title: Smad7 interrupts TGF-β signaling in intestinal macrophages and promotes inflammatory activation of these cells during necrotizing enterocolitis.
abstract: Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants. Based on our recent findings of increased Smad7 expression in surgically resected bowel affected by NEC, we hypothesized that NEC macrophages undergo inflammatory activation because increased Smad7 expression renders these cells resistant to normal, gut-specific, transforming growth factor (TGF)-β-mediated suppression of inflammatory pathways.
  
  
  
  We used surgically resected human NEC tissue, murine models of NEC-like injury, bone marrow-derived and intestinal macrophages, and RAW264.7 cells. Smad7 and IκB kinase-beta (IKK-β) were measured by quantitative PCR, western blots, and immunohistochemistry. Promoter activation was confirmed in luciferase reporter and chromatin immunoprecipitation assays.
  
  
  
  NEC macrophages showed increased Smad7 expression, particularly in areas with severe tissue damage and high bacterial load. Lipopolysaccharide-induced Smad7 expression suppressed TGF-β signaling and augmented nuclear factor-kappa B (NF-κB) activation and cytokine production in macrophages. Smad7-mediated NF-κB activation was likely mediated via increased expression of IKK-β, which, further increased Smad7 expression in a feed-forward loop. We show that Smad7 induced IKK-β expression through direct binding to the IKK-β promoter and its transcriptional activation.
  
  
  
  Smad7 expression in NEC macrophages interrupts TGF-β signaling and promotes NF-κB-mediated inflammatory signaling in these cells through increased expression of IKK-β.
authors: Department of Pediatrics, University of Illinois at Chicago, Chicago, Illinois.|Department of Pediatrics, Morsani College of Medicine, University of South Florida, Tampa, Florida.
authors: Krishnan
authors: K
authors: MohanKumar
authors: Department of Pediatrics, University of Illinois at Chicago, Chicago, Illinois.|Department of Pediatrics, Morsani College of Medicine, University of South Florida, Tampa, Florida.
authors: Kopperuncholan
authors: K
authors: Namachivayam
authors: Department of Pharmaceutical Sciences, College of Pharmacy, University of South Florida, Tampa, Florida.
authors: Kalyan C
authors: KC
authors: Chapalamadugu
authors: Department of Pathology, University of Illinois at Chicago, Chicago, Illinois.
authors: Steven A
authors: SA
authors: Garzon
authors: Department of Pediatrics, Baylor College of Medicine, Houston, Texas.
authors: Muralidhar H
authors: MH
authors: Premkumar
authors: Department of Pharmaceutical Sciences, College of Pharmacy, University of South Florida, Tampa, Florida.
authors: Srinivas M
authors: SM
authors: Tipparaju
authors: Department of Pediatrics, University of Illinois at Chicago, Chicago, Illinois.|Department of Pediatrics, Morsani College of Medicine, University of South Florida, Tampa, Florida.|Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida.|Department of Community and Family Health, College of Public Health, University of South Florida, Tampa, Florida.
authors: Akhil
authors: 0000-0003-1502-7663
authors: A
authors: Maheshwari
mesh_terms: D000818:Animals; D020345:Enterocolitis, Necrotizing / Q000378:metabolism*; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D007249:Inflammation; D007413:Intestinal Mucosa / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D000067996:RAW 264.7 Cells; D015398:Signal Transduction; D051906:Smad7 Protein / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D008070:Lipopolysaccharides; D016328:NF-kappa B; C497806:SMAD7 protein, human; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; D016212:Transforming Growth Factor beta; D051550:I-kappa B Kinase