Study on the expression level of zonula occludens 1 and zonula occludens 1 related nucleic acid binding protein in alveolar epithelial cells in hyperoxia induced bronchopulmonary dysplasia newborn rats

Objective Previous studies have found abnormal proliferation and transdifferentiation of alveolar epithelial cells(AECs)in hyperoxic lung injury of neonatal rats.The purpose of this study was to clarify the expression of zonula occludens 1(ZO-1) and ZO-1 related nucleic acid binding protein(ZONAB)in AECs in hyperoxic lung injury model, in order to investigate its effect on the proliferation and transdifferentiation of AECs in the injured lung tissue. Methods Full-term neonatal Wistar rats were randomly divided into two groups within 12 h after birth, model group(inhaled oxygen concentration 85%)and control group(inhaled air). Lung specimens were collected at 7, 14 and 21 days after exposure.The expression of ZONAB in typeⅡalveolar epithelial cells(AECⅡ)was observed by double immunofluorescence staining.At the same time, AEC Ⅱ was isolated from lung tissues of animal models at these time points, and the expression levels of ZO-1, ZONAB protein and mRNA in lung tissues and AECⅡof the two groups were detected by Western blot and Real-Time PCR.In addition, AEC Ⅱ was isolated from lung tissue of normal newborn rats and then divided into model group(85% oxygen concentration)and control group(21% oxygen concentration). After 48 hours of culture in vitro, the expression levels of ZO-1, ZONAB protein and mRNA were detected, and the expression level and location of ZONAB were observed by immunofluorescence staining. Results Double immunofluorescence staining showed that the expression of ZONAB in AECⅡin model group was significantly lower than that in control group.The protein and mRNA expression levels of ZO-1 and ZONAB in AECⅡisolated from lung tissue of model group were both significantly lower than those from control group, starting from 7 d after hyperoxia exposure.AECⅡisolated from lung tissue of normal newborn rats, were then incubated for 48 hours under hyperoxia or normoxia in vitro, the protein and mRNA expression levels of ZO-1 and ZONAB significantly decreased in model group compared with those in control group.The results of immunofluorescence staining showed that the expression of ZONAB was higher in AECⅡof the control group, and ZONAB was mostly located in the junction and nucleus of cells, while the expression of ZONAB in the model group significantly decreased than that in the control group, and the expression sites were clustered in the cytoplasm, with little expression in the junction and nucleus. Conclusion ZO-1, as a tight junction-related protein, is down-regulated in hyperoxic lung injury model.In addition to destroying pulmonary epithelial barrier to mediate pulmonary edema, it also participated in the regulation of proliferation and differentiation of AECs by regulating transcription factor ZONAB, suggesting that this may be another pathway leading to hyperoxic lung injury. Key words: Hyperoxia; Alveolar epithelial cell; Transdifferentiation; Zonula occludens 1; Zonula occludens 1 related nucleic acid binding protein