Neuron Secrete Exosomes Containing MiR-9-5p To Promote Polarization Of M1 Microglia In Depression

Background:Depression(MDD)is a common but serious psychological disorder,and the failure of some patients to respond effectively to known treatments may be due to a lack of mechanistic understanding of MDD pathogenesis and progression.Neuroinflammation is currently an important component mechanism in the development of MDD.Exosomal transfer of MDD-associated microRNAs(miRNAs)from neurons to microglia might exacerbate neuronal cell inflammatory injury.This study intends to investigate the etiological role and potential mechanisms by which neuronal cells transmit core microRNAs by virtue of shuttle carrier exosomes(Exo)to regulate microglia polarization and thereby influence the neuroinflammatory state.Methods:Exosomes were identified using transmission electron microscopy,protein immunoblot analysis and NTA particle size analysis.Exosomes of serum from depressed patients were labeled in vitro to verify the uptake capacity of BV2 and its polarizing effect.Sequence identification revealed differentially expressed miRNAs in serum exosomes from depressed patients and healthy subjects.qRT-PCR was used to further validate and screen for target miR-95p.A co-culture system was established between PC12 and BV2 cells,and it was observed that BV2 microglia internalized PC 12 neuronal cell-derived exosomes,while miR-9-5p was successfully transferred.The regulatory role of miR-9-5p on microglia polarization.The target gene of miR-9-5p was predicted by TargetScan target gene prediction database,and the target target gene SOCS2 was screened.qRT-PCR,WB and rescue assays were used to investigate the interaction between miR-9-5p and the target gene SOCS2.Immunofluorescence assay was used to study the effect of polarized BV2 cells on PC12 damage.Adeno-associated virus(AAV)-mediated overexpression of miR-9-5p polarized microglia toward the M1 phenotype and exacerbated depressive symptoms in chronic unpredictable mild stress(CUMS)mouse mode.Results:1.MDD patient-derived serum and serum exosomes promoted M1 polarization of microglia similarly,but the effect of serum exosomes was more pronounced.Exosomes from depressed cell models induced M1 cell polarization in vivo.2.Sequencing analysis and qRT-PCR verified that miR-9-5p expression was increased in serum exosomes from depressed patients.miR-9-5p was identified as a potential functional exosome vector.3.PC12 cells promoted M1 polarization of BV2 microglia via exosomal transport of miR-95p.4.miR-9-5p was upregulated in microglia and promotes M1 polarization in vitro and in vivo.5.miR-9-5p targets and regulates SOCS2,activated STAT3 pathway and increased M1 polarization.6.M1 polarized microglia resulted in the accumulation of PC 12 cell damages.Conclusion:Our study demonstrated that miR-9-5p was transferred from PC12 cells to BV2 microglia in an exosomal manner,which targetd SOCS2 and induced JAK/STAT3 pathway activation,thereby promoting M1 polarization and further neuronal damage.The regulation of microglia polarization by miR-9-5p was a key factor promoting the occurrence and development of MDD,and its expression and secretion might be novel therapeutic targets for MDD.