Expression of renal aquaporins is down-regulated in children with congenital hydronephrosis

OBJECTIVE: This study investigated mRNA and protein expression of four renal aquaporin isoforms [AQP1, 2, 3 and 4 (AQP1-4)] in congenital hydronephrotic kidneys (HK) due to pelviureteral junction obstruction and normal control kidneys.

MATERIAL AND METHODS: The expression of AQP1-4 was evaluated in 22 children (15 boys, seven girls, aged 58.9+/-54.3 months) using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) techniques, immunoblotting and immunohistochemistry. Hydronephrosis was graded by ultrasound according to the Society for Fetal Urology.

RESULTS: Both RT-PCR and immunoblotting showed significantly reduced mRNA and protein expression of AQP1-4 in grade IV compared with those in grade III HK and controls. Sequencing demonstrated 99% homology of AQP1-4 with those in GenBank. Positive immunoreactivity of AQP1 was found in plasma membranes of the proximal tubule, thin descending limb of Henle and descending vasa recta; AQP2 in the apical membrane of collecting duct principal cells; and AQP3 and 4 in the basolateral membrane of the same cells. In kidneys with grade IV hydronephrosis there was reduction in the protein abundance of all four AQP isoforms which was more pronounced compared with the protein abundance seen in kidneys with grade III hydronephrosis and control kidneys.

CONCLUSION: The expression of AQP1-4 mRNA and protein abundance is reduced in proportion with the degree of hydronephrosis graded by ultrasound in human congenital HK.