Membrane properties and coupling of macroglia in the optic nerve.

We established a longitudinal acute slice preparation of transgenic mouse optic nerve to characterize membrane properties and coupling of glial cells by patch-clamp and dye-filling, complemented by immunohistochemistry. Unlike in cortex or hippocampus, the majority of EGFP + cells in optic nerve of the hGFAP-EGFP transgenic mouse, a tool to identify astrocytes, were characterized by time and voltage dependent K-currents including A-type K-currents, properties previously described for NG2 glia. Indeed, the majority of transgene expressing cells in optic nerve were immunopositive for NG2 proteoglycan, whereas only a minority show GFAP immunoreactivity.

In situ Patch-seq analysis of microglia reveals a lack of stress genes as found in FACS-isolated microglia.

We applied the patch-seq technique to harvest transcripts from individual microglial cells from cortex, hippocampus and corpus callosum of acute brain slices from adult mice. After recording membrane currents with the patch-clamp technique, the cytoplasm was collected via the pipette and underwent adapted SMART-seq2 preparation with subsequent sequencing. On average, 4138 genes were detected in 113 cells from hippocampus, corpus callosum and cortex, including microglia markers such as Tmem119, P2ry12 and Siglec-H.

Neurofibromin 1 mutations impair the function of human induced pluripotent stem cell-derived microglia.

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition caused by germline mutations in the neurofibromin 1 (NF1) gene. Children with NF1 are prone to the development of multiple nervous system abnormalities, including autism and brain tumors, which could reflect the effect of NF1 mutation on microglia function. Using heterozygous Nf1-mutant mice, we previously demonstrated that impaired purinergic signaling underlies deficits in microglia process extension and phagocytosis in situ.

Cesium activates the neurotransmitter receptor for glycine.

The monovalent cations sodium and potassium are crucial for the proper functioning of excitable cells, but, in addition, other monovalent alkali metal ions such as cesium and lithium can also affect neuronal physiology. For instance, there have been recent reports of adverse effects resulting from self-administered high concentrations of cesium in disease conditions, prompting the Food and Drug Administration (FDA) to issue an alert concerning cesium chloride. As we recently found that the monovalent cation NH activates glycine receptors (GlyRs), we investigated the effects of alkali metal ions on the function of the GlyR, which belongs to one of the most widely distributed neurotransmitter receptors in the peripheral and central nervous systems.

Sex-specific microglia state in the Neuroligin-4 knock-out mouse model of autism spectrum disorder.

Neuroligin-4 (NLGN4) loss-of-function mutations are associated with monogenic heritable autism spectrum disorder (ASD) and cause alterations in both synaptic and behavioral phenotypes. Microglia, the resident CNS macrophages, are implicated in ASD development and progression. Here we studied the impact of NLGN4 loss in a mouse model, focusing on microglia phenotype and function in both male and female mice.

Neurofibromatosis type 1-dependent alterations in mouse microglia function are not cell-intrinsic.

We previously discovered a sex-by-genotype defect in microglia function using a heterozygous germline knockout mouse model of Neurofibromatosis type 1 (Nf1 ± mice), in which only microglia from male Nf1 ± mice exhibited defects in purinergic signaling. Herein, we leveraged an unbiased proteomic approach to demonstrate that male, but not female, heterozygous Nf1 ± microglia exhibit differences in protein expression, which largely reflect pathways involved in cytoskeletal organization. In keeping with these predicted defects in cytoskeletal function, only male Nf1 ± microglia had reduced process arborization and surveillance capacity.

Microglia sense neuronal activity via GABA in the early postnatal hippocampus.

Microglia, the resident macrophages in the central nervous system, express receptors for classical neurotransmitters, such as γ-aminobutyric acid (GABA) and glutamate, suggesting that they sense synaptic activity. To detect microglial Ca responses to neuronal activity, we generate transgenic mouse lines expressing the fluorescent Ca indicator GCaMP6m, specifically in microglia and demonstrate that electrical stimulation of the Schaffer collateral pathway results in microglial Ca responses in early postnatal but not adult hippocampus. Preceding the microglial responses, we also observe similar Ca responses in astrocytes, and both are sensitive to tetrodotoxin.

Histamine triggers microglial responses indirectly via astrocytes and purinergic signaling.

Histamine is a monoaminergic neurotransmitter which is released within the entire brain from ascending axons originating in the tuberomammillary nucleus in a sleep state-dependent fashion. Besides the modulation of neuronal firing patterns, brain histamine levels are also thought to modulate functions of glial cells. Microglia are the innate immune cells and professional phagocytes of the central nervous system, and histamine was previously shown to have multiple effects on microglial functions in health and disease.

Down-regulation of Aquaporin-1 mediates a microglial phenotype switch affecting glioma growth.

Aquaporin 1 (AQP1), a transmembrane protein that forms water channels, has previously been shown to facilitate growth and progression of many types of tumors by modulating tumor cell migration, proliferation and angiogenesis. Here, we determined the impact of AQP1 expression in the tumor environment on the progression of brain tumors. Primary microglia from wild type(WT) and AQP1 knockout(KO) mice were used to test AQP1 effect on microglia function by using Western blot, quantative PCR, in an experimental in vivo mouse glioma model and organotypic brain slice culture.

Neurofibromatosis 1 - Mutant microglia exhibit sexually-dimorphic cyclic AMP-dependent purinergic defects.

As critical regulators of brain homeostasis, microglia are influenced by numerous factors, including sex and genetic mutations. To study the impact of these factors on microglia biology, we employed genetically engineered mice that model Neurofibromatosis type 1 (NF1), a disorder characterized by clinically relevant sexually dimorphic differences. While microglia phagocytic activity was reduced in both male and female heterozygous Nf1 mutant (Nf1+/-) mice, purinergic control of phagocytosis was only affected in male Nf1+/- mice.

The VGF-derived Peptide TLQP21 Impairs Purinergic Control of Chemotaxis and Phagocytosis in Mouse Microglia.

Microglial cells are considered as sensors of brain pathology by detecting any sign of brain lesions, infections, or dysfunction and can influence the onset and progression of neurological diseases. They are capable of sensing their neuronal environment via many different signaling molecules, such as neurotransmitters, neurohormones and neuropeptides. The neuropeptide VGF has been associated with many metabolic and neurological disorders.

Correction to: Comprehensive gene expression meta-analysis identifies signature genes that distinguish microglia from peripheral monocytes/macrophages in health and glioma.

The original publication of this article [1] contained 3 minor errors in Figs. 1, 3 and 5. In this correction article the updated figures are published.

let-7 MicroRNAs Regulate Microglial Function and Suppress Glioma Growth through Toll-Like Receptor 7.

Microglia express Toll-like receptors (TLRs) that sense pathogen- and host-derived factors, including single-stranded RNA. In the brain, let-7 microRNA (miRNA) family members are abundantly expressed, and some have recently been shown to serve as TLR7 ligands. We investigated whether let-7 miRNA family members differentially control microglia biology in health and disease.

Tenascin C regulates multiple microglial functions involving TLR4 signaling and HDAC1.

Tenascin C (Tnc) is an extracellular matrix glycoprotein, expressed in the CNS during development, as well as in the setting of inflammation, fibrosis and cancer, which operates as an activator of Toll-like receptor 4 (TLR4). Although TLR4 is highly expressed in microglia, the effect of Tnc on microglia has not been elucidated to date. Herein, we demonstrate that Tnc regulates microglial phagocytic activity at an early postnatal age (P4), and that this process is partially dependent on microglial TLR4 expression.

Corrigendum: A Novel RNA Editing Sensor Tool and a Specific Agonist Determine Neuronal Protein Expression of RNA-Edited Glycine Receptors and Identify a Genomic APOBEC1 Dimorphism as a New Genetic Risk Factor of Epilepsy.

[This corrects the article DOI: 10.3389/fnmol.2017.

Comprehensive gene expression meta-analysis identifies signature genes that distinguish microglia from peripheral monocytes/macrophages in health and glioma.

Monocytes/macrophages have begun to emerge as key cellular modulators of brain homeostasis and central nervous system (CNS) disease. In the healthy brain, resident microglia are the predominant macrophage cell population; however, under conditions of blood-brain barrier leakage, peripheral monocytes/macrophages can infiltrate the brain and participate in CNS disease pathogenesis. Distinguishing these two populations is often challenging, owing to a paucity of universally accepted and reliable markers.

Athymic mice reveal a requirement for T-cell-microglia interactions in establishing a microenvironment supportive of low-grade glioma growth.

Pediatric low-grade gliomas (LGGs) frequently do not engraft in immunocompromised mice, limiting their use as an experimental platform. In contrast, murine Neurofibromatosis-1 () optic LGG stem cells (o-GSCs) form glioma-like lesions in wild-type, but not athymic, mice following transplantation. Here, we show that the inability of athymic mice to support o-GSC engraftment results from impaired microglia/macrophage function, including reduced expression of Ccr2 and Ccl5, both of which are required for o-GSC engraftment and optic glioma growth.

Oligodendrocytes in the Mouse Corpus Callosum Maintain Axonal Function by Delivery of Glucose.

In the optic nerve, oligodendrocytes maintain axonal function by supplying lactate as an energy substrate. Here, we report that, in acute brain slices of the mouse corpus callosum, exogenous glucose deprivation (EGD) abolished compound action potentials (CAPs), which neither lactate nor pyruvate could prevent. Loading an oligodendrocyte with 20 mM glucose using a patch pipette prevented EGD-mediated CAP reduction in about 70% of experiments.

A Novel RNA Editing Sensor Tool and a Specific Agonist Determine Neuronal Protein Expression of RNA-Edited Glycine Receptors and Identify a Genomic APOBEC1 Dimorphism as a New Genetic Risk Factor of Epilepsy.

C-to-U RNA editing of glycine receptors (GlyR) can play an important role in disease progression of temporal lobe epilepsy (TLE) as it may contribute in a neuron type-specific way to neuropsychiatric symptoms of the disease. It is therefore necessary to develop tools that allow identification of neuron types that express RNA-edited GlyR protein. In this study, we identify NH as agonist of C-to-U RNA edited GlyRs.

S-sulfocysteine/NMDA receptor-dependent signaling underlies neurodegeneration in molybdenum cofactor deficiency.

Molybdenum cofactor deficiency (MoCD) is an autosomal recessive inborn error of metabolism characterized by neurodegeneration and death in early childhood. The rapid and progressive neurodegeneration in MoCD presents a major clinical challenge and may relate to the poor understanding of the molecular mechanisms involved. Recently, we reported that treating patients with cyclic pyranopterin monophosphate (cPMP) is a successful therapy for a subset of infants with MoCD and prevents irreversible brain damage.

Changes in phagocytosis and potassium channel activity in microglia of 5xFAD mice indicate alterations in purinergic signaling in a mouse model of Alzheimer's disease.

As the immunocompetent cells of the central nervous system, microglia accumulate at amyloid beta plaques in Alzheimer's disease (AD) and acquire a morphological phenotype of activated microglia. Recent functional studies, however, indicate that in mouse models of amyloidosis and AD, these cells are rather dysfunctional indicated by a reduced phagocytic activity. Here, we report that this reduction in phagocytic activity is associated with perturbed purinergic receptor signaling, since phagocytosis could be stimulated by P2Y receptor activation in control, but not in 5xFAD transgenic animals, an animal model of amyloid deposition.

Human iPSC-Derived Neural Progenitors Are an Effective Drug Discovery Model for Neurological mtDNA Disorders.

Mitochondrial DNA (mtDNA) mutations frequently cause neurological diseases. Modeling of these defects has been difficult because of the challenges associated with engineering mtDNA. We show here that neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (iPSCs) retain the parental mtDNA profile and exhibit a metabolic switch toward oxidative phosphorylation.

Spontaneous Ca transients in mouse microglia.

Microglia are the resident immune cells in the central nervous system and many of their physiological functions are known to be linked to intracellular calcium (Ca) signaling. Here we show that isolated and purified mouse microglia-either freshly or cultured-display spontaneous and transient Ca elevations lasting for around ten to twenty seconds and occurring at frequencies of around five to ten events per hour and cell. The events were absent after depletion of internal Ca stores, by phospholipase C (PLC) inhibition or blockade of inositol-1,4,5-trisphosphate receptors (IPRs), but not by removal of extracellular Ca, indicating that Ca is released from endoplasmic reticulum intracellular stores.

Electrophysiological Signature of Homomeric and Heteromeric Glycine Receptor Channels.

Glycine receptors are chloride-permeable, ligand-gated ion channels and contribute to the inhibition of neuronal firing in the central nervous system or to facilitation of neurotransmitter release if expressed at presynaptic sites. Recent structure-function studies have provided detailed insights into the mechanisms of channel gating, desensitization, and ion permeation. However, most of the work has focused only on comparing a few isoforms, and among studies, different cellular expression systems were used.

Identification of Parvalbumin Interneurons as Cellular Substrate of Fear Memory Persistence.

Parvalbumin-positive (PV) basket cells provide perisomatic inhibition in the cortex and hippocampus and control generation of memory-related network activity patterns, such as sharp wave ripples (SPW-R). Deterioration of this class of fast-spiking interneurons has been observed in neuropsychiatric disorders and evidence from animal models suggests their involvement in the acquisition and extinction of fear memories. Here, we used mice with neuron type-targeted expression of the presynaptic gain-of-function glycine receptor RNA variant GlyR α3L(185L)to genetically enhance the network activity of PV interneurons.