Changes in mitochondrial energy utilization in young and old worker honeybees (Apis mellifera)

Age-related flexibility of energetic metabolism in the honey bee Apis mellifera

The mechanisms that underpin aging are still elusive. In this study, we suggest that the ability of mitochondria to oxidize different substrates, which is known as metabolic flexibility, is involved in this process. To verify our hypothesis, we used honey bees (Apis mellifera carnica) at different ages, to assess mitochondrial oxygen consumption and enzymatic activities of key enzymes of the energetic metabolism as well as ATP5A1 content (subunit of ATP synthase) and adenylic energy charge (AEC). We also measured mRNA abundance of genes involved in mitochondrial functions and the antioxidant system. Our results demonstrated that mitochondrial respiration increased with age and favored respiration through complexes I and II of the electron transport system (ETS) while glycerol-3-phosphate (G3P) oxidation was relatively decreased. In addition, glycolytic, tricarboxylic acid cycle and ETS enzymatic activities increased, which was associated with higher ATP5A1 content and AEC. Furthermore, we detected an early decrease in the mRNA abundance of subunits of NADH ubiquinone oxidoreductase subunit B2 (NDUFB2, complex I), mitochondrial cytochrome b (CYTB, complex III) of the ETS as well as superoxide dismutase 1 and a later decrease for vitellogenin, catalase and mitochondrial cytochrome c oxidase subunit 1 (COX1, complex IV). Thus, our study suggests that the energetic metabolism is optimized with aging in honey bees, mainly through quantitative and qualitative mitochondrial changes, rather than showing signs of senescence. Moreover, aging modulated metabolic flexibility, which might reflect an underpinning mechanism that explains lifespan disparities between the different castes of worker bees.

1H NMR Profiling of Honey Bee Bodies Revealed Metabolic Differences between Summer and Winter Bees

Simple Summary

The European honey bee, Apis mellifera, is well-known to have two distinct populations in temperate climate zone: short-living summer bees and long-living winter bees. Several biological factors related to the different lifespans of the two populations have been studied. However, the link between the metabolic changes and basic physiological features in the bodies of summer bees and winter bees is limited. This study aimed to identify the metabolic fingerprints that characterize summer and winter bees using proton nuclear magnetic resonance (¹H NMR) spectroscopy. In total, we found 28 significantly changed metabolites between the two populations. The results suggest that the metabolites detected in honey bee bodies can distinguish the summer and winter bees. Changes in carbohydrates, amino acids, choline-containing compounds, and an unknown compound were noticeable during the transition from summer bees to winter bees. The results from this study give us a broad perspective on honey bee metabolism that will support future research related to honey bee lifespan and overwintering management.

Abstract

In temperate climates, honey bee workers of the species Apis mellifera have different lifespans depending on the seasonal phenotype: summer bees (short lifespan) and winter bees (long lifespan). Many studies have revealed the biochemical parameters involved in the lifespan differentiation of summer and winter bees. However, comprehensive information regarding the metabolic changes occurring in their bodies between the two is limited. This study used proton nuclear magnetic resonance (¹H NMR) spectroscopy to analyze the metabolic differences between summer and winter bees of the same age. The multivariate analysis showed that summer and winter bees could be distinguished based on their metabolic profiles. Among the 36 metabolites found, 28 metabolites have displayed significant changes from summer to winter bees. Compared to summer bees, trehalose in winter bees showed 1.9 times higher concentration, and all amino acids except for proline and alanine showed decreased patterns. We have also detected an unknown compound, with a CH₃ singlet at 2.83 ppm, which is a potential biomarker that is about 13 times higher in summer bees. Our results show that the metabolites in summer and winter bees have distinctive characteristics; this information could provide new insights and support further studies on honey bee longevity and overwintering.

MS275 as Class I HDAC inhibitor displayed therapeutic potential on malignant ascites by iTRAQ-based quantitative proteomic analysis

Background

Malignant ascites is a manifestation of end stage events in a variety of cancers and is associated with significant morbidity. Epigenetic modulators play a key role in cancer initiation and progression, among which histone deacetylases (HDACs) are considered as one of the most important regulators for various cancer development, such as liver cancer, ovarian cancer, and pancreatic cancer et al. Thus, in this paper, we sought to explore the therapeutic effect of HDAC inhibitor on malignant ascites.

Methods

In this report, we tested the therapeutic effect of different isoform selective HDAC inhibitors (Class I HDACI MS275, Class IIa HDACI MC1568, pan-HDAC inhibitors SAHA) on malignant ascites in vitro and in vivo. We further used proteome analysis to find the potential mechanisms for malignant ascites therapy.

Results

Among the different isoform-selective HDAC inhibitors, the class I selective HDACI, MS275, exhibited preferential inhibition on various ascites cells. MS275 could induce cell cycle arrest in G0/G1 phase and promote apoptosis on ascites cells. Through proteome analysis, we found MS275 could downregulate proteins related to cell cycle progression, such as CDK4, CDC20, CCND1; MS275 could upregulate pro-apoptosis proteins such as PAPR1, LMNB2 and AIFM1; in addition, MS275 could change the expression of tumorigenic proteins related to the specific malignant ascites bearing tumors, such as TSP1 and CDK4 for bladder cancer. We then confirmed that abemaciclib (CDK4/6 selective inhibitor) could inhibit the proliferation of ascites cells, and the combination of abemaciclib and MS275 had synergistic anti-tumor effect. Finally, we found that MS275 could in vivo inhibit malignant ascites progression (ascites volume: 2.9 ± 1.0 mL vs 7.5 ± 1.2 mL, p < 0.01), tumor growth, and prolong 66% of the life-span when compared with the untreated group.

Conclusion

This present research revealed that the class I selective HDAC inhibitor, MS275, could effectively inhibit malignant ascites development and tumor growth via multiple pathways. These results indicated that HDACI could have great potential for clinical therapy of malignant ascites.

The trophocytes and oenocytes of worker and queen honey bees (Apis mellifera) exhibit distinct age-associated transcriptome profiles

Despite the identical genomic context, trophocytes and oenocytes in worker bees exhibit aging-related phenotypes, in contrast to the longevity phenotypes in queen bees. To explore this phenomenon at the molecular level, we evaluated the age-associated transcriptomes of trophocytes and oenocytes in worker bees and queen bees using high-throughput RNA-sequencing technology (RNA-seq). The results showed that (i) while gene expression profiles were different between worker and queen bees, they remained similar between young and old counterparts; (ii) worker bees express a high proportion of low-abundance genes, whereas queen bee transcriptomes display a high proportion of moderate-expression genes; (iii) genes were upregulated to a greater extent in queen bees vs. worker bees; and (iv) distinct aging-related and longevity-related candidate genes were found in worker and queen bees. These results provide new insights into the cellular aging and longevity of trophocytes and oenocytes in honey bees. Identification of aging-associated biomarker genes also constitutes a basis for translational research of aging in higher organisms.

Differential expression of antioxidant system genes in honey bee (Apis mellifera L.) caste development mitigates ROS-mediated oxidative damage in queen larvae

The expression of morphological differences between the castes of social bees is triggered by dietary regimes that differentially activate nutrient-sensing pathways and the endocrine system, resulting in differential gene expression during larval development. In the honey bee, Apis mellifera, mitochondrial activity in the larval fat body has been postulated as a link that integrates nutrient-sensing via hypoxia signaling. To understand regulatory mechanisms in this link, we measured reactive oxygen species (ROS) levels, oxidative damage to proteins, the cellular redox environment, and the expression of genes encoding antioxidant factors in the fat body of queen and worker larvae. Despite higher mean H₂O₂ levels in queens, there were no differences in ROS-mediated protein carboxylation levels between the two castes. This can be explained by their higher expression of antioxidant genes (MnSOD, CuZnSOD, catalase, and Gst1) and the lower ratio between reduced and oxidized glutathione (GSH/GSSG). In worker larvae, the GSG/GSSH ratio is elevated and antioxidant gene expression is delayed. Hence, the higher ROS production resulting from the higher respiratory metabolism in queen larvae is effectively counterbalanced by the up-regulation of antioxidant genes, avoiding oxidative damage. In contrast, the delay in antioxidant gene expression in worker larvae may explain their endogenous hypoxia response.

A critical look at proximate causes of social insect senescence: damage accumulation or hyperfunction?

Social insects have received attention for their extreme lifespan variation and reversal of the fecundity/longevity trade-off. However, proximate causes of senescence in general are disputed, and social insects often fail to meet the predictions of prevailing models. We present evidence for and against the long-held free radical theory of aging in social insects, and consider the application of the competing hyperfunction theory. Current results present problems for both theories, and a more complex picture of the biological processes involved emerges. The eusocial life style might allow colonies to allocate damage in ways that create seemingly senescence-free life histories. Only experimental approaches characterizing multiple senescence factors simultaneously will shed light on how social insects defy the conventions of senescence.

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.

Energy-regulated molecules maintain young status in the trophocytes and fat cells of old queen honeybees

Queen honeybees (Apis mellifera) have much longer lifespans than worker bees. Energy-regulated molecules in the trophocytes and fat cells of workers during aging have been determined, but are unknown in queen bees. In the present study, energy-regulated molecules were evaluated in the trophocytes and fat cells of young and old queen bees. Adenosine monophosphate-activated protein kinase α2 (AMPK-α2), phosphorylated AMPK-α2 (pAMPK-α2), and cAMP-specific phosphodiesterases activity increased with aging. The pAMPK-α2/AMPK-α2 ratio and AMPK activity; adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) concentrations; the ADP/ATP ratio and the AMP/ATP ratio; the cyclic adenosine monophosphate concentration; forkhead box protein O expression; Silent information regulator T1 (SirT1) expression and activity; and peroxisome proliferator-activated receptor-α (PPAR-α) expression were not significantly different between young and old queen bees. These results show that energy-regulated molecules maintain a youthful status in the trophocytes and fat cells of queen bees during aging. These cells seem to have longevity-promoting mechanisms and may clarify the secret of longevity in queen bees.

Oxidative stress and anti-oxidant enzyme activities in the trophocytes and fat cells of queen honeybees (Apis mellifera)

Trophocytes and fat cells of queen honeybees have been used for delayed cellular senescence studies, but their oxidative stress and anti-oxidant enzyme activities with advancing age are unknown. In this study, we assayed reactive oxygen species (ROS) and anti-oxidant enzymes in the trophocytes and fat cells of young and old queens. Young queens had lower ROS levels, lower superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, and higher thioredoxin reductase (TR) activity compared to old queens. These results show that oxidative stress and anti-oxidant enzyme activities in trophocytes and fat cells increase with advancing age in queens and suggest that an increase in oxidative stress and a consequent increase in stress defense mechanisms are associated with the longevity of queen honeybees.

Extracellular visfatin has nicotinamide phosphoribosyltransferase enzymatic activity and is neuroprotective against ischemic injury

AIM

Visfatin, a novel adipokine, is predominantly produced by visceral adipose tissue and exists in intracellular and extracellular compartments. The intracellular form of visfatin is proved to be nicotinamide phosphoribosyltransferase (NAMPT) and exhibits neuroprotection through maintaining intracellular NAD(+) pool. However, whether extracellular form of visfatin has NAMPT activity and the effect of extracellular visfatin in cerebral ischemia are unknown.

METHODS AND RESULTS

Plasma concentrations of visfatin, NAD(+) , and ATP were increased in mice upon cerebral ischemia. Cultured glia, but not neuron, was able to secrete visfatin. Oxygen-glucose deprivation (OGD) stress increased the secretion of visfatin from glia. Extracellular recombinant mouse wild-type visfatin, but not mouse H247A-mutant enzymatic-dead visfatin, had NAMPT enzymatic function in vitro. Treatment of wild-type visfatin, but not H247A-mutant enzymatic-dead visfatin, significantly attenuated detrimental effect of OGD on the cell viability and apoptosis in both cultured mouse neuron and glia. Treatment of neutralizing antibody, abolished the protective effect of extracellular visfatin on cell viability, but failed to block the antiapoptotic effect of extracellular visfatin. At last, we observed that plasma visfatin concentrations decreased in 6-month-old but not 3-month-old SHR-SP compared with that in age-matched Wistar-Kyoto rats. Inhibition of NAMPT enzymatic function of visfatin (by FK866) accelerated the occurrence of stroke in SHR-SP.

CONCLUSIONS

Extracellular visfatin has NAMPT enzymatic activity and maybe be neuroprotective just as intracellular visfatin in cerebral ischemic injury.

Changes in energy-regulated molecules in the trophocytes and fat cells of young and old worker honeybees (Apis mellifera)

Trophocytes and fat cells of honeybees (Apis mellifera) have been used for cellular senescence studies, but the changes in the expression, concentration, and activity of cellular energy-regulated molecules that occur with aging in worker bees is unknown. In this study, energy-regulated molecules were evaluated in the trophocytes and fat cells of young and old workers. The results showed that (i) adenosine monophosphate-activated protein kinase-α2 (AMPK-α2) expression increased with aging, whereas phosphorylated AMPK-α2 expression, the phosphorylated AMPK/AMPK ratio, and AMPK activity decreased with aging; (ii) adenosine diphosphate and adenosine triphosphate concentrations decreased with aging, the AMP concentration was unchanged, the adenosine diphosphate/adenosine triphosphate ratio did not change with aging, and the AMP/adenosine triphosphate ratio increased with aging; (iii) the cyclic AMP concentration decreased with aging, and cyclic AMP-specific phosphodiesterases activity increased with aging; (iv) silent information regulator 2 (Sir2) expression increased with aging, whereas its activity decreased with aging; and (v) peroxisome proliferator-activated receptor-α expression decreased with aging. These results show that the trophocytes and fat cells of young workers have higher cellular energy status and express higher levels of energy-regulated molecules than those of old workers and that aging results in a decline in the energy status of trophocytes and fat cells in worker honeybees.