Hydrogen peroxide stimulates activity and alters behavior in Drosophila melanogaster

Understanding photoluminescent carbon nanodots interaction with Human Corneal Epithelial cells and Drosophila melanogaster model

The employment of photoluminescent carbon nanodots (PL-CNDs) in biomedical applications is a new trend of research, specifically in delivering and tracking the drug of interest at the target site. On the other hand, the determination of in vitro and in vivo biocompatibility of the highly utilized nanomaterial is of utmost priority. In the present work, we described the synthesis, optical and surface morphological characterization, and determination of toxicity of PL-CNDs derived from egg white on the in vitro Human Corneal Epithelial (HCE) cells, and in vivo Drosophila melanogaster (D. melanogaster) model. The in-house developed PL-CNDs were blue photoluminescent under excitation at 365 nm and showed an emission peak at 420 nm. Further, HR-TEM analysis suggests the spherical shape of PL-CNDs with a lattice space of 0.26 nm, having a size of 2 nm determined from particle size analysis. The Tauc plot analysis calculated from absorption spectra suggests a band gap of ∼1.8 eV and ∼4.9 eV. The biocompatibility assay (20-250 μg/mL), cell apoptosis (20, 60, 100 μg/mL), and cell morphological (20, 60, 100 μg/mL) studies on HCE cells highlight the cytocompatibility of the PL-CNDs at various concentrations. The toxicity of PL-CNDs was evaluated using an in vivo genetic animal model, D. melanogaster. The oral treatment of 20-250 μg/mL concentrations of PL-CNDs did not induce any significant mortality and climbing defect in flies. In addition, dietary supplementation with PL-CNDs elicits a dose-dependent enhancement of antioxidant defense mechanisms confirmed by SOD and CAT, and the elevation of total antioxidant capacity. The measurement of Reactive Oxygen Species (ROS) in the brain and the gastrointestinal (GI) tract region suggests the non-toxic properties of PL-CNDs (50-100 μg/mL). In summary, PL-CNDs are non-toxic and have good bioavailability, they can be used for delivering drugs in conjugations due to their nano size.

Ameliorative Effects of Pearl Millet (Pennisetum glaucum L.) Against Hydrogen Peroxide Induced Cognitive Impairment and Oxidative Stress in Rats

Pearl millet (PM) (Pennisetum glaucum L.) contains a wide variety of bioactive compounds, such as polyphenols, mostly flavonoids and phenolic acids. In the present study, we investigated the effects of PM activity against hydrogen peroxide (H2O2)-induced behavior impairment and oxidative damage in rats. The rats were divided into four groups based on the treatments they received over 30 days: Control, H2O2, PM + H2O2, and PM. The phytochemical screening, total polyphenols content (TFC), and total flavonoid content (TFC) were determined using colorimetric analysis. All animals were subjected to behavioral test (elevated plus maze test). Thereafter, oxidative stress response (malondialdehyde [MDA], H2O2, and Thiol groups [-SH]) contents and antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) were estimated in brain, liver, and kidney tissues. We evaluated the levels of liver enzymes, such as alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT). Our investigation showed that PM is rich in total phenolic content and TFC and exhibited an important in vitro antioxidant activity. In vivo, we first found that H2O2-treated rat exhibited anxiogenic behavior in the elevated plus maze test and the genesis of oxidative stress in the brain, liver, and kidney was measured by an increase of MDA and antioxidant enzyme activity depletion, such as SOD and CAT. Moreover, H2O2 increased levels of liver enzymes (ALAT and ASAT). Pearl Mille administration improved emotional behavior impairments and significantly reversed H2O2-induced biochemical alterations. Thus, we suggest that the Pearl Mille may have an anxiolytic-like effect and prevent biochemical disorders associated from the oxidative stress (H2O2), confirming its potential therapeutic capability.

tRNA modification enzyme-dependent redox homeostasis regulates synapse formation and memory

Post-transcriptional modification of RNA regulates gene expression at multiple levels. ALKBH8 is a tRNA-modifying enzyme that methylates wobble uridines in a subset of tRNAs to modulate translation. Through methylation of tRNA-selenocysteine, ALKBH8 promotes selenoprotein synthesis and regulates redox homeostasis. Pathogenic variants in ALKBH8 have been linked to intellectual disability disorders in the human population, but the role of ALKBH8 in the nervous system is unknown. Through in vivo studies in Drosophila, we show that ALKBH8 controls oxidative stress in the brain to restrain synaptic growth and support learning and memory. ALKBH8 null animals lack wobble uridine methylation and exhibit reduced protein synthesis in the nervous system, including a specific decrease in selenoprotein levels. Either loss of ALKBH8 or independent disruption of selenoprotein synthesis results in ectopic synapse formation. Genetic expression of antioxidant enzymes fully suppresses synaptic overgrowth in ALKBH8 null animals, confirming oxidative stress as the underlying cause of dysregulation. ALKBH8 null animals also exhibit associative memory impairments that are reversed by pharmacological antioxidant treatment. Together, these findings demonstrate the critical role of tRNA wobble uridine modification in redox homeostasis in the developing nervous system and reveal antioxidants as a potential therapy for ALKBH8-associated intellectual disability.

Neurotoxicity of hexaconazole on rat brain: The aspect of biological rhythm

Hexaconazole is a widely used and frequently detected fungicide which is also reported to be persistent in environment. The toxicity of Hex to non-organisms such as reproductive toxicity, endocrine disrupting toxicity, and carcinogenic toxicity had been reported. However, study on the Hex-induced neurotoxicity is rare and the mechanism is still unclear. Therefore, in this study, environmental related concentrations of Hex were chosen to investigate the effects of Hex on nervous system from the aspect of biological rhythm under 90 d sub-chronic exposure. The results showed that Hex significantly affected the cognitive function of rats resulting in the deterioration of learning and memory ability and induced oxidative stress in rat brain. Moreover, the notable changes of neurotransmitters in rat brain suggested the disorder of nerve signaling conduction induced by Hex. The influence of Hex on biological rhythm was further detected which showed that levels of rhythm regulatory genes and proteins significantly disturbed at four monitored time periods. Based on these results, it was supposed that the underlying mechanism of Hex-induced cognitive dysfunction might through oxidative stress pathway. Our findings could systematically and comprehensively clarify the effects of Hex on nervous system and were helpful for prevention neurological diseases induced by triazole pesticides.

Correlated changes in stress resistance and biochemical parameters in response to long-term protein restriction in Drosophila melanogaster

Studies in fruit flies, Drosophila melanogaster, have observed considerable variation in the effect of dietary protein restriction (PR) on various fitness traits. In addition, not only are there inconsistent results relating lifespan to stress resistance, but also the long-term effects of PR are unexplored. We study PR implementation across generations (long term) hypothesizing that it will be beneficial for fitness traits, stress resistance and storage reserves due to nutritional plasticity transferred by parents to offspring in earlier Drosophila studies. By imposing two concentrations of PR diets (50% and 70% of control protein) from the pre-adult and adult (age 1 day) stages of the flies, we assessed the stage-specific and long-term effect of the imposed PR. All long-term PR flies showed increased resistance against the tested stressors (starvation, desiccation, H2O2-induced oxidative stress). In addition, we also found long-term PR-induced increased stress resistance across generations. The PR flies also possessed higher protein and triglyceride (TG) content, reduced glucose and unaffected glycogen levels. We also assayed the effect of returning the PR flies to control (AL) food for a single generation and assessed their biochemical parameters to witness the transient PR effect. It was seen that TG content upon reversal was similar to AL flies except for PRI70 males; however, the glucose levels of PR males increased, while they were consistently lower in females. Taken altogether, our study suggests that long-term PR implementation contributes to increased stress resistance and was found to influence storage reserves in D. melanogaster.

tRNA modification enzyme-dependent redox homeostasis regulates synapse formation and memory

Post-transcriptional modification of RNA regulates gene expression at multiple levels. ALKBH8 is a tRNA modifying enzyme that methylates wobble uridines in specific tRNAs to modulate translation. Through methylation of tRNA-selenocysteine, ALKBH8 promotes selenoprotein synthesis and regulates redox homeostasis. Pathogenic variants in ALKBH8 have been linked to intellectual disability disorders in the human population, but the role of ALKBH8 in the nervous system is unknown. Through in vivo studies in Drosophila, we show that ALKBH8 controls oxidative stress in the brain to restrain synaptic growth and support learning and memory. ALKBH8 null animals lack wobble uridine methylation and exhibit a global reduction in protein synthesis, including a specific decrease in selenoprotein levels. Loss of ALKBH8 or independent disruption of selenoprotein synthesis results in ectopic synapse formation. Genetic expression of antioxidant enzymes fully suppresses synaptic overgrowth in ALKBH8 null animals, confirming oxidative stress as the underlying cause of dysregulation. ALKBH8 animals also exhibit associative learning and memory impairments that are reversed by pharmacological antioxidant treatment. Together, these findings demonstrate the critical role of tRNA modification in redox homeostasis in the nervous system and reveal antioxidants as a potential therapy for ALKBH8-associated intellectual disability.

Neuroprotective effects of magnesium against stress induced by hydrogen peroxide in Wistar rat

INTRODUCTION

Oxidative stress has been implicated in the pathogenesis of diverse disease states. The present study was designed to examine the effects of magnesium sulphate (MgSO4) against hydrogen peroxide (H2O2) induced behaviour impairment and oxidative damage in rats.

MATERIAL AND METHODS

Eighteen rats were equally divided into three groups. The first group was kept as a control. In the second group, H2O2 was given in drinking water at 3% during 5 days. In the third group, rats were subjected to daily administration of H2O2 and MgSO4 (100 mg/kg; b.w) for 5 days. Animals were subjected to behavioural tests (elevated plus maze and open field). At the end of experiment, brains were extracted for oxidative stress biomarkers assessment including levels of malondialdéhyde and hydrogen peroxide and activities of superoxide dismutase and catalase.

RESULTS

Our findings showed that H2O2 treated rat exhibited anxiogenic behaviour and the genesis of free radicals in the brain. Magnesium showed amelioration against oxidative stress and significant decrease in anxiety levels.

DISCUSSION AND CONCLUSION

Stress is a powerful process that disrupts brain homeostasis by inducing oxidative stress and its appear that magnesium may have potential therapeutic benefits by reducing oxidative stress and inducing anxiolytic effect.

Tracking the flight and landing behaviour of western flower thrips in response to single and two-colour cues

Real-time 3D tracking and high-speed videography was used to examine the behaviour of a worldwide greenhouse pest, the western flower thrips (WFT), in response to different colours in the context of improving trap design. Measurements were taken of the number of landings on, and flight activity near, a lamp containing two LEDs of either the same colour or a combination of two colours presented side by side. Main findings show that landing patterns of WFT are different between colours, with landings on UV(+ red) as highly attractive stimulus being mostly distributed at the bottom half of the lamp, while for yellow also as very attractive and green as a 'neutral' stimulus, landings were clearly on the upper rim of the lamp. Additionally, a positive interaction with the UV-A(+ red) and yellow combination elicited the highest number of landings and flight time in front of the LED lamp. Conversely, a negative interaction was observed with decreased landings and flight time found for yellow when blue was present as the adjacent colour. Overall, differences between treatments were less obvious for flight times compared to number of landings, with tracking data suggesting that WFT might use different colours to orientate at different distances as they approach a visual stimulus.

Activation of the Cap'n'collar C pathway (Nrf2 pathway in vertebrates) signaling in insulin pathway compromised Drosophila melanogaster flies ameliorates the diabetic state upon pro-oxidant conditions

The insulin pathway is a crucial central system for metabolism and growth. The Nrf2 signaling pathway functions to counteract oxidative stress. Here we sought to study the consequences of an oxidative stress challenge to insulin compromised and control adult flies of different ages, varying the activation state of the Nrf2 pathway in flies, the Cap'n'collar C pathway. For this, we employed two different pro-oxidative conditions: 3 % hydrogen peroxide or 20 mM paraquat laced in the food. In both cases, wild type (control) flies die within a few days, yet there are significant differences between males and females, and also within flies of different ages (seven versus thirty days old flies). We repeated the same conditions with young (seven days old) flies that were heterozygous for a loss-of-function mutation in Keap1. There were no significant differences. We then tested two hypomorphic viable conditions of the insulin pathway (heteroallelic combination for the insulin receptor and the S6 Kinase), challenged in the same way: Whereas they also die in the pro-oxidant conditions, they fare significantly better when heterozygous for Keap1, in contrast to controls. We also monitored locomotion in all of these conditions, and, in general, found significant differences between flies without and with a mutant allele (heterozygous) for Keap1. Our results point to altered oxidative stress conditions in diabetic flies. These findings suggest that modest activation of the Cap'n'collar C pathway may be a treatment for diabetic symptoms.

Influence of Redox and Dopamine Regulation in Cocaine-Induced Phenotypes Using Drosophila

Reactive Oxidative Species (ROS) are produced during cellular metabolism and their amount is finely regulated because of negative consequences that ROS accumulation has on cellular functioning and survival. However, ROS play an important role in maintaining a healthy brain by participating in cellular signaling and regulating neuronal plasticity, which led to a shift in our understanding of ROS from being solely detrimental to having a more complex role in the brain. Here we use Drosophila melanogaster to investigate the influence of ROS on behavioral phenotypes induced by single or double exposure to volatilized cocaine (vCOC), sensitivity and locomotor sensitization (LS). Sensitivity and LS depend on glutathione antioxidant defense. Catalase activity and hydrogen peroxide (H₂O₂) accumulation play a minor role, but their presence is necessary in dopaminergic and serotonergic neurons for LS. Feeding flies the antioxidant quercetin completely abolishes LS confirming the permissive role of H₂O₂ in the development of LS. This can only partially be rescued by co-feeding H₂O₂ or the dopamine precursor 3,4-dihydroxy-L-phenylalanine (L-DA) showing coordinate and similar contribution of dopamine and H₂O₂. Genetic versatility of Drosophila can be used as a tool for more precise dissection of temporal, spatial and transcriptional events that regulate behaviors induced by vCOC.

Multi-Modal Regulation of Circadian Physiology by Interactive Features of Biological Clocks

The circadian clock is a fundamental biological timing mechanism that generates nearly 24 h rhythms of physiology and behaviors, including sleep/wake cycles, hormone secretion, and metabolism. Evolutionarily, the endogenous clock is thought to confer living organisms, including humans, with survival benefits by adapting internal rhythms to the day and night cycles of the local environment. Mirroring the evolutionary fitness bestowed by the circadian clock, daily mismatches between the internal body clock and environmental cycles, such as irregular work (e.g., night shift work) and life schedules (e.g., jet lag, mistimed eating), have been recognized to increase the risk of cardiac, metabolic, and neurological diseases. Moreover, increasing numbers of studies with cellular and animal models have detected the presence of functional circadian oscillators at multiple levels, ranging from individual neurons and fibroblasts to brain and peripheral organs. These oscillators are tightly coupled to timely modulate cellular and bodily responses to physiological and metabolic cues. In this review, we will discuss the roles of central and peripheral clocks in physiology and diseases, highlighting the dynamic regulatory interactions between circadian timing systems and multiple metabolic factors.

The Drosophila ERG channel seizure plays a role in the neuronal homeostatic stress response

Neuronal physiology is particularly sensitive to acute stressors that affect excitability, many of which can trigger seizures and epilepsies. Although intrinsic neuronal homeostasis plays an important role in maintaining overall nervous system robustness and its resistance to stressors, the specific genetic and molecular mechanisms that underlie these processes are not well understood. Here we used a reverse genetic approach in Drosophila to test the hypothesis that specific voltage-gated ion channels contribute to neuronal homeostasis, robustness, and stress resistance. We found that the activity of the voltage-gated potassium channel seizure (sei), an ortholog of the mammalian ERG channel family, is essential for protecting flies from acute heat-induced seizures. Although sei is broadly expressed in the nervous system, our data indicate that its impact on the organismal robustness to acute environmental stress is primarily mediated via its action in excitatory neurons, the octopaminergic system, as well as neuropile ensheathing and perineurial glia. Furthermore, our studies suggest that human mutations in the human ERG channel (hERG), which have been primarily implicated in the cardiac Long QT Syndrome (LQTS), may also contribute to the high incidence of seizures in LQTS patients via a cardiovascular-independent neurogenic pathway.

Carbohydrate Metabolic Compensation Coupled to High Tolerance to Oxidative Stress in Ticks

Reactive oxygen species (ROS) are natural byproducts of metabolism that have toxic effects well documented in mammals. In hematophagous arthropods, however, these processes are not largely understood. Here, we describe that Rhipicephalus microplus ticks and embryonic cell line (BME26) employ an adaptive metabolic compensation mechanism that confers tolerance to hydrogen peroxide (H2O2) at concentrations too high for others organisms. Tick survival and reproduction are not affected by H2O2 exposure, while BME26 cells morphology was only mildly altered by the treatment. Furthermore, H2O2-tolerant BME26 cells maintained their proliferative capacity unchanged. We evaluated several genes involved in gluconeogenesis, glycolysis, and pentose phosphate pathway, major pathways for carbohydrate catabolism and anabolism, describing a metabolic mechanism that explains such tolerance. Genetic and catalytic control of the genes and enzymes associated with these pathways are modulated by glucose uptake and energy resource availability. Transient increase in ROS levels, oxygen consumption, and ROS-scavenger enzymes, as well as decreased mitochondrial superoxide levels, were indicative of cell adaptation to high H2O2 exposure, and suggested a tolerance strategy developed by BME26 cells to cope with oxidative stress. Moreover, NADPH levels increased upon H2O2 challenge, and this phenomenon was sustained mainly by G6PDH activity. Interestingly, G6PDH knockdown in BME26 cells did not impair H2O2 tolerance, but generated an increase in NADP-ICDH transcription. In agreement with the hypothesis of a compensatory NADPH production in these cells, NADP-ICDH knockdown increased G6PDH relative transcript level. The present study unveils the first metabolic evidence of an adaptive mechanism to cope with high H2O2 exposure and maintain redox balance in ticks.

Sleep and circadian defects in a Drosophila model of mitochondrial encephalomyopathy

Mitochondrial encephalomyopathies (ME) are complex, incurable diseases characterized by severe bioenergetic distress that can affect the function of all major organ systems but is especially taxing to neuromuscular tissues. Animal models of MEs are rare, but the Drosophila ATP6¹ mutant is a stable, well-characterized genetic line that accurately models progressive human mitochondrial diseases such as Maternally-Inherited Leigh Syndrome (MILS), Neuropathy, Ataxia, and Retinitis Pigmentosa (NARP), and Familial Bilateral Striatal Necrosis (FBSN). While it is established that this model exhibits important hallmarks of ME, including excess cellular and mitochondrial reactive oxygen species, shortened lifespan, muscle degeneration, and stress-induced seizures, it is unknown whether it exhibits defects in sleep or circadian function. This is a clinically relevant question, as many neurological and neurodegenerative diseases are characterized by such disturbances, which can exacerbate other symptoms and worsen quality of life. Since Drosophila is highly amenable to sleep and circadian studies, we asked whether we could detect disease phenotypes in the circadian behaviors of ATP6¹. Indeed, we found that day-time and night-time activity and sleep are altered through disease progression, and that circadian patterns are disrupted at both the behavioral and neuronal levels. These results establish ATP6¹ as an important model of sleep and circadian disruption in ME that can be studied mechanistically at the molecular, cellular, and behavioral level to uncover underlying pathophysiology and test novel therapies.

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A Drosophila model of mitochondrial disease (ATP6¹) displays altered sleep patterns.

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ATP6¹ sleep quantity and consolidation are reduced in advanced disease.

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ATP6¹ is behaviorally arrhythmic under conditions of constant darkness.

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Selected neurons of the circadian circuit display altered daily firing rates in ATP6¹.

Interplay of ROS and behavioral pattern in fluoride exposed Drosophila melanogaster

Reactive oxygen species (ROS) is known to be associated with the process of aging and other health hazards. Organisms are compelled to compromise with body homeostasis when exposed to toxic substances. In the present study sodium fluoride (NaF) exposure (10-100 μgmL^-1) to Drosophila melanogaster in the parental (P) generation leads to increase in adult mortality and alteration in male-female ratio in the P and F1 (1st Filial) generation. Post-treatment alterations in selected behavioral traits (crawling, embedding and climbing) were observed in larvae and adults. Altered behavioral pattern was found to be associated with reduced mitochondrial activity and decreased number of viable brain cells in treated individuals. Interestingly, higher cholinesterase activities in treated males in comparison to females demonstrate a definite sex bias in NaF-induced response. Hyper-activation of antioxidant enzyme like catalase and reduced superoxide dismutase (SOD) and glutathione-s-transferase (GST) activity indicate a shift in the oxidative status after fluoride exposure. Additionally, increase in lipid peroxidation suggests enhancement in ROS which is further validated through increment in protein carbonyl content. Hence, the observations of the present study propose behavioral alterations resulting from increased ROS after chronic exposure to sub-lethal concentrations of NaF in D. melanogaster.

A bidirectional relationship between sleep and oxidative stress in Drosophila

Although sleep appears to be broadly conserved in animals, the physiological functions of sleep remain unclear. In this study, we sought to identify a physiological defect common to a diverse group of short-sleeping Drosophila mutants, which might provide insight into the function and regulation of sleep. We found that these short-sleeping mutants share a common phenotype of sensitivity to acute oxidative stress, exhibiting shorter survival times than controls. We further showed that increasing sleep in wild-type flies using genetic or pharmacological approaches increases survival after oxidative challenge. Moreover, reducing oxidative stress in the neurons of wild-type flies by overexpression of antioxidant genes reduces the amount of sleep. Together, these results support the hypothesis that a key function of sleep is to defend against oxidative stress and also point to a reciprocal role for reactive oxygen species (ROS) in neurons in the regulation of sleep.

Cap-n-Collar Promotes Tissue Regeneration by Regulating ROS and JNK Signaling in the Drosophila melanogaster Wing Imaginal Disc

Regeneration is a complex process that requires an organism to recognize and repair tissue damage, as well as grow and pattern new tissue. Here, we describe a genetic screen to identify novel regulators of regeneration. We ablated the Drosophila melanogaster larval wing primordium by inducing apoptosis in a spatially and temporally controlled manner and allowed the tissue to regenerate and repattern. To identify genes that regulate regeneration, we carried out a dominant-modifier screen by assessing the amount and quality of regeneration in adult wings heterozygous for isogenic deficiencies. We have identified 31 regions on the right arm of the third chromosome that modify the regenerative response. Interestingly, we observed several distinct phenotypes: mutants that regenerated poorly, mutants that regenerated faster or better than wild-type, and mutants that regenerated imperfectly and had patterning defects. We mapped one deficiency region to cap-n-collar (cnc), the Drosophila Nrf2 ortholog, which is required for regeneration. Cnc regulates reactive oxygen species levels in the regenerating epithelium, and affects c-Jun N-terminal protein kinase (JNK) signaling, growth, debris localization, and pupariation timing. Here, we present the results of our screen and propose a model wherein Cnc regulates regeneration by maintaining an optimal level of reactive oxygen species to promote JNK signaling.

Circadian modulation of proteasome activity and accumulation of oxidized protein in human embryonic kidney HEK 293 cells and primary dermal fibroblasts

The circadian system orchestrates the timing of physiological processes of an organism living in daily environmental changes. Disruption of circadian rhythmicity has been shown to result in increased oxidative stress and accelerated aging. The circadian regulation of antioxidant defenses suggests that other redox homeostasis elements such as oxidized protein degradation by the proteasome, could also be modulated by the circadian clock. Hence, we have investigated whether proteasome activities and oxidized protein levels would exhibit circadian rhythmicity in synchronized cultured mammalian cells and addressed the mechanisms underlying this process. Using synchronized human embryonic kidney HEK 293 cells and primary dermal fibroblasts, we have shown that the levels of carbonylated protein and proteasome activity vary rhythmically following a 24h period. Such a modulation of proteasome activity is explained, at least in part, by the circadian expression of both Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and the proteasome activator PA28αβ. HEK 293 cells showed an increased susceptibility to oxidative stress coincident with the circadian-dependent lower activity of the proteasome. Finally, in contrast to young fibroblasts, no circadian modulation of the proteasome activity and carbonylated protein levels was evidenced in senescent fibroblasts. This paper reports a novel role of the circadian system for regulating proteasome function. In addition, the observation that proteasome activity is modulated by the circadian clock opens new avenues for both the cancer and the aging fields, as exemplified by the rhythmic resistance of immortalized cells to oxidative stress and loss of rhythmicity of proteasome activity in senescent fibroblasts.

Interplay between cellular redox oscillations and circadian clocks

The circadian clock is a cellular timekeeping mechanism that helps organisms from bacteria to humans to organize their behaviour and physiology around the solar cycle. Current models for circadian timekeeping incorporate transcriptional/translational feedback loop mechanisms in the predominant model systems. However, recent evidence suggests that non-transcriptional oscillations such as metabolic and redox cycles may play a fundamental role in circadian timekeeping. Peroxiredoxins, an antioxidant protein family, undergo rhythmic oxidation on the circadian time scale in a variety of species, including bacteria, insects and mammals, but also in red blood cells, a naturally occurring, non-transcriptional system. The profound interconnectivity between circadian and redox pathways strongly suggests that a conserved timekeeping mechanism based on redox cycles could be integral to generating circadian rhythms.

UVA-induced reset of hydroxyl radical ultradian rhythm improves temporal lipid production in Chlorella vulgaris

We report for the first time that the endogenous, pseudo-steady-state, specific intracellular levels of the hydroxyl radical (si-OH) oscillate in an ultradian fashion (model system: the microalga, Chlorella vulgaris), and also characterize the various rhythm parameters. The ultradian rhythm in the endogenous levels of the si-OH occurred with an approximately 6 h period in the daily cycle of light and darkness. Further, we expected that the rhythm reset to a shorter period could rapidly switch the cellular redox states that could favor lipid accumulation. We reset the endogenous rhythm through entrainment with UVA radiation, and generated two new ultradian rhythms with periods of approximately 2.97 h and 3.8 h in the light phase and dark phase, respectively. The reset increased the window of maximum lipid accumulation from 6 h to 12 h concomitant with the onset of the ultradian rhythms. Further, the saturated fatty acid content increased approximately to 80% of total lipid content, corresponding to the peak maxima of the hydroxyl radical levels in the reset rhythm.

Fluctuating vs. continuous exposure to H₂O₂: the effects on mitochondrial membrane potential, intracellular calcium, and NF-κB in astroglia

The effects of H2O2 are widely studied in cell cultures and other in vitro systems. However, such investigations are performed with the assumption that H2O2 concentration is constant, which may not properly reflect in vivo settings, particularly in redox-turbulent microenvironments such as mitochondria. Here we introduced and tested a novel concept of fluctuating oxidative stress. We treated C6 astroglial cells and primary astrocytes with H2O2, using three regimes of exposure - continuous, as well as fluctuating at low or high rate, and evaluated mitochondrial membrane potential and other parameters of mitochondrial activity - respiration, reducing capacity, and superoxide production, as well as intracellular ATP, intracellular calcium, and NF-κB activation. When compared to continuous exposure, fluctuating H2O2 induced a pronounced hyperpolarization in mitochondria, whereas the activity of electron transport chain appears not to be significantly affected. H2O2 provoked a decrease of ATP level and an increase of intracellular calcium concentration, independently of the regime of treatment. However, fluctuating H2O2 induced a specific pattern of large-amplitude fluctuations of calcium concentration. An impact on NF-κB activation was observed for high rate fluctuations, whereas continuous and low rate fluctuating oxidative stress did not provoke significant effects. Presented results outline the (patho)physiological relevance of redox fluctuations.

Reactive oxygen species can modulate circadian phase and period in Neurospora crassa

Reactive oxygen species (ROS) may serve as signals coupling metabolism to other cell functions. In addition to being by-products of normal metabolism, they are generated at elevated levels under environmental stress situations. We analyzed how reactive oxygen species affect the circadian clock in the model organism Neurospora crassa. In light/dark cycles, an increase in the levels of reactive oxygen species advanced the phase of both the conidiation rhythm and the expression of the clock gene frequency. Our results indicate a dominant role of the superoxide anion in the control of the phase. Elevation of superoxide production resulted in the activation of protein phosphatase 2A, a regulator of the positive element of the circadian clock. Our data indicate that even under nonstress conditions, reactive oxygen species affect circadian timekeeping. Reduction of their basal levels results in a delay of the phase in light/dark cycles and a longer period under constant conditions. We show that under entrained conditions the phase depends on the temperature and reactive oxygen species contribute to this effect. Our results suggest that the superoxide anion is an important factor controlling the circadian oscillator and is able to reset the clock most probably by activating protein phosphatase 2A, thereby modulating the activity of the White Collar complex.

Expression of zinc-deficient human superoxide dismutase in Drosophila neurons produces a locomotor defect linked to mitochondrial dysfunction

More than 130 different mutations in the Cu/Zn superoxide dismutase (SOD1) gene have been associated with amyotrophic lateral sclerosis but the mechanism of this toxicity remains controversial. To gain insight into the importance of the zinc site in the pathogenesis of SOD1 in vivo, we generated a Drosophila model with transgenic expression of a zinc-deficient human SOD1. Expression of zinc-deficient SOD1 in Drosophila resulted in a progressive movement defect with associated mitochondrial cristae vacuolization and reductions in adenosine triphosphate (ATP) levels. Furthermore, these flies are sensitized to mitochondrial toxins, paraquat, and zinc. Importantly, we show that the zinc-deficient SOD1-induced motor defect can be ameliorated by supplementing the endogenous fly respiratory chain machinery with the single-subunit NADH-ubiquinone oxidoreductase from yeast (NADH is nicotinamide adenine dinucleotide, reduced form.). These results demonstrate that zinc-deficient SOD1 is neurotoxic in vivo and suggest that mitochondrial dysfunction plays a critical role in this toxicity. The robust behavioral, pathological, and biochemical phenotypes conferred by zinc-deficient SOD1 in Drosophila have general implications for the role of the zinc ion in familial and sporadic amyotrophic lateral sclerosis.

Oxidative stress adaptation with acute, chronic, and repeated stress

Oxidative stress adaptation, or hormesis, is an important mechanism by which cells and organisms respond to, and cope with, environmental and physiological shifts in the level of oxidative stress. Most studies of oxidative stress adaption have been limited to adaptation induced by acute stress. In contrast, many if not most environmental and physiological stresses are either repeated or chronic. In this study we find that both cultured mammalian cells and the fruit fly Drosophila melanogaster are capable of adapting to chronic or repeated stress by upregulating protective systems, such as their proteasomal proteolytic capacity to remove oxidized proteins. Repeated stress adaptation resulted in significant extension of adaptive responses. Repeated stresses must occur at sufficiently long intervals, however (12-h or more for MEF cells and 7 days or more for flies), for adaptation to be successful, and the levels of both repeated and chronic stress must be lower than is optimal for adaptation to acute stress. Regrettably, regimens of adaptation to both repeated and chronic stress that were successful for short-term survival in Drosophila nevertheless also caused significant reductions in life span for the flies. Thus, although both repeated and chronic stress can be tolerated, they may result in a shorter life.

Early mitochondrial dysfunction leads to altered redox chemistry underlying pathogenesis of TPI deficiency

Triose phosphate isomerase (TPI) is responsible for the interconversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate in glycolysis. Point mutations in this gene are associated with a glycolytic enzymopathy called TPI deficiency. This study utilizes a Drosophila melanogaster model of TPI deficiency; TPI(sugarkill) is a mutant allele with a missense mutation (M80T) that causes phenotypes similar to human TPI deficiency. In this study, the redox status of TPI(sugarkill) flies was examined and manipulated to provide insight into the pathogenesis of this disease. Our data show that TPI(sugarkill) animals exhibit higher levels of the oxidized forms of NAD(+), NADP(+) and glutathione in an age-dependent manner. Additionally, we demonstrate that mitochondrial redox state is significantly more oxidized in TPI(sugarkill) animals. We hypothesized that TPI(sugarkill) animals may be more sensitive to oxidative stress and that this may underlie the progressive nature of disease pathogenesis. The effect of oxidizing and reducing stressors on behavioral phenotypes of the TPI(sugarkill) animals was tested. As predicted, oxidative stress worsened these phenotypes. Importantly, we discovered that reducing stress improved the behavioral and longevity phenotypes of the mutant organism without having an effect on TPI(sugarkill) protein levels. Overall, these data suggest that reduced activity of TPI leads to an oxidized redox state in these mutants and that the alleviation of this stress using reducing compounds can improve the mutant phenotypes.

A conserved role for the 20S proteasome and Nrf2 transcription factor in oxidative stress adaptation in mammals, Caenorhabditis elegans and Drosophila melanogaster

In mammalian cells, hydrogen peroxide (H(2)O(2))-induced adaptation to oxidative stress is strongly dependent on an Nrf2 transcription factor-mediated increase in the 20S proteasome. Here, we report that both Caenorhabditis elegans nematode worms and Drosophila melanogaster fruit flies are also capable of adapting to oxidative stress with H(2)O(2) pre-treatment. As in mammalian cells, this adaptive response in worms and flies involves an increase in proteolytic activity and increased expression of the 20S proteasome, but not of the 26S proteasome. We also found that the increase in 20S proteasome expression in both worms and flies, as in mammalian cells, is important for the adaptive response, and that it is mediated by the SKN-1 and CNC-C orthologs of the mammalian Nrf2 transcription factor, respectively. These studies demonstrate that stress mechanisms operative in cell culture also apply in disparate intact organisms across a wide biological diversity.

Using GFP video to track 3D movement and conditional gene expression in free-moving flies

BACKGROUND

In vivo imaging and quantification of fluorescent reporter molecules is increasingly useful in biomedical research. For example, tracking animal movement in 3D with simultaneous quantification of fluorescent transgenic reporters allows for correlations between behavior, aging and gene expression. However implementation has been hindered in the past by the complexity of operating the systems.

RESULTS

We report significant technical improvements and user-friendly software (called FluoreScore) that enables tracking of 3D movement and the dynamics of gene expression in adult Drosophila, using two cameras and recorded GFP videos. Expression of a transgenic construct encoding eGFP was induced in free-moving adult flies using the Gene-Switch system and RU486 drug feeding. The time course of induction of eGFP expression was readily quantified from internal tissues including central nervous tissue.

CONCLUSIONS

FluoreScore should facilitate a variety of future studies involving quantification of movement behaviors and fluorescent molecules in free-moving animals.

Lifespan extension by preserving proliferative homeostasis in Drosophila

Regenerative processes are critical to maintain tissue homeostasis in high-turnover tissues. At the same time, proliferation of stem and progenitor cells has to be carefully controlled to prevent hyper-proliferative diseases. Mechanisms that ensure this balance, thus promoting proliferative homeostasis, are expected to be critical for longevity in metazoans. The intestinal epithelium of Drosophila provides an accessible model in which to test this prediction. In aging flies, the intestinal epithelium degenerates due to over-proliferation of intestinal stem cells (ISCs) and mis-differentiation of ISC daughter cells, resulting in intestinal dysplasia. Here we show that conditions that impair tissue renewal lead to lifespan shortening, whereas genetic manipulations that improve proliferative homeostasis extend lifespan. These include reduced Insulin/IGF or Jun-N-terminal Kinase (JNK) signaling activities, as well as over-expression of stress-protective genes in somatic stem cell lineages. Interestingly, proliferative activity in aging intestinal epithelia correlates with longevity over a range of genotypes, with maximal lifespan when intestinal proliferation is reduced but not completely inhibited. Our results highlight the importance of the balance between regenerative processes and strategies to prevent hyperproliferative disorders and demonstrate that promoting proliferative homeostasis in aging metazoans is a viable strategy to extend lifespan.

O fly, where art thou?

In this paper, the design of a real-time image acquisition system for tracking the movement of Drosophila in three-dimensional space is presented. The system uses three calibrated and synchronized cameras to detect multiple flies and integrates the detected fly silhouettes to construct the three-dimensional visual hull models of each fly. We used an extended Kalman filter to estimate the state of each fly, given past positions from the reconstructed fly visual hulls. The results show that our approach constructs the three-dimensional visual hull of each fly from the detected image silhouettes and robustly tracks them at real-time rates. The system is suitable for a more detailed analysis of fly behaviour.