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Ablation of mouse phosphomannose isomerase (Mpi) causes mannose 6-phosphate accumulation, toxicity, and embryonic lethality.

MPI encodes phosphomannose isomerase, which interconverts fructose 6-phosphate and mannose 6-phosphate (Man-6-P), used for glycoconjugate biosynthesis. MPI mutations in humans impair protein glycosylation causing congenital disorder of glycosylation Ib (CDG-Ib), but oral mannose supplements normalize glycosylation. To establish a mannose-responsive mouse model for CDG-Ib, we ablated Mpi and provided dams with mannose to rescue the anticipated defective glycosylation. Surprisingly, although glycosylation was normal, Mpi(-/-) embryos died around E11.5. Mannose supplementation even hastened their death, suggesting that man-nose was toxic. Mpi(-/-) embryos showed growth retardation and placental hyperplasia. More than 90% of Mpi(-/-) embryos failed to form yolk sac vasculature, and 35% failed chorioallantoic fusion. We generated primary embryonic fibroblasts to investigate the mechanisms leading to embryonic lethality and found that mannose caused a concentration- and time-dependent accumulation of Man 6-P in Mpi(-/-) fibroblasts. In parallel, ATP decreased by more than 70% after 24 h compared with Mpi(+/+) controls. In cell lysates, Man-6-P inhibited hexokinase (70%), phosphoglucose isomerase (65%), and glucose-6-phosphate dehydrogenase (85%), but not phosphofructokinase. Incubating intact Mpi(-/-) fibroblasts with 2-[(3)H]deoxyglucose confirmed mannose-dependent hexokinase inhibition. Our results in vitro suggest that mannose toxicity in Mpi(-/-) embryos is caused by Man-6-P accumulation, which inhibits glucose metabolism and depletes intracellular ATP. This was confirmed in E10.5 Mpi(-/-) embryos where Man-6-P increased more than 10 times, and ATP decreased by 50% compared with Mpi(+/+) littermates. Because Mpi ablation is embryonic lethal, a murine CDG-Ib model will require hypomorphic Mpi alleles.

Pubmed ID: 16339137


  • DeRossi C
  • Bode L
  • Eklund EA
  • Zhang F
  • Davis JA
  • Westphal V
  • Wang L
  • Borowsky AD
  • Freeze HH


The Journal of biological chemistry

Publication Data

March 3, 2006

Associated Grants

  • Agency: NIDDK NIH HHS, Id: R01 DK 065091
  • Agency: NIGMS NIH HHS, Id: R01 GM 55695

Mesh Terms

  • Adenosine Triphosphate
  • Animals
  • Carbohydrate Metabolism, Inborn Errors
  • Cells, Cultured
  • Embryo Loss
  • Embryo, Mammalian
  • Female
  • Fibroblasts
  • Gene Targeting
  • Genotype
  • Gestational Age
  • Hexokinase
  • Humans
  • Male
  • Mannose
  • Mannose-6-Phosphate Isomerase
  • Mannosephosphates
  • Mice
  • Mice, Knockout
  • Polysaccharides
  • Pregnancy