Heterogeneous human muscle fibroadipogenic progenitors include a DLK1 + subpopulation that prevents fatty infiltration after injury.

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

• Level A · Stronger Clinical Evidence
• Level B · Emerging clinical evidence with positive signals
• Level C · Early human research exploring benefits
• Level D · Scientific groundwork from lab and animal studies
• Emerging · Emerging topic under active research

Abstract (original English)

Fatty infiltration and fibrosis drive poor outcomes after chronic muscle injury. Here, we characterized fibroadipogenic progenitor cell (FAP) subpopulations from healthy and injured human rotator cuff muscle by single-cell RNA sequencing, full-spectrum flow cytometry, and functional assays and found distinct subpopulations, including a preadipogenic population that expresses delta-like noncanonical notch ligand 1 (DLK1 + ) and a prefibrogenic population that expresses decay-accelerating factor (CD55 + ). We used in vitro and flow cytometry experiments to show that human FAP lineages displayed unique surface marker expression across adipogenic and fibrogenic differentiation. In chronic human rotator cuff injury, expression of DLK1 RNA and DLK1 protein was decreased compared with that in healthy muscle. Overexpression of DLK1 in primary human FAPs suppressed differentiation into adipocytes in vitro, whereas DLK1 knockdown increased adipogenesis. In an immunodeficient murine model of glycerol-induced acute muscle injury, xenotransplantation of DLK1-overexpressing human FAPs into the injured murine muscle resulted in reduced fatty infiltration after 14 days by histological assessment, supporting a functional role for DLK1 in restraining adipogenesis. Together, we defined molecularly distinct, clinically relevant human FAP subpopulations, established DLK1 as a regulator of adipogeni

Evidence level

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

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