Mannosidosis is an inherited storage disorder in which a deficiency of lysosomal Alpha-mannosidase leads to the accumulation of mannose-rich oligosaccharides in many organs including brain. In contrast to many other lysosomal storage diseases, mannosidosis is not associated with progressive metal retardation or decreased longevity. This proposal examines the biochemical basis for these unusual clinical features by focusing on the nature and origin of the stored oligosaccharides, the relative storage burden in different tissues and the dynamics of excretion of mannose-terminal oligosaccharides. This will be accomplished by an integrated study at the level of the cell, the tissue and the whole body. At the cellular level, the ability of cultured mannosidosis fibroblasts to take up exogenous, labelled oligosaccharides and metabolize them to defined products will be studied. The most abundant oligosaccharide may be derived from complex glycoproteins by the action of an endomannosidase, and elucidation of the degradative pathway for complex oligosaccharides could have important implications for other glycoprotein storage diseases. A rat model of mannosidosis will be established by administration of swainsonine, a potent inhibitor of Alpha-mannosidase. This model will be utilized to examine the tissue distribution and metabolism of infused, labelled oligosaccharides. Measurements of oligosaccharide levels in CSF, serum and urine from bovine and human mannosidosis have indicated species differences. These measurements will be extended to compare the storage burden in individual tissues. The oligosaccharide differences between human and bovine urine will be further explored. Our previous studies have indicated a facilitated renal clearance of oligosaccharides in mannosidosis patients may exist which could be relevant to the neurological course of the disease. The role of the kidney in the clearance of deuterated trisaccharide from plasma will be explored in the rat model of mannosidosis and in clinical studies on two mannosidosis patients. Throughout these studies we will utilize micromethodology for HPLC analysis of oligosaccharide developed in this laboratory, together with GC-MS for structure determination.
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