Table 1.

Summary of the key characteristics of senescent cells.

Characteristic	Marker
Proliferative arrest	Low expression of Ki-67 or bromodeoxyuridine BrdU
Persistent activation of the DNA damage response	Activation of tumour suppressors, such as p53, p16INK4A, cyclins, and cyclin-dependent kinases
Heterochromatic foci (DNA becomes denser than normal)	Senescence-associated heterochromatic foci on DNA staining with DAPI
Cells become flattened and enlarged	Light microscopy changes
Altered metabolism including increased β-galactosidase activity, which is part of carbohydrate metabolism	Measurement of β-galactosidase levels
Senescence-associated secretory phenotype	Interleukins-1, -6, and -8, matrix metalloproteinases, plasminogen activator inhibitor-1