Role of AMACR (α-methylacyl-CoA racemase) and MFE-1 (peroxisomal multifunctional enzyme-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. Knockout mouse models deficient in AMACR (α-methylacyl-CoA racemase) or MFE-2 (peroxisomal multifunctional enzyme type 2), in which this β-oxidation pathway is prevented, display a residual C₂₄-bile acid pool which, although greatly reduced, implies the existence of alternative pathways of bile acid synthesis. One alternative pathway could involve Mfe-1 (peroxisomal multifunctional enzyme type 1) either with or without Amacr. To test this hypothesis, we generated a double knockout mouse model lacking both Amacr and Mfe-1 activities and studied the bile acid profiles in wild-type, Mfe-1 and Amacr single knockout mouse line and Mfe-1 and Amacr double knockout mouse lines. The total bile acid pool was decreased in Mfe-1^-/- mice compared with wild-type and the levels of mature C₂₄-bile acids were reduced in the double knockout mice when compared with Amacr-deficient mice. These results indicate that Mfe-1 can contribute to the synthesis of mature bile acids in both Amacr-dependent and Amacr-independent pathways.