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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Article Cardiology

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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Figure 7

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Competitive displacement of endogenous active PI3K by PI3Kγinact from βA...
Competitive displacement of endogenous active PI3K by PI3Kγinact from βARK1 prevents βAR dysfunction following 12 weeks of chronic pressure overload. (a) βAR density among WT and PI3Kγinact mice (WT and PI3Kγinact sham: n = 4; TAC: n = 4). *P < 0.005 WT TAC versus WT sham. (b) Basal (white bars) and ISO-stimulated (black bars) adenylyl cyclase activity in membrane fractions from WT (n = 8–10) and PI3Kγinact (n = 7–8) hearts. Adenylyl cyclase activity upon NaF stimulation: 185 ± 8 pmol/mg/min for WT-sham; 128 ± 10 pmol/mg/min for WT-TAC; 151 ± 6 pmol/mg/min for PI3Kγinact-sham; 162 ± 10 pmol/mg/min for PI3Kγinact-TAC. *P < 0.001 ISO versus basal. (c) Myocardial βAR/Gs coupling (percentage of high affinity) in sarcolemmal membranes prepared from hearts of WT sham (n = 3), WT TAC (n = 4), and PI3Kγinact (n = 3) mice. *P < 0.01 WT TAC versus either WT sham or PI3Kγinact TAC. (d) Proposed model of the mechanism by which overexpression of PI3Kγinact transgene prevents βAR downregulation. Overexpression of PI3Kγinact leads to a competitive displacement of all PI3K isoforms from the βARK1/PI3K complex. Following agonist stimulation, the translocation of βARK1 recruits inactive PI3K to the activated receptor complex attenuating receptor internalization. Inhibition of receptor internalization ultimately leads to receptor dephosphorylation and resensitization either at the cell surface or through enhanced cycling of receptor without being targeted for lysosomal degradation. Gs, Gαs subunit of heterotrimeric G protein.