Ependymal cells: biology and pathology

Non-Neoplastic Lesions of the Ependyma: A Neuropathological Overview

Non-neoplastic lesions of the ependyma have been neglected to date in comparison with neoplastic lesions derived from the ependyma, that is, ependymoma. The ependyma has a simple structure: mono-layered cuboidal cells covering the surface of the cerebral ventricles and the central canal of the spinal cord. In this review, the histopathological appearances of various non-neoplastic ependymal lesions are shown based on the author's personal experience, along with a review of the relevant literature. Following the introductory remarks about the normal histology and functions of ependymal cells including tanycytes, non-neoplastic lesions are then presented including, obliteration of the spinal central canal; the "ventriculus terminalis"; shedding of ependymal cells and "granular ependymitis"; "ependymal incorporation"; ependymal cells in hydrocephalus; ependymal reactions to various noxious stimuli; ependymal changes in cerebral dysgenesis; infections involving ependymal cells; glio-ependymal cyst; and finally, various intracellular inclusions in ependymal cells. Non-neoplastic ependymal lesions are intriguing and merit further investigations, which may provide deeper understanding of various brain lesions and of ependymal neoplasms.

IFN-γ signaling links ventriculomegaly to choroid plexus and ependyma dysfunction following maternal immune activation

Maternal immune activation (MIA) is a principal environmental risk factor contributing to autism spectrum disorder (ASD) and can be causally linked to ASD symptoms. In our study, we found that MIA triggered by poly (I: C) injection caused ventriculomegaly in offspring due to the dysfunction of the choroid plexus (Chp) and ependyma. We subsequently identified a sustained enhancement of interferon-γ (IFN-γ) signaling in the brain and serum of MIA offspring. Further study revealed that increased IFN-γ signaling could disrupt the barrier function of Chp epithelial cells by activating macrophages, and suppress the differentiation of primary ependymal cells via the signal transducer and activator of transcription 1/3 signaling. The effects of MIA on the offspring were mitigated by administration of IFNGR-blocking antibody in pregnant dams, while systemic maternal administration of IFN-γ was sufficient to mimic the effect of MIA. Overall, our findings revealed that ventriculomegaly caused by IFN-γ signaling could be a critical factor in compromising fetal brain development in MIA-induced ASD and provide a mechanistic framework for the association between maternal inflammation and abnormal development of ventricles in the offspring.

RGS22 maintains the physiological function of ependymal cells to prevent hydrocephalus

Ependymal cells line the wall of cerebral ventricles and ensure the unidirectional cerebrospinal fluid (CSF) flow by beating their motile cilia coordinately. The ependymal denudation or ciliary dysfunction causes hydrocephalus. Here, we report that the deficiency of regulator of G-protein signaling 22 (RGS22) results in severe congenital hydrocephalus in both mice and rats. Interestingly, RGS22 is specifically expressed in ependymal cells within the brain. Using conditional knock-out mice, we further demonstrate that the deletion of Rgs22 exclusively in nervous system is sufficient to induce hydrocephalus. Mechanistically, we show that Rgs22 deficiency leads to the ependymal denudation and impaired ciliogenesis. This phenomenon can be attributed to the excessive activation of lysophosphatidic acid receptor (LPAR) signaling under Rgs22-/- condition, as the LPAR blockade effectively alleviates hydrocephalus in Rgs22-/- rats. Therefore, our findings unveil a previously unrecognized role of RGS22 in the central nervous system, and present RGS22 as a potential diagnostic and therapeutic target for hydrocephalus.

Brain-wide cell-type-specific transcriptomic signatures of healthy ageing in mice

Biological ageing can be defined as a gradual loss of homeostasis across various aspects of molecular and cellular function1,2. Mammalian brains consist of thousands of cell types3, which may be differentially susceptible or resilient to ageing. Here we present a comprehensive single-cell RNA sequencing dataset containing roughly 1.2 million high-quality single-cell transcriptomes of brain cells from young adult and aged mice of both sexes, from regions spanning the forebrain, midbrain and hindbrain. High-resolution clustering of all cells results in 847 cell clusters and reveals at least 14 age-biased clusters that are mostly glial types. At the broader cell subclass and supertype levels, we find age-associated gene expression signatures and provide a list of 2,449 unique differentially expressed genes (age-DE genes) for many neuronal and non-neuronal cell types. Whereas most age-DE genes are unique to specific cell types, we observe common signatures with ageing across cell types, including a decrease in expression of genes related to neuronal structure and function in many neuron types, major astrocyte types and mature oligodendrocytes, and an increase in expression of genes related to immune function, antigen presentation, inflammation, and cell motility in immune cell types and some vascular cell types. Finally, we observe that some of the cell types that demonstrate the greatest sensitivity to ageing are concentrated around the third ventricle in the hypothalamus, including tanycytes, ependymal cells, and certain neuron types in the arcuate nucleus, dorsomedial nucleus and paraventricular nucleus that express genes canonically related to energy homeostasis. Many of these types demonstrate both a decrease in neuronal function and an increase in immune response. These findings suggest that the third ventricle in the hypothalamus may be a hub for ageing in the mouse brain. Overall, this study systematically delineates a dynamic landscape of cell-type-specific transcriptomic changes in the brain associated with normal ageing that will serve as a foundation for the investigation of functional changes in ageing and the interaction of ageing and disease.

Motile cilia modulate neuronal and astroglial activity in the zebrafish larval brain

The brain uses a specialized system to transport cerebrospinal fluid (CSF), consisting of interconnected ventricles lined by motile ciliated ependymal cells. These cells act jointly with CSF secretion and cardiac pressure gradients to regulate CSF dynamics. To date, the link between cilia-mediated CSF flow and brain function is poorly understood. Using zebrafish larvae as a model system, we identify that loss of ciliary motility does not alter progenitor proliferation, brain morphology, or spontaneous neural activity despite leading to an enlarged telencephalic ventricle. We observe altered neuronal responses to photic stimulations in the optic tectum and hindbrain and brain asymmetry defects in the habenula. Finally, we investigate astroglia since they contact CSF and regulate neuronal activity. Our analyses reveal a reduction in astroglial calcium signals during both spontaneous and light-evoked activity. Our findings highlight a role of motile cilia in regulating brain physiology through the modulation of neural and astroglial networks.

Characterizing progenitor cells in developing and injured spinal cord: Insights from single-nucleus transcriptomics and lineage tracing

Various mature tissue-resident cells exhibit progenitor characteristics following injury. However, the existence of endogenous stem cells with multiple lineage potentials in the adult spinal cord remains a compelling area of research. In this study, we present a cross-species investigation that extends from development to injury. We used single-nucleus transcriptomic sequencing and genetic lineage tracing to characterize neural cells in the spinal cord. Our findings show that ciliated ependymal cells lose neural progenitor gene signatures and proliferation ability following the differentiation of NPCs within the ventricular zone. By combining single-nucleus transcriptome datasets from the rhesus macaque spinal cord injury (SCI) model with developmental human spinal cord datasets, we revealed that ciliated ependymal cells respond minimally to injury and cannot revert to a developmental progenitor state. Intriguingly, we observed astrocytes transdifferentiating into mature oligodendrocytes postinjury through lineage tracing experiments. Further analysis identifies an intermediate-state glial cell population expressing both astrocyte and oligodendrocyte feature genes in adult spinal cords. The transition ratio from astrocytes into oligodendrocytes increased after remodeling injury microenvironment by functional scaffolds. Overall, our results highlight the remarkable multilineage potential of astrocytes in the adult spinal cord.

Genetic and molecular mechanisms of hydrocephalus

Hydrocephalus is a neurological condition caused by aberrant circulation and/or obstructed cerebrospinal fluid (CSF) flow after cerebral ventricle abnormal dilatation. In the past 50 years, the diagnosis and treatment of hydrocephalus have remained understudied and underreported, and little progress has been made with respect to prevention or treatment. Further research on the pathogenesis of hydrocephalus is essential for developing new diagnostic, preventive, and therapeutic strategies. Various genetic and molecular abnormalities contribute to the mechanisms of hydrocephalus, including gene deletions or mutations, the activation of cellular inflammatory signaling pathways, alterations in water channel proteins, and disruptions in iron metabolism. Several studies have demonstrated that modulating the expression of key proteins, including TGF-β, VEGF, Wnt, AQP, NF-κB, and NKCC, can significantly influence the onset and progression of hydrocephalus. This review summarizes and discusses key mechanisms that may be involved in the pathogenesis of hydrocephalus at both the genetic and molecular levels. While obstructive hydrocephalus can often be addressed by removing the obstruction, most cases require treatment strategies that involve merely slowing disease progression by correcting CSF circulation patterns. There have been few new research breakthroughs in the prevention and treatment of hydrocephalus.

Addressing the Effect of Exercise on Glial Cells: Focus on Ependymal Cells

A growing body of research highlights the positive impact of regular physical activity on improving physical and mental health. On the other hand, physical inactivity is one of the leading risk factors for noncommunicable diseases and death worldwide. Exercise profoundly impacts various body districts, including the central nervous system. Here, overwhelming evidence exists that physical exercise affects neurons and glial cells, by promoting their interaction. Physical exercise directly acts on ependymal cells by promoting their proliferation and activation, maintaing brain homeostasis in healthy animals and promote locomotor recovery after spinal cord injury. This review aims to describe the main anatomical characteristics and functions of ependymal cells and provide an overview of the effects of different types of physical exercise on glial cells, focusing on the ependymal cells.

Ezrin, a novel marker of ependymal cells, can be used to demonstrate their proliferation regulation after spinal cord injury in mice

Ependymal cells (EpCs), as a potential stem cell niche, have gained interest for their potential in vivo stem cell therapy for spinal cord injury (SCI). Heterogeneity of spinal EpCs may contribute to differences in the ability of spinal EpCs to proliferate, differentiate and transition after injury, while there is limited understanding of the regulation of these events. Our research found that ezrin (Ezr) was expressed highly in EpCs of the spinal cord, and its upregulation rapidly occurred after injury (6 h). It remained consistently highly expressed in proliferating EpCs, this occurs before pathological accumulation of it occurs in other glial and immune-related cells. Differential expression of Ezr, Arg3, Pvalb, Ccnd1, and Gmpr characterized distinct responses of EpCs to injury activity. Also, we uncovered the dynamic regulatory behavior of immature EpCs after injury. In contrast to constitutive expression in parenchymal tissues, injury factors upregulated guanosine monophosphate reductase (Gmpr) in arrested EpCs, unveiling a distinctive mechanism to regulate proliferation in EpCs following spinal cord injury.

Hydrocephalus: An update on latest progress in pathophysiological and therapeutic research

Hydrocephalus is a severe and life-threatening disease associated with the imbalance of CSF dynamics and affects millions globally at any age, including infants. One cause of pathology that is wide-ranging is genetic mutations to post-traumatic injury. The most effective current pharmacological treatments provide only symptomatic relief and do not address the underlying pathology. At the same time, surgical procedures such as VP shunts performed in lower-income countries are often poorly tolerated due to insufficient diagnostic resources and suboptimal outcomes partially attributable to inferior materials. These problems are compounded by an overall lack of funding that keeps high-quality medical devices out of reach for all but the most developed countries and even among those states. There is a massive variance in treatment effectiveness. This review indicates the necessity for innovative and low-cost, accessible treatment strategies to close these gaps, focusing on current advances in novel therapies, including Pharmacological, gene therapy, and nano-based technologies, which are currently at different stages of clinical trial phases. This review provides an overview of pathophysiology, current treatments, and promising new therapeutic strategies for hydrocephalus.

The periaxonal space as a conduit for cerebrospinal fluid flow to peripheral organs

Mechanisms controlling the movement of the cerebrospinal fluid (CSF) toward peripheral nerves are poorly characterized. We found that, in addition to the foramina Magendie and Luschka for CSF flow toward the subarachnoid space and glymphatic system, CSF outflow could also occur along periaxonal spaces (termed "PAS pathway") from the spinal cord to peripheral organs, such as the liver and pancreas. When interrogating the latter route, we found that serotonin, acting through 5-HT2B receptors expressed in ependymocytes that line the central canal, triggered Ca2+ signals to induce polymerization of F-actin, a cytoskeletal protein, to reduce the volume of ependymal cells. This paralleled an increased rate of PAS-mediated CSF redistribution toward peripheral organs. In the liver, CSF was received by hepatic stellate cells. CSF efflux toward peripheral organs through the PAS pathway represents a mechanism dynamically connecting the nervous system with the periphery. Our findings are compatible with the traditional theory of CSF efflux into the glymphatic system to clear metabolic waste from the cerebral parenchyma. Thus, we extend the knowledge of CSF flow and expand the understanding of connectivity between the CNS and peripheral organs.

Machine learning in prenatal MRI predicts postnatal ventricular abnormalities in fetuses with isolated ventriculomegaly

OBJECTIVES

To evaluate the intracranial structures and brain parenchyma radiomics surrounding the occipital horn of the lateral ventricle in normal fetuses (NFs) and fetuses with ventriculomegaly (FVs), as well as to predict postnatally enlarged lateral ventricle alterations in FVs.

METHODS

Between January 2014 and August 2023, 141 NFs and 101 FVs underwent 1.5 T balanced steady-state free precession (BSSFP), including 68 FVs with resolved lateral ventricles (FVM-resolved) and 33 FVs with stable lateral ventricles (FVM-stable). Demographic data and intracranial structures were analyzed. To predict the enlarged ventricle alterations of FVs postnatally, logistic regression models with 5-fold cross-validation were developed based on lateral ventricle morphology, blended-cortical or/and subcortical radiomics characteristics. Validation of the models' performance was conducted using the receiver operating characteristic curve (ROC), calibration curve, and decision curve analysis (DCA).

RESULTS

Significant alterations in cerebral structures were observed between NFs and FVs (p < 0.05), excluding the maximum frontal horn diameter (FD). However, there was no notable distinction between the FVM-resolved and FVM-stable groups (all p > 0.05). Based on subcortical-radiomics on the aberrant sides of FVs, this approach exhibited high efficacy in distinguishing NFs from FVs in the training/validation set, yielding an impressive AUC of 1/0.992. With an AUC value of 0.822/0.743 in the training/validation set, the Subcortical-radiomics model demonstrated its ability to predict lateral ventricle alterations in FVs, which had the greatest predictive advantages indicated by DCA.

CONCLUSIONS

Microstructural alterations in subcortical parenchyma associated with ventriculomegaly can serve as predictive indicators for postnatal lateral ventricle variations in FVs.

CLINICAL RELEVANCE STATEMENT

It is critical to gain pertinent information from a solitary fetal MRI to anticipate postnatal lateral ventricle alterations in fetuses with ventriculomegaly. This approach holds the potential to diminish the necessity for recurrent prenatal ultrasound or MRI examinations.

KEY POINTS

Fetal ventriculomegaly is a dynamic condition that affects postnatal neurodevelopment. Machine learning and subcortical-radiomics can predict postnatal alterations in the lateral ventricle. Machine learning, applied to single-fetal MRI, might reduce required antenatal testing.

The Role of CXCR3 in Nervous System-Related Diseases

Inflammatory chemokines are a group of G-protein receptor ligands characterized by conserved cysteine residues, which can be divided into four main subfamilies: CC, CXC, XC, and CX3C. The C-X-C chemokine receptor (CXCR) 3 and its ligands, C-X-C chemokine ligands (CXCLs), are widely expressed in both the peripheral nervous system (PNS) and central nervous system (CNS). This comprehensive literature review aims to examine the functions and pathways of CXCR3 and its ligands in nervous system-related diseases. In summary, while the related pathways and the expression levels of CXCR3 and its ligands are varied among different cells in PNS and CNS, the MPAK pathway is the core via which CXCR3 exerts physiological functions. It is not only the core pathway of CXCR3 after activation but also participates in the expression of CXCR3 ligands in the nervous system. In addition, despite CXCR3 being a common inflammatory chemokine receptor, there is no consensus on its precise roles in various diseases. This uncertainty may be attributable to distinct inflammatory characteristics, that inflammation simultaneously possesses the dual properties of damage induction and repair facilitation.

Ependymal cells: roles in central nervous system infections and therapeutic application

Ependymal cells are arranged along the inner surfaces of the ventricles and the central canal of the spinal cord, providing anatomical, physiological and immunological barriers that maintain cerebrospinal fluid (CSF) homeostasis. Based on this, studies have found that alterations in gene expression, cell junctions, cytokine secretion and metabolic disturbances can lead to dysfunction of ependymal cells, thereby participating in the onset and progression of central nervous system (CNS) infections. Additionally, ependymal cells can exhibit proliferative and regenerative potential as well as secretory functions during CNS injury, contributing to neuroprotection and post-injury recovery. Currently, studies on ependymal cell primarily focus on the basic investigations of their morphology, function and gene expression; however, there is a notable lack of clinical translational studies examining the molecular mechanisms by which ependymal cells are involved in disease onset and progression. This limits our understanding of ependymal cells in CNS infections and the development of therapeutic applications. Therefore, this review will discuss the molecular mechanism underlying the involvement of ependymal cells in CNS infections, and explore their potential for application in clinical treatment modalities.

Revisiting the Pathophysiology of Intracranial Hemorrhage in Fetuses with Chiari II Malformation: Novel Imaging Biomarkers of Disease Severity?

BACKGROUND AND PURPOSE

Intracranial hemorrhage (ICH) has emerged as a notable concern in Chiari II malformation (CM II), yet its origins and clinical implications remain elusive. This study aims to validate the in utero prevalence of ICH in CM II and investigate contributing factors, and visualize the findings in a network format.

MATERIALS AND METHODS

A single-center retrospective review of fetal MRI scans obtained in fetuses with CM II (presenting January 2007 to December 2022) was performed for ICH utilizing EPI-T2* blood-sensitive sequence. Fetuses with aqueduct stenosis (AS) were included as a control group. The incidence of ICH and corresponding gestational ages were compared between CM II and AS cases, and morphometric measurements (inner/outer CSF spaces, posterior fossa, venous structure) were compared among the 4 1:1 age-matched groups: CM II+ICH, CM II-ICH, AS+ICH, and AS-ICH. Additionally, a co-occurrence network was constructed to visualize associations between phenotypic features in ICH cases.

RESULTS

A total of 101 fetuses with CM II and 90 controls with AS at a median gestational age of 24.4 weeks and 22.8 weeks (P = .138) were included. Prevalence of ICH in fetuses with CM II was higher compared with the AS cases (28.7% versus 18.9%, P = .023), accompanied by congested veins (deep vein congestion mainly in young fetuses, and cortical veins may also be affected in older fetuses). ICH was notably correlated with specific anatomic features, essentially characterized by reduced outer CSF spaces and clivus-supraocciput angle. The co-occurrence network analysis reveals complex connections including bony defects, small posterior fossa dimensions, vermis ectopia, reduced CSF spaces, as well as venous congestion and venous sinus stenosis as pivotal components within the network.

CONCLUSIONS

The high prevalence of ICH-detected by fetal MRI-among fetuses with CM emphasizes the pathophysiologic importance of venous congestion, ICH, and vasogenic edema. As indicators of disease severity, these features may serve as helpful additional imaging biomarkers for the identification of potential candidates for fetal surgery.

Ependymal cells undergo astrocyte-like reactivity in response to neuroinflammation

Ependymal cells form a specialized brain-cerebrospinal fluid (CSF) interface and regulate local CSF microcirculation. It is becoming increasingly recognized that ependymal cells assume a reactive state in response to aging and disease, including conditions involving hypoxia, hydrocephalus, neurodegeneration, and neuroinflammation. Yet what transcriptional signatures govern these reactive states and whether this reactivity shares any similarities with classical descriptions of glial reactivity (i.e., in astrocytes) remain largely unexplored. Using single-cell transcriptomics, we interrogated this phenomenon by directly comparing the reactive ependymal cell transcriptome to the reactive astrocyte transcriptome using a well-established model of autoimmune-mediated neuroinflammation (MOG35-55 EAE). In doing so, we unveiled core glial reactivity-associated genes that defined the reactive ependymal cell and astrocyte response to MOG35-55 EAE. Interestingly, known reactive astrocyte genes from other CNS injury/disease contexts were also up-regulated by MOG35-55 EAE ependymal cells, suggesting that this state may be conserved in response to a variety of pathologies. We were also able to recapitulate features of the reactive ependymal cell state acutely using a classic neuroinflammatory cocktail (IFNγ/LPS) both in vitro and in vivo. Taken together, by comparing reactive ependymal cells and astrocytes, we identified a conserved signature underlying glial reactivity that was present in several neuroinflammatory contexts. Future work will explore the mechanisms driving ependymal reactivity and assess downstream functional consequences.

Bioavailability as Proof to Authorize the Clinical Testing of Neurodegenerative Drugs-Protocols and Advice for the FDA to Meet the ALS Act Vision

Although decades of intensive drug discovery efforts to treat neurodegenerative disorders (NDs) have failed, around half a million patients in more than 2000 studies continue being tested, costing over USD 100 billion, despite the conclusion that even those drugs which have been approved have no better effect than a placebo. The US Food and Drug Administration (FDA) has established multiple programs to innovate the treatment of rare diseases, particularly NDs, providing millions of USD in funding primarily by encouraging novel clinical trials to account for issues related to study sizes and adopting multi-arm studies to account for patient dropouts. Instead, the FDA should focus on the primary reason for failure: the poor bioavailability of drugs reaching the brain (generally 0.1% at most) due to the blood-brain barrier (BBB). There are several solutions to enhance entry into the brain, and the FDA must require proof of significant entry into the brain as the prerequisite to approving Investigational New Drug (IND) applications. The FDA should also rely on factors other than biomarkers to confirm efficacy, as these are rarely relevant to clinical use. This study summarizes how the drugs used to treat NDs can be made effective and how the FDA should change its guidelines for IND approval of these drugs.

Multiciliated ependymal cells: an update on biology and pathology in the adult brain

Mature multiciliated ependymal cells line the cerebral ventricles where they form a partial barrier between the cerebrospinal fluid (CSF) and brain parenchyma and regulate local CSF microcirculation through coordinated ciliary beating. Although the ependyma is a highly specialized brain interface with barrier, trophic, and perhaps even regenerative capacity, it remains a misfit in the canon of glial neurobiology. We provide an update to seminal reviews in the field by conducting a scoping review of the post-2010 mature multiciliated ependymal cell literature. We delineate how recent findings have either called into question or substantiated classical views of the ependymal cell. Beyond this synthesis, we document the basic methodologies and study characteristics used to describe multiciliated ependymal cells since 1980. Our review serves as a comprehensive resource for future investigations of mature multiciliated ependymal cells.

Cerebrospinal Fluid Dynamics Analysis Using Time-Spatial Labeling Inversion Pulse (Time-SLIP) Magnetic Resonance Imaging in Mice

Background/Objectives: Abnormalities in cerebrospinal fluid (CSF) dynamics cause diverse conditions, such as hydrocephalus, but the underlying mechanism is still unknown. Methods to study CSF dynamics in small animals have not been established due to the lack of an evaluation system. Therefore, the purpose of this research study is to establish the time-spatial labeling inversion pulse (Time-SLIP) MRI technique for the evaluation of CSF dynamics in mice. Methods: We performed the Time-SLIP technique on 10 wild-type mice and 20 Tiptoe-walking Yoshimura (TWY) mice, a mouse model of ossification of the posterior longitudinal ligament (OPLL). We defined the stir distance as the distance of CSF stirring and calculated the mean ± standard deviation. The intraclass correlation coefficient of intraobserver reliability was also calculated. Furthermore, in TWY mice, the correlation coefficient between stir distance and canal stenosis ratio (CSR) was calculated. Results: The stir distance was significantly lower in TWY mice at 12 weeks and 17 weeks of age (1.20 ± 0.16, 1.21 ± 0.06, and 1.21 ± 0.15 mm at 12 weeks and 1.32 ± 0.21, 1.28 ± 0.23, and 1.38 ± 0.31 mm at 17 weeks for examiners A, B, and C). The intrarater reliability of the three examiners was excellent (>0.90) and there was a strongly negative correlation between stir distance and CSR in TWY mice (>-0.80). Conclusions: In this study, we established the Time-SLIP technique in experimental mice. This technique allows for a better understanding of CSF dynamics in small laboratory animals.

Ventricular-subventricular zone stem cell niche adaptations in a mouse model of post-infectious hydrocephalus

Congenital post-infectious hydrocephalus (PIH) is a condition characterized by enlargement of the ventricular system, consequently imposing a burden on the associated stem cell niche, the ventricular-subventricular zone (V-SVZ). To investigate how the V-SVZ adapts in PIH, we developed a mouse model of influenza virus-induced PIH based on direct intracerebroventricular injection of mouse-adapted influenza virus at two distinct time points: embryonic day 16 (E16), when stem cells line the ventricle, and postnatal day 4 (P4), when an ependymal monolayer covers the ventricle surface and stem cells retain only a thin ventricle-contacting process. Global hydrocephalus with associated regions of astrogliosis along the lateral ventricle was found in 82% of the mice infected at P4. Increased ependymogenesis was observed at gliotic borders and throughout areas exhibiting intact ependyma based on tracking of newly divided cells. Additionally, in areas of intact ependyma, stem cell numbers were reduced; however, we found no significant reduction in new neurons reaching the olfactory bulb following onset of ventriculomegaly. At P4, injection of only the non-infectious viral component neuraminidase resulted in limited, region-specific ventriculomegaly due to absence of cell-to-cell transmission. In contrast, at E16 intracerebroventricular injection of influenza virus resulted in death at birth due to hypoxia and multiorgan hemorrhage, suggesting an age-dependent advantage in neonates, while the viral component neuraminidase resulted in minimal, or no, ventriculomegaly. In summary, we tracked acute adaptations of the V-SVZ stem cell niche following onset of ventriculomegaly and describe developmental changes that help mitigate the severity of congenital PIH.

Impact of aquaporin-4 and CD11c + microglia in the development of ependymal cells in the aqueduct: inferences to hydrocephalus

AQP4 is expressed in the endfeet membranes of subpial and perivascular astrocytes and in the ependymal cells that line the ventricular system. The sporadic appearance of obstructive congenital hydrocephalus (OCHC) has been observed in the offspring of AQP4-/- mice (KO) due to stenosis of Silvio's aqueduct. Here, we explore whether the lack of AQP4 expression leads to abnormal development of ependymal cells in the aqueduct of mice. We compared periaqueductal samples from wild-type and KO mice. The microarray-based transcriptome analysis reflected a large number of genes with differential expression (809). Gene sets (GS) associated with ependymal development, ciliary function and the immune system were specially modified qPCR confirmed reduced expression in the KO mice genes: (i) coding for transcription factors for ependymal differentiation (Rfx4 and FoxJ1), (ii) involved in the constitution of the central apparatus of the axoneme (Spag16 and Hydin), (iii) associated with ciliary assembly (Cfap43, Cfap69 and Ccdc170), and (iv) involved in intercellular junction complexes of the ependyma (Cdhr4). By contrast, genes such as Spp1, Gpnmb, Itgax, and Cd68, associated with a Cd11c-positive microglial population, were overexpressed in the KO mice. Electron microscopy and Immunofluorescence of vimentin and γ-tubulin revealed a disorganized ependyma in the KO mice, with changes in the intercellular complex union, unevenly orientated cilia, and variations in the planar cell polarity of the apical membrane. These structural alterations translate into reduced cilia beat frequency, which might alter cerebrospinal fluid movement. The presence of CD11c + microglia cells in the periaqueductal zone of mice during the first postnatal week is a novel finding. In AQP4-/- mice, these cells remain present around the aqueduct for an extended period, showing peak expression at P11. We propose that these cells play an important role in the normal development of the ependyma and that their overexpression in KO mice is crucial to reduce ependyma abnormalities that could otherwise contribute to the development of obstructive hydrocephalus.

Ciliogenesis defects after neurulation impact brain development and neuronal activity in larval zebrafish

Cilia are slender, hair-like structures extending from cell surfaces and playing essential roles in diverse physiological processes. Within the nervous system, primary cilia contribute to signaling and sensory perception, while motile cilia facilitate cerebrospinal fluid flow. Here, we investigated the impact of ciliary loss on neural circuit development using a zebrafish line displaying ciliogenesis defects. We found that cilia defects after neurulation affect neurogenesis and brain morphology, especially in the cerebellum, and lead to altered gene expression profiles. Using whole brain calcium imaging, we measured reduced light-evoked and spontaneous neuronal activity in all brain regions. By shedding light on the intricate role of cilia in neural circuit formation and function in the zebrafish, our work highlights their evolutionary conserved role in the brain and sets the stage for future analysis of ciliopathy models.

The role of glial cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has traditionally been considered a neuron-centric disease. This view is now outdated, with increasing recognition of cell autonomous and non-cell autonomous contributions of central and peripheral nervous system glia to ALS pathomechanisms. With glial research rapidly accelerating, we comprehensively interrogate the roles of astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells and satellite glia in nervous system physiology and ALS-associated pathology. Moreover, we highlight the inter-glial, glial-neuronal and inter-system polylogue which constitutes the healthy nervous system and destabilises in disease. We also propose classification based on function for complex glial reactive phenotypes and discuss the pre-requisite for integrative modelling to advance translation. Given the paucity of life-enhancing therapies currently available for ALS patients, we discuss the promising potential of harnessing glia in driving ALS therapeutic discovery.

Paediatric hydrocephalus

Hydrocephalus is classically considered as a failure of cerebrospinal fluid (CSF) homeostasis that results in the active expansion of the cerebral ventricles. Infants with hydrocephalus can present with progressive increases in head circumference whereas older children often present with signs and symptoms of elevated intracranial pressure. Congenital hydrocephalus is present at or near birth and some cases have been linked to gene mutations that disrupt brain morphogenesis and alter the biomechanics of the CSF-brain interface. Acquired hydrocephalus can develop at any time after birth, is often caused by central nervous system infection or haemorrhage and has been associated with blockage of CSF pathways and inflammation-dependent dysregulation of CSF secretion and clearance. Treatments for hydrocephalus mainly include surgical CSF shunting or endoscopic third ventriculostomy with or without choroid plexus cauterization. In utero treatment of fetal hydrocephalus is possible via surgical closure of associated neural tube defects. Long-term outcomes for children with hydrocephalus vary widely and depend on intrinsic (genetic) and extrinsic factors. Advances in genomics, brain imaging and other technologies are beginning to refine the definition of hydrocephalus, increase precision of prognostication and identify nonsurgical treatment strategies.

Cerebral furin deficiency causes hydrocephalus in mice

Furin is a pro-protein convertase that moves between the trans-Golgi network and cell surface in the secretory pathway. We have previously reported that cerebral overexpression of furin promotes cognitive functions in mice. Here, by generating the brain-specific furin conditional knockout (cKO) mice, we investigated the role of furin in brain development. We found that furin deficiency caused early death and growth retardation. Magnetic resonance imaging showed severe hydrocephalus. In the brain of furin cKO mice, impaired ciliogenesis and the derangement of microtubule structures appeared along with the down-regulated expression of RAB28, a ciliary vesicle protein. In line with the widespread neuronal loss, ependymal cell layers were damaged. Further proteomics analysis revealed that cell adhesion molecules including astrocyte-enriched ITGB8 and BCAR1 were altered in furin cKO mice; and astrocyte overgrowth was accompanied by the reduced expression of SOX9, indicating a disrupted differentiation into ependymal cells. Together, whereas alteration of RAB28 expression correlated with the role of vesicle trafficking in ciliogenesis, dysfunctional astrocytes might be involved in ependymal damage contributing to hydrocephalus in furin cKO mice. The structural and molecular alterations provided a clue for further studying the potential mechanisms of furin.

Loss of Katnal2 leads to ependymal ciliary hyperfunction and autism-related phenotypes in mice

Autism spectrum disorders (ASD) frequently accompany macrocephaly, which often involves hydrocephalic enlargement of brain ventricles. Katnal2 is a microtubule-regulatory protein strongly linked to ASD, but it remains unclear whether Katnal2 knockout (KO) in mice leads to microtubule- and ASD-related molecular, synaptic, brain, and behavioral phenotypes. We found that Katnal2-KO mice display ASD-like social communication deficits and age-dependent progressive ventricular enlargements. The latter involves increased length and beating frequency of motile cilia on ependymal cells lining ventricles. Katnal2-KO hippocampal neurons surrounded by enlarged lateral ventricles show progressive synaptic deficits that correlate with ASD-like transcriptomic changes involving synaptic gene down-regulation. Importantly, early postnatal Katnal2 re-expression prevents ciliary, ventricular, and behavioral phenotypes in Katnal2-KO adults, suggesting a causal relationship and a potential treatment. Therefore, Katnal2 negatively regulates ependymal ciliary function and its deletion in mice leads to ependymal ciliary hyperfunction and hydrocephalus accompanying ASD-related behavioral, synaptic, and transcriptomic changes.

Dmd mdx mice have defective oligodendrogenesis, delayed myelin compaction and persistent hypomyelination

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, resulting in the loss of dystrophin, a large cytosolic protein that links the cytoskeleton to extracellular matrix receptors in skeletal muscle. Aside from progressive muscle damage, many patients with DMD also have neurological deficits of unknown etiology. To investigate potential mechanisms for DMD neurological deficits, we assessed postnatal oligodendrogenesis and myelination in the Dmdmdx mouse model. In the ventricular-subventricular zone (V-SVZ) stem cell niche, we found that oligodendrocyte progenitor cell (OPC) production was deficient, with reduced OPC densities and proliferation, despite a normal stem cell niche organization. In the Dmdmdx corpus callosum, a large white matter tract adjacent to the V-SVZ, we also observed reduced OPC proliferation and fewer oligodendrocytes. Transmission electron microscopy further revealed significantly thinner myelin, an increased number of abnormal myelin structures and delayed myelin compaction, with hypomyelination persisting into adulthood. Our findings reveal alterations in oligodendrocyte development and myelination that support the hypothesis that changes in diffusion tensor imaging seen in patients with DMD reflect developmental changes in myelin architecture.

Design of a Stem Cell-Based Therapy for Ependymal Repair in Hydrocephalus Associated With Germinal Matrix Hemorrhages

BACKGROUND

In preterm birth germinal matrix hemorrhages (GMHs) and the consequent posthemorrhagic hydrocephalus (PHH), the neuroepithelium/ependyma development is disrupted. This work is aimed to explore the possibilities of ependymal repair in GMH/PHH using a combination of neural stem cells, ependymal progenitors (EpPs), and mesenchymal stem cells.

METHODS

GMH/PHH was induced in 4-day-old mice using collagenase, blood, or blood serum injections. PHH severity was characterized 2 weeks later using magnetic resonance, immunofluorescence, and protein expression quantification with mass spectrometry. Ependymal restoration and wall regeneration after stem cell treatments were tested in vivo and in an ex vivo experimental approach using ventricular walls from mice developing moderate and severe GMH/PHH. The effect of the GMH environment on EpP differentiation was tested in vitro. Two-tailed Student t or Wilcoxon-Mann-Whitney U test was used to find differences between the treated and nontreated groups. ANOVA and Kruskal-Wallis tests were used to compare >2 groups with post hoc Tukey and Dunn multiple comparison tests, respectively.

RESULTS

PHH severity was correlated with the extension of GMH and ependymal disruption (means, 88.22% severe versus 19.4% moderate). GMH/PHH hindered the survival rates of the transplanted neural stem cells/EpPs. New multiciliated ependymal cells could be generated from transplanted neural stem cells and more efficiently from EpPs (15% mean increase). Blood and TNFα (tumor necrosis factor alpha) negatively affected ciliogenesis in cells committed to ependyma differentiation (expressing Foxj1 [forkhead box J1] transcription factor). Pretreatment with mesenchymal stem cells improved the survival rates of EpPs and ependymal differentiation while reducing the edematous (means, 18% to 0.5% decrease in severe edema) and inflammatory conditions in the explants. The effectiveness of this therapeutical strategy was corroborated in vivo (means, 29% to 0% in severe edema).

CONCLUSIONS

In GMH/PHH, the ependyma can be restored and edema decreased from either neural stem cell or EpP transplantation in vitro and in vivo. Mesenchymal stem cell pretreatment improved the success of the ependymal restoration.

History of research concerning the ependyma: a view from inside the human brain

The history of research concerning ependymal cells is reviewed. Cilia were identified along the surface of the cerebral ventricles c1835. Numerous anatomical and histopathological studies in the late 1800's showed irregularities in the ependymal surface that were thought to be indicative of specific pathologies such as syphilis; this was subsequently disproven. The evolution of thoughts about functions of cilia, the possible role of ependyma in the brain-cerebrospinal fluid barrier, and the relationship of ependyma to the subventricular zone germinal cells is discussed. How advances in light and electron microscopy and cell culture contributed to our understanding of the ependyma is described. Discoveries of the supraependymal serotoninergic axon network and supraependymal macrophages are recounted. Finally, the consequences of loss of ependymal cells from different regions of the central nervous system are considered.

Leveraging Biomaterial Platforms to Study Aging-Related Neural and Muscular Degeneration

Aging is a complex multifactorial process that results in tissue function impairment across the whole organism. One of the common consequences of this process is the loss of muscle mass and the associated decline in muscle function, known as sarcopenia. Aging also presents with an increased risk of developing other pathological conditions such as neurodegeneration. Muscular and neuronal degeneration cause mobility issues and cognitive impairment, hence having a major impact on the quality of life of the older population. The development of novel therapies that can ameliorate the effects of aging is currently hindered by our limited knowledge of the underlying mechanisms and the use of models that fail to recapitulate the structure and composition of the cell microenvironment. The emergence of bioengineering techniques based on the use of biomimetic materials and biofabrication methods has opened the possibility of generating 3D models of muscular and nervous tissues that better mimic the native extracellular matrix. These platforms are particularly advantageous for drug testing and mechanistic studies. In this review, we discuss the developments made in the creation of 3D models of aging-related neuronal and muscular degeneration and we provide a perspective on the future directions for the field.

Formation and function of multiciliated cells

In vertebrates, multiciliated cells (MCCs) are terminally differentiated cells that line the airway tracts, brain ventricles, and reproductive ducts. Each MCC contains dozens to hundreds of motile cilia that beat in a synchronized manner to drive fluid flow across epithelia, the dysfunction of which is associated with a group of human diseases referred to as motile ciliopathies, such as primary cilia dyskinesia. Given the dynamic and complex process of multiciliogenesis, the biological events essential for forming multiple motile cilia are comparatively unelucidated. Thanks to advancements in genetic tools, omics technologies, and structural biology, significant progress has been achieved in the past decade in understanding the molecular mechanism underlying the regulation of multiple motile cilia formation. In this review, we discuss recent studies with ex vivo culture MCC and animal models, summarize current knowledge of multiciliogenesis, and particularly highlight recent advances and their implications.

Adenosine Stimulates Beating of Neonatal Brain-Derived Cilia through Adenosine A2B Receptor on the Cilia and Activation of Protein Kinase A Pathway

Motile cilia in the ependymal cells that line the brain ventricles play pivotal roles in cerebrospinal fluid (CSF) flow in well-defined directions. However, the substances and pathways which regulate their beating have not been well studied. Here, we used primary cultured cells derived from neonatal mouse brain that possess motile cilia and found that adenosine (ADO) stimulates ciliary beating by increasing the ciliary beat frequency (CBF) in a concentration-dependent manner, with the ED50 value being 5 µM. Ciliary beating stimulated by ADO was inhibited by A2B receptor (A2BR) antagonist MRS1754 without any inhibition by antagonists of other ADO receptor subtypes. The expression of A2BR on the cilia was also confirmed by immunofluorescence. The values of CBF were also increased by forskolin, which is an activator of adenylate cyclase, whereas they were not further increased by the addition of ADO. Furthermore, ciliary beating was not stimulated by ADO in the presence of a protein kinase A (PKA) inhibitors. These results altogether suggest that ADO stimulates ciliary beating through A2BR on the cilia, and activation of PKA.

Recommendations for reproducibility of cerebrospinal fluid extracellular vesicle studies

Cerebrospinal fluid (CSF) is a clear, transparent fluid derived from blood plasma that protects the brain and spinal cord against mechanical shock, provides buoyancy, clears metabolic waste and transports extracellular components to remote sites in the brain. Given its contact with the brain and the spinal cord, CSF is the most informative biofluid for studies of the central nervous system (CNS). In addition to other components, CSF contains extracellular vesicles (EVs) that carry bioactive cargoes (e.g., lipids, nucleic acids, proteins), and that can have biological functions within and beyond the CNS. Thus, CSF EVs likely serve as both mediators of and contributors to communication in the CNS. Accordingly, their potential as biomarkers for CNS diseases has stimulated much excitement for and attention to CSF EV research. However, studies on CSF EVs present unique challenges relative to EV studies in other biofluids, including the invasive nature of CSF collection, limited CSF volumes and the low numbers of EVs in CSF as compared to plasma. Here, the objectives of the International Society for Extracellular Vesicles CSF Task Force are to promote the reproducibility of CSF EV studies by providing current reporting and best practices, and recommendations and reporting guidelines, for CSF EV studies. To accomplish this, we created and distributed a world-wide survey to ISEV members to assess methods considered 'best practices' for CSF EVs, then performed a detailed literature review for CSF EV publications that was used to curate methods and resources. Based on responses to the survey and curated information from publications, the CSF Task Force herein provides recommendations and reporting guidelines to promote the reproducibility of CSF EV studies in seven domains: (i) CSF Collection, Processing, and Storage; (ii) CSF EV Separation/Concentration; (iii) CSF EV Size and Number Measurements; (iv) CSF EV Protein Studies; (v) CSF EV RNA Studies; (vi) CSF EV Omics Studies and (vii) CSF EV Functional Studies.

Convergent differentiation of multiciliated cells

Multiciliated cells (MCCs) are epithelial cells that control body fluid flow and contribute to the clearance of pathogenic microbes and other particles from the airways, egg transport in oviducts, and circulation of cerebrospinal fluid in the central nervous system. Although MCCs have shared functions to control fluid flow via coordinated motility of multiple ciliary structures, they are found in multiple mammalian tissues originating from distinct germ layers and differentiate via distinct developmental pathways. To understand the similarities and differences of MCCs in multiple tissues, we investigated single-cell transcriptome data of nasal epithelial cells, bronchial tubes, fallopian tubes, and ependymal cells in the subventricular zone from humans and mice by cross-species data integration. Expression of cilia-associated genes was indistinguishable between these MCCs, although cell populations had unique properties by the species and tissue, demonstrating that they share the same final differentiation status for ciliary functions. We further analyzed the final differentiation step of MCCs from their distinctive progenitors and confirmed their convergent gene set expression for ciliogenesis at the final step. These results may provide new insight into understanding ciliogenesis during the developmental process.

Homemade: building the structure of the neurogenic niche

Neural stem/progenitor cells live in an intricate cellular environment, the neurogenic niche, which supports their function and enables neurogenesis. The niche is made of a diversity of cell types, including neurons, glia and the vasculature, which are able to signal to and are structurally organised around neural stem/progenitor cells. While the focus has been on how individual cell types signal to and influence the behaviour of neural stem/progenitor cells, very little is actually known on how the niche is assembled during development from multiple cellular origins, and on the role of the resulting topology on these cells. This review proposes to draw a state-of-the art picture of this emerging field of research, with the aim to expose our knowledge on niche architecture and formation from different animal models (mouse, zebrafish and fruit fly). We will span its multiple aspects, from the existence and importance of local, adhesive interactions to the potential emergence of larger-scale topological properties through the careful assembly of diverse cellular and acellular components.

Adult neurogenesis research in China

Neural stem cells are multipotent stem cells that generate functional newborn neurons through a process called neurogenesis. Neurogenesis in the adult brain is tightly regulated and plays a pivotal role in the maintenance of brain function. Disruption of adult neurogenesis impairs cognitive function and is correlated with numerous neurologic disorders. Deciphering the mechanisms underlying adult neurogenesis not only advances our understanding of how the brain functions, but also offers new insight into neurologic diseases and potentially contributes to the development of effective treatments. The field of adult neurogenesis is experiencing significant growth in China. Chinese researchers have demonstrated a multitude of factors governing adult neurogenesis and revealed the underlying mechanisms of and correlations between adult neurogenesis and neurologic disorders. Here, we provide an overview of recent advancements in the field of adult neurogenesis due to Chinese scientists.

CWH43 Variants Are Associated With Disease Risk and Clinical Phenotypic Measures in Patients With Normal Pressure Hydrocephalus

Background and Objectives

Variants in the CWH43 gene have been associated with normal pressure hydrocephalus (NPH). We aimed to replicate these findings, identify additional CWH43 variants, and further define the clinical phenotype associated with CWH43 variants.

Methods

We determined the prevalence of CWH43 variants by whole-genome sequencing (WGS) in 94 patients with NPH. The odds of having CWH43 variant carriers develop NPH were determined through comparison with 532 Mayo Clinic Biobank volunteers without a history of NPH. For patients with NPH, we documented the head circumference, prevalence of disproportionate enlargement of subarachnoid hydrocephalus (DESH), microvascular changes on MRI quantified by the Fazekas scale, and ambulatory response to ventriculoperitoneal shunting.

Results

We identified rare (MAF <0.05) coding CWH43 variants in 15 patients with NPH. Ten patients (Leu533Terfs, n = 8; Lys696Asnfs, n = 2) harbored previously reported predicted loss-of-function variants, and combined burden analysis confirmed risk association with NPH (OR 2.60, 95% CI 1.12-6.03, p = 0.027). Additional missense variations observed included Ile292Thr (n = 2), Ala469Ser (n = 2), and Ala626Val (n = 1). Though not quite statistically significant, in single variable analysis, the odds of having a head circumference above the 75th percentile of normal controls was more than 5 times higher for CWH43 variant carriers compared with that for noncarriers (unadjusted OR 5.67, 95% CI 0.96-108.55, p = 0.057), and this was consistent after adjusting for sex and height (OR 5.42, 95% CI 0.87-106.37, p = 0.073). DESH was present in 56.7% of noncarriers and only 21.4% of carriers (p = 0.016), while sulcal trapping was also more prevalent among noncarriers (67.2% vs 35.7%, p = 0.030). All 8 of the 15 variant carriers who underwent ventriculoperitoneal shunting at our institution experienced ambulatory improvements.

Discussion

CWH43 variants are frequent in patients with NPH. Predicted loss-of-function mutations were the most common; we identified missense mutations that require further study. Our findings suggest that congenital factors, rather than malabsorption or vascular dysfunction, are primary contributors to the CWH43-related NPH clinical syndrome.

Organic cation transporter 2 contributes to SSRI antidepressant efficacy by controlling tryptophan availability in the brain

Selective serotonin reuptake inhibitors (SSRI) are common first-line treatments for major depression. However, a significant number of depressed patients do not respond adequately to these pharmacological treatments. In the present preclinical study, we demonstrate that organic cation transporter 2 (OCT2), an atypical monoamine transporter, contributes to the effects of SSRI by regulating the routing of the essential amino acid tryptophan to the brain. Contrarily to wild-type mice, OCT2-invalidated mice failed to respond to prolonged fluoxetine treatment in a chronic depression model induced by corticosterone exposure recapitulating core symptoms of depression, i.e., anhedonia, social withdrawal, anxiety, and memory impairment. After corticosterone and fluoxetine treatment, the levels of tryptophan and its metabolites serotonin and kynurenine were decreased in the brain of OCT2 mutant mice compared to wild-type mice and reciprocally tryptophan and kynurenine levels were increased in mutants' plasma. OCT2 was detected by immunofluorescence in several structures at the blood-cerebrospinal fluid (CSF) or brain-CSF interface. Tryptophan supplementation during fluoxetine treatment increased brain concentrations of tryptophan and, more discreetly, of 5-HT in wild-type and OCT2 mutant mice. Importantly, tryptophan supplementation improved the sensitivity to fluoxetine treatment of OCT2 mutant mice, impacting chiefly anhedonia and short-term memory. Western blot analysis showed that glycogen synthase kinase-3β (GSK3β) and mammalian/mechanistic target of rapamycin (mTOR) intracellular signaling was impaired in OCT2 mutant mice brain after corticosterone and fluoxetine treatment and, conversely, tryptophan supplementation recruited selectively the mTOR protein complex 2. This study provides the first evidence of the physiological relevance of OCT2-mediated tryptophan transport, and its biological consequences on serotonin homeostasis in the brain and SSRI efficacy.

Pathogenic role of autoantibodies at the ependyma in autoimmune disorders of the central nervous system

Ependymal cells make up the epithelial monolayer that lines the brain ventricles and the spinal cord central canal that are filled with cerebrospinal fluid. The ependyma has several functions, including regulating solute exchange between the cerebrospinal fluid and parenchyma, controlling microcirculation of cerebrospinal fluid via coordinated ciliary beating, and acting as a partial barrier. Dysregulation of these functions can lead to waste clearance impairment, cerebrospinal fluid accumulation, hydrocephalus, and more. A role for ependymal cells in a variety of neurological disorders has been proposed, including in neuromyelitis optica and multiple sclerosis, two autoimmune demyelinating diseases of the central nervous system, where periventricular damage is common. What is not known is the mechanisms behind how ependymal cells become dysregulated in these diseases. In neuromyelitis optica, it is well established that autoantibodies directed against Aquaporin-4 are drivers of disease, and it has been shown recently that these autoantibodies can drive ependymal cell dysregulation. We propose a similar mechanism is at play in multiple sclerosis, where autoantibodies targeting a glial cell protein called GlialCAM on ependymal cells are contributing to disease. GlialCAM shares high molecular similarities with the Epstein-Barr virus (EBV) protein EBNA1. EBV has recently been shown to be necessary for multiple sclerosis initiation, yet how EBV mediates pathogenesis, especially in the periventricular area, remains elusive. In this perspective article, we discuss how ependymal cells could be targeted by antibody-related autoimmune mechanisms in autoimmune demyelinating diseases and how this is implicated in ventricular/periventricular pathology.

Amyloid-β slows cilia movement along the ventricle, impairs fluid flow, and exacerbates its neurotoxicity in explant culture

Alzheimer's disease (AD) is characterized by extensive and selective death of neurons and deterioration of synapses and circuits in the brain. The Aβ1-42 concentration is higher in an AD brain than in cognitively normal elderly individuals, and Aβ1-42 exhibits neurotoxicity. Brain-derived Aβ is transported into the cerebrospinal fluid (CSF), and CSF flow is driven in part by the beating of cilia and CSF secretion into ventricles. Ventricles are lined with ependyma whose apical surface is covered with motile cilia. Herein, we constructed an experimental system to measure the movement of ependymal cilia and examined the effects of Aβ1-42 to the beating of cilia and neurons. The circadian rhythm of the beating frequency of ependymal cilia was detected using brain wall explant-cultures containing ependymal cilia and neurons; the beating frequency was high at midday and low at midnight. Aβ1-42 decreased the peak frequency of ciliary beating at midday and slightly increased it at midnight. Aβ1-42 exhibited neurotoxicity to neurons on the non-ciliated side of the explant culture, while the neurotoxicity was less evident in neurons on the ciliated side. The neurotoxic effect of Aβ1-42 was diminished when 1 mPa of shear stress was generated using a flow chamber system that mimicked the flow by cilia. These results indicate that Aβ1-42 affects the circadian rhythm of ciliary beating, decreases the medium flow by the cilia-beating, and enhances the neurotoxic action of Aβ1-42 in the brain explant culture.

Cell-type specific molecular signatures of aging revealed in a brain-wide transcriptomic cell-type atlas

Biological aging can be defined as a gradual loss of homeostasis across various aspects of molecular and cellular function. Aging is a complex and dynamic process which influences distinct cell types in a myriad of ways. The cellular architecture of the mammalian brain is heterogeneous and diverse, making it challenging to identify precise areas and cell types of the brain that are more susceptible to aging than others. Here, we present a high-resolution single-cell RNA sequencing dataset containing ~1.2 million high-quality single-cell transcriptomic profiles of brain cells from young adult and aged mice across both sexes, including areas spanning the forebrain, midbrain, and hindbrain. We find age-associated gene expression signatures across nearly all 130+ neuronal and non-neuronal cell subclasses we identified. We detect the greatest gene expression changes in non-neuronal cell types, suggesting that different cell types in the brain vary in their susceptibility to aging. We identify specific, age-enriched clusters within specific glial, vascular, and immune cell types from both cortical and subcortical regions of the brain, and specific gene expression changes associated with cell senescence, inflammation, decrease in new myelination, and decreased vasculature integrity. We also identify genes with expression changes across multiple cell subclasses, pointing to certain mechanisms of aging that may occur across wide regions or broad cell types of the brain. Finally, we discover the greatest gene expression changes in cell types localized to the third ventricle of the hypothalamus, including tanycytes, ependymal cells, and Tbx3+ neurons found in the arcuate nucleus that are part of the neuronal circuits regulating food intake and energy homeostasis. These findings suggest that the area surrounding the third ventricle in the hypothalamus may be a hub for aging in the mouse brain. Overall, we reveal a dynamic landscape of cell-type-specific transcriptomic changes in the brain associated with normal aging that will serve as a foundation for the investigation of functional changes in the aging process and the interaction of aging and diseases.

Mechanical loading of the ventricular wall as a spatial indicator for periventricular white matter degeneration

Progressive white matter degeneration in periventricular and deep white matter regions appears as white matter hyperintensities (WMH) on MRI scans. To date, periventricular WMHs are often associated with vascular dysfunction. Here, we demonstrate that ventricular inflation resulting from cerebral atrophy and hemodynamic pulsation with every heartbeat leads to a mechanical loading state of periventricular tissues that significantly affects the ventricular wall. Specifically, we present a physics-based modeling approach that provides a rationale for ependymal cell involvement in periventricular WMH formation. Building on eight previously created 2D finite element brain models, we introduce novel mechanomarkers for ependymal cell loading and geometric measures that characterize lateral ventricular shape. We show that our novel mechanomarkers, such as maximum ependymal cell deformations and maximum curvature of the ventricular wall, spatially overlap with periventricular WMH locations and are sensitive predictors for WMH formation. We also explore the role of the septum pellucidum in mitigating mechanical loading of the ventricular wall by constraining the radial expansion of the lateral ventricles during loading. Our models consistently show that ependymal cells are stretched thin only in the horns of the ventricles irrespective of ventricular shape. We therefore pose that periventricular WMH etiology is strongly linked to the deterioration of the over-stretched ventricular wall resulting in CSF leakage into periventricular white matter. Subsequent secondary damage mechanisms, including vascular degeneration, exacerbate lesion formation and lead to progressive growth into deep white matter regions.

Pretreatment and Posttreatment Factors Associated with Shunt-Dependent Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis

BACKGROUND

Hydrocephalus is a common complication after aneurysmal subarachnoid hemorrhage (aSAH). This study aimed to evaluate novel preoperative and postoperative risk factors for shunt-dependent hydrocephalus (SDHC) after aSAH via a systematic review and meta-analysis.

METHODS

A systematic search was conducted using PubMed and Embase databases for studies pertaining to aSAH and SDHC. Articles were assessed by meta-analysis if the number of risk factors for SDHC was reported by >4 studies and could be extracted separately for patients who did or did not develop SDHC.

RESULTS

Thirty-seven studies were included, comprising 12,667 patients with aSAH (SDHC 2214 vs. non-SDHC 10,453). In a primary analysis of 15 novel potential risk factors, 8 were identified to be significantly associated with increased prevalence of SDHC after aSAH, including high World Federation of Neurological Surgeons grades (odds ratio [OR], 2.43), hypertension (OR, 1.33), anterior cerebral artery (OR, 1.36), middle cerebral artery (OR, 0.65), and vertebrobasilar artery (2.21) involvement, decompressive craniectomy (OR, 3.27), delayed cerebral ischemia (OR, 1.65), and intracerebral hematoma (OR, 3.91).

CONCLUSIONS

Several new factors associated with increased odds of developing SDHC after aSAH were found to be significant. By providing evidence-based risk factors for shunt dependency, we describe an identifiable list of preoperative and postoperative prognosticators that may influence how surgeons recognize, treat, and manage patients with aSAH at high risk for developing SDHC.

Sickness behaviour and depression: An updated model of peripheral-central immunity interactions

Current research into mood disorders indicates that circulating immune mediators participating in the pathophysiology of chronic somatic disorders have potent influences on brain function. This paradigm has brought to the fore the use of anti-inflammatory therapies as adjunctive to standard antidepressant therapy to improve treatment efficacy, particularly in subjects that do not respond to standard medication. Such new practice requires biomarkers to tailor these new therapies to those most likely to benefit but also validated mechanisms of action describing the interaction between peripheral immunity and brain function to optimize target intervention. These mechanisms are generally studied in preclinical models that try to recapitulate the human disease, MDD, through peripherally induced sickness behaviour. In this proposal paper, after an appraisal of the data in rodent models and their adherence to the data in clinical cohorts, we put forward a modified model of periphery-brain interactions that goes beyond the currently established view of microglia cells as the drivers of depression. Instead, we suggest that, for most patients with mild levels of peripheral inflammation, brain barriers are the primary actors in the pathophysiology of the disease and in treatment resistance. We then highlight data gaps in this proposal and suggest novel lines of research.

Therapeutic strategies to recover ependymal barrier after inflammatory damage: relevance for recovering neurogenesis during development

The epithelium covering the surfaces of the cerebral ventricular system is known as the ependyma, and is essential for maintaining the physical and functional integrity of the central nervous system. Additionally, the ependyma plays an essential role in neurogenesis, neuroinflammatory modulation and neurodegenerative diseases. Ependyma barrier is severely affected by perinatal hemorrhages and infections that cross the blood brain barrier. The recovery and regeneration of ependyma after damage are key to stabilizing neuroinflammatory and neurodegenerative processes that are critical during early postnatal ages. Unfortunately, there are no effective therapies to regenerate this tissue in human patients. Here, the roles of the ependymal barrier in the context of neurogenesis and homeostasis are reviewed, and future research lines for development of actual therapeutic strategies are discussed.

Ependyma in Neurodegenerative Diseases, Radiation-Induced Brain Injury and as a Therapeutic Target for Neurotrophic Factors

The neuron loss caused by the progressive damage to the nervous system is proposed to be the main pathogenesis of neurodegenerative diseases. Ependyma is a layer of ciliated ependymal cells that participates in the formation of the brain-cerebrospinal fluid barrier (BCB). It functions to promotes the circulation of cerebrospinal fluid (CSF) and the material exchange between CSF and brain interstitial fluid. Radiation-induced brain injury (RIBI) shows obvious impairments of the blood-brain barrier (BBB). In the neuroinflammatory processes after acute brain injury, a large amount of complement proteins and infiltrated immune cells are circulated in the CSF to resist brain damage and promote substance exchange through the BCB. However, as the protective barrier lining the brain ventricles, the ependyma is extremely vulnerable to cytotoxic and cytolytic immune responses. When the ependyma is damaged, the integrity of BCB is destroyed, and the CSF flow and material exchange is affected, leading to brain microenvironment imbalance, which plays a vital role in the pathogenesis of neurodegenerative diseases. Epidermal growth factor (EGF) and other neurotrophic factors promote the differentiation and maturation of ependymal cells to maintain the integrity of the ependyma and the activity of ependymal cilia, and may have therapeutic potential in restoring the homeostasis of the brain microenvironment after RIBI or during the pathogenesis of neurodegenerative diseases.

Detection of galanin receptors in the spinal cord in experimental autoimmune encephalomyelitis

AIMS

The neuropeptide galanin is a widely distributed neurotransmitter/neuromodulator that regulates a variety of physiological processes and also participates in the regulation of stress responses. The aims of the present study were to investigate the expression of galanin receptors (GalR1, GalR2, GalR3) in the spinal cords in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE) using qPCR analysis and to determine GalR1 cellular localization (oligodendrocytes, microglia, astrocytes, ependymal cells, and endothelial cells in the capillaries) by immunohistochemistry.

METHODS

Twelve samples from the EAE group and 14 samples from the control group were analyzed. Spinal cords samples were obtained at the peak of the EAE disease.

RESULTS

The GalR1 mRNA level was significantly decreased in the EAE mice compared with the controls (P=0.016), whereas the mRNA levels of GalR2 and GalR3 were not significantly different for the EAE and the control mice. No significant correlations were found between the severity of the EAE disease and the mRNA levels of GalR1, GalR2 and GalR3. Immunochemical detection of the GalR1 revealed its expression in the ependymal and endothelial cells. Additionally, a weak GalR1 immunoreactivity was occasionally detected in the oligodendrocytes.

CONCLUSION

This study provides additional evidence of galanin involvement in EAE pathophysiology, but this has to be further investigated.

New aspects for the brain in Hartnup disease based on mining of high-resolution cellular mRNA expression data for SLC6A19

Hartnup disease is an autosomal recessive, metabolic disorder caused by mutations of the neutral amino acid transporter, SLC6A19/B0AT1. Reduced absorption in the intestine and kidney results in deficiencies in neutral amino acids and their down-stream metabolites, including niacin, associated with skin lesions and neurological symptoms. The effects on the nervous system such as ataxia have been related to systemic deficiencies of tryptophan (and other neutral amino acids) as no expression of the B0AT1 transporter was found in the brain. In the intestine, SLC6A19 cooperates with ACE2 which has received major attention as the cellular receptor for SARS-CoV-2. When transcriptomics data for ACE2 and its partner proteins were examined, a previously unrecognized expression of Slc6a19 mRNA in the ependymal cells of the mouse brain was encountered that is set into the context of neurological manifestations of Hartnup disease with this communication. A novel role for SLC6A19/B0AT1 in amino acid transport from CSF into ependymal cells is proposed and a role of niacin in ependymal cells highlighted.

Far from home: the role of glial mRNA localization in synaptic plasticity

Neurons and glia are highly polarized cells, whose distal cytoplasmic functional subdomains require specific proteins. Neurons have axonal and dendritic cytoplasmic extensions containing synapses whose plasticity is regulated efficiently by mRNA transport and localized translation. The principles behind these mechanisms are equally attractive for explaining rapid local regulation of distal glial cytoplasmic projections, independent of their cell nucleus. However, in contrast to neurons, mRNA localization has received little experimental attention in glia. Nevertheless, there are many functionally diverse glial subtypes containing extensive networks of long cytoplasmic projections with likely localized regulation that influence neurons and their synapses. Moreover, glia have many other neuron-like properties, including electrical activity, secretion of gliotransmitters and calcium signaling, influencing, for example, synaptic transmission, plasticity and axon pruning. Here, we review previous studies concerning glial transcripts with important roles in influencing synaptic plasticity, focusing on a few cases involving localized translation. We discuss a variety of important questions about mRNA transport and localized translation in glia that remain to be addressed, using cutting-edge tools already available for neurons.