Mild mitochondrial uncoupling and calorie restriction increase fasting eNOS, akt and mitochondrial biogenesis

Protective effects of 2,4-dinitrophenol in okadaic acid-induced cellular model of Alzheimer's disease

Alzheimer's disease (AD) research started several decades ago and despite the many efforts employed to develop new treatments or approaches to slow and/or revert disease progression, AD treatment remains an unsolved issue. Knowing that mitochondria loss of function is a central hub for many AD-associated pathophysiological processes, there has been renewed interest in exploring mitochondria as targets for intervention. In this perspective, the present study was aimed to investigate the possible beneficial effects of 2,4 dinitrophenol (DNP), a mitochondrial uncoupler agent, in an in vitro model of AD. Retinoic acid-induced differentiated SH-SY5Y cells were incubated with okadaic acid (OA), a neurotoxin often used as an AD experimental model, and/or with DNP. OA caused a decrease in neuronal cells viability, induced multiple mitochondrial anomalies including increased levels of reactive oxygen species, decreased bioenergetics and mitochondria content markers, and an altered mitochondria morphology. OA-treated cells also presented increased lipid peroxidation levels, and overactivation of tau related kinases (GSK3β, ERK1/2 and AMPK) alongside with a significant augment in tau protein phosphorylation levels. Interestingly, DNP co-treatment ameliorated and rescued OA-induced detrimental effects not only on mitochondria but also but also reinstated signaling pathways homeostasis and ameliorated tau pathology. Overall, our results show for the first time that DNP has the potential to preserve mitochondria homeostasis under a toxic insult, like OA exposure, as well as to reestablish cellular signaling homeostasis. These observations foster the idea that DNP, as a mitochondrial modulator, might represent a new avenue for treatment of AD.

Mitochondrial redox state, bioenergetics, and calcium transport in caloric restriction: A metabolic nexus

Mitochondria congregate central reactions in energy metabolism, many of which involve electron transfer. As such, they are expected to both respond to changes in nutrient supply and demand and also provide signals that integrate energy metabolism intracellularly. In this review, we discuss how mitochondrial bioenergetics and reactive oxygen species production is impacted by dietary interventions that change nutrient availability and impact on aging, such as calorie restriction. We also discuss how dietary interventions alter mitochondrial Ca2+ transport, regulating both mitochondrial and cytosolic processes modulated by this ion. Overall, a plethora of literature data support the idea that mitochondrial oxidants and calcium transport act as integrating signals coordinating the response to changes in nutritional supply and demand in cells, tissues, and animals.

Targeting mitochondrial shape: at the heart of cardioprotection

There remains an unmet need to identify novel therapeutic strategies capable of protecting the myocardium against the detrimental effects of acute ischemia-reperfusion injury (IRI), to reduce myocardial infarct (MI) size and prevent the onset of heart failure (HF) following acute myocardial infarction (AMI). In this regard, perturbations in mitochondrial morphology with an imbalance in mitochondrial fusion and fission can disrupt mitochondrial metabolism, calcium homeostasis, and reactive oxygen species production, factors which are all known to be critical determinants of cardiomyocyte death following acute myocardial IRI. As such, therapeutic approaches directed at preserving the morphology and functionality of mitochondria may provide an important strategy for cardioprotection. In this article, we provide an overview of the alterations in mitochondrial morphology which occur in response to acute myocardial IRI, and highlight the emerging therapeutic strategies for targeting mitochondrial shape to preserve mitochondrial function which have the future therapeutic potential to improve health outcomes in patients presenting with AMI.

Genetic perturbation of AMP biosynthesis extends lifespan and restores metabolic health in a naturally short-lived vertebrate

During aging, the loss of metabolic homeostasis drives a myriad of pathologies. A central regulator of cellular energy, the AMP-activated protein kinase (AMPK), orchestrates organismal metabolism. However, direct genetic manipulations of the AMPK complex in mice have, so far, produced detrimental phenotypes. Here, as an alternative approach, we alter energy homeostasis by manipulating the upstream nucleotide pool. Using the turquoise killifish, we mutate APRT, a key enzyme in AMP biosynthesis, and extend the lifespan of heterozygous males. Next, we apply an integrated omics approach to show that metabolic functions are rejuvenated in old mutants, which also display a fasting-like metabolic profile and resistance to high-fat diet. At the cellular level, heterozygous cells exhibit enhanced nutrient sensitivity, reduced ATP levels, and AMPK activation. Finally, lifelong intermittent fasting abolishes the longevity benefits. Our findings suggest that perturbing AMP biosynthesis may modulate vertebrate lifespan and propose APRT as a promising target for promoting metabolic health.

Effects of low-protein diet and feed restriction on mRNA expression of cationic amino acid transporters in porcine skeletal muscles

We investigated the effects of a low-protein diet and feed restriction on the mRNA expression of cationic amino acid transporters (CATs) in the longissimus dorsi (LD), rhomboideus (RH), and biceps femoris (BF) muscles of pigs. Eighteen piglets were divided into three groups: a control (CP21%), low-protein diet (LP, CP16%), and feed-restricted diet (FR, CP21%, 76% feed intake of control pigs) groups. The expression levels of CAT-1 in the LD and BF muscles of LP pigs were higher than that of control pigs, whereas that of FR pigs showed no difference. The CAT-2A expression levels in the RH muscle of FR pigs were higher than that of control pigs. The free lysine concentrations in all muscles of LP and FR pigs were lower than that of control pigs. To examine the factors that affect CATs mRNA expression, we evaluated the effects of lysine, arginine, insulin-like growth factor-I, and dexamethasone on the expression of CATs in C2C12 myotubes. CAT-1 expression levels increased in lysine and/or arginine deprivation. We show that CAT-1 and CAT-2A expression levels in skeletal muscles differ in response to dietary treatments and CAT-1 expression in skeletal muscles appears to increase in response to low free lysine concentrations.

The relationship between experimental 2,4-Dinitrophenol administration and neurological oxidative stress: in terms of dose, time and gender differences

Although 2,4-DNP is claimed to promote fast weight reduction, it is also related with an intolerable high risk of serious side effects to various tissues. On the other hand, it is known to have neuroprotective effects. These different effects of 2,4-DNP may be due to the administration conditions. For this reason, in this study, it was aimed for the first time to clarify the oxidative changes that occur in the brain during the use of 2,4-DNP, depending on the dose, time and gender. For this purpose, 60 Wistar rats (30 male, 30 female) were divided into ten groups: control groups, short-term/long-term groups and low dose/high dose groups. Except for the control groups, 2,4-DNP was administered to the other groups by oral gavage. End of the experiment, thiobarbituric acid-reactive substances (TBARs), glutathione (GSH), nitric oxide (NOx) and ascorbic acid (AA) levels were measured in the brain tissues of sacrificed animals. 2,4-DNP administration showed attenuation impact on oxidative stress depending on both dose, time and gender. It can be said that it is more beneficial in terms of neuroprotection, especially in the short-term and male groups. In conclusion, our findings suggest that, depending on the dose, time, and gender, 2,4-DNP may be beneficial in the treatment of neurodegenerative disorders.

Fifty Years of Research on Protonophores: Mitochondrial Uncoupling As a Basis for Therapeutic Action

Protonophores are compounds capable of electrogenic transport of protons across membranes. Protonophores have been intensively studied over the past 50 years owing to their ability to uncouple oxidation and phosphorylation in mitochondria and chloroplasts. The action mechanism of classical uncouplers, such as DNP and CCCP, in mitochondria is believed to be related to their protonophoric activity; i.e., their ability to transfer protons across the lipid part of the mitochondrial membrane. Given the recently revealed deviations in the correlation between the protonophoric activity of some uncouplers and their ability to stimulate mitochondrial respiration, this review addresses the involvement of some proteins of the inner mitochondrial membrane, such as the ATP/ADP antiporter, dicarboxylate carrier, and ATPase, in the uncoupling process. However, these deviations do not contradict the Mitchell theory but point to a more complex nature of the interaction of DNP, CCCP, and other uncouplers with mitochondrial membranes. Therefore, a detailed investigation of the action mechanism of uncouplers is required for a more successful pharmacological use, including their antibacterial, antiviral, anticancer, as well as cardio-, neuro-, and nephroprotective effects.

An energetics perspective on geroscience: mitochondrial protonmotive force and aging

Mitochondria are organelles that provide energy to cells through ATP production. Mitochondrial dysfunction has long been postulated to mediate cellular declines that drive biological aging. Many well-characterized hallmarks of aging may involve underlying energetic defects that stem from loss of mitochondrial function with age. Why and how mitochondrial function declines with age is an open question and one that has been difficult to answer. Mitochondria are powered by an electrochemical gradient across the inner mitochondrial membrane known as the protonmotive force (PMF). This gradient decreases with age in several experimental models. However, it is unclear if a diminished PMF is a cause or a consequence of aging. Herein, we briefly review and define mitochondrial function, we summarize how PMF changes with age in several models, and we highlight recent studies that implicate PMF in aging biology. We also identify barriers that must be addressed for the field to progress. Emerging technology permits more precise in vivo study of mitochondria that will allow better understanding of cause and effect in metabolic models of aging. Once cause and effect can be discerned more precisely, energetics approaches to combat aging may be developed to prevent or reverse functional decline.

Down syndrome is an oxidative phosphorylation disorder

Down syndrome is the most common genomic disorder of intellectual disability and is caused by trisomy of chromosome 21. Several genes in this chromosome repress mitochondrial biogenesis. The goal of this study was to evaluate whether early overexpression of these genes may cause a prenatal impairment of oxidative phosphorylation negatively affecting neurogenesis. Reduction in the mitochondrial energy production and a lower mitochondrial function have been reported in diverse tissues or cell types, and also at any age, including early fetuses, suggesting that a defect in oxidative phosphorylation is an early and general event in Down syndrome individuals. Moreover, many of the medical conditions associated with Down syndrome are also frequently found in patients with oxidative phosphorylation disease. Several drugs that enhance mitochondrial biogenesis are nowadays available and some of them have been already tested in mouse models of Down syndrome restoring neurogenesis and cognitive defects. Because neurogenesis relies on a correct mitochondrial function and critical periods of brain development occur mainly in the prenatal and early neonatal stages, therapeutic approaches intended to improve oxidative phosphorylation should be provided in these periods.

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Several chromosome 21-encoded proteins repress mitochondrial biogenesis.

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These proteins are overexpressed in fetal brains of Down syndrome (DS) individuals.

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Oxidative phosphorylation function is essential for neurogenesis.

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Upregulation of these proteins adversely impact on neurogenesis.

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Prenatal therapy with drugs inhibiting these proteins would increase DS neurogenesis.

Uncoupling proteins in the mitochondrial defense against oxidative stress

Oxidative stress is a major component of most major retinal diseases. Many extrinsic anti-oxidative strategies have been insufficient at counteracting one of the predominant intrinsic sources of reactive oxygen species (ROS), mitochondria. The proton gradient across the inner mitochondrial membrane is a key driving force for mitochondrial ROS production, and this gradient can be modulated by members of the mitochondrial uncoupling protein (UCP) family. Of the UCPs, UCP2 shows a widespread distribution and has been shown to uncouple oxidative phosphorylation, with concomitant decreases in ROS production. Genetic studies using transgenic and knockout mice have documented the ability of increased UCP2 activity to provide neuroprotection in models of a number of diseases, including retinal diseases, indicating that it is a strong candidate for a therapeutic target. Molecular studies have identified the structural mechanism of action of UCP2 and have detailed the ways in which its expression and activity can be controlled at the transcriptional, translational and posttranslational levels. These studies suggest a number of ways in control of UCP2 expression and activity can be used therapeutically for both acute and chronic conditions. The development of such therapeutic approaches will greatly increase the tools available to combat a broad range of serious retinal diseases.

Niclosamide ethanolamine attenuates systemic lupus erythematosus and lupus nephritis in MRL/lpr mice

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple organ involvement. Lupus nephritis (LN) is a severe manifestation of the disease and the most common cause of mortality in SLE patients. The etiology of LN is multifactorial and accumulating evidence suggests that mitochondrial dysfunction contributes to LN initiation and progression. Mild mitochondrial uncoupler niclosamide ethanolamine salt (NEN) has recently been shown to be efficacious in the treatment of both diabetic kidney disease and non-diabetic adriamycin nephropathy. However, its role in autoimmune kidney disease has not been explored. Here, we report for the first time that NEN attenuated SLE and lupus nephritis in MRL/lpr mice. NEN treatment reduced urinary protein excretion and attenuated glomerular lesions in this model. NEN treatment also decreased urinary excretion of tubular injury biomarkers NGAL and Kim-1, restored renal tubule phenotypic alterations, inhibited tubular proliferation, and suppressed renal interstitial inflammation and fibrosis. In addition, NEN diet supplementation restored redox imbalance, promoted mitochondrial biogenesis, and improved energy dysregulation in the kidney. Importantly, NEN prevented the enlargement of lymph nodes and the spleen, and decreased serum anti-dsDNA antibody levels in the MRL/lpr mice. Therefore, our data suggest that this mild mitochondrial uncoupling agent has great potential for translational application as a novel therapy for autoimmune disease.

MitoTimer-based high-content screen identifies two chemically-related benzothiophene derivatives that enhance basal mitophagy

Mitochondrial turnover is required for proper cellular function. Both mitochondrial biogenesis and mitophagy are impaired in several degenerative and age-related diseases. The search for mitophagy activators recently emerged as a new therapeutical approach; however, there is a lack in suitable tools to follow mitochondrial turnover in a high-throughput manner. We demonstrate that the fluorescent protein, MitoTimer, is a reliable and robust probe to follow mitochondrial turnover. The screening of 15 000 small molecules led us to two chemically-related benzothiophenes that stimulate basal mitophagy in the beta-cell line, INS1. Enhancing basal mitophagy was associated with improved mitochondrial function, higher Complex I activity and Complex II and III expressions in INS1 cells, as well as better insulin secretion performance in mouse islets. The possibility of further enhancing mitophagy in the absence of mitochondrial stressors points to the existence of a 'basal mitophagy spare capacity'. To this end, we found two small molecules that can be used as models to better understand the physiological regulation of mitophagy.

Mitochondrial adaptations in liver and skeletal muscle to pro-longevity nutritional and genetic interventions: the crosstalk between calorie restriction and CYB5R3 overexpression in transgenic mice

Calorie restriction without malnutrition (CR) is considered as the most effective nongenetic nor pharmacological intervention that promotes healthy aging phenotypes and can extend lifespan in most model organisms. Lifelong CR leads to an increase of cytochrome b₅ reductase-3 (CYB5R3) expression and activity. Overexpression of CYB5R3 confers some of the salutary effects of CR, although the mechanisms involved might be independent because key aspects of energy metabolism and lipid profiles of tissues go in opposite ways. It is thus important to study if some of the metabolic adaptations induced by CR are affected by CYB5R3 overexpression. CYB5R3 overexpression greatly preserved body and liver weight in mice under CR conditions. In liver, CR did not modify mitochondrial abundance, but lead to increased expression of mitofusin Mfn2 and TFAM, a transcription factor involved in mitochondrial biogenesis. These changes were prevented by CYB5R3 overexpression but resulted in a decreased expression of a different mitochondrial biogenesis-related transcription factor, Nrf1. In skeletal muscle, CR strongly increased mitochondrial mass, mitofusin Mfn1, and Nrf1. However, CYB5R3 mice on CR did not show increase in muscle mitochondrial mass, regardless of a clear increase in expression of TFAM and mitochondrial complexes in this tissue. Our results support that CYB5R3 overexpression significantly modifies the metabolic adaptations of mice to CR.

A single muscle contusion promotes an immediate alteration in mitochondrial bioenergetics response in skeletal muscle fibres with different metabolism

Skeletal muscle is the most abundant tissue in the human body and mechanical injuries are common; these are frequently of mechanical origins, such as contusion. However, the immediate mitochondrial response to injury and energetic substrate utilisation is still unclear. We evaluated the acute response in mitochondrial function after a single muscle contusion, either in fast twitch fibres (glycolytic metabolism), fast and slow twitch (oxidative and glycolytic metabolism), or slow twitch fibres (oxidative metabolism). Rats were assigned to two groups: control and Lesion (muscle contusion). We collected the gastrocnemius and soleus muscles. The fibres were analysed for mitochondrial respiration, lactate dehydrogenase (LDH), citrate synthase (CS) activity, Ca²⁺ uptake, and H₂O₂ production. We found that muscle injury was able to increase ATP synthesis-dependent and OXPHOS oxygen flux in the oxidative fibres when stimulated by complex I + II substrates. On the other hand, the muscle injury increased hydrogen peroxide (H₂O₂) production when compared to control fibres, and reduced citrate synthase activity; however, it did not change Ca²⁺ uptake. Surprisingly, injury in mixed fibres increased the OXPHOS and ATP synthesis oxygen consumption, and H₂O₂ production, but it reduced Ca²⁺ uptake. The injury in glycolytic fibres did not affect oxygen flux coupled to ATP synthesis, citrate synthase, and lactate dehydrogenase activity, but did reduce Ca²⁺ uptake. Finally, we demonstrated distinct mitochondrial responses between the different muscle fibres, indicating that the mitochondrial dynamics is related to flexibilities in metabolism, and that reactive oxygen species directly affect physiology and normal function.

Vitamin E supplementation and caloric restriction promotes regulation of insulin secretion and glycemic homeostasis by different mechanisms in rats

Vitamin E and caloric restriction have antioxidant effects in mammals. The aim of this study was to evaluate effects of vitamin E supplementation and caloric restriction upon insulin secretion and glucose homeostasis in rats. Male Wistar rats were distributed among the following groups: C, control group fed ad libitum; R, food quantity reduction of 40%; CV, control group supplemented with vitamin E [30 mg·kg^-1·day^-1]; and RV, food-restricted group supplemented with vitamin E. The experiments ran for 21 days. Glucose tolerance and insulin sensitivity was higher in the CV, R, and RV groups. Insulin secretion stimulated with different glucose concentrations was lower in the R and RV groups, compared with C and CV. In the presence of glucose and secretagogues, insulin secretion was higher in the CV group and was lower in the R and RV groups. An increase in insulin receptor occurred in the fat pad and muscle tissue of groups CV, R, and RV. Levels of hepatic insulin receptor and phospho-Akt protein were higher in groups R and RV, compared with C and CV, while muscle phospho-Akt was increased in the CV group. There was a reduction in hepatic RNA levels of the hepatocyte growth factor gene and insulin degrading enzyme in the R group, and increased levels of insulin degrading enzyme in the CV and RV groups. Thus, vitamin E supplementation and caloric restriction modulate insulin secretion by different mechanisms to maintain glucose homeostasis.

Tyrphostin AG17 inhibits adipocyte differentiation in vivo and in vitro

Background

Excessive subcutaneous adiposity in obesity is associated to positive white adipocyte tissue (WAT) differentiation (adipogenesis) and WAT expandability. Here, we hypothesized that supplementation with the insulin inhibitor and mitochondrial uncoupler, Tyrphostin (T-AG17), in vitro and in vivo inhibits adipogenesis and adipocyte hypertrophy.

Methods

We used a 3T3-L1 proadipocyte cell line to identify the potential effect of T-AG17 on adipocyte differentiation and fat accumulation in vitro. We evaluated the safety of T-AG17 and its effects on physiological and molecular metabolic parameters including hormonal profile, glucose levels, adipogenesis and adipocyte hypertrophy in a diet-induced obesity model using C57BL/6 mice.

Results

We found that T-AG17 is effective in preventing adipogenesis and lipid synthesis in the 3T3-L1 cell line, as evidenced by a significant decrease in oil red staining (p < 0.05). In obese C57BL/6 mice, oral administration of T-AG17 (0.175 mg/kg for 2 weeks) lead to decreased fat accumulation and WAT hypertrophy. Further, T-AG17 induced adipocyte apoptosis by activating caspase-3. In the hepatocytes of obese mice, T-AG17 promoted an increase in the size of lipid inclusions, which was accompanied by glycogen accumulation. T-AG17 did not alter serum biochemistry, including glucose, insulin, leptin, free fatty acids, creatinine, and aspartate aminotransferase.

Conclusion

T-AG17 promotes adipocyte apoptosis in vivo and is an effective modulator of adipocyte differentiation and WAT hypertrophy in vitro and in vivo. Therefore, T-AG17 may be useful as a pharmacological obesity treatment.

Study of respiratory chain dysfunction in heart disease

The relentlessly beating heart has the greatest oxygen consumption of any organ in the body at rest reflecting its huge metabolic turnover and energetic demands. The vast majority of its energy is produced and cycled in form of ATP which stems mainly from oxidative phosphorylation occurring at the respiratory chain in the mitochondria. A part from energy production, the respiratory chain is also the main source of reactive oxygen species and plays a pivotal role in the regulation of oxidative stress. Dysfunction of the respiratory chain is therefore found in most common heart conditions. The pathophysiology of mitochondrial respiratory chain dysfunction in hereditary cardiac mitochondrial disease, the aging heart, in LV hypertrophy and heart failure, and in ischaemia-reperfusion injury is reviewed. We introduce the practicing clinician to the complex physiology of the respiratory chain, highlight its impact on common cardiac disorders and review translational pharmacological and non-pharmacological treatment strategies.

Rapid regulation of substrate use for oxidative phosphorylation during a single session of high intensity interval or aerobic exercises in different rat skeletal muscles

Different exercise protocols lead to long-term adaptations that are related to increased mitochondrial content through the activation of mitochondrial biogenesis. However, immediate mitochondrial response to exercise and energetic substrate utilization is still unknown. We evaluate the mitochondrial physiology of two types rat skeletal muscle fibres immediately after a single session of high intensity interval exercise (HIIE) or aerobic exercise (AER). We found AER was able to reduce the ATP synthesis dependent oxygen flux in the tibialis (TA) when stimulated by complex I and II substrates. On the other hand, there was an increase of the maximum velocity (V_max) for glycerol-phosphate oxidation and V_max and affinity (K_M) of palmitoyl-carnitine oxidation (PC). The exercise did not affect oxygen flux coupled to ATP synthesis in red gastrocnemius (RG) but, surprisingly, reduced its affinity for PC, decreasing the apparent catalytic efficiency (V_max/K_M) of oxidation for PC. Neither exercise protocol was able to change the electron transfer system capacity of the mitochondria or markers of mitochondrial content. The AER group had increased H₂O₂ production compared to the SED and HIIE groups, with the mechanism being predominantly the escape of electrons through reverse flux in complex I and other sites in TA, and only through other sites in RG. There were no changes in the activities of antioxidant enzymes. Our results show that mitochondria from different muscles submitted to distinct exercise protocols show alterations in the specific fluxes of substrate utilization and oxygen metabolism, indicating that the dynamics of mitochondria are linked to the metabolic flexibility.

Mitochondrial form, function and signalling in aging

Aging is often accompanied by a decline in mitochondrial mass and function in different tissues. Additionally, cell resistance to stress is frequently found to be prevented by higher mitochondrial respiratory capacity. These correlations strongly suggest mitochondria are key players in aging and senescence, acting by regulating energy homeostasis, redox balance and signalling pathways central in these processes. However, mitochondria display a wide array of functions and signalling properties, and the roles of these different characteristics are still widely unexplored. Furthermore, differences in mitochondrial properties and responses between tissues and cell types, and how these affect whole body metabolism are also still poorly understood. This review uncovers aspects of mitochondrial biology that have an impact upon aging in model organisms and selected mammalian cells and tissues.

Investigating mitochondrial redox state using NADH and NADPH autofluorescence

The redox states of the NAD and NADP pyridine nucleotide pools play critical roles in defining the activity of energy producing pathways, in driving oxidative stress and in maintaining antioxidant defences. Broadly speaking, NAD is primarily engaged in regulating energy-producing catabolic processes, whilst NADP may be involved in both antioxidant defence and free radical generation. Defects in the balance of these pathways are associated with numerous diseases, from diabetes and neurodegenerative disease to heart disease and cancer. As such, a method to assess the abundance and redox state of these separate pools in living tissues would provide invaluable insight into the underlying pathophysiology. Experimentally, the intrinsic fluorescence of the reduced forms of both redox cofactors, NADH and NADPH, has been used for this purpose since the mid-twentieth century. In this review, we outline the modern implementation of these techniques for studying mitochondrial redox state in complex tissue preparations. As the fluorescence spectra of NADH and NADPH are indistinguishable, interpreting the signals resulting from their combined fluorescence, often labelled NAD(P)H, can be complex. We therefore discuss recent studies using fluorescence lifetime imaging microscopy (FLIM) which offer the potential to discriminate between the two separate pools. This technique provides increased metabolic information from cellular autofluorescence in biomedical investigations, offering biochemical insights into the changes in time-resolved NAD(P)H fluorescence signals observed in diseased tissues.

Mitochondrial Dysfunction in Alzheimer's Disease and the Rationale for Bioenergetics Based Therapies

Alzheimer’s disease (AD) is a debilitating neurodegenerative disorder characterized by the progressive loss of cholinergic neurons, leading to the onset of severe behavioral, motor and cognitive impairments. It is a pressing public health problem with no effective treatment. Existing therapies only provide symptomatic relief without being able to prevent, stop or reverse the pathologic process. While the molecular basis underlying this multifactorial neurodegenerative disorder remains a significant challenge, mitochondrial dysfunction appears to be a critical factor in the pathogenesis of this disease. It is therefore important to target mitochondrial dysfunction in the prodromal phase of AD to slow or prevent the neurodegenerative process and restore neuronal function. In this review, we discuss mechanisms of action and translational potential of current mitochondrial and bioenergetic therapeutics for AD including: mitochondrial enhancers to potentiate energy production; antioxidants to scavenge reactive oxygen species and reduce oxidative damage; glucose metabolism and substrate supply; and candidates that target apoptotic and mitophagy pathways to remove damaged mitochondria. While mitochondrial therapeutic strategies have shown promise at the preclinical stage, there has been little progress in clinical trials thus far.

Low Concentrations of Uncouplers of Oxidative Phosphorylation Prevent Inflammatory Activation of Endothelial Cells by Tumor Necrosis Factor

In endothelial cells, mitochondria play an important regulatory role in physiology as well as in pathophysiology related to excessive inflammation. We have studied the effect of low doses of mitochondrial uncouplers on inflammatory activation of endothelial cells using the classic uncouplers 2,4-dinitrophenol and 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole, as well as the mitochondria-targeted cationic uncoupler dodecyltriphenylphosphonium (C12TPP). All of these uncouplers suppressed the expression of E-selectin, adhesion molecules ICAM1 and VCAM1, as well as the adhesion of neutrophils to endothelium induced by tumor necrosis factor (TNF). The antiinflammatory action of the uncouplers was at least partially mediated by the inhibition of NFκB activation due to a decrease in phosphorylation of the inhibitory subunit IκBα. The dynamic concentration range for the inhibition of ICAM1 expression by C12TPP was three orders of magnitude higher compared to the classic uncouplers. Probably, the decrease in membrane potential inhibited the accumulation of penetrating cations into mitochondria, thus lowering the uncoupling activity and preventing further loss of mitochondrial potential. Membrane potential recovery after the removal of the uncouplers did not abolish its antiinflammatory action. Thus, mild uncoupling could induce TNF resistance in endothelial cells. We found no significant stimulation of mitochondrial biogenesis or autophagy by the uncouplers. However, we observed a decrease in the relative amount of fragmented mitochondria. The latter may significantly change the signaling properties of mitochondria. Earlier we showed that both classic and mitochondria-targeted antioxidants inhibited the TNF-induced NFκB-dependent activation of endothelium. The present data suggest that the antiinflammatory effect of mild uncoupling is related to its antioxidant action.

Chloroquine increases phosphorylation of AMPK and Akt in myotubes

Aims

There are reports that ataxia telangiectasia mutated (ATM) can activate the AMP-activated protein kinase (AMPK) and also Akt, two kinases that play integral parts in cardioprotection and metabolic function. We hypothesized that chloroquine and resveratrol, both known ATM activators, would also activate AMPK and Akt.

Main methods

Phosphorylation of AMPK and Akt was assessed after C2C12 myotubes were exposed to chloroquine or resveratrol. Additional experiments were done in cells expressing shRNA against ATM or in the presence of the ATM inhibitor KU55933. The effects of chloroquine on intracellular calcium were assessed with the fluorescent probe Calcium Green-1 AM.

Key findings

0.5 mM chloroquine increased AMPK phosphorylation by nearly four-fold (P < 0.05), and 0.25 mM chloroquine roughly doubled Akt phosphorylation (P < 0.05). Chloroquine also increased autophosphorylation of ATM by ∼50% (P < 0.05). Resveratrol (0.15 mM) increased AMPK phosphorylation about three-fold (P < 0.05) but in contrast to chloroquine sharply decreased Akt phosphorylation. Chloroquine increased AMPK and Akt phosphorylation in myotubes expressing shRNA against ATM that reduced ATM protein levels by about 90%. Likewise, chloroquine-stimulated phosphorylation of AMPK and Akt and resveratrol-stimulated phosphorylation of AMPK were not altered by inhibition of ATM. Chloroquine decreased intracellular calcium by >50% concomitant with a decrease in glucose transport.

Significance

These ATM-independent effects of chloroquine on AMPK and Akt and the additional effect to decrease intracellular calcium are likely to partially underlie the positive metabolic effects of chloroquine that have been reported in the literature.

IL-15Rα deficiency in skeletal muscle alters respiratory function and the proteome of mitochondrial subpopulations independent of changes to the mitochondrial genome

Interleukin-15 receptor alpha knockout (IL15RαKO) mice exhibit a greater skeletal muscle mitochondrial density with an altered mitochondrial morphology. However, the mechanism and functional impact of these changes have not been determined. In this study, we characterized the functional, proteomic, and genomic alterations in mitochondrial subpopulations isolated from the skeletal muscles of IL15RαKO mice and B6129 background control mice. State 3 respiration was greater in interfibrillar mitochondria and whole muscle ATP levels were greater in IL15RαKO mice supporting the increases in respiration rate. However, the state 3/state 4 ratio was lower, suggesting some degree of respiratory uncoupling. Proteomic analyses identified several markers independently in mitochondrial subpopulations that are associated with these functional alterations. Next Generation Sequencing of mtDNA revealed a high degree of similarity between the mitochondrial genomes of IL15RαKO mice and controls in terms of copy number, consensus coding and the presence of minor alleles, suggesting that the functional and proteomic alterations we observed occurred independent of alterations to the mitochondrial genome. These data provide additional evidence to implicate IL-15Rα as a regulator of skeletal muscle phenotypes through effects on the mitochondrion, and suggest these effects are driven by alterations to the mitochondrial proteome.

Artemisinin mimics calorie restriction to trigger mitochondrial biogenesis and compromise telomere shortening in mice

Calorie restriction is known to extend lifespan among organisms by a debating mechanism underlying nitric oxide-driven mitochondrial biogenesis. We report here that nitric oxide generators including artemisinin, sodium nitroprusside, and L-arginine mimics calorie restriction and resembles hydrogen peroxide to initiate the nitric oxide signaling cascades and elicit the global antioxidative responses in mice. The large quantities of antioxidant enzymes are correlated with the low levels of reactive oxygen species, which allow the down-regulation of tumor suppressors and accessory DNA repair partners, eventually leading to the compromise of telomere shortening. Accompanying with the up-regulation of signal transducers and respiratory chain signatures, mitochondrial biogenesis occurs with the elevation of adenosine triphosphate levels upon exposure of mouse skeletal muscles to the mimetics of calorie restriction. In conclusion, calorie restriction-triggered nitric oxide provides antioxidative protection and alleviates telomere attrition via mitochondrial biogenesis, thereby maintaining chromosomal stability and integrity, which are the hallmarks of longevity.

Artemisinin mimics calorie restriction to extend yeast lifespan via a dual-phase mode: a conclusion drawn from global transcriptome profiling

Calorie restriction (CR) promotes longevity among distinct organisms from yeast to mammals. Although CR-prolonged lifespan is believed to associate with enhanced respiratory activity, it is apparently controversial for accelerated energy consumption regardless of insufficient nutrient intake. In reconciling the contradiction of less food supply versus much metabolite dispense, we revealed a CR-based mode of dual-phase responses that encompass a phase of mitochondrial enhancement (ME) and a phase of post-mitochondrial enhancement (PME), which can be distinguished by the expression patterns and activity dynamics of mitochondrial signatures. ME is characterized by global antioxidative activation, and PME is denoted by systemic metabolic modulation. CR-mediated aging-delaying effects are replicated by artesunate, a semi-synthetic derivative of the antimalarial artemisinin that can alkylate heme-containing proteins, suggesting artesunate-heme conjugation functionally resembles nitric oxide-heme interaction. A correlation of artesunate-heme conjugation with cytochrome c oxidase activation has been established from adduct formation and activity alteration. Exogenous hydrogen peroxide also mimics CR to trigger antioxidant responses, affect signaling cascades, and alter respiratory rhythms, implying hydrogen peroxide is engaged in lifespan extension. Conclusively, artesunate mimics CR-triggered nitric oxide and hydrogen peroxide to induce antioxidative networks for scavenging reactive oxygen species and mitigating oxidative stress, thereby directing metabolic conversion from anabolism to catabolism, maintaining essential metabolic functionality, and extending life expectancy in yeast.

Nitric oxide, interorganelle communication, and energy flow: a novel route to slow aging

The mitochondrial lifecycle (mitochondrial biogenesis, dynamics, and removal by mitophagy) is carefully orchestrated to ensure the efficient generation of cellular energy and to maintain reactive oxygen species (ROS) production within an optimal range for cellular health. Based on latest research, these processes largely depend on mitochondrial interactions with other cell organelles, so that the ER- and peroxisome-mitochondrial connections might intervene in the control of cellular energy flow. Damaged organelles are cleared by autophagic mechanisms to assure the quality and proper function of the intracellular organelle pool. Nitric oxide (NO) generated through the endothelial nitric oxide synthase (eNOS) acts a gas signaling mediator to promote mitochondrial biogenesis and bioenergetics, with a favorable impact in diverse chronic diseases of the elderly. Obesity, diabetes and aging share common pathophysiological mechanisms, including mitochondrial impairment and dysfunctional eNOS. Here we review the evidences that eNOS-dependent mitochondrial biogenesis and quality control, and possibly the complex interplay among cellular organelles, may be affected by metabolic diseases and the aging processes, contributing to reduce healthspan and lifespan. Drugs or nutrients able to sustain the eNOS-NO generating system might contribute to maintain organelle homeostasis and represent novel preventive and/or therapeutic approaches to chronic age-related diseases.

Impact of caloric restriction on myocardial ischaemia/reperfusion injury and new therapeutic options to mimic its effects

Caloric restriction (CR) is the most reliable intervention to extend lifespan and prevent age-related disorders in various species from yeast to rodents. Short- and long-term CR confers cardio protection against ischaemia/reperfusion injury in young and even in aged rodents. A few human trials suggest that CR has the potential to mediate improvement of cardiac or vascular function and induce retardation of cardiac senescence also in humans. The underlying mechanisms are diverse and have not yet been clearly defined. Among the known mediators for the benefits of CR are NO, the AMP-activated PK, sirtuins and adiponectin. Mitochondria, which play a central role in such complex processes within the cell as apoptosis, ATP-production or oxidative stress, are centrally involved in many aspects of CR-induced protection against ischaemic injury. Here, we discuss the relevant literature regarding the protection against myocardial ischaemia/reperfusion injury conferred by CR. Furthermore, we will discuss drug targets to mimic CR and the possible role of calorie restriction in preserving cardiovascular function in humans.

The many roles of PGC-1α in muscle--recent developments

Skeletal muscle is the largest organ in the body and contributes to innumerable aspects of organismal biology. Muscle dysfunction engenders numerous diseases, including diabetes, cachexia, and sarcopenia. At the same time, skeletal muscle is also the main engine of exercise, one of the most efficacious interventions for prevention and treatment of a wide variety of diseases. The transcriptional coactivator PGC-1α has emerged as a key driver of metabolic programming in skeletal muscle, both in health and in disease. We review here the many aspects of PGC-1α function in skeletal muscle, with a focus on recent developments.

Mitochondrial uncoupling reduces exercise capacity despite several skeletal muscle metabolic adaptations

The effects of mitochondrial uncoupling on skeletal muscle mitochondrial adaptation and maximal exercise capacity are unknown. In this study, rats were divided into a control group (CTL, n = 8) and a group treated with 2,4-dinitrophenol, a mitochondrial uncoupler, for 28 days (DNP, 30 mg·kg−1·day−1in drinking water, n = 8). The DNP group had a significantly lower body mass ( P < 0.05) and a higher resting oxygen uptake (V̇o2, P < 0.005). The incremental treadmill test showed that maximal running speed and running economy ( P < 0.01) were impaired but that maximal V̇o2(V̇o2max) was higher in the DNP-treated rats ( P < 0.05). In skinned gastrocnemius fibers, basal respiration (V0) was higher ( P < 0.01) in the DNP-treated animals, whereas the acceptor control ratio (ACR, Vmax/V0) was significantly lower ( P < 0.05), indicating a reduction in OXPHOS efficiency. In skeletal muscle, DNP activated the mitochondrial biogenesis pathway, as indicated by changes in the mRNA expression of PGC1-α and -β, NRF-1 and −2, and TFAM, and increased the mRNA expression of cytochrome oxidase 1 ( P < 0.01). The expression of two mitochondrial proteins (prohibitin and Ndufs 3) was higher after DNP treatment. Mitochondrial fission 1 protein (Fis-1) was increased in the DNP group ( P < 0.01), but mitofusin-1 and -2 were unchanged. Histochemical staining for NADH dehydrogenase and succinate dehydrogenase activity in the gastrocnemius muscle revealed an increase in the proportion of oxidative fibers after DNP treatment. Our study shows that mitochondrial uncoupling induces several skeletal muscle adaptations, highlighting the role of mitochondrial coupling as a critical factor for maximal exercise capacities. These results emphasize the importance of investigating the qualitative aspects of mitochondrial function in addition to the amount of mitochondria.

The breathing heart - mitochondrial respiratory chain dysfunction in cardiac disease

The relentlessly beating heart has the greatest oxygen consumption of any organ in the body at rest reflecting its huge metabolic turnover and energetic demands. The vast majority of its energy is produced and cycled in form of ATP which stems mainly from oxidative phosphorylation occurring at the respiratory chain in the mitochondria. Apart from energy production, the respiratory chain is also the main source of reactive oxygen species and plays a pivotal role in the regulation of oxidative stress. Dysfunction of the respiratory chain is therefore found in most common heart conditions. The pathophysiology of mitochondrial respiratory chain dysfunction in hereditary cardiac mitochondrial disease, the ageing heart, in LV hypertrophy and heart failure, and in ischaemia-reperfusion injury is reviewed. We introduce the practising clinician to the complex physiology of the respiratory chain, highlight its impact on common cardiac disorders and review translational pharmacological and non-pharmacological treatment strategies.

The mitochondrial uncoupler 2,4-dinitrophenol attenuates sodium nitroprusside-induced toxicity in Drosophila melanogaster: potential involvement of free radicals

The toxicity of sodium nitroprusside (SNP) (an inducer of oxidative/nitrosative stress) and the attenuation of SNP effects by 2,4-dinitrophenol (DNP) (that induces mild uncoupling of respiration) were evaluated in the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with 1.0 mM SNP, 0.5 or 1.25 mM DNP, or with mixtures 1.0 mM SNP plus 0.5 or 1.25 mM DNP. Food supplementation with SNP decreased larval viability and pupation height whereas supplementation with DNP substantially reversed these changes. Biochemical analyses of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies emerged from control larvae and larvae fed on food supplemented with SNP, DNP, or SNP/DNP mixtures. Larval exposure to SNP lowered activities of aconitase, while the presence of DNP reduced the negative impact of SNP by raising aconitase activity back to near control levels. Larval treatment with SNP also elevated the contents of carbonyl protein, uric acid and low molecular mass thiols and produced higher activities of superoxide dismutase, glutathione S-transferase, glucose-6-phosphate dehydrogenase and thioredoxin reductase in adult flies. However, the presence of DNP in the food mixtures prevented SNP-induced changes in thioredoxin reductase and glucose-6-phosphate dehydrogenase activities, as well as uric acid and low-molecular-mass thiol content. The potential mechanisms by which DNP exerts protective effects against SNP toxicity are discussed.

Germline energetics, aging, and female infertility

The role of metabolism in ovarian aging is poorly described, despite the fact that ovaries fail earlier than most other organs. Growing interest in ovarian function is being driven by recent evidence that mammalian females routinely generate new oocytes during adult life through the activity of germline stem cells. In this perspective, we overview the female reproductive system as a powerful and clinically relevant model to understand links between aging and metabolism, and we discuss new concepts for how oocytes and their precursor cells might be altered metabolically to sustain or increase ovarian function and fertility in women.

Mitochondria as a source of reactive oxygen and nitrogen species: from molecular mechanisms to human health

Mitochondrially generated reactive oxygen species are involved in a myriad of signaling and damaging pathways in different tissues. In addition, mitochondria are an important target of reactive oxygen and nitrogen species. Here, we discuss basic mechanisms of mitochondrial oxidant generation and removal and the main factors affecting mitochondrial redox balance. We also discuss the interaction between mitochondrial reactive oxygen and nitrogen species, and the involvement of these oxidants in mitochondrial diseases, cancer, neurological, and cardiovascular disorders.

Redox-regulating sirtuins in aging, caloric restriction, and exercise

The consequence of decreased nicotinamide adenine dinucleotide (NAD(+)) levels as a result of oxidative challenge is altered activity of sirtuins, which, in turn, brings about a wide range of modifications in mammalian cellular metabolism. Sirtuins, especially SIRT1, deacetylate important transcription factors such as p53, forkhead homeobox type O proteins, nuclear factor κB, or peroxisome proliferator-activated receptor γ coactivator 1α (which controls the transcription of pro- and antioxidant enzymes, by which the cellular redox state is affected). The role of SIRT1 in DNA repair is enigmatic, because it activates Ku70 to cope with double-strand breaks, but deacetylation of apurinic/apyrimidinic endonuclease 1 and probably of 8-oxoguanine-DNA glycosylase 1 decreases the activity of these DNA repair enzymes. The protein-stabilizing effects of the NAD+-dependent lysine deacetylases are readily related to housekeeping and redox regulation. The role of sirtuins in caloric restriction (CR)-related longevity in yeast is currently under debate. However, in mammals, it seems certain that sirtuins are involved in many cellular processes that mediate longevity and disease prevention via the effects of CR through the vascular, neuronal, and muscular systems. Regular physical exercise-mediated health promotion also involves sirtuin-regulated pathways including the antioxidant-, macromolecular damage repair-, energy-, mitochondrial function-, and neuronal plasticity-associated pathways. This review critically evaluates these findings and points out the age-associated role of sirtuins.

Skeletal muscle function during exercise-fine-tuning of diverse subsystems by nitric oxide

Skeletal muscle is responsible for altered acute and chronic workload as induced by exercise. Skeletal muscle adaptations range from immediate change of contractility to structural adaptation to adjust the demanded performance capacities. These processes are regulated by mechanically and metabolically induced signaling pathways, which are more or less involved in all of these regulations. Nitric oxide is one of the central signaling molecules involved in functional and structural adaption in different cell types. It is mainly produced by nitric oxide synthases (NOS) and by non-enzymatic pathways also in skeletal muscle. The relevance of a NOS-dependent NO signaling in skeletal muscle is underlined by the differential subcellular expression of NOS1, NOS2, and NOS3, and the alteration of NO production provoked by changes of workload. In skeletal muscle, a variety of highly relevant tasks to maintain skeletal muscle integrity and proper signaling mechanisms during adaptation processes towards mechanical and metabolic stimulations are taken over by NO signaling. The NO signaling can be mediated by cGMP-dependent and -independent signaling, such as S-nitrosylation-dependent modulation of effector molecules involved in contractile and metabolic adaptation to exercise. In this review, we describe the most recent findings of NO signaling in skeletal muscle with a special emphasis on exercise conditions. However, to gain a more detailed understanding of the complex role of NO signaling for functional adaptation of skeletal muscle (during exercise), additional sophisticated studies are needed to provide deeper insights into NO-mediated signaling and the role of non-enzymatic-derived NO in skeletal muscle physiology.

Calorie restriction hysteretically primes aging Saccharomyces cerevisiae toward more effective oxidative metabolism

Calorie restriction (CR) is an intervention known to extend the lifespan of a wide variety of organisms. In S. cerevisiae, chronological lifespan is prolonged by decreasing glucose availability in the culture media, a model for CR. The mechanism has been proposed to involve an increase in the oxidative (versus fermentative) metabolism of glucose. Here, we measured wild-type and respiratory incompetent (ρ(0)) S. cerevisiae biomass formation, pH, oxygen and glucose consumption, and the evolution of ethanol, glycerol, acetate, pyruvate and succinate levels during the course of 28 days of chronological aging, aiming to identify metabolic changes responsible for the effects of CR. The concomitant and quantitative measurements allowed for calculations of conversion factors between different pairs of substrates and products, maximum specific substrate consumption and product formation rates and maximum specific growth rates. Interestingly, we found that the limitation of glucose availability in CR S. cerevisiae cultures hysteretically increases oxygen consumption rates many hours after the complete exhaustion of glucose from the media. Surprisingly, glucose-to-ethanol conversion and cellular growth supported by glucose were not quantitatively altered by CR. Instead, we found that CR primed the cells for earlier, faster and more efficient metabolism of respiratory substrates, especially ethanol. Since lifespan-enhancing effects of CR are absent in respiratory incompetent ρ(0) cells, we propose that the hysteretic effect of glucose limitation on oxidative metabolism is central toward chronological lifespan extension by CR in this yeast.

Maternal calorie restriction modulates placental mitochondrial biogenesis and bioenergetic efficiency: putative involvement in fetoplacental growth defects in rats

Low birth weight is associated with an increased risk for developing type 2 diabetes and metabolic diseases. The placental capacity to supply nutrients and oxygen to the fetus represents the main determiner of fetal growth. However, few studies have investigated the effects of maternal diet on the placenta. We explored placental adaptive proteomic processes implicated in response to maternal undernutrition. Rat term placentas from 70% food-restricted (FR30) mothers were used for a proteomic screen. Placental mitochondrial functions were evaluated using molecular and functional approaches, and ATP production was measured. FR30 drastically reduced placental and fetal weights. FR30 placentas displayed 14 proteins that were differentially expressed, including several mitochondrial proteins. FR30 induced a marked increase in placental mtDNA content and changes in mitochondrial functions, including modulation of the expression of genes implicated in biogenesis and bioenergetic pathways. FR30 mitochondria showed higher oxygen consumption but failed to maintain their ATP production. Maternal undernutrition induces placental mitochondrial abnormalities. Although an increase in biogenesis and bioenergetic efficiency was noted, placental ATP level was reduced. Our data suggest that placental mitochondrial defects may be implicated in fetoplacental pathologies.

Mitochondrial metabolism in aging: effect of dietary interventions

Mitochondrial energy metabolism and mitochondrially-derived oxidants have, for many years, been recognized as central toward the effects of aging. A body of recent work has focused on the relationship between mitochondrial redox state, aging and dietary interventions that affect lifespan. These studies have uncovered mechanisms through which diet alters mitochondrial metabolism, in addition to determining how these changes affect oxidant generation, which in itself has an impact on mitochondrial function in aged animals. Many of the studies conducted to date, however, are correlative, and it remains to be determined which of the energy metabolism and redox modifications induced by diet are central toward lifespan extent. Furthermore, dietary interventions used for laboratory animals are often unequal, and of difficult comparison with humans (for whom, by nature, no long-term sound scientific information on the effects of diet on mitochondrial redox state and aging is available). We hope future studies will be able to mechanistically characterize which energy metabolism and redox changes promoted by dietary interventions have positive lifespan effects, and translate these findings into human prevention and treatment of age-related disease.

Nitric oxide in skeletal muscle: role on mitochondrial biogenesis and function

Nitric oxide (NO) has been implicated in several cellular processes as a signaling molecule and also as a source of reactive nitrogen species (RNS). NO is produced by three isoenzymes called nitric oxide synthases (NOS), all present in skeletal muscle. While neuronal NOS (nNOS) and endothelial NOS (eNOS) are isoforms constitutively expressed, inducible NOS (iNOS) is mainly expressed during inflammatory responses. Recent studies have demonstrated that NO is also involved in the mitochondrial biogenesis pathway, having PGC-1α as the main signaling molecule. Increased NO synthesis has been demonstrated in the sarcolemma of skeletal muscle fiber and NO can also reversibly inhibit cytochrome c oxidase (Complex IV of the respiratory chain). Investigation on cultured skeletal myotubes treated with NO donors, NO precursors or NOS inhibitors have also showed a bimodal effect of NO that depends on the concentration used. The present review will discuss the new insights on NO roles on mitochondrial biogenesis and function in skeletal muscle. We will also focus on potential therapeutic strategies based on NO precursors or analogs to treat patients with myopathies and mitochondrial deficiency.

Is mitochondrial DNA content a potential biomarker of mitochondrial dysfunction?

Mitochondrial dysfunction is central to numerous diseases of oxidative stress. Changes in mitochondrial DNA (MtDNA) content, often measured as mitochondrial genome to nuclear genome ratio (Mt/N) using real time quantitative PCR, have been reported in a broad range of human diseases, such as diabetes and its complications, obesity, cancer, HIV complications, and ageing. We propose the hypothesis that MtDNA content in body fluids and tissues could be a biomarker of mitochondrial dysfunction and review the evidence supporting this theory. Increased reactive oxygen species resulting from an external trigger such as hyperglycaemia or increased fat in conditions of oxidative stress could lead to enhanced mitochondrial biogenesis, and increased Mt/N. Altered MtDNA levels may contribute to enhanced oxidative stress and inflammation and could play a pathogenic role in mitochondrial dysfunction and disease. Changes in Mt/N are detectable in circulating cells such as peripheral blood mononuclear cells and these could be used as surrogate to predict global changes in tissues and organs. We review a large number of studies reporting changes in MtDNA levels in body fluids such as circulating blood cells, cell free serum, saliva, sperm, and cerebrospinal fluid as well as in tumour and normal tissue samples. However, the data are often conflicting as the current methodology used to measure Mt/N can give false results because of one or more of the following reasons (1) use of mitochondrial primers which co-amplify nuclear pseudogenes (2) use of nuclear genes which are variable and/or duplicated in numerous locations (3) a dilution bias caused by the differing genome sizes of the mitochondrial and nuclear genome and (4) template preparation protocols which affect the yields of nuclear and mitochondrial genomes. Development of robust and reproducible methodology is needed to test the hypothesis that MtDNA content in body fluids is biomarker of mitochondrial dysfunction.

Nitrite activates AMP kinase to stimulate mitochondrial biogenesis independent of soluble guanylate cyclase

Nitrite, a dietary constituent and endogenous signaling molecule, mediates a number of physiological responses including modulation of ischemia/reperfusion injury, glucose tolerance, and vascular remodeling. Although the exact molecular mechanisms underlying nitrite's actions are unknown, the current paradigm suggests that these effects depend on the hypoxic reduction of nitrite to nitric oxide (NO). Mitochondrial biogenesis is a fundamental mechanism of cellular adaptation and repair. However, the effect of nitrite on mitochondrial number has not been explored. Herein, we report that nitrite stimulates mitochondrial biogenesis through a mechanism distinct from that of NO. We demonstrate that nitrite significantly increases cellular mitochondrial number by augmenting the activity of adenylate kinase, resulting in AMP kinase phosphorylation, downstream activation of sirtuin-1, and deacetylation of PGC1α, the master regulator of mitochondrial biogenesis. Unlike NO, nitrite-mediated biogenesis does not require the activation of soluble guanylate cyclase and results in the synthesis of more functionally efficient mitochondria. Further, we provide evidence that nitrite mediates biogenesis in vivo. In a rat model of carotid injury, 2 weeks of continuous oral nitrite treatment postinjury prevented the hyperproliferative response of smooth muscle cells. This protection was accompanied by a nitrite-dependent upregulation of PGC1α and increased mitochondrial number in the injured artery. These data are the first to demonstrate that nitrite mediates differential signaling compared to NO. They show that nitrite is a versatile regulator of mitochondrial function and number both in vivo and in vitro and suggest that nitrite-mediated biogenesis may play a protective role in the setting of vascular injury.

Caloric restriction and redox state: does this diet increase or decrease oxidant production?

Calorie restriction (CR) is well established to enhance the lifespan of a wide variety of organisms, although the mechanisms are still being uncovered. Recently, some authors have suggested that CR acts through hormesis, enhancing the production of reactive oxygen species (ROS), activating stress response pathways, and increasing lifespan. Here, we review the literature on the effects of CR and redox state. We find that there is no evidence in rodent models of CR that an increase in ROS production occurs. Furthermore, results in Caenorhabditis elegans and Saccharomyces cerevisiae suggesting that CR increases intracellular ROS are questionable, and probably cannot be resolved until adequate, artifact free, tools for real-time, quantitative, and selective measurements of intracellular ROS are developed. Overall, the largest body of work indicates that CR improves redox state, although it seems improbable that a global improvement in redox state is the mechanism through which CR enhances lifespan.

Calorie restriction increases cerebral mitochondrial respiratory capacity in a NO•-mediated mechanism: impact on neuronal survival

Calorie restriction (CR) enhances animal life span and prevents age-related diseases, including neurological decline. Recent evidence suggests that a mechanism involved in CR-induced life-span extension is NO(•)-stimulated mitochondrial biogenesis. We examine here the effects of CR on brain mitochondrial content. CR increased eNOS and nNOS and the content of mitochondrial proteins (cytochrome c oxidase, citrate synthase, and mitofusin) in the brain. Furthermore, we established an in vitro system to study the neurological effects of CR using serum extracted from animals on this diet. In cultured neurons, CR serum enhanced nNOS expression and increased levels of nitrite (a NO(•) product). CR serum also enhanced the levels of cytochrome c oxidase and increased citrate synthase activity and respiratory rates in neurons. CR serum effects were inhibited by L-NAME and mimicked by the NO(•) donor SNAP. Furthermore, both CR sera and SNAP were capable of improving neuronal survival. Overall, our results indicate that CR increases mitochondrial biogenesis in a NO(•)-mediated manner, resulting in enhanced reserve respiratory capacity and improved survival in neurons.

Mitochondria in vascular disease

Mitochondria are often regarded as the powerhouse of the cell by generating the ultimate energy transfer molecule, ATP, which is required for a multitude of cellular processes. However, the role of mitochondria goes beyond their capacity to create molecular fuel, to include the generation of reactive oxygen species, the regulation of calcium, and activation of cell death. Mitochondrial dysfunction is part of both normal and premature ageing, but can contribute to inflammation, cell senescence, and apoptosis. Cardiovascular disease, and in particular atherosclerosis, is characterized by DNA damage, inflammation, cell senescence, and apoptosis. Increasing evidence indicates that mitochondrial damage and dysfunction also occur in atherosclerosis and may contribute to the multiple pathological processes underlying the disease. This review summarizes the normal role of mitochondria, the causes and consequences of mitochondrial dysfunction, and the evidence for mitochondrial damage and dysfunction in vascular disease. Finally, we highlight areas of mitochondrial biology that may have therapeutic targets in vascular disease.