A Critical Role for TLR4 in the Pathogenesis of Necrotizing Enterocolitis by Modulating Intestinal Injury and Repair

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.

As shown, TLR4-mutant mice are protected from the development of NEC. NEC was experimentally induced in newborn TLR4-wild-type (C3H/HeOUJ, A and D) and TLR4-mutant (C3H/HeJ, B and F) mice. Breast-fed animals that were either TLR4-wild type (C) or TLR4-mutant (E) served as controls. The extent of intestinal inflammation was assessed on gross (A and B) and histological inspection of the intestine (C–F). G, Quantification of NEC severity as determined by a blinded observer and graded as 0 (normal), 1 (mild, separation of villus core without other abnormalities), 2 (moderate, villus core separation, submucosal edema, and sloughing of the epithelium), or 3 (severe, loss of villus, full thickness necrosis, or marked edema). Data are means _ SEM of at least four separate experiments with at least three animals per group. _, p _ 0.05 by ANOVA compared with formula/hypoxia-treated wild-type animals.
Leaphart CL, Cavallo J, Gribar SC, Cetin S, Li J, Branca MF, Dubowski TD, Sodhi CP, Hackam DJ
J Immunol
2007 Oct 1
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January 18, 2011
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Last Update
January 18, 2011