Yoda1 and phosphatidylserine exposure in red cells from patients with sickle cell anaemia

Phosphatidylserine (PS) exposure is increased in red cells from sickle cell anaemia (SCA) patients. Externalised PS is prothrombotic and attractive to phagocytes and activated endothelial cells and thus contributes to the anaemic and ischaemic complications of SCA. The mechanism of PS exposure remains uncertain but it can follow increased intracellular Ca(2+) concentration ([Ca(2+)](i)). Normally, [Ca(2+)](i) is maintained at very low levels but in sickle cells, Ca(2+) permeability is increased, especially following deoxygenation and sickling, mediated by a pathway sometimes called P(sickle). The molecular identity of P(sickle) is also unclear but recent work has implicated the mechanosensitive channel, PIEZO1. We used Yoda1, an PIEZO1 agonist, to investigate its role in sickle cells. Yoda1 caused an increase in [Ca(2+)](i) and PS exposure, which was inhibited by its antagonist Dooku1 and the PIEZO1 inhibitor GsMTx4, consistent with functional PIEZO1. However, PS exposure did not necessitate an increase in [Ca(2+)](i). Two PKC inhibitors were also tested, chelerytherine chloride and calphostin C. Both reduced PS exposure whilst chelerytherine chloride also reduced Yoda1-induced increases in [Ca(2+)](i). Findings are therefore consistent with the presence of PIEZO1 in sickle cells, able to mediate Ca(2+) entry but that PKC was also involved in both Ca(2+) entry and PS exposure.