Related Experiment Video
Updated: Jul 26, 2025
Isolation, Processing and Analysis of Murine Gingival Cells
Published on: July 2, 2013
Microglial cell response to experimental periodontal disease
Rawan Almarhoumi1,2,3, Carla Alvarez1,2, Theodore Harris1
1Forsyth Institute, 245 First Street, Cambridge, MA, 02142, USA.
Objectives:
Microglial activation is critical for modulating the neuroinflammatory process and the pathological progression of neurodegenerative diseases, such as Alzheimer's disease (AD). Microglia are involved in forming barriers around extracellular neuritic plaques and the phagocytosis of β-amyloid peptide (Aβ). In this study, we tested the hypothesis that periodontal disease (PD) as a source of infection alters inflammatory activation and Aβ phagocytosis by the microglial cells.
Methods:
Experimental PD was induced using ligatures in C57BL/6 mice for 1, 10, 20, and 30 days to assess the progression of PD. Animals without ligatures were used as controls. Maxillary bone loss and local periodontal tissue inflammation associated with the development of PD were confirmed by morphometric bone analysis and cytokine expression, respectively. The frequency and the total number of activated microglia (CD45+ CD11b+ MHCII+) in the brain were analyzed by flow cytometry. Mouse microglial cells (1 × 105) were incubated with heat-inactivated bacterial biofilm isolated from the ligatures retrieved from the teeth or with Klebsiella variicola, a relevant PD-associated bacteria in mice. Expression of pro-inflammatory cytokines, toll-like receptors (TLR), and receptors for phagocytosis was measured by quantitative PCR. The phagocytic capacity of microglia to uptake β-amyloid was analyzed by flow cytometry.
Results:
Ligature placement caused progressive periodontal disease and bone resorption that was already significant on day 1 post-ligation (p < 0.05) and continued to increase until day 30 (p < 0.0001). The severity of periodontal disease increased the frequency of activated microglia in the brains on day 30 by 36%. In parallel, heat-inactivated PD-associated total bacteria and Klebsiella variicola increased the expression of TNFα, IL-1β, IL-6, TLR2, and TLR9 in microglial cells (1.6-, 83-, 3.2-, 1.5-, 1.5-fold, respectively p < 0.01). Incubation of microglia with Klebsiella variicola increased the Aβ-phagocytosis by 394% and the expression of the phagocytic receptor MSR1 by 33-fold compared to the non-activated cells (p < 0.0001).
Conclusions:
We showed that inducing PD in mice results in microglia activation in vivo and that PD-associated bacteria directly promote a pro-inflammatory and phagocytic phenotype in microglia. These results support a direct role of PD-associated pathogens in neuroinflammation.
Insights
Periodontal disease (PD) in mice activates brain microglia, increasing inflammatory markers and enhancing the phagocytosis of amyloid-beta (Aβ). These findings suggest PD pathogens directly contribute to neuroinflammation, potentially impacting Alzheimer's disease progression.
Area of Science:
- Neuroimmunology
- Periodontal Medicine
- Alzheimer's Disease Research
Background:
- Microglial activation is crucial for managing neuroinflammation and the progression of neurodegenerative diseases like Alzheimer's disease (AD).
- Microglia play roles in forming barriers around amyloid plaques and phagocytosing beta-amyloid peptide (Aβ).
- The potential link between periodontal disease (PD) and neuroinflammation warrants investigation.
Purpose of the Study:
- To test the hypothesis that periodontal disease (PD) alters inflammatory activation and Aβ phagocytosis by microglial cells.
- To investigate the impact of PD-induced infection on microglial function in a mouse model.
Main Methods:
- Experimental PD was induced in C57BL/6 mice using ligatures, with assessments at 1, 10, 20, and 30 days.
- Bone loss and cytokine expression confirmed PD progression; microglial activation was analyzed via flow cytometry.
- Microglial cells were incubated with PD-associated bacteria or bacterial biofilm to measure inflammatory and phagocytic markers.
Main Results:
- Progressive PD and bone resorption were observed, correlating with increased frequency of activated microglia in the brain.
- PD-associated bacteria and Klebsiella variicola significantly increased pro-inflammatory cytokines (TNFα, IL-1β, IL-6) and TLRs (TLR2, TLR9) in microglia.
- Klebsiella variicola significantly enhanced Aβ-phagocytosis (394%) and MSR1 expression (33-fold) in microglial cells.
Conclusions:
- Inducing PD in mice leads to microglia activation in vivo.
- PD-associated bacteria directly induce a pro-inflammatory and phagocytic phenotype in microglia.
- These findings support a direct role for PD pathogens in driving neuroinflammation.
