Endothelial cells synthesize FVIII Scientific section designation: THROMBOSIS AND HEMOSTASIS Title: Murine coagulation factor VIII is synthesized in endothelial cells

The primary cellular source of FVIII biosynthesis is controversial, with contradictory evidence supporting an endothelial or hepatocyte origin. LMAN1 is a cargo receptor in the early secretory pathway that is responsible for the efficient secretion of FV and FVIII to the plasma. Lman1 mutations result in combined deficiency of FV and FVIII, with levels of both factors reduced to ~10-15% of normal in human patients. We generated Lman1 conditional knockout mice to characterize the FVIII secretion profiles of endothelial cells and hepatocytes. We demonstrate that endothelial cells are the primary biosynthetic source of murine FVIII, and that hepatocytes make no significant contribution to the plasma FVIII pool. Utilizing RiboTag mice and polyribosome immunoprecipitation, we performed endothelial cell-specific mRNA isolation and qPCR analyses to confirm that endothelial cells highly express F8, and to explore the heterogeneity of F8 expression in different vascular beds. We demonstrate that endothelial cells from multiple, but not all, tissues contribute to the plasma FVIII pool in the mouse. For personal use only. on July 15, 2017. by guest www.bloodjournal.org From