A procession of metabolic alterations accompanying muscle senescence in Manduca sexta

Dietary Supplementation with Lauric Acid Improves Aerobic Endurance in Sedentary Mice via Enhancing Fat Mobilization and Glyconeogenesis

BACKGROUND

Lauric acid (LA), a major, natural, medium-chain fatty acid, is considered an efficient energy substrate for intense exercise and in patients with long-chain fatty acid β-oxidation disorders. However, few studies have focused on the role of LA in exercise performance and related glucolipid metabolism in vivo.

OBJECTIVES

We aimed to investigate the effect of dietary supplementation with LA on exercise performance and related metabolic mechanisms.

METHODS

Male C57BL/6N mice (14 wk old) were fed a basal diet or a diet containing 1% LA, and a series of exercise tests, including a high-speed treadmill test, aerobic endurance exercises, a 4-limb hanging test, and acute aerobic exercises, were performed.

RESULTS

Dietary supplementation with 1.0% LA accelerated the recovery from fatigue after explosive exercise (P < 0.05) and improved aerobic endurance and muscle strength in sedentary mice (P = 0.039). Lauric acid intake not only changed muscle fatty acid profiles, including increases in C12:0 and n-6/n-3 PUFAs (P < 0.001) and reductions in C18:0, C20:4n-6, C22:6n-3, and n-3 PUFAs (P < 0.05) but also enhanced fat mobilization from adipose tissue and fatty acid oxidation in the liver, at least partly via the AMP-activated protein kinase-acetyl CoA carboxylase pathway (P < 0.05). Likewise, LA supplementation promoted liver glyconeogenesis and conserved muscular glycogen during acute aerobic exercise (P < 0.05), which was accompanied by an increase in the mitochondrial DNA copy number and Krebs cycle activity in skeletal muscle (P < 0.05).

CONCLUSIONS

Dietary supplemental LA serves as an efficient energy substrate for sedentary mice to improve aerobic exercise endurance and muscle strength through regulation of glucolipid metabolism. These findings imply that LA supplementation might be a promising nutritional strategy to improve aerobic exercise performance in sedentary people.

The Transcription of Flight Energy Metabolism Enzymes Declined with Aging While Enzyme Activity Increased in the Long-Distance Migratory Moth, Spodoptera frugiperda

Of all the things that can fly, the flight mechanisms of insects are possibly the least understood. By using RNAseq, we studied the aging-associated gene expression changes in the thorax of Spodoptera frugiperda females. Three possible flight energy metabolism pathways were constructed based on 32 key metabolic enzymes found in S. frugiperda. Differential expression analysis revealed up to 2000 DEGs within old females versus young ones. Expression and GO and KEGG enrichment analyses indicated that most genes and pathways related to energy metabolism and other biological processes, such as transport, redox, longevity and signaling pathway, were downregulated with aging. However, activity assay showed that the activities of all the five tested key enzymes increased with age. The age-associated transcriptional decrease and activity increase in these enzymes suggest that these enzymes are stable. S. frugiperda is a long-distance migrator, and a high activity of enzymes may be important to guarantee a high flight capacity. The activity ratio of GAPDH/HOAD ranged from 0.594 to 0.412, suggesting that lipid is the main fuel of this species, particularly in old individuals. Moreover, the expression of enzymes in the proline oxidation pathway increased with age, suggesting that this energy metabolic pathway also is important for this species or linked to some aging-specific processes. In addition, the expression of immunity- and repair-related genes also increased with age. This study established the overall transcriptome framework of the flight muscle and aging-associated expression change trajectories in an insect for the first time.

New insights into the biomineralization of mercury selenide nanoparticles through stable isotope analysis in giant petrel tissues

Tiemannite (HgSe) is considered the end-product of methylmercury (MeHg) demethylation in vertebrates. The biomineralization of HgSe nanoparticles (NPs) is understood to be an efficient MeHg detoxification mechanism; however, the process has not yet been fully elucidated. In order to contribute to the understanding of complex Hg metabolism and HgSe NPs formation, the Hg isotopic signatures of 40 samples of 11 giant petrels were measured. This seabird species is one of the largest avian scavengers in the Southern Ocean, highly exposed to MeHg through their diet, reaching Hg concentrations in the liver up to more than 900 µg g^-1. This work constitutes the first species-specific isotopic measurement (δ²⁰²Hg, Δ¹⁹⁹Hg) of HgSe NPs in seabirds and the largest characterization of this compound in biota. Similar δ²⁰²Hg values specifically associated to HgSe (δ²⁰²Hg_HgSe) and tissues (δ²⁰²Hg_bulk) dominated by inorganic Hg species were found, suggesting that no isotopic fractionation is induced during the biomineralization step from the precursor (demethylated) species. In contrast, the largest variations between δ²⁰²Hg_bulk and δ²⁰²Hg_HgSe were observed in muscle and brain tissues. This could be attributed to the higher fraction of Hg present as MeHg in these tissues. Hg-biomolecules screening highlights the importance of the isotopic characterization of these (unknown) complexes.

Proline as a Sparker Metabolite of Oxidative Metabolism during the Flight of the Bumblebee, Bombus impatiens

Several insect species use the amino acid proline as a major energy substrate. Although initially thought to be limited to blood-feeding dipterans, studies have revealed this capability is more widespread. Recent work with isolated flight muscle showed that the bumblebee Bombus impatiens can oxidize proline at a high rate. However, its role as a metabolic fuel to power flight is unclear. To elucidate the extent to which proline is oxidized to power flight and how its contribution changes during flight, we profiled 14 metabolites central to energy and proline metabolism at key time points in flight muscle and abdominal tissues. Ultra-high performance liquid chromatography-electrospray ionization-quadrupole time of flight mass spectrometry (UPLC-ESI-QTOF MS) analysis revealed that proline is likely used as a sparker metabolite of the tricarboxylic acid cycle at the onset of flight, whereby it supplements the intermediates of the cycle. Carbohydrates are the major energy substrates, which is evidenced by marked decreases in abdominal glycogen stores and a lack of alanine accumulation to replenish flight muscle proline. The time course of fuel stores and metabolites changes during flight highlights homeostatic regulation of energy substrates and patterns of changes in metabolic intermediates within pathways. This study clarifies the role of proline and carbohydrate metabolism during flight in hymenopterans, such as B. impatiens.

The Role of Peptide Hormones in Insect Lipid Metabolism

Lipids are the primary storage molecules and an essential source of energy in insects during reproduction, prolonged periods of flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. The fat body is primarily composed of adipocytes, which accumulate triacylglycerols in intracellular lipid droplets. Genomics and proteomics, together with functional analyses, such as RNA interference and CRISPR/Cas9-targeted genome editing, identified various genes involved in lipid metabolism and elucidated their functions. However, the endocrine control of insect lipid metabolism, in particular the roles of peptide hormones in lipogenesis and lipolysis are relatively less-known topics. In the current review, the neuropeptides that directly or indirectly affect insect lipid metabolism are introduced. The primary lipolytic and lipogenic peptide hormones are adipokinetic hormone and the brain insulin-like peptides (ILP2, ILP3, ILP5). Other neuropeptides, such as insulin-growth factor ILP6, neuropeptide F, allatostatin-A, corazonin, leucokinin, tachykinins and limostatin, might stimulate lipolysis, while diapause hormone-pheromone biosynthesis activating neuropeptide, short neuropeptide F, CCHamide-2, and the cytokines Unpaired 1 and Unpaired 2 might induce lipogenesis. Most of these peptides interact with one another, but mostly with insulin signaling, and therefore affect lipid metabolism indirectly. Peptide hormones are also involved in lipid metabolism during reproduction, flight, diapause, starvation, infections and immunity; these are also highlighted. The review concludes with a discussion of the potential of lipid metabolism-related peptide hormones in pest management.

Current Status and Future Prospects of Genome-Scale Metabolic Modeling to Optimize the Use of Mesenchymal Stem Cells in Regenerative Medicine

Mesenchymal stem cells are a promising source for externally grown tissue replacements and patient-specific immunomodulatory treatments. This promise has not yet been fulfilled in part due to production scaling issues and the need to maintain the correct phenotype after re-implantation. One aspect of extracorporeal growth that may be manipulated to optimize cell growth and differentiation is metabolism. The metabolism of MSCs changes during and in response to differentiation and immunomodulatory changes. MSC metabolism may be linked to functional differences but how this occurs and influences MSC function remains unclear. Understanding how MSC metabolism relates to cell function is however important as metabolite availability and environmental circumstances in the body may affect the success of implantation. Genome-scale constraint based metabolic modeling can be used as a tool to fill gaps in knowledge of MSC metabolism, acting as a framework to integrate and understand various data types (e.g., genomic, transcriptomic and metabolomic). These approaches have long been used to optimize the growth and productivity of bacterial production systems and are being increasingly used to provide insights into human health research. Production of tissue for implantation using MSCs requires both optimized production of cell mass and the understanding of the patient and phenotype specific metabolic situation. This review considers the current knowledge of MSC metabolism and how it may be optimized along with the current and future uses of genome scale constraint based metabolic modeling to further this aim.

High-precision isotopic analysis sheds new light on mercury metabolism in long-finned pilot whales (Globicephala melas)

Whales accumulate mercury (Hg), but do not seem to show immediate evidence of toxic effects. Analysis of different tissues (liver, kidney, muscle) and biofluids (blood, milk) from a pod of stranded long-finned pilot whales (Globicephala melas) showed accumulation of Hg as a function of age, with a significant decrease in the MeHg fraction. Isotopic analysis revealed remarkable differences between juvenile and adult whales. During the first period of life, Hg in the liver became isotopically lighter (δ²⁰²Hg decreased) with a strongly decreasing methylmercury (MeHg) fraction. We suggest this is due to preferential demethylation of MeHg with the lighter Hg isotopes and transport of MeHg to less sensitive organs, such as the muscles. Also changes in diet, with high MeHg intake in utero and during lactation, followed by increasing consumption of solid food contribute to this behavior. Interestingly, this trend in δ²⁰²Hg is reversed for livers of adult whales (increasing δ²⁰²Hg value), accompanied by a progressive decrease of δ²⁰²Hg in muscle at older ages. These total Hg (THg) isotopic trends suggest changes in the Hg metabolism of the long-finned pilot whales, development of (a) detoxification mechanism(s) (e.g., though the formation of HgSe particles), and Hg redistribution across the different organs.

Polyamines in Microalgae: Something Borrowed, Something New

Microalgae of different evolutionary origins are typically found in rivers, lakes, and oceans, providing more than 45% of global primary production. They provide not only a food source for animals, but also affect microbial ecosystems through symbioses with microorganisms or secretion of some metabolites. Derived from amino acids, polyamines are present in almost all types of organisms, where they play important roles in maintaining physiological functions or against stress. Microalgae can produce a variety of distinct polyamines, and the polyamine content is important to meet the physiological needs of microalgae and may also affect other species in the environment. In addition, some polyamines produced by microalgae have medical or nanotechnological applications. Previous studies on several types of microalgae have indicated that the putative polyamine metabolic pathways may be as complicated as the genomes of these organisms, which contain genes originating from plants, animals, and even bacteria. There are also several novel polyamine synthetic routes in microalgae. Understanding the nature of polyamines in microalgae will not only improve our knowledge of microalgal physiology and ecological function, but also provide valuable information for biotechnological applications.

Flight duration and flight muscle ultrastructure of unfed hawk moths

Flight muscle breakdown has been reported for many orders of insects, but the basis of this breakdown in insects with lifelong dependence on flight is less clear. Lepidopterans show such muscle changes across their lifespans, yet how this change affects the ability of these insects to complete their life cycles is not well documented. We investigated the changes in muscle function and ultrastructure of unfed aging adult hawk moths (Manduca sexta). Flight duration was examined in young, middle-aged, and advanced-aged unfed moths. After measurement of flight duration, the main flight muscle (dorsolongitudinal muscle) was collected and histologically prepared for transmission electron microscopy to compare several measurements of muscle ultrastructure among moths of different ages. Muscle function assays revealed significant positive correlations between muscle ultrastructure and flight distance that were greatest in middle-aged moths and least in young moths. In addition, changes in flight muscle ultrastructure were detected across treatment groups. The number of mitochondria in muscle cells peaked in middle-aged moths. Many wild M. sexta do not feed as adults; thus, understanding the changes in flight capacity and muscle ultrastructure in unfed moths provides a more complete understanding of the ecophysiology and resource allocation strategies of this species.