Correcting glucose-6-phosphate dehydrogenase deficiency with a small-molecule activator

A hidden cysteine in Fis1 targeted to prevent excessive mitochondrial fission and dysfunction under oxidative stress

Fis1-mediated mitochondrial localization of Drp1 and excessive mitochondrial fission occur in human pathologies associated with oxidative stress. However, it is not known how Fis1 detects oxidative stress and what structural changes in Fis1 enable mitochondrial recruitment of Drp1. We find that conformational change involving α1 helix in Fis1 exposes its only cysteine, Cys41. In the presence of oxidative stress, the exposed Cys41 in activated Fis1 forms a disulfide bridge and the Fis1 covalent homodimers cause increased mitochondrial fission through increased Drp1 recruitment to mitochondria. Our discovery of a small molecule, SP11, that binds only to activated Fis1 by engaging Cys41, and data from genetically engineered cell lines lacking Cys41 strongly suggest a role of Fis1 homodimerization in Drp1 recruitment to mitochondria and excessive mitochondrial fission. The structure of activated Fis1-SP11 complex further confirms these insights related to Cys41 being the sensor for oxidative stress. Importantly, SP11 preserves mitochondrial integrity and function in cells during oxidative stress and thus may serve as a candidate molecule for the development of treatment for diseases with underlying Fis1-mediated mitochondrial fragmentation and dysfunction.

A live bacteria enzyme assay for identification of human disease mutations and drug screening

Advances in high-throughput sequencing have enabled the identification of genetic variations associated with human disease. However, deciphering the functional significance of these variations remains challenging. Here we propose an alternative approach that uses humanized Escherichia coli to study human genetic enzymopathies and to screen candidate drug effects on metabolic targets. By replacing selected E. coli metabolic enzymes with their human orthologues and their sequence variants, we demonstrate that the growth rate of E. coli reflects the in vivo activity of heterologously expressed human enzymes. This approach accurately reflected enzyme activities of known sequence variants, enabling rapid screening of causal sequence variations associated with human diseases. This approach bridges the gap between in vitro assays and cell-based assays. Our findings suggest that the proposed approach using a humanized E. coli strain holds promise for drug discovery, offering a high-throughput and cost-effective platform for identifying new compounds targeting human enzymes. Continued research and innovation in this field have the potential to impact the development and practice of precision medicine.

NRF2 activation in the heart induces glucose metabolic reprogramming and reduces cardiac dysfunction via upregulation of the pentose phosphate pathway

AIMS

The transcription factor nuclear factor erythroid-derived 2-like 2 (NRF2) is well recognized as a master regulator of antioxidant responses and cytoprotective genes. Previous studies showed that NRF2 enhances the resistance of mouse hearts to chronic haemodynamic overload, at least in part by reducing oxidative stress. Evidence from other tissues suggests that NRF2 may modulate glucose intermediary metabolism but whether NRF2 has such effects in the heart is unclear. Here, we investigate the role of NRF2 in regulating glucose intermediary metabolism and cardiac function during disease stress.

METHODS AND RESULTS

Cardiomyocyte-specific Keap1 knockout (csKeap1KO) mice, deficient in the endogenous inhibitor of NRF2, were used as a novel model of constitutively active NRF2 signalling. Targeted metabolomics and isotopomer analysis were employed in studies with 13C6-glucose in csKeap1KO and wild-type mice. Pharmacological and genetic approaches were utilized in neonatal rat ventricular myocytes (NRVMs) to explore molecular mechanisms. We found that cardiac-specific activation of NRF2 redirected glucose metabolism towards the pentose phosphate pathway (PPP), a branch pathway of glycolysis, and mitigated pressure overload-induced cardiomyocyte death and cardiac dysfunction. Activation of NRF2 also protected against myocardial infarction-induced DNA damage in remote myocardium and cardiac dysfunction. In vitro, knockdown of Keap1 upregulated PPP enzymes and reduced cell death in NRVM subjected to chronic neurohumoral stimulation. These pro-survival effects were abolished by pharmacological inhibition of the PPP or silencing of the PPP rate-limiting enzyme glucose-6-phosphate dehydrogenase. Knockdown of NRF2 in NRVM increased stress-induced DNA damage, which was rescued by supplementing the cells with either nicotinamide adenine dinucleotide phosphate (NADPH) or nucleosides, the two main products of the PPP.

CONCLUSION

These results indicate that NRF2 regulates cardiac metabolic reprogramming by stimulating the diversion of glucose into the PPP, thereby generating NADPH and providing nucleotides to prevent stress-induced DNA damage and cardiac dysfunction.

Metabolic changes during cardiac regeneration in the axolotl

BACKGROUND

The axolotl is a prominent model organism of heart regeneration due to its ability to anatomically and functionally repair the heart after an injury that mimics human myocardial infarction. In humans, such an injury leads to permanent scarring. Cardiac regeneration has been linked to metabolism and the oxygenation state, but so far, these factors remain to be detailed in the axolotl model. In this descriptive study, we have investigated metabolic changes that occurred during cardiac regeneration in the axolotl.

RESULTS

We describe systemic and local cardiac metabolic changes after injury involving an early upregulation of glucose uptake and nucleotide biosynthesis followed by a later increase in acetate uptake. We detect several promising factors and metabolites for future studies and show that, unlike other popular animal models capable of intrinsic regeneration, the axolotl maintains its cardiac regenerative ability under hyperoxic conditions.

CONCLUSIONS

Axolotls undergo dynamic metabolic changes during the process of heart regeneration and display a robust reparative response to cardiac cryo-injury, which is unaffected by hyperoxia.

Enhancing NADPH to restore redox homeostasis and lysosomal function in G6PD-deficient microglia

Microglia, the immune cells of the central nervous system (CNS), play key roles in neurogenesis, myelination, synaptic transmission, immune surveillance, and neuroinflammation. Inflammatory responses in microglia can lead to oxidative stress and neurodegeneration, contributing to diseases like Parkinson's and Alzheimer's. The enzyme glucose-6-phosphate dehydrogenase (G6PD) is essential for producing nicotinamide adenine dinucleotide phosphate hydrogen (NADPH), which neutralizes oxidative stress. G6PD deficiency has been linked to several disorders, including neurological conditions. Our study shows that G6PD deficiency in microglia reduces NADPH levels, disrupting redox balance and lysosomal function. To address this, we explored alternative metabolic pathways by targeting enzymes like isocitrate dehydrogenase 1 (IDH1) and malic enzyme 1 (ME1), both crucial for NADPH production. Supplementing metabolites such as citric and malic acid improved NADPH levels, while small molecules like dieckol and resveratrol enhanced IDH1 and ME1 expression. The combination of these approaches restored redox homeostasis and lysosomal function, offering potential therapeutic strategies for G6PD deficiency.

In vitro inhibition potency of malononitrile derivatives on the activity of two pentose phosphate pathway enzymes: accompanied by molecular docking evaluation

Many disorders, including cancer and malaria, could be targeted via the pentose phosphate pathway (PPP), whose products are key in biosynthetic reactions in cells. The goal of this study was to find new PPP inhibitors. The inhibition effects of malononitrile derivatives on Glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) were analyzed through in vitro experiments. Besides, molecular docking studies were performed to predict the interactions having role in inhibition of compounds. K i constants of derivatives were found between 4.24 ± 0.46-69.63 ± 7.75 µM for G6PD and 1.91 ± 0.12-95.07 ± 11.08 µM for 6PGD. Derivatives indicated non-competitive inhibition on both enzymes except for compound 4. The findings of the molecular docking studies revealed that free-binding energy estimations agreed with in vitro data. The structure of these malononitrile derivatives may guide for drug discovery in targeting the PPP.

G6PD deficiency triggers dopamine loss and the initiation of Parkinson's disease pathogenesis

Loss of dopaminergic neurons in Parkinson's disease (PD) is preceded by loss of synaptic dopamine (DA) and accumulation of proteinaceous aggregates. Linking these deficits is critical to restoring DA signaling in PD. Using murine and human pluripotent stem cell (hPSC) models of PD coupled with human postmortem tissue, we show that accumulation of α-syn micro-aggregates impairs metabolic flux through the pentose phosphate pathway (PPP). This leads to decreased nicotinamide adenine dinucleotide phosphate (NADP/H) and glutathione (GSH) levels, resulting in DA oxidation and decreased total DA levels. We find that α-syn anchors the PPP enzyme G6PD to synaptic vesicles via the α-syn C terminus and that this interaction is lost in PD. Furthermore, G6PD clinical mutations are associated with PD diagnosis, and G6PD deletion phenocopies PD pathology. Finally, we show that restoring NADPH or GSH levels through genetic and pharmacological intervention blocks DA oxidation and rescues steady-state DA levels, identifying G6PD as a pharmacological target against PD.

p53-dependent crosstalk between DNA replication integrity and redox metabolism mediated through a NRF2-PARP1 axis

Mechanisms underlying p53-mediated protection of the replicating genome remain elusive, despite the quintessential role of p53 in maintaining genomic stability. Here, we uncover an unexpected function of p53 in curbing replication stress by limiting PARP1 activity and preventing the unscheduled degradation of deprotected stalled forks. We searched for p53-dependent factors and elucidated RRM2B as a prime factor. Deficiency in p53/RRM2B results in the activation of an NRF2 antioxidant transcriptional program, with a concomitant elevation in basal PARylation in cells. Dissecting the consequences of p53/RRM2B loss revealed a crosstalk between redox metabolism and genome integrity that is negotiated through a hitherto undescribed NRF2-PARP1 axis, and pinpoint G6PD as a primary oxidative stress-induced NRF2 target and activator of basal PARylation. This study elucidates how loss of p53 could be destabilizing for the replicating genome and, importantly, describes an unanticipated crosstalk between redox metabolism, PARP1 and p53 tumor suppressor pathway that is broadly relevant in cancers and can be leveraged therapeutically.

Histone deacetylase 7 activates 6-phosphogluconate dehydrogenase via an enzyme-independent mechanism that involves the N-terminal protein-protein interaction domain

Histone deacetylase 7 (HDAC7) is a member of the class IIa family of classical HDACs with important roles in cell development, differentiation, and activation, including in macrophages and other innate immune cells. HDAC7 and other class IIa HDACs act as transcriptional repressors in the nucleus but, in some cell types, they can also act in the cytoplasm to modify non-nuclear proteins and/or scaffold signalling complexes. In macrophages, HDAC7 is a cytoplasmic protein with both pro- and anti-inflammatory functions, with the latter activity involving activation of the pentose phosphate pathway (PPP) enzyme 6-phosphogluconate dehydrogenase (6PGD) and the generation of anti-inflammatory metabolite ribulose-5-phosphate. Here, we used ectopic expression systems and biochemical approaches to investigate the mechanism by which HDAC7 promotes 6PGD enzyme activity. We reveal that HDAC7 enzyme activity is not required for its activation of 6PGD and that the N-terminal protein-protein interaction domain of HDAC7 is sufficient to initiate this response. Mechanistically, the N-terminus of HDAC7 increases the affinity of 6PGD for NADP+, promotes the generation of a shorter form of 6PGD, and enhances the formation of higher order protein complexes, implicating its scaffolding function in engagement of the PPP. This contrasts with the pro-inflammatory function of HDAC7 in macrophages, in which it promotes deacetylation of the glycolytic enzyme pyruvate kinase M2 for inflammatory cytokine production.

Glucose-6-phosphate dehydrogenase and its 3D structures from crystallography and electron cryo-microscopy

Glucose-6-phosphate dehydrogenase (G6PD) is the first enzyme in the pentose phosphate pathway. It has been extensively studied by biochemical and structural techniques. 13 X-ray crystal structures and five electron cryo-microscopy structures in the PDB are focused on in this topical review. Two F420-dependent glucose-6-phosphate dehydrogenase (FGD) structures are also reported. The significant differences between human and parasite G6PDs can be exploited to find selective drugs against infections such as malaria and leishmaniasis. Furthermore, G6PD is a prognostic marker in several cancer types and is also considered to be a tumour target. On the other hand, FGD is considered to be a target against Mycobacterium tuberculosis and possesses a high biotechnological potential in biocatalysis and bioremediation.

G6PD deficiency mediated impairment of iNOS and lysosomal acidification affecting phagocytotic clearance in microglia in response to SARS-CoV-2

The glucose-6-phosphate dehydrogenase (G6PD) deficiency is X-linked and is the most common enzymatic deficiency disorder globally. It is a crucial enzyme for the pentose phosphate pathway and produces NADPH, which plays a vital role in regulating the oxidative stress of many cell types. The deficiency of G6PD primarily causes hemolytic anemia under oxidative stress triggered by food, drugs, or infection. G6PD-deficient patients infected with SARS-CoV-2 showed an increase in hemolysis and thrombosis. Patients also exhibited prolonged COVID-19 symptoms, ventilation support, neurological impacts, and high mortality. However, the mechanism of COVID-19 severity in G6PD deficient patients and its neurological manifestation is still ambiguous. Here, using a CRISPR-edited G6PD deficient human microglia cell culture model, we observed a significant reduction in NADPH level and an increase in basal reactive oxygen species (ROS) in microglia. Interestingly, the deficiency of the G6PD-NAPDH axis impairs induced nitric oxide synthase (iNOS) mediated nitric oxide (NO) production, which plays a fundamental role in inhibiting viral replication. Surprisingly, we also observed that the deficiency of the G6PD-NADPH axis reduced lysosomal acidification and free radical production, further abrogating the lysosomal clearance of viral particles. Thus, impairment of NO production, lysosomal functions, and redox dysregulation in G6PD deficient microglia altered innate immune response, promoting the severity of SARS-CoV-2 pathogenesis.

Deficiency of metabolic regulator PKM2 activates the pentose phosphate pathway and generates TCF1+ progenitor CD8+ T cells to improve immunotherapy

TCF1high progenitor CD8+ T cells mediate the efficacy of immunotherapy; however, the mechanisms that govern their generation and maintenance are poorly understood. Here, we show that targeting glycolysis through deletion of pyruvate kinase muscle 2 (PKM2) results in elevated pentose phosphate pathway (PPP) activity, leading to enrichment of a TCF1high progenitor-exhausted-like phenotype and increased responsiveness to PD-1 blockade in vivo. PKM2KO CD8+ T cells showed reduced glycolytic flux, accumulation of glycolytic intermediates and PPP metabolites and increased PPP cycling as determined by 1,2-13C glucose carbon tracing. Small molecule agonism of the PPP without acute glycolytic impairment skewed CD8+ T cells toward a TCF1high population, generated a unique transcriptional landscape and adoptive transfer of agonist-treated CD8+ T cells enhanced tumor control in mice in combination with PD-1 blockade and promoted tumor killing in patient-derived tumor organoids. Our study demonstrates a new metabolic reprogramming that contributes to a progenitor-like T cell state promoting immunotherapy efficacy.

Glucose-6-phosphate dehydrogenase alleviates epileptic seizures by repressing reactive oxygen species production to promote signal transducer and activator of transcription 1-mediated N-methyl-d-aspartic acid receptors inhibition

The pathogenesis of epilepsy remains unclear; however, a prevailing hypothesis suggests that the primary underlying cause is an imbalance between neuronal excitability and inhibition. Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway, which is primarily involved in deoxynucleic acid synthesis and antioxidant defense mechanisms and exhibits increased expression during the chronic phase of epilepsy, predominantly colocalizing with neurons. G6PD overexpression significantly reduces the frequency and duration of spontaneous recurrent seizures. Furthermore, G6PD overexpression enhances signal transducer and activator of transcription 1 (STAT1) expression, thus influencing N-methyl-d-aspartic acid receptors expression, and subsequently affecting seizure activity. Importantly, the regulation of STAT1 by G6PD appears to be mediated primarily through reactive oxygen species signaling pathways. Collectively, our findings highlight the pivotal role of G6PD in modulating epileptogenesis, and suggest its potential as a therapeutic target for epilepsy.

Environmentally responsive hydrogel promotes vascular normalization to enhance STING anti-tumor immunity

The immunosuppressive microenvironment of malignant tumors severely hampers the effectiveness of anti-tumor therapy. Moreover, abnormal tumor vasculature interacts with immune cells, forming a vicious cycle that further interferes with anti-tumor immunity and promotes tumor progression. Our pre-basic found excellent anti-tumor effects of c-di-AMP and RRx-001, respectively, and we further explored whether they could be combined synergistically for anti-tumor immunotherapy. We chose to load these two drugs on PVA-TSPBA hydrogel scaffolds that expressly release drugs within the tumor microenvironment by in situ injection. Studies have shown that c-di-AMP activates the STING pathway, enhances immune cell infiltration, and reverses tumor immunosuppression. Meanwhile, RRx-001 releases nitric oxide, which increases oxidative stress injury in tumor cells and promotes apoptosis. Moreover, the combination of the two presented more powerful pro-vascular normalization and reversed tumor immunosuppression than the drug alone. This study demonstrates a new design option for anti-tumor combination therapy and the potential of tumor environmentally responsive hydrogel scaffolds in combination with anti-tumor immunotherapy.

MAZ-mediated up-regulation of BCKDK reprograms glucose metabolism and promotes growth by regulating glucose-6-phosphate dehydrogenase stability in triple-negative breast cancer

Tumour metabolic reprogramming is pivotal for tumour survival and proliferation. Investigating potential molecular mechanisms within the heterogeneous and clinically aggressive triple-negative breast cancer (TNBC) subtype is essential to identifying novel therapeutic targets. Accordingly, we investigated the role of branched-chain α-keto acid dehydrogenase kinase (BCKDK) in promoting tumorigenesis in TNBC. We analysed The Cancer Genome Atlas dataset and immunohistochemically stained surgical specimens to investigate BCKDK expression and its prognostic implications in TNBC. The effects of BCKDK on tumorigenesis were assessed using cell viability, colony formation, apoptosis, and cell cycle assays, and subsequently validated in vivo. Metabolomic screening was performed via isotope tracer studies. The downstream target was confirmed using mass spectrometry and a co-immunoprecipitation experiment coupled with immunofluorescence analysis. Upstream transcription factors were also examined using chromatin immunoprecipitation and luciferase assays. BCKDK was upregulated in TNBC tumour tissues and associated with poor prognosis. BCKDK depletion led to reduced cell proliferation both in vitro and vivo. MYC-associated zinc finger protein (MAZ) was confirmed as the major transcription factor directly regulating BCKDK expression in TNBC. Mechanistically, BCKDK interacted with glucose-6-phosphate dehydrogenase (G6PD), leading to increased flux in the pentose phosphate pathway for macromolecule synthesis and detoxification of reactive oxygen species. Forced expression of G6PD rescued the growth defect in BCKDK-deficient cells. Notably, the small-molecule inhibitor of BCKDK, 3,6-dichlorobenzo(b)thiophene-2-carboxylic acid, exhibited anti-tumour effects in a patient-derived tumour xenograft model. Our findings hold significant promise for developing targeted therapies aimed at disrupting the MAZ/BCKDK/G6PD signalling pathway, offering potential advancements in treating TNBC through metabolic reprogramming.

The effects of morin and methotrexate on pentose phosphate pathway enzymes and GR/GST/TrxR enzyme activities: An in vivo and in silico study

In this study, the mechanisms by which the enzymes glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), glutathione reductase (GR), glutathione-S-transferase (GST), and thioredoxin reductase (TrxR) are inhibited by methotrexate (MTX) were investigated, as well as whether the antioxidant morin can mitigate or prevent these adverse effects in vivo and in silico. For 10 days, rats received oral doses of morin (50 and 100 mg/kg body weight). On the fifth day, a single intraperitoneal injection of MTX (20 mg/kg body weight) was administered to generate toxicity. Decreased activities of G6PD, 6PGD, GR, GST, and TrxR were associated with MTX-related toxicity while morin treatment increased the activity of the enzymes. The docking analysis indicated that H-bonds, pi-pi stacking, and pi-cation interactions were the dominant interactions in these enzyme-binding pockets. Furthermore, the docked poses of morin and MTX against GST were subjected to molecular dynamic simulations for 200 ns, to assess the stability of both complexes and also to predict key amino acid residues in the binding pockets throughout the simulation. The results of this study suggest that morin may be a viable means of alleviating the enzyme activities of important regulatory enzymes against MTX-induced toxicity.

Evaluating the relationship between Clinical G6PD enzyme activity and gene variants

Glucose-6-phosphate dehydrogenase (G6PD) is a the first and rate-limiting enzyme that plays a critical role in G6PD deficiency, the most common enzyme disorder worldwide, is related to intravascular hemolysis. To determine the clinical enzyme activity level in different G6PD variants, we evaluated 15 variant from 424 clinical blood samples by using multicolor melting curve analysis and DNA sequencing. The results showed that the enzyme activities of the hemizygous deficient were 1.5-2.4 U/gHb, which was significantly lower than those of the heterozygous (P < 0.001) and the compound heterozygous variants (P < 0.05). Since the hemizygous of c.1024C > T (Chinese-5) mutation affects the kinetic parameters of G6PD and increase utilization of analogues, its enzyme activity is more than those of other mutations that mutated in the β+α region of G6PD. The heterozygous enzyme levels ranged from 6.5-20.1 U/gHb; and there was no significant difference among different heterozygous variants (P > 0.05). The enzyme activity levels of the compound heterozygous mutation were mainly in the range of 1.7-3.8 U/gHb, which was much lower than that of the heterozygous mutation (P < 0.001). In summary, our findings revealed that the enzyme activity of G6PD in blood have a significant relationship with genotype of G6PD.

The evolution of small molecule enzyme activators

There is a myriad of enzymes within the body responsible for maintaining homeostasis by providing the means to convert substrates to products as and when required. Physiological enzymes are tightly controlled by many signaling pathways and their products subsequently control other pathways. Traditionally, most drug discovery efforts focus on identifying enzyme inhibitors, due to upregulation being prevalent in many diseases and the existence of endogenous substrates that can be modified to afford inhibitor compounds. As enzyme downregulation and reduction of endogenous activators are observed in multiple diseases, the identification of small molecules with the ability to activate enzymes has recently entered the medicinal chemistry toolbox to afford chemical probes and potential therapeutics as an alternative means to intervene in diseases. In this review we highlight the progress made in the identification and advancement of non-kinase enzyme activators and their potential in treating various disease states.

Acetylation-dependent coupling between G6PD activity and apoptotic signaling

Lysine acetylation has been discovered in thousands of non-histone human proteins, including most metabolic enzymes. Deciphering the functions of acetylation is key to understanding how metabolic cues mediate metabolic enzyme regulation and cellular signaling. Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, is acetylated on multiple lysine residues. Using site-specifically acetylated G6PD, we show that acetylation can activate (AcK89) and inhibit (AcK403) G6PD. Acetylation-dependent inactivation is explained by structural studies showing distortion of the dimeric structure and active site of G6PD. We provide evidence for acetylation-dependent K95/97 ubiquitylation of G6PD and Y503 phosphorylation, as well as interaction with p53 and induction of early apoptotic events. Notably, we found that the acetylation of a single lysine residue coordinates diverse acetylation-dependent processes. Our data provide an example of the complex roles of acetylation as a posttranslational modification that orchestrates the regulation of enzymatic activity, posttranslational modifications, and apoptotic signaling.

Deficiency of metabolic regulator PKM2 activates the pentose phosphate pathway and generates TCF1+ progenitor CD8+ T cells to improve checkpoint blockade

TCF1high progenitor CD8+ T cells mediate the efficacy of PD-1 blockade, however the mechanisms that govern their generation and maintenance are poorly understood. Here, we show that targeting glycolysis through deletion of pyruvate kinase muscle 2 (PKM2) results in elevated pentose phosphate pathway (PPP) activity, leading to enrichment of a TCF1high central memory-like phenotype and increased responsiveness to PD-1 blockade in vivo. PKM2KO CD8+ T cells showed reduced glycolytic flux, accumulation of glycolytic intermediates and PPP metabolites, and increased PPP cycling as determined by 1,2 13C glucose carbon tracing. Small molecule agonism of the PPP without acute glycolytic impairment skewed CD8+ T cells towards a TCF1high population, generated a unique transcriptional landscape, enhanced tumor control in mice in combination with PD-1 blockade, and promoted tumor killing in patient-derived tumor organoids. Our study demonstrates a new metabolic reprogramming that contributes to a progenitor-like T cell state amenable to checkpoint blockade.

The pentose phosphate pathway in health and disease

The pentose phosphate pathway (PPP) is a glucose-oxidizing pathway that runs in parallel to upper glycolysis to produce ribose 5-phosphate and nicotinamide adenine dinucleotide phosphate (NADPH). Ribose 5-phosphate is used for nucleotide synthesis, while NADPH is involved in redox homoeostasis as well as in promoting biosynthetic processes, such as the synthesis of tetrahydrofolate, deoxyribonucleotides, proline, fatty acids and cholesterol. Through NADPH, the PPP plays a critical role in suppressing oxidative stress, including in certain cancers, in which PPP inhibition may be therapeutically useful. Conversely, PPP-derived NADPH also supports purposeful cellular generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) for signalling and pathogen killing. Genetic deficiencies in the PPP occur relatively commonly in the committed pathway enzyme glucose-6-phosphate dehydrogenase (G6PD). G6PD deficiency typically manifests as haemolytic anaemia due to red cell oxidative damage but, in severe cases, also results in infections due to lack of leucocyte oxidative burst, highlighting the dual redox roles of the pathway in free radical production and detoxification. This Review discusses the PPP in mammals, covering its roles in biochemistry, physiology and disease.

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

Enzymes catalyze biochemical reactions and play critical roles in human health and disease. Enzyme variants and deficiencies can lead to variable expression of glycans, which can affect physiology, influence predilection for disease, and/or directly contribute to disease pathogenesis. Although certain well-characterized enzyme deficiencies result in overt disease, some of the most common enzyme deficiencies in humans form the basis of blood groups. These carbohydrate blood groups impact fundamental areas of clinical medicine, including the risk of infection and severity of infectious disease, bleeding risk, transfusion medicine, and tissue/organ transplantation. In this review, we examine the enzymes responsible for carbohydrate-based blood group antigen biosynthesis and their expression within the human population. We also consider the evolutionary selective pressures, e.g. malaria, that may account for the variation in carbohydrate structures and the implications of this biology for human disease.

Oxidants and Antioxidants in the Redox Biochemistry of Human Red Blood Cells

Red blood cells (RBCs) are exposed to both external and internal sources of oxidants that challenge their integrity and compromise their physiological function and supply of oxygen to tissues. Autoxidation of oxyhemoglobin is the main source of endogenous RBC oxidant production, yielding superoxide radical and then hydrogen peroxide. In addition, potent oxidants from other blood cells and the surrounding endothelium can reach the RBCs. Abundant and efficient enzymatic systems and low molecular weight antioxidants prevent most of the damage to the RBCs and also position the RBCs as a sink of vascular oxidants that allow the body to maintain a healthy circulatory system. Among the antioxidant enzymes, the thiol-dependent peroxidase peroxiredoxin 2, highly abundant in RBCs, is essential to keep the redox balance. A great part of the RBC antioxidant activity is supported by an active glucose metabolism that provides reducing power in the form of NADPH via the pentose phosphate pathway. There are several RBC defects and situations that generate oxidative stress conditions where the defense mechanisms are overwhelmed, and these include glucose-6-phosphate dehydrogenase deficiencies (favism), hemoglobinopathies like sickle cell disease and thalassemia, as well as packed RBCs for transfusion that suffer from storage lesions. These oxidative stress-associated pathologies of the RBCs underline the relevance of redox balance in these anucleated cells that lack a mechanism of DNA-inducible antioxidant response and rely on a complex and robust network of antioxidant systems.

Glutamine promotes O-GlcNAcylation of G6PD and inhibits AGR2 S-glutathionylation to maintain the intestinal mucus barrier in burned septic mice

Mucus forms the first line of defence of the intestinal mucosa barrier, and mucin is its core component. Glutamine is a vital energy substance for goblet cells; it can promote mucus synthesis and alleviate damage to the intestinal mucus barrier after burn injury, but its mechanism is not fully understood. This study focused on the molecular mechanisms underlying the effects of glutamine on the synthesis and modification of mucin 2 (MUC2) by using animal and cellular models of burn sepsis. We found that anterior gradient-2 (AGR2) plays a key role in the posttranslational modification of MUC2. Oxidative stress induced by burn sepsis enhanced the S-glutathionylation of AGR2, interfered with the processing and modification of MUC2 precursors by AGR2 and blocked the synthesis of mature MUC2. Further studies revealed that NADPH, catalysed by glucose-6-phosphate dehydrogenase (G6PD), is a key molecule in inhibiting oxidative stress and regulating AGR2 activity. Glutamine promotes O-linked N-acetylglucosamine (O-GlcNAc) modification of G6PD via the hexosamine pathway, which facilitates G6PD homodimer formation and increases NADPH synthesis, thereby inhibiting AGR2 S-glutathionylation and promoting MUC2 maturation, ultimately reducing damage to the intestinal mucus barrier after burn sepsis. Overall, we have demonstrated that the central mechanisms of glutamine in promoting MUC2 maturation and maintaining the intestinal mucus barrier are the enhancement of G6PD glycosylation and inhibition of AGR2 S-glutathionylation.

The Pursuit of Enzyme Activation: A Snapshot of the Gold Rush

A range of enzymes drive human physiology, and their activities are tightly regulated through numerous signaling pathways. Depending on the context, these pathways may activate or inhibit an enzyme as a way to ensure proper execution of cellular functions. From a drug discovery and development perspective, pharmacological inhibition of enzymes has been a focus of interest, as many diseases are associated with the upregulation of enzyme function. On the other hand, however, pharmacological activation of enzymes such as kinases and phosphatases has been of increasing interest. In this review, we discuss seven case studies that highlight pharmacological activation strategy, describe the binding modes and pharmacology of the activators, and comment on how this on-demand activation strategy complements the commonly pursued inhibition strategy, thus jointly enabling bidirectional modulation of specific target of interest. Going forward, we expect activators to play important roles as chemical probes and drug leads.

Glucose 6-P Dehydrogenase—An Antioxidant Enzyme with Regulatory Functions in Skeletal Muscle during Exercise

Hypomorphic Glucose 6-P dehydrogenase (G6PD) alleles, which cause G6PD deficiency, affect around one in twenty people worldwide. The high incidence of G6PD deficiency may reflect an evolutionary adaptation to the widespread prevalence of malaria, as G6PD-deficient red blood cells (RBCs) are hostile to the malaria parasites that infect humans. Although medical interest in this enzyme deficiency has been mainly focused on RBCs, more recent evidence suggests that there are broader implications for G6PD deficiency in health, including in skeletal muscle diseases. G6PD catalyzes the rate-limiting step in the pentose phosphate pathway (PPP), which provides the precursors of nucleotide synthesis for DNA replication as well as reduced nicotinamide adenine dinucleotide phosphate (NADPH). NADPH is involved in the detoxification of cellular reactive oxygen species (ROS) and de novo lipid synthesis. An association between increased PPP activity and the stimulation of cell growth has been reported in different tissues including the skeletal muscle, liver, and kidney. PPP activity is increased in skeletal muscle during embryogenesis, denervation, ischemia, mechanical overload, the injection of myonecrotic agents, and physical exercise. In fact, the highest relative increase in the activity of skeletal muscle enzymes after one bout of exhaustive exercise is that of G6PD, suggesting that the activation of the PPP occurs in skeletal muscle to provide substrates for muscle repair. The age-associated loss in muscle mass and strength leads to a decrease in G6PD activity and protein content in skeletal muscle. G6PD overexpression in Drosophila Melanogaster and mice protects against metabolic stress, oxidative damage, and age-associated functional decline, and results in an extended median lifespan. This review discusses whether the well-known positive effects of exercise training in skeletal muscle are mediated through an increase in G6PD.

G6PD deficiency: imbalance of functional dichotomy contributing to the severity of COVID-19

Human COVID-19 has affected more than 491 million people worldwide. It has caused over 6.1 million deaths and has especially perpetrated a high number of casualties among the elderly and those with comorbid illnesses. COVID-19 triggers a pro-oxidant response, leading to the production of reactive oxygen species (ROS) as a common innate defense mechanism. However, ROS are regulated by a key enzyme called G6PD via the production of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which controls the generation and removal of ROS in a tissue-specific manner. Therefore, a deficiency of G6PD can lead to the dysregulation of ROS, which causes a severe inflammatory response in COVID-19 patients. This report highlights the G6PD dichotomy in the regulation of ROS and inflammatory responses, as well as its deficiency in severity among COVID-19 patients.

Metabolic Reprogramming in Sickle Cell Diseases: Pathophysiology and Drug Discovery Opportunities

Sickle cell disease (SCD) is a genetic disorder that affects millions of individuals worldwide. Chronic anemia, hemolysis, and vasculopathy are associated with SCD, and their role has been well characterized. These symptoms stem from hemoglobin (Hb) polymerization, which is the primary event in the molecular pathogenesis of SCD and contributes to erythrocyte or red blood cell (RBC) sickling, stiffness, and vaso-occlusion. The disease is caused by a mutation at the sixth position of the β-globin gene, coding for sickle Hb (HbS) instead of normal adult Hb (HbA), which under hypoxic conditions polymerizes into rigid fibers to distort the shapes of the RBCs. Only a few therapies are available, with the universal effectiveness of recently approved therapies still being monitored. In this review, we first focus on how sickle RBCs have altered metabolism and then highlight how this understanding reveals potential targets involved in the pathogenesis of the disease, which can be leveraged to create novel therapeutics for SCD.

Molecular dynamics of G6PD variants from sub-Saharan Africa

Precision medicine uses genomic guidance to improve drug treatment safety and efficacy. Prior knowledge of genetic variant impact can enable such strategies, but current knowledge of African variants remains scarce. G6PD variants are linked to haemolytic adverse effects for a number of drugs commonly used in African populations. We have investigated a set of G6PD variants with structural bioinformatics techniques to further characterise variants with known effect, and gain insights into variants with unknown impact. We observed wide variations in patterns of root-mean-square deviation between wild-type and variant structures. Variants with known, highly deleterious impact show structural effects which may likely result in the destabilisation of the G6PD homodimer. The V68M and N126D variants (which are both common across African populations, and together form the A- haplotype) induce large conformational shifts in the catalytic NADP+ binding domain. We observed a greater impact for the haplotype than for each of the individual variants in these cases. A novel African variant (M207T) shows the potential to disrupt interactions within the protein core, urging further investigation. We explore how characterising the molecular impact of African G6PD variants can enable advanced strategies for precision medicine, as well as impact the use of novel therapeutics aiming to treat G6PD deficiency. This knowledge can assist in bridging current knowledge gaps, and aid to facilitate precision medicine applications in African populations.

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Assessment of African G6PD variation with structural bioinformatics.

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Molecular dynamics of 500 ns to explore molecular motions.

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Comparison of variants with known/unknown impact.

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Exploring mechanisms of impact.

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Knowledge building to enable G6PD precision medicine in Africa.

H3K9me3 represses G6PD expression to suppress the pentose phosphate pathway and ROS production to promote human mesothelioma growth

The role of glucose-6-phosphate dehydrogenase (G6PD) in human cancer is incompletely understood. In a metabolite screening, we observed that inhibition of H3K9 methylation suppressed aerobic glycolysis and enhances the PPP in human mesothelioma cells. Genome-wide screening identified G6PD as an H3K9me3 target gene whose expression is correlated with increased tumor cell apoptosis. Inhibition of aerobic glycolysis enzyme LDHA and G6PD had no significant effects on tumor cell survival. Ablation of G6PD had no significant effect on human mesothelioma and colon carcinoma xenograft growth in athymic mice. However, activation of G6PD with the G6PD-selective activator AG1 induced tumor cell death. AG1 increased tumor cell ROS production and the resultant extrinsic and intrinsic death pathways, mitochondrial processes, and unfolded protein response in tumor cells. Consistent with increased tumor cell death in vitro, AG1 suppressed human mesothelioma xenograft growth in a dose-dependent manner in vivo. Furthermore, AG1 treatment significantly increased tumor-bearing mouse survival in an intra-peritoneum xenograft athymic mouse model. Therefore, in human mesothelioma and colon carcinoma, G6PD is not essential for tumor growth. G6PD acts as a metabolic checkpoint to control metabolic flux towards the PPP to promote tumor cell apoptosis, and its expression is repressed by its promotor H3K9me3 deposition.

Stabilization of glucose-6-phosphate dehydrogenase oligomers enhances catalytic activity and stability of clinical variants

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic trait that can cause hemolytic anemia. To date, over 150 nonsynonymous mutations have been identified in G6PD, with pathogenic mutations clustering near the dimer and/or tetramer interface and the allosteric NADP+-binding site. Recently, our lab identified a small molecule that activates G6PD variants by stabilizing the allosteric NADP+ and dimer complex, suggesting therapeutics that target these regions may improve structural defects. Here, we elucidated the connection between allosteric NADP+ binding, oligomerization, and pathogenicity to determine whether oligomer stabilization can be used as a therapeutic strategy for G6PD deficiency (G6PDdef). We first solved the crystal structure for G6PDK403Q, a mutant that mimics the physiological acetylation of wild-type G6PD in erythrocytes and demonstrated that loss of allosteric NADP+ binding induces conformational changes in the dimer. These structural changes prevent tetramerization, are unique to Class I variants (the most severe form of G6PDdef), and cause the deactivation and destabilization of G6PD. We also introduced nonnative cysteines at the oligomer interfaces and found that the tetramer complex is more catalytically active and stable than the dimer. Furthermore, stabilizing the dimer and tetramer improved protein stability in clinical variants, regardless of clinical classification, with tetramerization also improving the activity of G6PDK403Q and Class I variants. These findings were validated using enzyme activity and thermostability assays, analytical size-exclusion chromatography (SEC), and SEC coupled with small-angle X-ray scattering (SEC-SAXS). Taken together, our findings suggest a potential therapeutic strategy for G6PDdef and provide a foundation for future drug discovery efforts.

Association of TNF-Alpha, MBL2, NOS2, and G6PD with Malaria Outcomes in People in Southern Ghana

Background

One major issue that has set back the gains of the numerous malaria control interventions that national malaria control programs have implemented is asymptomatic malaria. Certain host genetic factors are known to influence symptomatic malaria; however, not much is known about how host genetics influences the acquisition of asymptomatic malaria.

Methods

Genomic DNA was extracted from whole blood collected from 60 symptomatic and 149 nonfebrile (asymptomatic, N = 109, and uninfected, N = 40) volunteers aged between 2 and 69 years from a high (Obom) and a low (Asutsuare) malaria transmission setting in Southern Ghana. Restriction fragment length polymorphism (RFLP) was used to determine polymorphisms at the MBL2 54, TNF-α 308, NOS2 954, and G6PD 202/376 gene loci.

Results

Polymorphisms at the MBL2 54 and TNF-α 308 loci were significantly different amongst the three categories of volunteers in both Asutsuare (p = 0.006) and Obom (p=0.05). In Asutsuare, a low malaria transmission area, the allele G has significantly higher odds (3.15) of supporting asymptomatic malaria as against symptomatic malaria. There were significantly higher odds of TNF-α genotype GA being associated with symptomatic malaria as against asymptomatic malaria in both sites, Obom (p=0.027) and Asutsuare (p=0.027). The allele B of the G6PD gene was more prevalent in symptomatic rather than asymptomatic parasite-infected individuals in both Obom (p=0.001) and Asutsuare (p=0.003).

Conclusion

Individuals in Southern Ghana carrying the TNF-α 308 GA genotype are more likely to exhibit symptoms of malaria when infected with the malaria parasite as opposed to harboring an asymptomatic infection. Also, the B allele of the G6PD gene is likely to prevent a P. falciparum-infected person from exhibiting symptoms and thereby promote asymptomatic parasite carriage.

G6PD functions as a metabolic checkpoint to regulate granzyme B expression in tumor-specific cytotoxic T lymphocytes

Background

Granzyme B is a key effector of cytotoxic T lymphocytes (CTLs), and its expression level positively correlates with the response of patients with mesothelioma to immune checkpoint inhibitor immunotherapy. Whether metabolic pathways regulate Gzmb expression in CTLs is incompletely understood.

Methods

A tumor-specific CTL and tumor coculture model and a tumor-bearing mouse model were used to determine the role of glucose-6-phosphate dehydrogenase (G6PD) in CTL function and tumor immune evasion. A link between granzyme B expression and patient survival was analyzed in human patients with epithelioid mesothelioma.

Results

Mesothelioma cells alone are sufficient to activate tumor-specific CTLs and to enhance aerobic glycolysis to induce a PD-1^hi Gzmb^lo CTL phenotype. However, inhibition of lactate dehydrogenase A, the key enzyme of the aerobic glycolysis pathway, has no significant effect on tumor-induced CTL activation. Tumor cells induce H3K9me3 deposition at the promoter of G6pd, the gene that encodes the rate-limiting enzyme G6PD in the pentose phosphate pathway, to downregulate G6pd expression in tumor-specific CTLs. G6PD activation increases acetyl-coenzyme A (CoA) production to increase H3K9ac deposition at the Gzmb promoter and to increase Gzmb expression in tumor-specific CTLs converting them from a Gzmb^lo to a Gzmb^hi phenotype, thus increasing CTL tumor lytic activity. Activation of G6PD increases Gzmb⁺ tumor-specific CTLs and suppresses tumor growth in tumor-bearing mice. Consistent with these findings, GZMB expression level was found to correlate with increased survival in patients with epithelioid mesothelioma.

Conclusion

G6PD is a metabolic checkpoint in tumor-activated CTLs. The H3K9me3/G6PD/acetyl-CoA/H3K9ac/Gzmb pathway is particularly important in CTL activation and immune evasion in epithelioid mesothelioma.

Pentose Phosphate Pathway Regulates Tolerogenic Apoptotic Cell Clearance and Immune Tolerance

The efficient removal of apoptotic cells (ACs), a process termed as efferocytosis, is essential for immune homeostasis. While recent work has established an important interplay between efferocytosis and cellular metabolic changing, underlying mechanisms remain poorly known. Here, we discovered that pentose phosphate pathway (PPP) regulates tolerogenic ACs clearance and immune tolerance. ACs decreased levels of PPP-related genes and metabolites in macrophages. AG1, the agonist of PPP, increased the activity of PPP but greatly reduced macrophage phagocytosis of ACs and enhanced the inflammatory response during efferocytosis. miR-323-5p regulated the expression of PPP-related genes and its levels increased during efferocytosis. miR-323-5p inhibitor greatly promoted levels of PPP-related genes, reduced the macrophage phagocytosis of ACs, and increased inflammatory response during efferocytosis, suggesting that miR-323-5p was essential in regulating PPP activity and ACs clearance in macrophages. Correspondingly, the PPP agonist AG1 exacerbated the lupus-like symptoms in the AC-induced systemic lupus erythematosus (SLE) model. Our study reveals that regulating PPP-dependent metabolic reprogramming is critical for tolerogenic ACs phagocytosis and immune tolerance.

Combined effects of double mutations on catalytic activity and structural stability contribute to clinical manifestations of glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy in humans, affecting ~ 500 million worldwide. A detailed study of the structural stability and catalytic activity of G6PD variants is required to understand how different mutations cause varying degrees of enzyme deficiency, reflecting the response of G6PD variants to oxidative stress. Furthermore, for G6PD double variants, investigating how two mutations jointly cause severe enzyme deficiency is important. Here, we characterized the functional and structural properties of nine G6PD variants: G6PD Gaohe, G6PD Mahidol, G6PD Shoklo, G6PD Canton, G6PD Kaiping, G6PD Gaohe + Kaiping, G6PD Mahidol + Canton, G6PD Mahidol + Kaiping and G6PD Canton + Kaiping. All variants were less catalytically active and structurally stable than the wild type enzyme, with G6PD double mutations having a greater impact than single mutations. G6PD Shoklo and G6PD Canton + Kaiping were the least catalytically active single and double variants, respectively. The combined effects of two mutations were observed, with the Canton mutation reducing structural stability and the Kaiping mutation increasing it in the double mutations. Severe enzyme deficiency in the double mutants was mainly determined by the trade-off between protein stability and catalytic activity. Additionally, it was demonstrated that AG1, a G6PD activator, only marginally increased G6PD enzymatic activity and stability.

The effects of glucose-6-phosphate dehydrogenase deficiency on benzene-induced hematotoxicity in mice

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme deficiency. Our previous study revealed the level of G6PD changed in wild type (WT) mice after benzene exposure. In this study, the pentose phosphate pathway (PPP) in regulation of benzene-induced hematotoxicity was investigated and other potential pathways were discovered in a G6PD deficiency mouse model. WT and G6PD mutation (G6PD^mut) mice were exposed to benzene (diluted in corn oil) at doses of 0 and 160 mg/kg by subcutaneous injection for 5 days/week, 4 weeks. Peripheral blood samples and bone marrow cells (BMCs) were obtained and measured. The levels of nicotinamide adenine dinucleotide phosphate (NADPH),reduced glutathione (GSH) and malondialdehyde (MDA) were detected and comet assay was analyzed for DNA damage in BMCs. Finally, RNA sequencing (RNA-seq) of BMCs was performed. The results showed that white blood cells decreased significantly in G6PD^mut mice compared with WT mice after benzene treatment. The ratio of hematopoietic stem/progenitor cells significantly decreased in G6PD^mut mice exposed to benzene. The reduction of NADPH and GSH revealed the effect on PPP with G6PD deficiency, which then caused the increase of MDA and DNA damage. Finally, RNA-seq results suggested potential genes including SHROOM4, CAMK2B and REN1 played potential roles of G6PD deficiency on benzene-induced hematotoxicity. Renin-angiotensin system and cAMP signaling pathway were potentially involved in the process. Our study provides a better understanding for the effects of G6PD deficiency on benzene-induced hematotoxicity.

Perspective on the Structural Basis for Human Aldo-Keto Reductase 1B10 Inhibition

Human aldo-keto reductase 1B10 (AKR1B10) is overexpressed in many cancer types and is involved in chemoresistance. This makes AKR1B10 to be an interesting drug target and thus many enzyme inhibitors have been investigated. High-resolution crystallographic structures of AKR1B10 with various reversible inhibitors were deeply analyzed and compared to those of analogous complexes with aldose reductase (AR). In both enzymes, the active site included an anion-binding pocket and, in some cases, inhibitor binding caused the opening of a transient specificity pocket. Different structural conformers were revealed upon inhibitor binding, emphasizing the importance of the highly variable loops, which participate in the transient opening of additional binding subpockets. Two key differences between AKR1B10 and AR were observed regarding the role of external loops in inhibitor binding. The first corresponded to the alternative conformation of Trp112 (Trp111 in AR). The second difference dealt with loop A mobility, which defined a larger and more loosely packed subpocket in AKR1B10. From this analysis, the general features that a selective AKR1B10 inhibitor should comply with are the following: an anchoring moiety to the anion-binding pocket, keeping Trp112 in its native conformation (AKR1B10-like), and not opening the specificity pocket in AR.

Glucose 6-P dehydrogenase delays the onset of frailty by protecting against muscle damage

BACKGROUND

Frailty is a major age-associated syndrome leading to disability. Oxidative damage plays a significant role in the promotion of frailty. The cellular antioxidant system relies on reduced nicotinamide adenine dinucleotide phosphate (NADPH) that is highly dependent on glucose 6-P dehydrogenase (G6PD). The G6PD-overexpressing mouse (G6PD-Tg) is protected against metabolic stresses. Our aim was to examine whether this protection delays frailty.

METHODS

Old wild-type (WT) and G6PD-Tg mice were evaluated longitudinally in terms of frailty. Indirect calorimetry, transcriptomic profile, and different skeletal muscle quality markers and muscle regenerative capacity were also investigated.

RESULTS

The percentage of frail mice was significantly lower in the G6PD-Tg than in the WT genotype, especially in 26-month-old mice where 50% of the WT were frail vs. only 13% of the Tg ones (P < 0.001). Skeletal muscle transcriptomic analysis showed an up-regulation of respiratory chain and oxidative phosphorylation (P = 0.009) as well as glutathione metabolism (P = 0.035) pathways in the G6PD-Tg mice. Accordingly, the Tg animals exhibited an increase in reduced glutathione (34.5%, P < 0.01) and a decrease on its oxidized form (-69%, P < 0.05) and in lipid peroxidation (4-HNE: -20.5%, P < 0.05). The G6PD-Tg mice also showed reduced apoptosis (BAX/Bcl2: -25.5%, P < 0.05; and Bcl-xL: -20.5%, P < 0.05), lower levels of the intramuscular adipocyte marker FABP4 (-54.7%, P < 0.05), and increased markers of mitochondrial content (COX IV: 89.7%, P < 0.05; Grp75: 37.8%, P < 0.05) and mitochondrial OXPHOS complexes (CII: 81.25%, P < 0.01; CIII: 52.5%, P < 0.01; and CV: 37.2%, P < 0.05). Energy expenditure (-4.29%, P < 0.001) and the respiratory exchange ratio were lower (-13.4%, P < 0.0001) while the locomotor activity was higher (43.4%, P < 0.0001) in the 20-month-old Tg, indicating a major energetic advantage in these mice. Short-term exercise training in young C57BL76J mice induced a robust activation of G6PD in skeletal muscle (203.4%, P < 0.05), similar to that achieved in the G6PD-Tg mice (142.3%, P < 0.01).

CONCLUSIONS

Glucose 6-P dehydrogenase deficiency can be an underestimated risk factor for several human pathologies and even frailty. By overexpressing G6PD, we provide the first molecular model of robustness. Because G6PD is regulated by pharmacological and physiological interventions like exercise, our results provide molecular bases for interventions that by increasing G6PD will delay the onset of frailty.

G6PD distribution in sub-Saharan Africa and potential risks of using chloroquine/hydroxychloroquine based treatments for COVID-19

Chloroquine/hydroxychloroquine have been proposed as potential treatments for COVID-19. These drugs have warning labels for use in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Analysis of whole genome sequence data of 458 individuals from sub-Saharan Africa showed significant G6PD variation across the continent. We identified nine variants, of which four are potentially deleterious to G6PD function, and one (rs1050828) that is known to cause G6PD deficiency. We supplemented data for the rs1050828 variant with genotype array data from over 11,000 Africans. Although this variant is common in Africans overall, large allele frequency differences exist between sub-populations. African sub-populations in the same country can show significant differences in allele frequency (e.g. 16.0% in Tsonga vs 0.8% in Xhosa, both in South Africa, p = 2.4 × 10-3). The high prevalence of variants in the G6PD gene found in this analysis suggests that it may be a significant interaction factor in clinical trials of chloroquine and hydroxychloroquine for treatment of COVID-19 in Africans.

Newborn Screening for G6PD Deficiency in Xiamen, China: Prevalence, Variant Spectrum, and Genotype-Phenotype Correlations

Background: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common inherited enzymatic defect. The purpose of this study was to evaluate the profile of G6PD deficiency and investigate the factors associated with the accuracy of newborn screening (NBS) in Xiamen, China.

Methods: A total of 99,546 newborns were screened by modified fluorescent spot test at the Women and Children’s Hospital, Xiamen University. High-risk neonates were recalled for diagnosis by either a measurement of G6PD activity or genetic testing for the presence of pathogenic G6PD variants using a quantitative G6PD enzymatic assay or the MeltPro® G6PD assay, respectively.

Results: In the first-tier screening, 1,256 newborns were categorized as high risk. Of these, 1,051 were diagnosed with G6PD deficiency, indicating a prevalence of 1.39% in Xiamen, China. Among the 1,013 neonates who underwent genotyping, 851 carried hemizygous, heterozygous, homozygous, or compound heterozygous variants, for a positive predictive value (PPV) of 84.01%. In total, 12 variants and 32 genotypes were identified, and the six most common variants were c.1376G>T, c.1388G>A, c.95A>G, c.1024C>T, c.871G>A, and c.392G>T, which accounted for approximately 94% of the identified alleles. Different variants showed characteristic enzymatic activities, although high phenotypic heterogeneity was observed for each variant. The use of cold-chain transportation significantly improved the PPV of NBS.

Conclusions: We determined the profile of G6PD deficiency in Xiamen, including the prevalence, variant spectrum, and genotype-phenotype correlations and confirmed that maintaining a low temperature during sample transport is essential to ensure the high screening accuracy of NBS. Our data provides epidemiological, genotypic, phenotypic, and clinical practice references to standardize future interventions for G6PD deficiency.

A Novel Sesquiterpene Lactone Xanthatin-13-(pyrrolidine-2-carboxylic acid) Isolated from Burdock Leaf Up-Regulates Cells' Oxidative Stress Defense Pathway

The aim of our study was to identify novel molecules able to induce an adaptative response against oxidative stress during the first stages of metabolic syndrome. A cellular survival in vitro test against H₂O₂-based test was applied after pretreatment with various natural bitter Asteraceae extracts. This screening revealed potent protection from burdock leaf extract. Using chromatography and LC-MS—RMN, we then isolated and identified an original sesquiterpene lactone bioactive molecule: the Xanthatin-13-(pyrrolidine-2-carboxylic acid) (XPc). A real-time RT-qPCR experiment was carried out on three essential genes involved in oxidative stress protection: GPx, SOD, and G6PD. In presence of XPc, an over-expression of the G6PD gene was recorded, whereas no modification of the two others genes could be observed. A biochemical docking approach demonstrated that XPc had a high probability to directly interact with G6PD at different positions. One of the most probable docking sites corresponds precisely to the binding site of AG1, known to stabilize the G6PD dimeric form and enhance its activity. In conclusion, this novel sesquiterpene lactone XPc might be a promising prophylactic bioactive agent against oxidative stress and inflammation in chronic diseases such as metabolic syndrome or type 2 diabetes.

Glial Cell Line-Derived Neurotrophic Factor and Focal Ischemic Stroke

Focal ischemic stroke (FIS) is a leading cause of human debilitation and death. Following the onset of a FIS, the brain experiences a series of spatiotemporal changes which are exemplified in different pathological processes. One prominent feature of FIS is the development of reactive astrogliosis and glial scar formation in the peri-infarct region (PIR). During the subacute phase, astrocytes in PIR are activated, referred to as reactive astrocytes (RAs), exhibit changes in morphology (hypotrophy), show an increased proliferation capacity, and altered gene expression profile, a phenomenon known as reactive astrogliosis. Subsequently, the morphology of RAs remains stable, and proliferation starts to decline together with the formation of glial scars. Reactive astrogliosis and glial scar formation eventually cause substantial tissue remodeling and changes in permanent structure around the PIR. Glial cell line-derived neurotrophic factor (GDNF) was originally isolated from a rat glioma cell-line and regarded as a potent survival neurotrophic factor. Under normal conditions, GDNF is expressed in neurons but is upregulated in RAs after FIS. This review briefly describes properties of GDNF, its receptor-mediated signaling pathways, as well as recent studies regarding the role of RAs-derived GDNF in neuronal protection and brain recovery. These results provide evidence suggesting an important role of RA-derived GDNF in intrinsic brain repair and recovery after FIS, and thus targeting GDNF in RAs may be effective for stroke therapy.

Modeling human glucose-6-phosphate dehydrogenase mutations using C. elegans GSPD-1

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked, recessive condition that causes intermittent jaundice or hemolytic anemia because of low NADPH levels in red blood cells. We performed steady-state enzyme kinetics with the recombinant C. elegans ortholog of human G6PD, GSPD-1, and two mutants containing amino acid changes found in human patients. The K M values for glucose-6-phosphate were 100 ± 27 µM, 80 ± 22 µM, and 1000 ± 300 µM for the wild-type, D60N, and R252L GSPD-1 enzymes, respectively. The specific activities of the D60N and R252L mutants were 59% and 11%, respectively, of the wild-type value. Protein homology modeling suggested that the R252L mutation was more severe because the mutation caused a shift in the position of some active site residues. The D60N mutation may have affected the conformation of an outer loop of the enzyme. These data demonstrate that GSPD-1 is a promising model for human G6PD deficiencies, with the advantage that potential treatments could be studied in vivo in C. elegans.

Treatment strategies for glucose-6-phosphate dehydrogenase deficiency: past and future perspectives

Glucose-6-phosphate dehydrogenase (G6PD) maintains redox balance in a variety of cell types and is essential for erythrocyte resistance to oxidative stress. G6PD deficiency, caused by mutations in the G6PD gene, is present in ~400 million people worldwide, and can cause acute hemolytic anemia. Currently, there are no therapeutics for G6PD deficiency. We discuss the role of G6PD in hemolytic and nonhemolytic disorders, treatment strategies attempted over the years, and potential reasons for their failure. We also discuss potential pharmacological pathways, including glutathione (GSH) metabolism, compensatory NADPH production routes, transcriptional upregulation of the G6PD gene, highlighting potential drug targets. The needs and opportunities described here may motivate the development of a therapeutic for hematological and other chronic diseases associated with G6PD deficiency.

Metabolomic and transcriptional profiling reveals bioenergetic stress and activation of cell death and inflammatory pathways in vivo after neuronal deletion of NAMPT

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the NAD+ salvage pathway. Our previous study demonstrated that deletion of NAMPT gene in projection neurons using Thy1-NAMPT-/- conditional knockout (cKO) mice causes neuronal degeneration, muscle atrophy, neuromuscular junction abnormalities, paralysis and eventually death. Here we conducted a combined metabolomic and transcriptional profiling study in vivo in an attempt to further investigate the mechanism of neuronal degeneration at metabolite and mRNA levels after NAMPT deletion. Here using steady-state metabolomics, we demonstrate that deletion of NAMPT causes a significant decrease of NAD+ metabolome and bioenergetics, a buildup of metabolic intermediates upstream of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in glycolysis, and an increase of oxidative stress. RNA-seq shows that NAMPT deletion leads to the increase of mRNA levels of enzymes in NAD metabolism, in particular PARP family of NAD+ consumption enzymes, as well as glycolytic genes Glut1, Hk2 and PFBFK3 before GAPDH. GO, KEGG and GSEA analyses show the activations of apoptosis, inflammation and immune responsive pathways and the inhibition of neuronal/synaptic function in the cKO mice. The current study suggests that increased oxidative stress, apoptosis and neuroinflammation contribute to neurodegeneration and mouse death as a direct consequence of bioenergetic stress after NAMPT deletion.

Cell and Gene Therapy for Anemia: Hematopoietic Stem Cells and Gene Editing

Hereditary anemia has various manifestations, such as sickle cell disease (SCD), Fanconi anemia, glucose-6-phosphate dehydrogenase deficiency (G6PDD), and thalassemia. The available management strategies for these disorders are still unsatisfactory and do not eliminate the main causes. As genetic aberrations are the main causes of all forms of hereditary anemia, the optimal approach involves repairing the defective gene, possibly through the transplantation of normal hematopoietic stem cells (HSCs) from a normal matching donor or through gene therapy approaches (either in vivo or ex vivo) to correct the patient’s HSCs. To clearly illustrate the importance of cell and gene therapy in hereditary anemia, this paper provides a review of the genetic aberration, epidemiology, clinical features, current management, and cell and gene therapy endeavors related to SCD, thalassemia, Fanconi anemia, and G6PDD. Moreover, we expound the future research direction of HSC derivation from induced pluripotent stem cells (iPSCs), strategies to edit HSCs, gene therapy risk mitigation, and their clinical perspectives. In conclusion, gene-corrected hematopoietic stem cell transplantation has promising outcomes for SCD, Fanconi anemia, and thalassemia, and it may overcome the limitation of the source of allogenic bone marrow transplantation.

Long-range structural defects by pathogenic mutations in most severe glucose-6-phosphate dehydrogenase deficiency

Mechanism of the loss of activity of the most severe patient-derived mutants of glucose-6-phosphate dehydrogenase (G6PD) deficiency has remained elusive despite the availability of the G6PD structures for decades. Structural and biophysical investigations have revealed a common mechanism and dynamics of how these mutations hinder the substrate-binding site, reducing enzymatic activity. These are triggered by a long-distance propagation of structural defects at the dimer interface and the binding site of the noncatalytic cofactor. These structural distortions are found among all of the class I mutants investigated, providing critical clues for drug design to address G6PD deficiency by correcting the structural defects.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common blood disorder, presenting multiple symptoms, including hemolytic anemia. It affects 400 million people worldwide, with more than 160 single mutations reported in G6PD. The most severe mutations (about 70) are classified as class I, leading to more than 90% loss of activity of the wild-type G6PD. The crystal structure of G6PD reveals these mutations are located away from the active site, concentrating around the noncatalytic NADP⁺-binding site and the dimer interface. However, the molecular mechanisms of class I mutant dysfunction have remained elusive, hindering the development of efficient therapies. To resolve this, we performed integral structural characterization of five G6PD mutants, including four class I mutants, associated with the noncatalytic NADP⁺ and dimerization, using crystallography, small-angle X-ray scattering (SAXS), cryogenic electron microscopy (cryo-EM), and biophysical analyses. Comparisons with the structure and properties of the wild-type enzyme, together with molecular dynamics simulations, bring forward a universal mechanism for this severe G6PD deficiency due to the class I mutations. We highlight the role of the noncatalytic NADP⁺-binding site that is crucial for stabilization and ordering two β-strands in the dimer interface, which together communicate these distant structural aberrations to the active site through a network of additional interactions. This understanding elucidates potential paths for drug development targeting G6PD deficiency.