title: The proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha activate serotonin transporters.
abstract: Proinflammatory cytokines and serotonergic homeostasis have both been implicated in the pathophysiology of major psychiatric disorders. We have demonstrated that activation of p38 mitogen-activated protein kinase (MAPK) induces a catalytic activation of the serotonin transporter (SERT) arising from a reduction in the SERT Km for 5-hydroxytryptamine (5-HT). As inflammatory cytokines can activate p38 MAPK, we hypothesized that they might also activate neuronal SERT. Indeed, Interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) stimulated serotonin uptake in both the rat embryonic raphe cell line, RN46A, and in mouse midbrain and striatal synaptosomes. In RN46A cells, IL-1beta stimulated 5-HT uptake in a dose- and time-dependent manner, peaking in 20 min at 100 ng/ml. This was abolished by IL-1ra (20 ng/ml), an antagonist of the IL-1 receptor, and by SB203580 (5 microM), a p38 MAPK inhibitor. TNF-alpha also dose- and time-dependently stimulated 5-HT uptake that was only partially blocked by SB203580. Western blots showed that IL-1beta and TNF-alpha activated p38 MAPK, in an SB203580-sensitive manner. IL-1beta induced an SB203580-sensitive decrease in 5-HT Km with no significant change in Vmax. In contrast, TNF-alpha stimulation decreased 5-HT Km and increased SERT Vmax. SB203580 selectively blocked the TNF-alpha-induced change in SERT Km. In mouse midbrain and striatal synaptosomes, maximal stimulatory effects on 5-HT uptake occurred at lower concentrations (IL-1beta, 10 ng/ml; TNF-alpha, 20 ng/ml), and over shorter incubation times (10 min). As with RN46A cells, the effects of IL-1beta and TNF-alpha were completely (IL-1beta) or partially (TNF-alpha) blocked by SB203580. These results provide the first evidence that proinflammatory cytokines can acutely regulate neuronal SERT activity via p38 MAPK-linked pathways.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232-8645, USA.
authors.forename: Chong-Bin
authors.initials: CB
authors.lastname: Zhu
authors.forename: Randy D
authors.initials: RD
authors.lastname: Blakely
authors.forename: William A
authors.initials: WA
authors.lastname: Hewlett
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002460:Cell Line; D003342:Corpus Striatum / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007375:Interleukin-1 / Q000494:pharmacology*; D008636:Mesencephalon / Q000648:ultrastructure; D051379:Mice; D009474:Neurons / Q000187:drug effects*; D011903:Raphe Nuclei / Q000166:cytology; D051381:Rats; D012701:Serotonin / Q000378:metabolism / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D007375:Interleukin-1; D050486:Serotonin Plasma Membrane Transport Proteins; D014409:Tumor Necrosis Factor-alpha; D012701:Serotonin; D048051:p38 Mitogen-Activated Protein Kinases