Abstract 13309: Specific Deletion of Microrna1’S Biophysical Action Causes a Functional Deterioration of the Heart and Increases the Vulnerability to Arrhythmias

Abstract

MicroRNAs (miRs) are involved in most biological events via a broadly-recognized RNA interference (RNAi) mechanism. miR1, encoded by miR1-1 and miR1-2 genes, is the predominant miRs of the heart and plays a critical role in heart development and cardiac diseases. Previous studies of miRs have focused on the canonical RNAi mechanism. Recently, we discovered a novel biophysical action of miR and found that miR1 physically binds to Kir2.1 and directly suppresses the inward rectifier potassium current (I K1 ). However, the physiological significance of this newly-discovered biophysical action of miR remains unknown. Importantly, we found that a human single nucleotide polymorphism (hSNP)-hSNP14A/G (rs776480338), in which the 14th nucleotide of miR1 is mutated from A to G, specifically disrupts this biophysical action while maintaining its RNAi function. We then created a single nucleotide mutation of hSNP14A/G on mouse miR1-1 and miR1-2 genes by CRISPR/Cas9 technology and have successfully developed 14G-mutated homozygous transgenic mice (14G-Homo), in which the biophysical function of miR1 is specifically removed while the RNAi function is maintained. We found that 14G-Homo mice had higher mortality than wild-type (WT) mice. Echocardiogram showed that, compared to WT hearts, adult 14G-homo heart (2-month age) had significantly lower ejection fraction and fractional shortening with a thinner wall of the left ventricle, which became more severe at the age of 6 months; some mice developed severe heart failure. Surface ECG showed that 14G-Homo hearts had a slower heart rate and the prolonged QRS interval and QT interval. Optical mapping revealed a slower conduction velocity in the 14G-Homo heart with high inducibility of ventricular arrhythmias. Patch clamping of isolated ventricular cardiomyocytes showed that, compared to WT cells, 14G-homo cardiomyocytes had an increased amplitude and prolonged duration of action potential with bigger I K1 and L-type calcium currents. In conclusion, our discoveries demonstrate that the biophysical action of miR1 is deeply involved in maintaining the homeostasis of the heart. Specific deletion of the biophysical function causes a functional deterioration of the heart and increases the vulnerability to arrhythmias.