Heparan sulphate proteoglycans reside on the plasma membrane of all animal cells studied so far and are a major component of extracellular matrices. Studies of model organisms and human diseases have demonstrated their importance in development and normal physiology. A recurrent theme is the electrostatic interaction of the heparan sulphate chains with protein ligands, which affects metabolism, transport, information transfer, support and regulation in all organ systems. The importance of these interactions is exemplified by phenotypic studies of mice and humans bearing mutations in the core proteins or the biosynthetic enzymes responsible for assembling the heparan sulphate chains.

Heparan sulphate proteoglycans fine-tune mammalian physiology

▪ Abstract Virtually every cell type in metazoan organisms produces heparan sulfate. These complex polysaccharides provide docking sites for numerous protein ligands and receptors involved in diverse biological processes, including growth control, signal transduction, cell adhesion, hemostasis, and lipid metabolism. The binding sites consist of relatively small tracts of variably sulfated glucosamine and uronic acid residues in specific arrangements. Their formation occurs in a tissue-specific fashion, generated by the action of a large family of enzymes involved in nucleotide sugar metabolism, polymer formation (glycosyltransferases), and chain processing (sulfotransferases and an epimerase). New insights into the specificity and organization of the biosynthetic apparatus have emerged from genetic studies of cultured cells, nematodes, fruit flies, zebrafish, rodents, and humans. This review covers recent developments in the field and provides a resource for investigators interested in the incredible dive...

Order out of chaos: assembly of ligand binding sites in heparan sulfate.

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of ligands. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions. Here, we discuss changing views on the specificity of protein-heparan sulfate binding and the activity of HSPGs as receptors and coreceptors. Although few in number, heparan sulfate proteoglycans have profound effects at the cellular, tissue, and organismal level.

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Heparan Sulfate Proteoglycans

The availability of the human and mouse genome sequences has allowed the identification and comparison of their respective degradomes--the complete repertoire of proteases that are produced by these organisms. Because of the essential roles of proteolytic enzymes in the control of cell behaviour, survival and death, degradome analysis provides a useful framework for the global exploration of these protease-mediated functions in normal and pathological conditions.

Human and mouse proteases: a comparative genomic approach

Heparan sulfate (HS) appeared early in metazoan evolution. As such, many of the structural motifs (variably sulfated disaccharide subunits) that characterize HS (and heparin) were established early on and have been preserved in modern organisms. Thus, many of the biological functions associated with HS either occurred early in evolution or have depended on the subsequent evolution of the protein ligands that bind to the polysaccharide. Today, we know of literally hundreds of heparin-binding proteins, and many interactions have profound consequences in vertebrate and invertebrate physiology. This Perspective aims to provide an overview of HS structure, function, and biosynthesis and to set the stage for discussing the relationship between structure and function of these fascinating molecules and how altered HS biosynthesis and catabolism can lead to human disorders.

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Molecular diversity of heparan sulfate

Heparin is a sulphated polysaccharide, synthesized exclusively by connective-tissue-type mast cells1 and stored in the secretory granules in complex with histamine and various mast-cell proteases2. Although heparin has long been used as an antithrombotic drug, endogenous heparin is not present in the blood, so it cannot have a physiological role in regulating blood coagulation. The biosynthesis of heparin involves a series of enzymatic reactions, including sulphation at various positions1,3. The initial modification step, catalysed by the enzyme glucosaminyl N -deacetylase/N -sulphotransferase-2, NDST-2 (4–7), is essential for the subsequent reactions. Here we report that mice carrying a targeted disruption of the gene encoding NDST-2 are unable to synthesize sulphated heparin. These NDST-2-deficient mice are viable and fertile but have fewer connective-tissue-type mast cells; these cells have an altered morphology and contain severely reduced amounts of histamine and mast-cell proteases. Our results indicate that one site of physiological action for heparin could be inside connective-tissue-type mast cells, where its absence results in severe defects in the secretory granules.

Abnormal mast cells in mice deficient in a heparin-synthesizing enzyme

Altered storage of proteases in mast cells from mice lacking heparin: a possible role for heparin in carboxypeptidase A processing.

To study early events in mast cell / basophil development, the phenotype of a panel of murine cell lines at various stages of differentiation was determined. Based on the expression on various mast cell-specific proteases and several additional hematopoietic differentiation markers, the cell lines CFTL-15 and MCP5 / L were clearly identified as mast cells, although with a relatively immature phenotype. These two cell lines express the high-affinity IgE receptor alpha-chain, the mouse mast cell protease (MMCP)-5 and the carboxypeptidase A (CPA). Bone marrow-derived mast cells and the transplantable mast cell tumor MTC were shown to express the IgE receptor alpha-chain, MMCP-5 and CPA, as well as the mast cell tryptase MMCP-6 and the chymase MMCP-4, a protease expressed only during late stages of mast cell differentiation. These two cell types thus display a more mature mast cell phenotype. In contrast, the cell lines P815 and 32D cl3 did not express any mast cell differentiation markers. Interestingly, the IC-2 cell line was shown to express several markers for immature mast cells and in addition MMCP-8, a serine protease which may represent a marker for mouse basophils. By antibody staining, almost all IC-2 cells were shown to express MMCP-8. This indicates that individual cells may simultaneously express both mast cell and basophil markers. Moreover, these findings suggest that an early branch point in hematopoietic development where mast cells and basophils have a common precursor cell may exist.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-4141%282000012%2930%3A12%3C3396%3A%3AAID-IMMU3396%3E3.0.CO%3B2-O

Murine mast cell lines as indicators of early events in mast cell and basophil development.

Activation of the coagulation cascade, mediated by various monocyte/macrophage procoagulants, is an important component in the pathology of inflammatory disease. The type of procoagulant expressed may vary between different monocyte/macrophage subtypes and may differ depending on how the cells are treated. In the present study we show that both murine peritoneal macrophages and human adherent synovial cells from rheumatoid arthritis lesions express prothrombinase activity that was inhibited by anti-Factor X antibodies. Northern blot analysis showed that Factor X was transcribed by the murine peritoneal cells and Western blot analysis showed the presence of Factor X antigen. Further experiments showed that the prothrombinase activity was secreted by the cells into the medium in a detergent-sensitive form, suggesting that the prothrombinase is released on small lipid-containing vesicles.

Macrophages synthesize factor X and secrete factor X/Xa-containing prothrombinase activity into the surrounding medium.

A kinetic analysis of the expression of mast cell protease mRNA in the intestines of of Nippostrongylus brasiliensis infected rats.

Carolina Lunderius

Papers

Abnormal mast cells in mice deficient in a heparin-synthesizing enzyme

Altered storage of proteases in mast cells from mice lacking heparin: a possible role for heparin in carboxypeptidase A processing.

Murine mast cell lines as indicators of early events in mast cell and basophil development.

Macrophages synthesize factor X and secrete factor X/Xa-containing prothrombinase activity into the surrounding medium.

A kinetic analysis of the expression of mast cell protease mRNA in the intestines of Nippostrongylus brasiliensis-infected rats