Synergistic activation of glucose-6-phosphate dehydrogenase and NAD(P)H oxidase by Src kinase elevates superoxide in type 2 diabetic, Zucker fa/fa, rat liver

Abstract

Glucose metabolism through glycolysis and hexosamine pathway has been shown to be altered in type 2 diabetes. However, its fate through the pentose phosphate pathway (PPP) is currently unclear. In this study, we determined whether the activity of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the PPP, is modulated in the liver of Zucker obese fa/fa rats (9–11 weeks old). We found that G6PD expression and activity, NADPH levels and 6-phosphogluconate generation was significantly increased in liver of fa/fa rats. Inhibition of PI3 kinase and Src kinases decreased (P<0.05) G6PD activity in the fa/fa but not in the lean rat liver, suggesting that G6PD activity is regulated by PI3/Src kinase signaling pathways. G6PD-derived NADPH increased (P<0.05) superoxide anion levels by 70–90% in the fa/fa vs the lean rat liver, which was inhibited by NADPH oxidase inhibitor, gp91ds-tat (50 μM), and G6PD inhibitors, 6-aminonicotinamide (1 mM) and dihydroepiandrosterone (100 μM); therefore, indicating that elevated G6PD activity may be responsible for mediating superoxide generation. Interestingly, we also found a positive correlation between liver hypertrophy/increased G6PD activity (r2=0.77; P=0.0009) and liver hypertrophy/superoxide production (r2=0.51; P=0.0091) in fa/fa rats. Increased G6PD and NADPH oxidase expression and activity, in young hyper-glycemic and -insulinemic rats prior to the development of diabetes, appear to be contributing factors for the induction of oxidative stress. Since inhibition of G6PD activity decreases oxidative stress, we conclude that it behaves as a pro-oxidant in the fa/fa rat liver, in type 2 diabetes.

Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat

“…Although increased G6PdH activity might be thought to increase GSH levels, that is not the case here and suggests that depletion of oxidant buffers may be an early step in the downward spiral of mitochondrial function. Diabetes increases flux through the pentose shunt pathway in the heart, and this may be a significant source of oxidant stress within the cytosol (43,57,105). Glucose-6-phosphate dehydrogenase (G6PdH) is rate limiting in this pathway and in the present study its inhibition reduced glucose-induced mtDNA damage and restored cellular ATP production.…”

Glucose-6-Phosphate Dehydrogenase Deficiency Improves Insulin Resistance With Reduced Adipose Tissue Inflammation in Obesity

“…Furthermore, overexpression of G6PD in macrophages promotes oxidative stress and the expression of proinflammatory cytokines, which induce insulin resistance in adipocytes (24). Similarly, upregulation of G6PD in the liver, heart, and pancreatic b-cells of obese and diabetic animals also increases oxidative stress, which leads to functional defects in the respective tissues (12,25,26). Altogether, these findings suggest that anomalous G6PD upregulation in obese conditions might deteriorate energy homeostasis and oxidative stress, thereby accelerating metabolic complications.…”

“…Various pro-oxidative enzymes are known to be augmented in the adipose tissues of obese animals, whereas antioxidative processes related to ROS scavenging tend to be suppressed (9,10). Accordingly, treatment with NADPH oxidase inhibitors as well as antioxidant drugs attenuates ROS production and adipokine dysregulation, alleviating metabolic disorders such as insulin resistance in obesity (9,12). Thus it is likely that the imbalance between ROS production and scavenging in obese adipose tissue is closely associated with elevated adipose tissue inflammation and metabolic dysregulation.…”

Stress-Induced GSK3 Regulates the Redox Stress Response by Phosphorylating Glucose-6-Phosphate Dehydrogenase in Arabidopsis

“…G6PD is phosphorylated in animals and plants, which has been correlated with both enhanced (Ramnanan and Storey, 2006;Dieni and Storey, 2010;Gupte et al, 2011) and reduced activity (Hauschild and von Schaewen, 2003;Xu et al, 2005;Zhang et al, 2000). While different signaling pathways, including protein kinase C, protein kinase A, and Src kinase, have been implicated in regulating G6PD phosphorylation in animals under a variety of different conditions (Xu et al, 2005;Gupte et al, 2009Gupte et al, , 2011, the upstream regulator(s) of G6PD phosphorylation in plants have yet to be identified.…”