Effects Of Periodontitis On β-Amyloid Deposition In Alzheimer’s Disease Mice And Its Mechanism

Objective:Periodontitis is a chronic inflammation of periodontal tissue caused by bacterial plaque infection.The periodontal pathogen Porphyromonas gingivalis（P.gingivalis）can not only destroy periodontal support tissues,but also participate in the interaction between periodontitis and systemic diseases.Alzheimer’s disease（AD）is a chronic progressive neurodegeneration characterized by the deposition of amyloid-β（Aβ）protein in the hippocampus or cortex to form amyloid plaques.Recent studies have shown that periodontitis is a risk factor for AD,and its mechanism has become a research hotspot.The aim of this study was to investigate the effects of P.gingivalis-induced periodontitis on Aβdeposition in the brain,and to provide new insights into how periodontitis aggravates the development of AD.Methods:Clinical sample collection was used to detect the difference of Aβlevels in inflammatory and non-inflammatory gingival tissues.Gingival tissues were collected from patients with periodontitis and periodontal healthy individuals.The levels of Aβin gingival tissues was detected by IHC.And immunofluorescence（IF）was used to detect Aβlevels in macrophages of gingival tissues.We examined the changes of learning and memory ability and the difference of Aβdeposition in brain tissue between periodontitis model and control AD mice.Morris water maze（MWM）test was performed in APP/PS1mice with P.gingivalis-induced and silk ligature periodontitis and control APP/PS1 mice to detect the changes in learning and memory ability.Immunohistochemistry staining（IHC）was used to detect the Aβlevels in the brain after the mice were sacrificed.We also tested whether Aβinjected into the mouse gingival tissues could enter the brain.C57BL/6J mice were injected with 5-FAM-Aβ_1-42 oligomers or PBS into the gingiva and the fluorescence direction was observed by animal imaging system to determine whether it entered the brain at 0 min,4h and 48h.After sampling,the presence of 5-FAM-Aβ_1-42oligomers in brain tissue was observed by fluorescence inverted microscope.Results:1.The IHC results showed that Aβlevels were increased in the inflammatory gingival tissues compared with the non-inflammatory gingival tissues of the subjects.The results of IF detection of macrophages in inflamed gingival tissues showed that Aβwas highly expressed in macrophages in inflamed gingival tissues compared with non-inflamed gingival tissues.2.Compared with the control group,the escape latency time of MWM in APP/PS1 mice group with periodontitis was significantly longer（P<0.05）.The results of exploration test showed that the crossing times to platform in group with periodontitis was significantly less than that in control group（P<0.01）.The results of IHC showed that Aβplaque deposition in the brain of periodontitis group was increased.3.The results of in animal imaging showed that fluorescent labeling was detected in the brains of C57BL/6J mice 48 hours after injection of 5-FAM-Aβ_1-42oligomers into the gingival tissues compared with the control group.The frozen sections of brain tissue were further detected by immunofluorescence inverted microscope,and fluorescent labeling was detected in the brain tissue sections of mice injected with 5-FAM-Aβ_1-42oligomers.Conclusions:High levels of Aβin inflammatory gingival tissues may enter the brain and aggravate Aβdeposition,thereby aggravating Alzheimer’s disease.