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

RATIONALE

Ca signaling is a key and ubiquitous actor of cell organization and its modulation controls many cellular responses. SERCAs (sarco-endoplasmic reticulum Ca-ATPases) pump Ca into internal stores that play a major role in the cytosolic Ca 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 Ca mobilization from SERCA3-dependent stores was required for full platelet activation in weak stimulation conditions.

OBJECTIVE

To uncover the signaling mechanisms associated with Ca mobilization from SERCA3-dependent stores leading to ADP secretion.

METHODS AND RESULTS

Using platelets from wild-type or -deficient mice, we demonstrated that an early (within 5-10 s following stimulation) secretion of ADP specifically dependent on SERCA3 stored Ca is exclusively mobilized by nicotinic acid adenosine dinucleotide-phosphate (NAADP): both Ca 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, Ca 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 Ca mobilization pathway initiates an early ADP secretion, potentiating platelet activation, and a secondary wave of ADP secretion driven by both an IP3/SERCA2b-dependent Ca stores pathway and the NAADP/SERCA3 pathway. This does not exclude that Ca 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. Graphic Abstract: A graphic abstract is available for this article.