Ureteric bud derivatives express angiotensinogen and AT1 receptors

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.