Distinct Fibroadipogenic Progenitor Populations And Trajectories Characterize Regenerative And Non-regenerative Responses In The Ischemic Limb

Introduction: Skeletal muscle possesses the capacity for self-repair. This ability is impaired in chronic limb threatening ischemia (CLTI) patients. Myopathy in CLTI patients is associated with adverse clinical outcomes. Skeletal muscle regeneration requires multicellular interactions between muscle progenitor cells and other cell types. Fibroadipogenic progentiors (FAPs) represent a support cell type in the skeletal muscle niche; they modulate inflammatory and myogenic responses via the secretion of a paracrine factors. Hence, FAPs are an attractive therapeutic target for myopathies. We sought to characterize the temporal dynamics and transcriptional heterogeneity of FAPs in failed and successful skeletal muscle regeneration in the ischemic limb. Methods: We analyzed the FAP regenerative response in BALB/c (non-regenerative) and C57BL/6 (regenerative) mice undergoing hindlimb ischemia using single-cell RNA sequencing spanning 4 distinct time points. We also performed RNA velocity analysis to determine the cellular dynamics of FAP sub-populations during the repair process. Results: We identified 10 FAP populations in the ischemic limb, including specific regenerative and non-regenerative FAP sub-clusters. Gene ontology (GO) enrichment analysis demonstrated distinct transcriptional programs between regenerative and non-regenerative FAPs. Regenerative FAPs were enriched in extracellular matrix and angiogenesis pathways, while non-regenerative FAPs were enriched in chemotactic pathways. RNA velocity analysis demonstrated divergent FAP cellular trajectories. Conclusions: Our study maps the dynamic FAP response in the ischemic limb at single-cell resolution. We identify distinct transcriptional programs and cellular trajectories that are associated with failed and successful skeletal muscle repair. This provides a resource to investigate FAP mediated mechanisms of skeletal muscle regeneration in response to limb ischemia.