Abstract 16: Physiological Characterization of a Selective Knockout of the Intracellular Isoform of Renin in the Brain of Mice

Renin gene expression is regulated by two distinct promoter-first exon combinations that target renin for either secretion (exon 1a initiating secreted renin, sREN) or for cytoplasmic retention (exon 1b initiating intracellular renin, icREN). The icREN isoform is expressed predominantly in the brain and its expression is downregulated whereas sREN expression is upregulated by deoxycorticosterone (DOCA)-salt suggesting each isoform may be differentially regulated. We generated mice that conditionally lack icREN, but preserve sREN, by targeting a novel renin allele in ES cells by flanking exon-1b and its surrounding sequences (including the promoter) with loxP sites. Mice carrying this allele were first bred with flippase mice to remove the neo cassette and then with cre-recombinase mice to generate the null allele lacking icREN. The structure of the final allele was confirmed by Southern blot. There was no apparent lethality in the homozygous mice when heterozygous mice were intercrossed. Real time quantitative RT-PCR analysis revealed a loss of icREN mRNA in the brain, but a preservation of sREN mRNA in the kidney. Male icREN-KO mice were similar in size (n=4, 14.7±0.9 wk, 27.94±1.08 g) compared to littermate controls (n=7, 14.2±0.8 wk, 27.96±0.82 g, P=0.988), but by NMR exhibited reduced total and relative total fat mass (1.83±0.15 vs 3.00±0.12 g, or 6.6±0.7 vs 10.9±0.5 %, both P<0.001). Interestingly, interscapular brown adipose (289±77, n=5 vs 68±61 mg, n=9 P=0.04) and heart (162±12 vs 129±9 mg, P=0.04) masses were both increased in icREN-KO mice, possibly suggesting increased resting metabolic rate (RMR) and blood pressure. Liver and kidney masses were normal. Food intake was normal (3.25±0.28, n=4 vs 3.14±0.14, n=8 P=0.7), but preliminary tests uncovered trends toward increased RMR (7.67±0.75, n=4 vs 6.93±0.59 g/day, n=4 kcal/kg lean/hr, P=0.47) and glucose tolerance (2g/kg, 25768±3994, n=3 vs 33734±2854 mg/dL*min, n=8, P=0.157). Studies are ongoing to assess arterial pressure. Together these data suggest that this novel icREN isoform contributes to metabolic and possibly to cardiovascular control. Future studies using the conditional allele (icREN-flox) will provide an opportunity to dissect the neural circuits involved in these responses.