Unique translational modification of an invertebrate neuropeptide: a phosphorylated member of the adipokinetic hormone peptide family

Knockdown of the adipokinetic hormone receptor inhibits the reproduction of female Culex pipiens pallens (Diptera: Culicidae) by downregulating L-homoserine and serotonin levels

The adipokinetic hormone (AKH) receptor, interacting with AKH, regulates the metabolism of amino acids, carbohydrates, and lipids. The AKH receptor is abundant in mosquito primary and secondary sexual organs; however, the exact role of the AKH receptor in mosquito reproductive processes and the specific mechanisms involved are unclear. Among different tissues of adult female mosquitoes (Culex pipiens pallens), the ovaries and fat body showed high expression of the AKH receptor gene. Silencing this gene led to anti-reproductive effects, including abnormal ovarian morphology, reduced follicle number, and a decreased egg-laying count. Meanwhile, decreased yolk accumulation and iron deposition in the ovaries during the vitellogenesis phase were observed, accompanied by reduced expression levels of the vitellogenin-A1 precursor gene and transferrin gene. Liquid chromatography-mass spectrometry analysis revealed a decrease in L-homoserine and serotonin levels following AKH receptor gene knockdown, and supplementation with the above 2 metabolites partly rescued the anti-reproductive phenotype and increased the expression of the vitellogenin-A1 precursor gene and transferrin gene in the AKH receptor gene knockdown mosquitoes. Consistent with the gene knockdown results, Relugolix, an inhibitor of this receptor, likewise affected egg production. Herein, we revealed evidence for the function and potential mechanism of the AKH receptor during female mosquito reproduction, possibly offering an alternative method to control mosquitoes.

Authentication of a lophotrochozoan adipokinetic hormone receptor in a Gastropod, Aplysia californica

Gonadotropin-releasing hormone (GnRH) superfamily comprises multiple families of signaling peptides in both protostomes and deuterostomes. Among this superfamily, vertebrate GnRH stimulates reproduction, but other GnRH superfamily members elicit diverse pleiotropic effects. Within the GnRH superfamily members, adipokinetic hormone (AKH) and its receptor are well described in ecdysozoans but understudied in other lineages. To fill this knowledge gap, we deorphanized a putative receptor for a lophotrochozoan AKH in a gastropod mollusk, Aplysia californica, and named it Aplca-AKHR. Phylogenetic analysis revealed an orthologous relationship of Aplca-AKHR with ecdysozoan AKHRs and other putative lophotrochozoan AKHRs. Aplca-AKHR bound specifically to the previously identified Aplca-AKH with high affinity and activated the inositol phosphate pathway. Aplca-AKHR was expressed widely among central and peripheral tissues, but most prominently in several central ganglia and the heart. The expression of Aplca-AKHR was downregulated by a hyposaline challenge, consistent with a role in volume and fluid regulation previously described for its ligand, Aplca-AKH. In summary, this is the first pairing of a lophotrochozoan AKH with its cognate receptor. Expression data further support diverse central and peripheral roles, including volume and fluid control, of this ligand/receptor pair.

Oxidation Products of Tryptophan and Proline in Adipokinetic Hormones-Artifacts or Post-Translational Modifications?

BACKGROUND

Adipokinetic hormones (AKHs) regulate important physiological processes in insects. AKHs are short peptides with blocked termini and Trp in position 8. Often, proline occupies position 6. Few post-translational modifications have been found, including hydroxyproline ([Hyp6]) and kynurenine. Our recent data suggest that the Hyp- and Kyn-containing AKHs occur more often than originally thought and we here investigate if they are natural or artifactual.

METHODS

From crude extracts of the corpora cardiaca (CC) of various insect species, AKHs were analyzed using liquid chromatography coupled to high-resolution mass spectrometry (LC-MS). Synthetic [Hyp6]-AKHs were tested in an in vivo metabolic assay. Freshly dissected Periplaneta americana and Blaberus atropos CCs (with precautions taken against oxidation) were analyzed. B. atropos CC were placed into a depolarizing saline and the released AKHs were measured.

RESULTS

Hyp was detected in several decapeptides from cockroaches. The modified form accompanied the AKH at concentrations below 7%. The [Hyp6]-AKHs of B. atropos were present in fresh CC preparations and were shown to be releasable from the CC ex vivo. Synthetic [Hyp6]-containing peptides tested positively in a hypertrehalosemic bioassay. Hydroxyprolination was also detected for Manto-CC from the termite Kalotermes flavicollis and for Tetsu-AKH of the grasshopper, Tetrix subulata. Oxidized Trp-containing forms of Nicve-AKH were found in species of the burying beetle genus Nicrophorus.

CONCLUSIONS

Trp oxidation is known to occur easily during sample handling and is likely the reason for the present findings. For hydroxyprolination, however, the experimental evidence suggests endogenous processes.

Predicted novel hypertrehalosaemic peptides of cockroaches are verified by mass spectrometry

Small neuropeptides from the corpora cardiaca are responsible in cockroaches for the mobilisation of trehalose from the fat body into the haemolymph. Such hypertrehalosaemic hormones (HrTHs) belong to the large family of insect adipokinetic hormones (AKHs); a few HrTHs were previously sequenced from cockroaches, and from genomic and/or transcriptomic information one may predict the genes encoding HrTHs from more species. Definite elucidation of the primary structure of the mature peptide with putative modifications needs analytical chemical methods. In the current study, we use high-resolution mass spectrometry coupled with liquid chromatography to identify unequivocally the HrTHs of 13 cockroach species. Either genomic/transcriptomic information was available for most of the species examined, or from related species. We confirm predicted novel sequences and find hydroxyproline modification for the majority of the peptides. The novel decapeptides are structurally close to Bladi-HrTH, which is found in all seven of the investigated blaberid subfamilies. Bladi-HrTH and all the novel peptides elicit a hypertrehalosaemic response in Periplaneta americana, a blattid cockroach.

Mass Spectrometric Proof of Predicted Peptides: Novel Adipokinetic Hormones in Insects

The importance of insects in our ecosystems is undeniable. The indiscriminate use of broad-spectrum insecticides is a factor in the decline in insect biomass. We identify and sequence a prominent neuropeptide hormone in insects with an overarching goal to elucidate relatedness and create a database of bioactive peptides that could inform possible cross-activity in biological assays for the identification of a biorational lead compound. The major task of an adipokinetic hormone (AKH) in an insect is the regulation of metabolic events, such as carbohydrate and lipid breakdown in storage tissue during intense muscular work. From genomic and/or transcriptomic information one may predict the genes encoding neuropeptides such as the AKHs of insects. Definite elucidation of the primary structure of the mature peptide with putative post-translational modifications needs analytical chemical methods. Here we use high-resolution mass spectrometry coupled with liquid chromatography to identify unequivocally the AKHs of five insect species (one cockroach, two moths, and two flies) of which either genomic/transcriptomic information was available or sequences from related species. We confirm predicted sequences and discover novel AKH sequences, including one with a post-translational hydroxyproline modification. The additional sequences affirm an evolutionary pattern of dipteran AKHs and a conserved pattern in crambid moths.

Insects as a New Complex Model in Hormonal Basis of Obesity

Nowadays, one of the biggest problems in healthcare is an obesity epidemic. Consumption of cheap and low-quality energy-rich diets, low physical activity, and sedentary work favor an increase in the number of obesity cases within many populations/nations. This is a burden on society, public health, and the economy with many deleterious consequences. Thus, studies concerning this disorder are extremely needed, including searching for new, effective, and fitting models. Obesity may be related, among other factors, to disrupting adipocytes activity, disturbance of metabolic homeostasis, dysregulation of hormonal balance, cardiovascular problems, or disorders in nutrition which may lead to death. Because of the high complexity of obesity, it is not easy to find an ideal model for its studies which will be suitable for genetic and physiological analysis including specification of different compounds’ (hormones, neuropeptides) functions, as well as for signaling pathways analysis. In recent times, in search of new models for human diseases there has been more and more attention paid to insects, especially in neuro-endocrine regulation. It seems that this group of animals might also be a new model for human obesity. There are many arguments that insects are a good, multidirectional, and complex model for this disease. For example, insect models can have similar conservative signaling pathways (e.g., JAK-STAT signaling pathway), the presence of similar hormonal axis (e.g., brain–gut axis), or occurrence of structural and functional homologues between neuropeptides (e.g., neuropeptide F and human neuropeptide Y, insulin-like peptides, and human insulin) compared to humans. Here we give a hint to use insects as a model for obesity that can be used in multiple ways: as a source of genetic and peptidomic data about etiology and development correlated with obesity occurrence as well as a model for novel hormonal-based drug activity and their impact on mechanism of disease occurrence.

Novel members of the adipokinetic hormone family in beetles of the superfamily Scarabaeoidea

Eight beetle species of the superfamily Scarabaeoidea were investigated with respect to peptides belonging to the adipokinetic hormone (AKH) family in their neurohemal organs, the corpora cardiaca (CC). The following beetle families are represented: Scarabaeidae, Lucanidae, and Geotrupidae. AKH peptides were identified through a heterospecific trehalose-mobilizing bioassay and by sequence analyses, using liquid chromatography coupled to positive electrospray mass spectrometry (LC-ESI-MS) and analysis of the tandem MS² spectra obtained by collision-induced dissociation. All the beetle species have octapeptide AKHs; some have two AKHs, while others have only one. Novel AKH members were found in Euoniticellus intermedius and Circellium bacchus (family Scarabaeidae), as well as in Dorcus parallelipipedus (family Lucanidae). Two species of the family Geotrupidae and two species of the Scarabaeidae subfamily Cetoniinae contain one known AKH peptide, Melme-CC, while E. intermedius produces a novel peptide code named Euoin-AKH: pEINFTTGWamide. Two AKH peptides were each identified in CC of C. bacchus and D. parallelipipedus: the novel Cirba-AKH: pEFNFSAGWamide and the known peptide, Scade-CC-I in the former, and the novel Dorpa-AKH: pEVNYSPVW amide and the known peptide, Melme-CC in the latter. Kheper bonelli (subfamily Scarabaeinae) also has two AKHs, the known Scade-CC-I and Scade-CC-II. All the novel peptides were synthesized and the amino acid sequence assignments were unequivocally confirmed by co-elution of the synthetic peptides with their natural equivalent, and identical MS parameters of the two forms. The novel synthetic peptides are all active in inducing hypertrehalosemia in cockroaches.

Characterization and pharmacological analysis of two adipokinetic hormone receptor variants of the tsetse fly, Glossina morsitans morsitans

Adipokinetic hormones (AKH) are well known regulators of energy metabolism in insects. These neuropeptides are produced in the corpora cardiaca and perform their hormonal function by interacting with specific G protein-coupled receptors (GPCRs) at the cell membranes of target tissues, mainly the fat body. Here, we investigated the sequences, spatial and temporal distributions, and pharmacology of AKH neuropeptides and receptors in the tsetse fly, Glossina morsitans morsitans. The open reading frames of two splice variants of the Glomo-akh receptor (Glomo-akhr) gene and of the AKH neuropeptide encoding genes, gmmhrth and gmmakh, were cloned. Both tsetse AKHR isoforms show strong sequence conservation when compared to other insect AKHRs. Glomo-AKH prepropeptides also have the typical architecture of AKH precursors. In an in vitro Ca(2+) mobilization assay, Glomo-AKH neuropeptides activated each receptor isoform up to nanomolar concentrations. We identified structural features of tsetse AKH neuropeptides essential for receptor activation in vitro. Gene expression profiles suggest a function for AKH signaling in regulating Glossina energy metabolism, where AKH peptides are released from the corpora cardiaca and activate receptors mainly expressed in the fat body. This analysis of the ligand-receptor coupling, expression, and pharmacology of the two Glomo-AKHR variants facilitates further elucidation of the function of AKH in G. m. morsitans.

Two novel tyrosine-containing peptides (Tyr(4)) of the adipokinetic hormone family in beetles of the families Coccinellidae and Silphidae

Novel members of the adipokinetic hormone family of peptides have been identified from the corpora cardiaca (CC) of two species of beetles representing two families, the Silphidae and the Coccinellidae. A crude CC extract (0.3 gland equivalents) of the burying beetle, Nicrophorus vespilloides, was active in mobilizing trehalose in a heterologous assay using the cockroach Periplaneta americana, whereas the CC extract (0.5 gland equivalents) of the ladybird beetle, Harmonia axyridis, exhibited no hypertrehalosemic activity. Primary sequences of one adipokinetic hormone from each species were elucidated by liquid chromatography coupled to electrospray mass spectrometry (LC-MS). The multiple MS(N) electrospray mass data revealed an octapeptide with an unusual tyrosine residue at position 4 for each species: pGlu-Leu-Thr-Tyr-Ser-Thr-Gly-Trp amide for N. vespilloides (code-named Nicve-AKH) and pGlu-Ile-Asn-Tyr-Ser-Thr-Gly-Trp amide for H. axyridis (code-named Harax-AKH). Assignment of the correct sequences was confirmed by synthesis of the peptides and co-elution in reversed-phase high-performance liquid chromatography with fluorescence detection or by LC-MS. Moreover, synthetic peptides were shown to be active in the heterologous cockroach assay system, but Harax-AKH only at a dose of 30 pmol, which explains the negative result with the crude CC extract. It appears that the tyrosine residue at position 4 can be used as a diagnostic feature for certain beetle adipokinetic peptides, because this feature has not been found in another order other than Coleoptera.

A novel adipokinetic peptide from the corpus cardiacum of the primitive caeliferan pygmy grasshopper Tetrix subulata (Caelifera, Tetrigidae)

The basal caeliferan family Tetrigidae is investigated to identify neuropeptides belonging to the adipokinetic hormone (AKH) family. The pygmy grasshopper Tetrix subulata contains in its corpus cardiacum two octapeptides as revealed by liquid chromatography coupled to electrospray ionization mass spectrometry. The less abundant peptide is the well-known Schgr-AKH-II (pELNFSTGW amide) which is suggested to be the ancestral AKH of Caelifera and Ensifera. The second peptide, Tetsu-AKH (pEFNFTPGW amide), is novel and quite unusual with its third aromatic residue at position 2. It is thought to be autapomorphic for Caelifera. Tetsu-AKH has hyperlipemic activity in T. subulata and in Schistocerca gregaria.

Serine phosphorylation of CAPA pyrokinin in cockroaches-a taxon-specific posttranslational modification

In insects, posttranslational modifications of neuropeptides are largely restricted to C- and N-terminal amino acids. The most common modifications, N-terminal pyroglutamate formation and C-terminal α-amidation, may prevent a fast degradation of these messenger molecules. This is particularly important for peptide hormones. Other common posttranslational modifications of proteins such as glycosylation and phosphorylation seem to be very rare in insect neuropeptides. To check this assumption, we used a computer algorithm to search an extensive data set of MALDI-TOF mass spectra from cockroach tissues for ion signal patterns indicating peptide phosphorylation. The results verify that phosphorylation is indeed very rare. However, a candidate was found and experimentally verified as phosphorylated CAPA pyrokinin (GGGGpSGETSGMWFGPRL-NH2) in the cockroach Lamproblatta albipalpus (Blattidae, Lamproblattinae). Tandem mass spectrometry revealed the phosphorylation site as Ser(5). Phosphorylated CAPA pyrokinin was then also detected in most other cockroach lineages (e.g. Blaberidae, Polyphagidae) but not in closely related blattid species such as Periplaneta americana. This is remarkable since the sequence of CAPA pyrokinin is identical in Lamproblatta and Periplaneta. A consensus sequence of CAPA pyrokinins of cockroaches revealed a conserved motif that suggests phosphorylation by a Four-jointed/FAM20C related kinase.

Novel adipokinetic hormones in the kissing bugs Rhodnius prolixus, Triatoma infestans, Dipetalogaster maxima and Panstrongylus megistus

Peptides of the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) family were isolated and sequenced from the retrocerebral corpora cardiaca of four kissing bugs which are all vectors of the protozoan Trypanosoma cruzi responsible for Chagas' disease. The sequence of three novel AKHs were deduced from the multiple MS(N) electrospray mass data: the octapeptide pGlu-Leu-Thr-Phe-Ser-Thr-Asp-Trp amide (denoted Rhopr-AKH) in Rhodnius prolixus and Panstrongylus megistus, the nonapeptide pGlu-Leu-Thr-Phe-Thr-Pro-Asn-Trp-Gly amide (denoted Triin-AKH) in Triatoma infestans and the decapeptide pGlu-Leu-Thr-Phe-Ser-Asp-Gly-Trp-Gly-Asn amide (denoted Dipma-AKH) in Dipetalogaster maxima. The sequences were confirmed by identical behavior of natural and synthetic forms in reversed-phase HPLC and by CID-MS mass spectra. Conspecific injections of a dose of 10 pmol of the respective synthetic peptides resulted in a small but significant increase of the lipid concentration in the hemolymph. These experiments suggest that AKHs in kissing bugs act to regulate lipid metabolism, possibly during dispersal flights which is one of the mechanisms whereby the insects reach new outbreak areas.

Unique roles of glucagon and glucagon-like peptides: Parallels in understanding the functions of adipokinetic hormones in stress responses in insects

Glucagon is conventionally regarded as a hormone, counter regulatory in function to insulin and plays a critical anti-hypoglycemic role by maintaining glucose homeostasis in both animals and humans. Glucagon performs this function by increasing hepatic glucose output to the blood by stimulating glycogenolysis and gluconeogenesis in response to starvation. Additionally it plays a homeostatic role by decreasing glycogenesis and glycolysis in tandem to try and maintain optimal glucose levels. To perform this action, it also increases energy expenditure which is contrary to what one would expect and has actions which are unique and not entirely in agreement with its role in protection from hypoglycemia. Interestingly, glucagon-like peptides (GLP-1 and GLP-2) from the major fragment of proglucagon (in non-mammalian vertebrates, as well as in mammals) may also modulate response to stress in addition to their other physiological actions. These unique modes of action occur in response to psychological, metabolic and other stress situations and mirror the role of adipokinetic hormones (AKHs) in insects which perform a similar function. The findings on the anti-stress roles of glucagon and glucagon-like peptides in mammalian and non-mammalian vertebrates may throw light on the multiple stress responsive mechanisms which operate in a concerted manner under regulation by AKH in insects thus functioning as a stress responsive hormone while also maintaining organismal homeostasis.

Identification and functional characterization of two orphan G-protein-coupled receptors for adipokinetic hormones from silkworm Bombyx mori

Adipokinetic hormones (AKHs) are the best studied insect neuropeptides with the function of mobilizing lipids and carbohydrates during energy-expensive activities and modulating fundamental physiological processes, such as sugar homeostasis, lipid metabolism, and reproduction. Three distinct cDNAs encoding the prepro-Bombyx AKH1-3 have been cloned and confirmed by mass spectrometric methods. Our previous research suggested the Bombyx AKH receptor is activated by AKH1 and AKH2 with high affinity but by AKH3 with quite low affinity. In this study, using stable functional expression of the receptors in HEK293 cells, we have now identified AKH3 as a specific ligand for two orphan G-protein-coupled receptors, and we therefore named them AKHR2a and AKHR2b, respectively. We demonstrated that both AKHR2a and AKHR2b were activated by AKH3 at high affinity and by AKH1 and AKH2 at low affinity, leading to an increase of intracellular cAMP levels and activation of ERK1/2 and receptor internalization, but they were not activated by Bombyx corazonin. Conversely, the Bombyx corazonin receptor was activated by corazonin but not by AKH1-3. Quantitative RT-PCR revealed that AKHR2a and AKHR2b were both highly expressed in the testis but were also detected at low levels in other tissues. These results will lead to a better understanding of the AKH/AKHR system in the regulation of fundamental physiological processes.

Primary structure of an adipokinetic neuropeptide from the rhinoceros beetle, Oryctes rhinoceros L (Coleoptera: Dynastidae)

BACKGROUND

Neuropeptides play an important role in cellular communication in vertebrates. This is also true for insects in which many physiological, developmental and behavioral processes are affected by neuropeptides produced in neurosecretory cells of the retrocerebral complex. Small neuropeptides of the adipokinetic hormone/red pigment concentrating hormone family (AKH/RPCH) are one of the important groups of peptides that regulate physiological homeostasis.

PURPOSE

The present investigation was carried out to elucidate the primary structure of adipokinetic neuropeptides in the rhinoceros beetle, O. rhinoceros.

METHODS AND RESULTS

In the present investigation, an adipokinetic neuropeptide from the coconut pest, Oryctes rhinoceros was isolated from corpora cardiaca by HPLC; the chromatographic fractions were tested for adipokinetic activity in the plant bug, Iphita limbata in vivo. Two UV absorbance peaks were found to be significantly active in elevating haemolymph lipid levels. MALDI-MS analysis of the extract indicated that the molecular mass, 1003.70 Da is similar to the already known AKH from another beetle, Melolontha melolontha. MALDI-MS/MS analysis confirmed that its primary structure is exactly similar to the structure reported for the Melme-AKH (pE-L-N-Y-S-P-D-W-NH2).

COCLUSION

The findings suggest that the distribution of AKH peptides has shown that there exists a taxonomic order or family specificity. This data can be used as additional information to aid in the construction of phylogenetic trees by means of computer programme and protein parsimony algorithms.

The first decapeptide adipokinetic hormone (AKH) in Heteroptera: a novel AKH from a South African saucer bug, Laccocoris spurcus (Naucoridae, Laccocorinae)

A novel peptide of the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) family has been elucidated by mass spectrometry from the corpora cardiaca of an African saucer bug species, Laccocoris spurcus. It is the first decapeptide member found in the species-rich taxon Heteroptera, has the primary sequence pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp-Gly-Gly amide and is denoted as Lacsp-AKH. The first eight amino acids are identical to the octapeptide Anaim-AKH of the European saucer bug, Ilyocoris cimicoides. The synthetic peptide Lacsp-AKH elevates lipids upon injection into the hemolymph of L. spurcus at a low dose of 3 pmol. Swimming activity in this saucer bug also causes a significant increase in the lipid concentration in the hemolymph. Thus, both results point to an apparent function of the endogenous new decapeptide Lacsp-AKH in L. spurcus, namely, to regulate lipid mobilization. Isolation of an AKH peptide from the corpora cardiaca of the water bug Aphelocheirus aestivalis (Aphelocheiridae) resulted in the assignment of the octapeptide Anaim-AKH, supporting current phylogenies on the infraorder Nepomorpha.

Computational analysis and structure predictions of CHH-related peptides from Litopenaeus vannamei

The crustaceans produce several related peptides that belong to the crustacean hyperglycemic hormone (CHH) family. While these peptides have similar amino acid sequences, they have diverse biological functions that must arise, in part, from differences in the 3D shape of these peptides. However, it is generally accepted that peptides with a high degree of sequence similarity also have a similar 3-D structure. We used the solution structure of one peptide in the crustacean hyperglycemic hormone family, the molt-inhibiting hormone of the kuruma prawn (Marsupenaeus japonicus), to predict the shape of the five known peptides related to CHH in the Pacific white shrimp, Litopenaeus vannamei. The high similarity of the 3-D structures of these peptides suggests a common fold for the entire family. Nevertheless, minor differences in the shape of these peptides were observed, which may be the basis for their different biological properties.

Bombyx adipokinetic hormone receptor activates extracellular signal-regulated kinase 1 and 2 via G protein-dependent PKA and PKC but β-arrestin-independent pathways

Neuropeptides of the adipokinetic hormone (AKH) family are among the best studied hormone peptides. They play important roles in insect hemolymph sugar homeostasis, larval lipolysis, and storage-fat mobilization. Mechanistic investigations have shown that, upon AKH stimulation, adipokinetic hormone receptor (AKHR) couples to a Gs protein and enhances adenylate cyclase activity, leading to intracellular cAMP accumulation. However, the underlying molecular mechanism by which this signaling pathway connects to extracellular signal-regulated kinase 1/2 (ERK1/2) remains to be elucidated. Using HEK293 cells stably or transiently expressing AKHR, we demonstrated that activation of AKHR elicited transient phosphorylation of ERK1/2. Our investigation indicated that AKHR-mediated activation of ERK1/2 was significantly inhibited by H-89 (protein kinase A inhibitor), Go6983, and GF109203X (protein kinase C inhibitors) but not by U73122 (PLC inhibitor) or FIPI (PLD inhibitor). Moreover, AKHR-induced ERK1/2 phosphorylation was blocked by the calcium chelators EGTA and BAPTA-AM. Furthermore, ERK1/2 activation in both transiently and stably AKHR-expressing HEK293 cells was found to be sensitive to pretreatment of pertussis toxin, whereas AKHR-mediated ERK1/2 activation was insensitive to siRNA-induced knockdown of β-arrestins and to pretreatment of inhibitors of EGFR, Src, and PI3K. On the basis of our data, we propose that activated AKHR signals to ERK1/2 primarily via PKA- and calcium-involved PKC-dependent pathways. Our current study provides the first in-depth study defining the mechanisms of AKH-mediated ERK activation through the Bombyx AKHR.

Identification of myotropic neuropeptides from the brain and corpus cardiacum-corpus allatum complex of the beetle, Zophobas atratus

The neuropeptide profiles of the two major neuro-endocrinological organs, brain and retrocerebral complex corpus cardiacum-corpus allatum (CC/CA) of adult beetles, Zophobas atratus Fabricius (Coleoptera:Tenebrionidae) were analyzed by a combination of high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight tandem mass spectrometry (MALDI TOF/TOF MS). The homological semi-isolated heart bioassay was used to screen HPLC fractions for myotropic activity in tissues, revealing several cardiostimulatory and cardioinhibitory factors from both the brain and CC/CA. Analysis of HPLC fractions by MALDI-TOF MS identified seven mass ions that could be assigned to other known peptides: leucomyosuppressin (LMS), Tribolium castaneum pyrokinin 2, sulfakinin 1, myoinhibitory peptide 4, a truncated NVP-like peptide, Tenebrio molitor AKH and crustacean cardioactive peptide. In addition, two novel peptides, myosuppressin (pEDVEHVFLRFa), which differs from LMS by one amino acid (E for D at position 4) and pyrokinin-like peptide (LPHYTPRLa) were also identified. To establish cardioactive properties of some of the identified peptides, chemical synthesis was carried out and their activities were tested using the heart bioassay.

Hormonal regulation of energy metabolism in insects as a driving force for performance

Since all life processes depend on energy, the endocrine control of energy metabolism is one of the driving forces for the performance of an individual. Here, we review the literature on the key players in the endocrine regulation of energy homeostasis in insects, the adipokinetic hormones. These pleiotropic peptides not only control dynamic performance traits (flight, swimming, walking) but also regulatory performance traits (egg production, larval growth, and molting). Adipokinetic hormone is released into the hemolymph during intense muscular activity (flight) and also during apparently less energy-demanding locomotory activities, such as swimming and even walking, and, finally, activates the catabolic enzymes phosphorylase and/or triacylglycerol lipase that mobilize carbohydrates and/or lipids and proline, respectively. At the same time, anabolic processes such as the synthesis of protein, lipid, and glycogen are inhibited. Furthermore, adipokinetic hormones affect locomotory activity via neuromodulatory mechanisms that apparently employ biogenic amines. During oogenesis, it is thought that adipokinetic hormone performs similar tasks, because energetic substrates have to be mobilized and transported from the fat body to the ovaries in order to support oocyte growth. Inhibition of anabolic processes by exogenous adipokinetic hormone results in females that lay fewer and smaller eggs. Much less is known about the role of adipokinetic hormones during larval development and during molting but in this case energy homeostasis has to be tightly regulated as well: in general, during the early phase of a larval instar intake of food prevails and the energy stores of the fat body are established, whereas, prior to the molt, insects stop feeding and mobilize energy stores in the fat body, thereby fueling energy-demanding processes such as the formation of the new cuticle and the emergence from the old one. From the few data available to date, it is clear that adipokinetic hormones are involved in the regulation of these events in larvae.

Peptides of the adipokinetic hormone/red pigment-concentrating hormone family with special emphasis on Caelifera: primary sequences and functional considerations contrasting grasshoppers and locusts

The presented work is a hybrid of an overview and an original research paper. First, we review briefly the structure, biosynthesis, release, mode of action and function of those peptides that constitute the adipokinetic/red pigment-concentrating family. Second, we collate the data on primary sequences available for caeliferan orthoptera, i.e. grasshoppers and locusts, and add a number of new data from previously unpublished work. The data are interpreted in conjunction with morphological and molecular biology data with respect to phylogenetic relationships of these various taxa. Finally, we discuss the differences between the adipokinetic response of grasshoppers and locusts to corpus cardiacum extract or synthetic adipokinetic hormone with regard to flight ability, phase polymorphism, age, presence of adipokinetic hormones, lipophorin system and other parameters. It appears that the higher hyperlipaemic response is always correlated with pronounced flight ability.

Molecular and functional characterization of adipokinetic hormone receptor and its peptide ligands in Bombyx mori

Neuropeptides of the adipokinetic hormone (AKH) family are among the best studied hormone peptides, but its signaling pathways remain to be elucidated. In this study, we molecularly characterized the signaling of Bombyx AKH receptor (AKHR) and its peptide ligands in HEK293 cells. In HEK293 cells stably expressing AKHR, AKH1 stimulation not only led to a ligand concentration dependent mobilization of intracellular Ca(2+) and cAMP accumulation, but also elicited transient activation of extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. We observed that AKH receptor was rapidly internalized after AKH1 stimulation. We further demonstrated that AKH2 exhibited high activities in cAMP accumulation and ERK1/2 activation on AKHR comparable to AKH1, whereas AKH3 was much less effective.

The first identified neuropeptide in the insect order Megaloptera: a novel member of the adipokinetic hormone family in the alderfly Sialis lutaria

This is the first report on the structural identity of a neuropeptide of the insect order Megaloptera. A peptide was isolated and sequenced from the retrocerebral corpora cardiaca glands of the alderfly, Sialis lutaria. The sequence of the peptide was deduced from the multiple MS(N) electrospray mass data as that of an octapeptide: pGlu-Ile/Leu-Thr-Phe-Thr-Pro-Ser-Trp amide. The ambiguity about the amino acid at position 2, Leu or Ile, was solved by comparing retention time on reversed-phase HPLC and establishing co-elution with the synthetic Leu(2)-form which also had exactly the same MS(2) mass spectra as the natural peptide. The sequence represents a novel peptide of the adipokinetic hormone family which has already more than 40 members. Interestingly, the primary structure is identical to that predicted from genome information for the adipokinetic hormone of the yellow fever mosquito, Aedes aegypti. Since alderflies are not known for their active flight metabolism but produce a rather high number of eggs, it is anticipated that the alderfly is a good study object to establish a possible role of the novel peptide to regulate fat mobilization from the fat body and transport into the egg, thereby playing a role in the control of reproductive processes.

Neuropeptides of the beetle, Tenebrio molitor identified using MALDI-TOF mass spectrometry and deduced sequences from the Tribolium castaneum genome

Four neuropeptides were identified from the brain and corpora cardiaca-corpora allata (CC-CA) of the mealworm beetle Tenebrio molitor using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and information derived from the genome of the red flour beetle, Tribolium castaneum. Leucomyosuppressin (a FLRFamide), previously associated with cockroaches, but also subsequently identified from honey bee seen as a prominent peptide in both brain and CC-CA of T.molitor. A coding sequence for this peptide is found in the genome of T. castaneum. In addition, three FXPRLamides (pyrokinins), provisionally Tenmo-PK-1, Tenmo-PK-2 and Tenmo-PK-3 (HVVNFTPRLamide, SPPFAPRLamide, HL(I)SPFSPRLamide) were identified in both CC-CA and brain of T. molitor, again on the basis of predicted occurrence or similarity in T. castaneum. The sequence of Tenmo-PK-2 is the same as the PK-2 of the cockroach, Periplaneta americana. Other peptides readily predicted from the genome of T. castaneum include two AKH/HrTH peptides (Trica-AKH-1; pELNFSTDWamide and Trica-AKH-2; pELNFTPNWamide), the second of which is identical to Pyrap-AKH, an AKH-related peptide (Trica AKH-L; pEVTFSRDWPamide), two CRF-related diuretic factors (Trica-DH 37 and Trica-DH 47), the latter identical to Tenmo-DH 47, a putative antidiuretic factor (Trica-ADFb; LYDDGSYKPHVYGF-OH), two sulfakinin-like peptides (Trica-SK-1; pETSDDY(SO(3))GHLRFamide, and Trica SK-2; GEEPFDDYGHMRFamide), a potential allatostatin-C (Trica-AS; pESRYRQCYFNPISCF-OH), six allatostatin-B/myoinhibitory peptides (Trica-AST-B-1,2,3,4,5 & 6; DWNKDLHIWamide, GWNNLHEGWamide, AWQSLQSGWamide, NWGQFHGGWamide, SKWDNFRGSWamide, EPAWSNLGIWamide), an allatotropin-like peptide (Trica-ATL; GIEALKYHNMDLGTARGYamide), four 'CAPA'-related peptides (Trica-CAPA-1,2,3,4; NKLASVYALTPSLRVamide, RIGKMVSFPRIamide, PGANSGGMWFGPRLamide, SENFTPWAYIILNGEAPIIREVHYSPRLamide), proctolin (RYLPT), a potential SIFamide (Trica-SIFa; TYRKPPFNGSIFamide), an arginine-vasopressin-related peptide (Trica-AVP; CLITNCPRGamide) and an ITP-related peptide (Trica-ITP). No evidence was found for the presence of 'A' allatostatins (Y/FxFGLamides) or corazonin, either in T. molitor, or in the genome of T. castaneum.

A novel adipokinetic peptide in a water boatman (Heteroptera, Corixidae) and its bioanalogue in a saucer bug (Heteroptera, Naucoridae)

The corpora cardiaca (CC) of two water bug species, the water boatman Corixa punctata and the saucer bug Ilyocoris cimicoides, contain a substance that cause hyperlipemia in the migratory locust. The primary sequence of one octapeptide belonging to the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) family was deduced from the multiple MS(N) electrospray mass data of CC material from each species. Whereas the saucer bug contains the known octapeptide pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp amide, code-named Anaim-AKH, the water boatman has a novel peptide identified as pGlu-Leu/Ile-Asn-Phe-Ser-Pro-Ser-Trp amide, code-named Corpu-AKH. The ambiguity about the amino acid at position 2, i.e. Leu or Ile, in Corpu-AKH was solved by isolating the peptide in a single-step by reversed-phase HPLC and establishing co-elution with the synthetic peptide containing Leu at position 2. Functionally, the peptides regulate lipid mobilization, as evidenced by an adipokinetic effect after injecting synthetic Anaim-AKH and Corpu-AKH into the respective acceptor species. Swimming activity of I. cimicoides also causes hyperlipemia.