A role for gangliosides in development of the cerebral cortex and Niemann -Pick disease type C
Gondre-Lewis, Marjorie Claudine
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Glycosphingolipids (GSLs) are believed to play a critical role in normal embryonic development and in the maintenance of neuronal homeostasis. The overall objective of my thesis research was to elucidate the role that gangliosides, a subclass of GSLs, play during normal dendritic differentiation of developing cortical neurons and in the pathogenesis of Niemann-Pick disease type C (NPC), a metabolic disease that causes mental retardation. To address these issues I investigated the role of gangliosides in normal developing and diseased brain using immunocytochemistry, Golgi staining, confocal microscopy, microarray analysis and pharmacological treatments of cultured cortical neurons from normal and NPC-affected animals and of genetic mouse models in vivo .;In developing brain, by in vivo and in vitro methodologies, I show that GM2 ganglioside expression is temporally restricted to early differentiation events in mouse pyramidal neurons, and may have separate functions from GD2 or GD3 ganglioside. In the NPC mouse model, the induced reduction of GSL content in brain after treatment with ganglioside synthesis inhibitors, was sufficient to partially rescue the NPC phenotype and imply a significant role for accumulated GSLs in the pathogenesis of NPC1-mediated disease. In order to determine the subcellular relationship between gangliosides and cholesterol, a GalNacT-/-/NPC -/- double mutant mouse, unable to synthesize complex gangliosides was created. This genetic perturbation of ganglioside expression successfully reduced cholesterol accumulation, and in some animals increased longevity. By induction of an NPC phenotype after CaMKII inhibition I also show a possible linkage between the mechanism of NPC1 pathogenesis and CaMKII function.;The work presented in this thesis shows that gangliosides have important differential roles in specific stages of development. Their functions can be exerted either intracellularly or at the plasma membrane, and could be modulated by key proteins involved in dendritic stabilization. When cellular metabolism is impaired, and distribution of gangliosides is altered, severe neurological disease ensues. This disease state can be partially rescued by decreasing glycosphingolipid substrates available for biosynthesis of complex gangliosides.