Macrophages selectively stimulate ecto-5'-nucleotidase activity of cultured mesangial cells

Abstract

Because rat peritoneal macrophages exhibit a particular binding capacity to rat glomerular mesangial cells in vitro, we have studied the effect of macrophages on two plasma membrane enzymes, ecto-5'-nucleotidase and ecto-Mg2+ ATPase, or rat cultured mesangial cells. A marked increase of ecto-5'-nucleotidase activity was observed in cocultures of rat mesangial cells and peritoneal macrophages. In addition, macrophage-conditioned medium (MCM) produced a dose-dependent increase of mesangial cell ecto-5'-nucleotidase activity. In contrast, ecto-Mg2+ ATPase activity was unaffected. The effect of MCM on ecto-5'-nucleotidase activity was apparent after 24 hours and increased with time. Reversion was obtained by MCM withdrawal. Stimulation of ecto-5'-nucleotidase activity by MCM was inhibited by cycloheximide, which suggests that protein synthesis was required. Induction of enzyme activity by MCM depended in part on the presence of extracellular adenosine. The macrophage-released factor responsible for this effect was non-dialysable, heat-stable at 56 degrees C for 30 minutes but heat-inactivated at 100 degrees C for five minutes, inactivated in the presence of trypsin or protease V8, and adsorbed on charcoal. Its apparent molecular weight estimated by gel chromatography was close to 20 kD. MCM from resident macrophages was as potent as MCM from thioglycollate-elicited or zymosan-stimulated macrophages. This stimulatory effect was specific of macrophages since it was absent in the culture medium of rat fibroblasts or mouse thymocytes but present in that of mouse macrophages. These results suggest that peritoneal macrophages synthesize a factor which selectively stimulates ecto-5'-nucleotidase activity of glomerular mesangial cells.