Role of Siglec-7 in apoptosis in human platelets

• Published in: PloS one 2014-09, Vol.9 (9), p.e106239-e106239
• Main Authors: Nguyen, Kim Anh, Hamzeh-Cognasse, Hind, Palle, Sabine, Anselme-Bertrand, Isabelle, Arthaud, Charles-Antoine, Chavarin, Patricia, Pozzetto, Bruno, Garraud, Olivier, Cognasse, Fabrice
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; Acids; Antigens, Differentiation, Myelomonocytic - genetics; Antigens, Differentiation, Myelomonocytic - metabolism; Apoptosis; Apoptosis - genetics; Apoptosis - physiology; Bax protein; Bcl-2 protein; Binding sites; Biology and Life Sciences; Blood platelets; Blood Platelets - cytology; Blood Platelets - metabolism; Blood Platelets - ultrastructure; Cell activation; Cell morphology; Cells, Cultured; Confocal; Confocal microscopy; Crosslinking; Cytokines; Cytology; Cytometry; Depolarization; Electron microscopy; Flow cytometry; Hematology; Humans; Idiopathic thrombocytopenic purpura; Immune response; Immunoglobulins; Inflammation; Innate immunity; Kinases; Lectins; Lectins - genetics; Lectins - metabolism; Lesions; Ligands; Medicine and Health Sciences; Membrane potential; Membrane Potential, Mitochondrial; Membranes; Microscopy; Microscopy, Confocal; Mitochondria; NAD(P)H oxidase; Phosphatidylserine; Platelets; Protein kinase C; Proteins; Purpura; Receptors; Recruitment; Thrombocytopenic purpura; Thrombosis
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0106239

Platelets participate in tissue repair and innate immune responses. Sialic acid-binding immunoglobulin-like lectins (Siglecs) are well-characterized I-type lectins, which control apoptosis. We characterized the expression of Siglec-7 in human platelets isolated from healthy volunteers using flow cytometry and confocal microscopy. Siglec-7 is primarily expressed on α granular membranes and colocalized with CD62P. Siglec-7 expression was increased upon platelet activation and correlated closely with CD62P expression. Cross-linking Siglec-7 with its ligand, ganglioside, resulted in platelet apoptosis without any significant effects on activation, aggregation, cell morphology by electron microscopy analysis or secretion. We show that ganglioside triggered four key pathways leading to apoptosis in human platelets: (i) mitochondrial inner transmembrane potential (ΔΨm) depolarization; (ii) elevated expression of pro-apoptotic Bax and Bak proteins with reduced expression of anti-apoptotic Bcl-2 protein; (iii) phosphatidylserine exposure and (iv), microparticle formation. Inhibition of NAPDH oxidase, PI3K, or PKC rescued platelets from apoptosis induced by Siglec-7 recruitment, suggesting that the platelet receptors P2Y1 and GPIIbIIIa are essential for ganglioside-induced platelet apoptosis. The present work characterizes the role of Siglec-7 and platelet receptors in regulating apoptosis and death. Because some platelet pathology involves apoptosis (idiopathic thrombocytopenic purpura and possibly storage lesions), Siglec-7 might be a molecular target for therapeutic intervention/prevention.