Lipidomic features of honey bee and colony health during limited supplementary feeding

Honey bee nutritional health depends on nectar and pollen, which provide the main source of carbohydrates, proteins and lipids to individual bees. During malnutrition, insect metabolism accesses fat body reserves. However, this process in bees and its repercussions at the colony level are poorly understood. Using untargeted lipidomics and gene expression analysis, we examined the effects of different feeding treatments (starvation, sugar feeding and sugar + pollen feeding) on bees and correlated them with colony health indicators. We found that nutritional stress led to an increase in unsaturated triacylglycerols and diacylglycerols, as well as a decrease in free fatty acids in the bee fat body. Here, we hypothesise that stored lipids are made available through a process where unsaturations change lipid's structure. Increased gene expression of three lipid desaturases in response to malnutrition supports this hypothesis, as these desaturases may be involved in releasing fatty acyl chains for lipolysis. Although nutritional stress was evident in starving and sugar-fed bees at the colony and physiological level, only starved colonies presented long-term effects in honey production.

Phenotypic molecular features of long-lived animal species

One of the challenges facing science/biology today is uncovering the molecular bases that support and determine animal and human longevity. Nature, in offering a diversity of animal species that differ in longevity by more than 5 orders of magnitude, is the best 'experimental laboratory' to achieve this aim. Mammals, in particular, can differ by more than 200-fold in longevity. For this reason, most of the available evidence on this topic derives from comparative physiology studies. But why can human beings, for instance, reach 120 years whereas rats only last at best 4 years? How does nature change the longevity of species? Longevity is a species-specific feature resulting from an evolutionary process. Long-lived animal species, including humans, show adaptations at all levels of biological organization, from metabolites to genome, supported by signaling and regulatory networks. The structural and functional features that define a long-lived species may suggest that longevity is a programmed biological property.

Sterol and lipid metabolism in bees

BACKGROUND

Bees provide essential pollination services for many food crops and are critical in supporting wild plant diversity. However, the dietary landscape of pollen food sources for social and solitary bees has changed because of agricultural intensification and habitat loss. For this reason, understanding the basic nutrient metabolism and meeting the nutritional needs of bees is becoming an urgent requirement for agriculture and conservation. We know that pollen is the principal source of dietary fat and sterols for pollinators, but a precise understanding of what the essential nutrients are and how much is needed is not yet clear. Sterols are key for producing the hormones that control development and may be present in cell membranes, where fatty-acid-containing species are important structural and signalling molecules (phospholipids) or to supply, store and distribute energy (glycerides).

AIM OF THE REVIEW

In this critical review, we examine the current general understanding of sterol and lipid metabolism of social and solitary bees from a variety of literature sources and discuss implications for bee health.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We found that while eusocial bees are resilient to some dietary variation in sterol supply the scope for this is limited. The evidence of both de novo lipogenesis and a dietary need for particular fatty acids (FAs) shows that FA metabolism in insects is analogous to mammals but with distinct features. Bees rely on their dietary intake for essential sterols and lipids in a way that is dependent upon pollen availability.

Autophagy Is Required to Sustain Increased Intestinal Cell Proliferation during Phenotypic Plasticity Changes in Honey Bee (Apis mellifera)

Tissue phenotypic plasticity facilitates rapid adaptation of organisms to biotic and/or abiotic pressure. The reproductive capacity of honey bee workers (Apis mellifera) is plastic and responsive to pheromones produced by broods and the queen. Egg laying workers (ELWs), which could reactivate their ovaries and lay haploid eggs upon queen lost, have been commonly discussed from many aspects. However, it remains unclear whether midgut homeostasis in ELWs is affected during plastic changes. Here, we found that the expression of nutrition- and autophagy-related genes was up-regulated in the midguts of ELWs, compared with that in nurse workers (NWs) by RNA-sequencing. Furthermore, the area and number of autophagosomes were increased, along with significantly increased cell death in the midguts of ELWs. Moreover, cell cycle progression in the midguts of ELWs was increased compared with that in NWs. Consistent with the up-regulation of nutrition-related genes, the body and midgut sizes, and the number of intestinal proliferation cells of larvae reared with royal jelly (RJ) obviously increased more than those reared without RJ in vitro. Finally, cell proliferation was dramatically suppressed in the midguts of ELWs when autophagy was inhibited. Altogether, our data suggested that autophagy was induced and required to sustain cell proliferation in ELWs' midguts, thereby revealing the critical role of autophagy played in the intestines during phenotypic plasticity changes.

Chromatin accessibility-based characterisation of brain gene regulatory networks in three distinct honey bee polyphenisms

The honey bee genome has the capacity to produce three phenotypically distinct organisms (two diploid female castes: queen and worker, and a haploid male drone). Previous studies have implicated metabolic flux acting via epigenetic regulation in directing nutrition-driven phenotypic plasticity in the honey bee. However, the cis-acting DNA regulatory elements that establish tissue and polyphenism -specific epigenomes and gene expression programmes, remain unclear. Using a high resolution multiomic approach including assay for transposase-accessible chromatin by sequencing (ATAC-seq), RNA-seq and ChIP-seq, we produce the first genome-wide maps of the regulatory landscape across all three adult honey bee phenotypes identifying > 5000 regulatory regions in queen, 7500 in worker and 6500 in drone, with the vast majority of these sites located within intronic regions. These regions are defined by positive enrichment of H3K27ac and depletion of H3K4me3 and show a positive correlation with gene expression. Using ATAC-seq footprinting we determine queen, worker and drone -specific transcription factor occupancy and uncover novel phenotype-specific regulatory networks identifying two key nuclear receptors that have previously been implicated in caste-determination and adult behavioural maturation in honey bees; ecdysone receptor and ultraspiracle. Collectively, this study provides novel insights into key gene regulatory networks that are associated with these distinct polyphenisms in the honey bee.

Lipidomic specializations of honeybee (Apis mellifera) castes and ethotypes

Honeybees of the same colony combine a near-homogeneous genetic background with a high level of phenotypic plasticity, making them ideal models for functional lipidomics. The only external lipid source of the colony is pollen, a diet rich in polyunsaturated fatty acids (PUFA). It has been suggested that differences in exposure to pollen-derived PUFA could partly explain differences in longevity between honeybee castes. We here investigated whether the membrane composition of honeybees plays roles in the physiological adaptation to tasks of individuals within the colony. Membranes of cell heaters, a group of workers producing heat from their flight muscles to uphold brood nest temperature, were compared to those of different types of non-heaters. We found that the lipidomic profiles of these groups fall into clearly different "lipotypes", characterized by chain length and saturation of phospholipid-bound fatty acyl residues. The nutritional exposure to PUFA during early adult life and pupal development at the lower edge of the natural range of brood nest temperature both suppressed the expression of the cell heater-"lipotype". Because cardiolipins (CL) are the lipid class most clearly differentiating honeybee phenotypes, and CL plays central roles in mitochondrial function, dysfunction and aging, our findings could help to understand these processes in other animals and humans. Taken together, the lipidome analysis of different life stages of workers, fertile queens, and drones lead to the hypothesis that honeybee "lipotypes" might represent adaptations to different energetic profiles and the likelihood of exposure to low temperatures.

Lifespan prolonging mechanisms and insulin upregulation without fat accumulation in long-lived reproductives of a higher termite

Kings and queens of eusocial termites can live for decades, while queens sustain a nearly maximal fertility. To investigate the molecular mechanisms underlying their long lifespan, we carried out transcriptomics, lipidomics and metabolomics in Macrotermes natalensis on sterile short-lived workers, long-lived kings and five stages spanning twenty years of adult queen maturation. Reproductives share gene expression differences from workers in agreement with a reduction of several aging-related processes, involving upregulation of DNA damage repair and mitochondrial functions. Anti-oxidant gene expression is downregulated, while peroxidability of membranes in queens decreases. Against expectations, we observed an upregulated gene expression in fat bodies of reproductives of several components of the IIS pathway, including an insulin-like peptide, Ilp9. This pattern does not lead to deleterious fat storage in physogastric queens, while simple sugars dominate in their hemolymph and large amounts of resources are allocated towards oogenesis. Our findings support the notion that all processes causing aging need to be addressed simultaneously in order to prevent it.

Dose-Dependent Effects of Royal Jelly on Estrogen- and Progesterone-Induced Mammary Gland Hyperplasia in Rats

SCOPE

Royal jelly (RJ) has a wide range of biological functions, its effect on hyperplasia of the mammary gland (HMG) in mammals is unclear. This study aims to investigate the effect of RJ on HMG and the dose-response relationship of RJ in the treatment of HMG.

METHODS AND RESULTS

HMG rats are induced by intramuscular injection of estrogen (E2) and progesterone, and are treated with different doses of RJ (100, 200, 400, and 800 mg kg^-1 d^-1 ). As a result, RJ improves the expansion of acinar and breast tissue ducts, particularly at 100 and 800 mg kg^-1 d^-1 . These two doses also inhibit serum E2 and prolactin (PRL) secretion and increase serum progesterone secretion and the expression of estrogen receptor (ER)-β in the breast tissue. In addition, 800 mg kg^-1 d^-1 decrease and increase the mRNA expression of, respectively, hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary GnRH receptors (GnRH-R). The lowest dosage (100 mg kg^-1 d^-1 ) increases GnRH-R mRNA expression as well. However, the effects of 200 and 400 mg kg^-1 d^-1 RJ on the reproductive parameters of HMG are not significant, implying a dose-dependent effect.

CONCLUSION

RJ regulates endocrine dyscrasia in HMG rats and improves the breast tissue structure, indicating its potential in the prevention and treatment on HMG.

Non-targeted lipidomics and transcriptomics analysis reveal the molecular underpinnings of mandibular gland development in Apis mellifera ligustica

The mandibular gland is an important exocrine gland of worker bees, which mainly secretes fatty acids and pheromones. Lipids have important roles in energy storage, membrane structure stabilization, and signaling. However, molecular underpinnings of mandibular gland development and lipid remodeling at the different physiological stages of worker bees is still lacking. In this study, we used scanning and transmission electron microscopy to reveal the morphological changes in secretory cells, and liquid chromatography-mass spectrometry and RNA-seq to investigate the lipidome and gene transcripts during development. The morphology of secretory cells was flat in newly emerged workers, becoming vacuolated and turgid when they were activated in nurse bees and foragers. Transport vesicles became denser from newly emerged bees to 21-day worker bees. Concentrations of 10-HDA reached a maximum within 15d workers and changes in genes expression were consistent with 10-HDA content. Non-targeted lipidomics analysis of newly emerged, 6d, and 15d worker bees revealed that PC and TAG were the main lipids in mandibular gland, and lipids dramatically altered across developmental stages. TAG 54:4 was increased most strongly at 6d and 15d worker bees, meanwhile, the abundances of TAG 54:1 and TAG 54:2 were decreased sharply. Further, transcriptomics analysis showed that differentially expressed genes were significantly enriched in key nutrient metabolic pathways, particularly lipid metabolism, in 6d and 15d bees. This multi-omic perspective provides a unique resource and deeper insight into bee mandibular gland development and baseline data for further study of the mandibular gland in worker bees.

The Advanced Lipoxidation End-Product Malondialdehyde-Lysine in Aging and Longevity

The nonenzymatic adduction of malondialdehyde (MDA) to the protein amino groups leads to the formation of malondialdehyde-lysine (MDALys). The degree of unsaturation of biological membranes and the intracellular oxidative conditions are the main factors that modulate MDALys formation. The low concentration of this modification in the different cellular components, found in a wide diversity of tissues and animal species, is indicative of the presence of a complex network of cellular protection mechanisms that avoid its cytotoxic effects. In this review, we will focus on the chemistry of this lipoxidation-derived protein modification, the specificity of MDALys formation in proteins, the methodology used for its detection and quantification, the MDA-lipoxidized proteome, the metabolism of MDA-modified proteins, and the detrimental effects of this protein modification. We also propose that MDALys is an indicator of the rate of aging based on findings which demonstrate that (i) MDALys accumulates in tissues with age, (ii) the lower the concentration of MDALys the greater the longevity of the animal species, and (iii) its concentration is attenuated by anti-aging nutritional and pharmacological interventions.

The Lipidome Fingerprint of Longevity

Lipids were determinants in the appearance and evolution of life. Recent studies disclose the existence of a link between lipids and animal longevity. Findings from both comparative studies and genetics and nutritional interventions in invertebrates, vertebrates, and exceptionally long-lived animal species—humans included—demonstrate that both the cell membrane fatty acid profile and lipidome are a species-specific optimized evolutionary adaptation and traits associated with longevity. All these emerging observations point to lipids as a key target to study the molecular mechanisms underlying differences in longevity and suggest the existence of a lipidome profile of long life.

Special Significance of Non-Drosophila Insects in Aging

Aging is the leading risk factor of human chronic diseases. Understanding of aging process and mechanisms facilitates drug development and the prevention of aging-related diseases. Although many aging studies focus on fruit fly as a canonical insect system, minimal attention is paid to the potentially significant roles of other insects in aging research. As the most diverse group of animals, insects provide many aging types and important complementary systems for aging studies. Insect polyphenism represents a striking example of the natural variation in longevity and aging rate. The extreme intraspecific variations in the lifespan of social insects offer an opportunity to study how aging is differentially regulated by social factors. Insect flight, as an extremely high-intensity physical activity, is suitable for the investigation of the complex relationship between metabolic rate, oxidative stress, and aging. Moreover, as a "non-aging" state, insect diapause not only slows aging process during diapause phase but also affects adult longevity during/after diapause. In the past two decades, considerable progress has been made in understanding the molecular basis of aging regulation in insects. Herein, the recent research progress in non-Drosophila insect aging was reviewed, and its potential utilization in aging in the future was discussed.