Expression of factor VIII by murine liver sinusoidal endothelial cells

Factor VIII (MTI) is the procoagulant plasma glycoprotein that is missing o r decreased in hemophilia A. The cellular origin of fVIII synthesis is cont roversial. Liver transplantation cures hemophilia A, demonstrating that the liver is a major site of fVIII synthesis. We detected fVIII mRNA in purifi ed populations of murine liver sinusoidal endothelial cells (LSECs) and hep atocytes, but not Kupffer cells. LSECs and hepatocytes contained comparable numbers of fVIII mRNA (40 and 70 transcripts per cell, respectively) by qu antitative competitive reverse transcriptase-polymerase chain reaction anal ysis. There was not detectable mRNA for factor IX,a hepatocyte marker, in t he LSEC preparation, nor was there detectable mRNA for von Willebrand facto r, an endothelial cell marker, in the hepatocyte preparation. This excludes the possibility that detectable fVIII mRNA is due to cross-contamination i n the hepatocyte or LSEC preparations, Primary cultures of LSECs were estab lished in which fVIII mRNA levels were indistinguishable from purified LSEC s, LSECs secreted active fVIII into the culture medium. This finding repres ents the first demonstration of homologous expression of fVIII mRNA and pro tein in cell culture and should facilitate studies of fVIII gene regulation . Additionally, LSECs potentially are targets for a fVIII transgene during gene therapy of hemophilia A.