Analysis of cellular senescence in culture in vivo: the senescence-associated beta-galactosidase assay.

Replicative senescence, a process first described almost 40 years ago, entails irreversible growth arrest with sustained metabolic functions, and it is also associated with increased resistance to apoptotic signals. Interest in this process has increased greatly over the last 10 years, as it has been demonstrated that senescence can function as a potent tumor suppressor mechanism. Although mounting evidence suggests that the senescent phenotype is associated with an extraordinarily complex array of gene expression patterns and interactions with the microenvironment, there is only one widely accepted marker for distinguishing such cells in vitro and in vivo. This marker is the senescence-associated expression of a pH 6 beta-galactosidase (SA-beta-gal). Here, a method for analyzing SA-beta-gal expression in cultured cells and in human and animal tissues is described, and important parameters to consider when performing such assays are also highlighted.