Gangliosides may be involved in the pathogenesis of Parkinson's disease and related disorders, although the precise mechanisms governing this involvement remain unknown. In this study, we determined whether changes in endogenous ganglioside levels affect lysosomal pathology in a cellular model of synucleinopathy. For this purpose, dementia with Lewy body-linked P123H beta-synuclein (beta-syn) neuroblastoma cells transfected with alpha-synuclein were used as a model system because these cells were characterized as having extensive formation of lysosomal inclusions bodies. Treatment of these cells with D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), an inhibitor of glycosyl ceramide synthase, resulted in various features of lysosomal pathology, including compromised lysosomal activity, enhanced lysosomal membrane permeabilization, and increased cytotoxicity. Consistent with these findings, expression levels of lysosomal membrane proteins, ATP13A2 and LAMP-2, were significantly decreased, and electron microscopy demonstrated alterations in the lysosomal membrane structures. Furthermore, the accumulation of both P123H beta-syn and alpha-synuclein proteins was significant in PDMP-treated cells because of the suppressive effect of PDMP on the autophagy pathway. Finally, the detrimental effects of PDMP on lysosomal pathology were significantly ameliorated by the addition of gangliosides to the cultured cells. These data suggest that endogenous gangliosides may play protective roles against the lysosomal pathology of synucleinopathies.