Regulation Of LRP6 Expression By HDAC2 And Its Role In The Antagonism Of Gamma-aminobutyric Acid Against Alzheimer’s Disease

Objective: Alzheimer’s disease(AD)is a central neurodegenerative disorder characterized by extensive brain atrophy memory dysfunction and loss of cognitive functions.Up to now,the pathogenesis of AD is still unclear.The deposition of Beta-amyloid protein(Aβ)in the cerebral cortex and the hippocampus is the early pathological features of AD.The abnormal aggregation of Aβ in the brain and the destruction of neurons and synapses are the central link to induce memory and cognitive deficits in AD patients.Postsynaptic density protein 95(PSD95)is closely related to synaptic function,but its expression was low in AD hippocampus.Therefore,up-regulation the expression of PSD95 is expected to become one of the important targets for prevention and treatment of AD.Wnt/β-catenin signaling can up-regulate the expression of PSD95 and is closely related to synaptic plasticity.Wnt/β-catenin pathway mediated by Low density lipoprotein receptor-related protein 6(LRP6)is inhibited in the hippocampus of AD patients.It is reported that,up-regulation of LRP6 expression can enhance the Wnt/β-catenin signaling pathway in AD and up-regulate the expression of PSD95.Another study has shown that the Wnt/β-catenin signaling pathway is regulated by histone acetylation modification,but the specific mechanism remains unclear.HDAC2,a histone deacetylase,is considered to be the most closely related to AD.Whether HDAC2 can affect Wnt/β-catenin signaling by regulating LRP6 remains to be verified.Gamma-aminobutyric acid(GABA)is the most important inhibitory neurotransmitter in brains of mammals,as well as a functional food factor,which can inhibit HDAC2.Previous studies have confirmed that GABA has antagonistic effect on AD.Through vivo and vitro experiments,the study investigated whether GABA regulates the expression of LRP6 by inhibiting HDAC2,thereby enhancing Wnt/β-catenin signal,up-regulating PSD95 expression,and ultimately delaying the pathogenesis of AD.Methods: APP/PS1 transgenic AD model mice at 5 months of age were randomly divided into AD and AD+GABA groups.Wild-type mice were divided into WT and WT+GABA groups.10 mice in each group,half male and half female.Mice in AD+GABA and WT+GABA groups were given distilled water containing 0.1%GABA,and mice in AD and WT groups were given distilled water.After 6 months,mice in each group were given open-field experiment to identify behavioral changes.The mice were dissected after anesthesia and the brain tissue was dissected.The deposition of Aβ in hippocampus was detected by sulfurin T staining.Utilizing the RT-q PCR and WB methods to detect the levels of HDAC2,LRP6,β-catenin and PSD95.Human neuroblastoma cell lines(SH-SY5 Y cells)were cultured in vitro.SH-SY5 Y cells were treated with 20μM beta-amyloid protein(Aβ)and 20 n M GABA,set up a control group at the same time.Utilizing the RT-q PCR and WB methods to detect the levels of HDAC2,LRP6,β-catenin and PSD95.Transfect small interfering RNA(si RNA)to silence HDAC2 gene in SH-SY5 Y cells,set up a control group at the same time,utilizing the RT-q PCR and WB methods to detect the levels of LRP6,β-catenin and PSD95.Transfect si RNA to silence β-catenin gene in SH-SY5 Y cells,set up a control group at the same time,utilizing the RT-q PCR and WB methods to detect the level of PSD95.Results:1.Compared with WT group,the upright times,modifying times and moving distance of mice in AD group were reduced(P<0.01 or P<0.05).Compared with AD group,the upright times,modifying times and moving distance of mice in AD+GABA group were increased(P<0.01 or P<0.05).2.The number of Aβ plaques in hippocampus of mice in AD group was more than that in WT group(P<0.01);the number of Aβ plaques in hippocampal tissue of mice in AD+GABA group was less than that in AD group(P<0.01).3.Compared with WT group,the expressions of PSD95,LRP6 and β-catenin in hippocampus of mice in AD group were decreased(P<0.01),while the expression of HDAC2 was increased(P<0.01);compared with AD group,the expressions of LRP6,β-catenin and PSD95 in the hippocampus of mice in AD+GABA group were increased(P<0.01),while the expression of HDAC2 was decreased(P<0.01).4.Compared with the control group,the expressions of LRP6,β-catenin and PSD95 in SH-SY5 Y cells of Aβ treatment group were decreased(P<0.01),and the expression of HDAC2 was increased(P<0.01).GABA intervention can reverse the above changes.5.Compared with the control group,the expressions of LRP6,β-catenin and PSD95 in SH-SY5 Y cells of si-HDAC2 group were increased(P<0.01).6.Compared with the control group,the expression of PSD95 in SH-SY5 Y cells of si-β-catenin group was decreased(P<0.01).Conclusions: The mechanism of GABA antagonizing AD may be related to its inhibition of HDAC2,up-regulation of LRP6 expression,enhancement of Wnt/β-catenin signal transduction and up-regulation of PSD95 expression.