Abstract 429: MicroRNA Control of the Pacemaker Channel and Training-induced Bradycardia
Background: Athletes are prone to bradyarrythmias and have a higher-than-normal incidence of pacemaker implantation but the underlying mechanisms are poorly understood. In previous work we demonstrated a training-induced electrical remodelling of the sinoatrial node (SAN), including a down regulation of the key pacemaker channel HCN4 that carries the pacemaker current If. Here we investigated post-transcriptional regulation of HCN4 by microRNAs (miRNAs) in the trained SN.
Methods and Results: Mice subjected to 60-min swimming twice daily for 28 days (TM) were compared to parallel sedentary mice (SM).TM were bradycardic (cycle length in vivo: SM, 81±1.3 ms; TM, 102±3 ms; n=6, p<0.05). The cycle length of the isolated, denervated SAN (intrinsic heart rate) was also prolonged by exercise training (SM, 110±3 ms; TM, 150±5 ms; n=7, p<0.05). Deep sequencing for miRNAs on SAN punch biopsies revealed 10 differentially expressed miRNAs in TM vs SM (FDR adjusted P<0.05); 8 miRNAs were upregulated, 2 were downregulated. These findings were further confirmed by real-time PCR. We used the computation prediction tools Targetscan and Ingenuity Pathway Analysis to identify miR-423-5p and miR-486-3p as putative miRNAs participating in the post-transcriptional repression of HCN4 in the trained SAN. Both miRNAs had conserved seed sequences in the HCN4 3’UTR. To validate whether these miRNAs directly recognise the 3’UTR of HCN4, they were co-transfected with a construct containing HCN4 3’UTR fused downstream to a luciferase coding sequence in H9c2 cells. Transient transfection of precursor miR-423-5p and miR-486-3p decreased HCN4 3’UTR luciferase reporter activity in H9C2 cells by 47% and 22% respectively, compared with unaltered luciferase activity on co-transfection with control miR or miR-27a.
Conclusions: This is the first report of miRNA dysregulation in the trained SAN. We describe a novel molecular mechanism whereby an altered miRNA profile in the trained SAN promotes HCN4 downregulation and altered sinus automaticity. Data suggest miR-423-5p as a potential therapeutic target for bradyarrythmias in the athlete.
Author Disclosures: A. D’Souza: None. E. Gill: None. C. Cox: None. H. Dobrzynski: None. E. Cartwright: None. D. Oceandy: None. M.R. Boyett: None.
- © 2015 by American Heart Association, Inc.