Thiazolidinediones alter growth and epithelial cell integrity, independent of PPAR-γ and MAPK activation, in mouse M1 cortical collecting duct cells

Nasrallah R, Clark J, Corinaldi J, Paris G, Miura P, Jasmin BJ, Hebert RL. Thiazolidinediones alter growth and epithelial cell integrity, independent of PPAR-gamma and MAPK activation, in mouse M1 cortical collecting duct cells. Am J Physiol Renal Physiol 298: F1105-F1112, 2010. First published February 17, 2010; doi:10.1152/ajprenal.00735.2009.-Peroxisome proliferator-activated receptor (PPAR)-gamma is highly expressed in the collecting duct (CD), yet little is known about the effects of PPAR-gamma ligands, thiazolidinediones (TZDs), on CD cell structure and function. M1 mouse cortical CD cells were treated with 5 mu M troglitazone (TRO) and rosiglitazone (ROSI). First, growth was measured by [H-3] thymidine and [H-3] leucine incorporation, as well as analysis of cyclin D1 and the CDK inhibitor p27 by Western blot. [H-3] thymidine incorporation was reduced by 56 and 24% by TRO and ROSI at 6 h, and [H-3] leucine by 21 and 10%. A similar growth inhibition was also observed after 24 h for thymidine, but leucine was reduced by 48 and 24%, respectively. Likewise, cyclin D1 was diminished 60% by TRO, and p27 was elevated 1.6- and 1.7-fold in response to TRO and ROSI. Next, epithelial cell integrity was assessed by measuring different markers by Western blot analysis. While fibronectin and alpha-smooth muscle actin levels were unchanged, by 24 h E-cadherin was decreased by 50%, and beta-catenin levels were reduced 2- and 1.5-fold in response to TRO and ROSI, respectively. GW9662, a PPAR-gamma antagonist, did not reverse any of the TZD responses in M1 cells. Of interest, phosho-p38 levels were also elevated 2- fold in response to TRO and 2.3-fold to ROSI, but MAPK inhibition by PD98059 or SB203580 caused an additive inhibition of cell growth and did not alter E-cadherin or beta-catenin in response to TZDs. Finally, apoptotic death was assessed by Western blot, but cleaved caspase-3 levels were unchanged from 15 min to 24 h in response to TZDs, and TRO did not affect cell viability or reactive oxygen species generation. Our data suggest that TZDs cause a disruption of M1 cell integrity that is preceded by an inhibition of cell growth. This response is independent of p38 or PPAR-gamma activation.