Metformin Alleviates Radiation-Induced Skin Fibrosis via the Downregulation of FOXO3

BACKGROUND/AIMS

Radiation-induced skin fibrosis is a common side effect of clinical radiotherapy. Our previous next-generation sequencing (NGS) study demonstrated the reduced expression of the regulatory α subunit of phosphatidylinositol 3-kinase (PIK3r1) in irradiated murine skin. Metformin has been reported to target the PIK3-FOXO3 pathway. In this study, we investigated the effects of metformin on radiation-induced skin fibrosis.

METHODS

Metformin was orally administered to irradiated mice. Skin fibrosis was analyzed by staining with H&E and Masson's trichrome stain. The levels of cytokines and chemokines associated with fibrosis were analyzed by immunohistochemistry and quantitative RT-PCR. The roles of PIK3rl and FOXO3 in radiation-induced skin fibrosis were studied by overexpressing PIK3rl and transfecting FOXO3 siRNA in NIH3T3 cells and mouse-derived dermal fibroblasts (MDF).

RESULTS

The oral administration of metformin significantly reduced radiation-induced skin thickening and collagen accumulation and significantly reduced the radiation-induced expression of FOXO3 in murine skin. Additionally, the overexpression of PIK3r1 reduced the radiation-induced expression of FOXO3, while FOXO3 silencing decreased the radiation-induced expression of TGFβ in vitro.

CONCLUSIONS

The results indicated that metformin suppresses radiation-induced skin injuries by modulating the expression of FOXO3 through PIK3r1. Collectively, the data obtained in this study suggested that metformin could be a potent therapeutic agent for alleviating radiation-induced skin fibrosis.

Pro-apoptotic Noxa is involved in ablative focal irradiation-induced lung injury

Although lung injury including fibrosis is a well‐documented side effect of lung irradiation, the mechanisms underlying its pathology are poorly understood. X‐rays are known to cause apoptosis in the alveolar epithelial cells of irradiated lungs, which results in fibrosis due to the proliferation and differentiation of fibroblasts and the deposition of collagen. Apoptosis and BH3‐only pro‐apoptotic proteins have been implicated in the pathogenesis of pulmonary fibrosis. Recently, we have established a clinically analogous experimental model that reflects focal high‐dose irradiation of the ipsilateral lung. The goal of this study was to elucidate the mechanism underlying radiation‐induced lung injury based on this model. A radiation dose of 90 Gy was focally delivered to the left lung of C57BL/6 mice for 14 days. About 9 days after irradiation, the mice began to show increased levels of the pro‐apoptotic protein Noxa in the irradiated lung alongside increased apoptosis and fibrosis. Suppression of Noxa expression by small interfering RNA protected cells from radiation‐induced cell death and decreased expression of fibrogenic markers. Furthermore, we showed that reactive oxygen species participate in Noxa‐mediated, radiation‐induced cell death. Taken together, our results show that Noxa is involved in X‐ray‐induced lung injury.