title: Chlamydia trachomatis inhibits inducible NO synthase in human mesenchymal stem cells by stimulating polyamine synthesis.
abstract: Chlamydia trachomatis is considered the most common agent of sexually transmitted disease worldwide. As an obligate intracellular bacterium, it relies on the host for survival. Production of NO is an effective antimicrobial defense mechanism of the innate immune system. However, whether NO is able to arrest chlamydial growth remains unclear. Similarly, little is known about the mechanisms underlying subversion of cellular innate immunity by C. trachomatis. By analyzing protein and mRNA expression in infected human mesenchymal stem cells, combined with RNA interference and biochemical assays, we observed that infection with C. trachomatis led to downregulated expression of inducible NO synthase (iNOS) in human mesenchymal stem cells in vitro. Furthermore, infection upregulated the expression of the rate-limiting enzyme in the polyamine biosynthetic pathway, ornithine decarboxylase, diverting the iNOS substrate l-arginine toward the synthesis of polyamines. Inhibition of ornithine decarboxylase activity using small interfering RNA or the competitive inhibitor difluoromethylornithine restored iNOS protein expression and activity in infected cells and inhibited chlamydial growth. This inhibition was mediated through tyrosine nitration of chlamydial protein by peroxynitrite, an NO metabolite. Thus, Chlamydia evades innate immunity by inhibiting NO production through induction of the alternative polyamine pathway.
authors.affiliation: Department of Molecular Biology, Max Planck Institute for Infection Biology, 10117 Berlin, Germany.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Abu-Lubad
authors.affiliation: Department of Molecular Biology, Max Planck Institute for Infection Biology, 10117 Berlin, Germany meyer@mpiib-berlin.mpg.de al-zeer@mpiib-berlin.mpg.de.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Meyer
authors.affiliation: Department of Molecular Biology, Max Planck Institute for Infection Biology, 10117 Berlin, Germany meyer@mpiib-berlin.mpg.de al-zeer@mpiib-berlin.mpg.de.
authors.forename: Munir A
authors.initials: MA
authors.lastname: Al-Zeer
mesh_terms: D001120:Arginine / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D002690:Chlamydia Infections / Q000276:immunology; D002692:Chlamydia trachomatis / Q000254:growth & development / Q000276:immunology / Q000378:metabolism*; D000518:Eflornithine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000201:enzymology / Q000378:metabolism* / Q000382:microbiology; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D009955:Ornithine Decarboxylase / Q000096:biosynthesis* / Q000235:genetics; D065108:Ornithine Decarboxylase Inhibitors; D030421:Peroxynitrous Acid / Q000737:chemistry; D011073:Polyamines / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis; D034741:RNA, Small Interfering; D015854:Up-Regulation
chemical_list: D004791:Enzyme Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D030421:Peroxynitrous Acid; D001120:Arginine; D052247:Nitric Oxide Synthase Type II; D009955:Ornithine Decarboxylase; D000518:Eflornithine