The Mechanism Study Of Abnormal Differentiation Of Neural Precursor Cells In The Hippocampus Mediated By Interleukin-1? In Sepsis Neonatal Rats

Background:Neonatal sepsis may cause lasting neurological disorders in neonates.During perinatal period,the nervous system of neonate is still at developmental stage with the incomplete blood brain barrier,so serious infection contributes to neuronal inflammation leading to abnormal differentiation of neural precursor cells(NPCs),and subsequent disorder of neurogenesis,axonal and synaptic lesions.It might be one of the reasons for neuronal dysfunction induced by neonatal sepsis,however the molecular mechanism is still unclear.It is well documented that the Notch signaling is involved in proliferation and differentiation of NPCs.This study aimed to explore whether IL-1? would affect the lineage fate of hippocampal NPCs in the course of differentiation and,if so,whether this is via the Notch signal pathway.Methods:Sprague-Dawley rats at postnatal day 1(P1)were intraperitoneally injected with lipopolysaccharide(LPS)or PBS buffer as the matching control Immunofluorescence labeling and Western blot analysis were performed to assess the expression of IL-l? and its receptor IL-1R1 and the development of pro liferating and differentiated cells in the hippocampus at different time points after LPS administration Primary cultures of neural progenitor cells(NPCs)from P1 rats hippocanpus were also prepared to determine the effect of IL-1? on the differentiation of NPCs as well as the possible involvement of the Notch signaling pathway in the process.Results:The protein expression of IL-1? and its receptor IL-1R1 were upregulated at 1 and 3d,but it returned to normal level at 7d after LPS treatment compared with control.We examined the non-radial stem cells,neuroblasts or immature neurons,mature neurons,astrocytes and oligodendrocyte precursor cells(OPCs)labeled by their respective markers SOX2,DCX,NeuN,GFAP and NG2 by Western blot.The protein expression of SOX2,DCX,NeuN and NG2 were decreased while that of GFAP was increased in the hippocanmpus at 1 and 3d after LPS injection;however,the expression of GFAP was elevated until 28d.In vitro,IL-1R1 was expressed on IL-1?,treated and untreated NPCs.IL-1? treatment significantly upregulated IL-1R1 mRNA and protein expression which could be counteracted by IL-1Ra.Immunofluorescence showed that IL-1?exposure for 24 hours induced a decrease in neurospheres proliferation compared with controls,as assessed by co-localization of nestin and Ki-67.This was reversed by treatment with IL-1Ra.After the differentiation of NPCs for 4 d in vitro,Immunofluorescence and Western blot showed that administration of IL-1? upregulated the expression of GFAP and NG2;however,DCX and NeuN expression was decreased.In addition,the phenotype of neurons exposed to IL-1? was altered bearing fewer and shorter neurites(Fig.7 B,E)when compared with controls.Moreover,Western blot or real-time RT-PCR showed that IL-1? increased the expression of NICD,Hesl and Hes5 but repressed that of Ngnl and MashI,the phenomenon that was reversed by the y-secretase inhibitor,DAPT.DAPT and IL-lRa also counteractd the expressioin of DCX,NeuN,GFAP and NG2.Conclusion:The results suggest that immune cells-derived IL-1? engaging with IL-1R1 may repress the differentiation of hippocampal NPCs into neurons,and to adopt an alternative glial fate through activation of Notch signaling pathway in sepsis neonatal rats.It may be a possible mechanism that abnormal differentiation of NPCs in the hippocampus was mediated by interleukin-1? in neonatal sepsis.