Mitochondrial respiratory chain adjustment to cellular energy demand

Oocyte and cumulus cell cooperativity and metabolic plasticity under the direction of oocyte paracrine factors

Mammalian oocytes develop and mature in a mutually dependent relationship with surrounding cumulus cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble paracrine oocyte-secreted factors (OSFs). We characterized the molecular mechanisms by which two model OSFs, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Exposure to these OSFs during mouse oocyte maturation in vitro altered the proteomic and multispectral autofluorescence profiles of both the oocyte and cumulus cells. In oocytes, cumulin significantly upregulated proteins involved in nuclear function. In cumulus cells, both OSFs elicited marked upregulation of a variety of metabolic processes (mostly anabolic), including lipid, nucleotide, and carbohydrate metabolism, whereas mitochondrial metabolic processes were downregulated. The mitochondrial changes were validated by functional assays confirming altered mitochondrial morphology, respiration, and content while maintaining ATP homeostasis. Collectively, these data demonstrate that cumulin and BMP15 remodel cumulus cell metabolism, instructing them to upregulate their anabolic metabolic processes, while routine cellular functions are minimized in the oocyte during maturation, in preparation for ensuing embryonic development.NEW & NOTEWORTHY Oocyte-secreted factors (OSFs) promote oocyte and cumulus cell cooperativity by altering the molecular composition of both cell types. OSFs downregulate protein catabolic processes and upregulate processes associated with DNA binding, translation, and ribosome assembly in oocytes. In cumulus cells, OSFs alter mitochondrial number, morphology, and function, and enhance metabolic plasticity by upregulating anabolic pathways. Hence, the oocyte via OSFs, instructs cumulus cells to increase metabolic processes on its behalf, thereby subduing oocyte metabolism.

Isolation of Calenduloside E from Achyranthes bidentata Blume and its effects on LPS/D-GalN-induced acute liver injury in mice by regulating the AMPK-SIRT3 signaling pathway

BACKGROUND

Acute liver injury (ALI) is a frequent fatal liver disease with a high mortality. Calenduloside E (CE) is a pentacyclic triterpenoid derived from Achyranthes bidentata Blume. It has been found that liver injury is associated with mitochondrial dysfunction, and activation of the AMPK-SIRT3 signaling pathway protects the mitochondrial function to play a role in resistance to the disease. However, whether CE is protective against ALI through the AMPK-SIRT3 signaling pathway is unclear.

PURPOSE

To clarify the influences of Calenduloside E (CE) isolated from Achyranthes bidentata Blume on LPS/D-GalN-induced Acute liver injury (ALI).

METHODS

A mouse model of ALI was developed, intraperitoneal injection of 10 μg/kg LPS and 700 mg/kg D-GalN, histopathological, oxidative stress, and immune inflammation of the mice were monitored. The mechanism of CE influencing liver injury was investigated by examining the gut microbiota, mitochondrial dysfunction, and the AMPK-SIRT3 signaling pathway. The antagonistic effects of specific AMPK and SIRT3 blocker, as well as AMPKα1, AMPKα2, SIRT3 transfection-mediated silencing were investigated to confirm the role of the AMPK-SIRT3 signaling pathway in this process.

RESULTS

CE relieved liver pathological damage of mice and led to reduced oxidative stress and immune inflammation in mice, affected the balance of gut microbiota in mice with liver injury, as well as energy metabolism, and regulated mRNA and protein expressions of AMPK-SIRT3 signaling pathway. In addition, in vitro studies showed that CE relieved mitochondrial respiratory and protein expressions of AMPK-SIRT3 signaling pathway in LPS/D-GalN-induced AML12 and LX2 cells, and such effect was blocked by AMPK and SIRT3 inhibitors. Furthermore, silencing of AMPKα1, AMPKα2, and SIRT3 blocked the effects of CE. Overall, the influences of CE on mice with liver injury is tuned by the AMPK-SIRT3 signaling pathway.

CONCLUSION

CE mediates mitochondrial function and eventually regulate energy metabolism by regulating the AMPK-SIRT3 signaling pathway. The results of this study provide molecular evidences for application of CE in treatment of ALI and provide references to the drug development for ALI.

Metabolic design in a mammalian model of extreme metabolism, the North American least shrew (Cryptotis parva)

Mitochondrial adaptations are fundamental to differentiated function and energetic homeostasis in mammalian cells. But the mechanisms that underlie these relationships remain poorly understood. Here, we investigated organ-specific mitochondrial morphology, connectivity and protein composition in a model of extreme mammalian metabolism, the least shrew (Cryptotis parva). This was achieved through a combination of high-resolution 3D focused ion beam electron microscopy imaging and tandem mass tag mass spectrometry proteomics. We demonstrate that liver and kidney mitochondrial content are equivalent to the heart, permitting assessment of mitochondrial adaptations in different organs with similar metabolic demand. Muscle mitochondrial networks (cardiac and skeletal) are extensive, with a high incidence of nanotunnels - which collectively support the metabolism of large muscle cells. Mitochondrial networks were not detected in the liver and kidney as individual mitochondria are localized with sites of ATP consumption. This configuration is not observed in striated muscle, likely due to a homogeneous ATPase distribution and the structural requirements of contraction. These results demonstrate distinct, fundamental mitochondrial structural adaptations for similar metabolic demand that are dependent on the topology of energy utilization process in a mammalian model of extreme metabolism. KEY POINTS: Least shrews were studied to explore the relationship between metabolic function, mitochondrial morphology and protein content in different tissues. Liver and kidney mitochondrial content and enzymatic activity approaches that of the heart, indicating similar metabolic demand among tissues that contribute to basal and maximum metabolism. This allows an examination of mitochondrial structure and composition in tissues with similar maximum metabolic demands. Mitochondrial networks only occur in striated muscle. In contrast, the liver and kidney maintain individual mitochondria with limited reticulation. Muscle mitochondrial reticulation is the result of dense ATPase activity and cell-spanning myofibrils which require networking for adequate metabolic support. In contrast, liver and kidney ATPase activity is localized to the endoplasmic reticulum and basolateral membrane, respectively, generating a locally balanced energy conversion and utilization. Mitochondrial morphology is not driven by maximum metabolic demand, but by the cytosolic distribution of energy-utilizing systems set by the functions of the tissue.

Mitochondrial Costs of Being Hot: Effects of Acute Thermal Change on Liver Bioenergetics in Toads (Bufo bufo)

Global climatic warming is predicted to drive extreme thermal events, especially in temperate terrestrial environments. Hence, describing how physiological parameters are affected by acute temperature changes would allow us to understand the energy management of organisms facing such non-predictable and constraining events. As mitochondria play a key role in the conversion of energy from food into ATP but also produce harmful reactive oxygen species, the understanding of its functioning is crucial to determine the proximal causes of potential decline in an animal's performance. Here we studied the effects of acute temperature changes (between 20 and 30°C) on mitochondrial respiration, ATP synthesis rate, oxidative phosphorylation efficiency (ATP/O), and H2O2 generation in isolated liver mitochondria of a terrestrial ectotherm, the common toad (Bufo bufo). Using succinate as the respiratory substrate, we found that the mitochondrial rates of oxygen consumption, ATP synthesis, and H2O2 generation increased as the temperature increased, being 65, 52, and 66% higher at 30°C than at 20°C, respectively. We also found that the mitochondrial coupling efficiency (ATP/O) decreased, while the oxidative cost of ATP production (H2O2/ATP ratio) increased. The present results further indicate that between 40 and 60% of temperature effects on mitochondrial ATP production and H2O2 generation was at minima driven by an action on the oxidative capacity of the mitochondria. These results suggest that B. bufo may need to allocate extra energy to maintain ATP production and protect cells from oxidative stress, reducing the energy allocable performances.

Mitochondrial dysfunction is associated with long-term cognitive impairment in an animal sepsis model

Background: Several different mechanisms have been proposed to explain long-term cognitive impairment in sepsis survivors. The role of persisting mitochondrial dysfunction is not known. We thus sought to determine whether stimulation of mitochondrial dynamics improves mitochondrial function and long-term cognitive impairment in an experimental model of sepsis.

Methods: Sepsis was induced in adult Wistar rats by cecal ligation and perforation (CLP). Animals received intracerebroventricular injections of either rosiglitazone (biogenesis activator), rilmenidine, rapamycin (autophagy activators), or n-saline (sham control) once a day on days 7–9 after the septic insult. Cognitive impairment was assessed by inhibitory avoidance and object recognition tests. Animals were killed 24 h, 3 and 10 days after sepsis with the hippocampus and prefrontal cortex removed to determine mitochondrial function.

Results: Sepsis was associated with both acute (24 h) and late (10 days) brain mitochondrial dysfunction. Markers of mitochondrial biogenesis, autophagy and mitophagy were not up-regulated during these time points. Activation of biogenesis (rosiglitazone) or autophagy (rapamycin and rilmenidine) improved brain ATP levels and ex vivo oxygen consumption and the long-term cognitive impairment observed in sepsis survivors.

Conclusion: Long-term impairment of brain function is temporally related to mitochondrial dysfunction. Activators of autophagy and mitochondrial biogenesis could rescue animals from cognitive impairment.

Advances in understanding mechanisms of long-term sperm storage-the soft-shelled turtle model

Long-term sperm storage is a special reproductive strategy, which can extend the time window between mating and fertilization in some animal species. Spermatozoa of the soft-shelled turtle, Pelodiscus sinensis, can be stored in the epididymis and oviduct for at least six months and one year, respectively. How spermatozoa can be stored in vivo for such a prolonged period is yet to be explained. We analyze the mechanisms that contribute to long-term sperm storage in P. sinensis, and compare them with other species from three different perspectives: the spermatozoon itself, the storage microenvironment and the interaction between the spermatozoon and microenvironment. Characteristics of soft-shelled turtle spermatozoa itself, such as the huge cytoplasmic droplet with its content of several large lipid droplets (LDs) and onion-like mitochondira, facilitate long-term sperm storage. The microenvironment of reproductive tract, involving in the secretions, structural barriers, exosomes, androgen receptors, Toll-like receptors and survival factor Bcl-2, are important for the maintenance of spermatozoa long-term storage. Sperm heads are always embedded among the oviductal cilia and even intercalate into the apical hollowness of the ciliated cells, indicating that the ciliated cells support the stored spermatozoa. RNA seq is firstly used to detect the molecular mechanism of sperm storage, which shows that autophagy, apoptosis and immune take part in the long-term sperm storage in this species.

Life-time exposure to waterborne copper III: Effects on the energy metabolism of the killifish Poecilia vivipara

Copper ions (Cu) are essential to life maintenance, nonetheless, elevated concentrations can be hazardous. Acute and sub-chronic toxic effects of this metal are well known and are usually related to enzymatic inhibition, elevated ROS production and dysfunction of energy metabolism. Despite that, chronic studies are extremely rare. Therefore, the aim of this study was to assess the effects of chronic exposure to 5, 9 and 20 μg/L Cu (28 ad 345 days) on the energy metabolism and survival of the killifish Poecilia vivipara. To accomplish that, we evaluated the activity of enzymes related to aerobic (pyruvate kinase (PK); citrate synthase (CS)) and anaerobic metabolism (lactate dehydrogenase (LDH)) in whole-body (28 days) or in gills, liver and muscle (345 days) of exposed fish. Additionally, whole-body oxygen consumption was evaluated in fish exposed for 28 days and hepatic and muscular expression of genes involved in mitochondrial metabolism (cox I, II and III and atp5a1) was assessed in animals exposed for 345 days. Finally, final survival was evaluated. Following 28 days, Cu did not affect survival neither enzyme activities. However, increased whole-body oxygen consumption was observed in comparison to control condition. After 345 days, 76.8%, 63.9%, 60.9% and 0% survival were observed for control, 5, 9 and 20 μg/L groups, respectively. Animals exposed to 5 and 9 μg/L had a significant reduction in branchial and muscular LDH activity and in hepatic PK activity. Also, exposure to 9 μg/L significantly increased hepatic CS activity. For gene expression, Cu down-regulated muscular cox II (9 μg/L) and III (5 and 9 μg/L), and up-regulated hepatic atp5a1 (9 μg/L). Findings reported in the present study indicate that chronic exposure to Cu induces tissue-specific responses in key aspects of the energetic metabolism. In gills and muscle, Cu leads to reduced energy production through inhibition of anaerobic pathways and mitochondrial respiratory chain. This effect is paralleled by an increased ATP consumption in the liver, characterized by the augmented CS activity and atp5a1 expression. Finally, reduced PK activity indicate that oxidative stress may be involved with the observed outcomes.

Divergent gene expression in the gills of juvenile turbot (Psetta maxima) exposed to chronic severe hypercapnia indicates dose-dependent increase in intracellular oxidative stress and hypoxia

Elevated concentrations of carbon dioxide are a common stressor for fish and other aquatic animals. In particular, intensive aquaculture can impose prolonged periods of severe environmental hypercapnia, manifold exceeding CO₂ concentrations of natural habitats. In order to cope with this stressor, gills are essential and constitute the primary organ in the acclimatization process. Yet, despite a general understanding of changes in ion regulation, not much is known with regard to other cellular mechanisms. In this study, we apply RT-qPCR to investigate changes in the expression of several genes associated with metabolism, stress and immunity within gills of juvenile turbot (Psetta maxima) after an eight-week exposure to different concentrations of CO₂ (low = ∼3000 μatm, medium = ∼15,000 μatm and high = ∼25,000 μatm CO₂). Histological examination of the gill tissue only found a significant increase of hypertrophied secondary lamella in the highest tested treatment level. gene expression results, on the other hand, implied both, mutual and dose-dependent transcriptional adjustments. Comparable up-regulation of IL-1ß, LMP7 and Grim19 at medium and high hypercapnia indicated an increase of reactive oxygen species (ROS) within gill cells. Simultaneous increase in Akirin and PRDX transcripts at medium CO₂ indicated enhanced anti-oxidant activity and regulation of transcription, while reduced mRNA concentrations of COX, EF1α and STAT2 at high CO₂ denoted suppressed protein synthesis and reduced metabolic capacity. In addition to upregulated DFAD and ApoE expression, implying compensating repair measures, gills exposed to the highest tested treatment level seemed to operate close to or even beyond their maximum capacity. Thus, fitting the model of capacity limitation, our results provide evidence for accretive intracellular hypoxia and oxidative stress in the gills of turbot, dependent on the level of environmental hypercapnia. Further, genes, such as COX, may be valuable biomarkers when attempting to discriminate between a successful and an overpowered stress response.

Threshold effect in the H2O2 production of skeletal muscle mitochondria during fasting and refeeding

Under nutritional deprivation, the energetic benefits of reducing mitochondrial metabolism are often associated with enhanced harmful pro-oxidant effects and a subsequent long-term negative impact on cellular integrity. However, the flexibility of mitochondrial functioning under stress has rarely been explored during the transition from basal non-phosphorylating to maximal phosphorylating oxygen consumption. Here, we experimentally tested whether ducklings (Cairina moschata) fasted for 6 days and thereafter refed for 3 days, exhibited modifications to their mitochondrial fluxes, i.e. oxygen consumption, ATP synthesis, reactive oxygen species generation (ROS) and associated ratios, such as the electron leak (% ROS/O) and the oxidative cost of ATP production (% ROS/ATP). This was done at different steady state rate of oxidative phosphorylation in both pectoralis (glycolytic) and gastrocnemius (oxidative) muscles. Fasting induced a decrease in the rates of oxidative phosphorylation and maximal ROS release. All these changes were completely reversed by 3 days of refeeding. Yet, the fundamental finding of the present study is the existence of a clear threshold in ROS release and associated ratios, which remained low until a low level of mitochondrial activity is reached (30-40% of maximal oxidative phosphorylation activity).

Expression of mitofusin 2 in human sperm and its relationship to sperm motility and cryoprotective potentials

Mitofusin 2 is a kind of mitochondria membrane protein that has been implicated in maintenance of mitochondrial morphology and function. However, the expression and function of mitofusin 2 in human sperm are not well described at present. The aim of this study was to explore the location of mitofusin 2 in human sperm and to discover its relationship to human sperm functions like motility and cryoprotective potentials. Our result showed that mitofusin 2 is specifically localized in the 5-7 μm midpiece between the neck and main part of human sperm tail. The expression level of mitofusin 2 in human sperm was significantly different between the normozoospermia and asthenozoospermia groups ( P < 0.05); meanwhile, the sperm of the asthenozoospermia group had a lower mitochondrial membrane potential ( P < 0.05), but the results of TUNEL assay did not show significant difference between the two groups. Furthermore, we found that the expression level of mitofusin 2 in the freeze-resistant group (cryo-survival rate >40%) was significantly higher than that of the freeze-intolerant group (cryo-survival rate ≤40%) ( P < 0.05). These results demonstrate that the expression level of mitofusin 2 is related to motility and cryoprotective potentials of human sperm. Mitofusin 2 may play a crucial role in the function of human sperm, which needs further research to discover the mechanism. Impact statement The exact function of mitochondria in human sperm before and during fertilization process remains controversial. MFN2 is a kind of mitochondria membrane protein and participates in the regulation of mitochondrial morphology and function. In this study, we discover the relationship of MFN2 expression to human sperm motility and cryoprotective potentials. Our results suggest that MFN2 could be a new target for the mechanism research of asthenozoospermia. MFN2 may also serve as a protein marker predicting the ability of human sperm to sustain cryopreservation.

Modification of sperm morphology during long-term sperm storage in the reproductive tract of the Chinese soft-shelled turtle, Pelodiscus sinensis

Sperm storage in vivo extends the time window for fertilisation in several animal species, from a few days to several years. The underlying storage mechanisms, however, are largely unknown. In this study, spermatozoa from the epididymis and oviduct of Chinese soft-shelled turtles were investigated to identify potentially relevant morphological features and transformations at different stages of sperm storage. Large cytoplasmic droplets (CDs) containing lipid droplets (LDs) were attached to the midpiece of most spermatozoa in the epididymis, without migrating down the sperm tail. However, they were absent from the oviductal spermatozoa, suggesting that CDs with LDs may be a source of endogenous energy for epididymal spermatozoa. The onion-like mitochondria recovered their double-membrane morphology, with typical cristae, within the oviduct at a later stage of storage, thus implying that mitochondrial metabolism undergoes alterations during storage. Furthermore, a well developed fibrous sheath on the long principal piece was the integrating ultrastructure for glycolytic enzymes and substrates. These novel morphological characteristics may allow turtle spermatozoa to use diverse energy metabolism pathways at different stages of storage.

David and goliath: a mitochondrial coupling problem?

An organism's size, known to affect biological structures and processes from cellular metabolism to population dynamics, depends upon the duration and rate of growth. However, it is still poorly understood how mitochondrial function affects the energetic basis of growth, especially in ectotherms, which represent a huge majority of animal biodiversity. Here, we present an intraspecies comparison of neighboring populations of frogs (Rana temporaria) that have large differences in body mass even at the same age. By investigating liver mitochondrial bioenergetics, we find that frogs with high growth rates and large body sizes exhibit higher ATP synthesis rates and more efficient oxidative phosphorylation compared to the smaller frogs with low growth rates. This higher energy transduction efficiency is not associated with significant increased oxidative capacity or membrane potential values, but instead may rely on a higher mitochondrial phosphorylation system activity in combination with a lower inner membrane proton leakage. Overall, the present study introduces the mitochondrial energy transduction system as an important mechanism for balancing physiological and ecological trade-offs associated with body size. Whether phenotype differences in mitochondrial function result from local ecological constraints or reflect a natural genetic variability within wild populations of common frogs remains an open question. However, our findings highlight the need for closer consideration of all aspects of mitochondrial metabolism for a better understanding of the physiological basis of the link between size, metabolism, and energy production in wild-dwelling organisms.

Altered mitochondria morphology and cell metabolism in Apaf1-deficient cells

Background

Apaf1 (apoptotic protease activating factor 1) is the central component of the apoptosome, a multiprotein complex that activates procaspase-9 after cytochrome c release from the mitochondria in the intrinsic pathway of apoptosis. Other cellular roles, including a pro-survival role, have also been described for Apaf1, while the relative contribution of each function to cell death, but also to cell homeostatic conditions, remain to be clarified.

Methodology and Principal Findings

Here we examined the response to apoptosis induction of available embryonic fibroblasts from Apaf1 knockout mice (MEFS KO Apaf1). In the absence of Apaf1, cells showed mitochondria with an altered morphology that affects cytochrome c release and basal metabolic status.

Conclusions

We analysed mitochondrial features and cell death response to etoposide and ABT-737 in two different Apaf1-deficient MEFS, which differ in the immortalisation protocol. Unexpectedly, MEFS KO Apaf1 immortalised with the SV40 antigen (SV40IM-MEFS Apaf1) and those which spontaneously immortalised (SIM-MEFS Apaf1) respond differently to apoptotic stimuli, but both presented relevant differences at the mitochondria when compared to MEFS WT, indicating a role for Apaf1 at the mitochondria.

Cancer cachexia is associated with a decrease in skeletal muscle mitochondrial oxidative capacities without alteration of ATP production efficiency

BACKGROUND

Cancer cachexia is a complex syndrome related to a negative energy balance resulting in muscle wasting. Implication of muscle mitochondrial bioenergetics alterations during cancer cachexia was suggested. Therefore, the aim of this study was to explore the efficiency of oxidative phosphorylation in skeletal muscle mitochondria in a preclinical model of cancer cachexia.

METHODS

Berlin-Druckrey IX rats with peritoneal carcinosis (PC) were used as a model of cancer cachexia with healthy pair-fed rats (PF) as control. Hindlimb muscle morphology and fibre type composition were analysed in parallel with ubiquitin ligases and UCP gene expression. Oxidative phosphorylation was investigated in isolated muscle mitochondria by measuring oxygen consumption and ATP synthesis rate.

RESULTS

PC rats underwent significant muscle wasting affecting fast glycolytic muscles due to a reduction in fibre cross-sectional area. MuRF1 and MAFbx gene expression were significantly increased (9- and 3.5-fold, respectively) in the muscle of PC compared to PF rats. Oxygen consumption in non-phosphorylating state and the ATP/O were similar in both groups. Muscle UCP2 gene was overexpressed in PC rats. State III and the uncoupled state were significantly lower in muscle mitochondria from PC rats with a parallel reduction in complex IV activity (-30 %).

CONCLUSION

This study demonstrated that there was neither alteration in ATP synthesis efficiency nor mitochondrial uncoupling in skeletal muscle of cachectic rats despite UCP2 gene overexpression. Muscle mitochondrial oxidative capacities were reduced due to a decrease in complex IV activity. This mitochondrial bioenergetics alteration could participate to insulin resistance, lipid droplet accumulation and lactate production.

Dietary polyphenols preconditioning protects 3T3-L1 preadipocytes from mitochondrial alterations induced by oxidative stress

Numerous studies indicate that an increase in reactive oxygen species (ROS) significantly affects white adipose tissue biology and leads to an inflammatory profile and insulin resistance, which could contribute to obesity-associated diabetes and cardiovascular diseases. Mitochondria play a key role in adipose tissue energy metabolism and constitute the main source of cellular ROS such as H(2)O(2). Polyphenols constitute the most abundant antioxidants provided by the human diet. Indeed, they are widely distributed in fruits, vegetables and some plant-derived beverages such as coffee and tea. Thus, the biological effects of dietary polyphenols that may increase the antioxidant capacity of the body against obesity-induced oxidative stress are of high interest. Here, we studied the capacity of polyphenols to modulate the impact of oxidative stress on the mitochondria of preadipocytes, which are important cells governing the adipose tissue development for energy homeostasis. Whereas H(2)O(2) treatment induces a proliferation arrest associated with an increase in mitochondrial content in 3T3-L1 preadipocytes, preconditioning with some major dietary polyphenols totally or partially protects the cells against oxidative stress consequences. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Defective mitochondrial fusion, altered respiratory function, and distorted cristae structure in skin fibroblasts with heterozygous OPA1 mutations

Deleterious consequences of heterozygous OPA1 mutations responsible for autosomal dominant optic atrophy remain a matter of debate. Primary skin fibroblasts derived from patients have shown diverse mitochondrial alterations that were however difficult to resolve in a unifying scheme. To address the potential use of these cells as disease model, we undertook parallel and quantitative analyses of the diverse reported alterations in four fibroblast lines harboring different OPA1 mutations, nonsense or missense, in the guanosine triphosphatase or the C-terminal coiled-coil domains. We tackled several factors potentially underlying discordant reports and showed that fibroblasts with heterozygous OPA1 mutations present with several mitochondrial alterations. These included defective mitochondrial fusion during pharmacological challenge with the protonophore carbonyl cyanide m-chlorophenyl hydrazone, significant mitochondrial elongation with decreased OPA1 and DRP1 proteins, and abnormal mitochondrial fragmentation during glycolysis shortage or exogenous oxidative stress. Respiratory complex IV activity and subunits steady-state were decreased without alteration of the mitochondrial deoxyribonucleic acid size, amount or transcription. Physical link between OPA1 protein and oxidative phosphorylation was shown by reciprocal immunoprecipitation. Altered cristae structure coexisted with normal response to pro-apoptotic stimuli and expression of Bax or Bcl2 proteins. Skin fibroblasts with heterozygous OPA1 mutations thus share significant mitochondrial remodeling, and may therefore be useful for analyzing disease pathophysiology. Identifying whether the observed alterations are also present in ganglion retinal cells, and which of them underlies their degeneration process remains however an essential goal for therapeutic strategy.

Hepatic mitochondrial alterations and increased oxidative stress in nutritional diabetes-prone Psammomys obesus model

Mitochondrial dysfunction is considered to be a pivotal component of insulin resistance and associated metabolic diseases. Psammomys obesus is a relevant model of nutritional diabetes since these adult animals exhibit a state of insulin resistance when fed a standard laboratory chow, hypercaloric for them as compared to their natural food. In this context, alterations in bioenergetics were studied. Using liver mitochondria isolated from these rats fed such a diet for 18 weeks, oxygen consumption rates, activities of respiratory complexes, and content in cytochromes were examined. Levels of malondialdehyde (MDA) and gluthatione (GSH) were measured in tissue homogenates. Diabetic Psammomys showed a serious liver deterioration (hepatic mass accretion, lipids accumulation), accompanied by an enhanced oxidative stress (MDA increased, GSH depleted). On the other hand, both ADP-dependent and uncoupled respirations greatly diminished below control values, and the respiratory flux to cytochrome oxydase was mildly lowered. Furthermore, an inhibition of complexes I and III together with an activation of complex II were found. With emergence of oxidative stress, possibly related to a defect in oxidative phosphorylation, some molecular adjustments could contribute to alleviate, at least in part, the deleterious outcomes of insulin resistance in this gerbil species.

OXPHOS supercomplexes as a hallmark of the mitochondrial phenotype of adipogenic differentiated human MSCs

Mitochondria are essential organelles with multiple functions, especially in energy metabolism. Recently, an increasing number of data has highlighted the role of mitochondria for cellular differentiation processes. Metabolic differences between stem cells and mature derivatives require an adaptation of mitochondrial function during differentiation. In this study we investigated alterations of the mitochondrial phenotype of human mesenchymal stem cells undergoing adipogenic differentiation. Maturation of adipocytes is accompanied by mitochondrial biogenesis and an increase of oxidative metabolism. Adaptation of the mt phenotype during differentiation is reflected by changes in the distribution of the mitochondrial network as well as marked alterations of gene expression and organization of the oxidative phosphorylation system (OXPHOS). Distinct differences in the supramolecular organization forms of cytochrome c oxidase (COX) were detected using 2D blue native (BN)-PAGE analysis. Most remarkably we observed a significant increase in the abundance of OXPHOS supercomplexes in mitochondria, emphasizing the change of the mitochondrial phenotype during adipogenic differentiation.

PKCε promotes cardiac mitochondrial and metabolic adaptation to chronic hypobaric hypoxia by GSK3β inhibition

PKCε is central to cardioprotection. Sub-proteome analysis demonstrated co-localization of activated cardiac PKCε (aPKCε) with metabolic, mitochondrial, and cardioprotective modulators like hypoxia-inducible factor 1α (HIF-1α). aPKCε relocates to the mitochondrion, inactivating glycogen synthase kinase 3β (GSK3β) to modulate glycogen metabolism, hypertrophy and HIF-1α. However, there is no established mechanistic link between PKCε, p-GSK3β and HIF1-α. Here we hypothesized that cardiac-restricted aPKCε improves mitochondrial response to hypobaric hypoxia by altered substrate fuel selection via a GSK3β/HIF-1α-dependent mechanism. aPKCε and wild-type (WT) mice were exposed to 14 days of hypobaric hypoxia (45 kPa, 11% O(2)) and cardiac metabolism, functional parameters, p-GSK3β/HIF-1α expression, mitochondrial function and ultrastructure analyzed versus normoxic controls. Mitochondrial ADP-dependent respiration, ATP production and membrane potential were attenuated in hypoxic WT but maintained in hypoxic aPKCε mitochondria (P < 0.005, n = 8). Electron microscopy revealed a hypoxia-associated increase in mitochondrial number with ultrastructural disarray in WT versus aPKCε hearts. Concordantly, left ventricular work was diminished in hypoxic WT but not aPKCε mice (glucose only perfusions). However, addition of palmitate abrogated this (P < 0.05 vs. WT). aPKCε hearts displayed increased glucose utilization at baseline and with hypoxia. In parallel, p-GSK3β and HIF1-α peptide levels were increased in hypoxic aPKCε hearts versus WT. Our study demonstrates that modest, sustained PKCε activation blunts cardiac pathophysiologic responses usually observed in response to chronic hypoxia. Moreover, we propose that preferential glucose utilization by PKCε hearts is orchestrated by a p-GSK3β/HIF-1α-mediated mechanism, playing a crucial role to sustain contractile function in response to chronic hypobaric hypoxia.

Effects of a high-fat diet on energy metabolism and ROS production in rat liver

BACKGROUND & AIMS

A high-fat diet affects liver metabolism, leading to steatosis, a complex disorder related to insulin resistance and mitochondrial alterations. Steatosis is still poorly understood since diverse effects have been reported, depending on the different experimental models used.

METHODS

We hereby report the effects of an 8 week high-fat diet on liver energy metabolism in a rat model, investigated in both isolated mitochondria and hepatocytes.

RESULTS

Liver mass was unchanged but lipid content and composition were markedly affected. State-3 mitochondrial oxidative phosphorylation was inhibited, contrasting with unaffected cytochrome content. Oxidative phosphorylation stoichiometry was unaffected, as were ATPase and adenine nucleotide translocator proteins and mRNAs. Mitochondrial acylcarnitine-related H(2)O(2) production was substantially higher and the mitochondrial quinone pool was smaller and more reduced. Cellular consequences of these mitochondrial alterations were investigated in perifused, freshly isolated hepatocytes. Ketogenesis and fatty acid-dependent respiration were lower, indicating a lower β-oxidation rate contrasting with higher RNA contents of CD36, FABP, CPT-1, and AcylCoA dehydrogenases. Concomitantly, the cellular redox state was more reduced in the mitochondrial matrix but more oxidized in the cytosol: these opposing changes are in agreement with a significantly higher in situ mitochondrial proton motive force.

CONCLUSIONS

A high-fat diet results in both a decrease in mitochondrial quinone pool and a profound modification in mitochondrial lipid composition. These changes appear to play a key role in the resulting inhibition of fatty acid oxidation and of mitochondrial oxidative-phosphorylation associated with an increased mitochondrial ROS production. Mitochondrial quinone pool could have prospects as a crucial event, potentially leading to interesting therapeutic perspectives.

TNFα protects cardiac mitochondria independently of its cell surface receptors

Our novel proposal is that TNFα exerts a direct effect on mitochondrial respiratory function in the heart, independently of its cell surface receptors. TNFα-induced cardioprotection is known to involve reactive oxygen species (ROS) and sphingolipids. We therefore further propose that this direct mitochondrial effect is mediated via ROS and sphingolipids. The protective concentration of TNFα (0.5 ng/ml) was added to isolated heart mitochondria from black 6 × 129 mice (WT) and double TNF receptor knockout mice (TNFR1&2(-/-)). Respiratory parameters and inner mitochondrial membrane potential were analyzed in the presence/absence of two antioxidants, N-acetyl-L: -cysteine or N-tert-butyl-α-(2-sulfophenyl)nitrone or two antagonists of the sphingolipid pathway, N-oleoylethanolamine (NOE) or imipramine. In WT, TNFα reduced State 3 respiration from 279.3 ± 3 to 119.3 ± 2 (nmol O₂/mg protein/min), increased proton leak from 15.7 ± 0.6% (control) to 36.6 ± 4.4%, and decreased membrane potential by 20.5 ± 3.1% compared to control groups. In TNFR1&2(-/-) mice, TNFα reduced State 3 respiration from 205.2 ± 4 to 75.7 ± 1 (p < 0.05 vs. respective control). In WT mice, both antioxidants added with TNFα restored State 3 respiration to 269.2 ± 2 and 257.6 ± 2, respectively. Imipramine and NOE also restored State 3 respiration to 248.4 ± 2 and 249.0 ± 2, respectively (p < 0.01 vs. TNFα alone). Similarly, both antioxidant and inhibitors of the sphingolipid pathway restored the proton leak to pre-TNF values. TNFα-treated mitochondria or isolated cardiac muscle fibers showed an increase in respiration after anoxia-reoxygenation, but this effect was lost in the presence of an antioxidant or NOE. Similar data were obtained in TNFR1&2(-/-) mice. TNFα exerts a protective effect on respiratory function in isolated mitochondria subjected to an anoxia-reoxygenation insult. This effect appears to be independent of its cell surface receptors, but is likely to be mediated by ROS and sphingolipids.

Protection of mitochondrial system by Hippophae rhamnoides L. against radiation-induced oxidative damage in mice

The whole extract of the fresh berries of Hippophae rhamnoides L. (RH−3), which has been reported to provide protection to whole mice, various tissues, cells and cell organelles against lethal irradiation, was further investigated for its effects on mitochondria isolated from mouse liver. Superoxide anion, reduced (GSH) and oxidized glutathione (GSSG) levels, NADH-ubiquinone oxidoreductase (complex I), NADH-cytochrome c oxidoreductase (complex I/II), succinate-cytochrome c oxidoreductase (complex II/III), mitochondrial membrane potential (MMP), lipid peroxidation (LPx) and protein oxidation (PO) were determined for RH-3-mediated radioprotective manifestation. Pre-irradiation treatment of mice with RH-3 (30 mg kg−1, i.p.; single dose; −30 min) significantly inhibited the radiation-induced increase in superoxide anions, GSSG, thiobarbituric acid reactive substances (TBARS), complex I, complex I/III activity and MMP maximally at 4 h (P &lt; 0.05). This treatment inhibited the oxidation of proteins (P &lt; 0.05) at all the time periods studied here. This study suggests that pre-irradiation treatment of mice with RH-3 protects the functional integrity of mitochondria from radiation-induced oxidative stress.

Effects of Intrusive Force on Selected Determinants of Pulp Vitality

Objective: To determine the activity of aspartate aminotransferase (AST) in the pulp of orthodontically intruded teeth and to test the sensitivity of these teeth by means of electrical pulp testing (EPT).

Materials and Methods: The study sample consisted of 21 healthy subjects who needed extraction of first premolars for orthodontic reasons. In every subject, one premolar included in a 0.016″– 0.022″ stainless steel spring from the first molar and loaded by the force was regarded as a test tooth. The magnitude of the intrusive tipping force for every tooth was calculated with the use of ANSYS 10.0 software. The contralateral premolar was used as a control tooth. After 7 days, the spring was removed, and EPT was applied to test and control teeth. The teeth were extracted, and the dental pulp was removed. AST activity in the pulp was determined spectrophotometrically at 20°C.

Results: Estimated mean AST activity values ranged from 0.572 ± 0.097 U/mg in the test teeth to 0.348 ± 0.053 U/mg in the control teeth (P &lt; .01). The EPT test showed significant differences between test and control teeth (P &lt; .001). The mean estimated magnitude of the intrusive tipping force was 61 ± 4.5 g.

Conclusion: Seven days of orthodontic intrusion can cause metabolic changes in the pulp expressed by increased AST activity. The increased threshold in the pulp reaction to EPT indicates changes in the neural response of the pulp.

Cellular dysfunction in sepsis

Cellular dysfunction is a commonplace sequelum of sepsis and other systemic inflammatory conditions. Impaired energy production (related to mitochondrial inhibition, damage, and reduced protein turnover) appears to be a core mechanism underlying the development of organ dysfunction. The reduction in energy availability appears to trigger a metabolic shutdown that impairs normal functioning of the cell. This may well represent an adaptive mechanism analogous to hibernation that prevents a massive degree of cell death and thus enables eventual recovery in survivors.

High expression of thyroid hormone receptors and mitochondrial glycerol-3-phosphate dehydrogenase in the liver is linked to enhanced fatty acid oxidation in Lou/C, a rat strain resistant to obesity

Besides its well recognized role in lipid and carbohydrate metabolisms, glycerol is involved in the regulation of cellular energy homeostasis via glycerol-3-phosphate, a key metabolite in the translocation of reducing power across the mitochondrial inner membrane with mitochondrial glycerol-3-phosphate dehydrogenase. Here, we report a high rate of gluconeogenesis from glycerol and fatty acid oxidation in hepatocytes from Lou/C, a peculiar rat strain derived from Wistar, which is resistant to age- and diet-related obesity. This feature, associated with elevated cellular respiration and cytosolic ATP/ADP and NAD(+)/NADH ratios, was linked to a high expression and activity of mitochondrial glycerol-3-phosphate dehydrogenase. Interestingly, this strain exhibited high expression and protein content of thyroid hormone receptor, whereas circulating thyroid hormone levels were slightly decreased and hepatic thyroid hormone carrier MCT-8 mRNA levels were not modified. We propose that an enhanced liver thyroid hormone receptor in Lou/C may explain its unique resistance to obesity by increasing fatty acid oxidation and lowering liver oxidative phosphorylation stoichiometry at the translocation of reducing power into mitochondria.

Transcriptional co-expression and co-regulation of genes coding for components of the oxidative phosphorylation system

Background

The mitochondrial oxidative phosphorylation (OXPHOS) is critical for energy (ATP) production in eukaryotic cells. It was previously shown that genes coding for mitochondrial proteins involved in energy production co-express at the RNA level. Because the OXPHOS enzymes are multimeric complexes, we tested the hypothesis that genes coding for components of specific complexes are also co-regulated at the transcriptional level, and share common regulatory elements in their promoters.

Results

We observed for the first time that, not only OXPHOS genes as a group co-express, but there is a co-expression of genes within each of the five OXPHOS enzyme complexes, showing a higher degree of complexity in gene co-regulation. In silico analysis of homologous promoter sequences in mammals identified the likely core promoter elements for most genes encoding OXPHOS subunits/assembly factors. The results included a significant abundance of previously identified sites (e.g. NRF1, NRF2, ERRA and YY1), as well as several sites that had not been previously detected. Although we identified patterns that correlated to OXPHOS gene expression, we did not detect an OXPHOS complex-specific arrangement of transcription factor binding sites within the core promoter that could explain the tight co-expression of these functionally related genes.

Conclusion

This study mapped the core promoters of most OXPHOS related genes and provided an example of gene expression regulation based on the final protein arrangement within a linear metabolic pathway.

Mitochondrial adaptations to steatohepatitis induced by a methionine- and choline-deficient diet

Nonalcoholic fatty liver disease (NAFLD) has become common liver disease in Western countries. There is accumulating evidence that mitochondria play a key role in NAFLD. Nevertheless, the mitochondrial consequences of steatohepatitis are still unknown. The bioenergetic changes induced in a methionine- and choline-deficient diet (MCDD) model of steatohepatitis were studied in rats. Liver mitochondria from MCDD rats exhibited a higher rate of oxidative phosphorylation with various substrates, a rise in cytochrome oxidase (COX) activity, and an increased content in cytochrome aa3. This higher oxidative activity was associated with a low efficiency of the oxidative phosphorylation (ATP/O, i.e., number of ATP synthesized/natom O consumed). Addition of a low concentration of cyanide, a specific COX inhibitor, restored the efficiency of mitochondria from MCDD rats back to the control level. Furthermore, the relation between respiratory rate and protonmotive force (in the nonphosphorylating state) was shifted to the left in mitochondria from MCDD rats, with or without cyanide. These results indicated that, in MCDD rats, mitochondrial ATP synthesis efficiency was decreased in relation to both proton pump slipping at the COX level and increased proton leak although the relative contribution of each phenomenon could not be discriminated. MCDD mitochondria also showed a low reactive oxygen species production and a high lipid oxidation potential. We conclude that, in MCDD-fed rats, liver mitochondria exhibit an energy wastage that may contribute to limit steatosis and oxidative stress in this model of steatohepatitis.

Mitochondrial function and substrate availability

Carbohydrates and lipid oxidations support energy metabolism by distinct pathways exhibiting similarities and differences. Alterations of energy metabolism during sepsis are well recognized; however, failure of oxygen or substrate supply is not a prominent cause. The occurrence of a "mitochondrial cytopathy" induced by sepsis explains some of these abnormalities, which may represent a "metabolic hibernation," a potential strategy of defense during the very acute phase of the illness. Our view of the involvement of mitochondrial metabolism in cell signaling has evolved considerably. Because of the structure of the respiratory chain, the way electrons are provided (upstream or downstream of complex 1 [i.e., nicotinamide adenine dinucleotide {reduced form} or flavin adenine dinucleotide {reduced form}]) plays an important role in the regulation of several functions, including the yield of adenosine triphosphate synthesis and the production of reactive oxygen species. Moreover, the modern view of energy channeling and compartmentation in the cell may open attractive hypotheses regarding the changes in cellular energy distribution in pathologic states, such as sepsis.

On the biologic role of the reaction of NO with oxidized cytochrome c oxidase

The inhibition of cytochrome c oxidase (CcOX) by nitric oxide (NO) is analyzed with a mathematical model that simulates the metabolism in vivo. The main results were the following: (a) We derived novel equations for the catalysis of CcOX that can be used to predict CcOX inhibition in any tissue for any [NO] or [O(2)]; (b) Competitive inhibition (resulting from the reversible binding of NO to reduced CcOX) emerges has the sole relevant component of CcOX inhibition under state 3 in vivo; (c) In state 4, contribution of uncompetitive inhibition (resulting from the reaction of oxidized CcOX with NO) represents a significant nonmajority fraction of inhibition, being favored by high [O(2)]; and (d) The main biologic role of the reaction between NO and oxidized CcOX is to consume NO. By reducing [NO], this reaction stimulates, rather than inhibits, respiration. Finally, we propose that the biologic role of NO as an inhibitor of CcOX is twofold: in state 4, it avoids an excessive buildup of mitochondrial membrane potential that triggers rapid production of oxidants, and in state 3, increases the efficiency of oxidative phosphorylation by increasing the ADP/O ratio, supporting the therapeutic use of NO in situations in which mitochondria are dysfunctional.

Nitric oxide increases oxidative phosphorylation efficiency

We have studied the effect of nitric oxide (NO) and potassium cyanide (KCN) on oxidative phosphorylation efficiency. Concentrations of NO or KCN that decrease resting oxygen consumption by 10-20% increased oxidative phosphorylation efficiency in mitochondria oxidizing succinate or palmitoyl-L-carnitine, but not in mitochondria oxidizing malate plus glutamate. When compared to malate plus glutamate, succinate or palmitoyl-L-carnitine reduced the redox state of cytochrome oxidase. The relationship between membrane potential and oxygen consumption rates was measured at different degrees of ATP synthesis. The use of malate plus glutamate instead of succinate (that changes the H(+)/2e(-) stoichiometry of the respiratory chain) affected the relationship, whereas a change in membrane permeability did not affect it. NO or KCN also affected the relationship, suggesting that they change the H(+)/2e(-) stoichiometry of the respiratory chain. We propose that NO may be a natural short-term regulator of mitochondrial physiology that increases oxidative phosphorylation efficiency in a redox-sensitive manner by decreasing the slipping in the proton pumps.

Reduced expression of mitochondrial frataxin in mice exacerbates diet-induced obesity

Published evidence suggests that adiposity in humans may be linked to impaired energy expenditure for reasons widely unresolved. We have generated mice with a systemic impairment of oxidative phosphorylation (OXPHOS) due to aP2 cre-mediated targeted disruption, and unexpectedly ubiquitous reduction of mitochondrial frataxin protein expression. Only when maintained on a high-calorie diet resembling Westernized eating habits, these animals accumulate additional body fat, leading to increased body mass, and develop diabetes mellitus, despite the fact that both calorie uptake and physical activity were identical to that in control animals. This phenotype is caused by a mild but significant reduction in total energy expenditure paralleled by increased expression of ATP citrate lyase, a rate-limiting step in de novo synthesis of fatty acids and triglycerides. Taken together, these findings indicate that a limited impairment in oxidative metabolism within the mitochondria directly predisposes mammals to excessive body weight gain.

Mitochondrial energy metabolism in a model of undernutrition induced by dexamethasone

The present investigation was undertaken to evaluate whether mitochondrial energy metabolism is altered in a model of malnutrition induced by dexamethasone (DEX) treatment (1·5mg/kg per d for 5d). The gastrocnemius and liver mitochondria were isolated from DEX-treated, pair-fed (PF) and control (CON) rats. Body weight was reduced significantly more in the DEX-treated group (−16%) than in the PF group (−9%). DEX treatment increased liver mass (+59%v.PF, +23%v. CON) and decreased gastrocnemius mass. Moreover, in DEX-treated rats, liver mitochondria had an increased rate of non-phosphorylative O2consumption with all substrates (approximately +42%). There was no difference in enzymatic complex activities in liver mitochondria between rat groups. Collectively, these results suggest an increased proton leak and/or redox slipping in the liver mitochondria of DEX-treated rats. In addition, DEX decreased the thermodynamic coupling and efficiency of oxidative phosphorylation. We therefore suggest that this increase in the proton leak and/or redox slip in the liver is responsible for the decrease in the thermodynamic efficiency of energy conversion. In contrast, none of the variables of energy metabolism determined in gastrocnemius mitochondria was altered by DEX treatment. Therefore, it appears that DEX specifically affects mitochondrial energy metabolism in the liver.

Mitochondrial function, energy expenditure, aging and insulin resistance

Mitochondria are the cells' powerhouse that produce the ubiquitous energy currency (ATP) by consuming oxygen, producing water and building up the proton motive force. Oxygen consumption is a classical means of assessing energy expenditure, one component of energy balance. When energy balance is positive, weight increases. This is observed during the dynamic phase of obesity, and during body composition changes associated with aging. Whether intrinsic defaults in mitochondria occur is the matter of this review. Indeed, the ratio of ATP over oxygen consumed, which is not fixed, is one way of regulating heat release and ATP flux, but can also be the consequence of environmental conditions of mitochondrial work. For example, various hormones (T3, glucocorticoids), changes in lipid membrane composition, changes in food intake and exercise, and various drugs, can modify the ratio of ATP over oxygen consumed. Aging and insulin resistance are other regulators of this ratio. Finally there is a rising body of evidence linking diabetes to mitochondrial functions.

Hormonal regulation of mitochondrial energy production

PURPOSE OF REVIEW

It had been thought for a long time that thyroid hormones were the only ones to regulate energy production within mitochondria. Recent findings show that other hormones (steroids, leptin, insulin) regulate the efficiency of mitochondrial adenosine triphosphate production. Furthermore, a mismatch between oxygen consumption and energy intake may not be sufficient to understand body weight regulation. It appears that the efficiency of adenosine triphosphate production may play a role.

RECENT FINDINGS

Over the past 2 years a series of results argued that glucocorticoids influence energy balance, the efficiency of adenosine triphosphate production, and are thermogenic. The sites for this effect are discussed, probably both the liver and muscle. Evidence of the genes involved in this regulation is substantial for muscle but remains to be studied in the liver. On the other hand, leptin could be a thermogenic hormone, especially in situations of calorie restriction. Finally, recent data and opinions suggest that mitochondria and adenosine triphosphate production could be central in the pathogenesis of both insulin resistance and beta cell deficiency.

SUMMARY

The adaptation of mitochondrial adenosine triphosphate production appears to play a role in both diabetes and weight loss (voluntary and involuntary). Hormonal and nutritional manipulation could be a therapeutic possibility for weight management.

The yeast cAMP protein kinase Tpk3p is involved in the regulation of mitochondrial enzymatic content during growth

During aerobic cell growth, mitochondria must meet energy demand either by adjusting cellular mitochondrial content or by adjusting ATP production flux, allowing a constant growth yield. On respiratory substrate, the Ras/cAMP pathway has been shown to be involved in this process in the yeast Saccharomyces cerevisiae. We show that of the three cAMP protein kinase catalytic subunits, Tpk3p is the one specifically involved in the regulation of cellular mitochondrial content when energy demand decreases. In decreased energy demand, the Deltatpk3 mitochondrial enzymatic content decreases leading to a subsequent decrease in the cellular growth rate. Moreover, enzymatic content decreases in the Deltatpk3 isolated mitochondria, suggesting that the amount of cellular mitochondria is not affected, but rather that the mitochondria are modified. Our study points to an important decrease in the cytochrome c content in the Deltatpk3 mitochondria, which leads to a decrease in the slipping process at the level of cytochrome-c-oxidase.

Control of maximum metabolic rate in humans: dependence on performance phenotypes

Borrowing from metabolic control analysis the concept of control coefficients or ci values, defined as fractional change in MMR/fractional change in the capacity of any given step in ATP turnover, we used four performance phenotypes to compare mechanisms of control of aerobic maximum metabolic rate (MMR): (i) untrained sedentary (US) subjects, as a reference group against which to compare (ii) power trained (PT), (iii) endurance trained (ET), and (iv) high altitude adapted native (HA) subject groups. Sprinters represented the PT group; long distance runners illustrated the ET group; and Andean natives represented the HA group. Numerous recent studies have identified contributors to control on both the adenosine triphosphate (ATP) supply side and the ATP demand side of ATP turnover. From the best available evidence it appears that at MMR all five of the major steps in energy delivery (namely, ventilation, pulmonary diffusion, cardiac output, tissue capillary--mitochondrial O2 transfer, and aerobic cell metabolism per se) approach an upper functional ceiling, with control strength being distributed amongst the various O2 flux steps. On the energy demand side, the situation is somewhat simplified since at MMR approximately 90% of O2-based ATP synthesis is used for actomyosin (AM) and Ca2+ ATPases; at MMR these two ATP demand rates also appear to be near an upper functional ceiling. In consequence, at MMR the control contributions or ci values are distributed amongst all seven major steps in ATP supply and ATP demand pathways right to the point of fatigue. Relative to US (the reference group), in PT subjects at MMR control strength shifts towards O2 delivery steps (ventilation, pulmonary diffusion, and cardiac output); here physiological regulation clearly dominates MMR control. In contrast in ET and HA subjects at MMR control shifts towards the energy demand steps (AM and Ca2+ ATPases), and more control strength is focussed on tissue level ATP supply and ATP demand. One obvious advantage of the ET and HA biochemical-level control is improved metabolite homeostasis. Additionally, with some reserve capacity in the O2 delivery steps, the focussing of control on ATP turnover at the tissue level has allowed nature to improve on an 'endurance machine' design.

Polyunsaturated fatty acid deficiency reverses effects of alcohol on mitochondrial energy metabolism

BACKGROUND/AIMS

Polyunsaturated fatty acids (PUFA) deficiency is common in patients with alcoholic liver disease. The suitability of reversing such deficiency remains controversial. The aim was to investigate the role played by PUFA deficiency in the occurrence of alcohol-related mitochondrial dysfunction.

METHODS

Wistar rats were fed either a control diet with or without alcohol (control and ethanol groups) or a PUFA deficient diet with or without alcohol (PUFA deficient and PUFA deficient+ethanol groups). After 6 weeks, liver mitochondria were isolated for energetic studies and fatty acid analysis.

RESULTS

Mitochondria from ethanol fed rats showed a dramatic decrease in oxygen consumption rates and in cytochrome oxidase activity. PUFA deficiency showed an opposite picture. PUFA deficient+ethanol group roughly reach control values, regarding cytochrome oxidase activity and respiratory rates. The relationship between ATP synthesis and respiratory rate was shifted to the left in ethanol group and to the right in PUFA-deficient group. The plots of control and PUFA deficient+ethanol groups were overlapping. Phospholipid arachidonic over linoleic ratio closely correlated to cytochrome oxidase and oxygen uptake.

CONCLUSIONS

PUFA deficiency reverses alcohol-related mitochondrial dysfunction via an increase in phospholipid arachidonic over linoleic ratio, which raises cytochrome oxidase activity. Such deficiency may be an adaptive mechanism.

Contribution of the phosphorylable complex I in the growth phase-dependent respiration of C6 glioma cells in vitro

The energy metabolism of rat C6 glioma cells was investigated as a function of the growth phases. Three-dimensional cultures of C6 cells exhibited diminished respiration and respiratory capacity during the early growth phase, before reaching confluence. This decrease in respiration was neither due to changes in the respiratory complex content nor in the mitochondrial mass per se. Nevertheless, a quantitative correlation was found between cellular respiration and the rotenone-sensitive NADH ubiquinone oxidoreductase (i.e. complex I) activity. Immunoblot analysis showed that phosphorylation of the 18 kDa-subunit of this complex was associated with the growth-phase dependent modulation of complex I and respiratory activity in C6 cells. In addition, by using forskolin or dibutyryl cAMP, short-term activation of protein kinases A of C6 cells correlated with increased phosphorylation of the 18-kDa subunit of complex I, activated NADH ubiquinone oxidoreductase activity and stimulated cellular respiration. These findings suggest that complex I of C6 glioma cells is a key regulating step that modulates the oxidative phosphorylation capacity during growth phase transitions.

A turbo engine with automatic transmission? How to marry chemicomotion to the subtleties and robustness of life

Most genomes are much more complex than required for the minimum chemistry of life. Evolution has selected sophistication more than life itself. Could this also apply to bioenergetics? We first examine mechanisms through which bioenergetics could deliver sophistication. We illustrate possible benefits of the turbo-charging of catabolic pathways, of loose coupling, low-gear catabolism, automatic transmission in energy coupling, and of homeostasis. Mechanisms for such phenomena may reside at the level of individual proton pumps, or consist of rerouting of electrons over parallel pathways. The mechanisms may be confined to preexisting components, or involve the plasticity of gene expression that is so characteristic of most living organisms. These possible benefits lead us to the conjecture that also bioenergetics has evolved more for sophistication than for necessity. We next discuss a hitherto unresolved enigma, i.e. that bioenergetics does not seem to be critical for the physiological state. To decide on how critical bioenergetics is, we quantified the control exerted by catabolism on important physiological functions such as growth rate and growth yield. We also determined whether a growth inhibition mostly affected bioenergetics (catabolism) or anabolism; if ATP increases with growth rate, then growth should be considered energy (catabolism) limited. The experimental results for Escherichia coli pinpoint the enigma: its energy metabolism (catabolism) is not critical for growth rate. These results might suggest that because it has no direct control over cell function, bioenergetics is unimportant. Paradoxically however, in biology, highly important mechanisms tend to have little control on cell function, precisely because of that importance. Sophistication in terms of homeostatic mechanisms has evolved to guarantee robustness of the most important functions: The most important mechanisms are redundant in biology. Bioenergetics may be an excellent example of this paradox, in line with the above conjecture. It may be highly important and sophisticated. We then discuss work that has begun to focus on the sophistication of bioenergetics. Homeostasis of the energetics of DNA structure in E. coli is extensive. It relies both on preexisting components and on responsive gene expression. The vastly parallel electron-transfer network of Paracoccus denitrificans engages in sophisticated dynamic and hierarchical regulation. The growth yield of the organism can depend on which terminal oxidases are active. Effective proton translocation may vary due to rerouting of electrons. We conclude that much sophistication of bioenergetics will be discovered in this era of functional genomics.

Determination of mitochondrial reactive oxygen species: methodological aspects

The generation of Reactive Oxygen Species (ROS) as by-products in mitochondria Electron Transport Chain (ETC) has long been admitted as the cost of aerobic energy metabolism with oxidative damages as consequence. The purpose of this methodological review is to present some of the most widespread methods of ROS generation and to underline the limitations as well as some problems, identified with some experiments as examples, in the interpretation of such results. There is now no doubt that besides their pejorative role, ROS are involved in a variety of cellular processes for the continuous adaptation of the cell to its environment. Because ROS metabolism is a complex area (low production, instability of species, efficient antioxidant defense system, several places of production...) bias, variances and limitations in ROS measurements must be recognized in order to avoid artefactual conclusions, and especially to improve our understanding of physiological and pathophysiological mechanisms of such phenomenon.