Inhibition of glycosphingolipid biosynthesis reduces secretion of the beta-amyloid precursor protein and amyloid beta-peptide.

ABSTRACT

Alzheimer disease is associated with extracellular deposits of amyloid beta-peptides in the brain. Amyloid beta-peptides are generated by proteolytic processing of the beta-amyloid precursor protein by beta- and gamma-secretases. The cleavage by secretases occurs predominantly in post-Golgi secretory and endocytic compartments and is influenced by cholesterol, indicating a role of the membrane lipid composition in proteolytic processing of the beta-amyloid precursor protein. To analyze the role of glycosphingolipids in these processes we inhibited glycosyl ceramide synthase, which catalyzes the first step in glycosphingolipid biosynthesis. The depletion of glycosphingolipids markedly reduced the secretion of endogenous beta-amyloid precursor protein in different cell types, including human neuroblastoma SH-SY5Y cells. Importantly, secretion of amyloid beta-peptides was also strongly decreased by inhibition of glycosphingolipid biosynthesis. Conversely, the addition of exogenous brain gangliosides to cultured cells reversed these effects. Biochemical and cell biological experiments demonstrate that the pharmacological reduction of cellular glycosphingolipid levels inhibited maturation and cell surface transport of the beta-amyloid precursor protein. In the glycosphingolipid-deficient cell line GM95, cellular levels and maturation of beta-amyloid precursor protein were also significantly reduced as compared with normal B16 cells. Together, these data demonstrate that glycosphingolipids are implicated in the regulation of the subcellular transport of the beta-amyloid precursor protein in the secretory pathway and its proteolytic processing. Thus, enzymes involved in glycosphingolipid metabolism might represent targets to inhibit the production of amyloid beta-peptides.