Glucocorticoid-Induced Fetal Programming Alters the Functional Complement of Angiotensin Receptor Subtypes Within the Kidney

Abstract

Abstract-We examined the impact of fetal programming on the functional responses of renal angiotensin receptors. Fetal sheep were exposed in utero to betamethasone (BMX; 0.17 mg/kg) or control (CON) at 80 to 81 days gestation with full-term delivery. Renal nuclear and plasma membrane fractions were isolated from sheep age 1.0 to 1.5 years for receptor binding and fluorescence detection of reactive oxygen species (ROS) or nitric oxide (NO). Mean arterial blood pressure and blood pressure variability were significantly higher in the BMX-exposed adult offspring versus CON sheep. Key Words: angiotensin receptors Ⅲ kidney Ⅲ fetal programming Ⅲ hypertension G lucocorticoids have an important influence on cell maturation and differentiation, particularly in the developing lung. 1 Indeed, the treatment of mothers in immediate jeopardy of preterm delivery with synthetic glucocorticoids enhances fetal lung maturation and lessens respiratory distress syndrome, as well as substantially reduces neonatal mortality and morbidity; glucocorticoid administration is now standard care for women with preterm labor before 35 weeks gestation. However, a single course of antenatal corticosteroid is associated with higher blood pressure in adolescence and decreased insulin sensitivity and renal function in adulthood. 2,3 Experimental studies demonstrate that exposure of the fetus to elevated glucocorticoids during this critical period of gestation results in the development of elevated blood pressure once the offspring reaches adulthood. 4 In a wellcharacterized model of fetal programming, adult offspring of sheep exposed antenatally to the glucocorticoid betamethasone (BMX) exhibit increased mean arterial pressure (MAP) that is associated with reduced baroreflex sensitivity and an attenuated capacity to excrete sodium. 5-7 Furthermore, steroid-induced programming may selectively influence the enzymatic components of the renin-angiotensin system, such that the ratio of angiotensin-converting enzyme (ACE) to ACE2 is increased in the circulation and kidney favoring the Ang II-AT 1 receptor axis. 8,9 In this regard, sensitivity to Ang II and other stressors is enhanced in the offspring of glucocorticoid-exposed mothers. 9 -13 Indeed, acute treatment with an AT 1 receptor antagonist lowers blood pressure in adult exposed sheep at a therapeutic dose that does not influence pressure in the nonexposed adults. 5 We recently reported the increased expression of the angiotensin receptor subtype AT 1 , and a concomitant decrease in the AT 2 subtype within the kidney cortex of older (age 3-5 years) versus younger adult (age 1.5 years) sheep. 14 This altered receptor ratio was associated with an increased response in the Ang II-dependent release of reactive oxygen species (ROS) that was abolished by an AT 1 receptor antagonist. 14 In lieu of the functional role of glucocorticoids to influence tissue maturation, we hypothesize that antenatal exposure to glucocorticoids may influence renin-angiotensin system receptors to promote the development and/or...

Review:Novel roles of nuclear angiotensin receptors and signaling mechanisms

“…Functional studies on isolated renal nuclei suggest that at least a portion of the receptors may reside on the outer nuclear membrane with the ligand binding site oriented to the cytoplasm. Indeed, we find an immediate response in the fluorescent signal for ROS or NO upon addition of ANG II or ANG-(1-7) to rat and sheep renal nuclei (41)(42)(43). Moreover, the functional data are consistent with the demonstration of high-affinity binding sites on intact renal nuclei obtained from different laboratories using sucrose or iodixanol density gradient methods (43,61,71,107).…”

“…It is quite feasible that the AT 2 receptor itself, by competing for ANG II binding, may directly limit the actions of the ANG II-AT 1 receptor axis. In isolated nuclei, blockade of the AT 2 site with PD123319 exacerbated the ROS response to ANG II (42). These studies suggest the potential impact of the AT 2 receptor to buffer oxidative stress in renal nuclei.…”

“…Furthermore, Re et al (76) recently described the localization of functional GNRH receptors on the nuclear membrane of HEK293 cells; however, deletion of the NLS did not influence the distribution of the receptor to the nucleus. As previously mentioned, AT 2 receptors lack a canonical NLS and do not internalize following ligand activation, yet functional receptors are present on both renal and cardiac nuclei (42,96). The inability to demonstrate that internalized endothelin receptors traffic from the cell surface to the nucleus further supports an intracellular mechanism for nuclear expression of both ET-A and ET-B receptors on cardiomyocytes (3).…”

“…The proximal tubules are considered one of the primary cell types within the kidney to express all components of the RAS (66). In isolated nuclei from proximal tubules, we utilized the endogenous peptide substrates to demonstrate processing of ANG I to ANG II by ACE, direct formation of ANG-(1-7) from ANG I by the endopeptidase neprilysin, and the conversion of ANG II to ANG-(1-7) by ACE2 (42,43). Importantly, the activities of all three enzymes were comparable to that in whole proximal tubules using identical enzyme assays (88).…”

Biochemical evaluation of the renin-angiotensin system: the good, bad, and absolute?

“…3F). A similar approach was taken for the AT 7 /Mas receptor in isolated nuclei of the sheep kidney (55)(56)(57)(58). An alomone antibody (Alomone Labs, Tel Aviv, Israel) revealed Mas receptor expression along the tubular elements of the kidney that was abolished by antibody preabsorption with the immunogenic peptide; a single band (ϳ35 kDa) was evident on the full-length immunoblot of isolated nuclei (Fig.…”