title: The binding of the bone morphogenetic protein antagonist gremlin to kidney heparan sulfate: Such binding is not essential for BMP antagonism.
abstract: Gremlin-1, a bone morphogenetic protein (BMP) antagonist, has essential roles in kidney and limb bone development, and is important in chronic diseases including tissue fibrosis. It also functions as an activating ligand of the vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2), and binds strongly to the sulfated polysaccharide, heparin. Here we investigated the extent to which gremlin binds to the related polysaccharide heparan sulfate (HS), which unlike heparin is widely distributed spread within tissues. We determined that both highly sulfated HS and kidney HS are able to partially compete for the binding of heparin to gremlin, whereas low sulfated HS is a poor competitor. In further investigations of the interaction between gremlin and HS, we found that wild-type gremlin is able to bind broadly across the various regions of kidney in an HS-dependent manner, with particularly intense binding to tubular structures in the renal cortex. In a model of chronic kidney disease, fibrotic changes in the kidney result in a loss of gremlin binding sites. Gremlin mutants with reduced affinity for heparin showed negligible binding under the same conditions. These mutants nonetheless remain functional as BMP antagonists on C2C12 myoblastic cells transfected with a Smad 1 reporter gene construct. Overall our findings indicate that on secretion, gremlin will bind to HS structures on the cell surface and in the extracellular matrix, thus providing for a localised reservoir which can modulate BMP activity in a temporospatially restricted manner. Although binding of heparin/HS to gremlin has been shown elsewhere to be necessary for gremlin activation of VEGFR2, this does not appear to be essential for BMP antagonism by gremlin. Thus these sulfated polysaccharides differentially regulate the activities of gremlin.
authors.affiliation: Centre for Biomedical Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK.
authors.forename: Arnold Junior
authors.initials: AJ
authors.lastname: Tatsinkam
authors.affiliation: Centre for Biomedical Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK.
authors.forename: Naomi
authors.initials: N
authors.lastname: Rune
authors.affiliation: Centre for Biomedical Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK.
authors.forename: Joy
authors.initials: J
authors.lastname: Smith
authors.affiliation: UCL Centre for Nephrology, University College London, Royal Free Campus, Rowland Hill Street, London NW3 2PF, UK.
authors.forename: Jill T
authors.initials: JT
authors.lastname: Norman
authors.affiliation: Centre for Biomedical Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK.
authors.forename: Barbara
authors.initials: B
authors.lastname: Mulloy
authors.affiliation: Centre for Biomedical Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK. Electronic address: c.rider@rhul.ac.uk.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Rider
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D055415:Bone Morphogenetic Protein 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002460:Cell Line; D006497:Heparan Sulfate / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D051436:Renal Insufficiency, Chronic / Q000378:metabolism; D016207:Cytokines
chemical_list: D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D006497:Heparan Sulfate; D036341:Intercellular Signaling Peptides and Proteins; D050505:Mutant Proteins; C525810:Bmp4 protein, mouse; C113178:Grem1 protein, mouse; D016207:Cytokines
keywords: Bone morphogenetic protein; Gremlin; Heparan sulfate; Kidney; Renal cortex