Mechanism Of Delta4,Notch2,Notch4 In Premature Rat Lungs Exposed To Hyperoxia

Part 1 Expression of Delta4,Notch2,Notch4 in the early Stages of premature rat lung developmentObjective To explore the roles of the ligand--Delta4 and the the receptors--Notch2,Notch4 in the early stages of premature rat lung development.Methods Lung specimens from 18 d,20 d,21d fetuses and 1 d,7 d,14 d and 21d preterm Sprague-Dawley rats of day 21 of gestation(term rat of day 22 of gestation) were used(n=8). Tissue specimens were e used to evaluate the lung histological changes by HE staining,the expressions of Delta4 and Notch2,Notch4 by immunohistochemistry and the level of mRNA by reverse transcription polymerase chain reaction(RT-PCR).Results 1. Lungs of 18d fetuses the major airways developed centrifugally, blood capillaries began to appose to air ways; lungs of 20 d,21d fetuses and of 1d preterm rats. sac-like end segments showed progressive thinning of the epithelial linings, the lung is canalized with the multiplication of capillaries, and the cellularity of the interstitium decreased markedly with age; lungs of 7d,14d preterm rats the number of alveoli increased and became mature, the thickness of the blood-air barrier became thinner and thinner; 21d the alveoli septal was relatively thin at postnatal 21d and with few interstitial cells. 2. Delta4 exhibited significant differences between day gestational 18d and the other days(p<0.05), then were gradually weakened to trace;The expression of Notch2 was strongest at gestation 21d, then became weaker till postnatal 21d, it became weakest; Notch4 exhibited significant differences between day gestational 18d and the other days(p<0.05), then were gradually weakened to trace. 3. Relative abundance of Notch2,Notch4 were similar to the expression of their polypeptides(RT-PCR).Conclusions Delta4 and Notch2,Notch4 plays important roles during the early stages of lung development and might take part in the development of lung vascular. Part 2 The effects of hyperoxia on levels of Delta4,Notch2,Notch4 in premature Rat Lungs tissuesObjective To explore the roles of the ligand—Delta4 and the receptors—Notch2,Notch4 of Notch signanl in hyperoxia-induced lung injury in preterm rats.Methods At the postnatal 1d Sprague-Dawley preterm rats were randomly assigned to I : air group and II: hyperoxia group,exposed to about 85﹪of oxygen,temperature 25-26℃,humidity 60-70%,carbon dioxide concentration less than 5%.At 1,7,14,21d days after exposure,eight rats of each group were used to assess lung histologic changes,expression of Delta4 and Notch2,Notch4 in lungs by immunohistochemistry and the level of Delta4,Notch2,Notch4 andβ-actin mRNA by reverse transcription polymerase chain reaction(RT-PCR).Results Except 1d after exposure,hyperoxia group showed lung injury characterized by subacute alveolitis and inhibition of lung development. Expression of Delta4 in hyperoxia group was weaker than that in air group at 1 d, At 7,14,21d stronger ,at 1,7,14d Delta4 exhibited significant stronger(p<0.05)in hyperoxia than in air group; Expression of Notch2 in hyperoxia group was weaker than that in air group at every time point . At 1,7,14d the expressions of Notch2 exhibited significant difference(p<0.05)in hyperoxia than in air group; Expression of Notch4 in hyperoxia group was weaker than that in air group at 1 d, At 7,14,21d stronger ,at 1,7,14d Notch4 exhibited significant stronger(p<0.05)in hyperoxia than in air group. Relative abundance of Notch2,Notch4 and Delta4 mRNA in two groups were similar to the expression of their polypetides.Conclusions Prolonged 85﹪oxygen exposure resulted in abnormal expressions of Delta4 and Notch2,Notch4, which is likely to lead to the pathogenesis of hyperoxic lung injure espiacially in lung microvascular development In preterm rats.