Ambient temperature reduction extends lifespan via activating cellular degradation activity in an annual fish (Nothobranchius rachovii)

Identification of Isthmin1 in the small annual fish, Nothobranchius guentheri, as a novel biomarker of aging and its potential rejuvenation activity

Isthmin 1 (Ism1) has been shown to play roles in multiple biological processes including morphogenesis, hematopoiesis, antiviral immune response and suppression of tumor growth. However, it remains unknown if it plays any role in aging process. Here we showed for the first time that Ism1 was a new age-related biomarker, which decreased with age in fish, mice and humans. Interestingly, Ism1 was also useful to measure the "rejuvenated" age of fish Nothobranchius guentheri reversed by salidroside treatment and temperature reduction, providing additional evidence that Ism1 was an aging biomarker. In addition, we clearly showed that dietary intake of recombinant Ism1 had little effects on the body length and weight of aging N. guentheri, but it retarded the onset of age-related biomarkers and prolonged both the maximum and median lifespan of the fish. We also showed that Ism1 exerted its rejuvenation activity via the enhancement of antioxidant system. Collectively, our results indicate that Ism1 is not only is a novel biomarker of aging but also a potential rejuvenation factor capable of reversing aging of N. guentheri.

A higher mitochondrial content is associated with greater oxidative damage, oxidative defenses, protein synthesis and ATP turnover in resting skeletal muscle

An unavoidable consequence of aerobic metabolism is the production of reactive oxygen species (ROS). Mitochondria have historically been considered the primary source of ROS; however, recent literature has highlighted the uncertainty in primary ROS production sites and it is unclear how variation in mitochondrial density influences ROS-induced damage and protein turnover. Fish skeletal muscle is composed of distinct, highly aerobic red muscle and anaerobic white muscle, offering an excellent model system in which to evaluate the relationship of tissue aerobic capacity and ROS-induced damage under baseline conditions. The present study used a suite of indices to better understand potential consequences of aerobic tissue capacity in red and white muscle of the pinfish, Lagodon rhomboides. Red muscle had a 7-fold greater mitochondrial volume density than white muscle, and more oxidative damage despite also having higher activity of the antioxidant enzymes superoxide dismutase and catalase. The dominant protein degradation system appears to be tissue dependent. Lysosomal degradation markers and autophagosome volume density were greater in white muscle, while ubiquitin expression and 20S proteasome activity were significantly greater in red muscle. However, ubiquitin ligase expression was significantly higher in white muscle. Red muscle had a more than 2-fold greater rate of translation and total ATP turnover than white muscle, results that may be due in part to the higher mitochondrial density and the associated increase in oxidative damage. Together, these results support the concept that an elevated aerobic capacity is associated with greater oxidative damage and higher costs of protein turnover.

Thermal tolerance and routine oxygen consumption of convict cichlid, Archocentrus nigrofasciatus, acclimated to constant temperatures (20 °C and 30 °C) and a daily temperature cycle (20 °C → 30 °C)

Organismal temperature tolerance and metabolic responses are correlated to recent thermal history, but responses to thermal variability are less frequently assessed. There is great interest in whether organisms that experience greater thermal variability can gain metabolic or tolerance advantages through phenotypic plasticity. We compared thermal tolerance and routine aerobic metabolism of Convict cichlid acclimated for 2 weeks to constant 20 °C, constant 30 °C, or a daily cycle of 20 → 30 °C (1.7 °C/h). Acute routine mass-specific oxygen consumption ([Formula: see text]O₂) and critical thermal maxima/minima (CTMax/CTMin) were compared between groups, with cycle-acclimated fish sampled from the daily minimum (20 °C, 0900 h) and maximum (30 °C, 1600 h). Cycle-acclimated fish demonstrated statistically similar CTMax at the daily minimum and maximum (39.0 °C, 38.6 °C) but distinct CTMin values, with CTMin 2.4 °C higher for fish sampled from the daily 30 °C maximum (14.8 °C) compared to the daily 20 °C minimum (12.4 °C). Measured acutely at 30 °C, [Formula: see text]O₂ decreased with increasing acclimation temperature; 20 °C acclimated fish had an 85% higher average [Formula: see text]O₂ than 30 °C acclimated fish. Similarly, acute [Formula: see text]O₂ at 20 °C was 139% higher in 20 °C acclimated fish compared to 30 °C acclimated fish. Chronic [Formula: see text]O₂ was measured in separate fish continually across the 20 → 30 °C daily cycle for all 3 acclimation groups. Chronic [Formula: see text]O₂ responses were very similar between groups between average individual hourly values, as temperatures increased or decreased (1.7 °C/h). Acute [Formula: see text]O₂ and thermal tolerance responses highlight "classic" trends, but dynamic, chronic trials suggest acclimation history has little effect on the relative change in oxygen consumption during a thermal cycle. Our results strongly suggest that the minimum and maximum temperatures experienced more strongly influence fish physiology, rather than the thermal cycle itself. This research highlights the importance of collecting data in both cycling and static (constant) thermal conditions, and further research should seek to understand whether ectotherm metabolism does respond uniquely to fluctuating temperatures.

Extreme warm acclimation temperature alters oxygen consumption, micronucleus formation in erythrocytes, and gill morphology of rohu (Labeo rohita) fingerlings

Experiencing the seasonal variation and rapid global warming in the tropical climate is a common phenomenon which challenged the aquatic organisms to adapt the physiology and behavior. To investigate the effect of high-temperature acclimation, we selected Indian major carp, rohu (Labeo rohita), a commercially important freshwater aquaculture species. Oxygen consumptions, micronucleus formation in erythrocytes, and gill histopathology were observed in L. rohita fingerlings acclimated at three temperatures (30, 33, and 36 °C) for 30 days. Results showed that the highest acclimated temperature (36 °C) induced higher oxygen consumption and increased frequency of micronucleus formation in erythrocytes. Severity of different histological alterations (hyperplasia, epithelial necrosis, telangiectasis, epithelial lifting, and hypertrophy of chloride cells) in the gills was found to be increased in the highest acclimated temperature (36 °C). These findings indicate the temperature induced adaptive responses and climate vulnerability in a changing environment.

Nontraditional systems in aging research: an update

Research on the evolutionary and mechanistic aspects of aging and longevity has a reductionist nature, as the majority of knowledge originates from experiments on a relatively small number of systems and species. Good examples are the studies on the cellular, molecular, and genetic attributes of aging (senescence) that are primarily based on a narrow group of somatic cells, especially fibroblasts. Research on aging and/or longevity at the organismal level is dominated, in turn, by experiments on Drosophila melanogaster, worms (Caenorhabditis elegans), yeast (Saccharomyces cerevisiae), and higher organisms such as mice and humans. Other systems of aging, though numerous, constitute the minority. In this review, we collected and discussed a plethora of up-to-date findings about studies of aging, longevity, and sometimes even immortality in several valuable but less frequently used systems, including bacteria (Caulobacter crescentus, Escherichia coli), invertebrates (Turritopsis dohrnii, Hydra sp., Arctica islandica), fishes (Nothobranchius sp., Greenland shark), reptiles (giant tortoise), mammals (blind mole rats, naked mole rats, bats, elephants, killer whale), and even 3D organoids, to prove that they offer biogerontologists as much as the more conventional tools. At the same time, the diversified knowledge gained owing to research on those species may help to reconsider aging from a broader perspective, which should translate into a better understanding of this tremendously complex and clearly system-specific phenomenon.

Tissue-specific effects of temperature on proteasome function

Variation in ambient growth temperature can cause changes in normal animal physiology and cellular functions such as control of protein homeostasis. A key mechanism for maintaining proteostasis is the selective degradation of polyubiquitinated proteins, mediated by the ubiquitin-proteasome system (UPS). It is still largely unsolved how temperature changes affect the UPS at the organismal level. Caenorhabditis elegans nematodes are normally bred at 20 °C, but for some experimental conditions, 25 °C is often used. We studied the effect of 25 °C on C. elegans UPS by measuring proteasome activity and polyubiquitinated proteins both in vitro in whole animal lysates and in vivo in tissue-specific transgenic reporter strains. Our results show that an ambient temperature shift from 20 to 25 °C increases the UPS activity in the intestine, but not in the body wall muscle tissue, where a concomitant accumulation of polyubiquitinated proteins occurs. These changes in the UPS activity and levels of polyubiquitinated proteins were not detectable in whole animal lysates. The exposure of transgenic animals to 25 °C also induced ER stress reporter fluorescence, but not the fluorescence of a heat shock responsive reporter, albeit detection of a mild induction in hsp-16.2 mRNA levels. In conclusion, C. elegans exhibits tissue-specific responses of the UPS as an organismal strategy to cope with a rise in ambient temperature.

The cellular responses of autophagy, apoptosis, and 5-methylcytosine level in zebrafish cells upon nutrient deprivation stress

Here we reported the stress responses of nutrient deprivation and extended observation of autophagy, apoptosis, and DNA methylation in zebrafish embryonic fibroblast (ZF4) cells. Our results showed that serum deprivation resulted in the changes of cell shape and adherent ability, the suppressed cell growth and viability, and the inhibited proliferation and cell cycle. Besides, the appearance of lysosome and autophagosome/autolysosome with significantly increased expression of mRNAs (ulk1a, becn1, atg12, sqstm1, maplc3, and lamp1) and proteins (Atg12, Becn1, Sqstm1, and Lamp1) indicate the autophagic activity was boosted at initial stage but relatively weakened at 48 h of serum starvation. When autophagy no longer mitigate for the stress, cell apoptosis detected by the mRNA expression of caspases, Bcl-2/Bax expression, and Annexin V/PI was gradually enhanced to execute the death plan upon prolonged starvation process. Furthermore, the methyl group metabolism was increased in accordance with autophagic activity and was suppressed by enhanced apoptotic activity. These data suggested that the recycle activity induced by autophagy could compensate the substrates and reactions of DNA transmethylation, which obviously increased 5-methylcytosine (5 mC) level in ZF4 cells. In summary, our results discovered the cellular responses under prolonged serum starvation stress and elaborated the switch from autophagy to apoptosis and corresponding correlation with 5 mC level changes in teleost fish in vitro.

Dietary Intake of β-Glucans Can Prolong Lifespan and Exert an Antioxidant Action on Aged Fish Nothobranchius guentheri

One of the widely accepted conjectures regarding mechanisms of aging is probably the oxidative stress hypothesis. β-1,3-Glucans, well-known immunostimulants, have been shown to increase nonspecific immunity and resistance against infections or pathogenic bacteria in several fish species, but its antiaging function remains poorly understood. By feeding of β-1,3-glucans to the annual fish, Nothobranchius guentheri, we detected the survivorship of the fish and estimated the development of age-related biomarkers at different stages. We first showed that administration of β-1,3-glucans was able to prolong the lifespan of the fish (p < 0.05). We then showed that β-1,3-glucans clearly reduced the accumulation of lipofuscin in the gills and the senescence-associated β-galactosidase in the caudal fins. Moreover, β-1,3-glucans were able to lower the levels of protein oxidation, lipid peroxidation, and reactive oxygen species (ROS) in the muscles. Finally, β-1,3-glucans could promote the activities of the antioxidant enzymes, including catalase, superoxide dismutase, and glutathione peroxidase in the fish, and slow down the increase of P66shc, a critical factor involved in the regulation of intracellular ROS contents. These data together suggest for the first time that β-1,3-glucans can extend the lifespan, delay the onset of age-related biomarkers and exert an antioxidant action of the aged fish, N. guentheri. It also implies that β-1,3-glucans may be potentially useful for health care in the elderly, including extension of the lifespan.

Cellular degradation activity is maintained during aging in long-living queen bees

Queen honeybees (Apis mellifera) have a much longer lifespan than worker bees. Whether cellular degradation activity is involved in the longevity of queen bees is unknown. In the present study, cellular degradation activity was evaluated in the trophocytes and oenocytes of young and old queen bees. The results indicated that (i) 20S proteasome activity and the size of autophagic vacuoles decreased with aging, and (ii) there were no significant differences between young and old queen bees with regard to 20S proteasome expression or efficiency, polyubiquitin aggregate expression, microtubule-associated protein 1 light chain 3-II (LC3-II) expression, 70 kDa heat shock cognate protein (Hsc70) expression, the density of autophagic vacuoles, p62/SQSTM1 expression, the activity or density of lysosomes, or molecular target of rapamycin expression. These results indicate that cellular degradation activity maintains a youthful status in the trophocytes and oenocytes of queen bees during aging and that cellular degradation activity is involved in maintaining the longevity of queen bees.

Thermosensation and longevity

Temperature has profound effects on behavior and aging in both poikilotherms and homeotherms. To thrive under the ever fluctuating environmental temperatures, animals have evolved sophisticated mechanisms to sense and adapt to temperature changes. Animals sense temperature through various molecular thermosensors, such as thermosensitive transient receptor potential (TRP) channels expressed in neurons, keratinocytes, and intestine. These evolutionarily conserved thermosensitive TRP channels feature distinct activation thresholds, thereby covering a wide spectrum of ambient temperature. Temperature changes trigger complex thermosensory behaviors. Due to the simplicity of the nervous system in model organisms such as Caenorhabditis elegans and Drosophila, the mechanisms of thermosensory behaviors in these species have been extensively studied at the circuit and molecular levels. While much is known about temperature regulation of behavior, it remains largely unclear how temperature affects aging. Recent studies in C. elegans demonstrate that temperature modulation of longevity is not simply a passive thermodynamic phenomenon as suggested by the rate-of-living theory, but rather a process that is actively regulated by genes, including those encoding thermosensitive TRP channels. In this review, we discuss our current understanding of thermosensation and its role in aging.