title: The inhibitory neurotransmitter glycine modulates macrophage activity by activation of neutral amino acid transporters.
abstract: Glycine, an important inhibitory neurotransmitter in the mammalian central nervous system (CNS), has been shown to modulate peripheral immune cell responses. In that respect, glycine levels are increased in several neuroinflammatory disorders, such as amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). In this study, we show that glycine modulates macrophage effector functions implicated in CNS inflammation and in other, related inflammatory conditions. We demonstrate that glycine does not affect the production of reactive oxygen species but stimulates myelin phagocytosis and the production of the proinflammatory mediators nitric oxide (NO) and tumor necrosis factor (TNF)-alpha by rat macrophages. These effects of glycine are not mediated by the glycine receptor (GlyR) or by glycine transporters (GlyTs), as neither the GlyR antagonist strychnine nor the antagonist of GlyT1 (ALX5407) reverses the observed effects. In contrast, 2-aminoisobutyric acid, a substrate of neutral amino acid transporters (NAATs), inhibits the glycine-mediated enhancement of myelin phagocytosis as well as of NO and TNF-alpha production. In conclusion, our findings demonstrate that glycine modulates macrophage function through activation of NAATs. Glycine may thereby influence immunological processes in inflammatory diseases involving macrophage activation and demyelination, including MS and related conditions associated with altered glycine levels.
authors.affiliation: Biomedical Research Institute, Hasselt University, and School of Life Sciences, Transnationale Universiteit Limburg, Diepenbeek, Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: Carmans
authors.forename: Jerome J A
authors.initials: JJ
authors.lastname: Hendriks
authors.forename: Kristof
authors.initials: K
authors.lastname: Thewissen
authors.forename: Jimmy
authors.initials: J
authors.lastname: Van den Eynden
authors.forename: Piet
authors.initials: P
authors.lastname: Stinissen
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Rigo
authors.forename: Niels
authors.initials: N
authors.lastname: Hellings
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D005455:Fluorescent Antibody Technique; D005998:Glycine / Q000494:pharmacology*; D018684:Glycine Agents / Q000494:pharmacology; D007249:Inflammation / Q000473:pathology; D017737:Macrophages, Peritoneal / Q000187:drug effects*; D008297:Male; D009103:Multiple Sclerosis / Q000378:metabolism; D009186:Myelin Sheath / Q000502:physiology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009569:Nitric Oxide / Q000096:biosynthesis; D010587:Phagocytosis / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D018009:Receptors, Glycine / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013331:Strychnine / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D018684:Glycine Agents; D018377:Neurotransmitter Agents; D017382:Reactive Oxygen Species; D018009:Receptors, Glycine; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D013331:Strychnine; D005998:Glycine