miR‐124 Regulates Intracellular Calcium Leak and Mitochondrial Function in Heart Failure: A Novel Mechanism Underlying Ryanopathy

Intracellular calcium (Ca 2+ ) leak via type 2 ryanodine receptor (RyR2) is an established feature of heart failure (HF). Mounting evidence indicates that microRNAs (miRNAs) play an essential role in cardiovascular disease. However, a specific functional role of miRNAs in the regulation of intracellular Ca 2+ leak in HF has not been established. Study Objective Our hypothesis is that specific miRNAs can modulate the expression of proteins involved in the regulation of intracellular Ca 2+ leak via RyR2 in HF. Methods To verify our hypothesis, we measured circulating and tissue levels of a panel of miRNAs identified via bioinformatic approaches in mice undergoing coronary artery ligation or sham surgery and we tested both in vivo and ex vivo (in primary isolated adult cardiomyocytes), the miRNA‐mediated regulation of intracellular Ca 2+ leak via RyR2. Results Our computational analysis identified several miRNAs targeting RyR2 and its regulatory subunits. In our in vivo experiments, we observed a significant upregulation of miR‐124‐3p in both cardiac tissue and in the blood of HF mice compared to sham littermates. Combining bioinformatic evaluations and biological validations via luciferase assays, we demonstrated that miR‐124‐3p specifically targets FK‐506 binding protein 12.6 (FKBP12.6), a fundamental stabilizer of RyR2 channel, which reduces intracellular Ca 2+ leak. Importantly, cardiac and circulating levels of miR‐124‐3p were inversely correlated with myocardial function (assessed via both echocardiography and hemodynamic studies), and directly correlated with intracellular Ca 2+ leak measured in isolated cardiomyocytes (also in terms of Ca 2+ sparks). Strikingly, inhibition of miR‐124‐3p rescued the intracellular Ca 2+ leak observed in HF, reduced mitochondrial Ca 2+ overload, attenuated mitochondrial dysfunction/dysmorphology and oxidative stress, and ameliorated contractility. Conclusions Our data indicate for the first time that miR‐124 is a pivotal regulator of FKBP12.6, leading to a destabilization of RyR2 and subsequent intracellular Ca 2+ leak in post‐ischemic HF. Notably, the increased intracellular Ca 2+ leak via RyR2 caused mitochondrial Ca 2+ overload and mitochondrial dysfunction in HF, and these features were rescued by inhibition of miR‐124‐3p. These findings are highly relevant also in the clinical scenario since miR‐124‐3p has been recently associated ‐ although the underlying molecular mechanisms have not been defined ‐ with a significantly increased risk of cardiovascular disease and to poor outcome in patients admitted to cardiac intensive care. Support or Funding Information National Institutes of Health (NIH, R00 to G. Santulli).Functional role of miR‐124‐3p in the modulation of intracellular calcium (Ca 2+ ) leak via RyR2 in cardiac cardiomyocytes in heart failure (HF) The effects of a specific miR‐124‐3p antagomir, compared with a scramble control antagomir were evaluated in terms of FKBP12.6 bound to RyR2 (a), intracellular Ca 2+ leak (b), and mitochondrial Ca 2+ uptake (c). Data are shown as mean ± SEM; *:P < 0.05 (ANOVA, Tukey‐Kramer post hoc test).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .