NAADP/SERCA3-Dependent Ca2+Stores Pathway Specifically Controls Early Autocrine ADP Secretion Potentiating Platelet Activation

Abstract

Rationale: Ca2+signaling is a key and ubiquitous actor of cell organization and its modulation controls many cellular responses. SERCAs (sarco-endoplasmic reticulum Ca2+-ATPases) pump Ca2+into internal stores that play a major role in the cytosolic Ca2+concentration rise upon cell activation. Platelets exhibit 2 types of SERCAs, SERCA2b and SERCA3 (SERCA3 deficient mice), which may exert specific roles, yet ill-defined. We have recently shown that Ca2+mobilization from SERCA3-dependent stores was required for full platelet activation in weak stimulation conditions. Objective: To uncover the signaling mechanisms associated with Ca2+mobilization from SERCA3-dependent stores leading to ADP secretion. Methods and Results: Using platelets from wild-type or Serca3-deficient mice, we demonstrated that an early (within 5-10 s following stimulation) secretion of ADP specifically dependent on SERCA3 stored Ca2+is exclusively mobilized by nicotinic acid adenosine dinucleotide-phosphate (NAADP): Both Ca2+mobilization from SERCA3-dependent stores and primary ADP secretion are blocked by the NAADP receptor antagonist Ned-19, and reciprocally both are stimulated by permeant NAADP. In contrast, Ca2+mobilization from SERCA3-dependent stores and primary ADP secretion were unaffected by inhibition of the production of IP3 (inositol-1,4,5-trisphosphate) by phospholipase-C and accordingly were not stimulated by permeant IP3. Conclusions: Upon activation, an NAADP/SERCA3 Ca2+mobilization pathway initiates an early ADP secretion, potentiating platelet activation, and a secondary wave of ADP secretion driven by both an IP3/SERCA2b-dependent Ca2+stores pathway and the NAADP/SERCA3 pathway. This does not exclude that Ca2+mobilized from SERCA3 stores may also enhance platelet global reactivity to agonists. Because of its modulating effect on platelet activation, this NAADP-SERCA3 pathway may be a relevant target for anti-thrombotic therapy.