Porphyromonas Gingivalis Infection Induces The Accumulation Of Amyloid β In Macrophages

Objective:Chronic periodontitis is a destructive disease of dental support tissues which originated by dental plaque,generated by host immune-inflammatory responses and other factors,its occurrence and development were closely associated with general systemic disease.The main pathogen is Gram-negative anaerobic bacteria such as Porphyromonas gingivalis(P.gingivalis).Alzheimer’s disease is one of the most common progressive neurocognitive disorder disease,the abnormal accumulation of amyloid-β(Aβ)in the brain is the most significant pathological hallmark of Alzheimer’s disease(AD).Recently,studies have found that chronic periodontitis is associated with Alzheimer’s disease.We have demonstrated that chronic peripheral exposure to lipopolysaccharide(LPS)of P.gingivalis can induce the accumulation of Aβ in the brain.The objective of this experiment is to investigate whether chronic systemic P.gingivalis infection could induce the peripheral accumulation of Aβ in inflammatory macrophages.Methods:(In vivo)Animal models:12-month-old wild female mice were randomly divided into experimental group(n=10)and control group(n=10).The mice of experimental groups were intraperitoneally injected with.gingivalis for three weeks and the mice of control groups were intraperitoneally injected with the same amount of phosphate buffer at the same time course.1.Real-time PCR was used to test Toll-like receptor 2(TLR2),interleukin-1(IL-1)p,Aγ production related protein-amyloid precursor protein(APP),cathepsin B(Cat B)and Aβ-degrading enzymes(neprilysin,insulin degrading enzyme,angiotensin-converting enzyme)mRNA expression in the liver of mice after P.gingivalis infection.2.Immunofluorescence staining was used to observe the expression of TLR2,IL-1β,APP,Cat B and Aβ in liver macrophages of mice after P.gingivalis infection.(In vitro)P.gingivalis was used to infect mouse macrophage cell line RAW264.7.3.Real-time PCR was used to test the mRNA expression of TLR2 and IL-1β at different time points of macrophages RAW264.7 after.gingivalis infection.Western blotting was used to test the expression of pro-IL-1β and IL-1β in macrophages RAW264.7 which was pretreated with inhibitor of Cat B and inhibitor of nuclear factor-kappa B(NF-κB)after P.gingivalis infection.4.Real-time PCR was used to test the mRNA expression of APP and Cat B at different time points of macrophages RAW264.7 after P.gingivalis infection.Immunofluorescence staining was used to observe the expression of Aβ in macrophages RAW264.7 which was pretreated with inhibitor of Cat B and inhibitor of NF-κB after P.gingivalis infection.5.Immunofluorescence staining was used to observe the expression of APP,Cat B and Aβ in the macrophages of gingival tissues in chronic periodontitis patients.6.Graphpad Prism7 software was used to do one-way or two-way ANOVA of experimental results.Results:1.P.gingivalis infection increased the expression of TLR2,IL-1β,APP,Cat B and Aβ in the liver macrophages of mice,but did not alter the expression of Aβ-degrading enzymes(neprilysin,insulin degrading enzyme,angiotensin-converting enzyme)..gingivalis infection induced macrophages shifted to a pro-inflammatory phenotype.2.P.gingivalis infection increased the expression of TLR2,IL-1β,APP,Cat B and Aβ in cultured macrophages RAW264.7,and Cat B and NF-κB are involved in the regulation the expression of IL-1β and Aβ.3.High expression of APP,Cat B and Aβ in the macrophages of gingival tissues in chronic periodontitis patients.Conclusion:Chronic systemic P.gingivalis infection induces the accumulation of Aβ in inflammatory macrophages by activating NF-κB signaling pathway and Cat B,suggesting that macrophages may serve as a circulation Aβ pool under conditions of periodontitis.Cat B may be a novel therapeutic target for preventing periodontitis-related AD pathological processing by reducing peripheral Aβ as well as ameliorating neuroinflammation.