Integration of peroxisomes into an endomembrane system that governs cellular aging

Investigating D-Amino Acid Oxidase Expression and Interaction Network Analyses in Pathways Associated With Cellular Stress: Implications in the Biology of Aging

D-amino acid oxidase (DAO) is a flavoenzyme that metabolizes D-amino acids by oxidative deamination, producing hydrogen peroxide (H2O2) as a by-product. The generation of intracellular H2O2 may alter the redox-homeostasis mechanism of cells and increase the oxidative stress levels in tissues, associated with the pathogenesis of age-related diseases and organ decline. This study investigates the effect of DAO knockdown using clustered regularly interspaced short palindromic repeats (CRISPR) through an in silico approach on its protein-protein interactions (PPIs) and their potential roles in the process of aging. The target sequence and guide RNA of DAO were designed using the CCTop database, PPI analysis using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, Reactome biological pathway, protein docking using GalaxyTongDock database, and structure analysis. The translated target sequence of DAO lies between amino acids 43 to 50. The 10 proteins that were predicted to interact with DAO are involved in peroxisome pathways such as acyl-coenzyme A oxidase 1 (ACOX1), alanine-glyoxylate and serine-pyruvate aminotransferase (AGXT), catalase (CAT), carnitine O-acetyltransferase (CRAT), glyceronephosphate O-acyltransferase (GNPAT), hydroxyacid oxidase 1 (HAO1), hydroxyacid oxidase 2 (HAO2), trans-L-3-hydroxyproline dehydratase (L3HYPDH), polyamine oxidase (PAOX), and pipecolic acid and sarcosine oxidase (PIPOX). In summary, DAO mutation would most likely reduce activity with its interacting proteins that generate H2O2. However, DAO mutation may result in peroxisomal disorders, and thus, alternative techniques should be considered for an in vivo approach.

Peroxisomes Regulate Cellular Free Fatty Acids to Modulate Mast Cell TLR2, TLR4, and IgE-Mediated Activation

Mast cells are specialized, tissue resident, immune effector cells able to respond to a wide range of stimuli. MCs are involved in the regulation of a variety of physiological functions, including vasodilation, angiogenesis and pathogen elimination. In addition, MCs recruit and regulate the functions of many immune cells such as dendritic cells, macrophages, T cells, B cells and eosinophils through their selective production of multiple cytokines and chemokines. MCs generate and release multi-potent molecules, such as histamine, proteases, prostanoids, leukotrienes, heparin, and many cytokines, chemokines, and growth factors through both degranulation dependent and independent pathways. Recent studies suggested that metabolic shifts dictate the activation and granule content secretion by MCs, however the metabolic signaling promoting these events is at its infancy. Lipid metabolism is recognized as a pivotal immunometabolic regulator during immune cell activation. Peroxisomes are organelles found across all eukaryotes, with a pivotal role in lipid metabolism and the detoxification of reactive oxygen species. Peroxisomes are one of the emerging axes in immunometabolism. Here we identified the peroxisome as an essential player in MCs activation. We determined that lack of functional peroxisomes in murine MCs causes a significant reduction of interleukin-6, Tumor necrosis factor and InterleukinL-13 following immunoglobulin IgE-mediated and Toll like receptor 2 and 4 activation compared to the Wild type (WT) BMMCs. We linked these defects in cytokine release to defects in free fatty acids homeostasis. In conclusion, our study identified the importance of peroxisomal fatty acids homeostasis in regulating mast cell-mediated immune functions.

Beyond the cell factory: Homeostatic regulation of and by the UPRER

The endoplasmic reticulum (ER) is commonly referred to as the factory of the cell, as it is responsible for a large amount of protein and lipid synthesis. As a membrane-bound organelle, the ER has a distinct environment that is ideal for its functions in synthesizing these primary cellular components. Many different quality control machineries exist to maintain ER stability under the stresses associated with synthesizing, folding, and modifying complex proteins and lipids. The best understood of these mechanisms is the unfolded protein response of the ER (UPR^ER), in which transmembrane proteins serve as sensors, which trigger a coordinated transcriptional response of genes dedicated for mitigating the stress. As the name suggests, the UPR^ER is most well described as a functional response to protein misfolding stress. Here, we focus on recent findings and emerging themes in additional roles of the UPR^ER outside of protein homeostasis, including lipid homeostasis, autophagy, apoptosis, and immunity.

Discovery of fifteen new geroprotective plant extracts and identification of cellular processes they affect to prolong the chronological lifespan of budding yeast

In a quest for previously unknown geroprotective natural chemicals, we used a robust cell viability assay to search for commercially available plant extracts that can substantially prolong the chronological lifespan of budding yeast. Many of these plant extracts have been used in traditional Chinese and other herbal medicines or the Mediterranean and other customary diets. Our search led to a discovery of fifteen plant extracts that significantly extend the longevity of chronologically aging yeast not limited in calorie supply. We show that each of these longevity-extending plant extracts is a geroprotector that decreases the rate of yeast chronological aging and promotes a hormetic stress response. We also show that each of the fifteen geroprotective plant extracts mimics the longevity-extending, stress-protecting, metabolic and physiological effects of a caloric restriction diet but if added to yeast cultured under non-caloric restriction conditions. We provide evidence that the fifteen geroprotective plant extracts exhibit partially overlapping effects on a distinct set of longevity-defining cellular processes. These effects include a rise in coupled mitochondrial respiration, an altered age-related chronology of changes in reactive oxygen species abundance, protection of cellular macromolecules from oxidative damage, and an age-related increase in the resistance to long-term oxidative and thermal stresses.

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.

Characterization of a class III peroxidase from Artemisia annua: relevance to artemisinin metabolism and beyond

A class III peroxidase from Artemisia annua has been shown to indicate the possibility of cellular localization-based role diversity, which may have implications in artemisinin catabolism as well as lignification. Artemisia annua derives its importance from the antimalarial artemisinin. The -O-O- linkage in artemisinin makes peroxidases relevant to its metabolism. Earlier, we identified three peroxidase-coding genes from A. annua, whereby Aa547 showed higher expression in the low-artemisinin plant stage whereas Aa528 and Aa540 showed higher expression in the artemisinin-rich plant stage. Here we carried out tertiary structure homology modelling of the peroxidases for docking studies. Maximum binding affinity for artemisinin was shown by Aa547. Further, Aa547 showed greater binding affinity for post-artemisinin metabolite, deoxyartemisinin, as compared to pre-artemisinin metabolites (dihydroartemisinic hydroperoxide, artemisinic acid, dihydroartemisinic acid). It also showed significant binding affinity for the monolignol, coniferyl alcohol. Moreover, Aa547 expression was related inversely to artemisinin content and directly to total lignin content as indicated by its transient silencing and overexpression in A. annua. Artemisinin reduction assay also indicated inverse relationship between Aa547 expression and artemisinin content. Subcellular localization using GFP fusion suggested that Aa547 is peroxisomal. Nevertheless, dual localization (intracellular/extracellular) of Aa547 could not be ruled out due to its effect on both, artemisinin and lignin. Taken together, this indicates possibility of localization-based role diversity for Aa547, which may have implications in artemisinin catabolism as well as lignification in A. annua.

Neuronal Cells Rearrangement During Aging and Neurodegenerative Disease: Metabolism, Oxidative Stress and Organelles Dynamic

Brain cells normally respond adaptively to oxidative stress or bioenergetic challenges, resulting from ongoing activity in neuronal circuits. During aging and in neurodegenerative disorders, these mechanisms are compromised. In fact, neurons show unique age-related changes in functions and metabolism, resulting in greater susceptibility to insults and disease. Aging affects the nervous system as well as other organs. More precisely, as the nervous system ages, neuron metabolism may change, inducing glucose hypometabolism, impaired transport of critical substrates underlying metabolism, alterations in calcium signaling, and mitochondrial dysfunction. Moreover, in neuronal aging, an accumulation of impaired and aggregated proteins in the cytoplasm and in mitochondria is observed, as the result of oxidative stress: reduced antioxidant defenses and/or increase of reactive oxygen species (ROS). These changes lead to greater vulnerability of neurons in various regions of the brain and increased susceptibility to several diseases. Specifically, the first part of the review article will focus on the major neuronal cells’ rearrangements during aging in response to changes in metabolism and oxidative stress, while the second part will cover the neurodegenerative disease areas in detail.

Protective Effect of the Hexanic Extract of Eryngium carlinae Inflorescences In Vitro, in Yeast, and in Streptozotocin-Induced Diabetic Male Rats

In the present study, we investigated the composition and antioxidant activity of the hexanic extract of Eryngium carlinae inflorescences by employing in vitro assays to measure antioxidant capacity and 2,2-diphenyl-1-picrylhydrazyl scavenging activity. We also applied the hexanic extract to Saccharomyces cerevisiae, under hydrogen peroxide-induced stress. Finally, we tested the extract in male Wistar rats with and without streptozotocin-induced diabetes. The compounds in the hexanic extract were analyzed by gas-chromatography-mass spectrometry, which revealed mainly terpenes and sesquiterpenes, including (Z)β-farnesene (38.79%), β-pinene (17.53%), calamene (13.3%), and α-farnesene (10.38%). In vitro and in S. cerevisiae, the extract possessed antioxidant activity at different concentrations, compared to ascorbic acid (positive control). In normoglycemic and hyperglycemic rats, oral administration of 30 mg/kg of the extract reduced blood glucose levels; lipid peroxidation in liver, kidney and brain; protein carbonylation; and reactive oxygen species (ROS) production. It also increased catalase activity in the brain, kidneys and liver. These findings show that this hexanic extract of E. carlinae inflorescences possessed antioxidant properties.

Dysfunctional peroxisomes compromise gut structure and host defense by increased cell death and Tor-dependent autophagy

The gut has a central role in digestion and nutrient absorption, but it also serves in defending against pathogens, engages in mutually beneficial interactions with commensals, and is a major source of endocrine signals. Gut homeostasis is necessary for organismal health and changes to the gut are associated with conditions like obesity and diabetes and inflammatory illnesses like Crohn's disease. We report that peroxisomes, organelles involved in lipid metabolism and redox balance, are required to maintain gut epithelium homeostasis and renewal in Drosophila and for survival and development of the organism. Dysfunctional peroxisomes in gut epithelial cells activate Tor kinase-dependent autophagy that increases cell death and epithelial instability, which ultimately alter the composition of the intestinal microbiota, compromise immune pathways in the gut in response to infection, and affect organismal survival. Peroxisomes in the gut effectively function as hubs that coordinate responses from stress, metabolic, and immune signaling pathways to maintain enteric health and the functionality of the gut-microbe interface.

Some Metabolites Act as Second Messengers in Yeast Chronological Aging

The concentrations of some key metabolic intermediates play essential roles in regulating the longevity of the chronologically aging yeast Saccharomyces cerevisiae. These key metabolites are detected by certain ligand-specific protein sensors that respond to concentration changes of the key metabolites by altering the efficiencies of longevity-defining cellular processes. The concentrations of the key metabolites that affect yeast chronological aging are controlled spatially and temporally. Here, we analyze mechanisms through which the spatiotemporal dynamics of changes in the concentrations of the key metabolites influence yeast chronological lifespan. Our analysis indicates that a distinct set of metabolites can act as second messengers that define the pace of yeast chronological aging. Molecules that can operate both as intermediates of yeast metabolism and as second messengers of yeast chronological aging include reduced nicotinamide adenine dinucleotide phosphate (NADPH), glycerol, trehalose, hydrogen peroxide, amino acids, sphingolipids, spermidine, hydrogen sulfide, acetic acid, ethanol, free fatty acids, and diacylglycerol. We discuss several properties that these second messengers of yeast chronological aging have in common with second messengers of signal transduction. We outline how these second messengers of yeast chronological aging elicit changes in cell functionality and viability in response to changes in the nutrient, energy, stress, and proliferation status of the cell.

Six plant extracts delay yeast chronological aging through different signaling pathways

Our recent study has revealed six plant extracts that slow yeast chronological aging more efficiently than any chemical compound yet described. The rate of aging in yeast is controlled by an evolutionarily conserved network of integrated signaling pathways and protein kinases. Here, we assessed how single-gene-deletion mutations eliminating each of these pathways and kinases affect the aging-delaying efficiencies of the six plant extracts. Our findings imply that these extracts slow aging in the following ways: 1) plant extract 4 decreases the efficiency with which the pro-aging TORC1 pathway inhibits the anti-aging SNF1 pathway; 2) plant extract 5 mitigates two different branches of the pro-aging PKA pathway; 3) plant extract 6 coordinates processes that are not assimilated into the network of presently known signaling pathways/protein kinases; 4) plant extract 8 diminishes the inhibitory action of PKA on SNF1; 5) plant extract 12 intensifies the anti-aging protein kinase Rim15; and 6) plant extract 21 inhibits a form of the pro-aging protein kinase Sch9 that is activated by the pro-aging PKH1/2 pathway.

Discovery of plant extracts that greatly delay yeast chronological aging and have different effects on longevity-defining cellular processes

We discovered six plant extracts that increase yeast chronological lifespan to a significantly greater extent than any of the presently known longevity-extending chemical compounds. One of these extracts is the most potent longevity-extending pharmacological intervention yet described. We show that each of the six plant extracts is a geroprotector which delays the onset and decreases the rate of yeast chronological aging by eliciting a hormetic stress response. We also show that each of these extracts has different effects on cellular processes that define longevity in organisms across phyla. These effects include the following: 1) increased mitochondrial respiration and membrane potential; 2) augmented or reduced concentrations of reactive oxygen species; 3) decreased oxidative damage to cellular proteins, membrane lipids, and mitochondrial and nuclear genomes; 4) enhanced cell resistance to oxidative and thermal stresses; and 5) accelerated degradation of neutral lipids deposited in lipid droplets. Our findings provide new insights into mechanisms through which chemicals extracted from certain plants can slow biological aging.

Caloric restriction extends yeast chronological lifespan via a mechanism linking cellular aging to cell cycle regulation, maintenance of a quiescent state, entry into a non-quiescent state and survival in the non-quiescent state

A yeast culture grown in a nutrient-rich medium initially containing 2% glucose is not limited in calorie supply. When yeast cells cultured in this medium consume glucose, they undergo cell cycle arrest at a checkpoint in late G1 and differentiate into quiescent and non-quiescent cell populations. Studies of such differentiation have provided insights into mechanisms of yeast chronological aging under conditions of excessive calorie intake. Caloric restriction is an aging-delaying dietary intervention. Here, we assessed how caloric restriction influences the differentiation of chronologically aging yeast cultures into quiescent and non-quiescent cells, and how it affects their properties. We found that caloric restriction extends yeast chronological lifespan via a mechanism linking cellular aging to cell cycle regulation, maintenance of quiescence, entry into a non-quiescent state and survival in this state. Our findings suggest that caloric restriction delays yeast chronological aging by causing specific changes in the following: 1) a checkpoint in G1 for cell cycle arrest and entry into a quiescent state; 2) a growth phase in which high-density quiescent cells are committed to become low-density quiescent cells; 3) the differentiation of low-density quiescent cells into low-density non-quiescent cells; and 4) the conversion of high-density quiescent cells into high-density non-quiescent cells.

The respiratory chain inhibitor rotenone affects peroxisomal dynamics via its microtubule-destabilising activity

Peroxisomes and mitochondria in mammalian cells are closely linked subcellular organelles, which maintain a redox-sensitive relationship. Their interplay and role in ROS signalling are supposed to impact on age-related and degenerative disorders. Whereas the generation of peroxisome-derived oxidative stress can affect mitochondrial morphology and function, little is known about the impact of mitochondria-derived oxidative stress on peroxisomes. Here, we investigated the effect of the mitochondrial complex I inhibitor rotenone on peroxisomal and mitochondrial membrane dynamics. We show that rotenone treatment of COS-7 cells alters peroxisome morphology and distribution. However, this effect is related to its microtubule-destabilising activity rather than to the generation of oxidative stress. Rotenone also induced alterations in mitochondrial morphology, which-in contrast to its effect on peroxisomes-were dependent on the generation of ROS but independent of its microtubule-active properties. The importance of our findings for the peroxisome-mitochondria redox relationship and the interpretation of in cellulo and in vivo studies with rotenone, which is widely used to study Parkinson's disease, are discussed.

Mechanisms Underlying the Essential Role of Mitochondrial Membrane Lipids in Yeast Chronological Aging

The functional state of mitochondria is vital to cellular and organismal aging in eukaryotes across phyla. Studies in the yeast Saccharomyces cerevisiae have provided evidence that age-related changes in some aspects of mitochondrial functionality can create certain molecular signals. These signals can then define the rate of cellular aging by altering unidirectional and bidirectional communications between mitochondria and other organelles. Several aspects of mitochondrial functionality are known to impact the replicative and/or chronological modes of yeast aging. They include mitochondrial electron transport, membrane potential, reactive oxygen species, and protein synthesis and proteostasis, as well as mitochondrial synthesis of iron-sulfur clusters, amino acids, and NADPH. Our recent findings have revealed that the composition of mitochondrial membrane lipids is one of the key aspects of mitochondrial functionality affecting yeast chronological aging. We demonstrated that exogenously added lithocholic bile acid can delay chronological aging in yeast because it elicits specific changes in mitochondrial membrane lipids. These changes allow mitochondria to operate as signaling platforms that delay yeast chronological aging by orchestrating an institution and maintenance of a distinct cellular pattern. In this review, we discuss molecular and cellular mechanisms underlying the essential role of mitochondrial membrane lipids in yeast chronological aging.

Pex35 is a regulator of peroxisome abundance

Peroxisomes are cellular organelles with vital functions in lipid, amino acid and redox metabolism. The cellular formation and dynamics of peroxisomes are governed by PEX genes; however, the regulation of peroxisome abundance is still poorly understood. Here, we use a high-content microscopy screen in Saccharomyces cerevisiae to identify new regulators of peroxisome size and abundance. Our screen led to the identification of a previously uncharacterized gene, which we term PEX35, which affects peroxisome abundance. PEX35 encodes a peroxisomal membrane protein, a remote homolog to several curvature-generating human proteins. We systematically characterized the genetic and physical interactome as well as the metabolome of mutants in PEX35, and we found that Pex35 functionally interacts with the vesicle-budding-inducer Arf1. Our results highlight the functional interaction between peroxisomes and the secretory pathway.

Communications between Mitochondria, the Nucleus, Vacuoles, Peroxisomes, the Endoplasmic Reticulum, the Plasma Membrane, Lipid Droplets, and the Cytosol during Yeast Chronological Aging

Studies employing the budding yeast Saccharomyces cerevisiae as a model organism have provided deep insights into molecular mechanisms of cellular and organismal aging in multicellular eukaryotes and have demonstrated that the main features of biological aging are evolutionarily conserved. Aging in S. cerevisiae is studied by measuring replicative or chronological lifespan. Yeast replicative aging is likely to model aging of mitotically competent human cell types, while yeast chronological aging is believed to mimic aging of post-mitotic human cell types. Emergent evidence implies that various organelle-organelle and organelle-cytosol communications play essential roles in chronological aging of S. cerevisiae. The molecular mechanisms underlying the vital roles of intercompartmental communications in yeast chronological aging have begun to emerge. The scope of this review is to critically analyze recent progress in understanding such mechanisms. Our analysis suggests a model for how temporally and spatially coordinated movements of certain metabolites between various cellular compartments impact yeast chronological aging. In our model, diverse changes in these key metabolites are restricted to critical longevity-defining periods of chronological lifespan. In each of these periods, a limited set of proteins responds to such changes of the metabolites by altering the rate and efficiency of a certain cellular process essential for longevity regulation. Spatiotemporal dynamics of alterations in these longevity-defining cellular processes orchestrates the development and maintenance of a pro- or anti-aging cellular pattern.

Autophagic degradation of peroxisomes in mammals

Peroxisomes are essential organelles required for proper cell function in all eukaryotic organisms. They participate in a wide range of cellular processes including the metabolism of lipids and generation, as well as detoxification, of hydrogen peroxide (H2O2). Therefore, peroxisome homoeostasis, manifested by the precise and efficient control of peroxisome number and functionality, must be tightly regulated in response to environmental changes. Due to the existence of many physiological disorders and diseases associated with peroxisome homoeostasis imbalance, the dynamics of peroxisomes have been widely examined. The increasing volume of reports demonstrating significant involvement of the autophagy machinery in peroxisome removal leads us to summarize current knowledge of peroxisome degradation in mammalian cells. In this review we present current models of peroxisome degradation. We particularly focus on pexophagy-the selective clearance of peroxisomes through autophagy. We also critically discuss concepts of peroxisome recognition for pexophagy, including signalling and selectivity factors. Finally, we present examples of the pathological effects of pexophagy dysfunction and suggest promising future directions.

Lithocholic bile acid accumulated in yeast mitochondria orchestrates a development of an anti-aging cellular pattern by causing age-related changes in cellular proteome

We have previously revealed that exogenously added lithocholic bile acid (LCA) extends the chronological lifespan of the yeast Saccharomyces cerevisiae, accumulates in mitochondria and alters mitochondrial membrane lipidome. Here, we use quantitative mass spectrometry to show that LCA alters the age-related dynamics of changes in levels of many mitochondrial proteins, as well as numerous proteins in cellular locations outside of mitochondria. These proteins belong to 2 regulons, each modulated by a different mitochondrial dysfunction; we call them a partial mitochondrial dysfunction regulon and an oxidative stress regulon. We found that proteins constituting these regulons (1) can be divided into several "clusters", each of which denotes a distinct type of partial mitochondrial dysfunction that elicits a different signaling pathway mediated by a discrete set of transcription factors; (2) exhibit 3 different patterns of the age-related dynamics of changes in their cellular levels; and (3) are encoded by genes whose expression is regulated by the transcription factors Rtg1p/Rtg2p/Rtg3p, Sfp1p, Aft1p, Yap1p, Msn2p/Msn4p, Skn7p and Hog1p, each of which is essential for longevity extension by LCA. Our findings suggest that LCA-driven changes in mitochondrial lipidome alter mitochondrial proteome and functionality, thereby enabling mitochondria to operate as signaling organelles that orchestrate an establishment of an anti-aging transcriptional program for many longevity-defining nuclear genes. Based on these findings, we propose a model for how such LCA-driven changes early and late in life of chronologically aging yeast cause a stepwise development of an anti-aging cellular pattern and its maintenance throughout lifespan.

Cell-Nonautonomous Mechanisms Underlying Cellular and Organismal Aging

Cell-autonomous mechanisms underlying cellular and organismal aging in evolutionarily distant eukaryotes have been established; these mechanisms regulate longevity-defining processes within a single eukaryotic cell. Recent findings have provided valuable insight into cell-nonautonomous mechanisms modulating cellular and organismal aging in eukaryotes across phyla; these mechanisms involve a transmission of various longevity factors between different cells, tissues, and organisms. Herein, we review such cell-nonautonomous mechanisms of aging in eukaryotes. We discuss the following: (1) how low molecular weight transmissible longevity factors modulate aging and define longevity of cells in yeast populations cultured in liquid media or on solid surfaces, (2) how communications between proteostasis stress networks operating in neurons and nonneuronal somatic tissues define longevity of the nematode Caenorhabditis elegans by modulating the rates of aging in different tissues, and (3) how different bacterial species colonizing the gut lumen of C. elegans define nematode longevity by modulating the rate of organismal aging.

The different facets of organelle interplay-an overview of organelle interactions

Membrane-bound organelles such as mitochondria, peroxisomes, or the endoplasmic reticulum (ER) create distinct environments to promote specific cellular tasks such as ATP production, lipid breakdown, or protein export. During recent years, it has become evident that organelles are integrated into cellular networks regulating metabolism, intracellular signaling, cellular maintenance, cell fate decision, and pathogen defence. In order to facilitate such signaling events, specialized membrane regions between apposing organelles bear distinct sets of proteins to enable tethering and exchange of metabolites and signaling molecules. Such membrane associations between the mitochondria and a specialized site of the ER, the mitochondria associated-membrane (MAM), as well as between the ER and the plasma membrane (PAM) have been partially characterized at the molecular level. However, historical and recent observations imply that other organelles like peroxisomes, lysosomes, and lipid droplets might also be involved in the formation of such apposing membrane contact sites. Alternatively, reports on so-called mitochondria derived-vesicles (MDV) suggest alternative mechanisms of organelle interaction. Moreover, maintenance of cellular homeostasis requires the precise removal of aged organelles by autophagy—a process which involves the detection of ubiquitinated organelle proteins by the autophagosome membrane, representing another site of membrane associated-signaling. This review will summarize the available data on the existence and composition of organelle contact sites and the molecular specializations each site uses in order to provide a timely overview on the potential functions of organelle interaction.

Quasi-programmed aging of budding yeast: a trade-off between programmed processes of cell proliferation, differentiation, stress response, survival and death defines yeast lifespan

Recent findings suggest that evolutionarily distant organisms share the key features of the aging process and exhibit similar mechanisms of its modulation by certain genetic, dietary and pharmacological interventions. The scope of this review is to analyze mechanisms that in the yeast Saccharomyces cerevisiae underlie: (1) the replicative and chronological modes of aging; (2) the convergence of these 2 modes of aging into a single aging process; (3) a programmed differentiation of aging cell communities in liquid media and on solid surfaces; and (4) longevity-defining responses of cells to some chemical compounds released to an ecosystem by other organisms populating it. Based on such analysis, we conclude that all these mechanisms are programs for upholding the long-term survival of the entire yeast population inhabiting an ecological niche; however, none of these mechanisms is a ʺprogram of agingʺ - i.e., a program for progressing through consecutive steps of the aging process.

Antioxidant cytoprotection by peroxisomal peroxiredoxin-5

Peroxiredoxin-5 (PRDX5) is a thioredoxin peroxidase that reduces hydrogen peroxide, alkyl hydroperoxides, and peroxynitrite. This enzyme is present in the cytosol, mitochondria, peroxisomes, and nucleus in human cells. Antioxidant cytoprotective functions have been previously documented for cytosolic, mitochondrial, and nuclear mammalian PRDX5. However, the exact function of PRDX5 in peroxisomes is still not clear. The aim of this work was to determine the function of peroxisomal PRDX5 in mammalian cells and, more specifically, in glial cells. To study the role of PRDX5 in peroxisomes, the endogenous expression of PRDX5 in murine oligodendrocyte 158N cells was silenced by RNA interference. In addition, human PRDX5 was also overexpressed in peroxisomes using a vector coding for human PRDX5, whose unconventional peroxisomal targeting sequence 1 (PTS1; SQL) was replaced by the prototypical PTS1 SKL. Stable 158N clones were obtained. The antioxidant cytoprotective function of peroxisomal PRDX5 against peroxisomal and mitochondrial KillerRed-mediated reactive oxygen species production as well as H2O2 was examined using MTT viability assays, roGFP2, and C11-BOBIPY probes. Altogether our results show that peroxisomal PRDX5 protects 158N oligodendrocytes against peroxisomal and mitochondrial KillerRed- and H2O2-induced oxidative stress.

Redox interplay between mitochondria and peroxisomes

Reduction-oxidation or “redox” reactions are an integral part of a broad range of cellular processes such as gene expression, energy metabolism, protein import and folding, and autophagy. As many of these processes are intimately linked with cell fate decisions, transient or chronic changes in cellular redox equilibrium are likely to contribute to the initiation and progression of a plethora of human diseases. Since a long time, it is known that mitochondria are major players in redox regulation and signaling. More recently, it has become clear that also peroxisomes have the capacity to impact redox-linked physiological processes. To serve this function, peroxisomes cooperate with other organelles, including mitochondria. This review provides a comprehensive picture of what is currently known about the redox interplay between mitochondria and peroxisomes in mammals. We first outline the pro- and antioxidant systems of both organelles and how they may function as redox signaling nodes. Next, we critically review and discuss emerging evidence that peroxisomes and mitochondria share an intricate redox-sensitive relationship and cooperate in cell fate decisions. Key issues include possible physiological roles, messengers, and mechanisms. We also provide examples of how data mining of publicly-available datasets from “omics” technologies can be a powerful means to gain additional insights into potential redox signaling pathways between peroxisomes and mitochondria. Finally, we highlight the need for more studies that seek to clarify the mechanisms of how mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress. The outcome of such studies may open up exciting new avenues for the community of researchers working on cellular responses to organelle-derived oxidative stress, a research field in which the role of peroxisomes is currently highly underestimated and an issue of discussion.

Mechanisms by which different functional states of mitochondria define yeast longevity

Mitochondrial functionality is vital to organismal physiology. A body of evidence supports the notion that an age-related progressive decline in mitochondrial function is a hallmark of cellular and organismal aging in evolutionarily distant eukaryotes. Studies of the baker’s yeast Saccharomyces cerevisiae, a unicellular eukaryote, have led to discoveries of genes, signaling pathways and chemical compounds that modulate longevity-defining cellular processes in eukaryotic organisms across phyla. These studies have provided deep insights into mechanistic links that exist between different traits of mitochondrial functionality and cellular aging. The molecular mechanisms underlying the essential role of mitochondria as signaling organelles in yeast aging have begun to emerge. In this review, we discuss recent progress in understanding mechanisms by which different functional states of mitochondria define yeast longevity, outline the most important unanswered questions and suggest directions for future research.

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

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

Mechanisms underlying the anti-aging and anti-tumor effects of lithocholic bile acid

Bile acids are cholesterol-derived bioactive lipids that play essential roles in the maintenance of a heathy lifespan. These amphipathic molecules with detergent-like properties display numerous beneficial effects on various longevity- and healthspan-promoting processes in evolutionarily distant organisms. Recent studies revealed that lithocholic bile acid not only causes a considerable lifespan extension in yeast, but also exhibits a substantial cytotoxic effect in cultured cancer cells derived from different tissues and organisms. The molecular and cellular mechanisms underlying the robust anti-aging and anti-tumor effects of lithocholic acid have emerged. This review summarizes the current knowledge of these mechanisms, outlines the most important unanswered questions and suggests directions for future research.

Cell-autonomous mechanisms of chronological aging in the yeast Saccharomyces cerevisiae

A body of evidence supports the view that the signaling pathways governing cellular aging - as well as mechanisms of their modulation by longevity-extending genetic, dietary and pharmacological interventions - are conserved across species. The scope of this review is to critically analyze recent advances in our understanding of cell-autonomous mechanisms of chronological aging in the budding yeast Saccharomyces cerevisiae. Based on our analysis, we propose a concept of a biomolecular network underlying the chronology of cellular aging in yeast. The concept posits that such network progresses through a series of lifespan checkpoints. At each of these checkpoints, the intracellular concentrations of some key intermediates and products of certain metabolic pathways - as well as the rates of coordinated flow of such metabolites within an intricate network of intercompartmental communications - are monitored by some checkpoint-specific ʺmaster regulatorʺ proteins. The concept envisions that a synergistic action of these master regulator proteins at certain early-life and late-life checkpoints modulates the rates and efficiencies of progression of such processes as cell metabolism, growth, proliferation, stress resistance, macromolecular homeostasis, survival and death. The concept predicts that, by modulating these vital cellular processes throughout lifespan (i.e., prior to an arrest of cell growth and division, and following such arrest), the checkpoint-specific master regulator proteins orchestrate the development and maintenance of a pro- or anti-aging cellular pattern and, thus, define longevity of chronologically aging yeast.

Peroxisomes take shape

Peroxisomes carry out various oxidative reactions that are tightly regulated to adapt to the changing needs of the cell and varying external environments. Accordingly, they are remarkably fluid and can change dramatically in abundance, size, shape and content in response to numerous cues. These dynamics are controlled by multiple aspects of peroxisome biogenesis that are coordinately regulated with each other and with other cellular processes. Ongoing studies are deciphering the diverse molecular mechanisms that underlie biogenesis and how they cooperate to dynamically control peroxisome utility. These important challenges should lead to an understanding of peroxisome dynamics that can be capitalized upon for bioengineering and the development of therapies to improve human health.

Mitochondria are targets for peroxisome-derived oxidative stress in cultured mammalian cells

Many cellular processes are driven by spatially and temporally regulated redox-dependent signaling events. Although mounting evidence indicates that organelles such as the endoplasmic reticulum and mitochondria can function as signaling platforms for oxidative stress-regulated pathways, little is known about the role of peroxisomes in these processes. In this study, we employ targeted variants of the genetically encoded photosensitizer KillerRed to gain a better insight into the interplay between peroxisomes and cellular oxidative stress. We show that the phototoxic effects of peroxisomal KillerRed induce mitochondria-mediated cell death and that this process can be counteracted by targeted overexpression of a select set of antioxidant enzymes, including peroxisomal glutathione S-transferase kappa 1, superoxide dismutase 1, and mitochondrial catalase. We also present evidence that peroxisomal disease cell lines deficient in plasmalogen biosynthesis or peroxisome assembly are more sensitive to KillerRed-induced oxidative stress than control cells. Collectively, these findings confirm and extend previous observations suggesting that disturbances in peroxisomal redox control and metabolism can sensitize cells to oxidative stress. In addition, they lend strong support to the ideas that peroxisomes and mitochondria share a redox-sensitive relationship and that the redox communication between these organelles is not only mediated by diffusion of reactive oxygen species from one compartment to the other. Finally, these findings indicate that mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress, and this may have profound implications for our views on cellular aging and age-related diseases.

Lipids and cell death in yeast

Understanding lipid-induced malfunction represents a major challenge of today's biomedical research. The connection of lipids to cellular and organ dysfunction, cell death, and disease (often referred to as lipotoxicity) is more complex than the sole lipotoxic effects of excess free fatty acids and requires genetically tractable model systems for mechanistic investigation. We herein summarize recent advances in the field of lipid-induced toxicity that employ the established model system for cell death and aging research of budding yeast Saccharomyces cerevisiae. Studies in yeast have shed light on various aspects of lipotoxicity, including free fatty acid toxicity, sphingolipid-modulated cell death as well as the involvement of cardiolipin and lipid peroxidation in the mitochondrial pathways of apoptosis. Regimens used range from exogenously applied lipids, genetic modulation of lipolysis and triacylglyceride synthesis, variations in sphingolipid/ceramide metabolism as well as changes in peroxisome function by either genetic or pharmacological means. In future, the yeast model of programmed cell death will further contribute to the clarification of crucial questions of lipid-associated malfunction.

A network of interorganellar communications underlies cellular aging

Organelles within a eukaryotic cell respond to age-related intracellular stresses and environmental factors by altering their functional states to generate, direct and process the flow of interorganellar information that is essential for establishing a pro- or antiaging cellular pattern. The scope of this review is to critically analyze recent progress in understanding how various intercompartmental (i.e., organelle-organelle and organelle-cytosol) communications regulate cellular aging in evolutionarily distant eukaryotes. Our analysis suggests a model for an intricate network of intercompartmental communications that underly cellular aging in eukaryotic organisms across phyla. This proposed model posits that the numerous directed, coordinated and regulated organelle-organelle and organelle-cytosol communications integrated into this network define the long-term viability of a eukaryotic cell and, thus, are critical for regulating cellular aging.

Mitochondrial membrane lipidome defines yeast longevity

Our studies revealed that lithocholic acid (LCA), a bile acid, is a potent anti-aging natural compound that in yeast cultured under longevity-extending caloric restriction (CR) conditions acts in synergy with CR to enable a significant further increase in chronological lifespan. Here, we investigate a mechanism underlying this robust longevity-extending effect of LCA under CR. We found that exogenously added LCA enters yeast cells, is sorted to mitochondria, resides mainly in the inner mitochondrial membrane, and also associates with the outer mitochondrial membrane. LCA elicits an age-related remodeling of glycerophospholipid synthesis and movement within both mitochondrial membranes, thereby causing substantial changes in mitochondrial membrane lipidome and triggering major changes in mitochondrial size, number and morphology. In synergy, these changes in the membrane lipidome and morphology of mitochondria alter the age-related chronology of mitochondrial respiration, membrane potential, ATP synthesis and reactive oxygen species homeostasis. The LCA-driven alterations in the age-related dynamics of these vital mitochondrial processes extend yeast longevity. In sum, our findings suggest a mechanism underlying the ability of LCA to delay chronological aging in yeast by accumulating in both mitochondrial membranes and altering their glycerophospholipid compositions. We concluded that mitochondrial membrane lipidome plays an essential role in defining yeast longevity.

Peroxisome degradation in mammals: mechanisms of action, recent advances, and perspectives

Peroxisomes are remarkably dynamic organelles that participate in a diverse array of cellular processes, including the metabolism of lipids and reactive oxygen species. In order to regulate peroxisome function in response to changing nutritional and environmental stimuli, new organelles need to be formed and superfluous and dysfunctional organelles have to be selectively removed. Disturbances in any of these processes have been associated with the etiology and progression of various congenital neurodegenerative and age-related human disorders. The aim of this review is to critically explore our current knowledge of how peroxisomes are degraded in mammalian cells and how defects in this process may contribute to human disease. Some of the key issues highlighted include the current concepts of peroxisome removal, the peroxisome quality control mechanisms, the initial triggers for peroxisome degradation, the factors for dysfunctional peroxisome recognition, and the regulation of peroxisome homeostasis. We also dissect the functional and mechanistic relationship between different forms of selective organelle degradation and consider how lysosomal dysfunction may lead to defects in peroxisome turnover. In addition, we draw lessons from studies on other organisms and extrapolate this knowledge to mammals. Finally, we discuss the potential pathological implications of dysfunctional peroxisome degradation for human health.

Essential roles of peroxisomally produced and metabolized biomolecules in regulating yeast longevity

The essential role of the peroxisome in oxidizing fatty acids, maintaining reactive oxygen species homeostasis and replenishing tricarboxylic acid cycle intermediates is well known. Recent findings have broadened a spectrum of biomolecules that are synthesized and metabolized in peroxisomes. Emergent evidence supports the view that, by releasing various biomolecules known to modulate essential cellular processes, the peroxisome not only operates as an organizing platform for several developmental and differentiation programs but is also actively involved in defining the replicative and chronological age of a eukaryotic cell. The scope of this chapter is to summarize the evidence that the peroxisome defines yeast longevity by operating as a system controller that: (1) modulates levels of non-esterified fatty acids and diacylglycerol; (2) replenishes tricarboxylic acid cycle intermediates destined for mitochondria; and (3) contributes to the synthesis of polyamines. We critically evaluate molecular mechanisms underlying the essential role of peroxisomally produced and metabolized biomolecules in governing cellular aging in yeast.