Autocrine activation of human monocyte/macrophages by monocyte-derived microparticles and modulation by PPARγ ligands

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-KB activation (EMSA assay) were evaluated. Key Results Monocyte-derived MPs induced, in a concentration-dependent manner, oxygen radical production, cytokine release and NF-KB 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-KB activation) and anti-inflammatory (PPARγ expression) effects.