INSERM UMR 765, Paris, France.
PLoS One. 2013 May 30;8(5):e63810. doi: 10.1371/journal.pone.0063810. Print 2013.
It is established that proplatelets are formed from mature megakaryocytes (MK) as intermediates before platelet production. Recently, the presence of proplatelets was described in blood incubated in static conditions. We have previously demonstrated that platelet and proplatelet formation is upregulated by MK exposure to high shear rates (1800 s(-1)) on immobilized von Willebrand factor (VWF). The purpose of the present study was to investigate whether VWF is involved in the regulation of terminal platelet production in blood. To this end, Vwf (-/-) mice, a model of severe von Willebrand disease, were used to create a situation in which blood cells circulate in a vascular tree that is completely devoid of VWF. Murine platelets were isolated from Vwf (-/-) and Vwf (+/+) blood, exposed to VWF at 1800 s(-1) in a microfluidic platform, and examined by means of videomicroscopy, as well as fluorescence and activation studies. Proplatelets became visible within 5 minutes, representing 38% of all platelets after 12 minutes and 46% after 28 min. The proportion of proplatelets was 1.8-fold higher in blood from Vwf(-/-) mice than from Vwf(+/+) mice, suggesting a role of VWF in vivo. Fragmentation of these proplatelets into smaller discoid platelets was also observed in real-time. Platelets remained fully activatable by thrombin. Compensation of plasmatic VWF following hydrodynamic gene transfer in Vwf(-/-) mice reduced the percentage of proplatelets to wild-type levels. A thrombocytopenic mouse model was studied in the flow system, 7 days after a single 5-FU injection. Compared to untreated mouse blood, a 2-fold increase in the percentage of proplatelets was detected following exposure to 1800 s(-1) on VWF of samples from mice treated with 5-FU. In conclusion, VWF and shear stress together appear to upregulate proplatelet reorganization and platelet formation. This suggests a new function for VWF in vivo as regulator of bloodstream thrombopoiesis.
已有研究证实，前血小板是巨核细胞（MK）成熟过程中的中间产物，其在血小板生成之前形成。最近，在静态孵育的血液中发现了前血小板的存在。我们之前的研究表明，在固定的 von Willebrand 因子（VWF）上，MK 暴露于 1800 s(-1) 的高剪切速率下，可上调血小板和前血小板的形成。本研究的目的是探讨 VWF 是否参与了血液中终末血小板生成的调节。为此，使用 von Willebrand 病严重模型（Vwf(-/-)）的小鼠，在没有 VWF 的血管树中制造一种血细胞循环的情况。从小鼠血液中分离 Vwf(-/-)和 Vwf(+/+)血小板，在微流控平台上以 1800 s(-1)的速度暴露于 VWF，然后通过视频显微镜、荧光和激活研究进行检查。前血小板在 5 分钟内可见，12 分钟后代表所有血小板的 38%，28 分钟后占 46%。与 Vwf(+/+)小鼠相比，Vwf(-/-)小鼠血液中的前血小板比例高出 1.8 倍，这表明 VWF 在体内发挥作用。实时观察到这些前血小板碎裂成更小的盘状血小板。血小板仍然可以被凝血酶完全激活。Vwf(-/-)小鼠中经流体动力学基因转移补偿的血浆 VWF 将前血小板的比例降低至野生型水平。在流动系统中研究了血小板减少症的小鼠模型，在单次 5-FU 注射后 7 天。与未经处理的小鼠血液相比，在 5-FU 处理的小鼠血液中，暴露于 VWF 并以 1800 s(-1) 时，前血小板的比例增加了 2 倍。总之，VWF 和切应力一起上调前血小板重组和血小板形成。这表明 VWF 在体内具有新的功能，作为血液中血小板生成的调节剂。
