Fujii Toshihiro, Sakata Asuka, Nishimura Satoshi, Eto Koji, Nagata Shigekazu
Laboratory of Biochemistry & Immunology, Immunology Frontier Research Center, Osaka University, Osaka 565-0871, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Saitama 332-0012, Japan;
Center for Molecular Medicine, Jichi Medical University, Tochigi 329-0498, Japan;
Proc Natl Acad Sci U S A. 2015 Oct 13;112(41):12800-5. doi: 10.1073/pnas.1516594112. Epub 2015 Sep 28.
Phosphatidylserine (PtdSer) exposure on the surface of activated platelets requires the action of a phospholipid scramblase(s), and serves as a scaffold for the assembly of the tenase and prothrombinase complexes involved in blood coagulation. Here, we found that the activation of mouse platelets with thrombin/collagen or Ca(2+) ionophore at 20 °C induces PtdSer exposure without compromising plasma membrane integrity. Among five transmembrane protein 16 (TMEM16) members that support Ca(2+)-dependent phospholipid scrambling, TMEM16F was the only one that showed high expression in mouse platelets. Platelets from platelet-specific TMEM16F-deficient mice exhibited defects in activation-induced PtdSer exposure and microparticle shedding, although α-granule and dense granule release remained intact. The rate of tissue factor-induced thrombin generation by TMEM16F-deficient platelets was severely reduced, whereas thrombin-induced clot retraction was unaffected. The imaging of laser-induced thrombus formation in whole animals showed that PtdSer exposure on aggregated platelets was TMEM16F-dependent in vivo. The phenotypes of the platelet-specific TMEM16F-null mice resemble those of patients with Scott syndrome, a mild bleeding disorder, indicating that these mice may provide a useful model for human Scott syndrome.
活化血小板表面磷脂酰丝氨酸（PtdSer）的暴露需要磷脂翻转酶的作用，并作为参与血液凝固的凝血酶原酶和凝血酶原酶复合物组装的支架。在这里，我们发现，在20°C下用凝血酶/胶原蛋白或Ca（2+）离子载体激活小鼠血小板会诱导PtdSer暴露，而不会损害质膜完整性。在支持Ca（2+）依赖性磷脂翻转的五个跨膜蛋白16（TMEM16）成员中，TMEM16F是唯一在小鼠血小板中高表达的成员。来自血小板特异性TMEM16F缺陷小鼠的血小板在激活诱导的PtdSer暴露和微粒脱落方面表现出缺陷，尽管α颗粒和致密颗粒释放保持完整。TMEM16F缺陷血小板由组织因子诱导的凝血酶生成速率严重降低，而凝血酶诱导的血块收缩不受影响。对全动物激光诱导血栓形成的成像显示，聚集血小板上的PtdSer暴露在体内是TMEM16F依赖性的。血小板特异性TMEM16F基因敲除小鼠的表型与轻度出血性疾病斯科特综合征患者的表型相似，表明这些小鼠可能为人类斯科特综合征提供一个有用的模型。
