Angiotensinogen and Megalin Interactions Contribute to Atherosclerosis—Brief Report

Abstract

Objective— AGT (Angiotensinogen) is the unique precursor of the renin-angiotensin system that is sequentially cleaved by renin and ACE (angiotensin-converting enzyme) to produce Ang II (angiotensin II). In this study, we determined how these renin-angiotensin components interact with megalin in kidney to promote atherosclerosis. Approach and Results— AGT, renin, ACE, and megalin were present in the renal proximal convoluted tubules of wild-type mice. Hepatocyte-specific AGT deficiency abolished AGT protein accumulation in proximal tubules and diminished Ang II concentrations in kidney, while renin was increased. Megalin was most abundant in kidney and exclusively present on the apical side of proximal tubules. Inhibition of megalin by antisense oligonucleotides (ASOs) led to ablation of AGT and renin proteins in proximal tubules, while leading to striking increases of urine AGT and renin concentrations, and 70% reduction of renal Ang II concentrations. However, plasma Ang II concentrations were unaffected. To determine whether AGT and megalin interaction contributes to atherosclerosis, we used both male and female low-density lipoprotein receptor −/− mice fed a saturated fat-enriched diet and administered vehicles (PBS or control ASO) or megalin ASO. Inhibition of megalin did not affect plasma cholesterol concentrations, but profoundly reduced atherosclerotic lesion size in both male and female mice. Conclusions— These results reveal a regulatory role of megalin in the intrarenal renin-angiotensin homeostasis and atherogenesis, positing renal Ang II to be an important contributor to atherosclerosis that is mediated through AGT and megalin interactions.

Urinary Renin in Patients and Mice With Diabetic Kidney Disease

“…The concordant increase in urinary renin in an experimental model of diabetes mellitus and in human DKD associated with type 1 diabetes mellitus is in agreement with previous studies where key components of the RAS system including renin were similarly altered. 23,46,54 Renin-producing cells in adult life are restricted to the JGA localization, whereas in fetal life these cells are also found in large intrarenal arteries, inside the glomeruli, and in the interstitium. 6 As maturation continues, the number of renin-producing cells is reduced as they differentiate into arteriolar smooth muscle and mesangial cells and become progressively restricted to the JGA localization.…”

The Two Amino Acids Proximate to the Renin Cleavage Site of Human Angiotensinogen Do Not Affect Angiotensin II-mediated Functions in Mice

“…(3) The AAV vector encoding human AGT with a hepatocyte-specific promoter led to human AGT produced in hepatocytes, mimicking the normal processing of AGT production in liver and secretion to the circulation. 10,18 In hepAGT -/-mice infected with AAV containing human AGT, plasma human AGT concentrations were above 10 μg/ml, which were 3 -4-fold higher than plasma endogenous mouse AGT concentrations in wild type mice. Although mouse plasma renin concentrations were greatly elevated in hepAGT -/-mice compared with wild type mice due to removal of AngII-mediated negative feedback, the presence of human AGT did not correct plasma renin concentrations, elevate blood pressure, or contribute to the development of atherosclerosis.…”

“…The low plasma concentrations of mouse AGT were sufficient to enable normal growth and kidney development, but led to much lower blood pressure, compared to their wild type littermates. 4,9,10 Therefore, this mouse model is relevant to physiological regulation of the renin-angiotensin system. More importantly, our mouse model can address the caveats raised above in previous studies.…”

“…Development of hepatocyte-specific AGT deficient mice has been reported previously. 4,9,10 AGT floxed (termed "Agt f/f") x albumin-Cre -/-(hepAGT +/+) and Agt f/f x albumin-Cre +/-(hepAGT -/-) littermates were used for experiments described in this manuscript. Genotypes were determined prior to weaning and validated after termination by Cre PCR, and confirmed by measuring plasma AGT concentrations during the study and after termination.…”

Inhibition of Angiotensin II Dependent AT1a Receptor Stimulation Attenuates Thoracic Aortic Pathology in Fibrillin-1C1041G/+Mice

“…35 Inhibition of AGT synthesis by an ASO reduces plasma concentrations by approximately 90% in the postnatal phase with no observable toxicity as demonstrated in the present study and other reports. 24,36 Therefore, the use of ASO to deplete AGT demonstrated the need for the presence of angiotensin ligands to augment aortic pathology in Fbn1 C1041G/+ mice.…”