title: TNFR2 activates MLCK-dependent tight junction dysregulation to cause apoptosis-mediated barrier loss and experimental colitis.
abstract: OBJECTIVE
  Tight junction dysregulation and epithelial damage contribute to barrier loss in patients with inflammatory bowel disease. However, the mechanisms that regulate these processes and their relative contributions to disease pathogenesis are not completely understood. We investigated these processes using colitis models in mice.
  
  
  METHODS
  We induced colitis by adoptive transfer of CD4(+)CD45RB(hi) cells or administration of dextran sulfate sodium to mice, including those deficient in tumor necrosis factor receptor (TNFR) 1, TNFR2, or the long isoform of myosin light chain kinase (MLCK). Intestinal tissues and isolated epithelial cells were analyzed by immunoblot, immunofluorescence, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction assays.
  
  
  RESULTS
  Induction of immune-mediated colitis by CD4(+)CD45RB(hi) adoptive transfer increased intestinal permeability, epithelial expression of claudin-2, the long isoform of MLCK, and TNFR2 (but not TNFR1) and phosphorylation of the myosin II light chain. Long MLCK upregulation, myosin II light chain phosphorylation, barrier loss, and weight loss were attenuated in TNFR2(-/-) , but not TNFR1(-/-) , recipients of wild-type CD4(+)CD45RB(hi) cells. Similarly, long MLCK(-/-) mice had limited increases in myosin II light chain phosphorylation, claudin-2 expression, and intestinal permeability and delayed onset of adoptive transfer-induced colitis. However, coincident with onset of epithelial apoptosis, long MLCK(-/-) mice ultimately developed colitis. This indicates that disease progresses via apoptosis in the absence of MLCK-dependent tight junction regulation. In support of this conclusion, long MLCK(-/-) mice were not protected from epithelial apoptosis-mediated, damage-dependent dextran sulfate sodium colitis.
  
  
  CONCLUSIONS
  In immune-mediated inflammatory bowel disease models, TNFR2 signaling increases long MLCK expression, resulting in tight junction dysregulation, barrier loss, and induction of colitis. At advanced stages, colitis progresses by apoptosis and mucosal damage that result in tight junction- and MLCK-independent barrier loss. Therefore, barrier loss in immune-mediated colitis occurs via two temporally and morphologically distinct mechanisms. Differential targeting of these mechanisms can lead to improved inflammatory bowel disease therapies.
authors.affiliation: Shanghai Key Laboratory of Gastric Neoplasms, Shanghai Institute of Digestive Surgery, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Liping
authors.initials: L
authors.lastname: Su
authors.forename: Sam C
authors.initials: SC
authors.lastname: Nalle
authors.forename: Le
authors.initials: L
authors.lastname: Shen
authors.forename: Emily S
authors.initials: ES
authors.lastname: Turner
authors.forename: Gurminder
authors.initials: G
authors.lastname: Singh
authors.forename: Lydia A
authors.initials: LA
authors.lastname: Breskin
authors.forename: Ekaterina A
authors.initials: EA
authors.lastname: Khramtsova
authors.forename: Galina
authors.initials: G
authors.lastname: Khramtsova
authors.forename: Pei-Yun
authors.initials: PY
authors.lastname: Tsai
authors.forename: Yang-Xin
authors.initials: YX
authors.lastname: Fu
authors.forename: Clara
authors.initials: C
authors.lastname: Abraham
authors.forename: Jerrold R
authors.initials: JR
authors.lastname: Turner
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D062446:Claudin-2 / Q000378:metabolism; D003092:Colitis / Q000276:immunology / Q000378:metabolism / Q000503:physiopathology*; D016264:Dextran Sulfate; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D015212:Inflammatory Bowel Diseases; D007413:Intestinal Mucosa / Q000276:immunology / Q000378:metabolism / Q000503:physiopathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018994:Myosin Light Chains / Q000378:metabolism; D024462:Myosin Type II / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000235:genetics / Q000502:physiology*; D010539:Permeability; D010766:Phosphorylation; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000235:genetics / Q000502:physiology*; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D019108:Tight Junctions / Q000378:metabolism / Q000502:physiology*; D015854:Up-Regulation; D015431:Weight Loss
chemical_list: D062446:Claudin-2; D018994:Myosin Light Chains; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; C506236:Tnfrsf1a protein, mouse; D016264:Dextran Sulfate; D009219:Myosin-Light-Chain Kinase; D024462:Myosin Type II
keywords: CA-MLCK; DSS; Disease Progression; Epithelial Barrier; IBD; Inflammatory Bowel Disease; Intestinal Permeability; MLC; MLCK; Rag1; TNF; TNFR; constitutively active myosin light chain kinase; dextran sulfate sodium; inflammatory bowel disease; myosin II regulatory light chain; myosin light chain kinase; recombinase activating gene 1; tumor necrosis factor; tumor necrosis factor receptor