Appropriate Regulation of Human Renin Gene Expression and Secretion in 45-kb Human Renin Transgenic Mice

We generated transgenic mice with two P1 artificial chromosomes, each containing the human renin (HREN) gene and extending to ؊35 and ؊75 kilobase pairs, respectively. HREN protein production was restricted to juxtaglomerular cells of the kidney, and its expression was tightly regulated by angiotensin II and sodium. The magnitude of the up-and down-regulation in HREN mRNA caused by the stimuli tested was identical to the endogenous renin gene, suggesting tight physiological regulation. P1 artificial chromosome mice were mated with transgenic mice overexpressing human angiotensinogen to determine if there was a chronic compensatory down-regulation of the transgene. Despite a 3-fold down-regulation of HREN mRNA, plasma angiotensin II and blood pressure was modestly elevated in the double transgenic mice. Nevertheless, this elevation was significantly less than a different double transgenic model containing a poorly regulated HREN transgene. The increase in blood pressure, despite the decrease in HREN mRNA, suggests that the HREN gene can partially, but not completely, compensate for excess circulating angiotensinogen. These data suggest the possibility that increases in circulating or tissue angiotensinogen may cause an increase in blood pressure in humans, even in the presence of a functionally active servo-mechanism to downregulate HREN expression.

Section: Table II Mouse and Human Plasma Renin Activitycontrasting

confidence: 99%

Section: Fig 5 Copy Number-dependent Hren Expression In Kidneymentioning

confidence: 98%

Highly Regulated Cell Type-restricted Expression of Human Renin in Mice Containing 140- or 160-Kilobase Pair P1 Phage Artificial Chromosome Transgenes

Sinn

Davis

Sigmund

1999

“…Despite this renal cell specificity, ectopic expression in other tissues was evident and the transgenes were inappropriately regulated (46). Ectopic expression was eliminated and appropriate regulation restored in transgenic models employing substantially more 5Ј-flanking sequences (23,47). Similarly, transgenic mice containing constructs consisting only of short hREN 5Ј-flanking regions fused to reporter genes generally failed to exhibit correct expression (48,49).…”

Section: Discussionmentioning

confidence: 99%

The Human Renin Kidney Enhancer Is Required to Maintain Base-line Renin Expression but Is Dispensable for Tissue-specific, Cell-specific, and Regulated Expression

Zhoux

Davis

2006

Renin is the rate-limiting enzyme in the renin-angiotensin system and thus dictates the level of the pressor hormone angiotensin-II. The classical site of renin expression and secretion is the renal juxtaglomerular cell, where its expression is tightly regulated by physiological cues. An evolutionarily conserved transcriptional enhancer located 11 kb upstream of the human RENIN gene has been reported to markedly enhance transcription in renin expressing cells in vitro. However, its importance in vivo remains unclear. We tested whether this enhancer is required for appropriate tissue-and cell-specific expression, or for physiological regulation of the human RENIN gene. To accomplish this, we used a retrofitting technique employing homologous recombination in bacteria to delete the enhancer from a 160-kb P1-artificial chromosome containing human RENIN, two upstream genes and one downstream gene, and then generated two lines of transgenic mice. We previously showed that human renin expression in transgenic mice containing the wild type construct is tightly regulated as is expression of the linked genes. Deletion of the enhancer had no effect on tissue-specific expression of human RENIN, but using the downstream gene as an internal control, found that human RENIN mRNA levels were 3-10-fold decreased compared with constructs containing the enhancer. Despite this decrease in expression, renin protein remained localized to renal juxtaglomerular cells and was appropriately regulated by cues that either increase or decrease expression of renin. Our results suggest that sequences other than the enhancer may be necessary for tissue-specific, cell-specific, and regulated expression of human RENIN.Renin is the first and rate-limiting aspartyl protease in the renin-angiotensin system (RAS) 2 cascade that leads to the production of angiotensin-II (Ang-II) by the consecutive cleavage of angiotensinogen by renin and angiotensin-I by angiotensin converting enzyme. Ang-II is an important regulator of cardiovascular function, stimulating vasoconstriction, cardiac output, aldosterone synthesis, and sympathetic activity, thereby directly and indirectly enhancing peripheral vascular resistance and renal tubular water and salt reabsorption. The critical importance of the RAS is evidenced by gene targeted ablation of the RAS genes in mice. The elimination of any RAS gene in mice causes cardiovascular consequences that include hypotension and renal insufficiency, and developmental consequences including postnatal lethality (1-4). The cardiovascular and developmental defects can be complemented in mice by substitution of the mouse RAS with their human orthologs (5) or by targeted expression of Ang-II (6). In humans, genetic defects in the RAS were reported to cause renal tubular dysgenesis, hypotension, and early stillbirth (7). Consequently, both the mouse and human genetic data illustrate the importance of the system both developmentally and in adults.Renin is primarily expressed in renal juxtaglomerular (JG) cells in the wall of the af...

“…Following captopril administration, expression of each renin gene was derepressed. A 45-kb human renin transgene including 25 kb of upstream sequences was reported to exhibit appropriate regulation of expression and secretion in transgenic mice (31), whereas more recently, 140-and 160-kb human renin PAC transgenes (containing 35 and 75 kb of upstream sequences, respectively) were expressed in the kidney at levels equivalent to the endogenous mouse renin gene and were upregulated by captopril administration (32).…”

Section: Discussionmentioning

confidence: 99%

Granulation Rescue and Developmental Marking of Juxtaglomerular Cells Using “Piggy-BAC” Recombination of the Mouse RenLocus

Mullins¹,

Payne²,

Kotelevtseva³

et al. 2000