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 1

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Generation of transgenic mice with decreased cardiac βAR-localized PI3K ...
Generation of transgenic mice with decreased cardiac βAR-localized PI3K activity. (a) Diagram of the transgene construct containing the PI3Kγinact cDNA (upper panel). Southern (10 μg of DNA) and Western blots (100 μg of cytosolic extract) from WT and three transgenic founder lines using SV-40 probe and anti-PI3Kγ Ab, respectively (lower panel). (b and c) Basal levels of total PI3K (b) and PI3Kγ (c) activity in the LV relative to WT (n = 9, WT and transgenic lines); 2 mg of cytosolic extract was used for immunoprecipitation with PI3K Ab. *P < 0.05 versus WT; †P < 0.01 versus WT. (d) Basal βARK1-associated PI3K activity in the LV of WT (n = 6) and 180-fold overexpressing transgenic mice (n = 6); 4 mg of cytosolic extract was used for immunoprecipitation with βARK1 mAb. (e) Total PI3K, PI3Kγ, and βARK1-associated PI3K activity in the left LVs measured by their ability to phosphorylate PtdIns-4,5-P2 to PtdIns-3,4,5-P3. (f) Immunoblotting for PI3Kα or PI3Kγ following immunoprecipitation with βARK1 mAb from clarified myocardial lysates (3 mg). *P < 0.001 versus WT. IP, immunoprecipitation; αMHC, alpha myosin heavy chain promoter; K, Kozak sequence; C2, similar to type II C2 domain found in phospholipase Cδ1; X, catalytically inactive; ABR, adaptor binding region; RBD, ras-binding domain; HA, hemagglutinin epitope tag; PIP, phosphatidylinositol mono-phosphate; PIP2, phosphatidylinositol bis-phosphate; Ori, origin; Cont (plus control), immunoprecipitation of PI3Kα or PI3Kγ with its respective Ab and immunoblotted for PI3Kα or PI3Kγ; βARK, β-adrenergic receptor kinase.