Apolipoprotein E deficiency enhances the antigen-presenting capacity of Schwann cells

Molecular Characterization of Nodose Ganglia Development Reveals a Novel Population of Phox2b+ Glial Progenitors in Mice

The vagal ganglia, comprised of the superior (jugular) and inferior (nodose) ganglia of the vagus nerve, receive somatosensory information from the head and neck or viscerosensory information from the inner organs, respectively. Developmentally, the cranial neural crest gives rise to all vagal glial cells and to neurons of the jugular ganglia, while the epibranchial placode gives rise to neurons of the nodose ganglia. Crest-derived nodose glial progenitors can additionally generate autonomic neurons in the peripheral nervous system, but how these progenitors generate neurons is unknown. Here, we found that some Sox10+ neural crest-derived cells in, and surrounding, the nodose ganglion transiently expressed Phox2b, a master regulator of autonomic nervous system development, during early embryonic life. Our genetic lineage-tracing analysis in mice of either sex revealed that despite their common developmental origin and extreme spatial proximity, a substantial proportion of glial cells in the nodose, but not in the neighboring jugular ganglia, have a history of Phox2b expression. We used single-cell RNA-sequencing to demonstrate that these progenitors give rise to all major glial subtypes in the nodose ganglia, including Schwann cells, satellite glia, and glial precursors, and mapped their spatial distribution by in situ hybridization. Lastly, integration analysis revealed transcriptomic similarities between nodose and dorsal root ganglia glial subtypes and revealed immature nodose glial subtypes. Our work demonstrates that these crest-derived nodose glial progenitors transiently express Phox2b, give rise to the entire complement of nodose glial cells, and display a transcriptional program that may underlie their bipotent nature.

Human repair-related Schwann cells adopt functions of antigen-presenting cells in vitro

The plastic potential of Schwann cells (SCs) is increasingly recognized to play a role after nerve injury and in diseases of the peripheral nervous system. Reports on the interaction between immune cells and SCs indicate their involvement in inflammatory processes. However, the immunocompetence of human SCs has been primarily deduced from neuropathies, but whether after nerve injury SCs directly regulate an adaptive immune response is unknown. Here, we performed comprehensive analysis of immunomodulatory capacities of human repair-related SCs (hrSCs), which recapitulate SC response to nerve injury in vitro. We used our well-established culture model of primary hrSCs from human peripheral nerves and analyzed the transcriptome, secretome, and cell surface proteins for pathways and markers relevant in innate and adaptive immunity, performed phagocytosis assays, and monitored T-cell subset activation in allogeneic co-cultures. Our findings show that hrSCs are phagocytic, which is in line with high MHCII expression. Furthermore, hrSCs express co-regulatory proteins, such as CD40, CD80, B7H3, CD58, CD86, and HVEM, release a plethora of chemoattractants, matrix remodeling proteins and pro- as well as anti-inflammatory cytokines, and upregulate the T-cell inhibiting PD-L1 molecule upon pro-inflammatory stimulation with IFNγ. In contrast to monocytes, hrSC alone are not sufficient to trigger allogenic CD4⁺ and CD8⁺ T-cells, but limit number and activation status of exogenously activated T-cells. This study demonstrates that hrSCs possess features and functions typical for professional antigen-presenting cells in vitro, and suggest a new role of these cells as negative regulators of T-cell immunity during nerve regeneration.

Immunomodulation by Schwann cells in disease

Schwann cells are the principal glial cells of the peripheral nervous system which maintain neuronal homeostasis. Schwann cells support peripheral nerve functions and play a critical role in many pathological processes including injury-induced nerve repair, neurodegenerative diseases, infections, neuropathic pain and cancer. Schwann cells are implicated in a wide range of diseases due, in part, to their ability to interact and modulate immune cells. We discuss the accumulating examples of how Schwann cell regulation of the immune system initiates and facilitates the progression of various diseases. Furthermore, we highlight how Schwann cells may orchestrate an immunosuppressive tumor microenvironment by polarizing and modulating the activity of the dendritic cells.

The Origins and Vulnerabilities of Two Transmissible Cancers in Tasmanian Devils

Transmissible cancers are clonal lineages that spread through populations via contagious cancer cells. Although rare in nature, two facial tumor clones affect Tasmanian devils. Here we perform comparative genetic and functional characterization of these lineages. The two cancers have similar patterns of mutation and show no evidence of exposure to exogenous mutagens or viruses. Genes encoding PDGF receptors have copy number gains and are present on extrachromosomal double minutes. Drug screening indicates causative roles for receptor tyrosine kinases and sensitivity to inhibitors of DNA repair. Y chromosome loss from a male clone infecting a female host suggests immunoediting. These results imply that Tasmanian devils may have inherent susceptibility to transmissible cancers and present a suite of therapeutic compounds for use in conservation.

Modeling the Pathogenesis of Charcot-Marie-Tooth Disease Type 1A Using Patient-Specific iPSCs

Charcot-Marie-Tooth disease type 1A (CMT1A), one of the most frequent inherited peripheral neuropathies, is associated with PMP22 gene duplication. Previous studies of CMT1A mainly relied on rodent models, and it is not yet clear how PMP22 overexpression leads to the phenotype in patients. Here, we generated the human induced pluripotent stem cell (hiPSC) lines from two CMT1A patients as an in vitro cell model. We found that, unlike the normal control cells, CMT1A hiPSCs rarely generated Schwann cells through neural crest stem cells (NCSCs). Instead, CMT1A NCSCs produced numerous endoneurial fibroblast-like cells in the Schwann cell differentiation system, and similar results were obtained in a PMP22-overexpressing iPSC model. Therefore, despite the demyelination-remyelination and/or dysmyelination theory for CMT1A pathogenesis, developmental disabilities of Schwann cells may be considered as an underlying cause of CMT1A. Our results may have important implications for the uncovering of the underlying mechanism and the development of a promising therapeutic strategy for CMT1A neuropathy.

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Modeling CMT1A disease with PMP22 duplication using hiPSC-derived NCSCs

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PMP22 duplication may lead to Schwann cell developmental defect of NCSCs

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PMP22-overexpressing NCSCs recapitulate the phenotype of CMT1A NCSCs

Molecules involved in the crosstalk between immune- and peripheral nerve Schwann cells

Schwann cells are the myelinating glial cells of the peripheral nervous system and establish myelin sheaths on large caliber axons in order to accelerate their electrical signal propagation. Apart from this well described function, these cells revealed to exhibit a high degree of differentiation plasticity as they were shown to re- and dedifferentiate upon injury and disease as well as to actively participate in regenerative- and inflammatory processes. This review focuses on the crosstalk between glial- and immune cells observed in many peripheral nerve pathologies and summarizes functional evidences of molecules, regulators and factors involved in this process. We summarize data on Schwann cell's role presenting antigens, on interactions with the complement system, on Schwann cell surface molecules/receptors and on secreted factors involved in immune cell interactions or para-/autocrine signaling events, thus strengthening the view for a broader (patho) physiological role of this cell lineage.

Interleukin-17 impedes Schwann cell-mediated myelination

Background

Pro-inflammatory cytokines are known to have deleterious effects on Schwann cells (SCs). Interleukin 17 (IL-17) is a potent pro-inflammatory cytokine that exhibits relevant effects during inflammation in the peripheral nervous system (PNS), and IL-17-secreting cells have been reported within the endoneurium in proximity to the SCs.

Methods

Here, we analyzed the effects of IL-17 on myelination and the immunological properties of SCs. Dorsal root ganglia (DRG) co-cultures containing neurons and SCs from BL6 mice were used to define the impact of IL-17 on myelination and on SC differentiation; primary SCs were analyzed for RNA and protein expression to define the putative immunological alignment of the SCs.

Results

SCs were found to functionally express the IL-17 receptors A and B. In DRG cultures, stimulation with IL-17 resulted in reduced myelin synthesis, while pro-myelin gene expression was suppressed at the mRNA level. Neuronal outgrowth and SC viability, as well as structural myelin formation, remained unaffected. Co-cultures exhibited SC-relevant pro-inflammatory markers, such as matrix metalloproteinase 9 and SCs significantly increased the expression of the major histocompatibility complex (MHC) I and exhibited a slight, nonsignificant increase in expression of MHCII, and a transporter associated with antigen presentation (TAP) II molecules relevant for antigen processing and presentation.

Conclusions

IL-17 may act as a myelin-suppressive mediator in the peripheral nerve, directly propagating SC-mediated demyelination, paralleled by an inflammatory alignment of the SCs. Further analyses are warranted to elucidate the role of IL-17 during inflammation in the PNS in vivo, which could be useful in the development of target therapies.

A proteome map of primary cultured rat Schwann cells

Background

Schwann cells (SCs) are the principal glial cells of the peripheral nervous system with a wide range of biological functions. SCs play a key role in peripheral nerve regeneration and are involved in several hereditary peripheral neuropathies. The objective of this study was to gain new insight into the whole protein composition of SCs.

Results

Two-dimensional liquid chromatography coupled with tandem mass spectrometry (2D LC-MS/MS) was performed to identify the protein expressions in primary cultured SCs of rats. We identified a total of 1,232 proteins, which were categorized into 20 functional classes. We also used quantitative real time RT-PCR and Western blot analysis to validate some of proteomics-identified proteins.

Conclusion

We showed for the first time the proteome map of SCs. Our data could serve as a reference library to provide basic information for understanding SC biology.

Cross-talk between apolipoprotein E and cytokines

Apolipoprotein E (apoE) is a multifunctional glycosylated protein characterized by its wide tissue distribution. Despite its importance in lipid transport and atherosclerosis pathogenesis, apoE is associated with neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson disease, and autoimmune disorders such as multiple sclerosis and psoriasis. Among others, the role of apoE in modulating inflammation and oxidation is crucial in elucidating the risk factors of the above diseases since the function of apoE is closely linked with both proinflammatory and antiinflammatory cytokines. Moreover, apoE modulates inflammatory and immune responses in an isoform-dependent manner. Correspondingly, inflammatory cytokines can either upregulate or downregulate the production of apoE in various tissue types. However, studies on the interactions between apoE and cytokines occasionally yield conflicting results, highlighting the complex roles of apoE and cytokines in various disorders. The present paper summarizes the current knowledge about the cross-talk between apoE and cytokines, with emphasis on the effects of apoE on the Th1/Th2 balance.

Apolipoprotein E isoform-specific effects on cytokine and nitric oxide production from mouse Schwann cells after inflammatory stimulation

Previously, we reported that apolipoprotein E (apoE) deficiency increased the susceptibility to experimental autoimmune neuritis (EAN), an inflammatory autoimmune disorder of the peripheral nervous system (PNS) and an animal model for human Guillain-Barré syndrome (GBS) by affecting the antigen-presenting function of Schwann cells (SCs) via influence upon IL-6 production. To further elucidate the role of apoE in inflammation of the PNS, here we studied the effect of different isoforms of apoE on SCs in response to inflammatory stimulation. SCs from apoE2, E3 and E4 transgenic (Tg) and wild type (WT) mice were cultured, and their responses to stimulation by lipopolysaccharide (LPS) plus interferon (IFN)-γ were compared. Upon stimulation, the morphology of cultured SCs changed. Pronounced production of interleukin (IL)-6 and IL-10 within SCs, and of IL-6 and nitric oxide (NO) in the supernatants were found in an isoform-dependent manner (apoE3>apoE2≈apoE4). Further results indicated that both nuclear factor (NF) κB and Akt signaling pathways were involved in the process by the same isoform-dependent pattern. However, the expression of co-stimulatory molecules as showing the antigen-presenting capacity of SCs was not significantly different among these groups. In conclusion, SCs respond to inflammatory insults accompanied by increased productions of IL-6, IL-10 and NO in an apoE-isoform-dependent manner. SCs from apoE2 and apoE4 Tg mice seem to bear some dysfunction in producing cytokines (IL-6 and IL-10) and NO as compared with their apoE3 counterparts, probably resulting from their insufficiency to suppress the activation of NFκB and Akt pathways. Our findings may help to understand the role of different isoforms of apoE in inflammatory disorders of the PNS.

APOE ε3 attenuates experimental autoimmune neuritis by modulating T cell, macrophage and Schwann cell functions

Human apolipoprotein E (apoE) is a 34.2kDa glycosylated protein with three isoforms (apoE2, apoE3 and apoE4). Experimental autoimmune neuritis (EAN), an animal model for human Guillain-Barré syndrome, is an immune-mediated experimental disorder of the peripheral nervous system (PNS). Increased susceptibility to EAN in apoE deficient mice has been previously found. To elucidate the isoform-dependent effects of apoE on EAN, we used human apoE2, E3 and E4 transgenic mice (Tg) immunized with P0 peptide 180-199, as well as T cell proliferation test, macrophage and Schwann cell (SC) cultures to investigate the effects of apoE isoforms on the functions of T cells, macrophages and SCs both under naïve conditions and in EAN. Clinical signs of EAN were most severe in wild type (WT) C57BL/6 mice and apoE4 Tg mice, followed by apoE2 Tg mice and apoE3 Tg mice (WT≈E4>E2>E3, p<0.01). At the nadir of EAN, spleen weight and lymphocyte proliferation were in line with the clinical severity of the disease. Proliferation tests of purified T cells from naive mice stimulated with phytohemagglutinin or interleukin-12 showed isoform-specific differences (WT≈E4>E3≈E2, p<0.01). Macrophages from both naïve and EAN mice produced nitric oxide upon inflammatory stimulation with lipopolysaccharide, interferon-γ, polyinosinic:polycytidylic acid or combinations thereof, in an isoform-dependent manner (WT≈E4>E2>E3, p<0.01). Generalized intervention with 1400W, a specific inducible nitric oxide synthase inhibitor, significantly suppressed the clinical course of EAN in apoE2, E3 and E4 Tg mice and in WT mice. During the recovery stage of disease, the highest expression of CD178 (FasL) on SCs was found in apoE3 Tg mice. Our data support an isoform-dependent effect of apoE on EAN. This might be due to the isoform-specific effects of apoE on functions of T cells, macrophages and SCs, which contribute to the distinct clinical courses of EAN. ApoE3 might not only inhibit the onset and suppress the clinical severity of EAN, but also enhance the termination of immune responses in the PNS.

ApoD, a glia-derived apolipoprotein, is required for peripheral nerve functional integrity and a timely response to injury

Glial cells are a key element to the process of axonal regeneration, either promoting or inhibiting axonal growth. The study of glial derived factors induced by injury is important to understand the processes that allow or preclude regeneration, and can explain why the PNS has a remarkable ability to regenerate, while the CNS does not. In this work we focus on Apolipoprotein D (ApoD), a Lipocalin expressed by glial cells in the PNS and CNS. ApoD expression is strongly induced upon PNS injury, but its role has not been elucidated. Here we show that ApoD is required for: (1) the maintenance of peripheral nerve function and tissue homeostasis with age, and (2) an adequate and timely response to injury. We study crushed sciatic nerves at two ages using ApoD knock‐out and transgenic mice over‐expressing human ApoD. The lack of ApoD decreases motor nerve conduction velocity and the thickness of myelin sheath in intact nerves. Following injury, we analyze the functional recovery, the cellular processes, and the protein and mRNA expression profiles of a group of injury‐induced genes. ApoD helps to recover locomotor function after injury, promoting myelin clearance, and regulating the extent of angiogenesis and the number of macrophages recruited to the injury site. Axon regeneration and remyelination are delayed without ApoD and stimulated by excess ApoD. The mRNA and protein expression profiles reveal that ApoD is functionally connected in an age‐dependent manner to specific molecular programs triggered by injury. © 2010 Wiley‐Liss, Inc.

The role of apolipoprotein E in Guillain-Barré syndrome and experimental autoimmune neuritis

Apolipoprotein E (apoE) is a 34.2 kDa glycosylated protein characterized by its wide tissue distribution and multiple functions. ApoE has been widely studied in lipid metabolism, cardiocerebrovascular diseases, and neurodegenerative diseases like Alzheimer's disease and mild cognitive impairment, and so forth. Recently, a growing body of evidence has pointed to nonlipid related properties of apoE, including suppression of T cell proliferation, regulation of macrophage function, facilitation of lipid antigen presentation by CD1 molecules to natural killer T (NKT) cells, and modulation of inflammation and oxidation. By these properties, apoE impacts physiology and pathophysiology at multiple levels. The present paper summarizes updated studies on the immunoregulatory function of apoE, with special focus on isoform-specific effects of apoE on Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN).

Expression of antigen processing and presenting molecules by Schwann cells in inflammatory neuropathies

Schwann cells are the myelinating glia cells of the peripheral nervous system (PNS) and can become targets of an autoimmune response in inflammatory neuropathies like the Guillain-Barré syndrome (GBS). Professional antigen presenting cells (APCs) are known to promote autoimmune responses in target tissues by presenting self-antigens. Other cell types could participate in local autoimmune responses by acting as nonprofessional APCs. Using a combined approach of immunocytochemistry, immunohistochemistry, and flow cytometry analysis we demonstrate that human Schwann cells express the antigen processing and presenting machinery (APM) in vitro and in vivo. Moreover, cultured human Schwann cells increase the expression of proteasome subunit delta (Y), antigen peptide transporter TAP2, and HLA Class I and HLA Class II complexes in an inflammatory environment. In correlation with this observation, Schwann cells in sural nerve biopsies from GBS patients show increased expression of antigen processing and presenting molecules. Furthermore, cultured human Schwann cells can proteolytically digest fluorescently-labeled nonmammalian antigen ovalbumin. Taken together, our data suggest antigen processing and presentation as a possible function of Schwann cells that may contribute to (auto)immune responses within peripheral nerves.