Crosstalk between peroxisome proliferator-activated receptor-γ and mineralcorticoid receptor in TNF-α activated renal tubular cell.

INTRODUCTION: In our previous study, we observed the crosstalk between peroxisome proliferator-activated receptor-γ (PPAR-γ) and angiotensin II in activated renal tubular cells. The present study is aimed to further explore the crosstalk between PPAR-γ and mineralocorticoid receptor (MR) in tumor necrosis factor (TNF)-α activated renal tubular cells.
METHODS: Human proximal renal tubular epithelial cells HK-2 were cultured with the pre-treatment of PPAR-γ agonist, pioglitazone (5 μM), MR antagonist, eplerenone (5 μM), or their combined treatment, followed by activation with TNF-α (20 ng/ml). In the parallel experiment, PPAR-γ inhibitor GW9662 (25 µM) was used to study the independence of PPAR-γ. Gene expression and protein synthesis of intercellular adhesion molecule-1 (ICAM-1), interleukin-6 (IL-6), MR and PPAR-γ were measured by RT-PCR, ELISA and Western blot, respectively; nuclear factor κB (NF-κB) nuclear translocation activity in the nucleus was examined by EMSA assay.
RESULTS: TNF-α effectively activated HK-2 cells by up-regulating gene expression and protein synthesis of ICAM-1, IL-6 and MR and down-regulating PPAR-γ in a dose-dependent manner. TNF-α also significantly induced NF-κB nuclear translocation in HK-2 cells. Dual treatment of pioglitazone and eplerenone demonstrated synergistic effect on reducing ICAM-1 and IL-6 expression and alleviating NF-κB activation when compared with their monotherapies in TNF-α activated renal tubular cells. PPAR-γ antagonist, GW9662, significantly attenuated protective effect on ICAM-1, IL-6 and PPAR-γ expression by pioglitazone, eplerenone and their combined treatment.
CONCLUSIONS: Our data suggest that pioglitazone, in a PPAR-γ-dependent manner, trans-represses MR signaling by suppressing NF-κB activation. MR antagonist also restored PPAR-γ expression. Dual treatment of pioglitazone and eplerenone present better efficacy in attenuating excessive inflammatory response in activated renal tubular cells under stimulation of TNF-α than single treatment.