Neural Crest Cells Contribute an Astrocyte-like Glial Population to the Spleen

Heterophyllin B alleviates cognitive disorders in APP/PS1 model mice via the spleen-gut microbiota-brain axis

BACKGROUND

Accumulating evidence implicates both the brain-spleen axis and the gut microbiota-brain axis in Alzheimer's disease (AD) pathogenesis. While our previous work demonstrated heterophyllin B (HB) rectifies splenic Th1/Th2 imbalance and ameliorates cognitive deficits in Aβ1-42-induced AD mice, its potential modulation of the vagus nerve-spleen circuit remains unexplored.

METHODS

Using 8-month-old male APP/PS1 mice with/without splenic denervation (SD), we systematically investigated HB's therapeutic mechanisms via the spleen-gut microbiota-brain axis. Cognitive function was assessed through novel object recognition (ORT) and object location memory (OLT) tests. Immunofluorescence (IF) and enzyme-linked immunosorbent assay (ELISA) were employed to analyze Aβ plaques, phosphorylated tau (p-Tau) levels, and associated neuroinflammatory responses. Flow cytometry was utilized to examine the subtypes of splenic lymphocytes. Hematoxylin and eosin (H&E) staining, along with immunohistochemical (IHC) experiments, was conducted to evaluate the protective effects of HB on the intestinal barrier. Gut microbiota composition was analyzed using 16S rRNA sequencing.

RESULTS

HB administration significantly improved cognitive performance (ORT discrimination index: +28.7 %; OLT discrimination index: +26.6 %), reduced brain and serum Aβ1-42 and p-Tau levels, downregulated the Th1/Th2 ratio in the spleen, and alleviated intestinal permeability and neuroinflammation, which were abolished in SD APP/PS1 mice. Gut microbiota shifts showed HB-induced enrichment of cognition-associated Dubosiella and Muribaculaceae, with concurrent suppression of pathogenic Lachnospiraceae_NK4A136 and ASF356.

CONCLUSION

This study provides first evidence that HB ameliorates AD pathology through vagus nerve-dependent regulation of the spleen-gut microbiota-brain axis, establishing its multimodal therapeutic potential for neural-immune-gut circuit modulation in neurodegenerative diseases.

Peripheral nervous system glia in support of metabolic tissue functions

The peripheral nervous system (PNS) relays information between organs and tissues and the brain and spine to maintain homeostasis, regulate tissue functions, and respond to interoceptive and exteroceptive signals. Glial cells perform support roles to maintain nerve function, plasticity, and survival. The glia of the central nervous system (CNS) are well characterized, but PNS glia (PNSG) populations, particularly tissue-specific subtypes, are underexplored. PNSG are found in large nerves (such as the sciatic), the ganglia, and the tissues themselves, and can crosstalk with a range of cell types in addition to neurons. PNSG are also subject to phenotypic changes in response to signals from their local tissue environment, including metabolic changes. These topics and the importance of PNSG in metabolically active tissues, such as adipose, muscle, heart, and lymphatic tissues, are outlined in this review.

Astrocytes express aberrant immunoglobulins as putative gatekeeper of astrocytes to neuronal progenitor conversion

Using multi-omics analyses including RNAseq, RT-PCR, RACE-PCR, and shotgun proteomic with enrichment strategies, we demonstrated that newborn rat astrocytes produce neural immunoglobulin constant and variable heavy chains as well as light chains. However, their edification is different from the ones found in B cells and they resemble aberrant immunoglobulins observed in several cancers. Moreover, the complete enzymatic V(D)J recombination complex has also been identified in astrocytes. In addition, the constant heavy chain is also present in adult rat astrocytes, whereas in primary astrocytes from human fetus we identified constant and variable kappa chains as well as the substitution lambda chains known to be involved in pre-B cells. To gather insights into the function of these neural IgGs, CRISPR-Cas9 of IgG2B constant heavy chain encoding gene (Igh6), IgG2B overexpression, proximal labeling of rat astrocytes IgG2B and targets identification through 2D gels were performed. In Igh6 KO astrocytes, overrepresentation of factors involved in hematopoietic cells, neural stem cells, and the regulation of neuritogenesis have been identified. Moreover, overexpression of IgG2B in astrocytes induces the CRTC1-CREB-BDNF signaling pathway known to be involved in gliogenesis, whereas Igh6 KO triggers the BMP/YAP1/TEAD3 pathway activated in astrocytes dedifferentiation into neural progenitors. Proximal labeling experiments revealed that IgG2B is N-glycosylated by the OST complex, addressed to vesicle membranes containing the ATPase complex, and behaves partially like CD98hc through its association with LAT1. These experiments also suggest that proximal IgG2B-LAT1 interaction occurs concomitantly with MACO-1 and C2CD2L, at the heart of a potentially novel cell signaling platform. Finally, we demonstrated that these chains are synthesized individually and associated to recognize specific targets. Indeed, intermediate filaments Eif4a2 and Pdia6 involved in astrocyte fate constitute targets for these neural IgGs. Taken together, we hypothese that neural aberrant IgG chains may act as gatekeepers of astrocytes' fate.

Shared reproductive disruption, not neural crest or tameness, explains the domestication syndrome

Altered neural crest cell (NCC) behaviour is an increasingly cited explanation for the domestication syndrome in animals. However, recent authors have questioned this explanation, while others cast doubt on whether domestication syndrome even exists. Here, we review published literature concerning this syndrome and the NCC hypothesis, together with recent critiques of both. We synthesize these contributions and propose a novel interpretation, arguing shared trait changes under ancient domestication resulted primarily from shared disruption of wild reproductive regimes. We detail four primary selective pathways for 'reproductive disruption' under domestication and contrast these succinct and demonstrable mechanisms with cryptic genetic associations posited by the NCC hypothesis. In support of our perspective, we illustrate numerous important ways in which NCCs contribute to vertebrate reproductive phenotypes, and argue it is not surprising that features derived from these cells would be coincidentally altered under major selective regime changes, as occur in domestication. We then illustrate several pertinent examples of Darwin's 'unconscious selection' in action, and compare applied selection and phenotypic responses in each case. Lastly, we explore the ramifications of reproductive disruption for wider evolutionary discourse, including links to wild 'self-domestication' and 'island effect', and discuss outstanding questions.

Evolutionarily conserved concepts in glial cell biology

The evolutionary conservation of glial cells has been appreciated since Ramon y Cajal and Del Rio Hortega first described the morphological features of cells in the nervous system. We now appreciate that glial cells have essential roles throughout life in most nervous systems. The field of glial cell biology has grown exponentially in the last ten years. This new wealth of knowledge has been aided by seminal findings in non-mammalian model systems. Ultimately, such concepts help us to understand glia in mammalian nervous systems. Rather than summarizing the field of glial biology, I will first briefly introduce glia in non-mammalian models systems. Then, highlight seminal findings across the glial field that utilized non-mammalian model systems to advance our understanding of the mammalian nervous system. Finally, I will call attention to some recent findings that introduce new questions about glial cell biology that will be investigated for years to come.

Development and In Vitro Differentiation of Schwann Cells

Schwann cells are glial cells of the peripheral nervous system. They exist in several subtypes and perform a variety of functions in nerves. Their derivation and culture in vitro are interesting for applications ranging from disease modeling to tissue engineering. Since primary human Schwann cells are challenging to obtain in large quantities, in vitro differentiation from other cell types presents an alternative. Here, we first review the current knowledge on the developmental signaling mechanisms that determine neural crest and Schwann cell differentiation in vivo. Next, an overview of studies on the in vitro differentiation of Schwann cells from multipotent stem cell sources is provided. The molecules frequently used in those protocols and their involvement in the relevant signaling pathways are put into context and discussed. Focusing on hiPSC- and hESC-based studies, different protocols are described and compared, regarding cell sources, differentiation methods, characterization of cells, and protocol efficiency. A brief insight into developments regarding the culture and differentiation of Schwann cells in 3D is given. In summary, this contribution provides an overview of the current resources and methods for the differentiation of Schwann cells, it supports the comparison and refinement of protocols and aids the choice of suitable methods for specific applications.

Identification of astroglia-like cardiac nexus glia that are critical regulators of cardiac development and function

Glial cells are essential for functionality of the nervous system. Growing evidence underscores the importance of astrocytes; however, analogous astroglia in peripheral organs are poorly understood. Using confocal time-lapse imaging, fate mapping, and mutant genesis in a zebrafish model, we identify a neural crest-derived glial cell, termed nexus glia, which utilizes Meteorin signaling via Jak/Stat3 to drive differentiation and regulate heart rate and rhythm. Nexus glia are labeled with gfap, glast, and glutamine synthetase, markers that typically denote astroglia cells. Further, analysis of single-cell sequencing datasets of human and murine hearts across ages reveals astrocyte-like cells, which we confirm through a multispecies approach. We show that cardiac nexus glia at the outflow tract are critical regulators of both the sympathetic and parasympathetic system. These data establish the crucial role of glia on cardiac homeostasis and provide a description of nexus glia in the PNS.

A Review on the Vagus Nerve and Autonomic Nervous System During Fetal Development: Searching for Critical Windows

The autonomic nervous system (ANS) is one of the main biological systems that regulates the body's physiology. Autonomic nervous system regulatory capacity begins before birth as the sympathetic and parasympathetic activity contributes significantly to the fetus' development. In particular, several studies have shown how vagus nerve is involved in many vital processes during fetal, perinatal, and postnatal life: from the regulation of inflammation through the anti-inflammatory cholinergic pathway, which may affect the functioning of each organ, to the production of hormones involved in bioenergetic metabolism. In addition, the vagus nerve has been recognized as the primary afferent pathway capable of transmitting information to the brain from every organ of the body. Therefore, this hypothesis paper aims to review the development of ANS during fetal and perinatal life, focusing particularly on the vagus nerve, to identify possible "critical windows" that could impact its maturation. These "critical windows" could help clinicians know when to monitor fetuses to effectively assess the developmental status of both ANS and specifically the vagus nerve. In addition, this paper will focus on which factors-i.e., fetal characteristics and behaviors, maternal lifestyle and pathologies, placental health and dysfunction, labor, incubator conditions, and drug exposure-may have an impact on the development of the vagus during the above-mentioned "critical window" and how. This analysis could help clinicians and stakeholders define precise guidelines for improving the management of fetuses and newborns, particularly to reduce the potential adverse environmental impacts on ANS development that may lead to persistent long-term consequences. Since the development of ANS and the vagus influence have been shown to be reflected in cardiac variability, this paper will rely in particular on studies using fetal heart rate variability (fHRV) to monitor the continued growth and health of both animal and human fetuses. In fact, fHRV is a non-invasive marker whose changes have been associated with ANS development, vagal modulation, systemic and neurological inflammatory reactions, and even fetal distress during labor.

Efferent synaptic transmission at the vestibular type II hair cell synapse

In the vestibular peripheral organs, type I and type II hair cells (HCs) transmit incoming signals via glutamatergic quantal transmission onto afferent nerve fibers. Additionally, type I HCs transmit via "non-quantal" transmission to calyx afferent fibers, by accumulation of glutamate and potassium in the synaptic cleft. Vestibular efferent inputs originating in the brainstem contact type II HCs and vestibular afferents. Here, synaptic inputs to type II HCs were characterized by using electrical and optogenetic stimulation of efferent fibers combined with in vitro whole cell patch-clamp recording from type II HCs in the rodent vestibular crista. Properties of efferent synaptic currents in type II HCs were similar to those found in cochlear HCs and mediated by activation of α9-containing nicotinic acetylcholine receptors (nAChRs) and small-conductance calcium-activated potassium (SK) channels. While efferents showed a low probability of release at low frequencies of stimulation, repetitive stimulation resulted in facilitation and increased probability of release. Notably, the membrane potential of type II HCs during optogenetic stimulation of efferents showed a strong hyperpolarization in response to single pulses and was further enhanced by repetitive stimulation. Such efferent-mediated inhibition of type II HCs can provide a mechanism to adjust the contribution of signals from type I and type II HCs to vestibular nerve fibers, with a shift of the response to be more like that of calyx-only afferents with faster non-quantal responses.NEW & NOTEWORTHY Type II vestibular hair cells (HCs) receive inputs from efferent neurons in the brain stem. We used in vitro optogenetic and electrical stimulation of vestibular efferent fibers to study their synaptic inputs to type II HCs. Stimulation of efferents inhibited type II HCs, similar to efferent effects on cochlear HCs. We propose that efferent inputs adjust the contribution of signals from type I and II HCs to vestibular nerve fibers.

B-lymphocyte-intrinsic and -extrinsic defects in secretory immunoglobulin A production in the neural crest-conditional deletion of endothelin receptor B model of Hirschsprung-associated enterocolitis

Hirschsprung disease (HSCR) is a common cause of intestinal obstruction in the newborn. Hirschsprung-associated enterocolitis (HAEC) is a significant and life-threatening complication of HSCR, affecting up to 60% of patients. Animal models of endothelin receptor B (EdnrB) mutation reliably model human HSCR and HAEC. We previously demonstrated intestinal dysbiosis and a gut-specific deficiency of B-lymphocyte-produced secretory IgA (sIgA), the primary effector molecule of mucosal immunity, in mice with homozygous neural crest cell-conditional deletion of EdnrB (EdnrB^NCC-/-). To determine mechanisms for sIgA deficiency, we examined intrinsic and extrinsic aspects of B-lymphocyte development and function. Expression of the endothelin axis components [endothelin-1 (ET-1), endothelin-3 (ET-3), endothelin receptor A (EdnrA), EdnrB] were determined over a developmental time course. B-lymphocyte survival and Ig production were assayed in vitro. Polymeric Ig receptor (pIgR)-mediated IgA transport into the intestinal lumen was interrogated. We found endothelin axis component (EdnrA, EdnrB, ET-1, ET-3) expression in developing extramedullary hematopoietic organs and that some splenic B lymphocytes express EdnrB. Splenic B lymphocytes from EdnrB^NCC-/- mice showed no intrinsic defect in survival vs. wild-type (WT) B lymphocytes. In vitro stimulation of splenic B lymphocytes demonstrated decreased IgA, IgG, and IgM production in EdnrB^NCC-/- vs. WT mice. Additionally, small intestinal pIgR was decreased ∼50% in EdnrB^NCC-/- mice. These results suggest an intrinsic B-lymphocyte defect in antibody production as well as an extrinsic defect in IgA transport in the EdnrB^NCC-/- model of HAEC. Our results are consistent with human HAEC observations of decreased luminal sIgA and mouse models of other inflammatory bowel diseases, in which decreased pIgR is seen in concert with a dysregulated microbiota. Finally, our results suggest targeting the dysbiotic microbiome and pIgR-mediated sIgA transport as potential therapeutic approaches in prevention and treatment of HAEC.-Medrano, G., Cailleux, F., Guan, P., Kuruvilla, K., Barlow-Anacker, A. J., Gosain, A. B-lymphocyte-intrinsic and -extrinsic defects in secretory immunoglobulinA production in the neural crest-conditional deletion of endothelin receptor B model of Hirschsprung-associated enterocolitis.

Cluster expansion of apolipoprotein D (ApoD) genes in teleost fishes

BACKGROUND

Gene and genome duplication play important roles in the evolution of gene function. Compared to individual duplicated genes, gene clusters attract particular attention considering their frequent associations with innovation and adaptation. Here, we report for the first time the expansion of the apolipoprotein D (ApoD) ligand-transporter genes in a cluster manner specific to teleost fishes.

RESULTS

Based on comparative genomic and transcriptomic analyses, protein 3D structure comparison, positive selection detection and breakpoints detection, the single ApoD gene in the ancestor expanded into two clusters following a dynamic evolutionary pattern in teleost fishes. Orthologous genes show conserved expression patterns, whereas lineage-specific duplicated genes show tissue-specific expression patterns and even evolve new gene expression profiles. Positive selection occurred in branches before and after gene duplication, especially for lineage-specific duplicated genes. Cluster analyses based on protein 3D structure comparisons, especially comparisons of the four loops at the opening side, show gene duplication-segregating patterns. Duplicated ApoD genes are predicted to be associated with forkhead transcription factors and MAPK genes. ApoD clusters are located next to the breakpoints of genome rearrangements.

CONCLUSIONS

Here, we report the expansion of ApoD genes specific to teleost fishes in a cluster manner for the first time. Neofunctionalization and subfunctionalization were observed at both the protein and expression levels after duplication. Evidence from different aspects-i.e., abnormal expression-induced disease in humans, fish-specific expansion, predicted associations with forkhead transcription factors and MAPK genes, specific expression patterns in tissues related to sexual selection and adaptation, duplicated genes under positive selection and their location next to the breakpoints of genome rearrangements-suggests the potentially advantageous roles of ApoD genes in teleost fishes. The cluster expansion of ApoD genes specific to teleost fishes provides thus an ideal evo-devo model for studying gene duplication, cluster maintenance and new gene function emergence.

Postnatal neural crest stem cells from hair follicle interact with nerve tissue in vitro and in vivo

Neural crest stem cells that located in the postnatal hair follicle (HF-NCSC) are considered a promising tool for treatment of nervous system diseases and injuries. It is well known that HF-NCSC can be used in the spinal cord and sciatic nerve reparation but their ability to restore brain structures is poorly studied. In this article we are investigating the interaction between HF-NCSC and a nerve tissue (embryonic and adult). We have found out that HF-NCSC isolated from adult mice grow and differentiate in accordance with the mouse embryo developmental stage when co-cultured with the embryonic nerve tissue. The HF-NCSC migration is slower in the late embryonic tissue co-culture system compared to the early one. This phenomenon is related to the motor function of the cells but not to their proliferation level. We have demonstrated that the embryonic nerve tissue maintains HF-NCSC an undifferentiated status, while an adult brain tissue inhibits the cell proliferation and activates the differentiation processes. Besides, HF-NCSC pre-differentiated into the neuronal direction shows a higher survival and migration rate after the transplantation into the adult brain tissue compared to the undifferentiated HF-NCSC. Thus, we have investigated the postnatal HF-NCSC response to the nerve tissue microenvironment to analyze their possible application to the brain repair processes.

Schwann cell precursors in health and disease

Schwann cell precursors (SCPs) are frequently regarded as neural crest-derived cells (NCDCs) found in contact with axons during nerve formation. Nevertheless, cells with SCPs properties can be found up to the adulthood. They are well characterized with regard to both gene expression profile and cellular behavior -for instance, proliferation, migratory capabilities and survival requirements-. They differ in origin regarding their anatomic location: even though most of them are derived from migratory NCCs, there is also contribution of the boundary cap neural crest cells (bNCCs) to the skin and other tissues. Many functions are known for SCPs in normal development, including nerve fasciculation and target innervation, arterial branching patterning and differentiation, and other morphogenetic processes. In addition, SCPs are now known to be a source of many neural (glia, endoneural fibroblasts, melanocytes, visceral neurons, and chromaffin cells) and non-neural-like (mesenchymal stromal cells, able e.g., to generate dentine-producing odontoblasts) cell types. Until now no reports of endoderm-like derivatives were reported so far. Interestingly, in the Schwann cell lineage only early SCPs are likely able to differentiate into melanocytes and bone marrow mesenchymal stromal cells. We have also herein discussed the literature regarding their role in repair as well as in disease mechanisms, such as in diverse cancers. Moreover, many caveats in our knowledge of SCPs biology are highlighted all through this article. Future research should expand more into the relevance of SCPs in pathologies and in other regenerative mechanisms which might bring new unexpected clinically-relevant knowledge.

Quo vadis: tracing the fate of neural crest cells

The neural crest is a transient structure in vertebrate embryos that produces migratory cells with an astonishing developmental potential. While neural crest fate maps have originally been established through interspecies transplantation assays, dye labeling, and retroviral infection, more recent methods rely on approaches involving transgenesis and genome editing. These technologies allowed the identification of minor neural crest-derived cell populations in tissues of non-neural crest origin. Furthermore, in vivo multipotency at the single cell level and stage-dependent fate acquisitions were demonstrated using genetic technologies. Finally, recent reports indicate that neural crest-derived cells become activated in response to injury to secrete factors supporting tissue repair. Thus, neural crest-derived cells apparently contribute to tissue formation and regeneration by cell autonomous and non-autonomous mechanisms.