Apoptotic cells trigger the ABCA1/STAT6 pathway leading to PPAR-γ expression and activation in macrophages

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• Signal transducer and activator of transcription 6 (STAT6) regulates peroxisome proliferator-activated receptor gamma (PPAR-γ) gene expression in immune cells.
• The interaction between macrophages and apoptotic cells influences immune responses and gene expression.

Purpose of the Study:

• To investigate the proximal membrane signaling initiated in macrophages upon exposure to apoptotic cells.
• To elucidate the role of ATP-binding cassette transporter A1 (ABCA1) and STAT6 in enhancing PPAR-γ expression and activity.

Main Methods:

• Utilized specific siRNAs targeting ABCA1, STAT6, and PPAR-γ, along with their antagonists.
• Co-cultured mouse bone marrow-derived macrophages and RAW 264.7 cells with apoptotic or viable Jurkat cells.
• Assessed STAT6 phosphorylation, PPAR-γ, liver X receptor α (LXR-α), and ABCA1 expression at mRNA and protein levels.

Main Results:

• Apoptotic, but not viable, Jurkat cells induced STAT6 phosphorylation and PPAR-γ activation in macrophages.
• ABCA1 knockdown reduced apoptotic cell-induced STAT6 phosphorylation and PPAR-γ, LXR-α, and ABCA1 expression.
• Inhibition of STAT6 or PPAR-γ reversed the induction of PPAR-γ, LXR-α, and ABCA1 by apoptotic cells.

Conclusions:

• Apoptotic cells activate macrophages through the ABCA1/STAT6 signaling pathway.
• This activation leads to the subsequent activation of the PPAR-γ/LXR-α/ABCA1 pathway.
• Identified a novel signaling cascade crucial for macrophage response to apoptotic cells.