Generation of primary astrocyte cultures devoid of contaminating microglia

Nrf2 Regulates Basal Glutathione Production in Astrocytes

Astrocytes produce and export glutathione (GSH), an important thiol antioxidant essential for protecting neural cells from oxidative stress and maintaining optimal brain health. While it has been established that oxidative stress increases GSH production in astrocytes, with Nrf2 acting as a critical transcription factor regulating key components of the GSH synthetic pathway, the role of Nrf2 in controlling constitutive GSH synthetic and release mechanisms remains incompletely investigated. Our data show that naïve primary mouse astrocytes cultured from the cerebral cortices of Nrf2 knockout (Nrf2-/-) pups have significantly less intracellular and extracellular GSH levels when compared to astrocytes cultured from Nrf2 wild-type (Nrf2+/+) pups. Key components of the GSH synthetic pathway, including xCT (the substrate-specific light chain of the substrate-importing transporter, system xc-), glutamate-cysteine ligase [catalytic (GCLc) and modifying (GCLm) subunits], were affected. To wit: qRT-PCR analysis demonstrates that naïve Nrf2-/- astrocytes have significantly lower basal mRNA levels of xCT and both GCL subunits compared to naïve Nrf2+/+ astrocytes. No change in mRNA levels of glutathione synthetase (GS) or the GSH exporting transporter, Mrp1, was found. Western blot analysis reveals reduced protein levels of both subunits of GCL, while (seleno)cystine uptake into Nrf2-/- astrocytes was reduced compared to Nrf2+/+ astrocytes, confirming decreased system xc- activity. These findings suggest that Nrf2 regulates the basal production of GSH in astrocytes through constitutive transcriptional regulation of GCL and xCT.

Astrocytes Are the Source of TNF Mediating Homeostatic Synaptic Plasticity

Tumor necrosis factor α (TNF) mediates homeostatic synaptic plasticity (HSP) in response to chronic activity blockade, and prior work has established that it is released from glia. Here we demonstrate that astrocytes are the necessary source of TNF during HSP. Hippocampal cultures from rats of both sexes depleted of microglia still will increase TNF levels following activity deprivation and still express TTX-driven HSP. Slice cultures from mice of either sex with a conditional deletion of TNF from microglia also express HSP, but critically, slice cultures with a conditional deletion of TNF from astrocytes do not. In astrocytes, glutamate signaling is sufficient to reduce NFκB signaling and TNF mRNA levels. Further, chronic TTX treatment increases TNF in an NFκB-dependent manner, although NFκB signaling is dispensable for the neuronal response to TTX-driven HSP. Thus, astrocytes can sense neuronal activity through glutamate spillover and increase TNF production when activity falls, to drive HSP through the production of TNF.

Engineering circuits of human iPSC-derived neurons and rat primary glia

Novel in vitro platforms based on human neurons are needed to improve early drug testing and address the stalling drug discovery in neurological disorders. Topologically controlled circuits of human induced pluripotent stem cell (iPSC)-derived neurons have the potential to become such a testing system. In this work, we build in vitro co-cultured circuits of human iPSC-derived neurons and rat primary glial cells using microfabricated polydimethylsiloxane (PDMS) structures on microelectrode arrays (MEAs). Our PDMS microstructures are designed in the shape of a stomach, which guides axons in one direction and thereby facilitates the unidirectional flow of information. Such circuits are created by seeding either dissociated cells or pre-aggregated spheroids at different neuron-to-glia ratios. Furthermore, an antifouling coating is developed to prevent axonal overgrowth in undesired locations of the microstructure. We assess the electrophysiological properties of different types of circuits over more than 50 days, including their stimulation-induced neural activity. Finally, we demonstrate the inhibitory effect of magnesium chloride on the electrical activity of our iPSC circuits as a proof-of-concept for screening of neuroactive compounds.

Norepinephrine activates β1 -adrenergic receptors at the inner nuclear membrane in astrocytes

Norepinephrine exerts powerful influences on the metabolic, neuroprotective and immunoregulatory functions of astrocytes. Until recently, all effects of norepinephrine were believed to be mediated by receptors localized exclusively to the plasma membrane. However, recent studies in cardiomyocytes have identified adrenergic receptors localized to intracellular membranes, including Golgi and inner nuclear membranes, and have shown that norepinephrine can access these receptors via transporter-mediated uptake. We recently identified a high-capacity norepinephrine transporter, organic cation transporter 3 (OCT3), densely localized to outer nuclear membranes in astrocytes, suggesting that adrenergic signaling may also occur at the inner nuclear membrane in these cells. Here, we used immunofluorescence and western blot to show that β1 -adrenergic receptors are localized to astrocyte inner nuclear membranes; that key adrenergic signaling partners are present in astrocyte nuclei; and that OCT3 and other catecholamine transporters are localized to astrocyte plasma and nuclear membranes. To test the functionality of nuclear membrane β1 -adrenergic receptors, we monitored real-time protein kinase A (PKA) activity in astrocyte nuclei using a fluorescent biosensor. Treatment of astrocytes with norepinephrine induced rapid increases in PKA activity in the nuclear compartment. Pretreatment of astrocytes with inhibitors of catecholamine uptake blocked rapid norepinephrine-induced increases in nuclear PKA activity. These studies, the first to document functional adrenergic receptors at the nuclear membrane in any central nervous system cell, reveal a novel mechanism by which norepinephrine may directly influence nuclear processes. This mechanism may contribute to previously described neuroprotective, metabolic and immunoregulatory actions of norepinephrine.

Neurosurgical Approaches to Brain Tissue Harvesting for the Establishment of Cell Cultures in Neural Experimental Cell Models

In recent decades, cell biology has made rapid progress. Cell isolation and cultivation techniques, supported by modern laboratory procedures and experimental capabilities, provide a wide range of opportunities for in vitro research to study physiological and pathophysiological processes in health and disease. They can also be used very efficiently for the analysis of biomaterials. Before a new biomaterial is ready for implantation into tissues and widespread use in clinical practice, it must be extensively tested. Experimental cell models, which are a suitable testing ground and the first line of empirical exploration of new biomaterials, must contain suitable cells that form the basis of biomaterial testing. To isolate a stable and suitable cell culture, many steps are required. The first and one of the most important steps is the collection of donor tissue, usually during a surgical procedure. Thus, the collection is the foundation for the success of cell isolation. This article explains the sources and neurosurgical procedures for obtaining brain tissue samples for cell isolation techniques, which are essential for biomaterial testing procedures.

Advanced Bio-Based Polymers for Astrocyte Cell Models

The development of in vitro neural tissue analogs is of great interest for many biomedical engineering applications, including the tissue engineering of neural interfaces, treatment of neurodegenerative diseases, and in vitro evaluation of cell-material interactions. Since astrocytes play a crucial role in the regenerative processes of the central nervous system, the development of biomaterials that interact favorably with astrocytes is of great research interest. The sources of human astrocytes, suitable natural biomaterials, guidance scaffolds, and ligand patterned surfaces are discussed in the article. New findings in this field are essential for the future treatment of spinal cord and brain injuries.

Astrocyte-derived Wnt growth factors are required for endothelial blood-brain barrier maintenance

Maintenance of the endothelial blood-brain-barrier (BBB) through Wnt/β-catenin signalling is essential for neuronal function. The cells however, providing Wnt growth factors at the adult neurovascular unit (NVU) are poorly explored. Here we show by conditionally knocking out the evenness interrupted (Evi) gene in astrocytes (Evi^ΔAC) that astrocytic Wnt release is crucial for BBB and NVU integrity. Evi^ΔAC mice developed brain oedema and increased vascular tracer leakage. While brain vascularization and endothelial junctions were not altered in 10 and 40 week-old mice, endothelial caveolin(Cav)-1-mediated vesicle formation was increased in vivo and in vitro. Moreover, astrocytic end-feet were swollen, and aquaporin-4 distribution was disturbed, coinciding with decreased astrocytic Wnt activity. Vascular permeability correlated with increased neuronal activation by c-fos staining, indicative of altered neuronal function. Astrocyte-derived Wnts thus serve to maintain Wnt/β-catenin activity in endothelia and in astrocytes, thereby controlling Cav-1 expression, vesicular abundance, and end-feet integrity at the NVU.

HIF-1α is involved in blood-brain barrier dysfunction and paracellular migration of bacteria in pneumococcal meningitis

Bacterial meningitis is a deadly disease most commonly caused by Streptococcus pneumoniae, leading to severe neurological sequelae including cerebral edema, seizures, stroke, and mortality when untreated. Meningitis is initiated by the transfer of S. pneumoniae from blood to the brain across the blood-cerebrospinal fluid barrier or the blood-brain barrier (BBB). The underlying mechanisms are still poorly understood. Current treatment strategies include adjuvant dexamethasone for inflammation and cerebral edema, followed by antibiotics. The success of dexamethasone is however inconclusive, necessitating new therapies for controlling edema, the primary reason for neurological complications. Since we have previously shown a general activation of hypoxia inducible factor (HIF-1α) in bacterial infections, we hypothesized that HIF-1α, via induction of vascular endothelial growth factor (VEGF) is involved in transmigration of pathogens across the BBB. In human, murine meningitis brain samples, HIF-1α activation was observed by immunohistochemistry. S. pneumoniae infection in brain endothelial cells (EC) resulted in in vitro upregulation of HIF-1α/VEGF (Western blotting/qRT-PCR) associated with increased paracellular permeability (fluorometry, impedance measurements). This was supported by bacterial localization at cell-cell junctions in vitro and in vivo in brain ECs from mouse and humans (confocal, super-resolution, electron microscopy, live-cell imaging). Hematogenously infected mice showed increased permeability, S. pneumoniae deposition in the brain, along with upregulation of genes in the HIF-1α/VEGF pathway (RNA sequencing of brain microvessels). Inhibition of HIF-1α with echinomycin, siRNA in bEnd5 cells or using primary brain ECs from HIF-1α knock-out mice revealed reduced endothelial permeability and transmigration of S. pneumoniae. Therapeutic rescue using the HIF-1α inhibitor echinomycin resulted in increased survival and improvement of BBB function in S. pneumoniae-infected mice. We thus demonstrate paracellular migration of bacteria across BBB and a critical role for HIF-1α/VEGF therein and hence propose targeting this pathway to prevent BBB dysfunction and ensuing brain damage in infections.

Isolation and Culture of Astrocytes from Postnatal and Adult Mouse Brains

Astrocytes play fundamental roles in development and plasticity of the central nervous system. Dysfunction of astrocytes contributes to most of neurological diseases ranging from neurodegenerative diseases to psychological disorders. To better understand the involvement of astrocytes in both physiological and pathological conditions, and further elucidate their underlying mechanisms, it is critical to establish a reliable isolation and culture method for the cells. In this chapter, we describe the isolation and culture protocols of astrocytes from postnatal and adult mouse brains.

Mice lacking L-12/15-lipoxygenase show increased mortality during kindling despite demonstrating resistance to epileptogenesis

Objective

Studies have addressed the potential involvement of L-12/15-lipoxygenases (LOs), a polyunsaturated fatty acid metabolizing enzyme, in experimental models of acute stroke and chronic neurodegeneration; however, none to our knowledge has explored its role in epilepsy development. Thus, this study characterizes the cell-specific expression of L-12/15 -LO in the brain and examines its contribution to epileptogenesis.

Methods

L-12/15-LO messenger RNA (mRNA) and protein expression and activity were characterized via polymerase chain reaction (PCR), immunocytochemistry and enzyme-linked immunosorbent assay (ELISA), respectively. To assess its role in epileptogenesis, L-12/15 -LO-deficient mice and their wild-type littermates were treated with pentylenetetrazole (PTZ, ip) every other day for up to 43 days (kindling paradigm). The innate seizure threshold was assessed by the acute PTZ-induced seizure response of naive mice.

Results

L-12/15 -LO mRNA is expressed in hippocampal and cortical tissue from wild-type C57BL/6 mice. In addition, it is physically and functionally expressed by microglia, neurons, and brain microvessel endothelial cells, but not by astrocytes. Mice deficient in L-12/15 -LO were resistant to PTZ-induced kindling and demonstrated an elevated innate seizure threshold. Despite this, a significant increase in seizure-related mortality was observed during the kindling paradigm in L-12/15 -LO nulls relative to their wild-type littermates.

Significance

The present study is the first to detail the role of L-12/15-LO in the epileptogenic process. The results suggest that constitutive L-12/15-LO expression contributes to a lower innate set point for PTZ acute seizure generation, translating to higher rates of kindling acquisition. Nevertheless, increased seizure-related deaths in mice lacking activity of L-12/15-LO suggests that its products may influence endogenous mechanisms involved in termination of seizure activity.

Spontaneous Glutamatergic Synaptic Activity Regulates Constitutive COX-2 Expression in Neurons: OPPOSING ROLES FOR THE TRANSCRIPTION FACTORS CREB (cAMP RESPONSE ELEMENT BINDING) PROTEIN AND Sp1 (STIMULATORY PROTEIN-1)

Burgeoning evidence supports a role for cyclooxygenase metabolites in regulating membrane excitability in various forms of synaptic plasticity. Two cyclooxygenases, COX-1 and COX-2, catalyze the initial step in the metabolism of arachidonic acid to prostaglandins. COX-2 is generally considered inducible, but in glutamatergic neurons in some brain regions, including the cerebral cortex, it is constitutively expressed. However, the transcriptional mechanisms by which this occurs have not been elucidated. Here, we used quantitative PCR and also analyzed reporter gene expression in a mouse line carrying a construct consisting of a portion of the proximal promoter region of the mouse COX-2 gene upstream of luciferase cDNA to characterize COX-2 basal transcriptional regulation in cortical neurons. Extracts from the whole brain and from the cerebral cortex, hippocampus, and olfactory bulbs exhibited high luciferase activity. Moreover, constitutive COX-2 expression and luciferase activity were detected in cortical neurons, but not in cortical astrocytes, cultured from wild-type and transgenic mice, respectively. Constitutive COX-2 expression depended on spontaneous but not evoked excitatory synaptic activity and was shown to be N-methyl-d-aspartate receptor-dependent. Constitutive promoter activity was reduced in neurons transfected with a dominant-negative cAMP response element binding protein (CREB) and was eliminated by mutating the CRE-binding site on the COX-2 promoter. However, mutation of the stimulatory protein-1 (Sp1)-binding site resulted in an N-methyl-d-aspartate receptor-dependent enhancement of COX-2 promoter activity. Basal binding of the transcription factors CREB and Sp1 to the native neuronal COX-2 promoter was confirmed. In toto, our data suggest that spontaneous glutamatergic synaptic activity regulates constitutive neuronal COX-2 expression via Sp1 and CREB protein-dependent transcriptional mechanisms.

Sex Differences in Mouse Hippocampal Astrocytes after In-Vitro Ischemia

Astrogliosis following hypoxia/ischemia (HI)-related brain injury plays a role in increased morbidity and mortality in neonates. Recent clinical studies indicate that the severity of brain injury appear to be sex dependent, and that the male neonates are more susceptible to the effects of HI-related brain injury, resulting in more severe neurological outcomes as compared to females with comparable brain injuries. The development of reliable methods to isolate and maintain highly enriched populations of sexed hippocampal astrocytes is essential to understand the cellular basis of sex differences in the pathological consequences of neonatal HI. In this study, we describe a method for creating sex specific hippocampal astrocyte cultures that are subjected to a model of in-vitro ischemia, oxygen-glucose deprivation, followed by reoxygenation. Subsequent reactive astrogliosis was examined by immunostaining for the Glial Fibrillary Acidic Protein (GFAP) and S100B. This method provides a useful tool to study the role of male and female hippocampal astrocytes following neonatal HI, separately.

Angiopoietin-2-induced blood-brain barrier compromise and increased stroke size are rescued by VE-PTP-dependent restoration of Tie2 signaling

The homeostasis of the central nervous system is maintained by the blood-brain barrier (BBB). Angiopoietins (Ang-1/Ang-2) act as antagonizing molecules to regulate angiogenesis, vascular stability, vascular permeability and lymphatic integrity. However, the precise role of angiopoietin/Tie2 signaling at the BBB remains unclear. We investigated the influence of Ang-2 on BBB permeability in wild-type and gain-of-function (GOF) mice and demonstrated an increase in permeability by Ang-2, both in vitro and in vivo. Expression analysis of brain endothelial cells from Ang-2 GOF mice showed a downregulation of tight/adherens junction molecules and increased caveolin-1, a vesicular permeability-related molecule. Immunohistochemistry revealed reduced pericyte coverage in Ang-2 GOF mice that was supported by electron microscopy analyses, which demonstrated defective intra-endothelial junctions with increased vesicles and decreased/disrupted glycocalyx. These results demonstrate that Ang-2 mediates permeability via paracellular and transcellular routes. In patients suffering from stroke, a cerebrovascular disorder associated with BBB disruption, Ang-2 levels were upregulated. In mice, Ang-2 GOF resulted in increased infarct sizes and vessel permeability upon experimental stroke, implicating a role of Ang-2 in stroke pathophysiology. Increased permeability and stroke size were rescued by activation of Tie2 signaling using a vascular endothelial protein tyrosine phosphatase inhibitor and were independent of VE-cadherin phosphorylation. We thus identified Ang-2 as an endothelial cell-derived regulator of BBB permeability. We postulate that novel therapeutics targeting Tie2 signaling could be of potential use for opening the BBB for increased CNS drug delivery or tighten it in neurological disorders associated with cerebrovascular leakage and brain edema.

Interleukin 1β Regulation of the System xc- Substrate-specific Subunit, xCT, in Primary Mouse Astrocytes Involves the RNA-binding Protein HuR

System xc(-) is a heteromeric amino acid cystine/glutamate antiporter that is constitutively expressed by cells of the CNS, where it functions in the maintenance of intracellular glutathione and extracellular glutamate levels. We recently determined that the cytokine, IL-1β, increases the activity of system xc(-) in CNS astrocytes secondary to an up-regulation of its substrate-specific light chain, xCT, and that this occurs, in part, at the level of transcription. However, an in silico analysis of the murine xCT 3'-UTR identified numerous copies of adenine- and uridine-rich elements, raising the possibility that undefined trans-acting factors governing mRNA stability and translation may also contribute to xCT expression. Here we show that IL-1β increases the level of mRNA encoding xCT in primary cultures of astrocytes isolated from mouse cortex in association with an increase in xCT mRNA half-life. Additionally, IL-1β induces HuR translocation from the nucleus to the cytoplasm. RNA immunoprecipitation analysis reveals that HuR binds directly to the 3'-UTR of xCT in an IL-1β-dependent manner. Knockdown of endogenous HuR protein abrogates the IL-1β-mediated increase in xCT mRNA half-life, whereas overexpression of HuR in unstimulated primary mouse astrocytes doubles the half-life of constitutive xCT mRNA. This latter effect is accompanied by an increase in xCT protein levels, as well as a functional increase in system xc(-) activity. Altogether, these data support a critical role for HuR in mediating the IL-1β-induced stabilization of astrocyte xCT mRNA.

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System xc- Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc(-)) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc(-) expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes--either cultured alone or with neurons--to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc(-) mediates aglycemic neuronal cell death.

Interleukin-1β protects astrocytes against oxidant-induced injury via an NF-κB-dependent upregulation of glutathione synthesis

Astrocytes produce and export the antioxidant glutathione (GSH). Previously, we found that interleukin-1β (IL-1β) enhanced the expression of astrocyte system xc (-) , the transporter that delivers the rate-limiting substrate for GSH synthesis-cyst(e)ine. Herein, we demonstrate directly that IL-1β mediates a time-dependent increase in extracellular GSH levels in cortical astrocyte cultures, suggesting both enhanced synthesis and export. This increased GSH production was blocked by inhibition of nuclear factor-κB (NF-κB) activity but not by inhibition of p38 MAPK. To determine whether this increase could provide protection against oxidative stress, the oxidants tert-butyl hydroperoxide (tBOOH) and ferrous sulfate (FeSO4 ) were employed. IL-1β treatment prevented the increase in reactive oxygen species produced in astrocytes following tBOOH exposure. Additionally, the toxicity induced by tBOOH or FeSO4 exposure was significantly attenuated following treatment with IL-1β, an effect reversed by concomitant exposure to l-buthionine-S,R-sulfoximine (BSO), which prevented the IL-1β-mediated rise in GSH production. IL-1β failed to increase GSH or to provide protection against t-BOOH toxicity in astrocyte cultures derived from IL-1R1 null mutant mice. Overall, our data indicate that under certain conditions IL-1β may be an important stimulus for increasing astrocyte GSH production, and potentially, total antioxidant capacity in brain, via an NF-κB-dependent process.

LPS and IL-1 differentially activate mouse and human astrocytes: role of CD14

Treatment of cultures with toll-like receptor (TLR) ligands or cytokines has become a popular approach to investigate astrocyte neuroinflammatory responses and to simulate the neural environment in various CNS disorders. However, despite much effort, the mechanism of astrocyte activation such as their responses to the TLR ligands and IL-1 remain highly debated. We compared highly pure primary mouse and human astrocyte cultures in their ability to produce proinflammatory mediators (termed "A1") and immunoregulatory mediators (termed "A2") in response to LPS, poly IC, and IL-1 stimulation. In human astrocytes, IL-1 induced both A1 and A2 responses, poly IC induced mostly A2, and LPS induced neither. In mouse astrocytes, LPS induced mostly an A1-predominant response, poly IC induced both A1 and A2, and IL-1 neither. In addition, mouse astrocytes produce abundant IL-1 protein, whereas human astrocytes did not, despite robust IL-1 mRNA expression. Of the TLR4 receptor complex proteins, human astrocytes expressed TLR4 and MD2 but not CD14, whereas mouse astrocytes expressed all three. Mouse astrocyte CD14 (cell-associated and soluble) was potently upregulated by LPS. Silencing TLR4 or CD14 by siRNA suppressed LPS responses in mouse astrocytes. In vivo, astrocytes in LPS-injected mouse brains also expressed CD14. Our results show striking differences between human and mouse astrocytes in the use of TLR/IL-1R and subsequent downstream signaling and immune activation. IL-1 translational block in human astrocytes may be a built-in mechanism to prevent autocrine and paracrine cell activation and neuroinflammation. These results have important implications for translational research of human CNS diseases.

In vitro models of the blood-brain barrier

The blood-brain barrier (BBB) proper is composed of endothelial cells (ECs) of the cerebral microvasculature, which are interconnected by tight junctions (TJs) that in turn form a physical barrier restricting paracellular flux. Tight control of vascular permeability is essential for the homeostasis and functionality of the central nervous system (CNS). In vitro BBB models have been in use for decades and have been of great benefit in the process of investigating and understanding the cellular and molecular mechanisms underlying BBB establishment. BBB integrity changes can be addressed in vitro by determining cell monolayer permeability (Pe) to different solutes and measuring trans-endothelial electrical resistance (TEER).This chapter describes procedures that can be utilized for both freshly isolated mouse brain microvascular ECs (MBMECs) and murine or human brain EC lines (bEnd5 or hCMEC/D3), cultivated either as a single monolayer or in cocultivation with primary mouse astrocytes (ACs). It starts with detailed information on how to perform transwell cell culture, including coating of inserts and seeding of the ECs and ACs. Moreover, it encompasses instructions for electrical assessment of the in vitro BBB using the more recent cellZscope(®) device, which was traditionally performed with chopstick electrodes of voltohmmeter type (EVOM). From continuous impedance measurements, the cellZscope(®) device provides TEER (paracellular resistance) and cell membrane capacitance (Ccl-transcellular resistance), two independent measures of monolayer integrity. Additionally, this chapter provides guidance through subsequent experiments such as permeability analysis (Pe, flux), expression analysis (qRT-PCR and Western blotting), and localization analysis of BBB junction proteins (immunocytochemistry) using the same inserts subjected earlier to impedance analysis.As numerous diseases are associated with BBB breakdown, researchers aim to continuously improve and refine in vitro BBB models to mimic in vivo conditions as closely as possible. This chapter summarizes protocols with the intention to provide a collection of BBB in vitro assays that generate reproducible results not only with primary brain ECs but also with EC lines to open up the field for a broader spectrum of researchers who intend to investigate the BBB in vitro particularly aiming at therapeutic aspects.

Phenotypic transition of microglia into astrocyte-like cells associated with disease onset in a model of inherited ALS

Microglia and reactive astrocytes accumulate in the spinal cord of rats expressing the Amyotrophic lateral sclerosis (ALS)-linked SOD1 ^G93A mutation. We previously reported that the rapid progression of paralysis in ALS rats is associated with the appearance of proliferative astrocyte-like cells that surround motor neurons. These cells, designated as Aberrant Astrocytes (AbA cells) because of their atypical astrocytic phenotype, exhibit high toxicity to motor neurons. However, the cellular origin of AbA cells remains unknown. Because AbA cells are labeled with the proliferation marker Ki67, we analyzed the phenotypic makers of proliferating glial cells that surround motor neurons by immunohistochemistry. The number of Ki67 ⁺AbA cells sharply increased in symptomatic rats, displaying large cell bodies with processes embracing motor neurons. Most were co-labeled with astrocytic marker GFAP concurrently with the microglial markers Iba1 and CD163. Cultures of spinal cord prepared from symptomatic SOD1 ^G93A rats yielded large numbers of microglia expressing Iba1, CD11b, and CD68. Cells sorted for CD11b expression by flow cytometry transformed into AbA cells within two weeks. During these two weeks, the expression of microglial markers largely disappeared, while GFAP and S100β expression increased. The phenotypic transition to AbA cells was stimulated by forskolin. These findings provide evidence for a subpopulation of proliferating microglial cells in SOD1 ^G93A rats that undergo a phenotypic transition into AbA cells after onset of paralysis that may promote the fulminant disease progression. These cells could be a therapeutic target for slowing paralysis progression in ALS.

Depletion of microglia from primary cellular cultures

Primary cultures are an important in vitro tool to study cellular processes and interactions. These cultures are complex systems, composed of many cell types, including neurons, astrocytes, oligodendrocytes, microglia, NG2 cells, and endothelial cells. For some studies it is necessary to be able to study a pure culture of one cell type, or eliminate a particular cell type, to better understand its function. There exist cell culture protocols for making pure astrocyte or microglia cultures. Here we present two protocols to produce cultures depleted for microglia: in the first case, from a mixed astrocyte-microglia culture and, in the second, for eliminating microglia from neuronal cultures.