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

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.

Effect of time-restricted eating and intermittent fasting on cognitive function and mental health in older adults: A systematic review

Objective

Emerging evidence suggests that dietary interventions hold promise for promoting cognitive function and mental well-being in aging populations. This systematic review aimed to examine the potential relationship between Time-Restricted Eating (TRE) and Intermittent Fasting (IFA) with cognitive function and mental health in older adults.

Methods

A thorough exploration was undertaken on electronic databases such as PubMed, Scopus, Web of Science, Science Direct, and Google Scholar, up to October 2023, following PRISMA standards. The evaluation of the quality and potential bias in the incorporated articles involved the use of the Newcastle-Ottawa Scale and Consolidated Standards of Reporting Trials (CONSORT).

Results

From a total of 539 articles initially identified, eight studies met the eligibility criteria for inclusion in this review. Out of these eight studies, six focused on cognitive function, and 2 focused on mental health. The reviewed articles encompassed a wide range of population sizes, with the number of older adults studied varying from 10 to 1357, reflecting a diverse cohort of individuals. Conclusions.The findings suggest that TRE and IFA may have a positive impact on cognitive function and mental health in this population. However, additional research is needed to fully comprehend this relationship. Therefore, future research should specifically examine factors such as the duration and timing of the eating window in TRE, as well as the physical condition of older adults, to provide a more nuanced understanding of the cognitive and mental health benefits of TRE and IFA in older adults.

Unveiling the interplay of AMPK/SIRT1/PGC-1α axis in brain health: Promising targets against aging and NDDs

The escalating prevalence of neurodegenerative diseases (NDDs) within an aging global population presents a pressing challenge. The multifaceted pathophysiological mechanisms underlying these disorders, including oxidative stress, mitochondrial dysfunction, and neuroinflammation, remain complex and elusive. Among these, the AMPK/SIRT1/PGC-1α pathway emerges as a pivotal network implicated in neuroprotection against these destructive processes. This review sheds light on the potential therapeutic implications of targeting this axis, specifically emphasizing the promising role of flavonoids in mitigating NDD-related complications. Expanding beyond conventional pharmacological approaches, the exploration of non-pharmacological interventions such as exercise and calorie restriction (CR), coupled with the investigation of natural compounds, offers a beacon of hope. By strategically elucidating the intricate connections within these pathways, this review aims to pave the ways for novel multi-target agents and interventions, fostering a renewed optimism in the quest to combat and manage the debilitating impacts of NDDs on global health and well-being.

Intermittent fasting ameliorates neuronal ferroptosis and cognitive impairment in mice after traumatic brain injury

Ferroptosis, a newly characterized form of programmed cell death that results from lipid peroxidation and mitochondrial dysfunction, has been demonstrated to be involved in the pathogenesis of traumatic brain injury (TBI). Scientific evidence has shown that intermittent fasting (IF) reduces both the lipid peroxidation and the mitochondrial dysfunction, raising the question of whether IF affects the ferroptosis induced by TBI. Here, based on an established TBI animal model, we examine the effects of IF on the activation of ferroptosis pathway as well as related outcomes. We uncovered that a 1-mo IF elevated the protective Gpx4 and Hspb1 expression, and partly abolished the increase of Nfe2l2, Slc7a11, Alox8, Steap3, and Nox2 in the cortex, which were induced by TBI. Furthermore, the characteristic cellular damage induced by ferroptosis was alleviated by IF, as revealed by Perls' Prussian blue staining, Nissl staining, and transmission electron microscope examination. Consistently, we examined the outcomes of mice subjected to TBI and found an improved cognitive function of the IF mice. In sum, our study demonstrated, to our knowledge for the first time, that a 1-mo IF regimen partly ameliorates ferroptosis in the cortex of mice subjected to TBI, which potentially contributes to a lessening of cognitive impairment.

Ageing, Metabolic Dysfunction, and the Therapeutic Role of Antioxidants

The gradual ageing of the world population has been accompanied by a dramatic increase in the prevalence of obesity and metabolic diseases, especially type 2 diabetes. The adipose tissue dysfunction associated with ageing and obesity shares many common physiological features, including increased oxidative stress and inflammation. Understanding the mechanisms responsible for adipose tissue dysfunction in obesity may help elucidate the processes that contribute to the metabolic disturbances that occur with ageing. This, in turn, may help identify therapeutic targets for the treatment of obesity and age-related metabolic disorders. Because oxidative stress plays a critical role in these pathological processes, antioxidant dietary interventions could be of therapeutic value for the prevention and/or treatment of age-related diseases and obesity and their complications. In this chapter, we review the molecular and cellular mechanisms by which obesity predisposes individuals to accelerated ageing. Additionally, we critically review the potential of antioxidant dietary interventions to counteract obesity and ageing.

Effect of Tau Protein on Mitochondrial Functions

Alzheimer's disease is the most common age-related progressive neurodegenerative disorder of brain cortex and hippocampus leading to cognitive impairment. Accumulation of extracellular amyloid plaques and intraneuronal neurofibrillary tangles are believed to be the main hallmarks of the disease. Origin of Alzheimer's disease is not totally clear, multiple initiator factors are likely to exist. Intracellular impacts of Alzheimer's disease include mitochondrial dysfunction, oxidative stress, ER-stress, disruption of autophagy, severe metabolic challenges leading to massive neuronal apoptosis. Mitochondria are the key players in all these processes. This formed the basis for the so-called mitochondrial cascade hypothesis. This review provides current data on the molecular mechanisms of the development of Alzheimer's disease associated with mitochondria. Special attention was paid to the interaction between Tau protein and mitochondria, as well as to the promising therapeutic approaches aimed at preventing development of neurodegeneration.

Scientific Evidences of Calorie Restriction and Intermittent Fasting for Neuroprotection in Traumatic Brain Injury Animal Models: A Review of the Literature

It has widely been accepted that food restriction (FR) without malnutrition has multiple health benefits. Various calorie restriction (CR) and intermittent fasting (IF) regimens have recently been reported to exert neuroprotective effects in traumatic brain injury (TBI) through variable mechanisms. However, the evidence connecting CR or IF to neuroprotection in TBI as well as current issues remaining in this research field have yet to be reviewed in literature. The objective of our review was therefore to weigh the evidence that suggests the connection between CR/IF with recovery promotion following TBI. Medline, Google Scholar and Web of Science were searched from inception to 25 February 2022. An overwhelming number of results generated suggest that several types of CR/IF play a promising role in promoting post-TBI recovery. This recovery is believed to be achieved by alleviating mitochondrial dysfunction, promoting hippocampal neurogenesis, inhibiting glial cell responses, shaping neural cell plasticity, as well as targeting apoptosis and autophagy. Further, we represent our views on the current issues and provide thoughts on the future direction of this research field.

Ghrelin mediated hippocampal neurogenesis

The stomach hormone, ghrelin, which is released during food restriction, provides a link between circulating energy state and adaptive brain function. The maintenance of such homeostatic systems is essential for an organism to survive and thrive, and accumulating evidence points to ghrelin being a key regulator of adult hippocampal neurogenesis and memory function. Aberrant neurogenesis is linked to cognitive decline in aging and neurodegeneration. Therefore, identifying endogenous metabolic factors that regulate new adult-born neuron formation is an important objective in understanding the link between nutritional status and CNS function. Here, we review current developments in our understanding of ghrelin's role in regulating neurogenesis and memory function.

Enhanced hepatic respiratory capacity and altered lipid metabolism support metabolic homeostasis during short-term hypoxic stress

BACKGROUND

Tissue hypoxia is a key feature of several endemic hepatic diseases, including alcoholic and non-alcoholic fatty liver disease, and organ failure. Hypoxia imposes a severe metabolic challenge on the liver, potentially disrupting its capacity to carry out essential functions including fuel storage and the integration of lipid metabolism at the whole-body level. Mitochondrial respiratory function is understood to be critical in mediating the hepatic hypoxic response, yet the time-dependent nature of this response and the role of the respiratory chain in this remain unclear.

RESULTS

Here, we report that hepatic respiratory capacity is enhanced following short-term exposure to hypoxia (2 days, 10% O2) and is associated with increased abundance of the respiratory chain supercomplex III2+IV and increased cardiolipin levels. Suppression of this enhanced respiratory capacity, achieved via mild inhibition of mitochondrial complex III, disrupted metabolic homeostasis. Hypoxic exposure for 2 days led to accumulation of plasma and hepatic long chain acyl-carnitines. This was observed alongside depletion of hepatic triacylglycerol species with total chain lengths of 39-53 carbons, containing palmitic, palmitoleic, stearic, and oleic acids, which are associated with de novo lipogenesis. The changes to hepatic respiratory capacity and lipid metabolism following 2 days hypoxic exposure were transient, becoming resolved after 14 days in line with systemic acclimation to hypoxia and elevated circulating haemoglobin concentrations.

CONCLUSIONS

The liver maintains metabolic homeostasis in response to shorter term hypoxic exposure through transient enhancement of respiratory chain capacity and alterations to lipid metabolism. These findings may have implications in understanding and treating hepatic pathologies associated with hypoxia.

Global Proteomic Profile Integrated to Quantitative and Morphometric Assessment of Enteric Neurons: Investigation of the Mechanisms Involved in the Toxicity Induced by Acute Fluoride Exposure in the Duodenum

The enteric nervous system is responsible for controlling the gastrointestinal tract (GIT) functions. Enteric neuropathies are highly correlated to the development of several intestinal disturbances. Fluoride (F) is extensively applied for dental health improvement and its ingestion can promote systemic toxicity with mild to severe GIT symptomatology and neurotoxicity. Although F harmful effects have been published, there is no information regarding noxiousness of a high acute F exposure (25 mg F/kg) on enteric neurons and levels of expression of intestinal proteins in the duodenum. Quantitative proteomics of the duodenum wall associated to morphometric and quantitative analysis of enteric neurons displayed F effects of a high acute exposure. F-induced myenteric neuroplasticity was characterized by a decrease in the density of nitrergic neurons and morphometric alterations in the general populations of neurons, nitrergic neurons, and substance P varicosities. Proteomics demonstrated F-induced alterations in levels of expression of 356 proteins correlated to striated muscle cell differentiation; generation of precursor metabolites and energy; NADH and glutathione metabolic process and purine ribonucleoside triphosphate biosynthesis. The neurochemical role of several intestinal proteins was discussed specially related to the modulation of enteric neuroplasticity. The results provide a new perspective on cell signaling pathways of gastrointestinal symptomatology promoted by acute F toxicity.

Developmental programming: intrauterine caloric restriction promotes upregulation of mitochondrial sirtuin with mild effects on oxidative parameters in the ovaries and testes of offspring

According to the developmental origins of health and disease (DOHaD) hypothesis, changes in the maternal environment are known to reprogram the metabolic response of offspring. Known for its redox modulation, caloric restriction extends the lifespan of some species, which contributes to diminished cellular damage. Little is known about the effects of gestational caloric restriction, in terms of antioxidant parameters and molecular mechanisms of action, on the reproductive organs of offspring. This study assessed the effects of moderate (20%) caloric restriction on redox status parameters, molecular expression of sirtuin (SIRT) 1 and SIRT3 and histopathological markers in the ovaries and testes of adult rats that were subjected to gestational caloric restriction. Although enzyme activity was increased, ovaries from female pups contained high levels of oxidants, whereas testes from male pups had decreased antioxidant enzyme defences, as evidenced by diminished glyoxalase I activity and reduced glutathione content. Expression of SIRT3, a deacetylase enzyme related to cellular bioenergetics, was increased in both ovaries and testes. Previous studies have suggested that, in ovaries, diminished antioxidant metabolism can lead to premature ovarian failure. Unfortunately, there is little information regarding the redox profile in the testis. This study is the first to assess the redox network in both ovaries and testes, suggesting that, although intrauterine caloric restriction improves molecular mechanisms, it has a negative effect on the antioxidant network and redox status of reproductive organs of young adult rats.

Intermittent fasting promotes anxiolytic-like effects unrelated to synaptic mitochondrial function and BDNF support

Anxiety disorders are linked to mitochondrial dysfunction and decreased neurotrophic support. Since anxiolytic drugs target mitochondria, non-pharmacological approaches to improve mitochondrial metabolism such as intermittent fasting (IF) may cause parallel behavioral benefits against anxiety disorders. Here, we investigated whether a chronic IF regimen could induce anxiolytic-like effects concomitantly to modulation in mitochondrial bioenergetics and trophic signaling in mice brain. A total of 44 Male C57BL/6 J mice (180 days old) were assigned to two dietary regimens: a normal, ad libitum diet (AL group) and an alternate-day fasting (IF group), where animals underwent 10 cycles of 24 h food restriction followed by 24 h ad libitum access. Animals underwent the open field test, dark/light box and elevated plus maze tasks. Isolated nerve terminals were obtained from mice brain and used for mitochondrial respirometry, hydrogen peroxide production and assessment of membrane potential dynamics, calcium handling and western blotting. We showed that IF significantly alters total daily food intake and food consumption patterns but not body weight. There were no differences in the exploratory and locomotory parameters. Remarkably, animals from IF showed decreased anxiety-like behavior. Mitochondrial metabolic responses in different coupling states and parameters linked with H₂O₂ production, Ca²⁺ buffering and electric gradient were not different between groups. Finally, no alterations in molecular indicators of apoptotic death (Bax/Bcl-2 ratio) and neuroplasticity (proBDNF/BDNF and synaptophysin were observed). In conclusion, IF exerts anxiolytic-like effect not associated with modulation in synaptic neuronergetics or expression of neurotrophic proteins. These results highlight a potential benefit of intermittent fasting as a nutritional intervention in anxiety-related disorders.

Association between Time Restricted Feeding and Cognitive Status in Older Italian Adults

Background: Due to the increased life expectancy, the prevalence of aging-related health conditions, such as cognitive impairment, dementia and Alzheimer’s disease is increasing. Among the modifiable risk factors, dietary factors have proved to be of primary importance in preserving and improving mental health and cognitive status in older adults, possibly through the modulation of adult neurogenesis, neuronal plasticity and brain signaling. Feeding/fasting timing manipulation has emerged as an innovative strategy to counteract and treat cognitive decline. The aim of this study was to investigate the association between the timing of the feeding period and cognitive status in a cross-sectional cohort of adults living in the Mediterranean area. Methods: Demographic and dietary characteristics of 883 adults living in Southern Italy (Sicily) were analyzed. Food frequency questionnaires were used to calculate the time window between the first and the last meal of an average day. Participants with an eating time window duration of more than 10 h were then identified, as well as those with eating time restricted to less than 10 h (TRF). Results: After adjusting for potential confounding factors, individuals adherent to TRF were less likely to have cognitive impairment, compared to those with no eating time restrictions [odds ratio (OR) = 0.28; 95% confidence intervals (CI): 0.07–0.90]; a similar association was found for individuals having breakfast (OR = 0.37, 95% CI: 0.16–0.89), but not for those having dinner. Conclusions: The results of this study reveal that time restricted eating may be positively associated with cognitive status, and thus exert plausible effects on brain health.

Regulation of neuronal bioenergetics as a therapeutic strategy in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis are a heterogeneous group of debilitating disorders with multifactorial etiologies and pathogeneses that manifest distinct molecular mechanisms and clinical manifestations with abnormal protein dynamics and impaired bioenergetics. Mitochondrial dysfunction is emerging as an important feature in the etiopathogenesis of these age-related neurodegenerative diseases. The prevalence and incidence of these diseases is on the rise with the increasing global population and average lifespan. Although many therapeutic approaches have been tested, there are currently no effective treatment routes for the prevention or cure of these diseases. We present the current status of our knowledge and understanding of the involvement of mitochondrial dysfunction in these diseases and highlight recent advances in novel therapeutic strategies targeting neuronal bioenergetics as potential approach for treating these diseases.

Lifespan-extending interventions enhance lipid-supported mitochondrial respiration in Caenorhabditis elegans

Dietary restriction and reduced reproduction have been linked to long lifespans in the vast majority of species tested. Although decreased mitochondrial mass and/or function are hallmarks of aging, little is known about the mechanisms by which these organelles contribute to physiological aging or to the effects of lifespan-extending interventions, particularly with respect to oxidative phosphorylation and energy production. Here, we employed the nematode Caenorhabditis elegans to examine the effects of inhibition of germline proliferation and dietary restriction, both of which extend the lifespan of C. elegans, on mitochondrial respiratory activity in whole animals and isolated organelles. We found that oxygen consumption rates and mitochondrial mass were reduced in wild-type (WT) C. elegans subjected to bacterial deprivation (BD) compared with animals fed ad libitum (AL). In contrast, BD decreased the rate of oxygen uptake but not mitochondrial mass in germline-less glp-1(e2144ts) mutants. Interestingly, mitochondria isolated from animals subjected to BD and/or inhibition of germline proliferation showed no differences in complex I-mediated respiratory activity compared to control mitochondria, whereas both interventions enhanced the efficiency with which mitochondria utilized lipids as respiratory substrates. Notably, the combination of BD and inhibition of germline proliferation further increased mitochondrial lipid oxidation compared to either intervention alone. We also detected a striking correlation between lifespan extension in response to BD and/or inhibition of germline proliferation and the capacity of C. elegans to generate ATP from lipids. Our results thus suggest that the ability to oxidize lipids may be determinant in enhanced longevity.

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.

Supplementation with a putative calorie restriction mimetic micronutrient blend increases glutathione concentrations and improves neuroenergetics in brain of healthy middle-aged men and women

BACKGROUND

Caloric restriction (CR) without micronutrient deficiency has been shown to increase both lifespan and healthspan. In animals, CR has been demonstrated to increase glutathione (GSH), a neuroprotective antioxidant, in the brain and preserve brain mitochondrial function by altering neuroenergetics. In humans it has been associated with improvements in mood states and cognitive function. However, most CR studies have employed a 30-60% reduction in calories which is likely too stringent for most people to adhere to long-term. Thus, there is an unmet need for nutritional supplements which can mimic the biological effects of CR, without the need for calorie limitations.

AIM

The purpose of the present randomized, placebo-controlled clinical trial was to use Proton (¹H) Magnetic Resonance Spectroscopic (MRS) measurements to determine non-invasively whether a blend of micronutrients, a putative CR mimetic, positively modulates metabolites related to neuroprotection and neuroenergetics in the brain.

METHODS

Healthy middle-aged men and women (N = 63 [33 women]; age: 40-60 years) were randomized in a double-blind manner to 6 weeks supplementation with either the putative CR mimetic or placebo. At baseline and 6 weeks, subjects underwent MRS at 3 T to investigate changes in brain chemistry, including the neurometabolites: GSH, Glutamate (Glu), Glutamine (Gln) and N-Acetylaspartate (NAA).

RESULTS

GSH, a marker of antioxidant and cellular redox status, increased in the brain of participants in the supplement group. The supplement group also showed an increase in the Glu/Gln ratio, a marker of excitatory neurotransmission and bioenergetics. A trend for an increase in NAA/H₂O, a marker of neuronal integrity, was observed in females in the supplement group.

CONCLUSIONS

The present study reveals that 6-weeks daily supplementation with a micronutrient blend elicits positive changes in brain neurochemistry. This is the first study to demonstrate that a putative CR mimetic increases brain GSH concentrations and improves neuroprotection and neuroenergetics in the brain of healthy humans. This study was registered at www.clinicaltrials.gov as NCT02439983.

Lipase-like 5 enzyme controls mitochondrial activity in response to starvation in Caenorhabditis elegans

The C. elegans lipase-like 5 (lipl-5) gene is predicted to code for a lipase homologous to the human gastric acid lipase. Its expression was previously shown to be modulated by nutritional or immune cues, but nothing is known about its impact on the lipid landscape and ensuing functional consequences. In the present work, we used mutants lacking LIPL-5 protein and found that lipl-5 is important for normal lipidome composition as well as its remodeling in response to food deprivation. Particularly, lipids with signaling functions such as ceramides and mitochondrial lipids were affected by lipl-5 silencing. In comparison with wild type worms, animals lacking LIPL-5 were enriched in cardiolipins linked to polyunsaturated C20 fatty acids and coenzyme Q-9. Differences in mitochondrial lipid composition were accompanied by differences in mitochondrial activity as mitochondria from well-fed lipl-5 mutants were significantly more able to oxidize respiratory substrates when compared with mitochondria from well-fed wild type worms. Strikingly, starvation elicited important changes in mitochondrial activity in wild type worms, but not in lipl-5 worms. This indicates that this lipase is a determinant of mitochondrial functional remodeling in response to food withdrawal.

Aging, lifestyle and dementia

Aging is the greatest risk factor for most diseases including cancer, cardiovascular disorders, and neurodegenerative disease. There is emerging evidence that interventions that improve metabolic health with aging may also be effective for brain health. The most robust interventions are non-pharmacological and include limiting calorie or protein intake, increasing aerobic exercise, or environmental enrichment. In humans, dietary patterns including the Mediterranean, Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) and Okinawan diets are associated with improved age-related health and may reduce neurodegenerative disease including dementia. Rapamycin, metformin and resveratrol act on nutrient sensing pathways that improve cardiometabolic health and decrease the risk for age-associated disease. There is some evidence that they may reduce the risk for dementia in rodents. There is a growing recognition that improving metabolic function may be an effective way to optimize brain health during aging.

p66Shc Inactivation Modifies RNS Production, Regulates Sirt3 Activity, and Improves Mitochondrial Homeostasis, Delaying the Aging Process in Mouse Brain

Programmed and damage aging theories have traditionally been conceived as stand-alone schools of thought. However, the p66Shc adaptor protein has demonstrated that aging-regulating genes and reactive oxygen species (ROS) are closely interconnected, since its absence modifies metabolic homeostasis by providing oxidative stress resistance and promoting longevity. p66Shc(-/-) mice are a unique opportunity to further comprehend the bidirectional relationship between redox homeostasis and the imbalance of mitochondrial biogenesis and dynamics during aging. This study shows that brain mitochondria of p66Shc(-/-) aged mice exhibit a reduced alteration of redox balance with a decrease in both ROS generation and its detoxification activity. We also demonstrate a strong link between reactive nitrogen species (RNS) and mitochondrial function, morphology, and biogenesis, where low levels of ONOO- formation present in aged p66Shc(-/-) mouse brain prevent protein nitration, delaying the loss of biological functions characteristic of the aging process. Sirt3 modulates age-associated mitochondrial biology and function via lysine deacetylation of target proteins, and we show that its regulation depends on its nitration status and is benefited by the improved NAD+/NADH ratio in aged p66Shc(-/-) brain mitochondria. Low levels of protein nitration and acetylation could cause the metabolic homeostasis maintenance observed during aging in this group, thus increasing its lifespan.

Modulation of mitochondrial bioenergetics as a therapeutic strategy in Alzheimer's disease

Alzheimer's disease (AD) is an increasingly pressing worldwide public-health, social, political and economic concern. Despite significant investment in multiple traditional therapeutic strategies that have achieved success in preclinical models addressing the pathological hallmarks of the disease, these efforts have not translated into any effective disease-modifying therapies. This could be because interventions are being tested too late in the disease process. While existing therapies provide symptomatic and clinical benefit, they do not fully address the molecular abnormalities that occur in AD neurons. The pathophysiology of AD is complex; mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress are antecedent and potentially play a causal role in the disease pathogenesis. Dysfunctional mitochondria accumulate from the combination of impaired mitophagy, which can also induce injurious inflammatory responses, and inadequate neuronal mitochondrial biogenesis. Altering the metabolic capacity of the brain by modulating/potentiating its mitochondrial bioenergetics may be a strategy for disease prevention and treatment. We present insights into the mechanisms of mitochondrial dysfunction in AD brain as well as an overview of emerging treatments with the potential to prevent, delay or reverse the neurodegenerative process by targeting mitochondria.

Ghrelin mediated neuroprotection - A possible therapy for Parkinson's disease?

Parkinson's disease is a common age-related neurodegenerative disorder affecting 10 million people worldwide, but the mechanisms underlying its pathogenesis are still unclear. The disease is characterised by dopamine nerve cell loss in the mid-brain and intra-cellular accumulation of α-synuclein that results in motor and non-motor dysfunction. In this review, we discuss the neuroprotective effects of the stomach hormone, ghrelin, in models of Parkinson's disease. Recent findings suggest that it may modulate mitochondrial function and autophagic clearance of impaired organelle in response to changes in cellular energy balance. We consider the putative cellular mechanisms underlying ghrelin-action and the possible role of ghrelin mimetics in slowing or preventing Parkinson's disease progression. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Fat-specific Dicer deficiency accelerates aging and mitigates several effects of dietary restriction in mice

Aging increases the risk of type 2 diabetes, and this can be prevented by dietary restriction (DR). We have previously shown that DR inhibits the downregulation of miRNAs and their processing enzymes - mainly Dicer - that occurs with aging in mouse white adipose tissue (WAT). Here we used fat-specific Dicer knockout mice (AdicerKO) to understand the contributions of adipose tissue Dicer to the metabolic effects of aging and DR. Metabolomic data uncovered a clear distinction between the serum metabolite profiles of Lox control and AdicerKO mice, with a notable elevation of branched-chain amino acids (BCAA) in AdicerKO. These profiles were associated with reduced oxidative metabolism and increased lactate in WAT of AdicerKO mice and were accompanied by structural and functional changes in mitochondria, particularly under DR. AdicerKO mice displayed increased mTORC1 activation in WAT and skeletal muscle, where Dicer expression is not affected. This was accompanied by accelerated age-associated insulin resistance and premature mortality. Moreover, DR-induced insulin sensitivity was abrogated in AdicerKO mice. This was reverted by rapamycin injection, demonstrating that insulin resistance in AdicerKO mice is caused by mTORC1 hyperactivation. Our study evidences a DR-modulated role for WAT Dicer in controlling metabolism and insulin resistance.

Less is more: Caloric regulation of neurogenesis and adult brain function

Calorie intake is essential for regulating normal physiological processes and is fundamental to maintaining life. Indeed, both extremes of calorie intake result in increased morbidity and mortality. In this review, we discuss the effect of calorie intake on adult brain function, with an emphasis on the beneficial effects of mild calorie restriction. Recent findings relating to the regenerative and protective effects of the gastrointestinal hormone, ghrelin, suggest that it may underlie the beneficial effects of calorie restriction. We discuss the putative cellular mechanisms underlying the action of ghrelin and their possible role in supporting healthy brain ageing.

Symbiotic Origin of Aging

Normally aging cells are characterized by an unbalanced mitochondrial dynamic skewed toward punctate mitochondria. Genetic and pharmacological manipulation of mitochondrial fission/fusion cycles can contribute to both accelerated and decelerated cellular or organismal aging. In this work, we connect these experimental data with the symbiotic theory of mitochondrial origin to generate new insight into the evolutionary origin of aging. Mitochondria originated from autotrophic α-proteobacteria during an ancient endosymbiotic event early in eukaryote evolution. To expand beyond individual host cells, dividing α-proteobacteria initiated host cell lysis; apoptosis is a product of this original symbiont cell lytic exit program. Over the course of evolution, the host eukaryotic cell attenuated the harmful effect of symbiotic proto-mitochondria, and modern mitochondria are now functionally interdependent with eukaryotic cells; they retain their own circular genomes and independent replication timing. In nondividing differentiated or multipotent eukaryotic cells, intracellular mitochondria undergo repeated fission/fusion cycles, favoring fission as organisms age. The discordance between cellular quiescence and mitochondrial proliferation generates intracellular stress, eventually leading to a gradual decline in host cell performance and age-related pathology. Hence, aging evolved from a conflict between maintenance of a quiescent, nonproliferative state and the evolutionarily conserved propagation program driving the life cycle of former symbiotic organisms: mitochondria.

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.

PPAR mRNA Levels Are Modified by Dietary n-3 Fatty Acid Restriction and Energy Restriction in the Brain and Liver of Growing Rats

BACKGROUND

Without dietary sources of n-3 (ω-3) long-chain polyunsaturated fatty acids (LCPUFAs), α-linolenic acid (ALA; 18:3n-3) is the precursor for docosahexaenoic acid (DHA; 22:6n-3). It is not known how energy restriction (ER) affects ALA conversion to DHA.

OBJECTIVE

We tested the hypothesis that ER reduces n-3 LCPUFA concentrations in tissues of growing rats fed diets replete with and deficient in ALA.

METHODS

Male Sprague-Dawley rats (23 d old) were provided AIN93G diets (4 wk) made with soybean oil (SO; ALA sufficient) or corn oil (CO; ALA deficient) providing 16% of energy as fat. For each dietary oil, ER rats were individually pair-fed 75% of another rat's ad libitum (AL) intake. Fatty acid (FA) concentrations in brain regions, liver, and plasma were analyzed. Expression of peroxisome proliferator-activated receptors (PPARs), uncoupling proteins (UCPs), and mitochondrial DNA was analyzed in the brain and liver.

RESULTS

AL rats consuming CO had a 65% lower concentration of n-3 docosapentaenoic acid (22:5n-3) and a 10% lower DHA concentration in the cerebral cortex and cerebellum than did the SO-AL group. ER did not alter cerebral n-3 LCPUFA status. Liver n-3 LCPUFA concentrations were reduced in rats fed CO compared with SO. ER reduced hepatic linoleic acid (18:2n-6), ALA, and arachidonic acid (20:4n-6) regardless of oil. ER and n-3 FA deficiency had independent effects on the mRNA levels of Pparα, Pparβ/δ, and Pparγ in the liver, cerebral cortex, and cerebellum. ER reduced Ucp3 mRNA by nearly 50% in the cerebral cortex, cerebellum, and liver, and Ucp5 mRNA was 30% lower in the cerebellum of rats receiving the CO diet.

CONCLUSIONS

Small perturbations in PUFA concentration and ER modify the mRNA levels of Ppar and Ucp in the juvenile rat brain. More research is needed to identify the long-term physiologic and behavioral impacts of ER and PUFA restriction in the juvenile brain.

Contribution of mitochondrial oxidative stress to hypertension

PURPOSE OF REVIEW

In 1954 Harman proposed the free radical theory of aging, and in 1972 he suggested that mitochondria are both the source and the victim of toxic free radicals. Interestingly, hypertension is an age-associated disease and clinical data show that by age 70, 70% of the population has hypertension and this is accompanied by oxidative stress. Antioxidant therapy, however, is not currently available and common antioxidants such as ascorbate and vitamin E are ineffective in preventing hypertension. The present review focuses on the molecular mechanisms of mitochondrial oxidative stress and the therapeutic potential of targeting mitochondria in hypertension.

RECENT FINDINGS

Over the past several years, we have shown that the mitochondria become dysfunctional in hypertension and have defined a novel role of mitochondrial superoxide radicals in this disease. We have shown that genetic manipulation of mitochondrial antioxidant enzyme superoxide dismutase affects blood pressure, and have developed mitochondria-targeted therapies such as mitochondrial superoxide dismutase mimetics that effectively lower blood pressure. However, the specific mechanism of mitochondrial oxidative stress in hypertension remains unclear. Recent animal and clinical studies have demonstrated several hormonal, metabolic, inflammatory, and environmental pathways contributing to mitochondrial dysfunction and oxidative stress.

SUMMARY

Nutritional supplements, calorie restriction, and life style change are the most effective preventive strategies to improve mitochondrial function and reduce mitochondrial oxidative stress. Aging associated mitochondrial dysfunction, however, reduces the efficacy of these strategies. Therefore, we propose that new classes of mitochondria-targeted antioxidants can provide a high therapeutic potential to improve endothelial function and reduce hypertension.

Nutritional strategies to optimise cognitive function in the aging brain

Old age is the greatest risk factor for most neurodegenerative diseases. During recent decades there have been major advances in understanding the biology of aging, and the development of nutritional interventions that delay aging including calorie restriction (CR) and intermittent fasting (IF), and chemicals that influence pathways linking nutrition and aging processes. CR influences brain aging in many animal models and recent findings suggest that dietary interventions can influence brain health and dementia in older humans. The role of individual macronutrients in brain aging also has been studied, with conflicting results about the effects of dietary protein and carbohydrates. A new approach known as the Geometric Framework (GF) has been used to unravel the complex interactions between macronutrients (protein, fat, and carbohydrate) and total energy on outcomes such as aging. These studies have shown that low-protein, high-carbohydrate (LPHC) diets are optimal for lifespan in ad libitum fed animals, while total calories have minimal effect once macronutrients are taken into account. One of the primary purposes of this review is to explore the notion that macronutrients may have a more translational potential than CR and IF in humans, and therefore there is a pressing need to use GF to study the impact of diet on brain aging. Furthermore, given the growing recognition of the role of aging biology in dementia, such studies might provide a new approach for dietary interventions for optimizing brain health and preventing dementia in older people.

Diluted serum from calorie-restricted animals promotes mitochondrial β-cell adaptations and protect against glucolipotoxicity

β-cells quickly adjust insulin secretion to oscillations in nutrients carried by the blood, acting as fuel sensors. However, most studies of β-cell responses to nutrients do not discriminate between fuel levels and signaling components present in the circulation. Here we studied the effect of serum from calorie-restricted rats versus serum from rats fed ad libitum, diluted tenfold in the medium, which did not contribute significantly to the pool of nutrients, on β-cell mitochondrial function and dynamics under regular and high-nutrient culture conditions. Insulin secreting beta-cell derived line (INS1) cells incubated with serum from calorie-restricted rats (CR serum) showed higher levels of peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) and active nitric oxide synthase. The expression of mitofusin-2 (Mfn-2) and optic atrophy 1 (OPA-1), proteins involved in mitochondrial fusion, was increased, while the levels of the mitochondrial fission mediator dynamin related protein 1 (DRP-1) were reduced. Consistent with changes in mitochondrial dynamics protein levels, CR serum treatment increased mitochondrial fusion rates, as well as their length and connectivity. These changes in mitochondrial morphology were associated with prolonged glucose-stimulated insulin secretion and mitochondrial respiration. When combining CR serum and high levels of glucose and palmitate (20 and 0.4 mm, respectively), an in vitro model of type II diabetes, we observed that signaling promoted by CR serum was enough to overcome glucolipotoxicity, as indicated by CR-mediated prevention of mitochondrial fusion arrest and reduced respiratory function in INS1 cells under glucolipotoxicity. Overall, our results provide evidence that non-nutrient factors in serum have a major impact on β-cell mitochondrial adaptations to changes in metabolism.

Regional metabolic heterogeneity of the hippocampus is nonuniformly impacted by age and caloric restriction

The hippocampus is critical for cognition and memory formation and is vulnerable to age‐related atrophy and loss of function. These phenotypes are attenuated by caloric restriction (CR), a dietary intervention that delays aging. Here, we show significant regional effects in hippocampal energy metabolism that are responsive to age and CR, implicating metabolic pathways in neuronal protection. In situ mitochondrial cytochrome c oxidase activity was region specific and lower in aged mice, and the impact of age was region specific. Multiphoton laser scanning microscopy revealed region‐ and age‐specific differences in nicotinamide adenine dinucleotide (NAD)‐derived metabolic cofactors. Age‐related changes in metabolic parameters were temporally separated, with early and late events in the metabolic response to age. There was a significant regional impact of age to lower levels of PGC‐1α, a master mitochondrial regulator. Rather than reversing the impact of age, CR induced a distinct metabolic state with decreased cytochrome c oxidase activity and increased levels of NAD(P)H. Levels of hippocampal PGC‐1α were lower with CR, as were levels of GSK3β, a key regulator of PGC‐1α turnover and activity. Regional distribution and colocalization of PGC‐1α and GSK3β in mouse hippocampus was similar in monkeys. Furthermore, the impact of CR to lower levels of both PGC‐1α and GSK3β was also conserved. The studies presented here establish the hippocampus as a highly varied metabolic environment, reveal cell‐type and regional specificity in the metabolic response to age and delayed aging by CR, and suggest that PGC‐1α and GSK3β play a role in implementing the neuroprotective program induced by CR.

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.

Calorie restriction does not restore brain mitochondrial function in P301L tau mice, but it does decrease mitochondrial F0F1-ATPase activity

Calorie restriction (CR) has been shown to increase lifespan and delay aging phenotypes in many diverse eukaryotic species. In mouse models of Alzheimer's disease (AD), CR has been shown to decrease amyloid-beta and hyperphosphorylated tau levels and preserve cognitive function. Overexpression of human mutant tau protein has been shown to induce deficits in mitochondrial electron transport chain complex I activity. Therefore, experiments were performed to determine the effects of 4-month CR on brain mitochondrial function in Tg4510 mice, which express human P301L tau. Expression of mutant tau led to decreased ADP-stimulated respiratory rates, but not uncoupler-stimulated respiratory rates. The membrane potential was also slightly higher in mitochondria from the P301L tau mice. As shown previously, tau expression decreased mitochondrial complex I activity. The decreased complex I activity, decreased ADP-stimulated respiratory rate, and increased mitochondrial membrane potential occurring in mitochondria from Tg4510 mice were not restored by CR. However, the CR diet did result in a genotype independent decrease in mitochondrial F0F1-ATPase activity. This decrease in F0F1-ATPase activity was not due to lowered levels of the alpha or beta subunits of F0F1-ATPase. The possible mechanisms through which CR reduces the F0F1-ATPase activity in brain mitochondria are discussed.

RTG1- and RTG2-dependent retrograde signaling controls mitochondrial activity and stress resistance in Saccharomyces cerevisiae

Mitochondrial retrograde signaling is a communication pathway between the mitochondrion and the nucleus that regulates the expression of a subset of nuclear genes that codify mitochondrial proteins, mediating cell response to mitochondrial dysfunction. In Saccharomyces cerevisiae, the pathway depends on Rtg1p and Rtg3p, which together form the transcription factor that regulates gene expression, and Rtg2p, an activator of the pathway. Here, we provide novel studies aimed at assessing the functional impact of the lack of RTG-dependent signaling on mitochondrial activity. We show that mutants defective in RTG-dependent retrograde signaling present higher oxygen consumption and reduced hydrogen peroxide release in the stationary phase compared to wild-type cells. Interestingly, RTG mutants are less able to decompose hydrogen peroxide or maintain viability when challenged with hydrogen peroxide. Overall, our results indicate that RTG signaling is involved in the hormetic induction of antioxidant defenses and stress resistance.

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.

Metabolic disturbances in diseases with neurological involvement

Degeneration of specific neuronal populations and progressive nervous system dysfunction characterize neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. These findings are also reported in inherited diseases such as phenylketonuria and glutaric aciduria type I. The involvement of mitochondrial dysfunction in these diseases was reported, elicited by genetic alterations, exogenous toxins or buildup of toxic metabolites. In this review we shall discuss some metabolic alterations related to the pathophysiology of diseases with neurological involvement and aging process. These findings may help identifying early disease biomarkers and lead to more effective therapies to improve the quality of life of the patients affected by these devastating illnesses.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

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.

Dietary restriction in cerebral bioenergetics and redox state

The brain has a central role in the regulation of energy stability of the organism. It is the organ with the highest energetic demands, the most susceptible to energy deficits, and is responsible for coordinating behavioral and physiological responses related to food foraging and intake. Dietary interventions have been shown to be a very effective means to extend lifespan and delay the appearance of age-related pathological conditions, notably those associated with brain functional decline. The present review focuses on the effects of these interventions on brain metabolism and cerebral redox state, and summarizes the current literature dealing with dietary interventions on brain pathology.

Brain response to calorie restriction

Calorie restriction extends longevity and delays ageing in model organisms and mammals, opposing the onset and progression of an array of age-related diseases. These beneficial effects also extend to the maintenance of brain cognitive functions at later age and to the prevention, at least in rodents, of brain senescence and associated neurodegenerative disorders. In recent years, the molecular mechanisms underlying brain response to calorie restriction have begun to be elucidated, revealing the unanticipated role of a number of key nutrient sensors and nutrient-triggered signaling cascades in the translation of metabolic cues into cellular and molecular events that ultimately lead to increased cell resistance to stress, enhanced synaptic plasticity, and improved cognitive performance. Of note, the brain's role in CR also includes the activation of nutrient-sensitive hypothalamic circuitries and the implementation of neuroendocrine responses that impact the entire organism. The present review addresses emerging molecular themes in brain response to dietary restriction, and the implications of this knowledge for the understanding and the prevention of brain disorders associated with ageing and metabolic disease.

Hormesis in aging and neurodegeneration-a prodigy awaiting dissection

Hormesis describes the drug action of low dose stimulation and high dose inhibition. The hormesis phenomenon has been observed in a wide range of biological systems. Although known in its descriptive context, the underlying mode-of-action of hormesis is largely unexplored. Recently, the hormesis concept has been receiving increasing attention in the field of aging research. It has been proposed that within a certain concentration window, reactive oxygen species (ROS) or reactive nitrogen species (RNS) could act as major mediators of anti-aging and neuroprotective processes. Such hormetic phenomena could have potential therapeutic applications, if properly employed. Here, we review the current theories of hormetic phenomena in regard to aging and neurodegeneration, with the focus on its underlying mechanism. Facilitated by a simple mathematical model, we show for the first time that ROS-mediated hormesis can be explained by the addition of different biomolecular reactions including oxidative damage, MAPK signaling and autophagy stimulation. Due to their divergent scales, the optimal hormetic window is sensitive to each kinetic parameter, which may vary between individuals. Therefore, therapeutic utilization of hormesis requires quantitative characterizations in order to access the optimal hormetic window for each individual. This calls for a personalized medicine approach for a longer human healthspan.

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.

Facts and controversies in our understanding of how caloric restriction impacts the mitochondrion

Caloric restriction (CR) has pronounced benefits in promoting healthy aging. Amongst the most frequently implicated physiological mechanisms implicated in this benefit is altered mitochondrial function. Whereas a reduction in mitochondrial reactive oxygen species (ROS) production is a widely consistent effect of CR, an increase in mitochondrial biogenesis, which is accepted by many as fact, is contradicted on several levels, most critically by a lack of increase in mitochondrial protein synthesis rate in vivo. Furthermore, an increase in PGC-1α protein and markers of mitochondrial content with CR is a highly variable observation between studies. On the other hand, deacetylation of several mitochondrial proteins by the sirtuin, Sirt3, is an increasingly reported observation and at least so far, this observation is consistent between studies. Notwithstanding this point, the controversies evident in the published literature underscore the significant questions that remain in our understanding of how CR impacts the mitochondrion and suggest we have yet to fully understand the complexities herein.

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.

Is There a Link between Mitochondrial Reserve Respiratory Capacity and Aging?

Oxidative phosphorylation is an indispensable resource of ATP in tissues with high requirement of energy. If the ATP demand is not met, studies suggest that this will lead to senescence and cell death in the affected tissue. The term reserve respiratory capacity or spare respiratory capacity is used to describe the amount of extra ATP that can be produced by oxidative phosphorylation in case of a sudden increase in energy demand. Depletion of the reserve respiratory capacity has been related to a range of pathologies affecting high energy requiring tissues. During aging of an organism, and as a result of mitochondrial dysfunctions, the efficiency of oxidative phosphorylation declines. Based on examples from the energy requiring tissues such as brain, heart, and skeletal muscle, we propose that the age-related decline of oxidative phosphorylation decreases the reserve respiratory capacity of the affected tissue, sensitizes the cells to surges in ATP demand, and increases the risk of resulting pathologies.