Inhibition of receptor-localized PI3K preserves cardiac β-adrenergic receptor function and ameliorates pressure overload heart failure
Jeffrey J. Nienaber, … , Lan Mao, Howard A. Rockman
Jeffrey J. Nienaber, … , Lan Mao, Howard A. Rockman
Published October 1, 2003
Citation Information: J Clin Invest. 2003;112(7):1067-1079. https://doi.org/10.1172/JCI18213.
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Inhibition of receptor-localized PI3K preserves cardiac β-adrenergic receptor function and ameliorates pressure overload heart failure

Abstract

β-Adrenergic receptor (βAR) downregulation and desensitization are hallmarks of the failing heart. However, whether abnormalities in βAR function are mechanistically linked to the cause of heart failure is not known. We hypothesized that downregulation of cardiac βARs can be prevented through inhibition of PI3K activity within the receptor complex, because PI3K is necessary for βAR internalization. Here we show that in genetically modified mice, disrupting the recruitment of PI3K to agonist-activated βARs in vivo prevents receptor downregulation in response to chronic catecholamine administration and ameliorates the development of heart failure with pressure overload. Disruption of PI3K/βAR colocalization is required to preserve βAR signaling, since deletion of a single PI3K isoform (PI3Kγ knockout) is insufficient to prevent the recruitment of other PI3K isoforms and subsequent βAR downregulation with catecholamine stress. These data demonstrate a specific role for receptor-localized PI3K in the regulation of βAR turnover and show that abnormalities in βAR function are associated with the development of heart failure. Thus, a strategy that blocks the membrane translocation of PI3K and leads to the inhibition of βAR-localized PI3K activity represents a novel therapeutic approach to restore normal βAR signaling and preserve cardiac function in the pressure overloaded failing heart.

Authors

Jeffrey J. Nienaber, Hideo Tachibana, Sathyamangla V. Naga Prasad, Giovanni Esposito, Dianqing Wu, Lan Mao, Howard A. Rockman

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PI3Kγinact-overexpressing mice do not undergo βAR desensitization or dow...
PI3Kγinact-overexpressing mice do not undergo βAR desensitization or downregulation under conditions of chronic catecholamine administration. (a) In vivo hemodynamic studies showing βAR responsiveness as monitored by the increase in left ventricular contractility (LV dP/dtmax) in WT and PI3Kγinact mice following 7 days of ISO (closed circles: n = 9; closed squares: n = 7) or vehicle (open circles: n = 13; open squares: n = 8) treatment. *P < 0.0001 (two-way ANOVA) WT ISO versus PI3Kγinact ISO. (b) βARK1-associated PI3K activity in WT and PI3Kγinact ventricles (500 μg of membrane fraction) following 7 days of ISO (n = 6) or vehicle treatment (n = 5–6). Values are expressed relative to vehicle-treated WT. Immunoblotting the HA-epitope tag (PI3Kγinact) following immunoprecipitation with βARK1 from 500 μg of membrane fraction (upper immunoblot, IB: HA). *P < 0.001 ISO 7 days versus vehicle. (c) In vitro myocardial βARK1 activity measured by rhodopsin (Rho) phosphorylation in WT and PI3Kγinact mice following 7 days of ISO or vehicle treatment. (d) βAR density among WT and PI3Kγinact mice following 7 days of ISO administration (n = 6) or vehicle treatment (n = 5–6). *P < 0.05 ISO 7 days versus vehicle. (e) Basal (white bars) and in vitro ISO-stimulated (black bars) adenylyl cyclase activity in WT and PI3Kγinact mice following 7 days of ISO (n = 6) or vehicle treatment (n = 5–6). Adenylyl cyclase activity upon NaF stimulation: 257 ± 21 pmol/mg/min and 244 ± 18 pmol/mg/min for vehicle and ISO 7-day treatment, respectively, in WT; 242 ± 12 pmol/mg/min and 239 ± 24 pmol/mg/min for vehicle and ISO 7-day treatment, respectively, in PI3Kγinact mice. *P < 0.002 ISO versus basal. βARK1 (C5/1) mAb is directed against the catalytic site of βARK1 blocking its enzymatic activity.