Annual Fish as a Genetic Model for Aging

Prolonged Supplementation of Ozonated Sunflower Oil Bestows an Antiaging Effect, Improves Blood Lipid Profile and Spinal Deformities, and Protects Vital Organs of Zebrafish (Danio rerio) against Age-Related Degeneration: Two-Years Consumption Study

Ozonated sunflower oil (OSO) is renowned for its diverse therapeutic benefits. Nonetheless, the consequences of extended dietary intake of OSO have yet to be thoroughly investigated. Herein, the effect of 2-year dietary supplementation of OSO was examined on the survivability, obesity, skeletal deformities, swimming behavior, and liver, kidney, ovary, and testis function of zebrafish. Results showed that the zebrafish feed supplemented with 20% (wt/wt) OSO for 2 years emerged with higher survivability and body weight management compared to sunflower oil (SO) and normal diet (ND)-supplemented zebrafish. Radio imaging (X-ray)-based analysis revealed 2.6° and 15.2° lower spinal curvature in the OSO-supplemented groups than in the SO and ND-supplemented groups; consistently, OSO-supplemented zebrafish showed better swimming behavior. The histology analysis of the liver revealed the least fatty liver change and interleukin (IL)-6 generation in the OSO-supplemented group. Additionally, a significantly lower level of reactive oxygen species (ROS), apoptotic, and senescent cells were observed in the liver of the OSO-supplemented zebrafish. Also, no adverse effect on the kidney, testis, and ovary morphology was detected during 2 years of OSO consumption. Moreover, lower senescence with diminished ROS and apoptosis was noticed in the kidney and ovary in response to OSO consumption. The OSO supplementation was found to be effective in countering age-associated dyslipidemia by alleviating total cholesterol (TC), triglycerides (TG), low-density lipoproteins (LDL-C) and elevating high-density lipoproteins (HDL-C)/TC levels. Conclusively, prolonged OSO consumption showed no adverse effect on the morphology and functionality of vital organs; in fact, OSO supplementation displayed a protective effect against age-associated detrimental effects on spinal deformities, vital organ functionality, cell senescence, and the survivability of zebrafish.

Chronic Vitamin E Deficiency Dysregulates Purine, Phospholipid, and Amino Acid Metabolism in Aging Zebrafish Skeletal Muscle

Muscle wasting occurs with aging and may be a result of oxidative stress damage and potentially inadequate protection by lipophilic antioxidants, such as vitamin E. Previous studies have shown muscular abnormalities and behavioral defects in vitamin E-deficient adult zebrafish. To test the hypothesis that there is an interaction between muscle degeneration caused by aging and oxidative damage caused by vitamin E deficiency, we evaluated long-term vitamin E deficiency in the skeletal muscle of aging zebrafish using metabolomics. Zebrafish (55 days old) were fed E+ and E- diets for 12 or 18 months. Then, skeletal muscle samples were analyzed using UPLC-MS/MS. Data were analyzed to highlight metabolite and pathway changes seen with either aging or vitamin E status or both. We found that aging altered purines, various amino acids, and DHA-containing phospholipids. Vitamin E deficiency at 18 months was associated with changes in amino acid metabolism, specifically tryptophan pathways, systemic changes in the regulation of purine metabolism, and DHA-containing phospholipids. In sum, while both aging and induced vitamin E deficiency did have some overlap in altered and potentially dysregulated metabolic pathways, each factor also presented unique alterations, which require further study with more confirmatory approaches.

Evaluation of Age-Dependent Changes in the Coloration of Male Killifish Nothobranchius Guentheri Using New Photoprocessing Methods

Simple Summary

This paper proposes a new methodology for evaluating fish coloration, which allows us to identify differences in the intensity of coloration of specific areas of the body. Changes in fish coloration occur during growth and under the influence of environmental factors. Male fish belonging to the family Nothobranchius are characterized by extremely diverse coloration, depending on the age of the fish, environmental factors, and social hierarchical status. As the lifespan of this genus of fish is very short (12–14 months), studies on age-dependent changes are possible. In this study, we demonstrate correlations between the coloration of particular body zones of male Nothobranchius guentheri and age using new photofixation methods and image processing software. This methodology can be applied to other fish with unique coloration patterns, for example, family Cichlidae and order Cyprinodontiformes.

Abstract

Fish as model objects have found wide applications in biology and fundamental medicine and allow studies of behavioral and physiological responses to various environmental factors. Representatives of the genus Nothobranchius are one of the most convenient objects for such studies. Male fish belonging to the family Nothobranchiidae are characterized by extremely diverse coloration, which constantly changes, depending on the age of the fish, environmental factors, and social hierarchical status. These fish species are characterized by a short life cycle, which allows changes in coloration, an indicator of the ontogenesis stage, to be estimated. Existing methods of fish color assessments do not allow the intensity of coloration of particular body zones to be clearly differentiated. In the present study, we suggest a method of two-factor assessment of specific fish body zones using modified methods of photofixation and image processing software. We describe the protocol of the method and the results of its application to different-aged groups of male Nothobranchius guentheri. The coloration of selected areas (i.e., red spot on the gill cover (RSGC), black border on the caudal fin (BBCF), and white border on the dorsal fin (WBDF)) differed significantly according to the size and age of the fish (p < 0.05). The data obtained suggest that N. guentheri can be a model for studying aging by the intensity of body coloration in males.

Some Aspects of Development and Histological Structure of the Visual System of Nothobranchius Guentheri

In this, work some aspects of the development of the visual system of Nothobranchius guentheri at the main stages of ontogenesis were described for the first time. It was possible to establish that the formation of the visual system occurs similarly to other representatives of the order Cyprinodontiformes, but significantly differs in terms of the individual stages of embryogenesis due to the presence of diapause. In the postembryonic period, there is a further increase in the size of the fish's eyes and head, to the proportions characteristic of adult fish. The histological structure of the eye in adult N. guentheri practically does not differ from most teleost fish living in the same environmental conditions. The study of the structure of the retina showed the heterogeneity of the thickness of the temporal and nasal areas, which indicates the predominant role of peripheral vision. Morphoanatomical measurements of the body and eyes of N. guentheri showed that their correlation was conservative. This indicates an important role of the visual system for the survival of fish in natural conditions, both for the young and adults. In individuals of the older age group, a decrease in the amount of sodium (Na) and an increase in magnesium (Mg) and calcium (Ca) were found in the eye lens. Such changes in the elemental composition of the lens can be a sign of the initial stage of cataractogenesis and disturbances in the metabolism of lens fibers as a result of aging. This allows us to propose N. guentheri as a model for studying the structure, formation, and aging of the visual and nervous systems.

Exercise, programmed cell death and exhaustion of cardiomyocyte proliferation in aging zebrafish

Exercise may ameliorate the eventual heart failure inherent in human aging. In this study, we use zebrafish to understand how aging and exercise affect cardiomyocyte turnover and myocardial remodelling. We show that cardiomyocyte proliferation remains constant throughout life but that onset of fibrosis is associated with a late increase in apoptosis. These findings correlate with decreases in voluntary swimming activity, critical swimming speed (Ucrit), and increases in biomarkers of cardiac insufficiency. The ability to respond to severe physiological stress is also impaired with age. Although young adult fish respond with robust cardiomyocyte proliferation in response to enforced swimming, this is dramatically impaired in older fish and served by a smaller proliferation-competent cardiomyocyte population. Finally, we show that these aging responses can be improved through increased activity throughout adulthood. However, despite improvement in Ucrit and the proliferative response to stress, the size of the proliferating cardiomyocyte population remained unchanged. The zebrafish heart models human aging and reveals the important trade-off between preserving cardiovascular fitness through exercise at the expense of accelerated fibrotic change.

Comparative analysis of metabolic and transcriptomic features of Nothobranchius furzeri

Some species have a longer lifespan than others, but usually lifespan is correlated with typical body weight. Here, we study the lifetime evolution of the metabolic behaviour of Nothobranchius furzeri, a killifish with an extremely short lifespan with respect to other fishes, even when taking into account rescaling by body weight. Comparison of the gene expression patterns of N. furzeri with those of zebrafish Danio rerio and mouse (Mus musculus) shows that a broad set of metabolic genes and pathways are affected in N. furzeri during ageing in a way that is consistent with a global deregulation of chromatin. Computational analysis of the glycolysis pathway for the three species highlights a rapid increase in the metabolic activity during the lifetime of N. furzeri with respect to the other species. Our results highlight that the unusually short lifespan of N. furzeri is associated with peculiar patterns in the metabolic activities and in chromatin dynamics.

The turquoise killifish: a genetically tractable model for the study of aging

Lifespan is a remarkably diverse trait in nature, ranging from just hours in adult mayflies to hundreds of years in the Greenland shark and quahog clam. Great disparities in lifespan are often observed even among somewhat closely related species; for example, in the laboratory, wild-derived strains of the common house mouse have a maximum observed lifespan of approximately 6 years, while a similarly sized rodent, the naked mole rat, can live for over 30 years. Comparative biology of aging across the tree of life provides a tremendous opportunity for understanding the molecular and genetic basis underlying lifespan and aging. However, a lack of molecular and laboratory tools has limited the ability of researchers to take full advantage of the incredible diversity of aging phenotypes in nature. Recent developments in genomic technology have made it increasingly possible to study non-canonical model organisms for aging. One promising new genetic model organism amenable to a range of experimental interventions is the turquoise killifish (Nothobranchius furzeri). This fish species has a naturally short lifespan and undergoes a wide range of aging-related transformations. These fish have a fully sequenced genome and transcriptome, and killifish embryos are accessible to transgenesis and genome editing. Furthermore, different killifish species and populations show striking differences in lifespan, providing the opportunity for comparative analysis of aging. This Review introduces the natural life history of the turquoise killifish, its emerging applicability as an aging model system, the genetic tools that have been developed to study aging for this species and a summary of recent studies facilitated by these new tools.

Zebrafish Carrying pycr1 Gene Deficiency Display Aging and Multiple Behavioral Abnormalities

Aging is a natural process that internal gene control and external stimuli mediate. Clinical data pointed out that homozygotic or heterozygotic mutation in the pyrroline-5-carboxylate reductase 1 (PYCR1) gene in humans caused cutis laxa (ARCL) disease, with progeroid appearance, lax and wrinkled skin, joint laxity, osteopenia, and mental retardation phenotypes. In this study, we aimed to generate pycr1 knockout (KO) zebrafish and carried out biochemical characterizations and behavior analyses. Marked apoptosis and senescence were detected in pycr1 KO zebrafish, which started from embryos/larvae stage. Biochemical assays showed that adult pycr1 KO fish have significantly reduced proline and extracellular matrix contents, lowered energy, and diminished superoxide dismutase (SOD) and telomerase activity when compared to the wild type fish, which suggested the pycr1 KO fish may have dysfunction in mitochondria. The pycr1 KO fish were viable; however, displayed progeria-like phenotype from the 4 months old and reach 50% mortality around six months old. In adult stage, we found that pycr1 KO fish showed reduced locomotion activity, aggression, predator avoidance, social interaction interest, as well as dysregulated color preference and circadian rhythm. In summary, we have identified multiple behavioral alterations in a novel fish model for aging with pycr1 gene loss-of-function by behavioral tests. This animal model may not only provide a unique vertebrate model to screen potential anti-aging drugs in the future, but also be an excellent in vivo model towards a better understanding of the corresponding behavioral alterations that accompany aging.

Determination and reduced life expectancy model and molecular docking analyses of estrogenic potentials of 17β-estradiol, bisphenol A and nonylphenol on expression of vitellogenin gene (vtg1) in zebrafish

This study determined and evaluated the estrogenic potentials on hepatic vitellogenin gene (vtg1) of adult male zebrafish which were exposed to low level concentrations (ng/L-μg/L levels) of individual and binary mixtures of 17β-estradiol (E₂), bisphenol A (BPA) and nonylphenol (NP) through the use of reduced life expectancy (RLE) model and molecular docking analysis. The order of in vivo estrogenic potentials of individual and binary exposure of E₂, BPA and NP was as follows: E₂+BPA＞E₂＞E₂+NP＞BPA＞BPA + NP >>>NP. Binary mixtures of E₂, BPA and NP had weak synergistic effects under the exposure concentration ranges. With the expression of hepatic vtg1 gene, the hepatic toxicity was analyzed by using the RLE model. All plots of the linear RLE model had negative slopes indicating that EC₅₀ was negatively correlated with the natural logarithm of exposure time (lnET₅₀). The RLE model analyses can be useful to evaluate the exposure time effects of zebrafish by using EC₅₀ as toxicity endpoint. Molecular docking analysis revealed that the interaction potential of E₂ (Binding energy: -10.1 kcal/mol) for the zebrafish ERα-LBD was the most potent (stable), followed by BPA (-8.0 kcal/mol) and NP (-6.8 kcal/mol). Molecular docking analysis can be useful to understand interactive effects of E₂, BPA and NP.

The Power of Fish Models to Elucidate Skin Cancer Pathogenesis and Impact the Discovery of New Therapeutic Opportunities

Animal models play important roles in investigating the pathobiology of cancer, identifying relevant pathways, and developing novel therapeutic tools. Despite rapid progress in the understanding of disease mechanisms and technological advancement in drug discovery, negative trial outcomes are the most frequent incidences during a Phase III trial. Skin cancer is a potential life-threatening disease in humans and might be medically futile when tumors metastasize. This explains the low success rate of melanoma therapy amongst other malignancies. In the past decades, a number of skin cancer models in fish that showed a parallel development to the disease in humans have provided important insights into the fundamental biology of skin cancer and future treatment methods. With the diversity and breadth of advanced molecular genetic tools available in fish biology, fish skin cancer models will continue to be refined and expanded to keep pace with the rapid development of skin cancer research. This review begins with a brief introduction of molecular characteristics of skin cancers, followed by an overview of teleost models that have been used in the last decades in melanoma research. Next, we will detail the importance of the zebrafish (Danio rerio) animal model and other emerging fish models including platyfish (Xiphophorus sp.), and medaka (Oryzias latipes) in future cutaneous malignancy studies. The last part of this review provides the recent development and genome editing applications of skin cancer models in zebrafish and the progress in small molecule screening.

Comparison of captive lifespan, age-associated liver neoplasias and age-dependent gene expression between two annual fish species: Nothobranchius furzeri and Nothobranchius korthause

Nothobranchius is a genus of annual fish broadly distributed in South-Eastern Africa and found into temporary ponds generated during the rain seasons and their lifespan is limited by the duration of their habitats. Here we compared two Nothobranchius species from radically different environments: N. furzeri and N. korthausae. We found a large difference in life expectancy (29- against 71-weeks of median life span, 40- against 80-weeks of maximum lifespan, respectively), which correlates with a diverse timing in the onset of several age dependent processes: our data show that N. korthause longer lifespan is associated to retarded onset of age-dependent liver-neoplasia and slower down-regulation of collagen 1 alpha 2 (COL1A2) expression in the skin. On the other hand, the expression of cyclin B1 (CCNB1) in the brain was strongly age-regulated, but with similar profiles in N. furzeri and N. korthausae. In conclusion, our data suggest that the different ageing rate of two species of the same genus could be used as novel tool to investigate and better understand the genetic bases of some general mechanism leading to the complex ageing process, providing a strategy to unravel some of the genetic mechanisms regulating longevity and age-associate pathologies including neoplasias.

Transition to annual life history coincides with reduction in cell cycle speed during early cleavage in three independent clades of annual killifish

Background

Annual killifishes inhabit temporary ponds and their embryos survive the dry season encased in the mud by entering diapause, a process that arrests embryonic development during hostile conditions. Annual killifishes are present within three clades distributed in Africa (one East and one West of the Dahomey gap) and South America. Within each of these phylogenetic clades, a non-annual clade is sister taxon to a annual clade and therefore represent an example of convergent evolution.

Early cleavage of teleost embryos is characterized by a very fast cell cycle (15-30 minutes) and lack of G₁ and G₂ phases. Here, we decided to investigate rates of early cleavage in annual killifishes. In addition, we specifically tested whether also annual killifish embryos lack G₁ and G₂ phases.

Results

We used time lapse brightfield microscopy to investigate cell division kinetics during the first developmental stages of annual- and non-annual species belonging to the three different phylogenetic clades. Annual killifishes of all three clades showed cleavage times significantly longer when compared to their non-annual sister taxa (average 35 min vs. average 75 min). Using FUCCI fluorescent imaging of the cell cycle after microinjection in the annual species Nothobranchius furzeri, we demonstrate that the first 5 division are synchronous and do not show a G₁ phase. Cell cycle synchronization is lost after the 5th cleavage division.

Conclusions

Our results show, for the first time, that cell cycle rate during cleavage, a trait thought to be rather evolutionary conserved can undergo convergent evolutionary change in response to variations in life-history.

Nothobranchius as a model for aging studies. A review

In recent decades, the increase in human longevity has made it increasingly important to expand our knowledge on aging. To accomplish this, the use of animal models is essential, with the most common being mouse (phylogenetically similar to humans, and a model with a long life expectancy) and Caenorhabditis elegans (an invertebrate with a short life span, but quite removed from us in evolutionary terms). However, some sort of model is needed to bridge the differences between those mentioned above, achieving a balance between phylogenetic distance and life span. Fish of the genus Nothobranchius were suggested 10 years ago as a possible alternative for the study of the aging process. In the meantime, numerous studies have been conducted at different levels: behavioral (including the study of the rest-activity rhythm), populational, histochemical, biochemical and genetic, among others, with very positive results. This review compiles what we know about Nothobranchius to date, and examines its future prospects as a true alternative to the classic models for studies on aging.

Inhibitory effect of Lycium barbarum polysaccharides on cell apoptosis and senescence is potentially mediated by the p53 signaling pathway

Lycium barbarum (L. barbarum) fruit or extract has been regarded as a superior-grade Chinese medicine, used to modulate body immunity and for anti-aging purposes. However, the underlying molecular mechanisms behind these effects remain unclear. In the present study, L. barbarum polysaccharides (LBPs), considered a major contributor of L. barbarum effects, were used to elucidate its mechanism of action by phenotypic and senescence associated-β-galactosidase (SA-β-gal) assays, evaluation of survival rates in vivo and expression profiling of genes related to the p53 signaling pathway in a zebrafish model. Zebrafish embryos were continuously exposed to various concentrations of LBPs (1.0, 2.0, 3.0 and 4.0 mg/ml) for 3 days. The results of fluorescent acridine orange and SA-β-gal staining indicated that cell apoptosis and senescence mainly occur in the head at 24 hours post fertilization (hpf) and 72 hpf. In addition, resistance to replicative senescence was observed at low doses of LBPs, especially at the 3.0 mg/ml concentration. Furthermore, the expression of genes that relate to aging, such as p53, p21 and Bax, was decreased, while that of Mdm2 and TERT genes was increased after treatment with LBPs. The results demonstrated that the effects of LBPs on cell apoptosis and aging might be mediated by the p53-mediated pathway.

Age-related changes in mitochondrial membrane composition of Nothobranchius rachovii

Mitochondrial membrane composition may be a critical factor in the mechanisms of the aging process by influencing the propagation of reactions involved in mitochondrial function during periods of high stress. Changes affecting either lipid class or fatty acid compositions could affect phospholipid properties and alter mitochondrial function and cell viability. In the present study, mitochondrial membrane phospholipid compositions were analyzed throughout the life cycle of Nothobranchius rachovii. Mitochondrial phospholipids showed several changes with age. Proportions of cardiolipin decreased and those of sphingomyelin increased between 11- and 14-month-old fish. Fatty acid compositions of individual phospholipids in mitochondria were also significantly affected with age. These data suggest increasing damage to mitochondrial lipids during the life cycle of N. rachovii that could be one of the main factors related with and contributing to degraded mitochondrial function associated with the aging process.

The use of honeybees reared in a thermostatic chamber for aging studies

Honeybees (Apis mellifera) are an attractive model system for studying aging. However, the aging level of worker honeybees from the field hive is in dispute. To eliminate the influence of task performance and confirm the relationship between chronological age and aging, we reared newly emerged workers in a thermostat at 34°C throughout their lives. A survivorship curve was obtained, indicating that workers can be reared away from the field hive, and the only difference between these workers is age. To confirm that these workers can be used for aging studies, we assayed age-related molecules in the trophocytes and fat cells of young and old workers. Old workers expressed more senescence-associated β-galactosidase, lipofuscin granules, lipid peroxidation, and protein oxidation than young workers. Furthermore, cellular energy metabolism molecules were also assayed. Old workers exhibited less ATP concentration, β-oxidation, and microtubule-associated protein light chain 3 (LC3) than young workers. These results demonstrate that honeybees reared in a thermostatic chamber can be used for aging studies and cellular energy metabolism in the trophocytes and fat cells of workers changes with advancing age.

Prolonged life span among endemic Gasterosteus populations

Throughout their circumboreal coastal distribution, the threespine stickleback ( Gasterosteus aculeatus L., 1758) typically reproduce at 1 or 2 years of age (second or third summer) and die during the year of the reproductive cycle. Extending from a previous study on the Haida Gwaii archipelago, western Canada, that identified an exceptionally long life span (8 years) in a population of large-bodied threespine stickleback, we use pelvic spine annuli to examine age of the five largest adult stickleback of 12 additional populations comprising five populations with average-sized adults (45–60 mm standard length (SL)) and seven populations with large-bodied adult stickleback (>75 mm SL). Each of the small-bodied populations had a maximum age of 1 or 2 years typical for the taxon. Among the large-bodied populations, which also reached adult size in the 2nd year, adult stickleback in the populations ranged from 3 to 6 years, indicating extended longevity. Low productivity habitats and refuge against gape-limited piscivores, each of which theoretically predicts reduced rate of senescence, are associated with the greatest longevity among these populations. These data combined with the recent full genome sequence for stickleback provide opportunities for locating genetic markers for extended longevity.

Sleep and its regulation in zebrafish

The function of sleep remains a central enigma of modern biology, in spite of the obvious importance of sleep for normal physiology and cognition. The zebrafish has emerged as a promising new model for studying sleep, its changes with age, and the impact of sleep alterations on cognitive function. Recent studies of this diurnal vertebrate have provided new insights into the dual role of the pineal hormone melatonin and its receptors, regulating sleep in diurnal vertebrates through both homeostatic and circadian mechanisms. Research in zebrafish has also revealed interactions between melatonin and the hypocretin/orexin system, another important sleep-wake modulator. Future investigations should benefit from the conservation in zebrafish of mechanisms that regulate normal sleep, our extensive knowledge of their molecular biology, the availability of multiple transgenic and mutant phenotypes, and the feasibility of applying sensitive in vivo imaging techniques to record sleep-related neuronal activity in these optically transparent subjects. The established sensitivity of zebrafish to many pharmacological hypnotics should also contribute to the development of new, safe and effective sleep medications.

The short-lived annual fish Nothobranchius furzeri shows a typical teleost aging process reinforced by high incidence of age-dependent neoplasias

The annual fish Nothobranchius furzeri is the shortest-lived vertebrate which can be cultured in captivity. Here, we performed a histopathological analysis of age-related lesions in this species. Post-mortem analysis revealed lesions in liver (~90%), kidney (~75%), heart (~70%) and gonads (~40%) which are similar to those previously described in the small teleost Poecilia reticulata. In addition, a high incidence of neoplasias was observed in liver (~35%) and kidney (~25%). Different laboratory strains of N. furzeri show large genetic differences in longevity. Cross-sectional analysis revealed a clear age-dependent increase in the incidence of liver neoplasias which was accelerated in a short-lived strain. Cross-sectional analysis of gonads revealed sex-specific differences in the occurrence of lesions, with males being more severely affected than females. In conclusion, our analysis demonstrates that short life span in N. furzeri is a consequence of a typical teleost aging process which determines systemic failure of homeostasis functions rather than of a single organ or apparatus. Unlike other teleosts, however, this scenario is reinforced by high incidence of age-dependent neoplasias, making this species a promising model to analyze the molecular pathways of age-dependent spontaneous tumorigenesis.

Cats, "rats," and bats: the comparative biology of aging in the 21st century

Laboratory models have suggested a link between metabolism and life span in vertebrates, and it is well known that the evolution of specific life histories can be driven by metabolic factors. However, little is known regarding how the adoption of specific life-history strategies can shape aging and life span in populations facing different energetic demands from either a theoretical or a mechanistic viewpoint but significant insight can be gained by using a comparative approach. Comparative biology plays several roles in our understanding of the virtually ubiquitous phenomenon of aging in animals. First, it provides a critical evaluation of broad hypotheses concerning the evolutionary forces underlying the modulation of aging rate. Second, it suggests mechanistic hypotheses about processes of aging. Third, it illuminates particularly informative species because of their exceptionally slow or rapid aging rates to be interrogated about potentially novel mechanisms of aging. Although comparative biology has played a significant role in research on aging for more than a century, the new comparative biology of aging is poised to dwarf those earlier contributions, because: (1) new cellular and molecular techniques for investigating novel species are in place and more are being continually generated, (2) molecular systematics has resolved the phylogenetic relationships among a wide range of species, which allow for the implementation of analytic tools specialized for comparative biology, and (3) in addition to facilitating the construction of accurate phylogenies, the dramatic acceleration in DNA-sequencing technology is providing us with new tools for a comparative genomic approach to understanding aging.

Ambient temperature influences aging in an annual fish (Nothobranchius rachovii)

Extending lifespan by lowering ambient temperature in the habitat has been shown in a variety of organisms. Its mechanism, however, remains elusive. In this study, we examined the survivorship and the aging process of the annual fish (Nothobranchius rachovii) reared under high (30 degrees C), moderate (25 degrees C) and low (20 degrees C) ambient temperatures. The results showed that low ambient temperatures prolong survivorship, whereas high ambient temperatures shorten survivorship. At low ambient temperature, expression of senescence-associated beta-galactosidase, lipofuscin, reactive oxygen species, lipid peroxidation, protein oxidation, mitochondrial density and ADP/ATP ratio were reduced compared with those reared at high and moderate temperatures, whereas catalase activity, Mn-superoxide dismutase activities, mitochondrial membrane potential and the levels of ATP, ADP, Sirt1 and Forkhead box O expression were elevated. The expression levels of Hsp70 and CIRP showed no significant difference under any of the ambient temperatures tested. We concluded that cellular metabolism, energy utilization and gene expression are altered at lower ambient temperature, which is associated with the extension of lifespan of the annual fish.

Fish as model systems for the study of vertebrate apoptosis

Apoptosis is a process of pivotal importance for multi-cellular organisms and due to its implication in the development of cancer and degenerative disease it is intensively studied in humans and mammalian model systems. Invertebrate models of apoptosis have been well-studied, especially in C. elegans and D. melanogaster, but as these are evolutionarily distant from mammals the relevance of findings for human research is sometimes limited. Presently, a non-mammalian vertebrate model for studying apoptosis is missing. However, in the past few years an increasing number of studies on cell death in fish have been published and thus new model systems may emerge. This review aims at highlighting the most important of these findings, showing similarities and dissimilarities between fish and mammals, and will suggest topics for future research. In addition, the outstanding usefulness of fish as research models will be pointed out, hoping to spark future research on this exciting, often underrated group of vertebrates.

The short-lived fish Nothobranchius furzeri as a new model system for aging studies

Genetic and pharmacological research on aging is hampered by the lifespan of available vertebrate models. We recently initiated studies on Nothobranchius furzeri, a species with a maximum life expectancy in captivity of just three months which represents the shortest documented captive lifespan for a vertebrate. Further research on N. furzeri has demonstrated that 1. Short lifespan is tied with explosive growth and accelerated sexual maturation. 2. Short lifespan is correlated with expression of age-related behavioral and histological changes. 3. Lifespan and expression of age-related markers can be modulated by water temperature. 4. Resveratrol, a drug characterized for its life-extending action in Caenorhabditis elegans and Drosophila, increases lifespan and retards expression of age-related markers. 5. Aging-related genes can be easily isolated by homology cloning. Finally, different populations or species of Nothobranchius show large-scale differences in captive lifespan. In the last three years, N. furzeri has moved from biological curiosity to a promising model system for drug validation. Furthermore, this species occupies a favorable position in the Teleost's "tree of life". It is very close to the Japanese Medaka, and close to the pufferfishes and stickleback and might represent a very useful model for comparative genomics of aging.

Annual fishes of the genus Nothobranchius as a model system for aging research

Aging research in vertebrates is hampered by the lack of short-lived models. Annual fishes of the genus Nothobranchius live in East African seasonal ponds. Their life expectancy in the wild is limited by the duration of the wet season and their lifespan in captivity is also short. Nothobranchius are popular aquarium fishes and many different species are kept as captive strains, providing rich material for comparative studies. The present paper aims at reviving the interest in these fishes by reporting that: (1) Nothobranchius can be cultured, and their eggs stored dry at room temperature for months or years, offering inexpensive methods of embryo storage; (2) Nothobranchius show accelerated growth and expression of aging biomarkers at the level of histology and behaviour; (3) the species Nothobranchius furzeri has a maximum lifespan of only 3 months and offers the possibility to perform investigations thus far unthinkable in a vertebrate, such as drug screening with life-long pharmacological treatments and experimental evolution; (4) when the lifespan of different species is compared, a general correlation is found between wet season duration in their natural habitat and longevity in captivity; and (5) vertebrate aging-related genes, such as p66Shc and MTP, can be easily isolated in Nothobranchius by homology cloning. These fishes can become excellent models for aging studies. They can be employed to test the effects of experimental manipulation on aging at a pace comparable with that of Drosophila and to probe the effects of natural selection on the evolution of aging-related genes.

Salmon spawning migration and muscle protein metabolism: the August Krogh principle at work

The August Krogh principle, stating that for any particular question in biology, nature holds an ideal study system, was applied by choosing the anorexic, long-distance migration of salmon as a model to analyze protein degradation and amino acid metabolism. Reexamining an original study done over 20 years ago on migrating sockeye salmon (Oncorhynchus nerka), data on fish migration and starvation are reviewed and a general model is developed on how fish deal with muscle proteolysis. It is shown that lysosomal activation and degradation of muscle protein by lysosomal cathepsins, especially cathepsin D and sometimes cathepsin L, are responsible for the degradation of muscle protein during fish migration, maturation and starvation. This strategy is quite the opposite to mammalian muscle wasting, including starvation, uremia, cancer and others, where the ATP-ubiquitin proteasome in conjunction with ancillary systems, constitutes the overwhelming pathway for protein degradation in muscle. In mammals, the lysosome plays a bit part, if any. In contrast, the proteasome plays at best a subordinate role in muscle degradation in piscine systems. This diverging strategy is put into the context of fish metabolism in general, with its high amino acid turnover, reliance on amino acids as oxidative substrates and flux of amino acids from muscle via the liver into gonads during maturation. Brief focus is placed on structure, function and evolution of the key player in fishes: cathepsin D. The gene structure of piscine cathepsin D is outlined, focusing on the existence of duplicate, paralogous, cathepsin D genes in some species and analyzing the relationship between a female and liver-specific aspartyl protease and fish cathepsin Ds. Evolutionary relationships are developed between different groups of piscine cathepsins, aspartyl proteases and other cathepsins. Finally, based on specific changes in muscle enzymes in fish, including migrating salmon, common strategies of amino acid and carbon flux in fish muscle are pointed out, predicting some metabolic concepts that would make ideal application grounds for the August Krogh principle.

The use of mature zebrafish (Danio rerio) as a model for human aging and disease

Zebrafish (Danio rerio) have been extensively utilized for understanding mechanisms of development. These studies have led to a wealth of resources including genetic tools, informational databases, and husbandry methods. In spite of all these resources, zebrafish have been underutilized for exploring pathophysiology of disease and the aging process. Zebrafish offer several advantages over mammalian models for these studies, including the ability to perform saturation mutagenesis and the capability to contain thousands of animals in a small space. In this review, we will discuss the use of mature zebrafish as an animal model and provide specific examples to support this novel use of zebrafish. Examples include demonstrating that clinical pathology can be performed in mature zebrafish and that age-associated changes in heat shock response can be observed in zebrafish. These highlights demonstrate the utility of zebrafish as a model for disease and aging.