Genes controlling the metabolic switch in hibernating mammals

2004 ◽  
Vol 32 (6) ◽  
pp. 1021-1024 ◽  
Author(s):  
M.T. Andrews
Keyword(s):  
Low Temperature ◽  
Pyruvate Dehydrogenase ◽  
Ground Squirrel ◽  
Mammalian Cells ◽  
Lipolytic Activity ◽  
Tricarboxylic Acid Cycle ◽  
Ground Squirrels ◽  
Pyruvate Dehydrogenase Kinase ◽  
Body Temperatures ◽  
Triacylglycerol Lipase

Hibernating mammals have the ability to decrease their metabolic rate and survive up to 6 months without food in an inactive state where body temperatures approach 0°C. In hibernating 13-lined ground squirrels (Spermophilus tridecemlineatus), oxygen consumption holds at 1/30 to 1/50 of the aroused condition and heart rates are as low as 3–10 beats/min, compared with 200–300 beats/min when the animal is active. This seasonal adaptation requires a metabolic shift away from the oxidation of carbohydrates and towards the combustion of stored fatty acids as the primary source of energy. A key element in this fuel switch is the differential expression of the gene encoding pyruvate dehydrogenase kinase isoenzyme 4. Pyruvate dehydrogenase kinase isoenzyme 4 inhibits pyruvate dehydrogenase and thus minimizes carbohydrate oxidation by preventing the flow of glycolytic products into the tricarboxylic acid cycle. Hibernators also exploit the low-temperature activity of PTL (pancreatic triacylglycerol lipase) in both heart and white adipose tissue. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTL expressed in yeast. Enzymes from both humans and ground squirrel displayed high activity at temperatures as low as 0°C and showed Q10=1.2–1.5 over the temperature range 37–7°C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state.

Pancreatic triacylglycerol lipase in a hibernating mammal. II. Cold-adapted function and differential expression

2003 ◽  
Vol 16 (1) ◽  
pp. 131-140 ◽  
Author(s):  
Teresa L. Squire ◽  
Mark E. Lowe ◽  
Vernon W. Bauer ◽  
Matthew T. Andrews
Keyword(s):  
Low Temperature ◽  
High Activity ◽  
Ground Squirrel ◽  
Mammalian Cells ◽  
Lipolytic Activity ◽  
Tissue Expression ◽  
Ground Squirrels ◽  
Mrna Levels ◽  
Western Blots ◽  
Triacylglycerol Lipase

Thirteen-lined ground squirrels ( Spermophilus tridecemlineatus) exploit the low-temperature activity of pancreatic triacylglycerol lipase (PTL) during hibernation. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTLs expressed in yeast. Both the human and ground squirrel enzymes displayed high activity at temperatures as low as 0°C and showed Q10 values of 1.2–1.5 over a range of 37–7°C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state. Western blots show elevated levels of PTL protein during hibernation in both heart and white adipose tissue (WAT). Significant increases in PTL gene expression are seen in heart, WAT, and testes; but not in pancreas, where PTL mRNA levels are highest. Upregulation of PTL in testes is also accompanied by expression of the PTL-specific cofactor, colipase. The multi-tissue expression of PTL during hibernation supports its role as a key enzyme that shows high activity at low temperatures.

Digital transcriptome analysis indicates adaptive mechanisms in the heart of a hibernating mammal

2005 ◽  
Vol 23 (2) ◽  
pp. 227-234 ◽  
Author(s):  
Katharine M. Brauch ◽  
Nirish D. Dhruv ◽  
Eric A. Hanse ◽  
Matthew T. Andrews
Keyword(s):  
High Throughput Sequencing ◽  
Digital Gene Expression ◽  
Ground Squirrels ◽  
Pyruvate Dehydrogenase Kinase ◽  
Cdna Libraries ◽  
Body Temperatures ◽  
Triacylglycerol Lipase ◽  
Plasmic Reticulum ◽  
Comprehensive Survey ◽  
Dependent Protein

Survival of near-freezing body temperatures and reduced blood flow during hibernation is likely the result of changes in the expression of specific genes. In this study, we described a comprehensive survey of mRNAs in the heart of the thirteen-lined ground squirrel ( Spermophilus tridecemlineatus) before and during hibernation. The heart was chosen for this study because it is a contractile organ that must continue to work despite body temperatures of 5°C and the lack of food for periods of 5–6 mo. We used a digital gene expression assay involving high-throughput sequencing of directional cDNA libraries from hearts of active and hibernating ground squirrels to determine the identity and frequency of 3,532 expressed sequence tags (ESTs). Statistical analysis of the active and hibernating heart expression profile indicated the differential regulation of 48 genes based on a P ≤ 0.03 threshold. Several of the differentially expressed genes identified in this screen encode proteins that likely account for uninterrupted cardiac function during hibernation, including those involved in metabolism, contractility, Ca2+ handling, and low-temperature catalysis. A sampling of genes showing higher expression during hibernation includes phosphofructokinase, pancreatic triacylglycerol lipase, pyruvate dehydrogenase kinase 4 (PDK4), aldolase A, sarco(endo)plasmic reticulum Ca2+-ATPase 2a (SERCA2a), titin, and four-and-a-half LIM domains protein 2 (FHL2). Genes showing reduced levels of expression during hibernation include cyclin-dependent kinase 2-associated protein 1 (CDK2AP1), troponin C, phospholamban, Ca2+/calmodulin-dependent protein kinase II (CaMKII), calmodulin, and four subunits of cytochrome c oxidase.

scholarly journals Fibre-type specific modification of the activity and regulation of skeletal muscle pyruvate dehydrogenase kinase (PDK) by prolonged starvation and refeeding is associated with targeted regulation of PDK isoenzyme 4 expression

2000 ◽  
Vol 346 (3) ◽  
pp. 651-657 ◽  
Author(s):  
Mary C. SUGDEN ◽  
Alexandra KRAUS ◽  
Robert A. HARRIS ◽  
Mark J. HOLNESS
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Pyruvate Dehydrogenase ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Pyruvate Dehydrogenase Kinase ◽  
Acid Cycle ◽  
Slow Twitch ◽  
Fast Twitch ◽  
Anterior Tibialis

Using immunoblot analysis with antibodies raised against recombinant pyruvate dehydrogenase kinase (PDK) isoenzymes PDK2 and PDK4, we demonstrate selective changes in PDK isoenzyme expression in slow-twitch versus fast-twitch skeletal muscle types in response to prolonged (48 h) starvation and refeeding after starvation. Starvation increased PDK activity in both slow-twitch (soleus) and fast-twitch (anterior tibialis) skeletal muscle and was associated with loss of sensitivity of PDK to inhibition by pyruvate, with a greater effect in anterior tibialis. Starvation significantly increased PDK4 protein expression in both soleus and anterior tibialis, with a greater response in anterior tibialis. Starvation did not effect PDK2 protein expression in soleus, but modestly increased PDK2 expression in anterior tibialis. Refeeding for 4 h partially reversed the effect of 48-h starvation on PDK activity and PDK4 expression in both soleus and anterior tibialis, but the response was more marked in soleus than in anterior tibialis. Pyruvate sensitivity of PDK activity was also partially restored by refeeding, again with the greater response in soleus. It is concluded that targeted regulation of PDK4 isoenzyme expression in skeletal muscle in response to starvation and refeeding underlies the modulation of the regulatory characteristics of PDK in vivo. We propose that switching from a pyruvate-sensitive to a pyruvate-insensitive PDK isoenzyme in starvation (a) maintains a sufficiently high pyruvate concentration to ensure that the glucose → alanine → glucose cycle is not impaired, and (b) may ‘spare’ pyruvate for anaplerotic entry into the tricarboxylic acid cycle to support the entry of acetyl-CoA derived from fatty acid (FA) oxidation into the tricarboxylic acid cycle. We further speculate that FA oxidation by skeletal muscle is both forced and facilitated by upregulation of PDK4, which is perceived as an essential component of the operation of the glucose-FA cycle in starvation.

Isovolumetric performance of isolated ground squirrel and rat hearts at low temperature

1984 ◽  
Vol 247 (4) ◽  
pp. R722-R727 ◽  
Author(s):  
D. R. Caprette ◽  
J. B. Senturia
Keyword(s):  
Low Temperature ◽  
Ground Squirrel ◽  
Mechanical Performance ◽  
Cell Communication ◽  
Ventricular Myocardium ◽  
Ground Squirrels ◽  
Rat Hearts ◽  
Pulsus Alternans ◽  
Rate Of Increase ◽  
Developed Pressure

The effects of low temperature on mechanical performance of the isolated left ventricles of the 13-lined ground squirrel (a hibernator) and the rat (a nonhibernator) were studied. In addition, low-temperature performance of hearts from summer-active, winter-hibernating, and winter-active ground squirrels were compared. By measuring pressure (P) generated against a balloon inserted into the left ventricle, maximum developed pressure (DP) and maximum rate of increase of P (peak dP/dt) were determined over a temperature range of 5–20 degrees C. The DP and dP/dt of the rat ventricle exhibited significantly greater reduction in magnitude at reduced temperature, compared with those of ground squirrel ventricle. Rat, but not ground squirrel, hearts exhibited arrhythmias of various kinds, including extra-systoles, tachycardia, pulsus alternans, and periods of asystole. Hearts from winter-active ground squirrels developed greater pressures than those from winter-hibernating and summer-active animals. This evidence suggests that disruption of cell communication in the nonhibernator ventricular myocardium plays an important role in the failure of the nonhibernator heart at low body temperatures. Contractility of the seasonal hibernator's heart is influenced by both season and hibernation itself, possibly through shifts in myocardial metabolism. However, seasonal adaptations appear not to be required to confer the special resistance of the seasonal hibernator's heart to the deleterious effects of low temperature.

Identification and validation of differentially expressed transcripts in a hepatocyte model of cold-induced glycerol production in rainbow smelt (Osmerus mordax)

2011 ◽  
Vol 301 (4) ◽  
pp. R995-R1010 ◽  
Author(s):  
Jennifer R. Hall ◽  
Kathy A. Clow ◽  
Matthew L. Rise ◽  
William R. Driedzic
Keyword(s):  
Amino Acids ◽  
Low Temperature ◽  
Pyruvate Dehydrogenase ◽  
Cdna Array ◽  
Pyruvate Dehydrogenase Kinase ◽  
Osmerus Mordax ◽  
Type Ii ◽  
Glycerol Production ◽  
Rainbow Smelt ◽  
Transcript Levels

Rainbow smelt ( Osmerus mordax ) avoid freezing by producing antifreeze protein (AFP) and accumulating glycerol. Glyceroneogenesis occurs in liver via a branch in glycolysis and gluconeogenesis and is activated by low temperature. Hepatocytes were isolated from the livers of fish acclimated to 8°C. Cells were incubated at warm (8°C; nonglycerol accumulating) or cold (0.4°C; glycerol accumulating) temperature over a 72-h time course. Reciprocal suppression subtractive hybridization libraries enriched for cold-responsive transcripts were constructed at 72 h. Microarray analyses using a 16K salmonid cDNA array were performed at 24, 48, and 72 h. Expression of type II AFP and 21 carbohydrate, amino acid, or lipid metabolism-related transcripts were validated using quantitative RT-PCR. Type II AFP transcript levels were not directly temperature related. In cold cells, levels of the glucose synthesis transcript were transiently higher. Increased glycerol production was not associated with increased phosphofructokinase or cytosolic glycerol-3-phosphate dehydrogenase transcript levels. Levels of transcripts (phosphoenolpyruvate carboxykinase, mitochondrial malate dehydrogenase, alanine aminotransferase, glutamate dehydrogenase, and aquaglyceroporin 9) associated with mobilization of amino acids to fuel glycerol accumulation were all transiently higher, suggesting a common regulatory mechanism. In cold compared with warm cells, pyruvate dehydrogenase kinase [an inhibitor of pyruvate dehydrogenase (PDH)] transcript levels were 20-fold higher. Potent inhibition of PDH would direct pyruvate and oxaloacetate derived from amino acids to glycerol, as opposed to oxidation via the citric acid cycle. Levels of a transcript potentially encoding glycerol-3-phosphatase, an enzyme not yet characterized in any vertebrate species, were higher following cold incubation. Finally, this study also presents the novel finding of increased glutamine synthetase transcript levels in response to low temperature.

scholarly journals PDK2: An Underappreciated Regulator of Liver Metabolism

Livers ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 82-97
Author(s):  
Benjamin L. Woolbright ◽  
Robert A. Harris
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Mammalian Cells ◽  
Drug Targets ◽  
Pyruvate Dehydrogenase Complex ◽  
Liver Metabolism ◽  
Pyruvate Dehydrogenase Kinase ◽  
Metabolic Flexibility ◽  
Fed State ◽  
Disease States ◽  
Dehydrogenase Complex

Pyruvate metabolism is critical for all mammalian cells. The pyruvate dehydrogenase complex couples the pyruvate formed as the primary product of glycolysis to the formation of acetyl-CoA required as the primary substrate of the citric acid cycle. Dysregulation of this coupling contributes to alterations in metabolic flexibility in obesity, diabetes, cancer, and more. The pyruvate dehydrogenase kinase family of isozymes phosphorylate and inactive the pyruvate dehydrogenase complex in the mitochondria. This function makes them critical mediators of mitochondrial metabolism and drug targets in a number of disease states. The liver expresses multiple PDKs, predominantly PDK1 and PDK2 in the fed state and PDK1, PDK2, and PDK4 in the starved and diabetic states. PDK4 undergoes substantial transcriptional regulation in response to a diverse array of stimuli in most tissues. PDK2 has received less attention than PDK4 potentially due to the dramatic changes in transcriptional gene regulation. However, PDK2 is more responsive than the other PDKs to feedforward and feedback regulation by substrates and products of the pyruvate dehydrogenase complex. Although underappreciated, this makes PDK2 particularly important for the minute-to-minute fine control of the pyruvate dehydrogenase complex and a major contributor to metabolic flexibility. The purpose of this review is to characterize the underappreciated role of PDK2 in liver metabolism. We will focus on known biological actions and physiological roles as well as what roles PDK2 may play in disease states. We will also define current inhibitors and address their potential as therapeutic agents in the future.

Adaptations for hibernation in the depot fats of a ground squirrel (Spermophilus beldingi)

1991 ◽  
Vol 69 (11) ◽  
pp. 2707-2711 ◽  
Author(s):  
Craig L. Frank
Keyword(s):  
Fatty Acids ◽  
Adipose Tissue ◽  
Melting Point ◽  
Ground Squirrel ◽  
Unsaturated Fatty Acids ◽  
Ground Squirrels ◽  
Body Temperatures ◽  
Melting Points ◽  
Spermophilus Beldingi ◽  
Free Ranging

Ground squirrels are small herbivores that hibernate during winter. The ecological–nutritional limitations on hibernation are virtually unknown, but one constraint may be the melting point of stored fat. Lipids must be fluid to be metabolizable, and body temperatures maintained during hibernation are usually 30 °C below the melting point of typical mammalian fats. Fats containing greater amounts of unsaturated fatty acids, however, have correspondingly lower melting points. White adipose tissue was sampled from free-ranging Belding's ground squirrels, Spermophilus beldingi, during both the summer and fall. The lipids were twice as unsaturated as those of other rodent species, most of the increased unsaturation being due to the accumulation of plant-produced polyunsaturated fatty acids derived from the animals' diet. The melting points of S. beldingi fats were consequently 25 °C lower than those of other mammals. These results suggest that ground squirrels may depend upon their plant diet for the polyunsaturates necessary to produce the lipids with low melting points that are needed for hibernation.

Oxygen-dependent regulation of mitochondrial respiration by hypoxia-inducible factor 1

2007 ◽  
Vol 405 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Gregg L. Semenza
Keyword(s):  
Mitochondrial Respiration ◽  
Mammalian Cells ◽  
Tricarboxylic Acid Cycle ◽  
Hypoxia Inducible Factor ◽  
Mitochondrial Respiratory Chain ◽  
Pyruvate Dehydrogenase Kinase ◽  
Complex Iii ◽  
Metabolic Adaptation ◽  
Acetyl Coa ◽  
Hypoxia Inducible Factor 1

The survival of metazoan organisms is dependent upon the utilization of O2 as a substrate for COX (cytochrome c oxidase), which constitutes Complex IV of the mitochondrial respiratory chain. Premature transfer of electrons, either at Complex I or at Complex III, results in the increased generation of ROS (reactive oxygen species). Recent studies have identified two critical adaptations that may function to prevent excessive ROS production in hypoxic cells. First, expression of PDK1 [PDH (pyruvate dehydrogenase) kinase 1] is induced. PDK1 phosphorylates and inactivates PDH, the mitochondrial enzyme that converts pyruvate into acetyl-CoA. In combination with the hypoxia-induced expression of LDHA (lactate dehydrogenase A), which converts pyruvate into lactate, PDK1 reduces the delivery of acetyl-CoA to the tricarboxylic acid cycle, thus reducing the levels of NADH and FADH2 delivered to the electron-transport chain. Secondly, the subunit composition of COX is altered in hypoxic cells by increased expression of the COX4-2 subunit, which optimizes COX activity under hypoxic conditions, and increased degradation of the COX4-1 subunit, which optimizes COX activity under aerobic conditions. Hypoxia-inducible factor 1 controls the metabolic adaptation of mammalian cells to hypoxia by activating transcription of the genes encoding PDK1, LDHA, COX4-2 and LON, a mitochondrial protease that is required for the degradation of COX4-1. COX subunit switching occurs in yeast, but by a completely different regulatory mechanism, suggesting that selection for O2-dependent homoeostatic regulation of mitochondrial respiration is ancient and likely to be shared by all eukaryotic organisms.

scholarly journals Metabolic effects of bacitracin in isolated rat hepatocytes

1983 ◽  
Vol 216 (2) ◽  
pp. 369-375 ◽  
Author(s):  
L Agius ◽  
C Wilding ◽  
K G M M Alberti
Keyword(s):  
Fatty Acid ◽  
Pyruvate Dehydrogenase ◽  
Acid Metabolism ◽  
Tricarboxylic Acid Cycle ◽  
Rat Hepatocytes ◽  
Pyruvate Dehydrogenase Kinase ◽  
Metabolic Effects ◽  
Acid Oxidation ◽  
Isolated Rat Hepatocytes ◽  
Intracellular Processing

Bacitracin is a proteolytic inhibitor which interacts with the intracellular processing of insulin. Its effects on pyruvate, fatty acid and amino acid metabolism were examined in rat hepatocyte suspensions. Bacitracin (0.25-1.0 mM) increased the oxidation of [1-14C]pyruvate by 50-70% and presumably therefore increased the flux through pyruvate dehydrogenase. This was found both in the presence of extracellular Ca2+ and in its absence, but not in the presence of 2 mM-2-chloropropionate, which inhibits pyruvate dehydrogenase kinase. Insulin did not further stimulate [1-14C]pyruvate oxidation in the presence of 1 mM-bacitracin. Bacitracin decreased 14CO2 formation from [2-14C]pyruvate (20-40%) and [U-14C]palmitate (30-70%), suggesting a decreased flux through the tricarboxylic acid cycle. Fatty acid oxidation before acetyl-CoA formation was also decreased. Bacitracin decreased the incorporation of label from [3H]leucine into protein in the absence of insulin, but not in its presence. Bacitracin is commonly used in studies on insulin action. Our results suggest that in such studies the effects noted may be related not only to an interaction of bacitracin with the intracellular processing of insulin but also to direct metabolic effects of bacitracin independent of insulin.

scholarly journals Pyruvate dehydrogenase kinases (PDKs): an overview toward clinical applications

2021 ◽  
Vol 41 (4) ◽  
Author(s):  
Xiuxiu Wang ◽  
Xiaoyue Shen ◽  
Yuting Yan ◽  
Hongmin Li
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Metabolic Diseases ◽  
Tricarboxylic Acid Cycle ◽  
Pyruvate Dehydrogenase Complex ◽  
Pyruvate Dehydrogenase Kinase ◽  
Future Research ◽  
Cellular Energy ◽  
Cellular Energy Metabolism ◽  
Atp Generation

Abstract Pyruvate dehydrogenase kinase (PDK) can regulate the catalytic activity of pyruvate decarboxylation oxidation via the mitochondrial pyruvate dehydrogenase complex, and it further links glycolysis with the tricarboxylic acid cycle and ATP generation. This review seeks to elucidate the regulation of PDK activity in different species, mainly mammals, and the role of PDK inhibitors in preventing increased blood glucose, reducing injury caused by myocardial ischemia, and inducing apoptosis of tumor cells. Regulations of PDKs expression or activity represent a very promising approach for treatment of metabolic diseases including diabetes, heart failure, and cancer. The future research and development could be more focused on the biochemical understanding of the diseases, which would help understand the cellular energy metabolism and its regulation by pharmacological effectors of PDKs.

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