Chronic Periodontitis and Alzheimer Disease: A Putative Link of Serum Proteins Identification by 2D-DIGE Proteomics

Xianfang Rong; Liping Xiang; Yanfen Li; Hongfa Yang; Weijian Chen; Lei Li; Defeng Liang; Xincai Zhou

doi:10.3389/fnagi.2020.00248

Chronic Periodontitis and Alzheimer Disease: A Putative Link of Serum Proteins Identification by 2D-DIGE Proteomics

Front Aging Neurosci. 2020 Aug 21:12:248. doi: 10.3389/fnagi.2020.00248. eCollection 2020.

Authors

Xianfang Rong¹, Liping Xiang¹, Yanfen Li¹, Hongfa Yang², Weijian Chen¹, Lei Li¹, Defeng Liang¹, Xincai Zhou¹

Affiliations

¹ Department of Stomatology, Shenzhen Baoan Women's and Children's Hospital, Jinan University, Shenzhen, China.
² Department of Cardiology, The Second Affiliated Hospital of the University of South China, Hengyang, China.

Abstract

Increasing evidence indicates Chronic Periodontitis (CP) is a comorbidity of Alzheimer's disease (AD), which is the most common form of age-related dementia, and for the latter, effective diagnostic and treatment strategies are lacking. Although inflammation is present in both diseases, the exact mechanisms and cross-links between CP and AD are poorly understood; and a direct association between the two has not been reported. This study aimed to identify a direct serum proteins link between AD and CP. Two-dimensional differential in-gel electrophoresis was employed to analyze serum samples from 12 CP patients and 12 age-matched controls. Furthermore, to determine the molecular link between CP and AD, neuroblastoma SK-N-SH APPwt cells were treated with 1 μg/ml of lipopolysaccharide from Porphyromonas gingivalis (P.g-LPS). Ten differentially expressed proteins were identified in CP patients. Among them, nine proteins were up-regulated, and one protein was down-regulated. Of the 10 differentially expressed proteins, five proteins were reportedly involved in the pathology of AD: Cofilin-2, Cathepsin B, Clusterin, Triosephosphate isomerase, and inter-alpha-trypsin inhibitor heavy chain H4 (ITI-H4). Western blotting indicated significantly higher expression of Cofilin-2, Cathepsin B, and Clusterin and lower expression of ITI-H4 in the CP group than in the Control group. The serum concentration of Cathepsin B has a good correlation with MMSE scores. Moreover, the protein level of Cathepsin B (but not that of ADAM10 and BACE1) increased significantly along with a prominent increase in Aβ_1-40 and Aβ_1-42 in the cell lysates of P.g-LPS-treated SK-N-SH APPwt cells. Cathepsin B inhibition resulted in a sharp decrease in Aβ_1-40 and Aβ_1-42 in the cell lysates. Furthermore, TNF-α was one of the most important inflammatory cytokines for the P.g-LPS-induced Cathepsin B upregulation in SK-N-SH APPwt cells. These results show that CP and AD share an association, while Cathepsin B could be a key link between the two diseases. The discovery of the identical serum proteins provides a potential mechanism underlying the increased risk of AD in CP patients, which could be critical for elucidating the pathophysiology of AD.

Keywords: Alzheimer’s disease; Cathepsin B; biomarker; chronic periodontitis; two-dimensional differential in-gel electrophoresis.