Deletion of murine betaine-homocysteine S-methyltransferase in mice perturbs choline and 1-carbon metabolism, resulting in fatty liver and hepatocellular carcinoma

Betaine-homocysteine S-methyltransferase (BHMT) uses betaine to catalyze the degradation of homocysteine (Hcy). There are common genetic polymorphisms in the BHMT gene in humans. To model the phenotype of mice with a loss of BHMT function, we generated the first Bhmt-/- mouse. Deletion of the gene resulted in a 6-fold increase in hepatic and an 8-fold increase in plasma Hcy concentrations, suggesting the importance of BHMT in Hcy removal. Deletion of the gene resulted in a 43% reduction in hepatic S-adenosylmethionine (AdoMet) and a 3-fold increase in hepatic S-adenosylhomocysteine (AdoHcy) concentrations, resulting in a 75% reduction in methylation potential (AdoMet:AdoHcy). Bhmt-/- mice accumulated betaine in most tissues, including a 21-fold increase in the liver concentration compared to wildtype (WT). These mice had lower concentrations of choline, phosphocholine, glycerophosphocholine, phosphatidylcholine and sphingomyelin in several tissues. At 5 weeks of age, Bhmt-/- mice had 36% lower total hepatic phospholipid concentrations and a 6-fold increase in hepatic triacyglycerol concentrations compared to WT, which was due to a decrease in the secretion of very low density lipoproteins. At 1 year of age, 64% of Bhmt-/- mice had visible hepatic tumors. Histopathological analysis revealed that Bhmt-/- mice developed hepatocellular carcinoma (HCC) or carcinoma precursors. These results indicate that BHMT has an important role in Hcy, choline and one-carbon homeostasis. A lack of BHMT also affects susceptibility to fatty liver and HCC. We suggest that functional polymorphisms in BHMT that significantly reduce activity may have similar effects in humans.

Teng, Y.W., et al., Deletion of murine betaine-homocysteine S-methyltransferase in mice perturbs choline and 1-carbon metabolism, resulting in fatty liver and hepatocellular carcinoma. J Biol Chem, 2011. 286: p. 36258-67