Old fibroblasts secrete inflammatory cytokines that drive variability in reprogramming efficiency and may affect wound healing between old individuals

Abstract

Age-associated chronic inflammation (inflammaging) has emerged as a central hallmark of aging 1-3 , but its impact on specific cells is still largely unknown. Fibroblasts are present in all tissues and contribute to wound healing 4-6 . They are also the cell type that is mostly used for induced pluripotent stem cell (iPSC) reprogramming 7 -a process that has implications for regenerative medicine and rejuvenation strategies [8][9][10][11][12][13][14][15][16][17] . Here we show that primary fibroblasts from old mice secrete inflammatory cytokines and that there is an increased variability in reprogramming efficiency between fibroblast cultures from old individuals. Individual-toindividual variability is emerging as a key feature of old age 18-21 , which could reflect distinct aging trajectories, but the underlying causes remain unknown. To identify drivers of this variability, we perform a multi-omic assessment of young and old fibroblast cultures with different reprogramming efficiency. This approach, coupled with single cell transcriptomics, reveals that old fibroblast cultures are heterogeneous and show a greater proportion of 'activated fibroblasts' that secrete inflammatory cytokines, which correlates with reprogramming efficiency. We experimentally validate that activated fibroblasts express inflammatory cytokines in vivo and that their presence is linked to enhanced reprogramming efficiency in culture. Conditioned-media swapping experiments show that extrinsic factors secreted by activatedfibroblasts are more critical than intrinsic factors for the individual-to-individual variability in reprogramming efficiency, and we identify TNFα as a key inflammatory cytokine underlying this variability. Interestingly, old mice also exhibit variability in wound healing efficiency in vivo and old wounds show an increased subpopulation of activated fibroblasts with a unique TNFα signature. Our study shows that a switch in fibroblast composition, and the ratio of inflammatory cytokines they secrete, drives variability in reprogramming in vitro and may influence wound healing in vivo. These findings could help identify personalized strategies to improve iPSC generation and wound healing in older individuals.

In silico clinical trials for anti-aging therapies

“…The benefit/risk ratio of anti-aging strategies targeting inflammation (e.g., senolytics) or nutrient/metabolism-sensing pathways (e.g., DR/DRMs modulating the communication between metabolism and epigenetics) might be dictated by the pre-existing degree of epigenetic plasticity and phenotypic malleability of the different cell populations in aging tissues. Accordingly, the occurrence of intra- and inter-individual variability driven by sub-cellular/cellular (e.g., local availability of epigenetic substrates/cofactors and/or metabolic cues) and more systemic features (e.g., inflammation driven by senescent cells, activated fibroblasts or endothelial cells) begins to be understood as a consequence of different aging trajectories occurring in different tissue cell subpopulations [33]. This likely reflects changes in the short-range/paracrine communication between distinct cell types within a tissue, as well as between different individuals.…”