Binding of FUN14 Domain Containing 1 With Inositol 1,4,5-Trisphosphate Receptor in Mitochondria-Associated Endoplasmic Reticulum Membranes Maintains Mitochondrial Dynamics and Function in Hearts in Vivo.

Abstract

FUN14 domain containing 1 (FUNDC1) is a highly conserved outer mitochondrial membrane protein. The aim of this study is to examine whether FUNDC1 modulates the mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs), mitochondrial morphology, and function in cardiomyocytes and intact hearts. The impacts of FUNDC1 on MAMs formation and cardiac functions were studied in mouse neonatal cardiomyocytes, in mice with cardiomyocyte-specific <i>Fundc1</i> gene knockout (<i>Fundc1</i>^<i>f/Y</i><i>/Cre</i>^{<i>αMyHC+/-</i>} ), and in the cardiac tissues of the patients with heart failure. In mouse neonatal cardiomyocytes and intact hearts, FUNDC1 was localized in MAMs by binding to ER-resided inositol 1,4,5-trisphosphate type 2 receptor (IP₃R2). <i>Fundc1</i> ablation disrupted MAMs and reduced the levels of IP₃R2 and Ca²⁺ in both mitochondria and cytosol, whereas overexpression of <i>Fundc1</i> increased the levels of IP₃R2 and Ca²⁺ in both mitochondria and cytosol. Consistently, <i>Fundc1</i> ablation increased Ca²⁺ levels in ER, whereas <i>Fundc1</i> overexpression lowered ER Ca²⁺ levels. Further, <i>Fundc1</i> ablation in cardiomyocytes elongated mitochondria and compromised mitochondrial functions. Mechanistically, we found that <i>Fundc1</i> ablation-induced reduction of intracellular Ca²⁺ levels suppressed mitochondrial fission 1 protein (<i>Fis1</i>) expression and mitochondrial fission by reducing the binding of the cAMP response element binding protein (CREB) in the <i>Fis1</i> promoter. <i>Fundc1</i>^<i>f/Y</i><i>/Cre</i>^{<i>αMyHC+/-</i>} mice but not their littermate control mice (<i>Fundc1</i>^<i>wt/Y</i><i>/Cre</i>^{<i>αMyHC+/-</i>} ) exhibited cardiac dysfunction. The ligation of the left ventricle artery of <i>Fundc1</i>^<i>f/Y</i><i>/Cre</i>^{<i>αMyHC+/-</i>} mice caused more severe cardiac dysfunction than those in sham-treated <i>Fundc1</i>^<i>f/Y</i><i>/Cre</i>^{<i>αMyHC+/-</i>} mice. Finally, we found that the FUNDC1/MAMs/CREB/Fis1 signaling axis was significantly suppressed in patients with heart failure. We conclude that FUNDC1 binds to IP₃R2 to modulate ER Ca²⁺ release into mitochondria and cytosol. Further, a disruption of the FUNDC1 and IP₃R2 interaction lowers the levels of Ca²⁺ in mitochondria and cytosol, both of which instigate aberrant mitochondrial fission, mitochondrial dysfunction, cardiac dysfunction, and heart failure.