• Senescent cell formation is reframed as a metabolic fate driven by mitochondrial silencing. • Mitochondrial silencing elevates the MOMP threshold and limits apoptotic execution. • Senescence fixation occurs when ATP falls below the division threshold. • SASP emerges as a context-dependent secondary phenotype. • Senescence and cancer diverge from a shared apoptosis-evasive precursor state. Senescent cells accumulate in tissues with aging and contribute to functional decline through long-term survival and secretory activity. Cellular senescence is generally defined by irreversible cell-cycle arrest and the senescence-associated secretory phenotype (SASP). However, the metabolic basis that allows senescent cells to evade apoptotic elimination and persist for extended periods remains insufficiently integrated. Here we propose a hypothesis that positions mitochondrial silencing as a reversible precursor state that can precede senescence fixation. In this state, mitochondrial structure is largely preserved, while substrate influx and oxidative phosphorylation (OXPHOS) are gated. Mitochondria-derived reactive oxygen species (ROS) decrease or redistribute, and BAX/BAK-dependent mitochondrial outer membrane permeabilization (MOMP) becomes less likely to occur. Consequently, mitochondrial apoptotic execution becomes less likely. We further hypothesize that when ATP production falls below the energy demand required to complete cell division (the division threshold), cells drop out of the adaptive recovery process and become fixed in irreversible cell-cycle arrest, consistent with known senescence pathways. In contrast, cells that maintain ATP above the division threshold may persist under mitochondrial silencing, acquiring temporal persistence through apoptosis evasion and potentially diverging toward alternative pathological trajectories, including tumorigenesis. This framework links mitochondrial metabolic state, apoptotic execution capacity, and ATP-dependent fate determination, providing a unified and testable model for the origin and persistence of senescent cells in aging tissues.
Masato Hiki (Sun,) studied this question.