Survival protein anoctamin-6 controls multiple platelet responses including phospholipid scrambling and swelling

The Scott syndrome is characterized as a mild bleeding disorder associated with a low prothrombin consumption in blood. Platelets from Scott patients show a defect in Ca²⁺-induced phosphatidylserine (PS) exposure on the platelet surface and microparticle formation, but unchanged Ca²⁺ signaling and aggregation (1, 2). For long it has been recognized that the defective PS exposure in blood cells from Scott patients results from impaired phospholipid scrambling, a process that normally abolishes the asymmetric distribution of PS and phosphatidylethanolamine over the plasma membrane upon persistent elevation of cytosolic Ca²⁺. Consequence of the defective PS exposure is a markedly impaired procoagulant activity of platelets, which agrees with the bleeding phenotype (3). Recently, in two unrelated Scott syndrome patients, dysfunctional mutations have been identified in the ANO6 gene (alternatively named TMEM16F), which codes for the integral membrane protein anoctamin 6 (ANO6) (4, 5). The question can be raised if a gene defect in ANO6 alone is sufficient for the altered blood cell properties in the Scott syndrome. In the present article, we used several molecular and functional approaches to unravel the apparently multiple and non-redundant functions of ANO6 in platelets. We investigated the alterations in platelet properties of a Scott patient in comparison to platelets from healthy control subjects, and furthermore compared the platelet properties of several new strains of Ano6-deficient mice versus wild type mice.