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Apolipoprotein E suppresses the type I inflammatory response in vivo
Kamilah Ali1, Melissa Middleton, Ellen Puré
1Institute for Translational Medicine and Therapeutics, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6160, USA.
Circulation Research
|September 24, 2005
Summary
Apolipoprotein E (apoE) deficiency amplifies inflammatory responses to bacterial components. ApoE regulates key inflammatory signaling pathways, suggesting a role beyond cholesterol regulation in immune modulation.
Area of Science:
- Immunology
- Molecular Biology
- Cardiovascular Research
Background:
- Apolipoprotein E (apoE) is known for its role in cholesterol homeostasis and antiatherogenic properties.
- Emerging evidence suggests apoE also possesses anti-inflammatory functions potentially protecting against atherosclerosis independently of lipid metabolism.
Purpose of the Study:
- To investigate the role of apoE in modulating systemic inflammatory responses in vivo.
- To determine if apoE influences Toll-like receptor (TLR)-mediated cytokine production.
Main Methods:
- Comparison of inflammatory responses in apoE knockout mice and wild-type mice stimulated with lipopolysaccharide (LPS) and other TLR agonists.
- Analysis of pro-inflammatory cytokine mRNA and protein levels.
- Assessment of cytokine responses in hypercholesterolemic mice and apoE-reconstituted mice.
Main Results:
- ApoE-deficient mice exhibited significantly upregulated pro-inflammatory cytokines (TNF-α, IL-6, IL-12, IFN-γ) compared to wild-type mice after LPS stimulation.
- Hypercholesterolemia did not cause the exaggerated cytokine response, as seen in LDLr/apobec-1 double knockout mice.
- Reconstitution of hepatic apoE expression normalized LPS-induced IL-12p40 levels, and apoE selectively modulated TLR4- and TLR3-mediated IL-12 production.
Conclusions:
- Apolipoprotein E plays a crucial role in modulating the systemic type I inflammatory response in vivo.
- ApoE selectively regulates Toll-like receptor 4 and Toll-like receptor 3 signaling pathways, specifically impacting Interleukin-12 production.
- These findings indicate that apoE modulates the T helper-1 immune response through its regulation of IL-12.