Consistent differences in protein distribution along the longitudinal axis in symptomatic carotid atherosclerotic plaques

Identifying proteins associated with a complicated atherosclerotic plaque phenotype would provide potential biomarkers for detection of patients at elevated risk for clinically overt disease. We hypothesized that the protein content of carotid atherosclerotic tissue differs between complicated segments located in the internal carotid artery (ICA) and more stable segments in the common carotid artery (CCA). Using differential proteomics, we aimed to identify proteins differentially expressed between these segments of symptomatic carotid plaques. Ten snap-frozen human endarterectomies were divided into ICA and CCA segments and compared using two-dimensional differential gel electrophoresis and liquid chromatography-mass spectrometry. This study setup allowed pair-wise comparison of complicated and more stable atherosclerotic tissue from the same individual. We identified 19 proteins with differential distribution between ICA and CCA segments. Among the proteins more abundant in ICA were S100A10, ferritin light chain and fibrinogen. Among the proteins more abundant in CCA were ApoE, actin and l-lactate dehydrogenase B. Immunohistochemical staining revealed that S100A10 was expressed in endothelial cells, in clusters of macrophages and foam cells, and co-localized with the urokinase-type plasminogen activator receptor, uPAR. In conclusion, the results support the concept of comparing segments within plaques. The identified proteins constitute potential markers of complicated atherosclerotic lesions. The previously reported function of S100A10 to regulate plasmin activity affecting both angiogenesis and macrophage invasion, together with our observation of its accumulation in complicated plaque segments, warrants further studies of its potential role as a drug target for treatment of advanced atherosclerosis.

Research highlights
► Protein patterns differed longitudinally between carotid plaque segments.
► Proteins with differential expression between plaque segments were identified.
► The current approach allows linking of each protein to severity of atherosclerosis.
► The plasminogen receptor S100A10 was enriched in complicated plaque segments.