Prostaglandin E2 increases proximal tubule fluid reabsorption, and modulates cultured proximal tubule cell responses via EP1 and EP4 receptors

Renal prostaglandin (PG) E-2 regulates salt and water transport, and affects disease processes via EP1-4 receptors, but its role in the proximal tubule (PT) is unknown. Our study investigates the effects of PGE(2) on mouse PT fluid reabsorption, and its role in growth, sodium transporter expression, fibrosis, and oxidative stress in a mouse PT cell line (MCT). To determine which PGE(2) EP receptors are expressed in MCT, qPCR for EP1-4 was performed on cells stimulated for 24 h with PGE2 or transforming growth factor beta (TGF beta), a known mediator of PT injury in kidney disease. EP1 and EP4 were detected in MCT, but EP2 and EP3 are not expressed. EP1 was increased by PGE2 and TGF beta, but EP4 was unchanged. To confirm the involvement of EP1 and EP4, sulprostone (SLP, EP1/3 agonist), ONO8711 (EP1 antagonist), and EP1 and EP4 siRNA were used. We first show that PGE(2), SLP, and TGF beta reduced H-3-thymidine and H-3-leucine incorporation. The effects on cell-cycle regulators were examined by western blot. PGE(2) increased p27 via EP1 and EP4, but TGF beta increased p21; PGE(2)-induced p27 was attenuated by TGF beta. PGE(2) and SLP reduced cyclinE, while TGF beta increased cyclinD1, an effect attenuated by PGE(2) administration. Na-K-ATPase alpha 1 (NaK) was increased by PGE(2) via EP1 and EP4. TGF beta had no effect on NaK. Additionally, PGE(2) and TGF beta increased fibronectin levels, reaching 12-fold upon co-stimulation. EP1 siRNA abrogated PGE(2)-fibronectin. PGE(2) also increased ROS generation, and ONO-8711 blocked PGE(2)-ROS. Finally, PGE(2) significantly increased fluid reabsorption by 31 and 46% in isolated perfused mouse PT from C57BL/6 and FVB mice, respectively, and this was attenuated in FVB-EP1 null mice. Altogether PGE(2) acting on EP1 and EP4 receptors may prove to be important mediators of PT injury, and salt and water transport.