Shear stress is required for the endocytic uptake of the factor VIII-von Willebrand factor complex by macrophages
Article first published online: 4 SEP 2012
© 2012 International Society on Thrombosis and Haemostasis
Journal of Thrombosis and Haemostasis
Volume 10, Issue 9, pages 1929–1937, September 2012
How to Cite
CASTRO-NÚÑEZ, L., DIENAVA-VERDOOLD, I., HERCZENIK, E., MERTENS, K. and MEIJER, A. B. (2012), Shear stress is required for the endocytic uptake of the factor VIII-von Willebrand factor complex by macrophages. Journal of Thrombosis and Haemostasis, 10: 1929–1937. doi: 10.1111/j.1538-7836.2012.04860.x
- Issue published online: 4 SEP 2012
- Article first published online: 4 SEP 2012
- Accepted manuscript online: 20 JUL 2012 01:14AM EST
- Received 9 January 2012, accepted 3 July 2012
- factor VIII;
- shear stress;
- von Willebrand factor
Summary. Background: Low-density lipoprotein (LDL) receptor family members contribute to the cellular uptake of factor VIII. How von Willebrand factor fits into this endocytic pathway has remained poorly understood.
Objectives: It has been suggested that macrophages contribute to the clearance of the factor VIII (FVIII)-von Willebrand factor (VWF) complex. We now assessed the mechanisms of uptake employing human monocyte-derived macrophages.
Methods: A confocal microscopy study was employed to study the uptake by monocyte-derived macrophages of a functional green fluorescent FVIII-GFP derivative in the presence and absence of VWF.
Results: The results revealed that FVIII-GFP is internalized by macrophages. We found that FVIII-GFP co-localizes with LDL receptor-related protein (LRP), and that the LRP antagonist Receptor Associated Protein (RAP) blocks the uptake of FVIII-GFP. However, FVIII-GFP was not detected in the macrophages in the presence of VWF, suggesting that the FVIII-VWF complex is not internalized by these cells at all. Apart from static conditions, we also investigated the effect of shear stress on the uptake of FVIII-GFP in presence of VWF. Immunofluorescence studies demonstrated that VWF does not block endocytosis of FVIII-GFP under flow conditions. Moreover, VWF itself was also internalized by the macrophages. Strikingly, in the presence of RAP, endocytosis of FVIII-GFP and VWF was inhibited.
Conclusion: The results show that shear stress is required for macrophages to internalize both constituents of the FVIII-VWF complex.