Kidney Is the Only Source of Human Plasma Renin in 45-kb Human Renin Transgenic Mice

Abstract

Prorenin is expressed in certain extrarenal tissues, but normally only the kidneys process prorenin to renin and secrete renin into the circulation. Although transgenic animal lines containing the human renin (hREN) structural gene with either 0.9-kb or 3-kb 5'-flanking DNA express the transgene appropriately in renal juxtaglomerular cells and secrete hREN into the circulation, the source of the circulating renin is not known. In the present study, we observed that 13-kb hREN transgenic mice that contain the structural gene and 0.9-kb 5'-flanking DNA express hREN mRNA in many unusual tissues. We also observed that circulating hREN levels in 13-kb hREN mice increased after bilateral nephrectomy. These results suggested that the hREN gene is expressed at inappropriate locations where prorenin might be processed to renin. To determine if more distal sequences flanking the hREN gene might contribute to cell and tissue specificity, we used a 45-kb hREN genomic fragment that contained the structural gene and about 25-kb 5'- and 8-kb 3'-flanking DNA sequences to generate 3 separate transgenic lines that contained the intact transgene sequences. Ribonuclease protection assays revealed a much narrower tissue distribution of hREN expression than in the 13-kb hREN transgenic mice. In each 45-kb hREN line, hREN mRNA was present only in the kidney, adrenal, lung, eye, ovary, and brain. Moreover, 24 hours after nephrectomy, human plasma renin fell to very low levels, indistinguishable from those of nontransgenic littermates, indicating that their circulating hREN is of renal origin. These studies suggest that sequences flanking the structural gene, missing from previous hREN transgenic lines, suppress renin gene expression at inappropriate extrarenal sites where cellular proteases, to which prorenin is not normally exposed, could convert prorenin to renin, resulting in abnormal secretion of renin into the plasma.

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

“…We were surprised to find that HREN expression in the PAC mice was more restricted than in another transgenic model containing a 45-kb construct. The 45-kb construct extends from approximately 25 kb 5Ј to 8 kb 3Ј, and HREN expression in the lung exceeded the level of HREN expression in the kidney (27). These data suggest the possibility that regulatory elements or a locus control region outside the 45-kb region but included in the PAC constructs (extending from 35 kb 5Ј to 70 kb 3Ј of the gene) is necessary before a completely restricted pattern of expression is observed.…”

Identification of a Nuclear Orphan Receptor (Ear2) as a Negative Regulator of Renin Gene Transcription

“…42 Similarly, fusions between the human renin promoter and several different reporter genes that lack the enhancer are poorly expressed and regulated, whereas large genomic transgenes derived from P1 artificial chromosomes containing the enhancer are tightly regulated. 18,[43][44][45] Despite this suggestive evidence, experiments designed specifically to test the in vivo significance of the enhancer or one of its transcription factor binding sites has yet to be reported. Using homologous recombination in bacteria, we have recently modified a PAC clone containing the human renin gene by substitution of the enhancer sequence with a loxP511 site.…”

Physiology of Local Renin-Angiotensin Systems

“…Ultimate proof of the presence of local renin synthesis in the heart was to be expected by transgenic overexpression using the native renin promoter. Transgenic mice carrying a genomic human renin construct showed no cardiac renin expression (798), whereas transgenic rats carrying a genomic construct of the mouse Ren-2 gene under control of its own promoter expressed high levels of renin mRNA in the heart (549). This suggests that at least in some species, the heart is a site of extrarenal renin production.…”