title: Differential signal pathway activation and 5-HT function: the role of gut enterochromaffin cells as oxygen sensors.
abstract: The chemomechanosensory function of the gut enterochromaffin (EC) cell enables it to respond to dietary agents and mechanical stretch. We hypothesized that the EC cell, which also sensed alterations in luminal or mucosal oxygen level, was physiologically sensitive to fluctuations in O(2). Given that low oxygen levels induce 5-HT production and secretion through a hypoxia inducible factor 1α (HIF-1α)-dependent pathway, we also hypothesized that increasing O(2) would reduce 5-HT production and secretion. Isolated normal EC cells as well as the well-characterized EC cell model KRJ-I were used to examine HIF signaling (luciferase-assays), hypoxia transcriptional response element (HRE)-mediated transcription (PCR), signaling pathways (Western blot), and 5-HT release (ELISA) during exposure to different oxygen levels. Normal EC cells and KRJ-I cells express HIF-1α, and transient transfection with Renilla luciferase under HRE control identified a hypoxia-mediated pathway in these cells. PCR confirmed activation of HIF-downstream targets, GLUT1, IGF2, and VEGF under reduced O(2) levels (0.5%). Reducing O(2) also elevated 5-HT secretion (2-3.2-fold) as well as protein levels of HIF-1α (1.7-3-fold). Increasing O(2) to 100% inhibited HRE-mediated signaling, transcription, reduced 5-HT secretion, and significantly lowered HIF-1α levels (∼75% of control). NF-κB signaling was also elevated during hypoxia (1.2-1.6-fold), but no significant changes were noted in PKA/cAMP. We concluded that gut EC cells are oxygen responsive, and alterations in O(2) levels differentially activate HIF-1α and tryptophan hydroxylase 1, as well as NF-κB signaling. This results in alterations in 5-HT production and secretion and identifies that the chemomechanosensory role of EC cells extends to oxygen sensing.
authors.affiliation: Gastrointestinal Pathobiology Research Group, Yale Univ. School of Medicine, New Haven, CT 06510, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Haugen
authors.forename: Rikard
authors.initials: R
authors.lastname: Dammen
authors.forename: Bernhard
authors.initials: B
authors.lastname: Svejda
authors.forename: Bjorn I
authors.initials: BI
authors.lastname: Gustafsson
authors.forename: Roswitha
authors.initials: R
authors.lastname: Pfragner
authors.forename: Irvin
authors.initials: I
authors.lastname: Modlin
authors.forename: Mark
authors.initials: M
authors.lastname: Kidd
mesh_terms: D004759:Enterochromaffin Cells / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology; D016328:NF-kappa B / Q000502:physiology; D010100:Oxygen / Q000008:administration & dosage / Q000494:pharmacology*; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014365:Tryptophan Hydroxylase / Q000378:metabolism
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D012701:Serotonin; C497467:TPH1 protein, human; D014365:Tryptophan Hydroxylase; D010100:Oxygen