title: A role for adhesion and degranulation-promoting adapter protein in collagen-induced platelet activation mediated via integrin α(2) β(1).
abstract: BACKGROUND
  Collagen-induced platelet activation is a key step in the development of arterial thrombosis via its interaction with the receptors glycoprotein (GP)VI and integrin α(2) β(1) . Adhesion and degranulation-promoting adapter protein (ADAP) regulates α(IIb) β(3) in platelets and α(L) β(2) in T cells, and is phosphorylated in GPVI-deficient platelets activated by collagen.
  
  
  OBJECTIVE
  To determine whether ADAP plays a role in collagen-induced platelet activation and in the regulation and function of α(2) β(1).
  
  
  METHODS
  Using ADAP(-/-) mice and synthetic collagen peptides, we investigated the role of ADAP in platelet aggregation, adhesion, spreading, thromboxane synthesis, and tyrosine phosphorylation.
  
  
  CONCLUSIONS
  Platelet aggregation and phosphorylation of phospholipase Cγ2 induced by collagen were attenuated in ADAP(-/-) platelets. However, aggregation and signaling induced by collagen-related peptide (CRP), a GPVI-selective agonist, were largely unaffected. Platelet adhesion to CRP was also unaffected by ADAP deficiency. Adhesion to the α(2) β(1) -selective ligand GFOGER and to a peptide (III-04), which supports adhesion that is dependent on both GPVI and α(2) β(1), was reduced in ADAP(-/-) platelets. An impedance-based label-free detection technique, which measures adhesion and spreading of platelets, indicated that, in the absence of ADAP, spreading on GFOGER was also reduced. This was confirmed with non-fluorescent differential-interference contrast microscopy, which revealed reduced filpodia formation in ADAP(-/-) platelets adherent to GFOGER. This indicates that ADAP plays a role in mediating platelet activation via the collagen-binding integrin α(2) β(1). In addition, we found that ADAP(-/-) mice, which are mildly thrombocytopenic, have enlarged spleens as compared with wild-type animals. This may reflect increased removal of platelets from the circulation.
authors: School of Pharmacy, Queen's University Belfast, Belfast, UK. gavin.jarvis@cantab.net
authors: G E
authors: GE
authors: Jarvis
authors: D
authors: D
authors: Bihan
authors: S
authors: S
authors: Hamaia
authors: N
authors: N
authors: Pugh
authors: C J G
authors: CJ
authors: Ghevaert
authors: A C
authors: AC
authors: Pearce
authors: C E
authors: CE
authors: Hughes
authors: S P
authors: SP
authors: Watson
authors: J
authors: J
authors: Ware
authors: C E
authors: CE
authors: Rudd
authors: R W
authors: RW
authors: Farndale
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D007135:Immunoglobulin Variable Region / Q000235:genetics / Q000378:metabolism; D038982:Integrin alpha2beta1 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010455:Peptides / Q000378:metabolism; D051966:Phospholipase C gamma / Q000378:metabolism; D010766:Phosphorylation; D015539:Platelet Activation; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D013163:Splenomegaly / Q000235:genetics / Q000378:metabolism; D013921:Thrombocytopenia / Q000235:genetics / Q000378:metabolism; D013928:Thromboxane A2 / Q000378:metabolism; D013929:Thromboxane B2 / Q000378:metabolism; D013997:Time Factors; D014443:Tyrosine
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018955:CD36 Antigens; D002352:Carrier Proteins; C491468:Fyb protein, mouse; D007135:Immunoglobulin Variable Region; D038982:Integrin alpha2beta1; D010455:Peptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C435908:collagen-related peptide; D014443:Tyrosine; D013929:Thromboxane B2; D013928:Thromboxane A2; D003094:Collagen; D051966:Phospholipase C gamma