Adenylate kinase 1 gene deletion disrupts muscle energetic economy despite metabolic rearrangement

Adenylate kinase phosphate energy shuttle underlies energetic communication in flagellar axonemes

The complexities of energy transfer mechanisms in the flagella of mammalian sperm flagella have been intensively investigated and demonstrate significant diversity across species. Enzymatic shuttles, particularly adenylate kinase (AK) and creatine kinase (CK), are pivotal in the efficient transfer of intracellular ATP, showing distinct tissue- and species-specificity. Here, the expression profiles of AK and CK were investigated in mice and found to fall into four subgroups, of which Subgroup III AKs were observed to be unique to the male reproductive system and conserved across chordates. Both AK8 and AK9 were found to be indispensable to male reproduction after analysis of an infertile male cohort. Knockout mouse models showed that AK8 and AK9 were central to promoting sperm motility. Immunoprecipitation combined with mass spectrometry revealed that AK8 and AK9 interact with the radial spoke (RS) of the axoneme. Examination of various human and mouse sperm samples with substructural damage, including the presence of multiple RS subunits, showed that the head of radial spoke 3 acts as an adapter for AK9 in the flagellar axoneme. Using an ATP probe together with metabolomic analysis, it was found that AK8 and AK9 cooperatively regulated ATP transfer in the axoneme, and were concentrated at sites associated with energy consumption in the flagellum. These findings indicate a novel function for RS beyond its structural role, namely, the regulation of ATP transfer. In conclusion, the results expand the functional spectrum of AK proteins and suggest a fresh model regarding ATP transfer within mammalian flagella.

Genetic screening and metabolomics identify glial adenosine metabolism as a therapeutic target in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and lacks disease-modifying therapies. We developed a Drosophila model for identifying novel glial-based therapeutic targets for PD. Human alpha-synuclein is expressed in neurons and individual genes are independently knocked down in glia. We performed a forward genetic screen, knocking down the entire Drosophila kinome in glia in alpha-synuclein expressing flies. Among the top hits were five genes (Ak1, Ak6, Adk1, Adk2, and awd) involved in adenosine metabolism. Knockdown of each gene improved locomotor dysfunction, rescued neurodegeneration, and increased brain adenosine levels. We determined that the mechanism of neuroprotection involves adenosine itself, as opposed to a downstream metabolite. We dove deeper into the mechanism for one gene, Ak1, finding rescue of dopaminergic neuron loss, alpha-synuclein aggregation, and bioenergetic dysfunction after glial Ak1 knockdown. We performed metabolomics in Drosophila and in human PD patients, allowing us to comprehensively characterize changes in purine metabolism and identify potential biomarkers of dysfunctional adenosine metabolism in people. These experiments support glial adenosine as a novel therapeutic target in PD.

Deficiency in AK9 causes asthenozoospermia and male infertility by destabilising sperm nucleotide homeostasis

BACKGROUND

Asthenozoospermia is the primary cause of male infertility; however, its genetic aetiology remains poorly understood. Adenylate kinase 9 (AK9) is highly expressed in the testes of humans and mice and encodes a type of adenosine kinase that is functionally involved in cellular nucleotide homeostasis and energy metabolism. We aimed to assess whether AK9 is involved in asthenozoospermia.

METHODS

One-hundred-and-sixty-five Chinese men with idiopathic asthenozoospermia were recruited. Whole-exome sequencing (WES) and Sanger sequencing were performed for genetic analyses. Papanicolaou staining, Haematoxylin and eosin staining, scanning electron microscopy, and transmission electron microscopy were used to observe the sperm morphology and structure. Ak9-knockout mice were generated using CRISPR-Cas9. Sperm adenosine was detected by liquid chromatography-mass spectrometry. Targeted sperm metabolomics was performed. Intracytoplasmic sperm injection (ICSI) was used to treat patients.

FINDINGS

We identified five patients harbouring bi-allelic AK9 mutations. Spermatozoa from men harbouring bi-allelic AK9 mutations have a decreased ability to sustain nucleotide homeostasis. Moreover, bi-allelic AK9 mutations inhibit glycolysis in sperm. Ak9-knockout male mice also presented similar phenotypes of asthenozoospermia. Interestingly, ICSI was effective in bi-allelic AK9 mutant patients in achieving good pregnancy outcomes.

INTERPRETATION

Defects in AK9 induce asthenozoospermia with defects in nucleotide homeostasis and energy metabolism. This sterile phenotype could be rescued by ICSI.

FUNDING

The National Natural Science Foundation of China (82071697), Medical Innovation Project of Fujian Province (2020-CXB-051), open project of the NHC Key Laboratory of Male Reproduction and Genetics in Guangzhou (KF202004), Medical Research Foundation of Guangdong Province (A2021269), Guangdong Provincial Reproductive Science Institute Innovation Team grants (C-03), and Outstanding Young Talents Program of Capital Medical University (B2205).

Regulation of Adenine Nucleotide Metabolism by Adenylate Kinase Isozymes: Physiological Roles and Diseases

Adenylate kinase (AK) regulates adenine nucleotide metabolism and catalyzes the ATP + AMP ⇌ 2ADP reaction in a wide range of organisms and bacteria. AKs regulate adenine nucleotide ratios in different intracellular compartments and maintain the homeostasis of the intracellular nucleotide metabolism necessary for growth, differentiation, and motility. To date, nine isozymes have been identified and their functions have been analyzed. Moreover, the dynamics of the intracellular energy metabolism, diseases caused by AK mutations, the relationship with carcinogenesis, and circadian rhythms have recently been reported. This article summarizes the current knowledge regarding the physiological roles of AK isozymes in different diseases. In particular, this review focused on the symptoms caused by mutated AK isozymes in humans and phenotypic changes arising from altered gene expression in animal models. The future analysis of intracellular, extracellular, and intercellular energy metabolism with a focus on AK will aid in a wide range of new therapeutic approaches for various diseases, including cancer, lifestyle-related diseases, and aging.

Differential plasma protein expression after ingestion of essential amino acid-based dietary supplement verses whey protein in low physical functioning older adults

In a recent randomized, double-blind, placebo-controlled trial, we were able to demonstrate the superiority of a dietary supplement composed of essential amino acids (EAAs) over whey protein, in older adults with low physical function. In this paper, we describe the comparative plasma protein expression in the same subject groups of EAAs vs whey. The plasma proteomics data was generated using SOMA scan assay. A total of twenty proteins were found to be differentially expressed in both groups with a 1.5-fold change. Notably, five proteins showed a significantly higher fold change expression in the EAA group which included adenylate kinase isoenzyme 1, casein kinase II 2-alpha, Nascent polypeptide-associated complex subunit alpha, peroxiredoxin-1, and peroxiredoxin-6. These five proteins might have played a significant role in providing energy for the improved cardiac and muscle strength of older adults with LPF. On the other hand, fifteen proteins showed slightly lower fold change expression in the EAA group. Some of these 15 proteins regulate metabolism and were found to be associated with inflammation or other comorbidities. Gene Ontology (GO) enrichment analysis showed the association of these proteins with several biological processes. Furthermore, protein-protein interaction network analysis also showed distinct networks between upregulated and downregulated proteins. In conclusion, the important biological roles of the upregulated proteins plus better physical function of participants in the EAAs vs whey group demonstrated that EAAs have the potential to improve muscle strength and physical function in older adults. This study was registered with ClinicalTrials.gov: NCT03424265 "Nutritional interventions in heart failure."

Stable Isotope Tracing Uncovers Reduced γ/β-ATP Turnover and Metabolic Flux Through Mitochondrial-Linked Phosphotransfer Circuits in Aggressive Breast Cancer Cells

Changes in dynamics of ATP γ- and β-phosphoryl turnover and metabolic flux through phosphotransfer pathways in cancer cells are still unknown. Using ¹⁸O phosphometabolite tagging technology, we have discovered phosphotransfer dynamics in three breast cancer cell lines: MCF7 (non-aggressive), MDA-MB-231 (aggressive), and MCF10A (control). Contrary to high intracellular ATP levels, the ¹⁸O labeling method revealed a decreased γ- and β-ATP turnover in both breast cancer cells, compared to control. Lower β-ATP[¹⁸O] turnover indicates decreased adenylate kinase (AK) flux. Aggressive cancer cells had also reduced fluxes through hexokinase (HK) G-6-P[¹⁸O], creatine kinase (CK) [CrP[¹⁸O], and mitochondrial G-3-P[¹⁸O] substrate shuttle. Decreased CK metabolic flux was linked to the downregulation of mitochondrial MTCK1A in breast cancer cells. Despite the decreased overall phosphoryl flux, overexpression of HK2, AK2, and AK6 isoforms within cell compartments could promote aggressive breast cancer growth.

High and stable ATP levels prevent aberrant intracellular protein aggregation in yeast

Adenosine triphosphate (ATP) at millimolar levels has recently been implicated in the solubilization of cellular proteins. However, the significance of this high ATP level under physiological conditions and the mechanisms that maintain ATP remain unclear. We herein demonstrated that AMP-activated protein kinase (AMPK) and adenylate kinase (ADK) cooperated to maintain cellular ATP levels regardless of glucose levels. Single-cell imaging of ATP-reduced yeast mutants revealed that ATP levels in these mutants underwent stochastic and transient depletion, which promoted the cytotoxic aggregation of endogenous proteins and pathogenic proteins, such as huntingtin and α-synuclein. Moreover, pharmacological elevations in ATP levels in an ATP-reduced mutant prevented the accumulation of α-synuclein aggregates and its cytotoxicity. The present study demonstrates that cellular ATP homeostasis ensures proteostasis and revealed that suppressing the high volatility of cellular ATP levels prevented cytotoxic protein aggregation, implying that AMPK and ADK are important factors that prevent proteinopathies, such as neurodegenerative diseases.

Cells use a chemical called adenosine triphosphate (ATP) as a controllable source of energy. Like a battery, each ATP molecule contains a specific amount of energy that can be released when needed. Cells just need enough ATP to survive, but most cells store a lot more than they need. It is unclear why cells keep so much ATP, or whether this excess ATP has any other purpose.

To answer these questions, Takaine et al. identified mutants of the yeast Saccharomyces cerevisiae that had low levels of ATP, and studied how these cells differ from normal yeast The results showed that, in S. cerevisiae cells with lower and variable levels of ATP, proteins stick together, forming clumps. Proteins are molecules that perform diverse roles, keeping cells alive. When they clump together, they stop working and can cause cells to die. Further experiments showed that reducing the levels of ATP just for a short time increased the rate at which proteins stick together.

Taken together, Takaine et al.’s results suggest that ATP plays a role in stopping proteins from sticking together, explaining why cells may store excess ATP, since it could aid survival.

Protein clumps, also called aggregates, are a key feature of various illnesses, including neurodegenerative diseases such as Alzheimer’s. Takaine et al. provide a possible cause for why proteins aggregate in these diseases, which may be worth further study.

Adenylate kinase 1 overexpression increases locomotor activity in medaka fish

Maintenance of the energy balance is indispensable for cell survival and function. Adenylate kinase (Ak) is a ubiquitous enzyme highly conserved among many organisms. Ak plays an essential role in energy regulation by maintaining adenine nucleotide homeostasis in cells. However, its role at the whole organism level, especially in animal behavior, remains unclear. Here, we established a model using medaka fish (Oryzias latipes) to examine the function of Ak in environmental adaptation. Medaka overexpressing the major Ak isoform Ak1 exhibited increased locomotor activity compared to that of the wild type. Interestingly, this increase was temperature dependent. Our findings suggest that cellular energy balance can modulate locomotor activity.

Omics Technologies for High-Throughput-Screening of Cell-Biomaterial Interactions

Recent research effort in biomaterial development has largely focused on engineering bio-instructive materials to stimulate specific cell signaling. Assessing the biological performance of these materials using time-consuming and trial-and-error traditional...

Assessing the Interactions of Statins with Human Adenylate Kinase Isoenzyme 1: Fluorescence and Enzyme Kinetic Studies

Statins are the most effective cholesterol-lowering drugs. They also exert many pleiotropic effects, including anti-cancer and cardio- and neuro-protective. Numerous nano-sized drug delivery systems were developed to enhance the therapeutic potential of statins. Studies on possible interactions between statins and human proteins could provide a deeper insight into the pleiotropic and adverse effects of these drugs. Adenylate kinase (AK) was found to regulate HDL endocytosis, cellular metabolism, cardiovascular function and neurodegeneration. In this work, we investigated interactions between human adenylate kinase isoenzyme 1 (hAK1) and atorvastatin (AVS), fluvastatin (FVS), pravastatin (PVS), rosuvastatin (RVS) and simvastatin (SVS) with fluorescence spectroscopy. The tested statins quenched the intrinsic fluorescence of hAK1 by creating stable hAK1-statin complexes with the binding constants of the order of 10⁴ M⁻¹. The enzyme kinetic studies revealed that statins inhibited hAK1 with significantly different efficiencies, in a noncompetitive manner. Simvastatin inhibited hAK1 with the highest yield comparable to that reported for diadenosine pentaphosphate, the only known hAK1 inhibitor. The determined AK sensitivity to statins differed markedly between short and long type AKs, suggesting an essential role of the LID domain in the AK inhibition. Our studies might open new horizons for the development of new modulators of short type AKs.

EFFECT OF ADENYLATE KINASE 1 ON THE GROWTH AND DEVELOPMENT OF SCHISTOSOMA JAPONICUM SCHISTOSOMULUM

We investigated the effect of Schistosoma japonicum adenylate kinase 1 (Sjak1) on the growth and development of schistosomula. Quantitative real-time PCR showed that Sjak1 mRNA was expressed in 3-, 10-, 14-, 18-, and 21-day-old schistosomula, and its levels increased gradually with the development of S. japonicum. Using immunohistochemical techniques, ak1 protein was found to be mainly distributed in the tegument and some parenchymal tissues of the schistosomula. Double-stranded RNA-mediated knockdowns of ak1 decreased ak1 mRNA transcripts by more than 90%, and western blot results showed that expression of ak1 protein was decreased by 66%. Scanning electron microscopy following the RNA-mediated ak1 knockdown showed that the sensory papillae did not develop. Transmission electron microscopy showed a lower mean thickness of the tegument in the Sjak1 interference group than in the negative control group. Terminal deoxynucleotidyl transferase dUTP nick-end labeling suggested higher apoptosis in the interference group than the negative control group. These results showed that ak1 may be involved in the growth and development of S. japonicum schistosomula and especially in the development of the integument. Consequently, ak1 may be a potential target in developing prevention methods for schistosomiasis in the future.

Gas chromatography-mass spectrometry based 18O stable isotope labeling of Krebs cycle intermediates

New technologies permit determining metabolomic profiles of human diseases by fingerprinting metabolites levels. However, to fully understand metabolomic phenotypes, metabolite levels and turnover rates are necessary to know. Krebs cycle is the major hub of energy metabolism and cell signaling. Traditionally, ¹³C stable isotope labeled substrates were used to track the carbon turnover rates in Krebs cycle metabolites. In this study, for the first time we introduce H₂[¹⁸O] based stable isotope marker that permit tracking oxygen exchange rates in separate segments of Krebs cycle. The chromatographic and non-chromatographic parameters were systematically tested on the effect of labeling ratio of Krebs cycle mediators to increase selectivity and sensitivity of the method. We have developed a rapid, precise, and robust GC-MS method for determining the percentage of ¹⁸O incorporation to Krebs cycle metabolites. The developed method was applied to track the cancer-induced shift in the Krebs cycle dynamics of Caco-2 cells as compared to the control FHC cells revealing Warburg effects in Caco-2 cells. We demonstrate that unique information could be obtained using this newly developed ¹⁸O-labeling analytical technology by following the oxygen exchange rates of Krebs cycle metabolites. Thus, ¹⁸O-labeling of Krebs cycle metabolites expands the arsenal of techniques for monitoring the dynamics of cellular metabolism. Moreover, the developed method will allow to apply the ¹⁸O-labeling technique to numerous other metabolic pathways where oxygen exchange with water takes place.

Single-Cell Analysis of the Muscle Stem Cell Hierarchy Identifies Heterotypic Communication Signals Involved in Skeletal Muscle Regeneration

Muscle regeneration relies on the regulation of muscle stem cells (MuSCs) through paracrine signaling interactions. We analyzed muscle regeneration in mice using single-cell RNA sequencing (scRNA-seq) and generated over 34,000 single-cell transcriptomes spanning four time-points. We identified 15 distinct cell types including heterogenous populations of muscle stem and progenitor cells. We resolved a hierarchical map of these myogenic cells by trajectory inference and observed stage-specific regulatory programs within this continuum. Through ligand-receptor interaction analysis, we identified over 100 candidate regeneration-associated paracrine communication pairs between MuSCs and non-myogenic cells. We show that myogenic stem/progenitor cells exhibit heterogeneous expression of multiple Syndecan proteins in cycling myogenic cells, suggesting that Syndecans may coordinate myogenic fate regulation. We performed ligand stimulation in vitro and confirmed that three paracrine factors (FGF2, TGFβ1, and RSPO3) regulate myogenic cell proliferation in a Syndecan-dependent manner. Our study provides a scRNA-seq reference resource to investigate cell communication interactions in muscle regeneration.

Adenylate kinase AK2 isoform integral in embryo and adult heart homeostasis

Adenylate kinase2 (AK2) catalyzes trans-compartmental nucleotide exchange, but the functional implications of this mitochondrial intermembrane isoform is only partially understood. Here, transgenic AK2-/- null homozygosity was lethal early in embryo, indicating a mandatory role for intact AK2 in utero development. In the adult, conditional organ-specific ablation of AK2 precipitated abrupt heart failure with Krebs cycle and glycolytic metabolite buildup, suggesting a vital contribution to energy demanding cardiac performance. Depressed pump function recovered to pre-deletion levels overtime, suggestive of an adaptive response. Compensatory upregulation of phosphotransferase AK1, AK3, AK4 isozymes, creatine kinase isoforms, and hexokinase, along with remodeling of cell cycle/growth genes and mitochondrial ultrastructure supported organ rescue. Taken together, the requirement of AK2 in early embryonic stages, and the immediate collapse of heart performance in the AK2-deficient postnatal state underscore a primordial function of the AK2 isoform. Unsalvageable in embryo, loss of AK2 in the adult heart was recoverable, underscoring an AK2-integrated bioenergetics system with innate plasticity to maintain homeostasis on demand.

Protective effects of diet containing rutin against trichlorfon-induced muscle bioenergetics disruption and impairment on fatty acid profile of silver catfish Rhamdia quelen

Trichlorfon is an organophosphate insecticide that is widely used on fish farms to control parasitic infections. It has been detected in freshwater ecosystems as well as in fishery products. There is a growing body of evidence to suggest that certain feed additives may reduce or prevent pesticide-induced toxicity in fish. The aim of the present study was to determine whether acute exposure to trichlorfon would alter bioenergetic homeostasis and alter fatty acid profiles in muscles of silver catfish (Rhamdia quelen). We also sought to determine whether rutin prevents or reduces these effects. Cytosolic and mitochondrial creatine kinase (CK) and activities of complexes II-III and IV in muscle were significantly inhibited by exposure to 11 mg/L trichlorfon for 48 h compared to effects in the unexposed group. Total content of polyunsaturated fatty acids (omega-3 and omega-6) were significantly lower in muscle of silver catfish exposed to 11 mg/L trichlorfon for 48 h than in the unexposed group. Addition of 3 mg rutin/kg feed increased CK activity and prevented inhibition of complex IV activity, as well as preventing all alterations of muscle fatty acid profiles elicited by exposure to trichlorfon. No significant differences were observed between groups with respect to muscle adenylate kinase or pyruvate kinase activities, as well as total content of saturated and monounsaturated fatty acids. Our findings suggest that exposure (48 h) to 11 mg trichlorfon/L water inhibits cytosolic and mitochondrial CK activity in muscle. Trichlorfon also affects activities of complexes II-III and IV in respiratory chain, with important consequences for adenosine triphosphate production. The pesticide alters fatty acid profiles in the fish and endangers human consumers of the product. The most important finding of the present study is that inclusion of rutin improves bioenergetic homeostasis and muscle fatty acid profiles, suggesting that it reduces trichlorfon-induced muscle damage.

Adenylate kinase 1 deficiency disrupts mouse sperm motility under conditions of energy stress†

Mammalian spermatozoa are highly polarized cells characterized by compartmentalized cellular structures and energy metabolism. Adenylate kinase (AK), which interconverts two ADP molecules into stoichiometric amounts of ATP and AMP, plays a critical role in buffering adenine nucleotides throughout the tail to support flagellar motility. Yet the role of the major AK isoform, AK1, is still not well characterized. Here, by using a proteomic analysis of testis biopsy samples, we found that AK1 levels were significantly decreased in nonobstructive azoospermia patients. This result was further verified by immunohistochemical staining of AK1 on a tissue microarray. AK1 was found to be expressed in post-meiotic round and elongated spermatids in mouse testis and subsequent mature sperm in the epididymis. We then generated Ak1 knockout mice, which showed that AK1 deficiency did not induce any defects in testis development, spermatogenesis, or sperm morphology and motility under physiological conditions. We further investigated detergent-modeled epididymal sperm and included individual or mixed adenine nucleotides to mimic energy stress. When only ADP was available, Ak1 disruption largely compromised sperm motility, manifested as a smaller beating amplitude and higher beating frequency, which resulted in less effective forward swimming. The energy restriction/recover experiments with intact sperm further addressed this finding. Besides, decreased AK activity was observed in sperm of a male fertility disorder mouse model induced by cadmium chloride. These results cumulatively demonstrate that AK1 was dispensable for testis development, spermatogenesis, or sperm motility under physiological conditions, but was required for sperm to maintain a constant adenylate energy charge to support sperm motility under conditions of energy stress.

Role of adenylate kinase 1 in the integument development of Schistosoma japonicum schistosomula

Schistosomula antigens play an important role in the growth and development of Schistosoma japonicum. We investigated the role of S. japonicum adenylate kinase 1 (SjAK1) in the growth and development of schistosomula. Quantitative real-time PCR showed that SjAK1 mRNA was expressed in all schistosomula stages, but increased gradually with the development of S. japonicum schistosomula. Using immunohistochemical techniques, the AK1 protein was found to be mainly distributed in the tegument and in some parenchymal tissues of the schistosomula. Double-stranded RNA-mediated knockdown of AK1 reduced AK1 mRNA transcripts by more than 90%; western blot analysis demonstrated that AK1 protein expression decreased by 66%. Scanning electron microscopy following RNA-mediated AK1 knockdown demonstrated that the sensory papillae degenerated significantly. Transmission electron microscopy demonstrated that the mean thickness of the tegument in the SjAK1 interference group was lower than that in the negative control group. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) suggested that, compared with the negative control group, apoptosis increased in the interference group. These results show that AK1 may be involved in the growth and development of S. japonicum schistosomula, and thus may be a target when developing treatments for schistosomiasis.

High expression of AK1 predicts inferior prognosis in acute myeloid leukemia patients undergoing chemotherapy

The purpose of the present study was to investigate whether expression levels of adenylate kinase 1 (AK1) were associated with prognosis of acute myeloid leukemia (AML) in patients treated with chemotherapy or allogeneic hematopoietic stem cell transplantation (allo-HSCT). 85 AML patients with AK1 expression report who received chemotherapy-alone and 71 who underwent allo-HSCT from The Cancer Genome Atlas database were identified and grouped into either AK1high or AK1low based on their AK1 expression level relative to the median. Then, overall survival (OS) and event-free survival (EFS) were compared between patients with high vs. low AK1 expression. In the chemotherapy group, high AK1 expression was favorable for both EFS (P=0.016) and OS (P=0.014). In the allo-HSCT group, there was no association for AK1 expression levels and clinical outcomes. Further analyses suggested that in the high AK1 expression group, EFS and OS were longer in patients treated with allo-HSCT compared with those treated with chemotherapy (P=0.0011; P<0.0001, respectively), whereas no significant differences were observed in the low AK1 expression group. In summary, we reported AK1 as an independent unfavorable prognostic factor of AML patients undergoing chemotherapy, and its use could also facilitate clinical decision-making in selecting treatment for AML patients. Patients with high AK1 expression may be recommended for early allo-HSCT.

Involvement of the phosphoryl transfer network in gill bioenergetic imbalance of pacamã (Lophiosilurus alexandri) subjected to hypoxia: notable participation of creatine kinase

Hypoxia is among the most critical environmental stressors for fish in aquatic environments, and several energetic alterations have been associated with it. The aim of the present study was to evaluate the involvement of the phosphoryl transfer network and its effects on adenosine triphosphate (ATP)-dependent enzymes during hypoxia, as well as the role of oxidative stress in the activity of the phosphoryl transfer network in pacamã (Lophiosilurus alexandri) subjected to severe hypoxia. Branchial creatine kinase (CK; cytosolic and mitochondrial fractions), adenylate kinase (AK), and pyruvate kinase (PK) activities were inhibited after 72 h of exposure to hypoxia compared to their respective normoxia groups, and remained low (except for AK) after 24 and 72 h of re-oxygenation. Activities of the branchial sodium-potassium pump (Na⁺, K⁺-ATPase) and proton pump (H⁺-ATPase) were inhibited in fish exposed to 72 h of hypoxia compared to the normoxia group, remained inhibited after 24 h of re-oxygenation, and were restored to physiological levels after 72 h of re-oxygenation. Levels of branchial reactive oxygen species (ROS) were higher in fish exposed to hypoxia for 72 h compared to the normoxia group, and increased during re-oxygenation. Lipid peroxidation (LOOH) levels were higher in fish subjected to 72 h of hypoxia compared to the normoxia group, and remained higher during re-oxygenation. On the other hand, protein sulfhydryl (PSH) levels were lower in fish exposed to hypoxia for 72 h compared to the normoxia group, and remained low during re-oxygenation. Based on this evidence, inhibition of the activities of enzymes belonging to phosphoryl transfer network contributed to impairing energetic homeostasis linked to ATP production and ATP utilization in gills of pacamã subjected to hypoxia, and remained inhibited during re-oxygenation (except AK activity). Moreover, inhibition of the phosphoryl transfer network impaired activity of ATP-dependent enzymes, which can be mediated by ROS overproduction, lipid peroxidation, and oxidation of SH groups.

Effects of thymol supplementation on performance, mortality and branchial energetic metabolism in grass carp experimentally infected by Aeromonas hydrophila

We determined whether thymol supplementation of would minimize the negative effects of Aeromonas hydrophila infection on branchial energy metabolism, weight loss and mortality in grass carp (Ctenopharyngodon idella). We found that the infected fish all died, while 62.5% of those supplemented with 100 mg/kg thymol survived. Cytosolic and mitochondrial creatine kinase (CK) activities, as well as adenylate kinase (AK) and pyruvate kinase (PK) activities were significant lower in gills of A. hydrophila-infected fish than those of the control group, and adenosine triphosphate (ATP) levels were significant lower in the infected group. Finally, branchial reactive oxygen species (ROS) were significant higher in A. hydrophila-infected fish than in the control group. Supplementation with 100 and 300 mg thymol/kg diet prevented inhibition of branchial cytosolic and mitochondrial CK activities caused by infection, and also inhibited the reduction of branchial ATP levels. Supplementation with 100, 200 and 300 mg thymol/kg prevented the inhibition of branchial AK and PK activities induced by aeromonosis. Supplementation of 100 mg thymol/kg prevented weight loss after A. hydrophila infection. These data suggest that supplementation with 100 mg thymol/kg exerts potent bactericidal properties and augments longevity. Supplementation at all concentrations of thymol prevented A. hydrophila-induced branchial bioenergetics; nevertheless, higher concentrations were associated with side-effects.

Experimental infection by Neospora caninum in gerbil reduces activity of enzymes involved in energy metabolism

Neospora caninum is a protozoan that has tropism for the central nervous system. The aim of this study was to determine whether experimental infection of gerbils would interfere with activity of enzymes associated with energy metabolism. We randomized 20 gerbils into two groups (ten animals per group): the control group (healthy animals; uninfected) and the infected group (experimentally infected with dose 7.8 × 10² tachyzoites of N. caninum per gerbil). On day six and twelve post-infection (PI), brain and spleen tissues were collected for biochemical and histopathological analyses. No histopathological lesions were observed in the brains of infected animals; however, inflammatory infiltrates were found in the spleen. Significantly greater levels of reactive oxygen species (ROS) were observed in the brain and spleen of infected gerbils than in the control group at 12 days PI. Cytosolic creatine kinase (CK-CYT), mitochondrial creatine kinase (CK-MIT), and pyruvate kinase (PK) activities were lower in the brains of infected gerbils than in those of the control group on day 12 PI. There was significantly less CK-CYT activity in the spleens of infected gerbils on day 6 and 12 PI. Finally, there was significantly less sodium-potassium ion pump (Na⁺/K⁺ ATPase) activity in the brains and spleens of infected gerbils on day 12 PI. These data suggest that experimental infection with N. caninum interfered with energy metabolism associated with ATP homeostasis in the brain and spleen, directly or indirectly, apparently mediated by ROS overproduction, contributing to inhibition of Na⁺/K⁺ ATPase activity.

Caffeine supplementation in diet mitigates Aeromonas hydrophila-induced impairment of the gill phosphotransfer network in grass carp Ctenopharyngodon idella

Some evidence suggests the involvement of phosphotransfer network in the pathogenesis of fish bacterial diseases, catalyzed by creatine kinase (CK), pyruvate kinase (PK) and adenylate kinase (AK); nevertheless, the effects on fish affected by Aeromonas hydrophila remain unknown. Recent evidence suggested a potent protective effect of caffeine on the branchial phosphotransfer network of fish subjected to challenge conditions. Therefore, the aim of this study was to evaluate whether A. hydrophila infection impaired branchial bioenergetics. We also determined whether dietary supplementation with caffeine protected against A. hydrophila-induced gill bioenergetic imbalance. We found that branchial cytosolic CK and AK activities were significant lower in fish experimentally infected with A. hydrophila than in uninfected fish, while mitochondrial CK activity was significant higher. Branchial lactate dehydrogenase (LDH) activity and lactate levels were significant higher in fish experimentally infected by A. hydrophila than in uninfected fish, while sodium-potassium ion pump (Na⁺, K⁺-ATPase) activity and adenosine triphosphate (ATP) levels were significant lower. No significant difference was observed between groups with respect to branchial PK activity. The dietary supplementation with 8% caffeine improved the branchial CK (cytosolic and mitochondrial), AK, and LDH activities, as well as ATP levels, but did not prevent increases in branchial lactate levels or the inhibition of Na⁺, K⁺-ATPase activity elicited by aeromonosis. Based on this evidence, we believe that reduction of CK (cytosolic) and AK activities contributes to impairment of bioenergetic homeostasis, while augmentation of mitochondrial CK activity can be considered an attempt to prevent or reduce the energetic imbalance during aeromonosis caused by A. hydrophila. The use of 8% caffeine dietary supplementation improved the energetic metabolism via protective effects on CK and AK activities, avoiding the necessity of using anaerobic metabolism. In summary, 8% dietary caffeine can be used to improve branchial energetic homeostasis during aeromonosis caused by A. hydrophila.

Copper oxide and closantel prevent alterations in hepatic energetic metabolism and reduce inflammation in Haemonchus contortus infection

The aims of this study were to evaluate if the use of copper oxide wire particles, isolated or in association with closantel, in lambs infected with Haemonchus contortus enhances the anthelmintic efficacy of closantel, as well as to evaluate the effects of treatment in hepatic energy metabolism, inflammatory markers and hematological and biochemical tests. The lambs were randomly divided into five groups (6 animals each), as follows: uninfected animals (Control); animals infected with H. contortus (HC); infected and treated with closantel (HC + CL); infected and treated with copper oxide wire particles (HC + Cu); and infected and treated with closantel plus copper oxide wire particles (HC + CL + Cu). The animals of infected groups were infected orally with H. contortus (5,000 L3 -larvae) and on day 14 post infection (p.i) the treatments were initiated. The egg per gram of feces (EPG), butyrylcholinesterase (BuChE), myeloperoxidase (MPO), adenylate kinase (AK) and pyruvate kinase (PK) activities and hematological and biochemical tests were evaluated. Treatments with copper oxide (isolated and associated) were able to reduce the EPG count on days 28, 35, 42 and 49 p.i when compared to HC group, while closantel was able to reduce EPG only from day 35 p.i. Moreover, treatment with closantel (isolated or associated) was able to prevent the inhibition of hepatic AK and PK activities caused by H. contortus infection, which may contribute to efficient intracellular energetic communication in order to maintain the balance between cellular ATP consumption and production. Butyrylcholinesterase and MPO activities were higher in infected lambs compared to uninfected, while treated groups showed lower enzymatic activity compared to the group HC. The use of all therapeutic protocols was able to reduce the EPG count. Based on these evidences, the use of copper oxide plus closantel may be considered an alternative to treat lambs infected by H. contortus.

Intestinal injury caused by Eimeria spp. impairs the phosphotransfer network and gain weight in experimentally infected chicken chicks

Parasitic infections caused by protozoan belonging to genus Eimeria are considered important for the poultry industry, due to their severe intestinal lesions and high mortality rates, causing significant economic losses. Although several mechanisms of coccidiosis pathogenesis are known, the effects of this infection on intestinal enzymes linked to adenosine triphosphate (ATP) metabolism, as creatine kinase (CK), adenylate kinase (AK), and pyruvate kinase (PK), remain unknown. Thus, the aim of this study was to evaluate whether coccidiosis impairs enzymes linked ATP metabolism in the intestine of chicken chicks. For this, 42 animals that were 2 days old were divided into two groups: uninfected (the negative control group) and experimentally infected on second day of life (the positive control group). On days 5, 10, and 15 post-infection (PI), fecal samples were collected for oocyst counts; intestinal tissue was collected in order to evaluate CK, AK, and PK activities, as well as parameters of the oxidative stress and histopathology. On days 10 and 15 PI, infected animals showed high counts of oocysts in fecal samples and intestinal lesions compared to the control group. Cytosolic CK activity was higher in infected animals on days 10 and 15 PI compared to the control group, while mitochondrial CK activity was lower on days 5, 10, and 15 PI. Also, AK activity was lower in infected animals on days 10 and 15 PI compared to control group, while no differences were observed between groups regarding PK activity. In relation to parameters of oxidative stress, intestinal lipid peroxidation and reactive oxygen species levels were higher in infected animals on days 10 and 15 PI compared to the control group, while non-protein thiol levels were lower on day 10 PI. On the 15th day, infected animals had lower body weight (P < 0.05). Based on this evidence, inhibition of mitochondrial CK activity causes an impairment of intestinal energetic homeostasis possibly through depletion on ATP levels, although the cytosolic CK activity acted as an attempt to restore the mitochondrial ATP levels through a feedback mechanism. Moreover, the impairment on energy metabolism appears to be mediated by excessive production of intestinal ROS, as well as oxidation of lipids and thiol groups.

Development of Software for the In-Depth Analysis of Protein Dynamics as Determined by MALDI Mass Spectrometry-Based Hydrogen/Deuterium Exchange

Hydrogen/deuterium exchange (HDX) coupled with pepsin digestion is useful for rapidly analyzing the kinetic properties of small amounts of protein. However, the analysis of HDX by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is time-consuming due to a lack of dedicated software. Currently available software programs mainly calculate average mass shifts, even though the isotopic distribution width contains information regarding multiple protein conformations. Moreover, HDX reaction samples are typically composed of peptides that contain various numbers of deuterium atoms, which also hinders the rapid and comprehensive analysis of protein dynamics. We report here on the development of a software program "Scipas DX" that can be used to automatically analyze the hydrogen-deuterium isotopic distribution in peaks in HDX spectra and calculate the average number of atoms exchanged, the average deuteration ratio, the abundance ratio for exchanged atoms, and their fitted spectra with a high degree of accuracy within a few minutes. Analysis of the abundance ratio for exchanged atoms of a model protein, adenylate kinase 1, using Scipas DX indicate that the local structure at residues 83-106 and 107-117 are in a slow equilibrium, suggesting that these regions adopt multiple conformations that are involved in the stability and in switching between the active and inactive forms. Furthermore, precise HDX kinetics of the average deuteration ratio both confirmed the known induced conformations of two regions (residues 46-75 and 131-165) that are responsible for ligand binding and verified the novel structural dynamics of residues 107-117 and 166-196 following ligand binding to ligand-binding pockets 1 and 2, respectively. Collectively, these results highlight the usefulness and versatility of Scipas DX in MALDI-MS HDX-based analyses of protein dynamics.

Involvement of the phosphoryl transfer network on cardiac energetic metabolism during Staphylococcus aureus infection and its association to disease pathophysiology

Evidences have suggested that the phosphoryl transfer network by the enzymatic activities of creatine kinase (CK), adenylate kinase (AK), pyruvate kinase (PK), and lactate dehydrogenase (LDH), shows new perspectives to understand some disturbances in the energy metabolism during bacterial infections. Thus, the aim of this study was to evaluate whether Staphylococcus aureus infection in mice could alter serum and cardiac activities of these enzymes and their association to disease pathophysiology. For that, we measured total leukocytes, lymphocytes and neutrophils (just 48 h of infection) that were lower in infected animals after 48 and 72 h in infected mice compared with negative control, while total protein and globulin plasma levels were higher after 72 h of infection. The serum CK activity was higher in infected animals 48 and 72 h post-infection compared to the control group, as well as observed for mitochondrial cardiac CK activity. The serum PK activity was higher in infected animals after 72 h of infection compared to the control group, and lower in the cardiac tissue. The cardiac AK activity was lower in infected animals 48 h and 72 h post-infection compared to the control group, while serum and cardiac LDH activities were higher. Based on these evidences, it is possible to conclude that the stimulation of CK activity exerts a key role as an attempt to maintain the bioenergetic homeostasis by the production of phosphocreatine to avoid a rapid fall on the concentrations of total adenosine triphosphate. In summary, the phosphoryl transfer network can be considered a pathway involved in the improvement on tissue and cellular energy homeostasis of S. aureus-infected mice.

Intracellular Energy-Transfer Networks and High-Resolution Respirometry: A Convenient Approach for Studying Their Function

Compartmentalization of high-energy phosphate carriers between intracellular micro-compartments is a phenomenon that ensures efficient energy use. To connect these sites, creatine kinase (CK) and adenylate kinase (AK) energy-transfer networks, which are functionally coupled to oxidative phosphorylation (OXPHOS), could serve as important regulators of cellular energy fluxes. Here, we introduce how selective permeabilization of cellular outer membrane and high-resolution respirometry can be used to study functional coupling between CK or AK pathways and OXPHOS in different cells and tissues. Using the protocols presented here the ability of creatine or adenosine monophosphate to stimulate OXPHOS through CK and AK reactions, respectively, is easily observable and quantifiable. Additionally, functional coupling between hexokinase and mitochondria can be investigated by monitoring the effect of glucose on respiration. Taken together, high-resolution respirometry in combination with permeabilization is a convenient approach for investigating energy-transfer networks in small quantities of cells and tissues in health and in pathology.

Tissue oxidative damage mediates impairment on phosphotransfer network during thymol intake: Effects on hepatic and renal bioenergetics

Recent evidences demonstrated that ingestion of several monoterpenes cause hepatic and renal damage due to impairment on mitochondrial energy production, eliciting a collapse on adenosine triphosphate (ATP) synthesis and consequently impairment on bioenergetic homeostasis. Thus, the aim of this study was to evaluate whether phosphotransfer network, catalyzed by creatine kinase (CK), adenylate kinase (AK), and pyruvate kinase (PK), can be a pathway to explain hepatic and renal bioenergetics homeostasis impairment due to thymol ingestion. Daily intake of thymol (40 mg/kg) significantly cause a decreased kidney weight and relative kidney weight compared to control group. The same dose of thymol inhibited renal cytosolic and mitochondrial CK activity as well as renal PK activity compared to control group. Finally, thymol (40 mg/kg) elicited a significant increase on renal reactive oxygen species and lipid damage levels, as well as an inhibition on antioxidant capacity against peroxyl radicals and non-protein thiol levels, which did not occur liver. Doses of 10 and 20 mg/kg of thymol administered orally for 30 consecutive days non-changed these variables. Based on these evidence, the data supported that intake of a high dose of thymol severely inhibits cytosolic and mitochondrial CK activity, a crucial enzyme to maintain cellular energy homeostasis. Moreover, high dietary thymol intake impaired communication between CK isoenzymes, which inhibits the attempts to regenerate ATP or to facilitate the CK/PCr shuttle to improve the intracellular ATP utilization and consumption. Moreover, the inhibition of renal CK and PK activities appears to be mediated by the renal oxidation of lipids and thiol groups, as well as by the reduction of the renal antioxidant capacity.

Gill bioenergetics dysfunction and oxidative damage induced by thiamethoxam exposure as relevant toxicological mechanisms in freshwater silver catfish Rhamdia quelen

Thiamethoxam is a neonicotinoid pesticide utilized on a worldwide scale, it has been reported in freshwater ecosystems, and detected in fishery products. Nevertheless, there is a lack of information about thiamethoxam sublethal effects on the gills of freshwater fish, principally linked to energetic metabolism. In this context, creatine kinase (CK) is an enzyme of the phosphoryl transfer network that provides a temporal and spatial energy buffer to maintain cellular energy homeostasis in tissues with high energy requirements, such as gills. Based on this evidence, the aim of this study was to evaluate whether exposure to thiamethoxam impairs the cytosolic and mitochondrial CK activities in gills of Rhamdia quelen, and the involvement of oxidative stress in the energetic imbalance. Branchial CK (cytosolic and mitochondrial) activity and sodium‑potassium pump (Na⁺, K⁺-ATPase) were inhibited, and adenosine triphosphate (ATP) levels decreased after 96 h exposure to 1.125 and 3.75 μg/L thiamethoxam compared to the control group. Moreover, levels of branchial thiobarbituric acid reactive substances (TBARS) and protein carbonylation increased at 3.75 μg/L thiamethoxam after 96 h of exposure compared to the control group, while the non-protein thiol (NPSH) content did not differ between groups. It is important to emphasize that all evaluated parameters did not recover after 48 h in clean water. To summarize, the data presented here clearly demonstrated that thiamethoxan exposure severely impairs cytosolic and mitochondrial CK activities, a key enzyme for gill energy buffering to maintain cellular energy homeostasis, and this effect appears to be mediated by oxidation of lipid and protein molecules, which consequently thereby induces oxidative stress.

Changes in the cerebral phosphotransfer network impair energetic homeostasis in an aflatoxin B1-contaminated diet

The phosphotransfer network system, through the enzymes creatine kinase (CK), adenylate kinase (AK), and pyruvate kinase (PK), contributes to efficient intracellular energetic communication between cellular adenosine triphosphate (ATP) consumption and production in tissues with high energetic demand, such as cerebral tissue. Thus, the aim of this study was to evaluate whether aflatoxin B₁ (AFB₁) intoxication in diet negatively affects the cerebral phosphotransfer network related to impairment of cerebral ATP levels in silver catfish (Rhamdia quelen). Brain cytosolic CK activity decreased in animals fed with a diet contaminated with AFB₁ on days 14 and 21 post-feeding, while mitochondrial CK activity increased, when compared to the control group (basal diet). Also, cerebral AK and PK activity decreased in animals fed with a diet contaminated with AFB₁ on days 14 and 21 post-feeding, similarly to the results observed for cerebral ATP levels. Based on this evidence, inhibition of cerebral cytosolic CK activity is compensated by stimulation of mitochondrial CK activity in an attempt to prevent impairment of communication between sites of ATP generation and ATP utilization. The inhibition of cerebral AK and PK activity leads to impairment of cerebral energy homeostasis, decreasing the brain's ATP availability. Moreover, the absence of a reciprocal compensatory mechanism between these enzymes contributes to cerebral energetic imbalance, which may contribute to disease pathophysiology.

Thiamethoxam induced hepatic energy changes in silver catfish via impairment of the phosphoryl transfer network pathway: Toxicological effects on energetics homeostasis

Precise coupling of spatially separated intracellular adenosine triphosphate (ATP)-producing and ATP-consuming processes exerts a pivotal role in bioenergetic homeostasis of living organisms, and the phosphotransfer network pathway, catalyzed by adenylate kinase (AK) and pyruvate kinase (PK), is fundamental in cellular and tissue energetic homeostasis. Measurement of the phosphotransfer network can provide new information for understanding the alterations in hepatic energetic metabolism during exposition to insecticides, such as thiamethoxam. Therefore, the aim of this study was to evaluate whether exposition to thiamethoxam negatively affects the hepatic enzymes of the phosphotransfer network in silver catfish (Rhamdia quelen). Hepatic AK and PK activities were inhibited at 3.75 μg L^-1 after 24 h of exposure and at 1.125 and 3.75 μg L^-1 after 96 h of exposure compared with the control group. The hepatic ATP levels were decreased following 3.75 μg L^-1 thiamethoxam treatment after 24 h of exposure and at 1.125 and 3.75 μg L^-1 after 96 h of exposure compared with the control group. The enzymatic activity of the phosphotransfer network and ATP levels did not recover after 48 h of recovery in clean water. Thus, the inhibition of hepatic AK and PK activities by thiamethoxam caused impairment of energy homeostasis in liver tissue, decreasing hepatic ATP availability. Moreover, the absence of a mutual compensatory mechanism between these enzymes directly contributes to ATP depletion and to a severe energetic dysregulation, which may contribute to toxic effects caused by thiamethoxam.

Aeromonas caviae inhibits hepatic enzymes of the phosphotransfer network in experimentally infected silver catfish: Impairment on bioenergetics

Several studies have been demonstrated that phosphotransfer network, through the adenylate kinase (AK) and pyruvate kinase (PK) activities, allows for new perspectives leading to understanding of disease conditions associated with disturbances in energy metabolism, metabolic monitoring and signalling. In this sense, the aim of this study was to evaluate whether experimental infection by Aeromonas caviae alters hepatic AK and PK activities of silver catfish Rhamdia quelen. Hepatic AK and PK activities decreased in infected animals compared to uninfected animals, as well as the hepatic adenosine triphosphate (ATP) levels. Also, a severe hepatic damage was observed in the infected animals due to the presence of dilation and congestion of vessels, degeneration of hepatocytes and loss of liver parenchyma architecture and sinusoidal structure. Therefore, we have demonstrated, for the first time, that experimental infection by A. caviae inhibits key enzymes linked to the communication between sites of ATP generation and ATP utilization. Moreover, the absence of a reciprocal compensatory mechanism between these enzymes contributes directly to hepatic damage and for a severe energetic imbalance, which may contribute to disease pathophysiology.

Proteome analysis in dystrophic mdx mouse muscle reveals a drastic alteration of key metabolic and contractile proteins after chronic exercise and the potential modulation by anti-oxidant compounds

Weakness and fatigability are typical features of Duchenne muscular dystrophy patients and are aggravated in dystrophic mdx mice by chronic treadmill exercise. In the present study, we describe, the pattern of differentially abundant spots that is associated to the worsening of dystrophy phenotype induced by chronic exercise. Our proteomic analysis pointed out 34 protein spots with different abundance between sedentary and exercised mdx mice. These proteins belong mostly to glucose metabolism, energy production and sarcomere structure categories. Interestingly exercise induced an increase of typical fast twitch fiber proteins (Troponin T fast skeletal muscle, Troponin I fast skeletal muscle and Myozenin-1) combined with an increase of several glycolytic enzymes. Concerning energy transfer, Adenylate kinase, showed a marked decrease when compared with non-exercised mdx. The decline of this enzyme correlates with increased Creatin kinase enzyme, suggesting that a compensatory energy metabolism mechanism could be activated in mdx mouse skeletal muscle following exercise. In addition, we analysed muscles from exercised mdx mice treated with two natural anti-oxidant compounds, apocynin and taurine, that in our previous study, were proved to be beneficial on some pathology related parameters, and we showed that these compounds can counteract exercise-induced changes in the abundance of several proteins.

SIGNIFICANCE

Mdx mouse model of Duchenne muscular dystrophy shows a phenotype of the disorder milder than in human sufferers. This phenotype can be worsened by a different protocols of chronic exercise. These protocols can mimic the muscle progressive damage observed in humans, can allow studying the effects of inadequate training on dystrophic muscles and have been largely used to assess the ability of a drug to reduce the damage induced by exercise. In this study, we describe for the first time, the pattern of protein variation associated with the worsening of dystrophy phenotype induced by chronic exercise. Our proteomic analysis pointed out 34 protein spots with different amount between sedentary and exercised mdx mice. These proteins belong mostly to glucose metabolism, energy production and sarcomere structure categories and their variation indicates that mdx exercised muscle are not able to carry out the metabolic changes associated to fast-to-slow transition typically observed in aerobically trained muscle.

Human skeletal muscle fibre contractile properties and proteomic profile: adaptations to 3 weeks of unilateral lower limb suspension and active recovery

KEY POINTS

It is generally assumed that muscle fibres go through atrophy following disuse with a loss of specific force and an increase in unloaded shortening velocity. However, the underlying mechanisms remain to be clarified. Most studies have focused on events taking place during the development of disuse, whereas the subsequent recovery phase, which is equally important, has received little attention. Our findings support the hypotheses that the specific force of muscle fibres decreased following unilateral lower limb suspension (ULLS) and returned to normal after 3 weeks of active recovery as a result of a loss and recovery of myosin and actin content. Furthermore, muscle fibres went through extensive qualitative changes in muscle protein pattern following ULLS, and these were reversed by active recovery. Resistance training was very effective in restoring both muscle mass and qualitative muscle changes, indicating that long-term ULLS did not prevent the positive effect of exercise on human muscle.

ABSTRACT

Following disuse, muscle fibre function goes through adaptations such as a loss of specific force (PO /CSA) and an increase in unloaded shortening velocity, which could be a result of both quantitative changes (i.e. atrophy) and qualitative changes in protein pattern. The underlying mechanisms remain to be clarified. In addition, little is known about the recovery of muscle mass and strength following disuse. In the present study, we report an extensive dataset describing, in detail,the functional and protein content adaptations of skeletal muscle in response to both disuse and re-training. Eight young healthy subjects were subjected to 3 weeks of unilateral lower limb suspension (ULLS), a widely used human model of disuse skeletal muscle atrophy. Needle biopsies samples were taken from the vastus lateralis muscle Pre-ULLS, Post-ULLS and after 3 weeks of recovery during which heavy resistance training was performed. After disuse, cross-sectional area (CSA), PO /CSA and myosin concentration (MC) decreased in both type 1 and 2A skinned muscle fibres. After recovery, CSA and MC returned to levels comparable to those observed before disuse, whereas Po/CSA and unloaded shortening velocity reached a higher level. Myosin heavy chain isoform composition of muscle samples did not differ among the experimental groups. To study the mechanisms underlying such adaptations, a two-dimensional proteomic analysis was performed. ULLS induced a reduction of myofibrillar, metabolic (glycolytic and oxidative) and anti-oxidant defence system protein content. Resistance training was very effective in counteracting ULLS-induced alterations, indicating that long-term ULLS did not prevent the positive effect of exercise on human muscle.

Molecular cloning, subcellular localization and characterization of two adenylate kinases from cassava, Manihot esculenta Crantz cv. KU50

Adenylate kinase (ADK) is a phosphotransferase that plays an important role in cellular energy homeostasis. Many isozymes located in different subcellular compartments have been reported. In this study, we focus on the characterization of cassava (Manihot esculenta) ADKs. We found 15 ADKs that are publicly available in the African cassava genome database. We cloned two ADKs, namely MeADK1 and MeADK2, which are phylogenetically grouped together with the plastidial ADK in potato. Both MeADK1 and MeADK2 showed 66% identity in the amino acid sequences with plastidial ADK in potato. However, we demonstrated that they are localized to mitochondria using GFP fusions of MeADK1 and MeADK2. The Escherichia coli-produced recombinant MeADK1 and MeADK2 preferred forward reactions that produce ATP. They exhibited similar specific activities. The semi-quantitative RT-PCR analysis showed that MeADK1 and MeADK2 in 2-month-old leaves have similar expression patterns under a diurnal light-dark cycle. However, MeADK2 transcripts were expressed at much higher levels than MeADK1 in 5-month-old leaves and roots. Thus, we conclude that MeADK2 might play a vital role in energy homeostasis in cassava mitochondria.

Enzymes involved in metabolism of extracellular nucleotides and nucleosides: functional implications and measurement of activities

Extracellular nucleotides and nucleosides mediate diverse signaling effects in virtually all organs and tissues. Most models of purinergic signaling depend on functional interactions between distinct processes, including (i) the release of endogenous ATP and other nucleotides, (ii) triggering of signaling events via a series of nucleotide-selective ligand-gated P2X and metabotropic P2Y receptors as well as adenosine receptors and (iii) ectoenzymatic interconversion of purinergic agonists. The duration and magnitude of purinergic signaling is governed by a network of ectoenzymes, including the enzymes of the nucleoside triphosphate diphosphohydrolase (NTPDase) family, the nucleotide pyrophosphatase/phosphodiesterase (NPP) family, ecto-5'-nucleotidase/CD73, tissue-nonspecific alkaline phosphatase (TNAP), prostatic acid phosphatase (PAP) and other alkaline and acid phosphatases, adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP). Along with "classical" inactivating ectoenzymes, recent data provide evidence for the co-existence of a counteracting ATP-regenerating pathway comprising the enzymes of the adenylate kinase (AK) and nucleoside diphosphate kinase (NDPK/NME/NM23) families and ATP synthase. This review describes recent advances in this field, with special emphasis on purine-converting ectoenzymes as a complex and integrated network regulating purinergic signaling in such (patho)physiological states as immunomodulation, inflammation, tumorigenesis, arterial calcification and other diseases. The second part of this review provides a comprehensive overview and basic principles of major approaches employed for studying purinergic activities, including spectrophotometric Pi-liberating assays, high-performance liquid chromatographic (HPLC) and thin-layer chromatographic (TLC) analyses of purine substrates and metabolites, capillary electrophoresis, bioluminescent, fluorometric and electrochemical enzyme-coupled assays, histochemical staining, and further emphasizes their advantages, drawbacks and suitability for assaying a particular catalytic reaction.

Reticular dysgenesis-associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress

Rissone et al. demonstrate that adenylate kinase AK2, an enzyme mutated in reticular dysgenesis (RD) in humans, prevents oxidative stress during hematopoiesis. Using a zebrafish model, as well as induced pluripotent stem cells derived from an RD patient, they find that AK2 deficiency affects hematopoietic stem and progenitor development with increased oxidative stress. Antioxidant treatment rescues the hematopoietic phenotypes.

Adenylate kinases (AKs) are phosphotransferases that regulate the cellular adenine nucleotide composition and play a critical role in the energy homeostasis of all tissues. The AK2 isoenzyme is expressed in the mitochondrial intermembrane space and is mutated in reticular dysgenesis (RD), a rare form of severe combined immunodeficiency (SCID) in humans. RD is characterized by a maturation arrest in the myeloid and lymphoid lineages, leading to early onset, recurrent, and overwhelming infections. To gain insight into the pathophysiology of RD, we studied the effects of AK2 deficiency using the zebrafish model and induced pluripotent stem cells (iPSCs) derived from fibroblasts of an RD patient. In zebrafish, Ak2 deficiency affected hematopoietic stem and progenitor cell (HSPC) development with increased oxidative stress and apoptosis. AK2-deficient iPSCs recapitulated the characteristic myeloid maturation arrest at the promyelocyte stage and demonstrated an increased AMP/ADP ratio, indicative of an energy-depleted adenine nucleotide profile. Antioxidant treatment rescued the hematopoietic phenotypes in vivo in ak2 mutant zebrafish and restored differentiation of AK2-deficient iPSCs into mature granulocytes. Our results link hematopoietic cell fate in AK2 deficiency to cellular energy depletion and increased oxidative stress. This points to the potential use of antioxidants as a supportive therapeutic modality for patients with RD.

The sarcomeric M-region: a molecular command center for diverse cellular processes

The sarcomeric M-region anchors thick filaments and withstands the mechanical stress of contractions by deformation, thus enabling distribution of physiological forces along the length of thick filaments. While the role of the M-region in supporting myofibrillar structure and contractility is well established, its role in mediating additional cellular processes has only recently started to emerge. As such, M-region is the hub of key protein players contributing to cytoskeletal remodeling, signal transduction, mechanosensing, metabolism, and proteasomal degradation. Mutations in genes encoding M-region related proteins lead to development of severe and lethal cardiac and skeletal myopathies affecting mankind. Herein, we describe the main cellular processes taking place at the M-region, other than thick filament assembly, and discuss human myopathies associated with mutant or truncated M-region proteins.

Adenine nucleotide metabolism and a role for AMP in modulating flagellar waveforms in mouse sperm

While most ATP, the main energy source driving sperm motility, is derived from glycolysis and oxidative phosphorylation, the metabolic demands of the cell require the efficient use of power stored in high-energy phosphate bonds. In times of high energy consumption, adenylate kinase (AK) scavenges one ATP molecule by transphosphorylation of two molecules of ADP, simultaneously yielding one molecule of AMP as a by-product. Either ATP or ADP supported motility of detergent-modeled cauda epididymal mouse sperm, indicating that flagellar AKs are functional. However, the ensuing flagellar waveforms fueled by ATP or ADP were qualitatively different. Motility driven by ATP was rapid but restricted to the distal region of the sperm tail, whereas ADP produced slower and more fluid waves that propagated down the full flagellum. Characterization of wave patterns by tracing and superimposing the images of the flagella, quantifying the differences using digital image analysis, and computer-assisted sperm analysis revealed differences in the amplitude, periodicity, and propagation of the waves between detergent-modeled sperm treated with either ATP or ADP. Surprisingly, addition of AMP to the incubation medium containing ATP recapitulated the pattern of sperm motility seen with ADP alone. In addition to AK1 and AK2, which we previously demonstrated are present in outer dense fibers and mitochondrial sheath of the mouse sperm tail, we show that another AK, AK8, is present in a third flagellar compartment, the axoneme. These results extend the known regulators of sperm motility to include AMP, which may be operating through an AMP-activated protein kinase.

18O-assisted dynamic metabolomics for individualized diagnostics and treatment of human diseases

Technological innovations and translation of basic discoveries to clinical practice drive advances in medicine. Today's innovative technologies enable comprehensive screening of the genome, transcriptome, proteome, and metabolome. The detailed knowledge, converged in the integrated "omics" (genomics, transcriptomics, proteomics, and metabolomics), holds an immense potential for understanding mechanism of diseases, facilitating their early diagnostics, selecting personalized therapeutic strategies, and assessing their effectiveness. Metabolomics is the newest "omics" approach aimed to analyze large metabolite pools. The next generation of metabolomic screening requires technologies for high throughput and robust monitoring of metabolite levels and their fluxes. In this regard, stable isotope 18O-based metabolite tagging technology expands quantitative measurements of metabolite levels and turnover rates to all metabolites that include water as a reactant, most notably phosphometabolites. The obtained profiles and turnover rates are sensitive indicators of energy and metabolic imbalances like the ones created by genetic deficiencies, myocardial ischemia, heart failure, neurodegenerative disorders, etc. Here we describe and discuss briefly the potential use of dynamic phosphometabolomic platform for disease diagnostics currently under development at Mayo Clinic.

Identification and biochemical characterization of adenylate kinase 1 from Clonorchis sinensis

Adenylate kinase 1 is responsible for the conversion of AMP into ADP involved in purine metabolism. In the present study, adenylate kinase 1 gene (CsADK1) was isolated from an adult cDNA library of Clonorchis sinensis, and the recombinant protein was expressed in Escherichia coli. Bioinformatics analysis implied that the putative protein contained 197 amino acids, and some residues in conservative binding sites of CsADK1 were substituted. The structure modeling analysis showed that CsADK1 was composed of a core domain, an NMP-binding domain, and a LID domain, which was just a small loop. It demonstrated that CsADK1 was a short isoform of ADKs. Moreover, CsADK1 was identified as an excretory/secretory product by western blot analysis. Real-time quantitative PCR showed that expression level of CsADK1 at the stage of excysted metacercaria was higher than those of adult worm (18.8-folds, P<0.01), metacercariae (1.5-folds, P<0.01), and eggs (5.6-folds, P<0.01). In addition, histochemistry analysis showed that CsADK1 was extensively distributed in metacercariae and in the vitellaria and eggs of adult worms. The Km and Vmax value for substrate ADP were 2.2 mM and 0.9 mM/min, respectively. The optimal temperature and pH value were 37 °C and from 7.5 to 8.0, respectively. The enzyme activity was highly dependent on Mg2+, and the optimal concentration of Mg2+ was 2 mM. However, the enzyme activity was slightly activated by Ca2+, and Mn2+ has no effect on activity. For monovalent ions, activity was highly activated by K+ and NH4+, but slightly by Li+. Taken together, CsADK1 was a metal ion-dependent enzyme involved in purine metabolism, which was important for development and reproduction, and might be a potential candidate for drug target for clonorchiasis.

Sensitivity analysis of flux determination in heart by H₂ ¹⁸O -provided labeling using a dynamic Isotopologue model of energy transfer pathways

To characterize intracellular energy transfer in the heart, two organ-level methods have frequently been employed: inversion and saturation transfer, and dynamic labeling. Creatine kinase (CK) fluxes obtained by following oxygen labeling have been considerably smaller than the fluxes determined by saturation transfer. It has been proposed that dynamic labeling determines net flux through CK shuttle, whereas saturation transfer measures total unidirectional flux. However, to our knowledge, no sensitivity analysis of flux determination by oxygen labeling has been performed, limiting our ability to compare flux distributions predicted by different methods. Here we analyze oxygen labeling in a physiological heart phosphotransfer network with active CK and adenylate kinase (AdK) shuttles and establish which fluxes determine the labeling state. A mathematical model consisting of a system of ordinary differential equations was composed describing enrichment in each phosphoryl group and inorganic phosphate. By varying flux distributions in the model and calculating the labeling, we analyzed labeling sensitivity to different fluxes in the heart. We observed that the labeling state is predominantly sensitive to total unidirectional CK and AdK fluxes and not to net fluxes. We conclude that measuring dynamic incorporation of into the high-energy phosphotransfer network in heart does not permit unambiguous determination of energetic fluxes with a higher magnitude than the ATP synthase rate when the bidirectionality of fluxes is taken into account. Our analysis suggests that the flux distributions obtained using dynamic labeling, after removing the net flux assumption, are comparable with those from inversion and saturation transfer.

In heart, the movement of energy metabolites between force-producing myosin, other ATPases, and mitochondria is vital for its function and closely related to heart pathologies. In addition to diffusion, transport of ATP, ADP, Pi, and phosphocreatine occurs along parallel pathways such as the adenylate kinase and creatine kinase shuttles. Two organ-level methods have been developed to study the relative flux through these pathways. However, their results differ. It was recently demonstrated that studies often suffer from the exclusion of compartmentation from their metabolic models. One study overcame this limitation by using compartmental models and statistical methods on multiple experiments. Here, we analyzed the sensitivity of the other method - dynamic labeling of phosphoryl groups and inorganic phosphate. For that, we composed a mathematical model tracking enrichment of the metabolites and evaluated sensitivity of labeling to different flux distribution scenarios. Our study shows that the dynamic method provides a measure of total flux, and not net flux as presumed previously, making the fluxes predicted from both methods consistent. Importantly, conclusions derived on the basis of labeling analysis, particularly those regarding the net flux through the shuttles in control and pathological cases, need to be reevaluated.

Identification of a novel nuclear-localized adenylate kinase 6 from Arabidopsis thaliana as an essential stem growth factor

Adenylate kinase (AK; EC 2.7.4.3) is highly conserved across a wide range of organisms, including Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, and Homo sapiens. While AK6 orthologs play important roles in the growth of yeast and worms, the physiological function of AK6 in A. thaliana is still unknown. In this study, we first cloned and expressed Arabidopsis adenylate kinase 6 (AAK6). Enzyme assays revealed that AAK6 has characteristic adenylate kinase properties, with ATP as the preferred phosphate donor and AMP as the best phosphate acceptor. A subcellular localization assay demonstrated that AAK6 had a predominant nuclear localization. Through biochemical purification and mass spectrometry analysis, a putative homolog of the S. cerevisiae Rps14 protein was identified as a partner of AAK6. Most importantly, we observed that aak6 T-DNA insertion mutants had decreased stem growth compared with wild-type plants. These data indicate that AAK6 exhibits adenylate kinase activity and is an essential growth factor in Arabidopsis.

Metabolism of circulating ADP in the bloodstream is mediated via integrated actions of soluble adenylate kinase-1 and NTPDase1/CD39 activities

Extracellular ATP and ADP trigger inflammatory, vasodilatatory, and prothrombotic signaling events in the vasculature, and their turnover is governed by networks of membrane-associated enzymes. The contribution of soluble activities to intravascular nucleotide homeostasis remains controversial. By using thin-layer chromatographic assays, we revealed transphosphorylation of [γ-(32)P]ATP and AMP by human and murine sera, which was progressively inhibited by specific adenylate kinase (AK) inhibitor Ap(5)A. This phosphotransfer reaction was diminished markedly in serum from knockout mice lacking the major AK isoform, AK1, and in human serum immunodepleted of AK1. We also showed that ∼75% ADP in cell-free serum is metabolized via reversible AK1 reaction 2ADP ↔ ATP + AMP. The generated ATP and AMP are then metabolized through the coupled nucleotide pyrophosphatase/phosphodiesterase and 5'-nucleotidase/CD73 reactions, respectively. Constitutive presence of another nucleotide-converting enzyme, nucleoside triphosphate diphosphohydrolase-1 (NTPDase1, known as CD39), was ascertained by the relative deficiency of serum from CD39-null mice to dephosphorylate [(3)H]ADP and [γ-(32)P]ATP, and also by diminished [(3)H]ADP hydrolysis by human serum pretreated with NTPDase1 inhibitors, POM-1 and ARL-67156. In summary, we have identified hitherto unrecognized soluble forms of AK1 and NTPDase1/CD39 that contribute in the active cycling between the principal platelet-recruiting agent ADP and other circulating nucleotides.