Collagen-synthesizing cells in initial and advanced atherosclerotic lesions of human aorta

Accumulation of extracellular matrix, fibrosis, is regarded to be one of the major manifestations of atherosclerosis. Collagen type I is the predominant matrix component in human atherosclerotic plaques. In this work we have demonstrated procollagen type I expressing cells (PCI-cells) and studied their localization in grossly normal human aorta and atherosclerotic lesions: initial lesions, fatty streaks, fibrolipid lesions (fibrolipid plaque, fibroatheroma), fibrotic lesions (fibrous plaque). PCI-cells were revealed immunocytochemically using SPI.D8 monoclonal antibody against human procollagen type I. We failed to detect PCI-cells in the areas of grossly normal aorta and media underlying atherosclerotic lesions. Positively stained cells were shown in the areas of initial lesions, fatty streaks, fibrolipid and fibrous plaques. The largest amount of PCI-cells was revealed in fatty streaks. These cells were predominantly localized in the preluminal proteoglycan-rich intimal sublayer. Intimal cells in grossly normal regions formed a common cellular network contacting each other with their processes. The cellular network is found to be partly disintegrated in atherosclerotic lesions, which leads to the appearance of isolated cells. The share of isolated PCI-cells localized outside the intimal cellular network was higher in advanced lesions than in the areas of early atherosclerotic lesions. In initial lesions most of PCI-cells were identified as smooth muscle cells using antibodies to smooth muscle alpha-actin. In fatty streaks PCI-expressing smooth muscle cells were fewer in number. Much fewer cells double-stained with anti-alpha-actin and anti-PCI antibodies were found in fibrolipid and fibrous plaques. The proportion of these double stained cells was higher among total number of PCI-cells involved in the cellular network versus PCI-cells outside the network. The results of the study demonstrated that the most active de novo synthesis of interstitial collagen takes place in the regions of atherosclerotic lesions characterized by lipid deposition, which may lead to the further progression of atherosclerotic lesions.