Single-cell transcriptomic analysis reveals alterations to cellular dynamics and paracrine signaling in...

Radiation therapy causes long-term skeletal muscle atrophy and fibrosis in juvenile cancer survivors. The mechanisms responsible for the skeletal muscle late effects of radiation therapy are not well-understood and have prevented the development of effective treatments. Using single-cell RNA sequencing (scRNA-seq), we characterize cellular dynamics and communication in a murine model of therapeutic radiation at 24 h and 56 days post-irradiation (post-IR). We detected changes in muscle stem (satellite) cells (MuSCs) characterized by an acute preservation of committed MuSCs and long-term relative depletion of deep quiescent MuSCs. A conserved senescence Cdkn1a signature was observed in all muscle-resident cells post-IR. Genes related to fibroblast proliferation were upregulated and a fibrotic and senescent transcriptome persisted in fibro-adipogenic progenitors (FAPs) post-IR. Intercellular communication analysis revealed FAPs as the primary contributor of extracellular matrix (ECM) and target of monocyte/macrophage-derived transforming growth factor (TGF)-β signaling post-IR through TGF-βR2 on FAPs. Together, our findings provide insights into the potential mechanisms and intercellular communication responsible for radiation-induced muscle atrophy and fibrosis.NEW & NOTEWORTHY This work describes, for the first time, the transcriptional changes occurring following radiation exposure in the skeletal muscle microenvironment using scRNA-seq technology. We revelated that FAPs exhibited a profibrotic and senescent transcriptome. Radiation exposure led to a conserved and persistent Cdkn1a gene signature and impairs intercellular communication, increasing TGF-βR2 signaling in FAPs. These findings uncover potential mechanisms and intercellular communication responsible for long-term muscle impairments post-radiation, offering new targets for therapeutic intervention.