| Objective: To investigate changes of microRNA-1 (miR-1) and microRNA-21 (miR-21) expressions in human atrial fibrillation (AF).Methods: Right atrial appendages were obtained from rheumatic valvular heart disease patients with Mitral valve replacement (MVP) or Aortic valve replacement (AVP), 12 patients with sinus rhythm (SR) and 14 patients with chronic AF. Quantitative real time polymerase chain reaction (qRT-PCR) was applied to assess expressions of miR-1 and miR-21. The expressions of Kir2.1 and MMP-2 were tested by Western Blotting. Masson staining was used to estimate collagen deposition.Results: Histological sections showed significant increase in the size of atrial myocytes in AF patients, as well as abnormal arrangement of cells and increased interstitial collagen content. Masson staining also showed and an elevated collagen content in AF patients (collagen volume fraction, CVF: 14.1±0.01% vs. 8.3±0.01%, P<0.01). Expressions of miR-1 was decreased (relative expression: 0.684±0.086 vs. 1.761±0.146, P<0.01) while miR-21 was up-regualted (relative expression: 2.232±0.309 vs. 0.943±0.239, P<0.01) in AF patients. Kir2.1 and MMP-2 protein level were elevated in AF patients (Kir2.1 Protein/GAPDH ratio: 1.013±0.002 vs. 0.960±0.004, P<0.01, n=10; Protein/GAPDH ratio: 0.928±0.014 vs. 0.867±0.015, P<0.01, n=10). Expression of miR-1 was negatively correlated to that of Kir2.1 expression (r = -0.653, P<0.01). Expression of miR-21 was positively correlated to MMP-2 expression (r = 0.461, P<0.05). Additionally, positive correlation between MMP-2 expression and CVF was found (r = 0.456, P<0.05).Conclusion: Expression of miR-1 was down-regulated in AF patients, which may be associated with the increase in Kir2.1 protein expression. miR-21 level was significantly up-regulated, which may contribute to the increase in MMP-2 protein and collagen content in the atrium.
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