Serotonin stimulates mouse skeletal muscle 6-phosphofructo-1-kinase through tyrosine-phosphorylation of the enzyme altering its intracellular localization

Quantitative phosphoproteomic analysis of chicken DF-1 cells infected with Eimeria tenella, using tandem mass tag (TMT) and parallel reaction monitoring (PRM) mass spectrometry

Eimeria tenella is an obligate intracellular parasite which causes great harm to the poultry breeding industry. Protein phosphorylation plays a vital role in host cell-E. tenella interactions. However, no comprehensive phosphoproteomic analyses of host cells at various phases of E. tenella infection have been published. In this study, quantitative phosphoproteomic analysis of chicken embryo DF-1 fibroblasts that were uninfected (UI) or infected with E. tenella for 6 h (PI6, the early invasion phase) or 36 h (PI36, the trophozoite development phase) was conducted. A total of 10,122 phosphopeptides matched to 3,398 host cell phosphoproteins were identified and 13,437 phosphorylation sites were identified. Of these, 491, 1,253, and 275 differentially expressed phosphorylated proteins were identified in the PI6/UI, PI36/UI, and PI36/PI6 comparisons, respectively. KEGG pathway enrichment analysis showed that E. tenella modulated host cell processes through phosphorylation, including focal adhesion, regulation of the actin cytoskeleton, and FoxO signaling to support its early invasion phase, and modulating adherens junctions and the ErbB signaling pathway to favor its trophozoite development. These results enrich the data on the interaction between E. tenella and host cells and facilitate a better understanding of the molecular mechanisms underlying host-parasite relationships.

Ameliorating the impairment of glucose utilization in a high-fat diet-induced obesity model through the consumption of Tucum-do-Cerrado (Bactris Setosa Mart.)

INTRODUCTION

We evaluated the effect of Tucum-do-Cerrado on glucose metabolism homeostasis and its relationship with redox-inflammatory responses in a high-fat (HF) diet-induced obesity model.

RESULTS

The HF diet increased energy intake, feed efficiency, body weight, muscle and hepatic glycogen, insulin, homeostatic model assessment of insulin resistance (HOMA IR) and beta (β)-cell function, and gut catalase (CAT) activity, and decreased food intake, hepatic glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), and superoxide dismutase (SOD) activities, hepatic phosphoenolpyruvate carboxykinase 1 (Pck1), and intestinal solute carrier family 5 member 1 (Slc5a1) mRNA levels compared with the control diet. However, the HF diet with Tucum-do-Cerrado decreased hepatic glycogen, and increased hepatic GR activity, hepatic Slc2a2 mRNA levels and serum Tnfa compared with the HF diet. Tucum-do-Cerrado decreased muscle glycogen, intestinal CAT and GPX activities, muscle PFK-1 and HK activities, and increased hepatic protein (CARB) and intestinal lipid (MDA) oxidation, hepatic GST activity, serum antioxidant potential, hepatic phosphofructokinase-1 (PFK-1) activity, intestinal solute carrier family 2 member 2 (Slc2a2), tumor necrosis factor (Tnf), interleukin-1 beta (Il1b), muscle protein kinase AMP-activated alpha 1 (Prkaa1), solute carrier family 2 member 2 (Slc2a2) mRNA levels, and serum interleukin-6 (IL-6) levels, regardless of diet type.

CONCLUSION

Tucum-do-Cerrado consumption may ameliorate impaired glucose utilization in a HF diet-induced obesity model by increasing liver and muscle glucose uptake and oxidation. These data suggest that Tucum-do-Cerrado consumption improves muscle glucose oxidation in non-obese and obese rats. This response may be related to the improvement in the total antioxidant capacity of rats.

Gut-derived serotonin and its emerging roles in immune function, inflammation, metabolism and the gut-brain axis

PURPOSE OF REVIEW

To shed light on the recently uncovered diverse role of serotonin (5-hydroxytryptamine; 5-HT) in the regulation of immune functions, inflammation, metabolism, and gut-brain axis.

RECENT FINDINGS

Peripheral 5-HT which accounts for approximately 95% of the total is largely synthesized in the gut by enterochromaffin cells. Enterochromaffin cells release 5-HT in response to various stimuli including microbial products. Released 5-HT influences secretomotor, sensory and immune functions as well as inflammatory processes in the gut. 5-HT released from enterochromaffin cells enters circulation and is taken up and concentrated in platelets. 5-HT released from the activated platelets interacts with different organs to alter their metabolic activity. 5-HT also serves as a link in the gut-brain axis.

SUMMARY

Emerging evidence regarding the role of peripheral 5-HT in the regulation of various physiological and pathophysiological conditions opens up new targets for researchers to explore and for clinicians to treat and manage different diseases associated with the altered 5-HT signalling.

Inhibiting serotonin signaling through HTR2B in visceral adipose tissue improves obesity-related insulin resistance

Insulin resistance is a cornerstone of obesity-related complications such as type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease. A high rate of lipolysis is known to be associated with insulin resistance, and inhibiting adipose tissue lipolysis improves obesity-related insulin resistance. Here, we demonstrate that inhibition of serotonin (5-hydroxytryptamine [5-HT]) signaling through serotonin receptor 2B (HTR2B) in adipose tissues ameliorates insulin resistance by reducing lipolysis in visceral adipocytes. Chronic high-fat diet (HFD) feeding increased Htr2b expression in epididymal white adipose tissue, resulting in increased HTR2B signaling in visceral white adipose tissue. Moreover, HTR2B expression in white adipose tissue was increased in obese humans and positively correlated with metabolic parameters. We further found that adipocyte-specific Htr2b-knockout mice are resistant to HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Enhanced 5-HT signaling through HTR2B directly activated lipolysis through phosphorylation of hormone-sensitive lipase in visceral adipocytes. Moreover, treatment with a selective HTR2B antagonist attenuated HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Thus, adipose HTR2B signaling could be a potential therapeutic target for treatment of obesity-related insulin resistance.

Gut microbiota and its metabolites: Bridge of dietary nutrients and obesity-related diseases

While the incidence of obesity keeps increasing in both adults and children worldwide, obesity and its complications remain major threatens to human health. Over the past decades, accumulating evidence has demonstrated the importance of microorganisms and their metabolites in the pathogenesis of obesity and related diseases. There also is a significant body of evidence validating the efficacy of microbial based therapies for managing various diseases. In this review, we collected the key information pertinent to obesity-related bacteria, fermentation substrates and major metabolites generated by studies involving humans and/or mice. We then briefly described the possible molecular mechanisms by which microorganisms cause or inhibit obesity with a focus on microbial metabolites. Lastly, we summarized the advantages and disadvantages of the utilization of probiotics, plant extracts, and exercise in controlling obesity. We speculated that new targets and combined approaches (e.g. diet combined with exercise) could lead to more precise prevention and/or alleviation of obesity in future clinical research implications.

The effect of coffee consumption on glucose homeostasis and redox-inflammatory responses in high-fat diet-induced obese rats

Coffee effects on glucose homeostasis in obesity remain controversial. We investigated whether coffee mitigates the negative effects on glucose metabolism induced by a high-fat diet and the interrelationships with redox-inflammatory responses. Rats were treated with: control (CT-); coffee (CT+) 3.9 g of freeze-dried coffee/kg of diet; high-fat (HF-); or high-fat + coffee 3.9 g of freeze-dried coffee/kg of diet (HF+) diet. The high-fat diet increased weight gain, feed efficiency, HOMA β, muscle and hepatic glycogen, intestinal CAT and SOD activity, hepatic protein (CARB) and lipid oxidation (MDA), muscle Prkaa1 mRNA and IL6 levels, and decreased food intake, hepatic GR, GPX and SOD activities, intestinal CARB, intestinal Slc2a2 and Slc5a1 and hepatic Prkaa1 and Prkaa2 mRNA levels, hepatic glucose-6-phosphatase and muscle hexokinase (HK) activities, compared to the control diet. The high-fat diet with coffee increased hepatic GST activity and TNF and decreased IL6 and intestinal glucosidase activity compared with the high-fat diet. The coffee diet increased muscle glycogen, hepatic CARB and PEPCK activity, and decreased hepatic GR and SOD activities and intestinal CARB, compared with the control diet. Coffee increased insulin levels, HOMA IR/β, FRAP, muscle Prkaa1 mRNA levels and hepatic and muscle phosphofructokinase-1, and it decreased intestinal CAT, hepatic Slc2a2 mRNA levels and muscle HK activity, regardless of the diet type. In conclusion, chronic coffee consumption improves antioxidant and anti-inflammatory responses, but does not ameliorate glucose homeostasis in a high-fat diet-induced obesity model. In addition, coffee consumption increases insulin secretion and promotes muscle glycogen synthesis in rats maintained on a control diet.

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.

Serotonin activates glycolysis and mitochondria biogenesis in human breast cancer cells through activation of the Jak1/STAT3/ERK1/2 and adenylate cyclase/PKA, respectively

BACKGROUND

Although produced by several types of tumours, the role of serotonin on cancer biology is yet to be understood.

METHODS

The effects of serotonin (5-HT) on human breast cancer cells proliferation, signalling pathways and metabolic profile were evaluated by cytometry, western blotting, qPCR, enzymology and confocal microscopy.

RESULTS

Our results revealed that incubation of MCF-7 cells with 10 µM 5-HT increased cell growth rate by 28%, an effect that was prevented by the 5-HTR2A/C antagonist, ketanserin. Conversely, increasing concentrations of 5-HT promoted glucose consumption and lactate production by MCF-7 cells. We also showed that increased glucose metabolism is provoked by the upregulation of pyruvate kinase M2 (PKM2) isoform through 5-HTR2A/C-triggered activation of Jak1/STAT3 and ERK1/2 subcellular pathways. However, we noticed a decrease in the rate of produced lactate per consumed glucose as a function of the hormone concentration, suggesting a disruption of the Warburg effect. The latter effect is due to 5-HTR2A/C-dependent mitochondrial biogenesis and metabolism, which is triggered by adenylyl cyclase/PKA, enhancing the oxidation of lactate within these cells.

CONCLUSIONS

We showed that serotonin, through 5-HTR2A/C, interferes with breast cancer cells proliferation and metabolism by triggering two distinct signalling pathways: Jak1/STAT3 that boosts glycolysis through upregulation of PKM2, and adenylyl cyclase/PKA that enhances mitochondrial biogenesis.

Emerging Roles for Serotonin in Regulating Metabolism: New Implications for an Ancient Molecule

Serotonin is a phylogenetically ancient biogenic amine that has played an integral role in maintaining energy homeostasis for billions of years. In mammals, serotonin produced within the central nervous system regulates behavior, suppresses appetite, and promotes energy expenditure by increasing sympathetic drive to brown adipose tissue. In addition to these central circuits, emerging evidence also suggests an important role for peripheral serotonin as a factor that enhances nutrient absorption and storage. Specifically, glucose and fatty acids stimulate the release of serotonin from the duodenum, promoting gut peristalsis and nutrient absorption. Serotonin also enters the bloodstream and interacts with multiple organs, priming the body for energy storage by promoting insulin secretion and de novo lipogenesis in the liver and white adipose tissue, while reducing lipolysis and the metabolic activity of brown and beige adipose tissue. Collectively, peripheral serotonin acts as an endocrine factor to promote the efficient storage of energy by upregulating lipid anabolism. Pharmacological inhibition of serotonin synthesis or signaling in key metabolic tissues are potential drug targets for obesity, type 2 diabetes, and nonalcoholic fatty liver disease (NAFLD).

Integrating strategies of chemistry, biochemistry and metabolomics for characterization of the medication principle of "treating cold/heat syndrome with hot/cold herbs"

ETHNOPHARMACOLOGICAL RELEVANCE

"Treating cold syndrome with hot herbs & treating heat syndrome with cold herbs" is a fundamental medication principle of Chinese medicine. Scientists have been working hard to explore the scientific essence of this medication principle. However, researchers only focused on the herbs or syndrome individually, the intrinsic relationship between the cold/hot herbs and cold/heat syndrome received little attention. Consequently, the medication principle still lacked a scientific explanation.

AIM OF THE STUDY

The aim of present study was to explore the scientific essence involved in the medication principle.

MATERIALS AND METHODS

First, extracts of cold and hot herb_1-7 were analyzed using UPLC-Q-TOF/MS to research the chemical composition. Second, expression of enzymes relating glucose aerobic oxidation and respiratory chain were detected to assess the metabolic state of rats in cold herb, hot herb, cold syndrome and heat syndrome groups. Lastly, metabolomic approach was utilized to screen out biomarkers and related pathways shared between the cold and hot herb groups, the cold and heat syndrome groups, as well as the herb and syndrome groups.

RESULTS

The integrated results of chemistry, biochemistry and metabolomics study indicated that the cold (hot) herbs could remedy heat (cold) syndrome through inhibiting (promoting) arginine and proline metabolism and tryptophan metabolism, and the associated excessive (sluggish) material metabolism, ATP storage and generation in heat (cold) syndrome. The fundamental reason behind the differential efficacies of cold and hot herbs was the chemical composition and different contents of shared components.

CONCLUSIONS

The medication principle was scientifically elucidated from perspective of material and energy metabolism. Moreover, this integrated novel strategy provides a feasible approach for future research of Chinese medicinal herb.

DUSP6 mediates T cell receptor-engaged glycolysis and restrains TFH cell differentiation

Activated T cells undergo metabolic reprogramming and effector-cell differentiation but the factors involved are unclear. Utilizing mice lacking DUSP6 (DUSP6^-/-), we show that this phosphatase regulates T cell receptor (TCR) signaling to influence follicular helper T (T_FH) cell differentiation and T cell metabolism. In vitro, DUSP6^-/- CD4⁺ T_FH cells produced elevated IL-21. In vivo, T_FH cells were increased in DUSP6^-/- mice and in transgenic OTII-DUSP6^-/- mice at steady state. After immunization, DUSP6^-/- and OTII-DUSP6^-/- mice generated more T_FH cells and produced more antigen-specific IgG2 than controls. Activated DUSP6^-/- T cells showed enhanced JNK and p38 phosphorylation but impaired glycolysis. JNK or p38 inhibitors significantly reduced IL-21 production but did not restore glycolysis. TCR-stimulated DUSP6^-/- T cells could not induce phosphofructokinase activity and relied on glucose-independent fueling of mitochondrial respiration. Upon CD28 costimulation, activated DUSP6^-/- T cells did not undergo the metabolic commitment to glycolysis pathway to maintain viability. Unexpectedly, inhibition of fatty acid oxidation drastically lowered IL-21 production in DUSP6^-/- T_FH cells. Our findings suggest that DUSP6 connects TCR signaling to activation-induced metabolic commitment toward glycolysis and restrains T_FH cell differentiation via inhibiting IL-21 production.

The psychoactive drug 25B-NBOMe recapitulates rhabdomyolysis in zebrafish larvae

N-Benzyl-substituted 2C class phenethylamines (NBOMes) are psychoactive designer drugs, with strong hallucinogenic and stimulant effects, even at low doses. The designer drug, 2-(4-bromo-2, 5-dimethoxyphenyl)-N-(2-methoxybenzyl) ethanamine (25B-NBOMe) is considered to be one of the most potent agonists of the serotonin-2A (5-HT_2A) receptor. Recently, we reported the first lethal case of 25B-NBOMe intoxication with severe rhabdomyolysis, concluded by clinical, pathological and toxicological analyses. There are currently no good animal models that closely recapitulate serotonin receptor-dependent rhabdomyolysis. In the present study, we created animal models of rhabdomyolysis using zebrafish larvae to study the pathomechanism of rhabdomyolysis, and demonstrated that 25B-NBOMe can simulate lethal rhabdomyolysis in this animal. Treatment of the larvae with 25B-NBOMe decreased their survival rate, locomotion, altered birefringence of the skeletal muscle and immunostainings for dystroglycan (a myoseptal protein) and myosin heavy chain (a myofibril protein), which were consistent with rhabdomyolysis. This 25B-NBOMe-induced rhabdomyolysis was inhibited by the 5-HT_2A receptor antagonists ritanserin and aripirazole, but not by the 5-HT_1A + 5-HT_1B receptor antagonist propranolol and the 5-HT₃ receptor antagonist granisetron, indicating 5-HT_2A-dependent rhabdomyolysis. The 25B-NBOMe-treated zebrafish is, therefore, a highly useful model of rhabdomyolysis for studying the pathomechanism of rhabdomyolysis as well as for therapeutic drug screening.

Hexokinase and phosphofructokinase activity and intracellular distribution correlate with aggressiveness and invasiveness of human breast carcinoma

Glycolytic enzymes, such as hexokinase and phosphofructokinase, have been reported to be upregulated in many cancer types. Here, we evaluated these two enzymes in 54 breast cancer samples collected from volunteers subjected to mastectomy, and the results were correlated with the prognosis markers commonly used. We found that both enzymes positively correlate with the major markers for invasiveness and aggressiveness. For invasiveness, the enzymes activities increase in parallel to the tumor size. Moreover, we found augmented activities for both enzymes when the samples were extirpated from patients presenting lymph node involvement or occurrence of metastasis. For aggressiveness, we stained the samples for the estrogen and progesterone receptors, HER-2, p53 and Ki-67. The enzyme activities positively correlated with all markers but Ki-67. Finally, we conclude that these enzymes are good markers for breast cancer prognosis.

In vitro and in vivo study of epigallocatechin-3-gallate-induced apoptosis in aerobic glycolytic hepatocellular carcinoma cells involving inhibition of phosphofructokinase activity

Glycolysis, as an altered cancer cell-intrinsic metabolism, is an essential hallmark of cancer. Phosphofructokinase (PFK) is a metabolic sensor in the glycolytic pathway, and restricting the substrate availability for this enzyme has been researched extensively as a target for chemotherapy. In the present study, we investigated that the effects of epigallocatechin-3-gallate (EGCG), an active component of green tea, on inhibiting cell growth and inducing apoptosis by promoting a metabolic shift away from glycolysis in aerobic glycolytic hepatocellular carcinoma (HCC) cells. EGCG modulated the oligomeric structure of PFK, potentially leading to metabolic stress associated apoptosis and suggesting that EGCG acts by directly suppressing PFK activity. A PFK activity inhibitor enhanced the effect, while the allosteric activator reversed EGCG-induced HCC cell death. PFK siRNA knockdown-induced apoptosis was not reversed by the activator. EGCG enhanced the effect of sorafenib on cell growth inhibition in both aerobic glycolytic HCC cells and in a xenograft mouse model. The present study suggests a potential role for EGCG as an adjuvant in cancer therapy, which merits further investigation at the clinical level.

The roles of peripheral serotonin in metabolic homeostasis

Metabolic homeostasis in the organism is assured both by the nervous system and by hormones. Among a plethora of hormones regulating metabolism, serotonin presents a number of unique features. Unlike classical hormones serotonin is produced in different anatomical locations. In brain it acts as a neurotransmitter and in the periphery it can act as a hormone, auto- and/or paracrine factor, or intracellular signaling molecule. Serotonin does not cross the blood-brain barrier; therefore the two major pools of this bioamine remain separated. Although 95% of serotonin is produced in the periphery, its functions have been ignored until recently. Here we review the impact of the peripheral serotonin on the regulation of function of the organs involved in glucose and lipid homeostasis.

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

New potential eukaryotic substrates of the mycobacterial protein tyrosine phosphatase PtpA: hints of a bacterial modulation of macrophage bioenergetics state

The bacterial protein tyrosine phosphatase PtpA is a key virulence factor released by Mycobacterium tuberculosis in the cytosol of infected macrophages. So far only two unrelated macrophage components (VPS33B, GSK3α) have been identified as PtpA substrates. As tyrosine phosphatases are capable of using multiple substrates, we developed an improved methodology to pull down novel PtpA substrates from an enriched P-Y macrophage extract using the mutant PtpA D126A. This methodology reduced non-specific protein interactions allowing the identification of four novel putative PtpA substrates by MALDI-TOF-MS and nano LC-MS: three mitochondrial proteins - the trifunctional enzyme (TFP), the ATP synthase, and the sulfide quinone oxidoreductase - and the cytosolic 6-phosphofructokinase. All these proteins play a relevant role in cell energy metabolism. Using surface plasmon resonance, PtpA was found to bind immunopurified human TFP through its catalytic site since TFP-PtpA association was inhibited by a specific phosphatase inhibitor. Moreover, PtpA wt was capable of dephosphorylating immunopurified human TFP in vitro supporting that TFP may be a bona fide PtpA susbtrate. Overall, these results suggest a novel scenario where PtpA-mediated dephosphorylation may affect pathways involved in cell energy metabolism, particularly the beta oxidation of fatty acids through modulation of TFP activity and/or cell distribution.

Phosphofructokinase: a mediator of glycolytic flux in cancer progression

In view of the current limitations of cancer chemotherapy, there has been resurgent interest in re-visiting glycolysis to determine whether tumors could be killed by energy deprivation rather than solely by strategies to inhibit proliferation. Cancer cells exhibit a uniquely high rate of glucose utilization, converting it into lactate whose export subsequently creates an acidic extracellular environment that is thought to promote invasion and metastasis, in preference to its complete oxidation even in the presence of adequate oxygen supply. Reductive analysis of each step of glycolysis shows that, of the three rate limiting enzymes of the pathway, isoforms of phosphofructokinase may afford the greatest opportunity as targets to deprive cancer cells from essential energy and substrates for macromolecular synthesis for proliferation while allowing normal cells to survive. Strategies discussed include restricting the substrate for this enzyme. While prospects for monotherapy with glycolytic inhibitors are poor, combination therapy may be productive.

The structural and functional coordination of glycolytic enzymes in muscle: evidence of a metabolon?

Metabolism sustains life through enzyme-catalyzed chemical reactions within the cells of all organisms. The coupling of catalytic function to the structural organization of enzymes contributes to the kinetic optimization important to tissue-specific and whole-body function. This coupling is of paramount importance in the role that muscle plays in the success of Animalia. The structure and function of glycolytic enzyme complexes in anaerobic metabolism have long been regarded as a major regulatory element necessary for muscle activity and whole-body homeostasis. While the details of this complex remain to be elucidated through in vivo studies, this review will touch on recent studies that suggest the existence of such a complex and its structure. A potential model for glycolytic complexes and related subcomplexes is introduced.

Fluoxetine prevents dystrophic changes in a zebrafish model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a common and relentlessly progressive muscle disease. Some interventions have been identified that modestly slow progression and prolong survival, but more meaningful therapies are lacking. The goal of this study is to identify new therapeutic pathways for DMD using a zebrafish model of the disease. To accomplish this, we performed a non-biased drug screen in sapje, a zebrafish line with a recessive nonsense mutation in dystrophin. We identified 6 positive hits (out of 640 total drugs tested) by their ability to prevent abnormal birefringence in sapje. Follow-up analyses demonstrated that fluoxetine, a selective serotonin reuptake inhibitor (SSRI), provided the most substantial benefit. Morpholino-based experimentation confirmed that modulation of the serotonin pathway alone can prevent the dystrophic phenotype, and transcriptomic analysis revealed changes in calcium homeostasis as a potential mechanism. In all, we demonstrate that monoamine agonists can prevent disease in a vertebrate model of DMD. Given the safe and widespread use of SSRIs in clinical practice, our study identifies an attractive target pathway for therapy development.

Differential phosphofructokinase-1 isoenzyme patterns associated with glycolytic efficiency in human breast cancer and paracancer tissues

Cancers are characterized by an increasing glycolytic activity, which is called the Warburg effect. Although this phenomenon is well known, the mechanism of the enhanced rate of glycolysis in cancer has not yet been clearly recognized. The present study investigated the glycolytic rate, regulatory enzymatic activities and the expression of phosphofructokinase-1 (PFK-1) in human breast cancer and paracancer tissues. Human breast cancer tissues have an increased degree of glycolytic efficiency and regulatory enzymatic activities, which have been shown in previous studies. However, the present study identified a number of novel observations. The total PFK-1 levels were higher in human breast cancer tissues than in paracancer tissues, and further investigations revealed differential PFK-1 isoenzyme expression patterns between human breast cancer and paracancer tissues. The human breast cancer and paracancer tissues mainly expressed PFK-P and PFK-L isoforms, respectively. Linear-regression analysis showed that, depending on the pathological stage of breast cancer, the expression of PFK-P was significantly positively correlated with the activity of PFK-1. Thus, during the development of human breast cancer, the enhancement of glycolytic activity depends primarily on the conversion of the PFK-1, from PFK-L to PFK-P.

Pharmacometabolomic mapping of early biochemical changes induced by sertraline and placebo

In this study, we characterized early biochemical changes associated with sertraline and placebo administration and changes associated with a reduction in depressive symptoms in patients with major depressive disorder (MDD). MDD patients received sertraline or placebo in a double-blind 4-week trial; baseline, 1 week, and 4 weeks serum samples were profiled using a gas chromatography time of flight mass spectrometry metabolomics platform. Intermediates of TCA and urea cycles, fatty acids and intermediates of lipid biosynthesis, amino acids, sugars and gut-derived metabolites were changed after 1 and 4 weeks of treatment. Some of the changes were common to the sertraline- and placebo-treated groups. Changes after 4 weeks of treatment in both groups were more extensive. Pathway analysis in the sertraline group suggested an effect of drug on ABC and solute transporters, fatty acid receptors and transporters, G signaling molecules and regulation of lipid metabolism. Correlation between biochemical changes and treatment outcomes in the sertraline group suggested a strong association with changes in levels of branched chain amino acids (BCAAs), lower BCAAs levels correlated with better treatment outcomes; pathway analysis in this group revealed that methionine and tyrosine correlated with BCAAs. Lower levels of lactic acid, higher levels of TCA/urea cycle intermediates, and 3-hydroxybutanoic acid correlated with better treatment outcomes in placebo group. Results of this study indicate that biochemical changes induced by drug continue to evolve over 4 weeks of treatment and that might explain partially delayed response. Response to drug and response to placebo share common pathways but some pathways are more affected by drug treatment. BCAAs seem to be implicated in mechanisms of recovery from a depressed state following sertraline treatment.

Evidence of 5-HT components in human sperm: implications for protein tyrosine phosphorylation and the physiology of motility

Serotonin (5-hydroxytryptamine; C(10)H(12)N(2)O (5-HT)) is produced in the CNS and in some cells of peripheral tissues. In the mammalian male reproductive system, both 5-HT and tryptophan hydroxylase (TPH) have been described in Leydig cells of the testis and in principal cells of the caput epididymis. In capacitated hamster sperm, it has been shown that 5-HT promotes the acrosomal reaction. The aim of this work was to explore the existence of components of the serotoninergic system and their relevance in human sperm physiology. We used both immunocytochemistry and western blot to detect serotoninergic markers such as 5-HT, TPH1, MAO(A), 5-HT(1B), 5-HT(3), and 5HT(T); HPLC for TPH enzymatic activity; Computer Assisted Semen Analysis assays to measure sperm motility parameters and pharmacological approaches to show the effect of 5-HT in sperm motility and tyrosine phosphorylation was assessed by western blot. We found the presence of serotoninergic markers (5-HT, TPH1, MAO(A), 5-HT(1B), 5-HT(2A), 5-HT(3), 5-HT(T), and TPH enzymatic activity) in human sperm. In addition, we observed a significant increase in tyrosine phosphorylation and changes in sperm motility after 5-HT treatment. In conclusion, our data demonstrate the existence of components of a serotoninergic system in human sperm and support the notion for a functional role of 5-HT in mammalian sperm physiology, which can be modulated pharmacologically.

Serotonin regulates 6-phosphofructo-1-kinase activity in a PLC-PKC-CaMK II- and Janus kinase-dependent signaling pathway

Serotonin (5-HT) is a hormone that has been implicated in the regulation of many physiological and pathological events. One of the most intriguing properties of this hormone is its ability to up-regulate mitosis. Moreover, 5-HT stimulates glucose uptake and up-regulates PFK activity through the 5-HT(2A) receptor, resulting in the phosphorylation of a tyrosine residue of PFK and the intracellular redistribution of PFK within skeletal muscle. The present study investigated some of the signaling intermediates involved in the effects of 5-HT on 6-phosphofructo-1-kinase (PFK) regulation from skeletal muscle using kinetic assessments, immunoprecipitation, and western blotting assays. Our results demonstrate that 5-HT stimulates PFK from skeletal muscle via phospholipase C (PLC). The activation of PLC in skeletal muscle leads to the recruitment of protein kinase C (PKC) and calmodulin and the stimulation of calmodulin kinase II, which associates with PFK upon 5-HT action. Alternatively, 5-HT loses its ability to up-regulate PFK activity when Janus kinase is inhibited, suggesting that 5-HT is able to control glycolytic flux in the skeletal muscle of mice by recruiting different pathways and controlling PFK activity.

Herpes simplex type 1 activates glycolysis through engagement of the enzyme 6-phosphofructo-1-kinase (PFK-1)

Viruses such as HIV, HCV, Mayaro and HCMV affect cellular metabolic pathways, including glycolysis. Although some studies have suggested that the inhibition of glycolysis affects HSV-1 replication and that HSV-1-infected eyes have increased lactate production, the mechanisms by which HSV-1 induces glycolysis have never been investigated in detail. In this study, we observed an increase in glucose uptake, lactate efflux and ATP content in HSV-1-infected cells. HSV-1 triggered a MOI-dependent increase in the activity of phosphofructokinase-1 (PFK-1), a key rate-limiting enzyme of the glycolytic pathway. After HSV-1 infection, we observed increased PFK-1 expression, which increased PFK-1 total activity, and the phosphorylation of this enzyme at serine residues. HSV-1-induced glycolysis was associated with increased ATP content, and these events were critical for viral replication. In summary, our results suggest that HSV-1 triggers glycolysis through a different mechanism than other herpesviruses, such as HCMV. Thus, this study contributes to a better understanding of HSV-1 pathogenesis and provides insights into novel targets for antiviral therapy.

HIGHLIGHTS

►HSV-1 activates glycolysis by PFK-1 activation. ►In HSV-1-infected cells PFK-1 synthesis is up-regulated and phosphorylated at serine residues. ►PFK-1 knockdown impairs HSV-1 replication. ►HSV-1-mediated glycolysis activation increases ATP content.

Clotrimazole preferentially inhibits human breast cancer cell proliferation, viability and glycolysis

Background

Clotrimazole is an azole derivative with promising anti-cancer effects. This drug interferes with the activity of glycolytic enzymes altering their cellular distribution and inhibiting their activities. The aim of the present study was to analyze the effects of clotrimazole on the growth pattern of breast cancer cells correlating with their metabolic profiles.

Methodology/Principal Findings

Three cell lines derived from human breast tissue (MCF10A, MCF-7 and MDA-MB-231) that present increasingly aggressive profiles were used. Clotrimazole induces a dose-dependent decrease in glucose uptake in all three cell lines, with K_i values of 114.3±11.7, 77.1±7.8 and 37.8±4.2 µM for MCF10A, MCF-7 and MDA-MB-231, respectively. Furthermore, the drug also decreases intracellular ATP content and inhibits the major glycolytic enzymes, hexokinase, phosphofructokinase-1 and pyruvate kinase, especially in the highly metastatic cell line, MDA-MB-231. In this last cell lineage, clotrimazole attenuates the robust migratory response, an effect that is progressively attenuated in MCF-7 and MCF10A, respectively. Moreover, clotrimazole reduces the viability of breast cancer cells, which is more pronounced on MDA-MB-231.

Conclusions/Significance

Clotrimazole presents deleterious effects on two human breast cancer cell lines metabolism, growth and migration, where the most aggressive cell line is more affected by the drug. Moreover, clotrimazole presents little or no effect on a non-tumor human breast cell line. These results suggest, at least for these three cell lines studied, that the more aggressive the cell is the more effective clotrimazole is.

Muscle-type 6-phosphofructo-1-kinase and aldolase associate conferring catalytic advantages for both enzymes

6-Phosphofructo-1-kinase (PFK) and aldolase are two sequential glycolytic enzymes that associate forming heterotetramers containing a dimer of each enzyme. Although free PFK dimers present a negligible activity, once associated to aldolase these dimers are as active as the fully active tetrameric conformation of the enzyme. Here we show that aldolase-associated PFK dimers are not inhibited by clotrimazole, an antifungal azole derivative proposed as an antineoplastic drug due to its inhibitory effects on PFK. In the presence of aldolase, PFK is not modulated by its allosteric activators, ADP and fructose-2,6-bisphosphate, but is still inhibited by citrate and lactate. The association between the two enzymes also results on the twofold stimulation of aldolase maximal velocity and affinity for its substrate. These results suggest that the association between PFK and aldolase confers catalytic advantage for both enzymes and may contribute to the channeling of the glycolytic metabolism.

Clotrimazole disrupts glycolysis in human breast cancer without affecting non-tumoral tissues

Human breast cancer tissues, as well as normal tissues from the same patients, were treated with clotrimazole (CTZ) and have their capacities for glucose consumption and lactate production evaluated. This treatment strongly decreased the lactate production rate by tumor tissues (85% inhibition) without affecting the other measurements made, i.e. lactate production by control tissues or glucose consumption by both, control and tumor tissues. This result directly correlates with the inhibition promoted by CTZ on the activity of the major regulatory glycolytic enzyme 6-phosphofructo-1-kinase (PFK) that was observed in tumor tissues (84% inhibition) but not in control tissues. Fractionation of the tissues revealed that this inhibition does not occur in the soluble fraction of the enzyme, but is exclusive of a particulate fraction. It has been previously shown that the particulate fraction of PFK activity in tumors is associated to actin filaments (f-actin). Thus, we investigated whether CTZ would affect the association between PFK and f-actin and we found that the drug directly induces the dissociation of the two proteins in the same extent that it inhibits lactate production, total PFK activity and the particulate PFK activity. We concluded that CTZ disrupts glycolysis on human breast tumor tissues, inhibiting PFK activity by dissociating the enzyme from f-actin.

Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism

Phosphofructokinase (PFK) is a major regulatory glycolytic enzyme and is considered to be the pacemaker of glycolysis. This enzyme presents a puzzling regulatory mechanism that is modulated by a large variety of metabolites, drugs, and intracellular proteins. To date, the mammalian enzyme structure has not yet been resolved. However, it is known that PFK undergoes an intricate oligomerization process, shifting among monomers, dimers, tetramers, and more complex oligomeric structures. The equilibrium between PFK dimers and tetramers is directly correlated with the enzyme regulation, because the dimer exhibits very low catalytic activity, whereas the tetramer is fully active. Several PFK ligands modulate the enzyme, favoring the formation of its dimers or tetramers. The present review integrates recent findings regarding the regulatory aspects of muscle type PFK and discusses their relation to the control of metabolism.

Glucuronoxylomannan from Cryptococcus neoformans down-regulates the enzyme 6-phosphofructo-1-kinase of macrophages

The encapsulated yeast Cryptococcus neoformans is the causative agent of cryptococosis, an opportunistic life-threatening infection. C. neoformans is coated by a polysaccharide capsule mainly composed of glucuronoxylomannan (GXM). GXM is considered a key virulence factor of this pathogen. The present work aimed at evaluating the effects of GXM on the key glycolytic enzyme, 6-phosphofructo-1-kinase (PFK). GXM inhibited PFK activity in cultured murine macrophages in both dose- and time-dependent manners, which occurred in parallel to cell viability decrease. The polysaccharide also inhibited purified PFK, promoting a decrease on the enzyme affinity for its substrates. In macrophages GXM and PFK partially co-localized, suggesting that internalized polysaccharide directly may interact with this enzyme. The mechanism of PFK inhibition involved dissociation of tetramers into weakly active dimers, as revealed by fluorescence spectroscopy. Allosteric modulators of the enzyme able to stabilize its tetrameric conformation attenuated the inhibition promoted by GXM. Altogether, our results suggest that the mechanism of GXM-induced cell death involves the inhibition of the glycolytic flux.

Lactate downregulates the glycolytic enzymes hexokinase and phosphofructokinase in diverse tissues from mice

We examined the effects of lactate on the enzymatic activity of hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK) in various mouse tissues. Our results showed that lactate inhibited PFK activity in all the analyzed tissues. This inhibitory effect was observed in skeletal muscle even in the presence of insulin. Lactate directly inhibited the phosphorylation of PFK tyrosine residues in skeletal muscle, an important mechanism of the enzyme activation. Moreover, lactate indirectly inhibited HK activity, which resulted from its cellular redistribution, here attributed to alterations of HK structure. PK activity was not affected by lactate. The activity of HK and PFK is directly related to glucose metabolism. Thus, it is conceivable that lactate exposure can induce inhibition of glucose consumption in tissues.

Differential expression of phosphofructokinase-1 isoforms correlates with the glycolytic efficiency of breast cancer cells

Cancer cells are characterized by increased aerobic glycolysis, which correlates with a negative prognosis. Although this correlation is well known, the mechanism of the elevated rate of glycolysis in cancer and the role of glycolytic enzymes have yet to be determined. The present work aims to evaluate the activity of the major enzymes that regulate glycolysis in breast cancer cell lines of varying aggressiveness. MCF10A, MCF-7 and MDA-mb-231 are human breast-derived cell lines with non-tumorigenic, tumorigenic and metastatic profiles, respectively. These cell lines have increasing degrees of glycolytic efficiency, i.e., lactate produced per glucose consumed, corresponding to their metastatic potential. Although, there are no differences in phosphofructokinase (PFK) or pyruvate kinase (PK) activities, the activity of hexokinase (HK) activity is higher in both tumorigenic cell lines compared to MCF10A cells. No difference in HK activity is observed between MCF-7 and MDA-mb-231 cells, suggesting that the difference in their glycolytic efficiency could not be attributed to this enzyme. However, we find that expression of the PFK-L isoform directly and strongly correlates with aggressiveness and glycolytic efficiency in these cell lines. Thus, we conclude that glycolytic efficiency, which is important for the survival of cancer cells, depends primarily on the preferential expression of PFK-L over the M and P isoforms.

Clotrimazole potentiates the inhibitory effects of ATP on the key glycolytic enzyme 6-phosphofructo-1-kinase

Clotrimazole (CTZ) has been proposed as a potential anti-neoplastic agent, which inhibits glucose metabolism. The present work aimed to evaluate the effects of CTZ on the kinetic mechanism of 6-phosphofructo-1-kinase (PFK). We show that CTZ promotes a dose-dependent inhibition of PFK, presenting a K(i) of 28 +/- 2 microM. Inhibition occurs through the dissociation of the enzyme tetramers, as demonstrated through fluorescence spectroscopy and gel filtration chromatography. Moreover, the affinities of the enzyme for ATP and fructose-6-phosphate are reduced 50% and 30%, respectively. Furthermore, the affinity of PFK for ATP at the inhibitory site becomes 2-fold higher. Altogether, the results presented here suggest that PFK inhibition by CTZ involves a decrease in the affinity of PFK for its substrates at the catalytic site with the concomitant potentiation of the inhibitory properties of ATP.

Calmodulin upregulates skeletal muscle 6-phosphofructo-1-kinase reversing the inhibitory effects of allosteric modulators

6-phosphofructo-1-kinase (PFK) is a calmodulin (CaM)-binding protein that plays a key role on the regulation of glycolysis. Each PFK monomer binds two CaM molecules inducing the dissociation of the active tetrameric conformation of the enzyme into dimers, thus inhibiting it. Recently, we have reported that the binding of one CaM per PFK monomer promotes the dimerization of the enzyme although maintaining its full catalytic activity. The present work aims to understand the regulatory role of these active PFK dimers induced by CaM. We show that the inhibition of PFK activity by ATP (>1 mM) is abolished in the presence of CaM. CaM decreases the affinity of PFK for its substrates, fructose-6-phophate and ATP. Moreover, CaM activates PFK in the presence of citrate and lactate, two inhibitory metabolites that induce the dimerization of PFK tetramers, as well as potentiate the stimulatory action of ADP and fructose-2,6-bisphosphate. Under all the conditions tested CaM induces the formation of PFK dimers, supporting that these CaM-bound dimers are active and less susceptible to inhibition by allosteric ligands. In the end, we suggest that CaM binding to PFK, which is stimulated by Ca(2+), represents an important way to increase the glycolytic pathway in cells.

ATP and fructose-2,6-bisphosphate regulate skeletal muscle 6-phosphofructo-1-kinase by altering its quaternary structure

Recently, it has been demonstrated that fructose-2,6-bisphosphate (F2,6BP) protects skeletal muscle 6-phosphofructo-1-kinase (PFK) from thermal inactivation (50 degrees C) and against the deleterious effects of guanidinium hydrochloride (GdmCl). On the other hand, ATP, when added at its inhibitory concentrations, that is, >1 mM, enhanced either the thermal- or GdmCl-induced inactivation of PFK. Moreover, we concluded that these phenomena were probably due to the stabilization of PFK tetrameric structure by F2,6BP, and the dissociation of this structure into dimers induced by ATP. Aimed at elucidating the effects of F2,6BP and ATP on PFK at the structural and functional levels, the present work correlates the effects of these metabolites on the equilibrium between PFK dimers and tetramers to the regulation promoted on the enzyme catalytic activity. We show that ATP present a dual effect on PFK structure, favoring the formation of tetramer at stimulatory concentrations (up to 1 mM), and dissociating tetramers into dimers at inhibitory concentrations (>1 mM). Furthermore, F2,6BP counteracted this later ATP effect at either the structural or catalytic levels. Additionally, the effects of both F2,6BP or ATP on the equilibrium between PFK tetramers and dimers and on the enzyme activity presented a striking parallelism. Therefore, we concluded that modulation of PFK activity by ATP and F2,6BP is due to the effects of these ligands on PFK quaternary structure, altering the oligomeric equilibrium between PFK tetramers and dimers.