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Autocrine activation of human monocyte/macrophages by monocyte-derived microparticles and modulation by PPARγ ligands
C Bardelli1, A Amoruso, D Federici Canova
1Department of Medical Sciences, University A. Avogadro, Via Solaroli, Novara, Italy.
Background And Purpose:
Microparticles (MPs), small membrane-bound particles originating from different cell types during activation or apoptosis, mediate intercellular communication, exert pro-coagulant activity and affect inflammation and other pathophysiological conditions. Monocyte-derived MPs have undergone little investigation and, to our knowledge, have never been evaluated for their possible autocrine effects. Therefore, we assessed the ability of monocyte-derived MPs to stimulate human monocytes and monocyte-derived macrophages (MDM).
Experimental Approach:
MPs were generated from supernatants of human monocytes stimulated by the calcium ionophore A23187 (12 µM), and then characterized. Human monocytes and MDM of healthy donors were isolated by standard procedures. Cells were challenged by MPs or phorbol 12-myristate 13-acetate (PMA, used as standard stimulus), in the absence or presence of PPARγ agonists and antagonists. Superoxide anion production (measured spectrophotometrically), cytokine release (elisa), PPARγ protein expression (immunoblotting) and NF-κB activation (EMSA assay) were evaluated.
Key Results:
Monocyte-derived MPs induced, in a concentration-dependent manner, oxygen radical production, cytokine release and NF-κB activation in human monocytes and macrophages, with lower effects than PMA. In both cell types, the PPARγ agonists rosiglitazone and 15-deoxy-Δ(12,14) -prostaglandin J(2) (15d-PGJ(2) ) inhibited MPs-induced stimulation and this inhibition was reversed by a PPARγ antagonist. In human monocyte/macrophages, MPs as well as rosiglitazone and 15d-PGJ(2) induced PPARγ protein expression.
Conclusion And Implications:
In human monocyte/macrophages, monocyte-derived MPs exert an autocrine activation that was modulated by PPARγ ligands, inducing both pro-inflammatory (superoxide anion production, cytokine release and NF-κB activation) and anti-inflammatory (PPARγ expression) effects.
Insights
Monocyte-derived microparticles (MPs) activate human monocytes and macrophages, triggering inflammatory responses. PPARγ ligands modulate these effects, indicating a complex role in monocyte/macrophage function.
Area of Science:
- Immunology
- Cell Biology
Background:
- Microparticles (MPs) are cell-derived vesicles involved in intercellular communication, inflammation, and coagulation.
- Monocyte-derived MPs have been understudied, particularly regarding their autocrine effects on monocytes and macrophages.
Purpose of the Study:
- To investigate the autocrine effects of monocyte-derived MPs on human monocytes and monocyte-derived macrophages (MDM).
- To determine the role of Peroxisome proliferator-activated receptor gamma (PPARγ) in mediating these effects.
Main Methods:
- MPs were generated from activated human monocytes.
- Human monocytes and MDM were stimulated with MPs, and responses were measured.
- Superoxide anion production, cytokine release, PPARγ expression, and NF-κB activation were assessed.
- The effects of PPARγ agonists and antagonists were evaluated.
Main Results:
- Monocyte-derived MPs induced concentration-dependent superoxide anion production, cytokine release, and NF-κB activation in monocytes and MDM.
- PPARγ agonists (rosiglitazone, 15d-PGJ2) inhibited MP-induced activation, an effect reversed by a PPARγ antagonist.
- MPs, rosiglitazone, and 15d-PGJ2 increased PPARγ protein expression.
Conclusions:
- Monocyte-derived MPs exert autocrine effects on human monocytes and macrophages, promoting inflammation.
- PPARγ ligands modulate these autocrine effects, influencing both pro-inflammatory and anti-inflammatory pathways.
- This suggests a complex regulatory role for PPARγ in MP-mediated monocyte/macrophage activation.
