A Villin -Driven Fxr Transgene Modulates Enterohepatic Bile Acid Homeostasis and Response to an n -6-Enriched High-Fat Diet.

A diet high in n-6 polyunsaturated fatty acids (PUFAs) may contribute to inflammation and tissue damage associated with obesity and pathologies of the colon and liver. One contributing factor may be dysregulation by n-6 fatty acids of enterohepatic bile acid (BA) metabolism. The farnesoid X receptor (FXR) is a nuclear receptor that regulates BA homeostasis in the liver and intestine. This study aims to compare the effects on FXR regulation and BA metabolism of a palm oil-based diet providing 28% energy (28%E) from fat and low n-6 linoleic acid (LA, 2.5%E) (CNTL) with those of a soybean oil-based diet providing 50%E from fat and high (28%E) in LA (n-6HFD). Wild-type (WT) littermates and a transgenic mouse line overexpressing the Fxr alpha 1 isoform under the control of the intestine-specific Villin promoter (Fxr alpha 1(TG)) were fed the CNTL or n-6HFD starting at weaning through 16 weeks of age. Compared to the CNTL diet, the n-6HFD supports higher weight gain in both WT and Fxr alpha(TG) littermates; increases the expression of Fxr alpha 1/2, and peroxisome proliferator-activated receptor-gamma 1 (Ppar gamma 1) in the small intestine, Fxr alpha 1/2 in the colon, and cytochrome P4507A1 (Cyp7a1) and small heterodimer protein (Shp) in the liver; and augments the levels of total BA in the liver, and primary chenodeoxycholic (CDCA), cholic (CA), and beta-muricholic (beta MCA) acid in the cecum. Intestinal overexpression of the Fxra1(TG) augments expression of Shp and ileal bile acid-binding protein (Ibabp) in the small intestine and Ibabp in the proximal colon. Conversely, it antagonizes n-6HFD-dependent accumulation of intestinal and hepatic CDCA and CA; hepatic levels of Cyp7a1; and expression of Ppar gamma in the small intestine. We conclude that intestinal Fxr alpha 1 overexpression represses hepatic de novo BA synthesis and protects against n-6HFD-induced accumulation of human-specific primary bile acids in the cecum.