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Division of Pediatric Surgery, Department of Surgery, Children’s Hospital of Pittsburgh and the University of Pittsburgh School of Medicine, Pittsburgh, PA 15260
Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in preterm infants and is characterized by translocation of LPS across the inflamed intestine. We hypothesized that the LPS receptor (TLR4) plays a critical role in NEC development, and we sought to determine the mechanisms involved. We now demonstrate that NEC in mice and humans is associated with increased expression of TLR4 in the intestinal mucosa and that physiological stressors associated with NEC development, namely, exposure to LPS and hypoxia, sensitize the murine intestinal epithelium to LPS through up-regulation of TLR4. In support of a critical role for TLR4 in NEC development, TLR4-mutant C3H/HeJ mice were protected from the development of NEC compared with wild-type C3H/HeOUJ littermates. TLR4 activation in vitro led to increased enterocyte apoptosis and reduced enterocyte migration and proliferation, suggesting a role for TLR4 in intestinal repair. In support of this possibility, increased NEC severity in C3H/HeOUJ mice resulted from increased enterocyte apoptosis and reduced enterocyte restitution and proliferation after mucosal injury compared with mutant mice. TLR4 signaling also led to increased serine phosphorylation of intestinal focal adhesion kinase (FAK). Remarkably, TLR4 coimmunoprecipitated with FAK, and small interfering RNA-mediated FAK inhibition restored enterocyte migration after TLR4 activation, demonstrating that the FAK-TLR4 association regulates intestinal healing. These findings demonstrate a critical role for TLR4 in the development of NEC through effects on enterocyte injury and repair, identify a novel TLR4-FAK association in regulating enterocyte migration, and suggest TLR4/FAK as a therapeutic target in this disease.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 D.J.H. is supported by R01GM078238-01 from the National Institutes of Health and the State of Pennsylvania Tobacco Settlement Fund. C.L.L. is supported in part by the Loan Repayment Program for Pediatric Research of the National Institutes of Health. J.C. received an Administration on Aging Medical Student Research Award, and is supported by the Surgical Translational Research Training Program of the University of Pittsburgh.
2 Address correspondence and reprint requests to Dr. David J. Hackam, Division of Pediatric Surgery, Room 4A-486 DeSoto Wing, Children’s Hospital of Pittsburgh, Pittsburgh, PA 15213. E-mail address: david.hackam{at}chp.edu
3 Abbreviations used in this paper: NEC, necrotizing enterocolitis; FAK, focal adhesion kinase; ATRA, all-trans-retinoic acid; siRNA, small interfering RNA; XTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.
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