Making heads or tails of mitochondrial membranes in longevity and aging: a role for comparative studies

Lipid-mediated ex vivo cell surface engineering for augmented cellular functionalities

Once administrated, intercellular adhesion to recognize and/or arrest target cells is essential for specific treatments, especially for cancer or tumor. However, immune cells administrated into the tumor-microenvironment could lose their intrinsic functionalities such as target recognition ability, resulting in an ineffective cancer immunotherapy. Various manipulation techniques for decorating functional moieties onto cell surface and enhancing target recognition have been developed. A hydrophobic interaction-mediated ex-vivo cell surface engineering using lipid-based biomaterials could be a state-of-the-art engineering technique that could achieve high-efficiency cell surface modification by a single method without disturbance of intrinsic characteristics of cells. In this regard, this review provides design principles for the development of lipid-based biomaterials with a linear structure of lipid, polyethylene glycol, and functional group, strategies for the synthesis process, and their practical applications in biomedical engineering. Especially, we provide new insights into the development of a novel surface coating techniques for natural killer (NK) cells with engineering decoration of cancer targeting moieties on their cell surfaces. Among immune cells, NK cells are interesting cell population for substituting T cells because of their excellent safety and independent anticancer efficacy. Thus, optimal strategies to select cancer-type-specific targeting moieties and present them onto the surface of immune cells (especially, NK cells) using lipid-based biomaterials could provide additional tools to capture cancer cells for developing novel immune cell therapy products. Enhanced anticancer efficacies by surface-engineered NK cells have been demonstrated both in vitro and in vivo. Therefore, it could be speculated that recent progresses in cell surface modification technology via lipid-based biomaterials could strengthen immune surveillance and immune synapses for utilization in a next-generation cancer immunotherapy, beyond currently available genetic engineering tool such as chimeric antigen receptor-mediated immune cell modulation.

Deciphering therapeutic options for neurodegenerative diseases: insights from SIRT1

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD +)-dependent protein deacetylase that exerts biological effects through nucleoplasmic transfer. Recent studies have highlighted that SIRT1 deacetylates protein substrates to exert its neuroprotective effects, including decreased oxidative stress and inflammatory, increases autophagy, increases levels of nerve growth factors (correlated with behavioral changes), and maintains neural integrity (affects neuronal development and function) in aging or neurological disorder. In this review, we highlight the molecular mechanisms underlying the protective role of SIRT1 in modulating neurodegeneration, focusing on protein homeostasis, aging-related signaling pathways, neurogenesis, and synaptic plasticity. Meanwhile, the potential of targeting SIRT1 to block the occurrence and progression of neurodegenerative diseases is also discussed. Taken together, this review provides an up-to-date evaluation of our current understanding of the neuroprotective mechanisms of SIRT1 and also be involved in the potential therapeutic opportunities of AD and related neurodegenerative diseases.

Invited review: Thermal effects on oxidative stress in vertebrate ectotherms

Human-induced climate change is occurring rapidly. Ectothermic organisms are particularly vulnerable to these temperature changes due to their reliance on environmental temperature. The extent of ectothermic thermal adaptation and plasticity in the literature is well documented; however, the role of oxidative stress in these processes needs more attention. Oxidative stress occurs when reactive oxygen species, generated mainly through aerobic respiration, overwhelm antioxidant defences and damage crucial biomolecules. The effects of oxidative damage include the alteration of life-history traits and reductions in whole-organism fitness. Here we review the literature addressing experimental temperature effects on oxidative stress in vertebrate ectotherms. Acute and acclimation temperature treatments produce distinctly different results and highlight the role of phylogeny and thermal adaptation in shaping oxidative stress responses. Acute treatments on organisms adapted to stable environments generally produced significant oxidative stress responses, whilst organisms adapted to variable conditions exhibited capacity to cope with temperature changes and mitigate oxidative stress. In acclimation treatments, the temperature treatments higher than optimal temperatures tended to produce significantly less oxidative stress than lower temperatures in reptiles, whilst in some eurythermal fish species, no oxidative stress response was observed. These results highlight the importance of phylogeny and adaptation to past environmental conditions for temperature-dependent oxidative stress responses. We conclude with recommendations on experimental procedures to investigate these phenomena with reference to thermal plasticity, adaptation and biogeographic variation that provide the most significant benefits to adaptable populations. These results have potential conservation ramifications as they may shed light on the physiological effects of temperature alterations in some vertebrate ectotherms.

No Evidence for Trade-Offs Between Lifespan, Fecundity, and Basal Metabolic Rate Mediated by Liver Fatty Acid Composition in Birds

The fatty acid composition of biological membranes has been hypothesised to be a key molecular adaptation associated with the evolution of metabolic rates, ageing, and life span – the basis of the membrane pacemaker hypothesis (MPH). MPH proposes that highly unsaturated membranes enhance cellular metabolic processes while being more prone to oxidative damage, thereby increasing the rates of metabolism and ageing. MPH could, therefore, provide a mechanistic explanation for trade-offs between longevity, fecundity, and metabolic rates, predicting that short-lived species with fast metabolic rates and higher fecundity would have greater levels of membrane unsaturation. However, previous comparative studies testing MPH provide mixed evidence regarding the direction of covariation between fatty acid unsaturation and life span or metabolic rate. Moreover, some empirical studies suggest that an n-3/n-6 PUFA ratio or the fatty acid chain length, rather than the overall unsaturation, could be the key traits coevolving with life span. In this study, we tested the coevolution of liver fatty acid composition with maximum life span, annual fecundity, and basal metabolic rate (BMR), using a recently published data set comprising liver fatty acid composition of 106 avian species. While statistically controlling for the confounding effects of body mass and phylogeny, we found no support for long life span evolving with low fatty acid unsaturation and only very weak support for fatty acid unsaturation acting as a pacemaker of BMR. Moreover, our analysis provided no evidence for the previously reported links between life span and n-3 PUFA/total PUFA or MUFA proportion. Our results rather suggest that long life span evolves with long-chain fatty acids irrespective of their degree of unsaturation as life span was positively associated with at least one long-chain fatty acid of each type (i.e., SFA, MUFA, n-6 PUFA, and n-3 PUFA). Importantly, maximum life span, annual fecundity, and BMR were associated with different fatty acids or fatty acid indices, indicating that longevity, fecundity, and BMR coevolve with different aspects of fatty acid composition. Therefore, in addition to posing significant challenges to MPH, our results imply that fatty acid composition does not pose an evolutionary constraint underpinning life-history trade-offs at the molecular level.

Alterations of Lipid Metabolism With Age and Weight in Companion Dogs

The companion dog has recently been promoted as powerful translational model of aging. However, while dogs share environments with their human owners and develop many of the same age-related morbidities, little is known about the underlying mechanisms that drive their health and longevity. In addition, dogs have a well described phenotypic pattern in which small dogs live significantly longer than large dogs, such that weight can be used as a crude proxy for longevity. To investigate this pattern, we completed a small lipidomics study on 41 dogs in the Birmingham, Alabama, United States, area to determine individual circulating lipids that were associated with age and body weight. We discovered that sphingomyelins were significantly higher in large, short-lived dogs, independent of age, and triglycerides were higher in older dogs of all sizes. Our results point towards physiological differences that may explain a portion of the variation in longevity seen in companion dogs.

An Integrated Biomarker Approach Using Flounder to Improve Chemical Risk Assessments in the Heavily Polluted Seine Estuary

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk.

n-3 polyunsaturated fatty acids as modulators of thermogenesis in Ames dwarf mice

Lipids, commonly split into saturated and mono- and polyunsaturated fatty acids, are key constituents of all biological membranes, and their exact proportions in different tissues were previously shown to be related to lifespan in mammals. As a mechanism, it was put forward that long-chain and highly unsaturated n-3 fatty acids may act as "pacemakers" in membranes while the n-6 fatty acid class may act as a counterbalance. Previously, long-lived Ames dwarf mice (Prop1 df/df) were found to have lower n-3 fatty acids and higher n-6 throughout their tissues. We exposed 32 adult (8 months old) Ames dwarf mice to three isocaloric diets differing in their fatty acid composition (saturated vs. rich in n-3 and n-6) for 2 months while measuring their body masses, subcutaneous body temperatures and finally membrane fatty acid profiles. Prominently, we found that individuals from all three groups quickly increased their body masses by ca. 20% and had 0.45 °C higher subcutaneous body temperatures than at baseline (F_1,12,16 = 22.27; p < 0.001). Conceivably, experimental diets also largely reflected lipid composition found in the tissues with over 50% n-3 fatty acids in heart phospholipids from animals from the n-3-enriched feeding group. Our study indicates that fatty acid-enriched diets well affected body mass, subcutaneous body temperature and membrane fatty acid composition in Ames dwarf mice with no visible adverse effects on their health. Experimental feeding increased subcutaneous body fat and insulation, most likely explaining the higher subcutaneous temperatures.

Mechanisms by which PE21, an extract from the white willow Salix alba, delays chronological aging in budding yeast

We have recently found that PE21, an extract from the white willow Salix alba, slows chronological aging and prolongs longevity of the yeast Saccharomyces cerevisiae more efficiently than any of the previously known pharmacological interventions. Here, we investigated mechanisms through which PE21 delays yeast chronological aging and extends yeast longevity. We show that PE21 causes a remodeling of lipid metabolism in chronologically aging yeast, thereby instigating changes in the concentrations of several lipid classes. We demonstrate that such changes in the cellular lipidome initiate three mechanisms of aging delay and longevity extension. The first mechanism through which PE21 slows aging and prolongs longevity consists in its ability to decrease the intracellular concentration of free fatty acids. This postpones an age-related onset of liponecrotic cell death promoted by excessive concentrations of free fatty acids. The second mechanism of aging delay and longevity extension by PE21 consists in its ability to decrease the concentrations of triacylglycerols and to increase the concentrations of glycerophospholipids within the endoplasmic reticulum membrane. This activates the unfolded protein response system in the endoplasmic reticulum, which then decelerates an age-related decline in protein and lipid homeostasis and slows down an aging-associated deterioration of cell resistance to stress. The third mechanisms underlying aging delay and longevity extension by PE21 consists in its ability to change lipid concentrations in the mitochondrial membranes. This alters certain catabolic and anabolic processes in mitochondria, thus amending the pattern of aging-associated changes in several key aspects of mitochondrial functionality.

Dispersal capacity explains the evolution of lifespan variability

The evolutionary explanation for lifespan variation is still based on the antagonistic pleiotropy hypothesis, which has been challenged by several studies. Alternative models assume the existence of genes that favor aging and group benefits at the expense of reductions in individual lifespans. Here we propose a new model without making such assumptions. It considers that limited dispersal can generate, through reduced gene flow, spatial segregation of individual organisms according to lifespan. Individuals from subpopulations with shorter lifespan could thus resist collapse in a growing population better than individuals from subpopulations with longer lifespan, hence reducing lifespan variability within species. As species that disperse less may form more homogeneous subpopulations regarding lifespan, this may lead to a greater capacity to maximize lifespan that generates viable subpopulations, therefore creating negative associations between dispersal capacity and lifespan across species. We tested our model with individual-based simulations and a comparative study using empirical data of maximum lifespan and natal dispersal distance in 26 species of birds, controlling for the effects of genetic variability, body size, and phylogeny. Simulations resulted in maximum lifespans arising from lowest dispersal probabilities, and comparative analyses resulted in a negative association between lifespan and natal dispersal distance, thus consistent with our model. Our findings therefore suggest that the evolution of lifespan variability is the result of the ecological process of dispersal.

A Peculiar Formula of Essential Amino Acids Prevents Rosuvastatin Myopathy in Mice

AIMS

Myopathy, characterized by mitochondrial oxidative stress, occurs in ∼10% of statin-treated patients, and a major risk exists with potent statins such as rosuvastatin (Rvs). We sought to determine whether a peculiar branched-chain amino acid-enriched mixture (BCAAem), found to improve mitochondrial function and reduce oxidative stress in muscle of middle-aged mice, was able to prevent Rvs myopathy.

RESULTS

Dietary supplementation of BCAAem was able to prevent the structural and functional alterations of muscle induced by Rvs in young mice. Rvs-increased plasma 3-methylhistidine (a marker of muscular protein degradation) was prevented by BCAAem. This was obtained without changes of Rvs ability to reduce cholesterol and triglyceride levels in blood. Rather, BCAAem promotes de novo protein synthesis and reduces proteolysis in cultured myotubes. Morphological alterations of C2C12 cells induced by statin were counteracted by amino acids, as were the Rvs-increased atrogin-1 mRNA and protein levels. Moreover, BCAAem maintained mitochondrial mass and density and citrate synthase activity in skeletal muscle of Rvs-treated mice beside oxygen consumption and ATP levels in C2C12 cells exposed to statin. Notably, BCAAem assisted Rvs to reduce oxidative stress and to increase the anti-reactive oxygen species (ROS) defense system in skeletal muscle. Innovation and Conclusions: The complex interplay between proteostasis and antioxidant properties may underlie the mechanism by which a specific amino acid formula preserves mitochondrial efficiency and muscle health in Rvs-treated mice. Strategies aimed at promoting protein balance and controlling mitochondrial ROS level may be used as therapeutics for the treatment of muscular diseases involving mitochondrial dysfunction, such as statin myopathy. Antioxid. Redox Signal. 25, 595-608.

Looking Beyond Structure: Membrane Phospholipids of Skeletal Muscle Mitochondria

Skeletal muscle mitochondria are highly dynamic and are capable of tremendous expansion to meet cellular energetic demands. Such proliferation in mitochondrial mass requires a synchronized supply of enzymes and structural phospholipids. While transcriptional regulation of mitochondrial enzymes has been extensively studied, there is limited information on how mitochondrial membrane lipids are generated in skeletal muscle. Herein we describe how each class of phospholipids that constitute mitochondrial membranes are synthesized and/or imported, and summarize genetic evidence indicating that membrane phospholipid composition represents a significant modulator of skeletal muscle mitochondrial respiratory function. We also discuss how skeletal muscle mitochondrial phospholipids may mediate the effect of diet and exercise on oxidative metabolism.

Mitochondrial divergence between slow- and fast-aging garter snakes

Mitochondrial function has long been hypothesized to be intimately involved in aging processes--either directly through declining efficiency of mitochondrial respiration and ATP production with advancing age, or indirectly, e.g., through increased mitochondrial production of damaging free radicals with age. Yet we lack a comprehensive understanding of the evolution of mitochondrial genotypes and phenotypes across diverse animal models, particularly in species that have extremely labile physiology. Here, we measure mitochondrial genome-types and transcription in ecotypes of garter snakes (Thamnophis elegans) that are adapted to disparate habitats and have diverged in aging rates and lifespans despite residing in close proximity. Using two RNA-seq datasets, we (1) reconstruct the garter snake mitochondrial genome sequence and bioinformatically identify regulatory elements, (2) test for divergence of mitochondrial gene expression between the ecotypes and in response to heat stress, and (3) test for sequence divergence in mitochondrial protein-coding regions in these slow-aging (SA) and fast-aging (FA) naturally occurring ecotypes. At the nucleotide sequence level, we confirmed two (duplicated) mitochondrial control regions one of which contains a glucocorticoid response element (GRE). Gene expression of protein-coding genes was higher in FA snakes relative to SA snakes for most genes, but was neither affected by heat stress nor an interaction between heat stress and ecotype. SA and FA ecotypes had unique mitochondrial haplotypes with amino acid substitutions in both CYTB and ND5. The CYTB amino acid change (Isoleucine → Threonine) was highly segregated between ecotypes. This divergence of mitochondrial haplotypes between SA and FA snakes contrasts with nuclear gene-flow estimates, but correlates with previously reported divergence in mitochondrial function (mitochondrial oxygen consumption, ATP production, and reactive oxygen species consequences).

Long lifespans have evolved with long and monounsaturated fatty acids in birds

The evolution of lifespan is a central question in evolutionary biology, begging the question why there is so large variation among taxa. Specifically, a central quest is to unravel proximate causes of ageing. Here, we show that the degree of unsaturation of liver fatty acids predicts maximum lifespan in 107 bird species. In these birds, the degree of fatty acid unsaturation is positively related to maximum lifespan across species. This is due to a positive effect of monounsaturated fatty acid content, while polyunsaturated fatty acid content negatively correlates with maximum lifespan. Furthermore, fatty acid chain length unsuspectedly increases with maximum lifespan independently of degree of unsaturation. These findings tune theories on the proximate causes of ageing while providing evidence that the evolution of lifespan in birds occurs in association with fatty acid profiles. This suggests that studies of proximate and ultimate questions may facilitate our understanding of these central evolutionary questions.

The role of mitochondria in longevity and healthspan

The role of mitochondria in aging and disease remains contentious more than 40 years after the mitochondrial free radical theory of aging was first proposed. As part of a wider cross-journal series on contemporary mitochondrial biology, Longevity & Healthspan presents a thematic series of four reviews that discuss the evidence for and against the modern incarnations of the theory, and examine the relevance of mitochondrial membrane phospholipid unsaturation and the interactions of mitochondria with sex hormones.