Metabolic and functional consequences of adenylate kinase deficiency in skeletal muscle

2005 ◽  
Author(s):  
◽  
Chad R. Hancock
Keyword(s):  
Skeletal Muscle ◽  
Adenylate Kinase ◽  
Energy State ◽  
High Energy ◽  
Metabolic Signaling ◽  
University Of Missouri ◽  
Energy Demands ◽  
Ampk Phosphorylation ◽  
Functional Consequences ◽  
The University

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The primary function of skeletal muscle is to generate tension, and this ultimately occurs through ATP utilization. An increase in ADP and a depression in the cellular energy state are thought to be limited by the adenylate kinase (AK) reaction during high energy demands. AMP production through AK is also thought to be important for metabolic signaling, particularly during moderate energy demands. Thus, AK deficiency in muscle was evaluated during highly demanding and moderately demanding muscle contractions, using the AK1 knockout mouse (AK1-/-). The results demonstrate that AK deficiency leads to a marked elevation in free-ADP (1.5mM) at high energy demands, many fold greater than previously thought possible. These results call into question previously held views concerning the energy required for normal muscle function, because the performance was remarkably tolerant of ADP accumulation. At lower energy demands, AMPK phosphorylation was tempered in AK1-/- muscle consistent with reduced AMP production. Interestingly, other indicators of AMPK activity suggest that AMPK activation occurs normally, despite reduced AMPK phosphorylation. Thus, AK is critically important for the management of ADP during high energy demands, and may result in altered metabolic signaling at low energy demands.

Skeletal muscle contractile performance and ADP accumulation in adenylate kinase-deficient mice

2005 ◽  
Vol 288 (6) ◽  
pp. C1287-C1297 ◽  
Author(s):  
Chad R. Hancock ◽  
Edwin Janssen ◽  
Ronald L. Terjung
Keyword(s):  
Skeletal Muscle ◽  
Adenylate Kinase ◽  
Energy Demand ◽  
Adenine Nucleotide ◽  
Formation Rate ◽  
High Energy ◽  
Energy Demands ◽  
Whole Muscle ◽  
Muscle Contractile ◽  
Contractile Performance

The production of AMP by adenylate kinase (AK) and subsequent deamination by AMP deaminase limits ADP accumulation during conditions of high-energy demand in skeletal muscle. The goal of this study was to investigate the consequences of AK deficiency (−/−) on adenine nucleotide management and whole muscle function at high-energy demands. To do this, we examined isometric tetanic contractile performance of the gastrocnemius-plantaris-soleus (GPS) muscle group in situ in AK1−/− mice and wild-type (WT) controls over a range of contraction frequencies (30–120 tetani/min). We found that AK1−/− muscle exhibited a diminished inosine 5′-monophosphate formation rate (14% of WT) and an inordinate accumulation of ADP (∼1.5 mM) at the highest energy demands, compared with WT controls. AK-deficient muscle exhibited similar initial contractile performance (521 ± 9 and 521 ± 10 g tension in WT and AK1−/− muscle, respectively), followed by a significant slowing of relaxation kinetics at the highest energy demands relative to WT controls. This is consistent with a depressed capacity to sequester calcium in the presence of high ADP. However, the overall pattern of fatigue in AK1−/− mice was similar to WT control muscle. Our findings directly demonstrate the importance of AMP formation and subsequent deamination in limiting ADP accumulation. Whole muscle contractile performance was, however, remarkably tolerant of ADP accumulation markedly in excess of what normally occurs in skeletal muscle.

Abstract 392: Metabolic Signaling Mechanisms Governing Heart Regenerative Capacity

2015 ◽  
Vol 117 (suppl_1) ◽  
Author(s):  
Song Zhang ◽  
Petras Dzeja
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Network Formation ◽  
Energy State ◽  
High Energy ◽  
Cardiomyocyte Proliferation ◽  
Regenerative Capacity ◽  
Metabolic Signaling ◽  
Signaling Mechanisms ◽  
Cell Commitment

Energy metabolism and metabolic signaling circuits orchestrate cell commitment to self-renewal, lineage specification, differentiation and regeneration. When energy resources are plenty, cell can grow, proliferate and regenerate, however when energy is low - augmented adenylate kinase (AK)-mediated AMP signaling turns on AMPK which silences p53/p21/cyclin cell cycle metabolic checkpoint and halts cell division. Using mouse neonatal hearts, with high and low regenerative capacity, we have determined metabolomic profiles and dynamics of phosphotransfer circuits using 18O-phosphoryl labeling mass-spectrometric and 18O-assisted 31P NMR techniques. We demonstrate that loss of heart regenerative capacity after birth is associated with marked changes in heart AK-catalyzed phosphotransfer flux and AMP signaling along with changes in expression levels of p21, cyclin A and E and thymidine kinase. It appears, that in adult heart increased expression of AK isoforms (AK1, AK2 and AK1β) and augmented high energy phosphoryl and AMP signal dynamics is misread by AMPK-sensor as "low energy" state inducing blockade of cell cycle metabolic checkpoint and cardiomyocyte proliferation and renewal. Using AK-GFP constructs and immunocytochemistry we further demonstrate the distribution of AK1, AK1β, AK2 and AMPK between cytosol and nucleus and association with mitotic spindle and cytokinetic apparatus during cell division cycle. AK1 translocation to the nucleus, however, doesn’t occur in adult cardiomyocytes deficient in cytokinesis. Protein knockdown using siRNA indicates that AK2 is critical for cardiomyocyte mitochondrial biogenesis and network formation. Furthermore, we have discovered that deficiency of the AK2 isoform, which is localized in mitochondria intermembrane-intra-cristae space, arrests developmental programming and is embryonically lethal in mice. The uncovered shift in metabolic signaling mechanisms opens new avenues for targeted regulation of heart regenerative potential critical for repair of injured hearts.

scholarly journals Structural basis for ligand binding to an enzyme by a conformational selection pathway

2017 ◽  
Vol 114 (24) ◽  
pp. 6298-6303 ◽  
Author(s):  
Michael Kovermann ◽  
Christin Grundström ◽  
A. Elisabeth Sauer-Eriksson ◽  
Uwe H. Sauer ◽  
Magnus Wolf-Watz
Keyword(s):  
Ligand Binding ◽  
Adenylate Kinase ◽  
Energy State ◽  
High Energy ◽  
Structural Basis ◽  
Fast Time ◽  
X Ray ◽  
Conformational Selection ◽  
High Energy State ◽  
Energy States

Proteins can bind target molecules through either induced fit or conformational selection pathways. In the conformational selection model, a protein samples a scarcely populated high-energy state that resembles a target-bound conformation. In enzymatic catalysis, such high-energy states have been identified as crucial entities for activity and the dynamic interconversion between ground states and high-energy states can constitute the rate-limiting step for catalytic turnover. The transient nature of these states has precluded direct observation of their properties. Here, we present a molecular description of a high-energy enzyme state in a conformational selection pathway by an experimental strategy centered on NMR spectroscopy, protein engineering, and X-ray crystallography. Through the introduction of a disulfide bond, we succeeded in arresting the enzyme adenylate kinase in a closed high-energy conformation that is on-pathway for catalysis. A 1.9-Å X-ray structure of the arrested enzyme in complex with a transition state analog shows that catalytic sidechains are properly aligned for catalysis. We discovered that the structural sampling of the substrate free enzyme corresponds to the complete amplitude that is associated with formation of the closed and catalytically active state. In addition, we found that the trapped high-energy state displayed improved ligand binding affinity, compared with the wild-type enzyme, demonstrating that substrate binding to the high-energy state is not occluded by steric hindrance. Finally, we show that quenching of fast time scale motions observed upon ligand binding to adenylate kinase is dominated by enzyme–substrate interactions and not by intramolecular interactions resulting from the conformational change.

Abstract 122: Adenylate Kinase Isoform Network and AMP Metabolic Signaling in Heart Regeneration

2017 ◽  
Vol 121 (suppl_1) ◽  
Author(s):  
Song Zhang ◽  
Petras Dzeja
Keyword(s):  
Cell Cycle ◽  
Adenylate Kinase ◽  
Energy State ◽  
Cell Cycle Checkpoint ◽  
Heart Regeneration ◽  
Metabolic Signaling ◽  
Expression Levels ◽  
Atp Turnover ◽  
Signaling Mechanisms ◽  
Cycle Checkpoint

Metabolic signaling mechanisms of tissue regeneration is still an enigma. Energy state and metabolite signals regulate cell commitment to self-renewal, lineage specification, differentiation and regeneration. In a favorable metabolic environment, cells can grow and proliferate, however when energy is low - metabolic monitoring system sends signals to cell cycle checkpoint to halt cell division and preserve fuel resources. We demonstrate that loss of heart regenerative capacity after birth in mice is associated with marked changes in metabolome, AK-catalyzed phosphotransfer flux (β-ATP[ 18 O]), ATP turnover (γ-ATP[ 18 O]) and AMP-AMPK signaling along with changes in expression levels of p21, cyclins A and E, pGSK3β and thymidine kinase. Marked reduction of thymidine phosphorylation capacity prevents DNA synthesis and cell proliferation. It emerges, that in adult heart augmented ATP turnover and AMP signal dynamics is misread by AMPK-sensor as "low energy" state inducing blockade of cell cycle metabolic checkpoint and cardiomyocyte proliferation and regeneration after injury. This occurs through augmented adenylate kinase (AK)-mediated AMP signaling which turns on AMPK consequently silencing p53/p21/cyclin cell cycle checkpoint. Changes in expression levels AK1, AK1β, AK2 and AK5 isoforms occur with arrest of heart regeneration. Protein knockdown using siRNA and CRISPR/Cas9 approach indicates that AK2 is critical for cardiomyocyte mitochondrial biogenesis and network formation. Furthermore, we have discovered that deficiency of the AK2 isoform, which is localized in mitochondria intermembrane-intra-cristae space, arrests developmental programming and is embryonically lethal in mice. The uncovered shift in metabolic signaling mechanisms opens new avenues for targeted regulation of heart regenerative potential critical for repair of injured hearts.

Metabolic control over the oxygen consumption flux in intact skeletal muscle: in silico studies

2006 ◽  
Vol 291 (6) ◽  
pp. C1213-C1224 ◽  
Author(s):  
Piotr Liguzinski ◽  
Bernard Korzeniewski
Keyword(s):  
Skeletal Muscle ◽  
Oxygen Consumption ◽  
Oxidative Phosphorylation ◽  
Metabolic Control ◽  
In Silico ◽  
High Energy ◽  
Activation Mechanism ◽  
Atp Production ◽  
Atp Turnover ◽  
Energy Demands

It has been postulated previously that a direct activation of all oxidative phosphorylation complexes in parallel with the activation of ATP usage and substrate dehydrogenation (the so-called each-step activation) is the main mechanism responsible for adjusting the rate of ATP production by mitochondria to the current energy demand during rest-to-work transition in intact skeletal muscle in vivo. The present in silico study, using a computer model of oxidative phosphorylation developed previously, analyzes the impact of the each-step-activation mechanism on the distribution of control (defined within Metabolic Control Analysis) over the oxygen consumption flux among the components of the bioenergetic system in intact oxidative skeletal muscle at different energy demands. It is demonstrated that in the absence of each-step activation, the oxidative phosphorylation complexes take over from ATP usage most of the control over the respiration rate and oxidative ATP production at higher (but still physiological) energy demands. This leads to a saturation of oxidative phosphorylation, impossibility of a further acceleration of oxidative ATP synthesis, and dramatic drop in the phosphorylation potential. On the other hand, the each-step-activation mechanism allows maintenance of a high degree of the control exerted by ATP usage over the ATP turnover and oxygen consumption flux even at high energy demands and thus enables a potentially very large increase in ATP turnover. It is also shown that low oxygen concentration shifts the metabolic control from ATP usage to cytochrome oxidase and thus limits the oxidative ATP production.

Muscle phosphorus energy state in very-low-birth-weight infants: effect of exercise

1992 ◽  
Vol 262 (3) ◽  
pp. E289-E294 ◽  
Author(s):  
L. A. Bertocci ◽  
C. E. Mize ◽  
R. Uauy
Keyword(s):  
Skeletal Muscle ◽  
Birth Weight ◽  
Low Birth Weight ◽  
Very Low Birth Weight ◽  
Energy State ◽  
High Energy ◽  
High Energy Phosphates ◽  
Human Infants ◽  
Biochemical Basis ◽  
Vlbw Infants

Skeletal muscle hypotonia is a hallmark clinical finding in very-low-birth-weight (VLBW) human infants. Although the biochemical basis for this phenomenon is not completely understood, one hypothesis is that the phosphorylation potential is abnormally low in the skeletal muscle of these infants. Therefore, we used 31P-nuclear magnetic resonance (NMR) spectroscopy to measure phosphorus metabolites in the skeletal muscle of VLBW infants during rest and during reflex-induced muscle contractions. Compared with healthy larger infants or to adults, the total phosphorus NMR signal is lower in VLBW infants. In VLBW infants during rest, [PCr]/([PCr]+[Pi]), where PCr is phosphocreatine and brackets denote concentration, was 89% and [ATP]/[ADP][Pi] was 59% of that found in larger infants (P less than 0.05). During reflex-induced isometric contractions in VLBW infants, [PCr]/([PCr]+[Pi]) declined by 24% and [ATP]/[ADP][Pi] declined by 35% (P less than 0.05 vs. rest). In all conditions, muscle pH remained 7.1. Overall, the differences in skeletal muscle energy state during rest and the corresponding changes in concentration of high-energy phosphates during mild exercise suggest a very limited energy reserve in the hypotonic muscle of VLBW infants.

31P-NMR observation of free ADP during fatiguing, repetitive contractions of murine skeletal muscle lacking AK1

2005 ◽  
Vol 288 (6) ◽  
pp. C1298-C1304 ◽  
Author(s):  
Chad R. Hancock ◽  
Jeffrey J. Brault ◽  
Robert W. Wiseman ◽  
Ronald L. Terjung ◽  
Ronald A. Meyer
Keyword(s):  
Skeletal Muscle ◽  
Atp Synthesis ◽  
High Energy ◽  
High Yield ◽  
High Energy Phosphates ◽  
Cellular Processes ◽  
Calcium Sequestration ◽  
Energy Demands ◽  
Murine Skeletal Muscle ◽  
First Time

Metabolic control within skeletal muscle is designed to limit ADP accumulation even during conditions where ATP demand is out of balance with ATP synthesis. This is accomplished by the reactions of adenylate kinase (AK; ADP+ADP ↔ AMP+ATP) and AMP deaminase (AMP+H2O → NH3+IMP), which limit ADP accumulation under these conditions. The purpose of this study was to determine whether AK deficiency (AK−/−) would result in sufficient ADP accumulation to be visible using 31P-NMRS during the high energy demands of frequent in situ tetanic contractions. To do this we examined the high-energy phosphates of the gastrocnemius muscle in the knockout mouse with AK1−/− and wild-type (WT) control muscle over the course of 64 rapid (2/s) isometric tetanic contractions. Near-complete depletion of phosphocreatine was apparent after 16 contractions in both groups. By ∼40 contractions, ADP was clearly visible in AK1−/− muscle. This transient concentration of the NMR visible free ADP was estimated to be ∼1.7 mM, and represents the first time free ADP has been directly measured in contracting skeletal muscle. Such an increase in free ADP is severalfold greater than previously thought to occur. This large accumulation of free ADP also represents a significant reduction in energy available from ATP, and has implications on cellular processes that depend on a high yield of energy from ATP such as calcium sequestration. Remarkably, the AK1−/− and WT muscles exhibited similar fatigue profiles. Our findings suggest that skeletal muscle is surprisingly tolerant to a large increase in ADP and by extension, a decline in energy from ATP.

Modeling, characterization and evaluation of MU100 high-energy density ceramic nanodielectric for use in pulsed power applications

2017 ◽  
Author(s):  
◽  
Alexander B. Howard
Keyword(s):  
Energy Density ◽  
Dielectric Strength ◽  
High Energy ◽  
Pulsed Power ◽  
High Energy Density ◽  
Small Scale ◽  
University Of Missouri ◽  
High Dielectric ◽  
The University ◽  
Preparation And Evaluation

A high dielectric, nanodielectric, composite material, MU100, was developed by the University of Missouri for use in dielectric loaded antennas. Based on its dielectric strength and losses, MU100 had possible uses in the development for high energy-density capacitors. This work presents the theory behind, methods of preparation and evaluation, modeling and properties of MU100. MU100’s dielectric properties are explored in high energy-density pulsed power applications, compact high voltage capacitors. Small scale tests have shown the average dielectric strength of MU100 to be 225 kV/cm with a peak break down field of 328 kV/cm. When potted, these small-scale capacitors have lifetimes in excess of 800,000 discharges at 80% of their maximum rated field strength. This shows a remarkable development in the performance of high energy density capacitors for use in pulsed power applications.

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