title: Activated microglia cause reversible apoptosis of pheochromocytoma cells, inducing their cell death by phagocytosis.
abstract: Some apoptotic processes, such as phosphatidylserine exposure, are potentially reversible and do not necessarily lead to cell death. However, phosphatidylserine exposure can induce phagocytosis of a cell, resulting in cell death by phagocytosis: phagoptosis. Phagoptosis of neurons by microglia might contribute to neuropathology, whereas phagoptosis of tumour cells by macrophages might limit cancer. Here, we examined the mechanisms by which BV-2 microglia killed co-cultured pheochromocytoma (PC12) cells that were either undifferentiated or differentiated into neuronal cells. We found that microglia activated by lipopolysaccharide rapidly phagocytosed PC12 cells. Activated microglia caused reversible phosphatidylserine exposure on and reversible caspase activation in PC12 cells, and caspase inhibition prevented phosphatidylserine exposur and decreased subsequent phagocytosis. Nitric oxide was necessary and sufficient to induce the reversible phosphatidylserine exposure and phagocytosis. The PC12 cells were not dead at the time they were phagocytised, and inhibition of their phagocytosis left viable cells. Cell loss was inhibited by blocking phagocytosis mediated by phosphatidylserine, MFG-E8, vitronectin receptors or P2Y6 receptors. Thus, activated microglia can induce reversible apoptosis of target cells, which is insufficient to cause apoptotic cell death, but sufficient to induce their phagocytosis and therefore cell death by phagoptosis.
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
authors.forename: Tamara C
authors.initials: TC
authors.lastname: Hornik
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Vilalta
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK gcb3@cam.ac.uk.
authors.forename: Guy C
authors.initials: GC
authors.lastname: Brown
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D018920:Coculture Techniques; D004789:Enzyme Activation / Q000187:drug effects; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D017628:Microglia / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D008894:Milk Proteins / Q000378:metabolism; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism; D016716:PC12 Cells; D010587:Phagocytosis / Q000187:drug effects; D010673:Pheochromocytoma / Q000378:metabolism / Q000473:pathology*; D010718:Phosphatidylserines / Q000378:metabolism; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D019030:Receptors, Vitronectin / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000954:Antigens, Surface; D008070:Lipopolysaccharides; C499941:MFGE8 protein, rat; D008894:Milk Proteins; D010718:Phosphatidylserines; D018048:Receptors, Purinergic P2; D019030:Receptors, Vitronectin; D014409:Tumor Necrosis Factor-alpha; C099845:purinoceptor P2Y6; D009569:Nitric Oxide; D020169:Caspases
keywords: Cancer; Caspase; Inflammation; Neuroinflammation; Phagocytosis; Phosphatidylserine