Collagen synthesis in cultured mesothelial cells. Response to silica

Mesothelial cells were isolated from the peritoneal surface of rats using trypsinization. The cells were polygonal-shaped and proliferated rapidly forming confluent cultures. Application of colloidal silica to mesothelial cell cultures in doses known to induce peritoneal adhesion disease was injurious to the cells and reduced their synthesis of total proteins and collagen. This effect was dose dependent. Media from silica-treated mesothelial cells and granulation tissue fibroblasts were applied to similar but non-treated mesothelial cell and granulation tissue fibroblast cultures. Media from SiO2-treated mesothelial cells increased collagen synthesis markedly both in the mesothelial cell and fibroblast cultures compared with the control cultures as estimated from the incorporation of radioactive proline into hydroxy-proline-containing proteins. However, no stimulation of collagen synthesis was induced by media from the SiO2-treated granulation tissue fibroblasts. Similar effects are known to be induced in fibroblast cultured by media from silica-treated peritoneal macrophage cultures. The alkaline ribonuclease activities of the media were decreased in silica-treated mesothelial cell and macrophage cultures but not in the media of fibroblast cultures. These results suggest that mesothelial cells, like macrophages, can interfere with the protein synthesis of fibroblasts and thus contribute to the regeneration of mesothelium after injury and to the formation of adhesions.