Noninvasive Assessment of Antenatal Hydronephrosis in Mice Reveals a Critical Role for Robo2 in Maintaining Anti-Reflux Mechanism

Hang Wang,Cathy Mendelsohn,Juan Liu,David J Salant,Weining Lu,Qinggang Li

doi:10.1371/journal.pone.0024763

Abstract

Antenatal hydronephrosis and vesicoureteral reflux (VUR) are common renal tract birth defects. We recently showed that disruption of the Robo2 gene is associated with VUR in humans and antenatal hydronephrosis in knockout mice. However, the natural history, causal relationship and developmental origins of these clinical conditions remain largely unclear. Although the hydronephrosis phenotype in Robo2 knockout mice has been attributed to the coexistence of ureteral reflux and obstruction in the same mice, this hypothesis has not been tested experimentally. Here we used noninvasive high-resolution micro-ultrasonography and pathological analysis to follow the progression of antenatal hydronephrosis in individual Robo2-deficient mice from embryo to adulthood. We found that hydronephrosis progressed continuously after birth with no spontaneous resolution. With the use of a microbubble ultrasound contrast agent and ultrasound-guided percutaneous aspiration, we demonstrated that antenatal hydronephrosis in Robo2-deficient mice is caused by high-grade VUR resulting from a dilated and incompetent ureterovesical junction rather than ureteral obstruction. We further documented Robo2 expression around the developing ureterovesical junction and identified early dilatation of ureteral orifice structures as a potential fetal origin of antenatal hydronephrosis and VUR. Our results thus demonstrate that Robo2 is crucial for the formation of a normal ureteral orifice and for the maintenance of an effective anti-reflux mechanism. This study also establishes a reproducible genetic mouse model of progressive antenatal hydronephrosis and primary high-grade VUR.

Highlights

About one percent of human fetuses have congenital anomalies of the kidney and urinary tract (CAKUT), a family of birth defects comprising kidney anomalies such as antenatal hydronephrosis, duplex kidney and renal dysplasia, and ureteric defects such as vesicoureteral reflux (VUR) and urinary obstruction [1]
Antenatal hydronephrosis can be caused by a wide spectrum of renal and urological conditions ranging from transient dilatation of the fetal kidney collecting system that resolves spontaneously after birth to clinically significant urinary tract obstruction or VUR that leads to renal failure [6,7]
With rapid maturation of mouse embryonic kidney and urinary tract from E16.5 to birth, bilateral and unilateral antenatal hydronephrosis and duplex kidneys in Robo2 mutant embryos could be diagnosed starting at E17.5–18.5 (Fig. 1B–J)

Summary

Introduction

About one percent of human fetuses have congenital anomalies of the kidney and urinary tract (CAKUT), a family of birth defects comprising kidney anomalies such as antenatal hydronephrosis, duplex kidney and renal dysplasia, and ureteric defects such as vesicoureteral reflux (VUR) and urinary obstruction [1]. Antenatal hydronephrosis can be caused by a wide spectrum of renal and urological conditions ranging from transient dilatation of the fetal kidney collecting system that resolves spontaneously after birth to clinically significant urinary tract obstruction or VUR that leads to renal failure [6,7]. Despite the high incidence of antenatal hydronephrosis and VUR in the pediatric population, the natural history, causal relationship, developmental origins and genetic basis of these clinical conditions remain ill-defined [12,13,14]

Methods

Results

Conclusion