The essential role of the miRNA-208a/TARBP2/Sox6 axis in myosin expression in the end stage human heart failure

Abstract Despite diverse aetiologies, failing human hearts (HF) of various origins (coronary artery disease (CAD), dilated cardiomyopathy (DCM), restrictive cardiomyopathy, and hypertrophic cardiomyopathy (HCM)) exhibit impaired contractility and share alterations in MYH6, MYH7, and MYH7B gene expression. Here, we explore the miRNA-208a/TARBP2/Sox6 axis in regulating myosin expression within left ventricles of explanted human hearts. Methods Samples of left ventricles were obtained from explanted hearts of patients with terminal HF (NYHA III-IV) and reduced left ventricle ejection fraction (LVEF <25%) due to CAD (n=10), DCM (n=10), HCM (n=6), and controls (n=5). We analysed the expression of cardiac myosin heavy chains (MYH6, MYH7, MYH7B), cardiac damage markers (ANP, BNP), and heart-related MyoMiRs using quantitative real-time PCR. Results Pre-transplant data for the 31 subjects (25 male, 3 female) included: age 54.4±8.2y, BP 112±18/67±11 mmHg, HR 79±16 min-1, LVEF 27±14%, LVEDD 8.8±15.8mm, RVEDD 32.8±5.1mm, QRS 0.140±0.05s, QT 0.42±0.04s, NT-proBNP 5551±4259 ng/l. In all diseased groups, MYH6 mRNA was downregulated, while MYH7 and MHRT ncRNA were upregulated. We observed strong positive correlations between MYH7, MYH7B, and MHRT transcription, suggesting coordinated expression. The miRNA-208a/miRNA-208b ratio shifted heavily towards miRNA-208b in controls, with a similar effect for miRNA-499 and MYH7B. A strong negative correlation existed between miRNA-499 and MYH7B expression across HF samples. TARBP2 expression decreased slightly in all pathological groups, while Sox6 mRNA increased. Conclusion Elevated Sox6 expression may contribute to MYH6 downregulation and MYH7/MYH7B upregulation. Altered TARBP2 expression could promote cardiomyopathy via Sox6-mediated repression of cardiac slow-twitch myofiber proteins. Changes in miRNA-208a processing leading to Sox6 upregulation may inhibit Sox6-dependent myosin transcript expression.