Possible role of microparticles in neuroimmune signaling of microglial cells

Aim: Submicron fragments termed microparticles (MPs), derived from all major central nervous system cell types including neurons and glia (microglia, astrocytes, oligodendrocytes), have emerged as novel intercellular signaling agents. This study tested the hypothesis that MPs derived from activated microglia, which represent the mononuclear phagocyte system in the brain, could induce pro-inflammatory and cytotoxic responses of microglia in an autocrine or paracrine manner. Methods: Human THP-1 monocytic cells were used to model human microglia. MPs derived from these cells were reapplied to THP-1 cells and their secretion of neurotoxins and cytokines was measured. Results: When exposed to lipopolysaccharide (LPS) or mitochondrial transcription factor A in combination with interferon (IFN)-γ, THP-1 cells released MPs. When reapplied to THP-1 cells, MPs induced the release of secretions that were toxic to human SH-SY5Y neuroblastoma cells, as well as monocyte chemoattractant protein-1. The cytotoxicity of THP-1 cells induced by MPs derived from IFN-γ plus LPS-treated THP-1 donor cells was enhanced in the presence of IFN-γ. The MPs released by THP-1 cells were not directly toxic towards SH-SY5Y cells. Conclusion: Our data support the hypothesis that activated microglia-derived MPs could act as signaling agents that are recognized by microglia to cause pro-inflammatory and cytotoxic responses.