Platelet-derived microparticles are the most abundant type of microparticle in human blood and contribute to many biologically significant processes. Here, we report the first proteomic analysis of microparticles generated from activated platelets. Using 1D SDS-PAGE and liquid chromatography coupled to a linear ion trap mass spectrometer, the identification of 578 proteins was accomplished using a minimum of 5 MS/MS detections of at least two different peptides for each protein. These microparticles displayed many proteins intrinsic to and well-characterized on platelets. For example, microparticles in these experiments were found to contain membrane surface proteins including GPIIIa, GPIIb, and P-selectin, as well other platelet proteins such as the chemokines CXCL4, CXCL7, and CCL5. In addition, approximately 380 of the proteins identified were not found in two previous studies of the platelet proteome. Since several of the proteins detected here have been previously implicated in microparticle formation and/or pathological function, it is hoped that this study will help fuel future work concerning the possible role of microparticles in various disease states.
SummaryMicroparticles (MPs) are small membrane vesicles generated by essentially all cell types. In the plasma, most MPs are derived from platelets, but those from other sources, particularly leukocytes (macrophages, lymphocytes, and neutrophils), endothelial cells, and even smooth muscle cells can be detected and appear to play an important role in normal physiology and various diseases. In previous work we analyzed the proteome of MPs generated from isolated platelets (platelet MPs). Here, we report on a comparative analysis of microparticles isolated from plasma (plasma MPs) versus platelet MP using two complementary methods of comparative analysis. The first method, spectral count analysis, yielded 21 proteins detected in plasma MPs (with a total spectral count of 10 or greater) that were essentially absent in platelet MPs (with a total spectral count of 1 or 0). An additional two proteins (von Willebrand Factor, albumin) were present in both types of MPs but enriched in the plasma MPs. The second method, isotope-coded affinity tag (ICAT) labeling of proteins, supported the spectral count results for the more abundant proteins and provided better relative quantitation of differentially expressed proteins. Proteins present only in the plasma MPs include several associated with apoptosis (CD5-like antigen, galectin 3 binding protein, several complement components), iron transport (transferrin, transferrin receptor, haptoglobin), immune response (complement components, immunoglobulin J and kappa chains), and the coagulation process (protein S, coagulation factor VIII).
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