Abstract 015: Ctcf is Required for Renin Expression and Maintenance of the Structural Integrity of the Kidney

Abstract

Renin is crucial for the regulation of blood pressure and fluid electrolyte homeostasis. The transcriptional machinery that regulates renin expression and thus determines the identity of renin cells is not completely understood. CCCTC-binding factor ( Ctcf ), is an important chromatin organizer of genes that confer cell identity and tissue-specificity. Because Ctcf binds to several sites in the neighborhood of the renin locus, we hypothesized that Ctcf may regulate renin expression. To test this hypothesis, we generated mice with conditional deletion of Ctcf in cells of the renin lineage ( Ctcf cKO). Ctcf cKO mice showed fewer renin-positive cells as shown by immunostaining, and a 70% reduction of renin mRNA levels when compared to control mice (0.292 ± 0.246 vs 1.003 ± 0.097, p<0.001 ). In addition, plasma renin levels were significantly decreased in Ctcf cKO versus control mice (15276.544 ± 6778.735 pg/ml vs 62321.62 ± 21881.99 pg/ml, p<0.001 ). Consistent with reduced renin levels, Ctcf cKO mice had lower mean arterial pressures (60.09 ± 3.12 mmHg vs 75.07 ± 3.06 mmHg, p<0.001 ). The kidney/body weight ratio in Ctcf cKO mice was markedly reduced (1.05 ± 0.228 % vs 1.29 ± 0.074 %, p<0.05 ), indicating a more pronounced effect in kidney than in somatic growth (20.09 ± 1.47 g vs 22.95 ± 2.95 g, p<0.05 ). Masson’s trichrome staining revealed interstitial fibrosis coinciding with cortical depressions in Ctcf cKO kidneys. Moreover, PAS staining of Ctcf cKO kidneys showed dilated tubules with intraluminal casts, and areas with crowded sclerotic and crescent glomeruli surrounded by disorganized packed cells. Finally, Ctcf cKO mice exhibited renal failure evidenced by increased BUN (44.29 ± 17.62 mg/dL vs 26 ± 3.39 mg/dL, p<0.05) , and inability to concentrate their urine (448 ± 85.57 mOsm/kg vs 1519.33 ± 382.39 mOsm/kg, p<0.001 ). In summary, deletion of Ctcf in cells from the renin lineage leads to decreased endowment of renin-expressing cells accompanied by decreased circulating renin, hypotension, severe morphological abnormalities of the kidney and ultimately renal failure. We conclude that Ctcf is necessary for the appropriate expression of renin, control of renin cell number and structural integrity of the kidney.