Schwann cells (SCs) myelinate and provide trophic support to axons in the peripheral nervous system (PNS). Disrupted SC metabolism can lead to demyelination and axon degeneration, cardinal deficits in peripheral neuropathy. The lactate shuttle hypothesis proposes that glycolytic support cells supply lactate to axons to sustain their high metabolic demands. This transfer requires lactate dehydrogenase (LDH) to interconvert lactate and pyruvate in both SCs and neurons. To test the importance of lactate metabolism in the PNS, we selectively knocked out both LDHA and LDHB in ChAT-positive neurons, including motor neurons (MNs), Nav1.8-lineage sensory neurons (SNs), or SCs. Interestingly, motor axons and their synapses progressively degenerate when LDH is deleted from either MNs or SCs, but defects in Nav1.8-lineage sensory axons and their terminals are not observed when LDH is excised from either SNs or SCs. Deletion of LDH in SCs leads to decreased ATP in peripheral nerves despite marked accumulation of pyruvate and glycolytic intermediates, consistent with energetic deficits due to failed conversion of pyruvate to lactate. Cholinergic neuron-specific gene expression using ribosome affinity profiling (RiboTag) identified a strong response to metabolic compromise by activating axon-injury stress programs in LDH-deficient neurons. Finally, blocking axon degeneration in LDH-deficient mice by SARM1 deletion preserves axon morphology without ameliorating behavioral and electrophysiological defects, demonstrating functional decline of lactate-deprived axons that remain physically intact. These results show a differential requirement for SC-derived lactate by motor vs. sensory axons, suggesting that lactate availability could influence the course of motor neuron diseases.

Neuronal loss in multiple sclerosis (MS) is a key factor in the progression of disability. Axonal degeneration within MS lesions is central to progressive MS pathology, yet its mechanisms are not fully understood. Excess extracellular l-glutamate (GLUT) is neurotoxic due to overstimulation of GLUT receptors. Excitotoxicity, driven by GLUT, is a suspected contributor to several central nervous system (CNS) diseases. Astrocytic glutamate transporters EAAT-1 and EAAT-2 play crucial roles in managing extracellular GLUT, yet their role in chronic MS remains underexplored. Using the animal model experimental autoimmune encephalomyelitis (EAE) and advanced microscopy in live anesthetized mice, we examined GLUT-mediated neurotoxicity and protective mechanisms in chronic CNS lesions. By employing genetically encoded fluorescent biosensors, we visualized extracellular GLUT levels and axonal Ca2+ dynamics within the live mouse brain during EAE. In acute EAE, extracellular GLUT levels were high, while in chronic lesions, normalized GLUT levels together with sustained EAAT-2 upregulation were consistent with a protective astrocytic response. EAAT-2 inhibition in chronic lesions led to higher intra-axonal Ca2+ levels and morphological changes consistent with neuroaxonal injury, indicating that EAAT-2 upregulation may counter excitotoxicity and support neuroprotection. Post-mortem MS brain tissue analysis provided complementary evidence, showing elevated EAAT-1 and EAAT-2 expression in chronic MS lesions with expression patterns varying according to lesion type and cellularity. This study highlights astrocytic mechanisms that may contribute to neuroaxonal protection in MS tissue and suggests targeting GLUT transporters as a promising strategy to limit neurodegeneration in progressive MS.

Homeostasis of the vertebrate retina critically depends on two non-neuronal cell populations, Müller glia and the retinal pigment epithelium (RPE). Their opposing apical surfaces delineate the subretinal space, a specialized extracellular compartment housing the light-detecting outer segments of photoreceptors. Although the individual interactions between these supporting cells and photoreceptors have been extensively characterized, Müller glia and the RPE have long been presumed to remain physically separate in the healthy retina. Here, we challenge this assumption and present a revised model of the subretinal space architecture based on detailed FIB-SEM and confocal microscopy imaging of the zebrafish and mouse outer retina. We demonstrate that both Müller glia and the RPE extend long apical processes that not only contact one another but also collectively ensheath cone outer segments, forming a previously unrecognized tripartite interface. These contact regions are highly elaborated in fish and, while comparatively sparser, are still present in mouse. Developmentally, the growth and interdigitation of Müller glial and RPE apical processes follow the emergence of the outer segment in both species and, in mouse, coincides with the onset of visual function. Although glial-RPE interactions are enriched at cone-associated sites, their presence is not strictly dependent on cone localization in either species, suggesting they represent a fundamental feature of the vertebrate subretinal space. Together, these findings revise our understanding of the subretinal space cytoarchitecture and reveal a previously unappreciated structural interaction between Müller glia, RPE, and photoreceptors that is conserved across vertebrate species.

The etiological heterogeneity of autism spectrum disorder (ASD) complicates identifying core molecular mechanisms. We systematically integrated scRNA-seq data from 11 diverse genetic and environmental mouse (Mus musculus) models, encompassing > 300,000 cells across multiple brain regions and developmental stages. Using advanced computational harmonization (RPCA), we identified robust convergent transcriptomic signatures that transcend model-specific variability. Our findings reveal widespread alterations in neuronal communication pathways, specifically increased excitatory-inhibitory signaling involving PTN, SLIT, and PTPR pathways. Furthermore, cell-cell communication analysis via NicheNet prioritized ligand-receptor pairs associated with altered circuit excitability, offering a predictive blueprint of dysregulated intercellular crosstalk. Crucially, we identified significant glial involvement characterized by astrocyte function inhibition, marked by Aqp4 and Kcnj10 downregulation related to impaired water/potassium homeostasis and mature oligodendrocyte metabolic dysregulation through Olig family upregulation and enhanced oxidative phosphorylation. Differentially expressed genes (DEGs) significantly overlapped with SFARI-listed high-confidence risk genes, particularly within excitatory neuronal subtypes. Comparison with human postmortem single-nucleus data from the prefrontal and parietal cortices demonstrated conserved signatures related to impaired synaptic protein synthesis (GRIN2B, CAMK2A) and oligodendrocyte-mediated neurodevelopmental deficits (NRXN, DLGAP). This study confirms that E/I imbalance and glial dysfunction are universal cellular pathologies in ASD, providing a robust, large-scale reference for identifying novel therapeutic targets with single-cell resolution.

The mechanisms by which pathogenic T cells enter the immune-privileged retina at the onset of uveitis remain unclear. To identify regulatory targets that promote retinal inflammation, we established an experimental autoimmune uveoretinitis (EAU) model by immunizing C57BL/6J mice with IRBP651-670 and dynamically evaluated retinal inflammation after induction; fundus lesions were prominent, with the first 14 days representing the initiation phase, Days 14-28 the amplification phase, Days 28-35 the peak phase, and Days 35-42 the regression phase. We characterized retinal cellular alterations from the pre-inflammatory stage to the peak stage using single-cell transcriptomic analysis, and found that retinal immune cells changed in parallel with EAU severity, while immune-cell interactions were strongest on Day 14, especially between microglia and T cells through multiple chemokine-related pathways. We then identified key cell populations and candidate targets through integrated analyses and functional validation, and Ifi27l2a emerged as a core gene associated with inflammatory and immune responses in retinal microglia on Day 14. In vitro knockdown of Ifi27l2a in LPS-activated BV-2 cells reduced inflammatory mediator production and abolished Th1/Th17 induction. In vivo targeting of Ifi27l2a attenuated EAU severity and restored the balance of T-cell subsets. These findings indicate that microglia are highly activated before retinal inflammation becomes prominent and that Ifi27l2a regulates this early pathogenic process.

Adult hippocampal neurogenesis (AHN)-the lifelong generation of new neurons in the dentate gyrus (DG)-depends on the integrity of the subgranular zone (SGZ) neurogenic niche, which comprises astrocytes, microglia, oligodendroglial cells, and a dense vascular network. Although AHN declines during aging and is impaired in Alzheimer's disease (AD), the cell-type-specific alterations within the DG underlying this decline remain poorly characterized. Given the critical role of glycogen synthase kinase-3β (GSK-3β) in AD pathogenesis and AHN regulation, we studied how the overexpression of this kinase in dentate granule cells (DGCs) remodels the cellular and vascular composition of the DG throughout life. Using a layer-resolved approach (SGZ vs. granule cell layer (GCL)) and mice of distinct ages (4-30 months), we quantified glial densities, cellular contacts, vascular architecture, and cytokine profiles in wild-type (WT) and GSK-3β-overexpressing (GSK-3β-OE) mice. In the former, aging was associated with a layer-specific reorganization, characterized by progressive astrocyte loss in the SGZ, midlife increases in GCL microglia, a reduction in oligodendroglial progenitors, and enhanced SGZ vascularization. GSK-3β overexpression accelerated age-related changes, triggering premature SGZ astrocyte depletion by 4 months, broader disruption featuring reduced SGZ microglial and mature oligodendrocyte densities accompanied by increased microglial morphological complexity, vascular restructuring, and a shift toward a pro-inflammatory environment. Therefore, neuronal GSK-3β overexpression promoted a non-cell-autonomous reorganization of the DG, consistent with premature remodeling of the neurogenic niche. These results provide mechanistic insights into AHN failure in AD and point to the modulation of GSK-3β activity as a strategy to preserve DG integrity.

Traumatic spinal cord injury (SCI) is a complex and disabling condition with no curative therapy currently available. The mechanical damage of the primary injury phase is followed and exacerbated by a secondary injury phase, characterized by the release of free radicals and pro-inflammatory cytokines that lead to chronic inflammation. Microglia, as the resident immune cells of the central nervous system, play a critical role in orchestrating this inflammatory response. Studying their dynamics after SCI not only deepens our understanding of injury pathology but also advances the development of microglia-targeted immunotherapies. However, trauma-induced transcriptional and phenotypic changes mean that markers used to identify homeostatic microglia may be unreliable when applied to their reactive counterparts. Another major challenge lies within discriminating resident microglia from infiltrating monocyte-derived macrophages (MDM), which permeate the blood-spinal cord barrier (BSCB) after injury. In this review, we examine three key variables for selecting appropriate strategies for labeling microglia in mice: (i) time (in relation to injury); (ii) efficacy (within the chosen murine SCI model); and (iii) specificity (to microglia). We discuss the transcriptional landscape of murine microglia pre-injury and its alteration post-injury, evaluate the strengths and limitations of commonly used markers, and highlight emerging tools and approaches for studying microglia in preclinical murine SCI research.

Microglial "Off" signaling is crucial for maintaining microglia in a homeostatic state through the interaction of "Off" neuronal ligands with their corresponding microglial receptors. Dysregulation of "Off" signaling has been reported in both acute and chronic neuroinflammation; however, the influence of inflammatory mediators on this pathway remains underexplored. Here, we investigated whether chronic IL-6 or IL-10 overexpression modulates microglia-neuron "Off" signaling after FNA, thereby accounting for the previously observed differences in facial motoneuron (FMN) survival and microglial reactivity in transgenic mouse models (GFAP-IL6Tg and GFAP-IL10Tg). To this end, we examined the expression of the neuronal "Off" ligands CD200, CX3CL1, CD47, and CD22, as well as their corresponding microglial "Off" receptors CD200R, CX3CR1, SIRP-α, and CD45 in non-lesioned and axotomized GFAP-IL6Tg, GFAP-IL10Tg, and WT mice across multiple time points. Our analyses revealed the dynamic regulation of "Off" signaling in both neurons and microglia during microgliosis and FMN phagocytosis and showed temporally restricted strain-specific differences in CD47 expression across genotypes. Chronic IL-6 overproduction promoted a more phagocytic microglial phenotype, defined by downregulation of SIRPα and CX3CR1 alongside upregulated CD45 in the microglial population. In contrast, chronic IL-10 overproduction did not alter the expression of microglial "Off" receptors but induced an IL-10 dependent accelerated upregulation of neuronal CD47. Our findings highlight the CD47-SIRPα axis as a key regulator of FMN death via microglial phagocytosis and emphasize IL-10's neuroprotective potential role through enhanced neuronal CD47 signaling. Overall, this work positions the CD47-SIRPα axis as a potential therapeutic target to mitigate neuroinflammation-induced neuronal loss.

Myelin is a highly complex membranous structure wrapped around axons by oligodendrocytes or Schwann cells in the central and peripheral nervous system, respectively. Fluorescent labeling is widely used to study the structure and dynamics of myelin. Combining structural with functional imaging requires labeling of myelin with red fluorescence, as many functional sensors, including Ca2+ indicators and genetically encoded metabolite sensors, fluoresce in the green spectral range. However, in vivo tools enabling red fluorescent labeling of myelinating cells and their myelin sheaths remain limited. Here, we generated a set of seven transgenic mouse lines expressing a membrane-targeted variant of the red fluorescent protein tdTomato in myelinating oligodendrocytes and Schwann cells throughout the nervous system. The mouse lines provide a variety of expression patterns ranging from wide-spread labeling of myelin to a rather sparse expression, the latter enabling visualization of individual oligodendrocytes and their associated myelin sheaths. In the peripheral nervous system, the pattern of fluorescence in sciatic nerves indicates predominant localization of tdTomato to non-compact myelin compartments including the inner and outer tongues, paranodal loops and Schmidt-Lanterman incisures. In summary, our work provides a set of novel mouse lines with myelin labeled by red fluorescence, which are compatible with diverse imaging modalities in the green spectral range enabling integrated structural and functional imaging.

Myelin has the capacity to affect synapse number or plasticity across the lifespan. We report that disrupting oligodendrocyte (OL) and myelin maintenance from P57 (Plp-CreER[T2]:: Myrf[fl/fl] mice) induces myelin loss and impairs action potential conduction and gross motor performance. By studying sparsely labeled layer V pyramidal neurons in the primary motor cortex of P57 + 60 mice, we determined that apical and basal dendritic spine densities were normal; however, more were large, stable mushroom spines that generated larger amplitude miniature excitatory postsynaptic currents. When we instead prevented OL and myelin addition from P57 (Pdgfrα-CreER:: Myrf[fl/fl] mice), action potential conduction velocity, gross motor performance, and spine densities were normal; however, basal dendritic spine morphology was changed. Without adult myelination, the basal dendrites of P57 + 60 mice retained the morphological characteristics of dendrites in P57 + 0 mice, which have a higher proportion of thin, plastic spines. These data indicate that existing myelin imposes limits on the proportion of spines that become mushroom spines, allowing neurons to remain plastic, while adult myelination is required for spine stabilization within the basal but not apical dendritic compartment. These data show that myelin regulates synaptic plasticity within the motor circuit and offer a potential mechanism by which myelination can influence motor skill learning and/or recall.

Krabbe disease (KD) is a lysosomal storage disorder characterized by severe peripheral demyelination caused by mutations in galactosylceramidase (GALC), leading to the accumulation of galactosylceramide and psychosine. Although psychosine toxicity is central to KD pathology, additional mechanisms likely contribute to myelin dysfunction. Because Schwann cells (SCs) play a critical role in myelin maintenance, and GALC deficiency disrupts lysosomal function, we hypothesized that autophagy is altered in SCs during KD progression. Using a SC-specific Galc conditional knockout (Galc SC cKO) mouse model, we identified early changes in autophagy-related protein levels and increased autophagosome abundance during the pre-symptomatic phase, prior to detectable myelin abnormalities. To assess whether autophagy contributes to disease progression, we selectively deleted Atg7, an essential regulator of canonical autophagy, in SCs. Atg7 deletion alone did not affect myelin or behavior, but its loss in Galc SC cKO mice markedly worsened disease severity. Atg7-Galc SC cKO mice exhibited significantly thinner myelin and pronounced deficits in motor performance and nerve conduction, accompanied by altered steady-state levels of autophagy-associated proteins and functional decline. Notably, Atg7 deletion in Galc SC cKO mice did not further increase macrophage abundance, suggesting that the worsened myelin phenotype occurs without additional macrophage recruitment at this stage. Together, these findings demonstrate that autophagy-associated changes occur early in KD and ATG7-dependent pathways play a protective role during disease progression. Modulating ATG7-dependent pathways may therefore warrant further investigation as a strategy to support myelin maintenance in KD and related lysosomal disorders.

The zebrafish telencephalon is an excellent model for adult neurogenesis under physiological and regenerative conditions, as many pathways regulating neural stem cell behavior are conserved with mammalian neurogenic niches. Resident radial glial cells (RGCs) serve as neural stem cells in the adult brain and are readily accessible in vivo, because forebrain eversion repositions the ventricular zone to the dorsal surface. Recent studies have revealed substantial heterogeneity among RGCs, including activation-primed cells and deeply quiescent states during homeostasis. Here, we first review the evidence that four mechanisms control quiescence in pallial RGCs: Notch3-mediated lateral inhibition, the neuronal bone morphogenetic protein (BMP)-Id1 axis, the nuclear receptor Nr2f1b, and the secreted factor Midkine-a. The evidence supporting them is unequal, and we state its level for each before asking whether they act together. Notch-mediated lateral inhibition and neuronal BMP-Id1 signaling converge on her4.1, the clearest documented interaction among them, whereas Nr2f1b establishes a deeper dormancy program that resists Notch and BMP inhibition and protects a reserve stem cell pool. Midkine-a is proposed to reinforce quiescence, pending functional validation. Finally, we propose as a hypothesis that these mechanisms act as partially redundant inputs whose relative contributions determine quiescence depth and vary along the antero-posterior axis of the pallium. Together, these findings reframe quiescence as a spectrum of actively maintained conditions rather than a passive default state. These mechanisms are conserved across vertebrates, with implications for understanding why mammalian neural stem cell pools decline with age and injury.

Alexander disease (AxD) is a rare neurodegenerative disorder characterized by the pathological accumulation of Rosenthal fibers (RFs) and astrocytic inflammation. Despite advances in elucidating its genetic basis, effective therapeutic strategies remain limited. Recent studies indicate that astrocytes in AxD exhibit excessive mitochondrial fragmentation, which may cause mitochondrial dysfunction and inflammatory response. Photobiomodulation (PBM) has been shown to improve mitochondrial function and exert anti-inflammatory effects, suggesting it may be a promising candidate for the treatment of AxD. Here, we report that exposure to 1070-nm infrared light exerts therapeutic efficacy in AxD. Specifically, using the astrocytes derived from AxD patients and a mouse model of AxD, we demonstrate that PBM regulates AMPK/mTOR signaling and promotes mitophagy, thereby attenuating reactive oxygen species production from fragmented mitochondria and subsequent inflammatory status. This study suggests PBM may serve as a novel, non-invasive therapeutic approach for the treatment of AxD.

Neuroimmune responses critically shape the progression and outcome of ischemic stroke, yet the cell type-specific roles of myeloid populations remain incompletely defined. Cathepsin B (CatB), a lysosomal cysteine protease, has been implicated in neuroinflammation, but its contribution from distinct myeloid subsets is unclear. Transient middle cerebral artery occlusion (tMCAO) was induced in wild-type and CatB-deficient mice. Bone marrow chimeras were generated to selectively delete CatB in peripheral myeloid cells or resident microglia. Infarct severity, mortality, myeloid phenotypes, and transcriptional programs were assessed using flow cytometry, immunofluorescence, and bulk and cell type-resolved RNA sequencing. CatB expression was markedly upregulated in ischemic brain myeloid cells, with higher levels in infiltrating macrophages than in microglia. Selective deletion of CatB in peripheral myeloid cells, but not in microglia, significantly reduced infarct size, mortality, and pro-inflammatory gene expression after tMCAO. Transcriptomic analyses showed suppression of inflammatory pathways and preservation of neuronal signaling in mice lacking macrophage-derived CatB. Cell type-resolved RNA sequencing revealed that CatB deficiency shifted infiltrating macrophages toward a pro-resolving, tissue-repair phenotype characterized by increased expression of M2-associated genes, including Chil3. Consistently, CatB-deficient macrophages displayed enhanced pro-resolving polarization in response to ischemic neuron-derived signals in vitro. CatB was also elevated in circulating Ly6C[+] monocytes after stroke. These findings identify peripheral myeloid-derived CatB as a key driver of ischemic brain injury and a potential therapeutic target.

Myelin regulates neural signaling not only by enabling fast conduction but also by dynamically tuning axonal conduction velocity (CV) and thereby shaping spike timing. While activity-dependent myelination is thought to optimize neural communication, how changes in myelin translate into altered single-cell dynamics and plasticity remains unclear. Using a computational modeling approach, we show that disruptions of axonal CV reorganize presynaptic input correlations, leading to systematic changes in postsynaptic excitability, excitation-inhibition balance, and spike-timing-dependent plasticity. By spanning CV regimes associated with healthy myelination, demyelination, and excessive myelination, our simulations illustrate how both deficient and excessive CV could induce maladaptive neuronal dynamics. The incorporation of firing-rate homeostasis into our models further suggests distinct neuronal dynamic consequences for acute versus chronic myelin disruption. Ultimately, these results suggest that axonal CV may serve as a key mechanistic link between myelin plasticity and neural computation, offering a principled framework to interpret the functional consequences of myelin dysregulation in health and disease.