Differential transcriptomic profiling of lipid metabolism and collagen remodeling in fast- and slow-twitch skeletal muscles in aging.

Skeletal muscle function gradually declines with aging, presenting substantial health and societal challenges. Comparative analysis of how aging affects fast- and slow-twitch muscles remains lacking. We utilized 20-month-old mice to reveal the aging effects on muscle structure and fiber composition, followed by bulk RNA sequencing for fast- and slow-twitch muscles and integration with human single-cell RNA sequencing dataset providing a comparative analysis across species. In mouse slow-twitch muscles, aging induced a switch from fast to slow fibers and distinctively altered lipid metabolism in ceramide and triglyceride, with the upregulation of regulatory genes Gk and Ppargc1a also observed in human slow fibers. Additionally, both types of muscles exhibited common collagen deposition and fibrosis, possibly due to the imbalance between collagen synthesis and degradation. The extracellular matrix gene changes substantially overlapped between mice and humans in aging, yet also highlighted clear differences. This integrative analysis provides further understanding of aged fast- and slow-twitch muscles and offers new insights into the molecular changes in aging.