Senescence‐associated β‐galactosidase is lysosomal β‐galactosidase

TLDR

Replicative senescence limits somatic cell proliferation, and the widely used biomarker senescence‑associated β‑galactosidase (SA‑β‑gal) is defined by activity at pH 6.0, though its cellular origin remains unclear. We show that SA‑β‑gal activity originates from the lysosomal β‑D‑galactosidase encoded by GLB1, and that loss of GLB1 or defective lysosomal β‑galactosidase abolishes SA‑β‑gal expression in senescent cells, indicating that SA‑β‑gal is not essential for senescence.

Abstract

Summary Replicative senescence limits the proliferation of somatic cells passaged in culture and may reflect cellular aging in vivo . The most widely used biomarker for senescent and aging cells is senescence‐associated β‐galactosidase (SA‐β‐gal), which is defined as β‐galactosidase activity detectable at pH 6.0 in senescent cells, but the origin of SA‐β‐gal and its cellular roles in senescence are not known. We demonstrate here that SA‐β‐gal activity is expressed from GLB1 , the gene encoding lysosomal β‐D‐galactosidase, the activity of which is typically measured at acidic pH 4.5. Fibroblasts from patients with autosomal recessive G M1 ‐gangliosidosis, which have defective lysosomal β‐galactosidase, did not express SA‐β‐gal at late passages even though they underwent replicative senescence. In addition, late passage normal fibroblasts expressing small‐hairpin interfering RNA that depleted GLB1 mRNA underwent senescence but failed to express SA‐β‐gal. GLB1 mRNA depletion also prevented expression of SA‐β‐gal activity in HeLa cervical carcinoma cells induced to enter a senescent state by repression of their endogenous human papillomavirus E7 oncogene. SA‐β‐gal induction during senescence was due at least in part to increased expression of the lysosomal β‐galactosidase protein. These results also indicate that SA‐β‐gal is not required for senescence.