Mast Natalia, Anderson Kyle W, Lin Joseph B, Li Yong, Turko Illarion V, Tatsuoka Curtis, Bjorkhem Ingemar, Pikuleva Irina A
From the Departments of Ophthalmology and Visual Sciences and.
the Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
J Biol Chem. 2017 Mar 24;292(12):4913-4924. doi: 10.1074/jbc.M116.774760. Epub 2017 Feb 11.
Cytochrome P450 27A1 (CYP27A1 or sterol 27-hydroxylase) is a ubiquitous, multifunctional enzyme catalyzing regio- and stereospecific hydroxylation of different sterols. In humans, complete CYP27A1 deficiency leads to cerebrotendinous xanthomatosis or nodule formation in tendons and brain (preferentially in the cerebellum) rich in cholesterol and cholestanol, the 5α-saturated analog of cholesterol. In mice, xanthomas are not formed, despite a significant cholestanol increase in the brain and cerebellum. The mechanism behind cholestanol production has been clarified, yet little is known about its metabolism, except that CYP27A1 might metabolize cholestanol. It also is unclear why CYP27A1 deficiency results in preferential cholestanol accumulation in the cerebellum. We hypothesized that cholestanol might be metabolized by CYP46A1, the principal cholesterol 24-hydroxylase in the brain. We quantified sterols along with CYP27A1 and CYP46A1 in mouse models (, , , and two wild type strains) and human brain specimens. experiments with purified P450s were conducted as well. We demonstrate that CYP46A1 is involved in cholestanol removal from the brain and that several factors contribute to the preferential increase in cholestanol in the cerebellum arising from CYP27A1 deficiency. These factors include (i) low cerebellar abundance of CYP46A1 and high cerebellar abundance of CYP27A1, the lack of which probably selectively increases the cerebellar cholestanol production; (ii) spatial separation in the cerebellum of cholesterol/cholestanol-metabolizing P450s from a pool of metabolically available cholestanol; and (iii) weak cerebellar regulation of cholesterol biosynthesis. We identified a new physiological role of CYP46A1, an important brain enzyme and cytochrome P450 that could be activated pharmacologically.
细胞色素P450 27A1（CYP27A1或甾醇27 - 羟化酶）是一种普遍存在的多功能酶，可催化不同甾醇的区域和立体特异性羟基化反应。在人类中，CYP27A1完全缺乏会导致脑腱性黄瘤病，或在富含胆固醇和胆甾烷醇（胆固醇的5α - 饱和类似物）的肌腱和大脑（优先在小脑）中形成结节。在小鼠中，尽管大脑和小脑中胆甾烷醇显著增加，但不会形成黄瘤。胆甾烷醇产生的机制已经阐明，但除了CYP27A1可能代谢胆甾烷醇外，对其代谢知之甚少。此外，尚不清楚为什么CYP27A1缺乏会导致胆甾烷醇在小脑中优先积累。我们推测胆甾烷醇可能由大脑中主要的胆固醇24 - 羟化酶CYP46A1代谢。我们在小鼠模型（、、、和两个野生型品系）和人脑标本中对甾醇以及CYP27A1和CYP46A1进行了定量分析。还进行了纯化P450的实验。我们证明CYP46A1参与从大脑中清除胆甾烷醇，并且有几个因素导致了由于CYP27A1缺乏而在小脑中胆甾烷醇优先增加。这些因素包括：（i）CYP46A1在小脑中的丰度低，而CYP27A1在小脑中丰度高，缺乏CYP46A1可能选择性地增加小脑胆甾烷醇的产生；（ii）在小脑中，胆固醇/胆甾烷醇代谢的P450与可代谢的胆甾烷醇池在空间上分离；（iii）小脑对胆固醇生物合成的调节较弱。我们确定了CYP46A1的一种新的生理作用，CYP46A1是一种重要的脑酶和细胞色素P450，可通过药理学方法激活。
