miR-448 regulates potassium voltage-gated channel subfamily A member 4 (KCNA4) in ischemia and heart failure

BACKGROUND MicroRNA miR-448 mediates some of the effects of ischemia on arrhythmic risk. Potassium voltage-gated channel sub-family A member 4 (KCNA4) encodes a Kv1.4 current that opens in response to membrane depolarization and is essential for regulating the action potential duration in heart. KCNA4 has a miR-448 binding site.OBJECTIVE We investigated whether miR-448 was involved in the regulation of KCNA4 messenger RNA expression in ischemia.METHODS Quantitative real-time reverse-transcriptase polymerase chain reaction was used to investigate the expression of KCNA4 and miR-448. Pull-down assays were used to examine the interaction be-tween miR-448 and KCNA4. miR-448 decoy and binding site muta-tion were used to examine the specificity of the effect for KCNA4.RESULTS The expression of KCNA4 is diminished in ischemia and human heart failure tissues with ventricular tachycardia. Previously, we have shown that miR-448 is upregulated in ischemia and inhibi-tion can prevent arrhythmic risk after myocardial infarction. The 3'-untranslated region of KCNA4 has a conserved miR-448 binding site. miR-448 bound to this site directly and reduced KCNA4 expres-sion and the transient outward potassium current. Inhibition of miR-448 restored KCNA4.CONCLUSION These findings showed a link between Kv1.4 downre-gulation and miR-448-mediated upregulation in ischemia, suggest -ing a new mechanism for the antiarrhythmic effect of miR-448 inhibition.