Lipopolysaccharide Decreases Expression of the Farnesoid X Receptor and its Downstream Products

Author(s):
Michael Philippe-Auguste; Michelle Nguyen; Christopher P. Gayer

Background:

Farnesoid X receptor (FXR) is a nuclear bile acid receptor that has been shown to play a role in intestinal barrier integrity. Our lab has previously shown that lipopolysaccharide (LPS)-induced intestinal injury seen in wild type mice is attenuated in FXR knock out mice. Fibroblast growth factor 15/19 (Fgf15/19) and small heterodimer partner (SHP) are downstream FXR products that may be involved in the mechanism through which this attenuation occurs.

Hypothesis:

We hypothesized that LPS leads to FXR activation and upregulation of its downstream products Fgf15/19 and SHP.

Methods:

IEC-6 cells were treated with 100 uM GW4604, a potent FXR activator or 2 ng/mL LPS for 30 minutes, one, two, six and 24 hours. RNA was extracted with Trizol. Real-time PCR was used to measure mRNA expression of FXR, Fgf15/19 and SHP. IEC-6 cells were then treated with combined 100 uM GW4064 and 2 ng/mL of LPS for six hours. RNA extraction was performed with subsequent RT-PCR analysis.

Results:

IEC-6 cells treated with GW4064 showed an increase in mRNA expression of Fgf15/19 compared to control that peaked at six hours (40% increase, p<0.05). Cells treated with LPS showed a 90% decrease (p<0.0005) in Fgf15/19 expression compared to controls at six hours as well, which was opposite of what we expected since LPS had no effect on the barrier of FXR KO mice. We also noted a 50% decrease in FXR expression (p<0.05) with LPS treatment, but not until 24-hours. Interestingly, SHP mRNA expression decreased 70% (p<0.05), but at two hours with LPS administration. Finally, LPS blunted the effect of GW4064 on both Fgf15/19 and SHP expression when treated in combination

Conclusions:

These data suggest that LPS treatment blunts the activation of FXR as evidence by decreased expression of FXR and its downstream products Fgf15/19 and SHP, although this occurs at different time points. Future investigations will focus on how these effects alter intestinal barrier integrity during injury.