MitoSafe hypothesis: safeguarding mitochondrial morphology and innate immunity

Mitochondria divide and fuse, and the balance between these processes maintains mitochondrial morphology and function. Although the core fusion and division machinery is well established, how cells sense mitochondrial morphology and actively adjust it remains unclear. In this Opinion article, we propose a new conceptual framework, termed 'Mitochondrial Safeguard (MitoSafe)', in which cells monitor mitochondrial size and rebalance division and fusion through four branches: activation of fusion or inhibition of division in small mitochondria and activation of division or inhibition of fusion in enlarged mitochondria. Recent findings show that fusion is suppressed once mitochondria exceed a healthy size threshold. Dysregulation of this branch of MitoSafe, involving Parkin, PINK1, SLC25A3, SOD1, and cytochrome-c oxidase, causes mitochondrial enlargement, mitochondrial DNA release, and stimulator of interferon genes (STING)-mediated inflammation.