ROS-mediated glucose metabolic reprogram induces insulin resistance in type 2 diabetes.

Oxidative stress is known to contribute to insulin resistance in diabetes, however the mechanism is not clear. Here we show that reactive oxygen species (ROS) could reprogram the glucose metabolism through upregulating the pentose pathway so as to induce insulin resistance in type 2 diabetes (T2DM). By using streptozotocin-high fat diet (STZ-HFD) induced T2DM in rats, we show that diabetic rats exhibited high level of oxidative stress accompanied with insulin resistance. Hypoxia inducible factor (HIF-1α) protein expression as well as its downstream target glucokinase (GK), were upregulated; The glycogen synthesis increased accordingly; However the glycolysis was inhibited as indicated by decreased phosphofructokinase-1 (PFK-1), pyruvate kinase (PK), phospho-PFK-2/PFK-2 (p-PFK-2/PFK-2) ratio, lactate dehydrogenase (LDH) and pyruvate dehydrogenase kinase (PDK); Pyruvate dehydrogenase (PDH) which promotes pyruvate to generate acetyl-CoA declined as well. While phospho-acetyl-CoA carboxylase/acetyl-CoA carboxylase (p-ACC/ACC) ratio increased, meaning that lipid beta-oxidation increased. The pentose pathway was activated as indicated by increased G6PD activity and NADPH level. Our results suggest that diabetic rats countervail ROS stress through increasing pentose pathway, and reprogram the energy metabolic pathway from glycolysis into lipid oxidation in order to compensate the ATP requirement of the body, which causes insulin resistance.

Glutaredoxins concomitant with optimal ROS activate AMPK through S-glutathionylation to improve glucose metabolism in type 2 diabetes.

AMPK dysregulation contributes to the onset and development of type 2 diabetes (T2DM). AMPK is known to be activated by reactive oxygen species (ROS) and antioxidant interference. However the mechanism by which redox state mediates such contradictory result remains largely unknown. Here we used streptozotocin-high fat diet （STZ-HFD） induced-type 2 diabetic rats and cells lines (L02 and HEK 293) to explore the mechanism of redox-mediated AMPK activation. We show glutaredoxins (Grxs) concomitant with optimal ROS act as an essential mediator for AMPK activation. ROS level results in different mechanisms for AMPK activation. Under low ROS microenvironment, Grxs-mediated S-glutathionylation on AMPK-α catalytic subunit activates AMPK to improve glucose transportation and degradation while inhibiting glycogen synthesis and keeping redox balance. While, under high ROS microenvironment, AMPK is activated by an AMP-dependent mechanism, however sustained high level ROS also causes loss of AMPK protein. This finding provides evidence for a new approach to diabetes treatment by individual doses of ROS or antioxidant calibrated against the actual redox level in vivo. Moreover, the novel function of Grxs in promoting glucose metabolism may provide new target for T2DM treatment.

Redox homeostasis protects mitochondria through accelerating ROS conversion to enhance hypoxia resistance in cancer cells.

Mitochondria are the powerhouses of eukaryotic cells and the main source of reactive oxygen species (ROS) in hypoxic cells, participating in regulating redox homeostasis. The mechanism of tumor hypoxia tolerance, especially the role of mitochondria in tumor hypoxia resistance remains largely unknown. This study aimed to explore the role of mitochondria in tumor hypoxia resistance. We observed that glycolysis in hypoxic cancer cells was up-regulated more rapidly, with far lesser attenuation in aerobic oxidation, thus contributing to a more stable ATP/ADP ratio. In hypoxia, cancer cells rapidly convert hypoxia-induced O(2˙)(-) into H2O2. H2O2 is further decomposed by a relatively stronger antioxidant system, causing ROS levels to increase lesser compared to normal cells. The moderate ROS leads to an appropriate degree of autophagy, eliminating the damaged mitochondria and offering nutrients to promote mitochondria fusion, thus protects mitochondria and improves hypoxia tolerance in cancer. The functional mitochondria could enable tumor cells to flexibly switch between glycolysis and oxidative phosphorylation to meet the different physiological requirements during the hypoxia/re-oxygenation cycling of tumor growth.