Department of Cellular and Molecular Medicine, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
PLoS One. 2011;6(10):e26025. doi: 10.1371/journal.pone.0026025. Epub 2011 Oct 7.
Podocalyxin (Podxl) is a type I membrane sialoprotein of the CD34 family, originally described in the epithelial glomerular cells of the kidney (podocytes) in which it plays an important function. Podxl can also be found in megakaryocytes and platelets among other extrarenal places. The surface exposure of Podxl upon platelet activation suggested it could play some physiological role. To elucidate the function of Podxl in platelets, we generated mice with restricted ablation of the podxl gene in megakaryocytes using the Cre-LoxP gene targeting methodology. Mice with Podxl-null megakaryocytes did not show any apparent phenotypical change and their rates of growth, life span and fertility did not differ from the floxed controls. However, Podxl-null mice showed prolonged bleeding time and decreased platelet aggregation in response to physiological agonists. The number, size-distribution and polyploidy of Podxl-null megakaryocytes were similar to the floxed controls. Podxl-null platelets showed normal content of surface receptors and normal activation by agonists. However, the mice bearing Podxl-null platelets showed a significant retardation in the ferric chloride-induced occlusion of the carotid artery. Moreover, acute thrombosis induced by the i.v. injection of sublethal doses of collagen and phenylephrine produced a smaller fall in the number of circulating platelets in Podxl-null mice than in control mice. In addition, perfusion of uncoagulated blood from Podxl-null mice in parallel flow chamber showed reduced adhesion of platelets and formation of aggregates under high shear stress. It is concluded that platelet Podxl is involved in the control of hemostasis acting as a platelet co-stimulator, likely due to its pro-adhesive properties.
足细胞蛋白（Podxl）是 CD34 家族的一种 I 型膜唾液酸蛋白，最初在肾脏的上皮肾小球细胞（足细胞）中被描述，在足细胞中它发挥着重要的功能。Podxl 还可以在巨核细胞和血小板等肾脏以外的地方被发现。血小板激活时 Podxl 的表面暴露表明它可能发挥一些生理作用。为了阐明 Podxl 在血小板中的功能，我们使用 Cre-LoxP 基因靶向方法，在巨核细胞中对 podxl 基因进行了限制性敲除，从而生成了 Podxl 敲除的小鼠。Podxl 敲除的巨核细胞小鼠没有表现出任何明显的表型变化，它们的生长速度、寿命和繁殖力与 floxed 对照组没有差异。然而，Podxl 敲除小鼠的出血时间延长，对生理激动剂的血小板聚集减少。Podxl 敲除的巨核细胞的数量、大小分布和多倍体与 floxed 对照组相似。Podxl 敲除的血小板表面受体含量正常，对激动剂的激活正常。然而，携带 Podxl 敲除血小板的小鼠在三氯化铁诱导的颈动脉闭塞中显示出明显的延迟。此外，静脉注射亚致死剂量的胶原蛋白和苯肾上腺素诱导的急性血栓形成导致循环血小板数量的下降在 Podxl 敲除小鼠中比在对照小鼠中要小。此外，在平行流室中灌注未凝固的 Podxl 敲除小鼠的血液显示血小板黏附和在高剪切应力下形成聚集体的能力降低。结论是血小板 Podxl 参与了止血的控制，作为血小板共刺激物，可能是由于其促黏附特性。
