Functional Exploration of Conserved Sequences in the Distal Face of Angiotensinogen

Abstract

ABSTRACT Background Angiotensinogen (AGT) is an essential component in the renin-angiotensin system. AGT has highly conserved sequences in the loop and β-sheet regions among species; however, their functions have not been studied. Methods Adeno-associated viral vector (AAV) serotype 2/8 encoding mouse AGT with mutations of conserved sequences in the loop (AAV.loop-Mut), β-sheet (AAV.βsheet-Mut), or both regions (AAV.loop/βsheet-Mut) were injected into male hepatocyte-specific AGT deficient (hepAGT-/-) mice in an LDL receptor –/– background. AAV containing mouse wild-type AGT (AAV.mAGT) or a null vector (AAV.null) were used as controls. Two weeks after AAV administration, all mice were fed a Western diet for 12 weeks. To determine how AGT secretion is regulated in hepatocytes, AAVs containing the above mutations were transducted into HepG2 cells. Results In hepAGT-/– mice infected with AAV.loop-Mut or βsheet-Mut, plasma AGT concentrations, systolic blood pressure, and atherosclerosis were comparable to those in AAV.mAGT-infected mice. Surprisingly, plasma AGT concentrations, systolic blood pressure, and atherosclerotic lesion size in hepAGT-/– mice infected with AAV.loop/βsheet-Mut were not different from mice infected with AAV.null. In contrast, hepatic Agt mRNA abundance was elevated to a comparable magnitude as AAV.mAGT-infected mice. Immunostaining showed that AGT protein was accumulated trol and AAV containing wild-type mouse AGT as a positive control. We have demonstra ted consistently in this and previous studies tht located in the endoplasmic reticulum. Conclusions The conserved sequences in either the loop or β-sheet region individually have no effect on AGT regulation, but the conserved sequences in both regions synergistically contribute to the secretion of AGT from hepatocytes. HIGHLIGHTS The loop and β-sheet regions in the distal face of angiotensinogen (AGT) have highly conserved sequences across species. Mutations on either the loop or β-sheet regions do not affect plasma AGT concentrations, blood pressure, and atherosclerosis in hypercholesterolemic mice. The conserved sequences in the loop and β-sheet regions regulate the secretion of AGT from hepatocytes synergistically in vivo and in cultured cells.