Modulation of oxidative phosphorylation machinery signifies a prime mode of anti-ageing mechanism of calorie restriction in male rat liver mitochondria

Mechanisms underlying retardation of aging by dietary energy restriction

Moderate restriction of dietary energy intake, referred to here as dietary restriction (DR), delays aging and extends lifespan in experimental animals compared with a diet of ad libitum feeding (AL) control animals. Basic knowledge of the mechanisms underlying the effects of DR could be applicable to extending the healthspan in humans. This review highlights the importance of forkhead box O (FoxO) transcription factors downstream of the growth hormone-insulin-like growth factor 1 signaling in the effects of DR. Our lifespan studies in mice with heterozygous Foxo1 or Foxo3 gene knockout indicated differential roles of FoxO1 and FoxO3 in the tumor-inhibiting and life-extending effects of DR. Subsequent studies suggested a critical role of FoxO3 in metabolic and mitochondrial bioenergetic adaptation to DR. Our studies also verified hypothalamic neuropeptide Y (Npy) as a vital neuropeptide showing pleiotropic and sexually dimorphic effects for extending the healthspan in the context of nutritional availability. Npy was necessary for DR to exert its effects in male and female mice; meanwhile, under AL conditions, the loss of Npy prevented obesity and insulin resistance only in female mice. Overnutrition disrupts FoxO- and Npy-associated metabolic and mitochondrial bioenergetic adaptive processes, causing the acceleration of aging and related diseases.

Native DIGE for Quantitative and Functional Analysis of Protein Interactomes

Protein-protein interactions and multiprotein assemblies of water-soluble and membrane proteins are inherent features of the proteome, which also impart functional heterogeneity. One needs to consider this aspect while studying changes in abundance and activities of proteins in response to any physiological stimulus. Abundance changes in the components of a given proteome can be best visualized and efficiently quantified using electrophoresis-based approaches. Here, we describe the method of Blue Native Difference Gel Electrophoresis to quantify changes in abundance and activity of proteins in the context of protein-protein interactions. This method confers an additional advantage to monitor quantitative changes in membrane proteins, which otherwise is a difficult task.

Nonlinear effects of environmental salinity on the gill transcriptome versus proteome of Oreochromis niloticus modulate epithelial cell turnover

A data-independent acquisition (DIA) assay library for targeted quantitation of thousands of Oreochromis niloticus gill proteins using a label- and gel-free workflow was generated and used to compare protein and mRNA abundances. This approach generated complimentary rather than redundant data for 1899 unique genes in gills of tilapia acclimated to freshwater and brackish water. Functional enrichment analyses identified mitochondrial energy metabolism, serine protease and immunity-related functions, and cytoskeleton/ extracellular matrix organization as major processes controlled by salinity in O. niloticus gills. Non-linearity in salinity-dependent transcriptome versus proteome regulation was revealed for specific functional groups of genes. The relationship was more linear for other molecular functions/ cellular processes, suggesting that the salinity-dependent regulation of O. niloticus gill function relies on post-transcriptional mechanisms for some functions/ processes more than others. This integrative systems biology approach can be adopted for other tissues and organisms to study cellular dynamics for many changing ecological contexts.

Mitochondria and Reactive Oxygen Species in Aging and Age-Related Diseases

Aging has been linked to several degenerative processes that, through the accumulation of molecular and cellular damage, can progressively lead to cell dysfunction and organ failure. Human aging is linked with a higher risk for individuals to develop cancer, neurodegenerative, cardiovascular, and metabolic disorders. The understanding of the molecular basis of aging and associated diseases has been one major challenge of scientific research over the last decades. Mitochondria, the center of oxidative metabolism and principal site of reactive oxygen species (ROS) production, are crucial both in health and in pathogenesis of many diseases. Redox signaling is important for the modulation of cell functions and several studies indicate a dual role for ROS in cell physiology. In fact, high concentrations of ROS are pathogenic and can cause severe damage to cell and organelle membranes, DNA, and proteins. On the other hand, moderate amounts of ROS are essential for the maintenance of several biological processes, including gene expression. In this review, we provide an update regarding the key roles of ROS-mitochondria cross talk in different fundamental physiological or pathological situations accompanying aging and highlighting that mitochondrial ROS may be a decisive target in clinical practice.

Oxygen Concentration and Oxidative Stress Modulate the Influence of Alzheimer's Disease Aβ1-42 Peptide on Human Cells

Reactive oxygen species (ROS) generated after exposure to ionizing radiation and toxic peptides, in mitochondrial metabolism and during aging contribute to damage of cell's structural and functional components and can lead to diseases. Monomers and small oligomers of amyloid beta (Aβ) peptide, players in Alzheimer's disease, are recently suggested to be involved in damaging of neurons, instead of extracellular Aβ plaques. We demonstrate that externally applied disaggregated Aβ_1–42 peptide interacts preferentially with acidic compartments (lysosomes). We compared standard cell cultivation (21% O₂) to more physiological cell cultivation (5% O₂). Cells did not exhibit a dramatic increase in ROS and change in glutathione level upon 4 μM Aβ peptide treatment, whereas exposure to 2 Gy X-rays increased ROS and changed glutathione level and ATP concentration. The occurrence of the 4977 bp deletion in mtDNA and significant protein carbonylation were specific effects of IR and more pronounced at 21% O₂. An increase in cell death after Aβ peptide treatment or irradiation was unexpectedly restored to the control level or below when both were combined, particularly at 5% O₂. Therefore, Aβ peptide at low concentration can trigger neuroprotective mechanisms in cells exposed to radiation. Oxygen concentration is an important modulator of cellular responses to stress.

Native DIGE: Efficient Tool to Elucidate Protein Interactomes

Protein-protein interactions and multi-protein assemblies are inherent features of proteomes, involving soluble and membrane proteins. This imparts structural and functional heterogeneity to the proteome. One needs to consider this aspect while studying changes in abundance or activities of proteins in response to any physiological stimulus. Abundance changes in components of a given proteome can be best visualized and quantified using electrophoresis-based approaches. Here, we describe the method of Blue Native Difference Gel Electrophoresis (BN DIGE) to quantify abundance changes in proteins in the context of protein-protein interactions. This method confers an additional advantage to monitor quantitative changes in membrane proteins, which otherwise is a difficult task.

Native DIGE proteomic analysis of mitochondria from substantia nigra and striatum during neuronal degeneration and its compensation in an animal model of early Parkinson's disease

Cause of Parkinson's disease (PD) is still not understood. Motor symptoms are not observed at early stages of disease due to compensatory processes. Dysfunction of mitochondria was indicated already at preclinical PD. Selective toxin 6-OHDA was applied to kill dopaminergic neurons in substantia nigra and disturb neuronal transmission in striatum. Early phase of active degeneration and later stage, when surviving cells adapted to function normally, were analysed. 2D BN/SDS difference gel electrophoresis (DIGE) of mitochondrial proteome enabled to point out crucial processes involved at both time-points in dopaminergic structures. Marker proteins such as DPYSL2, HSP60, ATP1A3, EAAT2 indicated structural remodelling, cytoskeleton rearrangement, organelle trafficking, axon outgrowth and regeneration. Adaptations in dopaminergic and glutamatergic neurotransmission, recycling of synaptic vesicles, along with enlargement of mitochondria mass were proposed as causative for compensation. Changed expression of carbohydrates metabolism and oxidative phosphorylation proteins were described, including their protein-protein interactions and supercomplex assembly.

Adaptation within mitochondrial oxidative phosphorylation supercomplexes and membrane viscosity during degeneration of dopaminergic neurons in an animal model of early Parkinson's disease

In Parkinson's disease (PD) motor symptoms are not observed until loss of 70% of dopaminergic neurons in substantia nigra (SN), preventing early diagnosis. Mitochondrial dysfunction was indicated in neuropathological process already at early PD stages. Aging and oxidative stress, the main factors in PD pathogenesis, cause membrane stiffening, which could influence functioning of membrane-bound oxidative phosphorylation (OxPhos) complexes (Cxs) in mitochondria. In 6-OHDA rat model, medium-sized dopaminergic lesion was used to study mitochondrial membrane viscosity and changes at the level of OxPhos Cxs and their higher assembled states-supercomplexes (SCxs), during the early degeneration processes and after it. We observed loss of dopaminergic phenotype in SN and decreased dopamine level in striatum (STR) before actual death of neurons in SN. Behavioural deficits induced by lesion were reversed despite progressing neurodegeneration. Along with degeneration process in STR, mitochondrial Cx I performance and amount decreased in almost all forms of SCxs. Also, progressing decrease of Cx IV performance in SCxs (I1III2IV3-1, I1IV2-1) in STR was observed during degeneration. In SN, SCxs containing Cx I increased protein amount and a shifted individual Cx I1 into superassembled states. Importantly, mitochondrial membrane viscosity changed in parallel with altered SCxs performance. We show for the first time changes at the level of mitochondrial membrane viscosity influencing SCxs function after dopaminergic system degeneration. It implicates that altered mitochondrial membrane viscosity could play an important role in regulation of mitochondria functioning and pathomechanisms of PD. The data obtained are also discussed in relation to compensatory processes observed.

Subacute calorie restriction and rapamycin discordantly alter mouse liver proteome homeostasis and reverse aging effects

Calorie restriction (CR) and rapamycin (RP) extend lifespan and improve health across model organisms. Both treatments inhibit mammalian target of rapamycin (mTOR) signaling, a conserved longevity pathway and a key regulator of protein homeostasis, yet their effects on proteome homeostasis are relatively unknown. To comprehensively study the effects of aging, CR, and RP on protein homeostasis, we performed the first simultaneous measurement of mRNA translation, protein turnover, and abundance in livers of young (3 month) and old (25 month) mice subjected to 10-week RP or 40% CR. Protein abundance and turnover were measured in vivo using (2) H3 -leucine heavy isotope labeling followed by LC-MS/MS, and translation was assessed by polysome profiling. We observed 35-60% increased protein half-lives after CR and 15% increased half-lives after RP compared to age-matched controls. Surprisingly, the effects of RP and CR on protein turnover and abundance differed greatly between canonical pathways, with opposite effects in mitochondrial (mt) dysfunction and eIF2 signaling pathways. CR most closely recapitulated the young phenotype in the top pathways. Polysome profiles indicated that CR reduced polysome loading while RP increased polysome loading in young and old mice, suggesting distinct mechanisms of reduced protein synthesis. CR and RP both attenuated protein oxidative damage. Our findings collectively suggest that CR and RP extend lifespan in part through the reduction of protein synthetic burden and damage and a concomitant increase in protein quality. However, these results challenge the notion that RP is a faithful CR mimetic and highlight mechanistic differences between the two interventions.

Upregulation of cytochrome c oxidase subunit 6b1 (Cox6b1) and formation of mitochondrial supercomplexes: implication of Cox6b1 in the effect of calorie restriction

Calorie restriction (CR), a non-genetic intervention that promotes longevity in animals, may exert anti-aging effects by modulating mitochondrial function. Based on our prior mitochondrial proteome analysis, we focused on the potential roles of cytochrome c oxidase (Cox or Complex IV) subunit 6b1 on formation of mitochondrial supercomplexes comprised of Complex I, III, and IV. Blue native polyacrylamide gel electrophoresis followed by immunoblotting showed that the amount of Cox6b1 and the proportion of high molecular weight supercomplexes (SCs) comprised of Complexes I, III, and IV were increased in the liver of mice subjected to 30 % CR, compared with the liver of mice fed ad libitum. In in vitro experiments, in Cox6b1-overexpressing NIH3T3 (Cox6b1-3T3) cells, Cox6b1 was increased in the SC, III2IV1, and III2IV2 complexes and Cox was concomitantly recruited abundantly into the SC, compared with control (Con)-3T3 cells. The proportions of III2IV1, and III2IV2, relative to IV monomer were also increased in Cox6b1-3T3 cells. Cox6b1-3T3 cells showed increased oxygen consumption rates, Cox activity, and intracellular ATP concentrations, indicating enhanced mitochondrial respiration, compared with Con-3T3 cells. Despite the increased basal level of mitochondrial reactive oxygen species (ROS), cell viability after inducing oxidative stress was greater in Cox6b1-3T3 cells than in Con-3T3 cells, probably because of prompt activation of protective mechanisms, such as nuclear translocation of nuclear factor E2-related factor-2. These in vivo and in vitro studies show that Cox6b1 is involved in regulation of mitochondrial function by promoting the formation of SC, suggesting that Cox6b1 contributes to the anti-aging effects of CR.

Arginase I expression is upregulated by dietary restriction in the liver of mice as a function of age

Arginase is a cytosolic enzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. This reaction comprises the final step of the urea cycle, which provides the principal route for the disposal of nitrogenous waste from protein catabolism. The present study investigates the normal endogenous activity and expression level of arginase I as a function of age in the liver of 2-, 6-, and 18-month-old mice. The effect of dietary restriction (DR) on the expression of arginase I was also investigated in two age groups of mice, 2- and 18-month old. Arginase I activity was assessed spectrophotometrically, and the level of arginase I protein was further confirmed by Western blotting analyses. Arginase I mRNA level was measured using real-time PCR. Our results show that the arginase I activity (U/mg protein) and protein level in liver was higher in 2-month-old mice and decreased gradually with age. In contrast, arginase I mRNA was observed to be higher in the older mice as compared to the younger mice. DR was seen to upregulate the arginase I activity and expression in both 2- and 18-month-old mice. The findings concluded that arginase I is down-regulated with the advancement of age in the liver of mice and is upregulated by DR. This suggests that DR plays an important role in maintaining related metabolic processes as a function of age in mice.

Nordihydroguaiaretic Acid Extends the Lifespan of Drosophila and Mice, Increases Mortality-Related Tumors and Hemorrhagic Diathesis, and Alters Energy Homeostasis in Mice

Mesonordihydroguaiaretic acid (NDGA) extends murine lifespan. The studies reported here describe its dose dependence, effects on body weight, toxicity-related clinical chemistries, and mortality-related pathologies. In flies, we characterized its effects on lifespan, food consumption, body weight, and locomotion. B6C3F1 mice were fed AIN-93M diet supplemented with 1.5, 2.5, 3.5, or 4.5g NDGA/kg diet (1.59, 2.65, 3.71 and 4.77mg/kg body weight/day) beginning at 12 months of age. Only the 3.5mg/kg diet produced a highly significant increase in lifespan, as judged by either the Mantel–Cox log-rank test (p = .008) or the Gehan–Breslow–Wilcoxon test (p = .009). NDGA did not alter food intake, but dose-responsively reduced weight, suggesting it decreased the absorption or increased the utilization of calories. NDGA significantly increased the incidence of liver, lung, and thymus tumors, and peritoneal hemorrhagic diathesis found at necropsy. However, clinical chemistries found little evidence for overt toxicity. While NDGA was not overtly toxic at its therapeutic dosage, its association with severe end of life pathologies does not support the idea that NDGA consumption will increase human lifespan or health-span. The less toxic derivatives of NDGA which are under development should be explored as anti-aging therapeutics.

Proteome analysis in the assessment of ageing

Based on demographic trends, the societies in many developed countries are facing an increasing number and proportion of people over the age of 65. The raise in elderly populations along with improved health-care will be concomitant with an increased prevalence of ageing-associated chronic conditions like cardiovascular, renal, and respiratory diseases, arthritis, dementia, and diabetes mellitus. This is expected to pose unprecedented challenges both for individuals and societies and their health care systems. An ultimate goal of ageing research is therefore the understanding of physiological ageing and the achievement of 'healthy' ageing by decreasing age-related pathologies. However, on a molecular level, ageing is a complex multi-mechanistic process whose contributing factors may vary individually, partly overlap with pathological alterations, and are often poorly understood. Proteome analysis potentially allows modelling of these multifactorial processes. This review summarises recent proteomic research on age-related changes identified in animal models and human studies. We combined this information with pathway analysis to identify molecular mechanisms associated with ageing. We identified some molecular pathways that are affected in most or even all organs and others that are organ-specific. However, appropriately powered studies are needed to confirm these findings based in in silico evaluation.

Low abundance of the matrix arm of complex I in mitochondria predicts longevity in mice

Mitochondrial function is an important determinant of the ageing process; however, the mitochondrial properties that enable longevity are not well understood. Here we show that optimal assembly of mitochondrial complex I predicts longevity in mice. Using an unbiased high-coverage high-confidence approach, we demonstrate that electron transport chain proteins, especially the matrix arm subunits of complex I, are decreased in young long-living mice, which is associated with improved complex I assembly, higher complex I-linked state 3 oxygen consumption rates and decreased superoxide production, whereas the opposite is seen in old mice. Disruption of complex I assembly reduces oxidative metabolism with concomitant increase in mitochondrial superoxide production. This is rescued by knockdown of the mitochondrial chaperone, prohibitin. Disrupted complex I assembly causes premature senescence in primary cells. We propose that lower abundance of free catalytic complex I components supports complex I assembly, efficacy of substrate utilization and minimal ROS production, enabling enhanced longevity.

The effects of caloric restriction against ethanol-induced oxidative and nitrosative cardiotoxicity and plasma lipids in rats

Caloric restriction (CR) prevents or delays a wide range of aging-related diseases possibly through alleviation of oxidative stress. The aim of our study was to examine the effect of CR on oxidative and nitrosative cardiac damage in rats, induced by acute ethanol intoxication. Male Wistar rats were divided into following groups: control; calorie-restricted groups with intake of 60-70% (CR60-70) and 40-50% of daily energy needs (CR40-50); ethanol-treated group (E); calorie-restricted, ethanol-treated groups (CR60-70 + E, CR40-50 + E). Ethanol was administered in five doses of 2 g/kg every 12 h, while the duration of CR was five weeks before ethanol treatment. Malondialdehyde level was significantly lower in CR60-70 + E and significantly higher in CR40-50 + E vs. control. Nitrite and nitrate level was significantly higher in CR40-50 + E compared to control group. Activity of total superoxide dismutase (SOD) and its isoenzyme, copper/zinc-SOD (Cu/ZnSOD), was significantly higher in CR60-70 + E and lower in CR40-50 + E vs. control. Activity of manganese-SOD (MnSOD), that is also SOD isoenzyme, was significantly lower in  CR40-50 + E compared to control group. Plasma content of sulfhydryl (SH) groups was significantly higher in CR60-70 group vs. control. Plasma concentration of total cholesterol, triacylglycerol, low-density lipoproteins and high-density lipoproteins was significantly lower in CR60-70 group compared to control values. Food restriction to 60-70% of daily energy needs has a protective effect on acute ethanol-induced oxidative and nitrosative cardiac damage, at least partly due to alleviation of ethanol-induced decrease in SOD activity, while restriction to 40-50% of energy needs aggravates lipid peroxidation and nitrosative stress.

Updating the mitochondrial free radical theory of aging: an integrated view, key aspects, and confounding concepts

An updated version of the mitochondrial free radical theory of aging (MFRTA) and longevity is reviewed. Key aspects of the theory are emphasized. Another main focus concerns common misconceptions that can mislead investigators from other specialties, even to wrongly discard the theory. Those different issues include (i) the main reactive oxygen species (ROS)-generating site in the respiratory chain in relation to aging and longevity: complex I; (ii) the close vicinity or even contact between that site and the mitochondrial DNA, in relation to the lack of local efficacy of antioxidants and to sub-cellular compartmentation; (iii) the relationship between mitochondrial ROS production and oxygen consumption; (iv) recent criticisms on the MFRTA; (v) the widespread assumption that ROS are simple "by-products" of the mitochondrial respiratory chain; (vi) the unnecessary postulation of "vicious cycle" hypotheses of mitochondrial ROS generation which are not central to the free radical theory of aging; and (vii) the role of DNA repair concerning endogenous versus exogenous damage. After considering the large body of data already available, two general characteristics responsible for the high maintenance degree of long-lived animals emerge: (i) a low generation rate of endogenous damage: and (ii) the possession of tissue macromolecules that are highly resistant to oxidative modification.

The effect of calorie restriction on acute ethanol-induced oxidative and nitrosative liver injury in rats

The aim of our study was to examine the effect of calorie restriction (CR) on oxidative and nitrosative liver injury in rats, induced by acute ethanol intoxication. Male Wistar rats were divided into groups: (1) control; (2) calorie-restricted groups with intake of 60-70% (CR60-70) and 40-50% of daily energy needs (CR40-50); (3) ethanol-treated group (E); (4) calorie-restricted, ethanol-treated groups (E+CR60-70 and E+CR40-50). Ethanol was administered in 5 doses of 2g/kg every 12h, and duration of CR was 5 weeks before ethanol treatment. Malondialdehyde and nitrite and nitrate level were significantly lower in E+CR60-70 and higher in E+CR40-50 vs. E group. Liver reduced glutathione content and activity of both superoxide dismutase izoenzymes were significantly higher in E+CR60-70 and lower in E+CR40-50 vs. E group. Oxidative stress may be a potential mechanism of hormetic effects of CR on acute ethanol-induced liver injury.

Comparative analyses of protein complexes by blue native DIGE

Classically, DIGE is carried out on the basis of two-dimensional (2D) IEF/SDS PAGE. This allows comparative analyses of large protein sets. However, 2D IEF/SDS PAGE only poorly resolves hydrophobic proteins and is not compatible with native protein characterizations. Blue native PAGE represents a powerful alternative. Combined with CyDye labeling, blue native DIGE offers several useful applications like quantitative comparison of protein complexes of related protein fractions. Here we present a protocol for fluorophore labeling of native protein fractions for separation by blue native PAGE.

Modest inhibition of the growth hormone axis does not affect mitochondrial reactive oxygen species generation or redox state, unlike calorie restriction

AIM

Modest inhibition of the growth hormone (GH) axis by overexpression of the antisense GH gene in male Wistar rats reduced food intake and body weight, and lengthened the lifespan, even if fed ad libitum (AL). These findings were comparable with those induced by 30% calorie restriction (CR) in wild-type (WT) rats, suggesting importance of the GH signal pathway in the effect of CR. The present study evaluated the effects of GH inhibition and CR on mitochondrial oxidative stress and redox state in the liver.

METHODS

Transgenic and WT rats were fed AL or 30% CR diets from 6weeks of age. Liver tissues were collected at 6 and 24months of age. The mitochondria fraction was prepared from liver tissue homogenates. The total reactive oxygen species (ROS) generation, the protein levels of glutathione (GSH) and oxidized GSH (GSSG), and the superoxide dismutase 2 activity were measured.

RESULTS

The results revealed that CR, but not modest inhibition of GH, decreased mitochondrial ROS generation and increased the mitochondrial GSH redox potential.

CONCLUSION

The present study suggests that CR affects mitochondrial function and redox state through a pathway distinct from GH signaling.

Glucose reduction prevents replicative senescence and increases mitochondrial respiration in human mesenchymal stem cells

The unique self-renewal and multilineage differentiation potential of mesenchymal stem cells (MSCs) make them a promising candidate for cell therapy applications. However, during in vitro expansion of MSCs, replicative senescence may occur and will compromise the quality of the expanded cells. Because calorie restriction has been shown to effectively extend the life span of various organisms, the purpose of this study is to investigate the effect of glucose reduction on MSCs and the coordinated changes in energy utilization. It was found that the frequency of cycling cells was significantly increased, while senescence markers such as β-galactosidase activities and p16(INK4a) expression level were markedly reduced in MSCs under low-glucose culture condition. Quantitative real-time PCR analysis demonstrated the preserved trilineage differentiation potentials of MSCs after low-glucose treatment. Interestingly, the ability of osteogenic lineage commitment was improved, while the ability of adipogenic lineage commitment was delayed in MSCs after glucose reduction. In addition, we observed decreased lactate production, increased electron transport chain complexes expression, and increased oxygen consumption in MSCs after glucose reduction treatment. Increased antioxidant defensive responses were evidenced by increased antioxidant enzymes expression and decreased superoxide production after glucose reduction. Taken together, our findings suggest that MSCs utilize energy more efficiently under restricted glucose treatment and exhibit greater self-renewal and antisenescence abilities, while their differentiation potentials remain unaffected.