Angiotensin II requires PDGF-BB to induce DNA synthesis in rat mesangial cells cultured in an exogenous insulin-free medium

BACKGROUND: Mesangial cell proliferation is an important feature of chronicglomerular disease. Different cytokines and vasoactive substances have beenimplicated in mesangial cell proliferation. However, the role ofangiotensin II remains controversial. Furthermore, all the studies made todate have been performed using a medium supplemented with highconcentrations of insulin (5 micrograms/ml) in order to facilitatemesangial cell proliferation in vitro. As has recently been reported,insulin causes a change both in extracellular matrix composition and inmesangial cell phenotype, thus mimicking disease conditions. METHODS: Weexamined the effects of Ang II in synchronized and proliferating mesangialcells with and without growth factor (PDGF-BB, bFGF and/or insulin)supplementation and the effects of exogenous administration of insulin onmesangial proliferation by measuring the bromodeoxyuridine (BrdU) uptake.RESULTS: Angiotensin II itself caused no increase in BrdU incorporation.However, it exerted a significant synergistic effect on PDGF-BB-induced DNAsynthesis (P < 0.05) in quiescent medium and tended to stimulate BrdUuptake by proliferating cells (P = 0.09). BrdU incorporation significantlycorrelated with direct cell count (r = 0.95). PDGF-BB had the maximalstimulatory effect on DNA synthesis both in quiescent and in proliferativeculture conditions. The insulin dose (5 micrograms/ml) which has been shownto cause mesangial cell proliferation in vitro, caused an increase in BrdUincorporation by itself in quiescent medium. CONCLUSIONS: We conclude thatin an insulin-free medium, mimicking in vivo glomerular conditions, PDGF-BBor proliferative medium are needed to allow Ang II-induced DNA synthesis inmesangial cell culture.