Glia最新文献

Microglia, the resident immune cells of the central nervous system (CNS), are in constant survey of their environment. Extracellular nucleotides, released by stressed and damaged neurons, act as danger signals to microglia through various purinergic/pyrimidinergic receptors. In the CNS, the UDP receptor P2Y6 is mostly expressed in microglia, where its activation induces phagocytosis, a homeostatic function that is dysregulated in several neurodegenerative diseases and in chronic pain. Yet, modulatory mechanisms impacting P2Y6 activity remain to be identified. The microglial β2 adrenergic receptor (ADRB2) for norepinephrine represents a promising candidate for modulation of P2Y6 receptors. Our calcium imaging data indicate that exposure to the ADRB2 agonist isoproterenol inhibits the calcium transients evoked by activation of Gq-coupled P2Y6 receptors in primary mouse microglia. This functional modulation, suppressed by the selective ADRB2 antagonist ICI-118551, is conserved in human iPSC-derived microglia. Accordingly, we observed that the phagocytotic activity induced by P2Y6 is reduced by ADRB2 signaling in both mouse and human microglia. Finally, we report that ADRB2 activation is linked to a decrease in P2Y6 mRNA expression. These findings provide evidence that metabotropic and transcriptional crosstalks between nucleotide and adrenergic transductions control microglial responses in the CNS, potentially contributing to the pathophysiology of neuro-immune disorders and chronic pain conditions.

A disproportionate percentage of adolescents are diagnosed with human immunodeficiency virus (HIV) in the United States each year. Preexposure prophylaxis (PrEP), an antiretroviral regimen, is effective at preventing the transmission of HIV to adolescents at substantial risk for acquiring HIV. However, other select antiretrovirals have been shown to cause white matter deficits in experimental models. Adolescents taking PrEP are uniquely vulnerable to myelin impairments as the adolescent brain undergoes high rates of myelination. Here, we report that PrEP significantly reduced oligodendrocyte maturation in adolescent rats. Furthermore, cultures of primary rat oligodendrocyte progenitors treated with PrEP showed inhibited oligodendrocyte differentiation through deacidification of lysosomes resulting in lysosomal accumulation of myelin proteins. Acidic nanoparticle co-administration with PrEP prevented PrEP-induced oligodendrocyte maturation impairments both in vivo and in vitro. These studies suggest uninfected adolescents are vulnerable to PrEP-induced oligodendrocyte impairments and identify maintenance of lysosome pH as a critical factor in antiretroviral design.

Status epilepticus (SE) is a severe condition that results in uncontrollable cerebral edema and cognitive dysfunction. Recent studies suggest that the localization of aquaporin-4 (AQP4) in astrocytic endfeet plays a crucial role in regulating blood-brain water transport and cell volume control, particularly along perivascular pathways. However, the signaling mechanisms underlying AQP4 localization remain poorly understood. In this study, we utilized the genetically encoded fluorescent calcium (Ca²⁺) indicator GCaMp6f to investigate Ca²⁺ signals in astrocytic somata, processes, and endfeet during SE induction and observed enhanced Ca²⁺ signals in both the somata and perivascular endfeet of astrocytes. We employed genetic knockout of TRPM4 (Trpm4 ^-/- ) and glibenclamide treatment to explore the role of sulfonylurea receptor 1 transient receptor potential melastatin-4 (SUR1-TRPM4) channel in these Ca²⁺ responses. Both approaches significantly suppressed the Ca²⁺ signals in the astrocytic endfeet and reduced perivascular expression of the Ca²⁺-related signaling pathway sensor calmodulin (CaM). Furthermore, we found that AQP4 localization was no longer confined to the domains of astrocytic endfeet following SE. Inhibition of SUR1-TRPM4 through pharmacological blockade or gene deletion restored the subcellular localization of AQP4, reduced cerebral edema, and improved cognitive outcomes post-SE. Our findings suggest that SUR1-TRPM4 plays a pivotal role in regulating astrocytic Ca²⁺ signals and mediating the aberrant expression and subcellular localization of astrocytic AQP4 along perivascular pathways. Together, these findings demonstrate a novel molecular mechanism underscoring SUR1-TRPM4 therapy in the treatment of SE characterized by dysregulated Ca²⁺ signaling in astrocytic endfeet.

Astrocytes swell in response to elevations in extracellular K⁺ concentration. This K⁺-induced swelling is widely believed to be due to astrocytic K⁺ uptake, even if the underlying mechanisms are not fully understood. Conflicting results pertaining to the role of the brain water channel AQP4 in K⁺-induced swelling have been presented. This calls for revisiting the effect of AQP4 on K⁺-induced astrocytic swelling dynamics. In this study, we performed two-photon microscopy of acute hippocampal slices from wildtype (WT) and Aqp4 ^−/− mice to assess astrocytic swelling in response to medium high 10 mM and pathologically high 50 mM [K⁺] solutions. We demonstrate that K⁺-induced swelling is attenuated in Aqp4 ^−/− astrocytes exposed to 10 mM [K⁺]_o compared to WT. In slices exposed to 50 mM [K⁺]_o, peak swelling was similar between the two genotypes, whereas the cell volume recovery was more complete in Aqp4 ^−/− astrocytes. We demonstrate that the two [K⁺] concentrations elicit fundamentally different astrocytic Ca²⁺ signaling responses, and that the Ca²⁺ signaling response differs between the genotypes in the 10 mM [K⁺]_o scenario. Our findings suggest that K⁺-induced astrocytic swelling has different mechanistic underpinnings, depending on the K⁺ concentration to which the astrocytes are exposed, and that altered astrocytic Ca²⁺ signaling is a putative mechanism involved.

Neuroinflammation, particularly astrocyte reactivity, is increasingly linked to schizophrenia (SCZ). Yet, the crosstalk between astrocytes and microglia in SCZ, especially under pro-inflammatory conditions, remains unclear. Here, we employed human induced-pluripotent stem cells to compare how astrocytes from five age-matched individuals with SCZ and five neurotypical controls, upon stimulation with TNF-α, affected microglial biology. TNF-α stimulation of SCZ astrocytes, relative to their control counterparts, triggered increased mRNA expression of pro-inflammatory cytokines and CX3CL1. Interestingly, transcriptomic and gene set enrichment analyses revealed that reactive SCZ astrocytes promoted the downregulation of biological processes associated with immune cell proliferation and activation, phagocytosis, and cell migration in induced microglial-like cells (iMGs). Under such conditions, iMGs assumed a dystrophic/senescent-like phenotype, which was associated with accelerated transcriptional aging. Functional validations showed that TNF-α-stimulated SCZ astrocytes promoted reduced synaptoneurosomes phagocytosis by iMGs. Interestingly, while both reactive control and SCZ astrocytes were capable of inducing significant microglial migration in a CX3CR1-dependent manner, TNF-α-stimulated SCZ astrocytes failed to promote greater iMG chemotaxis, compared with their stimulated control counterparts, despite secreting more than twice as much CX3CL1. This was likely due to SCZ astrocytes triggering reduction in CX3CR1 plasma membrane levels in iMGs. Altogether, these findings suggest that astrocytes contribute to SCZ pathology by altering normal microglial function and inducing a dystrophic phenotype.

Cover Illustration: Oligodendrocyte binds to laminin on the perivascular basement membrane in the murine cortex at the age of postnatal day 16 (red: CC-1; green: laminin alpha-2; blue: DAPI). (See Sasaki, B., et al, https://doi.org/10.1002/glia.70027)

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder involving multiple cell types in the central nervous system. The key pathological features of ALS include the degeneration of motor neurons and the initiation and propagation of neuroinflammation mediated by nonneuronal cell types such as microglia. Currently, the specific mechanisms underlying the involvement of microglia in neuroinflammation in ALS are unclear. Consequently, we generated several human-induced pluripotent stem cell (iPSC) derived motor neuron and microglia cocultures. We utilized ALS patient-derived iPSCs carrying a common genetic variant, the hexanucleotide repeat expansion (HRE) in C9ORF72, as well as C9ORF72 knockout (KO) iPSC lines. iPSC-derived motor neurons and microglia demonstrated expression of cell type-specific markers and were functional. Phenotypic assessments on motor neurons and microglia in mono- and cocultures identified dysfunction in the expression and secretion of inflammatory cytokines and chemokines in lipopolysaccharide (LPS)-stimulated C9ORF72 HRE and C9ORF72 KO microglia. Analysis of single-cell RNA sequencing data from microglia and motor neuron cocultures revealed cell type-specific transcriptomic changes. Specifically, we detected the removal of an LPS-responsive microglia subpopulation, correlating with a dampened inflammatory response in C9ORF72 HRE and C9ORF72 KO microglia. Overall, our results support the critical role of microglia-mediated neuroinflammation in ALS pathology, and our iPSC-derived models should prove a valuable platform for further mechanistic studies of ALS-associated pathways.

THY1 is a cell surface protein of mature neurons. Although the Thy1 promoter is widely used as a neuron-specific promoter for transgenic expression, the role of the endogenous THY1 protein in the brain remains largely unknown. As THY1 receptors are expressed on astrocytes, THY1 may mediate signaling between both cell types. We therefore investigated the role of THY1 signaling in neuron-astrocyte communication using a full as well as a neuron-specific Thy1-knockout mouse model. Compared to wild-type mice, aged individuals of both strains exhibited an increased expression of a subset of astrocyte activation-associated genes, such as glial fibrillary acidic protein (Gfap), vimentin (Vim), and tenascin C (Tnc), whereas others appeared unaffected. Importantly, a cortical injury caused a permanent astrocytic activation in mice with neuronal Thy1 deletion, reflected by persistent high GFAP expression. The THY1-associated modulation of gene expression was confirmed in primary astrocytes cultured with or without recombinant THY1. Moreover, functional assays indicate that THY1 inhibits astrocyte proliferation while promoting apoptosis. Interaction of neuronal THY1 with ITGB1 on astrocytes was identified to be responsible for the THY1-mediated control of astrocyte activation. These data strongly suggest that THY1-bearing neurons keep astrocytes in a quiescent state. Consequently, a depletion of THY1 supports the development of a partially activated astrocyte phenotype characterized by increased expression of intermediate filaments, increased proliferative capacity, and reduced cell death. Our findings demonstrate that neuronal THY1 is a still unrecognized novel regulator in the communication between astrocytes and neurons involved in the maintenance and restoration of tissue homeostasis in the brain.