The SIRT3-ATAD3A axis regulates MAM dynamics and mitochondrial calcium homeostasis in cardiac hypertrophy

Mitochondria are energy-producing organelles that are mobile and harbor dynamic network structures. Although mitochondria and endoplasmic reticulum (ER) play distinct cellular roles, they are physically connected to maintain functional homeostasis. Abnormal changes in this interaction have been linked to pathological states, including cardiac hypertrophy. However, the exact regulatory molecules and mechanisms are yet to be elucidated. Here, we report that ATPase family AAA-domain containing protein 3A (ATAD3A) is an essential regulator of ER-mitochondria interplay within the mitochondria-associated membrane (MAM). ATAD3A prevents isoproterenol (ISO)-induced mitochondrial calcium accumulation, improving mitochondrial dysfunction and ER stress, which preserves cardiac function and attenuates cardiac hypertrophy. We also find that ATAD3A is a new substrate of NAD⁺-dependent deacetylase Sirtuin 3 (SIRT3). Notably, the heart mitochondria of SIRT3 knockout mice exhibited excessive formation of MAMs. Mechanistically, ATAD3A specifically undergoes acetylation, which reduces self-oligomerization and promotes cardiac hypertrophy. ATAD3A oligomerization is disrupted by acetylation at K134 site, and ATAD3A monomer closely interacts with the IP3R1-GRP75-VDAC1 complex, which leads to mitochondrial calcium overload and dysfunction. In summary, ATAD3A localizes to the MAMs, where it protects the homeostasis of ER-mitochondria contacts, quenching mitochondrial calcium overload and keeping mitochondrial bioenergetics unresponsive to ER stress. The SIRT3-ATAD3A axis represents a potential therapeutic target for cardiac hypertrophy.