A brief harvesting-freezing delay significantly alters the kidney metabolome and leads to false positive and negative results.

Abnormalities in distinct metabolic pathways have been associated with many forms of kidney disease. Metabolomics analyses can be used to determine organ-specific metabolic fingerprints. However, conventional harvesting methods depend on post-euthanasia tissue harvest, which results in ischemia conditions and metabolome changes that could introduce artifacts into the final studies. We optimized a clamp-freezing technique for kidney harvesting and freezing, significantly reducing ischemia and freezing times and granting a closer snapshot of in vivo metabolism. In this study, we characterized and compared the metabolome of kidneys harvested using our approach vs. traditional techniques to determine which metabolites are preferentially affected by a brief lapse of ischemia and freezing delay and which are more stable. We used Sprague Dawley rats as a model of wild-type (WT) kidneys and PCK, polycystic kidney disease (PKD) rats as a model of CKD kidneys. Finally, we compared the metabolic profile of clamp-frozen and delayed WT and PKD-kidneys to determine which metabolic changes are most likely observed in vivo in PKD and which could be subjected to false positive or negative results. Our data indicate that a short harvesting-freezing delay is sufficient to impart profound metabolic changes in WT and PKD kidneys. Interestingly, while the delay had a similar effect in WT and PKD, there were notable differences, leading to false positive and negative results when comparing these genotypes. The data obtained indicate that the quick clamp-freezing technique for kidney metabolomics provides a more accurate interpretation of the in vivo metabolic changes associated with the disease state.

Pyruvate dehydrogenase kinase regulates vascular inflammation in atherosclerosis and increases cardiovascular risk.

AIMS: Recent studies have revealed a close connection between cellular metabolism and the chronic inflammatory process of atherosclerosis. While the link between systemic metabolism and atherosclerosis is well established, the implications of altered metabolism in the artery wall are less understood. Pyruvate dehydrogenase kinase (PDK)-dependent inhibition of pyruvate dehydrogenase (PDH) has been identified as a major metabolic step regulating inflammation. Whether the PDK/PDH axis plays a role in vascular inflammation and atherosclerotic cardiovascular disease remains unclear. METHODS AND RESULTS: Gene profiling of human atherosclerotic plaques revealed a strong correlation between PDK1 and PDK4 transcript levels and the expression of pro-inflammatory and destabilizing genes. Remarkably, the PDK1 and PDK4 expression correlated with a more vulnerable plaque phenotype, and PDK1 expression was found to predict future major adverse cardiovascular events. Using the small-molecule PDK inhibitor dichloroacetate (DCA) that restores arterial PDH activity, we demonstrated that the PDK/PDH axis is a major immunometabolic pathway, regulating immune cell polarization, plaque development, and fibrous cap formation in Apoe-/- mice. Surprisingly, we discovered that DCA regulates succinate release and mitigates its GPR91-dependent signals promoting NLRP3 inflammasome activation and IL-1ß secretion by macrophages in the plaque. CONCLUSIONS: We have demonstrated for the first time that the PDK/PDH axis is associated with vascular inflammation in humans and particularly that the PDK1 isozyme is associated with more severe disease and could predict secondary cardiovascular events. Moreover, we demonstrate that targeting the PDK/PDH axis with DCA skews the immune system, inhibits vascular inflammation and atherogenesis, and promotes plaque stability features in Apoe-/- mice. These results point toward a promising treatment to combat atherosclerosis.

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

Changes in dynamics of ATP γ- and ß-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 ß-ATP turnover in both breast cancer cells, compared to control. Lower ß-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.

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.

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.

Partial inhibition of mitochondrial complex I ameliorates Alzheimer's disease pathology and cognition in APP/PS1 female mice.

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder without a cure. Here we show that mitochondrial respiratory chain complex I is an important small molecule druggable target in AD. Partial inhibition of complex I triggers the AMP-activated protein kinase-dependent signaling network leading to neuroprotection in symptomatic APP/PS1 female mice, a translational model of AD. Treatment of symptomatic APP/PS1 mice with complex I inhibitor improved energy homeostasis, synaptic activity, long-term potentiation, dendritic spine maturation, cognitive function and proteostasis, and reduced oxidative stress and inflammation in brain and periphery, ultimately blocking the ongoing neurodegeneration. Therapeutic efficacy in vivo was monitored using translational biomarkers FDG-PET, 31P NMR, and metabolomics. Cross-validation of the mouse and the human transcriptomic data from the NIH Accelerating Medicines Partnership-AD database demonstrated that pathways improved by the treatment in APP/PS1 mice, including the immune system response and neurotransmission, represent mechanisms essential for therapeutic efficacy in AD patients.

CFAP45 deficiency causes situs abnormalities and asthenospermia by disrupting an axonemal adenine nucleotide homeostasis module.

Axonemal dynein ATPases direct ciliary and flagellar beating via adenosine triphosphate (ATP) hydrolysis. The modulatory effect of adenosine monophosphate (AMP) and adenosine diphosphate (ADP) on flagellar beating is not fully understood. Here, we describe a deficiency of cilia and flagella associated protein 45 (CFAP45) in humans and mice that presents a motile ciliopathy featuring situs inversus totalis and asthenospermia. CFAP45-deficient cilia and flagella show normal morphology and axonemal ultrastructure. Proteomic profiling links CFAP45 to an axonemal module including dynein ATPases and adenylate kinase as well as CFAP52, whose mutations cause a similar ciliopathy. CFAP45 binds AMP in vitro, consistent with structural modelling that identifies an AMP-binding interface between CFAP45 and AK8. Microtubule sliding of dyskinetic sperm from Cfap45-/- mice is rescued with the addition of either AMP or ADP with ATP, compared to ATP alone. We propose that CFAP45 supports mammalian ciliary and flagellar beating via an adenine nucleotide homeostasis module.

Adenylate Kinase and Metabolic Signaling in Cancer Cells.

A hallmark of cancer cells is the ability to rewire their bioenergetics and metabolic signaling circuits to fuel their uncontrolled proliferation and metastasis. Adenylate kinase (AK) is the critical enzyme in the metabolic monitoring of cellular adenine nucleotide homeostasis. It also directs AK→ AMP→ AMPK signaling controlling cell cycle and proliferation, and ATP energy transfer from mitochondria to distribute energy among cellular processes. The significance of AK isoform network in the regulation of a variety of cellular processes, which include cell differentiation and motility, is rapidly growing. Adenylate kinase 2 (AK2) isoform, localized in intermembrane and intra-cristae space, is vital for mitochondria nucleotide exchange and ATP export. AK2 deficiency disrupts cell energetics, causes severe human diseases, and is embryonically lethal in mice, signifying the importance of catalyzed phosphotransfer in cellular energetics. Suppression of AK phosphotransfer and AMP generation in cancer cells and consequently signaling through AMPK could be an important factor in the initiation of cancerous transformation, unleashing uncontrolled cell cycle and growth. Evidence also builds up that shift in AK isoforms is used later by cancer cells for rewiring energy metabolism to support their high proliferation activity and tumor progression. As cell motility is an energy-consuming process, positioning of AK isoforms to increased energy consumption sites could be an essential factor to incline cancer cells to metastases. In this review, we summarize recent advances in studies of the significance of AK isoforms involved in cancer cell metabolism, metabolic signaling, metastatic potential, and a therapeutic target.

Glycolytic Stimulation Is Not a Requirement for M2 Macrophage Differentiation.

Enhanced glucose uptake and a switch to glycolysis are key traits of M1 macrophages, whereas enhanced fatty acid oxidation and oxidative phosphorylation are the main metabolic characteristics of M2 macrophages. Recent studies challenge this traditional view, indicating that glycolysis may also be critically important for M2 macrophage differentiation, based on experiments with 2-DG. Here we confirm the inhibitory effect of 2-DG on glycolysis, but also demonstrate that 2-DG impairs oxidative phosphorylation and significantly reduces 13C-labeled Krebs cycle metabolites and intracellular ATP levels. These metabolic derangements were associated with reduced JAK-STAT6 pathway activity and M2 differentiation marker expression. While glucose deprivation and glucose substitution with galactose effectively suppressed glycolytic activity, there was no effective suppression of oxidative phosphorylation, intracellular ATP levels, STAT6 phosphorylation, and M2 differentiation marker expression. These data indicate that glycolytic stimulation is not required for M2 macrophage differentiation as long as oxidative phosphorylation remains active.

Interferon Gamma Induces Reversible Metabolic Reprogramming of M1 Macrophages to Sustain Cell Viability and Pro-Inflammatory Activity.

Classical activation of M1 macrophages with lipopolysaccharide (LPS) is associated with a metabolic switch from oxidative phosphorylation to glycolysis. However, the generalizability of such metabolic remodeling to other modes of M1 macrophage stimulation, e.g. type II interferons (IFNs) such as IFNγ, has remained unknown as has the functional significance of aerobic glycolysis during macrophage activation. Here we demonstrate that IFNγ induces a rapid activation of aerobic glycolysis followed by a reduction in oxidative phosphorylation in M1 macrophages. Elevated glycolytic flux sustains cell viability and inflammatory activity, while limiting reliance on mitochondrial oxidative metabolism. Adenosine triphosphate (ATP) distributed by aerobic glycolysis is critical for sustaining IFN-γ triggered JAK (Janus tyrosine kinase)-STAT-1 (Signal Transducer and Activator of Transcription 1) signaling with phosphorylation of the transcription factor STAT-1 as its signature trait. Inhibition of aerobic glycolysis not only blocks the M1 phenotype and pro-inflammatory cytokine/chemokine production in murine macrophages and also human monocytes/macrophages. These findings extend on the potential functional role of immuno-metabolism from LPS- to IFNγ-linked diseases such as atherosclerosis and autoimmune disease.

Genetic Depletion of Adipocyte Creatine Metabolism Inhibits Diet-Induced Thermogenesis and Drives Obesity.

Diet-induced thermogenesis is an important homeostatic mechanism that limits weight gain in response to caloric excess and contributes to the relative stability of body weight in most individuals. We previously demonstrated that creatine enhances energy expenditure through stimulation of mitochondrial ATP turnover, but the physiological role and importance of creatine energetics in adipose tissue have not been explored. Here, we have inactivated the first and rate-limiting enzyme of creatine biosynthesis, glycine amidinotransferase (GATM), selectively in fat (Adipo-Gatm KO). Adipo-Gatm KO mice are prone to diet-induced obesity due to the suppression of elevated energy expenditure that occurs in response to high-calorie feeding. This is paralleled by a blunted capacity for ß3-adrenergic activation of metabolic rate, which is rescued by dietary creatine supplementation. These results provide strong in vivo genetic support for a role of GATM and creatine metabolism in energy expenditure, diet-induced thermogenesis, and defense against diet-induced obesity.

The Modulating Effects of Cardiac Resynchronization Therapy on Myocardial Metabolism in Heart Failure.

Heart failure (HF) is associated with changes in cardiac substrate utilization and energy metabolism, including a decline in high-energy phosphate content, mitochondrial dysfunction, and phosphotransfer enzyme deficiency. A shift toward glucose metabolism was noted in the end stage of HF in animals, although HF in humans may not be associated with a shift toward predominant glucose utilization. Deficiencies of micronutrients are well-established causes of cardiomyopathy. Correction of these deficits can improve heart function. The genes governing the energy metabolism were predominantly underexpressed in nonischemic cardiomyopathy and hypertrophic cardiomyopathy but were overexpressed in ischemic cardiomyopathy. Cardiac resynchronization therapy (CRT) has been proven to increase cardiac efficiency without increasing myocardial oxygen consumption. Altered myocardial metabolism is normalized by CRT to improve ventricular function.

Decline of Phosphotransfer and Substrate Supply Metabolic Circuits Hinders ATP Cycling in Aging Myocardium.

Integration of mitochondria with cytosolic ATP-consuming/ATP-sensing and substrate supply processes is critical for muscle bioenergetics and electrical activity. Whether age-dependent muscle weakness and increased electrical instability depends on perturbations in cellular energetic circuits is unknown. To define energetic remodeling of aged atrial myocardium we tracked dynamics of ATP synthesis-utilization, substrate supply, and phosphotransfer circuits through adenylate kinase (AK), creatine kinase (CK), and glycolytic/glycogenolytic pathways using 18O stable isotope-based phosphometabolomic technology. Samples of intact atrial myocardium from adult and aged rats were subjected to 18O-labeling procedure at resting basal state, and analyzed using the 18O-assisted HPLC-GC/MS technique. Characteristics for aging atria were lower inorganic phosphate Pi[18O], γ-ATP[18O], ß-ADP[18O], and creatine phosphate CrP[18O] 18O-labeling rates indicating diminished ATP utilization-synthesis and AK and CK phosphotransfer fluxes. Shift in dynamics of glycolytic phosphotransfer was reflected in the diminished G6P[18O] turnover with relatively constant glycogenolytic flux or G1P[18O] 18O-labeling. Labeling of G3P[18O], an indicator of G3P-shuttle activity and substrate supply to mitochondria, was depressed in aged myocardium. Aged atrial myocardium displayed reduced incorporation of 18O into second (18O2), third (18O3), and fourth (18O4) positions of Pi[18O] and a lower Pi[18O]/γ-ATP[18 O]-labeling ratio, indicating delayed energetic communication and ATP cycling between mitochondria and cellular ATPases. Adrenergic stress alleviated diminished CK flux, AK catalyzed ß-ATP turnover and energetic communication in aging atria. Thus, 18O-assisted phosphometabolomics uncovered simultaneous phosphotransfer through AK, CK, and glycolytic pathways and G3P substrate shuttle deficits hindering energetic communication and ATP cycling, which may underlie energetic vulnerability of aging atrial myocardium.

Modulation of mitochondrial complex I activity averts cognitive decline in multiple animal models of familial Alzheimer's Disease.

Development of therapeutic strategies to prevent Alzheimer's Disease (AD) is of great importance. We show that mild inhibition of mitochondrial complex I with small molecule CP2 reduces levels of amyloid beta and phospho-Tau and averts cognitive decline in three animal models of familial AD. Low-mass molecular dynamics simulations and biochemical studies confirmed that CP2 competes with flavin mononucleotide for binding to the redox center of complex I leading to elevated AMP/ATP ratio and activation of AMP-activated protein kinase in neurons and mouse brain without inducing oxidative damage or inflammation. Furthermore, modulation of complex I activity augmented mitochondrial bioenergetics increasing coupling efficiency of respiratory chain and neuronal resistance to stress. Concomitant reduction of glycogen synthase kinase 3ß activity and restoration of axonal trafficking resulted in elevated levels of neurotrophic factors and synaptic proteins in adult AD mice. Our results suggest metabolic reprogramming induced by modulation of mitochondrial complex I activity represents promising therapeutic strategy for AD.

Cardiac resynchronization therapy induces adaptive metabolic transitions in the metabolomic profile of heart failure.

BACKGROUND: Heart failure (HF) is associated with ventricular dyssynchrony and energetic inefficiency, which can be alleviated by cardiac resynchronization therapy (CRT). The aim of this study was to determine the metabolomic signature in HF and its prognostic value regarding the response to CRT. METHODS AND RESULTS: This prospective study consisted of 24 patients undergoing CRT for advanced HF and 10 control patients who underwent catheter ablation for supraventricular arrhythmia but not CRT. Blood samples were collected before and 3 months after CRT. Metabolomic profiling of plasma samples was performed with the use of gas chromatography-mass spectrometry and nuclear magnetic resonance. The plasma metabolomic profile was altered in the HF patients, with a distinct panel of metabolites, including Krebs cycle and lipid, amino acid, and nucleotide metabolism. CRT improved the metabolomic profile. The succinate-glutamate ratio, an index of Krebs cycle activity, improved from 0.58 ± 0.13 to 2.84 ± 0.60 (P < .05). The glucose-palmitate ratio, an indicator of the balance between glycolytic and fatty acid metabolism, increased from 0.96 ± 0.05 to 1.54 ± 0.09 (P < .01). Compared with nonresponders to CRT, responders had a distinct baseline plasma metabolomic profile, including higher isoleucine, phenylalanine, leucine, glucose, and valine levels and lower glutamate levels at baseline (P < .05). CONCLUSIONS: CRT improves the plasma metabolomic profile of HF patients, indicating harmonization of myocardial energy substrate metabolism. CRT responders may have a favorable metabolomic profile as a potential biomarker for predicting CRT outcome.

Metabolic plasticity in stem cell homeostasis and differentiation.

Plasticity in energy metabolism allows stem cells to match the divergent demands of self-renewal and lineage specification. Beyond a role in energetic support, new evidence implicates nutrient-responsive metabolites as mediators of crosstalk between metabolic flux, cellular signaling, and epigenetic regulation of cell fate. Stem cell metabolism also offers a potential target for controlling tissue homeostasis and regeneration in aging and disease. In this Perspective, we cover recent progress establishing an emerging relationship between stem cell metabolism and cell fate control.