Autophagy gene Atg7 regulates the development of radiation‐induced skin injury and fibrosis of skin

BACKGROUND: Radiation‐induced skin injury, which may progress to fibrosis, is a severe side effect of radiotherapy in patients with cancer. However, currently, there is a lack of preventive or curative treatments for this injury. Meanwhile, the mechanisms underlying this injury remain poorly understood. Here, we elucidated whether autophagy is essential for the development of radiation‐induced skin injury and the potential molecular pathways and mechanisms involved. METHODS AND RESULTS: We used the myofibroblast‐specific Atg7 knockout (namely, conditional Atg7 knockout) mice irradiated with a single electron beam irradiation dose of 30 Gy. Vaseline‐based 0.2% rapamycin ointment was topically applied once daily from the day of irradiation for 30 days. On day 30 post irradiation, skin tissues were harvested for further analysis. In vitro, human foreskin fibroblast cells were treated with rapamycin (100 nM) for 24 h and pretreated with 3‐MA (5 mM) for 12 h. Macroscopic skin manifestations, histological changes, and fibrosis markers at the mRNA and protein expression levels were measured. Post irradiation, the myofibroblast‐specific autophagy‐deficient (Atg7(Flox/Flox) Cre(+)) mice had increased fibrosis marker (COL1A1, CTGF, TGF‐β1, and α‐SMA) levels in the irradiated area and had more severe macroscopic skin manifestations than the control group (Atg7(Flox/Flox) Cre(−)) mice. Treatment with an autophagy agonist rapamycin attenuated macroscopic skin injury scores and skin fibrosis marker levels with decreased epidermal thickness and dermal collagen deposition in Atg7(Flox/Flox) Cre(+) mice compared with the vehicle control. Moreover, in vitro experiment results were consistent with the in vivo results. Together with studies at the molecular level, we found that these changes involved the Akt/mTOR pathway. In addition, this phenomenon might also relate to Nrf2‐autophagy signaling pathway under oxidative stress conditions. CONCLUSION: In conclusion, Atg7 and autophagy‐related mechanisms confer radioprotection, and reactivation of the autophagy process can be a novel therapeutic strategy to reduce and prevent the occurrence of radiodermatitis, particularly skin fibrosis, in patients with cancer.