Mitochondrial Metabolic Efficiency Research Articles

Comparative mitogenomics of Clupeoid fish provides insights into the adaptive evolution of mitochondrial oxidative phosphorylation (OXPHOS) genes and codon usage in the heterogeneous habitats.

Clupeoid fish can be considered excellent candidates to understand the role of mitochondrial DNA in adaptive evolution, as they have colonized different habitats (marine, brackish, freshwater, tropical and temperate regions) over millions of years. Here, we investigate patterns of tRNA location, codon usage bias, and lineage-specific diversifying selection signals to provide novel insights into how evolutionary improvements of mitochondrial metabolic efficiency have allowed clupeids to adapt to different habitats. Based on whole mitogenome data of 70 Clupeoids with a global distribution we find that purifying selection was the dominant force acting and that the mutational deamination pressure in mtDNA was stronger than the codon/amino acid constraints. The codon usage pattern appears evolved to achieve high translational efficiency (codon/amino acid-related constraints), as indicated by the complementarity of most codons to the GT-saturated tRNA anticodon sites (retained by deamination-induced pressure) and usage of the codons of the tRNA genes situated near to the control region (fixed by deamination pressure) where transcription efficiency was high. The observed shift in codon preference patterns between marine and euryhaline/freshwater Clupeoids indicates possible selection for improved translational efficiency in mitochondrial genes while adapting to low-salinity habitats. This mitogenomic plasticity and enhanced efficiency of the metabolic machinery may have contributed to the evolutionary success and abundance of Clupeoid fish.

Metabolic regulation in mitochondria as a prospective way of body rejuvenation

Scientists around the world are looking for ways to achieve high-quality and active longevity. The complexity of these searches is associated with the lack of unified concept of aging mechanisms, the problem of extrapolating the results of studies of geroprotectors from model organisms to humans. Therefore, modern medicine can only slow down the aging process so far. Nevertheless, it has been proven that disturbances in the functioning of mitochondria are an important link in the pathogenesis of aging; therefore, regulation of their metabolism is a promising way of rejuvenating the body. A decrease in protein synthesis and a general decrease in the intensity of the oxidative enzymes action are interrelated. Energy production for the protein and DNA synthesis decreases with a decrease in the intensity of oxidative processes. Dysfunction of mitochondrial adaptive reactions also develops with age, which may be associated with the low efficiency of the NADH dehydrogenase complex – NADH ubiquinone oxidoreductase, which catalyzes the transfer of electrons from NADH to ubiquinone/coenzyme Q10, resulting in a decrease in electron transport and an increase of active oxygen forms. Coenzyme Q10 reducing plays a very important role in the aging process, as it is an antioxidant and, unlike other antioxidants, is produced in the body. An increase in mitochondrial biogenesis, as well as an increase in the rate and efficiency of mitochondrial metabolism (with a calorie restricted diet for example) helps to improve the energy supply of cells and prolong life.A drug based on xylitol Xylate can be a source of triglycerophosphate by metabolism through the pentose phosphate cycle and thereby reduce the amount of free fatty acids that can be oxidized into acetyl-CoA, increases the content of adenosine triphosphate acid and other adenine nucleotides in liver, and has a pronounced antiketogenic effect. It can reduce intoxication and improve microcirculation, which is especially important for high-quality and active longevity.Activation of mitochondrial metabolism is a promising direction in the aging prevention, since it allows balancing metabolic processes not only in cells, but also in body as a whole.

Inorganic nitrate and nitrite supplementation fails to improve skeletal muscle mitochondrial efficiency in mice and humans

BackgroundInorganic nitrate, abundant in leafy green vegetables and beetroot, is thought to have protective health benefits. Adherence to a Mediterranean diet reduces the incidence and severity of coronary artery disease, whereas supplementation with nitrate can improve submaximal exercise performance. Once ingested, oral commensal bacteria may reduce nitrate to nitrite, which may subsequently be reduced to nitric oxide during conditions of hypoxia and in the presence of “nitrite reductases” such as heme- and molybdenum-containing enzymes.ObjectiveWe aimed to explore the putative effects of inorganic nitrate and nitrite on mitochondrial function in skeletal muscle.MethodsMice were subjected to a nitrate/nitrite-depleted diet for 2 wk, then supplemented with sodium nitrate, sodium nitrite, or sodium chloride (1 g/L) in drinking water ad libitum for 7 d before killing. Skeletal muscle mitochondrial function and expression of uncoupling protein (UCP) 3, ADP/ATP carrier protein (AAC) 1 and AAC2, and pyruvate dehydrogenase (PDH) were assessed by respirometry and Western blotting. Studies were also undertaken in human skeletal muscle biopsies from a cohort of coronary artery bypass graft patients treated with either sodium nitrite (30-min infusion of 10 μmol/min) or vehicle [0.9% (wt:vol) saline] 24 h before surgery.ResultsNeither sodium nitrate nor sodium nitrite supplementation altered mitochondrial coupling efficiency in murine skeletal muscle, and expression of UCP3, AAC1, or AAC2, and PDH phosphorylation status did not differ between the nitrite and saline groups. Similar results were observed in human samples.ConclusionsSodium nitrite failed to improve mitochondrial metabolic efficiency, rendering this mechanism implausible for the purported exercise benefits of dietary nitrate supplementation. This trial was registered at clinicaltrials.gov as NCT04001283.

A model of mitochondrial O2 consumption and ATP generation in rat proximal tubule cells.

Oxygen tension in the kidney is mostly determined by O2 consumption (Qo2), which is, in turn, closely linked to tubular Na+ reabsorption. The objective of the present study was to develop a model of mitochondrial function in the proximal tubule (PT) cells of the rat renal cortex to gain more insight into the coupling between Qo2, ATP formation (GATP), ATP hydrolysis (QATP), and Na+ transport in the PT. The present model correctly predicts in vitro and in vivo measurements of Qo2, GATP, and ATP and Pi concentrations in PT cells. Our simulations suggest that O2 levels are not rate limiting in the proximal convoluted tubule, absent large metabolic perturbations. The model predicts that the rate of ATP hydrolysis and cytoplasmic pH each substantially regulate the GATP-to-Qo2 ratio, a key determinant of the number of Na+ moles actively reabsorbed per mole of O2 consumed. An isolated increase in QATP or in cytoplasmic pH raises the GATP-to-Qo2 ratio. Thus, variations in Na+ reabsorption and pH along the PT may, per se, generate axial heterogeneities in the efficiency of mitochondrial metabolism and Na+ transport. Our results also indicate that the GATP-to-Qo2 ratio is strongly impacted not only by H+ leak permeability, which reflects mitochondrial uncoupling, but also by K+ leak pathways. Simulations suggest that the negative impact of increased uncoupling in the diabetic kidney on mitochondrial metabolic efficiency is partly counterbalanced by increased rates of Na+ transport and ATP consumption. This model provides a framework to investigate the role of mitochondrial dysfunction in acute and chronic renal diseases.

The mitochondrial metabolic function of DJ-1 is modulated by 14-3-3β.

Mitochondrial metabolic plasticity is a key adaptive mechanism in response to changes in cellular metabolic demand. Changes in mitochondrial metabolic efficiency have been linked to pathophysiological conditions, including cancer, neurodegeneration, and obesity. The ubiquitously expressed DJ-1 (Parkinsonism-associated deglycase) is known as a Parkinson's disease gene and an oncogene. The pleiotropic functions of DJ-1 include reactive oxygen species scavenging, RNA binding, chaperone activity, endocytosis, and modulation of major signaling pathways involved in cell survival and metabolism. Nevertheless, how these functions are linked to the role of DJ-1 in mitochondrial plasticity is not fully understood. In this study, we describe an interaction between DJ-1 and 14-3-3β that regulates the localization of DJ-1, in a hypoxia-dependent manner, either to the cytosol or to mitochondria. This interaction acts as a modulator of mitochondrial metabolic efficiency and a switch between glycolysis and oxidative phosphorylation. Modulation of this novel molecular mechanism of mitochondrial metabolic efficiency is potentially involved in the neuroprotective function of DJ-1 as well as its role in proliferation of cancer cells.-Weinert, M., Millet, A., Jonas, E. A., Alavian, K. N. The mitochondrial metabolic function of DJ-1 is modulated by 14-3-3β.

DJ1 regulates Neuronal Mitochondrial Bioenergetic Efficiency

The progressive loss of midbrain dopaminergic neurons is the hallmark of Parkinson's disease (PD). Defects in mitochondrial electron transport and mitochondrial DNA replication predispose to the onset of PD. The protein products of several PD genes, including Parkin, Pink1 and DJ1 are known to localize to mitochondria; pathological mutations in these genes may disrupt mitochondrial function. In a previous study we found that the anti-apoptotic protein Bcl-xL enhances the efficiency of neuronal energy metabolism by increasing total cellular ATP levels while decreasing cellular oxygen use. Bcl-xL produces this effect in part through a direct interaction with the beta subunit of the F1Fo ATP synthase. The interaction causes a decrease in leak of H+ ions across the mitochondrial inner membrane, correlated with an increase in coupling of oxidative phosphorylation. We now show that the Parkinson's disease gene-encoded protein, DJ1 (PARK7), is also associated with the ATP synthase complex and has a similar regulatory effect on enzymatic activity of the synthase and on the coupling of oxidation to phosphorylation. Pathological mutations of DJ1 may disrupt mitochondrial efficiency leading to neurodegeneration of mesencephalic dopaminergic neurons. The exact site of the leak inhibited by Bcl-xL and DJ1 is now being determined, but likely resides in or adjacent to the c-subunit ring of the ATP synthase Fo. Improved mitochondrial metabolic efficiency that accompanies decreases in H+ leak may result in long lasting changes in synaptic efficacy and survival in both healthy and at-risk neurons, suggesting a role for leak regulation in future therapeutic interventions.

Bcl-xL Determines the Metabolic Efficiency of Neurons, through Interaction with Mitochondrial ATP Synthase

The anti-apoptotic BCL-2 family protein, Bcl-xL, is highly expressed in the brain. Beside its anti-apoptotic function, Bcl-xL may contribute to activity-dependent normal functioning of neurons. In this study, using a set of gain and loss of function experiments, we find that, in hippocampal neurons, Bcl-xL enhances the efficiency of neuronal energy metabolism by increasing total cellular ATP levels, while decreasing cellular oxygen use. This effect is due to the presence of Bcl-xL in the mitochondrial inner membrane, co-localized with the (F1F0) ATP synthase, shown by immunocytochemistry and immune-electron microscopy. The interaction causes a decrease in leak of H+ ions across the mitochondrial inner membrane. The decreased leak is correlated with an increase in coupling of oxidative phosphorylation. In contrast, inhibition of Bcl-xL by pharmacological or genetic means increases a leak conductance measured by patch clamping the membrane of submitochondrial particles enriched in ATP synthase complexes (SMVs). Leaky SMVs demonstrate attenuated ability to sequester H+ during ATP hydrolysis. Additionally, Bcl-xL protein directly increases ATPase activity of the purified synthase complexes, while inhibition of endogenous Bcl-xL decreases synthase activity. The exact site of the leak is being determined by cross-linking studies and by patch clamping individual protein components of the ATP synthase reconstituted into artificial lipid vesicles. Improved mitochondrial metabolic efficiency of neurons accompanying changes in leak level may result in long lasting changes in synaptic efficacy in both physiological and pathological conditions.

Glucose regulates enzymatic sources of mitochondrial NADPH in skeletal muscle cells; a novel role for glucose‐6‐phosphate dehydrogenase

Reduced nicotinamide adenine dinucleotide (NADPH) is a functionally important metabolite required to support numerous cellular processes. However, despite the identification of numerous NADPH-producing enzymes, the mechanisms underlying how the organellar pools of NADPH are maintained remain elusive. Here, we have identified glucose-6-phosphate dehydrogenase (G6PDH) as an important source of NADPH in mitochondria. Activity analysis, submitochondrial fractionation, fluorescence microscopy, and protease sensitivity assays revealed that G6PDH is localized to the mitochondrial matrix. 6-ANAM, a specific G6PDH inhibitor, depleted mitochondrial NADPH pools and increased oxidative stress revealing the importance of G6PDH in NADPH maintenance. We also show that glucose availability and differences in metabolic state modulate the enzymatic sources of NADPH in mitochondria. Indeed, cells cultured in high glucose (HG) not only adopted a glycolytic phenotype but also relied heavily on matrix-associated G6PDH as a source of NADPH. In contrast, cells exposed to low-glucose (LG) concentrations, which displayed increased oxygen consumption, mitochondrial metabolic efficiency, and decreased glycolysis, relied predominantly on isocitrate dehydrogenase (ICDH) as the principal NADPH-producing enzyme in the mitochondria. Culturing glycolytic cells in LG for 48 h decreased G6PDH and increased ICDH protein levels in the mitochondria, further pointing to the regulatory role of glucose. 2-Deoxyglucose treatment also prevented the increase of mitochondrial G6PDH in response to HG. The role of glucose in regulating enzymatic sources of mitochondrial NADPH pool maintenance was confirmed using human myotubes from obese adults with a history of type 2 diabetes mellitus (post-T2DM). Myotubes from post-T2DM participants failed to increase mitochondrial G6PDH in response to HG in contrast to mitochondria in myotubes from control participants (non-T2DM). Hence, we not only identified a matrix-associated G6PDH but also provide evidence that metabolic state/glucose availability modulate enzymatic sources of NADPH.

BCL-xL Regulates ATP Synthase and Synaptic Efficiency

Anti-apoptotic BCL-2 family proteins such as BCL-xL play a crucial role in protecting cells from death. High levels of expression of BCL-xL are also key to the maintenance of life of certain cancer cells. Healthy adult neurons also contain high levels of BCL-xL, suggesting that BCL-xL plays a role in daily neuronal function. We have found previously that over-expression of BCL-xL in cultured neurons causes an increase in the number and size of synapses and an increase in synaptic activity, providing evidence that BCL-xL causes long term changes in synaptic efficacy and structure. We now describe that in cultured hippocampal neurons, BCL-xL overexpression enhances the availability of total cellular ATP by increasing the ATP/ADP ratio. BCL-xL specifically enhances mitochondrial ATP production even while producing a marked decrease in cellular oxygen use. Although BCL-xL is usually thought to function in the mitochondrial outer membrane, our findings suggest that it creates an increase in the efficiency of cellular energy metabolism by direct protein-protein interaction with the ATP synthase beta subunit at the inner membrane. We find that recombinant BCL-xL protein increases native brain ATP synthase enzymatic activity and that pharmacological inhibitors of BCL-xL decrease the enzymatic activity of the synthase complex. In patch clamp recordings of the isolated synthasomes, ATP seals a membrane ion leak that could decrease synthase efficiency. In contrast, BCL-xL inhibitors increase the leak. The leak is different from the oligomycin-sensitive H+ ion pathway, and is not sensitive to the membrane permeant ANT inhibitor, bongkrekic acid, or to inhibitors of MitoKATP. Our findings suggest that BCL-xL improves the efficiency of mitochondrial metabolism by helping to seal a leak in the ATP synthase complex. This may allow for increased synthesis of synaptic components during long term increases in synaptic activity.

Bcl-xl Regulates ATP Synthase Activity at the Inner Mitochondrial Membrane

Anti-apoptotic BCL-2 family proteins such as BCL-xL play a crucial role in protecting cells from death. High levels of expression of BCL-xL are key to the maintenance of life of certain cancer cells, but whether BCL-xL protects cells from death simply by sequestering pro-apoptotic molecules, or by producing a growth phenotype is controversial. Although adult neurons resist oncogenic transformation, they contain high levels of BCL-xL and overexpression of BCL-xL in cultured neurons causes an increase in the number and size of synapses and an increase in synaptic activity, suggesting that BCL-xL enhances the availability of ATP for synaptic events while also in some way enhancing synaptic growth. We describe herein that in cultured hippocampal neurons, BCL-xL overexpression promotes biosynthetic metabolism, increases mitochondrial growth, and enhances the availability of total cellular ATP by increasing the ATP/ADP ratio. BCL-xL specifically enhances mitochondrial ATP production even while producing a marked decrease in cellular oxygen use. Although BCL-xL is usually thought to function in the mitochondrial outer membrane, our findings suggest that it creates a super-efficient state of cellular energy metabolism by direct protein-protein interaction with the ATP synthase at the inner membrane. We find that recombinant BCL-xL protein increases native brain ATP synthase enzymatic activity and that a pharmacological inhibitor of BCL-xL decreases the enzymatic activity of the synthase complex. In patch clamp recordings of the isolated synthasome ATP enhances membrane conductance and a BCL-xL inhibitor decreases the conductance. Our findings suggest that BCL-xL improves the efficiency of mitochondrial metabolism. This allows the neuron to continue to produce ATP needed for synaptic activity during biosynthesis of synaptic components. It remains to be determined if this type of BCL-xL-induced metabolic phenotype is recapitulated in cancer cells.

Effects of amiodarone on cardiac function and mitochondrial oxidative phosphorylation during ischemia and reperfusion.

This study was carried out in order to determine if the efficiency of amiodarone, a class III antiarrhythmic agent, is associated with changes in mitochondrial oxidative phosphorylation. A population of 30 rats were treated with amiodarone (100 mg/kg/day) for 5 days. A second population receiving only vehicle was used as control. The hearts were perfused according to the working mode. After 15 min of normoxic perfusion, the left main coronary artery was ligated and the ligation was maintained for 20 min. The ligation was removed and reperfusion continued for a further 30 min. The electrocardiogram was monitored continuously. At the end of perfusion, the ischemic and non ischemic areas were visually separated and mitochondria were harvested from each area. Their oxidative and energy metabolism were assessed with palmitoylcarnitine as substrate in 2 respiration media differing in their free calcium concentration (0 or 0.34 microm). In normoxic conditions, amiodarone treatment increased the cardiac metabolic efficiency (mechanical work to oxygen consumption ratio). The local ischemia decreased the aortic and coronary flows without modifying the cardiac metabolic efficiency. Amiodarone treatment maintained the aortic flow at a significantly higher value; the duration of severe arrhythmias was significantly decreased by the drug. The reperfusion of the ischemic area allowed the partial recovery of fluid dynamics. The coronary flow was restored to 89% of the pre ischemic value. Conversely, the aortic flow never exceeded that measured at the end of ischemia, partly due to the important development of severe arrhythmias. The recovery of aortic flow and metabolic efficiency during reperfusion was improved by amiodarone treatment; ventricular tachycardia and fibrillation duration were reduced. In the mitochondria issued from the normoxic area, the energy metabolism was not altered by the amiodarone treatment, but the presence of calcium in the respiration medium modified the oxidative phosphorylation. The divalent cation slightly decreased the state III respiration rate and increased noticeably the state IV respiration rate. This was associated with an important mitochondrial AMP production and maintenance of ADP in the respiration medium. This energy wasting was reported to decrease the mitochondrial metabolic efficiency. After an ischemia-reperfusion sequence, mitochondrial oxidation phosphorylation was reduced and amiodarone treatment amplified this decrease. This was presumably due to an increased mitochondrial calcium accumulation. Thus, the beneficial properties of amiodarone during reperfusion are supposed to be due to a protection against the deleterious effect of excess matrix calcium on mitochondrial energy metabolism.

Mitochondrial aspects of cold acclimation in Pieris brassicae (Lepidoptera) during diapause and post-diapause imaginal development

1.1.|Exposure to cold during diapause led to an improvement in the efficiency of mitochondrial metabolism. After 2 months of diapause, several differences at the mitochondrial level were observed between pupae kept at 5 or 20°C.2.2.|After 60 days of diapause at 5°C, mitochondrial respiratory activity was higher than in pupae left at 20°C, cytochrome c oxidase activity was 2.5 times greater and there was a higher quantity of mitochondrial proteins.3.3.|During imaginal development, pupae which were placed at low temperatures when diapausing show a greater and more rapid increase in the quantity and activity of the mitochondria.