The Degradative Pathway of Gangliosides GM1 and GM2 in Neuro2a Cells by Sialidase

Abstract: Gangliosides GM1 [3H‐labeled at the sphingosine (Sph) moiety] and GM2 [3H‐labeled at the Sph or N‐acetylgalactosamine (GalNAc) moiety] were administered to cultured Neuro2a cells for varying pulse (1–4 h) and chase (up to 4 h) periods, and their metabolic processing was followed. The main and earliest formed 3H‐metabolites of [Sph‐3H]GM1 were GM2, asialo‐GM1, asialo‐GM2, and lactose‐ceramide, and those of [Sph‐3H]GM2 were asialo‐GM2 and lactose‐ceramide. The asialo‐GM1 and asialo‐GM2 formed were isolated and chemically characterized. [3H]Asialo‐GM2 was produced in identical amounts after treatment with equimolar [Sph‐3H]GM2 and [GalNAc‐3H]GM2. At low temperature or in the presence of chloroquine, the formation of all 3H‐metabolites, including asialo‐GM2 and asialo‐GM1, was undetectable, indicating that ganglioside metabolic processing was an endocytosis‐ and lysosome‐dependent process. These results demonstrate that in Neuro2a cells exogenous GM1 (and GM2) is mainly degraded through the pathway GM1 → GM2 → asialo‐GM2 →→ Sph, with a minor fraction of GM1 undergoing degradation with the sequence GM1 → asialo‐GM1 → asialo‐GM2 →→ Sph. These findings are consistent with the hypothesis that Neuro2a cells contain a sialidase (likely of lysosomal nature) affecting ganglioside GM1 and GM2. The sialidase‐mediated degradative pathway of GM1 and GM2 in Neuro2a cells might be related to the tumoral nature of these cells.