The immune landscape of murine skeletal muscle regeneration and aging

Age-related alterations in the immune system are starting to emerge as key contributors to impairments found in aged organs. A decline in regenerative capacity is a hallmark of tissue aging, however the contribution of immune aging to regenerative failure is just starting to be explored. Here, we applied a strategy combining single-cell RNA-sequencing with flow cytometry and functional assays to perform a complete analysis of the immune environment in the aged regenerating skeletal muscle, with time and single cell resolution. Our results identified previously undescribed immune cell types in the skeletal muscle and revealed an unanticipated complexity and functional heterogeneity in immune populations, that have been regarded as homogeneous. Furthermore, we uncovered a profound remodeling of both myeloid and lymphoid compartments in aging. These discoveries challenge established notions on immune regulation of skeletal muscle regeneration, providing a new set of potential targets to improve skeletal muscle health and regenerative capacity in aging. The CD45+ population (all immune cells) were fluorescence-activated cell sorting (FACS)-purified from non-injured and injured SkM at 1, 3 and 5 days post-injury from yg (3mo) and aged (25mo) mice. These samples were used to prepare scRNAseq libraries using 10× Chromium technology.