The Research Of The Signal Transduction Pathway In Brain Inflammatory Response Modulated By Alzheimer’s Disease Related Receptor TREM2

Alzheimer’s Disease(AD)is a chronic and progressive neurodegenerative disorder caused by a variety of factors,which is characterized by extracellular senile plaques(SP)and intracellular neurofibrillary tangles(NFT).Due to the sharp increase in the number of people suffering from AD,the unknown etiology,the unaddressed pathological mechanism,and the ineffective medicine to cure AD,individuals,families,and society will face the overwhelming economic burden.Neuroinflammation is widely considered to be one of the main causes of AD.Microglia,the immune cells in the central nervous system(CNS),monitor the homeostasis of the microenvironment,participate in synaptic plasticity,and release the neurotrophic factors and inflammatory factors.Studies have shown that the inflammatory response in the brain of AD patients is significantly higher than that in normal people,and there are a large number of overactivated microglia.Inflammatory cytokines released by activated microglia cells surrounding the senile plaques damage the surrounding neurons and aggravate the cognitive impairment.Therefore,understanding the mechanism of microglia in the process of neuroinflammation may provide a new therapeutic target for AD.Genome-wide association studies have shown that the triggering receptor expressed on myeloid cells 2(TREM2),as an AD risk factor,is second only to the APOE4.R47H,the TREM2 variant,increases the risk of AD.TREM2,a transmembrane receptor selectively expressed on the surface of myeloid cells,mainly expressed in microglial cells in the central nervous system and involved in microglial cell function such as proliferation,phagocytosis,survival,and cytokine release.The ligands of TREM2 include phospholipids,beta-amyloid,apolipoprotein E,and apoptotic neurons.The interaction of ligand and TREM2 can activate signaling adaptor protein DAP 12 to regulate the downstream signaling molecules inducing a series of intracellular reactions.PI3K/AKT signaling pathway,downstream pathway of TREM2,is involved in microglial cell activation and the expression of inflammatory cytokines.FoxO3a,a downstream molecule of AKT,is also involved in microglia activation.Recent research has shown that Punicalagin(PU)inhibits the release of inflammatory cytokines in macrophage by inhibiting the FoxO3a/autophagy signaling pathway.Thus,we hypothesized that TREM2 regulates neuroinflammatory response in microglia through the PI3K/AKT/FoxO3a signaling pathway.The experiment to verify the hypothesis is divided into two parts:in vivo and in vitro.(1):TREM2 regulates the pro-inflammatory response via the PI3K/AKT/FoxO3a axis in vivo.Firstly,the expression of pro-inflammatory cytokines and the neuroinflammation-associated factor was used to evaluate the neuroinflammation of the 5xFAD mouse model at 6-7 months old.Secondly,the adeno-associated virus was injected into the hippocampal DG region of 5xFAD mice using stereotaxic technology to inhibit the expression of TREM2.Then,the effect of TREM2 deficiency on the levels of inflammatory cytokine and the PI3K/AKT/FoxO3a signaling pathway was investigated in 5xFAD mice by western blot,qPCR,and immunofluorescence to identify that the defect in TRME2 inactivated the PI3K/AKT/FoxO3a signaling pathway.(2)TREM2 regulates the pro-inflammatory response via the PI3K/AKT/FoxO3a axis in vitro.Firstly,the plasmid of overexpressing TREM2 was transfected into BV2 cells,while western blot and qPCR were used to detect its effect on the inflammatory response and PI3K/AKT/FoxO3a signaling pathway.Then,FoxO3a nuclear translocation and microglia phenotype affecting by TREM2 was detected by immunofluorescence.As a whole,the results of this study indicate that TREM2 inhibits the levels of inflammatory cytokine by activating the PI3K/AKT/FoxO3a signaling pathway and inactivating FoxO3a.This study provides a new pathological molecular mechanism of TREM2 in neuroinflammation and a potential therapeutic target for AD.