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Introduction: Ureteropelvic junction (UPJ) obstruction is the most common cause of congenital hydronephrosis in the newborn. Failure of transmission of peristaltic waves across the UPJ leads to the accumulation of urine in the kidney and dilatation of the renal pelvis. Although the exact mechanism of pelviureteral peristalsis is poorly understood, it is believed that ureteral motility requires coordinated interaction of interstitial cells of Cajal-like cells (ICC-LCs), smooth muscle cells (SMCs) and neuronal cells. ICC-LCs are pacemaker cells conducting and amplifying pacemaker activity in pelviureteral peristalsis. Hyperpolarization-activated cyclic nucleotide-gated channels (HCN), a family of 4 isoforms (HCN1-4), are a type of voltage-gated ion channels that are important for the regulation of pacemaker cell activity. HCN3 channels have recently been shown to play a fundamental role in coordinating peristalsis in the upper urinary tract in the mouse. We designed this study to investigate the hypothesis that HCN3 channels are expressed in the normal human UPJ and that HCN3 expression is altered in congenital UPJ obstruction.
Material and Methods: After obtaining ethical approval, 22 human intrinsic UPJ obstruction specimens and 11 control UPJ specimens were obtained. Cryosections were stained with antibodies to HCN1, HCN2, HCN3, HCN4 and c-kit. Confocal-immunofluoresence-double staining including 3D-reconstruction was performed. Protein expression was assessed by western blot.
Results: Western blot revealed high levels of HCN3 protein expression in controls and barely detectable levels of HCN3 in UPJ obstruction (Fig. 1A). Confocal-immunofluoresence-double staining revealed that HCN3 was expressed in ICCs of the human UPJ and confirmed that HCN3 positive cells were markedly decreased in UPJ obstructed specimens compared to controls (Fig. 1B). There was absence of HCN1 expression in both UPJ obstruction and controls. HCN2 and HCN4 protein expression levels and immunohistochemical expression in UPJ obstruction were not different from controls.
Conclusion: We provide evidence, for the first time, of the presence of HCN3 in the human UPJ. Altered HCN3 expression observed in ICCs in UPJ obstruction suggests that inhibition of HCN3 activity across UPJ may perturb upper urinary tract peristalsis and cause hydronephrosis.