Abstract 1353: The Phosphoinositide 3-Kinases (PI3K)-AKT Signaling Pathway may Explain Arrhythmic Changes in Cardiac-Specific Angiotensin Converting Enzyme (ACE) Overexpression Mice (ACE 8/8)
Introduction: Elevated angiotensin II (AngII) is associated with increased arrhythmic risk. We created a model of excess myocardial AngII by cardiac overexpression of angiotensin converting enzyme (ACE). Homozygous ACE 8/8 mice have slow conduction, show conduction blocks, are prone to ventricular tachycardia and sudden death, and show a profound reductions in the gap junctional protein connexin 43 (Cx43) levels and phosphorylation. In this study, we attempted to define the signaling cascade responsible for this phenotype.
Methods: After baseline phenotyping by surface electrocardiography and invasive intracardiac electrophysiol-ogy, the heart was extracted from a group of ACE 8/8 mice and wild-type littermate controls. A mitogen-activated protein (MAP) kinase antibody microarray system was used for high throughput screening of candidate kinases. The result of the microarray analysis was confirmed and further expanded by immunoblotting.
Results: The antibody microarray identified two candidate kinases that were activated in ACE 8/8 mice: glycogen synthase kinase 3 (GSK-3) and ribosomal S6 kinase (p90RSK). Since both kinases are related to PI3K-AKT pathway, we probed this pathway using immunoblotting for total or phosphorylated proteins. We observed increases in phospho-AKT (3.6 fold, 95% confidence interval 1.3–5.9), phospho-GSK-3 (2.1, CI 1.0 –3.2), phospho-S6 (3.5, CI 2.1– 4.2), the transcriptional factor phospho-FoxO1 (2.4, CI 1.3–3.6), and the microtubular protein β-tubulin (3.2, CI 2.1– 4.2). There was no significant change in total β-catenin and phosphorylated p38, c-Jun N-terminal kinases (JNK), the mammalian target of rapamycin (mTOR), and nitric oxide synthase. Furthermore, we observed an upregulation of the epidermal growth factor (EGF) receptor (2.3, CI 1.8 –2.8), which activates PI3K-AKT pathway through extracellular signal-regulated kinases 1/2 (phospho-ERK1/2 was increase 6.3 fold, CI 3.5–13.3).
Conclusions: Activation of PI3K-AKT signaling pathway is associated with suppression of Cx43 and increased arrhythmic risk in ACE 8/8 mice. It is likely that the EGF/ERK pathway is, at least partly, responsible for the activation of the PI3K-AKT in this model.