ATP Usage Research Articles

Structural and functional insights into the T-even type bacteriophage topoisomerase II.

T-even type bacteriophages are virulent phages commonly used as model organisms, playing a crucial role in understanding various biological processes. One such process involves the regulation of DNA topology during phage replication upon host infection, governed by type IIA DNA topoisomerases. In spite of various studies on prokaryotic and eukaryotic counterparts, viral topoisomerase II remains insufficiently understood, especially the unique domain composition of T4 phage. In this study, we determine the cryo-EM structures of topoisomerase II from T4 and T6 phages, including full-length structures of both apo and DNA-binding states which have never been determined before. Together with other conformational states, these structures provide an explicit blueprint of mechanisms of phage topoisomerase II. Particularly, the asymmetric dimeric interactions observed in cryo-EM structures of T6 phage topoisomerase II ATPase domain and central domain bound with DNA shed light on the asynchronous ATP usage and asynchronous cleavage of the G-segment DNA, respectively. The elucidation of phage topoisomerase II's structures and functions not only enhances our understanding of mechanisms and evolutionary parallels with prokaryotic and eukaryotic homologs but also highlights its potential as a model for developing type IIA topoisomerase inhibitors.

Pi-based biochemical mechanism of endurance-training-induced improvement of running performance in humans.

Endurance training improves running performance in distances where oxidative phosphorylation (OXPHOS) is the main ATP source. Here, a dynamic computer model is used to assess possible biochemical mechanisms underlying this improvement. The dynamic computer model is based on the "Pi double-threshold" mechanism of muscle fatigue, according to which the additional ATP usage appears when (1) inorganic phosphate (Pi) exceeds a critical value (Picrit); (2) exercise is terminated because of fatigue, when Pi reaches a peak value (Pipeak); (3) the Pi increase and additional ATP usage increase mutually stimulate each other. The endurance-training-induced increase in oxidative phosphorylation (OXPHOS) activity attenuates the reaching of Pipeak by Pi (and thus of O2max by O2) at increased power output. This in turn allows a greater work intensity, and thus higher speed, to be achieved before exercise is terminated because of fatigue at the end of the 1500m run. Thus, identical total work is performed in a shorter time. Probably, endurance training also lowers Pipeak, which improves the homeostasis of "bioenergetic" muscle metabolites: ADP, PCr, Pi and H+ ions. The present dynamic computer model generates clear predictions of metabolic changes that limit performance during 1500m running. It contributes to our mechanistic understanding of training-induced improvement in running performance and stimulates further physiological experimental studies.

Sex-specific resilience of neocortex to food restriction.

Mammals have evolved sex-specific adaptations to reduce energy usage in times of food scarcity. These adaptations are well described for peripheral tissue, though much less is known about how the energy-expensive brain adapts to food restriction, and how such adaptations differ across the sexes. Here, we examined how food restriction impacts energy usage and function in the primary visual cortex (V1) of adult male and female mice. Molecular analysis and RNA sequencing in V1 revealed that in males, but not in females, food restriction significantly modulated canonical, energy-regulating pathways, including pathways associated waith AMP-activated protein kinase, peroxisome proliferator-activated receptor alpha, mammalian target of rapamycin, and oxidative phosphorylation. Moreover, we found that in contrast to males, food restriction in females did not significantly affect V1 ATP usage or visual coding precision (assessed by orientation selectivity). Decreased serum leptin is known to be necessary for triggering energy-saving changes in V1 during food restriction. Consistent with this, we found significantly decreased serum leptin in food-restricted males but no significant change in food-restricted females. Collectively, our findings demonstrate that cortical function and energy usage in female mice are more resilient to food restriction than in males. The neocortex, therefore, contributes to sex-specific, energy-saving adaptations in response to food restriction.

Sex-specific resilience of neocortex to food restriction

Mammals have evolved sex-specific adaptations to reduce energy usage in times of food scarcity. These adaptations are well described for peripheral tissue, though much less is known about how the energy-expensive brain adapts to food restriction, and how such adaptations differ across the sexes. Here, we examined how food restriction impacts energy usage and function in the primary visual cortex (V1) of adult male and female mice. Molecular analysis and RNA sequencing in V1 revealed that in males, but not in females, food restriction significantly modulated canonical, energy-regulating pathways, including pathways associated waith AMP-activated protein kinase, peroxisome proliferator-activated receptor alpha, mammalian target of rapamycin, and oxidative phosphorylation. Moreover, we found that in contrast to males, food restriction in females did not significantly affect V1 ATP usage or visual coding precision (assessed by orientation selectivity). Decreased serum leptin is known to be necessary for triggering energy-saving changes in V1 during food restriction. Consistent with this, we found significantly decreased serum leptin in food-restricted males but no significant change in food-restricted females. Collectively, our findings demonstrate that cortical function and energy usage in female mice are more resilient to food restriction than in males. The neocortex, therefore, contributes to sex-specific, energy-saving adaptations in response to food restriction.

Sarcomere model: Fluctuations drive energy consumption in striated muscle under constant load.

There are many in vitro tools to measure the amount of force developed by engineered cardiac or skeletal muscle tissues or cells. The work required to generate these forces is normally considered to be equal to the work required to deform the substrate on which the muscle is cultured. However, this approach ignores the amount of energy it takes to generate a constant force with no ongoing substrate deformation, and as a result, drastically underestimates the amount of energy, and therefore the amount of ATP, needed for the contraction. The importance of this contribution to the total work can be easily illustrated by holding aloft a heavy book and feeling muscle fatigue relatively quickly. We hypothesize that the ATP usage during constant loads is driven by fluctuations of the actin-myosin motor inside the basic contractile unit of the muscle—the sarcomere. To test and explore this hypothesis, we built a model of the half sarcomere that can track developed external force and ATP consumption as a function of time. To ensure that the results could be analyzed in situations of varying ATP, ADP, Pi availability, the model was formulated with a physiologically relevant distribution of free energy between the various states of the cross-bridge. The results of our model demonstrate the importance of considering fluctuations when calculating work performed by muscle. Further, the model provides a platform, unavailable with previous sarcomere models, to test the consequences of independently changing the amount of available ATP while at the same time manipulating the amount ADP and Pi present. These results will impact further development of techniques to analyze in vitro force generation by striated muscle.

V̇O2 (non-)linear increase in ramp-incremental exercise vs. V̇O2 slow component in constant-power exercise: Underlying mechanisms

A computer model of the skeletal muscle bioenergetic system involving the Pi double-threshold mechanism of muscle fatigue was used to study the V̇O2 (non-)linear increase in time in ramp-incremental exercise as compared to the V̇O2 slow component in constant-power exercise. The Pi double-threshold mechanism applies to both constant-power and ramp-incremental exercise. The additional ATP usage is initiated at a significantly higher ATP usage activity (power output), determining the moderate/heavy exercise border, in ramp-incremental, than in constant-power exercise. A significantly lowered additional ATP usage activity or elevated glycolysis stimulation at the highest power outputs in ramp-incremental exercise in relation to constant-power exercise can additionally explain the much smaller (or zero) V̇O2 non-linearity in ramp-incremental exercise, than V̇O2 slow component in constant-power exercise. The V̇O2 (non-)linearity in ramp-incremental exercise and V̇O2 slow component in constant-power exercise is a derivative of a balance between the additional ATP usage and ATP production by anaerobic glycolysis.

Condensin pinches a short negatively supercoiled DNA loop during each round of ATP usage

Condensin, an SMC (structural maintenance of chromosomes) protein complex, extrudes DNA loops using an ATP‐dependent mechanism that remains to be elucidated. Here, we show how condensin activity alters the topology of the interacting DNA. High condensin concentrations restrain positive DNA supercoils. However, in experimental conditions of DNA loop extrusion, condensin restrains negative supercoils. Namely, following ATP‐mediated loading onto DNA, each condensin complex constrains a DNA linking number difference (∆Lk) of −0.4. This ∆Lk increases to −0.8 during ATP binding and resets to −0.4 upon ATP hydrolysis. These changes in DNA topology do not involve DNA unwinding, do not spread outside the condensin‐DNA complex and can occur in the absence of the condensin subunit Ycg1. These findings indicate that during ATP binding, a short DNA domain delimited by condensin is pinched into a negatively supercoiled loop. We propose that this loop is the feeding segment of DNA that is subsequently merged to enlarge an extruding loop. Such a “pinch and merge” mechanism implies that two DNA‐binding sites produce the feeding loop, while a third site, plausibly involving Ycg1, might anchor the extruding loop.

Effect of High Viscosity on Energy Metabolism and Kinematics of Spermatozoa from Three Mouse Species Incubated under Capacitating Conditions

In order to sustain motility and prepare for fertilization, sperm require energy. The characterization of sperm ATP production and usage in mouse species revealed substantial differences in metabolic pathways that can be differentially affected by capacitation. Moreover, spermatozoa encounter different environments with varying viscoelastic properties in the female reproductive tract. Here, we examine whether viscosity affects sperm ATP levels and kinematics during capacitation in vitro. Sperm from three mouse species (Mus musculus, M. spretus, M. spicilegus) were incubated under capacitating conditions in a modified Tyrode's medium containing bicarbonate, glucose, pyruvate, lactate, and bovine serum albumin (mT-BH) or in a bicarbonate-free medium as a non-capacitating control. Viscosity was increased with the inclusion of polyvinylpyrrolidone. ATP was measured with a bioluminescence kit, and kinematics were examined with a computer-aided sperm analysis system. In M. musculus sperm, ATP declined during capacitation, but no differences were found between non-capacitating and capacitating sperm. In contrast, in M. spretus and M. spicilegus, ATP levels decreased in capacitating sperm. Increasing viscosity in the medium did not modify the timing or proportion of cells undergoing capacitation but did result in additional time- and concentration-dependent decreases in ATP in M. spretus and M. spicilegus under capacitating conditions. Additionally, increased viscosity altered both velocity and trajectory descriptors. The limited impact of capacitation and higher viscosity on M. musculus sperm ATP and kinematics could be related to the low intensity of postcopulatory sexual selection in this species. Responses seen in the other two species could be linked to the ability of their sperm to perform better under enhanced selective pressures.

Sensitivity of V̇O2max, critical power and V̇O2 on-kinetics to O2 concentration/delivery and other factors in skeletal muscle

Relative sensitivities of the maximal oxygen uptake (V̇O2max), critical power (CP) and transition time of the primary phase II of the V̇O2 on-kinetics (t0.63) to selected factors in skeletal muscle are simulated using a computer model of the skeletal muscle bioenergetic system. In normoxia, V̇O2max is significantly positively sensitive to peak Pi (Pipeak, Pi at which exercise is terminated because of fatigue), OXPHOS (oxidative phosphorylation) activity (kOX) and ESA (each-step-activation) intensity (AOXmax), and negatively sensitive to the accessible phosphate (and total creatine) pool (Pacc). CP is additionally moderately positively sensitive to critical Pi (Picrit, Pi at which the additional ATP usage appears) and negatively sensitive to the additional ATP usage activity (kadd). t0.63 is significantly positively sensitive to Pacc and negatively to kOX and AOXmax. The positive sensitivity of V̇O2max and CP, and negative sensitivity of t0.63 to O2 concentration/delivery is low at normoxic and hyperoxic O2 levels, but increases significantly at severely hypoxic O2 levels.

Skeletal muscle biochemical origin of exercise intensity domains and their relation to whole-body V̇O2 kinetics.

This article presents the biochemical intra-skeletal-muscle basis of exercise intensity domains: moderate (M), heavy (H), very heavy (VH) and severe (S). Threshold origins are mediated by a ‘Pi double-threshold’ mechanism of muscle fatigue, which assumes (1) additional ATP usage, underlying muscle V̇O2 and metabolite slow components, is initiated when inorganic phosphate (Pi) exceeds a critical value (Picrit); (2) exercise is terminated because of fatigue, when Pi reaches a peak value (Pipeak); and (3) the Pi increase and additional ATP usage increase mutually stimulate each other forming a positive feedback. M/H and H/VH borders are defined by Pi on-kinetics in relation to Picrit and Pipeak. The values of the ATP usage activity, proportional to power output (PO), for the M/H, H/VH and VH/S borders are lowest in untrained muscle and highest in well-trained muscle. The metabolic range between the M/H and H/VH border (or ‘H space’) decreases with muscle training, while the difference between the H/VH and VH/S border (or ‘VH space’) is only weakly dependent on training status. The absolute magnitude of the muscle V̇O2 slow-component, absent in M exercise, rises gradually with PO to a maximal value in H exercise, and then decreases with PO in VH and S exercise. Simulations of untrained, physically active and well-trained muscle demonstrate that the muscle M/H border need not be identical to the whole-body M/H border determined from pulmonary V̇O2 on-kinetics and blood lactate, while suggesting that the biochemical origins of the H/VH border reside within skeletal muscle and correspond to whole-body critical power.

Proton magnetic resonance spectroscopy assessment of neonatal brain metabolism during cardiopulmonary bypass surgery.

Here, we report on the development and performance of a robust 3-T single-voxel proton magnetic resonance spectroscopy (1 H MRS) experimental protocol and data analysis pipeline for quantifying brain metabolism during cardiopulmonary bypass (CPB) surgery in a neonatal porcine model, with the overall goal of elucidating primary mechanisms of brain injury associated with these procedures. The specific aims were to assess which metabolic processes can be reliably interrogated by 1 H MRS on a 3-T clinical scanner and to provide an initial assessment of brain metabolism during deep hypothermia cardiac arrest (DHCA) surgery and recovery. Fourteen neonatal pigs underwent CPB surgery while placed in a 3-T MRI scanner for 18, 28, and 37°C DHCA studies under hyperglycemic, euglycemic, and hypoglycemic conditions. Total imaging times, including baseline measurements, circulatory arrest (CA), and recovery averaged 3h/animal, during which 30-40 single-voxel 1 H MRS spectra (sLASER pulse sequence, TR/TE = 2000/30 ms, 64 or 128 averages) were acquired from a 2.2-cc right midbrain voxel. 1 H MRS at 3T was able to reliably quantify (1) anaerobic metabolism via depletion of brain glucose and the associated build-up of lactate during CA, (2) phosphocreatine (PCr) to creatine (Cr) conversion during CA and subsequent recovery upon reperfusion, (3) a robust increase in the glutamine-to-glutamate (Gln/Glu) ratio during the post-CA recovery period, and (4) a broadening of the water peak during CA. In vivo 1 H MRS at 3T can reliably quantify subtle metabolic brain changes previously deemed challenging to interrogate, including brain glucose concentrations even under hypoglycemic conditions, ATP usage via the conversion of PCr to Cr, and differential changes in Glu and Gln. Observed metabolic changes during CPB surgery of a neonatal porcine model provide new insights into possible mechanisms for prevention of neuronal injury.

Phosphate Dysregulation and Neurocognitive Sequelae.

The endocrine regulator proteins, fibroblast growth factor 23 (FGF23) and Klotho have been well studied as mediators of phosphate metabolism. FGF23 has been implicated in the renal excretion of phosphate by limiting the docking of sodium-dependent phosphate transporters, Npt2a and Npt2c, into the luminal side of renal proximal tubular epithelial cells. By limiting Npt2a/c activity in the renal tubular epithelial cells, phosphate is reabsorbed at lower rates and is excreted at higher rates. The action of Klotho is relatively less understood but has been implicated as an FGF23 cofactor in receptor binding. Klotho is mostly synthesized in the distal tubules of the nephron relative to FGF23's activity in proximal renal tubules. The neurological sequelae due to alterations in the FGF23-Klotho axis may be explained by the direct effects of these phosphate-regulating proteins on neuronal tissues or by the roles of these proteins in phosphate metabolism. Hyperphosphatemia has been associated with vascular wall stiffness that may alter blood flow and weakenvessels in the brain. In contrast, hypophosphatemia may alter ATP usage and metabolism in the central nervous system (CNS), leading to neurological compromise. Altered levels of FGF23 and Klotho have both been associated with neurocognitive decline, clinical dementia, memory loss, and poor executive function in humans. Furthermore, FGF23 and Klotho dysregulation has been linked to structural and functional changes of the cardiovascular system with an increased risk of stroke. Subsequent research should focus on characterizing the neuropathology associated with alterations in the FGF23-Klotho system and dysregulated phosphate metabolism.

Mechanisms of the effect of oxidative phosphorylation deficiencies on the skeletal muscle bioenergetic system in patients with mitochondrial myopathies.

Simulations carried out using a previously developed model of the skeletal muscle bioenergetic system, involving the "inorganic phosphate (Pi) double-threshold" mechanism of muscle fatigue, lead to the conclusion that a decrease in the oxidative phosphorylation (OXPHOS) activity, caused by mutations in mitochondrial or nuclear DNA, is the main mechanism underlying the changes in the kinetic properties of the system in mitochondrial myopathies (MM). These changes generally involve the very-heavy-exercise-like behavior and exercise termination because of fatigue at low work intensities. In particular, a sufficiently large (at a given work intensity) decrease in OXPHOS activity leads to slowing of the primary phase II of the oxygen uptake (V̇o2) on-kinetics, decrease in maximal V̇o2 (V̇o2max), appearance of the slow component of the V̇o2 on-kinetics, exercise intolerance, and lactic acidosis at relatively low power outputs encountered in experimental studies in patients with MM. Thus, the "Pi double-threshold" mechanism of muscle fatigue is able to account, at least semiquantitatively, for various kinetic effects of inborn OXPHOS deficiencies of the skeletal muscle bioenergetic system. Exercise can be potentially lengthened and V̇o2max elevated in patients with MM through an increase in peak Pi (Pipeak), at which exercise is terminated because of fatigue. Generally, a mechanism underlying the kinetic effects of OXPHOS deficiencies on the skeletal muscle bioenergetic system in MM is proposed that was absent in the literature.NEW & NOTEWORTHY A mechanism of the OXPHOS deficiencies-induced changes of the skeletal muscle bioenergetic system in patients with mitochondrial myopathies (MM), namely, appearance of the slow component of the V̇o2 on-kinetics at relatively low work intensities, slowed primary phase II of the V̇o2 on-kinetics, lowered V̇o2max, and lactic acidosis is proposed. It involves a decrease in OXPHOS activity acting through the "Pi double-threshold" mechanism of muscle fatigue comprising initiation of the additional ATP usage and termination of exercise.

Vasoplegia induces high energy demand and depletes cardiac energetics: a new insight into physiological concepts of cardiac work and a model for acute heart failure?

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): British Heart Foundation Background / Introduction Hearts subjected to constant high workload will, over time, fail. We hypothesized vasoplegia would create a high cardiac energy demand and deplete cardiac energy reserves, a mechanism causing failure. With 31Phosphorus Magnetic Resonance Spectroscopy, we can measure energy: ATP usage (via creatine kinase flux) and reserves of phosphocreatine (PCr/ATP ratio). Methods: Ten healthy volunteers were recruited mean age 37, mean BMI 22.4, 5 male, 5 female. A nitrate vasodilator (Glyceryl trinitrate, GTN) was used to induce vasoplegia, with MRI and MRS measurements taken before and during. Results There was reduced preload (falls in end diastolic volume and right atrial area) and afterload (mean blood pressure fall 14mmHg, p <0.0001). Subjects mounted reflex tachycardia (mean heart rate rise 9bpm, p < 0.0001) and inotropy (mean baseline ejection fraction increase 5%, p = 0.0002) hence cardiac output and rate pressure product were maintained (baseline CO 6.24 ± 1.45 L/min vs GTN 6.49 ± 1.43 L/min, p = 0.37; baseline RPP = 6929 ± 976 mmHg.bpm vs GTN 7214 ± 1051 mmHg.bpm, p = 0.06). There was a 58% increase in Creatine Kinase activity (kf) (baseline 0.158 s-1 vs GTN 0.249 s-1, p = 0.006) and CK flux (baseline 1.79 ± 0.78 umol/g/s vs GTN 2.59 ± 1.07 umol/g/s, p = 0.03), demonstrating increased ATP transfer. PCr/ATP fell (from 2.17 ± 0.2 to 1.99 ± 0.22, p = 0.027). Baseline PCr/ATP positively correlated with the change in stroke volume (R2 = 0.66, p = 0.005) during administration of GTN. In addition, whilst at rest, CK kf correlated with rate pressure product (R2 = 0.56, p = 0.03), there was no correlation seen during GTN. Conclusions We have shown vasoplegia increases energy demand upon the heart, despite unchanged cardiac output and rate pressure product. Further, we have shown a fall in Phosphocreatine/ATP ratio, suggesting this ATP transfer outstripped oxidative phosphorylation and the phosphocreatine pool was depleted in order to maintain ATP delivery. We speculate that progressive depletion of energetics in the context of high energy demand drives hearts under constant stress into failure. In addition, we demonstrate that the magnitude of the resting phosphocreatine pool relates to ability to augment stroke volume during stress and suggest that this may be protective against a decline into failure. Further work is needed, but PCr/ATP may be an important biomarker for treatments that target myocardial energetics to protect against failure. Abstract Figure 1

Sisyphus observed: Unraveling the high ATP usage of an RNA chaperone

DEAD-box proteins are nonprocessive RNA helicases that can function as RNA chaperones by coupling ATP binding and hydrolysis to structural reorganization of RNA. Here, Jarmoskaite et al. quantify the ATP utilization of an RNA chaperone during refolding of a misfolded ribozyme substrate. Strikingly, 100 ATP hydrolysis events are needed per successfully refolded ribozyme, suggesting that each round of unfolding requires ten ATP molecules, since 90% of substrate unfolding cycles only lead back to the kinetically favored misfolded state. This near-Sisyphean effort reveals a potentially conserved model for RNA reorganization by RNA chaperones.

Increased myocardial fat supply improves cardiac energetics and function in heart failure

Abstract Introduction The failing heart is starved of energy, in part accounting for its contractile dysfunction. Reduced uptake of fat and sugar required for energy production has frequently been demonstrated in heart failure, therefore altering metabolism of glucose and/or fat is therefore attractive as a therapy. We hypothesized increasing glucose supply would be beneficial over increasing fat supply so measured ATP usage (via PCr/ATP ratio and flux through creatine kinase) and cardiac function during fat emulsion infusion or euglycaemic hyperinsulinaemic clamp. Methods 11 patients with a diagnosis of heart failure and nonischaemic cardiomyopathy were recruited, mean age 66 (range 49–80), mean BMI 27.7 (range 21.3–37.5), F:M 3:8, 3 diabetic and 8 non-diabetic. On the first visit they had a baseline cardiac magnetic resonance (CMR), collecting cardiac volumes and function, then were randomised to receive either fat infusion or euglycaemic clamp. Following an hour of infusion, CMR was repeated followed by 31P cardiac magnetic resonance spectroscopy, then a dobutamine stress sequence at 65% maximum heart rate. They received the alternate infusion at the next visit. Results Data was normally distributed. Baseline ejection fraction was 37±9%. PCr/ATP ratio was greater with the fat infusion compared to euglycaemic clamp (1.82±0.26 vs 1.68±0.24, p=0.04). Fat emulsion infusion also brought about a greater ejection fraction increase over the baseline, compared to the euglycaemic clamp in which there was little difference (+5.3±5.3% vs −0.6±3.1%, p=0.004). Calculated cardiac work was greater in the fat infusion group than the Insulin/glucose group (682±156 L.mmHg/min vs 581±85 L.mmHg/min, p=0.009). There was no significant difference in creatine kinase first order rate constant (fat infusion 0.2±0.09/s vs euglycaemic clamp 0.16±0.07/s, p=0.32) nor creatine kinase flux (fat infusion 1.85±0.92 μmol/g/s vs euglycaemic clamp 1.46±0.58 μmol/g/s, p=0.22). The increment in cardiac output on stress over baseline was not significantly different between arms (fat infusion +3.39±3.07 L/min vs euglycaemic clamp +3.08±2.57 L/min, p=0.42). The PCr/ATP ratio showed positive correlation with the stress ejection fraction (R2=0.656, p=0.001), but not with resting ejection fraction. Conclusions Increased supply of fat to the myocardium brought about improved contractility and cardiac energetics compared to an increased glucose supply. The increase in PCr/ATP ratio would imply (given ATP concentrations are kept constant in the myocardium) there is a greater availability of phosphocreatine, suggesting increased mitochondrial ATP synthesis. These results were unexpected as it has traditionally been thought that increased glucose metabolism would yield greater cardiac function in the failing heart. These data suggest targeting myocardial fat metabolism may provide novel treatments for cardiac dysfunction. Figure 1 Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): British Heart Foundation

Tissue-specific changes in Ca2+-ATPase and Na+/K+-ATPase activities in freshwater African catfish Clarias gariepinus juvenile exposed to oxadiazon

BackgroundThis study investigated the effect of sublethal concentrations (0.0, 0.3, 0.6, and 1.2 mg·L-1) of herbicide oxadiazon (ODZ) on the activities of Ca2+-ATPase and Na+/K+-ATPase in juvenile Clarias gariepinus.MethodsOne hundred eighty juveniles of Clarias gariepinus (mean weight 58.88 ± 1.24 g and mean length 22.34 ± 1.52 cm) were randomly divided into four groups and exposed to sublethal concentrations (0.00, 0.3, 0.6, and 1.2 mg·L-1 ODZ) for 21 days in a static renewal bioassay system in which the herbicide and water were replaced completely every day. The changes in Ca2+- and Na+/K+-ATPase activities in the gill, kidney, liver, and heart of the fish were assayed on days 1, 7, 14, and 21.ResultThe result showed significant alteration in the activity of these membrane-bound enzymes. There was duration and concentration-dependent significant (p < 0.05) increase in Ca2+-ATPase activity in the treatment groups when compared with the control. The Na+/K+-ATPase activity was significantly (p < 0.05) inhibited in all the tissues when compared with control. The observed alterations in the activities of both Ca2+-ATPase and Na+/K+-ATPase in this study may be indication of impaired ionic transport and imbalance in the fish which may trigger other biochemical, physiological, and even neurological consequences that may compromise several body functions.ConclusionThe alteration of the ATPase activities in C. gariepinus by ODZ is likely to affect the ATP usage and energy metabolism in the fish serious repercussions on Ca2+ homeostasis, Na+/K+ sodium pump, and Ca2+/Na+ exchanger The results suggested that assay of the enzymes could be used as a biomarker of water pollution.

SO082LATENT TRANSFORMING GROWTH FACTOR BETA BINDING PROTEIN (LTBP4) CAN REGULATE RENAL FIBROSIS AND ALTER INFLAMMATION AND MITOCHONDRIAL DYSFUNCTION IN CHRONIC KIDNEY DISEASE (CKD)

Abstract Background and Aims: Transforming growth factor beta (TGF-beta) has been well known as a key factor for fibrosis and inflammation. LTBPs regulate TGF-beta signalling in complicated ways. Disruption and loss of LTBP4 expression is associated with abnormal accumulation of extracellular matrix (ECM) and altered TGF-beta activation. However, the role of LTBP4 in chronic kidney disease remains largely unknown. We aim to explore the mechanisms of LTBP4-related regulation in kidney disease. Method: To investigate the impact of LTBP4 on tubulointeresitial fibrosis (TIF), we generated LTBP4-overexpression human renal proximal tubule cells (HK-2), treated with exogenous TGF-beta and established a fibroblasts-HK-2 co-culture system using rat fibroblasts (NRK-49F) and HK-2 cells. Moreover, to create TIF model, we performed unilateral ureteral ligation (UUO) in Ltbp4S-/- mice and wild-type (WT) mice to check ECM deposition and phenotypic alterations. In addition, we performed RNA-Sequencing analysis to understand transcriptomic changes associate with LTBP4 overexpression. Results: Up-regulation of Ltbp4 in fibrotic kidney was noted in TIF model with UUO and in renal tissue with diabetic nephropathy. LTBP4-overexpression reduced epithelial-mesenchymal transition (EMT) with showing increased epithelial-cadherin, reduced vimentin and collagen I in the co-culture system. Moreover, higher expression of fibronectin, collagen I and alpha-smooth muscle actin (alpha-SMA) were noted in fibrotic kidneys in Ltbp4S-/- mice compared with changes in WT mice, suggesting inflammation condition could be altered by the absence of Ltbp4S. The inflammatory change in renal tissue in UUO model was studied with F4/80 stain. Increased macrophage infiltration and increased monocyte chemoattractant protein-1 (MCP-1) expression were detected in Ltbp4S-/- mice compared with that in WT mice. In addition, LTBP4-overexpression reduced mitochondrial biogenesis. Conclusion: Ltbp4 acted as a regulator of fibrosis and inflammation in fibrotic kidneys. TGF-beta- induced EMT were clearly enhanced in ltbp4 deficient environments, accompanied with reduced macrophage infiltration, which could be the major mechanism related to LTBP4/TGF-beta pathways. Furthermore, altered ATP production and usage as well as mitochondria respiration could be regulated by LTBP4 in renal failure.

Exceeding a "critical" muscle Pi: implications for [Formula: see text] and metabolite slow components, muscle fatigue and the power-duration relationship.

The consequences of the assumption that the additional ATP usage, underlying the slow component of oxygen consumption ([Formula: see text]) and metabolite on-kinetics, starts when cytosolic inorganic phosphate (Pi) exceeds a certain "critical" Pi concentration, and muscle work terminates because of fatigue when Pi exceeds a certain, higher, "peak" Pi concentration are investigated. A previously developed computer model of the myocyte bioenergetic system is used. Simulated time courses of muscle [Formula: see text], cytosolic ADP, pH, PCr and Pi at various ATP usage activities agreed well with experimental data. Computer simulations resulted in a hyperbolic power-duration relationship, with critical power (CP) as an asymptote. CP was increased, and phase II [Formula: see text] on-kinetics was accelerated, by progressive increase in oxygen tension (hyperoxia). Pi is a major factor responsible for the slow component of the [Formula: see text] and metabolite on-kinetics, fatigue-related muscle work termination and hyperbolic power-duration relationship. The successful generation of experimental system properties suggests that the additional ATP usage, underlying the slow component, indeed starts when cytosolic Pi exceeds a "critical" Pi concentration, and muscle work terminates when Pi exceeds a "peak" Pi concentration. The contribution of other factors, such as cytosolic acidification, or glycogen depletion and central fatigue should not be excluded. Thus, a detailed quantitative unifying mechanism underlying various phenomena related to skeletal muscle fatigue and exercise tolerance is offered that was absent in the literature. This mechanism is driven by reciprocal stimulation of Pi increase and additional ATP usage when "critical" Pi is exceeded.

Mitochondria supply ATP to the ER through a mechanism antagonized by cytosolic Ca2.

The endoplasmic reticulum (ER) imports ATP and uses energy from ATP hydrolysis for protein folding and trafficking. However, little is known about how this vital ATP transport occurs across the ER membrane. Here, using three commonly used cell lines (CHO, INS1 and HeLa), we report that ATP enters the ER lumen through a cytosolic Ca2+-antagonized mechanism, or CaATiER (Ca2+-Antagonized Transport into ER). Significantly, we show that mitochondria supply ATP to the ER and a SERCA-dependent Ca2+ gradient across the ER membrane is necessary for ATP transport into the ER, through SLC35B1/AXER. We propose that under physiological conditions, increases in cytosolic Ca2+ inhibit ATP import into the ER lumen to limit ER ATP consumption. Furthermore, the ATP level in the ER is readily depleted by oxidative phosphorylation (OxPhos) inhibitors and that ER protein misfolding increases ATP uptake from mitochondria into the ER. These findings suggest that ATP usage in the ER may increase mitochondrial OxPhos while decreasing glycolysis, i.e. an 'anti-Warburg' effect.