ASN NEURO最新文献

Galectin-3 (Gal-3) is a protein expressed by glia that belongs to an ancient family. Gal-3 recognises molecular patterns on pathogens due to the high degree of its binding specificity with carbohydrate recognition domains. Thus, in sponges as well as other invertebrates, galectins are an important component of the primitive innate immune system. Whereas Gal-3's function in driving mammalian inflammation is well known, its function in warding off bacterial and viral infections is not well appreciated. One route of brain infection is via the cerebrospinal fluid brain interface (CSFBI) which is primarily composed of ependymal cells (EC). ECs express high levels of Gal-3, and their motile cilia are compromised in Gal-3 KOs. In this mini-review, we discuss fundamentally important potential roles of Gal-3 in pathogen recognition at the CSFBI and suggest avenues of further study.

The g-ratio, defined as the ratio of an axon's diameter to the total fiber diameter (axon plus myelin), is a key metric for assessing myelin integrity and axonal conduction velocity in both the central and peripheral nervous systems. Deviations from the physiological range often signal underlying pathology. Despite its diagnostic importance, there is currently no standardized, open-source tool for g-ratio analysis from post-segmented electron microscopy images. To address this gap, we developed MyeliMetric, a Python-based, user-friendly toolbox that streamlines g-ratio data preprocessing and integrates biologically informed validation, requiring minimal statistical expertise to operate without introducing common analytical errors. It is built on the principle that g-ratios exhibit relative consistency across varying axon diameters in healthy conditions. To rigorously assess this relationship, MyeliMetric implements a binning strategy that groups axons into biologically relevant diameter cohorts, enabling the detection of size-dependent deviations in g-ratio distributions. This approach addresses common limitations in conventional analyses, including insufficient sampling, pseudo-replication, and artifacts such as misleading regression slopes. Validation using both synthetic and published datasets from rodent models of demyelination demonstrated the tool's accuracy, reproducibility, and biological relevance. Synthetic data yielded expected outcomes, and in experimental models, MyeliMetric reliably detected reductions in myelin thickness through g-ratio shifts while minimizing artifacts, thereby providing biologically meaningful insights. It is available on GitHub: https://github.com/Intakhar-Ahmad/NeuroMyelin-G-Ratio-Analysis-Toolkit.

Most studies involving myelin g ratios over the past 120 years assume this metric enumerates differences in myelin thickness (larger g ratio = thinner myelin) with axon or fiber diameter. And, moreover, such changes are directly correlated with internodal function (conduction velocity). However, such assumptions are warranted only in the absence of experimental errors and artifacts (i.e. under theoretical conditions). In reality, g ratios can easily under- or overestimate the rate of change for this relation in excess of 10%, especially for small caliber fibers. Typical analyses of myelin internodes rely on an explicit mathematical model, $g \text{ratio}=\frac{D_A}{D_F}\text{,}$ where D_A is axon diameter and D_F is fiber diameter (myelin plus axon). Shown recently and herein, this model approximates normal physiological conditions only when the axon-fiber diameter relation is directly proportional, whence it is concordant with the axomyelin unit model. However, in transient or non-steady states (development/aging, disease or myelin plasticity) with linear but not directly proportional relations, g ratios may not accurately describe myelin structure. Acceptance of this counterintuitive assertion is predicated on a detailed understanding of the g ratio - its origins, properties and the biology represented - which has been heretofore unexplored. In light of such g ratio limitations, and toward consistency with experimental data, two more reliable metrics are proposed, the myelin g_c ratio and the g' cline. But irrespective which of metric is preferred , the analysis herein shows that the axon-to-fiber diameter ratio under normal physiological conditions is a constant for all fiber diameters.

In light of the increasing importance for measuring myelin g ratios - the ratio of axon-to-fiber (axon + myelin) diameters in myelin internodes - to understand normal physiology, disease states, repair mechanisms and myelin plasticity, there is urgent need to minimize processing and statistical artifacts in current methodologies. Many contemporary studies fall prey to a variety of artifacts, reducing study outcome robustness and slowing development of novel therapeutics. Underlying causes stem from a lack of understanding of the myelin g ratio, which has persisted more than a century. An extended exploratory data analysis from first principles (the axon-fiber diameter relation) is presented herein and has major consequences for interpreting published g ratio studies. Indeed, a model of the myelin internode naturally emerges because of (1) the strong positive correlation between axon and fiber diameters and (2) the demonstration that the relation between these variables is one of direct proportionality. From this model, a robust framework for data analysis, interpretation and understanding allows specific predictions about myelin internode structure under normal physiological conditions. Further, the model establishes that a regression fit to g ratio plots has zero slope, and it identifies the underlying causes of several data processing artifacts that can be mitigated by plotting g ratios against fiber diameter (not axon diameter). Hypothesis testing can then be used for extending the model and evaluating myelin internodal properties under pathophysiological conditions (forthcoming). For without a statistical model as anchor, hypothesis testing is aimless like a rudderless ship on the ocean.

Despite tremendous progress in characterizing the myriad cellular structures in the nervous system, a full appreciation of the interdependent and intricate interactions between these structures is as yet unfulfilled. Indeed, few more so than the interaction between the myelin internode and its ensheathed axon. More than a half-century after the ultrastructural characterization of this axomyelin unit, we lack a reliable understanding of the physiological properties, the significance and consequence of pathobiological processes, and the means to gauge success or failure of interventions designed to mitigate disease. Herein, we highlight shortcomings in the most common statistical procedures used to characterize the myelin g ratio, with particular emphasis on the underlying principles of simple linear regression. These shortcomings lead to insensitive detection and/or ambiguous interpretation of normal physiology, disease mechanisms and remedial methodologies. To address these problems, we syndicate insights from early seminal myelin studies and use a statistical model of the axomyelin unit that is established in Gow (2025). Herein, we develop and demonstrate a statistically-robust analysis pipeline with which to examine and interpret axomyelin physiology and pathobiology in two disease states, experimental autoimmune encephalomyelitis and the rumpshaker mouse model of leukodystrophy. On a cautionary note, our pipeline is a relatively simple and streamlined approach that is not necessarily a panacea for all g ratio analyses. Rather, it approximates a minimum effort needed to elucidate departures from normal physiology and to determine if more comprehensive studies may lead to deeper insights.

Cre-reporter strategies in transgenic mice are widely used to assess the specificity of gene promoter activities, and for fate-mapping studies during development and under injury conditions. The ribosome tagging strategy, RiboTag, is a transgenic approach, in which a hemagglutinin (HA) tag fused to the endogenous ribosomal protein, RPL22, is expressed through the Cre/loxP system. To profile RiboTag reporter expression in oligodendrocyte lineage cells (OLCs), we generated NG2^Cre:Rpl22^HA, Pdgfra^CreERT:Rpl22^HA, and Plp^CreERT:Rpl22^HA mice. We found that NG2^Cre:Rpl22^HA displayed strong HA reporter expression in OLCs and neuronal subpopulations in the postnatal CNS. Tamoxifen administration into Pdgfra^CreERT:Rpl22^HA and Plp^CreERT:Rpl22^HA mice led to widespread HA reporter expression in oligodendrocyte precursor cells (OPCs) and oligodendrocytes, respectively, throughout the brain and spinal cord. Following focal demyelinating injury, Pdgfra^CreERT:Rpl22^HA mice exhibited HA labeling in OPCs, with a gradual increase in oligodendrocyte labeling during remyelination. In contrast, Plp^CreERT:Rpl22^HA exhibited oligodendrocyte labeling in lesions and throughout the CNS parenchyma, presenting a challenge in distinguishing newly generated oligodendrocytes during remyelination from pre-existing oligodendrocytes. Notably, HA expression was induced in oligodendrocytes, but not OPCs in demyelinated lesions of Plp^CreERT:Rpl22^HA mice even when the demyelinating injury was conducted several days after tamoxifen had cleared. This suggests a potential regulation of gene expression in OPCs in demyelinated lesions, in which Rpl22^HA translation may be prevented until oligodendrocyte differentiation occurs. Overall, the RiboTag reporter demonstrates high sensitivity and stability, and its potential application should be carefully considered in relation to the experimental model, timeline in which it will be used, and cell tracking conditions.

Central nervous system (CNS) demyelination occurs in numerous conditions including multiple sclerosis (MS). CNS remyelination involves recruitment and maturation of oligodendrocyte progenitor cells (OPCs). Remyelination often fails in part due to the inhibition of OPC maturation into myelinating oligodendrocytes (OLs). Digestion products of the glycosaminoglycan hyaluronan (HA), generated by hyaluronidase activity, block OPC maturation and remyelination. Here, we aimed to identify which hyaluronidases are elevated in demyelinating lesions and to test if they influence OPC maturation and remyelination. We find that the Cell Migration Inducing and hyaluronan binding Protein (CEMIP) is elevated in demyelinating lesions in mice with experimental autoimmune encephalomyelitis during peak disease when neuroinflammatory mediators, including tumor necrosis factor-α (TNFα), are at high levels. CEMIP expression is also elevated in demyelinated MS patient lesions. CEMIP is expressed by OPCs, and TNFα induces increased CEMIP expression by OPCs. Both increased CEMIP expression and HA fragments generated by CEMIP block OPC maturation into OLs. CEMIP-derived HA fragments also prevent remyelination in vivo. These data indicate that CEMIP blocks remyelination by generating bioactive HA fragments that inhibit OPC maturation. CEMIP is therefore a potential target for therapies aimed at promoting remyelination.

The mechanisms that govern whether T cells cross blood-brain barrier (BBB) endothelium by transcellular versus paracellular routes are unclear. Caveolin-1 is a membrane scaffolding and signaling protein associated with transcellular transmigration through the endothelial cytoplasm. Here, we report that the neuroinflammatory chemokine CXCL10 induced transcellular, caveolar transmigration of CXCR3+ CD4+ T cells. Specifically, data revealed that CXCL10-induced transcellular transmigration requires expression of Caveolin-1 and ICAM-1 in brain endothelial cells and of the CXCL10 receptor, CXCR3, and LFA-1 in T cells. Moreover, Caveolin-1 promoted CXCL10 aggregation into brain endothelial cytoplasmic stores, providing a mechanism for activation and recruitment of CXCR3+ T cells to migrate at cytoplasmic locations, distal to cell-cell junctions. Consistent with our in vitro data, genetic ablation of Caveolin-1 reduces infiltration of CXCR3+ CD4+ T cells into the CNS in experimental autoimmune encephalomyelitis. Our findings establish a novel mechanism by which brain endothelial cells utilize Caveolin-1 dependent CXCL10 intracellular stores to license T cells for transcellular migration across the blood-brain barrier.

People living with HIV (PLWH) experience HIV-associated neurocognitive disorders (HAND), even though combination antiretroviral therapy (cART) suppresses HIV replication. HIV-1 transactivator of transcription (HIV-1 Tat) contributes to the development of HAND through neuroinflammatory and neurotoxic mechanisms. C-C chemokine 5 receptor (CCR5) is important in immune cell targeting and is a co-receptor for HIV viral entry into CD4+ cells. Notably, CCR5 has been implicated in cognition unrelated to HIV infection. Inhibition of CCR5 has been shown to improve learning and memory. To test whether CCR5 is involved in cognitive changes in HAND, we used a non-infectious, transgenic model in which HIV-1 Tat is inducibly expressed. Well-powered cohorts of male and female mice were placed on a diet containing doxycycline to induce Tat expression for 8-wks. Males showed Tat-mediated deficits in the Barnes maze test of spatial learning and memory; females showed no impairments. Deficits in the males were fully reversed by the CCR5 antagonist, maraviroc (MVC). Tat-mediated deficits were not found in novel object recognition or contextual fear conditioning in either sex. Based on earlier work, we hypothesized that MVC might increase brain-derived neurotrophic factor (BDNF), which is essential in maintaining synaptodendritic function. MVC did increase the mBDNF to proBDNF ratio in males, perhaps contributing to improved cognition.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects more than 50 million people worldwide. One of the hallmark features of AD is the accumulation of amyloid β-peptide (Aβ) protein in the brain. P-glycoprotein (P-gp) is a membrane-bound protein expressed in various tissues, including the cerebrovascular endothelium. It plays a crucial role in the efflux of toxic substances, including Aβ, from the brain. Aberrations in P-gp levels or activity have been implicated in the pathogenesis of AD by promoting the accumulation of Aβ in the brain. Therefore, modulating the P-gp function represents a promising therapeutic strategy for treating AD. P-gp has multiple substrate binding sites, creating the potential for substrates to fall into complementation groups based on these sites; two substrates in the same complementation group may compete with one other, but two substrates in different groups may exhibit cooperativity. Thus, a given P-gp substrate may interfere with Aβ efflux whereas another may promote clearance. These threats and opportunities, as well as other aspects of P-gp relevance to AD, are discussed here.