In vivo reprogramming is a promising approach for tissue regeneration in response to injury. Several examples of in vivo reprogramming have been reported in a variety of lineages, but some including skeletal muscle have so far proven refractory. Here, we show that acute and chronic injury enables transcription-factor-mediated reprogramming in skeletal muscle. Lineage tracing indicates that this response frequently originates from Pax7+ muscle stem cells. Injury is associated with accumulation of senescent cells, and advanced aging or local irradiation further enhanced in vivo reprogramming, while selective elimination of senescent cells reduced reprogramming efficiency. The effect of senescence appears to be, at least in part, due to the release of interleukin 6 (IL-6), suggesting a potential link with the senescence-associated secretory phenotype. Collectively, our findings highlight a beneficial paracrine effect of injury-induced senescence on cellular plasticity, which will be important for devising strategies for reprogramming-based tissue repair.
Cellular senescence is an irreversible growth arrest with a highly dynamic secretome, termed the senescence-associated secretory phenotype (SASP). Senescence has been implicated in somatic reprogramming to pluripotency. The cell-intrinsic proliferation arrest is a barrier for reprogramming, whereas the SASP facilitates the cell fate conversion in nonsenescent cells. However, the mechanisms by which reprogramming-induced senescence regulates cell plasticity are not well understood. Here, we have further investigated how the heterogeneity of paracrine senescence impacts reprogramming. We show that senescence promotes in vitro reprogramming in a stress-dependent manner. We identified a catalog of SASP factors and pathways potentially involved in the cell fate conversion using an unbiased proteomic analysis. Amphiregulin (AREG), a growth factor frequently secreted by the senescent cells, promotes in vitro reprogramming by accelerating proliferation and MET via the EGFR signaling pathway. Of note, AREG treatment diminished the negative effect of donor age on reprogramming. Finally, AREG enhances in vivo reprogramming in the skeletal muscle. Hence, senescence could facilitate cellular plasticity via various SASP factors to promote reprogramming and tissue repair.
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