Abstract P160: Deficiency Of Angiotensin-converting Enzyme In Renal Proximal Convoluted Tubules Does Not Attenuate Atherosclerosis In Mice

Abstract

Objective: Angiotensin-converting enzyme (ACE) is the enzyme to generate Angiotensin II (AngII), an important contributor to atherosclerosis. ACE is present in all 3 segments (S1, S2, and S3) of proximal tubular cells (PTCs), and AngII concentrations are higher in kidney than in plasma. The purpose of this study was to determine whether ACE in PTCs contributes to atherosclerosis in mice. Approach and Results: Female ACE floxed mice and male Ndrg1-Cre ERT2 +/- transgenic mice were bred to generate ACE f/f x Ndrg1-Cre ERT2 -/- (PTC-ACE +/+ ) and ACE f/f x Ndrg1-Cre ERT2 +/- (PTC-ACE -/- ) littermates. Male PTC-ACE +/+ (n=7) and PTC-ACE -/- (n=10) littermates in an LDL receptor -/- background were used for atherosclerosis study. After Cre genotyping using tail DNA, mice (both Cre ERT2 -/- and Cre ERT2 +/- ) were injected with 150 mg/kg/day of tamoxifen for 5 consecutive days at the age of 4-6 weeks. Two weeks after the last injection of tamoxifen, mice were fed a Western diet (Envigo, Diet #TD.88137) for 12 weeks to induce hypercholesterolemia. Blood pressure was measured using a tail-cuff system. No difference of blood pressure was detected between the two genotypes (PTC-ACE +/+ vs. PTC-ACE -/- : 126 ± 4 vs. 125 ± 3 mmHg; P = 0.763). All study mice were hypercholesterolemic, but plasma cholesterol concentrations were not different between the two genotypes (PTC-ACE +/+ vs. PTC-ACE -/- : 1376 ± 119 vs. 1543 ± 93 mg/dl; P = 0.28). PTC-specific deletion of ACE was confirmed after termination using immunostaining of ACE. In mice with Ndrg1-Cre ERT2 transgene, immunostaining of ACE in kidney section showed an absence of ACE in S1 and S2 of PTCs, but ACE protein in S3 remained. Deletion of ACE in S1 and S2 of PTCs did not change hypercholesterolemia-induced atherosclerosis in the ascending and aortic arch regions (PTC-ACE +/+ vs. PTC-ACE -/- : 9.6 ± 0.9% vs. 7.0 ± 1.9%; P = 0.13 by Mann-Whitney Rank Sum Test), as measured using an en face method. Conclusion: ACE deficiency in S1 and S2 of renal proximal tubular cells had no effect on atherosclerosis in hypercholesterolemic mice. Since ACE is more abundant in S3 than in S1 and S2 of PTCs, it would be important to determine the role of ACE in the S3 segment.