Abstract
Senescent cells drive age-related tissue dysfunction via the induction of a chronic senescenceassociated secretory phenotype (SASP). The cyclin-dependent kinase inhibitors p21(Cip1) and p16(Ink4a) have long served as markers of cellular senescence. However, their individual roles remain incompletely elucidated. Thus, we conducted a comprehensive examination of multiple single-cell RNA sequencing (scRNA-seq) datasets spanning both murine and human tissues during aging. Our analysis revealed that p21(Cip1) and p16(Ink4a) transcripts demonstrate significant heterogeneity across distinct cell types and tissues, frequently exhibiting a lack of co-expression. Moreover, we identified tissue-specific variations in SASP profiles linked to p21(Cip1) or p16(Ink4a) expression. Our study underscores the extraordinary diversity of cellular senescence and the SASP, emphasizing that these phenomena are inherently cell- and tissue-dependent. However, a few SASP factors consistently contribute to a shared "core" SASP. These findings highlight the need for a more nuanced investigation of senescence across a wide array of biological contexts.