Borchiellini A, Fijnvandraat K, ten Cate J W, Pajkrt D, van Deventer S J, Pasterkamp G, Meijer-Huizinga F, Zwart-Huinink L, Voorberg J, van Mourik J A
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam, The Netherlands.
Blood. 1996 Oct 15;88(8):2951-8.
The results of studies with cultured endothelial cells have shown that most von Willebrand factor (vWF) synthesized is directly secreted (constitutive pathway) and consists of both mature vWF, its precursor molecule pro-vWF, and the cleaved vWF prosequence. Only fully processed, functionally mature vWF is stored within the cell, together with the propeptide, and leaves the cell only on stimulation (regulated secretion). Both in resting and stimulated cultured endothelial cells, the stoichiometry of the released propeptide to the released mature vWF is essentially equimolar. In the present study, we have measured the molar ratio of propeptide to mature vWF in vivo, both under resting conditions and conditions that reflect activation of the endothelium. To this end, we devised a method that allows the measurement of the propeptide (vW antigen II) on a quantitative, is, molar basis, using purified recombinant propeptide as a standard. Our results show that the molar concentration of the propeptide in normal plasma is about one tenth of the concentration of mature vWF (expressed as half-dimer concentration). This ratio is approximately 1:1 in the medium of cultured endothelial cells. On administration in healthy subjects of either 1-deamino-8-D-arginine vasopressin or endotoxin, both agents being known to elicit an intravascular increase of vWF, the molar ratio of propeptide to mature vWF increased fourfold to fivefold. The propeptide concentration returned to baseline values after about 6 to 7 hours of injection of each stimulus, whereas the increase of mature vWF was much more sustained. Because the respective half-lives of mature vWF and its propeptide clearly differ, measurement of the concentration of these proteins could provide a means to assess the extent of activation of the endothelium under physiological and pathophysiological conditions.
对培养的内皮细胞进行的研究结果表明，合成的大多数血管性血友病因子（vWF）直接分泌（组成型途径），包括成熟的vWF、其前体分子前vWF以及切割后的vWF前序列。只有经过完全加工、功能成熟的vWF与前肽一起储存在细胞内，并且仅在受到刺激时才离开细胞（调节性分泌）。在静息和受刺激的培养内皮细胞中，释放的前肽与释放的成熟vWF的化学计量比基本为等摩尔。在本研究中，我们测量了体内静息条件下以及反映内皮激活的条件下前肽与成熟vWF的摩尔比。为此，我们设计了一种方法，以纯化的重组前肽为标准，能够在定量、即摩尔基础上测量前肽（vW抗原II）。我们的结果表明，正常血浆中前肽的摩尔浓度约为成熟vWF浓度的十分之一（以半二聚体浓度表示）。在培养的内皮细胞培养基中，该比例约为1:1。在健康受试者中给予1-去氨基-8-D-精氨酸加压素或内毒素，已知这两种物质都会引起血管内vWF增加，前肽与成熟vWF的摩尔比增加了四倍至五倍。在注射每种刺激物约6至7小时后，前肽浓度恢复到基线值，而成熟vWF的增加则更为持久。由于成熟vWF及其前肽各自的半衰期明显不同，测量这些蛋白质的浓度可以提供一种手段来评估生理和病理生理条件下内皮激活的程度。
