title: Sialylation of neurites inhibits complement-mediated macrophage removal in a human macrophage-neuron Co-Culture System.
abstract: The complement system has been implicated in the removal of dysfunctional synapses and neurites during development and in disease processes in the mouse, but it is unclear how far the mouse data can be transferred to humans. Here, we co-cultured macrophages derived from human THP1 monocytes and neurons derived from human induced pluripotent stem cells, to study the role of the complement system in a human model. Components of the complement system were expressed by the human macrophages and human neuronal culture, while receptors of the complement cascade were expressed by human macrophages as shown via gene transcript analysis and flow cytometry. We mimicked pathological conditions leading to an altered glycocalyx by treatment of human neurons with sialidases. Desialylated human neurites were opsonized by the complement component C1q. Furthermore, human neurites with an intact sialic acid cap remained untouched, while desialylated human neurites were removed and ingested by human macrophages. While blockage of the complement receptor 1 (CD35) had no effect, blockage of CD11b as part of the complement receptor 3 (CR3) reversed the effect on macrophage phagocytosis of desialylated human neurites. Data demonstrate that in the human system sialylation of the neuronal glycocalyx serves as an inhibitory flag for complement binding and CR3-mediated phagocytosis by macrophages.
authors.affiliation: Neural Regeneration Group, Institute of Reconstructive Neurobiology, University Hospital Bonn, University of Bonn, Bonn, 53127, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Linnartz-Gerlach
authors.affiliation: Neural Regeneration Group, Institute of Reconstructive Neurobiology, University Hospital Bonn, University of Bonn, Bonn, 53127, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Schuy
authors.affiliation: Neural Regeneration Group, Institute of Reconstructive Neurobiology, University Hospital Bonn, University of Bonn, Bonn, 53127, Germany.
authors.forename: Anahita
authors.initials: A
authors.lastname: Shahraz
authors.affiliation: Department of Molecular Biology and Biochemistry, Institute for Immunology, University of California, Irvine, California, 92697, USA.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Tenner
authors.affiliation: Neural Regeneration Group, Institute of Reconstructive Neurobiology, University Hospital Bonn, University of Bonn, Bonn, 53127, Germany.
authors.forename: Harald
authors.identifier: http://orcid.org/0000-0002-5071-5202
authors.initials: H
authors.lastname: Neumann
mesh_terms: D039481:CD11b Antigen / Q000378:metabolism; D018920:Coculture Techniques; D015922:Complement C1q / Q000378:metabolism; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000502:physiology; D016177:Macrophage-1 Antigen / Q000378:metabolism; D008264:Macrophages / Q000502:physiology*; D009000:Monocytes / Q000502:physiology; D009081:Mucolipidoses / Q000378:metabolism*; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D058953:Neural Stem Cells / Q000502:physiology; D016501:Neurites / Q000502:physiology*; D055495:Neurogenesis / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010587:Phagocytosis / Q000502:physiology*; D017463:Receptors, Complement 3b / Q000378:metabolism
chemical_list: D039481:CD11b Antigen; C509991:CR1 protein, human; C509295:ITGAM protein, human; D016177:Macrophage-1 Antigen; D017463:Receptors, Complement 3b; D015922:Complement C1q; D019158:N-Acetylneuraminic Acid
keywords: complement; human; macrophage; neurons; phagocytosis; sialic acid