• Register
X
Forgot Password

If you have forgotten your password you can enter your email here and get a temporary password sent to your email.

X

Leaving Community

Are you sure you want to leave this community? Leaving the community will revoke any permissions you have been granted in this community.

No
Yes

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

Authors

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

Journal

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