Knockout of the primary sclerosing cholangitis-risk gene Fut2 causes liver disease in mice

The etiopathogenesis of primary sclerosing cholangitis is unknown. Genetic variants of fucosyltransferase 2 (FUT2) have been identified in genome-wide association studies as risk factors for primary sclerosing cholangitis. We investigated the role of Fut2 in murine liver pathophysiology by studying Fut2-/- mice. Fut2-/- mice were viable and fertile, had lower body weight than wild-type (wt) littermates and gray fur. Half of the Fut2-/- mice showed serum bile salt levels 40 times higher than wt (Fut2-/-high ), whereas the remainder were normocholanemic (Fut2-/-low ). Fut2-/- mice showed normal serum liver tests, bile flow, biliary bile salt secretion, fecal bile salt loss, and expression of major hepatocellular bile salt transporters and cytochrome P450 7a1, the key regulator of bile salt synthesis, indicating that elevated serum bile salts in Fut2-/-high mice were not explained by cholestasis. Fut2-/-high mice, but not Fut2-/-low mice, were sensitive to hydrophobic bile salt feeding (0.3% glycochenodeoxycholate); they rapidly lost weight and showed elevation of serum liver tests (alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase) and areas of liver parenchymal necrosis. Histomorphological evaluation revealed the presence of paraportal shunting vessels, increased numbers of portal vascular structures, wall thickening of some portal arteries, and periductal fibrosis in Fut2-/-high mice more than Fut2-/-low mice and not wt mice. Unconjugated bilirubin and ammonia were or tended to be elevated in Fut2-/-high mice only. Portosystemic shunting was demonstrated by portal angiography, which disclosed virtually complete portosystemic shunting in Fut2-/-high mice, discrete portosystemic shunting in Fut2-/-low mice, and no shunting in wt littermates.

CONCLUSION

Liver pathology in Fut2-/- mice is dominated by consequences of portosystemic shunting resulting in microcirculatory disturbances, mild (secondary) periductal fibrosis, and sensitivity toward human bile salt toxicity. (Hepatology 2017;66:542-554).

Fucosyltransferase 2: a genetic risk factor for primary sclerosing cholangitis and Crohn's disease--a comprehensive review

Fucosyltransferase 2 (FUT2) mediates the inclusion of fucose in sugar moieties of glycoproteins and glycolipids. ABO blood group antigens and host-microbe interactions are influenced by FUT2 activity. About 20 % of the population has a "non-secretor" status caused by inactivating variants of FUT2 on both alleles. The non-sense mutation G428A and the missense mutation A385T are responsible for the vast majority of the non-secretor status in Caucasians, Africans, and Asians, respectively. Non-secretor individuals do not secrete fucose-positive antigens and lack fucosylation in epithelia. They also appear to be protected against a number of infectious diseases, such as Norovirus and Rotavirus infections. In recent years, genome-wide association studies (GWAS) identified inactivating variants at the FUT2 locus to be associated with primary sclerosing cholangitis (PSC), Crohn's disease (CD), and biochemical markers of biliary damage. These associations are intriguing given the important roles of fucosylated glycans in host-microbe interactions and membrane stability. Non-secretors have a reduced fecal content of Bifidobacteria. The intestinal bacterial composition of CD patients resembles the one of non-secretors, with an increase in Firmicutes and decreases in Proteobacteria and Actinobacteria. Non-secretor individuals lack fucosylated glycans at the surface of biliary epithelium and display a different bacterial composition of bile compared to secretors. Notably, an intact biliary epithelial glycocalix is relevant for a stable 'biliary HCO3 (-) umbrella' to protect against toxic effects of hydrophobic bile salt monomers. Here, the biology of FUT2 will be discussed as well as hypotheses to explain the role of FUT2 in the pathophysiology of PSC and Crohn's disease.