Abstract 17816: KChIP2 Regulates Cardiac Excitability and Ion Channel Dysregulation by Novel Transcriptional Regulation of miR-34s
Cardiac ion channel dysregulation is a hallmark of heart failure. Consistently, the disease yields dramatic decline in Ito through loss in Kv4 and its auxiliary partner K+ channel interacting protein 2 (KChIP2), amongst a host of many other transcriptional changes. Notably, a subset of transcriptional changes in heart failure can be elicited by directly silencing KChIP2 in the absence of disease signaling, suggesting a potential transcriptional capacity for KChIP2. Further, disparity between resulting transcript and protein patterns suggests a mechanism compatible with modified miRNA activity. Considering members of the KChIP family behave as transcriptional repressors, we hypothesized that KChIP2 regulates discrete miRNAs which in turn regulate cardiac excitability. We show here that in vitro knock-down of KChIP2 by siRNA in neonatal rat ventricular myocytes (NRVM) produced elevations in miRs-34b/c. Reporter assays of the cloned polycistronic promoter for miR-34b/c reinforced KChIP2 repression, while the effect was abolished by deletion of the putative downstream regulatory element (DRE) in the promoter. Chromatin immunoprecipitation followed by PCR confirmed physical interaction of KChIP2 to the promoter site. We investigated the consequence of KChIP2 regulation via miR-34b/c by expressing precursors in NRVM or human induced cardiomyocytes, which reduced INa and Ito by targeting the transcripts for Nav1.5 and Navβ1, and Kv4.3. To identify if this pathway is implicated under pathophysiologic conditions, NRVMs were exposed to 100 μM phenylephrine (PE) for 48 hrs, significantly reducing KChIP2, Nav1.5, Navβ1, and Kv4.3, while elevating miR-34b/c. Returning KChIP2 expression by adenovirus normalized these changes back towards baseline, implicating the coordinated regulation of these gene targets by KChIP2. Critically, our results highlight the physiologic relevance of this pathway in a disease setting where KChIP2 loss is common. These observations describe a novel mechanism where KChIP2 regulates a host of cardiac genes through transcriptional control of miRNAs, potentially explaining electrical remodeling observed in myocardial infarction or hypertrophy and heart failure where KChIP2 is reduced.
Author Disclosures: D. Nassal: None. H. Liu: None. X. Wan: None. E. Ficker: None. I. Deschenes: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.