Increased biosynthesis of pyruvate kinase under hypoxic conditions in mammalian cells

Proteomic changes in the brain of the western painted turtle (Chrysemys picta bellii) during exposure to anoxia

During anoxia, overall protein synthesis is almost undetectable in the brain of the western painted turtle. The aim of this investigation was to address the question of whether there are alterations to specific proteins by comparing the normoxic and anoxic brain proteomes. Reductions in creatine kinase, hexokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase reflected the reduced production of adenosine triphosphate (ATP) during anoxia while the reduction in transitional endoplasmic reticulum ATPase reflected the conservation of ATP or possibly a decrease in intracellular Ca(2+). In terms of neural protection programed cell death 6 interacting protein (PDCD6IP; a protein associated with apoptosis), dihydropyrimidinase-like protein, t-complex protein, and guanine nucleotide protein G(o) subunit alpha (Go alpha; proteins associated with neural degradation and impaired cognitive function) also declined. A decline in actin, gelsolin, and PDCD6IP, together with an increase in tubulin, also provided evidence for the induction of a neurological repair response. Although these proteomic alterations show some similarities with the crucian carp (another anoxia-tolerant species), there are species-specific responses, which supports the theory of no single strategy for anoxia tolerance. These findings also suggest the anoxic turtle brain could be an etiological model for investigating mammalian hypoxic damage and clinical neurological disorders.

Effect of proline analogues on activity of human prolyl hydroxylase and the regulation of HIF signal transduction pathway

Hypoxia inducible factor 1 (HIF-1) plays a pivotal role in cellular responses to hypoxia. Prolyl hydroxylase 3 (PHD3) degrades HIF-1α under normoxic conditions through the hydroxylation of HIF-1α for proteolysis. Inhibiting PHD3 activity is crucial for up-regulating HIF-1α, thereby acting as a potential target for treating hypoxia-related diseases. In this study, two proline analogues (PA1 and PA2) were screened as PHD3 inhibitors with apparent EC50 values of 1.53 and 3.17 µM respectively, indicating good inhibition potency. Nine proteins, significantly regulated by PA1, were identified using 2-DE coupled with MALDI-TOF/TOF MS. Pyruvate kinase isozymes M1/M2 (PKM) and alpha-enolase 1 (ENO1), which are key modulators of glycolysis, are directly regulated by HIF-1α. Moreover, VEGF, a signal protein stimulating angiogenesis, was strongly promoted by PA1. Our findings suggest that PA1 stabilized HIF-1α as well as up-regulated glycolysis and angiogenesis proteins. Herein, for the first time, we systematically studied proline analogue PA1 as a PHD3 inhibitor, which provides innovative evidence for the treatment of HIF-related diseases.

Anti-hypoxic activity of the ethanol extract from Portulaca oleracea in mice

AIM OF THE STUDY

To investigate the effects of the ethanol extract from Portulaca oleracea (EEPO) on hypoxia models mice and to find the possible mechanism of its anti-hypoxic actions so as to elucidate the anti-hypoxia activity and provide scientific basis for the clinical use of Portulaca oleracea.

MATERIALS AND METHODS

EEPO was evaluated on anti-hypoxic activity in several hypoxia mice models, including closed normobaric hypoxia and sodium nitrite or potassium cyanide toxicosis. To verify the possible mechanism(s), we detected the activities of pyruvate kinase (PK), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and the level of adenosine triphosphate (ATP) in mice cortices.

RESULTS

Given orally, the EEPO at doses of 100, 200, 400 mg/kg could dose-dependently enhance the survival time of mice in both of the normobaric and chemical hypoxia models. The activity of the glycolysis enzymes and the level of ATP were higher than those of the control. In the pentobarbital sodium-induced sleeping time test and the open-field test, EEPO neither significantly enhanced the pentobarbital sodium-induced sleeping time nor impaired the motor performance, indicating that the observed anti-hypoxic activity was unlikely due to sedation or motor abnormality.

CONCLUSIONS

These results demonstrated that the EEPO possessed notable anti-hypoxic activity, which might be related to promoting the activity of the key enzymes in glycolysis and improving the level of ATP in hypoxic mice.

The activity and kinetics of pyruvate kinase in hypoxic newborns

Pyruvate kinase (PK) plays a key role in erythrocytes, which obtain most of their energy from glycolysis. This study investigated erythrocyte energy metabolism in hypoxic newborns, measuring pyruvate kinase activity, kinetic, and ATP levels in hypoxia. Forty-nine babies who had cord pH value lower than 7.2 and Apgar scores lower than 7 in the first minute were accepted as the hypoxic group, and 48 babies who had cord pH value higher than 7.2 and an Apgar score higher than 7 in the first minute were taken as controls. The erythrocyte mean PK activity was found to be lower (16.9+/-8.5 [5.8-47.9] EU/gHb) in the hypoxic group than the control group (21.3+/-10.9 [3.9-44.3] EU/gHb) (p<.05). The mean ATP value of hypoxic group was higher (19.2+/-11.3 [3.9-37.6] mM) compared to control group (13.8+/-7.16 [3.9-28.7] mM). In the kinetic study, with different ADP concentrations in the control group, the substrate amount (Km) that is needed to reach the half-maximum of enzyme activity (Vmax=27.7 Eu/gHb) was found to be 2.70 mM, but it was 1.47 mM to reach Vmax (22.7 Eu/gHb) in the hypoxic group. Vmax was 41.67 Eu/gHb and Km was 8.33 mM in the control group at different PEP concentrations, whereas Vmax was 21.7 Eu/gHb and Km was 0.89 mM in the hypoxic group. Increase in the ATP level while ePK activity decreases, suggesting that glycolysis increases in hypoxia. In the kinetic study, the substrate amount needed for reaching the half-maximum of enzyme activity was less in the hypoxic group, probably suggests that pyruvate kinase increases glycolysis by increasing its affinity to the substrates. In this way, erythrocytes may gain the energy required for oxygen delivery to tissues and maintaining ion gradient. This arrangement possibly proceeds from sygmoidal structure of pyruvate kinase.

Pyruvate kinase activity in cerebral hemispheres and cerebellum-brainstem of normal and hypoxic-ischemic newborn rats

Energy metabolism is affected in hypoxia-ischemia. Changes in the tissue concentrations of the high-energy phosphate reserves occur early during the course of the metabolic insult and with concurrent increases in cellular ADP and AMP leading glycolysis. It has been shown that enzymes of glycolysis tend to be regulated in hypoxia and ischemia. In this study we determined pyruvate kinase (PK) activity, one of the main enzymes in glycolysis, in brain tissues of healthy (n = 15) and hypoxic-ischemic (n = 18) 7-day-old newborn rats. Left common carotid artery was ligated in the hypoxic-ischemic group and after 2 hours rats were exposed to hypoxia in a chamber at 34-36 degrees C with 8% oxygen in nitrogen. The rats were decapitated after 2 hours of hypoxia and right and left cerebral hemispheres (CH) and cerebellum-brain stem (C-BS) were removed. Pyruvate kinase activity was significantly higher in C-BSs than CHs in both groups (p < 0.00005). There was no significant difference in enzyme activities of either CHs or C-BS of hypoxic-ischemic group compared to control healthy group (p > 0.05). In conclusion, brain pyruvate kinase activity did not change in hypoxia-ischemia and suggests that PK of brain differs from other tissues where it usually increases in hypoxiaischemia.

Effect of protein kinases on lactate dehydrogenase activity in cortical neurons during hypoxia

Our previous work shows that delta-opioid receptor (DOR) protects cortical neurons from hypoxic insults. Since an enhanced anaerobic capacity is important for neurons to adapt to the reduction of oxidative phosphorylation, we asked whether DOR plays a role in neuronal regulation of anaerobic capacity, thus protecting neurons from O(2) deprivation. Indeed, there is evidence suggesting that DOR may regulate protein kinase A (PKA) and C (PKC), which are involved in regulation of lactate dehydrogenase (LDH). However, little is known regarding the role of DOR and protein kinases in the regulation of glycolytic and related enzymes. As a first step, the present studies were performed in primary cultures of rat cortical neurons to clarify two issues: (1) Are protein kinases involved in the regulation of LDH activity in hypoxia? and (2) Does DOR affect LDH activity in hypoxic neurons? The results showed that PKC activation yielded substantial increases in normoxic LDH activity and significantly augmented LDH activity in hypoxic neurons, while PKC inhibition decreased LDH activity in both normoxic and hypoxic neurons. PKA activation significantly increased LDH activity in normoxic neurons and further elevated LDH activity in hypoxic neurons. However, PKA inhibition did not decrease in LDH activity in either normoxic or hypoxic neurons. Although DOR inhibition slightly reduced LDH activity in normoxia, DOR activation or inactivation did not alter LDH activity in hypoxic neurons. These data suggest that in cortical neurons, (i) PKC up-regulates LDH activity and plays an important role in its up-regulation during hypoxia; (ii) PKA is less likely involved in the regulation of LDH activity during hypoxia although its stimulation may slightly increase LDH activity and (iii) DOR does not contribute to LDH activity up-regulation during hypoxia.

Astrocytes respond to hypoxia by increasing glycolytic capacity

Astrocytes cope more readily with hypoxic insults than do neurons. We hypothesized that astrocytes can upregulate their glycolytic capacity, allowing anaerobic glycolysis to provide sufficient ATP for cell survival as well as for carrying out critical functions such as taking up glutamate. To test this hypothesis, astrocytes were subjected to hypoxia for 5 hr. Lactate dehydrogenase (LDH) and pyruvate kinase activities increased 3- to 4-fold. Examination of LDH isoenzyme patterns determined that it was the anaerobic isoenzymes that were upregulated. To determine whether increase in enzyme activity translates into increased glycolytic capacity, astrocytes were subjected to varying time periods of hypoxia, and glucose uptake was measured under conditions where astrocytes were forced to consume more ATP. This demonstrated that 8 hr of hypoxia resulted in a doubling of glycolytic capacity. We suggest that how quickly astrocytes upregulate glycolytic capacity may determine whether or not neurons within the stroke penumbra survive.

Regulation of ATP synthase subunit e gene expression by hypoxia: cell differentiation stage-specific control

Using the technique of differential display, we identified genes that are expressed differentially under normoxic and hypoxic conditions. One regulated gene encoded subunit e of mitochondrial F1F0-ATP synthase (subunit e). The hypoxia-mediated regulation of subunit e expression in C2C12 cells was influenced by the stage of cellular differentiation. Under normoxic conditions, subunit e expression was markedly upregulated during the transition from myoblast to myotube. After exposure to hypoxia for 24 h, subunit e mRNA expression markedly decreased (>70%) in C2C12 myotubes. In contrast, subunit e mRNA levels increased slightly in response to hypoxia in C2C12 myoblasts. Studies performed with primary rat cardiocytes demonstrated that expression of subunit e mRNA and a cardiac-enriched related transcript was downregulated after a hypoxic exposure. We conclude that expression of subunit e is regulated, at the pretranslational level, by oxygen availability via cell differentiation stage-specific mechanisms consistent with the proposed regulatory role of this protein in cellular ATP production.

Adaptation of chondrocytes to low oxygen tension: relationship between hypoxia and cellular metabolism

In endochondral bone, the growth cartilage is the site of rapid growth. Since the vascular supply to the cartilage is limited, it is widely assumed that cells of the cartilage are hypoxic and that limitations in the oxygen supply regulate the energetic state of the maturing cells. In this report, we evaluate the effects of oxygen tension on chondrocyte energy metabolism, thiol status, and expression of transcription elements, HIF and AP-1. Imposition of an hypoxic environment on cultured chondrocytes caused a proportional increase in glucose utilization and elevated levels of lactate synthesis. Although we observed a statistical increase in the activities of phosphofructokinase, pyruvate kinase, lactate dehydrogenase, and creatine kinase after exposure to lowered oxygen concentrations, the effect was small. The cultured cells exhibited a decreased utilization of glutamine, possibly due to down regulation of mitochondrial function and inhibition of oxidative deamination. With respect to total energy generation, we noted that these cells are quite capable of maintaining the energy charge of the cell at low oxygen tensions. Indeed, no changes in the absolute quantity of adenine nucleotides or the energy charge ratio was observed. Hypoxia caused a decrease in the glutathione content of cultured chondrocytes and a concomitant rise in cell and medium cysteine levels. It is likely that the fall in cell glutathione level is due to decreased synthesis of the tripeptide under reduced oxygen stress and the limited supply of glutamate. The observed rise in cellular and medium cysteine levels probably reflects an increase in the rate of degradation of glutathione and a decrease in synthesis of the peptide. To explore how cells transduce these metabolic effects, gel retardation assays were used to study chondrocyte HIF and AP-1 binding activities. Chondrocyte nuclear preparations bound an HIF-oligonucleotide; however, at low oxygen tensions, no increase in HIF binding was observed. In addition, we found that AP-1 binding activities in chondrocytes exposed to low oxygen tensions was elevated, although the response was lower than that exhibited by fibroblasts exposed to the same range of oxygen concentrations. We compared these results to HIF and AP-1 binding by cells in the growth plate. There was strong HIF and AP-1 binding throughout the plate, but no evidence of selective binding to any one zone. The results of the study lend strong support to the view that chondrocytes are very well adapted to low oxygen tensions; thus, under hypoxic conditions, there is a high level of expression of both HIF and AP-1, and energy conservation appears to be near-maximum.

Tumor metabolism: the lessons of magnetic resonance spectroscopy

For many years after Warburg's classic work, it was generally assumed that tumors produced large amounts of lactic acid and consequently had an acidic intracellular pHi. However, with the advent of Magnetic Resonance Spectroscopy (MRS), a non-invasive in vivo measure of tissue pH became available and demonstrated that in both human and animal tumors, pHi was higher (> 7.0) than pH epsilon (< 6.8), in contrast to normal tissues (e.g., liver) in which pHi (approximately 7.2) is lower than pH epsilon (approximately 7.4). This result has been confirmed in animal tumors using an MRS-visible extracellular marker, 3-aminopropyl phosphonate. The pH gradient across the tumor cell membrane is part of an interrelated system of ionic gradients and measurements made by both 31P MRS and by conventional analysis in Morris hepatoma 9618a and in livers demonstrated that the following ions also changed: compared with liver the Na+ content was 2-fold higher, K+ was 20% lower, total Ca2+ was 8-fold higher (7.4 mumol/g wet wt) and total Pi 2-fold higher (8.5 mumol/g wet wt), suggesting the presence of insoluble calcium phosphate, HCO3- was lower, total Mg2+ was similar in both tissues, but free [Mg2+] (calculated by two different methods) was approximately 5-fold lower in the hepatoma, as was [ATP]/[ADP][P(i)]. Because of an inadequate blood supply, tumors are often hypoxic with impaired Krebs cycle activity, low [ATP]/[ADP][P(i)] and rely mainly on glycolysis for energy. The rapid production and subsequent export of anionic lactate-from the tumor cell would be accompanied by H+. This would account for reversal of the proton gradient and activation of the Na+/H+ exchange. The elevated [Na+]i would decrease the Na+/Ca2+ exchange, which would in turn tend to cause the accumulation of Ca2+ (and P(i)). Such calcification is a very common feature of tumor pathology. The data indicate the change in gradient of one ion (H+) involves alterations in the linked equilibria of many ions and also of energy metabolites and offers new insights into properties of tumors important both diagnostically and therapeutically.

Hypoxia and cobalt stimulate lactate dehydrogenase (LDH) activity in vascular smooth muscle cells

O2 plays a dominant role in the metabolism and viability of cells; changes in O2 supply lead to many physiological responses in the cell. Recent reports have shown that hypoxia induces the transcription of a number of genes, among them those for the glycolytic enzymes. We have investigated signalling events that may lead to enhanced activity of lactate dehydrogenase (LDH) in cultured vascular smooth muscle (VSM) cells derived from rat aorta, grown under hypoxic conditions (1% versus 20% O2). LDH was chosen because this enzyme exhibits one of the largest increases in activity among the glycolytic enzymes after hypoxic stimulation of cells. Hypoxic exposure of VSM cells for 24 h resulted in a 2-fold increase in LDH activity and in a 2.5-fold increase in intracellular cAMP levels. Agents that activate adenylate cyclase, such as forskolin, cholera toxin and 1-methyl-3-isobutylxanthine (IBMX), and thus increase cAMP production, significantly induced LDH activity. Moreover, induction of LDH activity by hypoxia was prevented in the presence of the protein kinase A inhibitor N-[2-(methyl-amino)ethyl]-5-isoquinolinsulphonamide dihydrochloride (H-8), and the cyclooxygenase inhibitor indomethacin. In contrast to the cAMP-stimulating agents, stable cGMP analogues (dibutyryl-cGMP, 8-bromo-cGMP), activators of protein kinase C [12-O-tetradecanoylphorbol-13-acetate (TPA), and 1-oleoyl-2-acetyl-glycerol (OAG), and the calcium ionophore ionomycin did not alter LDH activity in VSM cells kept at 20% O2. A dose-dependent increase in LDH activity was also observed in normoxic cells exposed to cobalt chloride (50-200 microM), indicating that a metal binding protein might be involved in this signalling cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of insulin and dexamethasone in the control of pyruvate kinase activity and glucose metabolism in sheep adipose tissue

1. The Vmax. activity of pyruvate kinase of sheep adipose tissue increased during tissue culture up to 48 h; the increase was blocked by actinomycin D (an inhibitor of transcription) and was promoted by insulin and antagonized by dexamethasone. 2. In contrast with their effects on pyruvate kinase, insulin and dexamethasone acted synergistically to increase the activity of glucose-6-phosphate dehydrogenase of sheep adipose tissue maintained in culture. 3. Insulin stimulated, whereas dexamethasone inhibited, glucose utilization by sheep adipose tissue maintained in culture; the two agents were mutually antagonistic, and their effects were prevented by actinomycin D. 4. Antimycin A (an inhibitor of the electron-transport chain) stimulated glucose uptake and lactate output by sheep adipose tissue in the presence of dexamethasone and insulin, suggesting that the effects of dexamethasone on glucose utilization by sheep adipose tissue were not due to an inhibition of glucose transport. 5. Comparison of these findings with previous studies on the endocrine control of hepatic pyruvate kinase shows that there are major differences in the control of these Vmax. activities in liver and adipose tissue. 6. Although glucocorticoid hormones inhibit glucose utilization themselves and can antagonize the stimulatory effects of insulin on glucose utilization in adipose tissue from both sheep and rats, there appear to be major differences in the sites of action of these hormones in the two species.

Regulation of glycolytic enzyme RNA transcriptional rates by oxygen availability in skeletal muscle cells

Cytoplasmic beta-actin and five glycolytic enzyme cDNAs were isolated from a rat skeletal muscle cDNA library and together with a genomic clone of rat cytochrome c were used as probes to quantitate the respective RNA transcription rates in isolated nuclei run off transcription assays from stationary cells cultured under normal or 2% oxygen. The transcription rates of lactate dehydrogenase, pyruvate kinase, triosephosphate isomerase and aldolase increased by 2-5 fold during the 72 hr exposure to 2% oxygen. There was a small increase in actin RNA transcription while both cytochrome c and glyceraldehyde-3-phosphate dehydrogenase RNA transcription rates decreased. Since previous studies demonstrated an increase in steady state glyceraldehyde-3-phosphate dehydrogenase RNA during low O2 exposure it is concluded that the level of this RNA is regulated post transcriptionally whereas the other four glycolytic enzyme RNAs are regulated at least partially at the level of transcription by oxygen availability. The relative transcriptional rates of the RNAs in this study are related to their cellular RNA and protein concentrations.

Glycolytic activity and enhancement of serotonin uptake by endothelial cells exposed to hypoxia/anoxia

Serotonin (5-HT) uptake by bovine pulmonary artery endothelial cells in culture was stimulated several fold by exposure of cells for 24 hours to 0-3% O2. The cells appeared normal morphologically, excluded trypan blue dye, showed normal levels of release of lactate dehydrogenase, and contained normal amounts of adenosine triphosphate (ATP). Incubation of cells with iodoacetate (3-5 microM), an inhibitor of glycolytic metabolism, prevented the stimulation of 5-HT uptake but did not impair cellular proliferation. A similar, but less pronounced, effect was produced by 1 mM deoxyglucose. On the other hand, the mitochondrial inhibitors antimycin A, sodium azide, potassium cyanide, and 2,4-dinitrophenol inhibited cellular replication similar to the effect of anoxia but did not alter the stimulation of 5-HT uptake. 5-HT uptake correlated strongly with lactate production by the cells exposed to anoxia (r = 0.98). We conclude that stimulation of 5-HT uptake by prolonged exposure of the endothelial cell to hypoxia/anoxia causes alteration of a membrane function (serotonin transport) of the endothelial cell. This alteration is associated with enhanced glycolytic activity of the cell during exposure to hypoxia. The mechanism for translation of enhanced glycolysis to later stimulation of 5-HT uptake remains to be determined. Endothelial cellular replication is dependent on aerobic metabolism.

Effects of hypoxia and hyperoxia on proteoglycan production by bovine pulmonary artery endothelial cells

Bovine pulmonary artery endothelial cells in culture were used to assess the influence of oxygen tension on proteoglycan synthesis. Cells exposed to 3% O2 (hypoxia) for 72 h and then labeled with [35S]sulfate for 5 h accumulated significantly less [35S]proteoglycan in medium than cells exposed to 20% O2 (control). This decrease was due primarily to a reduction in heparan sulfate. Cells exposed to 80% O2 (hyperoxia) for 72 h secreted slightly more [35S]proteoglycan into medium than controls. Greater accumulation of chondroitin sulfate was responsible for the increase. The amount of cell-associated proteoglycan did not change significantly in cells cultured in 3% or 80% O2 as compared with control cells cultured in 20% O2. Proteoglycans produced by hypoxia- or hyperoxia-treated cells were found to be similar in size to proteoglycans produced by cells cultured at 20% O2. Glycosaminoglycan sulfation, as measured by ion-exchange chromatography, did not appear to change with varying oxygen tensions. Our results demonstrate that production of proteoglycans secreted by endothelial cells in culture is sensitive to oxygen tension.