Aim of the Study:
Determining the mechanisms underpinning antenatally detected pelvi-ureteric junction obstruction (PUJO) is important as distinguishing which children need a pyeloplasty can be challenging, and delayed treatment causes morbidity. This research investigates the role of aquaporin (AQP) water channels in the pathobiology of PUJO.
Following ethical approval (Licences:I57B0BE74, 30/2787), partial unilateral ureteric obstruction (n=12) or sham procedure (n=6) was performed in neonatal rats. At 5 weeks of age intra-renal pelvis pressure was assessed and bilateral nephroureterectomy performed. Kidney and renal pelvis AQP isoform expression was evaluated by qRT-PCR, Western Blotting and Immunohistochemistry. Urine AQP1 excretion at 4 weeks was analysed by ELISA.
Moderately hydronephrotic kidneys demonstrated increased pressure (8.3 +/- 2.9mmHg vs sham 0.5 +/- 0.1mmHg, p<0.05) and normal histology. Severely hydronephrotic kidneys displayed reduced glomeruli/field of view (1.6 +/- 0.7 vs sham 4.1 +/- 0.2, p<0.05) and increased interstitial fibrosis (27.3 +/- 13% per section vs sham 0.2 +/- 0.1%, p<0.05).
Renal AQP1 (0.32+0.137/-0.096 fold of sham, p<0.05), AQP2 (0.21+0.175/-0.095 fold of sham, p<0.05) and AQP6 (0.35+0.295/-0.160 fold of sham, p<0.05) mRNA relative expression, and AQP4 protein expression (optical density 5976 +/-2188 vs sham 18400 +/-3046, p<0.05), were downregulated in severe hydronephrosis.
AQP1 and 3 were localised to the vasculature and urothelium of normal renal pelvis respectively. Relative mRNA expression of both isoforms was reduced in moderate (AQP1 0.63+0.046/-0.043 fold of sham, p<0.05, AQP3 0.48+0.050/-0.046 fold of sham, p<0.05) and severe hydronephrosis (AQP1 0.48+0.042/-0.039 fold of sham, p<0.05, AQP3 0.34+0.035/-0.032 fold of sham, p<0.05).
Urinary AQP1 excretion was not significantly changed in any hydronephrotic state.
Urothelial renal pelvis AQP expression is diminished in hydronephrotic states. Mechanistically this is detrimental as it will not allow hydrostatic pressure release. Increasing expression could be therapeutically beneficial.