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Published on: May 31, 2018
CD14 recycling modulates LPS-induced inflammatory responses of murine macrophages
Anna Ciesielska1, Marta Krawczyk1, Hanna Sas-Nowosielska2
1Laboratory of Molecular Membrane Biology, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland.
Abstract:
TLR4 is activated by the bacterial endotoxin lipopolysaccharide (LPS) and triggers two proinflammatory signaling cascades: a MyD88-dependent one in the plasma membrane, and the following TRIF-dependent one in endosomes. An inadequate inflammatory reaction can be detrimental for the organism by leading to sepsis. Therefore, novel approaches to therapeutic modulation of TLR4 signaling are being sought after. The TLR4 activity is tightly connected with the presence of CD14, a GPI-anchored protein that transfers LPS monomers to the receptor and controls its endocytosis. In this study we focused on CD14 trafficking as a still poorly understood factor affecting TLR4 activity. Two independent assays were used to show that after endocytosis CD14 can recycle back to the plasma membrane in both unstimulated and stimulated cells. This route of CD14 trafficking can be controlled by sorting nexins (SNX) 1, 2 and 6, and is important for maintaining the surface level and the total level of CD14, but can also affect the amount of TLR4. Silencing of these SNXs attenuated especially the CD14-dependent endosomal signaling of TLR4, making them a new target for therapeutic regulation of the inflammatory response of macrophages to LPS.
Insights
Toll-like receptor 4 (TLR4) signaling, crucial for immune response, is modulated by CD14 trafficking. Sorting nexins (SNX) regulate CD14 recycling, impacting TLR4 activity and offering new therapeutic targets for inflammatory diseases.
Area of Science:
- Immunology
- Cell Biology
- Molecular Medicine
Background:
- Toll-like receptor 4 (TLR4) activation by lipopolysaccharide (LPS) initiates inflammatory signaling via MyD88-dependent and TRIF-dependent pathways.
- CD14, a protein essential for LPS transfer to TLR4, influences receptor activity and endocytosis.
- Dysregulated TLR4 signaling can lead to severe conditions like sepsis, necessitating therapeutic strategies.
Purpose of the Study:
- To investigate the role of CD14 trafficking in regulating TLR4 signaling.
- To identify molecular mechanisms controlling CD14 recycling and its impact on TLR4 surface levels.
- To explore sorting nexins (SNX) as potential regulators of TLR4-mediated inflammation.
Main Methods:
- Utilized two independent assays to track CD14 trafficking post-endocytosis.
- Investigated the influence of sorting nexins (SNX 1, 2, and 6) on CD14 recycling.
- Assessed the effect of SNX modulation on surface and total CD14 levels, as well as TLR4 expression.
- Examined the impact of SNX silencing on TLR4 signaling pathways, particularly the CD14-dependent endosomal route.
Main Results:
- Demonstrated that CD14 recycles to the plasma membrane in both unstimulated and LPS-stimulated cells.
- Showed that sorting nexins (SNX 1, 2, and 6) control this CD14 trafficking pathway.
- Found that SNX activity is critical for maintaining CD14 levels and influences TLR4 expression.
- Revealed that silencing SNXs attenuates CD14-dependent endosomal TLR4 signaling.
Conclusions:
- CD14 trafficking and recycling are key regulators of TLR4 activity.
- Sorting nexins (SNX 1, 2, and 6) represent novel targets for modulating TLR4-mediated inflammatory responses.
- Targeting SNX-mediated CD14 recycling offers a potential therapeutic strategy for inflammatory conditions like sepsis.
