ResolvinE1 and LipoxinA4 Reverse Porphyromonas gingivalis-induced Microglial Cell Activation

Objectives: Alzheimer’s disease (AD) is characterized by the accumulation of extracellular neuritic plaques mainly composed by β-amyloid peptide (Aβ) surrounded by activated microglia. Pro-resolving lipid mediators (SPMs; Resolvin E1- RvE1 and Lipoxin A4-LxA4) decreased the neuroinflammation and the formation of Aβ plaques. Porphyromonas gingivalis (Pg) was identified as a risk factor for developing Aβ plaques and Pg lipopolysaccharide (LPS) was detected in human AD brains. The aim of this study was to determine the impact of RvE1 and LxA4 on Pg- mediated microglial cell activation and Aβ phagocytosis.
Methods: BV2 murine microglia cells (2.5x10⁵) were pre-treated with 100nM RvE1, LxA4 or both for 1 hour followed by Pg-LPS or heat-killed Pg for additional 23 hours. RAW264.7 cells were used as non-microglial murine macrophages The RNA was extracted for analysis of pro-inflammatory cytokine mRNA expression levels. The cytokine release was measured by multiplex immunoassay. For Aβ phagocytosis analysis, 1ug/mL of HiLyte Fluor 488 β-amyloid was supplemented for additional 2 hours. The frequency of β-amyloid⁺ BV2 cells was analyzed by flow cytometry.
Results: The mRNA expression of TNFα, IL-1β and IL-6 was significantly increased in microglial cells in response to heat-killed-Pg compared to the Pg-LPS (1.8, 12, 15 fold changes, respectively) while non-microglial cells showed significantly higher response to the Pg-LPS than the heat-killed Pg. Pg-LPS increased the levels of TNFα, MCP-1, and GM-CSF (p<0.05). The combined treatment with RvE1 and LxA4 resulted in a reduction of cytokines to normal levels. Pg-LPS significantly decreased the Aβ-phagocytosis compared to the non-activated cells by 4-fold. The combined treatment with RvE1+LxA4 increased the Aβ-phagocytosis by 2-fold in microglia cells activated with heat-killed Pg (p<0.05).
Conclusions: Periodontal bacteria can stimulate the microglial cell function. SPMs promote Aβ-phagocytosis and restore microglial cell function suggesting a novel therapeutic strategy in controlling the neuroinflammatory process.