**6.1.2 Bladder outlet obstruction models**

Surgical introduction of a bladder outlet obstruction has been investigated in fetal sheep, immature guinea pigs, and young rats (Cendron et al., 1994; Kitagawa et al., 2001; Kitagawa et al., 2004; Mostwin et al., 1991; O'Connor et al., 1997). As in ureteral obstruction models, the effects of these urethral manipulations are also highly dependent on the timing and severity of the obstruction. Experimental urethral ligation resulted in a spectrum of findings ranging from minimal renal pathology to hydronephrosis, renal dysplasia, pulmonary hypoplasia and/or Potter's sequence. Unfortunately, the data on surgical models of *in utero* bladder outlet obstruction are limited by small numbers of animals, and by the lack of complementary genetic studies since many of the large animal models are not easily amenable to genetic manipulation.

#### **6.2 Chemically-induced models**

The antineoplastic anthracycline antibiotic Adriamycin has well-known teratogenic effects, and has been used in pregnant rats to generate an animal model of congenital obstructive nephropathy (Kajbafzadeh et al., 2011; Thompson et al., 1978). At Adriamycin dosages above 1.5mg/kg/d, bladder hypoplasia or agenesis occurs in all offspring, but fetal viability is low. At decreased doses, Kajbafzadeh et al. (2011) observed a high frequency of hydronephrosis with coexisting bladder anomalies and minimal fetal lethality. The kidneys of these animals demonstrated cortical thinning and cystic dilatation of collecting ducts. However, Adriamycin-treated rats display multiple extrarenal anomalies consistent with the VATER/VACTERL association, including vertebral defects, anal atresia, tracheoesophageal

Congenital Obstructive Nephropathy: Clinical Perspectives and Animal Models 19

Mice lacking either of the two angiotensin receptors likewise develop abnormal renal phenotypes. The Agtr2 knockout has incomplete penetrance, with approximately 2-20% of mutant mice demonstrating a wide spectrum of renal and urological anomalies including UPJ stenosis or megaureter as well as multicystic dysplastic kidney, hypoplastic kidney, VUR, or duplicated ureter (Nishimura, et al., 1999). Deficiency of Agtr1 produces a renal phenotype with some features similar to that seen in complete UUO, including papillary atrophy, medullary thinning, calyceal enlargement, tubulointerstitial apoptosis, macrophage infiltration, and fibrosis. The Agtr1 mutant also demonstrates hypertrophy of the renal vasculature, a feature not seen in UUO models. There is some evidence supporting a role for Agtr1 in promoting growth and contractility of smooth muscle cells (Miyazaki & Ichikawa, 2001), but the relative contributions of primary effects of the mutation on renal development and secondary consequences of a possible functional obstruction in these mice remain unclear. Agtr1 knockout mice also display significant extrarenal abnormalities, including poor weight gain, marked hypotension, and increased frequency of ventral septal defects

Our laboratory has identified a unique transgenic mouse model of congenital obstructive nephropathy designated the megabladder (*mgb*) mouse (Ingraham et al., 2010; Singh et al., 2007). As shown in Figure 7, these mice develop a nonfunctional, over-distended bladder due to a bladder-specific defect in smooth muscle differentiation. This leads to a functional lower urinary tract obstruction, antenatal hydronephrosis, and signs of renal failure evident shortly after birth. Male *mgb* homozygotes develop early renal insufficiency and rarely

Megabladder mice closely mirror the pathophysiology associated with a lower urinary tract obstruction in several key respects (Ingraham, et al., 2010; Singh, et al., 2007). *Mgb-/-* mice develop a functional obstruction of the lower urinary tract that leads to hydroureteronephrosis during embryogenesis. *Mgb-/-* mice are born with histopathological evidence of renal injury, indicating that their kidneys possess preexisting pathological changes resulting from *in utero* obstruction. The obstruction and its renal consequences develop within the uterine and fetal environment, in contrast to the postnatal timing of obstruction in UUO and many genetic models of obstructive nephropathy. *Mgb-/-* mice preferentially develop right-sided hydronephrosis reminiscent of the "pop-off" mechanism theorized in children with PUV and secondary unilateral VUR (Greenfield, et al., 1983). *Mgb-/-* mice also exhibit a variable clinical course, in much the same way that children with seemingly identical obstructive lesions may have very different clinical outcomes. Male *mgb-/-* mice can be rescued from the complications of renal failure and early demise by cutaneous vesicostomy, but of the vesicostomized animals that survive the perioperative period, approximately 40% die within the first two weeks despite a patent stoma and no apparent surgical complications. This result is reminiscent of the fact that 27% to 70% of children with PUV will have progressive CKD despite surgery (Ansari, et al., 2010; Kousidis, et al., 2008; Parkhouse, et al., 1988; Roth, et al., 2001; Sanna-Cherchi, et al., 2009). Finally, *mgb-/-* mice possess no extrarenal features to complicate their utilization as a functional model of congenital obstructive nephropathy. Taken together, these observations suggest that *mgb-/-* mice represent an excellent experimental model for the study of the pathophysiological events associated with congenital obstructive nephropathy involving the

survive beyond 4-6 weeks, whereas females may live a year or longer.

(Tsuchida et al., 1998).

lower urinary tract.

**6.3.3 Megabladder mouse** 

fistula with esophageal atresia, and radial limb dysplasia, which complicates application of this approach to modeling congenital obstructive nephropathy.
