Examination of Abnormal Dolichol Metabolism in Infantile Batten Disease Caused by Palmitoyl Protein Thioesterase-1 (PPT1) Deficiency
Cho, Steve Kyungrae
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The neuronal ceroid lipofuscinosis (NCLs, also known collectively as Batten disease) are a group of lysosomal storage disorders characterized by the accumulation of autofluorescent storage material in the brain. Although a number of genes underlying different forms of NCL have been cloned, the underlying mechanism for the neurodegeneration is still unknown. The most severe form of NCL (infantile NCL) is caused by mutations in the CLN1/PPT1 gene, which encodes a soluble lysosomal hydrolase (palmitoyl protein thioesterase-1) that removes fatty acids from lipid modified proteins in the lysosome. It has been postulated that abnormal dolichol metabolism might be involved in NCL pathogenesis because high levels of dolichol phosphate (Dol-P) and lipid linked oligosaccharides (LLOs) accumulate in NCL patients including infantile NCL. Here, a possible relationship between fatty acid and dolichol metabolism in the neuropathogenesis of NCL has been explored by analyzing LLOs from mouse models of Batten disease and other non-NCL lysosomal storage diseases (LSDs), and by characterizing a unique fusion protein consisting of PPT1 and a dolichol metabolizing enzyme (DOLPP1) in Schizosaccharomyces pombe, which we named pdf1 (for ppt1-dolpp1 fusion1). To do this, first, I characterized S. pombe pdf1 by ablating the pdf1 gene and studying the function of each of the proteins (PPT1 and DOLPP1) independently. These results revealed that PPT1 and DOLPP1 may be co-regulated in lower organisms but the functional relationship in higher eukaryotes remains unclear. To further explore the relationship between PPT1 and DOLPP1 in mammalian cells, I cloned the mammalian ortholog of DOLPP1 and subsequently characterized the mouse Dolpp1p. Finally, I characterized and analyzed LLOs in various mouse models of NCL by FACE (fluorophore assisted carbohydrate electrophoresis). It was shown that LLOs accumulated in PPT1-deficient mouse brain and the level of LLO accumulation was 14.5-fold higher as compared to wild type brain. Despite the striking accumulation of LLOs in PPT1-deficient brain compared to age-matched controls, I also found that the LLOs encompassed only 0.3% of the autofluorescent storage material by mass. Therefore, the abnormal dolichol catabolism is most likely a secondary phenotype to PPT1 deficiency during the pathogenesis of infantile Batten disease.