GR and MR), are members of the nuclear receptor superfamily and act in large measure as transcription factors. The outcome of MR/GR action on the genome depends on interaction with members from different protein families, which are of crucial importance for cross-talk with other neuronal and hormonal signals that impinge on the glucocorticoid sensitive circuitry. Relevant interacting proteins include other transcription factors that may either tether the receptor to the DNA, or that bind in the vicinity of GR and MR to tune the transcriptional response. In addition, transcriptional coregulator proteins constitute the actual signal transduction pathway to the transcription machinery. We review the current evidence for involvement of individual coregulators in GR-dependent effects on stress responses, and learning and memory. We discuss the use of in vitro and in silico tools to predict those coregulators that are of importance for particular brain processes. Finally, we discuss the potential of selective receptor modulators that may only allow a subset of all interactions, thus allowing more selective targeting of glucocorticoid-dependent processes in the brain.

Gonadectomy differentially regulates steroid receptor coactivator-1 and synaptic proteins in the hippocampus of adult female and male C57BL/6 mice

Hippocampus is one of the most important structures that mediates learning and memory, cognition, and mental behaviors and profoundly regulated by sex hormones in a sex-specific manner, but the mechanism of underlying sex differences regulation is still unclear. We have previously reported that in the male and female mice, steroid receptor coactivator-1 (SRC-1) and some key synaptic proteins share similar developmental profile in the hippocampus, but how circulating sex hormones affect hippocampal SRC-1 as well as these synaptic proteins remain unclear. In this study, we examined how gonad sex hormones regulate hippocampal SRC-1, synaptophysin, PSD-95, and AMPA receptor subtype GluR1 by using immunohistochemistry and Western blot. The results showed that in the female mice, ovariectomy affected hippocampal SRC-1 and GluR1 were only detected at 2 weeks post operation, then it recovered to sham level; synaptophysin was unaffected at any timepoint examined; significant decrease of PSD-95 was only detected at 4 weeks post operation. However, in the male hippocampus, SRC-1 and PSD-95 were decreased from one week and lasted to 4 weeks after orchidectomy, GluR1 decreased from 2 weeks after orchidectomy, but synaptophysin remained unchanged as in the females. Correlation analysis showed the profiles of SRC-1 were positively correlated with GluR1 of the females, PSD-95 and GluR1 of the males, respectively. The above results suggested a distinct regulatory mode between female and male gonad hormones in the regulation of hippocampal SRC-1 and synaptic proteins, which may be one of the mechanisms contributing to the dimorphism of hippocampus during development and ageing.

Differential expression levels of synaptophysin through developmental stages in hippocampal region of mouse brain

The formation of neural synapses according to the development and growth of neurite were usually studied with various markers. Of these markers, synaptophysin is a kind of synaptic protein located in the synaptic vesicle of neuron or neuroendocrine cell known to be distributed consistently in all neural synapses. The purpose of this study was to investigate differential expression levels and patterns of synaptic marker (synaptophysin) in the mouse hippocampal region according to the developmental stages of embryonic, neonatal, and adulthood respectively. In the embryonic and neonatal groups, synaptophysin immunofluorescence was almost defined to cornu ammonis subfields (CA1 and CA3) of hippocampus and subiculum proper in the hippocampal region. However in dentate gyrus, synaptophysin immunoreactivities were insignificant or absent in all developmental stages. In embryonic and neonatal hippocampus, the intensities of immunofluorescence were significantly different between molecular and oriens layers. Furthermore, those intensities were decreased considerably in both layers of neonatal group compared to embryonic. The results from this study will contribute to characterizing synaptogenic activities in the central nervous system through developmental stages.