Vesicoureteral Reflux and Other Urinary Tract Malformations in Mice Compound Heterozygous for Pax2 and Emx2

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of chronic kidney disease in children. This disease group includes a spectrum of urinary tract defects including vesicoureteral reflux, duplex kidneys and other developmental defects that can be found alone or in combination. To identify new regulators of CAKUT, we tested the genetic cooperativity between several key regulators of urogenital system development in mice. We found a high incidence of urinary tract anomalies in Pax2;Emx2 compound heterozygous mice that are not found in single heterozygous mice. Pax2+/−;Emx2+/− mice harbor duplex systems associated with urinary tract obstruction, bifid ureter and a high penetrance of vesicoureteral reflux. Remarkably, most compound heterozygous mice refluxed at low intravesical pressure. Early analysis of Pax2+/−;Emx2+/− embryos point to ureter budding defects as the primary cause of urinary tract anomalies. We additionally establish Pax2 as a direct regulator of Emx2 expression in the Wolffian duct. Together, these results identify a haploinsufficient genetic combination resulting in CAKUT-like phenotype, including a high sensitivity to vesicoureteral reflux. As both genes are located on human chromosome 10q, which is lost in a proportion of VUR patients, these findings may help understand VUR and CAKUT in humans

The position of ureteric budding and its relationship to vesico-ureteric reflux and kidney defects in mice

Vesico-ureteric reflux (VUR) is a congenital urinary tract defect that results in the retrograde flow of urine from the bladder to the kidneys. It is a defect in the formation of the uretero-vesical junction such that the ureter does not insert properly into the bladder. VUR affects up to 1% of the population and patients are at increased risk of developing recurrent urinary tract infections, hypertension, and end-stage renal disease. Patients with VUR frequently have malformed kidneys and short intravesical ureters, one component of the uretero-vesical junction. The co-occurrence of these defects suggests that they arise from a common developmental mechanism, notably, abnormal formation of the ureteric bud. The ureteric bud develops into both the kidney and the urinary tract. We hypothesize that proper ureteric bud development is critical for the formation of a normal kidney and an intact uretero-vesical junction. We identified VUR in two mouse lines at birth: the Pax21Neu+/- mouse and the inbred C3H/HeJ mouse. At postnatal day 1, Pax21Neu+/- and C3H/HeJ mice had a 32% and 100% incidence of VUR, respectively. Control mice (CD1 and C57BL/6J) had a 6.25% and 0% incidence of VUR, respectively. We measured kidney size in all mice tested for VUR and Pax21Neu+/- mice had small malformed kidneys while C3H/HeJ mice had small but no malformed kidneys at birth when compared to controls. Both refluxing mouse models had significantly shorter intravesical ureters compared to controls, providing evidence for a defective uretero-vesical junction. To understand the embryonic origin of VUR, we characterized the position of the ureteric bud along the mesonephric duct. At embryonic day 10.5, both Pax21Neu+/- and C3H/HeJ embryos had ureteric buds that exited from a more caudal position along the mesonephric duct compared to controls. Furthermore, detailed analysis of the developing kidney and urinary tracts revealed that bLe reflux vésico-rénal est un défaut de l'appareil urinaire, dontl'urine remonte anormalement depuis la vessie vers les reins. Le reflux est causé par un défaut dans la formation de la jonction entre la vessie et l'uretère. Le reflux vésico-rénal est une anomalie génétique humaine, affectant près de 1% de la population. Les patients sont susceptibles de développer des infections urinaires, de l'hypertension, et de la néphropathie. Ils sont aussi sujets à des malformations rénales et peuvent présenter des anomalies au niveau de la jonction entre la vessie et l'uretère (uretères intravésicaux courts). Étant donné que ces malformations se manifestent ensemble, il a été suggéré qu'elles résultent toutes d'un mécanisme commun. Les reins et l'appareil urinaire se développent à partir du bourgeon urétéral. Nous présumons que le développement normal du bourgeon urétéral est important pour la formation adéquate aussi bien du rein que de la jonction entre la vessie et l'uretère. Deux lignées de souris atteintes de reflux vésico-rénal ont été identifiées: la souris Pax21Neu+/- et la souris consanguine C3H/HeJ. À la naissance, les souris Pax21Neu+/- et C3H/HeJ avaient une incidence de reflux vésico-rénal, respectivement, de 32% et 100%. Les souris qui servaient de contrôle (CD1 et C57BL/6J) avaient, respectivement, une incidence de 6.25% et 0%. Lorsque nous avons mesuré la taille des reins pour toutes les souris, nous nous sommes aperçus que les souris Pax21Neu+/- et C3H/HeJ avaient des reins plus petits comparativement aux contrôles. Elles avaient aussi des uretères intravésicaux plus courts que ceux des contrôles, ce qui confirme la présence d'un défaut dans la formation de la jonction entre la vessie et l'uretère. Nous avons également caractérisé la position du bourgeon urétéral. Au stade embryonnaire 10.5, les bourgeons urétéraux des souris Pax21Neu