Abstract 12379: AT1-AA (Angiotensin II Type 1 Receptor Autoantibody) Aggravates Abdominal Aortic Aneurysm Through Activating AT1R/Gq Allosterically

Background: Angiotensin II type 1 receptor (AT1R) is a key mediator of the rennin-angiotensin-aldosterone system (RAAS). Autoantibodies against AT1R (AT1-AA), as an activator of AT1R, was found in abdominal aortic aneurysm (AAA) related diseases, such as hypertension and atherosclerosis. However, the role of AT1-AA in AAA is still unclear. Methods: We used angiotensin II (AngII)-infused male ApoE -/- mice model of AAA. Ultrasonography measurement, histological assessment, western blot, qRT-PCR and RNA sequencing were used to assess the severity of AAA. Nanoluciferase-based bioluminescence resonance energy transfer (NanoBRET) assay, radio assay of receptors and homogeneous time resolved fluorescence (HTRF) were used to measure the activation feature of AT1R and the affinity of AT1R with AT1-AA or AngII. Results: AT1-AA increased the incidence of AAA (vehicle vs. AT1-AA: 47% vs. 81%; P<0.05), which can be attenuated by AT1R blocker Candesartan. Furthermore, AT1-AA greatly increased severity of AAA, due to augmenting the diameter of abdominal aorta and the degradation of elastin by enhancing the expression of MMP2/9 (matrix metalloproteinase) and the accumulation of inflammatory cells. And AT1-AA could induce phenotypic switch of smooth muscle cells. But AT1-AA does not increase the plasma level of AngII. Mechanically, AT1-AA enhanced AngII-induced recruitment of Gq, but not β-arrestin1/2. AT1-AA potentiated the AngII-mediated Gq-dependent inositol phosphate (EC50 shift=3.829 nM) and the activation of PKC and ERK1/2. The responses were abolished by AT1R blocker and Gq inhibitor. The affinity of AT1-AA for the AT1R in cells was calculated to be 75.49 ± 4.7 nM. AT1-AA cannot compete for the binding of AngII to AT1R. However, AT1-AA significantly potentiated the binding of AngII with AT1R allosterically (mean K D ± SEM: 34.11 ± 0.9765 nM at 0 nM AT1-AA vs. 25.63 ± 1.826 nM at 100 nM AT1-AA; p<0.05), without altering the maximum binding. Conclusion: AT1-AA, as an allosteric activator of AT1R, promotes AAA through increasing the affinity of AngII with AT1R and activating Gq biasedly.