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Glycogen storage disease type Ib (GSD-Ib) is caused by mutations of the glucose-6-phosphate transporter (G6PT) and characterized by disrupted glucose homeostasis, neutropenia, and neutrophil dysfunction. To investigate the role of G6PT in human adipose-derived mesenchymal stem cells (hMSCs), the G6PT gene was mutated by CRISPR/Cas9 technology and single cell-derived G6PT-/- hMSCs were established. G6PT-/- hMSCs have significantly increased cell proliferation but impaired adipogenesis and osteogenesis. These phenotypes are associated with two mechanisms: i) metabolic reprogramming in G6PT-/- hMSCs causing a metabolic shift toward glycolysis rather than oxidative phosphorylation and ii) increased cyclooxygenase-2-derived prostaglandin E2 secretion in G6PT-/- hMSCs. This study demonstrates that G6PT is essential for proliferation and differentiation of MSCs, providing important insights into the GSD-Ib phenotypes.

Very recently we have proposed [Hemrika et al. (1997) Proc. Natl. Acad. Sci. USA 94, 2145–2149] that the active site of the vanadate-containing chloroperoxidase from the fungus Curvularia inaequalis, of which the tertiary structure is known, is structurally very similar to that of the membrane-bound mammalian glucose-6-phosphatases for which no structural data are available. The proposed active site of glucose-6-phosphatase, however, is incompatible with the six transmembrane–helix topology model that is currently used. Here we present a new topology model for glucose-6-phosphatase which is in agreement with all available data.

This study aimed at directly assessing glucose 6-phosphate (G6P) transport by intact rat liver microsomes. Tracer uptake from labeled G6P occurred with T 1/2 values that proved insensitive to unlabeled G6P or 100 μM vanadate, and could not be activated over background levels by intravesicular phosphate in the complete absence of G6P hydrolysis. [ 32 P]Phosphate efflux was similarly unaffected by G6P or phosphate in the incubation medium. We conclude that the gene product responsible for glycogen storage disease type Ib is functionally distinct from the bacterial hexose phosphate transporter, which operates as an obligatory phosphate:phosphate or G6P:phosphate exchanger.

Glycogen storage disease (GSD) 1b is the deficiency of endoplasmic reticulum glucose-6-phosphate (G6P) transport. We here report the structure of the gene encoding a protein likely to be responsible for G6P transport, and its mapping to human chromosome 11q23.3. The gene is composed of nine exons spanning a genomic region of approximately 4 kb. Primers based on the genomic sequence were used in single strand conformation polymorphism (SSCP) analysis and mutations were found in six out of seven GSD 1b patients analysed.

There are differences in the kinetic properties of the liver and brain microsomal glucose-6-phosphate transport systems suggesting the possibility of tissue specific isoforms. The availability of a human liver cDNA sequence which is mutated in patients with deficiencies of liver microsomal glucose-6-phosphate transport (glycogen storage disease 1b) made it possible to determine if a brain isoform exists. Northern blots of liver and brain RNA revealed that the mRNA of the brain form is slightly longer than the liver one. Isolation and sequencing of the respective human brain cDNA revealed that the brain protein has an additional 22 amino acid sequence.

The glucose-6-phosphatase enzyme protein of the human hepatic microsomal glucose-6-phosphatase system was identified as a 36.5 kDa polypeptide. The 36.5 kDa glucose-6-phosphatase enzyme protein was shown to be absent in the microsomes isolated from a patient previously diagnosed as having a type 1a glycogen storage disease.