Walden Charlotte M, Sandhoff Roger, Chuang Chia-Chen, Yildiz Yildiz, Butters Terry D, Dwek Raymond A, Platt Frances M, van der Spoel Aarnoud C
Departments of Biochemistry and Pharmacology, University of Oxford, Mansfield Road, Oxford, United Kingdom.
J Biol Chem. 2007 Nov 9;282(45):32655-64. doi: 10.1074/jbc.M702387200. Epub 2007 Sep 11.
One of the hallmarks of male germ cell development is the formation of a specialized secretory organelle, the acrosome. This process can be pharmacologically disturbed in C57BL/6 mice, and thus infertility can be induced, by small molecular sugar-like compounds (alkylated imino sugars). Here the biochemical basis of this effect has been investigated. Our findings suggest that in vivo alkylated imino sugars primarily interact with the non-lysosomal glucosylceramidase. This enzyme cleaves glucosylceramide into glucose and ceramide, is sensitive to imino sugars in vitro, and has been characterized as beta-glucosidase 2 (GBA2). Imino sugars raised the level of glucosylceramide in brain, spleen, and testis, in a dose-dependent fashion. In testis, multiple species of glucosylceramide were similarly elevated, those having long acyl chains (C16-24), as well as those with very long polyunsaturated acyl chains (C28-30:5). Both of these GlcCer species were also increased in the testes from GBA2-deficient mice. When considering that the very long polyunsaturated sphingolipids are restricted to germ cells, these results indicate that in the testis GBA2 is present in both somatic and germ cells. Furthermore, in all mouse strains tested imino sugar treatment caused a rise in testicular glucosylceramide, even in a number of strains, of which the males remain fertile after drug administration. Therefore, it appears that acrosome formation can be derailed by accumulation of glucosylceramide in an extralysosomal localization, and that the sensitivity of male germ cells to glucosylceramide is genetically determined.
雄性生殖细胞发育的一个标志性特征是形成一种特殊的分泌细胞器——顶体。在C57BL/6小鼠中，这个过程会受到小分子糖样化合物（烷基化亚氨基糖）的药理学干扰，从而导致不育。在此，我们研究了这种效应的生化基础。我们的研究结果表明，在体内，烷基化亚氨基糖主要与非溶酶体葡萄糖神经酰胺酶相互作用。这种酶将葡萄糖神经酰胺裂解为葡萄糖和神经酰胺，在体外对亚氨基糖敏感，并且已被鉴定为β-葡萄糖苷酶2（GBA2）。亚氨基糖以剂量依赖的方式提高了脑、脾和睾丸中葡萄糖神经酰胺的水平。在睾丸中，多种葡萄糖神经酰胺同样升高，包括那些具有长酰基链（C16 - 24）的以及那些具有非常长的多不饱和酰基链（C28 - 30:5）的。这两种葡萄糖神经酰胺在GBA2缺陷小鼠的睾丸中也有所增加。考虑到非常长的多不饱和鞘脂仅限于生殖细胞，这些结果表明在睾丸中，GBA2存在于体细胞和生殖细胞中。此外，在所有测试的小鼠品系中，亚氨基糖处理都会导致睾丸中葡萄糖神经酰胺升高，即使在一些品系中，雄性小鼠在给药后仍保持生育能力。因此，似乎顶体形成可能会因葡萄糖神经酰胺在溶酶体外定位的积累而受阻，并且雄性生殖细胞对葡萄糖神经酰胺的敏感性是由基因决定的。
