Proteomics of the TRAP-induced platelet releasate

Upon stimulation, platelets release the soluble content of their cytoplasmic granules along with microparticles. This sub-proteome is of interest since many of its constituents are associated with coagulation, (tumor) angiogenesis, cell growth and adhesion. Previously, differential - antibody-based - serum analysis has yielded information on the proteins released from platelets upon stimulation. A promising alternative strategy is formed by identifying the proteins released by freshly isolated platelets from blood using proteomics. Here we report on the analysis of the thrombin receptor activating peptide (TRAP)-induced releasate from 3 different volunteers using high resolution, high mass accuracy hybrid LTQ-FT mass spectrometry in a GeLC-MS/MS workflow. We obtained an activated platelet releasate proteome comprising a total of 716 identified proteins with 225 proteins present in the releasate of 3/3 volunteers. This core dataset is characterized by gene ontology mining and signal peptide analysis. Meta-analysis of our dataset and two published datasets of platelet a-granules and microparticles reveals that 55% of our platelet releasate proteins can be annotated using these previous platelet subproteome data, of the remaining releasate proteome 5% overlaps with a published platelet secretome while 40% of our data consists of novel releasate proteins. This high-accuracy activated platelet releasate proteome represents the largest and most comprehensive analysis to date. This approach offers unique possibilities to analyse the role of platelet-secreted proteins in physiology and in diseases such as atherosclerosis and cancer.