Department of Genetics and Genomic Sciences, Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY, 10029, USA.
The Donald B. and Catherine C. Marron Cancer Metabolism Center, Memorial Sloan Kettering Cancer Center, New York, NY, 10065, USA.
Cell Mol Life Sci. 2021 Jul;78(14):5631-5646. doi: 10.1007/s00018-021-03869-9. Epub 2021 Jun 10.
Peroxisomes play an essential role in the β-oxidation of dicarboxylic acids (DCAs), which are metabolites formed upon ω-oxidation of fatty acids. Genetic evidence linking transporters and enzymes to specific DCA β-oxidation steps is generally lacking. Moreover, the physiological functions of DCA metabolism remain largely unknown. In this study, we aimed to characterize the DCA β-oxidation pathway in human cells, and to evaluate the biological role of DCA metabolism using mice deficient in the peroxisomal L-bifunctional protein (Ehhadh KO mice). In vitro experiments using HEK-293 KO cell lines demonstrate that ABCD3 and ACOX1 are essential in DCA β-oxidation, whereas both the bifunctional proteins (EHHADH and HSD17B4) and the thiolases (ACAA1 and SCPx) have overlapping functions and their contribution may depend on expression level. We also show that medium-chain 3-hydroxydicarboxylic aciduria is a prominent feature of EHHADH deficiency in mice most notably upon inhibition of mitochondrial fatty acid oxidation. Using stable isotope tracing methodology, we confirmed that products of peroxisomal DCA β-oxidation can be transported to mitochondria for further metabolism. Finally, we show that, in liver, Ehhadh KO mice have increased mRNA and protein expression of cholesterol biosynthesis enzymes with decreased (in females) or similar (in males) rate of cholesterol synthesis. We conclude that EHHADH plays an essential role in the metabolism of medium-chain DCAs and postulate that peroxisomal DCA β-oxidation is a regulator of hepatic cholesterol biosynthesis.
过氧化物酶体在二羧酸 (DCA) 的β-氧化中发挥着重要作用，DCA 是脂肪酸 ω-氧化形成的代谢物。将转运蛋白和酶与特定 DCA β-氧化步骤联系起来的遗传证据通常是缺乏的。此外，DCA 代谢的生理功能在很大程度上仍然未知。在这项研究中，我们旨在表征人细胞中的 DCA β-氧化途径，并使用过氧化物酶体 L-双功能蛋白缺陷的小鼠 (Ehhadh KO 小鼠) 评估 DCA 代谢的生物学作用。使用 HEK-293 KO 细胞系的体外实验表明，ABCD3 和 ACOX1 是 DCA β-氧化所必需的，而双功能蛋白 (EHHADH 和 HSD17B4) 和硫酯酶 (ACAA1 和 SCPx) 具有重叠的功能，其贡献可能取决于表达水平。我们还表明，中链 3-羟基二羧酸尿症是小鼠 EHHADH 缺乏的一个显著特征，尤其是在抑制线粒体脂肪酸氧化时。使用稳定同位素示踪方法，我们证实过氧化物酶体 DCA β-氧化的产物可以被转运到线粒体进行进一步代谢。最后，我们表明，在肝脏中，Ehhadh KO 小鼠的胆固醇生物合成酶的 mRNA 和蛋白表达增加，胆固醇合成率降低（在雌性中）或相似（在雄性中）。我们得出结论，EHHADH 在中链 DCA 的代谢中起着至关重要的作用，并推测过氧化物酶体 DCA β-氧化是肝脏胆固醇生物合成的调节剂。
