Proline synthesis in fat body of Leptinotarsa decemlineata

Metabolic Rate Suppression and Maintenance of Flight Muscle Metabolic Capacity during Diapause in Bumble Bee (Bombus impatiens) Queens

AbstractThe common eastern bumble bee (Bombus impatiens) queens endure cold winter months by entering a diapause state. During this overwintering period, these animals use stored energy reserves while maintaining a low metabolic rate. This study investigates changes in the metabolic rate of bumble bee queens during diapause-like laboratory conditions and the potential reorganization of the flight muscle metabolic properties during this period. We first confirmed the hypometabolic state of queens during diapause in the laboratory, which lowered their resting metabolic rate to less than 5% of normal resting values. Body mass decreased during diapause, body composition changed where carbohydrates decreased initially, and later protein declined, with a similar trend for lipid content. Using cellular respirometry, we determined the capacity of the flight muscle cells of bumble bee queens to use various metabolic fuels and whether this capacity changes during the progression of diapause to favor stored lipid-derived substrates. Queens showed a low capacity to oxidize the amino acid proline, compared with workers, and their capacity to oxidize all metabolic substrates did not change during a 4-mo diapause period in the laboratory. We also show no detectable ability to oxidize fatty acid by flight muscle mitochondria in this species. The metabolic properties of flight muscle tissue were further characterized using metabolic enzyme activity profiles showing little change during diapause, indicating that profound metabolic suppression is induced without major changes in muscle metabolic phenotypes. Overall, B. impatiens queens undergo diapause while maintaining flight muscle capacity under the conditions used.

Functional insight and cell-specific expression of the adipokinetic hormone/corazonin-related peptide in the human disease vector mosquito, Aedes aegypti

The adipokinetic hormone/corazonin-related peptide (ACP) is an insect neuropeptide structurally intermediate between corazonin (CRZ) and adipokinetic hormone (AKH). Unlike the AKH and CRZ signaling systems that are widely known for their roles in the mobilization of energy substrates and stress responses, respectively, the main role of ACP and its receptor (ACPR) remains unclear in most arthropods. The current study aimed to localize the distribution of ACP in the nervous system and provide insight into its physiological roles in the disease vector mosquito, Aedes aegypti. Immunohistochemical analysis and fluorescence in situ hybridization localized the ACP peptide and transcript within a number of cells in the central nervous system, including two pairs of laterally positioned neurons in the protocerebrum of the brain and a few ventrally localized neurons within the pro- and mesothoracic regions of the fused thoracic ganglia. Further, extensive ACP-immunoreactive axonal projections with prominent blebs and varicosities were observed traversing the abdominal ganglia. Given the prominent enrichment of ACPR expression within the abdominal ganglia of adult A. aegypti mosquitoes as determined previously, the current results indicate that ACP may function as a neurotransmitter and/or neuromodulator facilitating communication between the brain and posterior regions of the nervous system. In an effort to elucidate a functional role for ACP signaling, biochemical measurement of energy substrates in female mosquitoes revealed a reduction in abdominal fat body in response to ACP that matched the actions of AKH, but interestingly, a corresponding hypertrehalosaemic effect was only found in response to AKH since ACP did not influence circulating carbohydrate levels. Comparatively, both ACP and AKH led to a significant increase in haemolymph carbohydrate levels in male mosquitoes while both peptides had no influence on their glycogen stores. Neither ACP nor AKH influenced circulating or stored lipid levels in both male and female mosquitoes. Collectively, these results reveal ACP signaling in mosquitoes may have complex sex-specific actions, and future research should aim to expand knowledge on the role of this understudied neuropeptide.

Diapause differentially modulates the transcriptomes of fat body and flight muscle in the Colorado potato beetle

Many temperate insects, such as the Colorado potato beetle, enter diapause in winter, during which they arrest their development, suppress their metabolic rate and have high stress tolerance. Diapause phenotypes can be transcriptionally regulated, however many studies to date report only whole animal gene expression rather than tissue-specific processes during diapause. We used RNA-seq to measure gene expression in fat body and flight muscle of diapausing and non-diapausing beetles. We used differential expression and GO enrichment analyses to evaluate longstanding hypotheses about the mechanisms that drive arrested development, changes in energy metabolism, and increased stress tolerance during diapause. We found evidence of G2/M cell cycle arrest, juvenile hormone catabolism, increased antioxidant metabolism, epigenetic modification, transposable element regulation, and cytoskeletal remodeling in both the fat body and flight muscle of diapausing beetles. Beetles differentially modulated the fat body and flight muscle transcriptomes during diapause with fat body playing a larger role in the hypoxia response and immunity, whereas flight muscle had higher abundance of transcripts related to the chaperone response and proteostasis. Our transcriptome provides evidence for distinct roles and responses of fat body and flight muscle during diapause in the Colorado potato beetle, and we provide testable hypotheses for biological processes that appear to drive diapause phenotypes in insects.

Evidence for non-colligative function of small cryoprotectants in a freeze-tolerant insect

Freeze tolerance, the ability to survive internal ice formation, facilitates survival of some insects in cold habitats. Low-molecular-weight cryoprotectants such as sugars, polyols and amino acids are hypothesized to facilitate freeze tolerance, but their in vivo function is poorly understood. Here, we use a combination of metabolomics and manipulative experiments in vivo and ex vivo to examine the function of multiple cryoprotectants in the spring field cricket Gryllus veletis. Cold-acclimated G. veletis are freeze-tolerant and accumulate myo-inositol, proline and trehalose in their haemolymph and fat body. Injecting freeze-tolerant crickets with proline and trehalose increases survival of freezing to lower temperatures or for longer times. Similarly, exogenous myo-inositol and trehalose increase ex vivo freezing survival of fat body cells from freeze-tolerant crickets. No cryoprotectant (alone or in combination) is sufficient to confer freeze tolerance on non-acclimated, freeze-intolerant G. veletis. Given that each cryoprotectant differentially impacts survival in the frozen state, we conclude that small cryoprotectants are not interchangeable and likely function non-colligatively in insect freeze tolerance. Our study is the first to experimentally demonstrate the importance of non-colligative cryoprotectant function for insect freeze tolerance both in vivo and ex vivo, with implications for choosing new molecules for cryopreservation.

How crickets become freeze tolerant: The transcriptomic underpinnings of acclimation in Gryllus veletis

Some ectotherms can survive internal ice formation. In temperate regions, freeze tolerance is often induced by decreasing temperature and/or photoperiod during autumn. However, we have limited understanding of how seasonal changes in physiology contribute to freeze tolerance, and how these changes are regulated. During a six week autumn-like acclimation, late-instar juveniles of the spring field cricket Gryllus veletis (Orthoptera: Gryllidae) become freeze tolerant, which is correlated with accumulation of low molecular weight cryoprotectants, elevation of the temperature at which freezing begins, and metabolic rate suppression. We used RNA-Seq to assemble a de novo transcriptome of this emerging laboratory model for freeze tolerance research. We then focused on gene expression during acclimation in fat body tissue due to its role in cryoprotectant production and regulation of energetics. Acclimated G. veletis differentially expressed >3000 transcripts in fat body. This differential expression may contribute to metabolic suppression in acclimated G. veletis, but we did not detect changes in expression that would support cryoprotectant accumulation or enhanced control of ice formation, suggesting that these latter processes are regulated post-transcriptionally. Acclimated G. veletis differentially regulated transcripts that likely coordinate additional freeze tolerance mechanisms, including upregulation of enzymes that may promote membrane and cytoskeletal remodelling, cryoprotectant transporters, cytoprotective proteins, and antioxidants. Thus, while accumulation of cryoprotectants and controlling ice formation are commonly associated with insect freeze tolerance, our results support the hypothesis that many other systems contribute to surviving internal ice formation. Together, this information suggests new avenues for understanding the mechanisms underlying insect freeze tolerance.

Knocking down a putative Δ(1) -pyrroline-5-carboxylate dehydrogenase gene by RNA interference inhibits flight and causes adult lethality in the Colorado potato beetle Leptinotarsa decemlineata (Say)

BACKGROUND

Leptinotarsa decemlineata is an able disperser by flight. Novel control strategies must be explored to control the damage and inhibit the dispersal efficiently. Proline is a major energy substrate during flight. Δ-Pyrroline-5-carboxylate dehydrogenase (P5CDh) catalyses the second step of proline degradation for the production of ATP.

RESULTS

A full-length Ldp5cdh cDNA was cloned. Ldp5cdh was ubiquitously expressed in the eggs, the first through fourth larval instars, wandering larvae, pupae and adults. In the adults, Ldp5cdh mRNA was widely distributed in thorax muscles, midgut, foregut, hindgut, Malpighian tubules, ventral ganglion, fat body and epidermis, with the expression levels from the highest to the lowest. Two double-stranded RNAs (dsRNAs) (dsLdp5cdh1 and dsLdp5cdh2) targeting Ldp5cdh were constructed and bacterially expressed. Ingestion of dsLdp5cdh1 and dsLdp5cdh2 successfully silenced Ldp5cdh, significantly increased the contents of proline, arginine and alanine, but strongly decreased the contents of asparate, asparagine, glutamate and glutamine in the haemolymph. Moreover, knocking down Ldp5cdh significantly reduced ATP content, decreased flight speed, shortened flight distance and increased adult mortality.

CONCLUSIONS

It seems that identified Ldp5cdh encodes a functional P5CDh enzyme, and Ldp5cdh may serve as a potential target for dsRNA-based pesticide for controlling the damage and dispersal of L. decemlineata adults. © 2014 Society of Chemical Industry.

A putative Δ1-pyrroline-5-carboxylate synthetase involved in the biosynthesis of proline and arginine in Leptinotarsa decemlineata

Delta 1-pyrroline-5-carboxylate synthetase (P5CS) catalyzes the conversion of glutamate (Glu) to Glu semialdehyde (GSA). GSA spontaneously cyclizes to form P5C. P5C is then reduced to proline (Pro) or is converted to ornithine, the intermediate for arginine (Arg) biosynthesis. In the present study, a full-length Ldp5cs complementary DNA was cloned from the Colorado potato beetle Leptinotarsa decemlineata, a notorious insect defoliator of potato in most potato-growing regions of the world. Ldp5cs encodes a 792-amino-acid protein which shares high identity to homologues from other insect species. Quantitative reverse transcription polymerase chain reaction revealed that Ldp5cs was ubiquitously expressed in the eggs, first to fourth-instar larvae, wandering larvae, pupae and sexually mature adults. In the adults, Ldp5cs mRNA levels were higher in the fat body, foregut, midgut and hindgut, moderate in the ventral ganglion, lower in the thorax muscles, epidermis and Malpighian tubules. Two double-stranded RNAs (dsRNAs) (dsLdp5cs1 and dsLdp5cs2) targeting Ldp5cs were constructed and bacterially expressed. Ingestion during 3 consecutive days of dsLdp5cs1 or dsLdp5cs2 successfully silenced Ldp5cs, significantly reduced the contents of Pro and Arg in the hemolymph, decreased flight speed and shortened flight distance of the resulting adults. Furthermore, knocking down Ldp5cs significantly increased adult mortality. Thus, our results suggest that identified Ldp5cs encodes a functional P5CS enzyme that is involved in the biosynthesis of Pro and Arg in L. decemlineata.

Metabolic pathways in Anopheles stephensi mitochondria

No studies have been performed on the mitochondria of malaria vector mosquitoes. This information would be valuable in understanding mosquito aging and detoxification of insecticides, two parameters that have a significant impact on malaria parasite transmission in endemic regions. In the present study, we report the analyses of respiration and oxidative phosphorylation in mitochondria of cultured cells [ASE (Anopheles stephensi Mos. 43) cell line] from A. stephensi, a major vector of malaria in India, South-East Asia and parts of the Middle East. ASE cell mitochondria share many features in common with mammalian muscle mitochondria, despite the fact that these cells are of larval origin. However, two major differences with mammalian mitochondria were apparent. One, the glycerol-phosphate shuttle plays as major a role in NADH oxidation in ASE cell mitochondria as it does in insect muscle mitochondria. In contrast, mammalian white muscle mitochondria depend primarily on lactate dehydrogenase, whereas red muscle mitochondria depend on the malate-oxaloacetate shuttle. Two, ASE mitochondria were able to oxidize proline at a rate comparable with that of alpha-glycerophosphate. However, the proline pathway appeared to differ from the currently accepted pathway, in that oxoglutarate could be catabolized completely by the tricarboxylic acid cycle or via transamination, depending on the ATP need.

Analysis of fat body transcriptome from the adult tsetse fly, Glossina morsitans morsitans

Tsetse flies (Diptera: Glossinidia) are vectors of pathogenic African trypanosomes. To develop a foundation for tsetse physiology, a normalized expressed sequence tag (EST) library was constructed from fat body tissue of immune-stimulated Glossina morsitans morsitans. Analysis of 20,257 high-quality ESTs yielded 6372 unique genes comprised of 3059 tentative consensus (TC) sequences and 3313 singletons (available at http://aksoylab.yale.edu). We analysed the putative fat body transcriptome based on homology to other gene products with known functions available in the public domain. In particular, we describe the immune-related products, reproductive function related yolk proteins and milk-gland protein, iron metabolism regulating ferritins and transferrin, and tsetse's major energy source proline biosynthesis. Expression analysis of the three yolk proteins indicates that all are detected in females, while only the yolk protein with similarity to lipases, is expressed in males. Milk gland protein, apparently important for larval nutrition, however, is primarily synthesized by accessory milk gland tissue.

Activation of triacylglycerol lipase in the fat body of a beetle by adipokinetic hormone

The activation of triacylglycerol lipase and the stimulation of proline synthesis in the fat body of the fruit beetle Pachnoda sinuata by the endogenous octapeptide hormone Melme-CC (pQLNYSPDWa), which belongs to the family of insect adipokinetic hormones, were studied, and the correlation of both events investigated. At rest, the activity of triacylglycerol lipase in the fat body of the beetle was higher than in the fat body of the American cockroach, Periplaneta americana, but lower than in the migratory locust, Locusta migratoria. Triacylglycerol lipase of the beetle is activated by: (a) injection of synthetic Melme-CC and (b) the stimulus of flight. Activation of lipase by Melme-CC is time-dependent. Injection of cpt-cAMP activates triacylglycerol lipase in the fat body and causes an increase in the concentration of proline in the haemolymph at the expense of alanine. In contrast, injection of F-inositol-1,4,5-phosphate does not affect the activation state of lipase, nor the levels of amino acids in the haemolymph. High doses of octopamine do not activate lipase. Furthermore, activity of fat body lipase and proline concentration in the haemolymph both follow a circadian rhythm: both parameters are high in the morning, whereas they are low in the evening. When transfer of Melme-CC, released from the corpora cardiaca, to the thorax/abdomen is prevented by neck-ligation, the activity of lipase, as well as the circulating proline levels are low. Regression analysis revealed that activity of triacylglycerol lipase is positively correlated to proline concentration in the haemolymph, whereas there is a negative correlation of the enzyme activity and alanine level in the haemolymph. From these results we conclude that the activation of fat body triacylglycerol lipase by Melme-CC in P. sinuata stimulates proline synthesis. Proline is one of the major substrates to power flight activity in the beetle.

Mitochondria: aerobic and anaerobic design--lessons from molluscs and fishes

The contributions of Peter Hochachka to the development of comparative and adaptational biochemistry are substantial. In particular, he and his academic offspring made major contributions to the understanding of the metabolism of molluscs and fishes. These two large taxonomic groups each have marine, freshwater and terrestrial/semiterrestrial representatives, and their mitochondrial metabolism has been shaped by these environmental conditions. In particular, the importance of amino acids and lipids as energy sources has interesting correlations with the environment and the osmotic strategy used. In marine molluscs, amino acids are important aerobic energy sources, and are used as osmolytes and participate in anaerobic metabolism. In marine elasmobranchs, amino acids and ketone bodies, but not lipids per se, are important energy sources in extrahepatic tissues. Marine and freshwater teleost fish by contrast use lipids as an extrahepatic energy source with minimal use of ketone bodies. Furthermore, ketone bodies are important in the metabolism of freshwater and terrestrial but not marine molluscs. The bases for these different metabolic plans may lie in the solute systems used by the different groups (e.g. amino acids in marine molluscs and urea in marine elasmobranchs). The various metabolic options used by fishes and molluscs indicate the plasticity of metabolic design in an environmental context.

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).

Effect of pyriproxyfen and photoperiod on free amino acid concentrations and proteins in the hemolymph of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

A North Dakota strain of the Colorado potato beetle, Leptinotarsa decemlineata (Say), was reared under both short- (8L:16D) and long-day (17L:7D) conditions. Age-related and pyriproxyfen- (JHA-) induced changes in hemolymph free amino acids and proteins were examined. Under a short-day photoperiod, the total free amino acid concentration in the hemolymph increased gradually up to 20 days of adult life, but the long-day beetles showed marked increases during the first 10 days and then decreased afterwards. Proline, glutamine and valine were the most abundant free amino acids in both sexes of beetles held under either short- or long-day photoregims. JHA treatment of diapausing adults, held under either short- or long-day conditions after treatment, terminated diapause as indicated by re-emergence from the vermiculite, feeding, mating, changes in free amino acid levels, the disappearance of diapause protein 1 and appearance of vitellogenin in the hemolymph. Furthermore, most of the JHA-treated females held under long-day conditions also matured oocytes and oviposited, but those held under short-day conditions did not.

Amino acid levels during learning and memory consolidation of an aversive conditioning task in crickets

We followed the titer of free amino acids in nervous ganglia and hemolymph of the cricket Pteronemobius sp. at different times during and after a shock avoidance training that included one experimental group and three controls. The results showed that Tau, urea, Thr, His, GABA, and an unidentified compound (Q) increased their titer in ganglia and hemolymph during training, whereas Ala, Arg, Val, Glu, Ser, and one or all of the group formed by Cys, Phe, Ile, Leu, and Trp decreased theirs concomitantly to memory consolidation. The difference in the rate of experimental insects and their yoked slaves to consolidate the learned task was reflected in the changes of the titers of the amino acids mentioned above. The data add to the evidence for a direct involvement of these amino acids in modulating the memory consolidation process.

Glutamine and glutamate metabolism in normal and heat shock conditions inDrosophila Kc cells: Conditions supporting glutamine synthesis maximize heat shock polypeptide expression

We have previously reported that Drosophila Kc cells require glutamine for maximal expression of heat shock proteins in stressed conditions (Sanders and Kon: J. Cell. Physiol. 146:180-190, 1991). The mechanism of this effect has been investigated by comparing the metabolic utilization of glutamine in conditions which support hsp expression with that of glutamate in conditions where up to 100-fold less hsp is synthesized. This comparison showed that free ammonia was generated by cells incubated in the presence of glutamine in 37 degrees C (heat shock) conditions, but not at 25 degrees C, and not in the presence of glutamate in either normal or heat shock conditions. There was no difference in the amount of [14C]O2 generated from either [14C]-labeled amino acid in the tricarboxylic acid cycle, but three- to four-fold more alanine was synthesized in cells incubated in glutamine than in glutamate. Treating the cells with aminotransferase inhibitors to artificially increase NH3 release raised hsp expression in the presence of glutamate to maximal levels characteristic of glutamine. This potentiation correlated with inhibition of alanine aminotransferase. Since only NH3 production correlated with hsp expression in heat shock conditions in the presence of glutamine, and NH3 addition to glutamate also resulted in maximal hsp expression, we measured glutamine production in glutamate plus NH3 and observed net glutamine synthesis. The supposition that glutamine itself is responsible for the regulatory changes supporting maximal hsp expression was supported by the finding that the glutamine analog, 6-diazo-5-oxo-L-norleucine (DON), mimicked the effects of glutamine. We conclude that glutamine imposes regulatory changes which alter nitrogen metabolism and support hsp expression in Kc cells.