Cytokines regulate cysteine cathepsins during TLR responses

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Toll-like receptor (TLR) activation is crucial for innate immunity but exacerbates inflammatory diseases.
• Cysteine cathepsins (Cat B, L, S) are lysosomal proteases involved in physiological processes and upregulated in inflammation and cancer.
• Macrophages, with high cathepsin expression, significantly contribute to inflammation and tissue damage in chronic inflammatory diseases.

Purpose of the Study:

• To investigate the impact of Toll-like receptor (TLR) activation on macrophage cysteine cathepsin (Cat B, L, S) activities.
• To elucidate the role of TLR-induced cytokines in regulating cathepsin proteolytic activity.

Main Methods:

• Utilized live-cell enzymatic assays to measure intracellular cathepsin activities in macrophages.
• Stimulated macrophages with TLR2, TLR3, and TLR4 ligands.
• Assessed the effect of neutralizing antibodies against TNF-α, IL-1β, and IFN-β on cathepsin activity.

Main Results:

• TLR2, TLR3, and TLR4 ligand stimulation differentially increased intracellular cathepsin B, L, and S activities.
• TLR4-induced cytokines enhanced cathepsin proteolytic activity without altering mRNA expression of cathepsins or their inhibitors.
• Neutralizing antibodies against TNF-α, IL-1β, and IFN-β differentially reduced cathepsin upregulation.

Conclusions:

• Cytokines induced by both MyD88-dependent and -independent signaling pathways regulate macrophage cathepsin activities following TLR stimulation.
• This highlights a novel mechanism by which TLRs influence macrophage function in inflammatory contexts.