Ureteric bud derivatives express angiotensinogen and AT1 receptors

1 Departments of Pediatrics 2 Physiology 3 Pathology, Tulane University School of Medicine, New Orleans, Louisiana 70112 Inactivation of the renin-angiotensin system interferes with the morphogenesis of the renal medulla. Thus ureteric bud (UB) derivatives may be a target for angiotensin production and action. To begin to test this hypothesis, we examined the cellular expression of angiotensinogen (Ao) and AT 1 receptor proteins during rat metanephrogenesis by immunohistochemistry. In addition, we tested whether UB-derived cells in culture express the Ao and AT 1 proteins. On embryonic day E15 , Ao and AT 1 are expressed in the UB branches and stromal mesenchyme. S-shaped bodies, including the vascular cleft, express AT 1 but not Ao. The metanephric mesenchyme and pretubular aggregates are Ao negative and AT 1 negative. Expression of Ao and AT 1 in UB branches and ampullae is also observed on E16 . However, UB expression of Ao is transient and is no longer detectable in the developing distal nephron beyond E17 . On E17 , both Ao and AT 1 are expressed in capillary loop glomeruli and proximal tubules, whereas UB branches express AT 1 only. By E18 , the majority of Ao immunoreactivity is clustered in terminally differentiated proximal tubules, whereas AT 1 receptors are expressed in both proximal and distal nephron segments. The specificity of Ao and AT 1 staining was documented by the elimination/attenuation of immunoreactivity after preadsorption of the primary antibodies with their respective antigens. Consistent with the in vivo findings, the AT 1 protein is abundantly expressed in cellular lysates of mouse UB ( E11.5 ) and IMCD3 (adult) cells. Moreover, AT 1 receptors in UB and IMCD3 cells are functional, since angiotensin II treatment elicits the tyrosine phosphorylation of the mitogen-activated protein kinases, ERK1/2. To our knowledge, this is the first demonstration of Ao and AT 1 protein expression in the developing distal nephron. Angiotensin II may have a paracrine role in the ontogeny of the collecting system. nephrogenesis; renal medulla; collecting duct; proximal tubule; immunohistochemistry