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Adipokinetic hormone counteracts oxidative stress elicited in insects by hydrogen peroxide: in vivo and in vitro study

The involvement of members of Adipokinetic hormone (AKH) family in regulation of response to oxidative stress (OS) was investigated in the present study. OS was elicited in the insect body by exogenous application of hydrogen peroxide. In vivo experiments reveal that injection of hydrogen peroxide into the haemocoel of the firebug, Pyrrhocoris apterus, increases the level of AKH in the central nervous system (CNS) and in the haemolymph. The injection of hydrogen peroxide also increases the mortality of experimental bugs, whereas co-injection of hydrogen peroxide with Pyrap-AKH reduces mortality to control levels. Importantly, an increase in haemolymph protein carbonyl (an OS biomarker) levels is decreased to control levels when hydrogen peroxide is co-injected with Pyrap-AKH. Similar results were obtained using in vitro experiments. OS biomarkers such as malondialdehyde and protein carbonyls were significantly enhanced upon exposure of isolated CNS to hydrogen peroxide in vitro, whereas co-treatment of the CNS with hydrogen peroxide and Pyrap-AKH reduces their level significantly. Catalase activity was measured as well and the same pattern was observed. The results of the present study provide strong support on the feedback regulation between oxidative stressors and AKH action, and implicate AKH in counteracting OS

Mode of action of adipokinetic hormone at the sub-cellular level in potentiating anti-oxidative responses in insects.

Adipokinetic hormones (AKHs) are neuropeptides from the arthropod AKH/RPCH (adipokinetic hormone/ red pigment concentrating hormone) family. The typical AKH is an octa-, nona- or decamer that is synthesized, stored and released by the neurosecretory cells of the corpora cardiaca (CC) connected to the brain and primarily involved in the mobilization of energy reserves from the fat body in insects. In addition to its well established role in energy metabolism, AKH has also been implicated to be involved in stress responses specifically to oxidative stress. Oxidative stress induced elevation of AKH levels as well as a modulation of biomarkers of oxidative damage following exogenous application of AKH have been demonstrated. However, the discrete steps involved in the mode of action of AKH in triggering an anti-oxidative response is far from clear. Given the role of AKH as a neuroendocrine factor that mediates a response to oxidative stress, the mode of action of AKH at the sub-cellular level was investigated. Using isolated central nervous system (brain) as an in vitro model, we establish that AKH can potentiate an anti-oxidative response to oxidative stress. Further, we also demonstrate that AKH uses a conserved signal transduction mechanism involving both protein kinase C (PKC) and cyclic adenosine monophosphate (cAMP) and by mobilizing both intra as well as extra-cellular Ca2+ stores to elaborate its anti-oxidative response. Finally, using the genetically tractable fruit fly Drosophila melanogaster, we demonstrate through RNAi mediated knockdown of AKH synthesis as well as overexpression of AKH using the GAL4/UAS system, that the fork-head box transcription factor (dFoXO) might function downstream of AKH signaling in its stress responsive role. These results implicate AKH as a stress hormone while offering possibilities to further identify specific regulatory mechanisms and downstream effector molecules. Since stress signaling pathways are conserved, insights obtained from such studies on insects will offer some unique avenues for understanding stress responses and related pathologies in vertebrates including humans

Development of cercariae (Trematoda) in the first intermediate host: current knowledge and perspectives

Annotation: The aim of this work is to present an overview of trematode life-cycles with emphasis on life-strategies that trematodes use for dispersion in the environment and for transmission to the next host. Life-cycles of trematodes are controlled by numerous abiotic and biotic factors, with temperature undoubtedly playing the key role in controlling transmission of developmental stages, including cercarial production in snail intermediate hosts

Lost in Translation: Defects in Transfer RNA Modifications and Neurological Disorders

Transfer RNAs (tRNAs) are key molecules participating in protein synthesis. To augment their functionality they undergo extensive post-transcriptional modifications and, as such, are subject to regulation at multiple levels including transcription, transcript processing, localization and ribonucleoside base modification. Post-transcriptional enzyme-catalyzed modification of tRNA occurs at a number of base and sugar positions and influences specific anticodon–codon interactions and regulates translation, its efficiency and fidelity. This phenomenon of nucleoside modification is most remarkable and results in a rich structural diversity of tRNA of which over 100 modified nucleosides have been characterized. Most often these hypermodified nucleosides are found in the wobble position of tRNAs, where they play a direct role in codon recognition as well as in maintaining translational efficiency and fidelity, etc. Several recent studies have pointed to a link between defects in tRNA modifications and human diseases including neurological disorders. Therefore, defects in tRNA modifications in humans need intensive characterization at the enzymatic and mechanistic level in order to pave the way to understand how lack of such modifications are associated with neurological disorders with the ultimate goal of gaining insights into therapeutic interventions

Hormonal Regulation of Response to Oxidative Stress in Insects—An Update

Insects, like other organisms, must deal with a wide variety of potentially challenging environmental factors during the course of their life. An important example of such a challenge is the phenomenon of oxidative stress. This review summarizes the current knowledge on the role of adipokinetic hormones (AKH) as principal stress responsive hormones in insects involved in activation of anti-oxidative stress response pathways. Emphasis is placed on an analysis of oxidative stress experimentally induced by various stressors and monitored by suitable biomarkers, and on detailed characterization of AKH’s role in the anti-stress reactions. These reactions are characterized by a significant increase of AKH levels in the insect body, and by effective reversal of the markers—disturbed by the stressors—after co-application of the stressor with AKH. A plausible mechanism of AKH action in the anti-oxidative stress response is discussed as well: this probably involves simultaneous employment of both protein kinase C and cyclic adenosine 3′,5′-monophosphate pathways in the presence of extra and intra-cellular Ca2+ stores, with the possible involvement of the FoxO transcription factors. The role of other insect hormones in the anti-oxidative defense reactions is also discussed