Diabetes-associated mitochondrial DNA mutation A3243G impairs cellular metabolic pathways necessary for beta cell function

Abstract

Aims/hypothesis Mitochondrial DNA (mtDNA) mutations cause several diseases, including mitochondrial inherited diabetes and deafness (MIDD), typically associated with the mtDNA A3243G point mutation on tRNALeu gene. The common hypothesis to explain the link between the genotype and the phenotype is that the mutation might impair mitochondrial metabolism expressly required for beta cell functions. However, this assumption has not yet been tested. Methods We used clonal osteosarcoma cytosolic hybrid cells (namely cybrids) harbouring mitochondria derived from MIDD patients and containing either exclusively wild-type or mutated (A3243G) mtDNA. According to the importance of mitochondrial metabolism in beta cells, we studied the impact of the mutation on key parameters by comparing stimulation of these cybrids by the main insulin secretagogue glucose and the mitochondrial substrate pyruvate. Results Compared with control mtDNA from the same patient, the A3243G mutation markedly modified metabolic pathways leading to a high glycolytic rate (2.8-fold increase), increased lactate production (2.5-fold), and reduced glucose oxidation (−83%). We also observed impaired NADH responses (−56%), negligible mitochondrial membrane potential, and reduced, only transient ATP generation. Moreover, cybrid cells carrying patient-derived mutant mtDNA exhibited deranged cell calcium handling with increased cytosolic loads (1.4-fold higher), and elevated reactive oxygen species (2.6-fold increase) under glucose deprivation. Conclusions/interpretation The present study demonstrates that the mtDNA A3243G mutation impairs crucial metabolic events required for proper cell functions, such as coupling of glucose recognition to insulin secretion.

Transient Oxidative Stress Damages Mitochondrial Machinery Inducing Persistent β-Cell Dysfunction

“…Subsequent endogenous ROS generation might contribute to prolongation of oxidative damages, correlating with reduction of respiratory chain complex proteins detected over a period of 3 days after stress. Previous studies reported that ROS production is associated with electron transport chain inhibition and mtDNA mutations (17,37,38). Accordingly, blockade of the respiratory chain allows electrons to be transferred directly to molecular oxygen to form superoxide (39).…”

“…has been shown that mitochondrial respiration chain dysfunction may be associated with increased ROS levels (17), suggesting that transient exogenous oxidative stress might favor endogenous ROS generation from altered mitochondria. To test this hypothesis, H 2 O 2 production from INS-1E mitochondria was measured with mitochondrial electron donors NADH (5 mM) and succinate (5 mM).…”

“…Damages to mitochondrial DNA (mtDNA) induce mutations that in turn may favor ROS generation, although the contribution of mtDNA mutations to ROS generation remains unclear. We previously reported that patient-derived mitochondrial A3243G mutation, causing mitochondrial inherited diabetes, is responsible for defective mitochondrial metabolism associated with elevated ROS levels and reduced antioxidant enzyme expression (17). On the other hand, mtDNA mutator mice exhibit accelerated aging without changes in superoxide levels in embryonic fibroblasts (18), showing that ROS generation can be dissociated from mtDNA mutations.…”

Peroxisome proliferator-activated receptor α (PPARα) protects against oleate-induced INS-1E beta cell dysfunction by preserving carbohydrate metabolism

“…The rate of glucose oxidation over a period of 1 h was measured as described [30]. Radiolabelled CO 2 released from cells was measured using [U- 14 C]glucose as substrate and 14 CO 2 production was measured with an LKB-Wallac 1217 Rackbeta counter.…”

Mitochondrial Actions for Fat Browning and Energy Expenditure in White Adipose Tissue

“…The main sources of known mitochondriarelated diseases comprise electron transport chain (ETC) malfunction, impaired ATP generation, imbalance between reactive oxygen species (ROS) generation and sequestration, mutations in the nuclear and mitochondrial genomes and unbalanced mitochondrial turnover [26][27][28]. These conditions include hypercholesterolemia, hypertriacylglyceridemia [29], hepatic cytolysis and steatosis [30], myoclonic epilepsy with ragged-red fibers (MERFF), mitochondrial encephalomyopathy, lactic acidosis, and stroke-like syndrome (MELAS), mitochondrial inherited diabetes and deafness (MIDD) and T2DM [20,26,27]. Mitochondria dysfunction due to mitochondrial DNA (mtDNA) mutations and reduced oxidative metabolism is also related to various types of cancer, including breast cancer [31][32][33].…”