Major glycan structure underlying expression of the Lewis X epitope in the developing brain is O-mannose-linked glycans on phosphacan/RPTPβ.
TL;DR: The results revealed the importance of O-mannosylated glycan chains in the presentation of functional glycan epitopes in the brain.
Abstract: Glycosylation is a major protein modification. Although proteins are glycosylated/further modulated by several glycosyltransferases during trafficking from the endoplasmic reticulum to the Golgi apparatus, a certain glycan epitope has only been detected on a limited number of proteins. Of these glycan epitopes, Lewis X is highly expressed in the early stage of a developing brain and plays important roles in cell-cell interaction. The Lewis X epitope is comprised of a trisaccharide (Galβ1-4 (Fucα1-3) GlcNAc), and a key enzyme for the expression of this epitope is α1,3-fucosyltransferase 9. However, the scaffolding glycan structure responsible for the formation of the Lewis X epitope as well as its major carrier protein has not been fully characterized in the nervous system. Here we showed that the Lewis X epitope was mainly expressed on phosphacan/receptor protein tyrosine phosphatase β (RPTPβ) in the developing mouse brain. Expression of the Lewis X epitope was markedly reduced in β1,4-galactosyltransferase 2 (β4GalT2) gene-deficient mice, which indicated that β4GalT2 is a major galactosyltransferase required for the Lewis X epitope. We also showed that the Lewis X epitope almost disappeared due to the knockout of protein O-mannose β1,2-N-acetylglucosaminyltransferase 1, an N-acetylglucosaminyltransferase essential for the synthesis of O-mannosylated glycans, which indicated that the O-mannosylated glycan is responsible for presenting the Lewis X epitope. Since O-mannosylated glycans on phosphacan/RPTPβ could also present human natural killer-1, another glycan epitope specifically expressed in the nervous system, our results revealed the importance of O-mannosylated glycan chains in the presentation of functional glycan epitopes in the brain.
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TL;DR: Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given and mucins and their glycosylation patterns are considered as instructive proof-of-principle case.
Abstract: Proteins undergo co- and posttranslational modifications, and their glycosylation is the most frequent and structurally variegated type. Histochemically, the detection of glycan presence has first been performed by stains. The availability of carbohydrate-specific tools (lectins, monoclonal antibodies) has revolutionized glycophenotyping, allowing monitoring of distinct structures. The different types of protein glycosylation in Eukaryotes are described. Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given. In particular, mucins and their glycosylation patterns are considered as instructive proof-of-principle case. The tissue and cellular location of glycoprotein biosynthesis and metabolism is reviewed, with attention to new findings in goblet cells. Finally, protein glycosylation in disease is documented, with selected examples, where aberrant glycan expression impacts on normal function to let disease pathology become manifest. The histological applications adopted in these studies are emphasized throughout the text.
108 citations
Cites background from "Major glycan structure underlying e..."
...…Yanagisawa) coding Galβ1,4(Fucα1,3)GlcNAcβ1- (Yu and Yanagisawa 2006), while O-mannosylation is also a significant feature of α-dystroglycan in the nervous system, where it mediates cell-extracellular matrix contact (Hennet 2009; Panin and Wells 2014; Praissman and Wells 2014; Yaji et al. 2015)....
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...Neural stem cells express CD15 (Yu and Yanagisawa) coding Galβ1,4(Fucα1,3)GlcNAcβ1- (Yu and Yanagisawa 2006), while O-mannosylation is also a significant feature of α-dystroglycan in the nervous system, where it mediates cell-extracellular matrix contact (Hennet 2009; Panin and Wells 2014; Praissman and Wells 2014; Yaji et al. 2015)....
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TL;DR: This review will focus on recent discoveries delineating the various enzymes, structures and functions associated with O-mannose-initiated glycoproteins, and discusses the evolution of this pathway.
Abstract: The post-translational glycosylation of select proteins by O-linked mannose (O-mannose or O-man) is a conserved modification from yeast to humans and has been shown to be necessary for proper development and growth. The most well studied O-mannosylated mammalian protein is α-dystroglycan (α-DG). Hypoglycosylation of α-DG results in varying severities of congenital muscular dystrophies, cancer progression and metastasis, and inhibited entry and infection of certain arenaviruses. Defects in the gene products responsible for post-translational modification of α-DG, primarily glycosyltransferases, are the basis for these diseases. The multitude of clinical phenotypes resulting from defective O-mannosylation highlights the biomedical significance of this unique modification. Elucidation of the various O-mannose biosynthetic pathways is imperative to understanding a broad range of human diseases and for the development of novel therapeutics. In this review, we will focus on recent discoveries delineating the various enzymes, structures and functions associated with O-mannose-initiated glycoproteins. Additionally, we discuss current gaps in our knowledge of mammalian O-mannosylation, discuss the evolution of this pathway, and illustrate the utility and limitations of model systems to study functions of O-mannosylation.
72 citations
TL;DR: GDP-l-fucose synthase is an autoantigen recognized by cerebrospinal fluid–infiltrating CD4+ T cells from HLA-DRB3*–positive patients with multiple sclerosis, and the possible role of this antigen as an inducer or driver of pathogenic autoimmune responses in multiple sclerosis is suggested.
Abstract: Multiple sclerosis is an immune-mediated autoimmune disease of the central nervous system that develops in genetically susceptible individuals and likely requires environmental triggers. The autoantigens and molecular mimics triggering the autoimmune response in multiple sclerosis remain incompletely understood. By using a brain-infiltrating CD4 + T cell clone that is clonally expanded in multiple sclerosis brain lesions and a systematic approach for the identification of its target antigens, positional scanning peptide libraries in combination with biometrical analysis, we have identified guanosine diphosphate (GDP)–l-fucose synthase as an autoantigen that is recognized by cerebrospinal fluid–infiltrating CD4 + T cells from HLA-DRB3*–positive patients. Significant associations were found between reactivity to GDP-l-fucose synthase peptides and DRB3*02:02 expression, along with reactivity against an immunodominant myelin basic protein peptide. These results, coupled with the cross-recognition of homologous peptides from gut microbiota, suggest a possible role of this antigen as an inducer or driver of pathogenic autoimmune responses in multiple sclerosis.
66 citations
TL;DR: It is shown that LeX‐glycosylated LRP1 is also expressed in the stem cell compartment of the developing spinal cord and has broader functions in the developing CNS, suggesting that LRP 1 facilitates NSPCs differentiation via interaction with apolipoprotein E (ApoE).
Abstract: The LDL family of receptors and its member low-density lipoprotein receptor-related protein 1 (LRP1) have classically been associated with a modulation of lipoprotein metabolism. Current studies, however, indicate diverse functions for this receptor in various aspects of cellular activities, including cell proliferation, migration, differentiation, and survival. LRP1 is essential for normal neuronal function in the adult CNS, whereas the role of LRP1 in development remained unclear. Previously, we have observed an upregulation of LewisX (LeX) glycosylated LRP1 in the stem cells of the developing cortex and demonstrated its importance for oligodendrocyte differentiation. In the current study, we show that LeX-glycosylated LRP1 is also expressed in the stem cell compartment of the developing spinal cord and has broader functions in the developing CNS. We have investigated the basic properties of LRP1 conditional knockout on the neural stem/progenitor cells (NSPCs) from the cortex and the spinal cord, created by means of Cre-loxp-mediated recombination in vitro. The functional status of LRP1-deficient cells has been studied using proliferation, differentiation, and apoptosis assays. LRP1 deficient NSPCs from both CNS regions demonstrated altered differentiation profiles. Their differentiation capacity toward oligodendrocyte progenitor cells (OPCs), mature oligodendrocytes and neurons was reduced. In contrast, astrocyte differentiation was promoted. Moreover, LRP1 deletion had a negative effect on NSPCs proliferation and survival. Our observations suggest that LRP1 facilitates NSPCs differentiation via interaction with apolipoprotein E (ApoE). Upon ApoE4 stimulation wild type NSPCs generated more oligodendrocytes, but LRP1 knockout cells showed no response. The effect of ApoE seems to be independent of cholesterol uptake, but is rather mediated by downstream MAPK and Akt activation. GLIA 2016 GLIA 2016;64:1363-1380.
46 citations
Cites background from "Major glycan structure underlying e..."
...We confirmed already known LeX presenting proteins such as phosphacan, tenascin-C, and L1-CAM (Garwood et al., 1999; Hennen et al., 2013; Streit et al., 1990; Yaji et al., 2015)....
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TL;DR: O-mannosyl glycan has a novel, unique structure that is important for the maintenance of brain and muscle functions that has opened up a new field in glycoscience.
45 citations
References
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TL;DR: A unique strategy using nuclease-mediated gene editing of a human cell line to reduce the structural heterogeneity of O-Man glycans and to probe the O- man glycoproteome is presented, and it is found that the important cadherin and plexin families of cell membrane receptors are O-mannosylated.
Abstract: The metazoan O-mannose (O-Man) glycoproteome is largely unknown. It has been shown that up to 30% of brain O-glycans are of the O-Man type, but essentially only alpha-dystroglycan (α-DG) of the dystrophin–glycoprotein complex is well characterized as an O-Man glycoprotein. Defects in O-Man glycosylation underlie congenital muscular dystrophies and considerable efforts have been devoted to explore this O-glycoproteome without much success. Here, we used our SimpleCell strategy using nuclease-mediated gene editing of a human cell line (MDA-MB-231) to reduce the structural heterogeneity of O-Man glycans and to probe the O-Man glycoproteome. In this breast cancer cell line we found that O-Man glycosylation is primarily found on cadherins and plexins on β-strands in extracellular cadherin and Ig-like, plexin and transcription factor domains. The positions and evolutionary conservation of O-Man glycans in cadherins suggest that they play important functional roles for this large group of cell adhesion glycoproteins, which can now be addressed. The developed O-Man SimpleCell strategy is applicable to most types of cell lines and enables proteome-wide discovery of O-Man protein glycosylation.
138 citations
TL;DR: There appears to be in higher eukaryotes a major alternative pathway related to the yeast-type protein O-mannosylation, the enzymatic basis and functional importance of which now require investigation.
Abstract: Di- to heptasaccharides isolated from total nondialyzable brain glycopeptides after release by alkaline borohydride treatment have been subjected to mass spectrometric and nuclear magnetic resonance spectroscopic analyses supplemented by TLC-MS analyses of derived neoglycolipids. A family of Manol-terminating oligosaccharides has been revealed which includes novel sequences with a 2, 6-disubstituted Manol: In contrast to the Manol-terminating HNK-1 antigen-positive chains described previously that occur as a minor population [Yuen, C.-T., Chai, W., Loveless, R.W., Lawson, A.M., Margolis, R.U. & Feizi, T. (1997) J. Biol. Chem. 272, 8924-8931], the above oligosaccharides are abundant. The ratio of these compounds to the classical N-acetylgalactosaminitol-terminating oligosaccharides is about 1 : 3. Thus, there appears to be in higher eukaryotes a major alternative pathway related to the yeast-type protein O-mannosylation, the enzymatic basis and functional importance of which now require investigation.
134 citations
"Major glycan structure underlying e..." refers background in this paper
...The O-mannose-linked glycan is highly enriched in the brain with 1/3 of all O-glycans in the brain being estimated to be O-mannose-linked ones (Chai et al. 1999)....
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...The O-mannose-linked glycan is highly enriched in the brain with 1/3 of all O-glycans in the brain being estimated to be O-mannose-linked ones (Chai et al. 1999)....
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TL;DR: There is a relationship in these cells between poly-N-acetyllactosamine chain length and the degree and type of sialylation of these chains, and it is found that immobilized tomato lectin interacts with high affinity with glycopeptides containing three or more linear units of the repeating disaccharide and thereby allows for a separation of glycopesptides on the basis of the length of the chain.
128 citations
"Major glycan structure underlying e..." refers methods in this paper
...Tomato lectin, Lycopersicon esculentum lectin (LEL) is specific to polyLacNAc (Merkle and Cummings 1987), and, thus, was used for this comparison....
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TL;DR: Mannose-linked Lewis X is the latest in an increasing list of oligosaccharide recognition “tags” that have been shown to be expressed on cranin (dystroglycan) purified from brain.
126 citations
"Major glycan structure underlying e..." refers background in this paper
...…250 kDa), L1 cell adhesion molecule (L1-CAM, approximately 140 kDa), and LRP-1 (515 kDa α-subunit and 85 kDa β-subunit) (Hennen et al. 2011; Hennen et al. 2013), and also on O-mannosylated glycans of CD24 (approximately 30 kDa) or α-DG (100-120 kDa) (Smalheiser et al. 1998; Bleckmann et al. 2009)....
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TL;DR: The authors discuss the implications of several neuronal CAMs and extracellular matrix proteins that combine to form cell-recognition complexes for intercellular signaling, and the regulation of RPTP activity by cell-cell and cell-ECM contact.
108 citations
"Major glycan structure underlying e..." refers background in this paper
...Phosphacan, one of the major soluble CSPGs in the brain, is a secreted-type splicing variant of receptor protein tyrosine phosphatase β (RPTPβ) that is also modified by CS chains (Krueger and Saito 1992; Barnea et al. 1994; Peles et al. 1998)....
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