Farnesoid-X Receptor Inhibition Allows Uninhibited Epidermal Growth Factor Activity

Author(s):
Oswaldo Escobar; Michelle Nguyen; Christopher P. Gayer

Background:

Cell migration and proliferation are components of intestinal restitution that promote the integrity of the intestinal barrier. We have previously shown that activation of the epidermal growth factor receptor (EGFR) pathway increases cell migration in a COX-2 and Erk-dependent fashion, while activation of the nuclear farnesoid-X receptor (FXR) interferes with the EGFR pathway.

Hypothesis:

We hypothesize that FXR activation will decrease cell proliferation and migration through inhibition of the EGFR pathway, leading to exacerbation of intestinal barrier injury. We will test this hypothesis using both in vitro and in vivo models of injury.

Methods:

Rat intestinal cells (IEC-6) were serum-starved for 24-48 hours and treated with vehicle control, GW4064 (FXR agonist), or guggulsterone (FXR antagonist) for 24 hours. Proliferation was measured using a crystal violet staining assay, and migration was measured using a modified wounding assay. Wild-type C57BL/6 (WT) mice received intraperitoneal injections of 30 mg/kg lipopolysaccharide (LPS) to induce peritonitis, 30 mg/kg GW4064, or the combination. Terminal ileal mucosal scrapings were harvested 16 hours after treatment. Phosphorylated Erk (pErk) and COX-2 were measured via Western blot. Statistical comparisons were done using ANOVA.

Results:

In vitro, guggulsterone-induced FXR inhibition increased cell proliferation compared to control or GW4064-induced FXR activation. FXR inhibition also allowed increased cell migration in IEC-6 cells. In vivo, both pErk and COX-2 levels were decreased in mice treated with GW4064, and further decreased in mice treated with the combination of LPS+GW4064, as measured by Western blot. We have previously shown that pErk and COX-2 epithelial expression increased with ursodeoxycholic acid (UDCA)-induced EGFR activation, leading to improved migration and barrier function.

Conclusions:

We conclude that FXR inhibition increases cell migration and proliferation, possibly through uninhibited activity of the EGFR pathway. In contrast, FXR activation decreases cell migration and proliferation, while decreasing pErk and COX-2 levels. In our lab, this change is seen when barrier function worsens. FXR may be a valuable target in treatment of intestinal diseases, such as necrotizing enterocolitis and inflammatory bowel disease.