In aging research, there has long been a need for better biomarkers that can detect and confirm the presence of senescent cells. This has become particularly urgent in recent years due to the meteoric rise of the senescent cell-clearing therapies known as senolytics.

Traditional ways of measuring senescent cell populations are problematic and have multiple shortfalls, so the development of better biomarkers is very important. Today, we share a new publication in which researchers take a step towards developing such a biomarker [1].


The activation of cellular senescence throughout the lifespan promotes tumor suppression, whereas the persistence of senescent cells contributes to aspects of aging. This theory has been limited, however, by an inability to identify and isolate individual senescent cells within an intact organism. Toward that end, we generated a murine reporter strain by “knocking-in” a fluorochrome, tandem-dimer Tomato (tdTom), into exon 1α of the p16INK4a locus. We used this allele (p16tdTom) for the enumeration, isolation, and characterization of individual p16INK4a-expressing cells (tdTom+). The half-life of the knocked-in transcript was shorter than that of the endogenous p16INK4a mRNA, and therefore reporter expression better correlated with p16INK4a promoter activation than p16INK4a transcript abundance. The frequency of tdTom+ cells increased with serial passage in cultured murine embryo fibroblasts from p16tdTom/+ mice. In adult mice, tdTom+ cells could be readily detected at low frequency in many tissues, and the frequency of these cells increased with aging. Using an in vivo model of peritoneal inflammation, we compared the phenotype of cells with or without activation of p16INK4a and found that tdTom+ macrophages exhibited some features of senescence, including reduced proliferation, senescence-associated β-galactosidase (SA-β-gal) activation, and increased mRNA expression of a subset of transcripts encoding factors involved in SA-secretory phenotype (SASP). These results indicate that cells harboring activation of the p16INK4a promoter accumulate with aging and inflammation in vivo, and display characteristics of senescence.

In brief, these researchers have demonstrated that most senescent cells display a number of hallmarks of cellular senescence, namely p16INK4a activation, reduced replication, and the expression of the senescence-associated secretory phenotype (SASP). They also identified a link between p16INK4a promoter activation and the presence and level of SASP, which shows the potential for p16INK4a as a biomarker for senescent cells.

They finally suggest that the p16tdTom allele enables the identification and isolation of cells that have high levels of p16INK4a promoter activity.


As we have mentioned many times, there is an urgent need to develop therapies against the harms of aging, but we must also develop better biomarkers that will help us to confirm the efficacy of such therapies. This study is a solid step towards developing such a biomarker.


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[1] Liu, J. Y., Souroullas, G. P., Diekman, B. O., Krishnamurthy, J., Hall, B. M., Sorrentino, J. A., … & Sharpless, N. E. (2019). Cells exhibiting strong p16INK4a promoter activation in vivo display features of senescence. Proceedings of the National Academy of Sciences, 201818313.

About the author

Steve Hill

Steve serves on the LEAF Board of Directors and is the Editor in Chief, coordinating the daily news articles and social media content of the organization. He is an active journalist in the aging research and biotechnology field and has to date written over 500 articles on the topic as well as attending various medical industry conferences. In 2019 he was listed in the top 100 journalists covering biomedicine and longevity research in the industry report – Top-100 Journalists covering advanced biomedicine and longevity created by the Aging Analytics Agency. His work has been featured in H+ magazine, Psychology Today, Singularity Weblog, Standpoint Magazine, and, Keep me Prime, and New Economy Magazine. Steve has a background in project management and administration which has helped him to build a united team for effective fundraising and content creation, while his additional knowledge of biology and statistical data analysis allows him to carefully assess and coordinate the scientific groups involved in the project. In 2015 he led the Major Mouse Testing Program (MMTP) for the International Longevity Alliance and in 2016 helped the team of the SENS Research Foundation to reach their goal for the OncoSENS campaign for cancer research.
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