Abstract 13489: Restoration of β-Adrenergic Receptor Signaling in Gravin Knockout Mice with Failing Hearts
Gravin, an A kinase anchoring protein, facilitates PKA phosphorylation of substrates to mediate cardiac contraction and relaxation as well as facilitates the desensitization of the β2-AR. In heart failure, alterations in β-AR signaling and density result in reduced cardiac function. Thus, we hypothesized that knockout of gravin would block β-AR desensitization and rescue impaired contractility in failing hearts. Therefore, we measured various aspects of the β-AR signaling pathway such as density and affinity of the β-AR subtypes and cAMP production in gravin knockout mice treated with isoproterenol (ISO; 30 mg/kg/day x 14 days) to induce heart failure. All experiments were performed with n=5. The WT treatment group (WT ISO) had significantly higher total β-AR density (WT control: 103.53±8.20; WT ISO: 209.52±27.70; KO control: 118.62±8.60; KO ISO: 146.25±22.40; fmol/mg; p=0.01) but significantly lower affinity, when compared to the gravin KO treatment group (KO ISO) and the WT and KO controls (WT control: 0.30±0.06; WT ISO: 0.66±0.07; KO control: 0.34±0.06; KO ISO: 0.23±0.04; nM; p=0.002). Additionally, the gravin KO ISO group had a significantly higher percentage of β1-ARs than the WT treatment group (WT ISO: 25.33%±5.9; KO ISO: 61%±3.2; p=0.007). However, both treatment groups had significantly decreased β1-AR affinity (WT ISO: 1.33±0.30; KO ISO: 1.35±0.20; nM; p=0.014). Similarly, the KO ISO group had a significantly increased percentage of β2-ARs compared to the WT ISO group (WT ISO: 31%±3.8; KO ISO: 57.4%±4.6; p=0.002). However, there was no difference in β2-AR affinity between the two groups. Both the WT and the gravin KO treatment group had significantly lower basal cAMP production when compared to their respective controls (WT control: 0.68±0.09; WT ISO: 0.32±0.05; KO control: 0.66±0.02; KO ISO: 0.24±0.03; pmol/mg; p=0.0001). However, when cAMP production was acutely stimulated by the addition of ISO, the gravin KO ISO group, but not the WT ISO group, responded similarly to control groups (WT control: 3.29±0.023; WT ISO: 1.74±0.18; KO control: 2.42±0.37; KO ISO: 2.48; pmol/mg±0.65; p=0.005). In conclusion, these data indicate that knockout of gravin results in the normalization of β-AR signaling even in the presence of chronic β-AR stimulation.
- © 2011 by American Heart Association, Inc.