Cardiac AKAP12 Signalosome Overexpression Exacerbates Isoproterenol Induced Heart Failure
Authors: Qasim Hanan , Dinakar Iyer , McConnell Bradley K. 
Published: April 2020

Background

Heart failure (HF), defined as an impaired ability of the heart to efficiently pump blood, is responsible for 1 out of 8 deaths per year in the U.S.A. and is the major cause of death globally. Physiologically, stimulation of β‐adrenergic receptors (β‐AR) by catecholamines, epinephrine (EP) and norepinephrine (NE), increases cardiac contractility. However, in HF, chronic β‐AR stimulation leads to reduced cardiac function due in part to the desensitization of these receptors. Previous in vivo studies reported by our group showed enhanced cardiac function after Isoproterenol (ISO) induced HF in male mice lacking functional cardiac AKAP12 compared to wild‐type (WT) mice. In this study, we aim to investigate the impact of cardiac AKAP12 overexpression (oxAKAP12‐Tg) on HF progression in both male and female mice and understand the underlying mechanisms involved. Our central hypothesis is that cardiac AKAP12 overexpression is involved in heart failure progression by influencing signaling downstream β‐AR.

Methods

WT and oxAKAP12‐Tg mice (8–10) weeks old males and females were categorized into three groups; subcutaneous ISO osmotic pump group (ISO; 60 mg/kg/day X 14‐days), vehicle group (ascorbic acid 0.0002% X 14‐days), and sham group (no subcutaneous pump). Echocardiography and ECG were obtained from all groups 2‐days before subcutaneous insertion of the osmotic pumps as well as 7‐days and 14‐days after the osmotic pump insertion, followed by tissue harvest on the 14‐day. Adult mouse ventricular homogenates were used for protein expression levels analysis. Furthermore, CRISPR‐cas9 technology was used to overexpress AKAP12 into AC16 cells, a human cardiomyocyte cell line, to assess gene expression levels upon overnight treatment with 100 nmol of ISO.

Results

Cardiac overexpression of AKAP12 in both males and females reduced left ventricular ejection fraction (EF) and fractional shortening (FS). Both males and females treated with ISO and overexpressing AKAP12 had a 22.7±2% reduction in EF and 14.5±2.5% reduction in FS after 14‐days of chronic ISO treatment when compared to control groups. However, the pattern of this decline in cardiac function was different between male mice and female mice; where male mice showed a slow decline in cardiac function over the two week period of chronic ISO treatment while female mice showed a steep decline within the first week of chronic ISO treatment that plateaued during the second week of treatment. Protein expression levels of β‐arrestin1 and β‐arrestin2 were significantly lower in cardiac homogenates of ISO treated oxAKAP12‐Tg when compared to ISO treated WT male and female mice, respectively. No significant differences were observed between control groups. This observation was further supported by QPCR gene expression studies; where we observed a 40% reduction of β‐arrestin‐1 gene expression in ISO treated AC16 overexpressing AKAP12 when compared to the ISO treated WT AC16 cells.

Conclusions

Cardiac overexpression of AKAP12 negatively influences systolic function in both male and female mice, potentially through affecting the β‐arrestin signaling pathway. Thus, AKAP12 might be involved in biased signaling downstream β‐AR which could serve as a potential target for designing drugs to ameliorate HF.