Glucosylceramide modulates membrane traffic along the endocytic pathway

Area of Science:

• Cellular biology
• Molecular medicine
• Biochemistry

Background:

• Glycosphingolipids are normally trafficked to the Golgi apparatus but are mistargeted to lysosomes in sphingolipidoses.
• Substrate reduction therapy aims to inhibit glucosylceramide synthase using imino sugars to mitigate storage diseases.
• Gaucher disease, caused by glucocerebrosidase deficiency, leads to glucosylceramide accumulation, yet lactosylceramide transport in Gaucher fibroblasts is typically normal.

Purpose of the Study:

• To investigate the impact of glycosphingolipid accumulation on intracellular trafficking.
• To understand the effects of imino sugar inhibitors on sphingolipid endocytosis.
• To explore the role of glucosylceramide in regulating membrane transport.

Main Methods:

• Studied sphingolipid endocytosis in fibroblast and macrophage models of Gaucher disease.
• Treated cells with conduritol B epoxide (a glucocerebrosidase inhibitor) and N-butyldeoxygalactonojirimycin (NB-DGJ, a glycosphingolipid biosynthesis inhibitor).
• Analyzed the endocytic targeting of lactosylceramide in response to inhibitor treatments.

Main Results:

• Inhibiting glucocerebrosidase with conduritol B epoxide caused lactosylceramide mistargeting from the Golgi to lysosomes.
• Co-treatment with conduritol B epoxide and low-dose NB-DGJ restored lactosylceramide trafficking to the Golgi.
• High-dose NB-DGJ alone induced lysosomal targeting of lactosylceramide, independent of conduritol B epoxide.

Conclusions:

• Both elevated and reduced glucosylceramide levels significantly alter lactosylceramide endocytic targeting.
• Glucosylceramide plays a crucial role in regulating membrane transport pathways.
• These findings have implications for substrate reduction therapy in sphingolipidoses.