Anxa7 Regulates Platelet Lipid Metabolism And Ca2+ Release In Arterial Thrombosis

Rationale: Platelet activation after contact to subendothelial collagen leads to acute arterial thrombosis. ANXA7 (Annexin A7) is a phospholipid-binding protein participating in the regulation of intracellular Ca2+ and exocytosis. Objective: The present study aimed to determine the role of ANXA7 in platelet Ca2+ signaling and lipid metabolism during platelet activation in arterial thrombosis using the ANXA7 inhibitor 6-amino-2,3-dihydro-3-hydroxymethyl-1,4-benzoxazine (ABO) and gene-targeted mice lacking Anxa7 (Anxa7(-/-)). Methods and Results: ANXA7 is strongly expressed in platelets. Functionally, luminescence aggregometry revealed significantly abrogated aggregation and secretion of ABO-treated or Anxa7(-/-) platelets when compared with untreated or Anxa7(+/+) platelets after activation with collagen or the GPVI (glycoprotein VI)-specific agonist collagen-related peptide. Furthermore, while both thrombus formation on collagen-coated surfaces under high arterial shear rates in ABO-treated or Anxa7-deficient whole blood, and thrombotic vascular occlusion after FeCl3-induced injury in vivo in Anxa7(-/-) bone marrow chimeric mice were significantly diminished, no prolongation of bleeding time was observed in ABO-treated or Anxa7(-/-) mice. Fura-2-AM spectrofluorimetry unraveled a blunted [Ca2+](i) increase in ABO-treated or Anxa7(-/-) platelets after GPVI stimulation. Due to an abolished phospholipase C gamma 2 phosphorylation, Anxa7(-/-) platelets displayed abrogated intracellular Ca2+ mobilization following collagen-related peptide-dependent platelet activation. Quantitative lipidomics analysis further revealed that ANXA7 critically affects platelet oxylipin metabolism following GPVI-dependent platelet activation. Anxa7(-/-) platelets showed a significantly reduced generation of several bioactive metabolites, particularly thromboxane A(2) and 12(S)-hydroxy-eicosatetraenoic acid. Finally, defective phospholipase C gamma 2 phosphorylation and blunted [Ca2+](i) increase in Anxa7(-/-) platelets could be rescued by exogenous addition of 12(S)-hydroxy-eicosatetraenoic acid, indicating that ANXA7 is a critical regulator of the platelet 12-lipoxygenase in GPVI-dependent platelet Ca2+ signaling during arterial thrombosis. Conclusions: The present study unravels ANXA7 as a regulator of oxylipin metabolism and Ca2+-dependent platelet activation downstream of GPVI. ANXA7 plays an important role in platelet signaling during arterial thrombosis and thus may reflect a promising target for novel antiplatelet strategies.