Fig. 1: Characteristics of normal cells vs. characteristics of senescent cells.

The characteristics of normal cells include: normal cell morphology, clear boundaries, intact structures of the cell nucleus and cell membrane, and evenly distributed and moderate numbers of intracellular organelles such as mitochondria, Golgi apparatus, and endoplasmic reticulum. Senescent cell features include: The prolonged arrest of the cell cycle is achieved through the upregulation of the p21 and p16 cell cycle inhibitors. The oxidative damage is identified by the elevation in reactive oxygen species (ROS) levels. The upregulation of the BCL-2 family of antiapoptotic proteins induces resistance to apoptosis. Senescence-associated heterochromatin foci (SAHF) and a senescence-associated secretory phenotype (SASP). Metabolic changes, which encompass the accumulation of senescence-associated β-galactosidase (SA-β-gal), are evident. Morphological changes. A signaling cascade, known as the DNA damage response (DDR), can be defined as a series of events triggered by DNA damage.