Compensatory control of associated ion channel mRNAs regulates cardiac excitability

Normal function of the heart is achieved by the orchestrated activity of ion channels and disruption in their functional expression can lead to life-threatening arrhythmias. We have found a cotranslational interaction between KCNH2, SCN5A, CACNA1C, and KCNQ1 transcripts respectively encoding the human ERG (hERG) potassium channel, NaV1.5 sodium channel, CaV1,2 calcium channel and KV7.1 potassium channel in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Additionally, mRNA levels and current densities from these channels exhibit an interesting co-knockdown effect upon silencing of KCNH2 or SCN5A. Here, we hypothesize that co-depletion of associated transcripts and serves a compensatory role, preventing an imbalance of ion channels that could trigger arrhythmia. To test this, we recorded electrophysiological activity on a multielectrode array (MEA) from iPSC-CMs monolayers serving as proxy for cardiac tissue. Direct block of hERG channels with IC50 concentrations of dofetilide significantly prolonged a proxy for action potential duration (pAPD) and increased beat-to-beat variability, both markers of pro-arrhythmia. In contrast, transduction of KCNH2 shRNA resulted in no change in the pAPD, or an unexpected shortening, despite a reduction of hERG mRNA levels by ∼60% determined by qPCR. Reduction of SCN5A mRNA levels similarly evoked little change in action potential parameters. These results suggest that mRNA association during biogenesis acts as a mechanism to maintain cardiac electrophysiology homeostasis. Ongoing experiments are aimed at elucidating the mechanism by which shRNA leads to coordinate depletion of associated transcripts. Supported by NIH/NHLBI R01HL131403 (GAR).