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Introduction and Review of Biological Background
Published in Luke R. Bucci, Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
Proteoglycans (PGs) are ubiquitous components of all connective tissues. PGs are one of the three major components of connective tissues, the others being collagen and cells. PGs form highly structured gels that occupy large amounts of space, especially in amorphous ground substance. PGs are very large aggregates of proteins and glycosaminoglycans (GAGs) that comprise a small percentage of tissues by weight, but exert an effect far larger than their concentration implies. PGs make up 10% of dry weight in articular cartilage and around 1% of dry weight in bones, tendons, and ligaments. Formerly called mucoproteins, PGs stain intensely with cationic dyes toluidine blue and safranin O due to their high electronegativity. PGs are more than simply structural elements of connective tissues. Smaller PGs serve as cross-linking agents in connective tissues, and others serve as membrane-associated markers involved in cell-cell and cell-matrix interactions. Three types of PGs have been found: (1) aggrecan; (2) small PGs (decorin, biglycan, and fibromodulin); and (3) membrane-associated PGs (glypican, perlecan, serglycin, syndecan).79,83 All are composed of GAG chains bound to core proteins.
Differential Expression of Proteoglycans on the Surface of Malignant Cells and in the Tumor Stroma
Published in Róza Ádány, Tumor Matrix Biology, 2017
ECM PGs are highly hydrophilic, determining the actual hydration of the connective tissue. Attachment and detachment of cells to and from a cell community may also be a function related to PGs. CSPGs of the ECM are able to inhibit cell attachment.18,19 The role of the PGs on the cell surface is not exactly known. These PGs can be glycanated with CS, HS, or with both, such as in the case of syndecan,20 which is the best known cell surface PG. Syndecan and the majority of cell surface PGs are transmembrane proteins with small intracellular domains containing tyrosine residue. This raises the possibility that syndecan can act as a cell surface receptor. Syndecan has at least two functions, both related to the HS chains. Via this GAG chain it binds to various matrix elements,21 anchoring the cells to their anatomical site. HS chains are also able to bind basic fibroblast growth factor (bFGF) and serve as low-affinity receptors for this growth factor.22 This binding is inevitably necessary to the interaction of FGF with its high-affinity receptor.23 A similar function is suggested for betaglycan,24 the type III receptor of TGF-β, which is also a “hybrid” PG, and it binds TGF-β via its protein core and presents the growth factor for the high-affinity receptors;25 furthermore, the HS chain of the molecule binds FGF, as well.26 Fibroglycan is a HSPG found on the cell surface of human lung fibroblasts.27 Its transmembrane domain is quite homologous with that of the syndecan family. It seems that this proteoglycan is the major cell surface PG of hepatocytes, as well.28 Amphyglycan has been recently cloned, and its name refers to its ubiquitous presence on the cell surface.29 Glypican differs from the PGs listed above, because it binds to the cell surface via inositolphosphate.30 Inositolphosphate-bound HSPG, once appeared on the cell surface, has been demonstrated to reenter the cytoplasm, and its HS chains reach the nucleus, where they may act as growth-regulatory molecules.31,32 There are CSPGs on the cell surface like the melanoma PG,33 or PG of neuronal tissues.34 Serglycin is the best known intracellular PG, located in the granules of mast cells, macrophages, natural killer (NK) cells acting as inhibitors of certain proteases.35 A specific group of PGs is the family of facultative PGs, where glycanation is not obligatory and they can be found in both forms, like CD44, HCAM, I chain of HLA-DR, type IX collagen, thrombomodulin.36 In these cases the significance of glycanation is only partially understood.
Platelet activation by charged ligands and nanoparticles: platelet glycoprotein receptors as pattern recognition receptors
Published in Platelets, 2021
Samantha J. Montague, Pushpa Patel, Eleyna M. Martin, Alexandre Slater, Lourdes Garcia Quintanilla, Gina Perrella, Caroline Kardeby, Magdolna Nagy, Diego Mezzano, Paula M. Mendes, Steve P. Watson
GPVI is a member of the immunoglobulin (Ig) receptor superfamily expressed on platelets and megakaryocytes and best known as a receptor for collagen.67 GPVI is activated by a diverse range of endogenous and exogenous ligands (Table 3), including fibrin and fibrinogen,68–70 extracellular matrix proteins (laminin, fibronectin, galectin-371 and vitronectin67,72), positively charged histones1 and the neuronal proteins, reelin and β-amyloid.73,74 Negatively charged molecules, such as chondroitin sulfate, heparins and small polyanions block fibrin-mediated aggregation and GPVI shedding, supporting a role for charge-mediated GPVI activation.75 Furthermore, serglycin, a sulfated proteoglycan contained in platelet α-granules, also appears to be important in charge neutralization and regulation of charge-mediated GPVI shedding, as convulxin-mediated GPVI shedding is increased in serglycin knock-out mice.76
Increased levels of serum serglycin and agrin is associated with adverse perinatal outcome in early onset preeclampsia
Published in Fetal and Pediatric Pathology, 2019
Basak Gumus Guler, Sibel Ozler
Serglycin was first found in the yolk sac [34]. Hematopoietic cells are made in the yolk sac, and serglycin is found in the cytoplasm and plasma membranes of these cells [35]. It has roles in the secretion of chemokines and cytokines [36], ligation of CD44 receptor on the cell surface, and fibronectin and collagen in ECM [37]. Schick et al. demonstrated its deposition in the vesicles of endothelial cells of the umbilical vein and its similar distribution with tissue plasminogen activator. Its secretion was found to be increased in the culture media in the presence of TNF-alpha [38]. At the 9th day of the embryogenesis, it was expressed in decidual and parietal endodermal cells which may suggest its role in decidual function in the early post-implantation process [39, 40].
CD44 receptor-targeted novel drug delivery strategies for rheumatoid arthritis therapy
Published in Expert Opinion on Drug Delivery, 2021
Srividya Gorantla, Ganesh Gorantla, Ranendra N. Saha, Gautam Singhvi
Chondroitin sulfate (CS) is a water-soluble, unbranched sulfated anionic glycosaminoglycan composed of alternating 4-linked β- d-glucuronic acid, and 3-linked N-acetyl galactosamine disaccharide units with varied sulfate positions [12]. The sulfate group imparts hydrophilicity, and was found on the fourth and sixth positions in CS, which are named CS A and CS C, respectively. Serglycin comprises CS-A and CS-C chains bound to a centrally positioned Ser-Gly repeat. Toyama et al. reported that the binding ability of serglycin to CD44 is independent of its CS composition [13].