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

Interplay between vesicoureteric reflux and kidney infection in the development of reflux nephropathy in mice

SUMMARY Vesicoureteric reflux (VUR) is a common congenital defect of the urinary tract that is usually discovered after a child develops a urinary tract infection. It is associated with reflux nephropathy, a renal lesion characterized by the presence of chronic tubulointersitial inflammation and fibrosis. Most patients are diagnosed with reflux nephropathy after one or more febrile urinary tract infections, suggesting a potential role for infection in its development. We have recently shown that the C3H mouse has a 100% incidence of VUR. Here, we evaluate the roles of VUR and uropathogenic Escherichia coli infection in the development of reflux nephropathy in the C3H mouse. We find that VUR in combination with sustained kidney infection is crucial to the development of reflux nephropathy, whereas sterile reflux alone fails to induce reflux nephropathy. A single bout of kidney infection without reflux fails to induce reflux nephropathy. The host immune response to infection was examined in two refluxing C3H substrains, HeN and HeJ. HeJ mice, which have a defect in innate immunity and bacterial clearance, demonstrate more significant renal inflammation and reflux nephropathy compared with HeN mice. These studies demonstrate the crucial synergy between VUR, sustained kidney infection and the host immune response in the development of reflux nephropathy in a mouse model of VUR

The C3H/HeJ inbred mouse is a model of vesico-ureteric reflux with a susceptibility locus on chromosome 12

Vesico-ureteric reflux is the most common congenital anomaly of the urinary tract, characterized by a defective uretero-vesical junction with retrograde urine flow from the bladder toward the kidneys. Because there is strong evidence for a genetic basis for some cases of vesico-ureteric reflux, we screened 11 inbred mouse strains for reflux and kidney size and identified one strain, C3H/HeJ, that has a 100 percent incidence of vesico-ureteric reflux with otherwise normal kidneys at birth. These mice are predisposed to reflux as a result of a defective uretero-vesical junction characterized by a short intravesical ureter. This defect results from a delay in urinary tract development initially manifested by a ureteric bud arising from a more caudal location along the mesonephric duct. In contrast, C57BL/6J mice (resistant to reflux at birth) have long intravesical ureters, normally positioned ureteric buds, and no delay in urinary tract development. Genome-wide and additional fine mapping of backcross mice, derived from C3H/HeJ and C57BL/6J crosses, identified a significant reflux susceptibility locus, Vurm1, on chromosome 12 (peak logarithm of the odds=7.39). The C3H/HeJ mouse is a model of vesico-ureteric reflux without renal malformation, and further characterization of this model will allow for the identification of a pathway important for urinary tract development, a finding that will serve as a model for the human disorder