Role Of Notch Pathway On Hyperoxia-Induced Immature Brain Damage In Newborn Mice

PART ONE:THE ACTIVATION OF NOTCH PATHWAY IN IMMATURE BRAIN DAMAGE INDUCED BY HYPEROXIAObjective:To detect the activation of Notch pathway in immature brain damage induced by hyperoxia exposure.Methods:3-day-old wild-type C57BL/10J mice were subjected to hyperoxia(90%) for 48 h, and devided into control group(A) and hyperoxia group(H). The mice’s body/brain weight of both groups were measured at P3, P5, P12, P28; co-expression of Caspase-3 and NG2 were observed by double-labelling immunofluorescence technique; expression of NICD and Hes1 at mRNA level were detected by quantitative real-time PCR(qRT-PCR).Results:The body/brain weight decreased significantly in H group compared with A group on P5 and P12 (P<0.05). Though the body weight has no difference between both group on P28, the brain weight of H group mice were still lower than that of A group (P<0.05). Immunofluorescence showed more co-expression of Caspase-3 and NG2 in H group compared with A group. Meanwhile, the expression of NICD and Hes1 were both upregulated in H group compared to A group (P<0.05).Conclusion:Notch pathway may be involved in the dysplasia of body/brain weight and the apoptosis of OPCs induced by hyperoxia in newborn mice.PART TWO:THE CHANGE OF IMMATURE BRAIN DAMAGE INDUCED BY HYPEROXIA AFTER THE DAPT INHIBITION OF NOTCH PATHWAYObjective:To observe the change of immature brain damage induced by hyperoxia after the DAPT inhibition of Notch pathway.Methods:3-day-old wild-type C57BL/10J mice were subjected to hyperoxia (90%) for 48 h, and divided into control group(A), hyperoxia group(H), DAPT group(DA) and DAPT+hyperoxia group(DH). DA and DH group were pretreated with DAPT(10mg/kg, i.p) once before hyperoxia exposure. Expression of NICD and Hesl at mRNA level were detected by qRT-PCR. The mice’s body/brain weight of both groups were measured at P3, P5, P12 and P28; Expression of NG2 and MBP were detected by double-labelling immunofluorescence technique to observe the maturity of OL at P12. Morris water maze was used to evaluate the ability of spatial learning and memory at P28.Results:1. The expression of NICD and Hesl mRNA decreased significantly in DH group compared with H group (P<0.05).2. Pretreatment with DAPT reduced the body/brain weight decrease induced by hyperoxia exposure (P<0.05).3. There were more expression of NG2 and less expression of MBP in H group compared with A group. However, the above change reduced significantly with the pretreatment of DAPT.4. The time and the distance of escape latency of H group after training were longer than that of A group (P<0.05), and in target quadrant and the number of times through virtual platform were smaller compared to that of the control (P<0.05). What’s more, indexes mentioned above were significant improved in DH group (P<0.05).Conclusion:Notch pathway was involved in the pathological process of immature brain damage induced by hyperoxia exposure, which is characterized by increased number of apoptotic OPCs, dysmaturity of OPCs, and the poor ability of spatial learning and memory. Inhibiting the activation of Notch pathway by DAPT reduced the histology and behavioral change induced by hyperoxia in immature brain.