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Transcellular propagation of fibrillar α-synuclein from enteroendocrine to neuronal cells requires cell-to-cell contact and is Rab35-dependent.
Parkinson's disease (PD) is a neurodegenerative condition featured by motor dysfunction, death of midbrain dopaminergic neurons and accumulation of α-synuclein (αSyn) aggregates. Growing evidence suggests that PD diagnosis happens late in the disease progression and that the pathology may originate much earlier in the enteric nervous system (ENS) before advancing to the brain, via autonomic fibers. It was recently described that a specific cell type from the gut epithelium named enteroendocrine cells (EECs) possess many neuron-like properties including αSyn expression. By facing the gut lumen and being directly connected with αSyn-containing enteric neurons in a synaptic manner, EECs form a neural circuit between the gastrointestinal tract and the ENS, thereby being a possible key player in the outcome of PD in the gut. We have characterized the progression and the cellular mechanisms involved in αSyn pre-formed fibrils (PFFs) transfer from EECs to neuronal cells. We show that brain organoids efficiently internalize αSyn PFF seeds which triggers the formation of larger intracellular inclusions. In addition, in the enteroendocrine cell line STC-1 and in the neuronal cell line SH-SY5Y, αSyn PFFs induced intracellular calcium (Ca2+) oscillations on an extracellular Ca2+ source-dependent manner and triggered αSyn fibrils internalization by endocytosis. We characterized the spread of αSyn PFFs from enteroendocrine to neuronal cells and showed that this process is dependent on physical cell-to-cell contact and on Rab35 GTPase. Lastly, inhibition of Rab35 increases the clearance of αSyn fibrils by redirecting them to the lysosomal compartment. Therefore, our results reveal mechanisms that contribute to the understanding of how seeded αSyn fibrils promote the progression of αSyn pathology from EECs to neuronal cells shifting the focus of PD etiology to the ENS.
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Protection against stroke-induced blood-brain barrier disruption by Guanxinning injection and its active-component combination via TLR4/NF-κB/MMP9-mediated neuroinflammation.
BACKGROUND: The blood-brain barrier (BBB) is essential for central nervous system (CNS) homeostasis, yet neuroinflammatory mechanisms driving BBB disruption remain poorly understood. PURPOSE: To explore the oxygen-glucose deprivation/reoxygenation (OGD/R)-induced BBB dysfunction and evaluate the therapeutic effects of Guanxinning injection (GXNI), a Danshen-Chuanxiong herbal combination, targeting neuroinflammatory pathways. METHODS: A 3D-BBB organoid composed of human brain microvascular endothelial cells, human astrocytes, and primary human brain microvascular pericytes was constructed, and conditions for OGD/R that simulate ischemic stroke were established. Structure and function of the in vitro BBB were evaluated by morphology, paracellular permeability, and tight junction proteins ZO-1, claudin-5, and occludin expression. In vivo, infarct volume and BBB leakage were measured in a mid-cerebral artery occlusion-induced cerebral ischemia-reperfusion injury model. RNA-seq and network pharmacology analysis were used to identify key genes and pathways for ischemic BBB disruption. HPLC-MS was performed to identify and quantify active components. Molecular docking, SPR, and molecular dynamics were performed to predict and confirm the interaction of active compounds and target proteins. RESULTS: A Danshen-Chuanxiong double herbal medicine, GXNI, mitigated these effects, restoring transport capacity, reducing oxidative stress (ROS), and enhancing basement membrane components (laminin, collagen IV). In vivo, GXNI alleviated cerebral ischemia-reperfusion injury (CIRI), decreasing BBB leakage, infarct volume, and neurological deficits. The pivotal role of TLR4/NF-κB/MMP9 neuroinflammatory axis for GXNI BBB protection was identified through transcriptomic analysis and validated via immunofluorescence in BBB spheroids. Molecular docking revealed Danshen-derived salvianolic acid B (SAB) as a high-affinity MMP9 binder, confirmed by quantitative binding assays. The SAB and Chuanxiong-derived senkyunolide I (SI) combination achieved more prominent upregulation of tight junction proteins and suppression of MMP9. CONCLUSION: Our findings further confirm neuroinflammation as a central driver of ischemic BBB damage and demonstrate that GXNI preserves BBB integrity by targeting TLR4/NF-κB/MMP9 signaling in 3D models and CIRI mice, with SAB-SI synergistically contributing to enhanced therapeutic efficacy.
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CK2 inhibition suppresses glial inflammation in models of neuroinflammation and neurodegeneration.
Neuroinflammation plays a key role in Alzheimer's disease (AD) and many other neurodegenerative disorders. Chronic activation of astrocytes and microglia fuels neuronal damage via cytokine secretion, oxidative stress, and proteolysis, yet glial inflammatory regulation remains poorly understood. Using chemoproteomics, we identified CK2, particularly the brain-enriched catalytic subunit CK2α2, as a key driver of astrocytic inflammation. CK2 enhances NF-κB activity by phosphorylating NF-κB S529 and IκBα S32, promoting pro-inflammatory gene expression. Genetic or chemical CK2 inhibition dampens inflammation, including IL-6 and IL-8 expression in a TNFα acute neuroinflammation mouse model. CK2α2 is upregulated in AD postmortem tissues and patient-derived astrocytes. AD astrocytes exhibit a hyperinflammatory state that can be attenuated by CK2 inhibition. Overexpression of CK2α2 in cortical organoids mimics AD pathology, whereas CK2 inhibition using the potent, selective, and brain-penetrant probe TAL606 rescues inflammatory markers in AD APP/PS1 mice. These findings position CK2 as a central regulator of neuroinflammation and a promising therapeutic target for AD and related disorders.
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Cilia, ciliopathies and hedgehog-related forebrain developmental disorders.
Development of the forebrain critically depends on the Sonic Hedgehog (Shh) signaling pathway, as illustrated in humans by the frequent perturbation of this pathway in holoprosencephaly, a condition defined as a defect in the formation of midline structures of the forebrain and face. The Shh pathway requires functional primary cilia, microtubule-based organelles present on virtually every cell and acting as cellular antennae to receive and transduce diverse chemical, mechanical or light signals. The dysfunction of cilia in humans leads to inherited diseases called ciliopathies, which often affect many organs and show diverse manifestations including forebrain malformations for the most severe forms. The purpose of this review is to provide the reader with a framework to understand the developmental origin of the forebrain defects observed in severe ciliopathies with respect to perturbations of the Shh pathway. We propose that many of these defects can be interpreted as an imbalance in the ratio of activator to repressor forms of the Gli transcription factors, which are effectors of the Shh pathway. We also discuss the complexity of ciliopathies and their relationships with forebrain disorders such as holoprosencephaly or malformations of cortical development, and emphasize the need for a closer examination of forebrain defects in ciliopathies, not only through the lens of animal models but also taking advantage of the increasing potential of the research on human tissues and organoids.
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Expression Analysis Highlights AXL as a Candidate Zika Virus Entry Receptor in Neural Stem Cells.
The recent outbreak of Zika virus (ZIKV) in Brazil has been linked to substantial increases in fetal abnormalities and microcephaly. However, information about the underlying molecular and cellular mechanisms connecting viral infection to these defects remains limited. In this study we have examined the expression of receptors implicated in cell entry of several enveloped viruses including ZIKV across diverse cell types in the developing brain. Using single-cell RNA-seq and immunohistochemistry, we found that the candidate viral entry receptor AXL is highly expressed by human radial glial cells, astrocytes, endothelial cells, and microglia in developing human cortex and by progenitor cells in developing retina. We also show that AXL expression in radial glia is conserved in developing mouse and ferret cortex and in human stem cell-derived cerebral organoids, highlighting multiple experimental systems that could be applied to study mechanisms of ZIKV infectivity and effects on brain development.
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eSPRESSO: topological clustering of single-cell transcriptomics data to reveal informative genes for spatio-temporal architectures of cells.
BACKGROUND: Bioinformatics capability to analyze spatio-temporal dynamics of gene expression is essential in understanding animal development. Animal cells are spatially organized as functional tissues where cellular gene expression data contain information that governs morphogenesis during the developmental process. Although several computational tissue reconstruction methods using transcriptomics data have been proposed, those methods have been ineffective in arranging cells in their correct positions in tissues or organs unless spatial information is explicitly provided. RESULTS: This study demonstrates stochastic self-organizing map clustering with Markov chain Monte Carlo calculations for optimizing informative genes effectively reconstruct any spatio-temporal topology of cells from their transcriptome profiles with only a coarse topological guideline. The method, eSPRESSO (enhanced SPatial REconstruction by Stochastic Self-Organizing Map), provides a powerful in silico spatio-temporal tissue reconstruction capability, as confirmed by using human embryonic heart and mouse embryo, brain, embryonic heart, and liver lobule with generally high reproducibility (average max. accuracy = 92.0%), while revealing topologically informative genes, or spatial discriminator genes. Furthermore, eSPRESSO was used for temporal analysis of human pancreatic organoids to infer rational developmental trajectories with several candidate 'temporal' discriminator genes responsible for various cell type differentiations. CONCLUSIONS: eSPRESSO provides a novel strategy for analyzing mechanisms underlying the spatio-temporal formation of cellular organizations.
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Human intermediate progenitor diversity during cortical development.
Studies of the spatiotemporal, transcriptomic, and morphological diversity of radial glia (RG) have spurred our current models of human corticogenesis. In the developing cortex, neural intermediate progenitor cells (nIPCs) are a neuron-producing transit-amplifying cell type born in the germinal zones of the cortex from RG. The potential diversity of the nIPC population, that produces a significant portion of excitatory cortical neurons, is understudied, particularly in the developing human brain. Here we explore the spatiotemporal, transcriptomic, and morphological variation that exists within the human nIPC population and provide a resource for future studies. We observe that the spatial distribution of nIPCs in the cortex changes abruptly around gestational week (GW) 19/20, marking a distinct shift in cellular distribution and organization during late neurogenesis. We also identify five transcriptomic subtypes, one of which appears at this spatiotemporal transition. Finally, we observe a diversity of nIPC morphologies that do not correlate with specific transcriptomic subtypes. These results provide an analysis of the spatiotemporal, transcriptional, and morphological diversity of nIPCs in developing brain tissue and provide an atlas of nIPC subtypes in the developing human cortex that can benchmark in vitro models of human development such as cerebral organoids and help inform future studies of how nIPCs contribute to cortical neurogenesis.
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Embryonic mouse medial neocortex as a model system for studying the radial glial scaffold in fetal human neocortex.
Neocortex is the evolutionarily newest region in the brain, and is a structure with diversified size and morphology among mammalian species. Humans have the biggest neocortex compared to the body size, and their neocortex has many foldings, that is, gyri and sulci. Despite the recent methodological advances in in vitro models such as cerebral organoids, mice have been continuously used as a model system for studying human neocortical development because of the accessibility and practicality of in vivo gene manipulation. The commonly studied neocortical region, the lateral neocortex, generally recapitulates the developmental process of the human neocortex, however, there are several important factors missing in the lateral neocortex. First, basal (outer) radial glia (bRG), which are the main cell type providing the radial scaffold to the migrating neurons in the fetal human neocortex, are very few in the mouse lateral neocortex, thus the radial glial scaffold is different from the fetal human neocortex. Second, as a consequence of the difference in the radial glial scaffold, migrating neurons might exhibit different migratory behavior and thus distribution. To overcome those problems, we propose the mouse medial neocortex, where we have earlier revealed an abundance of bRG similar to the fetal human neocortex, as an alternative model system. We found that similar to the fetal human neocortex, the radial glial scaffold, neuronal migration and neuronal distribution are tangentially scattered in the mouse medial neocortex. Taken together, the embryonic mouse medial neocortex could be a suitable and accessible in vivo model system to study human neocortical development and its pathogenesis.
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Neural progenitor cells and their role in the development and evolutionary expansion of the neocortex.
The evolutionary expansion of the mammalian brain, notably the neocortex, provides a platform for the higher cognitive abilities that characterize humans. Cortical expansion is accompanied by increased folding of the pial surface, which gives rise to a gyrencephalic (folded) rather than lissencephalic (unfolded) neocortex. This expansion reflects the prolonged and increased proliferation of neural stem and progenitor cells (NPCs). Distinct classes of NPCs can be distinguished based on either cell biological criteria (apical progenitors [APs], basal progenitors [BPs]) or lineage (primary progenitors and secondary progenitors). Cortical expansion in development and evolution is linked to an increased abundance and proliferative capacity of BPs, notably basal radial glial cells, a recently characterized type of secondary progenitor derived from apical radial glial cells, the primary progenitors. To gain insight into the molecular basis underlying the prolonged and increased proliferation of NPCs and in particular BPs, comparative genomic and transcriptomic approaches, mostly for human versus mouse, have been employed and applied to specific NPC types and subpopulations. These have revealed two principal sets of molecular changes. One concerns differences in the expression of common genes between species with different degrees of cortical expansion. The other comprises human-specific genes or genomic regulatory sequences. Various systems that allow functional testing of these genomic and gene expression differences between species have emerged, including transient and stable transgenesis, genome editing, cerebral organoids, and organotypic slice cultures. These provide future avenues for uncovering the molecular basis of cortical expansion. WIREs Dev Biol 2017, 6:e256. doi: 10.1002/wdev.256 For further resources related to this article, please visit the WIREs website.
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LRP4 is an entry receptor for multiple encephalitic alphaviruses.
Encephalitic alphaviruses, including Eastern equine encephalitis virus (EEEV), cause severe neurological disease with high mortality rates, and thus are a public health threat. Although members of the low-density lipoprotein receptor (LDLR) family, including VLDLR, LRP8 (ApoER2), and LDLR recently were identified as receptors for EEEV, residual infection in receptor-deficient cells suggests that additional entry factors exist. Using a CRISPR-based activation screen, we identified LDLR-related protein 4 (LRP4) as a candidate entry factor for EEEV and several related alphaviruses (Western equine encephalitis, Semliki Forest, and Sindbis viruses). LRP4 mediates viral attachment and internalization, and its ligand-binding domain binds directly to virions. Soluble LRP4 decoy proteins potently inhibit EEEV infection in primary mouse neuronal cells, male mice, and human brain organoids, suggesting possible therapeutic applications. Mammalian and avian LRP4 orthologs demonstrate conserved functions in promoting EEEV infection, supporting a possible role in its host range of infection and transmission. Our findings establish LRP4 as a shared entry receptor for multiple alphaviruses and expand our understanding of alphavirus tropism, pathogenesis, and countermeasure development.