Expression of Smooth Muscle α-Actin and the Proliferative Activity of Human Smooth Muscle Cells in Culture Is Influenced by Endothelial-Cell and Fibroblast-Conditioned Medium

Abstract

The relationship between cell density and the expression of smooth-muscle-specific α-actin (SMA) was studied in cultivated human smooth muscle cells (SMC) by indirect immunofluorescence microscopy. Moreover, the influence of an underlying subconfluent and confluent endothelial cell and fibroblast layer on SMA expression and proliferation of SMC was examined. The results demonstrate that the number of SMC expressing SMA correlates with the cell density, e.g. the higher the cell density the higher the number of SMA-expressing cells. This behaviour of SMC was independent of the age of the culture and could be observed over several subsequently established passages in the form of a periodic SMA expression. While underlying layers of subconfluent endothelial cells and fibroblasts neither influenced the growth rate nor SMA expression of SMC, confluent layers of both cell types retarded the expression of SMA and significantly stimulated the proliferative activity of SMC. The results suggest that the interactions between the three cell types present in the arterial wall have to be taken into account when studying complex pathological processes such as atherogenesis in vitro.