No abstract

Aims/hypothesis. The electrons of the glycolysis-derived reduced form of NADH are transferred to mitochondria through the NADH shuttle system. There are two NADH shuttles: the glycerol phosphate and malate-aspartate shuttle. Mice with a targeted disruption of mitochondrial glycerol-3-phosphate dehydrogenase, a rate-limiting enzyme of the glycerol phosphate shuttle, are not diabetic and have normal islet glucoseinduced secretion. In this study, we analyzed if environmental factors, such as a high carbohydrate diet could contribute to the development of Type 2 diabetes mellitus in mice with a specific defective genetic background. Methods. The mice were fed with a high carbohydrate diet for 1 and 6 months, and several biochemical parameters were analysed. The mitochondrial respiratory activity was assayed by polarography; and the islet function was studied by islet perifusion and pancreas perfusion.Results. The high carbohydrate diet induced hyperglycaemia, hyperinsulinaemia, and islet hyperplasia in the wild-type and heterozygote mice. Activity of the respiratory chain complex I also increased in these mice. In contrast, these effects were not observed in the null mice fed with the diet; in addition, these null mice had an increased insulin sensitivity compared to wild-type mice. Conclusion/interpretation. The phenotype of the mice with an impairment of NADH shuttles does not worsen when fed a high carbohydrate diet; moreover, the diet does not compromise islet function. [Diabetologia (2003[Diabetologia ( ) 46:1394[Diabetologia ( -1401 Keywords High carbohydrate diet, mitochondrial metabolism, mGPDH, beta cell, glycerol phosphate shuttle, insulin secretion. A. Barberà and M. Gudayol have contributed equally to this paper Diabetologia

Ca2+-responsive mitochondrial FAD-linked glycerophosphate dehydrogenase (mGPDH) is a key component of the pancreatic beta-cell glucose-sensing device. The purpose of this study was to examine the association of mutations in the cDNA coding for the FAD-binding domain of mGPDH and to explore the functional consequences of these mutations in vitro. To investigate this association in type 2 diabetes mellitus, we studied a cohort of 168 patients with type 2 diabetes and 179 glucose-tolerant control subjects of Spanish Caucasian origin by single-stranded conformational polymorphism analysis. In vitro site-directed mutagenesis was performed in the mGPDH cDNA sequence to reproduce those mutations that produce amino acid changes in a patient with type 2 diabetes. We detected mutations in the mGPDH FAD-binding domain in a single patient, resulting in a Gly to Arg amino acid change at positions 77, 78, and 81 and a Thr to Pro at position 90. In vitro expression of the mutated constructs in Xenopus oocytes resulted in a significantly lower enzymatic activity than in cells expressing the wild-type form of the enzyme. Our results indicate that although mutations in the mGPDH gene do not appear to have a major role in type 2 diabetes mellitus, the reduction in mGPDH enzymatic activity associated with the newly described mGPDH mutations suggests that they may contribute to the disease in some patients.