Distinct proteome features of plasma microparticles

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Abstract
Plasma microparticles (MPs) are spherical cell membrane fragments derived from either apoptotic or activated cells. Characterized by a rich phospholipid moiety and many protein constituents, MPs normally circulate in the blood and contribute to numerous physiological processes. In disease states, MPs derived from the injured organ likely contain valuable markers for determining the site, type, and extent of disease pathology. However, the basic protein characteristics of plasma MPs have yet to be described. In this study, MPs from a pooled plasma sample derived from 16 healthy donors, all of group A blood type, were prepared by ultracentrifugation. Flow cytometry confirmed that a majority of these MPs are smaller than 1 µm. Factor Xa generation assay revealed the presence of tissue factor activity in these MPs, confirming MPs' role in initiating blood coagulation. The MP proteome was analyzed by two‐dimensional (2‐D) gel electrophoresis performed in triplicate, and compared with a 2‐D gel of pooled whole plasma and blood platelets. Overall, plasma MPs displayed distinct protein features and a greater number of protein spots (1021–1055) than that detected in whole plasma (331–370). Protein spots expressed in high abundance in the MP proteome were then excised and submitted for protein identity determination. This process provided protein identification for 169 protein spots and reported their relative protein quantities within the MP proteome. These 169 protein spots represented 83 different proteins and their respective isoforms. Thirty of these proteins have never before been reported in previous proteome analyses of human plasma. These results provide unprecedented information on the MP proteome and create a basis for future studies to understand MP biology and pathophysiology.