Increased expression and internalization of the endotoxin coreceptor CD14 in enterocytes occur as an early event in the development of experimental necrotizing enterocolitis.
BACKGROUND
The early signaling events in the development of necrotizing enterocolitis (NEC) remain undefined. We have recently shown that the endotoxin (lipopolysaccharide [LPS]) receptor toll-like receptor 4 (TLR4) on enterocytes is critical in the pathogenesis of experimental NEC. Given that the membrane receptor CD14 is known to facilitate the activation of TLR4, we now hypothesize that endotoxemia induces an early upregulation of CD14 in enterocytes and that this participates in the early intestinal inflammatory response in the development of NEC.


METHODS
IEC-6 enterocytes were treated with LPS (50 microg/mL), and the subcellular localization of CD14 and TLR4 was assessed by confocal microscopy. C57/Bl6 or CD14-/- mice were treated with LPS (5 mg/kg), whereas experimental NEC was induced using a combination of gavage formula feeding and intermittent hypoxia. CD14 expression was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse transcriptase-polymerase chain reaction, and interleukin 6 was quantified by enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction.


RESULTS
Exposure of IEC-6 enterocytes to LPS led to an initial, transient increase in CD14 expression. The early increase in CD14 expression was associated with internalization of CD14 to a perinuclear compartment where increased colocalization with TLR4 was noted. The in vivo significance of these findings is suggested as treatment of mice with LPS led to an early increase in CD14 expression in the intestinal mucosa, whereas the persistent endotoxemia of experimental NEC was associated with decreased CD14 expression within enterocytes.


CONCLUSIONS
LPS signaling in the enterocyte is marked by an early, transient increase in expression of CD14 and redistribution of the receptor. This process may contribute to the early activation of the intestinal inflammatory response that is observed in the development of NEC.
Department of Surgery, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Kevin P
KP
Mollen
Steven C
SC
Gribar
Rahul J
RJ
Anand
David J
DJ
Kaczorowski
Jeffrey W
JW
Kohler
Maria F
MF
Branca
Theresa D
TD
Dubowski
Chhinder P
CP
Sodhi
David J
DJ
Hackam
D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D019446:Endotoxemia / Q000503:physiopathology*; D004731:Endotoxins; D020345:Enterocolitis, Necrotizing / Q000235:genetics* / Q000503:physiopathology; D020895:Enterocytes / Q000166:cytology / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism / Q000503:physiopathology; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D011336:Probability; D011897:Random Allocation; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
D004731:Endotoxins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4