Influence of macrophages and macrophage-modified collagen I on the adhesion and proliferation of vascular smooth muscle cells in culture

The adhesion, proliferation and morphology of rat vascular smooth muscle ce lls (VSMC) in cocultures with macrophages or in cultures on type I collagen modified by activated macrophages were evaluated. In the first set of expe riments, rat alveolar macrophages were added to 24-hour-old VSMC cultures. Between days 2 and 5 after VSMC seeding, the population densities and doubl ing times of cells were similar in both VSMC-macrophage and pure VSMC cultu res. However, from day 5, the cocultures proliferated about two times more rapidly and on day 7, they reached higher cell population density by 40%. T he pure macrophage cultures did not proliferate. In the second set of exper iments, rat alveolar macrophages were activated by non-toxic TiO2 dust to p roduce reactive oxygen species and incubated for 120 min with collagen I. T he collagen was then adsorbed on plastic culture dishes and seeded with VSM C. The collagen exposed for 10 min only, the unmodified collagen and pure c ulture dishes were used as control growth supports. On all four tested subs trates, the number of initially adhered cells was similar, but on the colla gen modified for 120 min, the cells were less spread. Moreover, on day 2 to 3 after seeding, some cells on this collagen became vacuolated and detache d spontaneously from the growth support. The remaining VSMC, however, rapid ly proliferated, so that on day 9, the cell population density on 120-min-m odified collagen was similar as on both control collagens and significantly higher compared to that on uncoated dishes. Our results suggest that 1. Th e delayed growth-stimulating effect of macrophages on VSMC-macrophage mixed population is probably due to autocrine production of mitogens by both cel l types rather than due to an acute effect of short-living oxygen radicals released from macrophages immediately after adding to VSMC cultures. 2. The effect of collagen I exposed to activated macrophages for 120 min is sligh tly cytotoxic, which could, however, stimulate a release of mitogens from d amaged as well as surviving VSMC.