From molecular damage to regulatory constraint: epigenetic and metabolic limits of cellular plasticity in aging.

Aging is most often portrayed as the progressive buildup of molecular damage, yet this conventional view leaves much unexplained. Over time, cells and tissues appear to lose the regulatory flexibility that allows them to adapt, repair, and reconfigure their functional states. Genomic instability, metabolic imbalance, mitochondrial dysfunction, and proteostatic decline converge on aging, but their effects focus on chromatin organization, transcriptional coordination, and signaling networks that maintain cellular identity. In this review, we propose that aging can be usefully viewed as a progressive restriction of epigenetic and regulatory plasticity, rather than as the simple accumulation of lesions. Pathways such as Wnt signaling, TET-dependent DNA demethylation, and metabolic sensors including AMPK, mTOR, and sirtuins create an interconnected landscape that links environmental and metabolic conditions with long-term cellular behavior. As this landscape becomes increasingly rigid and constrained, cells retain viability but lose their capacity for dynamic responses, stabilizing in low-plasticity states that include cellular senescence. Framing aging as a shift from adaptive plasticity toward regulatory rigidity offers a possible integrative lens on classical hallmarks and epigenetic aging signatures, without replacing existing models. Rather than targeting individual hallmarks in isolation, future approaches may need to complement hallmark-focused strategies by restoring dynamic balance within epigenetic and signaling networks that preserve tissue-level homeostasis and regenerative potential, thereby suggesting specific, testable predictions for interventions acting on metabolic-epigenetic axes.