Abstract 259: KChIP2 is a Key Transcriptional Regulator of Cardiac Excitability Under Normal and Pathogenic Conditions

Abstract

Introduction: Arrhythmogenesis is the primary cause of death in patients with acquired heart disease, and is the consequence of profound dysregulation of both depolarizing and repolarizing currents. Reduction in expression of the auxiliary subunit K+ channel interacting protein 2 (KChIP2), which regulates the transient outward K+ current (Ito), is a common and early event in many cardiac pathologies. Notably, transcriptional changes observed in heart disease can be elicited through direct KChIP2 silencing without disease signaling, suggesting novel transcriptional capacity for KChIP2. Methods and Results: A miRNA microarray was conducted on neonatal rat ventricular myocytes (NRVM) following in vitro silencing of KChIP2, identifying the miR-34 family as a potential transcriptional target of KChIP2. qPCR confirmed reduction in miR-34b/c when over-expressing KChIP2 and increase following silencing. Luciferase assays conducted on the promoter for miR-34b/c reinforced KChIP2 repression on the promoter, while chromatin immunoprecipitation identified direct interaction of KChIP2 on the promoter. Previous studies show modified expression of KChIP2 can lead to changes in several ion channel subunits. Therefore, we investigated if this was the consequence of KChIP2 regulation via miR-34. Expression of miR-34b/c precursors reduced transcript levels of Nav1.5 and Navβ1, and reduced protein levels for Kv4.3, resulting in loss of INa and Ito. To determine the relevance in disease signaling, NRVMs were exposed to 100 μM phenylephrine for 48 hrs, significantly reducing KChIP2, Nav1.5, Navβ1, and Kv4.3, while elevating miR-34b/c. Maintaining KChIP2 expression by adenovirus or blocking miR-34 activity with antagomirs rescued the changes in channel expression. Consequently, miR-34 inhibition rescued the induction of sustained arrhythmias observed in a 2D culture of myocytes through the maintenance of cardiac excitability. Conclusion: Collectively, these observations identify dysregulation of the KChIP2/miR-34 axis as a nodal event in the development of electrical dysfunction that characterize cardiac pathologies, and further identifies miR-34 as a viable therapeutic target for managing arrhythmogenesis in patients with heart disease.