Glucose-6-phosphate isomerase deficiency results in mTOR activation, failed translocation of lipin 1α to the nucleus and hypersensitivity to glucose: Implications for the inherited glycolytic disease

Abstract

Inherited glucose-6-phosphate isomerase (GPI) deficiency is the second most frequent glycolytic erythroenzymopathy in humans. Patients present with non-spherocytic anemia of variable severity and with neuromuscular dysfunction. We previously described Chinese hamster (CHO) cell lines with mutations in GPI and loss of GPI activity. This resulted in a temperature sensitivity and severe reduction in the synthesis of glycerolipids due to a reduction in phosphatidate phosphatase (PAP). In the current article we attempt to describe the nature of this pleiotropic effect. We cloned and sequenced the CHO lipin 1 cDNA, a gene that codes for PAP activity. Overexpression of lipin 1 in the GPI-deficient cell line, GroD1 resulted in increased PAP activity, however it failed to restore glycerolipid biosynthesis. Fluorescent microscopy showed a failure of GPI-deficient cells to localize lipin 1α to the nucleus. We also found that glucose-6-phosphate levels in GroD1 cells were 10-fold over normal. Lowering glucose levels in the growth medium partially restored glycerolipid biosynthesis and nuclear localization of lipin 1α. Western blot analysis of the elements within the mTOR pathway, which influences lipin 1 activity, was consistent with an abnormal activation of this system. Combined, these data suggest that GPI deficiency results in an accumulation of glucose-6-phosphate, and possibly other glucose-derived metabolites, leading to activation of mTOR and sequestration of lipin 1 to the cytosol, preventing its proper functioning. These results shed light on the mechanism underlying the pathologies associated with inherited GPI deficiency and the variability in the severity of the symptoms observed in these patients.

MicroRNA-217 Promotes Ethanol-induced Fat Accumulation in Hepatocytes by Down-regulating SIRT1

“…Nuclei were visualized with DAPI staining (blue). Consistent with the findings reported by others (19,(27)(28)(29)(30)(31), lipin-1␣ was localized in both the cytoplasm and the nucleus of AML-12 cells (Fig. 9, A and B).…”

“…Lipin-1 is a bifunctional molecule that regulates lipid metabolism as a phosphatidic acid phosphohydrolase type enzyme in the cytosol and a transcriptional co-activator in the nucleus (23)(24)(25)(26)(27)(28)(29)(30)(31). In recent years, lipin-1 has emerged as a major player in the development of both alcoholic and non-alcoholic fatty liver diseases (9,19,(23)(24)(25)(26)(27)(28)(29)(30)(31).…”

“…Lipin-1␣ is a nucleocytoplasmic shuttling protein (19,(27)(28)(29)(30)(31). To investigate whether miR-217 governs lipin-1␣ nucleocytoplasmic shuttling, AML-12 cells were co-transfected with control vector or HA-lipin-1␣ plasmid with or without the presence of ethanol.…”

Hexokinase II integrates energy metabolism and cellular protection: Akting on mitochondria and TORCing to autophagy

“…176 Glycerolipid deficiency is suggested to be associated with non-spherocytic hemolytic anemia in GPI-deficient patients. 177 In addition, nuclear lipin-1 interacts with transcription factors to regulate genes, thereby regulating fatty acid oxidation and lipogenesis. 176 These complex transcriptional events mediated by mTORC1/lipin-1 would also relate to the pathologies in GPI-deficient patients.…”

Physico-chemical properties and amino acid profiles of sap from Tunisian date palm

“…However, the increase in fructose content was lower than the one recorded for glucose. This result could presumably be ascribed to glucose -6-phosphate isomerase activity, a non rate-limiting enzyme in glycolysis, which catalyses the reversible isomerisation of glucose-6-phosphate to fructose-6-phosphate (Haller et al, 2011). Such invertase and glucose-6-phosphate isomerase activities could be attributed to the proteins involved in glycolysis and related to Saccharomyces cerevisiae which belongs to the natural microflora of date palm sap (Ben Thabet et al, 2010b).…”