CERAMIDE AND ITS INTERCONVERTIBLE METABOLITE SPHINGOSINE FUNCTION AS INDISPENSABLE LIPID FACTORS INVOLVED IN SURVIVAL AND DENDRITIC DIFFERENTIATION OF CEREBELLAR PURKINJE-CELLS

Ceramide generated from sphingomyelin has emerged as a new but conserv ed type of biologically active lipid. We previously found that endogen ous sphingolipids are required for the normal growth of cultured cereb ellar Purkinje neurons and that sphingomyelin is present abundantly in the somatodendritic region of these cells. To gain further insight in to a potential role of the sphingomyelin/ceramide pathway, we investig ated the effects of depletion of sphingolipids on the phenotypic growt h and survival of immature Purkinje cells and the ability of ceramide or other sphingolipids to antagonize these effects. Inhibition of cera mide synthesis by ISP-1, a specific inhibitor of serine palmitoyltrans ferase, decreased cellular levels of sphingolipids. This treatment res ulted in a decrease in cell survival accompanied by an induction of ap optotic cell death and aberrant dendritic differentiation of Purkinje cells with no detectable changes in other cerebellar neurons. Cell-per meable ceramides, sphingosine, or sphingomyelin overcame these abnorma lities more effectively than other sphingolipids when added simultaneo usly with ISP-1. Exposure to bacterial sphingomyelinase in turn enhanc ed cell survival and dendritic branching complexity of Purkinje cells at different optimal concentrations. Furthermore, cell-permeable ceram ide acted synergistically with the neurotrophin family, which has been previously shown to support Purkinje cell survival. These observation s suggest that ceramide is a requisite for the survival and the dendri tic differentiation of Purkinje cells.