Objective  To establish a mice model of radiation-induced pulmonary fibrosis (RIPF) with small-animal X-ray irradiators.

Methods  Twenty-four C57BL/6J mice were randomly classified into four groups. One group received sham irradiation (control group, n=6), and the other three groups were irradiated with a single dose of X-ray in the right lung by small-animal X-ray irradiators (20 Gy irradiation group, n=6; 22 Gy irradiation group, n=6; 24 Gy irradiation group, n=6). The mice were sacrificed 120 days after irradiation and lung tissues were extracted. Observe the body weight, the pathological changes in the right lung tissue of mice after irradiation stained with hematoxylin-eosin and Masson′s trichrome; Western blot and real-time quantitative polymerase chain reaction were used to detect the expression of fibronectin 1 (FN1) and α-smooth muscle actin (α-SMA) fibrosis related proteins in mice lung tissue. Detecting changes in hydroxyproline contents, and transforming growth factor beta 1 (TGF-β1) signaling pathway in lung tissue. Quantitative data were analyzed by one-way ANOVA.

Results  At two weeks after irradiation, mice in the control group had a body weight of (28.8±3.3) g. Mice in the 20, 22, and 24 Gy irradiation groups had body weights of (26.2±4.6), (26.4±3.3), and (26.6±3.3) g, respectively. The difference was not statistically significant (F=0.654, P>0.05). Compared with the control group, the right lung tissue of the irradiated groups mice showed structural damage to the alveoli, thickening of the alveolar septa, and significant deposition of collagen fibers. The expression levels of fibrosis related proteins, FN1, and α-SMA significantly increased in the lungs from radiation-injured groups. The transcription levels of FN1 in the 24 Gy irradiation group was significantly higher than those in the control group and the difference was statistically significant (2^−ΔΔCt: (2.1±0.6) vs. (0.6±0.1), F=12.470, P<0.05). The transcription levels of α-SMA in the 20 Gy irradiation group were significantly higher than those in the control group and the difference was statistically significant (2^−ΔΔCt: (2.1±0.7) vs. (1.1±0.3), F=4.320, P<0.05). Moreover, the hydroxyproline contents was (500.2±17.1) μg/mg in the right lung of control group, and it significantly increased in the right lung of mice in the 20, 22, and 24 Gy irradiation groups, with values of (1199.7±159.2), (1357.1±36.8), and (1649.3±213.4) μg/mg, respectively. Compared with the control group, the hydroxyproline contents in the right lung tissues of mice in different dose X-ray irradiation groups increased significantly, and the differences were statistically significant (F=13.170, P<0.001), accompanied by the activation of the TGF-β1 signaling pathway. The above results show that the mice model of RIPF was successfully established.

Conclusion  Severe fibrosis occurred in the right lungs of mice at 120 days after irradiation (20–24 Gy), indicating a mice RIPF model can be successful established.