Summary
Microparticles (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).
Keywords
Secretion / exocytosis - platelet activation markers - vascular cell markers