Cdkn1a transcript variant 2 is a marker of aging and cellular senescence

Abstract

Cellular senescence is a cell fate response characterized by a permanent cell cycle arrest driven primarily the by cell cycle inhibitor and tumor suppressor proteins p16 Ink4a and p21 Cip1/Waf1 . In mice, the p21 Cip1/Waf1 encoding locus, Cdkn1a , is known to generate two transcripts that produce identical proteins, but one of these transcript variants is poorly characterized. We show that the Cdkn1a transcript variant 2, but not the better-studied variant 1, is selectively elevated during natural aging across multiple mouse tissues. Importantly, mouse cells induced to senescence in culture by genotoxic stress (ionizing radiation or doxorubicin) upregulated both transcripts, but with different temporal dynamics: variant 1 responded nearly immediately to genotoxic stress, whereas variant 2 increased much more slowly as cells acquired senescent characteristics. Upon treating mice systemically with doxorubicin, which induces widespread cellular senescence in vivo , variant 2 increased to a larger extent than variant 1. Variant 2 levels were also more sensitive to the senolytic drug ABT-263 in naturally aged mice. Thus, variant 2 is a novel and more sensitive marker than variant 1 or total p21 Cip1/Waf1 protein for assessing the senescent cell burden and clearance in mice.

Targeted clearance of p21‐ but not p16‐positive senescent cells prevents radiation‐induced osteoporosis and increased marrow adiposity

“…These data demonstrated that although radiation induced both transgenes in bone and AP20187 cleared p21 Cip1 -and p16 Ink4a -expressing cells (which also expressed Egfp), senescent osteocytes, assessed using the TAF assay(Chandra et al, 2020;Farr et al, 2016), were only reduced in the p21-ATTAC mice. These data further demonstrate that although both our transgene promoters and the endogenous p21 Cip1 and p16 Ink4a promoters are upregulated following radiation(Chandra et al, 2020;López-Domínguez et al, 2021), it is p21 Cip1 that drives senescence in radiation-induced bone damage. Clearance of these cells prevents osteocyte senescence and the downstream consequences (i.e., increased SASP and bone loss).…”

“…does differ following radiation both in vitro (López-Domínguez et al, 2021) and in vivo (Chandra et al, 2020). Thus, in cultured mouse dermal fibroblasts, levels of p21 Cip1 mRNA were induced within 3 h of radiation, whereas p16 Ink4a transcripts increased much later, ~50-h post-radiation (López-Domínguez et al, 2021).…”

Dynamic Spatiotemporal Expression Pattern of the Senescence-Associated Factor p16Ink4a in Development and Aging

“…Upregulation of p16/p19 and p21 is widely accepted as a marker of aging and senescence [16,[72][73][74]. In human tissue samples, P16 was detected in endocrine and exocrine pancreas, skin, kidneys, liver, intestine, spleen, brain, and lung.…”

Ageing, cellular senescence and chronic kidney disease: experimental evidence

“…The histone acetyltransferase KAT7, a genetic and epigenetic marker of senescence, is upregulated in murine models of ageing [28]. Cdkn1a transcript variant 2 is accumulated and activated during ageing and could be used for the diagnosis of ageing-related diseases [29].…”