βb-arrestin-biased agonism of the angiotensin receptor induced by mechanical stress

β-Arrestins, which were originally characterized as terminators of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptor (GPCR) signaling, also act as important signal transducers. An emerging concept in GPCR signaling is β-arrestin-biased agonism, in which specific ligand-activated GPCR conformational states selectively signal through β-arrestins, rather than through G proteins. Here, we show that mechanical stretch induced β-arrestin-biased signaling downstream of angiotensin II type I receptors (AT1Rs) in the absence of ligand or G protein activation. Mechanical stretch triggered an AT1Rmediated conformational change in β-arrestin similar to that induced by a β-arrestin-biased ligand to selectively stimulate receptor signaling in the absence of detectable G protein activation. Hearts from mice lacking β-arrestin or AT1Rs failed to induce responses to mechanical stretch, as shown by blunted extracellular signal-regulated kinase and Akt activation, impaired transactivation of the epidermal growth factor receptor, and enhancedmyocyte apoptosis. These data show that the heart responds to acute increases in mechanical stress by activating β-arrestin-mediated cell survival signals.