Glia最新文献

Microglial cells are the phagocytic cells of the brain that under physiological conditions participate in brain homeostasis and surveillance. Under pathogenic states, microglia undergoes strong morphological and transcriptional changes potentially leading to sustained neuroinflammation, brain damage, and cognitive disorders. Postnatal and adult Zika virus (ZIKV) brain infection is characterized by the induction of reactive microglia associated with brain inflammation, synapse loss and neuropathogenesis. Contrary to neurons, microglial cells are not infected by ZIKV thus raising the question of the mechanism governing ZIKV-induced microglia's reactivity. In this work, we have questioned the role of exogenous, neuronal type I interferons (IFNs-I) in regulating ZIKV-induced microglia's reactivity. Primary cultured microglial cells were either treated with conditioned media from ZIKV-infected mature neurons or co-cultured with ZIKV-infected neurons. Using either an antibody directed against the IFNAR receptor that neutralizes the IFNs-I response or Ifnar−/−microglial cells, we demonstrate that IFNs-I produced by ZIKV-infected neurons are the main regulators of the phagocytic capacity and the pro-inflammatory gene expression profile of reactive, non-infected microglial cells. We identify protein kinase R (PKR), whose expression is activated by IFNs-I, as a major regulator of the phagocytic capacity, pro-inflammatory response, and morphological changes of microglia induced by IFNs-I while up-regulating STAT1 phosphorylation and IRF1 expression. Results obtained herein in vitro with primary cultured cells and in vivo in ZIKV-infected adult immunocompetent mice, unravel a role for IFNs-I and PKR in directly regulating microglia's reactivity that could be at work in other infectious and non-infectious brain pathologies.

The molecules that constitute myelin are critical for the integrity of axon/myelin-units and thus speed and precision of impulse propagation. In the CNS, the protein composition of oligodendrocyte-derived myelin has evolutionarily diverged and differs from that in the PNS. Here, we hypothesized that the CNS myelin proteome also displays variations within the same species. We thus used quantitative mass spectrometry to compare myelin purified from mouse brains at three developmental timepoints, from brains of male and female mice, and from four CNS regions. We find that most structural myelin proteins are of approximately similar abundance across all tested conditions. However, the abundance of multiple other proteins differs markedly over time, implying that the myelin proteome matures between P18 and P75 and then remains relatively constant until at least 6 months of age. Myelin maturation involves a decrease of cytoskeleton-associated proteins involved in sheath growth and wrapping, along with an increase of all subunits of the septin filament that stabilizes mature myelin, and of multiple other proteins which potentially exert protective functions. Among the latter, quinoid dihydropteridine reductase (QDPR) emerges as a highly specific marker for mature oligodendrocytes and myelin. Conversely, female and male mice display essentially similar myelin proteomes. Across the four CNS regions analyzed, we note that spinal cord myelin exhibits a comparatively high abundance of HCN2-channels, required for particularly long sheaths. These findings show that CNS myelination involves developmental maturation of myelin protein composition, and regional differences, but absence of evidence for sexual dimorphism.

Formation of myelin by Schwann cells is tightly coupled to peripheral nervous system development and is important for neuronal function and long-term maintenance. Perturbation of myelin causes a number of specific disorders that are among the most prevalent diseases affecting the nervous system. Schwann cells synthesize myelin lipids de novo rather than relying on uptake of circulating lipids, yet one unresolved matter is how acetyl CoA, a central metabolite in lipid formation is generated during myelin formation and maintenance. Recent studies have shown that glucose-derived acetyl CoA itself is not required for myelination. However, the importance of mitochondrially-derived acetyl CoA has never been tested for myelination in vivo. Therefore, we have developed a Schwann cell-specific knockout of the ATP citrate lyase (Acly) gene to determine the importance of mitochondrial metabolism to supply acetyl CoA in nerve development. Intriguingly, the ACLY pathway is important for myelin maintenance rather than myelin formation. In addition, ACLY is required to maintain expression of a myelin-associated gene program and to inhibit activation of the latent Schwann cell injury program.

Substantial advances in technology are permitting a high resolution understanding of the salience of glia, and have helped us to transcend decades of predominantly neuron-centric research. In particular, recent advances in ‘omic’ technologies have enabled unique insights into glial biology, shedding light on the cellular and molecular aspects of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Here, we review studies using omic techniques to attempt to understand the role of glia in ALS across different model systems and post mortem tissue. We also address caveats that should be considered when interpreting such studies, and how some of these may be mitigated through either using a multi-omic approach and/or careful low throughput, high fidelity orthogonal validation with particular emphasis on functional validation. Finally, we consider emerging technologies and their potential relevance in deepening our understanding of glia in ALS.

Alexander disease (AxD) is a rare and severe neurodegenerative disorder caused by mutations in glial fibrillary acidic protein (GFAP). While the exact disease mechanism remains unknown, previous studies suggest that mutant GFAP influences many cellular processes, including cytoskeleton stability, mechanosensing, metabolism, and proteasome function. While most studies have primarily focused on GFAP-expressing astrocytes, GFAP is also expressed by radial glia and neural progenitor cells, prompting questions about the impact of GFAP mutations on central nervous system (CNS) development. In this study, we observed impaired differentiation of astrocytes and neurons in co-cultures of astrocytes and neurons, as well as in neural organoids, both generated from AxD patient-derived induced pluripotent stem (iPS) cells with a GFAP^R239C mutation. Leveraging single-cell RNA sequencing (scRNA-seq), we identified distinct cell populations and transcriptomic differences between the mutant GFAP cultures and a corrected isogenic control. These findings were supported by results obtained with immunocytochemistry and proteomics. In co-cultures, the GFAP^R239C mutation resulted in an increased abundance of immature cells, while in unguided neural organoids and cortical organoids, we observed altered lineage commitment and reduced abundance of astrocytes. Gene expression analysis revealed increased stress susceptibility, cytoskeletal abnormalities, and altered extracellular matrix and cell–cell communication patterns in the AxD cultures, which also exhibited higher cell death after stress. Overall, our results point to altered cell differentiation in AxD patient-derived iPS-cell models, opening new avenues for AxD research.

Astrocytes are a highly abundant cell type in the brain and spinal cord. Like neurons, astrocytes can be molecularly and functionally distinct to fulfill specialized roles. Recent technical advances in sequencing-based single cell assays have driven an explosion of omics data characterizing astrocytes in the healthy, aged, injured, and diseased central nervous system. In this review, we will discuss recent studies which have furthered our understanding of astrocyte biology and heterogeneity, as well as discuss the limitations and challenges of sequencing-based single cell and spatial genomics methods and their potential future utility.

Neurotoxic A1 reactive astrocytes are induced by inflammatory stimuli. Leptin has been confirmed to have neuroprotective properties. However, its effect on the activation of A1 astrocytes in infectious inflammation is unclear. In the current study, astrocytes cultured from postnatal day 1 Sprague–Dawley rats were stimulated with lipopolysaccharide (LPS) to induce an acute in vitro inflammatory response. Leptin was applied 6 h later to observe its protective effects. The viability of the astrocytes was assessed. A1 astrocyte activation was determined by analyzing the gene expression of C3, H2-D1, H2-T23, and Serping 1 and secretion of pro-inflammatory cytokines IL-6 and TNF-α. The levels of phospho-p38 (pp38) and nuclear factor-κB (NF-κB) phosphor-p65 (pp65) were measured to explore the possible signaling pathways. Additionally, an LPS-induced inflammatory animal model was established to investigate the in vivo effects of leptin on A1 astrocytic activation. Results showed that in the in vitro culture system, LPS stimulation caused elevated expression of A1 astrocyte-specific genes and the secretion of pro-inflammatory cytokines, indicating the activation of A1 astrocytes. Leptin treatment significantly reversed the LPS induced upregulation in a dose-dependent manner. Similarly, LPS upregulated pp38, NF-κB pp65 protein and inflammatory cytokines were successfully reduced by leptin. In the LPS-induced animal model, the amelioratory effect of leptin on A1 astrocyte activation and inflammation was further confirmed, showed by the reduced sickness behaviors, A1 astrocyte genesis and inflammatory cytokines in vivo. Our results demonstrate that leptin efficiently inhibits LPS-induced neurotoxic activation of A1 astrocytes and neuroinflammation by suppressing p38-MAPK signaling pathway.

Microglia, the resident immune cells in the brain, dynamically adapt their morphology based on their functional state. This study explored the relationship between microglial morphology and sleep–wake cycles in mice. Using Iba1 immunostaining to identify microglia, we quantified morphological changes in microglia at different timepoints in multiple brain regions (cortex, hippocampus, basal forebrain, hindbrain, and cerebellum) in B6 male mice using semi-automated 3D structural analysis. Simultaneously, in a separate group, we monitored wake and sleep stage-specific brain activity using EEG/EMG recordings. During natural sleep–wake cycles, we observed increased microglial complexity (enlarged volume, territorial coverage, and ramification) during wakefulness, characterized by high-frequency theta (8–12 Hz) and gamma activity (30–80 Hz). Conversely, during NREM sleep, which is dominated by delta activity (0.5–4 Hz), microglia displayed reduced complexity. Notably, this pattern was absent in brain regions lacking direct functional connections to areas generating vigilance stage-dependent thalamocortical oscillations. We then extended wakefulness to decouple circadian influence from sleep–wake-specific neuronal activity. This procedure attenuated the decrease in microglial complexity observed during natural sleep, suggesting a crucial role for neuronal activity. Subsequent recovery sleep restored microglial features, independent of the time of day (zeitgeber time). These findings reveal a dynamic interplay between vigilance stage-specific thalamocortical activity and microglial morphology across various brain regions. This suggests a potential role for microglia in sleep regulation and warrants further investigation to understand the underlying mechanisms.

Cover Illustration: Representative images of immunofluorescent staining for glial fibrillary acidic protein (GFAP) (green), Iba-1(red) and DAPI (blue) in cultured primary astrocytes from TREM2-GFAP-knockout mice. Over 95% of the cultured cells were identified as astrocytes and no Iba-1 positive cells (microglia) were observed in the cultures. (See Li, L., et al, https://doi.org/10.1002/glia.24597)

Sialylation plays an important role in self-recognition, as well as keeping the complement and innate immune systems in check. It is unclear whether the reduced sialylation seen during aging and in mice heterozygous for the null mutant of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (Gne+/−), an essential enzyme for sialic acid biosynthesis, contributes to retinal inflammation and degeneration. We found a reduction of polysialic acid and trisialic acid expression in several retinal layers in Gne+/− mice at 9 months of age compared to Gne+/+ wildtype (WT) mice, which was associated with a higher microglial expression of the lysosomal marker CD68. Furthermore, the total number of rod bipolar cells was reduced in 12 months old Gne+/− mice in comparison to WT mice, demonstrating loss of these retinal interneurons. Transcriptome analysis showed up-regulation of complement, inflammation, and apoptosis-related pathways in the retinas of Gne+/− mice. Particularly, increased gene transcript levels of the complement factors C3 and C4 and the pro-inflammatory cytokine Il-1β were observed by semi-quantitative real-time polymerase chain reaction (sqRT-PCR) in 9 months old Gne+/− mice compared to WT mice. The increased expression of CD68, loss of rod bipolar cells, and increased gene transcription of complement factor C4, were all prevented after crossing Gne+/− mice with complement factor C3-deficient animals. In conclusion, our data show that retinal hyposialylation in 9 and 12 months old Gne+/− mice was associated with complement-related inflammation and lysosomal microglia response, as well as rod bipolar cells loss, which was absent after genetic deletion of complement factor C3.