Glucose-6-phosphate dehydrogenase modulates vascular endothelial growth factor-mediated angiogenesis

Glucose-6-phosphate dehydrogenase (G6PD), the first enzyme of the pentose phosphate pathway, is the principal intracellular source of NADPH. NADPH is utilized as a cofactor by vascular endothelial cell nitric-oxide synthase (eNOS) to generate nitric oxide (NO*). To determine whether G6PD modulates NO*-mediated angiogenesis, we decreased G6PD expression in bovine aortic endothelial cells using an antisense oligodeoxynucleotide to G6PD or increased G6PD expression by adenoviral gene transfer, and we examined vascular endothelial growth factor (VEGF)-stimulated endothelial cell proliferation, migration, and capillary-like tube formation. Deficient G6PD activity was associated with a significant decrease in endothelial cell proliferation, migration, and tube formation, whereas increased G6PD activity promoted these processes. VEGF-stimulated eNOS activity and NO* production were decreased significantly in endothelial cells with deficient G6PD activity and enhanced in G6PD-overexpressing cells. In addition, G6PD-deficient cells demonstrated decreased tyrosine phosphorylation of the VEGF receptor Flk-1/KDR, Akt, and eNOS compared with cells with normal G6PD activity, whereas overexpression of G6PD enhanced phosphorylation of Flk-1/KDR, Akt, and eNOS. In the Pretsch mouse, a murine model of G6PD deficiency, vessel outgrowth from thoracic aorta segments was impaired compared with C3H wild-type mice. In an in vivo Matrigel angiogenesis assay, cell migration into the plugs was inhibited significantly in G6PD-deficient mice compared with wild-type mice, and gene transfer of G6PD restored the wild-type phenotype in G6PD-deficient mice. These findings demonstrate that G6PD modulates angiogenesis and may represent a novel angiogenic regulator.     

Increasing Glucose 6-Phosphate Dehydrogenase Activity Restores Redox Balance in Vascular Endothelial Cells Exposed to High Glucose

Previous studies have shown that high glucose increases reactive oxygen species (ROS) in endothelial cells that contributes to vascular dysfunction and atherosclerosis. Accumulation of ROS is due to dysregulated redox balance between ROS-producing systems and antioxidant systems. Previous research from our laboratory has shown that high glucose decreases the principal cellular reductant, NADPH by impairing the activity of glucose 6-phosphate dehydrogenase (G6PD). We and others also have shown that the high glucose-induced decrease in G6PD activity is mediated, at least in part, by cAMP-dependent protein kinase A (PKA). As both the major antioxidant enzymes and NADPH oxidase, a major source of ROS, use NADPH as substrate, we explored whether G6PD activity was a critical mediator of redox balance. We found that overexpression of G6PD by pAD-G6PD infection restored redox balance. Moreover inhibition of PKA decreased ROS accumulation and increased redox enzymes, while not altering the protein expression level of redox enzymes. Interestingly, high glucose stimulated an increase in NADPH oxidase (NOX) and colocalization of G6PD with NOX, which was inhibited by the PKA inhibitor. Lastly, inhibition of PKA ameliorated high glucose mediated increase in cell death and inhibition of cell growth. These studies illustrate that increasing G6PD activity restores redox balance in endothelial cells exposed to high glucose, which is a potentially important therapeutic target to protect ECs from the deleterious effects of high glucose.     

Glucose-6-phosphate dehydrogenase and the oxidative pentose phosphate cycle protect cells against apoptosis induced by low doses of ionizing radiation

The initial and rate-limiting enzyme of the oxidative pentose phosphate shunt, glucose-6-phosphate dehydrogenase (G6PD), is inhibited by NADPH and stimulated by NADP(+). Hence, under normal growth conditions, where NADPH levels exceed NADP(+) levels by as much as 100-fold, the activity of the pentose phosphate cycle is extremely low. However, during oxidant stress, pentose phosphate cycle activity can increase by as much as 200-fold over basal levels, to maintain the cytosolic reducing environment. G6PD-deficient (G6PD(-)) cell lines are sensitive to toxicity induced by chemical oxidants and ionizing radiation. Compared to wild-type CHO cells, enhanced sensitivity to ionizing radiation was observed for G6PD(-) cells exposed to single-dose or fractionated radiation. Fitting the single-dose radiation response data to the linear-quadratic model of radiation-induced cytotoxicity, we found that the G6PD(-) cells exhibited a significant enhancement in the alpha component of radiation-induced cell killing, while the values obtained for the beta component were similar in both the G6PD(-) and wild-type CHO cell lines. Here we report that the enhanced alpha component of radiation-induced cell killing is associated with a significant increase in the incidence of ionizing radiation-induced apoptosis in the G6PD(-) cells. These data suggest that G6PD and the oxidative pentose phosphate shunt protect cells from ionizing radiation-induced cell killing by limiting the incidence of radiation-induced apoptosis. The sensitivity to radiation-induced apoptosis was lost when the cDNA for wild-type G6PD was transfected into the G6PD(-) cell lines. Depleting GSH with l-BSO enhanced apoptosis of K1 cells while having no effect in the G6PD(-) cell line     

G6PD缺陷抑制人黑色素瘤细胞裸鼠移植瘤的生长

敲减葡糖6-磷酸脱氢酶(G6PD)表达的人黑色素瘤A375细胞(A375-G6PDΔ) 呈现生长增殖抑制和凋亡率升高. 为明确G6PD缺陷对裸鼠体内成瘤的影响及其可能机制,用A375-WT与A375-G6PDΔ细胞制作裸鼠荷瘤模型,观察体内瘤体生长,real-time PCR、免疫组织化学染色与紫外分光光度法分别检测瘤体组织G6PD mRNA、G6PD蛋白及酶活性,Western 印迹分析凋亡相关蛋白,分光光度法测定NADPH和GSH/GSSG水平. 结果显示,A375-G6PDΔ细胞注射组的裸鼠成瘤时间延长,瘤体生长明显减慢,瘤体的体积与质量显著低于A375 WT细胞注射组（P <0.01）;与A375-WT细胞注射组相比,A375 G6PDΔ细胞注射组的裸鼠瘤体组织中G6PD mRNA表达、G6PD阳性细胞数与G6PD活性分别降低了87.10%、77.20%与75.77%（P<0.01）,G6PD、p53和Bcl-2的表达分别降低了67.92%、65.54%和62.32%（P<0.01）,Fas升高了86.38%（P<0.01）,NADPH和GSH/GSSG分别降低了74.37%和86.02%（P<0.01）. 结果提示,G6PD缺陷可能通过减少核酸等合成的原料、改变细胞内氧化还原状态及凋亡相关蛋白表达抑制裸鼠瘤体生长与增殖,这为黑色素瘤发生和治疗研究提供了新的线索.     

G6PD缺陷通过Caspase-3和PARP-1诱导人黑色素瘤细胞凋亡

葡糖-6-磷酸脱氢酶(G6PD)在许多肿瘤细胞中高表达,但其发生的作用机理目前仍然不明确.以正常人表皮黑色素细胞(HEM)、野生型人黑色素瘤A375细胞(A375-WT)和G6PD缺陷的A375细胞(A375-G6PDΔ)为对象,经real-time PCR、Western印迹和紫外分光光度法分析显示,A375-WT细胞的mRNA、G6PD蛋白和G6PD活性分别是HEM细胞的1.89倍(P0.05)、6.86倍(P0.01)和2.30倍(P0.05).Annexin V/PI流式细胞仪和Western印迹测定表明,A375-G6PDΔ的凋亡率是A375-WT的5.10倍(P0.01),活化半胱氨酸蛋白酶3(caspase-3)增高1.84倍(P0.01)以及89 kD多聚二磷酸腺苷核糖聚合酶-1(PARP-1)生成增加2.87倍(P0.01).分光光度法分析显示,A375-G6PDΔ的NADPH和GSH分别降低了72.30%(P0.01)和27.39%(P0.05),并伴有75.43%的H2O2增高(P0.01).结果提示,G6PD在黑色素瘤细胞中高表达和高活性,而敲减G6PD表达通过caspase-3和PARP-1信号诱发人黑色素瘤细胞凋亡,这为深入揭示黑色素瘤的发生机理提供了新思路。     

High glucose inhibits glucose-6-phosphate dehydrogenase via cAMP in aortic endothelial cells

Recent studies have shown that hyperglycemia is a principal cause of cellular damage in patients with diabetes mellitus. A major consequence of hyperglycemia is increased oxidative stress. Glucose-6-phosphate dehydrogenase (G6PD) plays an essential role in the regulation of oxidative stress by primarily regulating NADPH, the main intracellular reductant. In this paper we show that increased glucose (10-25 mm) caused inhibition of G6PD resulting in decreased NADPH levels in bovine aortic endothelial cells (BAEC). Inhibition was seen within 15 min. High glucose-induced inhibition of G6PD predisposed cells to cell death. High glucose via increased activity of adenylate cyclase also stimulated an increase in cAMP levels in BAEC. Agents that increased cAMP caused a decrease in G6PD activity. Inhibition of cAMP-dependent protein kinase A ameliorated the high glucose-induced inhibition of G6PD. Finally, high glucose stimulated phosphorylation of G6PD. These results suggest that, in BAEC, high glucose stimulated increased cAMP, which led to increased protein kinase A activity, phosphorylation of G6PD, and inhibition of G6PD activity. We conclude that these changes in G6PD activity play an important role in high glucose-induced cell damage/death.     

A VGF-derived peptide attenuates development of type 2 diabetes via enhancement of islet β-cell survival and function

Deterioration of functional islet β-cell mass is the final step in progression to Type 2 diabetes. We previously reported that overexpression of Nkx6.1 in rat islets has the dual effects of enhancing glucose-stimulated insulin secretion (GSIS) and increasing β-cell replication. Here we show that Nkx6.1 strongly upregulates the prohormone VGF in rat islets and that VGF is both necessary and sufficient for Nkx6.1-mediated enhancement of GSIS. Moreover, the VGF-derived peptide TLQP-21 potentiates GSIS in rat and human islets and improves glucose tolerance in vivo. Chronic injection of TLQP-21 in prediabetic ZDF rats preserves islet mass and slows diabetes onset. TLQP-21 prevents islet cell apoptosis by a pathway similar to that used by GLP-1, but independent of the GLP-1, GIP, or VIP receptors. Unlike GLP-1, TLQP-21 does not inhibit gastric emptying or increase heart rate. We conclude that TLQP-21 is a targeted agent for enhancing islet β-cell survival and function.     

Glucose-dependent Protection by Dietary Selenium against Haemolysis of Rat Erythrocytes <Emphasis Type="Italic">in vitro</Emphasis>

THE occurrence in man of drug-induced haemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficient erythrocytes¹ suggested the possibility of an analogy to the haemolysis which occurs in vitamin E deficient red blood cells. Cohen and Hochstein² have shown that haemolysis in G6PD deficient cells is associated with the inability of the cell to generate adequate reduced glutathione (GSH) through GSSG reductase because of the impaired generation of NADPH. Moreover, there is evidence that glucose protects red blood cells from haemolysis by its ability to provide NADPH through G6PD which subsequently generates GSH³. The G6PD deficient cell, however, cannot maintain an adequate concentration of GSH in the cell, even in the presence of glucose⁴, whereas the normal cell can maintain a normal concentration of GSH in the presence of glucose, preserving the integrity of the red blood cell. Vitamin E protects red blood cells from haemolysis whether supplied in vivo or in vitro and its effect has usually been demonstrated without glucose in the incubation medium. Although selenium prevents many of the same deficiency symptoms as vitamin E, it has not been uniformly effective in preventing the in vitro haemolysis of red blood cells. If a protective action of selenium against haemolysis were dependent on the presence of GSH, or if selenium were involved in the generation of GSH, selenium would not be expected to prevent haemolysis unless glucose was present in the incubation medium to provide a constant source of NADPH for the generation of GSH from GSSG through GSSG reductase (Fig. 1).     

Suppression of interleukin-1 beta-induced nitric oxide production in RINm5F cells by inhibition of glucose-6-phosphate dehydrogenase

In rat pancreatic islets and insulin-producing cell lines, IL-1beta induces expression of inducible nitric oxide synthase and NO production leading to impairment of glucose-stimulated insulin release and decreased cell survival. NADPH is an obligatory cosubstrate for iNOS synthesis of NO. We hypothesized that IL-1beta stimulates an increase in activity of NADPH-producing enzyme(s) prior to NO production and that this increase is necessary for NO production. Using rat insulin-secreting RINm5F cells, we found that (1) IL-1beta caused a biphasic change in the NADPH level (increased by 6 h and decreased after prolonged incubation in the presence of 2 ng/mL IL-1beta); (2) IL-1beta stimulated increased activity of glucose-6-phosphate dehydrogenase (G6PD) in a time- and dose-dependent manner, and G6PD expression was increased by about 80% after exposure to 2 ng/mL IL-1beta for 18 h: (3) IL-1beta-stimulated NO production was positively correlated with increased G6PD activity; (4) IL-1beta did not cause any significant change in enzyme activity of another NADPH-producing enzyme, malic enzyme; (5) IL-1beta-induced NO production was significantly reduced either by inhibiting G6PD activity using an inhibitor of G6PD (dehydroepiandrosterone) or by inhibiting G6PD expression using an antisense oligonucleotide to G6PD mRNA; and (6) IL-1beta stimulated a decrease in the cAMP level. 8-Bromo-cAMP caused decreased G6PD activity, and the protein kinase A inhibitor H89 led to a increase in G6PD activity in RINm5F cells. In conclusion, our data show that IL-1beta stimulated G6PD activity and expression level, providing NADPH that is required by iNOS for NO production in RINm5F cells. Also, inhibition of the cAMP-dependent PKA signal pathway is involved in an IL-1beta-stimulated increase in G6PD activity.     

Inhibition of Calcium/Calmodulin-Dependent Protein Kinase IIα Suppresses Oxidative Stress in Cerebral Ischemic Rats Through Targeting Glucose 6-Phosphate Dehydrogenase

Ischemic stroke is a leading cause of mortality and morbidity worldwide, and oxidative stress plays a significant role in the ischemia stage and reperfusion stage. Previous studies have indicated that both calcium/calmodulin-dependent protein kinase II (CaMKII) and glucose 6-phosphate dehydrogenase (G6PD) are involved in the oxidative stress. Thus, the aim of this study was to investigate the roles of CaMKIIα, an important isoform of CaMKII, and G6PD in a rat model of middle cerebral artery occlusion (MCAO). Intracerebroventricular injection of small interfering ribonucleic acid (siRNA) for CaMKIIα was performed at 48 h pre-MCAO surgery. Immunofluorescence Staining and western blot were performed to detect the expression of p-CaMKIIα and G6PD in the cortices. 2, 3, 5-Triphenyltetrazolium chloride (TTC) staining was performed to investigate the infarct volume. In addition, neurological deficit, reactive oxygen species (ROS), ratio of reduced-to-oxidized glutathione (GSH/GSSG) and ratio of reduced-to-oxidized oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP⁺) were assessed. The results indicated that both p-CaMKIIα and G6PD were widely located in the neurons and astrocytes, and their expression was gradually increased in the cortices after MCAO, which was accompanied by increased level of ROS and decreased levels of GSH/GSSG and NADPH/NADP⁺. However, after treatment with siRNA for CaMKIIα, p-CaMKIIα expression was decreased and G6PD expression was increased. Moreover, inhibition of CaMKIIα improved the neurological deficit, reduced the infarct volume, decreased the level of ROS and increased the levels of GSH/GSSG and NADPH/NADP⁺. The results suggested that CaMKIIα inhibition exerted neuroprotective effects through regulating G6PD expression, which provides a new target for prevention and treatment of stroke.

     

Modulation of doxorubicin resistance by the glucose-6-phosphate dehydrogenase activity

How anti-neoplastic agents induce MDR (multidrug resistance) in cancer cells and the role of GSH (glutathione) in the activation of pumps such as the MRPs (MDR-associated proteins) are still open questions. In the present paper we illustrate that a doxorubicin-resistant human colon cancer cell line (HT29-DX), exhibiting decreased doxorubicin accumulation, increased intracellular GSH content, and increased MRP1 and MRP2 expression in comparison with doxorubicin-sensitive HT29 cells, shows increased activity of the PPP (pentose phosphate pathway) and of G6PD (glucose-6-phosphate dehydrogenase). We observed the onset of MDR in HT29 cells overexpressing G6PD which was accompanied by an increase in GSH. The G6PD inhibitors DHEA (dehydroepiandrosterone) and 6-AN (6-aminonicotinamide) reversed the increase of G6PD and GSH and inhibited MDR both in HT29-DX cells and in HT29 cells overexpressing G6PD. In our opinion, these results suggest that the activation of the PPP and an increased activity of G6PD are necessary to some MDR cells to keep the GSH content high, which is in turn necessary to extrude anticancer drugs out of the cell. We think that our data provide a new further mechanism for GSH increase and its effects on MDR acquisition.     

Knockdown of glucose-6-phosphate dehydrogenase (G6PD) following cerebral ischemic reperfusion: the pros and cons

NADPH derived from glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, has been implicated not only to promote reduced glutathione (GSH) but also enhance oxidative stress in specific cellular conditions. In this study, the effects of G6PD antisense oligodeoxynucleotides (AS-ODNs) was examined on the CA1 pyramidal neurons following transient cerebral ischemia. Specifically knockdown of G6PD protein expression in hippocampus CA1 subregion at early reperfusion period (1-24 h) with a strategy to pre-treated G6PD AS-ODNs significantly reduced G6PD activity and NADPH level, an effect correlated with attenuation of NADPH oxidase activation and superoxide anion production. Concomitantly, pre-treatment of G6PD AS-ODNs markedly reduced oxidative DNA damage and the delayed neuronal cell death in rat hippocampal CA1 region induced by global cerebral ischemia. By contrast, knockdown of G6PD protein at late reperfusion period (48-96 h) increased oxidative DNA damage and exacerbated the ischemia-induced neuronal cell death in hippocampal CA1 region, an effect associated with reduced NADPH level and GSH/GSSG ratio. These findings indicate that G6PD not only plays a role in oxidative neuronal damage but also a neuroprotective role during different ischemic reperfusion period. Therefore, G6PD mediated oxidative response and redox regulation in the hippocampal CA1 act as the two sides of the same coin and may represent two potential applications of G6PD during different stage of cerebral ischemic reperfusion.     

TLQP-21, a VGF-derived peptide, stimulates exocrine pancreatic secretion in the rat

The aims of this paper were to study: (1) the effects of TLQP-21 (non-acronic name), the C-terminal region of the VGF (non-acronic name), polypeptide (from residue 557 to 576 of VGF), on in vitro amylase release from rat isolated pancreatic lobules and acinar cells; (2) the mechanism through which TLQP-21 regulates exocrine pancreatic secretion, by using the muscarinic receptor antagonist atropine (10(-6)M) and the cyclo-oxygenase inhibitor, indomethacin (10(-6)M). On pancreatic lobules of rats, concentrations of TLQP-21 from 10(-7) to 10(-5)M significantly (p<0.05) induced a 2-3-fold increase of baseline pancreatic amylase release, measured at the end of 60 min incubation period. Co-incubation with atropine 10(-6)M did not antagonise the enzyme outflow induced by the peptide. On the contrary, co-incubation of TLQP-21 (10(-7) and 10(-6)M) with indomethacin, at concentration of 10(-6)M, which alone did not modify enzyme secretion, completely suppressed the increase of amylase evoked by TLQP-21 on pancreatic lobules. On rat pancreatic acinar cells, TLQP-21, at all the concentrations tested, was unable to affect exocrine pancreatic secretion, indicating an indirect mechanism of action on acinar cells. These results put in evidence, for the first time, that TLQP-21, a VGF-derived peptide, modulates exocrine pancreatic secretion in rats through a stimulatory mechanism involving prostaglandin release. In conclusion, TLQP-21 could be included among the neurohumoral signals regulating pancreatic exocrine secretion, and increases the knowledge concerning the systems controlling this function.     

The anti-cancer drug, doxorubicin, causes oxidant stress-induced endothelial dysfunction

The anticancer drug doxorubicin (DOX) is toxic to target cells, but also causes endothelial dysfunction and edema, secondary to oxidative stress in the vascular wall. Thus, the mechanism of action of this drug may involve chemotoxicity to both cancer cells and to the endothelium. Indeed, we found that the permeability of monolayers of bovine pulmonary artery endothelial cells (BPAEC) to albumin was increased by approximately 10-fold above control, following 24-h exposure to clinically relevant concentrations of DOX (up to 1 microM). DOX also caused >4-fold increases in lactate dehydrogenase leakage and large decreases in ATP and reduced glutathione (GSH) in BPAECs, which paralleled the increases in endothelial permeability. A large part of the ATP loss could be attributed to DOX-induced hydrogen peroxide production which inhibited key thiol-enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and glucose-6-phosphate dehydrogenase (G6PDH). Depletion of reduced nicotinamide adenine dinucleotide phosphate (NADPH) appeared to be a major factor leading to DOX-induced GSH depletion. At low concentrations, the sulfhydryl reagent, iodoacetate (IA), inhibited GAPDH, caused a decrease in ATP and increased permeability, without inhibiting G6PDH or decreasing GSH. These results, coupled with those of previous work on a related quinone, menadione, suggest that depletion of either GSH or ATP may lead independently to endothelial dysfunction during chemotherapy, contributing to the cardiotoxicity and other systemic side-effects of the drug.     

Blood glutathione redox status in gestational hypertension

Gestational hypertension during the third trimester reflects an exaggerated maternal inflammatory response to pregnancy. We hypothesized that oxidative stress present even in normal pregnancy becomes uncompensated in hypertensive patients. A glucose-6-phosphate dehydrogenase (G6PD) activity sufficient to meet the increased reductive equivalent need of the cells is indispensable for defense against oxidative stress. The erythrocyte glutathione redox system was studied, where G6PD is the only NADPH source. The glutathione (GSH) redox status was measured both in vivo and after an in vitro oxidative challenge in pregnant women with gestational hypertension (n = 19) vs. normotensive pregnant subjects (n = 18) and controls (n = 20). An erythrocyte GSH depletion with an increase in the oxidized form (GSSG) resulted in an elevated ratio GSSG/GSH (0.305 +/- 0.057; mean +/- SD) in hypertensive pregnant women vs. normotensive pregnant or control subjects (0.154 +/- 0.025; 0.168 +/- 0.073; p <.001). In hypertensive pregnant patients, a "GSH stability" decrease after an in vitro oxidative challenge suggested a reduced GSH recycling capacity resulting from an insufficient NADPH supply. The erythrocyte GSSG/GSH ratio may serve as an early and sensitive parameter of the oxidative imbalance and a relevant target for future clinical trials to control the effects of antioxidant treatment in women at increased risk of the pre-eclampsia syndrome.     

Glucose-6-phosphate dehydrogenase-deficient cells show an increased propensity for oxidant-induced senescence

Glucose-6-phosphate dehydrogenase (G6PD) is involved in the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) and the maintenance of cellular redox balance. We previously showed that G6PD-deficient fibroblasts undergo growth retardation and premature cellular senescence. In the present study, we demonstrate abatement of both the intracellular G6PD activity and the ratio NADPH/NADP(+) during the serial passage of G6PD-deficient cells. This was accompanied by a significant increase in the level of 8-hydroxy-2-deoxyguanosine (8-OHdG). This suggests that the lowered resistance to oxidative stress and accumulative oxidative damage may account for the premature senescence of these cells. Consistent with this, the G6PD-deficient cells had an increased propensity for hydrogen peroxide (H(2)O(2))-induced senescence; these cells exhibited such senescent phenotypes as large, flattened morphology and increased senescence-associated beta-galactosidase (SA-beta-Gal) staining. Decreases in both the intracellular G6PD activity and the NADPH/NADP(+) ratio were concomitant with an increase in 8-OHdG level in H(2)O(2)-induced senescent cells. Exogenous expression of G6PD protected the deficient cells from stress-induced senescence. No significant telomere shortening occurred upon repetitive treatment with H(2)O(2). Simultaneous induction of p16(INK4a) and p53 was detected in G6PD-deficient but not in normal fibroblasts during H(2)O(2)-induced senescence. Our findings support the notion that G6PD status, and thus proper redox balance, is a determinant of cellular senescence.     

SIRT5 promotes IDH2 desuccinylation and G6PD deglutarylation to enhance cellular antioxidant defense

Excess in mitochondrial reactive oxygen species (ROS) is considered as a major cause of cellular oxidative stress. NADPH, the main intracellular reductant, has a key role in keeping glutathione in its reduced form GSH, which scavenges ROS and thus protects the cell from oxidative damage. Here, we report that SIRT5 desuccinylates and deglutarylates isocitrate dehydrogenase 2 (IDH2) and glucose‐6‐phosphate dehydrogenase (G6PD), respectively, and thus activates both NADPH‐producing enzymes. Moreover, we show that knockdown or knockout of SIRT5 leads to high levels of cellular ROS. SIRT5 inactivation leads to the inhibition of IDH2 and G6PD, thereby decreasing NADPH production, lowering GSH, impairing the ability to scavenge ROS, and increasing cellular susceptibility to oxidative stress. Our study uncovers a SIRT5‐dependent mechanism that regulates cellular NADPH homeostasis and redox potential by promoting IDH2 desuccinylation and G6PD deglutarylation.     

Regulation of G6PD acetylation by SIRT2 and KAT9 modulates NADPH homeostasis and cell survival during oxidative stress

Glucose‐6‐phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway (PPP) and plays an essential role in the oxidative stress response by producing NADPH, the main intracellular reductant. G6PD deficiency is the most common human enzyme defect, affecting more than 400 million people worldwide. Here, we show that G6PD is negatively regulated by acetylation on lysine 403 (K403), an evolutionarily conserved residue. The K403 acetylated G6PD is incapable of forming active dimers and displays a complete loss of activity. Knockdown of G6PD sensitizes cells to oxidative stress, and re‐expression of wild‐type G6PD, but not the K403 acetylation mimetic mutant, rescues cells from oxidative injury. Moreover, we show that cells sense extracellular oxidative stimuli to decrease G6PD acetylation in a SIRT2‐dependent manner. The SIRT2‐mediated deacetylation and activation of G6PD stimulates PPP to supply cytosolic NADPH to counteract oxidative damage and protect mouse erythrocytes. We also identified KAT9/ELP3 as a potential acetyltransferase of G6PD. Our study uncovers a previously unknown mechanism by which acetylation negatively regulates G6PD activity to maintain cellular NADPH homeostasis during oxidative stress.