Abstract Body: The study of renin cell identity and function often requires the isolation of this rare cell type –0.01% of the kidney cells. Multicistronic constructs are commonly used to express reporter genes in mice. They consist of two or more genes linked by 2A peptide sequences, which produce separate proteins through a ribosomal skipping mechanism. Here, we report on the generation of a mouse model to label renin-expressing cells with a bright fluorescent reporter for the tracking and isolation of renin cells.
Ren1^ctdTomato mice were generated by inserting a bicistronic T2A-tdTomato knock-in cassette upstream of the TGA stop codon of the Ren1^c gene.
Kidneys from adult heterozygous (het) Ren1^ctdTomato mice showed tdTomato signal confined to the JG area under basal conditions, and extending along the afferent arterioles and in the intraglomerular mesangium upon treatment with captopril + low-salt diet to induce the endocrine transformation of renin cells. Unexpectedly, homozygous (homo) mice exhibited increased tdTomato signal that extended in the afferent arterioles and the mesangium even under normal physiological conditions, and progressive thickening of the kidney arterioles with age. Despite reduced Renin immunostaining in the renal cortex, homo mice exhibited significantly higher kidney Ren1 mRNA (7.9 ± 1.2 vs 1.2 ± 0.6, p<0.0001) and circulating Renin levels (121.7 ± 44.0 vs 66.7 ± 29.4 ng/ml, p<0.003) when compared to het controls. Moreover, homo mice showed significantly lower blood pressure measured under anesthesia (62.3 ± 5.9 vs 90.0 ± 5.7 mmHg, p<0.0001), and Ang I plasma levels (159.3 ± 34.8 vs 500.0 ± 184.1 pmol/L, p<0.05), indicating compromised Renin activity. The concentric arteriolar hypertrophy phenotype observed in these mice is identical to that described when RAS is genetically or pharmacologically inhibited, including the presence of mutations in the renin gene. Unlike mice with global deletion of renin, these animals did not require neonatal saline injections to survive and did not develop other kidney abnormalities, indicating that the bicistronic approach rendered a renin hypomorphic mouse.

Ren1^ctdTomato mice constitute an excellent model for the labeling of renin-expressing cells and for the study of the mechanisms involved in the development of concentric vascular hypertrophy under RAS inhibition. In addition, this model may provide a better understanding of factors controlling renin protein folding, stability, packaging, and release.