Figure 1.

The nine “hallmarks” of cell fitness. Healthy cells rely on a balance between survival checkpoints and aberrant hallmarks. A total of nine factors have been defined: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication (represented by circles in matching colors). Skewing of this equilibrium generates a progressively senescent phenotype as a result of age-related checkpoint dysfunction driving cellular toxicity.