TLR4 Response to LPS Is Reinforced by Urokinase Receptor

Area of Science:

• Immunology
• Cell Biology
• Molecular Medicine

Background:

• The role of urokinase-type plasminogen activator receptor (uPAR) in inflammation is recognized, but its precise mechanisms remain unclear.
• uPAR, a receptor for urokinase-plasminogen activator (uPA), is anchored to the cell membrane via glycosylphosphatidylinositol (GPI).

Purpose of the Study:

• To investigate the molecular mechanisms linking uPAR to innate immune responses.
• To determine if uPAR interacts with Toll-like receptor 4 (TLR4) and influences TLR4-mediated signaling.

Main Methods:

• Investigated the interaction between uPAR and TLR4 using co-immunoprecipitation and proximity ligation assays.
• Assessed the impact of uPAR downregulation on lipopolysaccharide (LPS)-induced TLR4 signaling, NFκB activation, and inflammatory mediator secretion in vitro.
• Evaluated the role of uPAR in a mouse model of polymicrobial sepsis (cecal ligation and puncture) and assessed survival, inflammatory response, and organ function.

Main Results:

• Demonstrated that uPAR is part of the TLR4 interactome, physically associating with TLR4 on the cell membrane.
• Downregulation of uPAR significantly reduced LPS-induced TLR4 signaling, NFκB activation, and inflammatory cytokine production.
• uPAR knockout mice exhibited improved survival rates, reduced inflammation, and better organ function in a sepsis model.
• Identified CD36 as a scavenger receptor that colocalizes with uPAR and TLR4.

Conclusions:

• uPAR plays a critical role in modulating innate immunity through its interaction with TLR4.
• This uPAR-TLR4 axis represents a novel therapeutic target for managing inflammatory conditions and sepsis.
• Targeting the interaction between uPAR and TLR4 could lead to improved treatment strategies for sepsis and other inflammatory diseases.