Increased Pyruvate Kinase Activity Research Articles

Age-Related Changes in the Glycolytic Enzymes of M2-Isoform of Pyruvate Kinase and Fructose-1,6-Bisphosphate Aldolase: Implications to Age-Related Macular Degeneration.

Prior studies have emphasized a bioenergetic crisis in the retinal pigment epithelium (RPE) as a critical factor in the development of age-related macular degeneration (AMD). The isoforms Fructose-1,6-bisphosphate aldolase C (ALDOC) and pyruvate kinase M2 (PKM2) have been proposed to play a role in AMD pathogenesis. While PKM2 and ALDOC are crucial for aerobic glycolysis in the neural retina, they are not as essential for the RPE. In this study, we examined the expression and activity of PKM2 and ALDOC in both young and aged RPE cells, as well as in the retina and RPE tissue of mice, including an experimentally induced AMD mouse model. Our findings reveal an upregulation in PKM2 and ALDOC expression, accompanied by increased pyruvate kinase activity, in the aged and AMD mouse RPE. Conversely, there is a decrease in ALDOC expression but an increase in PKM2 expression and pyruvate kinase activity in the aged and AMD retina. Overall, our study indicates that aged and AMD RPE cells tend to favor aerobic glycolysis, while this tendency is diminished in the aged and AMD retina. These results underscore the significance of targeting PKM2 and ALDOC in the RPE as a promising therapeutic approach to address the bioenergetic crisis and prevent vision loss in AMD.

Integrated Metabolomics, Transcriptome and Functional Analysis Reveal Key Genes Are Involved in Tree Age-Induced Amino Acid Accumulation in Torreya grandis Nuts

Torreya grandis is native Chinese tree species of economic significance, renowned for its long lifespan and the rich nutritional value of its nuts. In this study, we analyzed the morphological characteristics, metabolites, associated gene expressions, and regulatory mechanism in nuts from young (10 years old) and old (1000 years old) T. grandis trees. We observed that the length, width, and weight of nuts from older trees were considerably greater than those from younger trees. Metabolomic analysis revealed that the concentrations of 18 amino acids and derivatives (including histidine and serine) in nuts from older trees were markedly higher than those in nuts from younger trees. Transcriptome and metabolomic correlation analysis identified 16 genes, including TgPK (pyruvate kinase), TgGAPDH (glyceraldehyde 3-phosphate dehydrogenase), and others, which exhibit higher expression levels in older trees compared to younger trees, as confirmed by qRT-PCR. These genes are associated with the biosynthesis of histidine, glutamic acid, tryptophan, and serine. Transient expression of TgPK in tobacco led to increased pyruvate kinase activity and amino acid content (histidine, tryptophan, and serine). Additionally, dual-luciferase assays and yeast one-hybrid results demonstrated that TgWRKY21 positively regulates TgPK expression by directly binding to the TgPK promoter. These findings not only demonstrate the nutritional differences between nuts from young and old trees but also offer fresh insights into the development of nutritional sources and functional components based on nuts from old trees, enriching our understanding of the potential benefits of utilizing nuts from older trees.

The Pyruvate Kinase (PK) Activator AG-946 Improves PK Properties and Red Blood Cell (RBC) Characteristics upon Ex Vivo treatment of RBCs from Patients with Myelodysplastic Syndromes

Background: Myelodysplastic syndromes (MDS) consist of a heterogenous group of clonal myeloid malignancies, characterized by dysplasia, ineffective hematopoiesis and cytopenias. MDS patients frequently suffer from anemia, directly affecting quality of life. The limited therapeutic options often do not result in the desired clinical improvement. Interestingly, in MDS the activity of the red blood cell (RBC) enzyme pyruvate kinase (PK), a key regulatory enzyme of glycolysis, may be decreased. The activation of PK via small molecules is hypothesized to be beneficial in a wide range of anemias. Currently, a phase 2a, open-label, proof of concept trial is running on the use of the PK activator AG-946 in low-risk MDS patients (NCT05490446). In light of these developments, we investigated the effect of ex vivo treatment of MDS RBCs with AG-946. Objectives: To evaluate RBC PK and cellular properties of patients with MDS, and to determine the effect of ex vivo treatment with the PK activator AG-946. Methods: Eleven low-risk non-transfusion dependent MDS patients and six healthy controls (HCs) were studied. Baseline PK activity and PK thermostability were measured in RBC lysates of purified RBCs, under V max conditions (phosphoenolpyruvate (PEP) 5mM final concentration). Hexokinase (HK) activity was included to relate PK activity to mean RBC age. Ex vivo treatment was performed by incubating MDS RBCs for 16 hours at 37 °C in presence or absence of the PK activator AG-946 (10μM or 5μM) using dimethylsulfoxide (DMSO) as a blank. Effect was assessed by measuring PK activity (using a final concentration of PEP 0.5mM) and levels of adenosine triphosphate (ATP) (LC-MS/MS). Functional RBC analysis was performed by osmotic gradient ektacytometry (Lorrca MaxSis). To investigate the effect on PK thermostability, RBC lysates were incubated with AG-946 (2μM or 1μM) or DMSO, after which residual PK activity was measured (PEP 0.5mM). The effect of AG-946 on erythroid development was studied using peripheral blood mononuclear cells, cultured in MethoCult TM H4434 medium for 14 days in the presence or absence of AG-946 (10μM or 625nM, DMSO as blank). Differences between conditions were determined using Unpaired T-test, ANOVA with Dunnett's test or Kruskal-Wallis with Dunn's test via GraphPad Prism. Results: Mean PK/HK ratio was significantly lower in RBCs from MDS patients compared to HCs (6.1 (SD 1.8) versus 10.5 (SD 1.5), p<0.001). Upon ex vivo treatment, PK activity significantly increased (independent of dosage) when compared to DMSO (10μM AG-946, mean increase 30% ( p<0.001); 5μM, 28% ( p<0.0001)) (Figure 1A). MDS RBCs displayed decreased PK thermostability at baseline under V max conditions (HCs 79% residual activity versus 68% in MDS, p<0.01). This was restored by ex vivo treatment with AG-946 (DMSO, 33% residual activity, 2μM AG-946, 85% ( p<0.0001); 1μM, 87% ( p<0.0001)). The increase in PK activity was accompanied by significantly increased ATP levels (N=10, DMSO, mean ATP 14.9 μg/mL RBC; 10μM AG-946, 21.0 μg/mL RBC ( p<0.01); 5μM, 21.1 μg/mL RBC ( p<0.01)) (Figure 1B). Functionally, RBC properties improved upon ex vivo treatment with AG-946 as reflected by the modest yet significant increase in O hyper, indicating improved hydration status (10μM AG-946, mean increase 2.3% ( p<0.001); 5μM, 2.9% ( p<0.0001)). To date, culture assays were performed in 8 patients; 3/8 showed an increase in the number of burst forming units-erythroid (BFU-Es) upon treatment with AG-946 when compared to DMSO. The percentual increases differed per patient: increase of 25% with 10μM AG946 and 150% with 625nM, increase of 40% (10μM) and 39% (625nM), and for the third an increase of 22% (10μM) and 39% (625nM). Conclusion: Our findings show that RBCs from MDS patients have decreased PK activity and thermostability. We demonstrate that ex vivo treatment with AG-946 increases PK activity and ATP levels and restores PK thermostability. Moreover, ex vivo treatment with AG-946 improves RBC hydration, suggesting that improved energy status directly improves RBC functional properties. The preliminary results of the culture assay could indicate that in certain patients, dyserythropoiesis may be ameliorated upon PK activation. To better understand the effects on erythropoiesis additional experiments are required. In conclusion, our data might support a rationale for the use of PK activators as a novel therapeutic option for MDS.

AG-946, an Activator of Pyruvate Kinase, Improves Ineffective Erythropoiesis in the Bone Marrow of Mouse Models of Myelodysplastic Syndromes

Background: Myelodysplastic syndromes (MDS) are a heterogeneous group of hematologic malignancies characterized by ineffective erythropoiesis. Anemia is the most common cytopenia and major clinical problem in MDS. Acquired pyruvate kinase (PK) deficiency has been observed in MDS, and a direct impact on the glycolytic pathway in the pathogenesis of anemia associated with MDS has been demonstrated. AG-946 is an investigational, small-molecule, allosteric activator of PK that has the potential to enhance red blood cell (RBC) functionality and survival by increasing glycolysis and adenosine triphosphate (ATP) production, and improve differentiation of erythroid cells in bone marrow, potentially improving anemia caused by ineffective erythropoiesis in MDS. Previous findings showed that RBCs from patients with MDS treated ex-vivo with AG-946, led to an increase in PK activity. Here, we used two MDS-related mouse models to evaluate the effects of the PK activator AG-946 in this mechanism of anemia. Aim: Evaluate the effect of AG-946 treatment on impaired erythropoiesis in the bone marrow of two mouse models of MDS. Methods:NUP98-HOXD13 (NHD13) is a fusion gene mutation observed in some patients with MDS. Mouse models with this mutation develop key characteristics of MDS such as impaired erythropoiesis and progressive anemia leading to malignant leukemia around 12 months of age. Male and female NHD13 and C57BL/6J mice were placed on 0.006% AG-946 (approximate dose 10 mg/kg/day) formulated diet starting at 10 months given ad libitum and continuing for 3 months. Numbers of animals for wild type (WT) Control, WT AG-946, NHD13 Control, NHD13 AG-946 were 10, 10, 13, and 11, respectively.Polg D257A (Polg) mouse model, while not a mutation observed in patients with MDS, does display many key features of MDS, such as impaired erythropoiesis and progressive anemia. Male and female Polg mice were placed on 0.006% AG-946 (approximate dose 10 mg/kg/day) formulated diet starting at 4 months given ad libitum and continuing for 8 months. Numbers of animals for WT Control, WT AG-946, Polg Control, Polg AG-946 were 10, 10, 19, and 18, respectively. Bone marrow from 1 femur per mouse was collected and analyzed by flow cytometry. Bone marrow cell pellets were washed and treated with ACK lysing buffer prior to staining. Samples with fewer than 1000 Ter119+ events were removed from analysis due to insufficient cell count. Bone marrow erythroblast populations were gated using Single Cells/Live/B220-/Ter119+/CD44 vs FSC, which were then gated into three populations: basophilic erythroblasts (BasoE), polychromatic erythroblasts (PolyE), and orthochromatic erythroblasts and reticulocytes (OrthoE + Retic). Results:No differences in any erythroblast populations were observed between untreated WT and NHD13 mice. No changes in the BasoE population were observed in WT or NHD13 mice. The PolyE population in NHD13 mice treated with AG-946 was significantly decreased compared with both the NHD13 and WT untreated mice (p=0.0021 and 0.0003, respectively). NHD13 mice treated with AG-946 showed significant increases in the OrthoE + Retic populations over the untreated NHD13 mice (p=0.0275).No differences in BasoE or OrthoE + Retic populations were observed between untreated WT and Polg mice while the PolyE population was significantly decreased in Polg mice compared with WT (p<0.0001). The BasoE population was significantly decreased in Polg mice treated with AG-946 compared with untreated Polg (p=0.0002). No difference in PolyE population was observed in Polg mice with AG-946. OrthoE + Retic population was significantly increased in Polg mice treated with AG-946 compared with WT and Polg untreated mice (p=0.0001 and 0.0304, respectively). Data graphed as average +/- SEM. Conclusions: Our data suggest AG-946 treatment improves erythroblast maturation in two MDS mouse models as demonstrated by a reduction in early-stage erythroblasts (BasoE, PolyE) coupled with an increase in late-stage erythroblast populations (OrthoE + Retic). These data are the first to suggest that PK activation by AG-946 could improve ineffective erythropoiesis in MDS.

Biochemical and Metabolomic Analysis of Glycolytic Activity in Red Blood Cells from Low-Risk Myelodysplastic Syndromes (LR-MDS) Patients and in-Vitro Effect of the Pyruvate Kinase Activator AG-946

Background: Anemia is the most common cytopenia occurring in 80%-85% of patients (pts) with LR-MDS and therapeutic strategies remain limited. Beyond defective maturation, preliminary data has shown decreased glycolytic activity in MDS-RBCs. Glycolytic pathway is the prominent metabolic cascade in RBCs and is currently targeted with PK activators in clinical trials of congenital anaemias which are also marked by ineffective erythropoiesis like MDS. AG946 is an investigational, potent activator of PK with potential to enhance RBC functionality and survival by increasing glycolysis. Aim: Evaluate enzymatic activity of the glycolytic pathway in pts with anemia due to LR-MDS and in-vitro effect of pyruvate kinase (PK) activator (AG946) in RBCs cultures of LR-MDS pts. Methods In part A, 66 anemic pts (i.e., Hb<11 g/dL) diagnosed with MDS according to WHO 2022 were enrolled in the study and sampled for peripheral blood >4 weeks after the last RBC unit to reduce blood donor contamination. The determination of activities of RBC enzymes hexokinase (HK) and PK (the initial and terminal steps of glycolytic pathway), and of ATP levels was performed by standard spectrophotometric method according to Beutler et al, 1984. 2,3DPG levels were tested by (2,3-BPG) ELISA kit (ElisaGenie, IE). In part B, purified RBC or whole blood of 10 LRMDS pts and 5 healthy controls (HC) were incubated for 6 and 24 h at 37°C in presence or absence of AG946 in phosphate-buffered saline containing 1% glucose, 170 mg/L adenine, and 5.25 g/L mannitol (AGAM, pH 7.40). RBC were incubated with 1, 5 and 50 uM of AG946 for up to 24 h, at 37°C. After 6 and 24 h, enzymatic activities (HK, PK) and ATP levels were measured. Additionally, metabolomic analysis was performed by LC-MS on extracts from blood samples for each condition. Results Part A: Pts were mainly elderly males (median age 80yr, range 58-92), and mostly belonged to IPSS-R low (78%) and very low/low groups (85%). PK activity (median 13.7 IU/gHb, 7.5-35.9) was reduced in 35% of cases and HK activity (median 2.3 IU/gHb, 0.8-8.1) was increased in 91%, resulting in an abnormally reduced PK/HK ratio in majority of pts (95%). Notably, ATP levels (median 3.4 umol/gHb, 1.3-6.5) were also reduced in 33/56 tested patients (59%), whilst 2,3DPG levels were close to the upper limit of the normal range (median 389 nmol/gHb, 318-639). Conclusions: Our data demonstrates decreased glycolytic activity in a large cohort of anemic pts with LR-MDS versus HC, with reduced PK activity in 1/3 of cases, decreased PK/HK ratio in nearly all subjects, and reduced ATP in 2/3 of pts. Furthermore, in vitro incubation with AG946 led to an increase in PK activity and PK/HK ratio and stable ATP levels in RBCs of LR-MDS pts across all WHO classifications. Metabolomic analysis confirmed an altered RBC-metabolic status of MDS versus HC at baseline with possible modulation of glycolysis by AG946, further supporting a potential therapeutic role of PK Activation with AG946 in LR-MDS.

Red Blood Cell Pyruvate Kinase Properties in Sickle Cell Disease - of Mice and Men

Background: Townes and Berkeley mouse models of sickle cell disease (SCD) are commonly used to study SCD pathophysiology and to develop novel therapies. Although the pathophysiology in these models is similar to the human disease, there are distinct differences. For example, Townes SS mice have higher ATP and lower 2,3-diphosphyglycerate (2,3-DPG) levels compared to Townes AA mice. This contrasts with SCD patients, who show lower ATP and higher 2,3-DPG levels, suggesting potential differences between human and murine red blood cell (RBC) metabolism. Pyruvate kinase (PK), a key ATP-generating enzyme in glycolysis, is a target for novel SCD therapies. While PK activators have been shown to increase hemoglobin in clinical trials, such treatments do not consistently lead to the same hematological change in mouse models, further indicating that PK properties may differ between SCD mouse models and human patients. A detailed comparative characterization of PK and glycolytic metabolites in murine SCD models and SCD patients is therefore important. Aim: To study PK properties in murine and human SCD RBCs. Methods: Wild-type (C57BL/6J), Townes (AA and SS) and Berkeley mice (non-sickling and sickling) were used. Human blood was obtained from healthy controls (HbAA) and untreated SCD patients (HbSS). Hematological parameters were measured using the Sysmex hematology analyzer. PK (Vmax, 5mM substrate) and hexokinase (HK) activity, and PK thermostability (53°C) were measured in purified RBCs. Levels of ATP, 2,3-DPG, as well as reduced glutathione (GSH) were measured by targeted LC-MS/MS and spectrophotometry, respectively. P50 (oxygen tension at which 50% of hemoglobin is saturated with oxygen) was measured with the Hemox analyzer (TCS). Statistical analysis was performed in Graphpad Prism 9.4.1. by Welch's t-test. Results: Samples from 17 wild-type mice, 21 Townes mice (10 AA, 11 SS), 15 Berkeley mice (7 non-sickling, 8 sickling) and 12 human subjects (6 HbAA, 6 HbSS) were included. Both Townes and Berkeley SCD mice showed increased PK activity (Table 1; p<0.0001). This may be attributed to their high reticulocyte counts (Townes SS vs. AA: 43% vs. 4%; Berkeley sickling vs. non-sickling: 30% vs. 6%), because when normalizing PK activity to that of HK, another RBC age-dependent enzyme, no genotype differences were found in these mouse models. This lack of PK/HK difference was in sharp contrast with our finding in human controls vs. SCD patients (Table 1). Notably, both Berkeley sickling and non-sickling mice had lower PK/HK ratio than their Townes counterparts (p<0.0001). Mouse PK thermostability was markedly reduced compared to that of human, and PK from the two sickling mice was less stable than their non-sickling controls (Fig. 1). Moreover, both sickling mice showed higher ATP/2,3-DPG ratio (Table 1; p<0.01). This was again in direct contrast with our observation using human blood, where SCD patients had lower ATP/2,3-DPG ratio than healthy controls (p<0.05). Even though there was no difference in ATP/2,3-DPG ratio between the two SCD models, Townes SS mice had significantly lower 2,3-DPG and higher ATP levels than Townes AA mice, whereas Berkeley sickling mice only had significantly higher ATP level compared to their controls. Furthermore, sickling mice had lower P50 value compared to non-sickling mice, reflecting a higher oxygen affinity. This also contrasted with human SCD patients, who had higher P50 value than healthy controls (Table 1). GSH levels were increased in both SCD patients and sickling mice, although the elevation was more pronounced in sickling mice (Table 1). Conclusions: This study reveals important distinctions between mouse models and humans: no differences in PK/HK ratio between sickling and non-sickling mice, and an overall lower PK thermostability in mice. Furthermore, this study shows significant changes in 2,3-DPG content (important for oxygen affinity), energy level (ATP), oxygen affinity (P50) and antioxidant level (GSH) when comparing sickling to non-sickling mice. Sickling mice also have higher ATP/2,3-DPG ratio, which contrasts with SCD patients. These differences should be considered when studying PK activators in SCD mouse models and extrapolating results from SCD mouse models to humans.

The pyruvate kinase activator mitapivat reduces hemolysis and improves anemia in a β-thalassemia mouse model

Anemia in β-thalassemia is related to ineffective erythropoiesis and reduced red cell survival. Excess free heme and accumulation of unpaired α-globin chains impose substantial oxidative stress on β-thalassemic erythroblasts and erythrocytes, impacting cell metabolism. We hypothesized that increased pyruvate kinase activity induced by mitapivat (AG-348) in the Hbbth3/+ mouse model for β-thalassemia would reduce chronic hemolysis and ineffective erythropoiesis through stimulation of red cell glycolytic metabolism. Oral mitapivat administration ameliorated ineffective erythropoiesis and anemia in Hbbth3/+ mice. Increased ATP, reduced reactive oxygen species production, and reduced markers of mitochondrial dysfunction associated with improved mitochondrial clearance suggested enhanced metabolism following mitapivat administration in β-thalassemia. The amelioration of responsiveness to erythropoietin resulted in reduced soluble erythroferrone, increased liver Hamp expression, and diminished liver iron overload. Mitapivat reduced duodenal Dmt1 expression potentially by activating the pyruvate kinase M2-HIF2α axis, representing a mechanism additional to Hamp in controlling iron absorption and preventing β-thalassemia-related liver iron overload. In ex vivo studies on erythroid precursors from patients with β-thalassemia, mitapivat enhanced erythropoiesis, promoted erythroid maturation, and decreased apoptosis. Overall, pyruvate kinase activation as a treatment modality for β-thalassemia in preclinical model systems had multiple beneficial effects in the erythropoietic compartment and beyond, providing a strong scientific basis for further clinical trials.

Impact of the Whole Genome Duplication Event on PYK Activity and Effects of a PYK1 Mutation on Metabolism in S. cerevisiae.

Background: Evolution of aerobic fermentation (crabtree effect) in yeast is associated with the whole genome duplication (WGD) event, suggesting that duplication of certain genes may have altered yeast metabolism. The pyruvate kinase (PYK) gene is associated with alterations in cell metabolism, and duplicated during the WGD, generating PYK1 and PYK2. Thus, the impact of WGD on PYK activity and role of PYK in yeast metabolism were explored.Methods: PYK activity in the presence or absence of fructose-1,6-bisphosphate (FBP) was compared between pre- and post-WGD yeast. Glucose consumption, ethanol production, and oxygen consumption were measured in wildtype yeast and yeast with a T403E point mutation, which alters FBP binding affinity.Results: FBP stimulated increased PYK activity in pre-WGD yeast and in the PYK1 isoforms of post-WGD yeast, but not in the PYK2 isoforms of post-WGD yeast. Compared to wildtype, T403E mutant yeast displayed reduced glucose consumption, reduced ethanol production, and increased mitochondrial metabolism.Conclusion: The WGD event impacted the sensitivity of PYK activity to FBP. Mutations in the FBP binding domain of PYK induce metabolic shifts that favor respiration and suppress fermentation.

ОСОБЕННОСТИ ВОЗДЕЙСТВИЯ ДЕЦИМЕТРОВЫХ ЭЛЕКТРОМАГНИТНЫХ ВОЛН НА АКТИВНОСТЬ ПИРУВАТКИНАЗЫ МОЗГА КРЫС В ОНТОГЕНЕЗЕ

The effect of decimetric microwaves (DMW) on the activity of pyruvate kinase (PK), one of the energy supply enzymes, was investigated in the brain structures of 3-, 6-, and 24-month-old white non-linear rats. Experimental rats were exposed on a daily basis for 20 min to 10 and 30 μW/cm² of DMW irradiation over a period of 10 days. It was established that PK activity in the cortical and subcortical brain structures, which differ in their oxygen supply, morphofunctional and phylogenetic characteristics, reacts differently to the effect of DMW: at 10 μW/cm² it increases while at 30 μW/cm² it decreases. In mitochondrial subcellular fractions of the brain structures, PK activity was lower at 10 μW/cm² than at 30 μW/cm². In cytosolic subcellular fractions, no significant differences were revealed in PK activity at different intensities of DMW irradiation, while these indicators, taken separately, were significantly different compared to the control (p < 0.01; p < 0.001). There are two alternative assumptions to account for the obtained results. The increased PK activity in the brain structures studied may reflect a metabolic adaptation aimed at protecting the structural integrity and functional components of nerve cells from detrimental effects of DMW irradiation. Conversely, a lack of energy due to a drop in PK activity, in turn, causes various negative secondary metabolic changes and free-radical oxidation in nerve cells. Our data indicate that both at 10 and 30 μW/cm² of DMW irradiation, endogenous signals in the rat brain are directed from cortical to subcortical structures, but PK activity does not recover to the control values. It is hypothesized that under the effect of DMW, the cerebellum, orbital and sensorimotor cortices serve as donors, while the limbic cortex and hypothalamus are acceptors in the system of signal transduction.

Metabolic and Non-metabolic Roles of Pyruvate Kinase M2 Isoform in Diabetic Retinopathy

The main therapeutic goal for diabetic retinopathy (DR) is to prevent vision loss in patients with diabetes mellitus. Identifying the visual complications at a preclinical juncture will offer an early therapeutic window for diagnosis and intervention. Very recently, we found that pyruvate kinase M2 isoform (PKM2) regulates visual function through regulation of a key enzyme, phosphodiesterase 6β (Pde6β), involved in modulating photoreceptor functions. A recent study showed that the activation of PKM2 protects mitochondrial integrity in diabetic nephropathy. In the present study, we examined the role of PKM2 in DR in a mouse model that has both phenotypes of obesity and type II diabetes. In DR, we found decreased expression of PKM2 and Pde6β expression, but not PKM1. Consistent with decreased Pde6β expression, the db/db mice had reduced rod photoreceptor function. We found increased pyruvate kinase activity and a decreased ratio of reduced/oxidized redox in db/db mouse retina compared with control retinas. There was no significant difference in the levels of lactate between db/db and control mouse retina. Our findings suggest that reduced expression of PKM2 with unchanged PKM1 expression might be responsible for higher pyruvate kinase activity in db/db mouse retina. Our studies suggest that PKM2 has a role in DR. The results support that PKM2 may serve as a therapeutic target in the treatment of DR.

Decreased Activity and Stability of Pyruvate Kinase in Hereditary Hemolytic Anemia: A Potential Target for Therapy By AG-348 (Mitapivat), an Allosteric Activator of Red Blood Cell Pyruvate Kinase

Background: Reactive oxygen species (ROS) play an important role in the complex and multifactorial pathophysiology of hereditary hemolytic anemia like sickle cell disease (SCD), β-thalassemia and hereditary xerocytosis (HX). Increased intracellular levels of oxidative stress disrupt normal cell functioning and may contribute to premature red blood cell (RBC) clearance from the circulation. Pyruvate kinase (PK) is a key regulatory enzyme of glycolysis, the cell's main source of energy. Because PK is very sensitive to redox balance we hypothesized that increased levels of oxidative stress in SCD, β-thalassemia and HX impairs proper enzyme function, thereby compromizing RBC energy metabolism. This may contribute to disease pathophysiology. Aims: To investigate if secondary deficiency of PK is common in SCD, thalassemia, and HX, and to investigate if PK in these disorders is able to respond to treatment with the allosteric PK activator AG-348 (mitapivat). Methods: Enzymatic activities of red cell PK and hexokinase (HK) were measured together with PK-thermostability in order to assess relative PK activity and enzyme stability. Purified RBCs were incubated with AG-348 (3.33μM) for 24 hours after which PK activity and ATP response was measured. RBCs of SCD patients were also analyzed with the oxygenscan, a newly developed method that characterizes individual sickling behavior by oxygen gradient ektacytometry (Rab et al, Am J Hematol, 2019). Individual tendency to sickle is reflected by Point-of-Sickling (PoS) that indicates the specific pO2 at which RBCs start to sickle during deoxygenation under shear stress. Results: Thirty-eight patients and 21 healthy controls (HC) were included. The patient cohort consisted of patients homozygous for HbS (HbSS, n=26), patients compound heterozygous for HbS and HbC (HbSC, n=4), β-thalassemia major (regularly transfused, n=3), and hereditary xerocytosis (n=5). Patients showed reticulocytosis and, in line with this, a concomitant increase in HK activity. In contrast however, relative PK activity was decreased significantly compared to HK in HbSS, β-thalassemia and HX patients, but not in HbSC patients (Figure 1A). PK thermostability was significantly decreased compared to healthy controls in HbSS patients and patients with HX (Figure 1B). In HbSC and β-thalassemia patients, PK-thermostability was comparable to HC. PK thermostability strongly correlated with absolute reticulocyte count (ARC), indicating that patients displaying the highest degree of PK instability had the highest reticulocyte count (Figure 1C). This suggests that in general, a higher degree of PK instability is associated with more severe anemia due to a high hemolytic rate. In SCD patients, PK-thermostability inversely correlated with PoS, indicating that decreased PK stability is associated with sickling at higher pO2 (r=-0.646, p&amp;lt;0.001, Figure 1F). When purified RBCs were incubated with 3.33μM of the allosteric PK-activator AG-348, an increase in PK activity was seen in all patients and HCs, with a mean increase of 122% in HbSS (range 111-139%, n=6), 137% in β-thalassemia (n=1), 163% in HX (range 152-174%, n=2) and 143% in HC (range 113-173%, n=9, Figure 1E). Accordingly, ATP-levels increased in all patients and HCs, with a mean increase of 133% in HbSS (range 125-141%, n=5), 144% patient with β-thalassemia (n=1), 121% in HX (range 112-129, n=3), and 132% in HCs (range 101-149%, n=9, Figure 1E). Conclusion: PK enzyme activity and stability is compromised in patients with various forms of hereditary hemolytic anemia. This implies that PK stability and, hence, compromised red cell metabolism could contribute to the complex pathophysiology of these diseases. In SCD patients, reduced PK-thermostability is associated with higher PoS, which we previously have shown to be associated with more severe disease (Rab et al, Am J Hematol, 2019, ASH 2019 abstract ID128870). This is confirmed by the correlation of decreased PK-thermostability with increased reticulocyte count as presented in this study. Current studies are in progress to further substantiate the underlying mechanism(s) involved, and to investigate whether AG-348 may ameliorate clinical features such as hemolysis, sickling tendency and iron overload. Disclosures Rab: RR Mechatronics: Research Funding. Bos:RR Mechatronics: Research Funding. Kosinski:Agios Pharmaceuticals, Inc: Employment, Other: Stakeholder. Kung:Agios Pharmaceuticals, Inc: Employment, Other: Stakeholder. van Beers:Agios Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Research Funding; RR Mechatronics: Research Funding. van Wijk:Agios Pharmaceuticals: Consultancy, Research Funding; RR Mechatronics: Research Funding.

PS1519 DECREASED ACTIVITY AND STABILITY OF PYRUVATE KINASE IN SICKLE CELL DISEASE AND THALASSEMIA: A POTENTIAL TARGET FOR THERAPY

Background:Reactive oxygen species (ROS) play an important role in the complex and multifactorial pathophysiology of sickle cell disease (SCD) and thalassemia. In SCD, auto‐oxidation of red blood cell (RBC) hemoglobin produces high levels of ROS that exceed anti‐oxidant capacity. In β–thalassemia, auto‐oxidation of unpaired α‐globins produces high levels of ROS. Increased intracellular levels of oxidative stress disrupt normal cell functioning and may contribute to premature clearance from the circulation. Pyruvate kinase (PK) is a key regulatory enzyme of glycolysis, the cell's only source of energy. Because PK is very sensitive to redox balance we hypothesized that increased levels of oxidative stress in hemoglobinopathies impairs proper enzyme function and thereby compromizes RBC energy metabolism. This may contribute to disease pathophysiology.Aims:To investigate if secondary deficiency of PK is common in SCD and thalassemia, and to investigate if PK in these disorders is able to respond to treatment with the allosteric PK activator AG‐348.Methods:Enzymatic activities of red cell PK and hexokinase (HK) were measured together with PK thermal stability (residual activity of PK) in order to assess relative PK activity and enzyme stability. RBC lysates were incubated with AG‐348 (3.33 uM) for 2 hours after which PK thermal stability, PK activity and ATP response was measured. Red blood cells of SCD patients were also analyzed with the oxygenscan, a newly developed method that characterizes individual sickling behavior (Rab et al, Am J Hematol, 2019).Results:Twenty‐eight patients and 18 healthy controls (HC) were included. The patient cohort consisted of patients with HbSS (n = 16), HbS/β‐thalassemia (n = 1), β‐thalassemia major (n = 3, regularly transfused), and HbSC (n = 3). Patients showed reticulocytosis and a concomitant increase in HK activity. However, PK activity was relatively decreased significantly compared to HK in SCD and β‐thalassemia patients, but not in HbSC patients (Figure 1A). PK thermal stability also was significantly decreased in SCD patients compared to healthy controls. In HbSC and β‐thalassemia patients PK‐thermal stability was comparable to HC (Figure 1B). When purified RBCs were incubated with 3.33uM of the allosteric PK‐activator AG‐348 an increase in PK activity was seen in all patients and HCs, with a median of 122% in SCD (range 120–138%, n = 3), 127% in β‐thalassemia and 142% in HC (range 130–166%, n = 5, Figure 1D). Accordingly, ATP‐levels increased in all patients and HCs, with a median of 126% in SCD (range 121–129%, n = 3), 146% in 1 patient with β‐thalassemia, and 122% in HCs (range 100–148%). In SCD patients PK‐thermal stability inversely correlated significantly with oxygenscan parameters, in particular the point‐of‐sickling (PoS). This indicates that RBCs tend to sickle at a higher pO2 when PK is more unstable. Interestingly, the 3 patients with most stable PK are HbSC patients (2) and a HbS/dβ‐thalassemia patient with HbF levels of 35% (Figure 1C).Summary/Conclusion:PK enzyme activity and stability is compromised in patients with SCD and β‐thalassemia. In SCD, reduced PK thermal stability is associated with higher PoS, which is associated with more severe disease. Current studies are in progress to further substantiate the underlying mechanism(s), and to investigate whether AG‐348 may ameliorate pathophysiological features such as hemolysis and sickling tendency.image

A Potential Role for α-Amylase in Amyloid-β-Induced Astrocytic Glycogenolysis and Activation.

Astrocytes produce and store the energy reserve glycogen. However, abnormal large glycogen units accumulate if the production or degradation of glycogen is disturbed, a finding often seen in patients with Alzheimer's disease (AD). We have shown increased activity of glycogen degrading α-amylase in AD patients and α-amylase positive glial cells adjacent to AD characteristic amyloid-β (Aβ) plaques. Investigate the role of α-amylase in astrocytic glycogenolysis in presence of Aβ. Presence of α-amylase and large glycogen units in postmortem entorhinal cortex from AD patients and non-demented controls were analyzed by immunohistological stainings. Impact of different Aβ42 aggregation forms on enzymatic activity (α-amylase, pyruvate kinase, and lactate dehydrogenase), lactate secretion, and accumulation of large glycogen units in cultured astrocytes were analyzed by activity assays, ELISA, and immunocytochemistry, respectively. AD patients showed increased number of α-amylase positive glial cells. The glial cells co-expressed the astrocytic marker glial fibrillary acidic protein, displayed hypertrophic features, and increased amount of large glycogen units. We further found increased load of large glycogen units, α-amylase immunoreactivity and α-amylase activity in cultured astrocytes stimulated with fibril Aβ42, with increased pyruvate kinase activity, but unaltered lactate release as downstream events. The fibril Aβ42-induced α-amylase activity was attenuated by β-adrenergic receptor antagonist propranolol. We hypothesize that astrocytes respond to fibril Aβ42 in Aβ plaques by increasing their α-amylase production to either liberate energy or regulate functions needed in reactive processes. These findings indicate α-amylase as an important actor involved in AD associated neuroinflammation.

Glucose Catabolism in Liver Tumors Induced by c-MYC Can Be Sustained by Various PKM1/PKM2 Ratios and Pyruvate Kinase Activities.

Different pyruvate kinase isoforms are expressed in a tissue-specific manner, with pyruvate kinase M2 (PKM2) suggested to be the predominant isoform in proliferating cells and cancer cells. Because of differential regulation of enzymatic activities, PKM2, but not PKM1, has been thought to favor cell proliferation. However, the role of PKM2 in tumorigenesis has been recently challenged. Here we report that increased glucose catabolism through glycolysis and increased pyruvate kinase activity in c-MYC-driven liver tumors are associated with increased expression of both PKM1 and PKM2 isoforms and decreased expression of the liver-specific isoform of pyruvate kinase, PKL. Depletion of PKM2 at the time of c-MYC overexpression in murine livers did not affect c-MYC-induced tumorigenesis and resulted in liver tumor formation with decreased pyruvate kinase activity and decreased catabolism of glucose into alanine and the Krebs cycle. An increased PKM1/PKM2 ratio by ectopic PKM1 expression further decreased glucose flux into serine biosynthesis and increased flux into lactate and the Krebs cycle, resulting in reduced total levels of serine. However, these changes also did not affect c-MYC-induced liver tumor development. These results suggest that increased expression of PKM2 is not required to support c-MYC-induced tumorigenesis in the liver and that various PKM1/PKM2 ratios and pyruvate kinase activities can sustain glucose catabolism required for this process. Cancer Res; 77(16); 4355-64. ©2017 AACR.

Reduction in cardiolipin decreases mitochondrial spare respiratory capacity and increases glucose transport into and across human brain cerebral microvascular endothelial cells.

Microvessel endothelial cells form part of the blood-brain barrier, a restrictively permeable interface that allows transport of only specific compounds into the brain. Cardiolipin is a mitochondrial phospholipid required for function of the electron transport chain and ATP generation. We examined the role of cardiolipin in maintaining mitochondrial function necessary to support barrier properties of brain microvessel endothelial cells. Knockdown of the terminal enzyme of cardiolipin synthesis, cardiolipin synthase, in hCMEC/D3 cells resulted in decreased cellular cardiolipin levels compared to controls. The reduction in cardiolipin resulted in decreased mitochondrial spare respiratory capacity, increased pyruvate kinase activity, and increased 2-deoxy-[(3) H]glucose uptake and glucose transporter-1 expression and localization to membranes in hCMEC/D3 cells compared to controls. The mechanism for the increase in glucose uptake was an increase in adenosine-5'-monophosphate kinase and protein kinase B activity and decreased glycogen synthase kinase 3 beta activity. Knockdown of cardiolipin synthase did not affect permeability of fluorescent dextran across confluent hCMEC/D3 monolayers grown on Transwell(®) inserts. In contrast, knockdown of cardiolipin synthase resulted in an increase in 2-deoxy-[(3) H]glucose transport across these monolayers compared to controls. The data indicate that in hCMEC/D3 cells, spare respiratory capacity is dependent on cardiolipin. In addition, reduction in cardiolipin in these cells alters their cellular energy status and this results in increased glucose transport into and across hCMEC/D3 monolayers. Microvessel endothelial cells form part of the blood-brain barrier, a restrictively permeable interface that allows transport of only specific compounds into the brain. In human adult brain endothelial cell hCMEC/D3 monolayers cultured on Transwell(®) plates, knockdown of cardiolipin synthase results in decrease in mitochondrial cardiolipin and decreased mitochondrial spare respiratory capacity. The reduced cardiolipin results in an increased activity of adenosine monophosphate kinase (pAMPK) and protein kinase B (pAKT) and decreased activity of glycogen synthase kinase 3 beta (pGSK3β) which results in elevated glucose transporter-1 (GLUT-1) expression and association with membranes. This in turn increases 2-dexoyglucose uptake from the apical medium into the cells with a resultant 2-deoxyglucose movement into the basolateral medium.

CD43 activates moonlight functions of pyruvate kinase (P1113)

Abstract CD43 is the most abundant costimulatory molecule on the T cell surface; it transduces activation signals through its cytoplasmic domain, modulating the outcome of T cell responses. CD43 KO mice revealed a positive role for CD43 in T cell migration and in the regulation of cell number and homeostasis. The aim of this study was to identify new signaling pathways modulated by CD43. Protein expression profiles of normal human CD4+ T cells stimulated through TCR and CD43 identified changes in 189 proteins. Bioinformatic analysis revealed that glucose metabolism was significantly represented. We evaluated pyruvate kinase (PK) and lactate dehydrogenase (LDH) activities, as well as glucose uptake. TCR+CD43 stimulated cells showed a 1.5 fold increase in PK activity, but only a moderate increase in LDH activity and glucose uptake. Interestingly, tyrosine phosphorylation of PK triggers its ability to phosphorylate Stat3. Phosphorylation of Y105 of PK and of Y705 of Stat3 was induced in response to TCR+CD43 and TCR+CD28. Since phosphorylation of Y705 of Stat3 by PK induces MEK5 transcription, we evaluated the MEK5/ERK5 pathway activation by measuring the levels of pCREB at S133, an ERK5 target. CREB pS133 was increased in TCR+CD43 and TCR+CD28 stimulated T cells. Altogether, our results show that CD43 regulates monosaccharide metabolism, as well as moonlight functions of metabolic enzymes.

Effects of alanine aminotransferase inhibition on the intermediary metabolism inSparus auratathrough dietary amino-oxyacetate supplementation

In liver, through the reaction catalysed by alanine aminotransferase (ALT), alanine becomes an effective precursor for gluconeogenesis. In the present study amino-oxyacetate (AOA) was used to evaluate its effect on liver ALT activity of the carnivorous fish Sparus aurata. Moreover, the derived metabolic effects on metabolites and other key enzymes of glycolysis, gluconeogenesis and the pentose phosphate pathway were also studied. A dose-effect-dependent inhibition of AOA on hepatic cytosolic and mitochondrial ALT activity was observed in vitro. In vivo, AOA behaved as an inhibitor of hepatic cytosolic ALT activity. A long-term exposure to AOA increased pyruvate kinase activity in the liver irrespective of the composition of the diet supplied to fish. 1H NMR studies showed that inclusion of AOA to the diet decreased the hepatic levels of alanine, glutamate and glycogen. Moreover, 2H NMR analysis indicated a higher renewal rate for alanine in the liver of fish fed with a high-carbohydrate/low-protein diet, while AOA decreased alanine 2H-enrichment irrespective of the diet. The present study indicates that AOA-dependent inhibition of the cytosolic ALT activity could help to increase the use of dietary carbohydrate nutrients.

CDC19 encoding pyruvate kinase is important for high-temperature tolerance in Saccharomyces cerevisiae

Use of thermotolerant strains is a promising way to reduce the cost of maintaining optimum temperatures in the fermentation process. Here we investigated genetically a Saccharomyces cerevisiae strain showing a high-temperature (41°C) growth (Htg(+)) phenotype and the result suggested that the Htg(+) phenotype of this Htg(+) strain is dominant and under the control of most probably six genes, designated HTG1 to HTG6. As compared with a Htg(-) strain, the Htg(+) strain showed a higher survival rate after exposure to heat shock at 48°C. Moreover, the Htg(+) strain exhibited a significantly high content of trehalose when cultured at high temperature and stronger resistance to Congo Red, an agent that interferes with cell wall construction. These results suggest that a strengthened cell wall in combination with increased trehalose accumulation can support growth at high temperature. The gene CDC19, encoding pyruvate kinase, was cloned as the HTG2 gene. The CDC19 allele from the Htg(+) strain possessed five base changes in its upstream region, and two base changes resulting in silent mutations in its coding region. Interestingly, the latter base changes are probably responsible for the increased pyruvate kinase activity of the Htg(+) strain. The possible mechanism leading to this increased activity and to the Htg(+) phenotype, which may lead to the activation of energy metabolism to maintain cellular homeostasis, is discussed.

Reduced gluconeogenesis and lactate clearance in Huntington's disease

We studied systemic and brain glucose and lactate metabolism in Huntington's disease (HD) patients in response to ergometer cycling. Following termination of exercise, blood glucose increased abruptly in control subjects, but no peak was seen in any of the HD patients (2.0±0.5 vs. 0.0±0.2mM, P<2×10−6). No difference was seen in brain metabolism parameters. Reduced hepatic glucose output in the HD mouse model R6/2 following a lactate challenge, combined with reduced phosphoenolpyruvate carboxykinase and increased pyruvate kinase activity in the mouse liver suggest a reduced capacity for gluconeogenesis in HD, possibly contributing to the clinical symptoms of HD. We propose that blood glucose concentration in the recovery from exercise can be applied as a liver function test in HD patients.

Blackspot seabream ( Pagellus bogaraveo) lipogenic and glycolytic pathways appear to be more related to dietary protein level than dietary starch type

The lipogenic potential of carbohydrate type on blackspot seabream was determined using two isolipidic (10%) and isonitrogenous (45%) diets containing either crude (CS) or gelatinized corn starch (GS). A third diet containing a lower protein level (35%) and gelatinized starch (GS) was also tested to determine if any lipogenic effect detected was due to carbohydrate and not from excess dietary protein. The three diets were formulated to have similar energy (21 kJ g − 1 DM) content. Triplicate groups of fish (24 g initial body weight) were fed each dietary treatment by hand to apparent satiety for 90 days. Both starch type and dietary protein level significantly affected growth. Fish fed the CS diet increased voluntary feed intake (VFI) and digestible protein intake resulting in both higher final body weight (FBW) and daily growth index (DGI). Although the lower protein level (35%) increased VFI, this increase was not enough to reach the same digestible protein intake observed in fish fed the high protein level (45%), resulting in lower FBW and DGI. Despite the differences observed in growth, nutrient gain and hence whole body composition were not affected by starch type (CS vs GS) or dietary protein level (35 vs 45%). Similarly, glycaemia was not affected by starch type or dietary protein level in any of the treatments, with the highest values being observed at 4 h post feeding. On the other hand, both starch type and dietary protein level significantly affected insulin levels 2 h after feeding. Plasma lipid levels showed no significant differences at 2 and 24 h post feeding, regardless of dietary treatment. A reduction of 10% dietary protein level (45 to 35%) markedly depressed (> 40%) hepatic activities of lipogenic enzymes (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME; fatty acid synthetase, FAS), and significantly increased PK activities at each postprandial time (2, 4 and 24 h). Starch type did not cause any significant effect on hexokinase (HK), glucokinase (GK), pyruvate kinase (PK) (glycolysis) or glucose-6-phosphatase (G6Pase) (gluconeogenesis) postprandial hepatic activities. Blackspot seabream lipogenic and glycolytic pathway regulation appear to be more related to dietary protein level than to dietary starch type.