The Experts below are selected from a list of 25791 Experts worldwide ranked by ideXlab platform
Kenneth B. Storey - One of the best experts on this subject based on the ideXlab platform.
-
nrf2 activates antioxidant enzymes in the Anoxia tolerant red eared slider turtle trachemys scripta elegans
2021Co-Authors: Sarah A Breedon, Hanane Hadjmoussa, Kenneth B. StoreyAbstract:The freshwater red-eared slider turtle, Trachemys scripta elegans, experiences weeks to months of Anoxia at the bottom of ice-locked bodies of water in the winter. While this introduces Anoxia-reoxygenation cycles similar to the ischemia-reperfusion events that mammals experience, T. s. elegans does not suffer any apparent tissue damage. To survive prolonged Anoxia and prevent cellular damage associated with reactive oxygen species, these turtles have developed numerous adaptions, including highly effective antioxidant defenses. Herein, we examined the subcellular localization and protein expression of nuclear factor erythroid-2-related factor 2 (Nrf2), a central transcription factor responsible for modulating cellular antioxidant responses, that was found to be upregulated and localized to the nucleus in anoxic turtles. Additionally, we examined protein levels of glutathione S-transferases (GSTs) and manganese superoxide dismutase (MnSOD) antioxidant enzymes in anoxic liver, kidney, heart, and skeletal muscle tissues. MnSOD levels were significantly higher in heart and muscle during Anoxia, and the four GST isozymes (GSTK1, GSTT1, GSTP1, and GSTM3) were elevated in a tissue-specific manner during Anoxia and/or aerobic recovery. Together, these results indicate that Nrf2 is likely involved in activating downstream antioxidant genes in response to anoxic stress. These results provide a possible Nrf2-mediated transcriptional mechanism that supports existing findings of enhanced antioxidant defenses that allow T. s. elegans to cope with Anoxia-reoxygenation cycles, and subsequent oxidative stress.
-
Purification and Regulation of Pyruvate Kinase from the Foot Muscle of the Anoxia and Freeze Tolerant Marine Snail, Littorina littorea
2020Co-Authors: Michael B. Smolinski, Anchal Varma, Stuart R. Green, Kenneth B. StoreyAbstract:The intertidal marine snail, Littorina littorea , has evolved to survive bouts of Anoxia and extracellular freezing brought about by changing tides and subsequent exposure to harsh environmental conditions. Survival in these anoxic conditions depends on the animals entering a state of metabolic rate depression in order to maintain an appropriate energy production-consumption balance during periods of limited oxygen availability. This study investigated the kinetic, physical, and regulatory properties of pyruvate kinase (PK), which catalyzes the final reaction of aerobic glycolysis, from foot muscle of L. littorea to determine if the enzyme is differentially regulated in response to Anoxia and freezing exposure. PK purified from foot muscle of anoxic animals exhibited a lower affinity for its substrate phosphoenolpyruvate than PK from control and frozen animals. PK from anoxic animals was also more sensitive to a number of allosteric regulators, including alanine and aspartate, which are key anaerobic metabolites in L. littorea . Furthermore, PK purified from anoxic and frozen animals exhibited greater stability compared to the non-stressed control animals, determined through high-temperature incubation studies. Phosphorylation of threonine and tyrosine residues was also assessed and demonstrated that levels of threonine phosphorylation of PK from anoxic animals were significantly higher than those of PK from control and frozen animals, suggesting a potential mechanism for regulating PK activity. Taken together, these results suggest that PK plays a role in suppressing metabolic rate in these animals during environmental Anoxia exposure.
-
Regulation of crayfish, Orconectes virilis, tail muscle lactate dehydrogenase (LDH) in response to anoxic conditions is associated with alterations in phosphorylation patterns.
2016Co-Authors: Stuart R. Green, Kenneth B. StoreyAbstract:Lactate dehydrogenase (LDH), the terminal enzyme of anaerobic glycolysis, has a crucial role in sustaining ATP production by glycolysis during periods of Anoxia via regenerating NAD+ through the production of lactate. The present study examined the effects of prolonged (20h) anoxic submergence on LDH from the tail muscle of an Anoxia-tolerant crayfish (Orconectes virilis). LDH was purified to homogeneity from tail muscle of both aerobic control and anoxic crayfish in a three step process. Analysis of the kinetic parameters and the stability of LDH showed that the Vmax in the pyruvate-reducing direction was significantly higher for the enzyme from anoxic crayfish whereas in the lactate-oxidizing direction the Vmax was significantly higher for the control enzyme. Differential scanning fluorimetry was used to assess thermal unfolding of crayfish LDH. The results showed that the enzyme from control muscle had a significantly higher melting temperature (greater thermal stability) than the anoxic enzyme form, suggesting that there was a structural difference between the two enzyme forms. Immunoblotting of purified LDH implicated post-translational modification as the reason for this difference; purified LDH from aerobic control crayfish showed significantly higher amounts of serine/threonine phosphorylation than did the anoxic enzyme form. This study provides evidence for Anoxia-induced modifications of crayfish muscle LDH that may contribute significantly to modulating enzyme function under anoxic conditions.
-
the role of dna methylation during Anoxia tolerance in a freshwater turtle trachemys scripta elegans
2016Co-Authors: Sanoji Wijenayake, Kenneth B. StoreyAbstract:Oxygen deprivation is a lethal stress that only a few animals can tolerate for extended periods. This study focuses on analyzing the role of DNA methylation in aiding natural Anoxia tolerance in a champion vertebrate anaerobe, the red-eared slider turtle (Trachemys scripta elegans). We examined the relative expression and total enzymatic activity of four DNA methyltransferases (DNMT1, DNMT2, DNMT3a and DNMT3b), two methyl-binding domain proteins (MBD1 and MBD2), and relative genomic levels of 5-methylcytosine under control, 5 h anoxic, and 20 h anoxic conditions in liver, heart, and white skeletal muscle (n = 4, p < 0.05). In liver, protein expression of DNMT1, DNMT2, MBD1, and MBD2 rose significantly by two- to fourfold after 5 h anoxic submergence compared to normoxic-control conditions. In heart, 5 h Anoxia submergence resulted in a 1.4-fold increase in DNMT3a levels and a significant decrease in MBD1 and MBD2 levels to ~30 % of control values. In white muscle, DNMT3a and DNMT3b increased threefold and MBD1 levels increased by 50 % in response to 5 h Anoxia. Total DNMT activity rose by 0.6–2.0-fold in liver and white muscle and likewise global 5mC levels significantly increased in liver and white muscle under 5 and 20 h Anoxia. The results demonstrate an overall increase in DNA methylation, DNMT protein expression and enzymatic activity in response to 5 and 20 h Anoxia in liver and white muscle indicating a potential downregulation of gene expression via this epigenetic mechanism during oxygen deprivation.
-
hexokinase regulation in the hepatopancreas and foot muscle of the Anoxia tolerant marine mollusc littorina littorea
2013Co-Authors: Judeh L Lama, Ryan A V Bell, Kenneth B. StoreyAbstract:Hexokinase from the hepatopancreas and foot muscle of Littorina littorea undergoes stable modification of its kinetic and structural properties in response to prolonged oxygen deprivation. In the hepatopancreas, a reduction in the Km glucose for hexokinase from the anoxic animal suggests a more active enzyme form during Anoxia. Conversely, in the foot muscle, an increase in Km ATP and a decrease in Vmax for anoxic snail hexokinase were consistent with a less active enzyme form during Anoxia. In either case, the molecular basis for the stable modification of hexokinase kinetics is reversible phosphorylation. The activation of endogenous PKC and AMPK increased the Km glucose for anoxic hepatopancreas hexokinase to a value that was similar to the control Km glucose. Alternatively, stimulation of endogenous PKA, PKG, and CamK for control foot muscle hexokinase increased the Km ATP to a value similar to that seen for the anoxic enzyme form. In both tissues, activation of endogenous phosphatases reversed the effects of protein kinases. Dephosphorylation and activation of hepatopancreas hexokinase during Anoxia may allow for increased shunting of glucose-6-phosphate into the pentose phosphate pathway, thereby producing reducing equivalents of NADPH needed for antioxidant defense upon tissue re-oxygenation. Conversely, phosphorylation and inhibition of foot muscle hexokinase during Anoxia may reflect the decreased need for glucose oxidation during hypometabolism.
Leslie T Buck - One of the best experts on this subject based on the ideXlab platform.
-
mitochondrial matrix ph acidifies during Anoxia and is maintained by the f1fo atpase in Anoxia tolerant painted turtle cortical neurons
2019Co-Authors: Peter John Hawrysh, Leslie T BuckAbstract:The western painted turtle (Chrysemys picta bellii) can survive extended periods of Anoxia via a series of mechanisms that serve to reduce its energetic needs. Central to these mechanisms is the response of mitochondria, which depolarize in response to Anoxia in turtle pyramidal neurons due to an influx of K+. It is currently unknown how mitochondrial matrix pH is affected by this response and we hypothesized that matrix pH acidifies during Anoxia due to increased K+/H+ exchanger activity. Inhibition of K+/H+ exchange via quinine led to a collapse of mitochondrial membrane potential (Ψm) during oxygenated conditions in turtle cortical neurons, as indicated by rhodamine-123 fluorescence, and this occurred twice as quickly during Anoxia which indicates an elevation in K+ conductance. Mitochondrial matrix pH acidified during Anoxia, as indicated by SNARF-1 fluorescence imaged via confocal microscopy, and further acidification occurred during Anoxia when the F1Fo-ATPase was inhibited with oligomycin-A, indicating that ΔpH collapse is prevented during anoxic conditions. Collectively, these results indicate that the mitochondrial proton electrochemical gradient is actively preserved during Anoxia to prevent a collapse of Ψm and ΔpH.
-
proteomic changes in the brain of the western painted turtle chrysemys picta bellii during exposure to Anoxia
2015Co-Authors: Richard W Smith, David W Hogg, Phil Cash, Leslie T BuckAbstract: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.
-
endogenous gaba a and gaba b receptor mediated electrical suppression is critical to neuronal Anoxia tolerance
2011Co-Authors: Matthew E Pamenter, David W Hogg, Jake Ormond, Damian S Shin, Melanie A Woodin, Leslie T BuckAbstract:Anoxic insults cause hyperexcitability and cell death in mammalian neurons. Conversely, in Anoxia-tolerant turtle brain, spontaneous electrical activity is suppressed by Anoxia (i.e., spike arrest; SA) and cell death does not occur. The mechanism(s) of SA is unknown but likely involves GABAergic synaptic transmission, because GABA concentration increases dramatically in anoxic turtle brain. We investigated this possibility in turtle cortical neurons exposed to Anoxia and/or GABAA/B receptor (GABAR) modulators. Anoxia increased endogenous slow phasic GABAergic activity, and both Anoxia and GABA reversibly induced SA by increasing GABAAR-mediated postsynaptic activity and Cl− conductance, which eliminated the Cl− driving force by depolarizing membrane potential (∼8 mV) to GABA receptor reversal potential (∼−81 mV), and dampened excitatory potentials via shunting inhibition. In addition, both Anoxia and GABA decreased excitatory postsynaptic activity, likely via GABABR-mediated inhibition of presynaptic glutamate release. In combination, these mechanisms increased the stimulation required to elicit an action potential >20-fold, and excitatory activity decreased >70% despite membrane potential depolarization. In contrast, anoxic neurons cotreated with GABAA+BR antagonists underwent seizure-like events, deleterious Ca2+ influx, and cell death, a phenotype consistent with excitotoxic cell death in anoxic mammalian brain. We conclude that increased endogenous GABA release during Anoxia mediates SA by activating an inhibitory postsynaptic shunt and inhibiting presynaptic glutamate release. This represents a natural adaptive mechanism in which to explore strategies to protect mammalian brain from low-oxygen insults.
Anthony P Farrell - One of the best experts on this subject based on the ideXlab platform.
-
na k atpase activity in the anoxic turtle trachemys scripta brain at different acclimation temperature
2017Co-Authors: Jonathan A W Stecyk, Anthony P Farrell, Matti VornanenAbstract:Survival of prolonged Anoxia requires a balance between cellular ATP demand and anaerobic ATP supply from glycolysis, especially in critical tissues such as the brain. To add insight into the ATP demand of the brain of the Anoxia-tolerant red-eared slider turtle (Trachemys scripta) during prolonged periods of anoxic submergence, we quantified and compared the number of Na+-K+-ATPase units and their molecular activity in brain tissue from turtles acclimated to either 21°C or 5°C and exposed to either normoxia or Anoxia (6h 21°C; 14days at 5°C). Na+-K+-ATPase activity and density per g tissue were similar at 21°C and 5°C in normoxic turtles. Likewise, Anoxia exposure at 21°C did not induce any change in Na+-K+-ATPase activity or density. In contrast, prolonged Anoxia at 5°C significantly reduced Na+-K+-ATPase activity by 55%, which was largely driven by a 50% reduction of the number of Na+-K+-ATPase units without a change in the activity of existing Na+-K+-ATPase pumps or α-subunit composition. These findings are consistent with the "channel arrest" hypothesis to reduce turtle brain Na+-K+-ATPase activity during prolonged, but not short-term Anoxia, a change that likely helps them overwinter under low temperature, anoxic conditions.
-
cardiac responses to Anoxia in the pacific hagfish eptatretus stoutii
2010Co-Authors: Erik Sandblom, Anthony P FarrellAbstract:In the absence of any previous study of the cardiac status of hagfishes during prolonged Anoxia and because of their propensity for oxygen-depleted environments, the present study tested the hypothesis that the Pacific hagfish Eptatretus stoutii maintains cardiac performance during prolonged Anoxia. Heart rate was halved from the routine value of 10.4±1.3 beats min–1 by the sixth hour of an anoxic period and then remained stable for a further 30 h. Cardiac stroke volume increased from routine (1.3±0.1 ml kg–1) to partially compensate the anoxic bradycardia, such that cardiac output decreased by only 33% from the routine value of 12.3±0.9 ml min–1 kg–1. Cardiac power output decreased by only 25% from the routine value of 0.26±0.02 mW g–1. During recovery from prolonged Anoxia, cardiac output and heart rate increased to peak values within 1.5 h. Thus, the Pacific hagfish should be acknowledged as hypoxic tolerant in terms of its ability to maintain around 70% of their normoxic cardiac performance during prolonged Anoxia. This is only the second fish species to be so classified. * f H : heart rate M v : ventricular mass P 50 : P O2 at which hemoglobin is 50% saturated with oxygen P O2 : partial pressure of oxygen PO : power output P va : ventral aortic pressure ![Graphic][1] : cardiac output RMR : routine metabolic rate V s : stroke volume [1]: /embed/inline-graphic-30.gif
-
α adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtle trachemys scripta during anoxic submergence at 5 c and 21 c
2004Co-Authors: Jonathan A W Stecyk, Johannes Overgaard, Anthony P Farrell, Tobias WangAbstract:SUMMARY Anoxic exposure in the Anoxia-tolerant freshwater turtle is attended by substantial decreases in heart rate and blood flows, but systemic blood pressure (Psys) only decreases marginally due to an increase in systemic peripheral resistance (Rsys). Here, we investigate the role of the α-adrenergic system in modulating Rsys during Anoxia at 5°C and 21°C in the turtle Trachemys scripta, and also describe how Anoxia affects relative systemic blood flow distribution (%Qsys) and absolute tissue blood flows. Turtles were instrumented with an arterial cannula for measurement of Psys and ultrasonic flow probes on major systemic blood vessels for determination of systemic cardiac output (Qsys). α-Adrenergic tone was assessed from vascular injections of α-adrenergic agonists and antagonists (phenylephrine and phentolamine, respectively) during normoxia and following either 6 h (21°C) or 12 days (5°C) of anoxic submergence. Coloured microspheres, injected through a left atrial cannula during normoxia and Anoxia, as well as after α-adrenergic stimulation and blockade during Anoxia at both temperatures, were used to determine relative and absolute tissue blood flows. Anoxia was associated with an increased Rsys and functional α-adrenergic vasoactivity at both acclimation temperatures. However, while Anoxia at 21°C was associated with a high systemicα -adrenergic tone, the progressive increase of Rsys at 5°C was not mediated by α-adrenergic control. A redistribution of blood flow away from ancillary vascular beds towards more vital circulations occurred with Anoxia at both acclimation temperatures. %Qsys and absolute blood flow were reduced to the digestive and urogenital tissues (approximately 2- to 15-fold), while %Qsys and absolute blood flows to the heart and brain were maintained at normoxic levels. The importance of liver and muscle glycogen stores in fueling anaerobic metabolism were indicated by increases in %Qsys to the muscle at 21°C (1.3-fold) and liver at 5°C (1.7-fold). As well, the crucial importance of the turtle shell as a buffer reserve during anoxic submergence was indicated by 40-50% of Qsys being directed towards the shell during Anoxia at both 5°C and 21°C. α-Adrenergic stimulation and blockade during Anoxia caused few changes in %Qsys and absolute tissue blood flow. However, there was evidence of α-adrenergic vasoactivity contributing to blood flow regulation to the liver and shell during anoxic submergence at 5°C.
Donald C Jackson - One of the best experts on this subject based on the ideXlab platform.
-
the metabolic consequences of repeated anoxic stress in the western painted turtle chrysemys picta bellii
2017Co-Authors: Daniel E Warren, Donald C JacksonAbstract:The painted turtle is known for its extreme tolerance to Anoxia, but it is unknown whether previous experience with anoxic stress might alter physiological performance during or following a test bout of Anoxia. Repeatedly subjecting 25°C-acclimated painted turtles to 2h of anoxic stress every other day for 19days (10 submergence bouts total) caused resting levels of liver glycogen to decrease by 17% and liver citrate synthase (CS) and cytochrome oxidase (COX) activities to increase by 33% and 112%, respectively. When the repeatedly submerged turtles were studied during a subsequent anoxic stress test, liver COX and CS activities decreased during Anoxia to the same levels of naive turtles, which were unchanged, and remained there throughout metabolic recovery. There were no effects of the repeated Anoxia treatment on any of the other measured variables, which included lactate dehydrogenase and phosphofructokinase activities in liver, skeletal muscle, and ventricle, blood acid-base status, hemoglobin, hematocrit and plasma ion (Na, K, Ca, Mg, Cl) and metabolite concentrations (lactate, glucose, free-fatty acids), before, during, or after the anoxic stress test. We conclude that although painted turtles can show a physiological reaction to repeated anoxic stress, the changes appear to have no measurable effect on anaerobic physiological performance or ability to recover from Anoxia.
-
bone and shell contribution to lactic acid buffering of submerged turtles chrysemys picta bellii at 3 c
2000Co-Authors: Donald C Jackson, Carlos E Crocker, Gordon R UltschAbstract:To evaluate shell and bone buffering of lactic acid during acidosis at 3°C, turtles were submerged in anoxic or aerated water and tested at intervals for blood acid-base status and plasma ions and for bone and shell percent water, percent ash, and concentrations of lactate, Ca2+, Mg2+, Pi, Na+, and K+. After 125 days, plasma lactate concentration rose from 1.6 ± 0.2 mM (mean ± SE) to 155.2 ± 10.8 mM in the anoxic group but only to 25.2 ± 6.4 mM in the aerated group. The acid-base state of the normoxic animals was stable after 25 days of submergence. Plasma calcium concentration ([Ca2+]) rose during Anoxia from 3.2 ± 0.2 to 46.0 ± 0.6 mM and [Mg2+] from 2.7 ± 0.2 to 12.2 ± 0.6 mM. Both shell and bone accumulated lactate to concentrations of 135.6 ± 35.2 and 163.6 ± 5.1 mmol/kg wet wt, respectively, after 125 days Anoxia. Shell and bone [Na+] both fell during Anoxia but the fate of this Na+ is uncertain because plasma [Na+] also fell. No other shell ions changed significantly in concentration, although the ...
Harvey A Millar - One of the best experts on this subject based on the ideXlab platform.
-
differential molecular responses of rice and wheat coleoptiles to Anoxia reveal novel metabolic adaptations in amino acid metabolism for tissue tolerance
2011Co-Authors: Rachel N Shingakiwells, Shaobai Huang, Nicolas L Taylor, Adam J Carroll, Wenxu Zhou, Harvey A MillarAbstract:Rice (Oryza sativa) and wheat (Triticum aestivum) are the most important starch crops in world agriculture. While both germinate with an anatomically similar coleoptile, this tissue defines the early Anoxia tolerance of rice and the Anoxia intolerance of wheat seedlings. We combined protein and metabolite profiling analysis to compare the differences in response to Anoxia between the rice and wheat coleoptiles. Rice coleoptiles responded to Anoxia dramatically, not only at the level of protein synthesis but also at the level of altered metabolite pools, while the wheat response to Anoxia was slight in comparison. We found significant increases in the abundance of proteins in rice coleoptiles related to protein translation and antioxidant defense and an accumulation of a set of enzymes involved in serine, glycine, and alanine biosynthesis from glyceraldehyde-3-phosphate or pyruvate, which correlates with an observed accumulation of these amino acids in anoxic rice. We show a positive effect on wheat root Anoxia tolerance by exogenous addition of these amino acids, indicating that their synthesis could be linked to rice Anoxia tolerance. The potential role of amino acid biosynthesis contributing to Anoxia tolerance in cells is discussed.
-
protein synthesis by rice coleoptiles during prolonged Anoxia implications for glycolysis growth and energy utilization
2005Co-Authors: Shaobai Huang, Hank Greenway, Timothy D Colmer, Harvey A MillarAbstract:• Background and Aims Anoxia-tolerant plant tissues synthesize a number of proteins during Anoxia, in addition to the ‘classical anaerobic proteins’ involved in glycolysis and fermentation. The present study used a model system of rice coleoptile tips to elucidate patterns of protein synthesis in this Anoxia-tolerant plant tissue. • Methods Coleoptile tips 7–11 mm long were excised from intact seedlings exposed to Anoxia, or excised from hypoxically pre-treated seedlings and then exposed to Anoxia for 72 h. Total proteins or 35S-labelled proteins were extracted, separated using two-dimensional isoelectric focusing/SDS–polyacrylamide gel electrophoresis and analysed using mass spectrometry. • Key Results The coleoptile tips excised after intact seedlings had been exposed to Anoxia for 72 h had a similar proteome to tips that were first excised and then exposed to Anoxia. After 72 h Anoxia, Bowman–Birk trypsin inhibitors and a glycine-rich RNA-binding protein decreased in abundance, whereas a nucleoside diphosphate kinase and several proteins with unknown functions were strongly enhanced. Using [35S]methionine as label, proteins synthesized at high levels in Anoxia, and also in aeration, included a nucleoside diphosphate kinase, a glycine-rich RNA-binding protein, a putative elicitor-inducible protein and a putative actin-depolymerizing factor. Proteins synthesized predominately in Anoxia included a pyruvate orthophosphate dikinase (PPDK), alcohol dehydrogenase 1 and 2, fructose 1,6-bisphosphate aldolase and a protein of unknown function. • Conclusion The induction of PPDK in anoxic rice coleoptiles might, in combination with pyruvate kinase (PK), enable operation of a ‘substrate cycle’ producing PPi from ATP. Production of PPi would (a) direct energy to crucial transport processes across the tonoplast (i.e. the H+-PPiase); (b) be required for sucrose hydrolysis via sucrose synthase; and (c) enable acceleration of glycolysis, via pyrophosphate:fructose 6-phosphate 1-phosphotransferase (PFP) acting in parallel with phosphofructokinase (PFK), thus enhancing ATP production in anoxic rice coleoptiles; ATP production would need to be increased if there was a substantial requirement for PPi.