Adolescent stress accelerates postpartum novelty recognition impairment in 5xFAD mice.

Pregnancy and the postpartum period induce physiological changes that can influence women's cognitive functions. Alzheimer's disease (AD) has a higher prevalence in women and is exacerbated by early life stress. In the present study, we found that late adolescent social isolation combined with the experience of pregnancy and delivery accelerates the onset of cognitive deficits in 5xFAD dams, particularly affecting their ability to recognize novelty. These cognitive deficits manifested as early as 16 weeks, earlier than the usual timeline for these mice, and were closely associated with increased levels of corticosterone, suggesting dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Notably, the presence of ß-amyloid plaques in brain regions associated with novelty recognition did not significantly contribute to these deficits. This highlights the potential role of stress and HPA axis dysregulation in the development of cognitive impairments related to AD, and underscores the need for further investigation.

Applying Proteomics and Computational Approaches to Identify Novel Targets in Blast-Associated Post-Traumatic Epilepsy.

Traumatic brain injury (TBI) can lead to post-traumatic epilepsy (PTE). Blast TBI (bTBI) found in Veterans presents with several complications, including cognitive and behavioral disturbances and PTE; however, the underlying mechanisms that drive the long-term sequelae are not well understood. Using an unbiased proteomics approach in a mouse model of repeated bTBI (rbTBI), this study addresses this gap in the knowledge. After rbTBI, mice were monitored using continuous, uninterrupted video-EEG for up to four months. Following this period, we collected cortex and hippocampus tissues from three groups of mice: those with post-traumatic epilepsy (PTE+), those without epilepsy (PTE-), and the control group (sham). Hundreds of differentially expressed proteins were identified in the cortex and hippocampus of PTE+ and PTE- relative to sham. Focusing on protein pathways unique to PTE+, pathways related to mitochondrial function, post-translational modifications, and transport were disrupted. Computational metabolic modeling using dysregulated protein expression predicted mitochondrial proton pump dysregulation, suggesting electron transport chain dysregulation in the epileptic tissue relative to PTE-. Finally, data mining enabled the identification of several novel and previously validated TBI and epilepsy biomarkers in our data set, many of which were found to already be targeted by drugs in various phases of clinical testing. These findings highlight novel proteins and protein pathways that may drive the chronic PTE sequelae following rbTBI.

Astrocyte-mediated mechanisms contribute to traumatic brain injury pathology.

Astrocytes respond to traumatic brain injury (TBI) with changes to their molecular make-up and cell biology, which results in changes in astrocyte function. These changes can be adaptive, initiating repair processes in the brain, or detrimental, causing secondary damage including neuronal death or abnormal neuronal activity. The response of astrocytes to TBI is often-but not always-accompanied by the upregulation of intermediate filaments, including glial fibrillary acidic protein (GFAP) and vimentin. Because GFAP is often upregulated in the context of nervous system disturbance, reactive astrogliosis is sometimes treated as an "all-or-none" process. However, the extent of astrocytes' cellular, molecular, and physiological adjustments is not equal for each TBI type or even for each astrocyte within the same injured brain. Additionally, new research highlights that different neurological injuries and diseases result in entirely distinctive and sometimes divergent astrocyte changes. Thus, extrapolating findings on astrocyte biology from one pathological context to another is problematic. We summarize the current knowledge about astrocyte responses specific to TBI and point out open questions that the field should tackle to better understand how astrocytes shape TBI outcomes. We address the astrocyte response to focal versus diffuse TBI and heterogeneity of reactive astrocytes within the same brain, the role of intermediate filament upregulation, functional changes to astrocyte function including potassium and glutamate homeostasis, blood-brain barrier maintenance and repair, metabolism, and reactive oxygen species detoxification, sex differences, and factors influencing astrocyte proliferation after TBI. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Atypical Neurogenesis, Astrogliosis, and Excessive Hilar Interneuron Loss Are Associated with the Development of Post-Traumatic Epilepsy.

BACKGROUND: Traumatic brain injury (TBI) remains a significant risk factor for post-traumatic epilepsy (PTE). The pathophysiological mechanisms underlying the injury-induced epileptogenesis are under investigation. The dentate gyrus-a structure that is highly susceptible to injury-has been implicated in the evolution of seizure development. METHODS: Utilizing the murine unilateral focal control cortical impact (CCI) injury, we evaluated seizure onset using 24/7 EEG video analysis at 2-4 months post-injury. Cellular changes in the dentate gyrus and hilus of the hippocampus were quantified by unbiased stereology and Imaris image analysis to evaluate Prox1-positive cell migration, astrocyte branching, and morphology, as well as neuronal loss at four months post-injury. Isolation of region-specific astrocytes and RNA-Seq were performed to determine differential gene expression in animals that developed post-traumatic epilepsy (PTE+) vs. those animals that did not (PTE-), which may be associated with epileptogenesis. RESULTS: CCI injury resulted in 37% PTE incidence, which increased with injury severity and hippocampal damage. Histological assessments uncovered a significant loss of hilar interneurons that coincided with aberrant migration of Prox1-positive granule cells and reduced astroglial branching in PTE+ compared to PTE- mice. We uniquely identified Cst3 as a PTE+-specific gene signature in astrocytes across all brain regions, which showed increased astroglial expression in the PTE+ hilus. CONCLUSIONS: These findings suggest that epileptogenesis may emerge following TBI due to distinct aberrant cellular remodeling events and key molecular changes in the dentate gyrus of the hippocampus.

Astrocyte Endfeet in Brain Function and Pathology: Open Questions.

Astrocyte endfeet enwrap the entire vascular tree within the central nervous system, where they perform important functions in regulating the blood-brain barrier (BBB), cerebral blood flow, nutrient uptake, and waste clearance. Accordingly, astrocyte endfeet contain specialized organelles and proteins, including local protein translation machinery and highly organized scaffold proteins, which anchor channels, transporters, receptors, and enzymes critical for astrocyte-vascular interactions. Many neurological diseases are characterized by the loss of polarization of specific endfoot proteins, vascular dysregulation, BBB disruption, altered waste clearance, or, in extreme cases, loss of endfoot coverage. A role for astrocyte endfeet has been demonstrated or postulated in many of these conditions. This review provides an overview of the development, composition, function, and pathological changes of astrocyte endfeet and highlights the gaps in our knowledge that future research should address.

Building Leadership Skills in Research Groups.

The academic research enterprise currently suffers from a culture of "academic bullying" and an unprecedented worldwide mental health crisis among trainees and faculty. These struggles, in part, result from a lack of leadership skills. Mental health, well-being, intrinsic motivation, and engagement at work are linked to three fundamental needs of self-determination: autonomy, competence, and relatedness. A great leader will first ensure they are meeting their own needs and, secondly, will support their team members in increasing their needs without decreasing autonomy. This article is a practical "how-to" guide for researchers at every stage of the academic career path. It distinguishes management from leadership and addresses three key leadership competencies related to the self-determination needs: 1. Increasing one's personal power as a foundation for autonomy, 2. building a culture of belonging and psychological safety to nurture relatedness, and 3. supporting and encouraging the need for competence by enabling people to self-evaluate performance and direct professional growth. © 2022 Wiley Periodicals LLC.

Mild Traumatic Brain Injury-Induced Disruption of the Blood-Brain Barrier Triggers an Atypical Neuronal Response.

Mild TBI (mTBI), which affects 75% of TBI survivors or more than 50 million people worldwide each year, can lead to consequences including sleep disturbances, cognitive impairment, mood swings, and post-traumatic epilepsy in a subset of patients. To interrupt the progression of these comorbidities, identifying early pathological events is key. Recent studies have shown that microbleeds, caused by mechanical impact, persist for months after mTBI and are correlated to worse mTBI outcomes. However, the impact of mTBI-induced blood-brain barrier damage on neurons is yet to be revealed. We used a well-characterized mouse model of mTBI that presents with frequent and widespread but size-restricted damage to the blood-brain barrier to assess how neurons respond to exposure of blood-borne factors in this pathological context. We used immunohistochemistry and histology to assess the expression of neuronal proteins in excitatory and inhibitory neurons after mTBI. We observed that the expression of NeuN, Parvalbumin, and CamKII was lost within minutes in areas with blood-brain barrier disruption. Yet, the neurons remained alive and could be detected using a fluorescent Nissl staining even 6 months later. A similar phenotype was observed after exposure of neurons to blood-borne factors due to endothelial cell ablation in the absence of a mechanical impact, suggesting that entrance of blood-borne factors into the brain is sufficient to induce the neuronal atypical response. Changes in postsynaptic spines were observed indicative of functional changes. Thus, this study demonstrates That exposure of neurons to blood-borne factors causes a rapid and sustained loss of neuronal proteins and changes in spine morphology in the absence of neurodegeneration, a finding that is likely relevant to many neuropathologies.

Mild Traumatic Brain Injury/Concussion Initiates an Atypical Astrocyte Response Caused by Blood-Brain Barrier Dysfunction.

Mild traumatic brain injury/concussion (mTBI) accounts for 70-90% of all reported TBI cases and causes long-lasting neurological consequences in 10-40% of patients. Recent clinical studies revealed increased blood-brain barrier (BBB) permeability in mTBI patients, which correlated with secondary damage after mTBI. However, the cascade of cellular events initiated by exposure to blood-borne factors resulting in sustained damage is not fully understood. We previously reported that astrocytes respond atypically to mTBI, rapidly losing many proteins essential to their homeostatic function, while classic scar formation does not occur. Here, we tested the hypothesis that mTBI-induced BBB damage causes atypical astrocytes through exposure to blood-borne factors. Using an mTBI mouse model, two-photon imaging, an endothelial cell-specific genetic ablation approach, and serum-free primary astrocyte cultures, we demonstrated that areas with atypical astrocytes coincide with BBB damage and that exposure of astrocytes to plasma proteins is sufficient to initiate loss of astrocyte homeostatic proteins. Although mTBI resulted in frequent impairment of both physical and metabolic BBB properties and leakage of small-sized blood-borne factors, deposition of the coagulation factor fibrinogen or vessel rupture were rare. Surprisingly, even months after mTBI, BBB repair did not occur in areas with atypical astrocytes. Together, these findings implicate that even relatively small BBB disturbances are sustained long term, and render nearby astrocytes dysfunctional, likely at the cost of neuronal health and function.

Astrocytes are necessary for blood-brain barrier maintenance in the adult mouse brain.

In the adult brain, multiple cell types are known to produce factors that regulate blood-brain barrier (BBB) properties, including astrocytes. Yet several recent studies disputed a role for mature astrocytes at the BBB. To determine if astrocytes contribute a nonredundant and necessary function in maintaining the adult BBB, we used a mouse model of tamoxifen-inducible astrocyte ablation. In adult mice, tamoxifen induction caused sparse apoptotic astrocyte cell death within 2 hr. Indicative of BBB damage, leakage of the small molecule Cadaverine, and the large plasma protein fibrinogen into the brain parenchyma indicative of BBB damage was detected as early as astrocyte ablation was present. Vessels within and close to regions of astrocyte loss had lower expression of the tight junction protein zonula occludens-1 while endothelial glucose transporter 1 expression was undisturbed. Cadaverine leakage persisted for several weeks suggesting a lack of barrier repair. This is consistent with the finding that ablated astrocytes were not replaced. Adjacent astrocytes responded with partial nonproliferative astrogliosis, characterized by morphological changes and delayed phosphorylation of STAT3, which restricted dye leakage to the brain and vessel surface areas lacking coverage by astrocytes 1 month after ablation. In conclusion, astrocytes are necessary to maintain BBB integrity in the adult brain. BBB-regulating factors secreted by other cell types, such as pericytes, are not sufficient to compensate for astrocyte loss.

Leveraging Zebrafish To Study Bona Fide Astrocytes.

In a recent study, Chen and colleagues demonstrated that zebrafish spinal cord radial glia differentiate into cells that are similar to mammalian astrocytes. This study highlights the validity of the zebrafish model for discovering molecular mechanisms governing astrocyte function.

Inducing Post-Traumatic Epilepsy in a Mouse Model of Repetitive Diffuse Traumatic Brain Injury.

Traumatic brain injury (TBI) is a leading cause of acquired epilepsy. TBI can result in a focal or diffuse brain injury. Focal injury is a result of direct mechanical forces, sometimes penetrating through the cranium, creating a direct lesion in the brain tissue. These are visible during brain imaging as areas with contusion, laceration, and hemorrhage. Focal lesions induce neuronal death and glial scar formation and are present in 20%-25% of all people who incur a TBI. However, in the majority of TBI cases, injury is caused by acceleration-deceleration forces and subsequent tissue shearing, resulting in nonfocal, diffuse damage. A subpopulation of TBI patients continues to develop post-traumatic epilepsy (PTE) after a latency period of months or years. Currently, it is impossible to predict which patients will develop PTE, and seizures in PTE patients are challenging to control, necessitating further research. Until recently, the field was limited to only two animal/rodent models with validated spontaneous post-traumatic seizures, both presenting with large focal lesions with massive tissue loss in the cortex and sometimes subcortical structures. In contrast to these approaches, it was determined that diffuse TBI induced using a modified weight drop model is sufficient to initiate development of spontaneous convulsive and non-convulsive seizures, even in the absence of focal lesions or tissue loss. Similar to human patients with acquired post-traumatic epilepsy, this model presents with a latency period after injury before seizure onset. In this protocol, the community will be provided with a new model of post-traumatic epilepsy, detailing how to induce diffuse non-lesional TBI followed by continuous long-term video-electroencephalographic animal monitoring over the course of several months. This protocol will detail animal handling, the weight drop procedure, the electrode placement for two acquisition systems, and the frequent challenges encountered during each of the steps of surgery, postoperative monitoring, and data acquisition.

Potassium and glutamate transport is impaired in scar-forming tumor-associated astrocytes.

Unprovoked recurrent seizures are a serious comorbidity affecting most patients who suffer from glioma, a primary brain tumor composed of malignant glial cells. Cellular mechanisms contributing to the development of recurrent spontaneous seizures include the release of the excitatory neurotransmitter glutamate from glioma into extracellular space. Under physiological conditions, astrocytes express two high affinity glutamate transporters, Glt-1 and Glast, which are responsible for the removal of excess extracellular glutamate. In the context of neurological disease or brain injury, astrocytes become reactive which can negatively affect neuronal function, causing hyperexcitability and/or death. Using electrophysiology, immunohistochemistry, fluorescent in situ hybridization, and Western blot analysis in different orthotopic xenograft and allograft models of human and mouse gliomas, we find that peritumoral astrocytes exhibit astrocyte scar formation characterized by proliferation, cellular hypertrophy, process elongation, and increased GFAP and pSTAT3. Overall, peritumoral reactive astrocytes show a significant reduction in glutamate and potassium uptake, as well as decreased glutamine synthetase activity. A subset of peritumoral astrocytes displayed a depolarized resting membrane potential, further contributing to reduced potassium and glutamate homeostasis. These changes may contribute to the propagation of peritumoral neuronal hyperexcitability and excitotoxic death.

Dynamic UTR Usage Regulates Alternative Translation to Modulate Gap Junction Formation during Stress and Aging.

Connexin43 (Cx43; gene name GJA1) is the most ubiquitously expressed gap junction protein, and understanding of its regulation largely falls under transcription and post-translational modification. In addition to Cx43, Gja1 mRNA encodes internally translated isoforms regulating gap junction formation, whose expression is modulated by TGF-ß. Here, using RLM-RACE, we identify distinct Gja1 transcripts differing only in 5' UTR length, of which two are upregulated during TGF-ß exposure and hypoxia. Introduction of these transcripts into Gja1-/- cells phenocopies the response of Gja1 to TGF-ß with reduced internal translation initiation. Inhibiting pathways downstream of TGF-ß selectively regulates levels of Gja1 transcript isoforms and translation products. Reporter assays reveal enhanced translation of full-length Cx43 from shorter Gja1 5' UTR isoforms. We also observe a correlation among UTR selection, translation, and reduced gap junction formation in aged heart tissue. These data elucidate a relationship between transcript isoform expression and translation initiation regulating intercellular communication.

Imaging and Manipulating Astrocyte Function In Vivo in the Context of CNS Injury.

Astrocytes are glial cells carrying out complex homeostatic functions in the healthy and diseased central nervous system (CNS). It has so far been impossible to reliably culture adult astrocytes and the results of studies on astrocytes outside of their normal environment are challenging to interpret. Consequently, most culture studies use astrocytes isolated from postnatal rodents. Yet cultured astrocytes do not display their complex three-dimensional in vivo morphology, and transcriptomes of cultured astrocytes vary significantly from those of acutely isolated astrocytes (Cahoy et al., J Neurosci 28:264-278, 2008). Astrocyte isolation for culture experiments, and the cutting of acute brain slices, induces astrocyte reactivity similar to a severe acute injury. In response to CNS injury, such as moderate or severe focal traumatic brain injury (TBI), astrocytes can change in cell number, physiological state, gene and protein expression, secretome, and morphology, in a process termed reactive astrogliosis. This makes the use of methods that inherently induce astrogliosis (e.g., dissociation of brain tissue for culture or sectioning of brains for acute brain slices) challenging, especially when conditions are studied that present with changes in astrocyte function that are milder and/or of a different nature.In this methods chapter, we will describe a technical approach that allows one to study astrocytes in the intact brain using two-photon in vivo imaging. We will use mild TBI as an example of how to use this approach to compare astrocyte function in the same animal before and after an injury.Here we describe the use of a noninvasive label-free method (Choi et al., J Biomed Opt 16:075003, 2011) to increase astrocyte Ca2+ using optical femtosecond pulsed laser activation. We will provide systematic instruction of the surgical technique, which when done properly, allows in vivo astrocyte imaging in the same experimental animal before the injury as well as over the course of days, weeks, and even months after injury. We will also elaborate on challenges in astrocytic Ca2+ imaging and how different image acquisition settings can affect the readout of astrocyte Ca2+ oscillations.

Repetitive Diffuse Mild Traumatic Brain Injury Causes an Atypical Astrocyte Response and Spontaneous Recurrent Seizures.

Focal traumatic brain injury (TBI) induces astrogliosis, a process essential to protecting uninjured brain areas from secondary damage. However, astrogliosis can cause loss of astrocyte homeostatic functions and possibly contributes to comorbidities such as posttraumatic epilepsy (PTE). Scar-forming astrocytes seal focal injuries off from healthy brain tissue. It is these glial scars that are associated with epilepsy originating in the cerebral cortex and hippocampus. However, the vast majority of human TBIs also present with diffuse brain injury caused by acceleration-deceleration forces leading to tissue shearing. The resulting diffuse tissue damage may be intrinsically different from focal lesions that would trigger glial scar formation. Here, we used mice of both sexes in a model of repetitive mild/concussive closed-head TBI, which only induced diffuse injury, to test the hypothesis that astrocytes respond uniquely to diffuse TBI and that diffuse TBI is sufficient to cause PTE. Astrocytes did not form scars and classic astrogliosis characterized by upregulation of glial fibrillary acidic protein was limited. Surprisingly, an unrelated population of atypical reactive astrocytes was characterized by the lack of glial fibrillary acidic protein expression, rapid and sustained downregulation of homeostatic proteins and impaired astrocyte coupling. After a latency period, a subset of mice developed spontaneous recurrent seizures reminiscent of PTE in human TBI patients. Seizing mice had larger areas of atypical astrocytes compared with nonseizing mice, suggesting that these atypical astrocytes might contribute to epileptogenesis after diffuse TBI.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) is a leading cause of acquired epilepsies. Reactive astrocytes have long been associated with seizures and epilepsy in patients, particularly after focal/lesional brain injury. However, most TBIs also include nonfocal, diffuse injuries. Here, we showed that repetitive diffuse TBI is sufficient for the development of spontaneous recurrent seizures in a subset of mice. We identified an atypical response of astrocytes induced by diffuse TBI characterized by the rapid loss of homeostatic proteins and lack of astrocyte coupling while reactive astrocyte markers or glial scar formation was absent. Areas with atypical astrocytes were larger in animals that later developed seizures suggesting that this response may be one root cause of epileptogenesis after diffuse TBI.

Astroglial Scarring and Seizures: A Cell Biological Perspective on Epilepsy.

Epilepsy is among the most prevalent chronic neurological diseases and affects an estimated 2.2 million people in the United States alone. About one third of patients are resistant to currently available antiepileptic drugs, which are exclusively targeting neuronal function. Yet, reactive astrocytes have emerged as potential contributors to neuronal hyperexcitability and seizures. Astrocytes react to any kind of CNS insult with a range of cellular adjustments to form a scar and protect uninjured brain regions. This process changes astrocyte physiology and can affect neuronal network function in various ways. Traumatic brain injury and stroke, both conditions that trigger astroglial scar formation, are leading causes of acquired epilepsies and surgical removal of this glial scar in patients with drug-resistant epilepsy can alleviate the seizures. This review will summarize the currently available evidence suggesting that epilepsy is not a disease of neurons alone, but that astrocytes, glial cells in the brain, can be major contributors to the disease, especially when they adopt a reactive state in response to central nervous system insult.

Glia as drivers of abnormal neuronal activity.

Reactive astrocytes have been proposed to become incompetent bystanders in epilepsy as a result of cellular changes rendering them unable to perform important housekeeping functions. Indeed, successful surgical treatment of mesiotemporal lobe epilepsy hinges on the removal of the glial scar. New research now extends the role of astrocytes, suggesting that they may drive the disease process by impairing the inhibitory action of neuronal GABA receptors. Here we discuss studies that include hyperexcitability resulting from impaired supply of astrocytic glutamine for neuronal GABA synthesis, and epilepsy resulting from genetically induced astrogliosis or malignant transformation, both of which render the inhibitory neurotransmitter GABA excitatory. In these examples, glial cells alter the expression or function of neuronal proteins involved in excitability. Although epilepsy has traditionally been thought of as a disease caused by changes in neuronal properties exclusively, these new findings challenge us to consider the contribution of glial cells as drivers of epileptogenesis in acquired epilepsies.

Vascular amyloidosis impairs the gliovascular unit in a mouse model of Alzheimer's disease.

Reduced cerebral blood flow impairs cognitive function and ultimately causes irreparable damage to brain tissue. The gliovascular unit, composed of neural and vascular cells, assures sufficient blood supply to active brain regions. Astrocytes, vascular smooth muscle cells, and pericytes are important players within the gliovascular unit modulating vessel diameters. While the importance of the gliovascular unit and the signals involved in regulating local blood flow to match neuronal activity is now well recognized, surprisingly little is known about this interface in disease. Alzheimer's disease is associated with reduced cerebral blood flow. Here, we studied how the gliovascular unit is affected in a mouse model of Alzheimer's disease, using a combination of ex vivo and in vivo imaging approaches. We specifically labelled vascular amyloid in living mice using the dye methoxy-XO4. We elicited vessel responses ex vivo using either pharmacological stimuli or cell-specific calcium uncaging in vascular smooth muscle cells or astrocytes. Multi-photon in vivo imaging through a cranial window allowed us to complement our ex vivo data in the presence of blood flow after label-free optical activation of vascular smooth muscle cells in the intact brain. We found that vascular amyloid deposits separated astrocyte end-feet from the endothelial vessel wall. High-resolution 3D images demonstrated that vascular amyloid developed in ring-like structures around the vessel circumference, essentially forming a rigid cast. Where vascular amyloid was present, stimulation of astrocytes or vascular smooth muscle cells via ex vivo Ca(2+) uncaging or in vivo optical activation produced only poor vascular responses. Strikingly, vessel segments that were unaffected by vascular amyloid responded to the same extent as vessels from age-matched control animals. We conclude that while astrocytes can still release vasoactive substances, vascular amyloid deposits render blood vessels rigid and reduce the dynamic range of affected vessel segments. These results demonstrate a mechanism that could account in part for the reduction in cerebral blood flow in patients with Alzheimer's disease.media-1vid110.1093/brain/awv327_video_abstractawv327_video_abstract.

SLC7A11 expression is associated with seizures and predicts poor survival in patients with malignant glioma.

Glioma is the most common malignant primary brain tumor. Its rapid growth is aided by tumor-mediated glutamate release, creating peritumoral excitotoxic cell death and vacating space for tumor expansion. Glioma glutamate release may also be responsible for seizures, which complicate the clinical course for many patients and are often the presenting symptom. A hypothesized glutamate release pathway is the cystine/glutamate transporter System xc (-) (SXC), responsible for the cellular synthesis of glutathione (GSH). However, the relationship of SXC-mediated glutamate release, seizures, and tumor growth remains unclear. Probing expression of SLC7A11/xCT, the catalytic subunit of SXC, in patient and mouse-propagated tissues, we found that ~50% of patient tumors have elevated SLC7A11 expression. Compared with tumors lacking this transporter, in vivo propagated and intracranially implanted SLC7A11-expressing tumors grew faster, produced pronounced peritumoral glutamate excitotoxicity, induced seizures, and shortened overall survival. In agreement with animal data, increased SLC7A11 expression predicted shorter patient survival according to genomic data in the REMBRANDT (National Institutes of Health Repository for Molecular Brain Neoplasia Data) database. In a clinical pilot study, we used magnetic resonance spectroscopy to determine SXC-mediated glutamate release by measuring acute changes in glutamate after administration of the U.S. Food and Drug Administration-approved SXC inhibitor, sulfasalazine (SAS). In nine glioma patients with biopsy-confirmed SXC expression, we found that expression positively correlates with glutamate release, which is acutely inhibited with oral SAS. These data suggest that SXC is the major pathway for glutamate release from gliomas and that SLC7A11 expression predicts accelerated growth and tumor-associated seizures.

Reactive astrogliosis causes the development of spontaneous seizures.

Epilepsy is one of the most common chronic neurologic diseases, yet approximately one-third of affected patients do not respond to anticonvulsive drugs that target neurons or neuronal circuits. Reactive astrocytes are commonly found in putative epileptic foci and have been hypothesized to be disease contributors because they lose essential homeostatic capabilities. However, since brain pathology induces astrocytes to become reactive, it is difficult to distinguish whether astrogliosis is a cause or a consequence of epileptogenesis. We now present a mouse model of genetically induced, widespread chronic astrogliosis after conditional deletion of ß1-integrin (Itgß1). In these mice, astrogliosis occurs in the absence of other pathologies and without BBB breach or significant inflammation. Electroencephalography with simultaneous video recording revealed that these mice develop spontaneous seizures during the first six postnatal weeks of life and brain slices show neuronal hyperexcitability. This was not observed in mice with neuronal-targeted ß1-integrin deletion, supporting the hypothesis that astrogliosis is sufficient to induce epileptic seizures. Whole-cell patch-clamp recordings from astrocytes further suggest that the heightened excitability was associated with impaired astrocytic glutamate uptake. Moreover, the relative expression of the cation-chloride cotransporters (CCC) NKCC1 (Slc12a2) and KCC2 (Slc12a5), which are responsible for establishing the neuronal Cl(-) gradient that governs GABAergic inhibition were altered and the NKCC1 inhibitor bumetanide eliminated seizures in a subgroup of mice. These data suggest that a shift in the relative expression of neuronal NKCC1 and KCC2, similar to that observed in immature neurons during development, may contribute to astrogliosis-associated seizures.