Lipopolysaccharides stimulate adrenomedullin synthesis in intestinal epithelial cells: release kinetics and secretion polarity.
Adrenomedullin (AM), a potent vasodilator peptide initially isolated from a human pheochromocytoma, functions as an antimicrobial peptide in host defense. In this study, we investigated changes in AM levels in intestinal epithelial cells and the mechanism of its secretion and cellular polarity after exposure to lipopolysaccharides (LPS). When a rat small intestinal cell line (IEC-18 cells) was exposed to LPS, enzyme-linked immunosorbent assay revealed a dose-dependent increase in AM together with an increase in AM mRNA expression, as determined by real-time polymerase chain reaction. Up-regulation of AM by LPS was dose-dependently inhibited by LY294002, PD98059, SP600125 and calphostin-C, suggesting the involvement of the phosphatidylinositol 3 kinase, extracellular signal-regulated kinase, c-Jun NH2-terminal kinase and protein kinase C pathways, respectively, in this process. When polarized IEC-18 cells in a Transwell chamber were stimulated with LPS, AM secretion was directed primarily toward the side of LPS administration (either the apical or basolateral side). In situ hybridization revealed that AM mRNA was expressed in epithelial cells and in the connective tissue in the lamina propria of the jejunum after intraperitoneal or oral administration of LPS. Higher levels of AM mRNA expression were observed in rats treated with LPS via the intraperitoneal route, compared with those treated via the oral route. These findings suggest that intestinal AM plays an important role in mucosal defense in the case of intestinal luminal infection, as well as in the modulation of hemodynamics in endotoxemia.
Department of Gastroenterology, Tokyo Dental College, Ichikawa General Hospital, 5-11-13 Sugano Ichikawa, Chiba 272-8513, Japan.
Hiroshi
H
Kishikawa
Jiro
J
Nishida
Hitoshi
H
Ichikawa
Shogo
S
Kaida
Tetsuo
T
Morishita
Soichiro
S
Miura
Toshifumi
T
Hibi
D053607:Adrenomedullin / Q000096:biosynthesis*; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D017403:In Situ Hybridization; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008070:Lipopolysaccharides / Q000235:genetics / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats
D017931:DNA Primers; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D053607:Adrenomedullin