Intracellular osteopontin negatively regulates toll-like receptor 4-mediated inflammatory response via regulating GSK3β and 4EBP1 phosphorylation

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Toll-like receptors (TLRs) are crucial for host defense but their inappropriate activation can lead to inflammatory and autoimmune diseases.
• Osteopontin (OPN) is an inflammatory cytokine, yet its specific role in TLR-mediated immune responses remains unclear.
• Understanding OPN's function in TLR signaling is vital for developing targeted therapies for inflammatory conditions.

Purpose of the Study:

• To investigate the role of osteopontin (OPN) in Toll-like receptor (TLR)-mediated inflammatory responses.
• To elucidate the regulatory mechanism of intracellular OPN (iOPN) in lipopolysaccharide (LPS)-induced inflammation.
• To determine the signaling pathways affected by OPN deficiency in macrophages.

Main Methods:

• Comparison of pro-inflammatory cytokine levels in OPN-deficient (OPN-/-) and wild-type (WT) macrophages after lipopolysaccharide (LPS) stimulation.
• Analysis of Akt and GSK3β phosphorylation levels in OPN-/- and WT macrophages.
• Assessment of 4EBP1 phosphorylation status as a downstream target of Akt signaling.

Main Results:

• OPN-/- macrophages exhibited significantly higher levels of pro-inflammatory cytokines upon LPS stimulation.
• Intracellular OPN (iOPN) isoform was identified as a negative regulator of LPS-induced inflammatory responses.
• OPN deficiency led to reduced Akt phosphorylation and increased GSK3β phosphorylation, impacting downstream targets like 4EBP1.

Conclusions:

• Intracellular OPN (iOPN) functions as a negative regulator, inhibiting TLR4-mediated inflammatory responses.
• iOPN modulates the Akt/GSK3β/4EBP1 signaling pathway to control inflammation.
• These findings highlight a novel mechanism by which OPN regulates innate immune responses.