Abstract
Sphingolipid activator protein-1 (SAP-1) stimulates enzymatic hydrolysis of sphingolipids including sulfatide. In this study, subcellular localization of the disease-specific inclusions and SAP-1 in cultured skin fibroblasts from a patient with metachromatic leukodystrophy (MLD), sulfatide storage disease, was examined by immunoelectronmicroscopy. When stained with antibody to SAP-1, acid phosphatase positive membrane-bound vesicles were stained in both the controls and MLD cells, indicating that SAP-1 was localized in lysosomes. After sulfatide loading (20μg/ml) for 7 days to MLD cells, 273 lysosomes in a cell were examined regarding the correlation of SAP-1 staining and specific sulfatide inclusions with 6-7nm periodicity. SAP-1 and specific sulfatide inclusions were simultaneously observed in 59% of total lysosome vesicles examined (164 out of 273) and positive staining of SAP-1 was observed in 92% of lysosomes with specific sulfatide inclusion (164 out of 178). These results demonstrated a positive correlation between SAP-1 staining and specific inclusions and suggested the possible induction of a secondary increase of SAP-1 in lysosomes by the pathological storage of sulfatide.
