Accumulation of Glucosylceramide in Murine Testis, Caused by Inhibition of β-Glucosidase 2

Abstract

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 ␤-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.

β-Glucosylceramide ameliorates liver inflammation in murine autoimmune cholangitis

“…Most glycosphingolipids are synthesized from glucosylation of ceramide to form glucosylceramide which, in turn, serves as the source of complex glycosylated sphingolipids (e.g. gangliosides GM3 and GM1) [21,22]. Structurally, glucosylceramide has a sphingosine and ceramide backbone with one or more sugar residues at the 1-hydroxyl position in a b-glycosidic linkage.…”

1-O-acylceramides are natural components of human and mouse epidermis

“…Correspondingly, loss of neutral glucosylceramidase then would lead to decreased substrate availability and concomitantly lower 1-O-acylceramide levels. Previously, elevated steady-state GlcCer levels were reported for liver and testis of neutral glucosylceramidase-defi cient mice ( 20,28,29 ), but were also observed in the spleen, kidney, and brain of these mice (unpublished observations). In epidermis, we analyzed GlcCers with a Cer anchor also present in 1-O-acylceramides and observed a 2-to 3-fold increase in mutants.…”

Identification of Niemann-Pick C1 disease biomarkers through sphingolipid profiling

“…On the other hand, MC species, which accumulated in the brain tissue of miglustat-treated Npc1 Ϫ / Ϫ mice, were elevated in the plasma and more profoundly in the CSF following initiation of miglustat. While elevation of plasma and CSF MC species at fi rst seems counterintuitive in light of miglustat's proposed mechanism of action through inhibition of glucosylceramide synthase, the enzyme responsible for conversion of CER to glucosylceramide ( 29 ), a number of reports have shown an increase of glucosylceramide in brain tissue in response to treatment with iminosugar-based inhibitors (e.g., miglustat) (45)(46)(47). There is mounting evidence that the increased glucosylceramide is due to inhibition of GBA2, a glucosylceramidase that is abundant particularly in the brain and is responsible for maintenance of glycosphingolipid homeostasis.…”