Background: In pancreatic β-cells under diabetic conditions, metabolic stressors cause mitochondrial dysfunction and reduce oxidative phosphorylation, resulting in impaired intracellular metabolism. It has been suggested that aberrant activation of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) plays a role in this impairment. However, the pathological significance of PFKFB3 activation and its flexibility are not clear.

Methods: Eight-week-old ob/ob mice were fed a standard chow ad lib or the same diet restricted to 2 g/day, or tofogliflozin added chow ad lib for 4 weeks. The body mass and glucose tolerance were compared among the groups. The expression of glycolytic enzymes in the pancreatic islets was evaluated using western blotting, immunohistochemistry and DNA microarray analysis. Next, INS-1 cells were cultured in medium containing a low (5.5 mM; low-G) or a high (22 mM: high-G) glucose concentration, or high-G with PFKFB3 inhibiter (3PO) for 48 hours. The expression of mafa and pdx-1 were evaluated using real time PCR.

Results: Ad lib-fed mice showed hyperglycemia and greater weight gain than food restricted mice and tofogliflozin treated mice. The expression of PFKFB3 and other glycolytic enzymes were higher in ad lib-fed mice, whereas such aberrant expression were suppressed by restricted feeding and tofogliflozin. DNA microarray analysis revealed increased expression of genes related to glycolytic pathway in ad lib-fed mice. However, these changes were corrected in a restricted diet and tofogliflozin groups. In INS-1 cells, high-G caused elevated pfkfb3 and decreased mafa and pdx-1 expression compared with low-G exposure. Inhibition of glycolytic pathway by 3PO in high-G environment did not normalize the defect of mafa and pdx-1.

Conclusion: The intracellular metabolic changes in pancreatic β cells associated with obesity and diabetes are flexible and may compensate for glucose intolerance.


K.Chiba: None. H.Nomoto: Speaker's Bureau; Novo Nordisk, Sumitomo Pharma, Co., Ltd. R.Izumihara: None. H.Kameda: None. H.Miyoshi: Research Support; Abbott, LifeScan Diabetes Institute, Taisho Pharmaceutical Holdings Co., Ltd., Speaker's Bureau; AstraZeneca, Boehringer Ingelheim Japan, Inc., Eli Lilly Japan K.K., Kowa Company, Ltd., MSD Life Science Foundation, Novo Nordisk, Ono Pharmaceutical Co., Ltd., Sanofi K.K., Mitsubishi Tanabe Pharma Corporation. A.Nakamura: Research Support; Abbott Japan Co., Ltd., Boehringer Ingelheim Japan, Inc., Daiichi Sankyo, Taisho Pharmaceutical Holdings Co., Ltd., Teijin Pharma Limited, Kowa Company, Ltd., Mitsubishi Tanabe Pharma Corporation. T.Atsumi: Speaker's Bureau; Eli Lilly Japan K.K., Kowa Company, Ltd.

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