Abstract 3819: Mechanical Stretch Activates β-arrestin-mediated Signaling of the AT1 Receptor
In the heart, mechanical stretch is an important stimulus for activation of hypertrophic signaling. Here, we identify a mechanism by which mechanical stretch induces angiotensin II type I receptor (AT1R) signaling in a Gq independent, but G protein-coupled receptor kinase (GRK) and β-arrestin (βarr) dependent manner. In vitro experiments utilized cyclic and osmotic stretch in HEK-293 cells stably expressing AT1Rs. Ex vivo experiments in Langendorff-perfused mouse hearts used tensile stretch applied via a LV balloon for 10 minutes. In AT1R HEK-293 cells, stretch caused ligand independent AT1R internalization and βarr-GFP translocation to the membrane. Absence of stretch-induced Gq activation was also documented using the highly sensitive fluorescent based diacylglycerol receptor assay. In AT1R HEK-293 cells, activation of phospho-ERK (pERK) in response to mechanical stretch was abrogated by siRNA targeting βarr1/2. In ex vivo heart experiments, mechanical stretch induced a robust pERK response WT mice, which was absent in AT1R KO mice (Fig A⇓). Moreover, hearts from both βarr 2 and GRK5 KO mice failed to show pERK activation in response to mechanical stretch (Fig B–C⇓). To confirm the absence of released angiotensin II ligand, pre-infusion with enalapril or added enalapril to perfusion buffer had no effect on stretch-induced pERK expression (Fig D⇓). Lastly, a robust pERK expression was observed in hearts from beta adrenergic KO mice following stretch. In conclusion, these findings suggest that mechanical stretch in the heart induces a ligand independent conformational change in the AT1R, which is able to activate β-arrestin mediated signaling down the ERK pathway.