Neurodegeneration Induced by Clustering of Sialylated Glycosylphosphatidylinositols of Prion Proteins

The transmissible spongiform encephalopathies, more commonly known as the prion diseases, are associated with the production and aggregation of disease-related isoforms of the prion protein (PrPSc). The mechanisms by which PrPSc accumulation causes neurodegeneration in these diseases are poorly understood. In cultured neurons, the addition of PrPSc alters cell membranes, increasing cholesterol, activating cytoplasmic phospholipase A(2) (cPLA(2)), and triggering synapse damage. These effects of PrPSc are dependent upon its glycosylphosphatidylinositol (GPI) anchor, suggesting that it is the increased density of GPIs that occurs following the aggregation of PrPSc molecules that triggers neurodegeneration. This hypothesis was supported by observations that cross-linkage of the normal cellular prion protein (PrPC) also increased membrane cholesterol, activated cPLA2, and triggered synapse damage. These effects were not seen after cross-linkage of Thy-1, another GPI-anchored protein, and were dependent on the GPI anchor attached to PrPC containing two acyl chains and sialic acid. We propose that the aggregation of PrPSc, or the cross-linkage of PrPC, causes the clustering of sialic acid-containing GPI anchors at high densities, resulting in altered membrane composition, the pathological activation of cPLA(2), and synapse damage.