Glia最新文献

Astrocytes regulate extracellular potassium (K⁺) through multiple mechanisms operating across distinct spatiotemporal scales, yet whether this regulation exhibits regional and circadian specificity remains unclear. Using real-time K⁺ measurements combined with electrophysiology and immunohistochemistry in astrocytes, we characterize K⁺ buffering by astrocytes across the dorsoventral hippocampal axis at three circadian times. We report that hippocampal CA1 stratum radiatum astrocytes possess different functional K⁺ buffering capacities depending on both anatomical location and time of day. At the early light phase (ZT3), the ventral hippocampus (VH) exhibits faster K⁺ accumulation and greater peak amplitudes than the dorsal hippocampus (DH) in response to similar neuronal network activity. This regional divergence is driven by reduced Kir4.1 channel function in VH astrocytes, which persists across all measured time points, and which is partially compensated by enhanced Na⁺/K⁺-ATPase activity specifically at ZT3. Gap junction coupling between astrocytes shows regional and time-dependent variation, with elevated coupling in VH at ZT3 that subsequently normalizes. Kir4.1 protein expression exhibits circadian dynamics. In contrast to the steady, high levels of Kir4.1 observed in the DH, the VH shows a gradual increase in expression across the light–dark cycle. These findings establish astrocytic K⁺ buffering as a multiscale phenomenon integrating regional heterogeneity with circadian regulation, with implications for understanding regional and temporal differences in network excitability, particularly in epilepsy.

Astrocytes play essential roles in brain function and disorders. Yet, compared to neurons, our knowledge of the physiological and pathological signaling mechanisms in astrocytes remains limited. As a major challenge, the ultrathin (~10–100 nm) processes of astrocytes render high-throughput quantitative molecular imaging within well-defined cellular contexts very difficult. Here, we introduce a single-molecule localization microscopy-based methodology that achieves unprecedented resolution of the intricate astrocytic arbor in intact brain circuits. Postnatal tagging of the plasma membrane by electroporation in mice resulted in selective and sparse labeling of hippocampal astrocytes and enabled the complete visualization of individual astrocytes with nanoscale precision by using STochastic Optical Reconstruction Microscopy (STORM). We also developed high-yield and easy-to-implement approaches to segment, measure, analyze, and visualize nanoscale molecular information within astrocytic compartments. As a proof-of-concept, we could readily differentiate between synaptic and astrocytic proteins by using dual-color STORM super-resolution imaging. Moreover, we identified cell-type-specific differences in the distribution of monoacylglycerol lipase (MAGL), an enzyme regulating synaptic plasticity in neurons and coupling endocannabinoid signaling to prostaglandin signaling in astrocytes. Our findings demonstrate the feasibility of nanoscale molecular measurements within ultrathin astrocytic processes. Moreover, the results provide insights into the synapse-independent nanoscale arrangement of the astrocytic MAGL pool that controls neuroinflammatory processes.

A key feature of brain development is the refinement of exuberant synapses, known as synapse pruning. This phenomenon is executed by microglia, the resident immune cells of the brain. Evidence that microglia prune retinal inputs via activation of the complement cascade in the dorsolateral geniculate nucleus (dLGN) has led to the widely held view that complement-dependent synapse pruning occurs ubiquitously in the brain. However, evidence for developmental complement-dependent pruning in regions outside of the dLGN is largely absent. Here, we tested for complement-dependent synapse pruning by microglia in the hippocampus, a central region for learning and memory. We hypothesized that complement-dependent pruning by microglia occurs at VGLUT2⁺ synapses, where complement proteins are enriched in the hippocampus. We analyzed mice genetically lacking the central complement component C3 (C3^-/-) that have broad inhibition of complement cascade activity. We found that microglia-mediated VGLUT2 engulfment was not significantly impaired in C3^-/- compared to wildtype (WT) mice in the hippocampus in both late postnatal development and early adulthood. Further, functional synapse properties were not significantly altered in C3^-/- compared to WT mice. Finally, we tested whether a complement-dependent pruning mechanism could be induced in the hippocampus via peripheral inflammation. Lipopolysaccharide (LPS) injections induced a neuroinflammatory phenotype associated with loss of VGLUT2⁺ synapses. However, in an LPS-induced neuroinflammatory state, VGLUT2⁺ synapse pruning by microglia was not affected in C3^-/- mice. These findings uncover that C3 is not ubiquitously required for synapse engulfment in physiological and neuroinflammatory conditions in the hippocampus.

Understanding how high-risk individuals are protected from Alzheimer's disease (AD) may illuminate potential therapeutic targets. We identified protective genetic variants in SH3RF3/POSH2 that delayed the onset of AD among individuals carrying the PSEN1^G206A mutation. SH3RF3 acts as a JNK pathway scaffold and activates NFκB signaling. While the effects of SH3RF3 knockdown in human neurons were subtle, including decreased pTau S422, knockdown in human microglia significantly reduced inflammatory cytokines in response to either a viral mimic or oAβ42. This was associated with reduced activation of JNK and NFκB pathways in response to these stimuli. Pharmacological inhibition of JNK or NFκB signaling phenocopied SH3RF3 knockdown. We also found PSEN1^G206A microglia had a reduced inflammatory response to oAβ42. Thus, further reduction of microglial inflammatory responses in PSEN1^G206A mutant carriers by protective variants in SH3RF3 might reduce the link between amyloid and neuroinflammation to subsequently delay the onset of AD.

Microglia are dynamic cells that respond both transcriptionally and morphologically to acute brain injury as well as to chronic neurodegenerative conditions. Upon activation, they become less ramified, more rounded, and accumulate intracellular lipid droplets. In this hypothesis paper, we propose that the formation of these lipid droplets supports the redistribution of plasma membrane lipids required during morphological remodeling. We rely on original and published studies of microglial morphology under conditions of aging, acute activation, and chronic activation. In ex vivo brain slices, microglia responded to either ATP or acute Aβ injections within minutes by extending their proximal processes toward the stimulus while simultaneously retracting their distal processes into their cell bodies. Chronic exposure to Aβ in mouse models of amyloid reduced microglial branching alongside a two- to three-fold loss of surface area. Transcriptomic analyses showed that activated microglia upregulate genes involved in fatty acid synthesis and fatty acid activation, both processes that are necessary in the production of triacylglycerol. Integrating these new and published analyses of microglia, we developed a hypothesis in which plasma membrane phospholipids are redistributed during acute activation and, during chronic activation, they are metabolized to triacylglycerol into lipid droplets. Tests of this hypothesis, through various pharmacological and genetic approaches, would contribute to our understanding of lipid droplets in cells that undergo substantial morphological changes.

HIV-associated neurocognitive disorders (HAND) remain prevalent in people with HIV (PWH) despite effective antiretroviral therapy, suggesting that persistent immune activation contributes to ongoing neurological dysfunction. Maladaptive trained immunity (TRIM), long-term innate immune reprogramming characterized by sustained inflammatory responses, metabolic rewiring, and epigenetic remodeling, has been proposed as a sustaining mechanism. We performed single-nucleus RNA-seq and ATAC-seq on post-mortem brain from PWH with HIV-associated dementia (HAD) or asymptomatic neurocognitive impairment (ANI) and compared these data with published HIV-uninfected (PWoH) datasets. In PWH versus PWoH, glia, led by microglia, showed enrichment of innate immune signaling and upregulation of inflammatory mediators including NLRP3, TLR2, and TLR4. In parallel, glia showed coordinated cholesterol remodeling, with efflux transporter and apolipoprotein upregulation alongside LDLR downregulation, and partial microglial glycolytic reprogramming (PFKFB3, HK2, PGK1 upregulation). Chromatin accessibility profiling showed concordant gains at inflammatory, cholesterol regulatory (notably RXRA and APOE), and glycolytic loci. The HAD versus ANI comparison revealed selective reorganization rather than uniform amplification, with increased lipid scavenger receptor accessibility in oligodendrocytes and reduced accessibility at cholesterol efflux and glycolytic loci. Neurons exhibited predominantly bystander epigenetic changes. Three features distinguish this pattern from chronic inflammation alone and align it with trained immunity hallmarks: concordant transcriptional and chromatin-level priming at inflammatory loci, parallel rewiring of glycolytic and cholesterol metabolism, and persistence despite long-term viral suppression. These multiomic data are consistent with maladaptive trained immunity sustaining neuroinflammation in HAND, though functional validation is required.

The Alzheimer's disease protective P522R PLCG2 coding variant (rs72824905) is downstream of TREM2, but how it confers disease protection is poorly understood. Using a Plcg2-R522 knock-in mouse and Plcg2-P522 control on both wildtype and Alzheimer's disease-like App^NL-G-F amyloidosis mouse backgrounds, aged mice were assayed for amyloid load, microglial activity, and synaptic integrity. In the absence of Alzheimer's disease-like pathology, the R522 variant increased microglial coverage and was associated with reduced ramification complexity, fewer terminal points, and elevated lysosomal CD68 expression. On the App^NL-G-F background, total amyloid burden was unaffected, but expression of the R522 variant led to increased plaque compaction compared to the P522 common variant. The protective R522 variant was also associated with: enhanced microglial engagement with less compact amyloid plaques; reduced microglial localisation around highly compacted plaques; protection from amyloid-induced synapse loss; and decreased engulfment of synaptic material by microglia. Our data indicate a significant direct PLCγ2 role in controlling microglial-plaque interactions and synaptic protection downstream of amyloid deposition, prioritizing it as a therapeutic target, potentially as an adjunct to other approaches, such as those targeting amyloid.