Effect of cell density on growth regulation of human glomerular epithelial cells. Inhibition of growth by dbcAMP and cAMP-elevating agonists

Abstract

Glomerular epithelial cells (GEC) play an important role in the development of focal glomerular sclerosis. A variety of growth factors and the local cellular enviroment contribute to growth regulation and development of GEC. To understand whether responsiveness of GEC to growth factors might be modulated by cell density, we investigated the influence of epidermal growth factor (EGF) on cell proliferation, as well as the role of transforming growth factor beta (TGFβ) on growth modulation in human visceral GEC in culture plated at different cell densities. Proliferation of cells was determined by [ 3H]thymidine incorporation. EGF and serum exhibited a dose-dependent stimulation independent of cell density in culture. Additon of TGFβ in concentrations greater than 0.1 ng/ml to cells prestimulated with EGF (1 ng/ml) and plated at densities of 18,000 and 50,000 cells per cm 2 was followed by a significant growth inhibition. Inhibition. In contrast, cells plated at 5,000 cells per cm 2 were not inhibited upon stimulation by TGPβ in this concentration (0.1 and 1.0 ng/ml). Heparin markedly inhibited serum-stimulated cell proliferation in concentrations of 1, 10, and 100 U/ml. De- N-sulphated- and low molecular weight heparin as weel as glycosaminoglycans and sulpahted polysaccharides (chondroitin sulphate A, B, C, heparan sulphate, dextran sulphate, and hyaluronic acid) failed to inhibit growth. Furthermore, proliferation of human GEC was significantly inhibited by the cAMP analogue dbcAMP (0.1 and 1 mM) and the cAMP-elevating agonists cholera toxin (250 ng/ml) and forskolin (10 and 100 μM). 1,9-Dideoxyforskolin had no effect. These experiments suggest that cell density may play an important role in human GEC growth regulation and that intracellular cAMP generation seems to be a mediator of growth inhibition.