Murine coagulation factor VIII is synthesized in endothelial cells

Abstract

• Lman1 tissue-specific knockout mice reveal that endothelial cells, not hepatocytes, are the primary source of FVIII biosynthesis.• F8 gene expression is heterogeneous among endothelial cell populations in different tissues.The primary cellular source of factor VIII (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 factor V (FV) and FVIII to the plasma. Lman1 mutations result in combined deficiency of FV and FVIII, with levels of both factors reduced to ∼10% to 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 messenger RNA isolation and quantitative polymerase chain reaction 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. (Blood. 2014;123(24):3697-3705)

CHD4-regulated plasmin activation impacts lymphovenous hemostasis and hepatic vascular integrity

“…Finally, it is worth noting that the liver is the key site of synthesis of most proteins required for the regulation of coagulation and fibrinolysis. Because hepatocytes and sinusoidal endothelial cells produce clotting and inhibitory factors that circulate in the bloodstream (41,42), liver injury and disease result in diminished production of these factors and subsequently a variety of coagulation disorders (7,43). Therefore, the plasmin-induced liver damage we detected in Chd4 fl/fl Lyve1-Cre + livers as early as E13.5 may contribute to the deficit of fibrin-rich LV thrombi we detected in those embryos.…”

Extrahepatic sources of factor VIII potentially contribute to the coagulation cascade correcting the bleeding phenotype of mice with hemophilia A

“…5 On the other hand, transplantation of liver from hemophilic donors, either dogs 6 or humans, 7 into healthy subjects does not cause hemophilia, indicating that FVIII is also produced in extrahepatic sites. Recent studies using a cell therapy approach 8,9 or cell typespecific knockout experiments indicated that FVIII is produced largely in liver sinusoidal endothelial cells (LSEC); 10,11 although FVIII mRNA was present in endothelial cells of kidneys, spleen and lungs, it was absent in endothelial cells of the brain and heart. 10,[12][13][14][15] These findings were in agreement with studies showing that hemophilic patients benefited from transplantation of the spleen in the long-term.…”

The search for the origin of factor VIII synthesis and its impact on therapeutic strategies for hemophilia A

“…In particular, high expression of the HOXA9 gene is a highly significant marker of poor prognosis in acute myeloid leukemia, 1 and dysregulation of HOXA9 appears to play a central role in several distinct leukemias. These include acute myeloid leukemia and acute lymphoblastic leukemias caused by translocations of the Mixed Lineage Leukemia (MLL) gene, [2][3][4] fusions of the HOXA9 gene that produce a novel HOXA9-NUP98 fusion protein in acute myeloid leukemia, 5 and T-cell acute lymphoblastic leukemias that have translocations between the TCRβ and HOXA9/A10 loci. 6 Interestingly however, despite this seemingly central role in a subset of acute leukemias, Hoxa9 expression alone is only weakly oncogenic in mouse leukemia models and usually requires a second "hit" via overexpression of Meis1, 7,8 or in some cases Pbx3.…”

“…[4][5][6] The overall conclusion was that liver sinusoid endothelial cells (LSEC), not hepatocytes, are the main cellular source of hepatic factor VIII. Here, in a unique set of experiments, the authors demonstrated that transplant of non-parenchymal cells (a mix of Küpffer cells and LSEC), improved circulating factor VIII levels, but infusion of isolated hepatocyte did not.…”

“…[4][5][6] In this issue of the journal, Zanolini and colleagues provide new insight into both the hepatic and hematopoietic-derived cellular origin of circulating factor VIII. 7 Using multiple sources of hematopoietic cells (bonemarrow derived or cord blood CD34 + cells) from humans, they identified (by both mRNA and immunofluorescence staining of protein) that monocytes and monocyte-derived macrophages are the main cells of the hematopoietic system responsible for factor VIII.…”