Abstract 11076: Cardiac AKAP12 Overexpression Reduces Cyclic Amp Accumulation in the Vicinity of β 2 Ar

Abstract

Introduction: In Heart Failure (HF), signaling downstream the β 2- Adrenergic Receptor (β 2 AR) is critical. Sympathetic stimulation of β 2 AR triggers Protein Kinase A (PKA) dependent phosphorylation of proteins that regulate cardiac function. Cyclic adenosine monophosphate (cAMP) accumulation in the vicinity of β 2 AR is crucial for PKA stimulation. cAMP levels are regulated in part by phosphodiesterases (PDEs). A Kinase Anchoring Protein 12 (AKAP12) has been reported to directly bind β 2 AR, PKA, and PDE4. Previously, we reported that cardiac overexpression of AKAP12 (oxAKAP12) in both male and female mice reduced left ventricular ejection fraction (EF) and fractional shortening (FS) significantly after 14-days of chronic Isoproterenol treatment when compared to control groups. Hypothesis: AKAP12 overexpression progresses HF development by reducing local cAMP levels in the vicinity of β 2 AR. Methods: AC16 cells (Human ventricular cell lines) were grouped into [1] control group or [2] cells stably transfected to overexpress human AKAP12 (oxAKAP12). cAMP accumulation in real-time downstream the β 2 AR was detected for 60 minutes in live cells using the luciferase-based biosensor (GloSensor) post-treatment with 10μM Epinephrine (EPI). Additionally, cells were pre-treated for 2 hours with either 10μM Rolipram (selective PDE4 inhibitor) or 0.1mM IBMX (non-selective PDE inhibitor) followed by 10μM EPI treatment. Results: oxAKAP12 cells (expressing AKAP12 protein 3 folds higher than controls) had significantly lower maximum cAMP accumulation post-EPI treatment downstream the β 2 AR (2.06 ± 0.32) compared to controls (9.04 ± 0.73), [p=0.0001]. Rolipram pretreatment increased cAMP levels in the oxAKAP12 group to (3.75± 0.72), however, the control group was still significantly higher (9.63 ± 0.95), [p=0.0032]. IBMX pretreatment increased cAMP levels in the oxAKAP12 group to (6.94 ± 1.55) which wasn’t significantly different from the control group (9.75 ± 2.52), [p=0.4152]. Conclusions: Cardiac overexpression of AKAP12 significantly reduces cAMP levels downstream of the β 2 AR. Potentially through scaffolding other PDEs aside from PDE4.