Adenylyl cyclase 6 deficiency ameliorates polycystic kidney disease

Abstract

cAMP is an important mediator of cystogenesis in polycystic kidney disease (PKD). Several adenylyl cyclase (AC) isoforms could mediate cAMP accumulation in PKD, and identification of a specific pathogenic AC isoform is of therapeutic interest. We investigated the role of AC6 in a mouse model of PKD that is homozygous for the loxP-flanked PKD1 gene and heterozygous for an aquaporin-2-Cre recombinase transgene to achieve collecting duct-specific gene targeting. Collecting duct-specific knockout of polycystin-1 caused massive renal cyst formation, kidney enlargement, and severe kidney failure, with a mean survival time of 2 months. In contrast, coincident collecting duct-specific knockout of polycystin-1 and AC6 (also homozygous for the floxed ADCY6 gene) markedly decreased kidney size and cystogenesis, improved renal function, reduced activation of the B-Raf/ERK/MEK pathway, and greatly increased survival. Absence of collecting duct AC6 did not alter urinary cAMP excretion or kidney cAMP concentration. In conclusion, AC6 is a key mediator of cyst formation and renal injury in a model of PKD.

Figure 1.

AC6 KO improves survival and lessens kidney disease in PKD KO mice. Coincident AC6 KO reduced kidney and cyst size. A shows representative images from 15 different kidneys of each genotype. B shows activated caspase 3 (apoptosis) or proliferating cell nuclear antigen (PCNA; proliferation), both of which are green, and AQP2 (red; to help show cyst walls, although not all cyst walls are red) staining in representative kidney sections from five different kidneys of each genotype. C shows mouse survival probability (all animals are PKD KO; legend shows AC6 genotype; n=26–52 per data point). D shows BUN at 33 days of age (n=15–27). *P<0.05 versus PKD KO alone.

Figure 2.

AC6 KO reduces expression of B-Raf/ERK/MEK in PKD KO mice. A shows Western analysis for B-Raf, phospho–B-Raf, ERK1/2, phospho-ERK1/2, MEK1/2, phosphor-MEK1/2, and β-actin in whole kidneys from 33-day-old PKD KO and PKD/AC6 KO mice (n=6 per group). WT, one wild-type mouse lane. B shows densitometry analysis, normalizing to β-actin, for each blot. *P<0.05 versus PKD KO.