Role of α-Methylacyl-CoA Racemase (Amacr) and peroxisomal Multifunctional Enzyme 1 (Mfe-1) in bile acid synthesis in mice

Cholesterol is catabolized to bile acids by peroxisomal β-oxidation in which the side-chain of C27-bile acid intermediates is shortened by three carbon atoms to form mature C24-bile acids. Knock-out mouse models deficient in α-methylacyl coenzyme A racemase (Amacr) or multifunctional enzyme type 2 (Mfe-2), in which this β-oxidation pathway is prevented, display a residual mature C24-bile acid pool although greatly reduced, which implies the existence of alternative pathways of bile acid synthesis. One alternative pathway could involve peroxisomal multifunctional enzyme type 1 (Mfe-1) either with or without Amacr. To test this hypothesis, we generated a double knock-out mouse model lacking both Amacr and Mfe-1 activities and studied the bile acid profiles in wild-type, Mfe-1 and Amacr single knock-out and Mfe-1 and Amacr double knock-out mouse lines. The total bile acid pool was decreased in Mfe-1 -/- mice compared to wild-type and the levels of mature C24-bile acids were reduced in the double knock-out mice when compared to Amacr-deficient mice. These results indicate that peroxisomal Mfe-1 can contribute to the synthesis of mature bile acids in both an Amacr–dependent and an Amacr-independent manner