Absence of female-specific protein in the hemolymph of stable fly Stomoxys calcitrans (L.) (Diptera: Muscidae)

Changes, during the reproductive cycle, in fat body, hemolymph, and ovarian proteins of the stable fly Stomoxys calcitrans were characterized quantitatively and qualitatively using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Protein content of all three tissues increased after blood feeding. Fat body protein increased first, followed by hemolymph and ovarian proteins. SDS-PAGE failed to identify vitellogenin in both female hemolymph and fat body samples. No single protein or group of proteins predominated at any stage of the reproductive cycle. Comparisons between male and female stable fly hemolymph and fat body proteins failed to detect female-specific proteins. Female-specific proteins, however, were detected in the hemolymph of four other species of Diptera.     

Retinoid metabolism and nuclear receptor responses: New insights into coordinated regulation of the PPAR-RXR complex

Retinoids, naturally-occurring vitamin A derivatives, regulate metabolism by activating specific nuclear receptors, including the retinoic acid receptor (RAR) and the retinoid X receptor (RXR). RXR, an obligate heterodimeric partner for other nuclear receptors, including peroxisome proliferator-activated receptors (PPARs), helps coordinate energy balance. Recently, many groups have identified new connections between retinoid metabolism and PPAR responses. We found that retinaldehyde (Rald), a molecule that can yield RA through the action of retinaldehyde dehydrogenases (Raldh), is present in fat in vivo and can inhibit PPAR gamma-induced adipogenesis. In vitro, Rald inhibits RXR and PPAR gamma activation. Raldh1-deficient mice have increased Rald levels in fat, higher metabolic rates and body temperatures, and are protected against diet-induced obesity and insulin resistance. Interestingly, one specific asymmetric beta-carotene cleavage product, apo-14'-carotenal, can also inhibit PPAR gamma and PPAR alpha responses. These data highlight how pathways of beta-carotene metabolism and specific retinoid metabolites may have direct distinct metabolic effects.     

Regulation of feeding and metabolism by neuronal and peripheral clocks in Drosophila

Studies in mammals have indicated a connection between circadian clocks and feeding behavior, but the nature of the interaction and its relationship to nutrient metabolism are not understood. In Drosophila, clock proteins are expressed in many metabolically important tissues but have not been linked to metabolic processes. Here we demonstrate that Drosophila feeding behavior displays a 24 hr circadian rhythm that is regulated by clocks in digestive/metabolic tissues. Flies lacking clocks in these tissues, in particular in the fat body, also display increased food consumption but have decreased levels of glycogen and a higher sensitivity to starvation. Interestingly, glycogen levels and starvation sensitivity are also affected by clocks in neuronal cells, but the effects of neuronal clocks generally oppose those of the fat body. We propose that the input of neuronal clocks and clocks in metabolic tissues is coordinated to provide effective energy homeostasis.     

Energy metabolism and the evolution of reproductive suppression in the human female

Reproduction places severe demands on the energy metabolism in human females. When physical work entails higher energy expenditure, not enough energy will be left for the support of the reproductive processes and temporal suppression of the reproductive function is expected. While energy needed for reproduction may be obtained by increases in energy intake, utilization of fat reserves, or reallocation of energy from basal metabolism, several environmental or physiological constraints render such solutions unlikely. For human ancestors increases in energy intake were limited by availability of food, by labor of food preparation and by metabolic ceilings to energy assimilation. Energy stored as fat may support only a fraction of the requirements for reproduction (especially lactation). Effects of intense physical activity on basal metabolism may also interfere with fat accumulation during pregnancy. Finally, the female physiology may experience demands on increasing the basal metabolism as a consequence of physical activity and, at the same time, on decreasing the basal metabolism, when energy to support the ongoing pregnancy or lactation is inadequate. The resulting metabolic dilemmas could constitute a plausible cause for the occurrence of reproductive suppression in response to physical activity. It is, therefore, likely that allocating enough energy to the reproductive processes during periods when energy expenditure rises may be difficult due to physiological and bioenergetic constraints. Females attempting pregnancy in such conditions may compromise their lifetime reproductive output. A reproductive suppression occurring in low energy availability situations may thus represent an adaptive rather then a pathological response.     

Changes in the biochemical composition of fat body stores during adult development of female crickets, Gryllus bimaculatus

Age-dependent changes in the fat body composition and aspects of lipogenesis in the free abdominal fat body of female crickets, Gryllus bimaculatus, were studied. Lipid, protein, glycogen, and free carbohydrate content of the fat body, and fat body wet weight increased simultaneously and sharply from day 0 onwards and were doubled/almost doubled by day 2 after adult emergence. Lipogenic activity of the fat body, fat body weight, and the energy stores in the fat body peaked on day 2, except for free carbohydrate, which peaked on day 3. On day 2, the fat body was mainly comprised of lipid (53.8%) and protein (6.6%), while glycogen and free carbohydrate together contributed less than 1% of the fat body wet weight. After peaking, both lipogenesis and energy stores decreased in a synchronous manner. The depletion of the fat body energy stores and the consequent decrease in the fat body weight were concomitant with a fast and massive gain in ovary weight (day 2: 19.5 +/- 1.5 mg; day 4: 332.8 +/- 31.5 mg) due to the vitellogenic oocyte growth that started on day 2. Our data clearly underline the importance of the free abdominal fat body as a source of energy for reproduction in the cricket. Fat body fatty acid synthase activity coincided with lipogenic activity. Adipokinetic hormone inhibits lipid synthesis in the fat body, but treatment of the fat body with adipokinetic hormone in vitro showed no consistent effect on fatty acid synthase activity.     

Changes in the fat body during the post-embryonic development of the predator Toxorhynchites theobaldi (Dyar & Knab) (Diptera: Culicidae)

Several studies have focused on understanding the biochemistry and morphology of the fat body of the hematophagous mosquito Aedes aegypti (L.) (Diptera: Culicidae). In contrast, few studies, if any, have focused on morphological characters of the fat body in other mosquitoes, especially non-hematophagous taxa such as the culicid Toxorhynchites. Larvae of Toxorhynchites prey upon the larvae of other mosquito species and are used in vector mosquito control. We investigated aspects of the fat body trophocytes, including the morphometric analyses of the lipid droplets, protein granules and nuclei, during Toxorhynchites theobaldi (Dyar & Knab) post-embryonic development. Following the body weight increase from larval stage L2 to L4, the size of lipid droplets within the trophocytes also increase, and are likely the result of lipogenesis. Lipid droplets decrease in size during L4 to the female pupal stage and increase once again during the period from newly-emerged to mature adult females. Protein granules are observed for the first time in female pupae, and their appearance might be related to protein storage during metamorphosis. The size of the nucleus of trophocytes also increases during larval development, followed by a decrease during metamorphosis and an additional increase as adult female ages. In conclusion, the morphology of the fat body of T. theobaldi changes according to the developmental stage. Our study provides for the first time important insights into T. theobaldi fat body development and contributes to understand this species biology.     

A Critical Role of the Nuclear Receptor HR3 in Regulation of Gonadotrophic Cycles of the Mosquito Aedes aegypti

The orphan nuclear receptor HR3 is essential for developmental switches during insect development and metamorphosis regulated by 20-hydroxyecdysone (20E). Reproduction of female mosquitoes of the major vector of Dengue fever, Aedes aegypti, is cyclic because of its dependence on blood feeding. 20E is an important hormone regulating vitellogenic events in this mosquito; however, any role for HR3 in 20E-driven reproductive events has not been known. Using RNA interference (RNAi) approach, we demonstrated that Aedes HR3 plays a critical role in a timely termination of expression of the vitellogenin (Vg) gene encoding the major yolk protein precursor. It is also important for downregulation of the Target-of-Rapamycin pathway and activation of programmed autophagy in the Aedes fat body at the end of vitellogenesis. HR3 is critical in activating betaFTZ-F1, EcRB and USPA, the expressions of which are highly elevated at the end of vitellogenesis. RNAi depletion of HR3 (iHR3) prior to the first gonadotrophic cycle affects a normal progression of the second gonadotrophic cycle. Most of ovaries 24 h post second blood meal from iHR3 females in the second cycle were small with follicles that were only slightly different in length from of those of resting stage. In addition, these iHR3 females laid a significantly reduced number of eggs per mosquito as compared to those of iMal and the wild type. Our results indicate an important role of HR3 in regulation of 20E-regulated developmental switches during reproductive cycles of A. aegypti females.     

NONSULFATED SULFAKININ CHANGES METABOLIC PARAMETERS OF INSECT FAT BODY MITOCHONDRIA

We investigated the effect of neuropeptide, the nonsulfated sulfakinin (SK) Zopat‐SK‐1 (pETSDDYGHLRFa) on the mitochondrial oxidative metabolism in the Zophobas atratus larval fat body. Mitochondria were isolated from beetle fat bodies 2 and 24 h after hormone injection. The administration of 20 pmol of Zopat‐SK‐1 to feeding larvae led to decreased mitochondrial oxidative activities in larval fat body. Diminished activities of citrate synthase and the cytochrome pathway, that is, nonphosphorylating and phosphorylating respiration during succinate oxidation, were observed. However, the effect of Zopat‐SK‐1 was more pronounced in fat body of insects after 24 h since hormone application. In hormone‐treated larval fat bodies, mitochondrial respiration was decreased at the level of respiratory chain and the TCA cycle as well as at the level of mitochondrial biogenesis, as indicated by decreased activities of mitochondrial marker enzymes in fat body homogenates. The inhibition of succinate oxidation may indicate the role of Zopat‐SK‐1 in the regulation of mitochondrial complex II activity. Moreover, decreased respiratory chain activity was accompanied by the reduced activity of mitochondrial energy‐dissipating pathway, uncoupling protein 4. The observed decrease in mitochondrial oxidative metabolism may reflect the Zopat‐SK‐1‐induced reduction in the metabolic rate of larval fat body linked to actual energetic demands of animal.     

Metabolomics characterization of energy metabolism reveals glycogen accumulation in gut-microbiota-lacking mice

Microbiota in the gut are considered an important environmental factor associated with host metabolism and physiology. Although gut microbiota are known to contribute to hepatic lipogenesis and fat storage, little is known about how the condition influences the deposition of glycogen in the liver. To better understand and characterize the host energy metabolism in guts lacking microbiota, we compared the liver metabolome of specific pathogen-free and germ-free mice by gas chromatography-mass spectrometry combined with partial least-squares discriminant analysis. We identified 30 of 52 highly reproducible peaks in chromatograms of liver tissue extracts from the two groups of mice. The two groups showed significant differences in metabolic profile. Changes in liver metabolism involved metabolites such as amino acids, fatty acids, organic acids and carbohydrates. The metabolic profile of germ-free mice suggests that they synthesize glycogen and accumulate it in the liver through gluconeogenesis and glycogenesis. Our findings shed light on a new perspective of the role of gut microbiota in energy metabolism and will be useful to help study probiotics, obesity and metabolic diseases.     

Mobilization of carbohydrates in tissues of female silkworms, Bombyx mori, during metamorphosis

The metabolic activity and mobilization of carbohydrates among tissues of female silkworms were examined during metamorphosis by injecting radioactive ¹⁴C-glucose as a tracer. The isotope injected was incorporated into various tissues with varying degrees and reached a relatively stable state in all tissues tested in about 240 min. The metabolic activities analysed by 4 hr pulse labelling were different for different tissues and ages; in glycogen synthetic activity midgut was highest on the day of the larval-pupal ecdysis, the fat body 2 days later, and ovaries a further 4 days later.When the isotope was injected on the day of larval-pupal ecdysis, it was found predominantly in glycogen first in the midgut, then in the fat body, and finally in the ovaries, proceeding through development. The total radioactivity recovered in the glycogen fractions from these tissues was almost constant throughout development. Ovariectomy caused a rise in synthesis of both glycogen and trehalose in the fat body during the second half of development.From these results it is proposed that the dermand of developing ovaries for carbohydrates exerts a controlling influence over mobilization of glycogen in the fat body.     

Progress and perspective on cyanobacterial glycogen metabolism engineering

As important oxygenic photoautotrophs, cyanobacteria are also generally considered as one of the most promising microbial chassis for photosynthetic biomanufacturing. Diverse synthetic biology and metabolic engineering approaches have been developed to enable the efficient harnessing of carbon and energy flow toward the synthesis of desired metabolites in cyanobacterial cell factories. Glycogen metabolism works as the most important natural carbon sink mechanism and reserve carbon source, storing a large portion of carbon and energy from the Calvin-Benson-Bassham (CBB) cycle, and thus is traditionally recognized as a promising engineering target to optimize the efficacy of cyanobacterial cell factories. Multiple strategies and approaches have been designed and adopted to engineer glycogen metabolism in cyanobacteria, leading to the successful regulation of glycogen synthesis and storage contents in cyanobacteria cells. However, disturbed glycogen metabolism results in weakened cellular physiological functionalities, thereby diminishing the robustness of metabolism. In addition, the effects of glycogen removal as a metabolic engineering strategy to enhance photosynthetic biosynthesis are still controversial. This review focuses on the efforts and effects of glycogen metabolism engineering on the physiology and metabolism of cyanobacterial chassis strains and cell factories. The perspectives and prospects provided herein are expected to inspire novel strategies and tools to achieve ideal control over carbon and energy flow for biomanufacturing.     

Caste specific differences in fat body glycogen metabolism of the bumblebee,Bombus terrestris

Bumblebee queens of Bombus terrestris store large amounts of glycogen in the fat body during the first days after eclosion. The accumulation of the reserves is complete prior to hibernation. Comparative studies on the glycogen metabolism in queens and workers show that the increased activity of UDP-glucose: glycogen 4-α-d-glucosyltransferase (EC 2.4.1.11) could account for glycogen accumulation in queens. The enzymatic activities are nearly the same in newly emerged bees, significant differences between castes are detected by day three after eclosion. The activity of glycogen phosphorylase (EC 2.4.1.1), in contrast, is not different between the castes. After injection of juvenile hormone into newly emerged queens the activity of UDP-glucose:glycogen 4-α-d-glucosyltransferase remains low and no glycogen is accumulated in the fat body. Since eggs are formed simultaneously, the lowered activity of the enzyme is thought to depend on the changed metabolism of the fat body related to induced oogenesis.     

Hormones regulating structural changes in the adipocytes of the female earwig Labidura riparia

Changes in periovarian fat body fine structure occur during the reproductive cycle of the female earwig Labidura riparia. During the process of vitellogenesis, high levels of protein synthesis are seen in the adipocytes. Simultaneously, the formerly osmiophilic lipid droplets become non-osmiophilic, while an osmiophilic material diffuses from lipid droplets to the cisternae of the rough endoplasmic reticulum (RER). These structural features alter during non-vitellogenic periods: RER and Golgi apparatus regress and seem to be inactive. Lipid droplets are once again osmiophilic and no material enters into RER cisternae. Using microsurgical manipulations, hormonal treatments and light and electron microscopy, we have investigated the regulation of these changes. The neuroendocrine cerebral centre pars intercerebralis, by the action of the juvenile hormone of the corpus allatum. triggers protein metabolism. Another neuroendocrine center, the pars lateralis. and the hormone 20-hydroxyecdysone, regulate structural lipid droplet changes in the adipocytes.     

Fuel mobilization for energy metabolism in the silkmoth, Bombyx mori, during reproductive processes

Flight muscles of male moth, B. mori seem to utilize carbohydrate preferentially as a source of energy for all its acrobatic movements during the search for female moth. Depletion of triacylglycerol from flight muscles without affecting its level from fat body suggests that this lipid fraction serves as a source of energy in flight muscles during insemination processes. Significant depletion of triacylglycerol and glycogen from flight muscles of female moth after egg laying indicates that they are used to meet the energy requirement of female during oviposition activity. Depletion of proteins from flight muscles of male and female insects suggest that these proteins are transported to the accessory reproductive glands to meet their protein demand.     

Peculiarities of metabolism of the microsporidia Nosema grylli during the intracellular development

A long adaptation of Microsporidia to intracellular development supposes the host-derived ATP dependence of merogony and sporogony stages. To prove this assumption the activities of ten carbohydrate and energy metabolism enzymes were compared in the microsporidia Nosema grylli intracellular stages and mature spores. This species infects the fat body of crickets Gryllus bimaculatus. We have demonstrated lower activities of glycolytic enzymes, phosphoglucomutase and glucose-6-PhDH in the metabolically active meronts and sporonts than in the dormant mature spores. Low glycolysis level indicates that carbohydrate catabolism is not a principal mechanism of ATP supply in the N. grylli intracellular stages. Furthermore, we have not revealed a preferable expenditure of glycogen in comparison with triglycerides in infected cricket fat bodies. The N. grylli infection causes an equal reduction of glycogen and lipid content approximately in 2-3 times. Microsporidia have not mitochondria, Krebs cycle and electron-transport chain. Therefore they are not able to utilise fat reserves for ATP production. It seems to be proposed that microsporidia consume exogenous ATP which is produced by host cell metabolic system. The N. grylli infection provokes an increase of ATP content and ratio of ATP/ADP concentrations in cricket fat bodies approximately in 4 times. These data indicates a rise of host cell energy metabolism rate during the infection.