Overexpression of angiotensinogen in proximal tubule leads to sodium-sensitivity of blood pressure.

摘要

Common genetic variation in angiotensinogen (AGT) predispose to essential hypertension EH in humans. Understanding the mechanism at play will require demonstration in experimental animals with phenotypic expression closely replicating the human condition. AGT is differentially regulated at various sites. Hence apportionment of systemic vs. intrarenal mechanisms to AGT-mediated predisposition to EH is of fundamental relevance for drug targeting in the treatment of EH.;Research Aims. In an initial step to test this hypothesis, Dr. Lalouel and colleagues have already generated transgenic mice mouse (m) AGT in liver (L), the leading source of systemic AGT under normal diet. They have shown that constitutive mAGT overexpression affects both plasma AGT levels and BP, in the range seen in humans and in Smithies' 3-copy animals, in sodium-sensitive C57BL/6J (B6) but not in the sodium-resistant A/J backgrounds.;Our specific aim was to complement these studies by generating and analyzing animals that overexpress homospecific mAGT in PT. This was achieved by placing the coding sequence of mouse AGT downstream from an internal ribosomal entry site (IRES) in the 3' UTR of the KAP gene by gene targeting. To set the stage for future research, we also developed an animal model that affords constitutive overexpression of homospecific mouse renin (mREN) in distal nephron.;Results. We developed animals with overexpression of mAGT restricted to PT. We showed that the increased expression of mAGT was within physiological range. Having concluded this validation, we showed that restricted overexpression of mAGT in PT led to volume-sensitivity of BP. Manifestation of the genetic effect required both high sodium intake and expression in a sodium-sensitive background. We also developed animals that overexpress mREN in distal nephron.;Hypothesis. We propose that variation in AGT expression in the physiologic range, with normal feedback regulation of renin at play, leads, whether in humans or mouse, to moderate but chronic differences in plasma volume regulation and BP through the interplay of both systemic and renal mechanisms to an extent that varies with (1) gender, (2) genetic background, (3) dietary sodium and (4) duration of disease and aging.