Abstract 17767: A MiR-31-dependent Loss of Dystrophin & Nnos in the Human Atria Plays a Key Role in Atrial Fibrillation-induced Electrical Remodelling

Abstract

Background: Management of atrial fibrillation (AF) remains a challenge. AF remodels the atrial electrical properties, thereby increasing resistance to treatment. Although remodeling has long been a target for therapeutic intervention in AF, the mechanisms driving this phenomenon are incompletely understood. Methods & Results: Using atrial samples from 351 patients (73 AF), and 67 goats (34 AF), we show that atrial-specific upregulation of miR31 causes dystrophin (DYS) translational repression and accelerates mRNA degradation of neuronal nitric oxide synthase (nNOS) leading to a profound reduction in NO availability. Six prediction algorithms and reporter assays established DYS and nNOS as miR-31 targets. In atrial myocytes from patients with AF (hAFm), both DYS and nNOS bind to miR-31 within the RNA induced silencing complex (RISC). In actinomycin D-treated myocytes from patients in sinus rhythm (hSRm), miR31 accelerated nNOS (but not DYS) mRNA decay. mRNA of nNOS (but not DYS) & protein content of nNOS, DYS & DYS associated proteins were significantly reduced in hAFm. Inhibition of miR31 in hAFm restored both DYS & nNOS protein. Protection of the nNOS miR31 binding site with a target site blocker (TSB) restored nNOS mRNA and protein (but not DYS), whereas, DYS-TSB increased both DYS and nNOS protein (but not mRNA), in keeping with an effect of DYS restoration on nNOS protein stability. Indeed, K48-linked polyubiquitination of nNOS was increased in hAFm & prevented by proteasome inhibition with MG132. NOS: inhibition (SMTC, 100 nmol) or transfection with a miR31 mimic was employed to evaluate the impact of these findings on atrial electrical properties. Both interventions shortened action potential duration (APD90) and abolished rate-dependency of the APD90 in hSRm but not in hAFm. By contrast, miR31 inhibition restored APD & APD rate-dependency in hAFm (both reversed by SMTC) but had no effect on hSRm. In mice (n=126), nNOS gene deletion or inhibition shortened atrial APD90 & lead to a 2-fold increase in AF inducibility in response to atrial burst pacing. Conclusions: These findings identify atrial-specific upregulation of miR31 in human AF as a key mechanism causing atrial loss of dystrophin and nNOS, which, in turn, lead to the electrical phenotype begetting AF.