title: Serotonin regulates innate immune responses of colon epithelial cells through Nox2-derived reactive oxygen species.
abstract: Changes in serotonin (5-hydroxytryptamine, 5-HT) content in the gut of patients with inflammatory bowel disease (IBD) and animal models of colitis suggest an important role of 5-HT in the pathogenesis of IBD. In this study, we examined the role and mechanism of action of 5-HT in the inflammatory response of colon epithelial cells in vitro and in vivo. In colon epithelial cells (CCD 841, HT-29, Caco-2), direct application of 5-HT induced production of reactive oxygen species (ROS) and monocyte-epithelial adhesion, an initial event of inflammation, which were blocked not only by 5-HT receptor antagonists (tropisetron, RS39604, and SB269970), antioxidants (ascorbic acid, apocynin), and various inhibitors of NADPH oxidase (DPI), CREB (KG-501), and NF-κB (PDTC), but also by transfection with Nox2 siRNA. Nox2-derived production of ROS corresponded with the rapid and brief activation of Rac. In addition, 5-HT induced Nox2, p67(phox), and Duox2 without altering the level of Nox1 or Duox1 in colon epithelial cells, and silencing of Nox2 suppressed 5-HT-induced Duox2 increase. 5-HT also induced an increase in the expression of MCP-1, IL-8, and ICAM-1 and a decrease in E-cadherin expression. Exogenous application of 5-HT to rat colon through the rectum caused a minimal level of inflammation, which was demonstrated by histological examination, MPO activity, and inflammatory cytokine induction. However, 5-HT combined with a low dose of 2,4,6-trinitrobenzene sulfonic acid (TNBS), the level of which caused a minimal level of colitis, exaggerated colon inflammation accompanied by much more enhanced induction of inflammatory cytokines, IL-6, IL-8, and MCP-1, indicating that colon epithelial cells directly exposed to 5-HT are primed toward inflammation. In the colon at the lesion site, treatment with 5-HT resulted in an increase in the level of epithelial Nox2 but not of constitutively expressed Nox1, which is the opposite result of TNBS treatment. Furthermore, 5-HT treatment of Nox2-knockout mice did not induce colon inflammation, in contrast to 5-HT-treated wild-type mice. The results demonstrate that colon epithelial cells directly exposed to 5-HT are primed for inflammatory reactions, which is an important innate immune response, and the underlying mechanism for the priming is associated with Nox2-activated signaling pathways, including ERK/p38 MAPK, NF-κB, and CREB.
authors: College of Pharmacy, Yeungnam University, Gyeongsan 712-749, South Korea.
authors: Sushil Chandra
authors: SC
authors: Regmi
authors: College of Pharmacy, Yeungnam University, Gyeongsan 712-749, South Korea.
authors: Su-Young
authors: SY
authors: Park
authors: Department of Anatomy and Histology, Daegu Hany University, Gyeongsan 712-715, South Korea.
authors: Sae Kwang
authors: SK
authors: Ku
authors: College of Pharmacy, Yeungnam University, Gyeongsan 712-749, South Korea. Electronic address: jakim@yu.ac.kr.
authors: Jung-Ae
authors: JA
authors: Kim
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D002448:Cell Adhesion / Q000235:genetics / Q000276:immunology; D003092:Colitis / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D003106:Colon / Q000378:metabolism / Q000473:pathology; D004847:Epithelial Cells; D019073:HT29 Cells; D006801:Humans; D007113:Immunity, Innate; D015212:Inflammatory Bowel Diseases / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012701:Serotonin / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D008562:Membrane Glycoproteins; D017382:Reactive Oxygen Species; D012701:Serotonin; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D048051:p38 Mitogen-Activated Protein Kinases
keywords: 5-HT; Free radicals; Inflammatory bowel disease; Innate immune response; Nox2; Reactive oxygen species