Stimulation of mesothelial cells proliferation by endogenous growth factor(s)

We have attempted to determine whether human mesothelial cells (MC) have the power to influence their own proliferation. A serum-free medium was conditioned with the mesothelial monolayer for 24 hours and then applied to proliferating MC. Conditioned medium increased proliferation rate of MC. When the medium was heated at 60°C for 60 minutes, the growth-promoting activity of the conditioned medium decreased by 50%, suggesting that MC produce at least 2 growth factors, 1 heat-labile and the other heat-stable. When MC were exposed continuously to a medium containing 90 mM glucose growth factor, production was decreased by 35%. However, when the cells were exposed to glucose only on alternate days, growth-factor production was similar to that in the control medium. On the other hand, MC exposed continuously for 10 days to 90 mM of glucose exhibited a weaker response to endogenous growth factor, even in a normotonic medium with low glucose concentration. Our results suggest that MC synthesize factor(s), which stimulate their own proliferation, and that high glucose concentrations interfere with this production and the subsequent action of growth factor.