Formation of extracellular matrix by cultured rat mesangial cells.

Formation of extracellular matrix (ECM) by mesangial cells (MCs) contributes to progressive glomerulosclerosis. The authors investigated the production and distribution of ECM constituents by cultured rat MCs, using immunocytochemistry and immunoelectron microscopy. Staining for all ECM constituents increased after serum feeding. Localization was strictly intracellular until confluency, when extracellular deposition of collagen IV and laminin appeared, followed by fibronectin and collagen III. In parallel, the intracellular staining for these proteins diminished markedly. Neither extracellular deposition nor intracellular loss was observed for collagen I and thrombospondin. On surfaces coated with collagen IV or laminin, extracellular deposition of ECM constituents clearly preceded confluency. These results indicate that synthesis of ECM constituents parallels MC growth, and that extracellular deposition of ECM occurs at cell-cell contact. Collagen IV or laminin secreted by MCs in the substratum accelerates production and facilitates secretion of other ECM constituents in an autocrine fashion.