Genetic Deletion of the Prostaglandin EP3 Receptor in the Kidney Tubule of Adult Mice Has No Impact on Kidney Water Handling

Abstract

Prostaglandin E2 (PGE2) is an important lipid mediator modulating various aspects of kidney function. PGE2 exerts its effects via four PGE2 receptors, EP1-EP4. The EP3 receptor is expressed in the thick ascending limb (TAL) and the collecting duct, where it is proposed to inhibit cAMP generation and NaCl and water reabsorption. However, EP3 is also expressed in endothelial cells of arteries and arterioles, which also play a role in kidney function. Therefore, to assess the tubular role of EP3 in adult mice we generated a mouse model based on the Pax8Cre system with doxycycline-dependent deletion of EP3 along the renal tubule and assessed their renal phenotype in respect to water handling. RNAscope confirmed that EP3 was highly expressed in cortical and medullary TAL and collecting ducts, but it was non-detected in proximal tubule and thin limbs. Two weeks after treatment with doxycycline, EP3 mRNA expression was reduced by >80% in whole kidney (RT-q-PCR) and non-detectable (RNAscope) in tubules of knockout mice compared to control mice. There were no compensatory changes in other EP receptors. Under basal conditions, there were no significant differences in food and water intake, bodyweight, urinary output or plasma and urine biochemistries in both male or female control and knockout mice. There were no differences between genotypes in their renal handling of water during an acute water load, or in their response to the vasopressin V2 receptor agonist dDAVP. Rats drinking 1% NaCl for several days in combination with an EP3 antagonist have increased urine output (Hao et al., 2016). However, relative to controls, we could not detect significant differences in urine volume or osmolality in tubular EP3 knockout mice during 1% NaCl intake. In conclusion, EP3 in the renal tubule is not important for renal water handling or compensatory mechanisms exist. This new model provides a novel tool for examination of the role of EP3 in other aspects of renal function or kidney disease independently of potential developmental abnormalities or systemic effects.