A mammalian fatty acid hydroxylase responsible for the formation of α-hydroxylated galactosylceramide in myelin
A mammalian fatty acid hydroxylase responsible for the formation of α-hydroxylated galactosylceramide in myelin
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DOI：
10.1042/bj20041451
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发表时间：
2005-05-15
影响因子：
4.1
通讯作者：
Gieselmann, V
中科院分区：
文献类型：
--
作者：
Eckhardt, M;Yaghootfam, A;Gieselmann, V
羟基化是神经酰胺在脑、皮肤、肠道和肾脏中的一种丰富的修饰。羟基化发生在鞘氨醇碱基的C-4或酰胺连接的脂肪酸内。在髓磷脂中，神经酰胺的羟基化仅在脂肪酸部分的α-C原子处发现。α-羟基化β-糖苷是髓鞘中最丰富的脂质。然而，这种修饰的功能作用尚不清楚。基于与酵母C-26脂肪酸羟化酶的序列相似性，我们鉴定了编码FA 2 H（脂肪酸2-羟化酶）的鼠cDNA。在CHO细胞（中国仓鼠卵巢细胞）中转染FA 2 H cDNA导致含有己糖神经酰胺的α-羟基化脂肪酸的形成。EGFP（增强型绿色荧光蛋白）-FA 2 H融合蛋白与钙连接蛋白共定位，表明该酶存在于内质网中。FA 2 H在脑、胃、皮肤、肾和睾丸中表达，即在已知合成脂肪酸α-羟基化鞘脂的组织中表达。其在脑中表达的时间过程与髓鞘特异性基因的表达密切相关，在2-3周龄时达到最大值。这与所报道的发育中大脑中脂肪酸α-羟化酶活性的时间过程一致。脑切片的原位杂交显示FA 2 H在白色物质中表达。因此，我们的研究结果强烈表明，FA 2 H是负责在哺乳动物大脑的少突胶质细胞中形成α-羟基化神经酰胺的酶。它的进一步表征将提供深入了解α-羟基化修饰在髓鞘，皮肤和其他器官中的功能作用。
Hydroxylation is an abundant modification of the ceramides in brain, skin, intestinal tract and kidney. Hydroxylation occurs at the sphingosine base at C-4 or within the amide-linked fatty acid. In myelin, hydroxylation of ceramide is exclusively found at the alpha-C atom of the fatty acid moiety. a-Hydroxylated cerebrosides are the most abundant lipids in the myelin sheath. The functional role of this modification, however, is not known. On the basis of sequence similarity to a yeast C-26 fatty acid hydroxylase, we have identified a murine cDNA encoding FA2H (fatty acid 2-hydroxylase). Transfection of FA2H cDNA in CHO cells (Chinese-hamster ovary cells) led to the formation of alpha-hydroxylated fatty acid containing hexosylceramide. An EGFP (enhanced green fluorescent protein)-FA2H fusion protein co-localized with calnexin, indicating that the enzyme resides in the endoplasmic reticulum. FA2H is expressed in brain, stomach, skin, kidney and testis, i.e. in tissues known to synthesize fatty acid alpha-hydroxylated sphingolipids. The time course of its expression in brain closely follows the expression of myelin-specific genes, reaching a maximum at 2-3 weeks of age. This is in agreement with the reported time course of fatty acid alpha-hydroxylase activity in the developing brain. In situ hybridization of brain sections showed expression of FA2H in the white matter. Our results thus strongly suggest that FA2H is the enzyme responsible for the formation of alpha-hydroxylated ceramide in oligodendrocytes of the mammalian brain. Its further characterization will provide insight into the functional role of alpha-hydroxylation modification in myelin, skin and other organs.