Rat and human HARE/stabilin-2 are clearance receptors for high- and low-molecular-weight heparins.
The human hyaluronic acid (HA) receptor for endocytosis (HARE/stabilin-2) is the primary clearance receptor for systemic HA, chondroitin sulfates, and heparin, but not for heparan sulfate or keratan sulfate (Harris EN, Weigel JA, Weigel PH. J Biol Chem 283: 17341-17350, 2008). HARE is expressed in the sinusoidal endothelial cells (SECs) of liver and lymph nodes where it acts as a scavenger for uptake and degradation of glycosaminoglycans, both as free chains and proteoglycan fragments. Unfractionated heparin (UFH; approximately 14 kDa) and low-molecular-weight heparin (LMWH; approximately 4 kDa) are commonly used in treatments for thrombosis and cancer and in surgical and dialysis procedures. The reported half-lives of UFH and LMWH in the blood are approximately 1 h and 2-6 h, respectively. In this study, we demonstrate that anti-HARE antibodies specifically block the uptake of LMWH and UFH by isolated rat liver SECs and by human 293 cells expressing recombinant human HARE (hHARE). hHARE has a significant affinity (K(d) = 10 microM) for LMWH, and higher affinity (K(d) = 0.06 microM) for the larger UFH. Rat liver SECs or cells expressing the recombinant 190-kDa HARE isoform internalized both UFH and LMWH, and both heparins cross-compete with each other, suggesting that they share the same binding sites. These cellular results were confirmed in ELISA-like assays using purified soluble 190-hHARE ectodomain. We conclude that both UFH and LMWH are cleared by HARE/Stab2 and that the differences in the affinities of HARE binding to LMWH and UFH likely explain the longer in vivo circulating half-life of LMWH compared with UFH.
Dept. of Biochemistry, The Oklahoma Center for Medical Glycobiology, Univ. of Oklahoma Health Sciences Center, Oklahoma City, OK 73190, USA. edward-harris@ouhsc.edu
Edward N
EN
Harris
Bruce A
BA
Baggenstoss
Paul H
PH
Weigel
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D001667:Binding, Competitive; D015816:Cell Adhesion Molecules, Neuronal / Q000502:physiology*; D002460:Cell Line; D016264:Dextran Sulfate / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D042783:Endothelial Cells / Q000378:metabolism; D017984:Enoxaparin / Q000737:chemistry / Q000378:metabolism; D006493:Heparin / Q000737:chemistry / Q000378:metabolism*; D006495:Heparin, Low-Molecular-Weight / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000502:physiology*; D008027:Light; D008077:Lipoproteins, LDL / Q000378:metabolism; D008099:Liver / Q000166:cytology; D008970:Molecular Weight; D011485:Protein Binding; D020033:Protein Isoforms / Q000276:immunology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000502:physiology*; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism; D012542:Scattering, Radiation; D014162:Transfection
D000911:Antibodies, Monoclonal; D015816:Cell Adhesion Molecules, Neuronal; D017984:Enoxaparin; D006495:Heparin, Low-Molecular-Weight; D018960:Hyaluronan Receptors; D008077:Lipoproteins, LDL; D020033:Protein Isoforms; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C449927:STAB2 protein, human; C032629:acetyl-LDL; C037680:heparin receptor; C472814:hyaluronan receptor 175-kDa, rat; D006493:Heparin; D016264:Dextran Sulfate