Figure 1.

Distinct stressors which inflict alterations at the DNA level, during the lifespan, independently of the status of a cell (young or aged). Signals initiated in response are mediated by the G-protein coupled receptors. Subsequently, five highly specialized mechanisms are activated, and three specific NAD-consuming enzymes are used for re-establishing and maintaining the integrity of the human genome. Based on the type-related stressor, cells are subjected to a distinct type of withdrawal (red, green, or purple border).