P16 positive microglia population identified in the aged mouse brain

Senescent cells are in a state of permanent cell cycle arrest, which is mediated by the Cyclin Dependent Kinase (CDK)4/6 inhibitor p16. During ageing, p16-expressing (P16pos) cells accumulate in tissues and promote multiple age-related pathologies, including neurodegenerative diseases. We evaluated the accumulation and the phenotype of senescent cells in the aged brain with a transgenic reporter mouse (p16-3MR), which allows for isolation of P16poscells. First, we showed that the number of P16pos cells is significantly increased in old brains. Second, using bulk RNAseq, we demonstrated that P16pos cells express high levels of inflammatory and lysosomal genes. Third, using single-cell RNAseq, we identified P16pos brain cells as being primarily microglia. Interestingly, the transcriptional profile of P16pos microglia cells is distinct from cell type signatures associated with senescence or defined microglia populations. Taken together, our study provides evidence for the accumulation of a novel P16pos microglia population in the aging brain, which could result in loss of tissue homeostasis and contribute to brain dysfunction. Bulk RNAseq of RFPneg and RFPpos cells from brains from p16–3MR mice with a C57BL/6 background (n=5). Single-cell RNAseq of the total viable population brain cells and RFPpos brain cells from 5 mice pooled.