PO-01-123 THE BIOPHYSICAL ACTION OF MICRORNA IS ESSENTIAL TO MAINTAIN THE NORMAL FUNCTION AND ELECTROPHYSIOLOGY OF THE HEART

Abstract

MicroRNAs (miRs) regulate most (if not all) biological events via a broadly-recoginized RNA interference (RNAi) mechnism. miR1, encoded by miR1-1 and miR1-2 genes, is the predominant miRs of the heart and plays critical roles 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 directly binds to ion channels physically modulates the electrophysiology of cardiomyocytes. There is an arrhythmia-associated human single nucleotide polymorphism (hSNP)–hSNP14A/G (rs776480338) on mature miR1, in which the 14th nucleotide of miR1 is mutated from A to G. We found that hSNP14A/G specifically disrupts this biophysical action while maintaining its RNAi function. To define the specific physiological significance of the biophysical action of miR1 in regulating the function of the heart. By using CRISPR/Cas9 technology, we created single nucleotide mutation of hSNP14A/G on mouse miR1-1 and miR1-2 genes and have successfully developed 14G-mutated homozygous transgenic mice (14G-Homo, miR1-114G/G;miR1-214G/G), in which the biophysical function of miR1 is specifically removed while the RNAi function is maintained. The function of whole heart was evaluated by echocardiagram and surface ECG. Cellular electrophysiology and contraction of isolated cardiomyocytes were studied by patch clamping and IonOptix. 14G-Homo mice had higher mortality than wildtype (WT) mice. Compared to WT hearts, adult 14G-homo heart (2-month age) had significantly lower ejection fraction and fractional shortening with thinner wall of 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 slower heart rate and the prolonged QRS interval and QT interval. Optial mapping revealed a slower conduction velocity in 14G-Homo heart with a high inducibility of ventricular arrhythmias. Patch clamping of isolated ventricular cardiomyocytes showed that, compared to WT cells, 14G-Homo cardiomyocytes had a prolonged duration to action potention with DADs. Compared to WT cells, 14G-Homo myocytes had bigger IK1 and IL-Ca2+ and showed faster Ca2+ transients. A specific delection of miR’s biophysical fuction leads to arrhythmia and heart failure. Beyond the RNAi, miRs are ion channel modulators; the biophysical action of miRs is deeply involved in maintaining the homeostasis of the heart.