Heterodimerization With 5-HT 2B R Is Indispensable for β 2 AR-Mediated Cardioprotection

Rationale: The β 2 -adrenoceptor (β 2 -AR), a prototypical GPCR (G protein-coupled receptor), couples to both G s and G i proteins. Stimulation of the β 2 -AR is beneficial to humans and animals with heart failure presumably because it activates the downstream G i -PI3K-Akt cell survival pathway. Cardiac β 2 -AR signaling can be regulated by crosstalk or heterodimerization with other GPCRs, but the physiological and pathophysiological significance of this type of regulation has not been sufficiently demonstrated. Objective: Here, we aim to investigate the potential cardioprotective effect of β 2 -adrenergic stimulation with a subtype-selective agonist, (R,R’)-4-methoxy-1-naphthylfenoterol (MNF), and to decipher the underlying mechanism with a particular emphasis on the role of heterodimerization of β 2 -ARs with another GPCR, 5-hydroxytryptamine receptors 2B (5-HT 2B Rs). Methods and Results: Using pharmacological, genetic and biophysical protein-protein interaction approaches, we studied the cardioprotective effect of the β 2 -agonist, MNF, and explored the underlying mechanism in both in vivo in mice and cultured rodent cardiomyocytes insulted with doxorubicin, hydrogen peroxide (H 2 O 2 ) or ischemia/reperfusion. In doxorubicin (Dox)-treated mice, MNF reduced mortality and body weight loss, while improving cardiac function and cardiomyocyte viability. MNF also alleviated myocardial ischemia/reperfusion injury. In cultured rodent cardiomyocytes, MNF inhibited DNA damage and cell death caused by Dox, H 2 O 2 or hypoxia/reoxygenation. Mechanistically, we found that MNF or another β 2 -agonist zinterol markedly promoted heterodimerization of β 2 -ARs with 5-HT 2B Rs. Upregulation of the heterodimerized 5-HT 2B Rs and β 2 -ARs enhanced β 2 -AR-stimulated G i -Akt signaling and cardioprotection while knockdown or pharmacological inhibition of the 5-HT 2B R attenuated β 2 -AR-stimulated G i signaling and cardioprotection. Conclusions: These data demonstrate that the β 2 -AR-stimulated cardioprotective G i signaling depends on the heterodimerization of β 2 -ARs and 5-HT 2B Rs.