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Identifier 000426563
Title Μελέτη φαινοτύπου διαγονιδιακών μυών που εκφράζουν την αγρίου τύπου hGDH2 (WT-hGDH2)
Alternative Title Study of transgenic mice carrying Glud2
Author Πετράκη Ζωή
Thesis advisor Σπανάκη, Κλεάνθη
Reviewer Καραγωγέως, Δόμνα
Καστελλάκης, Ανδρέας
Καρδάσης , Δημήτριος
Μήτσιας, Παναγιώτης
Νότας, Γεώργιος
Ζαγανάς, Ιωάννης
Abstract Mammalian glutamate dehydrogenase 1 (GDH1) is a mitochondrial enzyme that catalyzes the reversible oxidative deamination of glutamate to α-ketoglutarate and ammonia using NAD+/NADP+ as cofactor .It links amino acid with carbohydrate metabolism, contributing to Krebs cycle anaplerosis, energy production, ammonia handling and redox homeostasis. While most mammals possess a single GDH1 protein (hGDH1 in the human) that is highly expressed in the liver, humans and other primates have acquired, via duplication, an hGDH2 isoenzyme with distinct functional properties and tissue expression profile. The novel hGDH2 underwent rapid evolutionary adaptation, acquiring unique properties that enable enhanced enzyme function under conditions inhibitory to its ancestor hGDH1. These are though to provide a biological advantage to humans with hGDH2 evolution occurring concomitantly with human brain development. hGDH2 is co-expressed with hGDH1 in human brain, kidney, testis and steroidogenic organs, but not in liver. To better understand the role of hGDH2 in human biology, we generated a transgenic mouse model expressing hGDH2 by inserting a human DNA segment containing the GLUD2 gene and it regulatory elements into their genome. Study of the GLUD2 Tg mice brain using double IF and confocal microscopy, revealed a hGDH2 cellular expression pattern similar to that observed in human brain. These observations provided credence to the hypothesis that, by finding a suitable promoter in the X chromosome, the duplicated GLUD2 gene diversified its roles in human tissues. In light of these considerations, we explored the hGDH2 expression in non-neural organs (including pancreatic tissue) of Tg mice and the effect of GLUD2 gene on glucose homeostasis. Using specific antibodies we observed that hGDH2 is co-expressed with the endogenous murine GDH1 in pancreatic β-cells of Tg mice. Fasting blood glucose (FBG) levels were lower and of a narrower range in Tg (95% CI: 90.6-96.8 mg/dL; N=26) than in WT (95% CI: 136.2-151.4 mg/dL; N=23; p<0.0001), closely resembling those of healthy humans. GLUD2 also protected the host mouse from developing diabetes with advancing age. Tg animals maintained 2.6-fold higher fasting serum insulin levels (mean±SD: 1.63±0.15 ng/ml; N=12) than Wt mice (0.63±0.05 ng/ml; N=12; p b 0.0001). Glucose loading (1 mg/g, given i.p.) induced comparable serum insulin increases in Tg and Wt mice, suggesting no significant GLUD2 effect on glucose-stimulated insulin release. L-leucine (0.25 mg/g given orally) induced a 2-fold increase in the serum insulin of the Wt mice, implying significant activation of the endogenous GDH1. However, L-leucine had little effect on the high insulin levels of the Tg mice, suggesting that, under the high ADP levels that prevail in β-cells in the fasting state, glutamate flux through hGDH2 is close to maximal. Hence, the present data, showing that GLUD2 expression in Tg mice improves in vivo glucose homeostasis by boosting fasting serum insulin levels, suggest that evolutionary adaptation of hGDH2 has enabled humans to achieve narrow-range euglycemia by regulating glutamate-mediated basal insulin secretion.
Language Greek
Subject Body weight
Glucose homeostasis
Διαγονιδιακοί μύες
Ομοιόσταση γλυκόζης
Σωματικό βάρος
Issue date 2019-12-11
Collection   Faculty/Department--School of Medicine--Department of Medicine--Doctoral theses
  Type of Work--Doctoral theses
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