Glomerular epithelial cell products stimulate mesangial cell proliferation in culture

Glomerular epithelial cells (GEC) and mesangial cells (MC) are both invoked in glomerular diseases. To elucidate potential interactions between these glomerular cell types, we examined whether products of GEC affect the proliferative activity of MC. We found that cultured rat GEC secrete soluble factors into the supernate (GEC-CM) that induce proliferation of quiescent rat MC. The mitogenic activity was trypsin sensitive and partially heat-labile. Biochemical analysis of GEG-CM by gel filtration HPLC, reverse phase HPLC, and isoelectric focusing revealed at least three mitogenic fractions as well as inhibitory activity present in GEC-CM. Competitive binding assays with I-125-labeled PDGF did not show significant amounts of PDGF in GEC-CM. The biochemical features of the GEC-derived MC growth factors are distinct from IL-6, PDGF, bFGF, and endothelin, previously described GEC-derived MC growth factors. Additionally, significant contributions of known growth factors such as IL-1, IL-2, IL-3, IL-4, IL-5, TNF alpha, TGF beta, and GM-CSF are unlikely. The results indicate that GEC produce several biochemically-distinct MC growth regulators. While these epithelial cell-derived mitogens for MC require further characterization, they may play an important role in the regulation of MC replication, such as during embryogenesis and glomerular disease.