The Mechanism Of Astrocytes In Olfactory Bulb Neurogenesis Injury Induced By Diesel Exhaust

Background and objectiveAir pollution has been associated with occurrence and development of neurodegenerative diseases and mental disorders,the olfactory bulb(OB)injury is proposed to be one of early symptom and biomarkers of these diseases.Diesel exhaust(DE)as the main source of air pollution has been found to impaired the olfactory bulb.In adult,the structure and function of olfactory bulb can be maintained with continuous neurogenesis in rostral migration stream(RMS).In RMS astrocytes ensheath chains of neuroblasts control proliferation and migration to the OB,diferentiate into interneurons.Whether DE inhalation induces the OB damage by damaging RMS and the role of astrocytes in RMS in OB damage triggered by DE inhalation are still unclear.Therefore,this study aimed to investigate how DE inhalation induces the OB toxicity by damaging RMS and the action mechanisms of astrocytes in the RMS using in vivo and in vitro models.MethodsA total of 40 C57BL/6 mice were randomly divided into four groups with exposure to DE by systemic inhalation:Control group(filtered air),low exposure group(750μg/m~3),medium exposure group(1500μg/m~3)and high exposure group(3000μg/m~3).The mice inhalation exposed to DE was performed 1h/d for 28 days.HE staining was performed to observe after DE exposed pathological changes in OB tissue.In situ end labeling(Td T-mediated d UTP nick End labeling,TUNEL)staining was used to observe the apoptosis in the OB.Immunofluorescence staining with doublecortin(DCX)was used to observe the effect of DE exposure on the neuroblasts in the RMS,the Ki67 was used to detect the effect of DE exposure on the neurons proliferation in RMS.RNA-Seq was exhibited to explore the mechanisms of OB damage caused by DE.The astrocyte activation in RMS were observed by immunofluorescence staining with glial fibrillary acidic protein(GFAP).The changes of DLK1(Delta-like 1 homolog)factors secreted by astrocytes were studied by immunofluorescence.A model of primary astrocytes and N2A cells in vitro was constructed,cell proliferation and migration were detected by CCK8 and cell scratch test.DLK1 factors in the supernatant of the conditioned medium was detected by enzyme-linked immunosorbent assay(ELISA).At the same time,DLK1 protein was added to verify that DE affects neuronal proliferation and migration by interfering with DLK1 secretion from astrocytes.Results1.Structural damage of OB in mice caused by DE exposure,the interneurons in the granule cell layer of olfactory bulb became disordered;and the number of periglomerular cells in the glomerular layer of olfactory bulb decreased,neuronal apoptosis increased.2.DE exposure results cells disordered in RMS in mice,the number of neuroblast was decreased and the arrangement was disoriented,and the function of the RMS was inhibited.3.DE exposure results TNF-αinflammatory pathway activated in mice RMS,astrocytes were activated in RMS,and the morphology changed from resting state to activating.4.DE exposure decreased the expression of DLK1 in RMS and SVZ.5.In the co-culture model of primary astrocytes and N2A cells in vitro,the DE treatment Astrocytes conditioned medium decreased the proliferation ability and migration of N2A cells.6.Astrocytes were exposed to DE for 24 h,the expression of DLK1 protein was down and the secretion of DLK1 factor in the culture supernatant was decreased.Meanwhile astrocytes were activated and the content of TNF-αand IL-6 in the supernatant of the medium was significantly higher.The intervention experiments confirmed that reduced astrocyte DLK1secretion induced by DE exposure inhibits proliferation and migration of N2A cells.ConclusionDE exposure decreased the secretion of astrocyte DLK1 factor in mouse RMS,causing RMS structural damage and neuronal proliferation and migration dysfunction,while DE exposure led to astrocyte activation and inhibition of RMS neurogenesis,eventually lead to olfactory bulb structural damage.In the current study,we investigates that the abnormal structure and function of RMS play a key role in DE induced OB toxicity,moreover the inhibition of DLK1 secretion by astrocytes are involved in DE-induced RMS damage and provide a new direction for the study of the mechanism of DE induced OB toxicity.