Cox-2 is regulated by Toll-like receptor-4 (TLR4) signaling: Role in proliferation and apoptosis in the intestine.
OBJECTIVE
We recently showed that mice deficient in Toll-like receptor 4 (TLR4) or its adapter molecule MyD88 have increased signs of colitis compared with wild-type (WT) mice after dextran sodium sulfate (DSS)-induced injury. We wished to test the hypothesis that cyclooxygenase 2 (Cox-2)-derived prostaglandin E2 (PGE2) is important in TLR4-related mucosal repair.


METHODS
Cox-2 expression was analyzed by real-time polymerase chain reaction, immunohistochemistry, Western blotting, and luciferase reporter constructs. Small interfering RNA was used to inhibit expression of MyD88. TLR4-/- or WT mice were given 2.5% DSS for 7 days. Proliferation and apoptosis were assessed using bromodeoxyuridine staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays, respectively. PGE2 was given orally to DSS-treated mice.


RESULTS
Intestinal epithelial cell lines up-regulated Cox-2 expression in a TLR4- and MyD88-dependent fashion. Lipopolysaccharide-mediated stimulation of PGE2 production was blocked by a selective Cox-2 inhibitor or small interfering RNA against MyD88. After DSS injury, Cox-2 expression increased only in WT mice. TLR4-/- mice have significantly reduced proliferation and increased apoptosis after DSS injury compared with WT mice. PGE2 supplementation of TLR4-/- mice resulted in improvement in clinical signs of colitis and restoration of proliferation and apoptosis to WT values. The mechanism for improved epithelial repair may be through PGE2-dependent activation of the epidermal growth factor receptor.


CONCLUSIONS
We describe an important link between TLR4 signaling and Cox-2 expression in the gut. TLR4 and MyD88 signaling are required for optimal proliferation and protection against apoptosis in the injured intestine. Although TLR4 signaling is beneficial in the short term, chronic signaling through TLR4 may lower the threshold for colitis-associated cancer.
Fukata
Masayuki
M
Inflammatory Bowel Disease Center, Division of Gastroenterology, New York, New York, USA.
Chen
Anli
A
Klepper
Arielle
A
Krishnareddy
Suneeta
S
Vamadevan
Arunan S
AS
Thomas
Lisa S
LS
Xu
Ruliang
R
Inoue
Hiroyasu
H
Arditi
Moshe
M
Dannenberg
Andrew J
AJ
Abreu
Maria T
MT
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation; D003092:Colitis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D051546:Cyclooxygenase 2 / Q000235:genetics* / Q000378:metabolism; D016264:Dextran Sulfate / Q000633:toxicity; D015232:Dinoprostone / Q000096:biosynthesis; D004195:Disease Models, Animal; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics*; D012720:Severity of Illness Index; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C507779:MYD88 protein, human; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D051197:Toll-Like Receptor 4; D012313:RNA; D016264:Dextran Sulfate; D051546:Cyclooxygenase 2; D015232:Dinoprostone