In eukaryotes Pyridoxal kinase produces the active form of vitamin B6 named Pyridoxal 5¿-phosphate (PLP) which is implicated in numerous metabolic reactions. In Drosophila mutations in dPdxk gene cause chromosome aberrations (CABs), increase glucose content in larval hemolymph and cause insulin resistance. Studies suggesting that vitamin B6 supplementation influences glucose tolerance in pregnant women prompted us to investigate PDXK in women with gestational diabetes (GD). We performed a screening by sequencing PDXK in 400 GDM women and identified a novel PDXK variant (A243G) in two women. By considering the wide evolutionarily conservation of molecules and pathways involved in glucose homeostasis maintenance and the finding that human PDXK gene inserted in dPdxk1 flies is able to rescue hyperglycemia, we reasoned that Drosophila is a robust model to validate this variant. Thus, the purpose of this project is to express the A243G PDXK variant in a dPdxk1 mutant background and to investigate if it is able to rescue hyperglycemia and insulin resistance. Diabetes causes oxidative stress resulting in the production of oxygen reactive species (ROS) which in turn cause DNA and chromosome damage. We previously demonstrated that in dPdxk1 mutants hyperglycemia induces the accumulation of Advanced Glycation End product (AGEs) which in turn elicit the formation of CABs. Thus, in the present project we will also verify if the expression of A243G PDXK variant impacts on CABs and AGE accumulation. We will also assay whether supplementation with PLP precursors (PL, PM and PN), influence the rescue of hyperglycemia and CABs in A243G expressing cells in order to obtain indications on the putative biochemical defect of the mutant protein that will be subsequently investigate. The validation of A343G in Drosophila will provide us a first indication of the association between PDXK gene and diabetes that will be in the future deeply addressed in human cells.
The association of PDXK to diabetes in the future could promote the screening for PDXK variants not only in GDM women but also in patients clinically classified as MODY (maturity onset diabetes of the young) [19] or in families with diabetes in multiple consecutive generations but negative to the search of known MODY genes. Specific genotype-phenotype correlations have provided multiple benefits for carriers of mutations in many of known monogenic diabetes genes including refined genetic counseling, custom-made therapeutic strategies, and valuable prognosis of chronic diabetes complications. We predict that the validation of PDXK as novel diabetes gene may extend the aforementioned benefits to mutation carriers, and likely provide indications for the therapeutic use of vitamin B6 in monogenic diabetes and other forms of diabetes like gestational diabetes and type 2 diabetes.
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