Gap Junction Protein Expression in Hyperoxia-Exposed Neonatal Rat Lung Tissue

Abstract Bronchopulmonary dysplasia (BPD) is a common devastating pulmonary complication in preterm infants. Gap junction is involved in many lung diseases. In this study, we examine the expression of gap junction proteins, including connexin 26 (Cx26), connexin 32 (Cx32), connexin 43 (Cx43), and connexin 46 (Cx46) in neonatal rat lung tissue. Neonatal rats were kept in either 21% (normoxia) or 85% O2(hyperoxia) continuously from postnatal day (PN) 1 to 14. The neonatal rats of normoxia group had well-formed alveoli and a normal RAC value. Distal lung histology in neonatal rats in the hyperoxia group showed fewer and larger alveoli with a lower RAC value (P < 0.01). Compared with the normoxia group, the ROS level and MDA level were significantly higher (P < 0.01), and the GSH level was remarkably lower (P < 0.01) in the hyperoxia group. The statistical analysis of TUNEL staining and apoptosis index (AI) results indicated that AI was significantly higher in the hyperoxia group than in the normoxia group (P < 0.01). Cx26, Cx32, Cx43, and Cx46 mRNAs levels in the hyperoxia group were higher than those in the normoxia group (P < 0.01). Immunohistochemical results suggested that Cx26, Cx32, Cx43, and Cx46 were expressed in the lung tissue of both normoxic and hyperoxic neonatal rats. Immunofluorescence double-staining results suggested that Cx26 was expressed in both alveolar type I (ATI) and alveolar type II (ATII) cells. Nevertheless, its expression was mainly enriched in ATII cells. Cx32 was expressed in ATII cells only. Cx43 was expressed in both ATI and ATII cells. Cx46 was expressed in both ATI and ATII cells, but mainly in ATI cells. The Cx32 mRNA level was positively correlated with ROS level (P < 0.01), positively correlated with AI level (P < 0.01), and negatively correlated with RAC value (P< 0.01). We found that Cx32 was expressed only in ATII cells and was closely related to oxidative stress, apoptosis, and alveolar development. Cx32 may be involved in the development of BPD and may be a novel target for BPD management.