Rat mesangial cells in vitro synthesize a spectrum of proteoglycan species including those of the basement membrane and interstitium.

Accumulation of extracellular matrix within the mesangium is an important event in the development of glomerular disease. In this report we have used indirect immunofluorescence to positively identify a number of constituents of the mesangial matrix synthesized by rat mesangial cells (RMC) in vitro including laminin, fibronectin, type IV collagen and the basement membrane heparan sulphate proteoglycan (BM-HSPG) known as perlecan. In addition, using Mab 2B5 we demonstrate that RMC synthesize a specific basement membrane chondroitin sulfate (BM-CSPG), a matrix component that in normal animals is localized in the mesangium but is not found in the pericapillary glomerular basement membrane (GBM). Further characterization of the proteoglycans synthesized by RMC in vitro revealed: (i) a second large CSPG, identified as versican; (ii) two small dermatan sulphate proteoglycans identified as biglycan and decorin, which together account for the majority of the proteoglycans; (iii) a large HSPG-I, probably related to perlecan; and (iv) a small HSPG-II. The cell layer proteoglycans can be sub-divided into a class that are probably free in the membrane, and a class of anchored molecules of the extracellular matrix or stabilized by cytoskeletal elements.