Liu L, Choi H, Bernardo A, Bergeron A L, Nolasco L, Ruan C, Moake J L, Dong J-F
Department of Medicine, Thrombosis Research Section, Baylor College of Medicine, Houston, TX 77030, USA.
J Thromb Haemost. 2005 Nov;3(11):2536-44. doi: 10.1111/j.1538-7836.2005.01561.x. Epub 2005 Sep 13.
The adhesion ligand von Willebrand factor (VWF) is synthesized and stored in vascular endothelial cells and megakaryocytes/platelets. As in endothelial cells, platelet VWF also contains ultra-large (UL) multimers that are hyperactive in aggregating platelets. ULVWF in platelet lysates of thrombin-stimulated platelets was only detected in the presence of EDTA, suggesting that ULVWF is cleaved by a divalent cation-dependent protease. A recent study shows that platelets contain the VWF-cleaving metalloprotease ADAMTS-13, but its activity remains unknown. In this study, we show that platelet lysates cleave endothelial cell-derived ULVWF under static and flow conditions. This activity is inhibited by EDTA and by an ADAMTS-13 antibody from the plasma of a patient with acquired TTP. ADAMTS-13 was detected in platelet lysates and on the platelet surface by four antibodies that bind to different domains of the metalloprotease. Expression of ADAMTS-13 on the platelet surface increases significantly upon platelet activation by the thrombin receptor-activating peptide, but not by ADP. These results demonstrate that platelets contain functionally active ADAMTS-13. This intrinsic activity may be physiologically important to prevent the sudden release of hyperactive ULVWF from platelets and serves as the second pool of ADAMTS-13 to encounter the increase in ULVWF release from endothelial cells.
黏附配体血管性血友病因子（VWF）在内皮细胞和巨核细胞/血小板中合成并储存。与内皮细胞一样，血小板VWF也含有超大（UL）多聚体，这些多聚体在聚集血小板方面具有高活性。仅在存在乙二胺四乙酸（EDTA）的情况下，才能在凝血酶刺激的血小板裂解物中检测到ULVWF，这表明ULVWF被一种二价阳离子依赖性蛋白酶切割。最近的一项研究表明，血小板含有VWF切割金属蛋白酶ADAMTS-13，但其活性尚不清楚。在本研究中，我们表明血小板裂解物在静态和流动条件下均可切割内皮细胞衍生的ULVWF。这种活性受到EDTA和来自一名获得性血栓性血小板减少性紫癜（TTP）患者血浆中的ADAMTS-13抗体的抑制。通过四种与该金属蛋白酶不同结构域结合的抗体，在血小板裂解物和血小板表面检测到了ADAMTS-13。凝血酶受体激活肽激活血小板后，血小板表面ADAMTS-13的表达显著增加，但二磷酸腺苷（ADP）激活血小板后则不然。这些结果表明血小板含有功能活性的ADAMTS-13。这种内在活性在生理上可能对防止血小板中高活性ULVWF的突然释放很重要，并作为ADAMTS-13的第二个来源，以应对内皮细胞释放的ULVWF增加的情况。
