Regulation of Scn5a by Micrornas: Mir-219 Modulates Scn5a Transcript Expression and the Effects of Flecainide Intoxication in Mice

Abstract

Background: The human cardiac action potential in atrial and ventricular cells is initiated by a fastactivating fast-inactivating Na+ current generated by the Nav1.5/SCN5A channel, in association with its β1/SCN1B subunit. The role of Nav1.5 in the etiology of many cardiac diseases strongly suggests that proper regulation of cell biology and function of the channel is critical for normal cardiac function. Hence, numerous recent studies have focused on the regulatory mechanisms of Nav1.5 biosynthetic and degradation processes as well as its subcellular localization. Objective: To investigate the role of microRNAs on the Scn5a/Nav1.5 post trancriptional regulation. Methods: qPCR, immunohistochemical and electrophysiological measurements of distinct microRNA gain-of-function experiments. Results: Functional studies in HL-1 cardiomyocytes and luciferase assays in fibroblasts demonstrate that Scn5a is directly (miR-98, miR-106, miR-200, miR-219) and indirectly (miR-125 and miR-153) regulated by multiple microRNAs displaying distinct time-dependent profiles. Co-transfection experiments, demonstrated that miR-219 and miR-200 have independent opposite effects on Scn5a expression modulation. Among all microRNAs studied, only miR-219 increases Scn5a expression levels, leading to altered contraction rhythm of HL-1 cardiomyocytes. Electrophysiological analyses in HL-1 cells revealed that miR-219 increases sodium current (INa). In vivo administration of miR-219 does not alter normal cardiac rhythm but abolishes some of the effects of flecainide intoxication in mice, particularly QRS prolongation. Conclusions: This study demonstrates the involvement of multiple microRNAs on the regulation of Scn5a. Particularly, miR-219 increases Scn5a/Nav1.5 transcript and protein expression. Our data suggest that microRNAs, such as miR-219, constitute a promising therapeutical tool to treat sodium cardiac arrhythmias.