A Malpighian Tubule-Specific P450 Gene SlCYP9A75a Contributes to Xenobiotic Tolerance in Spodoptera litura.

Phytophagous insects are more predisposed to evolve insecticide resistance than other insect species due to the "preadaptation hypothesis". Cytochrome P450 monooxygenases have been strongly implicated in insecticide and phytochemical detoxification in insects. In this study, RNA-seq results reveal that P450s of Spodoptera litura, especially the CYP3 clan, are dominant in cyantraniliprole, nicotine, and gossypol detoxification. The expression of a Malpighian tubule-specific P450 gene, SlCYP9A75a, is significantly upregulated in xenobiotic treatments except α-cypermethrin. The gain-of-function and loss-of-function analyses indicate that SlCYP9A75a contributes to cyantraniliprole, nicotine, and α-cypermethrin tolerance, and SlCYP9A75a is capable of binding to these xenobiotics. This study indicates the roles of inducible SlCYP9A75a in detoxifying man-made insecticides and phytochemicals and may provide an insight into the development of cross-tolerance in omnivorous insects.

Cytotoxic and genotoxic effects of a pendimethalin-based herbicide in Apis mellifera.

Public concern about the effects of pesticides on non-target organisms has increased in the recent years. Nevertheless, there is a limited number of studies that address the actual toxic effects of herbicides on insects. This study investigated the side effects of herbicides on non-target organisms inhabiting agroecosystems and performing essential ecological and economic functions such as crop pollination. We analysed morphological alterations in the gut, Malpighian tubules and circulating haemocytes of Apis mellifera workers as markers of exposure effects. A commercial formulation of a pendimethalin-based herbicide (PND) was administered orally under laboratory conditions at a realistic concentration admitted in the field (330gL-1 of active ingredient., 4 L ha-1 for cereal and vegetable crops). The worker bees were exposed to a single application of PND for a period of one week, to simulate the exposure that can occur when foraging bees accidentally drink drops of contaminated water upon treatments. Histopathological analyses of the midgut, ileum and Malpighian tubules showed alterations over time (from 24 to 72 h after the beginning of exposure) such as loss of epithelial organisation, cellular vacuolisation and altered pyknotic nuclei as well as disruption of the peritrophic membrane over time. Semiquantitative analyses of the midgut showed a significant increase in the organ injury index 24 and 72 h after the initial exposure in PND-exposed bees compared to control bees. In addition, a change in positivity to Gram staining was observed in the midgut histological sections. A recovery of cytotoxic effects was observed one week after the initial exposure, which was favoured by the periodic renewal of the intestinal epithelium and the herbicide dissipation time. Cytochemical staining with Giemsa of haemocytes from PND-treated workers over 24 and 72 h showed significant nuclear alterations such as lobed or polymorphic nuclei and micronuclei compared to bees in the control group. These results show that the dose of PND used to protect crops from weeds can lead to significant cytotoxic and genotoxic effects in non-target organisms such as honey bees. In croplands, the sublethal effects on cell morphology can impair vital physiological processes such as nutrition, osmoregulation, and resistance to pathogens, contributing to the decline in biodiversity and abundance of species that play a prominent ecological role, such as pollinators.

Proteotranscriptomic analyses of the midgut and Malpighian tubules after a sublethal concentration of Cry1Ab exposure on Spodoptera litura.

BACKGROUND: Cry1Ab has emerged as a bio-insecticide to control Spodoptera litura (Lepidoptera: Noctuidae). However, the sublethal effects of Cry1Ab on the physiological changes and molecular level of S. litura have not been well documented. Our aims in this study were to assess the sublethal effect of Cry1Ab on S. litura, including midgut and Malpighian tubules as targets. RESULTS: After sublethal Cry1Ab exposure, distinct histological alterations were mainly observed in the midgut. Furthermore, the results of comparative RNA sequencing and tandem mass tag-based proteomics showed that, in the midgut, most differential expression genes (DEGs) were up-regulated and significantly enriched in the serine protease activity pathway, and up-regulated differential expression proteins (DEPs) were mainly associated with the oxidative phosphorylation pathway, whereas the down-regulated involved in the ribosome pathways. In the Malpighian tubules, DEGs and DEPs were significantly enriched in the ribosome pathway. We proposed that ribosome may act as a universal target in energy metabolism with other pathways via the results of protein-protein interaction analysis. Further, by verification of the mRNA expression of some Cry protein receptor and detoxification genes after Cry1Ab treatment, it was suggested that the ribosomal proteins (RPs) possibly participate in influencing the Bt-resistance of S. litura larvae under sublethal Cry1Ab exposure. CONCLUSION: Under sublethal Cry1Ab exposure, the midgut of S. litura was damaged, and the proteotranscriptomic analysis elucidated that Cry1Ab disrupted the energy homeostasis of larvae. Furthermore, we emphasized the potential role of ribosomes in sublethal Cry1Ab exposure. © 2024 Society of Chemical Industry.

Lead (Pb2+)-induced calcium oxalate crystallization ex vivo is ameliorated via inositol 1,4,5-trisphosphate receptor (InsP3R) knockdown in a Drosophila melanogaster model of nephrolithiasis.

Nephrolithiasis causes severe pain and is a highly recurrent pathophysiological state. Calcium-containing stones, specifically calcium oxalate (CaOx), is the most common type accounting for approximately 75 % of stone composition. Genetic predisposition, gender, geographic region, diet, and low fluid intake all contribute to disease pathogenesis. However, exposure to environmental pollutants as a contribution to kidney stone formation remains insufficiently studied. Lead (Pb2+) is of particular interest as epidemiological data indicate that low-level exposure (BLL = 0.48-3.85 µM) confers a 35 % increased risk of developing CaOx nephrolithiasis. However, mechanisms underlying this association have yet to be elucidated. Drosophila melanogaster provide a useful genetic model where major molecular pathophysiological pathways can be efficiently studied. Malpighian tubules (MT) were isolated from either Wild-Type or InsP3R knockdown flies and treated with oxalate (5 mM) ± Pb2+ (2µM) for 1 h. Following exposure, MTs were imaged and crystals quantified. CaOx crystal number and total area were significantly increased (˜5-fold) in Pb2+(pre-treatment) + oxalate-exposed MTs when compared to oxalate alone controls. However, CaOx crystal number and total crystal area in Pb2+ + oxalate-exposed InsP3R knockdown MTs were significantly decreased (˜3-fold) indicating the role for principal cell-specific InsP3R-mediated Ca2+ mobilization as a mechanism for Pb2+-induced increases in CaOx crystallization inset model of nephrolithiasis.

Effects of sodium valproate on the chromatin of Triatoma infestans (Klug, 1834) (Hemiptera, Reduviidae) under in vitro culture conditions.

Sodium valproate (VPA) is a classic anticonvulsive, a histone deacetylase inhibitor, and a chromatin remodeling inducer. When injected into specimens of Triatoma infestans, a vector of Chagas disease, VPA affects the chromatin supraorganization of chromocenter heterochromatin in only a few cells of the Malpighian tubules. To test whether this result was explained by the inaccessibility of all of the organ's cells to the drug, we investigated the nuclear phenotypes and global acetylation of lysine 9 in histone H3 (H3K9ac) in Malpighian tubules cultivated in vitro for 1-24 h in the presence of 0.05 mM-1 mM VPA. The present results revealed that the chromatin decondensation event in the chromocenter body, which was detected only under low VPA concentrations up to a 4-h treatment, was not frequent during organ culture, similar to the results for injected insects. Cultivation of T. infestans Malpighian tubules in vitro for 24 h revealed inadequate for cell preservation even in the absence of the drug. Immunofluorescence signals for H3K9ac following VPA treatment showed a slightly increased intensity in the euchromatin, but were never detected in the chromocenter bodies, except with great intensity at their periphery, where the 18S rDNA is located. In conclusion, when VPA affects the chromocenter heterochromatin in this animal cell model, it occurs through a pathway that excludes a classic global H3K9ac mark. Investigation of nonhistone proteins associated with histone methylation marks is still required to further explain the differential response of T. infestans chromatin to VPA.

Development of a Drosophila melanogaster based model for the assessment of cadmium and mercury mediated renal tubular toxicity.

Xenobiotic mediated renal toxicity is one of the major health concerns to the organisms, including humans. New chemicals with nephrotoxic potential are continuously being added to the list of existing nephrotoxicants. To predict the nephrotoxicity of these new chemicals, reliable and cost-effective alternative animal models are required. It is a prerequisite for the identification and assessment of these compounds as potential nephrotoxicants to prevent renal toxicity in the exposed population. Drosophila melanogaster, a genetically tractable invertebrate animal model, has a renal system functionally analogous to humans. The Malpighian tubules (MTs) of D. melanogaster are similar to the tubular part of nephron of the human kidney. Besides, it recapitulates the renal toxicity hallmark with mammals when exposed to known nephrotoxicants. In this study, first instar larvae of D. melanogaster (Oregon R) were exposed to different concentrations of two well-known nephrotoxicants, cadmium (Cd) and mercury (Hg). Akin to higher organisms, Cd and Hg exposure to D. melanogaster produce similar phenotypes. MTs of exposed D. melanogaster larvae exhibited increased oxidative stress, activated cellular antioxidant defense mechanism, GSH depletion, increased cleaved caspase-3 expression, increased DEVDase activity and increased cell death. The functional status of MTs was assessed by fluid secretion rate (FSR), efflux activity of transporter protein, mitochondrial membrane potential (MMP), ATP level and expression of junctional protein (Dlg). All the phenotypes observed in MTs of D. melanogaster larvae recapitulate the phenotypes observed in higher organisms. Increased uric acid level, the hallmark of renal dysfunction, was also observed in exposed larvae. Taken together, the study suggests that MTs of D. melanogaster may be used as a functional model to evaluate xenobiotic mediated nephrotoxicity.

Development of Aedes aegypti (Diptera: Culicidae) mosquito larvae in high ammonia sewage in septic tanks causes alterations in ammonia excretion, ammonia transporter expression, and osmoregulation.

Larvae of the disease vector mosquito, Aedes aegypti (L.) readily develop in ammonia rich sewage in the British Virgin Islands. To understand how the larvae survive in ammonia levels that are lethal to most animals, an examination of ammonia excretory physiology in larvae collected from septic-water and freshwater was carried out. A. aegypti larvae were found to be remarkably plastic in dealing with high external ammonia through the modulation of NH4+ excretion at the anal papillae, measured using the scanning ion-selective electrode technique (SIET), and NH4+ secretion in the primary urine by the Malpighian tubules when developing in septicwater. Ammonia transporters, Amt and Rh proteins, are expressed in ionoregulatory and excretory organs, with increases in Rh protein, Na+-K+-ATPase, and V-type-H+-ATPase expression observed in the Malpighian tubules, hindgut, and anal papillae in septic-water larvae. A comparative approach using laboratory A. aegypti larvae reared in high ammonia septic-water revealed similar responses to collected A. aegypti with regard to altered ammonia secretion and hemolymph ion composition. Results suggest that the observed alterations in excretory physiology of larvae developing in septic-water is a consequence of the high ammonia levels and that A. aegypti larvae may rely on ammonia transporting proteins coupled to active transport to survive in septic-water.

Physiological effects of biostable kinin and CAPA analogs in the Chagas disease vector, Rhodnius prolixus.

In the Chagas disease vector Rhodnius prolixus, the kinin and CAPA family of neuropeptides are implicated in feeding and diuresis-related behaviours, with Rhopr-kinins stimulating contractions of the midgut, salivary glands, and hindgut, and RhoprCAPA-2 functioning as an anti-diuretic hormone. The current study examined the effects of kinin and CAPA neuropeptides and their analogs on feeding and diuresis, and on hindgut contractions and MT fluid secretion in R. prolixus. The biostable Aib-containing kinin analog 2139[Φ1]wp-2 was found to have antifeedant effects, and to be more potent than Rhopr-kinin 2 in stimulating hindgut contractions. The CAPA analog 2129-SP3[Φ3]wp-2 induced the intake of a larger blood meal, and increased the rate of post-prandial rapid diuresis. RhoprCAPA-2, but not its analog, potentiated hindgut contractions induced by Rhopr-kinin 2. Potentiation was observed with the CAPA analog on 5-HT-stimulated increases in frequency of hindgut contractions, whereas RhoprCAPA-2 inhibited this 5-HT-mediated stimulation. The CAPA analog induced hindgut contractions and prevented the inhibition induced by RhoprCAPA-2 on 5-HT-stimulated MT secretion. These results demonstrate novel interactions between Rhopr-kinin and RhoprCAPA-2 on the hindgut, possibly influencing post-feeding excretion. The kinin analog is a potent agonist of the kinin receptor, and the CAPA analog an antagonist of the CAPA receptor. The use of neuropeptide mimetics is a promising approach to vector control as they can disrupt behaviours, and the effects of these neuropeptide analogs highlight their value as lead compounds, given their ability to interfere with epidemiologically-relevant behaviours.

Spinosad-mediated effects on the walking ability, midgut, and Malpighian tubules of Africanized honey bee workers.

BACKGROUND: The global decline in Apis mellifera colonies is attributed to multiple factors, including pesticides. The bioinsecticide spinosad was initially recognized as safe for non-target organisms; however, its toxicity has been changing this view. Here, we investigated the survival, behavioral changes, and structural changes in the midgut and Malpighian tubules of A. mellifera treated orally with a spinosad formulation. RESULTS: The field-recommended concentration of spinosad killed 100% of the bees. The 5% and 50% lethal concentrations (LC5 and LC50 , respectively) of spinosad altered the behavioral activity, reducing the walking distance and velocity, and increased the resting time in comparison to the control. The LC50 caused disorganization of the epithelia of tested organs and induced oxidative stress and cell death. CONCLUSIONS: The present work provides new insights into the debate about the role of bioinsecticides in the mortality of Africanized honey bees. Even at very low concentrations, the spinosad formulation was toxic to the vital organs midgut and Malpighian tubules and adversely affected walking behavior. This detailed evaluation of the impact of the bioinsecticide on A. mellifera will contribute to the clarification of disturbances probably caused by spinosad formulations, which can be used to develop more sustainable protocols in agriculture. © 2017 Society of Chemical Industry.

A Drosophila genetic model of nephrolithiasis: transcriptional changes in response to diet induced stone formation.

BACKGROUND: Urolithiasis is a significant healthcare issue but the pathophysiology of stone disease remains poorly understood. Drosophila Malpighian tubules were known to share similar physiological function to human renal tubules. We have used Drosophila as a genetic model to study the transcriptional response to stone formation secondary to dietary manipulation. METHODS: Wild-type male flies were raised on standard medium supplemented with lithogenic agents: control, sodium oxalate (NaOx) and ethylene glycol (EG). At 2 weeks, Malpighian tubules were dissected under polarized microscope to visualize crystals. The parallel group was dissected for RNA extraction and subsequent next-generation RNA sequencing. RESULTS: Crystal formation was visualized in 20%(±2.2) of flies on control diet, 73%(±3.6) on NaOx diet and 84%(±2.2) on EG diet. Differentially expressed genes were identified in flies fed with NaOx and EG diet comparing with the control group. Fifty-eight genes were differentially expressed (FDR <0.05, p < 0.05) in NaOx diet and 20 genes in EG diet. The molecular function of differentially expressed genes were assessed. Among these, Nervana 3, Eaat1 (Excitatory amino acid transporter 1), CG7912, CG5404, CG3036 worked as ion transmembrane transporters, which were possibly involved in stone pathogenesis. CONCLUSIONS: We have shown that by dietary modification, stone formation can be manipulated and visualized in Drosophila Malpighian tubules. This genetic model could be potentially used to identify the candidate genes that influence stone risk hence providing more insight to the pathogenesis of human stone disease.

Structural and functional alterations in Malpighian tubules as biomarkers of environmental pollution: synopsis and prospective.

Although a number of biomarkers of pollutant exposure have been identified in invertebrate species, little is known about the effect on Malpighian tubules playing an essential role in excretion and osmoregulation. Analyses of structural and functional alterations on this organ can be useful to predict the effects at the organism and population level in monitoring studies of environmental pollution. The aim of the present review is to provide a synthesis of existing knowledge on cellular damages induced by xenobiotics in Malpighian tubules both under laboratory and field conditions. We compared studies of exposure to pesticides and heavy metals as mainly environmental contaminants from anthropogenic activities. This report provided evidence that the exposure to xenobiotics has an effect on this organ and reinforces the need for further research integrating molecular biomarkers with analysis on Malpighian tubules. Copyright © 2017 John Wiley & Sons, Ltd.

Identification of multiple functional receptors for tyramine on an insect secretory epithelium.

The biogenic amine tyramine (TA) regulates many aspects of invertebrate physiology and development. Although three TA receptor subtypes have been identified (TAR1-3), specific receptors have not been linked to physiological responses in native tissue. In the Malpighian (renal) tubule of Drosophila melanogaster, TA activates a transepithelial chloride conductance, resulting in diuresis and depolarization of the transepithelial potential. In the current work, mutation or RNAi-mediated knockdown in the stellate cells of the tubule of TAR2 (tyrR, CG7431) resulted in a dramatic reduction, but not elimination, of the TA-mediated depolarization. Mutation or knockdown of TAR3 (tyrRII, CG16766) had no effect. However, deletion of both genes, or knockdown of TAR3 on a TAR2 mutant background, eliminated the TA responses. Thus while TAR2 is responsible for the majority of the TA sensitivity of the tubule, TAR3 also contributes to the response. Knockdown or mutation of TAR2 also eliminated the response of tubules to the related amine octopamine (OA), indicating that OA can activate TAR2. This finding contrasts to reports that heterologously expressed TAR2 is highly selective for TA over OA. This is the first report of TA receptor function in a native tissue and indicates unexpected complexity in the physiology of the Malpighian tubule.

Functional studies of Drosophila zinc transporters reveal the mechanism for zinc excretion in Malpighian tubules.

BACKGROUND: Zinc is an essential metal involved in many physiological processes. Previous work has identified a set of zinc transporters involved in Drosophila dietary zinc absorption. However, zinc excretion and reabsorption, the other two important processes to maintain zinc homeostasis, are not as well understood. In this work, we screened all the potential zinc transporter Zip (SLC39) and ZnT (SLC30) members for their likely roles in zinc excretion in Malpighian tubules, an insect organ functionally analogous to mammalian kidneys. RESULTS: Zip71B (CG10006, most homologous to hZIP5), in addition to the previously characterized ZnT35C (CG3994), was identified as being critical in zinc excretion. Tubule-specific knockdown of Zip71B/dZip5 reduces zinc accumulation in the tubules, but increases zinc levels in the body, resulting in survival defect under zinc excess conditions. Zip71B/dZip5 is localized to the plasma membrane at the basolateral side of the tubules, and is functionally epistatic to the apically localized ZnT35C in regulating the tubule zinc homeostasis. Our results indicate that Zip71B/dZip5 is involved in zinc import into the tubular cells from the circulation, and ZnT35C in turn effluxes the tubular zinc out. Notably, mammalian ZIP5, which is expressed in the kidney, functions analogously to Zip71B/dZip5 in the fly while hZIP4 cannot complement the loss of Zip71B/dZip5 function. Furthermore, Zip71B/dZip5 expression is regulated by zinc so that, in response to toxic levels of zinc, the tubules can increase zinc efflux capability. We also characterized the role of dZnT1 (CG17723) in zinc reabsorption in Malpighian tubules. Finally, using a tubule calcification model, we were able to show that knockdown of Zip71B/dZip5 or ZnT35C was able to mitigate stone formation, consistent with their roles in tubular zinc homeostasis. CONCLUSIONS: Our results start to sketch out a relatively complete picture of the zinc excretion process in Drosophila Malpighian tubules, and may provide a reference for relevant mammalian studies.

The orphan pentameric ligand-gated ion channel pHCl-2 is gated by pH and regulates fluid secretion in Drosophila Malpighian tubules.

Pentameric ligand-gated ion channels (pLGICs) constitute a large protein superfamily in metazoa whose role as neurotransmitter receptors mediating rapid, ionotropic synaptic transmission has been extensively studied. Although the vast majority of pLGICs appear to be neurotransmitter receptors, the identification of pLGICs in non-neuronal tissues and homologous pLGIC-like proteins in prokaryotes points to biological functions, possibly ancestral, that are independent of neuronal signalling. Here, we report the molecular and physiological characterization of a highly divergent, orphan pLGIC subunit encoded by the pHCl-2 (CG11340) gene, in Drosophila melanogaster We show that pHCl-2 forms a channel that is insensitive to a wide array of neurotransmitters, but is instead gated by changes in extracellular pH. pHCl-2 is expressed in the Malpighian tubules, which are non-innervated renal-type secretory tissues. We demonstrate that pHCl-2 is localized to the apical membrane of the epithelial principal cells of the tubules and that loss of pHCl-2 reduces urine production during diuresis. Our data implicate pHCl-2 as an important source of chloride conductance required for proper urine production, highlighting a novel role for pLGICs in epithelial tissues regulating fluid secretion and osmotic homeostasis.

Allatostatin-C antagonizes the synergistic myostimulatory effect of allatotropin and serotonin in Rhodnius prolixus (Stal).

Haematophagous insects can ingest large quantities of blood in a single meal producing a large quantity of urine in the following hours to eliminate the excess of water and mineral ions incorporated. The excretory activity of the Malpighian tubules is facilitated by an increase in haemolymph circulation as a result of the intensification of aorta contractions, combined with an increase of anterior midgut peristaltic waves. We have recently shown that haemolymph circulation during post-prandial diuresis is modulated by the synergistic activity of allatotropin (AT) and serotonin, resulting in an increase in aorta and crop contraction rates. In the present study we describe the antagonistic effect of allatostatin-C (AST-C) on the increase of aorta frequency of contractions induced by serotonin/AT in Rhodnius prolixus. The administration of AST-C counteracted the increase in the frequency induced by the treatment with serotonin/AT, but did not affect the increase in frequency induced by the administration of serotonin alone, suggesting that AST-C is altering the synergism between serotonin and AT. Furthermore, the administration of AST-C during post-prandial diuresis decreases the number of peristaltic waves of the anterior midgut. The AST-C putative receptor is expressed in the hindgut, midgut and dorsal vessel, three critical organs involved in post-prandial diuresis. All together these findings provide evidence that AST-C plays a key role as a myoregulatory and cardioregulatory peptide in R. prolixus.

Spinosad Induces Antioxidative Response and Ultrastructure Changes in Males of Red Palm Weevil Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae).

The red palm weevil, Rhynchophorus ferrugineus, is of great concern worldwide, especially in the Middle East, where dates are a strategic crop. Despite their ecological hazard, insecticides remain the most effective means of control. A bioinsecticide of bacterial origin, spinosad is effective against several pests, and its efficacy against male R. ferrugineus was assessed in the present study. The antioxidative responses of key enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) to spinosad were investigated in the midgut and testes, and the effects of this insecticide on the cell ultrastructure of the midgut, Malpighian tubules, and testes were also determined. The lethal concentration 50 of spinosad was measured at 58.8 ppm, and the insecticide inhibited the activities of CAT, SOD, and GST in the midgut. However, no significant changes in the activities of these enzymes were observed in the testes. Spinosad treatment resulted in concentration-dependent changes in the cellular organelles of the midgut, Malpighian tubules, and testes of R. ferrugineus, and some of these effects were similar to those exerted by other xenobiotics. However, specific changes were observed as a result of spinosad treatment, including an increase in the number and size of concretions in Malpighian tubule cells and the occasional absence of the central pair of microtubules in the axonemes of sperm tails. This study introduces spinosad for potential use as an insecticide within an integrated control program against male red palm weevils. Additionally, the study provides biochemical and ultrastructural evidence for use in the development of bioindicators.

Localization and role of inward rectifier K(+) channels in Malpighian tubules of the yellow fever mosquito Aedes aegypti.

Malpighian tubules of adult female yellow fever mosquitoes Aedes aegypti express three inward rectifier K(+) (Kir) channel subunits: AeKir1, AeKir2B and AeKir3. Here we 1) elucidate the cellular and membrane localization of these three channels in the Malpighian tubules, and 2) characterize the effects of small molecule inhibitors of AeKir1 and AeKir2B channels (VU compounds) on the transepithelial secretion of fluid and electrolytes and the electrophysiology of isolated Malpighian tubules. Using subunit-specific antibodies, we found that AeKir1 and AeKir2B localize exclusively to the basolateral membranes of stellate cells and principal cells, respectively; AeKir3 localizes within intracellular compartments of both principal and stellate cells. In isolated tubules bathed in a Ringer solution containing 34 mM K(+), the peritubular application of VU590 (10 µM), a selective inhibitor of AeKir1, inhibited transepithelial fluid secretion 120 min later. The inhibition brings rates of transepithelial KCl and fluid secretion to 54% of the control without a change in transepithelial NaCl secretion. VU590 had no effect on the basolateral membrane voltage (Vbl) of principal cells, but it significantly reduced the cell input conductance (gin) to values 63% of the control within ∼90 min. In contrast, the peritubular application of VU625 (10 µM), an inhibitor of both AeKir1 and AeKir2B, started to inhibit transepithelial fluid secretion as early as 60 min later. At 120 min after treatment, VU625 was more efficacious than VU590, inhibiting transepithelial KCl and fluid secretion to ∼35% of the control without a change in transepithelial NaCl secretion. Moreover, VU625 caused the Vbl and gin of principal cells to respectively drop to values 62% and 56% of the control values within only ∼30 min. Comparing the effects of VU590 with those of VU625 allowed us to estimate that AeKir1 and AeKir2B respectively contribute to 46% and 20% of the transepithelial K(+) secretion when the tubules are bathed in a Ringer solution containing 34 mM K(+). Thus, we uncover an important role of AeKir1 and stellate cells in transepithelial K(+) transport under conditions of peritubular K(+) challenge. The physiological role of AeKir3 in intracellular membranes of both stellate and principal cells remains to be determined.

Early gene Broad complex plays a key role in regulating the immune response triggered by ecdysone in the Malpighian tubules of Drosophila melanogaster.

In insects, humoral response to injury is accomplished by the production of antimicrobial peptides (AMPs) which are secreted in the hemolymph to eliminate the pathogen. Drosophila Malpighian tubules (MTs), however, are unique immune organs that show constitutive expression of AMPs even in unchallenged conditions and the onset of immune response is developmental stage dependent. Earlier reports have shown ecdysone positively regulates immune response after pathogenic challenge however, a robust response requires prior potentiation by the hormone. Here we provide evidence to show that MTs do not require prior potentiation with ecdysone hormone for expression of AMPs and they respond to ecdysone very fast even without immune challenge, although the different AMPs Diptericin, Cecropin, Attacin, Drosocin show differential expression in response to ecdysone. We show that early gene Broad complex (BR-C) could be regulating the IMD pathway by activating Relish and physically interacting with it to activate AMPs expression. BR-C depletion from Malpighian tubules renders the flies susceptible to infection. We also show that in MTs ecdysone signaling is transduced by EcR-B1 and B2. In the absence of ecdysone signaling the IMD pathway associated genes are down regulated and activation and translocation of transcription factor Relish is also affected.

A Drosophila model identifies a critical role for zinc in mineralization for kidney stone disease.

Ectopic calcification is a driving force for a variety of diseases, including kidney stones and atherosclerosis, but initiating factors remain largely unknown. Given its importance in seemingly divergent disease processes, identifying fundamental principal actors for ectopic calcification may have broad translational significance. Here we establish a Drosophila melanogaster model for ectopic calcification by inhibiting xanthine dehydrogenase whose deficiency leads to kidney stones in humans and dogs. Micro X-ray absorption near edge spectroscopy (µXANES) synchrotron analyses revealed high enrichment of zinc in the Drosophila equivalent of kidney stones, which was also observed in human kidney stones and Randall's plaques (early calcifications seen in human kidneys thought to be the precursor for renal stones). To further test the role of zinc in driving mineralization, we inhibited zinc transporter genes in the ZnT family and observed suppression of Drosophila stone formation. Taken together, genetic, dietary, and pharmacologic interventions to lower zinc confirm a critical role for zinc in driving the process of heterogeneous nucleation that eventually leads to stone formation. Our findings open a novel perspective on the etiology of urinary stones and related diseases, which may lead to the identification of new preventive and therapeutic approaches.

Excretion of NaCl and KCl loads in mosquitoes. 2. Effects of the small molecule Kir channel modulator VU573 and its inactive analog VU342.

The effect of two small molecules VU342 and VU573 on renal functions in the yellow fever mosquito Aedes aegypti was investigated in vitro and in vivo. In isolated Malpighian tubules, VU342 (10 µM) had no effect on the transepithelial secretion of Na(+), K(+), Cl(-), and water. In contrast, 10 µM VU573 first stimulated and then inhibited the transepithelial secretion of fluid when the tubules were bathed in Na(+)-rich or K(+)-rich Ringer solution. The early stimulation was blocked by bumetanide, suggesting the transient stimulation of Na-K-2Cl cotransport, and the late inhibition of fluid secretion was consistent with the known block of AeKir1, an Aedes inward rectifier K(+) channel, by VU573. VU342 and VU573 at a hemolymph concentration of about 11 µM had no effect on the diuresis triggered by hemolymph Na(+) or K(+) loads. VU342 at a hemolymph concentration of 420 µM had no effect on the diuresis elicited by hemolymph Na(+) or K(+) loads. In contrast, the same concentration of VU573 significantly diminished the Na(+) diuresis by inhibiting the urinary excretion of Na(+), Cl(-), and water. In K(+)-loaded mosquitoes, 420 µM VU573 significantly diminished the K(+) diuresis by inhibiting the urinary excretion of K(+), Na(+), Cl(-), and water. We conclude that 1) the effects of VU573 observed in isolated Malpighian tubules are overwhelmed in vivo by the diuresis triggered with the coinjection of Na(+) and K(+) loads, and 2) at a hemolymph concentration of 420 µM VU573 affects Kir channels systemically, including those that might be involved in the release of diuretic hormones.