Peroxisome Proliferator-Activated Receptor γ Antagonists Decrease Na+Transport via the Epithelial Na+Channel

Abstract

The epithelial sodium channel (ENaC) is believed to represent the rate-limiting step for sodium absorption in the renal collecting duct. Consequently, ENaC is a central effector affecting systemic blood volume and pressure. Sodium and water transport are dysregulated in diabetes mellitus. Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists are currently used in the treatment of type 2 diabetes, although their use remains limited by fluid retention. The effects of PPARgamma agonists on ENaC activity remain controversial. Although PPARgamma agonists were shown to stimulate ENaC-mediated renal salt absorption, probably via the serum- and glucocorticoid-regulated kinase 1, other studies reported that the PPARgamma agonist-induced fluid retention is independent of ENaC activity. Here we confirmed that four chemically distinct PPARgamma agonists [pioglitazone, rosiglitazone, troglitazone, and 15-deoxy-Delta12,14-prostaglandin J2 (PGJ2)] do not enhance Na+ transport in cultured renal collecting duct principal mpkCCDc14 cells, as assessed by short-circuit current measurements. However, the PPARgamma antagonist 2-chloro-5-nitro-N-4-pyridinyl-benzamide (T0070907), and to a lesser extent 2-chloro-5-nitrobenzanilide (GW9662), were found to decrease Na+ reabsorption across mpkCCDc14 cell layers. Furthermore, pretreatment of monolayers with T0070907 diminished the insulin-stimulated sodium transport. PPARgamma agonist PGJ2 did not enhance insulin-stimulated Na+ flux via ENaC. We also show that PPARgamma enhances ENaC activity when all three subunits are reconstituted in Chinese hamster ovary (CHO) cells. GW9662 inhibits ENaC activity when ENaC subunits are coexpressed in CHO cells with PPARgamma. In contrast, rosiglitazone has no effect on ENaC activity. We conclude that PPARgamma activity is important for maintaining basal and insulin-dependent transepithelial Na+ transport and ENaC activity.