Background: Ca²⁺ signaling is key to cell organization, and its modulation controls many cellular responses. Sarco-endoplasmic reticulum Ca²⁺-ATPases (SERCAs) pump cytosolic Ca²⁺ into internal stores that in turn regulate cytosolic Ca²⁺ concentration rise upon cell activation. Platelets exhibit 2 types of SERCAs, SERCA2b and SERCA3, 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.

Aims: The aim of this study was to uncover the signaling mechanism involved in the mobilization of Ca²⁺ from SERCA3-dependent stores leading to an early ADP secretion that acts as an autocrine loop to potentiate platelet activation.

Methods: Mouse wild-type or SERCA3-deficient platelets, or human platelets were tested for calcium mobilization, secretion and aggregation in presence of different inhibitors.

Results: We demonstrate that an early (5 to 10 seconds following stimulation) ADP secretion is specifically dependent on SERCA3 stored Ca²⁺ exclusively mobilized by nicotinic acid adenosine dinucleotide phosphate (NAADP), both being blocked by the NAADP receptor antagonist Ned-19, and conversely stimulated by permeant NAADP. In contrast, Ca²⁺ mobilization from SERCA3-dependent stores and primary ADP secretion were unaffected by inhibition of the production of inositol-1,4,5-trisphosphate (IP3) by phospholipase-C, and accordingly were not stimulated by permeant IP3. On the contrary, late ADP secretion and SERCA2b-dependent Ca²⁺ stores mobilization were blocked by phospholipase C inhibition or conversely stimulated by permeant IP3 and not by NAADP. Finally, platelet incubation with NAADP and IP3 triggered ADP secretion to a level comparable to thrombin stimulation.

Conclusions: An early ADP secretion, specifically driven by an NAADP/SERCA3 Ca²⁺ mobilization pathway, potentiates platelet activation via a secondary wave of ADP secretion driven by an IP3/SERCA2b-dependent Ca²⁺ stores pathway. Because of its modulating effect on platelet activation, this NAADP-SERCA3 pathway may be a relevant target for future anti-thrombotic therapy.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/naadp-serca3-dependent-ca2-stores-pathway-specifically-controls-early-autocrine-adp-secretion-potentiating-platelet-activation/