The Role Of Interleukin1in The Formation Of Cortical Dysplasia

Cortical dysplasia (CD) is one of the most common causes in children withrefractory epilepsy. The typical pathological changes in CD are disorders ofcortical plate layer structural and ectopic neurons. Neuronal migration plays animportant role in the formation of lamellar structure in the cortex and aberrantneuronal migration may thus contribute to the development of CD.A majority of studies aimed to reveal the underlying mechanisms of corticaldysplasia have focused on genetic factors. For example, certain gene mutation,such as Lis1or DCX mutation, may play a crucial role in the formation of CD.However, established gene mutations can not explain the underlying etiology ofall patients with CD. Moreover, there is no such effective gene therapy for CD atpresent. Thus, further investigations of other factors associated with aberrantneuronal migration may provide new clues for the prevention and treatment ofCD.Our group had focused on the relationship between inflammation andaberrant neuronal migration for a long time. We found that interleukin1beta (IL-1β), which is a pro-inflammatory cytokines, plays an important role in theaberrant neuronal migration after status epilepticus (SE). What’s more, IL-1βplays an attractive effect on the migration of cultured cortical neurons in vitro.These results suggested that IL-1may be involved in aberrant neuronal migrationin CD formation. It had been reported that the expression of IL-1and IL1R1wereelevated in the brain section removed from the CD patients. However, the role ofIL-1in the formation of CD is not clear.ObjectivesThe purpose of this study was to confirm the expression pattern of IL-1indeveloping cortex and observe the effect of lamellar structure and neuronalmigration when the IL1R1, the functional receptor of IL-1β,was down-regulated.Then, we investigated the mechanism of IL-1βinvolved in neuronal migrationby observing the effect of radial glia structure, the proliferation of newbornneurons, and the morphology of neural cells when the IL1R1was down-regulated.Finally, the possible downstream signal pathway was discussed.MethodsWe established the animal model of CD by giving overdose gama-irradiationto E16pregnant rats, using the normal pups and normal adult rats as control.RT-PCR and western were used to examine the expression pattern of IL-1βandIL1R1in developing cortex. Specific siRNAs, in utero eletroporation,immunohistology, and western were employed to investigate the effect ofneuronal migration and the possible mechanism. Transwell assay was used toconfirm whether RhoA signal pathway was involved in the downstreammechanism. Results1. There were10%pups in CD group underwent the spontaneous seizuresafter their mothers received overdose γ-irradiation at E16. Other pups appearedto be more excited than the normal pups and normal adult rats. The lamellarstructure in the CD group was in chaos and the cortex became thinner than thenormal pups. Neural nodes can be found in the II/III layers, CA2/CA3region insome rats. These results revealed that we established the CD animal modelsuccessfully.2. The mRNA level of IL-1βin CD was higher than that in normal pups atthe same period, and that in normal adult rats from E17-P7. As time passed by,the expression level of IL-1βdeclined in CD group and normal pups. There wasno significance between CD group and normal adult rats at E28. The westernresults showed that the IL-1βproteinis higher in CD group than that in normalpups and normal adult rats at P0.IL1R1can be found expressed in all the three groups. The expression patternof IL1R1is similar to IL-1β. As time passed by, the mRNA level of IL-1R1declined in CD group and normal pups. There is no significance of IL1R1mRNAlevel among the three groups at P7. However, unlike IL-1β，the expression ofIL1R1protein has no differences in the three groups.3. The western results suggested us that the siRNA plasmids andover-expression plasmids of human IL1R1were established successfully. Afterwe down-regulated the expression of IL1R1in neural precursors by in uteroelectroporation，the migration of newborn neurons appeared to be obviouslyabnormal. The newborn neurons should have migrated to the II/III layers incortex at that stage, but most of them (about62%) remained in ventricular zone (VZ)、subventricular zone（SVZ）和white matter（WM）at P5. This phenotypecan be rescued by over human IL1R1plasmids which can not be interfered by thesiRNA sequence。Most of neurons (about84%) can migrate to the II/III layers inthe cortex as usual.4. We found that down-regulated IL1R1had only slight effect on thelamellar structure，while no effect on the structureof radial glia cells, theproliferation of newborn neurons, and the morphology of neural cells when theIL1R1was down-regulated. After examining the IL-1β expression in differentlayer of cortex by Western, we found that the distribution of IL-1βas a ladderpattern, which suggested that the IL-1β might be involved in the aberrantmigration in CD by affecting the direction of migration.5. The result of Transwell shows that IL-1βhad an attractive effect on thecortical neurons in vitro, However, clostridium difficile Toxin B(Cdt B), ainhabitator of RhoAsignal pathway, had a negtive effect on the phenotype above.These results suggested that IL-1β may be involved in the aberrant migration inCD by RhoA signal pathway.ConclusionOur results indicate that abnormal expression of IL-1β in developing cortexmay affect the direction of neuronal migration through RhoA pathway signalling.This study also suggests that inflammation ralated aberrant neuronal migrationmay be a common cause of CD. The data may provide us new clues for theprevention and treatment of CD.