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Human endothelial cells synthesize and release ADAMTS‐13

Summary.  Hepatic stellate cells have been considered to be a primary source for human plasma ADAMTS‐13, the von Willebrand factor (VWF)‐cleaving metalloprotease. In this study, ADAMTS‐13 antigen was detected by immunofluorescence in both venous (HUVECs) and arterial endothelial cells (HUAECs) using both polyclonal antibodies made against peptides found in various domains of human ADAMTS‐13, as well as by a monoclonal antibody against the ADAMTS‐13 metalloprotease domain. ADAMTS‐13 antigen had an intra‐cellular distribution in endothelial cells distinct from the Weibel–Palade body location of VWF, and was released from the cells during 48 h in culture. The mRNA for ADAMTS13 was detected in HUVECs and HUAECs using reverse transcription‐polymerase chain reaction (RT‐PCR), indicating that the enzyme is synthesized in these cells. The ADAMTS‐13 protein was immunoprecipitated from HUVECs and had an approximate Mr of 170 kDa, similar to the molecular mass of recombinant ADAMTS‐13. The ADAMTS‐13 in HUVEC and HUAEC lysates had enzymatic activity using both static and flow assays. We conclude that ADAMTS‐13 is synthesized in human endothelial cells, and released constitutively. The vast number of endothelial cells in the body may be an important source of ADAMTS‐13.