The Mechanism Study Of Interleukin-1β Mediated By E3 Ubiquitin Ligase Siah1 In Synaptic Transmission Disorder Of Hippocampus In Sepsis Neonatal Rats

Neonatal sepsis is one of the leading causes of neonatal death.The specific molecular mechanism of cognitive dysfunction in the late stage of neonatal sepsis remains unclear.Synaptic transmission in the hippocampus is closely related to learning and memory functions,in while multiple synaptic proteins are involved.Damage to synaptic proteins and disruption of synaptic morphological structures can affect normal synaptic transmission.E3 ubiquitin ligase Siahl has been shown to be closely related to synaptophysin(Syn).Interleukin-1β(IL-1β)plays an important role in the relationship between neuroinflammation and cognitive dysfunction.Objective:To confirm the presence of synaptic transmission disorders is in the hippocampus of sepsis animal models,including synaptic damage and synaptic destruction.At the same time,inflammation occuring in the hippocampus to release IL-1β;IL-1β has been shown to cause abnormal expression of synaptic proteins in vitro.The expression level of Syn can be down-regulated by p-ERK which leads to increased expression of Siahl.Methods:Sprague-Dawley(SD)pups(Pld)were randomly divided into control group and sepsis model group.The sepsis model was induced by intraperitoneal injection of SD Pld pups with 1 mg/kg LPS,and the control group was intraperitoneally injected with an equal dose of 0.01 M phosphate buffer(PBS).The expression of IL-β,interleukin-1 receptor 1(IL-1R1),interleukin-6(IL-6),tumor necrosis factor-α(TNF-α),inducible nitric oxide synthase(iNOS),and synapse-related proteins:Syn,synaptophysin-related protein-25(SNAP-25),synaptic fusion protein 1A(syntinla),post-synaptic dense-95(PSD-95),post-synaptic membrane receptor N-methyl-D-aspariate receptor(NMDAR)in the hippocampus of the control and sepsis groups at different time points were detected by Immunofluorescence staining or Western blot.Nissl staining,Golgi staining and transmission electron microscopy were used to observe the number of neurons,dendritic morphology and submicroscopic structure of hippocampal synapses.Rats of P1d were isolated from the hippocampus and cultured in primary neurons.After interleukin-1β intervention,the effects of interleukin-1β on neurons,as well as the role of ERK signaling pathway and Siahl in this process were explored.Results:This study found that the protein expression levels of IL-1β,IL-1R1,IL-6,TNF-α,and iNOS were increased in the hippocampus at 1,2,and 3 days after LPS injection.And increased protein expression of IL-1β is associated with activated microglia.By western blotting,expression levels of pre-synapse-associated proteins including Syn,SNAP-25 and postsynaptic NMDAR expression were significantly reduced in the hippocampus in septic brain.Golgi-Cox staining showed that the number of dendritic spines associated with the pyramidal neurons in the CAl region of the hippocampus was obviously decreased at 28 d after LPS administration.By electron microscopy,the number of synapse and synaptic vesicles was noticeably reduced in the CAl of hippocampus;some synaptic vesicles in the latter appeared swollen indicative of anomalous changes.In Nissl-stained sections,the number of neurons remained relatively unchanged in the CAl and CA3 of hippocampus at 7,14,and 28 days after LPS administration,when compared with their matching control.The protein expression levels of Syn and SNAP-25 in neurons were decreased and fewer dendritic branches were detected by scanning electron microscopy after IL-1βtreatment.However,this effect could be antagonized by IL-1Ra.Meanwhile,the mRNA levels of synapse-related proteins were no significant change in each group.Siahl protein expression in primary cultured neurons was increased after IL-1βadministration,while IL-IRa could antagonize the up-regulation induced by IL-1β.IL-1β administration could up-regulate the phosphorylation of ERK at 40 minutes in primary neurons.Treatment with PD98059 and ubiquitination inhibitor MG 132 alone could antagonize IL-1β-mediated increase in Siahl protein expression and decrease in Syn protein expression.Conclusions:Our study showed that inflammatory response in the hippocampus of sepsis-induced neonatal rats released interleukin-1β,which activated IL-1R signalling pathway to activate ERK phosphorylation and up-regulate Siahl expression to increase Syn ubiquitination and degradation,leading to synapses Transmission disorders,which may be a the mechanism of cognitive dysfunction in the late stage of neonatal sepsis.