SA-β-Gal (Senescence-associated β-galactosidase)

Senescence-associated β-galactosidase (SA-β-Gal) is an enzyme activity detectable at pH 6.0 that reflects the increased lysosomal content and elevated expression of lysosomal β-galactosidase (encoded by GLB1) found in senescent cells. First described in 1995 by Dimri and colleagues, it became the most widely used single histochemical marker for senescent cells in tissue sections and cell culture due to its relative ease of detection. SA-β-Gal activity is not exclusive to senescent cells — it can also appear under conditions of quiescence, overconfluence or lysosomal stress — so it is best used alongside complementary markers such as p21, p16^INK4a, SASP components and heterochromatin foci for reliable senescence identification.