Abstract:

Objective To investigate the effect of Porphyromonas gingivalis (P. gingivalis) on Th17/Treg imbalance and vascular endothelial function in ApoE^-/- mice. Methods Eight-week-old ApoE^-/- mice were inoculated orally with P. gingivalis every other day and received high-fat diet for 8 weeks. The alveolar bone loss was assessed by Micro-CT and the oral microflora of mice was analyzed by 16S rRNA sequencing technology. HE staining and oil red O staining were used to detect plaque formation in ApoE^-/- mice. The total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels of mice were detected by biochemical detection technology. Real-time quantitative PCR (qRT-PCR) and immunohistochemistry (IHC) were used to detect the indicators of endothelial injury in the model aortic plaques, including vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), matrix metallopeptidase (MMP)-2 and MMP-9. The relative proportions of Th17 and Treg in aortic plaque and spleen were detected by IHC, qRT-PCR and flow cytometry, including interleukin-17 (IL-17), retinoic acid related orphan receptor γt (RORγt) and forkhead box P3 (Foxp3). Results In ApoE^-/- mice infected with P. gingivalis, the severity of alveolar bone loss was increased (P<0.01); the diversity of oral microbiota was decreased (P<0.05), and the composition of oral microbiota was changed. The proportion of atherosclerotic plaque area was increased (P<0.01), paralleled by elevated serum levels of TG, TC and LDL-C (P<0.05), alongside a significant decrease in HDL-C (P<0.01). Aortic plaques exhibited upregulated protein expression of VCAM and ICAM as well as heightened mRNA levels of ICAM, VCAM, MMP-2 and MMP-9 (P<0.05). The levels of IL-17 related protein and RORγt transcriptional activity in aortic plaque were increased (P<0.01), while the levels of Foxp3 related protein and gene were decreased (P<0.01). The ratio of Th17/Treg cells in spleen was imbalanced (P<0.05). Conclusion Periodontitis caused by the imbalance of the oral flora of ApoE^-/- mice induced by P. gingivalis can cause Th17/Treg imbalance in aortic plaque and exacerbate the endothelial dysfunction during atherosclerosis.

Key words: Porphyromonas gingivalis, atherosclerosis, imbalance of Th17/Treg, endothelial dysfunction, oral bacterial dysbiosis