To investigate the dynamic expression of DNA damage repair protein Nijmegen breakage syndrome protein 1(NBS1) in the neonatal rats with bronchopulmonary dysplasia(BPD), and its influence on the development and progression of BPD.

Newborn rats were randomly divided into the BPD model group(n=50) and the control group(n=50) within 12 h after birth.The inhaled oxygen concentration was 80%-85% in the model group, and the control group inhaled air.In the two groups, lung tissue samples were collected on days 1, 3, 7, 10 and 14, and isolated, purified and cultured alveolar epithelial type Ⅱ cells(AEC Ⅱ). We observed pulmonary morphological changes under light microscope and evaluated alveolar development degree by radiate alveolar counts(RAC). Immunohistochemistry and cell immunofluorescence were used to observe the localization and expression of NBS1.Western blot and real-time quantitative PCR were used to detect the expression level of NBS1.

Compared with the control group, the RAC value in the model group was decreased significantly from 7 d after birth(control group 7.58±1.24, model group 5.42±1.24, P<0.01). Immunohistochemistry showed that NBS1 protein was mainly located in the nucleus of alveolar epithelial cells.In the model group, NBS1 was mainly expressed in the nucleus on the 1st day.With the prolonged exposure time, the number of cytoplasmic staining cells increased and the expression in the nucleus decreased.Cell immunofluorescence farther showed that NBS1 protein was mainly located in the nucleus in AEC Ⅱ.Compared with the control group, cytoplasmic staining in model group was enhanced from 3 d, while nuclear staining was gradually weakened, and was mainly located in the cytoplasm at 14 d. Western blot results showed that the expression of NBS1 protein in the model group peaked at 1 d compared to the control group(control group 0.72±0.29, model group 1.28±0.22, P<0.01), and then gradually decreased, with lower expression at 14 d compared to the control group(control group 0.73±0.19, model group 0.49±0.11, P<0.05). Similarly, the mRNA expression level of NBS1 in the model group peaked at 1 d compared to the control group(control group 1.00±0.00, model group 1.18±0.06, P<0.01), and then gradually decreased, with lower expression at 14 d than that in the control group(control group 1.07±0.13, model group 0.76±0.11, P<0.05).

In the neonatal rats with BPD, the down-regulation expression and nuclear enrichment disorder of NBS1 may affect the DNA damage response and be one of the mechanisms mediating the onset of oxidative stress damage in BPD.

Nijmegen breakage syndrome protein 1; DNA damage; Bronchopulmonary dysplasia; Newborn rat