The specificity of monoclonal antibody A2B5 to c-series gangliosides

Deciphering the Action of Neuraminidase in Glioblastoma Models

Glioblastoma (GBM) contains cancer stem cells (CSC) that are resistant to treatment. GBM CSC expresses glycolipids recognized by the A2B5 antibody. A2B5, induced by the enzyme ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyl transferase 3 (ST8Sia3), plays a crucial role in the proliferation, migration, clonogenicity and tumorigenesis of GBM CSC. Our aim was to characterize the resulting effects of neuraminidase that removes A2B5 in order to target GBM CSC. To this end, we set up a GBM organotypic slice model; quantified A2B5 expression by flow cytometry in U87-MG, U87-ST8Sia3 and GBM CSC lines, treated or not by neuraminidase; performed RNAseq and DNA methylation profiling; and analyzed the ganglioside expression by liquid chromatography-mass spectrometry in these cell lines, treated or not with neuraminidase. Results demonstrated that neuraminidase decreased A2B5 expression, tumor size and regrowth after surgical removal in the organotypic slice model but did not induce a distinct transcriptomic or epigenetic signature in GBM CSC lines. RNAseq analysis revealed that OLIG2, CHI3L1, TIMP3, TNFAIP2, and TNFAIP6 transcripts were significantly overexpressed in U87-ST8Sia3 compared to U87-MG. RT-qPCR confirmed these results and demonstrated that neuraminidase decreased gene expression in GBM CSC lines. Moreover, neuraminidase drastically reduced ganglioside expression in GBM CSC lines. Neuraminidase, by its pleiotropic action, is an attractive local treatment against GBM.

Ganglioside Microdomains on Cellular and Intracellular Membranes Regulate Neuronal Cell Fate Determination

Gangliosides are sialylated glycosphingolipids (GSLs) with essential but enigmatic functions in brain activities and neural stem cell (NSC) maintenance. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of NSC activity and differentiation. The primary localization of gangliosides is on cell-surface microdomains and the drastic dose and composition changes during neural differentiation strongly suggest that they are not only important as biomarkers, but also are involved in modulating NSC fate determination. Ganglioside GD3 is the predominant species in NSCs and GD3-synthase knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal. Since morphological changes during neurogenesis require a huge amount of energy, mitochondrial functions are vital for neurogenesis. We discovered that a mitochondrial fission protein, the dynamin-related protein-1 (Drp1), as a novel GD3-binding protein, and GD3 regulates mitochondrial dynamics. Furthermore, we discovered that GM1 ganglioside promotes neuronal differentiation by an epigenetic regulatory mechanism. Nuclear GM1 binds with acetylated histones on the promoters of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase) as well as on the NeuroD1 genes in differentiated neurons. In addition, epigenetic activation of the GalNAcT gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. GM1 is indeed localized in the nucleus where it can interact with transcriptionally active histones. Interestingly, GM1 could induce epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of nuclear receptor related 1 (Nurr1, also known as NR4A2), a dopaminergic neuron-associated transcription factor, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression. GM1 interacts with active chromatin via acetylated histones to recruit transcription factors at the nuclear periphery, resulting in changes in gene expression for neuronal differentiation. The significance is that multifunctional gangliosides modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides could regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains.

PRC2-dependent regulation of ganglioside expression during dedifferentiation contributes to the proliferation and migration of vascular smooth muscle cells

Phenotypic switching between contractile (differentiated state) and proliferative (dedifferentiated state) vascular smooth muscle cells (VSMCs) is a hallmark of vascular remodeling that contributes to atherosclerotic diseases. Gangliosides, a group of glycosphingolipids, have been detected in atherosclerotic lesions and are suspected to contribute to the disease process. However, the underlying mechanism, specifically with respect to their role in VSMC phenotype switching, is not clear. In this study, we sought to reveal the endogenous expression of gangliosides and their functional significance in VSMCs during atherosclerosis. We found that switching from the contractile to proliferative phenotype was accompanied by upregulation of a- and b-series gangliosides, which in turn, were regulated by polycomb repressor complex 2 (PRC2). Downregulation of ganglioside expression using an siRNA targeting ST3GAL5, which is required for the synthesis of a- and b-series gangliosides, attenuated the proliferation and migration of dedifferentiated VSMCs. Therefore, we concluded that the increased expression of a- and b-series gangliosides via PRC2 activity during dedifferentiation is involved in the proliferation and migration of VSMCs. Gangliosides may be an effective target in VSMCs for atherosclerosis prevention and treatment.

Comprehensive Analysis of Oligo/Polysialylglycoconjugates in Cancer Cell Lines

In cancer cells, cell-surface sialylation is altered, including a change in oligo/polysialic acid (oligo/polySia) structures. Since they are unique and rarely expressed in normal cells, oligo/polySia structures may serve as promising novel biomarkers and targets for therapies. For the diagnosis and treatment of the disease, a precise understanding of the oligo/polySia structures in cancer cells is necessary. In this study, flow cytometric analysis and gene expression datasets were obtained from sixteen different cancer cell lines. These datasets demonstrated the ability to predict glycan structures and their sialylation status. Our results also revealed that sialylation patterns are unique to each cancer cell line. Thus, we can suggest promising combinations of antibody and cancer cell for glycan prediction. However, the precise prediction of minor glycans need to be further explored.

A2B5 Expression in Central Nervous System and Gliomas

A2B5 IgM recognizes c-series gangliosides with three sialic acids. The aim of this review was to focus on A2B5 expression in the central nervous system and gliomas. In brain development, A2B5+ cells are recorded in areas containing multipotent neural stem cells (NSC). In adults, A2B5+ cells persist in neurogenic areas and in white matter where it identifies oligodendrocyte precursor cells (OPCs) but also cells with NSC properties. Although the expression of A2B5 has been widely studied in culture, where it characterizes bipotential glial progenitor cells, its expression in vivo is less characterized mainly because of technical issues. A new interest was given to the NSCs and OPCs since the discovery of cancer stem cells (CSC) in gliomas. Among other cell surface molecules, A2B5 has been identified as an accurate marker to identify glioma CSCs. We and others have shown that all types of gliomas express A2B5, and that only A2B5+ cells, and not A2B5- cells, can generate a tumor after orthotopic implantation in immunocompromised animals. Moreover, A2B5 epitope expression is positively correlated with stemness and tumor growth. This review highlights that A2B5 is an attractive target to tackle glioma CSCs, and a better characterization of its expression in the developing and adult CNS will benefit to a better understanding of gliomagenesis.

Galectins and Their Ligand Glycoconjugates in the Central Nervous System Under Physiological and Pathological Conditions

Galectins are β-galactoside-binding lectins consisting of 15 members in mammals. Galectin-1,-3,-4,-8, and -9 are predominantly expressed in the central nervous system (CNS) and regulate various physiological and pathological events. This review summarizes the current knowledge of the cellular expression and role of galectins in the CNS, and discusses their functions in neurite outgrowth, myelination, and neural stem/progenitor cell niches, as well as in ischemic/hypoxic/traumatic injuries and neurodegenerative diseases such as multiple sclerosis. Galectins are expressed in both neurons and glial cells. Galectin-1 is mainly expressed in motoneurons, whereas galectin-3-positive neurons are broadly distributed throughout the brain, especially in the hypothalamus, indicating its function in the regulation of homeostasis, stress response, and the endocrine/autonomic system. Astrocytes predominantly contain galectin-1, and galectin-3 and−9 are upregulated along with its activation. Activated, but not resting, microglia contain galectin-3, supporting its phagocytic activity. Galectin-1,−3, and -4 are characteristically expressed during oligodendrocyte differentiation. Galectin-3 from microglia promotes oligodendrocyte differentiation and myelination, while galectin-1 and axonal galectin-4 suppress its differentiation and myelination. Galectin-1- and- 3-positive cells are involved in neural stem cell niche formation in the subventricular zone and hippocampal dentate gyrus, and the migration of newly generated neurons and glial cells to the olfactory bulb or damaged lesions. In neurodegenerative diseases, galectin-1,-8, and -9 have neuroprotective and anti-inflammatory activities. Galectin-3 facilitates pro-inflammatory action; however, it also plays an important role during the recovery period. Several ligand glycoconjugates have been identified so far such as laminin, integrins, neural cell adhesion molecule L1, sulfatide, neuropilin-1/plexinA4 receptor complex, triggering receptor on myeloid cells 2, and T cell immunoglobulin and mucin domain. N-glycan branching on lymphocytes and oligodendroglial progenitors mediated by β1,6-N-acetylglucosaminyltransferase V (Mgat5/GnTV) influences galectin-binding, modulating inflammatory responses and remyelination in neurodegenerative diseases. De-sulfated galactosaminoglycans such as keratan sulfate are potential ligands for galectins, especially galectin-3, regulating neural regeneration. Galectins have multitudinous functions depending on cell type and context as well as post-translational modifications, including oxidization, phosphorylation, S-nitrosylation, and cleavage, but there should be certain rules in the expression patterns of galectins and their ligand glycoconjugates, possibly related to glucose metabolism in cells.

Myelination of regenerating optic nerve axons occurs in conjunction with an increase of the oligodendrocyte precursor cell population in the adult mice

Recently, regeneration of CNS tracts has been partially accomplished by strategies of intrinsic neuronal growth stimulation. However, restoration of function is dependent on proper myelination of regenerating axons. Previous work from our group (Goulart et al., 2018) has shown an increase in oligodendrocyte staining in the regenerating optic nerve, 2 weeks after crush, in animals that were submitted to conditional deletion of pten gene in retinal ganglion cells and intravitreal injection of zymosan + cAMP. Thus, in the present study we aimed to investigate the maturation of the oligodendroglial lineage and myelination during the regeneration of the optic nerve under the same conditions of our previous work. We showed that the combined treatment promoted an increase of myelinated fibers within the optic nerve, 12 weeks after lesion, as well as an increase in Sox10 positive cells. Early-OPCs, positive to A2B5, were also increased at 12 weeks, whereas O4 positive, late-OPCs, were increased from 2 until 12 weeks after crush. At 12 weeks after crush, the optic nerve of Regenerating group presented more CC1 positive oligodendrocytes and increased MRF positive myelinating oligodendrocytes, culminating in CTB traced regenerating axons superimposed to MBP staining, suggestive of myelination. Thus, our work showed that conditional deletion of pten gene in retinal ganglion cells and intravitreal inflammatory stimuli + cAMP stimulate full maturation of the olidodendroglial lineage, from OPC proliferation and differentiation to myelination of regenerating CNS axons.

Lipid-specific IgMs induce antiviral responses in the CNS: implications for progressive multifocal leukoencephalopathy in multiple sclerosis

Progressive multi-focal leukoencephalopathy (PML) is a potentially fatal encephalitis caused by JC polyomavirus (JCV). PML principally affects people with a compromised immune system, such as patients with multiple sclerosis (MS) receiving treatment with natalizumab. However, intrathecal synthesis of lipid-reactive IgM in MS patients is associated with a markedly lower incidence of natalizumab-associated PML compared to those without this antibody repertoire. Here we demonstrate that a subset of lipid-reactive human and murine IgMs induce a functional anti-viral response that inhibits replication of encephalitic Alpha and Orthobunyaviruses in multi-cellular central nervous system cultures. These lipid-specific IgMs trigger microglia to produce IFN-β in a cGAS-STING-dependent manner, which induces an IFN-α/β-receptor 1-dependent antiviral response in glia and neurons. These data identify lipid-reactive IgM as a mediator of anti-viral activity in the nervous system and provide a rational explanation why intrathecal synthesis of lipid-reactive IgM correlates with a reduced incidence of iatrogenic PML in MS.

Reduced sialylation triggers homeostatic synapse and neuronal loss in middle-aged mice

Sialic acid-binding Ig-like lectin (Siglec) receptors are linked to neurodegenerative processes, but the role of sialic acids in physiological aging is still not fully understood. We investigated the impact of reduced sialylation in the brain of mice heterozygous for the enzyme glucosamine-2-epimerase/N-acetylmannosamine kinase (GNE+/-) that is essential for sialic acid biosynthesis. We demonstrate that GNE+/- mice have hyposialylation in different brain regions, less synapses in the hippocampus and reduced microglial arborization already at 6 months followed by increased loss of neurons at 12 months. A transcriptomic analysis revealed no pro-inflammatory changes indicating an innate homeostatic immune process leading to the removal of synapses and neurons in GNE+/- mice during aging. Crossbreeding with complement C3-deficient mice rescued the earlier onset of neuronal and synaptic loss as well as the changes in microglial arborization. Thus, sialic acids of the glycocalyx contribute to brain homeostasis and act as a recognition system for the innate immune system in the brain.

Glycolipids Recognized by A2B5 Antibody Promote Proliferation, Migration, and Clonogenicity in Glioblastoma Cells

A2B5+ cells isolated from human glioblastomas exhibit cancer stem cell properties. The A2B5 epitope belongs to the sialoganglioside family and is synthetized by the ST8 alpha-N-acetyl-neuraminidase α-2,8-sialyltransferase 3 (ST8SIA3) enzyme. Glycolipids represent attractive targets for solid tumors; therefore, the aim of this study was to decipher A2B5 function in glioblastomas. To this end, we developed cell lines expressing various levels of A2B5 either by genetically manipulating ST8SIA3 or by using neuraminidase. The overexpression of ST8SIA3 in low-A2B5-expressing cells resulted in a dramatic increase of A2B5 immunoreactivity. ST8SIA3 overexpression increased cell proliferation, migration, and clonogenicity in vitro and tumor growth when cells were intracranially grafted. Conversely, lentiviral ST8SIA3 inactivation in low-A2B5-expressing cells resulted in reduced proliferation, migration, and clonogenicity in vitro and extended mouse survival. Furthermore, in the shST8SIA3 cells, we found an active apoptotic phenotype. In high-A2B5-expressing cancer stem cells, lentiviral delivery of shST8SIA3 stopped cell growth. Neuraminidase treatment, which modifies the A2B5 epitope, impaired cell survival, proliferation, self-renewal, and migration. Our findings prove the crucial role of the A2B5 epitope in the promotion of proliferation, migration, clonogenicity, and tumorigenesis, pointing at A2B5 as an attractive therapeutic target for glioblastomas.

The crosstalk between glycosphingolipids and neural stem cells

Until a few years ago, the majority of cell functions were envisioned as the result of protein and DNA activity. The cell membranes were considered as a mere structure of support and/or separation. In the last years, the function of cell membranes has, however, received more attention and their components of lipid nature have also been depicted as important cell mediators and the membrane organization was described as an important determinant for membrane-anchored proteins activity. In particular, because of their high diversity, glycosphingolipids offer a wide possibility of regulation. Specifically, the role of glycosphingolipids, in the fine-tuning of neuron activity, has recently received deep attention. For their pivotal role in vertebrate and mammals neural development, neural stem cells regulation is of main interest especially concerning their further functions in neurological pathology progression and treatment. Glycosphingolipids expression present a developmental regulation. In this view, glycosphingolipids can hold an important role in neural stem cells features because of their heterogeneity and their consequent capacity for eclectic interaction with other cell components.

Grey matter OPCs are less mature and less sensitive to IFNγ than white matter OPCs: consequences for remyelination

Multiple sclerosis (MS) is a chronic inflammatory disease characterized by the formation of demyelinated lesions in the central nervous system. At later stages of the disease repair in the form of remyelination often fails, which leads to axonal degeneration and neurological disability. For the regeneration of myelin, oligodendrocyte progenitor cells (OPCs) have to migrate, proliferate and differentiate into remyelinating oligodendrocytes. Remyelination occurs faster and is more extensive in grey matter (GM) lesions than in white matter (WM) lesions. Here, we examined differences in neonatal OPCs from GM (gmOPCs) and WM (wmOPCs), both intrinsically and in response to environmental (injury) signals. We show that gmOPCs are less mature than wmOPCs, both on morphological and on gene-expression level. Additionally, gmOPCs proliferate more and differentiate slower than wmOPCs. When exposed to astrocyte-secreted signals wmOPC, but not gmOPC, migration decreases. In addition, wmOPCs are more sensitive to the detrimental effects of IFNγ treatment on proliferation, differentiation, and process arborisation, which is potentiated by TNFα. Our results demonstrate that OPCs from GM and WM differ both intrinsically and in response to their environment, which may contribute to the difference in remyelination efficiency between GM and WM MS lesions.

Gangliosides in Nerve Cell Specification

The central nervous system is generated from progenitor cells that are recognized as neural stem cells (NSCs). NSCs are defined as undifferentiated neural cells that are characterized by the capacity for self-renewal and multipotency. Throughout neural development, NSCs undergo proliferation, migration, and cellular differentiation, and dynamic changes are observed in the composition of carbohydrate-rich molecules, including gangliosides. Gangliosides are sialic acid-containing glycosphingolipids with essential and multifaceted functions in brain development and NSC maintenance, which reflects the complexity of brain development. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of ganglioside biosynthesis in NSCs. We found that GD3 is the predominant ganglioside species in NSCs (>80%) and modulates NSC proliferation by interacting with epidermal growth factor receptor signaling. In postnatal brain, GD3 is required for long-term maintenance of NSCs. Deficiency in GD3 leads to developmental and behavioral deficits, such as depression. The synthesis of GD3 is switched to the synthesis of complex, brain-type gangliosides, namely, GM1, GD1a, GD1b, and GT1b, resulting in terminal differentiation and loss of "stemness" of NSCs. In this process, GM1 is augmented by a novel GM1-modulated epigenetic gene regulation mechanism of glycosyltransferases at a later differentiation stage. Consequently, our research suggests that stage-specific gangliosides play specific roles in maintaining NSC activities and in cell fate determination.

Quiescence of adult oligodendrocyte precursor cells requires thyroid hormone and hypoxia to activate Runx1

The adult mammalian central nervous system (CNS) contains a population of slowly dividing oligodendrocyte precursor cells (OPCs), i.e., adult OPCs, which supply new oligodendrocytes throughout the life of animal. While adult OPCs develop from rapidly dividing perinatal OPCs, the mechanisms underlying their quiescence remain unknown. Here, we show that perinatal rodent OPCs cultured with thyroid hormone (TH) under hypoxia become quiescent and acquire adult OPCs-like characteristics. The cyclin-dependent kinase inhibitor p15/INK4b plays crucial roles in the TH-dependent cell cycle deceleration in OPCs under hypoxia. Klf9 is a direct target of TH-dependent signaling. Under hypoxic conditions, hypoxia-inducible factors mediates runt-related transcription factor 1 activity to induce G1 arrest in OPCs through enhancing TH-dependent p15/INK4b expression. As adult OPCs display phenotypes of adult somatic stem cells in the CNS, the current results shed light on environmental requirements for the quiescence of adult somatic stem cells during their development from actively proliferating stem/progenitor cells.

A2B5+/GFAP+ Cells of Rat Spinal Cord Share a Similar Lipid Profile with Progenitor Cells: A Comparative Lipidomic Study

The central nervous system (CNS) harbors multiple glial fibrillary acidic protein (GFAP) expressing cell types. In addition to the most abundant cell type of the CNS, the astrocytes, various stem cells and progenitor cells also contain GFAP+ populations. Here, in order to distinguish between two types of GFAP expressing cells with or without the expression of the A2B5 antigens, we performed lipidomic analyses on A2B5+/GFAP+ and A2B5-/GFAP+ cells from rat spinal cord. First, A2B5+/GFAP- progenitors were exposed to the leukemia inhibitory factor (LIF) or bone morphogenetic protein (BMP) to induce their differentiation to A2B5+/GFAP+ cells or A2B5-/GFAP+ astrocytes, respectively. The cells were then analyzed for changes in their phospholipid, sphingolipid or acyl chain profiles by mass spectrometry and gas chromatography. Compared to A2B5+/GFAP- progenitors, A2B5-/GFAP+ astrocytes contained higher amounts of ether phospholipids (especially the species containing arachidonic acid) and sphingomyelin, which may indicate characteristics of cellular differentiation and inability for multipotency. In comparison, principal component analyses revealed that the lipid composition of A2B5+/GFAP+ cells retained many of the characteristics of A2B5+/GFAP- progenitors, but their lipid profile was different from that of A2B5-/GFAP+ astrocytes. Thus, our study demonstrated that two GFAP+ cell populations have distinct lipid profiles with the A2B5+/GFAP+ cells sharing a phospholipid profile with progenitors rather than astrocytes. The progenitor cells may require regulated low levels of lipids known to mediate signaling functions in differentiated cells, and the precursor lipid profiles may serve as one measure of the differentiation capacity of a cell population.

Ganglioside-Dependent Neural Stem Cell Proliferation in Alzheimer's Disease Model Mice

The aggregation and formation of amyloid plaques by amyloid β-peptides (Aβs) is believed to be one of the pathological hallmarks of Alzheimer's disease (AD). Intriguingly, Aβs have also been shown to possess proliferative effects on neural stem cells (NSCs). Many essential cellular processes in NSCs, such as fate determination and proliferation, are heavily influenced by cell surface glycoconjugates, including gangliosides. It has recently been shown that Aβ1-42 alters several key glycosyltransferases and glycosidases. To further define the effects of Aβs and to clarify the potential mechanisms of action of those peptides on NSCs, NSCs were cultured from embryonic brains of the double-transgenic mouse model of AD [B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J] coexpressing mutants of amyloid precursor protein (APPswe) and presenilin1 (PSEN1dE9). We found that Aβs not only promoted cell proliferation but also altered expression of several key glycogenes for glycoconjugate metabolism, such as sialyltransferases II and III (ST-II & -III) in AD NSCs. In addition, we found upregulation of epidermal growth factor receptor and Notch1 intracellular domain. Moreover, the increased expression of ST-II and -III coincided with the elevated levels of c-series gangliosides (A2B5+ antigens) in AD NSCs. Further, we revealed that epidermal growth factor signaling and gangliosides are necessary components on Aβ-stimulated NSC proliferation. Our present study has thus provided a novel mechanism for the upregulation of c-series ganglioside expression and increases in several NSC markers to account for the proliferative effect of Aβs on NSCs in AD mouse brain. These observations support the potential beneficial effects of Aβs and gangliosides in promoting neurogenesis in AD brain.

A natural human IgM that binds to gangliosides is therapeutic in murine models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, fatal neurological disease that primarily affects spinal cord anterior horn cells and their axons for which there is no treatment. Here we report the use of a recombinant natural human IgM that binds to the surface of neurons and supports neurite extension, rHIgM12, as a therapeutic strategy in murine models of human ALS. A single 200 µg intraperitoneal dose of rHIgM12 increases survival in two independent genetic-based mutant SOD1 mouse strains (SOD1G86R and SOD1G93A) by 8 and 10 days, delays the onset of neurological deficits by 16 days, delays the onset of weight loss by 5 days, and preserves spinal cord axons and anterior horn neurons. Immuno-overlay of thin layer chromatography and surface plasmon resonance show that rHIgM12 binds with high affinity to the complex gangliosides GD1a and GT1b. Addition of rHIgM12 to neurons in culture increases α-tubulin tyrosination levels, suggesting an alteration of microtubule dynamics. We previously reported that a single peripheral dose of rHIgM12 preserved neurological function in a murine model of demyelination with axon loss. Because rHIgM12 improves three different models of neurological disease, we propose that the IgM might act late in the cascade of neuronal stress and/or death by a broad mechanism.

Summary: A single peripheral dose of a recombinant natural human IgM increases lifespan and delays neurological deficits in mouse models of human ALS.

Human-derived natural antibodies: biomarkers and potential therapeutics

The immune system generates antibodies and antigen-specific T-cells as basic elements of the immune networks that differentiate self from non-self in a finely tuned manner. The antigen-specific nature of immune responses ensures that normal immune activation contains non-self when tolerating self. Here we review the B-1 subset of lymphocytes which produce self-reactive antibodies. By analyzing the IgM class of natural antibodies that recognize antigens from the nervous system, we emphasize that natural antibodies are biomarkers of how the immune system monitors the host. The immune response activated against self can be detrimental when triggered in an autoimmune genetic background. In contrast, tuning immune activity with natural antibodies is a potential therapeutic strategy.

Zac1 regulates astroglial differentiation of neural stem cells through Socs3

Cell-fate decisions and differentiation of embryonic and adult neural stem cells (NSC) are tightly controlled by lineage-restricted and temporal factors that interact with cell-intrinsic programs and extracellular signals through multiple regulatory loops. Imprinted genes are important players in neurodevelopment and mental health although their molecular and cellular functions remain poorly understood. Here, we show that the paternally expressed transcriptional regulator Zac1 (zinc finger protein regulating apoptosis and cell cycle arrest) is transiently induced during astroglial and neuronal differentiation of embryonic and adult NSC lines. Thereby, Zac1 transactivates Socs3 (suppressor of cytokine signaling 3), a potent inhibitor of prodifferentiative Jak/Stat3 signaling, in a lineage-specific manner to prevent precocious astroglial differentiation. In vivo, Zac1 and Socs3 colocalize in the neocortical ventricular zone during incipient astrogliogenesis. Zac1 overexpression in primary NSCs delays astroglial differentiation whereas knockdown of Zac1 or Socs3 facilitates formation of astroglial cells. This negative feedback loop is unrelated to Zac1's cell cycle arrest function and specific to the Jak/Stat3 pathway. Hence, reinstating Jak/Stat3 signaling in the presence of increased Zac1 expression allows for timely astroglial differentiation. Overall, we suggest that the imprinted gene Zac1 curtails astroglial differentiation of NSCs in the developing and adult brain.

Amyloid β-peptide 1-42 modulates the proliferation of mouse neural stem cells: upregulation of fucosyltransferase IX and notch signaling

Amyloid β-peptides (Aβs) aggregate to form amyloid plaques, also known as senile plaques, which are a major pathological hallmark of Alzheimer's disease (AD). Aβs are reported to possess proliferation effects on neural stem cells (NSCs); however, this effect remains controversial. Thus, clarification of their physiological function is an important topic. We have systematically evaluated the effects of several putative bioactive Aβs (Aβ1-40, Aβ1-42, and Aβ25-35) on NSC proliferation. Treatment of NSCs with Aβ1-42 significantly increased the number of those cells (149 ± 10 %). This was not observed with Aβ1-40 which did not have any effects on the proliferative property of NSC. Aβ25-35, on the other hand, exhibited inhibitory effects on cellular proliferation. Since cell surface glycoconjugates, such as glycolipids, glycoproteins, and proteoglycans, are known to be important for maintaining cell fate determination, including cellular proliferation, in NSCs and they undergo dramatic changes during differentiation, we examined the effect of Aβs on a number of key glycoconjugate metabolizing enzymes. Significantly, we found for the first time that Aβ1-42 altered the expression of several key glycosyltransferases and glycosidases, including fucosyltransferase IX (FUT9), sialyltransferase III (ST-III), glucosylceramide ceramidase (GLCC), and mitochondrial sialidase (Neu4). FUT9 is a key enzyme for the synthesis of the Lewis X carbohydrate epitope, which is known to be expressed in stem cells. Aβ1-42 also stimulated the Notch1 intracellular domain (NICD) by upregulation of the expression of Musashi-1 and the paired box protein, Pax6. Thus, Aβ1-42 upregulates NSC proliferation by modulating the expression of several glycogenes involved in Notch signaling.

Transplantation of human glial restricted progenitors and derived astrocytes into a contusion model of spinal cord injury

Transplantation of neural progenitors remains a promising therapeutic approach to spinal cord injury (SCI), but the anatomical and functional evaluation of their effects is complex, particularly when using human cells. We investigated the outcome of transplanting human glial-restricted progenitors (hGRP) and astrocytes derived from hGRP (hGDA) in spinal cord contusion with respect to cell fate and host response using athymic rats to circumvent xenograft immune issues. Nine days after injury hGRP, hGDA, or medium were injected into the lesion center and rostral and caudal to the lesion, followed by behavioral testing for 8 weeks. Both hGRP and hGDA showed robust graft survival and extensive migration. The total number of cells increased 3.5-fold for hGRP, and twofold for hGDA, indicating graft expansion, but few proliferating cells remained by 8 weeks. Grafted cells differentiated into glia, predominantly astrocytes, and few remained at progenitor state. About 80% of grafted cells around the injury were glial fibrillary acidic protein (GFAP)-positive, gradually decreasing to 40-50% at a distance of 6 mm. Conversely, there were few graft-derived oligodendrocytes at the lesion, but their numbers increased away from the injury to 30-40%. Both cell grafts reduced cyst and scar formation at the injury site compared to controls. Microglia/macrophages were present at and around the lesion area, and axons grew along the spared tissue with no differences among groups. There were no significant improvements in motor function recovery as measured by the Basso, Beattie, and Bresnahan (BBB) scale and grid tests in all experimental groups. Cystometry revealed that hGRP grafts attenuated hyperactive bladder reflexes. Importantly, there was no increased sensory or tactile sensitivity associated with pain, and the hGDA group showed sensory function returning to normal. Although the improved lesion environment was not sufficient for robust functional recovery, the permissive properties and lack of sensory hypersensitivity indicate that human GRP and astrocytes remain promising candidates for therapy after SCI.

Sequential two-step multienzyme synthesis of tumor-associated sialyl T-antigens and derivatives

A series of α2-3-sialylated β1-3-linked galactosides, including sialyl T-antigens, 3'-sialyl galacto-N-biose, 3'-sialyl lacto-N-biose, and their derivatives containing natural and non-natural sialic acid forms have been synthesized from simple monosaccharides using an efficient sequential two-step multienzyme approach.

Human glial-restricted progenitors survive, proliferate, and preserve electrophysiological function in rats with focal inflammatory spinal cord demyelination

Transplantation of glial progenitor cells results in transplant-derived myelination and improved function in rodents with genetic dysmyelination or chemical demyelination. However, glial cell transplantation in adult CNS inflammatory demyelinating models has not been well studied. Here we transplanted human glial-restricted progenitor (hGRP) cells into the spinal cord of adult rats with inflammatory demyelination, and monitored cell fate in chemically immunosuppressed animals. We found that hGRPs migrate extensively, expand within inflammatory spinal cord lesions, do not form tumors, and adopt a mature glial phenotype, albeit at a low rate. Human GRP-transplanted rats, but not controls, exhibited preserved electrophysiological conduction across the spinal cord, though no differences in behavioral improvement were noted between the two groups. Although these hGRPs myelinated extensively after implantation into neonatal shiverer mouse brain, only marginal remyelination was observed in the inflammatory spinal cord demyelination model. The low rate of transplant-derived myelination in adult rat spinal cord may reflect host age, species, transplant environment/location, and/or immune suppression regime differences. We conclude that hGRPs have the capacity to myelinate dysmyelinated neonatal rodent brain and preserve conduction in the inflammatory demyelinated adult rodent spinal cord. The latter benefit is likely dependent on trophic support and suggests further exploration of potential of glial progenitors in animal models of chronic inflammatory demyelination.

Immunopanning selection of A2B5-positive cells increased the differentiation efficiency of induced pluripotent stem cells into oligodendrocytes

Oligodendrocytes are the myelinating cells of the central nervous system (CNS), and defects in these cells can result in CNS dysfunction. Although oligodendrocyte precursor cell (OPC) transplantation therapy is an effective cure for several disorders, there is no readily available source of these cells. Recent studies have described the generation of induced pluripotent stem cell (iPSC) from somatic cells, leading to speculation that this technique might become a novel therapeutic tool in regenerative medicine. In a previous study, we were able to produce O4 positive (O4(+)) oligodendrocytes from mouse iPSC in vitro. Unfortunately, the efficiency of differentiation achieved was relatively low (2.3%). In the current study, we improved the differentiation efficiency using a mouse monoclonal antibody (A2B5) to select cells of oligodendrocyte lineage. During in vitro differentiation, we purified A2B5-positive (A2B5(+)) cells by immunopanning from a mixed culture of iPSC-derived cells. This procedure increased the differentiation efficiency of O4(+) oligodendrocytes to 43.5%. We also examined the expression of myelin basic protein (MBP), a marker of mature oligodendrocytes. After 21 days of terminal differentiation, 62.3% of iPSC-derived O4(+) oligodendrocytes expressed MBP.

Isolation, characterization and preclinical development of human glial-restricted progenitor cells for treatment of neurological disorders

Aim: Glial-restricted progenitor cells (GRPs), a neural cell population that gives rise to astrocytes and oligodendrocytes both in vitro and in vivo, hold great promise as a cellular therapeutic for the treatment of demyelinating and neurodegenerative diseases of the CNS. The manufacturing and characterization protocols of human-derived GRPs (hGRPs; trade name Q-Cells®) for use in a clinical setting that adhere to rigorous standards for their isolation, propagation, characterization and storage are presented. Materials & methods: hGRPs, defined by their immunoreactivity with A2B5 antibodies, were isolated from fetal cadaver forebrain tissue of mice 17–24 weeks gestational age using Miltenyi paramagnetic bead cell separation technology. GRPs were grown in a defined xenobiotic-free medium for 6 days. At harvest, hGRPs were characterized using immunocytochemical techniques. Long-term cryopreservation and storage conditions, and viability upon freeze–thaw were determined. The phenotypic differentiation potential of hGRPs was determined by implantation experiments into the CNS of shiverer mice. Results: hGRPs were isolated from over 50 neural tissues of either sex during gestational ages of 17–24 weeks. Cells expanded out to 6 days in vitro in a xenobiotic-free medium demonstrated very consistent immunocytochemical profiles. No residual antibody used in the purification process was detected after 6 days of growth in vitro. GRPs could be frozen at up to 24 million cells/ml and were over 70% viable upon freeze–thaw. Thawed hGRPs transplanted into the brain of the dysmyelinated shiverer mouse model were observed to differentiate into both glial fibrillary acidic protein-positive astrocytes and myelin basic protein-positive oligodendrocytes; no human-derived NeuN-positive neuronal cells were observed and no abnormal cell proliferation was observed. Conclusion: We demonstrate that hGRPs can be consistently obtained, propagated, cryopreserved and characterized using protocols that can be transferred to a good laboratory practice/good manufacturing practice setting for the manufacture of clinical-grade hGRP cellular therapeutics. Functional data demonstrate that cells manufactured under these conditions are able to differentiate into appropriate cellular phenotypes in an animal model of dysmyelination.

Expression profiling of human glial precursors

BACKGROUND

We have generated gene expression databases for human glial precursors, neuronal precursors, astrocyte precursors and neural stem cells and focused on comparing the profile of glial precursors with that of other populations.

RESULTS

A total of 14 samples were analyzed. Each population, previously distinguished from each other by immunocytochemical analysis of cell surface markers, expressed genes related to their key differentiation pathways. For the glial precursor cell population, we identified 458 genes that were uniquely expressed. Expression of a subset of these individual genes was validated by RT-PCR. We also report genes encoding cell surface markers that may be useful for identification and purification of human glial precursor populations.

CONCLUSION

We provide gene expression profile for human glial precursors. Our data suggest several signaling pathways that are important for proliferation and differentiation of human glial precursors. Such information may be utilized to further purify glial precursor populations, optimize media formulation, or study the effects of glial differentiation.

The expression and functions of glycoconjugates in neural stem cells

The mammalian central nervous system is organized by a variety of cells such as neurons and glial cells. These cells are generated from a common progenitor, the neural stem cell (NSC). NSCs are defined as undifferentiated neural cells that are characterized by their high proliferative potential while retaining the capacity for self-renewal and multipotency. Glycoconjugates carrying carbohydrate antigens, including glycoproteins, glycolipids, and proteoglycans, are primarily localized on the plasma-membrane surface of cells and serve as excellent biomarkers at various stages of cellular differentiation. Moreover, they also play important functional roles in determining cell fate such as self-renewal, proliferation, and differentiation. In the present review, we discuss the expression pattern and possible functions of glycoconjugates and carbohydrate antigens in NSCs, with an emphasis on stage-specific embryonic antigen-1, human natural killer antigen-1, polysialic acid-neural cell-adhesion molecule, prominin-1, gp130, chondroitin sulfate proteoglycans, heparan sulfate proteoglycans, cystatin C, galectin-1, glycolipids, and Notch.

A set of glycoproteins recognized by A2B5 antibody with major bands at 55 and 76 kDa is overexpressed in human head and neck squamous cell carcinomas

A2B5 antibody was found to strongly label frozen sections of human head and neck squamous cell carcinomas. The low amount of glycolipids (c-series gangliosides and sulfatides) purified from the same tumors and reactive with A2B5 by immunostaining on thin-layer plates could not account for the high level of tissue labeling. Proteins were extracted from both normal tissues and squamous cell carcinomas and analyzed by Western blot with A2B5 antibody on PVDF membranes. The antibody was found to stain a set of glycoproteins with two major bands at 55 and 76 kDa present in normal tissues and overexpressed in carcinomas. Staining was abolished by prior treatment of the PVDF membranes either with Arthrobacter ureafaciens neuraminidase or with a solution of 10 mM periodate that is known to destroy carbohydrates. Our results show that the carbohydrate epitope recognized by A2B5 antibody can be displayed by both glycolipids and glycoproteins.

A novel heptasialosyl c-series ganglioside in embryonic chicken brain: its structure and stage-specific expression

A ganglioside of unknown structure (ganglioside X) was purified from chicken brain at embryonic day 12 (E12) and characterized for its structure. Ganglioside X was reactive with a monoclonal antibody A2B5 and migrated below GH1c on thin-layer chromatography (TLC). Extensive treatment of ganglioside X with Clostridium perfringens sialidase produced a single ganglioside product. This ganglioside was identified as GM1 based upon its chromatographic mobility and reactivity to cholera toxin B subunit and anti-GM1 antibody. Partial hydrolysis of ganglioside X by sialidase generated several degradation products including GH1c, GP1c, and GQ1c. Electrospray ionization (ESI)-mass spectrometry (MS) of the permethylated derivative of ganglioside X produced a triple-charged parent ion peak at m/z 1355, which corresponded with the gangliotetraose oligosaccharide structure having seven sialic acids and ceramide with the molecular mass of 566 (as non-methylated form). Collision-induced dissociation (CID)-MS(2) showed fragment ions including those at m/z 1066 and 1931; these two ions matched the structures of (NeuAc)(3)-Gal-Glc-Cer and (NeuAc)(4)-Gal-GalNAc, respectively. These structures were confirmed by CID-MS(3) of the corresponding peaks. Based upon these findings, the structure of ganglioside X was identified as NeuAc-NeuAc-NeuAc-NeuAc-Galbeta1-3GalNAcbeta1-4(NeuAc-NeuAc-NeuAcalpha2-3)Galbeta1-4Glcbeta1-1'Cer. This ganglioside was designated as GS1c. A developmental study demonstrated that GS1c was expressed in chicken brain during a period from E6 to E13 and thereafter decreased rapidly in its concentration. The present study suggests that GS1c may play a specific role in early development of chicken brain.

Occurrence and tissue distribution of c-series gangliosides in the common squid Todarodes pacificus

We have recently demonstrated that the common squid Todarodes pacificus express acidic lipids that were reactive with a monoclonal antibody A2B5. In the present study, two A2B5-reactive acidic lipids were isolated from squid hepatopancreatic tissue and characterized for their structures by methods including glycolipid overlay analysis, product analysis after sialidase treatment, and electrospray ionization-mass spectrometry (ESI-MS). Accordingly, the two acidic lipid were identified as GT3 and GQ1c, respectively. Another A2B5-reactive acidic lipid in the tissue was tentatively assigned to GT2 based upon its reactivity to A2B5 and chromatographic mobility on thin-layer chromatography. The composition and concentration of c-series gangliosides significantly differed among squid tissues (i.e. hepatopancreas, cerebral ganglion, eye lens, and mantle tissue). Interestingly, the percentages of c-series gangliosides within total gangliosides of hepatopancreas and cerebral ganglion were even higher than that of cod fish brain, which is known to be highly enriched with this ganglioside species. These findings strongly support the hypothesis that c-series gangliosides in squid tissues are not derived from ganglioside-containing food intake, but biosynthesized in a tissue-specific manner.

Characterization of nuclear gangliosides in rat brain: concentration, composition, and developmental changes

Nuclear gangliosides were characterized using two distinct fractions of large (N1) and small (N2) nuclear populations from rat brain. The ganglioside concentration of N1 nuclei from adult rat brain was 0.92 microg sialic acid/mg protein, which was about 3.8 times higher than that of N2 nuclei. N1 and N2 nuclear gangliosides showed similar compositional profiles; they contained major gangliosides of GM1, GD1a, GD1b, and GT1b, with GM3 in lesser amounts. c-Series gangliosides such as GT3, GQ1c, and GP1c were also detected in both nuclear preparations. Nuclear localization of gangliosides was confirmed by immunofluorescence with anti-GM1 antibody, cholera toxin B subunit, and c-series ganglioside-specific monoclonal antibody A2B5. Developmental changes of nuclear gangliosides were examined using rats of different ages ranging from embryonic day 14 (E14) to postnatal 7 weeks. The concentration of N1 nuclear gangliosides changed only slightly during development and did not correlate with that of whole-brain gangliosides. The developmental pattern of ganglioside composition of N1 nuclei was also distinguished from that of microsomal membranes; the ganglioside changes in N1 nuclei included reduced expression of di- and polysialogangliosides at E16 and higher proportions of GM3 at early and late stages of the period. These findings suggest that gangliosides in nuclear membranes are developmentally regulated in a distinct manner in brain cells.