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Published on: June 23, 2013
PPARα modulation of macrophage polarization and inflammatory signaling in mimic periodontitis
1Massachusetts Institute of Technology, Cambridge, United States.
Objective:
This study investigates the role of peroxisome proliferator-activated receptor alpha (PPARα) in regulating macrophage polarization and inflammatory signaling under stimulation by periodontal pathogens.
Methodology:
THP-1-derived macrophages were stimulated with Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) in the presence or absence of PPARα agonists fenofibrate and WY14643, or the antagonist GW6471. Protein expression levels of TNF-α, IL-10, and phosphorylated NF-κB were assessed by Western blot. Immunofluorescence staining was used to evaluate IL-10, NF-κB, and CD36 expression. Flow cytometry quantified changes in macrophage polarization markers, including CD14+CD86+ (M1) and CD68+CD206+/CD163+ (M2) populations. THP-1 cells transfected with a secreted embryonic alkaline phosphatase (SEAP) reporter plasmid were treated with Pg-LPS (1 μg/mL) ± fenofibrate (50 μM) to assess NF-κB/AP-1 activity. PPARα reporter cells were treated with increasing concentrations of GW590735 or WY14643 and exposed to TNF-α, LPS, or GW6471+LPS to evaluate PPARα transcriptional activity.
Results:
PPARα activation by fenofibrate reduced TNF-α expression in Pg-LPS-stimulated macrophages and attenuated NF-κB signaling via both TLR2 and TLR4 pathways. Fenofibrate significantly increased IL-10 and CD36 expression, inhibited Pg-LPS-induced NF-κB nuclear translocation, and promoted a phenotypic shift from pro-inflammatory M1 to anti-inflammatory M2 macrophages. Moreover, inflammatory stimuli such as TNF-α and LPS suppressed PPARα activity, which could be restored by potent PPARα agonists.
Conclusion:
These findings suggest that PPARα activation modulates macrophage polarization and suppresses inflammatory signaling in response to periodontal bacterial antigens.
Insights
Peroxisome proliferator-activated receptor alpha (PPARα) activation reduces inflammation and shifts macrophages to an anti-inflammatory state when exposed to periodontal pathogens. This suggests PPARα plays a key role in modulating immune responses to oral bacteria.
Area of Science:
- Immunology and Molecular Biology
- Periodontal Disease Pathogenesis
Background:
- Periodontal pathogens trigger inflammatory responses mediated by macrophages.
- Macrophage polarization into M1 (pro-inflammatory) and M2 (anti-inflammatory) phenotypes is crucial in host defense and tissue repair.
- Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor involved in metabolic and inflammatory processes.
Purpose of the Study:
- To investigate the role of PPARα in regulating macrophage polarization and inflammatory signaling.
- To determine how PPARα activation affects macrophage responses to periodontal pathogens like Porphyromonas gingivalis lipopolysaccharide (Pg-LPS).
Main Methods:
- THP-1 derived macrophages were stimulated with Pg-LPS and treated with PPARα agonists (fenofibrate, WY14643) or antagonist (GW6471).
- Protein expression (TNF-α, IL-10, p-NF-κB) and cellular localization (NF-κB, IL-10, CD36) were assessed via Western blot and immunofluorescence.
- Macrophage polarization (M1/M2 markers) was quantified by flow cytometry; NF-κB/AP-1 and PPARα transcriptional activity were measured using reporter assays.
Main Results:
- PPARα activation significantly reduced TNF-α expression and attenuated NF-κB signaling in response to Pg-LPS.
- Fenofibrate treatment increased IL-10 and CD36 expression, promoting a shift from M1 to M2 macrophage polarization.
- Inflammatory stimuli suppressed PPARα activity, which was restored by PPARα agonists.
Conclusions:
- PPARα activation effectively suppresses inflammatory signaling pathways (NF-κB) triggered by periodontal bacterial components.
- PPARα plays a critical role in modulating macrophage polarization towards an anti-inflammatory M2 phenotype.
- Targeting PPARα may represent a therapeutic strategy to control inflammation in periodontal diseases.
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