Astroglial cells as neuroendocrine targets in forebrain development: Implications for sex differences in psychiatric disease

Astrocytic glutamate transport is essential for the memory-enhancing effects of 17β-estradiol in ovariectomized mice

Infusion of 17β-estradiol (E2) into the dorsal hippocampus (DH) of ovariectomized (OVX) mice enhances memory consolidation, an effect that depends on rapid phosphorylation of extracellular signal-regulated kinase (ERK) and Akt. Astrocytic glutamate transporter 1 (GLT-1) modulates neurotransmission via glutamate uptake from the synaptic cleft. However, little is known about the contribution of DH astrocytes, and astrocytic glutamate transport, to the memory-enhancing effects of E2. This study was designed to test whether DH astrocytes contribute to estrogenic modulation of memory consolidation by determining the extent to which DH GLT-1 is necessary for E2 to enhance memory in object recognition and object placement tasks and trigger rapid phosphorylation events in DH astrocytes. OVX female mice were bilaterally cannulated into the DH or the DH and dorsal third ventricle (ICV). Post-training DH infusion of the GLT-1 inhibitor dihydrokainic acid (DHK) dose-dependently impaired memory consolidation in both tasks. Moreover, the memory-enhancing effects of ICV-infused E2 in each task were blocked by DH DHK infusion. E2 increased p42 ERK and Akt phosphorylation in DH astrocytes, and these effects were blocked by DHK. Results suggest the necessity of DH GLT-1 activity for object and spatial memory consolidation, and for E2 to enhance consolidation of these memories and to rapidly activate cell signaling in DH astrocytes. Findings indicate that astrocytic function in the DH of OVX females is necessary for memory formation and is regulated by E2, and suggest an essential role for DH astrocytic GLT-1 activity in the memory-enhancing effects of E2.

Proteomic evidence of depression-associated astrocytic dysfunction in the human male olfactory bulb

The olfactory bulb (OB), a major structure of the limbic system, has been understudied in human investigations of psychopathologies such as depression. To explore more directly the molecular features of the OB in depression, a global comparative proteome analysis was carried out with human post-mortem OB samples from 11 males having suffered from depression and 12 healthy controls. We identified 188 differentially abundant proteins (with adjusted p < 0.05) between depressed cases and controls. Gene ontology and gene enrichment analyses suggested that these proteins are involved in biological processes including the complement and coagulation cascades. Cell type enrichment analysis displayed a significant reduction in several canonical astrocytic proteins in OBs from depressed patients. Furthermore, using RNA-fluorescence in-situ hybridization, we observed a decrease in the percentage of ALDH1L1+ cells expressing canonical astrocytic markers including ALDOC, NFIA, GJA1 (connexin 43) and SLC1A3 (EAAT1). These results are consistent with previous reports of downregulated astrocytic marker expression in other brain regions in depressed patients. We also conducted a comparative phosphoproteomic analysis of OB samples and found a dysregulation of proteins involved in neuronal and astrocytic functions. To determine whether OB astrocytic abnormalities is specific to humans, we also performed proteomics on the OB of socially defeated male mice, a commonly used model of depression. Cell-type specific analysis revealed that in socially defeated animals, the most striking OB protein alterations were associated with oligodendrocyte-lineage cells rather than with astrocytes, highlighting an important species difference. Overall, this study further highlights cerebral astrocytic abnormalities as a consistent feature of depression in humans.

Fatty acid sensing in the brain: The role of glial-neuronal metabolic crosstalk and horizontal lipid flux

The central control of energy homeostasis is a regulatory axis that involves the sensing of nutrients, signaling molecules, adipokines, and neuropeptides by neurons in the metabolic centers of the hypothalamus. However, non-neuronal glial cells are also abundant in the hypothalamus and recent findings have underscored the importance of the metabolic crosstalk and horizontal lipid flux between glia and neurons to the downstream regulation of systemic metabolism. New transgenic models and high-resolution analyses of glial phenotype and function have revealed that glia sit at the nexus between lipid metabolism and neural function, and may markedly impact the brain's response to dietary lipids or the supply of brain-derived lipids. Glia comprise the main cellular compartment involved in lipid synthesis, lipoprotein production, and lipid processing in the brain. In brief, tanycytes provide an interface between peripheral lipids and neurons, astrocytes produce lipoproteins that transport lipids to neurons and other glia, oligodendrocytes use brain-derived and dietary lipids to myelinate axons and influence neuronal function, while microglia can remove unwanted lipids in the brain and contribute to lipid re-utilization through cholesterol efflux. Here, we review recent findings regarding glial-lipid transport and highlight the specific molecular factors necessary for lipid processing in the brain, and how dysregulation of glial-neuronal metabolic crosstalk contributes to imbalanced energy homeostasis. Furthering our understanding of glial lipid metabolism will guide the design of future studies that target horizontal lipid processing in the brain to ameliorate the risk of developing obesity and metabolic disease.

The role of estrogen in Alzheimer's disease pathogenesis and therapeutic potential in women

Estrogens are pivotal regulators of brain function throughout the lifespan, exerting profound effects from early embryonic development to aging. Extensive experimental evidence underscores the multifaceted protective roles of estrogens on neurons and neurotransmitter systems, particularly in the context of Alzheimer's disease (AD) pathogenesis. Studies have consistently revealed a greater risk of AD development in women compared to men, with postmenopausal women exhibiting heightened susceptibility. This connection between sex factors and long-term estrogen deprivation highlights the significance of estrogen signaling in AD progression. Estrogen's influence extends to key processes implicated in AD, including amyloid precursor protein (APP) processing and neuronal health maintenance mediated by brain-derived neurotrophic factor (BDNF). Reduced BDNF expression, often observed in AD, underscores estrogen's role in preserving neuronal integrity. Notably, hormone replacement therapy (HRT) has emerged as a sex-specific and time-dependent strategy for primary cardiovascular disease (CVD) prevention, offering an excellent risk profile against aging-related disorders like AD. Evidence suggests that HRT may mitigate AD onset and progression in postmenopausal women, further emphasizing the importance of estrogen signaling in AD pathophysiology. This review comprehensively examines the physiological and pathological changes associated with estrogen in AD, elucidating the therapeutic potential of estrogen-based interventions such as HRT. By synthesizing current knowledge, it aims to provide insights into the intricate interplay between estrogen signaling and AD pathogenesis, thereby informing future research directions and therapeutic strategies for this debilitating neurodegenerative disorder.

Neonatal estrogen induces male-like expression of astroglial markers of maturation and plasticity in the neocortex of female mice

Astroglia play a crucial role in various aspects of neurodevelopment including building, maintaining, and modulating neuronal circuits that underly complex behaviours in the neocortex. Telencephalic regions exhibit sex differences in neuronal networks that arise early in development. Astroglia express receptors for gonadal hormones responsible for the organization of sex differences, such as estrogen, placing them in a key position to modulate sex differences in the development of neuronal networks. Astroglial cells express specific proteins related to their morphology, function, and maturation. We have previously shown that P7-P14 is a key transition period for neocortical astroglial maturation and that males reach a mature phenotype earlier than females, at P7. In this study, we investigated whether administration of perinatal estradiol to female mice is sufficient to masculinize astroglial protein and gene expression related to maturation that we previously observed at P7. We found that canonical astroglial markers like glial fibrillary acidic protein and glutamine synthetase are not affected by perinatal estrogen, but markers of astroglial maturation, Vimentin, Aldh1a1, Dio2, and the number of actively dividing astroglia are masculinized by perinatal estradiol administration. These findings suggest that sex differences in neocortical astroglial maturation are at least in-part due to the role of perinatal estrogen. Given the higher prevalence of neurodevelopmental disorders in males compared to females and the involvement of astroglia in virtually all neurodevelopmental disorders, further research is needed to determine other contributions to sex differences in neocortical astroglial cells.

Environmental enrichment initiated in adolescence restores the reduced expression of synaptophysin and GFAP in the hippocampus of chronically stressed rats in a sex-specific manner

This study aims at investigating whether environmental enrichment (EE) initiated in adolescence can alter chronic unpredictable stress (CUS)-associated changes in astroglial and synaptic plasticity markers in male and female rats. To this end, we studied possible alterations in hippocampal glial fibrillary acidic protein (GFAP) and synaptophysin (SYN) in CUS rats previously housed in EE. Wistar rats on postnatal day (PND) 23 were housed for 10 weeks in standard housing (SH) or enriched conditions. On PND 66, animals were exposed to CUS for 4 weeks. SYN and GFAP expressions were evaluated in CA1 and CA3 subfields and dentate gyrus (DG). CUS reduced the expression of SYN in all hippocampal areas, whereas lower GFAP expression was evident only in CA1 and CA3. The reduced expression of SYN in DG and CA3 was evident to male SH/CUS rats, whereas the reduced GFAP expression in CA1 and CA3 was limited to SH/CUS females. EE housing increased the hippocampal expression of both markers and protected against CUS-associated decreases. Our findings indicate that the decreases in the expression of SYN and GFAP following CUS are region and sex-specific and underline the neuroprotective role of EE against these CUS-associated changes.

Aging, testosterone, and neuroplasticity: friend or foe?

Neuroplasticity or neural plasticity implicates the adaptive potential of the brain in response to extrinsic and intrinsic stimuli. The concept has been utilized in different contexts such as injury and neurological disease. Neuroplasticity mechanisms have been classified into neuroregenerative and function-restoring processes. In the context of injury, neuroplasticity has been defined in three post-injury epochs. Testosterone plays a key yet double-edged role in the regulation of several neuroplasticity alterations. Research has shown that testosterone levels are affected by numerous factors such as age, stress, surgical procedures on gonads, and pharmacological treatments. There is an ongoing debate for testosterone replacement therapy (TRT) in aging men; however, TRT is more useful in young individuals with testosterone deficit and more specific subgroups with cognitive dysfunction. Therefore, it is important to pay early attention to testosterone profile and precisely uncover its harms and benefits. In the present review, we discuss the influence of environmental factors, aging, and gender on testosterone-associated alterations in neuroplasticity, as well as the two-sided actions of testosterone in the nervous system. Finally, we provide practical insights for further study of pharmacological treatments for hormonal disorders focusing on restoring neuroplasticity.

Sex differences in developmental patterns of neocortical astroglia: A mouse translatome database

Astroglial cells are key players in the development and maintenance of neurons and neuronal networks. Astroglia express steroid hormone receptors and show rapid responses to hormonal manipulations. However, despite important sex differences in the cortex and hippocampus, few studies have examined sex differences in astroglial cells in telencephalic development. To characterize the cortical astroglial translatome in male and female mice across postnatal development, we use translating ribosome affinity purification together with RNA sequencing and immunohistochemistry to phenotype astroglia at six developmental time points. Overall, we find two distinct astroglial phenotypes between early (P1-P7) and late development (P14-adult), independent of sex. We also find sex differences in gene expression patterns across development that peak at P7 and appear to result from males reaching a mature astroglial phenotype earlier than females. These developmental sex differences could have an impact on the construction of neuronal networks and windows of vulnerability to perturbations and disease.

Saracatinib, a Src Tyrosine Kinase Inhibitor, as a Disease Modifier in the Rat DFP Model: Sex Differences, Neurobehavior, Gliosis, Neurodegeneration, and Nitro-Oxidative Stress

Diisopropylfluorophosphate (DFP), an organophosphate nerve agent (OPNA), exposure causes status epilepticus (SE) and epileptogenesis. In this study, we tested the protective effects of saracatinib (AZD0530), a Src kinase inhibitor, in mixed-sex or male-only Sprague Dawley rats exposed to 4-5 mg/kg DFP followed by 2 mg/kg atropine and 25 mg/kg 2-pralidoxime. Midazolam (3 mg/kg) was given to the mixed-sex cohort (1 h post-DFP) and male-only cohort (~30 min post-DFP). Saracatinib (20 mg/kg, oral, daily for 7 days) or vehicle was given two hours later and euthanized eight days or ten weeks post-DFP. Brain immunohistochemistry (IHC) showed increased microgliosis, astrogliosis, and neurodegeneration in DFP-treated animals. In the 10-week post-DFP male-only group, there were no significant differences between groups in the novel object recognition, Morris water maze, rotarod, or forced swim test. Brain IHC revealed significant mitigation by saracatinib in contrast to vehicle-treated DFP animals in microgliosis, astrogliosis, neurodegeneration, and nitro-oxidative stressors, such as inducible nitric oxide synthase, GP91phox, and 3-Nitrotyrosine. These findings suggest the protective effects of saracatinib on brain pathology seem to depend on the initial SE severity. Further studies on dose optimization, including extended treatment regimen depending on the SE severity, are required to determine its disease-modifying potential in OPNA models.

Androgen Effects on Neural Plasticity

Androgens are synthesized in the brain, gonads, and adrenal glands, in both sexes, exerting physiologically important effects on the structure and function of the central nervous system. These effects may contribute to the incidence and progression of neurological disorders such as autism spectrum disorder, schizophrenia, and Alzheimer's disease, which occur at different rates in males and females. This review briefly summarizes the current state of knowledge with respect to the neuroplastic effects of androgens, with particular emphasis on the hippocampus, which has been the focus of much of the research in this field.