Background: The collecting duct (CD) is a major site of both biosynthesis and action of prostaglandin E2 as highlighted by the predominant expression of COX-2 (cyclooxygenase-2) and some E-prostanoid (EP) subtypes at this nephron site. The purpose of this study was to determine the relevance and mechanism of CD COX-2/prostaglandin E2/EP1 signaling for the regulation of Na+ hemostasis during Na+ depletion.
Methods: Mice with Aqp2Cre-driven deletion of COX-2 (COX-2fl/flAqp2Cre+) or the EP1 subtype (EP1fl/flAqp2Cre+) were generated and the Na+-wasting phenotype of these mice during low-salt (LS) intake was examined. EP subtypes responsible for prostaglandin E2-induced local renin response were analyzed in primary cultured mouse inner medullary CD cells.
Results: Following 28-day LS intake, COX-2fl/flAqp2Cre+ mice exhibited a higher urinary Na+ excretion and lower cumulative Na+ balance, accompanied with suppressed intrarenal renin, AngII (angiotensin II), and aldosterone, expression of CYP11B2 (cytochrome P450 family 11 subfamily B member 2), and blunted expression of epithelial sodium channel subunits compared to floxed controls (COX-2fl/flAqp2Cre-), whereas no differences were observed for indices of systemic renin-angiotensin-aldosterone system. In cultured CD cells, exposure to prostaglandin E2 stimulated release of soluble (pro)renin receptor, prorenin/renin and aldosterone and the stimulation was more sensitive to antagonism of EP1 as compared other EP subtypes. Subsequently, EP1fl/flAqp2Cre+ mice largely recapitulated Na+-wasting phenotype seen in COX-2fl/flAqp2Cre+ mice.
Conclusions: The study for the first time reports that CD COX-2/EP1 pathway might play a key role in maintenance of Na+ homeostasis in the face of Na+ depletion, at least in part, through activation of intrarenal renin-angiotensin-aldosterone-system and epithelial sodium channel.
Keywords: EP1 receptor; collecting duct; cyclooxygenase-2; low salt; renin-angiotensin system.