miR-24 Regulates Macrophage Polarization and Plasticity

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• MicroRNAs (miRNAs) are key regulators of biological processes, including immunity.
• Previous studies indicated miR-24 inhibits phagocytosis and cytokine secretion in response to bacterial lipopolysaccharides (LPS).
• Environmental factors like cigarette smoke extract modify LPS structure, impacting macrophage responses.

Purpose of the Study:

• To investigate the role of miR-24 in macrophage polarization and plasticity.
• To understand how miR-24 influences macrophage activation states.
• To explore miR-24's impact on cytokine secretion and immune signaling.

Main Methods:

• Primary human macrophages were differentiated and transfected with miR-24 mimics or inhibitors.
• Macrophages were stimulated with various LPS types and cytokines.
• Macrophage activation, polarization, cytokine production, and protein expression were assessed.
• miR-24 expression was quantified using RT-PCR.

Main Results:

• LPS from different pathogens (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis) and modified LPS (Pg CSE) induced distinct cytokine and miR-24 expression levels.
• Overexpression of miR-24 inhibited LPS-induced cytokine secretion, an effect partially modulated by activation state.
• miR-24 promoted alternative macrophage activation (CD206 upregulation) and inhibited its downregulation during polarization shifts.
• miR-24 overexpression reduced the expression of the PI 3-kinase subunit p110δ.

Conclusions:

• LPS modifications by pathogens and environment alter macrophage miR-24 and cytokine expression.
• miR-24 acts as a negative regulator of classical macrophage activation and promotes alternative activation.
• The anti-inflammatory effect of miR-24 on cytokine secretion is dependent on the macrophage activation state and potentially involves p110δ signaling.
• Overexpression of miR-24 demonstrates a predominantly anti-inflammatory role in macrophages.