The mannose receptor on murine liver sinusoidal endothelial cells is the main denatured collagen clearance receptor.
The purpose of this study was to identify the receptor responsible for endocytosis of denatured collagen from blood. The major site of clearance of this material (at least 0.5 g/day in humans) is a receptor on liver sinusoidal endothelial cells (LSECs). We have now identified an 180-kDa endocytic receptor on LSECs, peptide mass fingerprinting of which revealed it to be the mannose receptor. Challenge of mannose-receptor knockout mice and their cultured LSECs revealed significantly reduced blood clearance and a complete absence of LSEC endocytosis of denatured collagen. Organ analysis of wild-type versus knockout mice after injection of denatured collagen revealed significantly reduced liver uptake in the knockout mice. Clearance/endocytosis of ligands for other receptors in these animals was as that for wild-type mice, and denatured collagen uptake in wild-type mice was not affected by other ligands of the mannose receptor, namely mannose and mannan. Furthermore, unlike that of mannose and mannan, endocytosis of denatured collagen by the mannose receptor is calcium independent. This suggests that the binding site for denatured collagen is distinct from that for mannose/mannan. Mannose receptors on LSECs appear to have less affinity for circulating triple helical type I collagen.


CONCLUSIONS
The mannose receptor is the main candidate for being the endocytic denatured collagen receptor on LSECs.
Malovic
Ivana
I
Department of Cell Biology and Histology, University of Tromsø, NO-9037 Tromsø, Norway.
Sørensen
Karen K
KK
Elvevold
Kjetil H
KH
Nedredal
Geir Ivar
GI
Paulsen
Steinar
S
Erofeev
Alexander V
AV
Smedsrød
Bård H
BH
McCourt
Peter A G
PA
D000818:Animals; D003094:Collagen / Q000737:chemistry / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D042783:Endothelial Cells / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008103:Liver Cirrhosis / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011489:Protein Denaturation; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D034421:Sus scrofa
D008562:Membrane Glycoproteins; C474081:Mrc2 protein, mouse; D011956:Receptors, Cell Surface; D003094:Collagen