Targeting miR-423-5p Reverses Exercise Training-Induced HCN4 Channel Remodeling and Sinus Bradycardia.

Alicia D’Souza,Alicia Lundby,Yu Zhang,Gwilym M Morris,Halina Dobrzynski,Hayley Bennett,Elizabeth J Cartwright,Mark R Boyett,Charlotte Cox,Anne Berit Johnsen,Nora Linscheid,Ashraf Kitmitto,Yanwen Wang,Delvac Oceandy,Ulrik Wisløff,Charles M Pearman,Oliver Monfredi,Abigail Robertson,Shin-Ichi Nakao ,Jamie S Mcphee ,Peter Noe Poulsen ,Sunil Jit R J Logantha ,Jo Coulson ,Paula Martins ,Jonathan T Elliott

doi:10.1161/circresaha.117.311607

Abstract

Downregulation of the pacemaking ion channel, HCN4 (hyperpolarization-activated cyclic nucleotide gated channel 4), and the corresponding ionic current, If, underlies exercise training-induced sinus bradycardia in rodents. If this occurs in humans, it could explain the increased incidence of bradyarrhythmias in veteran athletes, and it will be important to understand the underlying processes. To test the role of HCN4 in the training-induced bradycardia in human athletes and investigate the role of microRNAs (miRs) in the repression of HCN4. As in rodents, the intrinsic heart rate was significantly lower in human athletes than in nonathletes, and in all subjects, the rate-lowering effect of the HCN selective blocker, ivabradine, was significantly correlated with the intrinsic heart rate, consistent with HCN repression in athletes. Next-generation sequencing and quantitative real-time reverse transcription polymerase chain reaction showed remodeling of miRs in the sinus node of swim-trained mice. Computational predictions highlighted a prominent role for miR-423-5p. Interaction between miR-423-5p and HCN4 was confirmed by a dose-dependent reduction in HCN4 3'-untranslated region luciferase reporter activity on cotransfection with precursor miR-423-5p (abolished by mutation of predicted recognition elements). Knockdown of miR-423-5p with anti-miR-423-5p reversed training-induced bradycardia via rescue of HCN4 and If. Further experiments showed that in the sinus node of swim-trained mice, upregulation of miR-423-5p (intronic miR) and its host gene, NSRP1, is driven by an upregulation of the transcription factor Nkx2.5. HCN remodeling likely occurs in human athletes, as well as in rodent models. miR-423-5p contributes to training-induced bradycardia by targeting HCN4. This work presents the first evidence of miR control of HCN4 and heart rate. miR-423-5p could be a therapeutic target for pathological sinus node dysfunction in veteran athletes.

Highlights

Athletes are prone to cardiac arrhythmias and sinus bradycardia is the most common rhythm ‘disturbance’.1 In the long term, this physiological adaptation can become pathological as veteran athletes are more likely to have sinus node dysfunction and to need an electronic pacemaker implantation than nonathletes.[2,3,4] In two rodent models of exercise training, we previously demonstrated that the training-induced bradycardia is predominantly the result of a downregulation of the key pacemaking ion channel HCN4 and the corresponding ionic current in the sinus node.[5]
HCN remodelling likely occurs in human athletes as well as rodent models. miR-423-5p contributes to training-induced bradycardia by targeting HCN4
This work presents the first evidence of miR control of HCN4 and heart rate. miR-423-5p could be a therapeutic target for pathological sinus node dysfunction in veteran athletes

Summary

Introduction

Athletes are prone to cardiac arrhythmias and sinus bradycardia is the most common rhythm ‘disturbance’.1 In the long term, this physiological adaptation can become pathological as veteran athletes are more likely to have sinus node dysfunction and to need an electronic pacemaker implantation than nonathletes.[2,3,4] In two rodent models of exercise training, we previously demonstrated that the training-induced bradycardia is predominantly the result of a downregulation of the key pacemaking ion channel HCN4 and the corresponding ionic current (funny current, If) in the sinus node.[5]. Athletes are prone to cardiac arrhythmias and sinus bradycardia is the most common rhythm ‘disturbance’.1. What is responsible for the downregulation of HCN4 in the athlete? Some miRs have been implicated in ion channel remodelling.[7,8,9] We report here that the downregulation of HCN4 and If in trained mice is the result of an upregulation of miR-423-5p in the sinus node and the training-induced bradycardia can be reversed by targeting the miR-dependent HCN4 remodelling

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Conclusion