Macrophage LRP1 contributes to the clearance of von Willebrand factor

G Rastegarlari, JN Pegon, C Casari… - Blood, The Journal …, 2012 - ashpublications.org
G Rastegarlari, JN Pegon, C Casari, S Odouard, AM Navarrete, N Saint-Lu, BJ van Vlijmen…
Blood, The Journal of the American Society of Hematology, 2012ashpublications.org
The relationship between low-density lipoprotein receptor–related protein-1 (LRP1) and von
Willebrand factor (VWF) has remained elusive for years. Indeed, despite a reported absence
of interaction between both proteins, liver-specific deletion of LRP1 results in increased VWF
levels. To investigate this discrepancy, we used mice with a macrophage-specific deficiency
of LRP1 (macLRP1−) because we previously found that macrophages dominate VWF
clearance. Basal VWF levels were increased in macLRP1− mice compared with control mice …
Abstract
The relationship between low-density lipoprotein receptor–related protein-1 (LRP1) and von Willebrand factor (VWF) has remained elusive for years. Indeed, despite a reported absence of interaction between both proteins, liver-specific deletion of LRP1 results in increased VWF levels. To investigate this discrepancy, we used mice with a macrophage-specific deficiency of LRP1 (macLRP1) because we previously found that macrophages dominate VWF clearance. Basal VWF levels were increased in macLRP1 mice compared with control mice (1.6 ± 0.4 vs 1.0 ± 0.4 U/mL). Clearance experiments revealed that half-life of human VWF was significantly increased in macLRP1 mice. Ubiquitous blocking of LRP1 or additional lipoprotein receptors by overexpressing receptor-associated protein in macLRP1 mice did not result in further rise of VWF levels (0.1 ± 0.2 U/mL), in contrast to macLRP1+ mice (rise in VWF, 0.8 ± 0.4 U/mL). This points to macLRP1 being the only lipoprotein receptor regulating VWF levels. When testing the mechanism(s) involved, we observed that VWF-coated beads adhered efficiently to LRP1 but only when exposed to shear forces exceeding 2.5 dyne/cm2, implying the existence of shear stress-dependent interactions. Furthermore, a mechanism involving β2-integrins that binds both VWF and LRP1 also is implicated because inhibition of β2-integrins led to increased VWF levels in control (rise, 0.19 ± 0.16 U/mL) but not in macLRP1 mice (0.08 ± 0.15 U/mL).
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