Apoptotic processes direct the matrix-induced fibrogenic conversion of aged muscle stem cells. Mus musculus

The stiffening of the extracellular matrix (ECM) with age hinders muscle regeneration by causing intrinsic muscle stem cell (MuSC) dysfunction through a poorly understood mechanism. Here, young and aged MuSCs were seeded onto substrates engineered to mimic a soft and stiff ECM microenvironment to study those molecular changes using single-cell RNA-sequencing (scRNA). Data revealed the presence of a branching point within the trajectory leading to the emergence of an age-related fibroblastic population characterized by activation of the TNF-related apoptosis-inducing ligand (TRAIL) pathway, which was significantly activated in aged cells cultured on stiff substrates. Next, using the collagen cross-linking inhibitor beta-aminopropionitrile (BAPN) in vivo, we elucidated stiffness changes on TRAIL downstream apoptotic targets (caspase 8 and caspase 3) using immunostaining. TRAIL activity was significantly inhibited by BAPN in aged animals, indicating a complex mechanism of age-related declines in muscle function through inflammatory and apoptotic mediators.