Background: Because transforming growth factor beta (TGF-beta) has been shown to have a bimodal effect on mesangial cell (MC) proliferation, we studied its effect on MC apoptosis.
Methods: Cultured mouse MCs were used to evaluate the effect of TGF-beta. Morphologic evaluation of MC apoptosis was performed by staining cells with H-33342 and propidium iodide. To confirm the effect of TGF-beta on MC apoptosis, DNA was extracted from control and TGF-beta-treated MCs and run on gel electrophoresis. We evaluated the effect of NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, on TGF-beta-induced MC apoptosis to determine the role of NO and studied the effect of sodium nitroprusside (SNP) and SNAP (S-nitroso-N-acetyl-penicillamine) on MC apoptosis to confirm the effect of NO. We examined the role of p53 by studying the effect of TGF-beta on MCs derived from p53 knockout mice (p53KO-MC) as well as a normogenic strain (N-MC). We also examined the effect of TGF-beta, SNP, and SNAP on apoptosis of p53 mutant (MDAMB-231) and wild-type p53 (MCF-7) breast cancer cell lines. In addition, Western blots were generated from control, TGF-beta-treated, and SNAP-treated MCs and probed for the expression of p53.
Results: TGF-beta promoted MC apoptosis. Moreover, TGF-beta-treated MCs displayed integer multiples of 180 base pairs (ladder pattern). L-NAME inhibited TGF-beta-induced MC apoptosis. Furthermore, SNP and SNAP, NO donors, promoted MC apoptosis. TGF-beta also enhanced the MC expression of p53. TGF-beta induced only a moderate degree of apoptosis in MCs derived from p53KO-MC when compared with N-MCs. Similarly, the TGF-beta-induced apoptosis of MDAMB-231 was of a moderate degree when compared with MCF-7 cells.
Conclusions: We hypothesize that TGF-beta promotes MC apoptosis through NO generation and p53-dependent and -independent pathways.