KLRG1 identifies regulatory T cells with mitochondrial alterations that accumulate with aging

Recent works using single cell RNA sequencing (scRNAseq) technology have uncovered several subpopulations of CD4+ T cells that accumulate with aging, including activated regulatory T cells, effector memory T cells, exhausted T cells or cytotoxic T cells. These age-associated T cells are emerging as relevant players in the control of inflammaging and tissue senescence. Herein, based on information provided by scRNAseq data, we present a flow cytometry panel that allows the identification of age-associated T cell subsets in systematic larger analysis in mice. We use this panel to evaluate at single cell level mitochondrial and senescence marks in the different age-associated CD4 T cell subpopulations. Our analysis identifies a subpopulation of regulatory T cells (Tregs) that is characterized by the extracellular expression of the co-inhibitory molecule Killer cell lectin-like receptor subfamily G member 1 (KLRG1) and accumulates with aging in humans and mice. KLRG1-expressing Tregs display features of senescence such as mitochondrial alterations, increased expression of cell-cycle regulators and genomic DNA damage. Functionally, KLRG1+ Treg cells show a reduced suppressive activity in vivo accompanied by a pro-inflammatory phenotype in which FOXP3 expression is preserved but accompanied by the engagement of an inflammatory program. Overall design: To investigate a new Treg subset, we analysed the transcriptome of three different splenic Treg subsets (resting Tregs, activated Tregs and KLRG1+Tregs) sorted from 4 young and 4 old mice