Exogenous mannose does not raise steady state mannose-6-phosphate pools of normal or N-glycosylation-deficient human fibroblasts.
Increasing intracellular mannose-6-phosphate (Man-6-P) was previously reported to reduce the amount of the major lipid linked oligosaccharide (LLO) precursor of N-glycans; a loss that might decrease cellular N-glycosylation. If so, providing dietary mannose supplements to glycosylation-deficient patients might further impair their glycosylation. To address this question, we studied the effects of exogenous mannose on intracellular levels of Man-6-P, LLO, and N-glycosylation in human and mouse fibroblasts. Mannose (500microM) did not increase Man-6-P pools in human fibroblasts from controls or from patients with Congenital Disorders of Glycosylation (CDG), who have 90-95% deficiencies in either phosphomannomutase (CDG-Ia) or phosphomannose isomerase (MPI) (CDG-Ib), enzymes that both use Man-6-P as a substrate. In the extreme case of fibroblasts derived from Mpi null mice (<0.001% MPI activity), intracellular Man-6-P levels greatly increased in response to exogenous mannose, and this produced a dose-dependent decrease in the steady state level of the major LLO precursor. However, LLO loss did not decrease total protein N-glycosylation or that of a hypoglycosylation indicator protein, DNaseI. These results make it very unlikely that exogenous mannose could impair N-glycosylation in glycosylation-deficient CDG patients.
Higashidani
Aya
A
Department of Applied Biological Science, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan.
Bode
Lars
L
Nishikawa
Atsushi
A
Freeze
Hudson H
HH
D000818:Animals; D003850:Deoxyribonuclease I / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism*; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D008358:Mannose / Q000494:pharmacology*; D008359:Mannose-6-Phosphate Isomerase / Q000172:deficiency / Q000378:metabolism; D008360:Mannosephosphates / Q000378:metabolism*; D051379:Mice
D008070:Lipopolysaccharides; D008360:Mannosephosphates; C023023:lipid-linked oligosaccharides; C027693:mannose-6-phosphate; D003850:Deoxyribonuclease I; D008359:Mannose-6-Phosphate Isomerase; D008358:Mannose