Effect of aging on the oxidative phosphorylation pathway

Bioenergetic analysis of aged-phenotype skin in a rare syndromic cutis laxa

BACKGROUND

Skin aging is an inevitable phenomenon characterized by wrinkled skin and loss of elasticity. To date, several studies have been performed on skin aging to discover the underlying mechanisms and improve efficient preventive strategies and anti-aging therapeutics.

AIMS

Here, we aimed to investigate the modifications of oxidative phosphorylation and glycolysis which are the critical determinants of aging in aged-phenotype skin.

METHODS

Due to the complexity of the skin aging process, we performed bioenergetic measurements on aged-phenotype fibroblasts from an inherited cutis laxa syndrome which remarkably presents clinical features of normal aged skin. Bioenergetic analysis was performed on cutis laxa samples (n = 3) and healthy samples (n = 3) using Seahorse XFe24 Analyzer. We also compared the sensitivity of cultured aged-phenotype fibroblasts to normal cells in glucose withdrawal.

RESULTS

Our results show a significant increase in oxidative phosphorylation parameters but not glycolysis in the patient fibroblast cells implying increased energy demand and preferential dependence on mitochondrial respiration in those cells. Interestingly, we found the patient cells demonstrate hypersensitivity to glucose starvation, supporting their enhanced energy consumption.

CONCLUSIONS

In summary, our work suggested increased energy demand and higher oxidative phosphorylation in aged-phenotype cells which can be considered in anti-skin aging therapeutic design.

Mitochondrial respiration in human viable platelets--methodology and influence of gender, age and storage

Studying whole cell preparations with intact mitochondria and respiratory complexes has a clear benefit compared to isolated or disrupted mitochondria due to the dynamic interplay between mitochondria and other cellular compartments. Platelet mitochondria have a potential to serve as a source of human viable mitochondria when studying mitochondrial physiology and pathogenic mechanisms, as well as for the diagnostics of mitochondrial diseases. The objective of the present study was to perform a detailed evaluation of platelet mitochondrial respiration using high-resolution respirometry. Further, we aimed to explore the limits of sample size and the impact of storage as well as to establish a wide range of reference data from different pediatric and adult cohorts. Our results indicate that platelet mitochondria are well suited for ex-vivo analysis with the need for minute sample amounts and excellent reproducibility and stability.

Proteomic analysis of protein expression affected by peroxiredoxin V knock-down in hypoxic kidney

Peroxiredoxin V, an atypical thioredoxin peroxidase, is widely expressed in mammalian tissues. In addition, Prdx V is localized in mitochondria, peroxisome, cytosol, and the nucleus. Prdx V has been reported to protect a wide range of cellular environments as an antioxidant enzyme, and its dysfunctions may be implicated in several diseases, such as cancer, inflammation, and neurodegenerative disease. Identification and relative quantification of proteins affected by Prdx V may help identify novel signaling mechanisms that are important for oxidative stress response. However, the role of Prdx V in the modulation of hypoxia-related cellular response is not studied yet. To examine the function of endogenous Prdx V in hypoxic condition in vivo, we generated a transgenic mouse model with Prdx V siRNA expression controlled by U6 promoter. Of many tissues, the knockdown of Prdx V expression was displayed in the kidney, lung, and liver but not the spleen and skin. We conducted on the basis of nano-UPLC-MS(E) proteomic study to identify the Prdx V-affected protein networks in hypoxic kidneys. In this study, we identified protein networks associated with oxidative stress, fatty acid metabolism, and mitochondrial dysfunction. Our results indicated that Prdx V affected to regulation of kidney homeostasis under hypoxia stress.

Mitochondria in the elderly: Is acetylcarnitine a rejuvenator?

Endogenous acetylcarnitine is an indicator of acetyl-CoA synthesized by multiple metabolic pathways involving carbohydrates, amino acids, fatty acids, sterols, and ketone bodies, and utilized mainly by the tricarboxylic acid cycle. Acetylcarnitine supplementation has beneficial effects in elderly animals and humans, including restoration of mitochondrial content and function. These effects appear to be dose-dependent and occur even after short-term therapy. In order to set the stage for understanding the mechanism of action of acetylcarnitine, we review the metabolism and role of this compound. We suggest that acetylation of mitochondrial proteins leads to a specific increase in mitochondrial gene expression and mitochondrial protein synthesis. In the aged rat heart, this effect is translated to increased cytochrome b content, restoration of complex III activity, and oxidative phosphorylation, resulting in amelioration of the age-related mitochondrial defect.

Metabonomic study on ageing: NMR-based investigation into rat urinary metabolites and the effect of the total flavone of Epimedium

The aim of this work was to investigate the effects of ageing on rat urinary metabolites and to evaluate the anti-ageing effects of the total flavone of Epimedium (TFE). Proton nuclear magnetic resonance based metabonomic analyses was performed on urine from rats aged 4, 10, 18 and 24 months, and rats administered with TFE. By multivariate analysis, 26 characteristic resonances were found to be highly related with the age of rats, and ten of them were structurally postulated as creatinine, lactate, alanine, acetate, acetone, succinate, allantoin, methylamine, dimethylamine and trimethylamine-N-oxide; these metabolites involve creatinine metabolites, aliphatic amines metabolites and some important intermediates or end products of energy metabolism. Principal components analysis revealed that the metabolic profiles of 24-month-old rats treated with TFE closely resembled those of rats aged 18 months. In addition, most of these characteristic resonances were reset to younger levels by TFE intervention. The result suggests that TFE administration can markedly influence the ageing process and shows anti-ageing effects, which might due to the melioration of pyruyate metabolism and oxidative phosphorylation.

Oxidative phosphorylation and aging

This review addresses the data that support the presence and contribution of decreased mitochondrial oxidative phosphorylation during aging to impaired cellular metabolism. Aging impairs substrate oxidation, decreases cellular energy production and increases the production of reactive intermediates that are toxic to the cell. First, the basic principles of mitochondrial oxidative physiology are briefly reviewed. Second, the focus on the relationship of altered mitochondrial respiration to the increased production of reactive oxygen species that are employed by the "rate of living" and the "uncoupling to survive" theories of aging are discussed. Third, the impairment of function of respiration in aging is reviewed using an organ-based approach in mammalian systems. Fourth, the current state of knowledge regarding aging-induced alterations in the composition and function of key mitochondrial constituents is addressed. Model organisms, including C. elegans and D. melanogaster are included where pertinent. Fifth, these defects are related to knowledge regarding the production of reactive oxygen species from specific sites of the electron transport chain.

Mitochondrial dysfunctions during aging: vitamin E deficiency or caloric restriction--two different ways of modulating stress

Caloric restriction (CR), which has been demonstrated to offset the age-associated accrual of oxidative injury, involves a reduction in calory intake while maintaining adequate nutrition, preserves the activities of antioxidant enzymes in postmitotic tissues, maintains organ function, opposes the development of spontaneous diseases, and prolongs maximum life span in laboratory rodents. It has been proposed that reductions in Reactive Oxygen Species (ROS) production and cellular oxidative injury are central to the positive effects of CR. In the present investigation we studied the effect of CR and of a vitamin E deprived diet on mitochondrial structure and features in the liver of rats during aging, in order to ascertain the extent of modifications induced by these experimental conditions. CR rats displayed structural and functional mitochondrial properties (fatty acid pattern, respiratory chain activities, antioxidant levels, and hydroperoxide contents) similar to those of younger rats whilst vitamin E deficient rats appeared older than their own age. The mitochondria of the former, together with those of young rats, possessed the lowest Coenzyme Q9, hydroperoxide, and cytochrome contents as well as a suitable fatty acid membrane composition. Our study confirms that CR is a valuable tool in limiting aging-related free-radical damage also at mitochondrial liver level.

Age and sex influence on oxidative damage and functional status in human skeletal muscle

A reduction in muscle mass, with consequent decrease in strength and resistance, is commonly observed with advancing age. In this study we measured markers of oxidative damage to DNA, lipids and proteins, some antioxidant enzyme activities as well Ca2+ transport in sarcoplasmic reticulum membranes in muscle biopsies from vastus lateralis of young and elderly healthy subjects of both sexes in order to evaluate the presence of age- and sex-related differences. We found a significant increase in oxidation of DNA and lipids in the elderly group, more evident in males, and a reduction in catalase and glutathione transferase activities. The experiments on Ca2+ transport showed an abnormal functional response of aged muscle after exposure to caffeine, which increases the opening of Ca2+ channels, as well a reduced activity of the Ca2+ pump in elderly males. From these results we conclude that oxidative stress play an important role in muscle aging and that oxidative damage is much more evident in elderly males, suggesting a gender difference maybe related to hormonal factors.

Mitochondrial coenzyme Q content and aging

The main objective of this study was to determine the nature of the relationship between aging and mitochondrial coenzyme Q (CoQ) content. Mitochondria in the heart, skeletal muscle, kidney and brain of the mouse varied in both the amount of total CoQ (CoQ9 + CoQ10) content as well as in the ratio of the CoQ9 to CoQ10. CoQ content declined with age only in the skeletal muscle. Caloric restriction (CR) resulted in an increase in the amount of CoQ9 in skeletal muscle mitochondria. This effect was partially reversible upon termination of the caloric restriction regimen. Results suggest that a decrease in mitochondrial CoQ content is an integral aspect of aging in skeletal muscle.

Caloric restriction prevents age-associated accrual of oxidative damage to mouse skeletal muscle mitochondria

The purpose of this study was to understand the nature of the causes underlying the senescence-related decline in skeletal muscle mass and performance. Protein and lipid oxidative damage to upper hindlimb skeletal muscle mitochondria was compared between mice fed ad libitum and those restricted to 40% fewer calories--a regimen that increases life span by approximately 30-40% and attenuates the senescence-associated decrement in skeletal muscle mass and function. Oxidative damage to mitochondrial proteins, measured as amounts of protein carbonyls and loss of protein sulfhydryl content, and to mitochondrial lipids, determined as concentration of thiobarbituric acid reactive substances, significantly increased with age in the ad libitum-fed (AL) C57BL/6 mice. The rate of superoxide anion radical generation by submitochondrial particles increased whereas the activities of antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidase in muscle homogenates remained unaltered with age in the AL group. In calorically-restricted (CR) mice there was no age-associated increase in mitochondrial protein or lipid oxidative damage, or in superoxide anion radical generation. Crossover studies, involving the transfer of 18- to 22-month-old mice fed on the AL regimen to the CR regimen, and vice versa, indicated that the mitochondrial oxidative damage could not be reversed by CR or induced by AL feeding within a time frame of 6 weeks. Results of this study indicate that mitochondria in skeletal muscles accumulate significant amounts of oxidative damage during aging. Although such damage is largely irreversible, it can be prevented by restriction of caloric intake.

Oxidative stress and mitochondrial function in skeletal muscle: Effects of aging and exercise training

The rate of oxidative phosphorylation was investigated in isolated mitochondria from hindlimb muscles of young (4.5 mo) and old (26.5 mo) male Fischer 344 rats with or without endurance training. Further, the susceptibility of the muscle mitochondria to exogenous reactive oxygen species was examined. State 3 and 4 respiration, as well as the respiratory control index (RCI), were significantly lower in muscle mitochondria from aged vs. young rats (P<0.05), using either the site 1 substrates malate-pyruvate (M-P) and 2-oxoglutarate (2-OG), or the site 2 substrate succinate. In both young and old rats, training increased state 4 respiration with M-P, but had no effect on state 3 respiration, resulting in a reduction of RCI. Training also increased state 4 respiration with 2-OG and decreased RCI in young rats. When muscle mitochondria were exposed to superoxide radicals (O2 (·-)) and hydrogen peroxide (H2O2) generated by xanthine oxidase and hypoxanthine, or H2O2 alone in vitro, state 3 respiration and RCI in both age groups were severely hampered, but those from the old rats were inhibited to a less extent than the young rats. In contrast, state 4 respiration was impaired by O2 (·-) and/or H2O2 to a greater extent in the old rats. Muscle mitochondria from trained young rats showed a greater resistance to the O2 (· -) and/or H2O2-induced state 3 and RCI inhibition than those from untrained young rats. Muscle from aged rats had significantly higher total activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPX), and glutathione reductase than that from young rats, however, training increased SOD and GPX activities in young but not old rats. The results of this study suggest that mitochondrial capacity for oxidative phosphorylation is compromised in aging skeletal muscle. Further, the increased mitochondrial resistance to reactive oxygen species demonstrated in aged and young trained muscles may be attributed to enhanced antioxidant enzyme activities.

Age-related changes in the binding and uptake of Cu, Zn superoxide dismutase in rat liver cells

The present paper reports the effect of aging on receptor mediated endocytosis of Cu, Zn superoxide dismutase in rat liver cells. The fate of bovine Cu, Zn superoxide dismutase conjugated to colloidal gold was followed by electron microscopy in young (2 months) and old (24 months) rats in situ, in vivo and in vitro experiments. The use of different models for the study of the binding and internalization of the enzyme allowed to discriminate the contribution of each different liver cell type. The data obtained demonstrate that aging of the liver affects binding and uptake of this enzyme. In particular both the number of binding sites and the rate of internalization were depressed in old rats. Therefore, the hypothesis of therapeutic application of superoxide dismutase for age-related diseases needs to be revalued in view of the fact that receptor-mediated endocytosis of this protein is a mechanism affected by senescence.

Human epidermal cells progressively lose their cardiolipins during ageing without change in mitochondrial transmembrane potential

Mitochondria dysfunction is considered to be a major cause of the modifications that occur during cell ageing. For this reason, cardiolipin, a suitable marker of the chondriome, as well as the mitochondrial transmembrane potential were examined in keratinocytes obtained from 9- to 75-year-old women. The study was carried out by flow cytometry using two fluorescent mitochondria probes: nonyl acridine orange, which binds specifically to cardiolipin, and rhodamine 123, which is incorporated mainly in response to transmembrane potential. Cardiolipin levels in cells from elderly donors (75 years old) would be 57% lower (r = 0.540; P = 0.0002) than those in children (9 years old), while the inner transmembrane potential remained unchanged (r = 0.0394; P = 0.8017). The stability of the membrane potential may be explained by either or both of the following hypotheses: (i) the same pool of organelles able to maintain membrane potential is conserved even when cardiolipin levels decrease (ii) mitochondria membrane potential does indeed decrease with age but is compensated by glycolysis energy production. Finally, it may be stated that the fluorescent probes nonyl acridine orange and rhodamine 123 might be of interest in testing the phenotype of senescent cells and would be useful in screening the role of certain specific genes in cell ageing.

Hypotonic fragility of outer membrane and activation of external pathway of NADH oxidation in rat liver mitochondria are increased with age

Great importance is attached to structural and functional deterioration of mitochondria as a reason for ageing of an organism; the attention of many scientists has been concentrated on such questions as age changes in the system of oxidative phosphorylation, damage of mitochondrial DNA by free radicals generated in the respiratory chain and inclusion of some fragments of mitochondrial DNA into the nuclear genome. Mitochondrial high amplitude swelling in a cell under some extreme conditions can possibly play a very important role in mechanisms of deterioration of energy transformation function, in activation of lipid peroxidation and mitochondrial DNA damage as a result of outer membrane disruption and release of enzymes from the intermembrane space (e.g. superoxide dismutase amd adenylate kinase). In this work the age changes of the hypotonic fragility of the outer membrane of rat liver mitochondria and the activation of the external, rotenone-insensitive pathway of NADH oxidation have been examined. It is shown that the obligatory condition for activation of rotenone-insensitive NADH oxidation is a break in the outer membrane and that the rate of NADH oxidation substantially increases in the presence of physiological concentrations of Mg2+ which cause a multiple increase in the affinity of the inner membrane to cytochrome c. Research on the rate of rotenone-insensitive NADH oxidation with respect to the osmotic pressure, the ionic strength of the medium, the presence of Mg2+ ions and cytochrome c in the medium has demonstrated a considerable increase in the hypotonic fragility of the outer membrane of liver mitochondria with age in male rats. In female rats the age changes were insignificant. It is supposed that the damage to the outer membrane of mitochondria in cells can serve as one of the possible explanations of both decrease in the reliability of an aged organism under extreme conditions and sex differences of life-span.

Evidence for and against the causal involvement of mitochondrial DNA mutation in mammalian ageing

Current experimental evidence on the role of mitochondrial DNA mutation in ageing is assessed alongside reports implicating other genetic and non-genetic causes, including inter-relationships between the mitochondrial and nuclear genomes and their potential effect on mitochondrial structure and function. The role of a 5-kb mtDNA deletion, identified as age-dependent in a variety of human and other mammalian species, is specifically evaluated in the context of its functional effect in mitotic and non-mitotic adult tissue. Downstream effects of mitochondrial decline are considered in terms of the maintenance of ATP production. Associated sequelae then are discussed specifically with reference to restrictions in the supply of ribose moieties for DNA and RNA synthesis, and to disruption of NADPH production and hence cellular anti-oxidant defences.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative study of succinate-supported respiration and ATP/ADP translocation in liver mitochondria from adult and old rats

This study was undertaken to compare the rates of succinate-supported hepatic mitochondrial respiration between 12 months (adult) and 29 months (old) male Fischer 344 rats. Experiments were also performed to determine the activity of adenine nucleotide translocase and the effect of its inhibition on mitochondrial respiration. Succinate-supported state 3 mitochondrial respiration was found to decline 20% between 12 and 29 months of age in rat liver, along with a similar 25% decrease in the respiratory control ratio with age. Adenine nucleotide translocase activity is shown to decrease 39% from adult to old rat liver mitochondria. This decrease does not, however, account for the decline in state 3 respiration, since translocase activity is approximately 50% greater than state 3 respiration in both adult and old rats. Therefore, adenine nucleotide translocase is not rate-limiting for state 3 mitochondrial respiration. Neither the rate of succinate permeation into the mitochondrial nor the rate of electron transport is rate-limiting for state 3 respiration, indicated by the greatly increased oxygen consumption with addition of the uncoupler carbonyl cyanide m-chlorophenyl hydrazone (m-CCCP). These processes, therefore, are not responsible for the observed decline in state 3 respiration. The implications and possible cause of the age-related decrease in the maximal rate of ATP-synthesis are discussed.

An integrated theory of aging as the result of mitochondrial-DNA mutation in differentiated cells

We maintain that aging of humans and animals derives from a mutation or inactivation (probably followed by endonuclease digestion) of the mitochondrial genome of differentiated cells. This extranuclear somatic mutation hypothesis of aging is based on the finding that mitochondrial DNA (mtDNA) synthesis takes place at the inner mitochondrial membrane near the sites of formation of highly reactive oxygen species and their products, such as lipoperoxides and malonaldehyde. The mtDNA may be unable to counteract the damage inflicted by those by-products of respiration because, in contrast to the nuclear genome, it lacks histone protection and scission repair. Since the mitochondrial genome controls the synthesis of several hydrophobic proteins of the inner mitochondrial membrane, the postulated mutation, inactivation or loss of mtDNA will prevent the replication of the organelles. Thus deprived of the ability to regenerate their mitochondrial populations, the cells will sustain an irreversible decline in their bioenergetic ability, with concomitant senescent loss of physiological performance and eventual death. The above hypothesis is integrated with the concepts of Minot, Pearl and others in order to offer a more comprehensive view of aging.