Angiotensin II Type 1 Receptor–EGF Receptor Cross-Talk Regulates Ureteric Bud Branching Morphogenesis

Abstract

Angiotensinogen-, angiotensin-converting enzyme-, and angiotensin II (Ang II) type 1 receptor (AT 1 R)-deficient mice exhibit a dilated renal pelvis (hydronephrosis) and a small papilla. These abnormalities have been attributed to impaired development of the ureteral and pelvic smooth muscle. Defects in the growth and branching of the ureteric bud (UB), which gives rise to the collecting system, have not been examined carefully. This study tested the hypothesis that Ang II stimulates UB growth and branching in the intact metanephros. Immunohistochemistry demonstrated that embryonic mouse kidneys express AT 1 R in the UB and its branches. Embryonic day 11.5 metanephroi were microdissected from Hoxb7-green fluorescence protein mice and grown for 48 h in serum T he metanephros develops via reciprocal inductive interactions between the ureteric bud (UB) and the metanephrogenic mesenchyme (MM) (1,2). Signals from the MM induce UB outgrowth from the nephric duct and its elongation and entrance into the mesenchyme followed by repetitive branching to form the renal collecting system (ureter, pelvis, calyces, and collecting ducts). In turn, emerging UB tips induce surrounding mesenchymal cells to condense, aggregate, undergo mesenchymal-to-epithelial transition, and form nephrons (from the glomerulus to the distal tubule). Therefore, UB branching morphogenesis is critical in determining nephron number, and subtle defects in the efficiency and/or accuracy of this process potentially can have profound effects on the proper development of the metanephric kidney. Decreased nephron endowment is linked to hypertension and eventual progression to chronic renal failure (3,4). In addition, aberrant UB branching morphogenesis causes renal dysplasia, the leading cause of chronic renal failure in human infants.Genetic inactivation of the renin-angiotensin system (RAS) genes in mice causes abnormalities in the development of the ureter, renal pelvis, and papilla (5-9). Angiotensinogen-, angiotensin-converting enzyme (ACE)-, or angiotensin II (Ang II) type 1 receptor (AT 1 R)-deficient mice exhibit pelvic dilation (hydronephrosis) and a small papilla mimicking urinary tract obstruction. Elegant studies from Ichikawa's laboratory have suggested that absence of AT 1 R signaling in ureteral smooth muscle cells impairs pelvic-ureteral smooth muscle development and peristalsis (9). Mutations in the AT 2 R gene in mice and humans are associated with increased incidence of lower urinary tract anomalies, including double ureters and vesicoureteral reflux (10). These findings indicate that UB growth and development are a target for Ang II actions. Work that has performed by several laboratories, including ours, has revealed that the fetal kidney expresses a local RAS. Quantitative analysis of murine Ang II receptors AT 1 R and AT 2 R gene expression indicate that AT 1 R undergo a progressive increase during fetal and neonatal life, whereas AT 2 R are high in the fetus and decline significantly with maturation (11). Immunolocalization studies d...

Ontogeny of angiotensin-converting enzyme 2

“…Enhanced shedding may lead to increased secretion of ACE2 and lowering of its protein content. In addition, ACE2 protein abundance may be differentially regulated during ontogeny by the variation in the activity of peptidases, as shown for neutral peptidase activity in the rat kidney (35). In summary, the present study demonstrates that ACE2 is expressed in the developing kidney, heart, lung, and brain as early as on E12.5 in the mouse.…”

“…Organs were homogenized in cold lysis buffer containing a cocktail of enzyme inhibitors (35). The samples were centrifuged and the supernatants containing proteins (40 µg/lane) were resolved on 10% sodium dodecyl sulfate-polyacrylamide gels and transferred to nitrocellulose membranes.…”

Roles of mitogen-activated protein kinases and angiotensin II in renal development

“…Clinical and experimental evidence shows that the renin-angiotensin system participates in renal development (16)(17)(18)(19)(20)(21)(22). Greater angiotensinogen expression has been observed in the rat kidney during late gestation and the newborn period than in adult kidney.…”

“…The mRNA for the type 1 AII receptor (AT 1 ) has been detected in the renal glomeruli of newborn rats during cell proliferation and differentiation (20). Renal expression of the type 2 AII receptor (AT 2 ) increases during fetal life and decreases after birth (20), suggesting that AII modulates the growth of various cell types and tissues (21,22). Mutations in genes that encode components of the renin-angiotensin system are associated with autosomal recessive renal tubular dysgenesis (23).…”

Development of the kidney medulla

“…76,77 Although medullary hypoplasia and hydronephrosis observed in angiotensin (Ang) II AT1 receptor (AT1R)-deficient mice may result from impaired ureteral peristalsis due to hypoplastic ureteral smooth muscle layer, 78 our previous studies suggest that aberrant branching morphogenesis of the UB may also contribute to medullary defects observed in these mutants. 79 The possibility that medullary hypoplasia may be due in some cases to an intrinsic defect in medullary morphogenesis, rather than to urinary tract obstruction, is supported by the findings that Wnt7b-and Adamts 1/4-or Esrrg-null mice exhibit hypoplastic renal medulla at birth in the absence of structural abnormalities of the lower urinary tract. 9,25,34 Of interest, renal tubular dysgenesis, a congenital and frequently fatal human disease due to mutations in angiotensinogen, renin, angiotensinconverting enzyme or AT1R genes is characterized by collapsed medullary collecting ducts and abundant interstitial fibrosis that occur in the absence of papillary hypoplasia or hydronephrosis.…”