Balduini A, Pallotta I, Malara A, Lova P, Pecci A, Viarengo G, Balduini C L, Torti M
Department of Biochemistry, University of Pavia, Pavia, Italy.
J Thromb Haemost. 2008 Nov;6(11):1900-7. doi: 10.1111/j.1538-7836.2008.03132.x. Epub 2008 Aug 22.
Megakaryocytes release platelets from the tips of cytoplasmic extensions, called proplatelets. In humans, the regulation of this process is still poorly characterized.
To analyse the regulation of proplatelet formation by megakaryocyte adhesion to extracellular adhesive proteins through different membrane receptors.
Human megakaryocytes were obtained by differentiation of cord blood-derived CD34(+) cells, and proplatelet formation was evaluated by phase contrast and fluorescence microscopy.
We found that human megakaryocytes extended proplatelets in a time-dependent manner. Adhesion to fibrinogen, fibronectin or von Willebrand factor (VWF) anticipated the development of proplatelets, but dramatically limited both amplitude and duration of the process. Type I, but not type III or type IV, collagen totally suppressed proplatelet extension, and this effect was overcome by the myosin IIA antagonist blebbistatin. Integrin alphaIIbbeta3 was essential for megakaryocyte spreading on fibrinogen or VWF, but was not required for proplatelet formation. In contrast, proplatelet formation was prevented by blockade of GPIb-IX-V, or upon cleavage of GPIbalpha by the metalloproteinase mocarhagin. Membrane-associated VWF was detected exclusively on proplatelet-forming megakaryocytes, but not on round mature cells that do not extend proplatelets.
Our findings show that proplatelet formation in human megakaryocytes undergoes a complex spatio-temporal regulation orchestrated by adhesive proteins, GPIb-IX-V and myosin IIA.
巨核细胞从称为前血小板的细胞质延伸末端释放血小板。在人类中，这一过程的调控仍不清楚。
通过不同膜受体分析巨核细胞与细胞外黏附蛋白黏附对前血小板形成的调控。
通过脐带血来源的CD34(+)细胞分化获得人巨核细胞，通过相差显微镜和荧光显微镜评估前血小板形成。
我们发现人巨核细胞以时间依赖的方式延伸前血小板。与纤维蛋白原、纤连蛋白或血管性血友病因子（VWF）的黏附提前了前血小板的发育，但显著限制了该过程的幅度和持续时间。I型胶原而非III型或IV型胶原完全抑制前血小板延伸，并且肌球蛋白IIA拮抗剂blebbistatin可克服这种作用。整合素αIIbβ3对于巨核细胞在纤维蛋白原或VWF上的铺展至关重要，但对于前血小板形成并非必需。相反，阻断GPIb-IX-V或通过金属蛋白酶mocarhagin切割GPIbα可阻止前血小板形成。膜相关VWF仅在前血小板形成的巨核细胞上检测到，而在不延伸前血小板的圆形成熟细胞上未检测到。
我们的研究结果表明，人巨核细胞中的前血小板形成受到黏附蛋白、GPIb-IX-V和肌球蛋白IIA精心编排的复杂时空调控。
