OBJECTIVETo explore the expression of CASZ1 and its relationship with the pulmonary microvascular development in lung tissue of newborn rats exposed to hyperoxia which induced bronchopulmonary dysplasia (BPD).

METHODForty-eight newborn Sprague Dawley(SD) rats (male and female unlimited) were randomly divided into two groups: experimental group and control group according to random digits table with 24 in each.The rats in experimental group were exposed to high oxygen volume fraction of 800 ml/L and the rats in control group were exposed to normal air. Eight rats were randomly selected from each group on day 3 and 7 after oxygen exposure.The sections of lung were stained with HE method in order to assess lung histological changes, the alveolar development was evaluated by the number of radial alveolar count (RAC) and septal wall thickness. CD31 was detected by immunohistochemistry (IHC) method and the capillary density was calculated. The location, distribution and expression of CASZ1 in the lung tissue were detected by the immunohistochemistry, Western blotting, and quantitative PCR (qPCR).

RESULT(1) Stained by HE, lungs of experimental group showed destroyed alveoli, alveoli fusion and increased septal wall thickness, RAC were significantly lower than those in control group(14 d: septal wall thickness (12.69 ± 0.63) μm vs. (6.53 ± 0.16) μm, RAC 5.9 ± 0.4 vs. 8.4 ± 1.0, t = 19.046, 4.760, P both = 0.000). (2) CD31 protein was expressed predominantly in cytoplasm of pulmonary microvascular endothelial cells. The experimental group CD31 average optical density (AIOD) were decreased compared with control group((16.6 ± 1.6) × 10(3) vs.(40.1 ± 2.4) × 10(3), (18.1 ± 1.4) × 10(3) vs.(83.2 ± 5.2) × 10(3), (49.2 ± 5.4) × 10(3) vs.(136.2 ± 28.1) × 10(3), t=16.185, 16.066 and 6.078, P<0.01 for all comparisons). Capillary density in experimental group was also significantly decreased compared with control group ((3.84 ± 0.15)% vs.(6.01 ± 0.22)%, (4.17 ± 0.38)% vs.(6.15 ± 0.24)%, (5.43 ± 0.44)% vs. (9.13 ± 0.25)%, t = 16.124, 8.773 and 14.076, P all < 0.01). (3)RT-qPCR and Western blotting showed that the CASZ1 mRNA significantly increased in experimental group compared with control group(0.56 ± 0.17 vs. 1.00 ± 0.26, 0.32 ± 0.29 vs. 0.58 ± 0.14, 0.14 ± 0.22 vs. 0.56 ± 0.15, t=3.890, 3.303 and 2.388, P < 0.05 for all comparisons), and the protein expression of CASZ1 also significantly increased in experimental group compared with control group (0.65 ± 0.02 vs. 0.78 ± 0.23, 0.46 ± 0.03 vs. 0.75 ± 0.05, 0.34 ± 0.22 vs. 0.75 ± 0.04, t=6.200 and 10.485 and 14.998, P < 0.05 for all comparisons). (4)The protein level of CASZ1 in experimental group was positively correlated with capillary density (r=0.519, P<0.01).

CONCLUSIONCASZ1 is involved in the whole process of newborn rats BPD and may be linked to pulmonary microvascular dysplasia.