Expression Of Pyruvate Kinase Research Articles

Effects of small interfering RNA-mediated hepatic glucagon receptor inhibition on lipid metabolism in db/db mice

Hepatic glucose overproduction is a major characteristic of type 2 diabetes. Because glucagon is a key regulator for glucose homeostasis, antagonizing the glucagon receptor (GCGR) is a possible therapeutic strategy for the treatment of diabetes mellitus. To study the effect of hepatic GCGR inhibition on the regulation of lipid metabolism, we generated siRNA-mediated GCGR knockdown (si-GCGR) in the db/db mouse. The hepatic knockdown of GCGR markedly reduced plasma glucose levels; however, total plasma cholesterol was increased. The detailed lipid analysis showed an increase in the LDL fraction, and no change in VLDL HDL fractions. Further studies showed that the increase in LDL was the result of over-expression of hepatic lipogenic genes and elevated de novo lipid synthesis. Inhibition of hepatic glucagon signaling via siRNA-mediated GCGR knockdown had an effect on both glucose and lipid metabolism in db/db mice.

PKM2 Isoform-Specific Deletion Reveals a Differential Requirement for Pyruvate Kinase in Tumor Cells

The pyruvate kinase M2 isoform (PKM2) is expressed in cancer and plays a role in regulating anabolic metabolism. To determine whether PKM2 is required for tumor formation or growth, we generated mice with a conditional allele that abolishes PKM2 expression without disrupting PKM1 expression. PKM2 deletion accelerated mammary tumor formation in a Brca1-loss-driven model of breast cancer. PKM2 null tumors displayed heterogeneous PKM1 expression, with PKM1 found in nonproliferating tumor cells and no detectable pyruvate kinase expression in proliferating cells. This suggests that PKM2 is not necessary for tumor cell proliferation and implies that the inactive state of PKM2 is associated with the proliferating cell population within tumors, whereas nonproliferating tumor cells require active pyruvate kinase. Consistent with these findings, variable PKM2 expression and heterozygous PKM2 mutations are found in human tumors. These data suggest that regulation of PKM2 activity supports the different metabolic requirements of proliferating and nonproliferating tumor cells.

Molecular cloning, expression and activity of pyruvate kinase in grass carp Ctenopharyngodon idella: Effects of dietary carbohydrate level

The R/L type pyruvate kinase (PKLR) gene was cloned from liver of grass carp (Ctenopharyngodon idella) by degenerate oligonucleotide primed PCR, including a complete open reading frame (ORF) of 1617bp. Homological protein analysis showed that the PKLR in grass carp shared a high degree of sequence identity with other known PK sequences. In addition, tissue distribution analysis showed that the highest expression of the PKLR was detected in liver. Then triplicate groups of grass carp (9 tanks) were fed twice daily to satiation with 91.8, 192.9, and 402.6gkg−1 carbohydrate diets for 8weeks, respectively. Dietary 402.6gkg−1 carbohydrate decreased growth performance, feed intake and feed utilization. With increasing dietary carbohydrates, the hepatic PK activity and mRNA expression of grass carp were up-regulated significantly. The results indicated that the PKLR play a modulation role in the adaptation of hepatic glycolysis to dietary high carbohydrates in grass carp.

ADIPONECTIN REGULATION IN TYPE 2 DIABETIC RATS: EFFECTS OF INSULIN, METFORMIN AND DEXAMETHASONE

Adiponectin is a protein synthesized from adipose t issue, increases peripheral glucose utilization in liver and skeletal muscle. Adiponectin expression and sec retion are decreased during obesity and insulin resistance. In this study, the effect of insulin, m etformin and dexamethasone on serum lipid profiles was examined in Type 2 Diabetic (T2D) rats. T2D was induced by feeding rats a high fat diet for 4 weeks plus medium dose of Streptozotocin (STZ, 35 mk kg -1 BW). Adiponectin, adiponectin receptors (AdipoR-1 and AdipoR-2), leptin, Peroxisome Prolifrator Activated Receptor gamma (PPAR-γ), Hormone Sensitive Lipase (HSL), Pyruvate Kinase (PK), enolase and Glucose Trasporter-2 (GLUT-2) expression in epididymal adipose and liver tissue w ere examined using RT-PCR. Results showed that metformin improved insulin resistance by normalizin g serum lipid profiles in diabetic rats, while dexamethasone did not alter it. Metformin up-regula ted adiponectin, AdipoR-1 and AdipoR-2 expression, while insulin and dexamethasone down-regulated them. Leptin expression was decreased while PPAR γ, HSL, PK, enolase and GLUT-2 expression was increased by metformin administration. Dexamethasone failed to improve insulin resistance in T2D rats. I n conclusion, metformin ameliorates T2D through controlling adiponectin expression and its conseque nt genes of lipids and glucose metabolism.

Coagulanolide modulates hepatic glucose metabolism in C57BL/KsJ-db/dbmice

Increased hepatic glucose output is one of the major causes of fasting hyperglycemia in diabetic patients. In this study, we investigated the mechanism of action of coagulanolide on hepatic glucose, regulating enzymes in type 2 diabetic C57BL/KsJ-db/db (db/db) mice. Coagulanolide is an active component of Withania coagulans fruit. Oral administration of coagulanolide for 3 weeks decreases fasting blood glucose and plasma insulin significantly, and it improves glucose tolerance in the db/db mice group. The enzyme activity and protein expression of glucokinase and pyruvate kinase was significantly enhanced in coagulanolide-treated db/db group when compared with untreated one. On the other hand, activities and protein expression of fructose-1,6-bisphosphatase, glucose 6-phosphatase, phosphoenolpyruvate carboxykinase, and glycogen phosphorylase enzymes were significantly lowered in treated group. The treatment with coagulanolide also normalizes the concentrations of plasma cholesterol, triglyceride, free fatty acid, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol in the db/db mice. These findings suggested that the coagulanolide is useful in the control of fasting hyperglycemia in type 2 diabetes by regulating the production of hepatic glucose.

Changes in the Contents of Metabolites and Enzyme Activities in Rice Plants Responding to Rhizoctonia solani Kuhn Infection: Activation of Glycolysis and Connection to Phenylpropanoid Pathway

Rhizoctonia solani Kuhn causes sheath blight disease in rice, and genetic resistance against it is the most desirable characteristic. Current improvement efforts are based on analysis of polygenic quantitative trait loci (QTLs), but interpretation is limited by the lack of information on the changes in metabolic pathways. Our previous studies linked activation of the glycolytic pathway to enhanced generation of lignin in the phenylpropanoid pathway. The current studies investigated the regulation of glycolysis by examining the time course of changes in enzymatic activities and metabolite contents. The results showed that the activities of all glycolytic enzymes as well as fructose-6-phosphate (F-6-P), fructose-1,6-bisphosphate (F-1,6-P(2)), dihydroxyacetone phosphate (DHAP), glyceraldehyde-3-phosphate (GAP), 3-phosphoglycerate (3-PG), phosphoenolpyruvate (PEP) and pyruvate contents increased. These results combined with our previous findings that the expression of phosphoglucomutase (PGM), triosephosphate isomerase (TPI), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), enolase and pyruvate kinase (PK) increased after infection suggested that the additional establishment of glycolysis in the cytosol compartment occurred after infection. Further evidence for this was our recent findings that the increase in expression of the 6-phosphofructokinase (PFK) plastid isozyme Os06g05860 was accompanied by an increase in expression of three cytosolic PFK isozymes, i.e. Os01g09570, Os01g53680 and Os04g39420, as well as pyrophosphate-dependent phosphofrucokinase (PFP) isozymes Os08g25720 (α-subunit) and Os06g13810 (β-subunit) in infected rice plants of the resistant line. The results also showed that the reactions catalysed by PFK/PFP, aldolase, GAPDH + phosphoglycerate kinase (PGK) and PK in leaf sheaths of R. solani-infected rice plants were non-equilibrium reactions in vivo. This study showed that PGM, phosphoglucose isomerase (PGI), TPI and phosphoglycerate mutase (PGmu) + enolase could be regulated through coarse control whereas, PFK/PFP, aldolase, GAPDH + PGK and PK could be regulated through coarse and fine controls simultaneously.

Overexpression of the M2 isoform of pyruvate kinase is an adverse prognostic factor for signet ring cell gastric cancer

To investigate M2 isoform of pyruvate kinase (PKM2) expression in gastric cancers and evaluate its potential as a prognostic biomarker and an anticancer target. All tissue samples were derived from gastric cancer patients underwent curative gastrectomy as a primary treatment. Clinical and pathological information were obtained from the medical records. Gene expression microarray data from 60 cancer and 19 non-cancer gastric tissues were analyzed to evaluate the expression level of PKM2 mRNA. Tissue microarrays were constructed from 368 gastric cancer patients. Immunohistochemistry was used to measure PKM2 expression and PKM2 positivity of cancer was determined by proportion of PKM2-positive tumor cells and staining intensity. Association between PKM2 expression and the clinicopathological factors was evaluated and the correlation between PKM2 and cancer prognosis was evaluated. PKM2 mRNA levels were increased more than 2-fold in primary gastric cancers compared to adjacent normal tissues from the same patients (log transformed expression level: 7.6 ± 0.65 vs 6.3 ± 0.51, P < 0.001). Moreover, differentiated type cancers had significantly higher PKM2 mRNA compared to undifferentiated type cancers (log transformed expression level: 7.8 ± 0.70 vs 6.7 ± 0.71, P < 0.001). PKM2 protein was mainly localized in the cytoplasm of primary cancer cells and detected in 144 of 368 (39.1%) human gastric cancer cases. PKM2 expression was not related with stage (P = 0.811), but strongly correlated with gastric cancer differentiation (P < 0.001). Differentiated type cancers expressed more PKM2 protein than did the undifferentiated ones. Well differentiated adenocarcinoma showed 63.6% PKM2-positive cells; in contrast, signet-ring cell cancers showed only 17.7% PKM2-positive cells. Importantly, PKM2 expression was correlated with shorter overall survival (P < 0.05) independent of stage only in signet-ring cell cancers. PKM2 expression might be an adverse prognostic factor for signet-ring cell carcinomas. Its function and potential as a prognostic marker should be further verified in gastric cancer.

Pyruvate kinase expression (PKM1 and PKM2) in cancer-associated fibroblasts drives stromal nutrient production and tumor growth

We have previously demonstrated that enhanced aerobic glycolysis and/or autophagy in the tumor stroma supports epithelial cancer cell growth and aggressive behavior, via the secretion of high-energy metabolites. These nutrients include lactate and ketones, as well as chemical building blocks, such as amino acids (glutamine) and nucleotides. Lactate and ketones serve as fuel for cancer cell oxidative metabolism, and building blocks sustain the anabolic needs of rapidly proliferating cancer cells. We have termed these novel concepts the “Reverse Warburg Effect,” and the “Autophagic Tumor Stroma Model of Cancer Metabolism.” We have also identified a loss of stromal caveolin-1 (Cav-1) as a marker of stromal glycolysis and autophagy. The aim of the current study was to provide genetic evidence that enhanced glycolysis in stromal cells favors tumorigenesis. To this end, normal human fibroblasts were genetically-engineered to express the two isoforms of pyruvate kinase M (PKM1 and PKM2), a key enzyme in the glycolytic pathway. In a xenograft model, fibroblasts expressing PKM1 or PKM2 greatly promoted the growth of co-injected MDA-MB-231 breast cancer cells, without an increase in tumor angiogenesis. Interestingly, PKM1 and PKM2 promoted tumorigenesis by different mechanism(s). Expression of PKM1 enhanced the glycolytic power of stromal cells, with increased output of lactate. Analysis of tumor xenografts demonstrated that PKM1 fibroblasts greatly induced tumor inflammation, as judged by CD45 staining. In contrast, PKM2 did not lead to lactate accumulation, but triggered a “pseudo-starvation” response in stromal cells, with induction of an NFκB-dependent autophagic program, and increased output of the ketone body 3-hydroxy-buryrate. Strikingly, in situ evaluation of Complex IV activity in the tumor xenografts demonstrated that stromal PKM2 expression drives mitochondrial respiration specifically in tumor cells. Finally, immuno-histochemistry analysis of human breast cancer samples lacking stromal Cav-1 revealed PKM1 and PKM2 expression in the tumor stroma. Thus, our data indicate that a subset of human breast cancer patients with a loss of stromal Cav-1 show profound metabolic changes in the tumor microenvironment. As such, this subgroup of patients may benefit therapeutically from potent inhibitors targeting glycolysis, autophagy and/or mitochondrial activity (such as metformin).

The shock of vacuolar PrA on glycolytic flux, oxidative phosphorylation, and cell morphology by industrial Saccharomyces cerevisiae WZ65

Proteinase A (PrA) is one of the most significant vacuolar proteinase in S. cerevisiae, and it plays an important role in S. cerevisiae physiology and metabolism, especially under unfavorable environment. In this study, the differences in pyruvate kinase (PYK) level under fructose-1,6-diphosphate (FDP) induction and ATP synthesis block among SC1 (the wild-type yeast that was industrial Saccharomyces cerevisiae WZ65), SC2 (PEP4 partial deletion) and SC3 (PEP4 complete deletion) were examined. Results showed that the induction caused by FDP clearly increased PYK expression no matter for which strain, but the increasing effect is more significant for SC2 (P < 0.05). The comparative results of intracellular ATP accumulation showed that the induction by FDP may be affected at the presence of PrA. The block experiment of ATP synthesis showed that PYK activities in PEP4-modified strains are lower than that of the wild type, but the intracellular ATP levels in the wild-type one are generally higher than the PEP4-modified strains after rotenone treatment (P < 0.01). This implies that the effect of PrA deficiency on intracellular ATP accumulation was much more pronounced than the effect of rotenone on oxidative phosphorylation. The cell morphology of three strains was comparatively examined by means of transmission electron microscopy (TEM). The PEP4-modified strains possessed more vacuoles, and cell structure were more integrated than the wild-type strain. Current data preliminarily indicated that the deletion of PEP4 gene in industrial S. cerevisiae WZ65 may not only affected PYK expression but also modulated the oxidative phosphorylation flux.

Neuroglial Metabolic Compartmentation Underlying Leptin Deficiency in the Obese ob/ob Mice as Detected by Magnetic Resonance Imaging and Spectroscopy Methods

Manganese-Enhanced Magnetic Resonance Imaging (MEMRI), (1)H and (13)C High-Resolution-Magic Angle Spinning (HR-MAS) Spectroscopy, and genomic approaches were used to compare cerebral activation and neuronal and glial oxidative metabolism in ad libitum fed C57BL6/J leptin-deficient, genetically obese ob/ob mice. T(1)-weighted Magnetic Resonance Images across the hypothalamic Arcuate and the Ventromedial nuclei were acquired kinetically after manganese infusion. Neuroglial compartmentation was investigated in hypothalamic biopsies after intraperitoneal injections of [1-(13)C]glucose or [2-(13)C]acetate. Total RNA was extracted to determine the effects of leptin deficiency in the expression of representative genes coding for regulatory enzymes of hypothalamic energy pathways and glutamatergic neurotransmission. Manganese-Enhanced Magnetic Resonance Imaging revealed enhanced cerebral activation in the hypothalamic Arcuate and Ventromedial nuclei of the ob/ob mice. (13)C HR-MAS analysis showed increased (13)C accumulation in the hypothalamic glutamate and glutamine carbons of ob/ob mice after the administration of [1-(13)C]glucose, a primarily neuronal substrate. Hypothalamic expression of the genes coding for glucokinase, phosphofructokinase, pyruvate dehydrogenase, and glutamine synthase was not significantly altered while pyruvate kinase expression was slightly upregulated. In conclusion, leptin deficiency associated with obesity led to increased cerebral activation in the hypothalamic Arcuate and Ventromedial nuclei, concomitant with significant increases in neuronal oxidative metabolism and glutamatergic neurotransmission.

Hypermethylation of Hepatic Glucokinase and L-Type Pyruvate Kinase Promoters in High-Fat Diet–Induced Obese Rats

Obesity-dependent insulin resistance and type 2 diabetes mellitus are closely associated with decreased glucose utilization and down-regulation of hepatic glycolytic enzymes expression. Previously, we showed that DNA hypermethylation is involved in age-dependent susceptibility to hepatic insulin resistance and diabetes. However, what we cannot distinguish is whether the age-related obesity contributes to DNA hypermethylation in those natural aging rats. In the present study, we hypothesize that DNA methylation plays a crucial role in the regulation of glycolytic enzymes in the high-fat diet-induced obesity. Here, we report that DNA hypermethylation is correlated with a decline in hepatic glucokinase (Gck) and L-type pyruvate kinase (LPK) expression in high-fat diet-induced obese rats as compared with the control diet group. Down-regulation of Gck and LPK expression are reversed by the 5-aza-2'-deoxycytidine in the cell model of steatosis. These novel observations indicate that DNA methylation is involved in the development of metabolic diseases, such as obesity, insulin resistance, type 2 diabetes mellitus, and nonalcoholic steatohepatitis, suggesting that the hypermethylation level of Gck and LPK promoters may be a useful parameter for the evaluation of obesity-induced insulin resistance and fatty liver.

Kinetic and expression profiling of cytosolic pyruvate kinase enzyme during seed development of Indian mustard (Brassica juncea)

In the recent years tremendous progress has been achieved in deconstructing the oil biosynthetic pathways, majority of which is in Arabidopsis. Glycolysis is fundamental to this process as it is the cardinal supplier of precursors for fatty acid metabolism. Recent reports suggest that modification and expression of pyruvate kinase (PK), a crucial regulatory enzyme involved in glycolysis is one of the plausible ways to alter seed oil content in plants. In the present study we evaluated the kinetic behavior and expression profiling of pyruvate kinase, associated with seed development in a major oilseed crop B. juncea. Developmental profiling of the enzyme showed that enzyme activity was highest during middle stage (35 DAF) of seed development which is strongly corroborated by the expression profiling of the enzyme using RT-PCR approach. Oil accumulation pattern also correlated with the enzyme expression study. Comparative activity profiling from different tissues showed seedlings to have elevated activity than other tissues. For kinetic characterization, the enzyme was partially purified by 12.3 fold using DEAE-Sephadex column and showed a narrow pH optimum of 7.0. In presence of saturated substrate concentration, the enzyme exhibited hyperbolic kinetics for both ADP and PEP with Km (Michaelis constant value) for PEP and ADP was found to be 178.5 and 96.45 μM respectively. ATP and citrate are the most significant allosteric effectors of the partially purified PK. Study on isozymes of PK resulted in a single band.

Leukocyte pyruvate kinase expression is reduced in normal human pregnancy but not in pre-eclampsia.

Emerging evidence suggests that metabolism influences immune cell signaling and immunoregulation. To examine the immunoregulatory role of glycolysis in pregnancy, we evaluated the properties of pyruvate kinase in leukocytes from non-pregnant women and those with normal pregnancy and pre-eclampsia. We evaluated pyruvate kinase expression in lymphocytes and neutrophils from non-pregnant, pregnant, and pre-eclampsia patients using fluorescence microscopy and flow cytometry. Leukocyte pyruvate kinase activity and pyruvate concentrations were also evaluated. To study pyruvate's effect on signaling, we labeled Jurkat T cells with Ca(2+) dyes and measured cell responses in the presence of agents influencing intracellular pyruvate. The expression of pyruvate kinase is reduced in lymphocytes and neutrophils from normal pregnant women in comparison with those of non-pregnant women and pre-eclampsia patients. Similarly, the activity of pyruvate kinase and the intracellular pyruvate concentration are reduced in leukocytes of normal pregnant women in comparison with non-pregnant women and women with pre-eclampsia. Using Jurkat cells as a model of leukocyte signaling, we have shown that perturbations of intracellular pyruvate influence Ca(2+) signals. Normal pregnancy is characterized by reduced pyruvate kinase expression within lymphocytes and neutrophils. We speculate that reduced pyruvate kinase expression modifies immune cell responses due to reduced pyruvate concentrations.

Integration of insulin and amino acid signals that regulate hepatic metabolism-related gene expression in rainbow trout: role of TOR

Amino acids are considered to be regulators of metabolism in several species, and increasing importance has been accorded to the role of amino acids as signalling molecules regulating protein synthesis through the activation of the TOR transduction pathway. Using rainbow trout hepatocytes, we examined the ability of amino acids to regulate hepatic metabolism-related gene expression either alone or together with insulin, and the possible involvement of TOR. We demonstrated that amino acids alone regulate expression of several genes, including glucose-6-phosphatase, phosphoenolpyruvate carboxykinase, pyruvate kinase, 6-phospho-fructo-1-kinase and serine dehydratase, through an unknown molecular pathway that is independent of TOR activation. When insulin and amino acids were added together, a different pattern of regulation was observed that depended upon activation of the TOR pathway. This pattern included a dramatic up-regulation of lipogenic (fatty acid synthase, ATP-citrate lyase and sterol responsive element binding protein 1) and glycolytic (glucokinase, 6-phospho-fructo-1-kinase and pyruvate kinase) genes in a TOR-dependent manner. Regarding gluconeogenesis genes, only glucose-6-phosphatase was inhibited in a TOR-dependent manner by combination of insulin and amino acids and not by amino acids alone. This study is the first to demonstrate an important role of amino acids in combination with insulin in the molecular regulation of hepatic metabolism.

Genomic Analysis of an Attenuated Chlamydia abortus Live Vaccine Strain Reveals Defects in Central Metabolism and Surface Proteins

Comparative genomic analysis of a wild-type strain of the ovine pathogen Chlamydia abortus and its nitrosoguanidine-induced, temperature-sensitive, virulence-attenuated live vaccine derivative identified 22 single nucleotide polymorphisms unique to the mutant, including nine nonsynonymous mutations, one leading to a truncation of pmpG, which encodes a polymorphic membrane protein, and two intergenic mutations potentially affecting promoter sequences. Other nonsynonymous mutations mapped to a pmpG pseudogene and to predicted coding sequences encoding a putative lipoprotein, a sigma-54-dependent response regulator, a PhoH-like protein, a putative export protein, two tRNA synthetases, and a putative serine hydroxymethyltransferase. One of the intergenic mutations putatively affects transcription of two divergent genes encoding pyruvate kinase and a putative SOS response nuclease, respectively. These observations suggest that the temperature-sensitive phenotype and associated virulence attenuation of the vaccine strain result from disrupted metabolic activity due to altered pyruvate kinase expression and/or alteration in the function of one or more membrane proteins, most notably PmpG and a putative lipoprotein.

Caffeic acid phenethyl ester (CAPE) exhibits significant potential as an antidiabetic and liver-protective agent in streptozotocin-induced diabetic rats

Caffeic acid phenethyl ester (CAPE) was screened for hypoglycemic and liver-protective activity in streptozotocin (STZ)-induced diabetic rats. Diabetes was established by single dose STZ injection (45 mg kg −1 bw, i.p.) for 48 h. CAPE was injected at doses of 10, 20 and 30 μM kg −1 bw day −1 (i.p.) to the rats in CAPEI, CAPEII and CAPEIII groups 2 days after induction of diabetes and continued for 60 days, thereafter. It was found that diabetes down-regulated the expressions of glucokinase (7.8-fold) and pyruvate kinase (6.4-fold) in comparison to control, however, phoshoenolpyruvate carboxykinase mRNA levels were up-regulated by 2.2-fold. CAPE treatments enhanced the expressions of glucokinase (3.4–14.9-folds), and pyruvate kinase (3.2–12.8-folds) mRNAs in diabetic rats. However, phoshoenolpyruvate carboxykinase mRNA expression was decreased by CAPE to varying degrees (1.2–5.5-fold). CAPE increased (∼2-fold) the level of plasma insulin previously decreased by STZ treatment. Here we demonstrate that CAPE significantly decreased the fasting blood levels of glucose, alanine aminotransferase, cholesterol, and triglyceride induced by diabetes. CAPE increased the liver glycogen level lowered by diabetes. In histopathological evaluation of the liver, CAPE treatments were seen to reduce necrosis and anisonucleosis in hepatocytes, and connective tissue elevated in the portal region by diabetes. CAPE exhibits a significant potential as an antidiabetic agent by suppressing hepatic glucose output via inducing mRNA expression of glucokinase and pyruvate kinase, whilst inhibiting phoshoenolpyruvate carboxykinase in diabetes. CAPE also has the ability to decrease the harmful effects of diabetes on the liver of rats.

Increased Expression of Hepatic Scavenger Receptor B 1 and Apo A‐I in Streptozotocin‐induced Diabetic Rats

Elevated serum cholesterol levels and an increase in cardiovascular events are frequently seen in diabetes. We used microarray and RT‐PCR analysis to investigate the expression of key hepatic genes in the male Sprague‐Dawley rat, a predominantly HDL animal, in which diabetes was induced by injection of 65 mg/kg of streptozotocin. As expected, HMG‐CoA reductase, glucokinase, fatty acid synthase, acetyl CoA carboxylase, stearoyl CoA desaturase, pyruvate kinase and thyroid hormone responsive protein expression was decreased. On the other hand, expression of serine dehydratase, carnitine palmitoyl transferase, carnitine acetyltransferase, insulin‐like growth factor binding protein‐1, INSIG‐1 and 2, PPAR gamma coactivator 1 alpha, and ABCC‐3 was increased in the diabetic rats. The expression of scavenger receptor B 1 and Apo A‐I were increased about 3‐fold in the streptozotocin‐induced diabetic animals. This may be a consequence of the severe insulin deficiency which promotes robust lipolysis. These genes are critical to reverse cholesterol transport. Consistent with these findings, a decrease in hepatic scavenger receptor B 1 has been reported in an animal model of Type 2 diabetes with increased insulin levels. (This investigation was supported by NIH grant DK075414).

Decreased expression of cytosolic pyruvate kinase in potato tubers leads to a decline in pyruvate resulting in an in vivo repression of the alternative oxidase.

The aim of this work was to investigate the effect of decreased cytosolic pyruvate kinase (PKc) on potato (Solanum tuberosum) tuber metabolism. Transgenic potato plants with strongly reduced levels of PKc were generated by RNA interference gene silencing under the control of a tuber-specific promoter. Metabolite profiling showed that decreased PKc activity led to a decrease in the levels of pyruvate and some other organic acids involved in the tricarboxylic acid cycle. Flux analysis showed that this was accompanied by changes in carbon partitioning, with carbon flux being diverted from glycolysis toward starch synthesis. However, this metabolic shift was relatively small and hence did not result in enhanced starch levels in the tubers. Although total respiration rates and the ATP to ADP ratio were largely unchanged, transgenic tubers showed a strong decrease in the levels of alternative oxidase (AOX) protein and a corresponding decrease in the capacity of the alternative pathway of respiration. External feeding of pyruvate to tuber tissue or isolated mitochondria resulted in activation of the AOX pathway, both in the wild type and the PKc transgenic lines, providing direct evidence for the regulation of AOX by changes in pyruvate levels. Overall, these results provide evidence for a crucial role of PKc in the regulation of pyruvate levels as well as the level of the AOX in heterotrophic plant tissue, and furthermore reveal that these parameters are interlinked in vivo.

Male rats fed low or high carbohydrate diets for ten days did not differ in hepatic gene expression of enzymes associated with carbohydrate metabolism, but differed in peripheral insulin signaling

Our laboratory previously reported differential metabolic regulations in rats and humans fed low or high carbohydrate diets designed to meet DRI guidelines for macronutrients. This study examined the impact of short‐term feeding of low vs. high carbohydrate diets (LC vs. HC) on gene expression of liver enzymes involved in carbohydrate metabolism and insulin signaling in skeletal muscle and adipose. LC and HC diets consisted of 42:30:28 (carbohydrate:protein:fat as % energy) and 60:12:28, respectively. Male SD rats ~250 g were fed 3 times/d to mimic human meal patterns. After 10 d, samples were obtained at fasted (n=8) or 90 min after a 4 g meal (n=8). Plasma insulin, glucagon, glucose, and triacylglyceride were not different in fasted samples. Liver gene expression of PEPCK, pyruvate kinase, glucose‐6‐phosphatase, and fatty acid synthetase was not different between diets. Insulin and triacylglyceride increased 97% (P&lt;0.05) and 123% (P&lt;0.10) after the HC meal, respectively, but increased only 51% (P&lt;0.10) and 52% (P&lt;0.10) after the LC meal. In skeletal muscle, LC caused greater activation (p=0.01) of Akt and p70S6K (p&lt;0.05), while HC activated Akt (p&lt;0.05) in adipose. In summary, short‐term feeding of LC and HC diets elicited no differences in hepatic gene expression of enzymes for carbohydrate metabolism, but produced differential insulin signaling in skeletal muscle and adipose.Support: Unigen Pharmaceutical

The M2 splice isoform of pyruvate kinase is important for cancer metabolism and tumour growth

Many tumour cells have elevated rates of glucose uptake but reduced rates of oxidative phosphorylation. This persistence of high lactate production by tumours in the presence of oxygen, known as aerobic glycolysis, was first noted by Otto Warburg more than 75 yr ago. How tumour cells establish this altered metabolic phenotype and whether it is essential for tumorigenesis is as yet unknown. Here we show that a single switch in a splice isoform of the glycolytic enzyme pyruvate kinase is necessary for the shift in cellular metabolism to aerobic glycolysis and that this promotes tumorigenesis. Tumour cells have been shown to express exclusively the embryonic M2 isoform of pyruvate kinase. Here we use short hairpin RNA to knockdown pyruvate kinase M2 expression in human cancer cell lines and replace it with pyruvate kinase M1. Switching pyruvate kinase expression to the M1 (adult) isoform leads to reversal of the Warburg effect, as judged by reduced lactate production and increased oxygen consumption, and this correlates with a reduced ability to form tumours in nude mouse xenografts. These results demonstrate that M2 expression is necessary for aerobic glycolysis and that this metabolic phenotype provides a selective growth advantage for tumour cells in vivo.