Analysis of glycolipids metabolism in peroxisome-defective cells and its relation to pathogenesis of Zellweger syndrome

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We observed an increased amount of a-series gangliosides, GM2, GM1 and GD1a in the fibroblasts of patients with ZS and IRD. Gangliosides GM1 and GD1a were not contained in a detectable amount in normal subjects. A key step for the synthesis of a-series gangliosides is a transfer of GalNAc to ganglioside GM3, so we determined the level of ganglioside GM3 by immunohistochemical method. We found granular structure, which was positive toward antiganglioside GM3 antibody in the cytoplasm of the patients' fibroblasts. In the control cells, cell membrane was slightly positive toward anti-GM3 antibody. To clarify the metabolic bases of incresed amounts of glycolipids, we measured the ceramide glucosyltransferase and β-glucosidase activities in Z65 and CHO-K1 cells, and found that the former enzyme was responsible for the accumulation of glucocerebroside in Z65 cells. Then, we cloned the cDNA encoding ceramide glucosyltransferase from CHO-K1 cells, which exhibited sequence homology with the human gene product (98.7%). Northern blot analysis of ceramide glucosyltransferase revealed increased expression of it in Z65 cells compared with in CHO-K1 cells, probably causing the simultaneous increase in GM3. With an immunohistochemical procedure, GM3 was more strongly expressed in the cell membrane of Z65 cells than in that of CHO-K1 cells. These results may help to clarify the pathogenesis of PBD with respect to the functional roles of glycosphingolipids in cell differentiation, proliferation and apoptosis.