Effects of hyperoxia on erythropoietin receptor expression in lung development of neonatal rats

Abstract

Oxygen toxicity is thought to be a major contributing factor in the pathogenesis of bronchopulmonary dysplasia (BPD). Animal experiments reveal that erythropoietin (EPO) may have protective effects against hyperoxic lung injury, but the mechanisms remain unknown. The aim of this study was to evaluate effects of hyperoxia on erythropoietin receptor expression in lung development of neonatal rats. Several litters of Wistar pups were pooled together within 12 hours after birth and randomly divided into two groups (n = 24 in each): air-exposed control group and hyperoxia-exposed group. In hyperoxia-exposed group, the rats were exposed to 85% oxygen. Pups (n = 8) from each group were sacrificed on postnatal days 3, 7, and 14. The pulmonary histological and morphometric changes were observed after hematoxylin-eosin (HE) staining under light microscope. Radical alveolar counts (RAC) were compared between the two groups to evaluate the differences of alveolarization. Expressions of platelet endothelial cell adhesion molecule-1 (PECAM-1) and erythropoietin receptor (EPOR) in lung tissue were measured by immunohistochemistry. Expressions of EPOR mRNA and EPOR protein were measured by RT-PCR and Western blotting. In hyperoxia-exposed group, there were a few inflammatory cells infiltration in interstitium on day 3 and inflammatory response worsened on day 7. Alveolar and capillary hypoplasia and interstitial fibrosis were evident on day 14. RAC increased in air-exposed control group along with the age in days. RAC decreased from day 7 in hyperoxia-exposed group compared with air-exposed control group [(6.85 ± 1.04) vs. (7.33 ± 1.0), P < 0.01], which was more evident on day 14 [(6.20 ± 1.58) vs. (9.07 ± 0.69), P < 0.001]. Expression of PECAM-1 protein increased in air-exposed control group along with the age in days. But in hyperoxia-exposed group, it decreased on day 7 and 14 [(15.14 ± 1.51) vs. (31.47 ± 2.43), (11.04 ± 1.76) vs. (41.41 ± 3.83), P < 0.001] compared with air-exposed control group. Expression of EPOR on day 3 in air-exposed control group was the strongest and weakened gradually with the increase of postnatal days. Expression of EPOR in hyperoxia-exposed group decreased on day 3 and became more evident on day 7 and day 14 compared with air-exposed control group [(1.62 ± 0.04) vs. (1.82 ± 0.06), P < 0.05; (0.48 ± 0.01) vs. (1.10 ± 0.07), (0.39 ± 0.04) vs. (0.87 ± 0.03), P < 0.001]. Expression of EPOR mRNA on day 3 in air-exposed control group was the strongest and was decreased significantly in hyperoxia-exposed group compared with air-exposed control group at all time points [(0.87 ± 0.07) vs. (1.1 ± 0.17), (0.18 ± 0.07) vs. (0.36 ± 0.08), P < 0.01;(0.14 ± 0.05) vs. (0.36 ± 0.09), P < 0.001]. EPOR may participate in the modulation of normal lung development. Depressed expression of EPOR and PECAM-1 may be involved in the pathogenesis of alveolar and capillary hypoplasia induced by hyperoxia.