We reveal here a basic mechanism that has never been suggested in the literature and that explains neutropenia in G6PC3 and G6PT deficiencies: the lack of dephosphorylation of a non-canonical metabolite, (1,5-anhydroglucitol-6-phosphate; 1,5AG6P) which can easily be made from a major polyol present in blood (1,5-anhydroglucitol), strongly impairs glucose metabolism in neutrophils. In patients or mice with G6PC3 or G6PT deficiency, 1,5AG6P accumulates and inhibits the first step of glycolysis. This is particularly detrimental in neutrophils, since their energy metabolism depends almost entirely on glycolysis. Consistent with our findings, we observed that treatment with a 1,5-anhydroglucitol-lowering drug treats neutropenia in G6PC3-deficient mice. These mouse experiments now provide the ground for a proof of concept human study in G6PC3 deficient and GSD 1b patients using an SGLT2 inhibitor to lower blood 1,5-anhydroglucitol.
Illustration of the role played by 1,5-anhydroglucitol-6-phosphate accumulation in the neutropenia found in G6PC3 and G6PT deficiency. When patients are deficient in G6PT or G6PC3, 1,5AG6P accumulates in neutrophils to concentrations that strongly inhibit low-KM hexokinases, the enzymes catalyzing the first step of glycolysis. This depletes the intracellular pool of glucose-6-P in granulocytes, which likely decreases ATP production in glycolysis, as well as NADPH production in the pentose-P pathway and also UDP-glucose availability for protein glycosylation. This explains neutrophil dysfunction and neutropenia described in these patients.
When trying to understand many of the still mysterious Inborn Errors of Metabolism, it is important to be aware that quite a few enzymes in our cells act on substrates that resemble, but are not identical, to their physiological substrate, thereby leading to non-canonical, sometimes toxic metabolites. Our study highlights the essential role played by metabolite repair enzymes to maintain normal metabolic functions. It also demonstrates that the search for metabolite repair enzymes can lead to explanations for diseases that have remained until now completely mysterious. It is very likely that other diseases will reveal one day to be due to a defect in an as yet unknown metabolite repair process.
|Emile Van Schaftingen, Maria Veiga-da-Cunha & Guido Bommer|
Article describing this research
M. Veiga-da-Cunha, N. Chevalier, X. Stephenne, JP. Defour, N. Paczia, A. Ferster, Y. Achouri, J. P. Dewulf, C. L. Linster, G. T. Bommer, and E. Van Schaftingen