PO-615-02 MIR-144 KNOCKOUT LEADS TO INCREASED ARRHYTHMOGENICITY ASSOCIATED WITH IMPAIRED ATRIAL CALCIUM-HANDLING

Abstract

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Pathophysiology is still incompletely understood and consequently current AF therapeutics often lack efficacy. MicroRNAs are involved in various AF remodeling processes. In a screening study, we identified miR-144 to be significantly downregulated in AF patients. To investigate the effects of in vivo knockout (KO) of miR-144 on atrial electrophysiology and arrhythmogenesis. C57BL/6 wildtype, heterozygous or homozygous miR-144-KO mice were phenotyped by ECG, echocardiography, electrophysiological (EP) study, and cellular EP study. MiR-144 target genes were identified in silico, validated in vitro by luciferase assay and subsequently measured by qPCR from atrial tissue samples. miR-144 KO leads to left atrial enlargement ( 1.72 mm wt vs. 1.94 mm ko/ko, ****p <0.0001) and increased atrial susceptibility to tachyarrhythmia (2.79 % wt vs. 5.79 % ko/ko, *p=0.015) without affecting baseline parameters such as animal weight, heart mass, ECG parameters or left ventricular function. On a cellular level this is accompanied by decreased ICaL-triggered atrial calcium transient amplitudes (218.7 nM wt vs. 157.1 nM ko/ko, *p=0.014), a reduced atrial sarcoplasmatic reticulum (SR) calcium load (511.9 nM wt vs. 408.0 nM ko/ko, *p=0.038) and impaired function of atrial sarco/endoplasmic reticulum calcium ATPase (SERCA) (9.74 s-1 wt vs. 7.38 s-1 ko/ko, *p=0.024). Luciferase assay validated NOS1AP as miR-144 target (1.00 control vs 0.81 miR-144, **p=0.004) and tissue qPCR showed significant NOAS1AP upregulation in atrial tissues of KO-mice (right atrium 1.00 wt vs. 3.24 ko/ko, **p=0.0024; left atrium 1.00 wt vs. 2.86 ko/ko, ***p=0.0002). Our study uncovered that miR-144 KO leads to increased atrial arrythmogenicity in mice. This effect is accompanied by reduced calcium transient amplitudes, a reduced SR calcium load and impaired SERCA function. Remodeling processes involve NOS1AP upregulation which might directly link miR-144 KO to SERCA impairment via NOS1 dependent SERCA S-nitrosylation through NOS1AP upregulation. Additional studies are warranted to further investigate this signaling cascade and to determine whether this mechanism can be subject to pharmacological intervention.