Antimicrobial peptides increase tolerance to oxidant stress in Drosophila melanogaster

Investigating Sulforaphane's anti-virulence and anti-quorum sensing properties against Pseudomonas aeruginosa

Background

P. aeruginosa, a significant bacterium, can cause severe illness and resistance to antibiotics. Quorum sensing (QS) systems regulate virulence factors production. Targeting QS could reduce bacteria pathogenicity and prevent antibiotic resistance. Cruciferous vegetables contain sulforaphane, known for its anti-inflammatory, antioxidant, anticancer, and antimicrobial properties.

Aim

We aimed to examine the inhibitory influences of sulforaphane, at a sub-inhibitory concentration (¼ minimum inhibitory concentration, MIC), on virulence and QS in P. aeruginosa.

Materials and methods

The sulforaphane's anti-virulence actions at sub-inhibitory concentrations were explored in vitro and in vivo. A sub-MIC concentration of sulforaphane was combined with anti-pseudomonal drugs, and the results of this combination were assessed. The virtual affinity of sulforaphane for the receptors of QS was studied, and its effect on the expression of QS genes was quantified.

Results

Sulforaphane significantly decreased the biofilm formation, motility, ability to withstand oxidative stress, and the synthesis of virulence extracellular enzymes such as proteases, hemolysins, and elastase, as well as other virulence factors like pyocyanin. In addition, sulforaphane lessened the severity of P. aeruginosa infection in mice. Sulforaphane reduced the antipseudomonal antibiotics' MICs when used together, resulting in synergistic effects. The observed anti-virulence impacts were attributed to the ability of sulforaphane to inhibit QS via suppressing the QS genes' expression.

Conclusion

Sulforaphane shows promise as a potent anti-virulence and anti-QS agent that can be used alongside conventional antimicrobials to manage severe infections effectively. Furthermore, this study paves the way for further investigation of sulforaphane and similar structures as pharmacophores for anti-QS candidates.

Evaluating the Impact of Vitamin D3 on NF-κB and JAK/STAT Signaling Pathways in Drosophila melanogaster

This study delved into the consequences of prolonged administration of vitamin D3 on innate immune systems, particularly NF-κB and JAK/STAT, in Drosophila melanogaster. The outcomes indicated that vitamin D3 treatment exhibited a notable capacity to improve the survival of adult flies with compromised immune functions, a condition induced by the loss of PGRP-LB, particularly when the flies were exposed to heat-killed Escherichia coli. The PGRP-LBΔ mutant line that was treated with heat-killed E. coli experienced reduced survival. Treatment of heat-killed E. coli-treated PGRP-LBΔ with vitamin D3 resulted in improved survival, and this phenotypic feature might be due to the downregulation of gene expression in the NF-κB and JAK/STAT pathways. However, a higher concentration of vitamin D3 was associated with decreased survival, potentially linked to intricate immunological responses. The research also underscored the influence of vitamin D3 on the expression of antioxidant genes, sod1 and sod2, indicating an augmented resistance to oxidative stress. Further, this study revealed the effect of vitamin D3 on the reproductive status of the autoinflammatory model, showing an increase in pupae and adult flies with a treatment of 10 mM vitamin D3, suggesting the potential benefits of vitamin D3 on the reproductive profile. Overall, this study provides preliminary insights into the complex interactions between vitamin D3, immune pathways, oxidative responses in the cell, and reproduction in Drosophila.

Cecropin A Alleviates LPS-Induced Oxidative Stress and Apoptosis of Bovine Endometrial Epithelial Cells

Dairy cows receiving a prolonged high-concentrate diet express an elevated concentration of lipopolysaccharides (LPSs) in the peripheral blood circulation, accompanied by a series of systemic inflammatory responses; however, the specific impacts of inflammation are yet to be determined. Cecropin-like antimicrobial peptides have become a research hotspot regarding antimicrobial peptides because of their excellent anti-inflammatory activities, and cecropin A is a major member of the cecropin family. To elucidate the mechanism of cecropin A as anti-inflammatory under the condition of sub-acute ruminal acidosis (SARA) in dairy cows, we induced inflammation in bEECs with LPS (10 µg/mL) and then added cecropin A (25 µM). Afterwards, we detected three categories of indexes including oxidative stress indices, inflammation-related genes, and apoptosis-related genes in bovine endometrial epithelial cells (bEECs). The results indicated that cecropin A has the ability to reduce inflammatory factors TNF-α, IL-1β, and IL-8 and inhibit the MAPK pathway to alleviate inflammation. In addition, cecropin A is able to reduce reactive oxygen species (ROS) levels and alleviates LPS-induced oxidative stress and mitochondrial dysfunction by downregulating NADPH Oxidase (NOX), and upregulating catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD). Furthermore, cecropin A demonstrates the ability to inhibit apoptosis by suppressing the mitochondrial-dependent apoptotic pathway, specifically Fas/FasL-caspase-8/-3. The observed increase in the Bcl-2/Bax ratio, a known apoptosis regulator, further supports this finding. In conclusion, our study presents novel solutions for addressing inflammatory responses associated with SARA.

Cold-induced immune activation in chill-susceptible insects

Chilling injuries in chill-susceptible insects, like the model dipteran Drosophila melanogaster, have been well-documented as a consequence of stressful low temperature exposures. Cold stress also causes upregulation of genes in the insect immune pathways, some of which are also upregulated following other forms of sterile stress. The adaptive significance and underlying mechanisms surrounding cold-induced immune activation, however, are still unclear. Here, we review recent work on the roles of ROS, DAMPs, and AMPs in insect immune signalling or function. Using this emerging knowledge, we propose a conceptual model linking biochemical and molecular causes of immune activation to its consequences during and following cold stress.

Long-term sevoflurane exposure resulted in temporary rather than lasting cognitive impairment in Drosophila

Sevoflurane is the primary inhaled anesthetic used in pediatric surgery. It has been the focus of research since animal models studies found that it was neurotoxic to the developing brain two decades ago. However, whether pediatric general anesthesia can lead to permanent cognitive deficits remained a subject of heated debate. Therefore, our study aims to determine the lifetime neurotoxicity of early long-time sevoflurane exposure using a short-life-cycle animal model, Drosophila melanogaster. To investigate this question, we measured the lifetime changes of two-day-old flies' learning and memory abilities after anesthesia with 3 % sevoflurane for 6 h by the T-maze memory assay. We evaluated the apoptosis, levels of ATP and ROS, and related genes in the fly head. Our results suggest that 6 h 3 % sevoflurane exposure at a young age can only induce transient neuroapoptosis and cognitive deficits around the first week after anesthesia. But this brain damage recedes with time and vanishes in late life. We also found that the mRNA level of caspases and Bcl-2, ROS level, and ATP level increased during this temporary neuroapoptosis process. And mRNA levels of antioxidants, such as SOD2 and CAT, increased and decreased simultaneously with the rise and fall of the ROS level, indicating a possible contribution to the recovery from the sevoflurane impairment. In conclusion, our results suggest that one early prolonged sevoflurane-based general anesthesia can induce neuroapoptosis and learning and memory deficit transiently but not permanently in Drosophila.

Antimicrobial peptide cathelicidin LL-37 preserves intestinal barrier and organ function in rats with heat stroke

Global warming increases the incidence of heat stroke (HS) and HS causes the reduction of visceral blood flow during hyperthermia, leading to intestinal barrier disruption, microbial translocation, systemic inflammation and multiple organ failure. Cathelicidin LL-37 exhibits antimicrobial activities, helps innate immunity within the gut to maintain intestinal homeostasis, and augments intestinal wound healing and barrier function. Thus, we evaluated the effects and possible mechanisms of cathelicidin LL-37 on HS. Wistar rats were placed in a heating-chamber of 42 ̊C to induce HS. Changes in rectal temperature, hemodynamic parameters, and survival rate were measured during the experimental period. Blood samples and ilea were collected to analyze the effects of LL-37 on systemic inflammation, multiple organ dysfunction, and intestinal injury. Furthermore, LS174T and HT-29 cells were used to assess the underlying mechanisms. Our data showed cathelicidin LL-37 ameliorated the damage of intestinal cells induced by HS. Intestinal injury, systemic inflammation, and nitrosative stress (high nitric oxide level) caused by continuous hyperthermia were attenuated in HS rats treated with cathelicidin LL-37, and hence, improved multiple organ dysfunction, coagulopathy, and survival rate. These beneficial effects of cathelicidin LL-37 were attributed to the protection of intestinal goblet cells (by increasing transepithelial resistance, mucin-2 and Nrf2 expression) and the improvement of intestinal barrier function (less cyclooxygenase-2 expression and FITC-dextran translocation). Interestingly, high cathelicidin expression in the ileal samples of inflammatory bowel disease patients was associated with better clinical outcome. These results suggest that cathelicidin LL-37 could prevent heat stress-induced intestinal damage and heat-related illnesses.

Unraveling the Role of Antimicrobial Peptides in Insects

Antimicrobial peptides (AMPs) are short, mainly positively charged, amphipathic molecules. AMPs are important effectors of the immune response in insects with a broad spectrum of antibacterial, antifungal, and antiparasitic activity. In addition to these well-known roles, AMPs exhibit many other, often unobvious, functions in the host. They support insects in the elimination of viral infections. AMPs participate in the regulation of brain-controlled processes, e.g., sleep and non-associative learning. By influencing neuronal health, communication, and activity, they can affect the functioning of the insect nervous system. Expansion of the AMP repertoire and loss of their specificity is connected with the aging process and lifespan of insects. Moreover, AMPs take part in maintaining gut homeostasis, regulating the number of endosymbionts as well as reducing the number of foreign microbiota. In turn, the presence of AMPs in insect venom prevents the spread of infection in social insects, where the prey may be a source of pathogens.

Adult exposure of atrazine alone or in combination with carbohydrate diet hastens the onset/progression of type 2 diabetes in Drosophila

AIM

The combined impact of traditional and non-traditional risk factors of type 2 diabetes (T2D) on the development and progression of insulin resistance and associated complications is poorly understood. Therefore, we assessed the effect of moderately rich sugar diet coupled with environmental chemical exposure on the development and progression of T2D using Drosophila as a model organism.

MAIN METHODS

We reared newly eclosed Drosophila males on a diet containing atrazine (20 μg/ml; non-traditional risk factor) and/or moderately high sucrose (0.5 M/1 M; to mimic binge eating, Traditional risk factor) for 20-30 days. Subsequently, we assessed diabetic parameters, oxidative stress parameters and also the abundance of advanced glycation end products (AGEs) along with their receptor (RAGE) in these flies. For diabetic cardiomyopathy, we examined the pericardin (tissue fibrosis marker) level in Drosophila heart.

KEY FINDINGS

Flies reared on 20 μg/ml atrazine alone showed T2D hallmarks at 30 days. In contrast, flies reared on 0.5 M sucrose+ 20 μg/ml atrazine showed insulin resistance characterized by hyperglycemia and increased Drosophila insulin-like peptides along with reduced insulin signaling at 20 days, similar to those reared on high sucrose diet. In addition, both groups had high levels of oxidative stress and showed starvation response (converting triglycerides into fatty acids). Alarmingly, flies fed with sucrose+atrazine for 20 and 30 days had elevated pericardin in heart tissues, indicating early onset of diabetic complications such as cardiomyopathy.

SIGNIFICANCE

Lifestyle-chemical exposure synergistically impairs glucose metabolism, affects organisms' redox state and leads to the early onset of T2D and associated complications like cardiomyopathy.

Heightened immune surveillance in Drosophila melanogaster populations selected for faster development and extended longevity

Maximization of life-history traits is under constraints due to both, limitations of resource acquisition and the restricted pathways of resource allocation. Drosophila melanogaster has served as an excellent model organism to not only unravel various trade-offs among life history traits but also numerous aspects of host immune response. Drosophila larvae are semi-aquatic that live, feed and excrete inside the food source-often over-ripe fruits and vegetables that are rich in both commensal and pathogenic microbiota that can impact the larval survival. In this study, we have used six populations of D. melanogaster, three of which are selected for faster pre-adult development and extended adult longevity, and their three ancestral controls, to explore the impact of selection on the basal immune activity in the larval stage. The larvae from selected populations had nearly significantly upregulated plasmatocyte density, significantly higher percent phagocytosis, phagocytic index and higher transcript levels of Tep3, eater and NimC1. Selected populations also had significantly upregulated crystal cell number along with higher transcript of PPO2. Out of seven tested AMPs level, Drosomycin was significantly upregulated in selected populations while Drosocin was significantly higher in control populations. ROS levels were comparable in the selected and control populations. Our results strongly suggest that enhanced basal immune activity during larval stage manages the faster development and could be responsible for comparable larval survival of selected and control populations.

Vexed mutations promote degeneration of dopaminergic neurons through excessive activation of the innate immune response

The hallmark of Parkinson's disease (PD) is the loss of dopaminergic (DA) neurons in the brain. However, little is known about why DA neurons are selectively vulnerable to PD. We previously completed a screen identifying genes associated with the progressive degeneration of DA neurons. Here we describe the role of a previously uncharacterized gene, CG42339, in the loss of DA neurons using Drosophila Melanogaster. CG42339 mutants display a progressive loss of DA neurons and locomotor dysfunction, along with an accumulation of advanced glycation end products (AGEs) in the brain. Based on this phenotype, we refer to CG42339 as vexed. We demonstrate that vexed is specifically required within cortex glia to maintain neuronal viability. Loss of vexed function results in excessive activation of the innate immune response in the brain, leading to loss of DA neurons. We show that activation of the innate immune response leads to increased nitric oxide signaling and accumulation of AGEs, which ultimately result in neurodegeneration. These results provide further insight into the relationship between the role of the immune response in the central nervous system and how this impacts neuronal viability.

Expression of antimicrobial peptides associated with different susceptibilities to environmental chemicals in Drosophila suzukii and Drosophila melanogaster

Drosophila suzukii is a serious agricultural pest. The evolved morphology of the female D. suzukii assists in penetrating the surface of fresh fruit and spawns eggs with its unique ovipositor. Conversely, Drosophila melanogaster, a taxonomically close species with D. suzukii, largely inhabits decaying and fermenting fruits and is consistently exposed to extensive environmental chemicals, such as 2-phenylethanol, ethanol, and acetic acid, produced by microorganisms. Considering the distinct habitats of the two flies, D. suzukii is thought to be more susceptible to environmental chemicals than D. melanogaster. We investigated the significantly higher survival rate of D. melanogaster following exposure to 2-phenylethanol, ethanol, and acetic acid. A comparison of the expression of antimicrobial peptides (AMPs) between the two flies treated with chemicals established that AMPs were generally more abundantly induced in D. melanogaster than in D. suzukii, particularly in the gut and fat body. Among the AMPs, the induction of genes (Diptericin A, Diptericin B, and Metchnikowin), which are regulated by the immune deficiency (IMD) pathway, was significantly higher than that of Drosomycin, which belongs to the Toll pathway in chemical-treated D. melanogaster. A transgenic RNAi fly (D. melanogaster) with silenced expression of AMPs and Relish, a transcription factor of the IMD pathway, exhibited significantly reduced survival rates than the control fly. Our results suggest that AMPs regulated by the IMD pathway play an important role in the chemical tolerance of D. melanogaster, and these flies are adapted to their habitats by physiological response.

Pathogen within-host dynamics and disease outcome: what can we learn from insect studies?

Parasite proliferations within/on the host form the basis of the outcome of all infectious diseases. However, within-host dynamics are difficult to study in vertebrates, as it requires regularly following pathogen proliferation from the start of the infection and at the organismal level. Invertebrate models allow for this monitoring under controlled conditions using population approaches. These approaches offer the possibility to describe many parameters of the within-host dynamics, such as rate of proliferation, probability to control the infection, and average time at which the pathogen is controlled. New parameters such as the Pathogen Load Upon Death and the Set-Point Pathogen Load have emerged to characterize within-host dynamics and better understand disease outcome. While contextualizing the potential of studying within-host dynamics in insects to build fundamental knowledge, we review what we know about within-host dynamics using insect models, and what it can offer to our knowledge of infectious diseases.

Repurposing α-Adrenoreceptor Blockers as Promising Anti-Virulence Agents in Gram-Negative Bacteria

Antimicrobial resistance is among the world’s most urgent public health problems. Diminishing of the virulence of bacteria is a promising approach to decrease the development of bacterial resistance. Quorum sensing (QS) systems orchestrate the bacterial virulence in inducer–receptors manner. Bacteria can spy on the cells of the host by sensing adrenergic hormones and other neurotransmitters, and in turn, these neurotransmitters can induce bacterial pathogenesis. In this direction, α-adrenergic blockers were proposed as an anti-virulence agents through inhibiting the bacterial espionage. The current study aimed to explore the α-blockers’ anti-QS activities. Within comprehensive in silico investigation, the binding affinities of seven α-adrenoreceptor blockers were evaluated towards structurally different QS receptors. From the best docked α-blockers into QS receptors, terazosin was nominated to be subjected for further in vivo and in vitro anti-QS and anti-virulence activities against Chromobacterium violaceum and Pseudomonas aeruginosa. Terazosin showed a significant ability to diminish the QS-controlled pigment production in C. violaceum. Moreover, Terazosin decreased the P. aeruginosa biofilm formation and down-regulated its QS-encoding genes. Terazosin protected mice from the P. aeruginosa pathogenesis. In conclusion, α-adrenergic blockers are proposed as promising anti-virulence agents as they hinder QS receptors and inhibit bacterial espionage.

Calycosin Alleviates Paraquat-Induced Neurodegeneration by Improving Mitochondrial Functions and Regulating Autophagy in a Drosophila Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder with limited clinical treatments. The occurrence of PD includes both genetic and environmental toxins, such as the pesticides paraquat (PQ), as major contributors to PD pathology in both invertebrate and mammalian models. Calycosin, an isoflavone phytoestrogen, has multiple pharmacological properties, including neuroprotective activity. However, the paucity of information regarding the neuroprotective potential of calycosin on PQ-induced neurodegeneration led us to explore whether calycosin can mitigate PD-like phenotypes and the underlying molecular mechanisms. We used a PQ-induced PD model in Drosophila as a cost-effective in vivo screening platform to investigate the neuroprotective efficacy of natural compounds on PD. We reported that calycosin shows a protective role in preventing dopaminergic (DA) neuronal cell death in PQ-exposed Canton S flies. Calycosin-fed PQ-exposed flies exhibit significant resistance against PQ-induced mortality and locomotor deficits in terms of reduced oxidative stress, loss of DA neurons, the depletion of dopamine content, and phosphorylated JNK-caspase-3 levels. Additionally, mechanistic studies show that calycosin administration improves PQ-induced mitochondrial dysfunction and stimulates mitophagy and general autophagy with reduced pS6K and p4EBP1 levels, suggestive of a maintained energy balance between anabolic and catabolic processes, resulting in the inhibition of neuronal cell death. Collectively, this study substantiates the protective effect of calycosin against PQ-induced neurodegeneration by improving DA neurons' survival and reducing apoptosis, likely via autophagy induction, and it is implicated as a novel therapeutic application against toxin-induced PD pathogenesis.

Cr(VI)-induced DNA damage is lessened by the modulation of hsp70 via increased GSH de novo synthesis in Drosophila melanogaster

Hexavalent chromium [Cr(VI)] is a genotoxic chemical, and in the chemical-exposed organism, oxidative stress is one of the leading causative mechanisms of genotoxicity. Heat shock protein-70 (Hsp70) is reported to be modulated in environmental chemical exposed organisms. Inadequate information on the protective role of Hsp70 in chemical-induced DNA lesions prompted us to investigate this possibility in a well-studied genetically tractable in vivo model Drosophila melanogaster. In the midgut cells of Cr(VI)-exposed hsp70-knockout (KO), -knockdown (KD), and -overexpression Drosophila strains, no significant change in double-strand breaks generation was observed in comparison to similarly exposed w ¹¹¹⁸ and the respective genetic control strain after 48 h. Therefore, the role of hsp70 was investigated on oxidative DNA damage induction in the exposed organisms after 24 h. Oxidized DNA lesions (particularly oxidized purine-based lesions), 8-oxo-dG level, and oxidative stress endpoints were found to be significantly elevated in hsp70-KO and -KD strains in comparison to similarly exposed w ¹¹¹⁸ and respective genetic control strain. On the contrary, in ubiquitous hsp70-overexpression strain exposed to Cr(VI), these endpoints were significantly lowered concurrently with increased GSH level through elevated gclc, and gclm expression, Gclc level, and GCL activity. The study suggests that as a consequence of hsp70 overexpression, the augmented GSH level in cells vis-a-vis GSH de novo synthesis can counteract Cr(VI)-induced oxidized DNA lesions.

Multiple mechanisms drive genomic adaptation to extreme O2 levels in Drosophila melanogaster

To detect the genomic mechanisms underlying evolutionary dynamics of adaptation in sexually reproducing organisms, we analyze multigenerational whole genome sequences of Drosophila melanogaster adapting to extreme O₂ conditions over an experiment conducted for nearly two decades. We develop methods to analyze time-series genomics data and predict adaptive mechanisms. Here, we report a remarkable level of synchronicity in both hard and soft selective sweeps in replicate populations as well as the arrival of favorable de novo mutations that constitute a few asynchronized sweeps. We additionally make direct experimental observations of rare recombination events that combine multiple alleles on to a single, better-adapted haplotype. Based on the analyses of the genes in genomic intervals, we provide a deeper insight into the mechanisms of genome adaptation that allow complex organisms to survive harsh environments.

The genomic details of adaptation to extreme environments remain challenging to characterize. Using new methods to analyze flies experimentally evolved to survive extreme O₂ conditions, the authors find a surprising level of synchronicity in selective sweeps, de novo mutations and adaptive recombination events.

Enhanced antioxidant properties of sericin-cecropin fusion protein against oxidative stress in human adult dermal fibroblasts

Chronic exposure to UVB radiation causes photoaging, immunosuppression, and ultimately photocarcinogenisis through the generation of reactive oxygen species (ROS). The ability of natural compounds in neutralizing the effects of oxidative stress is being explored with increased interest. Silk sericin, a biopolymer is reported to have diverse biological properties. In an effort to make the silk sericin pure, more effective and multifunctional, we have recombinantly expressed both functional sericin as well as sericin-cecropin B fusion proteins. Herein, we studied the antioxidant and anti-UVB potential of recombinant sericin and sericin-cecropin B proteins against oxidative stress using human primary dermal fibroblast cells. Treating the cells with recombinant sericin (RS) or sericin-cecropin B (RSC) prior to exposure to UVB and H2O2, effectively increased the cell viability by approximately 30% and 50%, respectively, in comparison to non-treated control. The protective effects were further evident in terms of significant reduction of LDH in oxidatively challenged cells treated with RS and RSC. A reduction in LDH release of at least 16 and 33% was observed with RS and RSC treatments, respectively, in comparison to exposed control. Further, elevated levels of catalase and superoxide dismutase (SOD) activity were observed. Importantly, the RSC fusion protein exhibited enhanced protective effects than cells treated with RS alone. Our results demonstrate that the functional attributes of cecropin B along with sericin activity in the fusion protein conferred enhanced protection against UVB- and H2O2-induced oxidative damage in human dermal fibroblasts. The improved antioxidant activity of recombinant sericin fusion biopolymer has great potential as a promising therapeutic agent for ROS-induced skin diseases.

Amyloid-β peptides slightly affect lifespan or antimicrobial peptide gene expression in Drosophila melanogaster

Background

Beta-amyloid peptide (Aβ) is the key protein in the pathogenesis of Alzheimer’s disease, the most common age-related neurodegenerative disorder in humans. Aβ peptide induced pathological phenotypes in different model organisms include neurodegeneration and lifespan decrease. However, recent experimental evidence suggests that Aβ may utilize oligomerization and fibrillization to function as an antimicrobial peptide (AMP), and protect the host from infections. We used the power of Drosophila model to study mechanisms underlying a dual role for Aβ peptides.

Results

We investigated the effects of Drosophila treatment with three Aβ42 peptide isoforms, which differ in their ability to form oligomers and aggregates on the lifespan, locomotor activity and AMP genes expression. Aβ42 slightly decreased female’s median lifespan (by 4.5%), but the effect was not related to the toxicity of peptide isoform. The lifespan and relative levels of AMP gene expression in male flies as well as locomotor activity in both sexes were largely unaffected by Aβ42 peptide treatment. Regardless of the effects on lifespan, Aβ42 peptide treatment induced decrease in AMP genes expression in females, but the effects were not robust.

Conclusions

The results demonstrate that chronic treatment with Aβ42 peptides does not drastically affect fly aging or immunity.

The value of antimicrobial peptides in the age of resistance

Accelerating growth and global expansion of antimicrobial resistance has deepened the need for discovery of novel antimicrobial agents. Antimicrobial peptides have clear advantages over conventional antibiotics which include slower emergence of resistance, broad-spectrum antibiofilm activity, and the ability to favourably modulate the host immune response. Broad bacterial susceptibility to antimicrobial peptides offers an additional tool to expand knowledge about the evolution of antimicrobial resistance. Structural and functional limitations, combined with a stricter regulatory environment, have hampered the clinical translation of antimicrobial peptides as potential therapeutic agents. Existing computational and experimental tools attempt to ease the preclinical and clinical development of antimicrobial peptides as novel therapeutics. This Review identifies the benefits, challenges, and opportunities of using antimicrobial peptides against multidrug-resistant pathogens, highlights advances in the deployment of novel promising antimicrobial peptides, and underlines the needs and priorities in designing focused development strategies taking into account the most advanced tools available.

Identification of transcriptional responsive genes to acetic acid, ethanol, and 2-phenylethanol exposure in Drosophila melanogaster

The fruit fly, Drosophila melanogaster, is predominantly found in overripe, rotten, fermenting, or decaying fruits and is constantly exposed to chemical stressors such as acetic acid, ethanol, and 2-phenylethanol. D. melanogaster has been employed as a model system for studying the molecular bases of various types of chemical-induced tolerance. Expression profiling using Illumina sequencing has been performed for identifying changes in gene expression that may be associated with evolutionary adaptation to exposure of acetic acid, ethanol, and 2-phenylethanol. We identified a total of 457 differentially expressed genes that may affect sensitivity or tolerance to three chemicals in the chemical treatment group as opposed to the control group. Gene-set enrichment analysis revealed that the genes involved in metabolism, multicellular organism reproduction, olfaction, regulation of signal transduction, and stress tolerance were over-represented in response to chemical exposure. Furthermore, we also detected a coordinated upregulation of genes in the Toll- and Imd-signaling pathways after the chemical exposure. Quantitative reverse transcription PCR analysis revealed that the expression levels of nine genes within the set of genes identified by RNA sequencing were up- or downregulated owing to chemical exposure. Taken together, our data suggest that such differentially expressed genes are coordinately affected by chemical exposure. Transcriptional analyses after exposure of D. melanogaster with three chemicals provide unique insights into subsequent functional studies on the mechanisms underlying the evolutionary adaptation of insect species to environmental chemical stressors.

Cathelicidin attenuates hyperoxia-induced lung injury by inhibiting oxidative stress in newborn rats

PURPOSE

High concentrations of oxygen administered to newborn infants with respiratory failure increases oxidant stress and leads to lung injury, characterized by decreased alveolar and capillary development. Cathelicidin belongs to an important group of human antimicrobial peptides that exhibit antioxidant activity; its overexpression reduces hyperoxia-induced oxidative stress. This study evaluated the therapeutic effects of cathelicidin in hyperoxia-induced lung injury in newborn rats.

METHODS AND MATERIALS

Sprague Dawley rat pups were reared in either room air (RA) or hyperoxia (85% O₂) and then randomly treated with low-dose (4 mg/kg) and high-dose (8 mg/kg) cathelicidin in 0.05 mL of normal saline (NS) administered intraperitoneally on postnatal days 1-6. The following six groups were obtained: RA + NS, RA + low-dose cathelicidin, RA + high-dose cathelicidin, O₂ + NS, O₂ + low-dose cathelicidin, and O₂ + high-dose cathelicidin. Lungs were harvested for Western blot and histological analyses on postnatal day 7.

RESULTS

Compared with the RA-reared rats, the hyperoxia-reared rats exhibited significantly lower body weights, higher mean linear intercept (MLI), lung injury score, interleukin-6, and oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression but lower superoxide dismutase 1 (SOD1) and vascular endothelial growth factor (VEGF) protein expression and vascular density. Cathelicidin treatment attenuated hyperoxia-induced lung injury as demonstrated by lower MLI and injury score and higher VEGF expression and vascular density.

CONCLUSIONS

Cathelicidin attenuated hyperoxia-induced lung injury and caused a decrease in 8-OHdG and SOD1 protein expression, most likely by inhibiting oxidative stress in the lung.

Cathelicidin attenuates hyperoxia-induced kidney injury in newborn rats

Aim: Supplemental oxygen is often used to treat neonates with respiratory disorders. Human and animal studies have demonstrated that neonatal hyperoxia increases oxidative stress and induces damage and collagen deposition in kidney during the perinatal period. Cathelicidin LL-37 is one important group of human antimicrobial peptides which exhibits antioxidant activity and its overexpression resists hyperoxia-induced oxidative stress. This study was designed to evaluate the protective effects of cathelicidin in hyperoxia-induced kidney injury in newborn rats.

Methods: Sprague-Dawley rat pups were reared in either room air (RA) or hyperoxia (85% O₂) and were randomly treated with low-dose (4 mg/kg) and high-dose (8 mg/kg) cathelicidin in normal saline (NS) administered intraperitoneally on postnatal days 1–6. The following six groups were obtained: RA + NS, RA + low-dose cathelicidin, RA + high-dose cathelicidin, O₂ + NS, O₂ + low-dose cathelicidin, and O₂ + high-dose cathelicidin. Kidneys were taken for Western blot and histological analyses on postnatal day 7.

Results: The hyperoxia-reared rats exhibited significantly lower body weights and anti-inflammatory M2 macrophages, but the kidney injury scores, oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG)-positive cells, pro-inflammatory M1 macrophages, collagen deposition, and NF-κB expression were higher than did the RA-reared rats.

Conclusions: Cathelicidin treatment attenuated kidney injury as evidenced by lower kidney injury scores, 8-OHdG-positive cells, collagen deposition, and reversion of hyperoxia-induced M1/M2 macrophage polarization. The role of Cathelicidin in ameliorates kidney injury of the hyperoxia newborn rats was accompanied by decreased NF-κB expression, which probably through the modulating NF-κB activity in the kidney.

Candle soot derived carbon nanoparticles: An assessment of cellular and progressive toxicity using Drosophila melanogaster model

The biomedical demand of the nanomaterials is continuously increasing due to their wide range of applications in the field. However, before the implementation of these nanomaterials, toxicity assessment is essential for its safe usage. In the present study, the toxicity of carbon nanoparticles (CNPs) was investigated which was derived from candle soot and compared with commercially available multi-walled carbon nanotubes (CNTs) by using Drosophila melanogaster as a model system. First instar Drosophila larvae were exposed to CNPs as well as CNTs, and the toxic effects of these nanomaterials were compared. The result shows that both nanomaterials enhance the level of reactive oxygen species and oxidative stress in the Drosophila, which leads to the upregulation of heat shock proteins that may cause cytotoxicity in exposed Drosophila larvae. In contrast, exposure to CNPs and CNTs did not affect the developmental period of the larvae. Morphology of the internal organs, brain, gut and Malpighian tubules was also not altered in the exposed larvae. Similarly, no change observed in the cytoskeleton (F-actin) of these organs. Reproductive performance was slightly reduced in the case of CNPs compare to control. However, CNTs exposure did not show any significant effect on the reproductive performance of the flies that emerged from exposed larvae in comparison to control. Hence the study concludes that exposure to CNPs and CNTs cause a moderate level of cytotoxicity in Drosophila. The study also indicates that the inexpensive CNPs may use as an alternative to expensive CNTs for biomedical and biological applications.

Listening to your gut: immune challenge to the gut sensitizes body wall nociception in the caterpillar Manduca sexta

Immune-nociceptor connections are found in animals across phyla. Local inflammation and/or damage results in increased nociceptive sensitivity of the affected area. However, in mammals, immune responses far from peripheral nociceptors, such as immune responses in the gut, produce a general increase in peripheral nociceptive sensitivity. This phenomenon has not, to our knowledge, been found in other animal groups. We found that consuming heat-killed pathogens reduced the tactile force needed to induce a defensive strike in the caterpillar Manduca sexta. This increase in the nociceptive sensitivity of the body wall is probably part of the reconfiguration of behaviour and physiology that occurs during an immune response (e.g. sickness behaviour). This increase may help enhance anti-predator behaviour as molecular resources are shifted towards the immune system. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

A conserved role of the insulin-like signaling pathway in diet-dependent uric acid pathologies in Drosophila melanogaster

Elevated uric acid (UA) is a key risk factor for many disorders, including metabolic syndrome, gout and kidney stones. Despite frequent occurrence of these disorders, the genetic pathways influencing UA metabolism and the association with disease remain poorly understood. In humans, elevated UA levels resulted from the loss of the of the urate oxidase (Uro) gene around 15 million years ago. Therefore, we established a Drosophila melanogaster model with reduced expression of the orthologous Uro gene to study the pathogenesis arising from elevated UA. Reduced Uro expression in Drosophila resulted in elevated UA levels, accumulation of concretions in the excretory system, and shortening of lifespan when reared on diets containing high levels of yeast extract. Furthermore, high levels of dietary purines, but not protein or sugar, were sufficient to produce the same effects of shortened lifespan and concretion formation in the Drosophila model. The insulin-like signaling (ILS) pathway has been shown to respond to changes in nutrient status in several species. We observed that genetic suppression of ILS genes reduced both UA levels and concretion load in flies fed high levels of yeast extract. Further support for the role of the ILS pathway in modulating UA metabolism stems from a human candidate gene study identifying SNPs in the ILS genes AKT2 and FOXO3 being associated with serum UA levels or gout. Additionally, inhibition of the NADPH oxidase (NOX) gene rescued the reduced lifespan and concretion phenotypes in Uro knockdown flies. Thus, components of the ILS pathway and the downstream protein NOX represent potential therapeutic targets for treating UA associated pathologies, including gout and kidney stones, as well as extending human healthspan.

The antimicrobial peptide defensin cooperates with tumour necrosis factor to drive tumour cell death in Drosophila

Antimicrobial peptides (AMPs) are small cationic molecules best known as mediators of the innate defence against microbial infection. While in vitro and ex vivo evidence suggest AMPs’ capacity to kill cancer cells, in vivo demonstration of an anti-tumour role of endogenous AMPs is lacking. Using a Drosophila model of tumourigenesis, we demonstrate a role for the AMP Defensin in the control of tumour progression. Our results reveal that Tumour Necrosis Factor mediates exposure of phosphatidylserine (PS), which makes tumour cells selectively sensitive to the action of Defensin remotely secreted from tracheal and fat tissues. Defensin binds tumour cells in PS-enriched areas, provoking cell death and tumour regression. Altogether, our results provide the first in vivo demonstration for a role of an endogenous AMP as an anti-cancer agent, as well as a mechanism that explains tumour cell sensitivity to the action of AMPs.

Animals have a natural defence system – the immune system – that is needed to fight off disease-causing microbes, known as pathogens. One way the immune system attacks pathogens is by producing small microbe-killing molecules called antimicrobial peptides. These antimicrobial peptides carry a positive charge, which allows them to interact with and disrupt the negatively charged cell surfaces of many microbes. Healthy animal cells do not have these negatively charged components on their cell surface, which means they are invisible to antimicrobial peptides. Studies have reported that antimicrobial peptides can attack cancer cells grown in a dish. However, it was unclear whether they could fight cancer cells in a live animal.

Parvy et al. have now addressed this issue by studying tumours in the larvae of fruit flies. Flies with tumours made an antimicrobial peptide called Defensin, which normally helps to fight infections. When Parvy et al. deleted the gene coding for Defensin, less tumour cells were dying and the tumours became bigger. This result indicated that Defensin was protecting the fruit flies from tumours. Examining the tumours under the microscope showed that Defensin protein interacted with the membranes of tumour cells. Defensin was not, however, interacting with healthy cells.

Further analysis revealed that a negatively charged component of cell membranes called phosphatidylserine, which normally faces the inside of healthy cells, is exposed to the outer surface of tumour cells. This negatively charged molecule renders cancer cells visible to positively charged Defensin. Importantly, the exposure of the phosphatidylserine is mediated by the fly equivalent of a protein called Tumour Necrosis Factor, a key player in cancer biology. Defensin binding to tumour cells leads to their death.

These experiments in the fruit fly highlight key molecular mechanisms that allow antimicrobial peptides to fight cancer cells in a living organism. Because human tumour cells can also expose phosphatidylserine, these latest findings may open up the possibility of a new kind of anti-cancer therapy for patients.

Synergy and remarkable specificity of antimicrobial peptides in vivo using a systematic knockout approach

Antimicrobial peptides (AMPs) are host-encoded antibiotics that combat invading microorganisms. These short, cationic peptides have been implicated in many biological processes, primarily involving innate immunity. In vitro studies have shown AMPs kill bacteria and fungi at physiological concentrations, but little validation has been done in vivo. We utilized CRISPR gene editing to delete all known immune-inducible AMPs of Drosophila, namely: 4 Attacins, 4 Cecropins, 2 Diptericins, Drosocin, Drosomycin, Metchnikowin and Defensin. Using individual and multiple knockouts, including flies lacking all 14 AMP genes, we characterize the in vivo function of individual and groups of AMPs against diverse bacterial and fungal pathogens. We found that Drosophila AMPs act primarily against Gram-negative bacteria and fungi, contributing either additively or synergistically. We also describe remarkable specificity wherein certain AMPs contribute the bulk of microbicidal activity against specific pathogens, providing functional demonstrations of highly specific AMP-pathogen interactions in an in vivo setting.

Efflux pumps and antimicrobial resistance: Paradoxical components in systems genomics

Efflux pumps play a major role in the increasing antimicrobial resistance rendering a large number of drugs of no use. Large numbers of pathogens are becoming multidrug resistant due to inadequate dosage and use of the existing antimicrobials. This leads to the need for identifying new efflux pump inhibitors. Design of novel targeted therapies using inherent complexity involved in the biological network modeling has gained increasing importance in recent times. The predictive approaches should be used to determine antimicrobial activities with high pathogen specificity and microbicidal potency. Antimicrobial peptides, which are part of our innate immune system, have the ability to respond to infections and have gained much attention in making resistant strain sensitive to existing drugs. In this review paper, we outline evidences linking host-directed therapy with the efflux pump activity to infectious disease.

Mitotype Interacts With Diet to Influence Longevity, Fitness, and Mitochondrial Functions in Adult Female Drosophila

Mitochondrial DNA (mtDNA) and the dietary macronutrient ratio are known to influence a wide range of phenotypic traits including longevity, fitness and energy production. Commonly mtDNA mutations are posited to be selectively neutral or reduce fitness and, to date, no selectively advantageous mtDNA mutations have been experimentally demonstrated in adult female Drosophila. Here we propose that a ND V161L mutation interacted with diets differing in their macronutrient ratios to influence organismal physiology and mitochondrial traits, but further studies are required to definitively show no linked mtDNA mutations are functionally significant. We utilized two mtDNA types (mitotypes) fed either a 1:2 Protein: Carbohydrate (P:C) or 1:16 P:C diet. When fed the former diet, Dahomey females harboring the V161L mitotype lived longer than those with the Alstonville mitotype and had higher climbing, basal reactive oxygen species (ROS) and elevated glutathione S-transferase E1 expression. The short lived Alstonville females ate more, had higher walking speed and elevated mitochondrial functions as suggested by respiratory control ratio (RCR), mtDNA copy number and expression of mitochondrial transcription termination factor 3. In contrast, Dahomey females fed 1:16 P:C were shorter lived, had higher fecundity, walking speed and mitochondrial functions. They had reduced climbing. This result suggests that mtDNA cannot be assumed to be a strictly neutral evolutionary marker when the dietary macronutrient ratio of a species varies over time and space and supports the hypothesis that mtDNA diversity may reflect the amount of time since the last selective sweep rather than strictly demographic processes.

The interplay between immunity and aging in Drosophila

Here, we provide a brief review of the mechanistic connections between immunity and aging—a fundamental biological relationship that remains poorly understood—by considering two intertwined questions: how does aging affect immunity, and how does immunity affect aging? On the one hand, aging contributes to the deterioration of immune function and predisposes the organism to infections (“immuno-senescence”). On the other hand, excessive activation of the immune system can accelerate degenerative processes, cause inflammation and immunopathology, and thus promote aging (“inflammaging”). Interestingly, several recent lines of evidence support the hypothesis that restrained or curbed immune activity at old age (that is, optimized age-dependent immune homeostasis) might actually improve realized immune function and thereby promote longevity. We focus mainly on insights from Drosophila, a powerful genetic model system in which both immunity and aging have been extensively studied, and conclude by outlining several unresolved questions in the field.

The bacterium Wolbachia exploits host innate immunity to establish a symbiotic relationship with the dengue vector mosquito Aedes aegypti

A host's immune system plays a central role in shaping the composition of the microbiota and, in return, resident microbes influence immune responses. Symbiotic associations of the maternally transmitted bacterium Wolbachia occur with a wide range of arthropods. It is, however, absent from the dengue and Zika vector mosquito Aedes aegypti in nature. When Wolbachia is artificially forced to form symbiosis with this new mosquito host, it boosts the basal immune response and enhances the mosquito's resistance to pathogens, including dengue, Zika virus and malaria parasites. The mechanisms involved in establishing a symbiotic relationship between Wolbachia and A. aegypti, and the long-term outcomes of this interaction, are not well understood. Here, we have demonstrated that both the immune deficiency (IMD) and Toll pathways are activated by the Wolbachia strain wAlbB upon its introduction into A. aegypti. Silencing the Toll and IMD pathways via RNA interference reduces the wAlbB load. Notably, wAlbB induces peptidoglycan recognition protein (PGRP)-LE expression in the carcass of A. aegypti, and its silencing results in a reduction of symbiont load. Using transgenic mosquitoes with stage-specific induction of the IMD and Toll pathways, we have shown that elevated wAlbB infection in these mosquitoes is maintained via maternal transmission. These results indicate that host innate immunity is utilized to establish and promote host-microbial symbiosis. Our results will facilitate a long-term projection of the stability of the Wolbachia-A. aegypti mosquito system that is being developed to control dengue and Zika virus transmission to humans.

Antimicrobial peptides extend lifespan in Drosophila

Antimicrobial peptides (AMPs) are important defense molecules of the innate immune system. High levels of AMPs are induced in response to infections to fight pathogens, whereas moderate levels induced by metabolic stress are thought to shape commensal microbial communities at barrier tissues. We expressed single AMPs in adult flies either ubiquitously or in the gut by using the inducible GeneSwitch system to tightly regulate AMP expression. We found that activation of single AMPs, including Drosocin, resulted in a significant extension of Drosophila lifespan. These animals showed reduced activity of immune pathways over lifetime, less intestinal regenerative processes, reduced stress response and a delayed loss of gut barrier integrity. Furthermore, intestinal Drosocin induction protected the animals against infections with the natural Drosophila pathogen Pseudomonas entomophila, whereas a germ-reduced environment prevented the lifespan extending effect of Drosocin. Our study provides new insights into the crosstalk of innate immunity, intestinal homeostasis and ageing.

Mitochondrial peroxiredoxins are essential in regulating the relationship between Drosophila immunity and aging

Previously, we have shown that flies under-expressing the two mitochondrial peroxiredoxins (Prxs), dPrx3 and dPrx5, display increases in tissue-specific apoptosis and dramatically shortened life span, associated with a redox crisis, manifested as changes in GSH:GSSG and accumulation of protein mixed disulfides. To identify specific pathways responsible for the observed biological effects, we performed a transcriptome analysis. Functional clustering revealed a prominent group enriched for immunity-related genes, including a considerable number of NF-kB-dependent antimicrobial peptides (AMP) that are up-regulated in the Prx double mutant. Using qRT-PCR analysis we determined that the age-dependent changes in AMP levels in mutant flies were similar to those observed in controls when scaled to percentage of life span. To further clarify the role of Prx-dependent mitochondrial signaling, we expressed different forms of dPrx5, which unlike the uniquely mitochondrial dPrx3 is found in multiple subcellular compartments, including mitochondrion, nucleus and cytosol. Ectopic expression of dPrx5 in mitochondria but not nucleus or cytosol partially extended longevity under normal or oxidative stress conditions while complete restoration of life span occurred when all three forms of dPrx5 were expressed from the wild type dPrx5 transgene. When dPrx5 was expressed in mitochondria or in all three compartments, it substantially delayed the development of hyperactive immunity while expression of cytosolic or nuclear forms had no effect on the immune phenotype. The data suggest a critical role of mitochondria in development of chronic activation of the immune response triggered by impaired redox control.

Characterization of the effect of Cr(VI) on humoral innate immunity using Drosophila melanogaster

With the advancement of human race, different anthropogenic activities have heaped the environment with chemicals that can cause alteration in the immune system of exposed organism. As a first line of barrier, the evolutionary conserved innate immunity is crucial for the health of an organism. However, there is paucity of information regarding in vivo assessment of the effect of environmental chemicals on innate immunity. Therefore, we examined the effect of a widely used environmental chemical, Cr(VI), on humoral innate immune response using Drosophila melanogaster. The adverse effect of Cr(VI) on host humoral response was characterized by decreased gene expression of antimicrobial peptides (AMPs) in the exposed organism. Concurrently, a significantly decreased transcription of humoral pathway receptors (Toll and PGRP) and triglyceride level along with inhibition of antioxidant enzyme activities were observed in exposed organism. This in turn weakened the immune response of exposed organism that was manifested by their reduced resistance against bacterial infection. In addition, overexpression of the components of humoral immunity particularly Diptericin benefits Drosophila from Cr(VI)-induced humoral immune-suppressive effect. To our knowledge, this is the first report regarding negative impact of an environmental chemical on humoral innate immune response of Drosophila along with subsequent protection by AMPs, which may provide novel insight into host-chemical interactions. Also, our data validate the utility and sensitivity of Drosophila as a model that could be used for screening the possible risk of environmental chemicals on innate immunity with minimum ethical concern that can be further extrapolated to higher organisms.

Efficacy of methuselah gene mutation toward tolerance of dichlorvos exposure in Drosophila melanogaster

Adverse reports on the exposure of organisms to dichlorvos (DDVP; an organophosphate insecticide) necessitate studies of organismal resistance/tolerance by way of pharmacological or genetic means. In the context of genetic modulation, a mutation in methuselah (mth; encodes a class II G-protein-coupled receptor (GPCR)) is reported to extend (~35%) the life span of Drosophila melanogaster and enhance their resistance to oxidative stress induced by paraquat exposure (short term, high level). A lack of studies on organismal tolerance of DDVP by genetic modulation prompted us to examine the protective efficacy of mth mutation in exposed Drosophila. Flies were exposed to 1.5 and 15.0 ng/ml DDVP for 12-48 h to examine oxidative stress endpoints and chemical resistance. After prolonged exposure of flies to DDVP, antioxidant enzyme activities, oxidative stress, glutathione content, and locomotor performance were assayed at various days (0, 10, 20, 30, 40, 50) of age. Flies with the mth mutation (mth(1)) showed improved chemical resistance and rescued redox impairment after acute DDVP exposure. Exposed mth(1) flies exhibited improved life span along with enhanced antioxidant enzyme activities and rescued oxidative perturbations and locomotor insufficiency up to middle age (~20 days) over similarly exposed w(1118) flies. However, at late (≥30 days) age, these benefits were undermined. Further, similarly exposed mth-knockdown flies showed effects similar to those observed in mth(1) flies. This study provides evidence of tolerance in organisms carrying a mth mutation against prolonged DDVP exposure and further warrants examination of similar class II GPCR signaling facets toward better organismal health.

Transcriptome analysis reveals signature of adaptation to landscape fragmentation

We characterize allelic and gene expression variation between populations of the Glanville fritillary butterfly (Melitaea cinxia) from two fragmented and two continuous landscapes in northern Europe. The populations exhibit significant differences in their life history traits, e.g. butterflies from fragmented landscapes have higher flight metabolic rate and dispersal rate in the field, and higher larval growth rate, than butterflies from continuous landscapes. In fragmented landscapes, local populations are small and have a high risk of local extinction, and hence the long-term persistence at the landscape level is based on frequent re-colonization of vacant habitat patches, which is predicted to select for increased dispersal rate. Using RNA-seq data and a common garden experiment, we found that a large number of genes (1,841) were differentially expressed between the landscape types. Hexamerin genes, the expression of which has previously been shown to have high heritability and which correlate strongly with larval development time in the Glanville fritillary, had higher expression in fragmented than continuous landscapes. Genes that were more highly expressed in butterflies from newly-established than old local populations within a fragmented landscape were also more highly expressed, at the landscape level, in fragmented than continuous landscapes. This result suggests that recurrent extinctions and re-colonizations in fragmented landscapes select a for specific expression profile. Genes that were significantly up-regulated following an experimental flight treatment had higher basal expression in fragmented landscapes, indicating that these butterflies are genetically primed for frequent flight. Active flight causes oxidative stress, but butterflies from fragmented landscapes were more tolerant of hypoxia. We conclude that differences in gene expression between the landscape types reflect genomic adaptations to landscape fragmentation.

Long-term dietary exposure to low concentration of dichloroacetic acid promoted longevity and attenuated cellular and functional declines in aged Drosophila melanogaster

Dichloroacetic acid (DCA), a water disinfection by-product, has attained emphasis due to its prospect for clinical use against different diseases including cancer along with negative impact on organisms. However, these reports are based on the toxicological as well clinical data using comparatively higher concentrations of DCA without much of environmental relevance. Here, we evaluate cellular as well as organismal effects of DCA at environmentally and mild clinically relevant concentrations (0.02-20.0 μg/ml) using an established model organism, Drosophila melanogaster. Flies were fed on food mixed with test concentrations of DCA for 12-48 h to examine the induction of reactive oxygen species (ROS) generation, oxidative stress (OS), heat shock genes (hsps) and cell death along with organismal responses. We also examined locomotor performance, ROS generation, glutathione (GSH) depletion, expression of GSH-synthesizing genes (gclc and gclm), and hsps at different days (0, 10, 20, 30, 40, 50) of the age in flies after prolonged DCA exposure. We observed mild OS and induction of antioxidant defense system in 20.0 μg/ml DCA-exposed organism after 24 h. After prolonged exposure to DCA, exposed organism exhibited improved survival, elevated expression of hsp27, gclc, and gclm concomitant with lower ROS generation and GSH depletion and improved locomotor performance. Conversely, hsp27 knockdown flies exhibited reversal of the above end points. The study provides evidence for the attenuation of cellular and functional decline in aged Drosophila after prolonged DCA exposure and the effect of hsp27 modulation which further incites studies towards the therapeutic application of DCA.

Influence of continuous light treatment on expression of stress biomarkers in Atlantic cod

Continuous light treatment during early juvenile stages in Gadus morhua is a common farming management practice but the effects of these unnatural light conditions on fish stress have received scant attention. In the present study we investigated how continuous illumination affects transcription levels of key stress-related and antimicrobial peptide genes in juvenile Atlantic cod. Gene expression quantification by real-time PCR revealed higher levels of transcripts coding for antioxidant enzymes, namely superoxide dismutase, catalase and glutathione reductase in liver of fish reared under continuous illumination, concomitantly with a 43% decrease in glutathione content. Transcription of antimicrobial peptides such as piscidins, hepcidin and cathelicidin was also affected by constant illumination. Overall, the significant changes in liver transcript levels of these biomarkers in response to continuous light may be an adaptation to light stress.

The transposable element Bari-Jheh mediates oxidative stress response in Drosophila

Elucidating the fitness effects of natural genetic variants is one of the current major challenges in evolutionary biology. Understanding the interplay between genotype, phenotype and environment is necessary to make accurate predictions of important biological outcomes such as stress resistance or yield in economically important plants and animals, and disease in humans. Based on population frequency patterns and footprints of selection at the DNA level, the transposable element Bari-Jheh, inserted in the intergenic region of Juvenile Hormone Epoxy Hydrolase (Jheh) genes, was previously identified as putatively adaptive. However, the adaptive effect of this mutation remained elusive. In this work, we integrate information on transcription factor binding sites, available ChIP-Seq data, gene expression analyses and phenotypic assays to identify the functional and the mechanistic underpinnings of Bari-Jheh. We show that Bari-Jheh adds extra antioxidant response elements upstream of Jheh1 and Jheh2 genes. Accordingly, we find that Bari-Jheh is associated with upregulation of Jheh1 and Jheh2 and with resistance to oxidative stress induced by two different compounds relevant for natural D. melanogaster populations. We further show that TEs other than Bari-Jheh might be playing a role in the D. melanogaster response to oxidative stress. Overall our results contribute to the understanding of resistance to oxidative stress in natural populations and highlight the role of transposable elements in environmental adaptation. The replicability of fitness effects on different genetic backgrounds also suggests that epistatic interactions do not seem to dominate the genetic architecture of oxidative stress resistance.

Diminishing glutathione availability and age-associated decline in neuronal excitability

Oxidative stress is frequently implicated in diminished electrical excitability of aging neurons yet the foundations of this phenomenon are poorly understood. This study explored links between alterations in cellular thiol-redox state and age-associated decline in electrical excitability in identified neurons (right pedal dorsal 1 [RPeD1]) of the gastropod Lymnaea stagnalis. Intracellular thiol redox state was modulated with either dithiothreitol or membrane permeable ethyl ester of the antioxidant glutathione (et-GSH). Neuronal antioxidant demand was manipulated through induction of lipid peroxidation with 2,2'-azobis-2-methyl-propanimidamide-dihydrochloride (AAPH). Glutathione synthesis was manipulated with buthionine sulfoximine (BSO). We show that; glutathione content of snail brains declines with age, whereas pyroglutamate content increases; treatment with AAPH and BSO alone aggravated the natural low excitability state of old RPeD1, but only the combination of AAPH + BSO affected electrical excitability of young RPeD1; et-GSH reversed this effect in young RPeD1; et-GSH and dithiothreitol treatment reversed age-associated low excitability of old RPeD1. Together, these data argue for a tight association between glutathione availability and the regulation of neuronal electrical excitability and indicate perturbation of cellular thiol-redox metabolism as a key factor in neuronal functional decline in this gastropod model of biological aging.

Does hyperoxia selection cause adaptive alterations of mitochondrial electron transport chain activity leading to a reduction of superoxide production?

Prolonged hyperoxia exposure generates excessive reactive oxygen species (ROS) and potentially leads to oxidative injury in every organ. We have previously generated Drosophila melanogaster flies that tolerate extreme oxidative stress (90%-95% O₂), a lethal condition to naive flies, through a long-term laboratory selection. We found that hyperoxia-selected (S(O2)A) flies had a significantly longer lifespan in hyperoxia and paraquat-induced oxidative stress. Prolonged hyperoxia exposure induced a significant ROS accumulation and an increased expression of oxidative stress markers, including lipid peroxidation and protein carbonyl contents in control flies, but not in S(O2)A flies. Enzymatic assays revealed that antioxidant enzyme activity in S(O2)A flies was similar to that in control flies. However, in isolated mitochondria and using electron paramagnetic resonance, we observed that S(O2)A flies displayed a decreased superoxide yield during state 3 respiration as compared to control flies and that the activity of electron transport chain complex I and III was also inhibited in S(O2)A flies. Our observations lead to the hypothesis that decreased complex activity results in a decreased ROS production, which might be a major potential adaptive mechanism of hyperoxia tolerance.

Immune and stress response 'cross-talk' in the Drosophila Malpighian tubule

The success of insects is in large part due to their ability to survive environmental stress, including heat, cold, and dehydration. Insects are also exposed to infection, osmotic or oxidative stress, and to xenobiotics or toxins. The molecular mechanisms of stress sensing and response have been widely investigated in mammalian cell lines, and the area of stress research is now so vast to be beyond the scope of a single review article. However, the mechanisms by which stress inputs to the organism are sensed and integrated at the tissue and cellular level are less well understood. Increasingly, common molecular events between immune and other stress responses are observed in vivo; and much of this work stems of efforts in insect molecular science and physiology. We describe here the current knowledge in the area of immune and stress signalling and response at the level of the organism, tissue and cell, focussing on a key epithelial tissue in insects, the Malpighian tubule, and drawing together the known pathways that modulate responses to different stress insults. The tubules are critical for insect survival and are increasingly implicated in responses to multiple and distinct stress inputs. Importantly, as tubule function is central to survival, they are potentially key targets for insect control, which will be facilitated by increased understanding of the complexities of stress signalling in the organism.

Low-dose radiation induces Drosophila innate immunity through Toll pathway activation

Numerous studies report that exposing certain organisms to low-dose radiation induces beneficial effects on lifespan, tumorigenesis, and immunity. By analyzing survival after bacterial infection and antimicrobial peptide gene expression in irradiated flies, we demonstrate that low-dose irradiation of Drosophila enhances innate immunity. Low-dose irradiation of flies significantly increased resistance against gram-positive and gram-negative bacterial infections, as well as expression of several antimicrobial peptide genes. Additionally, low-dose irradiation also resulted in a specific increase in expression of key proteins of the Toll signaling pathway and phosphorylated forms of p38 and JNK. These results indicate that innate immunity is activated after low-dose irradiation through Toll signaling pathway in Drosophila.