title: Toll-like receptor 3 activation affects serotonin transporter activity and expression in human enterocyte-like Caco-2 cells.
abstract: Serotonin, a neurotransmitter/autocrineagent mainly synthesized by intestinal enterochromaffin cells, regulates the whole intestinal physiology. Toll-like receptor 3 (TLR3) also contributes to the intestinal physiology by modulating intestinal innate immunity responses. Both serotonin and TLR3 are involved in intestinal inflammatory processes; however, the role of TLR3 in the regulation of intestinal 5-HT availability remains unexplored. The present study analyzes the effect of TLR3 activation on serotonin transporter (SERT) activity in Caco-2 cells. Treatment with poly(I:C), dsRNA synthetic analogue and TLR3 ligand, was assayed and SERT activity determined by 5-HT uptake and transepithelial flux. SERT expression was analyzed by qRT-PCR and western blotting. Poly(I:C) short-term treatment inhibited SERT activity in the apical and basal membrane of epithelial cells and diminished SERT protein content in the membrane. SERT total protein and mRNA levels were not affected by poly(I:C), suggesting a post-translational alteration of SERT. The poly(I:C) effect on SERT activity did not appear to be mediated by PKC, cAMP, PKR or JNK signaling pathways; however, the p38 MAPK pathway seemed to be involved. Our results demonstrate that TLR3 inhibits SERT activity, which may increase 5-HT extracellular levels and contribute to the inflammatory response; however, 5-HT treatment did not affect TLR3 expression.
authors: Department of Pharmacology and Physiology, Faculty of Veterinary Sciences, University of Zaragoza, Zaragoza, Spain.
authors: Carmen
authors: C
authors: Mendoza
authors: Nyurky
authors: N
authors: Matheus
authors: Eva
authors: E
authors: Latorre
authors: Marta
authors: M
authors: Castro
authors: José Emilio
authors: JE
authors: Mesonero
authors: Ana Isabel
authors: AI
authors: Alcalde
mesh_terms: D018938:Caco-2 Cells; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020895:Enterocytes / Q000201:enzymology / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008871:Microvilli / Q000378:metabolism; D011070:Poly I-C / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D050486:Serotonin Plasma Membrane Transport Proteins; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; D012701:Serotonin; D000242:Cyclic AMP; D019892:eIF-2 Kinase; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases; D011070:Poly I-C