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 import ant 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 c ells (RMC) in vitro including laminin, fibronectin, type IV collagen a nd the basement membrane heparan sulphate proteoglycan (BM-HSPG) known as perlecan. In addition, using Mab 2B5 we demonstrate that RMC synth esize a specific basement membrane chondroitin sulfate (BM-CSPG), a ma trix component that in normal animals is localized in the mesangium bu t 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 d ecorin, which together account for the majority of the proteoglycans; (iii) a large HSPG-I, probably related to perlecan; and (iv) a small H SPG-II. The cell layer proteoglycans can be sub-divided into a class t hat are probably free in the membrane, and a class of anchored molecul es of the extracellular matrix or stabilized by cytoskeletal elements.