Study On The Acetylation Mechanism Of Smilagenin In The Treatment Of Alzheimer’s Disease

Brain-derived neurotrophic factor（BDNF）is a multifunctional neurotrophic factor which can regulate synaptic plasticity of neurons and play an important role in the growth and development of neurons.Smilagenin（SMI）,a traditional Chinese medicine for nourishing yin,is a kind of small steroidal saponins extracted from Rhizoma Anemarrhenae.Previous studies have shown that SMI can up-regulate the expression of BDNF in Aβintoxicated SH-SY5Y cells,but its mechanism is still unclear.Based on this,the expression and mechanism of BDNF in AD model regulated by SMI are discussed.In this study,APP/PS1 double transgenic mice were used as AD models in vivo.To study the neuroprotective effect of SMI on AD model,we firstly performed open field experiments,novel object recognition,Y maze and water maze experiments and observed that SMI could enhance the learning and memory ability of APP/PS1 mice as well as improve their cognitive impairment.Pathological results showed that SMI reduced the deposition ofβ-amyloid plaques in cortex and hippocampus of AD mouse models and promoted the expression of BDNF m RNA.Meanwhile,H₂O₂-injured SH-SY5Y cells and N2a/APP695 cells were chosen as AD cell models in vitro.We found SMI treatment could effectively inhibit the secretion of Aβ_1-42 in N2a/APP695 cells upregulate the decreased BDNF m RNA level.The mechanism of BDNF regulation by SMI was further explored.WB detection showed that SMI pretreatment could increase the level of H3AC and H4AC in AD model.The acetylation level of histone was mainly regulated by HDACs and HAT,WB showed that SMI could significantly increase the expression of P300 in AD model,but had no obvious effect on HDAC1/2/3 of AD mice.However,SMI could inhibit the activity of HDACs.Chromatin immunoprecipitation was employed to detect the acetylation level of histone H3 and H4 at the promoter sites of BDNF transcriptsⅠ,ⅡandⅣ.It was proved that SMI could increase the level of H3AC and H4AC at the promoter of BDNF gene transcriptomeⅣin AD model.To sum up,SMI can promote the histone acetylation level in the promoter region of BDNF gene by increasing the expression of P300 protein,further promoting the transcription and expression of BDNF gene and acting as neuron protection.It provides an important theoretical basis for the study of SMI in the treatment of Alzheimer’s disease.