EPIDERMAL GROWTH FACTOR (EGF) ATTENUATES LPS-MEDIATED SIGNALING IN ENTEROCYTES THROUGH REDUCED EXPRESSION OF TOLL LIKE RECEPTOR 4 DURING ENDOTOXEMIC STRESS

Abstract

Objective: EGF has been shown to protect the intestine during endotoxemia, although the mechanisms mediating this effect remain largely unexplored. We now hypothesize that EGF reduces LPS-mediated signaling in enterocytes, and sought to determine the mechanisms involved. Methods: TLR4 signaling and expression were assessed by treating IEC-6 cells with LPS (100 ng-50 μg/ml) ± EGF(50 nM) or injecting wild-type or TLR4-mutant mice with LPS (1-5 mg/kg) ± EGF (50 μg/kg), then probing for pERK, total ERK or TLR4. Results: LPS caused a dose-dependent increase in the expression of pERK in IEC-6 enterocytes, which was reversed when cells were pre-treated with EGF (Figure). These findings were also observed in vivo, as LPS injection resulted in a significant increase in the ileal mucosal expression of pERK of wild-type but not TLR4-mutant mice, which was decreased when animals were pre-injected with EGF but not saline. To understand the mechanisms underlying this effect, EGF caused a dose- and time-dependent decrease in the expression of TLR4 in IEC-6 cells as compared with untreated cells. Strikingly, injection of endotoxemic wild-type animals with EGF led to a significant decrease in the expression of TLR4 in the ileal mucosa which corresponded with the reduced pERK expression, which was not observed in saline injected or TLR4-mutant mice.FigureConclusions: EGF attenuates LPS-mediated signaling in vitro and in vivo through reduced expression of TLR4 in enterocytes. These findings shed light on the regulation of TLR4 signaling by growth factors, and suggest potential therapeutic insights in the management of intestinal dysfunction during endotoxemia.