The effects of synthetic locust adipokinetic hormone on dispersed locust fat body cell preparations: cAMP induction, lipid mobilization, and inhibition of protein synthesis

Ginsenoside Rg1 can reverse fatigue behavior in CFS rats by regulating EGFR and affecting Taurine and Mannose 6-phosphate metabolism

Background: Chronic fatigue syndrome (CFS) is characterized by significant and persistent fatigue. Ginseng is a traditional anti-fatigue Chinese medicine with a long history in Asia, as demonstrated by clinical and experimental studies. Ginsenoside Rg1 is mainly derived from ginseng, and its anti-fatigue metabolic mechanism has not been thoroughly explored. Methods: We performed non-targeted metabolomics of rat serum using LC-MS and multivariate data analysis to identify potential biomarkers and metabolic pathways. In addition, we implemented network pharmacological analysis to reveal the potential target of ginsenoside Rg1 in CFS rats. The expression levels of target proteins were measured by PCR and Western blotting. Results: Metabolomics analysis confirmed metabolic disorders in the serum of CFS rats. Ginsenoside Rg1 can regulate metabolic pathways to reverse metabolic biases in CFS rats. We found a total of 34 biomarkers, including key markers Taurine and Mannose 6-phosphate. AKT1, VEGFA and EGFR were identified as anti-fatigue targets of ginsenoside Rg1 using network pharmacological analysis. Finally, biological analysis showed that ginsenoside Rg1 was able to down-regulate the expression of EGFR. Conclusion: Our results suggest ginsenoside Rg1 has an anti-fatigue effect, impacting the metabolism of Taurine and Mannose 6-phosphate through EGFR regulation. This demonstrates ginsenoside Rg1 is a promising alternative treatment for patients presenting with chronic fatigue syndrome.

Adipokinetic Hormone Receptor Mediates Trehalose Homeostasis to Promote Vitellogenin Uptake by Oocytes in Nilaparvata lugens

Adipokinetic hormones (AKHs) are well known to mobilize lipids and carbohydrates for energy-consuming activities in insects. These neuropeptides exert their functions by interacting with AKH receptors (AKHRs) located on the plasma membrane of fat body cells, which regulates energy mobilization by stimulating lipolysis of triacylglycerols (TAG) to diacylglycerols (DAG) and conversion of glycogen into trehalose. Here, we investigated the roles of AKH/AKHR signaling system in trehalose metabolism and vitellogenesis during female reproduction in the brown planthopper, Nilaparvata lugens. Knockdown of AKHR expression by RNA interference (RNAi) resulted in a decrease of the circulating trehalose in hemolymph and significantly increased levels of two trehalases in fat bodies, indicating that the modulation of hemolymph trehalose levels by AKHR may be mediated by regulating trehalose degradation. In addition, adult females that had been injected with double-stranded RNA (dsRNA) for AKHR exhibited delayed oocyte maturation, prolonged pre-oviposition period, as well as decline in egg number and reduction in fecundity. Considering that these phenotypes resulting from AKHR silencing are similar to those of vitellogenin receptor (VgR) RNAi, we further analyzed a possible connection between AKHR and vitellogenesis. Knockdown of AKHR showed no effects on the Vg synthesis in fat bodies, whereas it significantly reduced the levels of VgR in ovaries. With RNAi-females, we observed an increase of Vg accumulation in hemolymph and a decrease of Vg deposition in ovaries. Moreover, the decrease in VgR expression and Vg incorporation by developing oocytes could be partially rescued by injection of trehalose into AKHR RNAi females. The present study has implicated trehalose in the AKH/AKHR signaling-mediated control of reproduction and provided new insight into mechanisms of AKH/AKHR regulation of trehalose metabolism in insect vitellogenesis, oocyte maturation and fecundity.

Cdk4 functions in multiple cell types to control Drosophila intestinal stem cell proliferation and differentiation

The proliferation of intestinal stem cells (ISCs) and differentiation of enteroblasts to form mature enteroendocrine cells and enterocytes in the Drosophila intestinal epithelium must be tightly regulated to maintain homeostasis. We show that genetic modulation of CyclinD/Cdk4 activity or mTOR-dependent signalling cell-autonomously regulates enterocyte growth, which influences ISC proliferation and enteroblast differentiation. Increased enterocyte growth results in higher numbers of ISCs and defective enterocyte growth reduces ISC abundance and proliferation in the midgut. Adult midguts deficient for Cdk4 show severe disruption of intestinal homeostasis characterised by decreased ISC self-renewal, enteroblast differentiation defects and low enteroendocrine cell and enterocyte numbers. The ISC/enteroblast phenotypes result from a combination of cell autonomous and non-autonomous requirements for Cdk4 function. One non-autonomous consequence of Cdk4-dependent deficient enterocyte growth is high expression of Delta in ISCs and Delta retention in enteroblasts. We postulate that aberrant activation of the Delta–Notch pathway is a possible partial cause of lost ISC stemness. These results support the idea that enterocytes contribute to a putative stem cell niche that maintains intestinal homeostasis in the Drosophila anterior midgut.

Summary: We identify that the growth status of absorptive enterocyte cells in the Drosophila intestine controls the proliferation and differentiation of stem and progenitor cells, thereby controlling organ homeostasis.

Age-dependent changes of fat body stores and the regulation of fat body lipid synthesis and mobilisation by adipokinetic hormone in the last larval instar of the cricket, Gryllus bimaculatus

Data on the hormonal regulation of the formation and mobilisation of fat body stores are presented and discussed in relation to general parameters of last instar larval development such as growth, food intake, and moulting. Crickets feed voraciously during the first half of the last larval stage. With the onset of feeding, fat body lipid synthesis increases, leading to increasing lipid stores in the fat body with a maximum reached on day 5. Lipid (42% of fat body fresh mass) is the main constituent of the fat body stores, followed by protein (6%) and glycogen (2%). During the second half of the last larval stage, feeding activity dramatically decreases, the glycogen reserves are depleted but lipid and protein reserves in the fat body remain at a high level except for the last day of the last larval stage when lipid and protein in the fat body are also largely depleted. The process of moulting consumes almost three quarters of the caloric equivalents that were acquired during the last larval stage. Adipokinetic hormone (AKH) inhibits effectively the synthesis of lipids in the larval fat body. Furthermore, AKH stimulates lipid mobilisation by activating fat body triacylglycerol lipase (TGL) in last larval and adult crickets. Both effects of AKH are weaker in larvae than in adults. This is the first report on the age-dependent basal activity of TGL in larval and adult insects. In addition, for the first time, an activation of TGL by AKH in a larval insect is shown.

Purification, characterisation and titre of the haemolymph juvenile hormone binding proteins from Schistocerca gregaria and Gryllus bimaculatus

Juvenile hormone binding proteins (JHBPs) were extracted from the haemolymph of adult desert locusts, Schistocerca gregaria, and Mediterranean field crickets, Gryllus bimaculatus. The JHBPs were purified by polyethyleneglycol precipitation, filtration through molecular weight cut off filters and chromatography on a HiTrap heparin column. The juvenile hormone (JH) binding activity of the extracts was measured using a hydroxyapatite assay and the purification progress was monitored by native gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The haemolymph JHBPs of both insects are hexamers composed of seemingly identical subunits. The JHBP of the locust has a native Mr of 480 kDa with subunits of 77 kDa, whereas the JHBP of the cricket has a Mr of 510 kDa with subunits of 81 kDa. The locust JHBP binds JH III with moderate affinity (KD = 19 nM). Competition for binding of JH II and JH I was about 2 and 5 times less, respectively. The cricket JHBP also has a moderate affinity for JH III (KD = 28 nM), but surprisingly, competition for binding of JH II was equal to that of JH III and JH I competed about 3 times higher. No sequence information was obtained for the locust JHBP, but the N-terminal sequence of the cricket JHBP shows ca. 56% sequence homology with a hexamerin from Calliphora vicina. Antisera raised against the purified JHBPs were used to measure age- and sex-dependent changes in haemolymph JHBP titres and to confirm that the JHBPs of both species are immunologically different.

Adipokinetic hormone inhibits the formation of energy stores and egg production in the cricket Gryllus bimaculatus

Adipokinetic hormones (AKHs) mobilise lipids, carbohydrates and/or proline from insect fat body stores. In addition, AKHs inhibit lipid and protein synthesis in the fat body. In the current study, 100 pmol homologous Grybi-AKH was injected twice daily into adult female crickets, Gryllus bimaculatus, starting on the day of adult emergence. The effects of the injected AKH on the formation of energy reserves in the fat body and on egg production were measured on day 4 after adult emergence. In comparison to water-injected control animals, lipid and protein content in the fat body of the AKH-injected crickets was significantly reduced, suggesting an inhibitory effect of AKH on the formation of lipid reserves and protein stores. The content of glycogen and free carbohydrate in the fat body was significantly higher in the AKH-injected animals. The most pronounced effect of the AKH-injections was a significant reduction of ovary mass, due to the retarded maturation of the oocytes and the significantly lower number of terminal oocytes produced. It is concluded that AKH inhibits egg production indirectly by interference with the formation of energy stores in the fat body that are mobilised to fuel egg production.

Mode of action of neuropeptides from the adipokinetic hormone family

Neuropeptides of the adipokinetic hormone (AKH) family regulate inter alia mobilisation of various substrates from stores in the fat body of insects during episodes of flight. How is this achieved? In insects which exclusively oxidise carbohydrates for flight (cockroaches), or which oxidise carbohydrates in conjunction with lipids (locusts) or proline (a number of beetles), the endogenous AKHs bind to a G(q)-protein-coupled receptor, activate a phospholipase C and the resulting inositol trisphosphate releases Ca(2+) from internal stores. In addition, influx of extracellular Ca(2+) is increased and, via a kinase cascade, glycogen phosphorylase is activated, glucose-1-phosphate produced, and transformed to trehalose, which is released into the haemolymph. In locusts, additionally, adenylate cyclase is activated and cyclic AMP is synthesised. In insects which use lipids for sustained flight (locust, tobacco hornworm moth) or proline for flight (certain beetles), adenylate cyclase is activated after the AKHs bind to their respective G(s)-protein-coupled receptor. The resulting cyclic AMP, together with the messengers intra- and extracellular Ca(2+), activate a triacylglycerol lipase, which results in the production of 1,2 diacylglycerols (in locusts, moths) or (hypothetically) free fatty acids (fruit beetle).

Synthesis of lipids in the fat body of Gryllus bimaculatus: age-dependency and regulation by adipokinetic hormone

The free abdominal fat body of adult female Mediterranean field crickets, Gryllus bimaculatus, synthesizes lipids from [1-(14)C]-acetate in vitro. Up to an age of 12h, the incorporation of acetate into lipids is very low and then rises to a maximum 24h after adult emergence. Thereafter, the incorporation of acetate decreases to moderate levels at day 2 and then slowly decreases until day 30. The adipokinetic hormone of G. bimaculatus (Grb-AKH) significantly inhibits the incorporation of acetate at a concentration of 10(-11) M; maximum inhibition (approximately 95%) is reached at 10(-8) M. The inhibiting effect of Grb-AKH is fast, dose-dependent, and reversible. The periovaric fat body shows a similar pattern of acetate incorporation, although rates of incorporation are lower; the incorporation can be inhibited by Grb-AKH as well. The segmental abdominal fat body and the fat body from the head both incorporate acetate into lipids at low rates that cannot be inhibited significantly by AKH. Prepurified brain extracts significantly inhibit acetate incorporation by free abdominal fat bodies at a concentration of 0.1 brain equivalent. Allatostatins and crustacean cardioactive peptide, which are both present in cricket brains, are not responsible for this inhibiting effect. Octopamine causes a dose-dependent inhibition of acetate incorporation whereas synephrine had no such effect. The inhibiting effect of Grb-AKH on the formation of lipid stores in the fat body and its consequences for reproductive processes are discussed.

Pheromone-producing cells in the silkmoth, Bombyx mori: identification and their morphological changes in response to pheromonotropic stimuli

A method to isolate functional clusters of viable pheromone gland cells of Bombyx mori was developed. The 8th-9th intersegmental invaginated membrane corresponding to the pheromone gland was dissected, trimmed and separated into two distinct layers, the outer and inner layers, by enzymatic digestion with papain. The outer layer mainly consists of cuticle, while the inner layer consists of homogeneous cells with many refractile granules. The solubilized microsome fraction prepared from the inner layer retained the ability to produce bombykol in vitro, whereas the outer layer fraction did not produce bombykol. Moreover, in tissue incubations, the inner layer - but not the outer layer - produced bombykol in response to the pheromonotropic peptide TKYFSPRLamide, ionomycin and calcium ionophore A23187. These results indicate that the inner-layer cells are indeed the pheromone-producing cells, which retain their functional integrity after separation with papain. These cells could be cultured successfully in Grace's medium for at least 5days.The presence or absence of pheromonotropic stimuli prior to dissection greatly influenced the size, number and distribution of refractile granules in the cytoplasm of the pheromone-producing cells. Staining with Nile Red proved that these refractile granules were lipid droplets. When pheromone production was studied under normal conditions or stimulated in decapitated females with pheromone-biosynthesis-activating neuorpeptide (PBAN) charge, the size of lipid droplets observed in the pheromone-producing cells reduced prominently and their number increased dramatically with time. By contrast, when pheromone production was suppressed by decapitation, the size and number of the lipid droplets remained constant. Lipid droplets observed in the pheromone-producing cells could be carriers of pheromone precursors and/or the pheromone bombykol. The present results suggest that the isolated cell preparation can be used for quantitative visualization of the cellular dynamics during pheromone production in B. mori.

New insights into adipokinetic hormone signaling

Flight activity of insects comprises one of the most intense biochemical processes known in nature, and therefore provides an attractive model system to study the hormonal regulation of metabolism during physical exercise. In long-distance flying insects, such as the migratory locust, both carbohydrate and lipid reserves are utilized as fuels for sustained flight activity. The mobilization of these energy stores in Locusta migratoria is mediated by three structurally related adipokinetic hormones (AKHs), which are all capable of stimulating the release of both carbohydrates and lipids from the fat body. To exert their effects intracellularly, these hormones induce a variety of signal transduction events, involving the activation of AKH receptors, GTP-binding proteins, cyclic AMP, inositol phosphates and Ca2+. In this review, we discuss recent advances in the research into AKH signaling. This not only includes the effects of the three AKHs on each of the signaling molecules, but also crosstalk between signaling cascades and the degradation rates of the hormones in the hemolymph. On the basis of the observed differences between the three AKHs, we have tried to construct a physiological model for their action in locusts, in order to answer a fundamental question in endocrinology: why do several structurally and functionally related peptide hormones co-exist in locusts (and animals in general), when apparently one single hormone would be sufficient to exert the desired effects? We suggest that the success of the migratory locust in performing long-distance flights is in part based on this neuropeptide multiplicity, with AKH-I being the strongest lipid-mobilizing hormone, AKH-II the most powerful carbohydrate mobilizer and AKH-III, a modulatory entity that predominantly serves to provide the animal with energy at rest.

Stimulation of glycogenolysis by three locust adipokinetic hormones involves Gs and cAMP

Insect adipokinetic hormones (AKHs) have been shown to mobilize fat body carbohydrate by glycogen phosphorylase activation. In this study, the signal transduction pathways of AKH-I, -II and -III from the migratory locust are further elucidated. We show that the AKHs enhance fat body cAMP levels in vitro. For all hormones, maximal levels are reached after 1 min and correspond to a 200% increase compared to resting levels. Although cAMP levels induced by massive doses of AKH-I, -II and -III are equal, AKH-III is the most potent when applied in a physiological dose. This difference in potency also applies to glycogen phosphorylase activation. Cholera toxin (CTX) likewise ennhaces cAMP levels and phosphorylase activity, however pertussis toxin (PTX) has no effect. Increases induced by CTX and AKH are not additive, suggesting that they share the same pathway. Phosphorylase activation by the AKHs is strongly attenuated by guanosine-5'-O-(2-thiodiphosphate) (GDP beta S). These results demonstrate a role for cAMP in AKH signal transduction and indicate that the AKH receptor(s) are coupled to cAMP formation and glycogen phosphorylase activation via the stimulatory guanine nucleotide-binding protein (Gs).

Hypertrehalosemic hormone effects on transcriptional activity in the fat body of the cockroach, Blaberus discoidalis

Gene expression was examined in the fat body of adult male Blaberus discoidalis cockroaches in response to the hypertrehalosemic hormone (HTH). HTH regulates a natural peak of heme synthesis in the fat body at day 4 of adult life. Inhibition of transcriptional activity by alpha-amanitin suppressed both the natural increase in heme biosynthesis at day 4, and the increase that was induced in decapitated animals by HTH administration. In contrast, the regimen of alpha-amanitin treatments that suppressed HTH-responsive heme biosynthesis had no effect on the ability of HTH to increase hemolymph carbohydrate. HTH administration to decapitated animals produced a 25% increase in total fat body RNA and a 3-fold increase in [3H]uridine incorporation. In vitro translation of fat body RNA showed that HTH increased the synthesis of polypeptides at 24, 60 and 77 kDa. The results suggest that HTH affects fat body heme synthesis through gene expression, and evidence was obtained for three polypeptides that increase in the fat body in response to HTH.

The preparation of trophocytes from disaggregated fat body of the cockroach (Periplaneta americana)

A method has been developed for disaggregating the fat body of the adult American cockroach, Periplaneta americana, using collagenase. The yield of cells is sensitive to the osmolarity of the dispersing medium and to the age of the cockroaches from which the fat bodies are taken. Trophocytes uncontaminated with other cells were obtained by taking advantage of the low density of these cells which causes them to float to the top of the dispersion medium. In contrast, the mycetocytes and urocytes being denser than the medium sink to the bottom. The trophocytes retain the ability to respond to the synthetic hyperglycaemic hormones, CCI and CCII, as shown by the activation of phosphorylase and the stimulation of trehalose efflux. The trophocytes incorporated leucine into protein secreted by the cells in a time dependent manner.

Effects of intestinal insulin-like peptide on glucose catabolism in mealworm larval fat body in vitro: dependence on extracellular Ca2+ for its stimulatory action

In vitro hormonally induced variations of glucose catabolism in mealworm fat body tissue were examined by a microradiorespirometric method. An insulin-like peptide (ILP) extracted from the midgut of last larval instar mealworm larvae significantly modified glucose catabolism and was dependent on energy metabolism and on the Ca2+ concentration in the culture medium. Using two different labelled substrate molecules, the stimulatory effects of ILP (compared with those of mammalian insulin) on the relative use of the pentose cycle as opposed to the glycolytic-citric acid cycle by the mealworm fat body were measured in vitro. Metabolic variations were evaluated using either [1-14C]glucose or [6-14C]glucose as substrates. Time course and dose-response curves of ILP and the hormonally induced variations in total CO2 and 14CO2 kinetics were determined. Modification in the specific radioactivity kinetics of 14CO2 derived from [1-14C] glucose and [6-14C]glucose molecules under hormonal effects were observed. As demonstrated in in vivo studies, ILP stimulated the relative utilization of the pentose cycle. However, this effect was observed much more rapidly, but for a shorter time, with fat body in vitro. Mammalian insulin produced similar, but not identical effects. Variations in transmembranous Ca2+ cellular exchanges, induced by either EGTA, nifedipine, or calcium ionophore ionomycin included in the culture medium, indicated that the stimulatory effects of ILP depends on this cation.

Ecdysteroids affect in vivo protein metabolism of the flight muscle of the tobacco hornworm (Manduca sexta)

Ecdysteroid growth promotion of the dorsolongitudinal flight muscle of Manduca sexta was studied by measuring in vivo protein metabolism using both "flooding-dose" and "non-carrier" techniques. These procedures differ in that the former method includes injection of non-labelled phenylalanine (30 micromoles/insect) together with the [3H]amino acid. Injected radioactivity plateaued in the haemolymph within 7 min. With the flooding-dose method, haemolymph and intramuscular specific radioactivities were similar between 15 min and 2 h. Incorporation of [3H]phenylalanine into muscle protein was linear with either method between 30 and 120 min. Fractional rates (%/12 h) of synthesis with the flooding-dose technique were best measured after 1 h because of the initial delay in radioactivity equilibration. Estimation of body phenylalanine turnover with the non-carrier method showed 24-53%/h which was negligible with the flooding-dose method. Since the two methods yielded similar rates of protein synthesis, the large injection of non-labelled amino acid did not alter the rate of synthesis. Because the flooding-dose technique requires only a single time point measurement, it is the preferred method. The decline and eventual cessation of flight-muscle growth was mostly a consequence of declining protein synthesis though degradation increased between 76-86 h before eclosion and was relatively rapid. This decline in muscle growth could be prevented by treating pupae with 20-hydroxyecdysone (10 micrograms/insect). Protein accretion was promoted by a decline of up to 80% in protein breakdown, which was offset in part by a concurrent though much smaller decrease in protein synthesis. Therefore, ecdysteroids may increase flight-muscle growth by inhibiting proteolysis.

Involvement of cyclic AMP-dependent protein kinase in prothoracicotropic hormone-stimulated ecdysone synthesis

Prothoracicotropic hormone (PTTH) is a brain neuropeptide that stimulates the prothoracic glands to synthesize ecdysone, an event that leads to insect molting. Both cyclic AMP (cAMP) and calcium have been implicated in PTTH action, with current evidence favoring cAMP as the messenger directly regulating ecdysone synthesis. To further define the role of cAMP in PTTH action, the activity of cAMP-dependent protein kinase (cAMP-PK) was examined in prothoracic glands from two developmental stages of the tobacco hornworm, Manduca sexta (day 3 fifth instar larvae and day 0 pupae). Prothoracic glands at each of these stages of development possess two forms of cAMP-PK which resemble the vertebrate type I and type II isozymes, with the latter being the predominant form (greater than 90%). Marked developmental differences exist in the degree of activation of soluble cAMP-PK following in vitro exposure of the prothoracic glands to PTTH. In larval glands, soluble cAMP-PK is activated within 3-10 min of initial exposure to doses of PTTH that stimulate ecdysone synthesis. By contrast, activation of soluble cAMP-PK in pupal glands occurs only when PTTH is administered in the presence of a phosphodiesterase inhibitor. Developmental differences in the activation of cAMP-PK by PTTH were qualitatively identical to previously observed differences in PTTH-stimulated accumulation of intracellular cAMP. The results suggest an involvement of soluble cAMP-PK in the response of day 3 fifth instar larval prothoracic glands to PTTH, but indicate a difference in the nature, intracellular location, or time course of activation, of hormone-sensitive protein kinase in day 0 pupal glands.