DNA microarray analysis of type 2 diabetes-related genes co-regulated between white blood cells and livers of diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats

An epigenomic signature of postprandial hyperglycemia in peripheral blood leukocytes

Postprandial hyperglycemia is known to be one of the earliest signs of abnormal glucose homeostasis associated with type 2 diabetes. This study aimed to assess clinical significance of a 1-h postprandial glucose level for the development of diabetes, and identify epigenetic biomarkers of postprandial hyperglycemia. We analyzed clinical data from the oral glucose tolerance tests for healthy subjects (n=4502). The ratio (Glu60/Glu0) of 1-h glucose levels to fasting glucose levels was significantly associated with an insulin sensitive index (QUICKI, quantitative insulin sensitivity check index) (β=0.055, P=1.25E-04) as well as a risk of future pre-diabetic and diabetic conversion. Next, DNA methylation profile analyses of 24 matched pairs of the high and low Glu60/Glu0 ratio subjects showed that specific DNA methylation levels in the promoter region of an olfactory receptor gene (olfactory receptor gene family10 member A4, OR10A4) were associated with the Glu60/Glu0 ratios (β=0.337, P=0.03). Moreover, acute oral glucose challenges decreased the DNA methylation levels of OR10A4 but not the global DNA methylation in peripheral leukocytes of healthy subjects (n=7), indicating that OR10A4 is a specific epigenomic target of postprandial hyperglycemia. This work suggests possible relevance of olfactory receptor genes to an earlier molecular biomarker of peripheral hyperglycemia and diabetic conversion.

Gene expression profiling in peripheral white blood cells in response to the intake of food with different glycemic index using a DNA microarray

BACKGROUND/AIMS

Transcriptomics technology in human nutrition intervention studies would allow for genome-wide screening of the effects of nutrients. We observed the time course of gene expression changes in peripheral white blood cells (WBC) to elucidate the metabolic changes in the postprandial state that are a reflection and a marker of whole body metabolic changes.

METHODS

In a randomized crossover study, 7 healthy subjects consumed test meals of glucose (GL), white rice (WR) and rolled barley (BAR), each containing 75 g of available carbohydrate, and water (WAT). Blood glucose, insulin and nonesterified fatty acid concentrations, as well as the subjective levels of fullness and hunger were measured. Microarray analysis of the WBC and the real-time PCR were examined during 360 min after the intake of the test meals.

RESULTS

The number of genes that changed more than 1.5-fold and the expression patterns in the time course were different between the GL, the WR and the BAR groups. Several genes involved in glycolysis and fatty acid β-oxidation were markedly changed after the intake of the GL, the WR and the BAR; however, these genes did not change at any time point in the WAT.

CONCLUSIONS

Gene expression profiling in the WBC can reflect food-related metabolic changes, even in the postprandial state.

Immunohistochemical localization of mitochondrial fatty acid β-oxidation enzymes in rat testis

The testis consists of two types of tissues, the interstitial tissue and the seminiferous tubule, which have different functions and are assumed to have different nutritional metabolism. The localization of enzymes of the mitochondrial fatty acid β-oxidation system in the testis was investigated to obtain a better understanding of nutrient metabolism in the testis. Adult rat testis tissues were subjected to immunoblot analysis for quantitation of the amounts of enzyme proteins, to DNA microarray analysis for gene expression, and to immunofluorescence and immunoelectron microscopy for localization. Quantitative analysis by immunoblot and DNA microarray revealed that enzymes occur abundantly in Leydig cells in the interstitial tissue but much less so in the seminiferous tubules. Immunohistochemistry revealed that Leydig cells in the interstitial tissue and Sertoli cells in the seminiferous tubules contain a full set of mitochondrial fatty acid β-oxidation enzymes in relatively plentiful amounts among the cells in the testis, but that this is not so in spermatogenic cells. This characteristic localization of the mitochondrial fatty acid β-oxidation system in the testis needs further elucidation in terms of a possible role for it in the nutritional metabolism of spermatogenesis.

BSTA promotes mTORC2-mediated phosphorylation of Akt1 to suppress expression of FoxC2 and stimulate adipocyte differentiation

Phosphorylation and activation of Akt1 is a crucial signaling event that promotes adipogenesis. However, neither the complex multistep process that leads to activation of Akt1 through phosphorylation at Thr³⁰⁸ and Ser⁴⁷³ nor the mechanism by which Akt1 stimulates adipogenesis is fully understood. We found that the BSD domain-containing signal transducer and Akt interactor (BSTA) promoted phosphorylation of Akt1 at Ser⁴⁷³ in various human and murine cells, and we uncovered a function for the BSD domain in BSTA-Akt1 complex formation. The mammalian target of rapamycin complex 2 (mTORC2) facilitated the phosphorylation of BSTA and its association with Akt1, and the BSTA-Akt1 interaction promoted the association of mTORC2 with Akt1 and phosphorylation of Akt1 at Ser⁴⁷³ in response to growth factor stimulation. Furthermore, analyses of bsta gene-trap murine embryonic stem cells revealed an essential function for BSTA and phosphorylation of Akt1 at Ser⁴⁷³ in promoting adipocyte differentiation, which required suppression of the expression of the gene encoding the transcription factor FoxC2. These findings indicate that BSTA is a molecular switch that promotes phosphorylation of Akt1 at Ser⁴⁷³ and reveal an mTORC2-BSTA-Akt1-FoxC2-mediated signaling mechanism that is critical for adipocyte differentiation.