miR-328 - a novel diagnostic and predictive atrial fibrillation biomarker in spontaneously hypertensive rats

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Romanian Ministry of Education and Research, CNCS-UEFISCDI PURPOSE: Atrial fibrillation (AF) is the most common cardiac arrhythmia and a major cause of morbidity and mortality worldwide. To date, there are no reliable biomarkers for the diagnosis and prediction of AF. Alterations in the atrial expression of various microRNAs contributes to the pathogenesis of AF, suggesting that certain miRNAs may emerge as promising AF diagnostic and/or predictive biomarkers. We aimed to evaluate miR-328 as a potential biomarker for the prediction and diagnosis of AF in an experimental model of spontaneous AF in rats. METHOD: Male spontaneously hypertensive rats (SHR) and their normotensive counterparts (WKY) were divided into 6 groups: young (12 weeks, n = 8 each), adult (26 weeks, n = 8 each), and elderly (46 weeks, n = 10 each) SHR and WKY. All animals were implanted with ECG radiotelemetry devices, the ECG was continuously monitored for 72 hours, and the number of spontaneous AF episodes was assessed. At the end of the protocol, blood and left atrium tissue samples were taken and miR-328 levels were quantified. miR-328 levels were normalized with U6 snRNA and compared between groups. Correlations between atrial and blood miR-328 levels, and between mir-328 levels and arrhythmic load were also assessed. RESULTS: None of the WKY rats and none of the young SHRs presented arrhythmic episodes; two of the adult SHRs and all elderly SHRs had spontaneous AF episodes. Young SHR and WKY rats had similar atrial miR-328 levels (p = 0.67). At adult age, atrial miR-328 levels were significantly higher in SHRs than in WKYs (1.20 ± 0.02 vs. 1.07 ± 0.04; p = 0.01). Between-groups differences were even higher in the elderly rats (1.59 ± 0.01 vs. 1.03 ± 0.03; p< 0.01). Among the SHRs, atrial miR-328 levels increased progressively with age (p = 0.02) and were strongly correlated with the circulating blood levels of miR-328 (r = 0.71; p = 0.04). Moreover, among the elderly SHRs, atrial miR-328 levels correlated positively with the number of arrhythmic episodes (r = 0.72; p< 0.01). CONCLUSIONS: The present study demonstrates a strong association between increased miR-328 expression levels and the presence and burden of AF in the hypertensive rats, suggesting that miR-328 could be a promising biomarker for the diagnosis of AF. Moreover, our results demonstrate that in this model the increase in miR-328 levels precedes the onset of AF, suggesting that dynamic evaluation of miR-328 could be used to predict AF, at least in a hypertensive context. Further studies will have to validate these results in clinical settings and to assess miR-328 manipulation as a potential prophylactic and/or therapeutic strategy in AF.