Defective Zn 2+ homeostasis in mouse and human platelets with α- and δ-storage pool diseases

Zinc (Zn 2+ ) can modulate platelet and coagulation activation pathways, including fibrin formation. Here, we studied the (patho)physiological consequences of abnormal platelet Zn 2+ storage and release. To visualize Zn 2+ storage in human and mouse platelets, the Zn 2+ specific fluorescent dye FluoZin3 was used. In resting platelets, the dye transiently accumulated into distinct cytosolic puncta, which were lost upon platelet activation. Platelets isolated from Unc13d −/− mice, characterized by combined defects of α/δ granular release, showed a markedly impaired Zn 2+ release upon activation. Platelets from Nbeal2 −/− mice mimicking Gray platelet syndrome (GPS), characterized by primarily loss of the α-granule content, had strongly reduced Zn 2+ levels, which was also confirmed in primary megakaryocytes. In human platelets isolated from patients with GPS, Hermansky-Pudlak Syndrome (HPS) and Storage Pool Disease (SPD) altered Zn 2+ homeostasis was detected. In turbidity and flow based assays, platelet-dependent fibrin formation was impaired in both Nbeal2 −/− and Unc13d −/− mice, and the impairment could be partially restored by extracellular Zn 2+ . Altogether, we conclude that the release of ionic Zn 2+ store from secretory granules upon platelet activation contributes to the procoagulant role of Zn 2+ in platelet-dependent fibrin formation.