H2AX and bronchopulmonary dysplasia: Immunofluorescence and western blotting analyses (Fig. 1B, C) showed that in the model group, γ-H2AX levels increased starting on day 3 and were significantly higher on day 7 (p < 0.05) and more pronounced on day 14 (p < 0.01), suggesting the accumulation of DSBs in the lungs of BPD rats over time.