Genetic Evidence That Lethality in Angiotensinogen-deficient Mice Is Due to Loss of Systemic but Not Renal Angiotensinogen

Abstract

Angiotensinogen (AGT)-deficient mice die shortly after birth presumably due to renal dysfunction caused by the presence of severe vascular and tubular lesions in the kidney. Because AGT is expressed in renal proximal tubule cells, we hypothesized that its loss may be the primary mediator of the lethal phenotype. We generated two models to test this hypothesis by breeding transgenic mice expressing human renin with mice expressing human AGT (hAGT) either systemically or kidneyspecifically. We then bred double transgenic mice with AGT؉/؊ mice, intercrossed the compound heterozygotes, and examined the offspring. We previously reported that the presence of the human renin and systemically expressed hAGT transgene complemented the lethality observed in AGT؊/؊ mice. On the contrary, we show herein that the presence of the human renin and kidney-specific hAGT transgene cannot rescue lethality in AGT؊/؊ mice. An analysis of newborns indicated that AGT؊/؊ mice were born in normal numbers, and collection of dead 10-day old pups revealed an enrichment in AGT؊/؊. Importantly, we demonstrated that angiotensinogen protein and functional angiotensin II was generated in the kidney, and the kidney-specific transgene was temporally expressed during renal development similar to the endogenous AGT gene. These data strongly support the notion that the loss of systemic AGT, but not intrarenal AGT, is responsible for death in the AGT؊/؊ mouse model. Taken together with our previous studies, we conclude that the intrarenal reninangiotensin system located in the proximal tubule plays an important role in blood pressure regulation and may cause hypertension if overexpressed, but may not be required for continued development of the kidney after birth.

Polymorphism in miR-31 and miR-584 binding site in the angiotensinogen gene differentially influences body fat distribution in both sexes

“…Interestingly, these differences were also depot specific with differences between omental and perigenital fatty tissue. The sex differences were also replicated in human fatty tissue (Park et al 2013) and may be linked to sex hormone regulation of AGT expression, which has been confirmed in laboratory rodents (Stavréus-Evers et al 2001;Ding et al 2001). The results of our study suggest that similar effects can be present in humans in the case of the ?11525 C/A (rs7079) polymorphism in miR-31 and miR-584 binding site of the angiotensinogen gene; sex-related differences in miRNA expression observed in the case of miR-31 (Rieger et al 2013) can be a contributing factor.…”

Brain-specific Restoration of Angiotensin II Corrects Renal Defects Seen in Angiotensinogen-deficient Mice

“…In contrast, 2C/AGT Ϫ/Ϫ (FVB) mice correct this decrease in urine osmolality (Fig. 7C), consistent with the known importance of circulating Ang II for kidney function (8). As previously reported, AGT Ϫ/Ϫ mice are unable to concentrate urine when deprived of water (Fig.…”

“…Because only limited tissues, including the brain, adrenal gland, and testis, express both the AT1 receptor isoforms in mice, it is possible that the effects of the RAS on renal development are mediated through one of these nonrenal tissues. Supporting this hypothesis, specific restoration of AGT in the circulation by targeting adipocytes (20) or multitissue restoration of AGT by using the ubiquitously expressed metallothionein promoter (21) or the native angiotensinogen promoter (22) prevents kidney abnormalities seen in AGT Ϫ/Ϫ mice, whereas targeted restoration of AGT only in the kidney of these animals does not prevent the renal anomalies (8). In the current study, we have used a novel transgenic strategy to directly address the ability of brain Ang II to correct the renal anomalies in AGT Ϫ/Ϫ mice and have compared these results to those obtained when Ang II is specifically restored in the circulation of these mice.…”

“…Newborn mice deficient for a RAS have histologically normal kidneys at birth and develop frank hydronephrosis in the first 3-5 weeks of life (8,33), a period when the newborn kidney must adapt to a much higher flux in fluid than it was exposed to in utero. Although both transgenic models reduce drinking behavior and urine output in the AGT Ϫ/Ϫ background, these values do not return to levels seen in control mice, and it seems unlikely that this partial reduction in urine flux could account for the complete disappearance of the hydronephrosis.…”

New approaches to genetic manipulation of mice: tissue-specific expression of ACE

“…Such a mouse would be null for ACE expression in other tissues not recognizing the new tissue-specific promoter. This is similar to creating a transgenic mouse and breeding it onto a knockout background, an approach that has been previously used to investigate the tissue-specific expression of angiotensinogen (13). Technically, we believed that our approach would be simpler for the study of ACE due to the reduced fertility present in the ACE knockout.…”