title: Mechanical stress is a pro-inflammatory stimulus in the gut: in vitro, in vivo and ex vivo evidence.
abstract: OBJECTIVE
  Inflammatory infiltrates and pro-inflammatory mediators are found increased in obstructive and functional bowel disorders, in which lumen distention is present. However, what caused the low level inflammation is not well known. We tested the hypothesis that lumen distention- associated mechanical stress may induce expression of specific inflammatory mediators in gut smooth muscle.
  
  
  METHODS
  Static mechanical stretch (18% elongation) was applied in vitro in primary culture of rat colonic circular smooth muscle cells (RCCSMCs) with a Flexercell FX-4000 Tension Plus System. Mechanical distention in vivo was induced in rats with an obstruction band placed in the distal colon.
  
  
  RESULTS
  In the primary culture of RCCSMCs, we found that static stretch significantly induced mRNA expression of iNOS, IL-6, and MCP-1 in 3 hours by 6.0(±1.4), 2.5(±0.5), and 2.2(±0.5) fold (n = 6∼8, p<0.05), respectively. However, gene expression of TNF-α, IL-1β, and IL-8 was not significantly affected by mechanical stretch. In the in vivo model of colon obstruction, we found that gene expression of iNOS, IL-6, and MCP-1 is also significantly increased in a time-dependent manner in the mechanically distended proximal segment, but not in the sham controls or distal segments. The conditioned medium from the muscle strips of the stretched proximal segment, but not the distal segment or control, significantly induced translocation and phosphorylation of NF-κB p65. This treatment further increased mRNA expression of inflammatory mediators in the naïve cells. However, treatment of the conditioned medium from the proximal segment with neutralizing antibody against rat IL-6 significantly attenuated the activation of NF-κB and gene expression of inflammatory mediators.
  
  
  CONCLUSIONS
  Our studies demonstrate that mechanical stress induces gene expression of inflammatory mediators i.e. iNOS, IL-6, and MCP-1 in colonic SMC. Further ex vivo study showed that mechanical stress functions as a pro-inflammatory stimulus in the gut.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas, United States of America.
authors.forename: You-Min
authors.initials: YM
authors.lastname: Lin
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas, United States of America.
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas, United States of America.
authors.forename: Xuan-Zheng
authors.initials: XZ
authors.lastname: Shi
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000494:pharmacology; D002478:Cells, Cultured; D018925:Chemokines / Q000235:genetics / Q000378:metabolism; D003106:Colon / Q000473:pathology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D041981:Gastrointestinal Tract / Q000187:drug effects / Q000473:pathology*; D007249:Inflammation / Q000473:pathology*; D018836:Inflammation Mediators / Q000378:metabolism; D007415:Intestinal Obstruction / Q000473:pathology; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D057134:Antibodies, Neutralizing; D018925:Chemokines; D017077:Culture Media, Conditioned; D018836:Inflammation Mediators; D016328:NF-kappa B; D012333:RNA, Messenger; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II