title: Irgm1 protects hematopoietic stem cells by negative regulation of IFN signaling.
abstract: The IFN-inducible immunity-related p47 GTPase Irgm1 has been linked to Crohn disease as well as susceptibility to tuberculosis. Previously we demonstrated that HSC quiescence and function are aberrant in mice lacking Irgm1. To investigate the molecular basis for these defects, we conducted microarray expression profiling of Irgm1-deficient HSCs. Cell-cycle and IFN-response genes are up-regulated in Irgm1(-/-) HSCs, consistent with dysregulated IFN signaling. To test the hypothesis that Irgm1 normally down-regulates IFN signaling in HSCs, we generated Irgm1(-/-)Ifngr1(-/-) and Irgm1(-/-)Stat1(-/-) double-knockout animals. Strikingly, hyperproliferation, self-renewal, and autophagy defects in Irgm1(-/-) HSCs were normalized in double-knockout animals. These defects were also abolished in Irgm1(-/-)Irgm3(-/-) double-knockout animals, indicating that Irgm1 may regulate Irgm3 activity. Furthermore, the number of HSCs was reduced in aged Irgm1(-/-) animals, suggesting that negative feedback inhibition of IFN signaling by Irgm1 is necessary to prevent hyperproliferation and depletion of the stem cell compartment. Collectively, our results indicate that Irgm1 is a powerful negative regulator of IFN-dependent stimulation in HSCs, with an essential role in preserving HSC number and function. The deleterious effects of excessive IFN signaling may explain how hematologic abnormalities arise in patients with inflammatory conditions.
authors.affiliation: Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Katherine Y
authors.initials: KY
authors.lastname: King
authors.forename: Megan T
authors.initials: MT
authors.lastname: Baldridge
authors.forename: David C
authors.initials: DC
authors.lastname: Weksberg
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Chambers
authors.forename: Georgi L
authors.initials: GL
authors.lastname: Lukov
authors.forename: Shihua
authors.initials: S
authors.lastname: Wu
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Boles
authors.forename: Sung Yun
authors.initials: SY
authors.lastname: Jung
authors.forename: Jun
authors.initials: J
authors.lastname: Qin
authors.forename: Dan
authors.initials: D
authors.lastname: Liu
authors.forename: Zhou
authors.initials: Z
authors.lastname: Songyang
authors.forename: N Tony
authors.initials: NT
authors.lastname: Eissa
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Taylor
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Goodell
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects / Q000235:genetics; D016026:Bone Marrow Transplantation; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D005434:Flow Cytometry; D019204:GTP-Binding Proteins / Q000172:deficiency / Q000235:genetics*; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D057809:HEK293 Cells; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007372:Interferons / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D017471:Receptors, Interferon / Q000172:deficiency / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050794:STAT1 Transcription Factor / Q000172:deficiency / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics*; D000096743:Interferon gamma Receptor
chemical_list: D019204:GTP-Binding Proteins; D007372:Interferons; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; D000096743:Interferon gamma Receptor; C096000:Ifi1 protein, mouse; C494080:Stat1 protein, mouse