Phosphofructokinase family genes in grass carp: Molecular identification and tissue-specific expression in response to glucose, insulin and glucagon

It is widely acknowledged that glucose serves as the primary energy source for organisms. However, fish exhibit persistent postprandial hyperglycemia and are thought to have low glucose tolerance. Glycolysis serves as the ubiquitous pathway for glucose catabolism, with phosphofructokinase (PFK) acting as a crucial rate-limiting enzyme in this process and playing an indispensable role. PFK is classified into three isoforms based on their major expression sites, i.e., PFKM (skeletal muscle type), PFKL (liver type) and PFKP (platelet type). In this study, grass carp (Ctenopharyngodon idella) was used as animal model and the open reading frame (ORF) sequences of six PFK genetic isoforms of grass carp were cloned. Real-time PCR was used to detect its tissue distribution, and expression changes in oral glucose tolerance test (OGTT), insulin and glucagon injection experiments. The results showed that the ORF of pfkla, pfklb, pfkma, pfkmb, pfkpa and pfkpb genes was 2343, 2340, 2355, 2331, 2364 and 2349 bp in length, respectively. The results of tissue distribution showed that pfkla and pfklb, homologous to mammalian pfkl, exhibited low expression levels in the liver of grass carp, but were expressed at the highest level in the brain. Muscle-type pfkma and pfkmb mRNA were found to be highly expressed in both red and white muscle, with pfkmb also exhibiting high expression levels in the heart, while platelet type pfkpa and pfkpb showed high mRNA abundances in the brain and heart. Oral glucose administration stimulated pfkma and pfkmb mRNA expression in the red muscle, and up-regulated pfklb mRNA levels in the liver at 3 h post treatment, but it suppressed liver-type and platelet-type PFK genes expression in the brain. The expression of pfkmb in white muscle and pfkmb and pfkpb in heart were promoted by insulin, whereas the expression of pfkla and pfkpb in the brain, pfkma and pfkmb in the red muscle, pfkma in the white muscle, and pfklb in the liver was suppressed by insulin. As for glucagon, it inhibited pfkma and pfkmb mRNA expression in the red muscle, as well as pfklb in the liver, but it up-regulated PFK genes expression in most tissues detected, such as brain (pfklb, pfkpa and pfkpb), white muscle (pfkma and pfkmb), liver (pfkla) and heart (pfkmb and pfkpb). Our results suggest that PFK family genes have different or even opposite expression patterns in response to glucose, insulin and glucagon stimulation in various tissues of grass carp, which may contribute to glucose intolerance in fish.

Pyrophosphate as allosteric regulator of ATP-phosphofructokinase in Clostridium thermocellum and other bacteria with ATP- and PPi-phosphofructokinases

The phosphofructokinase (Pfk) reaction represents one of the key regulatory points in glycolysis. While most organisms encode for Pfks that use ATP as phosphoryl donor, some organisms also encode for PP_i-dependent Pfks. Despite this central role, the biochemical characteristics as well as the physiological role of both Pfks is often not known. Clostridium thermocellum is an example of a microorganism that encodes for both Pfks, however, only PP_i-Pfk activity has been detected in cell-free extracts and little is known about the regulation and function of both enzymes. In this study, the ATP- and PP_i-Pfk of C. thermocellum were purified and biochemically characterized. No allosteric regulators were found for PP_i-Pfk amongst common effectors. With fructose-6-P, PP_i, fructose-1,6-bisP, and P_i PP_i-Pfk showed high specificity (K_M < 0.62 mM) and maximum activity (V_max > 156 U mg^-1). In contrast, ATP-Pfk showed much lower affinity (K_0.5 of 9.26 mM) and maximum activity (14.5 U mg^-1) with fructose-6-P. In addition to ATP, also GTP, UTP and ITP could be used as phosphoryl donors. The catalytic efficiency with GTP was 7-fold higher than with ATP, suggesting that GTP is the preferred substrate. The enzyme was activated by NH₄⁺, and pronounced inhibition was observed with GDP, FBP, PEP, and especially with PP_i (K_i of 0.007 mM). Characterization of purified ATP-Pfks originating from eleven different bacteria, encoding for only ATP-Pfk or for both ATP- and PP_i-Pfk, identified that PP_i inhibition of ATP-Pfks could be a common phenomenon for organisms with a PP_i-dependent glycolysis.

Analysis of differential proteins between non-capacitated and capacitated boar sperm and verification of the effect of phosphofructokinase on capacitation

The objective of this study was to analyze the differences in the proteins in non-capacitated and capacitated boar sperm and to identify the functions of the differential proteins and key capacitation proteins of boar sperm before and after capacitation. Transwell chambers were used to separate capacitated sperm proteins using a unique polycarbonate membrane. Meanwhile, isotopic tags for relative and absolute quantification combined with LC‒MS/MS analysis were used for quantitative determination of differential proteins. Through the comparative analysis of different databases, 475 different proteins were identified in non-capacitated sperm and capacitated sperm, of which 303 were significantly upregulated and 172 were significantly downregulated. These differentially-expressed proteins are mainly involved in redox processes, cell biosynthesis processes and cell aromatic compound metabolism biological processes. They also participate in the signaling pathways of phosphorylation, ketone synthesis and degradation, most of which interact to varying degrees. Among these differentially-expressed proteins, phosphofructokinase attracted our attention as a potential capacitated protein. We further verified that phosphofructokinase can promote boar sperm capacitation by immunoblotting.

Characterization of an Entner-Doudoroff pathway-activated Escherichia coli

BACKGROUND

Escherichia coli have both the Embden-Meyerhof-Parnas pathway (EMPP) and Entner-Doudoroff pathway (EDP) for glucose breakdown, while the EDP primarily remains inactive for glucose metabolism. However, EDP is a more favorable route than EMPP for the production of certain products.

RESULTS

EDP was activated by deleting the pfkAB genes in conjunction with subsequent adaptive laboratory evolution (ALE). The evolved strains acquired mutations in transcriptional regulatory genes for glycolytic process (crp, galR, and gntR) and in glycolysis-related genes (gnd, ptsG, and talB). The genotypic, transcriptomic and phenotypic analyses of those mutations deepen our understanding of their beneficial effects on cellulosic biomass bio-conversion. On top of these scientific understandings, we further engineered the strain to produce higher level of lycopene and 3-hydroxypropionic acid.

CONCLUSIONS

These results indicate that the E. coli strain has innate capability to use EDP in lieu of EMPP for glucose metabolism, and this versatility can be harnessed to further engineer E. coli for specific biotechnological applications.

Characterization of phosphofructokinase (PFK) from mud crab Scylla paramamosain and its role in mud crab dicistrovirus-1 proliferation

Phosphofructokinase (PFK), the key enzyme of glycolysis, can catalyze the irreversible transphosphorylation of fructose-6-phosphate forming fructose-1, 6-biphosphate. In the present study, a PFK gene from the mud crab Scylla paramamosain, named SpPFK, was cloned and characterized. The full length of SpPFK contained a 5'untranslated region (UTR) of 249 bp, an open reading frame of 2,859 bp, and a 3'UTR of 1,248 bp. The mRNA of SpPFK was highly expressed in the gill, followed by the hemocytes and muscle. The expression of SpPFK was significantly up-regulated after mud crab dicistrovirus-1 (MCDV-1) infection. Knocking down SpPFK in vivo by RNA interference significantly reduced the expression of lactate dehydrogenase after MCDV-1 infection. Furthermore, silencing of SpPFK in vivo increased the survival rate of mud crabs and decreased the MCDV-1 copies in the gill and hepatopancreas after MCDV-1 infection. All these results suggested that SpPFK could play an important role in the process of MCDV-1 proliferation in mud crab.

Circular RNA circPFKP promotes cell proliferation by activating IMPDH2 in prostate cancer

Prostate cancer (PCa), especially castration-resistant PCa, is a common and fatal disease. circRNAs had been confirmed to affect the proliferation of a variety of malignant tumors. Exploring the role of circRNAs in PCa progression and discovering new therapeutic targets are of great importance for the treatment of PCa. In the present study, we found that the expression of circPFKP was significantly increased in PCa tissues compared with adjacent noncancerous prostate tissues, and was correlated with the D'Amico risk classification, N stage, and prognostic stage group of PCa. CircPFKP promotes the proliferation of PCa cells in vitro and in vivo. Suppressing circPFKP induced the G1/S arrest of PCa cells. Mechanistically, circPFKP interacted with IMPDH2, promoted the biogenesis of guanine nucleotides. Moreover, the replenishment of intracellular guanine nucleotides pool reverses the inhibitory effect of knocking-down circPFKP on PCa cell proliferation. hnRNPF might promote circPFKP generation by binding to flanking Alu elements. Our results identify a novel functional interaction of circPFKP with IMPDH2, which promotes the proliferation of PCa cells.

Structural analysis and functional study of phosphofructokinase B (PfkB) from Mycobacterium marinum

Phosphofructokinase B (PfkB) belongs to the ribokinase family, which uses the phosphorylated sugar as substrate, and catalyzes fructose-6-phosphate into fructose-1,6-diphosphate. However, the structural basis of Mycobacterium marinum PfkB is not clear. Here, we found that the PfkB protein was monomeric in solution, which was different from most enzymes in this family. The crystal structure of PfkB protein from M. marinum was solved at a resolution of 2.21 Å. The PfkB structure consists of two domains, a major three-layered α/β/α sandwich-like domain characteristic of the ribokinase-like superfamily, and a second domain composed of four-stranded β sheets. Structural comparison analysis suggested that residues G236, A237, G238, and D239 could be critical for ATP catalysis and substrate binding of PfkB. Our current work provides new insights into understanding the mechanism of the glycolysis in M. marinum.

Genome-wide survey of the phosphofructokinase family in cassava and functional characterization in response to oxygen-deficient stress

BACKGROUND

Glycolytic pathway is common in all plant organs, especially in oxygen-deficient tissues. Phosphofructokinase (PFK) is a rate-limiting enzyme in the glycolytic pathway and catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate. Cassava (M. esculenta) root is a huge storage organ with low amount of oxygen. However, less is known about the functions of PFK from M. esculenta (MePFK). We conducted a systematic analysis of MePFK genes to explore the function of the MePFK gene family under hypoxic stress.

RESULTS

We identified 13 MePFK genes and characterised their sequence structure. The phylogenetic tree divided the 13 genes into two groups: nine were MePFKs and four were pyrophosphate-fructose-6-phosphate phosphotransferase (MePFPs). We confirmed by green fluorescent protein fusion protein expression that MePFK03 and MePFPA1 were localised in the chloroplast and cytoplasm, respectively. The expression profiles of the 13 MePFKs detected by quantitative reverse transcription polymerase chain reaction revealed that MePFK02, MePFK03, MePFPA1, MePFPB1 displayed higher expression in leaves, root and flower. The expression of MePFK03, MePFPA1 and MePFPB1 in tuber root increased gradually with plant growth. We confirmed that hypoxia occurred in the cassava root, and the concentration of oxygen was sharply decreasing from the outside to the inside root. The expression of MePFK03, MePFPA1 and MePFPB1 decreased with the decrease in the oxygen concentration in cassava root. Waterlogging stress treatment showed that the transcript level of PPi-dependent MePFP and MeSuSy were up-regulated remarkably and PPi-dependent glycolysis bypass was promoted.

CONCLUSION

A systematic survey of phylogenetic relation, molecular characterisation, chromosomal and subcellular localisation and cis-element prediction of MePFKs were performed in cassava. The expression profiles of MePFKs in different development stages, organs and under waterlogging stress showed that MePFPA1 plays an important role during the growth and development of cassava. Combined with the transcriptional level of MeSuSy, we found that pyrophosphate (PPi)-dependent glycolysis bypass was promoted when cassava was under waterlogging stress. The results would provide insights for further studying the function of MePFKs under hypoxic stress.

Biochemical Basis for Redox Regulation of Chloroplast-Localized Phosphofructokinase from Arabidopsis thaliana

Various proteins in plant chloroplasts are subject to thiol-based redox regulation, allowing light-responsive control of chloroplast functions. Most redox-regulated proteins are known to be reductively activated in the light in a thioredoxin (Trx)-dependent manner, but its regulatory network remains incompletely understood. Using a biochemical procedure, we here show that a specific form of phosphofructokinase (PFK) is a novel redox-regulated protein whose activity is suppressed upon reduction. PFK is a key enzyme in the glycolytic pathway. In Arabidopsis thaliana, PFK5 is targeted to chloroplasts and uniquely contains an insertion sequence harboring two Cys residues (Cys152 and Cys157) in the N-terminal region. Redox shift assays using a thiol-modifying reagent indicated that PFK5 is efficiently reduced by a specific type of Trx, namely, Trx-f. PFK5 enzyme activity was lowered with the Trx-f-dependent reduction. PFK5 redox regulation was bidirectional; PFK5 was also oxidized and activated by the recently identified Trx-like2/2-Cys peroxiredoxin pathway. Mass spectrometry-based peptide mapping analysis revealed that Cys152 and Cys157 are critical for the intramolecular disulfide bond formation in PFK5. The involvement of Cys152 and Cys157 in PFK5 redox regulation was further supported by a site-directed mutagenesis study. PFK5 catalyzes the reverse reaction of fructose 1,6-bisphosphatase (FBPase), which is reduced and activated specifically by Trx-f. Our data suggest that PFK5 redox regulation, together with that of FBPase, constitutes a checkpoint for switching light/dark metabolism in chloroplasts.

Discovery and development of tumor glycolysis rate-limiting enzyme inhibitors

Tumor cells mainly provide necessary energy and substances for rapid cell growth through aerobic perglycolysis rather than oxidative phosphorylation. This phenomenon is called the "Warburg effect". The mechanism of glycolysis in tumor cells is more complicated, which is caused by the comprehensive regulation of multiple factors. Abnormal enzyme metabolism is one of the main influencing factors and inhibiting the three main rate-limiting enzymes in glycolysis is thought to be important strategy for cancer treatment. Therefore, numerous inhibitors of glycolysis rate-limiting enzyme have been developed in recent years, such as the latest HKII inhibitor and PKM2 inhibitor Pachymic acid (PA) and N-(4-(3-(3-(methylamino)-3-oxopropyl)-5-(4'-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-pyrazol-1-yl)phenyl)propiolamide. The review focuses on source, structure-activity relationship, bioecological activity and mechanism of the three main rate-limiting enzymes inhibitors, and hopes to guide the future research on the design and synthesis of rate-limiting enzyme inhibitors.

Metabolic changes in triple negative breast cancer-focus on aerobic glycolysis

Among breast cancer subtypes, the triple negative breast cancer (TNBC) has the worst prognosis. In absence of any permitted targeted therapy, standard chemotherapy is the mainstay for TNBC treatment. Hence, there is a crucial need to identify potential druggable targets in TNBCs for its effective treatment. In recent times, metabolic reprogramming has emerged as cancer cells hallmark, wherein cancer cells display discrete metabolic phenotypes to fuel cell progression and metastasis. Altered glycolysis is one such phenotype, in which even in oxygen abundance majority of cancer cells harvest considerable amount of energy through elevated glycolytic-flux. In the present review, we attempt to summarize the role of key glycolytic enzymes i.e. HK, Hexokinase; PFK, Phosphofructokinase; PKM2, Pyruvate kinase isozyme type 2; and LDH, Lactate dehydrogenase in TNBCs, and possible therapeutic options presently available.

Middle aged turn point in parameters of oxidative stress and glucose catabolism in mouse cerebellum during lifespan: minor effects of every-other-day fasting

The cerebellum is considered to develop aging markers more slowly than other parts of the brain. Intensification of free radical processes and compromised bioenergetics, critical hallmarks of normal brain aging, may be slowed down by caloric restriction. This study aimed to evaluate the intensity of oxidative stress and the enzymatic potential to utilize glucose via glycolysis or the pentose phosphate pathway (PPP) in the cerebellum of mice under ad libitum versus every-other-day fasting (EODF) feeding regimens. Levels of lipid peroxides, activities of antioxidant and key glycolytic and PPP enzymes were measured in young (6-month), middle-aged (12-month) and old (18-month) C57BL/6J mice. The cerebellum showed the most dramatic increase in lipid peroxide levels, antioxidant capacity and PPP key enzyme activities and the sharpest decline in the activities of key glycolytic enzymes under transition from young to middle age but these changes slowed when transiting from middle to old age. A decrease in the activity of the key glycolytic enzyme phosphofructokinase was accompanied by a concomitant increase in the activities of hexokinase and glucose-6-phosphate dehydrogenase (G6PDH), which may suggest that during normal cerebellar aging glucose metabolism shifts from glycolysis to the pentose phosphate pathway. The data indicate that intensification of free radical processes in the cerebellum occurred by middle age and that activation of the PPP together with increased antioxidant capacity can help to resist these changes into old age. However, the EODF regime did not significantly modulate or alleviate any of the metabolic processes studied in this analysis of the aging cerebellum.

Target enzymes are stabilized by AfrLEA6 and a gain of α-helix coincides with protection by a group 3 LEA protein during incremental drying

Anhydrobiotic organisms accumulate late embryogenesis abundant (LEA) proteins, a family of intrinsically disordered proteins (IDPs) reported to improve cellular tolerance to water stress. Here we show that AfrLEA6, a Group 6 LEA protein only recently discovered in animals, protects lactate dehydrogenase (LDH), citrate synthase (CS) and phosphofructokinase (PFK) against damage during desiccation. In some cases, protection is enhanced by trehalose, a naturally-occurring protective solute. An open question is whether gain of secondary structure by LEA proteins during drying is a prerequisite for this stabilizing function. We used incremental drying (equilibration to a series of relative humidities, RH) to test the ability of AfrLEA2, a Group 3 LEA protein, to protect desiccation-sensitive PFK. AfrLEA2 was chosen due to its exceptional ability to protect PFK. In parallel, circular dichroism (CD) spectra were obtained for AfrLEA2 across the identical range of relative water contents. Protection of PFK by AfrLEA2, above that observed with trehalose and BSA, coincides with simultaneous gain of α-helix in AfrLEA2. At 100% RH, the CD spectrum for AfrLEA2 is typical of random coil, while at decreasing RH, the spectrum shows higher ellipticity at 191 nm and minima at 208 and 220 nm, diagnostic of α-helix. This study provides experimental evidence linking the gain of α-helix with stabilization of a target protein across a graded series of hydration states. Mechanistically, it is intriguing that certain other functions of these IDPs, like preventing aggregation of target proteins, can occur in fully hydrated cells and apparently do not require gain of α-helix.

Adriamycin inhibits glycolysis through downregulation of key enzymes in Saccharomyces cerevisiae

Adriamycin is a widely used drug for the treatment of various types of cancers, but its clinical application is limited because of irreversible dilated cardiomyopathy. The incidence of cardiomyopathy is a consequence of disrupted energy production, which could be related to the defects in glycogen, lipid and mucopolysaccharide metabolism. We explored the effect of Adriamycin on enzymes involved in glycolysis and apoptotic genes through molecular docking. We used Saccharomyces cerevisiae as model organism and studied the effect of Adriamycin on selected enzymes involved in glycolysis. The docking studies revealed that Adriamycin interacts with phosphofructokinase and enolase in an efficient manner. In phosphofructokinase, Adriamycin binds at the active site and with enolase the drug interacts at the cofactor-binding site (Mg²⁺) which might impair the activity of the enzyme. Gene expression studies revealed that Adriamycin causes the dysregulation of glycolysis through dysregulation of hexokinase, phosphoglycerate mutase, enolase and downregulation of pyruvate kinase. The drug shows a biphasic effect on the expression of genes enolase and pyruvate kinase. The impairment in glycolysis might reduce the ATP synthesis, and the cells might be deprived of energy. The condition is further worsened by elevated ROS levels triggering the cell to undergo apoptosis evidenced by downregulation of SOD and upregulation of BAX and caspase. In conclusion, our study reveals that Adriamycin impairs glycolysis and cause cell to undergo apoptosis due to oxidative stress in yeast cells.

Paroxetine binding and activation of phosphofructokinase implicates energy metabolism in antidepressant mode of action

Selective serotonin reuptake inhibitors (SSRIs) are the predominant drugs prescribed for Major Depressive Disorder. The immediate pharmacological target of SSRIs is the serotonin transporter. However, the delayed therapeutic effect and high rate of patient non-response make it highly likely that SSRIs also have other molecular targets that are yet to be identified. Cellular thermal shift assay (CETSA) is a method based on thermal stabilization of target proteins upon drug binding. In the present study, we show that the SSRI paroxetine binds to phosphofructokinase (PFK) protein using CETSA. We found that mouse brain PFK and recombinant human PFK proteins are stabilized by paroxetine incubation. Chronic paroxetine treatment also significantly increased mouse brain PFK thermal stability. Paroxetine significantly elevated in vitro and in vivo PFK activity. Levels of several metabolites in glutamate- and energy metabolism-related pathways are significantly correlated with PFK activity in mouse hippocampus. Our data show that paroxetine can bind to PFK and affect its activity. Implications of these results for the antidepressant mode of action of paroxetine are discussed.

At physiological concentrations, AMP increases phosphofructokinase-1 activity compared to fructose 2, 6-bisphosphate in postmortem porcine skeletal muscle

Phosphofructokinase-1 (PFK-1) is the most important enzyme controlling postmortem glycolysis in living skeletal muscle and is the most likely candidate for regulation of postmortem glycolysis. We investigated the regulation of PFK-1 activity by F-2, 6-BP and AMP under simulated postmortem conditions in porcine skeletal muscle. Six pigs were harvested and longissimus lumborum samples were collected immediately post-slaughter. PFK-1 activity was assayed using increasing concentrations of F-2, 6-BP or AMP, added to the buffer adjusted to different pH. Both F-2, 6-BP and AMP increased PFK-1 activity with increasing buffer pH from 5.5 to 7.0. A concentration of 50 μM F-2, 6-BP was required to increase PFK-1 activity which is very high compared to physiological concentration in the porcine skeletal muscle. However, physiological concentrations (50-150 μM) of AMP resulted in increased PFK-1 activity compared to 1-2 μM F-2, 6-BP. Thus, AMP may play a greater role in dictating the rate and extent of postmortem muscle glycolysis and pH decline as compared to F-2, 6-BP.

Brain and muscle adaptation to high-fat diets and exercise: Metabolic transporters, enzymes and substrates in the rat cortex and muscle

There is evidence suggesting that the effects of diet and physical activity on physical and mental well-being are the result of altered metabolic profiles. Though the central and peripheral systems work in tandem, the interactions between peripheral and central changes that lead to these altered states of well-being remains elusive. We measured changes in the metabolic profile of brain (cortex) and muscle (soleus and plantaris) tissue in rats following 5-weeks of treadmill exercise and/or a high-fat diet to evaluate peripheral and central interactions as well as identify any common adaptive mechanisms. To characterize changes in metabolic profiles, we measured relative changes in key metabolic enzymes (COX IV, hexokinase, LDHB, PFK), substrates (BHB, FFA, glucose, lactate, insulin, glycogen, BDNF) and transporters (MCT1, MCT2, MCT4, GLUT1, GLUT3). In the cortex, there was an increase in MCT1 and a decrease in glycogen following the high-fat diet, suggesting an increased reliance on monocarboxylates. Muscle changes were dependent muscle type. Within the plantaris, a high-fat diet increased the oxidative capacity of the muscle likely supported by increased glycolysis, whereas exercise increased the oxidative capacity of the muscle likely supported via increased glycogen synthesis. There was no effect of diet on soleus measurements, but exercise increased its oxidative capacity likely fueled by endogenous and exogenous monocarboxylates. For both the plantaris and soleus, combining exercise training and high-fat diet mediated results, resulting in a middling effect. Together, these results indicate the variable adaptions of two main metabolic pathways: glycolysis and oxidative phosphorylation. The results also suggest a dynamic relationship between the brain and body.

Sex-dimorphic moderate hypoglycemia preconditioning effects on Hippocampal CA1 neuron bio-energetic and anti-oxidant function

Hypoglycemia is a detrimental complication of rigorous management of type 1 diabetes mellitus. Moderate hypoglycemia (MH) preconditioning of male rats partially affords protection from loss of vulnerable brain neurons to severe hypoglycemia (SH). Current research investigated whether MH preconditioning exerts sex-dimorphic effects on hippocampal CA1 neuron bio-energetic and anti-oxidant responses to SH. SH up-regulated CA1 glucose or monocarboxylate transporter proteins in corresponding hypoglycemia-naïve male versus female rats; precedent MH amplified glucose transporter expression in SH irrespective of sex. Sex-differentiating SH effects on glycolytic and tricarboxylic pathway markers correlated with elevated tissue ATP content and diminished CA1 5'-AMP-activated protein kinase (AMPK) activation in females. MH-preconditioned suppression of mitochondrial energy pathway enzyme profiles and tissue ATP in SH rats coincided with amplified CA1 AMPK activity in both sexes. Anti-oxidative stress enzyme protein responses to SH were primarily sex-contingent; preconditioning amplified most of these profiles, yet exacerbated expression of lipid and protein oxidation markers in SH male and female rats, respectively. Results show that MH preconditioning abolishes female CA1 neuron neuroprotection of positive energy balance through SH, resulting in augmented CA1 AMPK activity and oxidative injury and diminished tissue ATP in hypoglycemia-conditioned versus naïve rats in each sex. It is unclear if SH elicits differential rates of CA1 neuronal destruction in the two sexes, or how MH may impact sex-specific cell loss. Further research is needed to determine if molecular mechanism(s) that maintain female CA1 neuron metabolic stability in the absence of MH preconditioning can be leveraged for therapeutic prevention of hypoglycemic nerve cell damage.

Neuronostatin Promotion Soluble Aβ1-42 Oligomers: Induced Dysfunctional Brain Glucose Metabolism in Mice

Neuronostatin (NST) is an endogenous peptide hormone, it has the ability to improve oligomeric Aβ (oAβ)-induced cognitive impairments and increase blood glucose levels in mice. However, the relationship between NST and oAβ regarding brain glucose metabolism has not yet been established. The present study defined the contributions of NST and oAβ in the brain glucose metabolism in mice. It was found that i.c.v. co-administration of NST (3 nmol/mouse) and oAβ (1 nmol/mouse) decreased the mRNA expressions of glucose-6-phosphate dehydrogenase and phosphofructokinase. The treatments were observed to reduce ATP production and the enzyme activities of glucose-6-phosphate dehydrogenase and hexokinase in both the cortex and hippocampus. Simultaneously, co-injection of NST and oAβ inhibited the mRNA and protein expression of glucose transporters GLUT3 and GLUT1 in the cortex and hippocampus. NST promoted the oAβ-induced decreased the cortical NeuN staining, while oAβ increased the levels of NST in both the cortex and hippocampus. I.c.v. co-administration of NST and oAβ led to increase the levels of GPR107 expression and the phosphorylation of PKA, Akt, PERK and eIF-2α in the cortex. These findings suggest that NST promoted oAβ-induced dysfunctional glucose metabolism through the GPR107/PKA/Akt signaling pathway and PERK/eIF2α axis in the brain, which thus contributes to metabolic dysfunction and Alzheimer's disease (AD) pathophysiology.

A novel microRNA and its pfk target control growth length in the freshwater shrimp Neocaridina heteropoda

MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate gene expression and play roles in a wide range of physiological processes, including ontogenesis. Herein, we discovered a novel miRNA, novel miR-26, which inhibits translation of the phosphofructokinase (PFK) gene by targeting the 3' untranslated region (UTR) of pfk directly, thereby inhibiting molting and body length growth of the freshwater shrimp Neocaridina heteropoda Lowering expression of pfk by RNA interference (RNAi) led to a longer ecdysis cycle and smaller individuals. This phenotype was mirrored in shrimps injected with novel miR-26 agomirs, but the opposite phenotype occurred in shrimps injected with novel miR-26 antagomirs (i.e. the ecdysis cycle was shortened and body length was increased). After injection of 20-hydroxyecdysone (ecdysone 20E), expression of the novel miR-26 was decreased, while expression of pfk was up-regulated, and the fructose-1,6-diphosphate metabolite of PFK accumulated correspondingly. Furthermore, expression of eIF2 (eukaryotic initiation factor 2) increased under stimulation with fructose-1,6-diphosphate, suggesting that protein synthesis was stimulated during this period. Taken together, our results suggest that the novel miR-26 regulates expression of pfk and thereby mediates the molting and growth of N. heteropoda.

Physiological phenotyping of mammalian cell lines by enzymatic activity fingerprinting of key carbohydrate metabolic enzymes: a pilot and feasibility study

Objective

Enzymatic fingerprinting of key enzymes of glucose metabolism is a valuable analysis tool in cell physiological phenotyping of plant samples. Yet, a similar approach for mammalian cell line samples is missing. In this study, we applied semi-high throughput enzyme activity assays that were originally designed for plant samples and tested their feasibility in extracts of six frequently used mammalian cell lines (Caco2, HaCaT, C2C12, HEK293, HepG2 and INS-1E).

Results

Enzyme activities for aldolase, hexokinase, glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, phosphoglucomutase, phosphofructokinase could be detected in samples of one or more mammalian cell lines. We characterized effects of sample dilution, assay temperature and repeated freeze–thaw cycles causing potential biases. After careful selection of experimental parameters, the presented semi-high throughput methods could be established as useful tool for physiological phenotyping of cultured mammalian cells.

Genome-wide identification, expression and functional analysis of the phosphofructokinase gene family in Chinese white pear (Pyrus bretschneideri)

Phosphofructokinase plays an essential role in sugar metabolism in plants. Plants possess two types of phosphofructokinase proteins for phosphorylation of fructose-6-phosphate, the pyrophosphate-dependent fructose-6-phosphate phosphotransferase (PFP), and the ATP-dependent phosphofructokinase (PFK). Until now, the gene evolution, expression patterns, and functions of phosphofructokinase proteins were unknown in pear. In this report, 14 phosphofructokinase genes were identified in pear. The phylogenetic tree indicated that the phosphofructokinase gene family could be grouped into two subfamilies, with 10 genes belonging to the PbPFK subfamily, and 4 genes belonging to the PbPFP subfamily. Conserved motifs and exon numbers of the phosphofructokinase were found in pear and other six species. The evolution analysis indicated that WGD/Segmental and dispersed duplications were the main duplication models for the phosphofructokinase genes expansion in pear and other six species. Analysis of cis-regulatory element sequences of all phosphofructokinase genes identified light regulation and the MYB binding site in the promoter of all pear phosphofructokinase genes, suggesting that phosphofructokinase might could be regulated by light and MYB transcription factors (TFs). Gene expression patterns revealed that PbPFP1 showed similar pattern with sorbitol contents, suggesting important contributions to sugar accumulation during fruit development. Further functional analysis indicated that the phosphofructokinase gene PbPFP1 was localized on plasma membrane compartment, indicating that PbPFP1 had function in plasma membrane. Transient transformation of PbPFP1 in pear fruits led to significant increases of fructose and sorbitol compared to controls. Overall, our study provides important insights into the gene expression patterns and important potential functions of phosphofructokinase for sugar accumulation in pear fruits, which will help to enrich understanding of sugar-related bio-pathways and lay the molecular basis for fruit quality improvement.

Insulin specifically regulates expression of liver and muscle phosphofructokinase isoforms

Phosphofructokinase (PFK) is a key regulatory enzyme of glycolysis, being considered the pacemaker of this pathway. In mammals, this enzyme exists as three different isoforms, PFKM, PFKL and PFKP, presenting different regulatory and catalytic properties. The expression of these isoforms is tissue-specific and vary according to the cell differentiation and signalization. Although it is known that the expression of the different PFK isoforms directly affects cell function, the information regarding the regulation of PFK isoforms expression is scarce. In the present work, we evaluate the role of insulin signalization on the expression of three PFK isoforms on skeletal muscle, liver, and epididymal white adipose tissue (eWAT) of mice. For this, Swiss mice were treated with streptozotocin (STZ) to disrupt pancreatic ß-cells and, thus, insulin production. Control group were treated with citrate buffer (STZ vehicle). These groups were then treated with insulin or saline twice a day for ten consecutive days when animals were euthanized and tissues used for the evaluation of PFK isoforms expression by quantitative PCR (qPCR). Our results revealed that the lack of insulin significantly impacted the expression of PFKL, presenting mild effects on PFKM and no effects on PFKP. The decrease of PFKL and PFKM mRNA levels observed on the group treated with STZ was reversed by the treatment with insulin. In conclusion, insulin, the most known regulator of glucose consumption, specifically regulates the expression of PFKL and PFKM, which impact the regulation of glycolysis in the cell.

ADP-dependent phosphofructokinases from the archaeal order Methanosarcinales display redundant glucokinase activity

The genome of Methanosarcinales organisms presents both ADP-dependent glucokinase and phosphofructokinase genes. However, Methanococcoides burtonii has a truncate glucokinase gene with a large deletion at the C-terminal, where the catalytic GXGD motif is located. Characterization of its phosphofructokinase annotated protein shows that is a bifunctional enzyme able to supply the absence of the glucokinase activity. Moreover, kinetic analyses of the phosphofructokinase annotated enzyme from, Methanohalobium evestigatum demonstrated that this enzyme is also bifunctional. The high conservation of the active site residues of all the enzymes from the order Methanosarcinales suggest that they should be bifunctional, as was previously reported for the ADP-dependent kinases from Methanococcales, highlighting the redundancy of the glucokinase activity in this archaeal group. The presence of active glycolytic enzymes would be important when glycogen storage of these organisms needs to be degraded to be used as energy source. Kinetic and structural information allows us to establish a substrate specificity signature that identifies specific GK or PFK, and bifunctional enzymes in this family.

Sodium ions activated phosphofructokinase leading to enhanced D-lactic acid production by Sporolactobacillus inulinus using sodium hydroxide as a neutralizing agent

Sporolactobacillus inulinus is a superior D-lactic acid-producing bacterium and proposed species for industrial production. The major pathway for D-lactic acid biosynthesis, glycolysis, is mainly regulated via the two irreversible steps catalyzed by the allosteric enzymes, phosphofructokinase (PFK) and pyruvate kinase. The activity level of PFK was significantly consistent with the cell growth and D-lactic acid production, indicating its vital role in control and regulation of glycolysis. In this study, the ATP-dependent PFK from S. inulinus was expressed in Escherichia coli and purified to homogeneity. The PFK was allosterically activated by both GDP and ADP and inhibited by phosphoenolpyruvate; the addition of activators could partly relieve the inhibition by phosphoenolpyruvate. Furthermore, monovalent cations could enhance the activity, and Na⁺ was the most efficient one. Considering this kind activation, NaOH was investigated as the neutralizer instead of the traditional neutralizer CaCO₃. In the early growth stage, the significant accelerated glucose consumption was achieved in the NaOH case probably for the enhanced activity of Na⁺-activated PFK. Using NaOH as the neutralizer at pH 6.5, the fermentation time was greatly shortened about 22 h; simultaneously, the glucose consumption rate and the D-lactic acid productivity were increased by 34 and 17%, respectively. This probably contributed to the increased pH and Na⁺-promoted activity of PFK. Thus, fermentations by S. inulinus using the NaOH neutralizer provide a green and highly efficient D-lactic acid production with easy subsequent purification.

Altered Erythrocyte Glycolytic Enzyme Activities in Type-II Diabetes

The activity of enzymes of glycolysis has been studied in erythrocytes from type-II diabetic patients in comparison with control. RBC lysate was the source of enzymes. In the diabetics the hexokinase (HK) activity increased 50 % while activities of phosphoglucoisomerase (PGI), phosphofructokinase (PFK) and aldolase (ALD) decreased by 37, 75 and 64 % respectively but were still several folds higher than that of HK. Hence, it is possible that in the diabetic erythrocytes the process of glycolysis could proceed in an unimpaired or in fact may be augmented due to increased levels of G6P. The lactate dehydrogenase (LDH) activity was comparatively high in both the groups; the diabetic group showed 85 % increase. In control group the HK, PFK and ALD activities showed strong positive correlation with blood sugar level while PGI activity did not show any correlation. In the diabetic group only PFK activity showed positive correlation. The LDH activity only in the control group showed positive correlation with marginal increase with increasing concentrations of glucose.

Analysis of the substrate inhibition of complete and partial types

A simple graphical method was described for determining the kinetic parameters of substrate inhibition of complete and partial types. The method consists of plotting experimental data as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v/\left( {V_{max} - v} \right)$$\end{document}v/Vmax-v versus the reciprocals of the substrate concentrations, where V_max represents the maximal velocity. The reaction rate constant of enzyme–substrate–inhibitor complex \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(k^{\prime } /k)$$\end{document}(k′/k) can be calculated from the ordinate intercept of the linear relationship between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v/\left( {V_{max} - v} \right)$$\end{document}v/Vmax-v and the reciprocal of the substrate concentrations at the higher and inhibitory concentrations of the substrate: partial type \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(k^{\prime } /k < 1)$$\end{document}(k′/k<1) of the substrate inhibition gives straight lines intersecting with the ordinate at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(k^{\prime } /k)/( 1- k^{\prime } /k)$$\end{document}(k′/k)/(1-k′/k), whereas complete substrate inhibition \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(k^{\prime } = 0)$$\end{document}(k′=0) yields straight lines converging on the origin. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K_{i}^{\prime }$$\end{document}Ki′ value also can be calculated from the slope by using the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$k^{\prime } /k$$\end{document}k′/k value determined. Validity of the method was confirmed by analyzing the substrate inhibition of phosphofructokinase II from E. coli. The present method provides a simple way for determining kinetic parameters of the substrate inhibition irrespective of complete and partial types.

Measurement of glycolysis reactants by high-throughput solid phase extraction with tandem mass spectrometry: Characterization of pyrophosphate-dependent phosphofructokinase as a case study

Glycolysis is a 10-step metabolic pathway involved in producing cellular energy. Many tumors exhibit accelerated glycolytic rates, and enzymes that participate in this pathway are focal points of cancer research. Here, a novel method for the measurement of glycolysis reactants from in vitro samples is presented. Fast and direct measurement is achieved by an automated system that couples on-line solid phase extraction (SPE) with tandem mass spectrometry (MS/MS). The single analytical method enables multiple reactants to be measured concurrently, sustains a cycle time of 8s, and permits the measurement of up to 10,000 samples per day. Concentration-response curves were conducted using standards for 10 metabolic intermediates, and the results demonstrate that the detection strategy has excellent sensitivity (average limit of detection = 5.4 nM), dynamic range (nanomolar to micromolar), and linear response (average R(2) = 0.998). To test the analysis method on reactions, pyrophosphate-dependent phosphofructokinase (PPi-PFK) was used as a model system. Data that corroborate the activation and inhibition of PPi-PFK are presented, and the ways in which SPE-MS/MS simplifies experimental design and interpretation are highlighted. In summary, the method for measuring metabolic intermediates described here demonstrates unprecedented speed, performance, and versatility.

Molecular and biochemical characterisation of abomasal nematode parasites Teladorsagia circumcincta and Haemonchus contortus phosphofructokinases and their recognition by the immune host

Full length cDNAs encoding phosphofructokinase (PFK) were cloned from Teladorsagia circumcincta (TcPFK) and Haemonchus contortus (HcPFK). TcPFK (2361 bp) and HcPFK (2367 bp) cDNA encoded 787 and 789 amino acid proteins respectively. The predicted amino acid sequences showed 98% similarity with each other and 70% with a Caenorhabditis elegans PFK. Substrate binding sites were completely conserved in both proteins. Soluble N-terminal His-tagged PFK proteins were expressed in Escherichia coli strain BL21, purified and characterised. The recombinant TcPFK and HcPFK had very similar kinetic properties: the pH optima were pH 7.0, Km for fructose 6-phosphate was 0.50 ± 0.01 and 0.55 ± 0.01 mM respectively when higher (inhibiting concentration, 0.3 mM) ATP concentration was used and the curve was sigmoidal. The Vmax for TcPFK and HcPFK were 1110 ± 16 and 910 ± 10 nM min(-1 )mg(-1) protein respectively. Lower ATP concentration (non-inhibiting, 0.01 mM) did not change the Vmax for TcPFK and HcPFK (890 ± 10 and 860 ± 12 nM min(-1 )mg(-1) protein) but the substrate affinity doubled and Km for fructose 6-phosphate were 0.20 ± 0.05 and 0.25 ± 0.01 mM respectively. Recognition of TcPFK and HcPFK by mucosal and serum antibodies in nematode exposed animals demonstrates antigenicity and suggests involvement in the host response to nematode infection.

Yeast phosphofructokinase-1 subunit Pfk2p is necessary for pH homeostasis and glucose-dependent vacuolar ATPase reassembly

V-ATPases are conserved ATP-driven proton pumps that acidify organelles. Yeast V-ATPase assembly and activity are glucose-dependent. Glucose depletion causes V-ATPase disassembly and its inactivation. Glucose readdition triggers reassembly and resumes proton transport and organelle acidification. We investigated the roles of the yeast phosphofructokinase-1 subunits Pfk1p and Pfk2p for V-ATPase function. The pfk1Δ and pfk2Δ mutants grew on glucose and assembled wild-type levels of V-ATPase pumps at the membrane. Both phosphofructokinase-1 subunits co-immunoprecipitated with V-ATPase in wild-type cells; upon deletion of one subunit, the other subunit retained binding to V-ATPase. The pfk2Δ cells exhibited a partial vma growth phenotype. In vitro ATP hydrolysis and proton transport were reduced by 35% in pfk2Δ membrane fractions; they were normal in pfk1Δ. In vivo, the pfk1Δ and pfk2Δ vacuoles were alkalinized and the cytosol acidified, suggestive of impaired V-ATPase proton transport. Overall the pH alterations were more dramatic in pfk2Δ than pfk1Δ at steady state and after readdition of glucose to glucose-deprived cells. Glucose-dependent reassembly was 50% reduced in pfk2Δ, and the vacuolar lumen was not acidified after reassembly. RAVE-assisted glucose-dependent reassembly and/or glucose signals were disturbed in pfk2Δ. Binding of disassembled V-ATPase (V1 domain) to its assembly factor RAVE (subunit Rav1p) was 5-fold enhanced, indicating that Pfk2p is necessary for V-ATPase regulation by glucose. Because Pfk1p and Pfk2p are necessary for V-ATPase proton transport at the vacuole in vivo, a role for glycolysis at regulating V-ATPase proton transport is discussed.

A fresh view of glycolysis and glucokinase regulation: history and current status

This minireview looks back at a century of glycolysis research with a focus on the mechanisms of flux regulation. Traditionally, glycolysis is regarded as a feeder pathway that prepares glucose for further catabolism and energy production. However, glycolysis is much more than that, in particular in those tissues that express the low affinity glucose-phosphorylating enzyme glucokinase. This enzyme equips the glycolytic pathway with a special steering function for the regulation of intermediary metabolism. In beta cells, glycolysis acts as a transducer for triggering and amplifying physiological glucose-induced insulin secretion. On the basis of these considerations, I have defined a glycolytic flux regulatory unit composed of the two fructose ester steps of this pathway with various enzymes and metabolites that regulate glycolysis.

Increased concentrations of fructose 2,6-bisphosphate contribute to the Warburg effect in phosphatase and tensin homolog (PTEN)-deficient cells

Unlike normal differentiated cells, tumor cells metabolize glucose via glycolysis under aerobic conditions, a hallmark of cancer known as the Warburg effect. Cells lacking the commonly mutated tumor suppressor PTEN exhibit a glycolytic phenotype reminiscent of the Warburg effect. This has been traditionally attributed to the hyperactivation of PI3K/Akt signaling that results from PTEN loss. Here, we propose a novel mechanism whereby the loss of PTEN negatively affects the activity of the E3 ligase APC/C-Cdh1, resulting in the stabilization of the enzyme PFKFB3 and increased synthesis of its product fructose 2,6-bisphosphate (F2,6P2). We discovered that when compared with wild-type cells, PTEN knock-out mouse embryonic fibroblasts (PTEN KO MEF) have 2-3-fold higher concentrations of F2,6P2, the most potent allosteric activator of the glycolytic enzyme phosphofructokinase-1 (PFK-1). Reintroduction of either wild-type or phosphatase mutant PTEN in the PTEN KO cells effectively lowers F2,6P2 to the wild-type levels and reduces their lactate production. PTEN KO cells were found to have high protein levels of PFKFB3, which directly contribute to the increased concentrations of F2,6P2. PTEN enhances interaction between PFKFB3 and Cdh1, and overexpression of Cdh1 down-regulates the PFKFB3 protein level in wild-type, but not in PTEN-deficient cells. Importantly, we found that the degradation of endogenous PFKFB3 in PTEN KO cells occurs at a slower rate than in wild-type cells. Our results suggest an important role for F2,6P2 in the metabolic reprogramming of PTEN-deficient cells that has important consequences for cell proliferation.

[Exercise-induced muscle pain due to phosphofrutokinase deficiency: Diagnostic contribution of metabolic explorations (exercise tests, 31P-nuclear magnetic resonance spectroscopy)]

INTRODUCTION

Muscle phosphofructokinase deficiency, the seventh member of the glycogen storage diseases family, is also called Tarui's disease (GSD VII).

METHODS

We studied two patients in two unrelated families with Tarui's disease, analyzing clinical features, CK level, EMG, muscle biopsy findings and molecular genetics features. Metabolic muscle explorations (forearm ischemic exercise test [FIET]; bicycle ergometer exercise test [EE]; 31P-nuclear magnetic resonance spectroscopy of calf muscle [31P-NMR-S]) are performed as appropriate.

RESULTS

Two patients, a 47-year-old man and a 38-year-old woman, complained of exercise-induced fatigue since childhood. The neurological examination was normal or showed light weakness. Laboratory studies showed increased CPK, serum uric acid and reticulocyte count without anemia. There was no increase in the blood lactate level during the FIET or the EE although there was a light increase in the respiratory exchange ratio during the EE. 31P-NMR-S revealed no intracellular acidification or accumulated intermediates such as phosphorylated monoesters (PME) known to be pathognomic for GSD VII. Two new mutations were identified.

DISCUSSION

FIET and EE were non-contributive to diagnosis, but 31P-NMR provided a characteristic spectra of Tarui's disease, in agreement with phosphofructokinase activity level in erythrocytes. Muscle biopsy does not always provide useful information for diagnosis. In these two cases, genetic studies failed to establish a genotype-phenotype correlation.

CONCLUSION

The search for phosphofructokinase deficiency should be continued throughout life in adults experiencing fatigability or weakness because of the severe disability for daily life activities caused by the late onset form.