TLR-mediated secretion of endoplasmic reticulum aminopeptidase 1 from macrophages

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Macrophages are crucial for host defense in immunological, inflammatory, and infectious conditions.
• Previous studies showed endoplasmic reticulum aminopeptidase 1 (ERAP1) secretion enhances macrophage phagocytosis.
• The mechanism of ERAP1 secretion induced by lipopolysaccharide (LPS) and interferon-gamma (IFN-γ) requires further investigation.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying LPS/IFN-γ-induced ERAP1 secretion from macrophages.
• To identify the signaling pathways and key mediators involved in ERAP1 secretion.

Main Methods:

• Utilized the murine macrophage cell line RAW264.7 and primary murine peritoneal macrophages.
• Investigated the role of Toll-like receptors (TLRs) using various agonists and antagonists (e.g., Polymyxin B).
• Assessed the involvement of cytokines (IFN-β, TNF-α) and intracellular signaling molecules (Ca2+, calmodulin) using knockout mice, neutralizing antibodies, and specific inhibitors/inducers.

Main Results:

• LPS/IFN-γ-induced ERAP1 secretion was suppressed by Polymyxin B, indicating TLR involvement.
• TLR agonists (Pam3CSK4, FSL-1, ODN1826) stimulated ERAP1 secretion.
• Neutralizing antibodies and knockout models confirmed the essential roles of IFN-β and TNF-α.
• Secretion was induced by calcium ionophore A23187 and thapsigargin, and inhibited by BAPTA-AM and calmodulin inhibitor W7, highlighting calcium/calmodulin pathway activation.

Conclusions:

• LPS/IFN-γ-induced ERAP1 secretion is mediated by TLRs.
• This process involves the induction of intermediate cytokines like IFN-β and TNF-α.
• Activation of the cytosolic Ca2+ and calmodulin signaling pathway is critical for ERAP1 secretion, contributing to enhanced macrophage function.