Enhancer rewiring orchestrates inflammation and loss of cell identity during muscle stem cell aging [CUT&RUN]

Loss of regeneration is a key feature of aging organs, often linked to stem cell exhaustion. Skeletal muscle stem cells (MuSCs) undergo age-related numerical and functional decline, contributing to reduced regenerative potential. Using low-input multi-omics, we systematically profiled the epigenome, transcriptome, and 3D genome of MuSCs from individual mice across 3 age groups (young, old, and geriatric) and both sexes. At baseline, young male MuSCs showed reduced expression of cell cycle-related mRNAs. In aged mice, particularly males, MuSCs exhibited early alterations (emerging during the transition from young to old age), including enhanced proinflammatory signaling, and loss of cell identity. Late alterations (emerging during the transition from old to geriatric age) included heightened inflammation, widespread enhancer activation, and extensive 3D genome rewiring. Proinflammatory pathways were enriched for interferon signaling and correlated with endogenous retroviral expression and NFκB activity. Late-stage epigenome and 3D genome rewiring reflected downstream degenerative changes in muscle organization, response to cytokines, and loss of myogenic identity. Thus, progressive molecular shifts may explain the aggravated proliferative deficit and functional impairment observed in MuSCs during aging.