MicroRNA Regulation of hERG-Related Current: Potential Role in Heart Failure-Associated Arrhythmias

Noha A Mourad, Purdue University

Abstract

Sudden cardiac death, mainly attributable to arrhythmic causes, underlies a large proportion of deaths among patients with heart failure (HF). HF is associated with electrical remodeling caused by a wide array of changes in cardiac ion channels, including a down-regulation of the hERG-related repolarizing potassium current IKr. The precise molecular mechanisms underlying the down-regulation of IKr in heart failure remain poorly understood. In this research, we examine a novel mechanism for the regulation of I Kr in heart failure by microRNA. MicroRNAs (miRs) are a group of small, non-coding RNAs that regulate gene expression at the post-transcriptional level. Through genome-wide profiling of microRNA expression, our lab has identified microRNA 362-3p (miR-362-3p) to be associated with a SNP previously linked to QT interval duration and a down-regulation of hERG mRNA. In addition, miR-362-3p has been shown to bind to the 3’ untranslated region of hERG and to downregulate hERG at the mRNA and protein levels. The effects of miR-362-3p on IKr function and its expression in the failing human heart are unknown. The primary objectives of this research were 1) to assess the functional effect of miR-362-3p on hERG-related current, and 2) to assess the expression of miR-362-3p in the failing human myocardium. The effects of miR-362-3p on hERG currents were assessed using cellular electrophysiology techniques in SK-Br-3 and HL-1 cells following transfection with either miR-362-3p mimic or negative control. In SK-Br-3 cells, peak inward IKr tail currents recorded at -120 mV 48 hours post-transfection were significantly lower in cells transfected with miR-362-3p compared to control (p=0.038). In HL-1 cells, there was no statistically significant difference in mean peak tail current amplitude between groups over the voltage range -40 to +50 mV at 24 hours following transfection (p=0.52). At 48 hours post-transfection, the mean peak tail current amplitude recorded over the voltage range from -40 to +50 mV was significantly lower in miR-362-3p-transfected cells compared to control cells (p<0.001). The mean ± SE peak tail current recorded at +20 mV in the miR-362-3p group was 2.2 ± 0.4 pA/pF compared to 4.1 ± 0.7 pA/pF in the control group (p=0.03). Quantitative RT-PCR was performed to investigate differences in miR-362-3p and hERG expression in ventricular tissue samples from failing and non-failing human hearts (control). The normalized expression of miR-362-3p was significantly higher in the heart failure with reduced ejection fraction (HFrEF) group compared to control with a mean fold change of 1.56 ± 0.28 (p=0.05). The normalized expression of hERG was significantly lower in the HFrEF group compared to control with a mean fold change in expression of 0.66 ± 0.28 (p=0.01). In this research, miR-362-3p has been identified as a candidate regulator of hERG function. Evidence is also presented that miR-362-3p is upregulated in the ventricular tissue of patients with heart failure. Further studies are needed to show the functional link between miR-362-3p and IKr in heart failure. Presence of a functional link would warrant evaluation of miR-362-3p as a novel therapeutic target for the prevention and/or treatment of arrhythmias in heart failure.

Degree

Ph.D.

Advisors

Overholser, Purdue University.

Subject Area

Molecular biology|Pharmacology

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