Vasopressin receptor subtype 2 activation increases cell proliferation in the renal medulla of AQP1 null mice

Aquaporin (AQP) 1 null mice have a defect in the renal concentrating gradient because of their inability to generate a hyperosmotic medullary interstitium. To determine the effect of vasopressin on renal medullary gene expression, in the absence of high local osmolarity, we infused 1-deamino-8-Darginine vasopressin (dDAVP), a V₂ receptor (V ₂R)-specific agonist, in AQP1 null mice for 7 days. cDNA microarray analysis was performed on the renal medullary tissue, and 5,140 genes of the possible 12,000 genes on the array were included in the analysis. In the renal medulla of AQP1 null mice, 245 transcripts were identified as increased by dDAVP infusion and 200 transcripts as decreased (1.5-fold or more). Quantitative real-time PCR measurements confirmed the increases seen for cyclin D1, early growth response gene 1, and activating transcription factor 3, genes associated with changes in cell cycle/growth. Changes in mRNA expression were correlated with changes in protein expression by semiquantitative immunoblotting; cyclin D1 and ATF3 were increased significantly in abundance following dDAVP infusion in the renal medulla of AQP1 null mice (161 and 461%, respectively). A significant increase in proliferation of medullary collecting ducts cells, following V ₂R activation, was identified by proliferating cell nuclear antigen immunohistochemistry; colocalization studies with AQP2 indicated that the increase in proliferation was primarily observed in principal cells of the inner medullary collecting duct (IMCD). V₂R activation, via dDAVP, increased AQP2 and AQP3 protein abundance in the cortical collecting ducts of AQP1 null mice. However, V₂R activation did not increase AQP2 protein abundance in the IMCD of AQP1 null mice.