A microfluidic chip-based capillary zone electrophoresis-mass spectrometry method for measuring adenosine 5'-Triphosphate and its similar nucleotide analogues.

BACKGROUND: Extracellular ATP is involved in disorders that cause inflammation of the airways and cough, thus limiting its release has therapeutic benefits. Standard luminescence-based ATP assays measure levels indirectly through enzyme degradation and do not provide a simultaneous readout for other nucleotide analogues. Conversely, mass spectrometry can provide direct ATP measurements, however, common RPLC and HILIC methods face issues because these molecules are unstable, metal-sensitive analytes which are often poorly retained. These difficulties have traditionally been overcome using passivation or ion-pairing chromatography, but these approaches can be problematic for LC systems. As a result, more effective analytical methods are needed. RESULTS: Here, we introduce a new application that uses microfluidic chip-based capillary zone electrophoresis-mass spectrometry (µCZE-MS) to measure ATP and its analogues simultaneously in biofluids. The commercially available ZipChip Interface and a High-Resolution Bare-glass microchip (ZipChip, HRB, 908 Devices Inc.) coupled to a Thermo Scientific Tribrid Orbitrap, were successfully used to separate and detect various nucleotide standards, as well as ATP, ADP, AMP, and adenosine in plasma and BALF obtained from naïve Brown Norway rats. The findings demonstrate that this approach can rapidly and directly detect ATP and its related nucleotide analogues, while also highlighting the need to preserve these molecules in biofluids with chelators like EDTA. In addition, we demonstrate that this µCZE-MS method is also suitable for detecting a variety of metabolites, revealing additional potential future applications. SIGNIFICANCE: This innovative µCZE-MS approach provides a robust new tool to directly measure ATP and other nucleotide analogues in biofluids. This can enable the study of eATP in human disease and potentially contribute to the creation of ATP-targeting therapies for airway illnesses.

Multiomics Characterization of a Less Invasive Microfluidic-Based Cell Sorting Technique.

Fluorescence-activated cell sorting (FACS) is a specialized technique to isolate specific cell subpopulations with a high level of recovery and accuracy. However, the cell sorting procedure can impact the viability and metabolic state of cells. Here, we performed a comparative study and evaluated the impact of traditional high-pressure charged droplet-based and microfluidic chip-based sorting on the metabolic and phosphoproteomic profile of different cell types. While microfluidic chip-based sorted cells more closely resembled the unsorted control group for most cell types tested, the droplet-based sorted cells showed significant metabolic and phosphoproteomic alterations. In particular, greater changes in redox and energy status were present in cells sorted with the droplet-based cell sorter along with larger shifts in proteostasis. 13C-isotope tracing analysis on cells recovering postsorting revealed that the sorter-induced suppression of mitochondrial TCA cycle activity recovered faster in the microfluidic chip-based sorted group. Apart from this, amino acid and lipid biosynthesis pathways were suppressed in sorted cells, with minimum impact and faster recovery in the microfluidic chip-based sorted group. These results indicate microfluidic chip-based sorting has a minimum impact on metabolism and is less disruptive compared to droplet-based sorting.

Effects of protein-coding variants on blood metabolite measurements and clinical biomarkers in the UK Biobank.

Genome-wide association studies (GWASs) have established the contribution of common and low-frequency variants to metabolic blood measurements in the UK Biobank (UKB). To complement existing GWAS findings, we assessed the contribution of rare protein-coding variants in relation to 355 metabolic blood measurements-including 325 predominantly lipid-related nuclear magnetic resonance (NMR)-derived blood metabolite measurements (Nightingale Health Plc) and 30 clinical blood biomarkers-using 412,393 exome sequences from four genetically diverse ancestries in the UKB. Gene-level collapsing analyses were conducted to evaluate a diverse range of rare-variant architectures for the metabolic blood measurements. Altogether, we identified significant associations (p < 1 × 10-8) for 205 distinct genes that involved 1,968 significant relationships for the Nightingale blood metabolite measurements and 331 for the clinical blood biomarkers. These include associations for rare non-synonymous variants in PLIN1 and CREB3L3 with lipid metabolite measurements and SYT7 with creatinine, among others, which may not only provide insights into novel biology but also deepen our understanding of established disease mechanisms. Of the study-wide significant clinical biomarker associations, 40% were not previously detected on analyzing coding variants in a GWAS in the same cohort, reinforcing the importance of studying rare variation to fully understand the genetic architecture of metabolic blood measurements.

A microbiome-dependent gut-brain pathway regulates motivation for exercise.

Exercise exerts a wide range of beneficial effects for healthy physiology1. However, the mechanisms regulating an individual's motivation to engage in physical activity remain incompletely understood. An important factor stimulating the engagement in both competitive and recreational exercise is the motivating pleasure derived from prolonged physical activity, which is triggered by exercise-induced neurochemical changes in the brain. Here, we report on the discovery of a gut-brain connection in mice that enhances exercise performance by augmenting dopamine signalling during physical activity. We find that microbiome-dependent production of endocannabinoid metabolites in the gut stimulates the activity of TRPV1-expressing sensory neurons and thereby elevates dopamine levels in the ventral striatum during exercise. Stimulation of this pathway improves running performance, whereas microbiome depletion, peripheral endocannabinoid receptor inhibition, ablation of spinal afferent neurons or dopamine blockade abrogate exercise capacity. These findings indicate that the rewarding properties of exercise are influenced by gut-derived interoceptive circuits and provide a microbiome-dependent explanation for interindividual variability in exercise performance. Our study also suggests that interoceptomimetic molecules that stimulate the transmission of gut-derived signals to the brain may enhance the motivation for exercise.

TLCD1 and TLCD2 regulate cellular phosphatidylethanolamine composition and promote the progression of non-alcoholic steatohepatitis.

The fatty acid composition of phosphatidylethanolamine (PE) determines cellular metabolism, oxidative stress, and inflammation. However, our understanding of how cells regulate PE composition is limited. Here, we identify a genetic locus on mouse chromosome 11, containing two poorly characterized genes Tlcd1 and Tlcd2, that strongly influences PE composition. We generated Tlcd1/2 double-knockout (DKO) mice and found that they have reduced levels of hepatic monounsaturated fatty acid (MUFA)-containing PE species. Mechanistically, TLCD1/2 proteins act cell intrinsically to promote the incorporation of MUFAs into PEs. Furthermore, TLCD1/2 interact with the mitochondria in an evolutionarily conserved manner and regulate mitochondrial PE composition. Lastly, we demonstrate the biological relevance of our findings in dietary models of metabolic disease, where Tlcd1/2 DKO mice display attenuated development of non-alcoholic steatohepatitis compared to controls. Overall, we identify TLCD1/2 proteins as key regulators of cellular PE composition, with our findings having broad implications in understanding and treating disease.

The aryl hydrocarbon receptor activates ceramide biosynthesis in mice contributing to hepatic lipogenesis.

Aryl hydrocarbon receptor (AHR) activation via 2,3,7,8-tetrachlorodibenzofuran (TCDF) induces the accumulation of hepatic lipids. Here we report that AHR activation by TCDF (24  µg/kg body weight given orally for five days) induced significant elevation of hepatic lipids including ceramides in mice, was associated with increased expression of key ceramide biosynthetic genes, and increased activity of their respective enzymes. Results from chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay (EMSA) and cell-based reporter luciferase assays indicated that AHR directly activated the serine palmitoyltransferase long chain base subunit 2 (Sptlc2, encodes serine palmitoyltransferase 2 (SPT2)) gene whose product catalyzes the initial rate-limiting step in de novo sphingolipid biosynthesis. Hepatic ceramide accumulation was further confirmed by mass spectrometry-based lipidomics. Taken together, our results revealed that AHR activation results in the up-regulation of Sptlc2, leading to ceramide accumulation, thus promoting lipogenesis, which can induce hepatic lipid accumulation.

Artemisinin-resistant K13 mutations rewire Plasmodium falciparum's intra-erythrocytic metabolic program to enhance survival.

The emergence and spread of artemisinin resistance, driven by mutations in Plasmodium falciparum K13, has compromised antimalarial efficacy and threatens the global malaria elimination campaign. By applying systems-based quantitative transcriptomics, proteomics, and metabolomics to a panel of isogenic K13 mutant or wild-type P. falciparum lines, we provide evidence that K13 mutations alter multiple aspects of the parasite's intra-erythrocytic developmental program. These changes impact cell-cycle periodicity, the unfolded protein response, protein degradation, vesicular trafficking, and mitochondrial metabolism. K13-mediated artemisinin resistance in the Cambodian Cam3.II line was reversed by atovaquone, a mitochondrial electron transport chain inhibitor. These results suggest that mitochondrial processes including damage sensing and anti-oxidant properties might augment the ability of mutant K13 to protect P. falciparum against artemisinin action by helping these parasites undergo temporary quiescence and accelerated growth recovery post drug elimination.

Quantitative Analysis of Bile Acid with UHPLC-MS/MS.

Bile acids are important end products of cholesterol metabolism, having been shown to serve as signaling molecules and intermediates between the host and the gut microbiota. Here we describe a robust and accurate method using ultrahigh-pressure liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) for the quantification of bile acids in stool/cecal and tissue samples.

Increased circulation time of Plasmodium falciparum underlies persistent asymptomatic infection in the dry season.

The dry season is a major challenge for Plasmodium falciparum parasites in many malaria endemic regions, where water availability limits mosquito vectors to only part of the year. How P. falciparum bridges two transmission seasons months apart, without being cleared by the human host or compromising host survival, is poorly understood. Here we show that low levels of P. falciparum parasites persist in the blood of asymptomatic Malian individuals during the 5- to 6-month dry season, rarely causing symptoms and minimally affecting the host immune response. Parasites isolated during the dry season are transcriptionally distinct from those of individuals with febrile malaria in the transmission season, coinciding with longer circulation within each replicative cycle of parasitized erythrocytes without adhering to the vascular endothelium. Low parasite levels during the dry season are not due to impaired replication but rather to increased splenic clearance of longer-circulating infected erythrocytes, which likely maintain parasitemias below clinical and immunological radar. We propose that P. falciparum virulence in areas of seasonal malaria transmission is regulated so that the parasite decreases its endothelial binding capacity, allowing increased splenic clearance and enabling several months of subclinical parasite persistence.

Impact of Facultative Bacteria on the Metabolic Function of an Obligate Insect-Bacterial Symbiosis.

Beneficial microorganisms associated with animals derive their nutritional requirements entirely from the animal host, but the impact of these microorganisms on host metabolism is largely unknown. The focus of this study was the experimentally tractable tripartite symbiosis between the pea aphid Acyrthosiphon pisum, its obligate intracellular bacterial symbiont Buchnera, and the facultative bacterium Hamiltonella which is localized primarily to the aphid hemolymph (blood). Metabolome experiments on, first, multiple aphid genotypes that naturally bear or lack Hamiltonella and, second, one aphid genotype from which Hamiltonella was experimentally eliminated revealed no significant effects of Hamiltonella on aphid metabolite profiles, indicating that Hamiltonella does not cause major reconfiguration of host metabolism. However, the titer of just one metabolite, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), displayed near-significant enrichment in Hamiltonella-positive aphids in both metabolome experiments. AICAR is a by-product of biosynthesis of the essential amino acid histidine in Buchnera and, hence, an index of histidine biosynthetic rates, suggesting that Buchnera-mediated histidine production is elevated in Hamiltonella-bearing aphids. Consistent with this prediction, aphids fed on [13C]histidine yielded a significantly elevated 12C/13C ratio of histidine in Hamiltonella-bearing aphids, indicative of increased (∼25%) histidine synthesized de novo by Buchnera However, in silico analysis predicted an increase of only 0.8% in Buchnera histidine synthesis in Hamiltonella-bearing aphids. We hypothesize that Hamiltonella imposes increased host demand for histidine, possibly for heightened immune-related functions. These results demonstrate that facultative bacteria can alter the dynamics of host metabolic interactions with co-occurring microorganisms, even when the overall metabolic homeostasis of the host is not substantially perturbed.IMPORTANCE Although microbial colonization of the internal tissues of animals generally causes septicemia and death, various animals are persistently associated with benign or beneficial microorganisms in their blood or internal organs. The metabolic consequences of these persistent associations for the animal host are largely unknown. Our research on the facultative bacterium Hamiltonella, localized primarily to the hemolymph of pea aphids, demonstrated that although Hamiltonella imposed no major reconfiguration of the aphid metabolome, it did alter the metabolic relations between the aphid and its obligate intracellular symbiont, Buchnera Specifically, Buchnera produced more histidine in Hamiltonella-positive aphids to support both Hamiltonella demand for histidine and Hamiltonella-induced increase in host demand. This study demonstrates how microorganisms associated with internal tissues of animals can influence specific aspects of metabolic interactions between the animal host and co-occurring microorganisms.

The microbiome modulating activity of bile acids.

Bile acids are potent antibacterial compounds and play an important role in shaping the microbial ecology of the gut. Here, we combined flow cytometry, growth rate measurements (OD600), and NMR- and mass spectrometry-based metabolomics to systematically profile the impact of bile acids on the microbiome using in vitro and in vivo models. This study confirmed that (1) unconjugated bile acids possess more potent antibacterial activity than conjugated bile acids; (2) Gram-positive bacteria are more sensitive to bile acids than Gram-negative bacteria; (3) some probiotic bacteria such as Lactobacillus and Bifidobacterium and 7α-dehydroxylating bacteria such as Clostridium scindens show bile acid resistance that is associated with activation of glycolysis. Moreover, we demonstrated that (4) as one of most hydrophobic bile acids, lithocholic acid (LCA) shows reduced toxicity to bacteria in the cecal microbiome in both in vivo and in vitro models; (5) bile acids directly and rapidly affect bacterial global metabolism including membrane damage, disrupted amino acid, nucleotide, and carbohydrate metabolism; and (6) in vivo, short-term exposure to bile acids significantly affected host metabolism via alterations of the bacterial community structure. This study systematically profiled interactions between bile acids and gut bacteria providing validation of previous observation and new insights into the interaction of bile acids with the microbiome and mechanisms related to bile acid tolerance.

Antimalarial pantothenamide metabolites target acetyl-coenzyme A biosynthesis in Plasmodium falciparum.

Malaria eradication is critically dependent on new therapeutics that target resistant Plasmodium parasites and block transmission of the disease. Here, we report that pantothenamide bioisosteres were active against blood-stage Plasmodium falciparum parasites and also blocked transmission of sexual stages to the mosquito vector. These compounds were resistant to degradation by serum pantetheinases, showed favorable pharmacokinetic properties, and cleared parasites in a humanized mouse model of P. falciparum infection. Metabolomics revealed that coenzyme A biosynthetic enzymes converted pantothenamides into coenzyme A analogs that interfered with parasite acetyl-coenzyme A anabolism. Resistant parasites generated in vitro showed mutations in acetyl-coenzyme A synthetase and acyl-coenzyme A synthetase 11. Introduction and reversion of these mutations in P. falciparum using CRISPR-Cas9 gene editing confirmed the roles of these enzymes in the sensitivity of the malaria parasites to pantothenamides. These pantothenamide compounds with a new mode of action may have potential as drugs against malaria parasites.

Erwinia amylovora Auxotrophic Mutant Exometabolomics and Virulence on Apples.

The Gram-negative bacterium Erwinia amylovora causes fire blight disease of apples and pears. While the virulence systems of E. amylovora have been studied extensively, relatively little is known about its parasitic behavior. The aim of this study was to identify primary metabolites that must be synthesized by this pathogen for full virulence. A series of auxotrophic E. amylovora mutants, representing 21 metabolic pathways, were isolated and characterized for metabolic defects and virulence in apple immature fruits and shoots. On detached apple fruitlets, mutants defective in arginine, guanine, hexosamine, isoleucine/valine, leucine, lysine, proline, purine, pyrimidine, sorbitol, threonine, tryptophan, and glucose metabolism had reduced virulence compared to the wild type, while mutants defective in asparagine, cysteine, glutamic acid, histidine, and serine biosynthesis were as virulent as the wild type. Auxotrophic mutant growth in apple fruitlet medium had a modest positive correlation with virulence in apple fruitlet tissues. Apple tree shoot inoculations with a representative subset of auxotrophs confirmed the apple fruitlet results. Compared to the wild type, auxotrophs defective in virulence caused an attenuated hypersensitive immune response in tobacco, with the exception of an arginine auxotroph. Metabolomic footprint analyses revealed that auxotrophic mutants which grew poorly in fruitlet medium nevertheless depleted environmental resources. Pretreatment of apple flowers with an arginine auxotroph inhibited the growth of the wild-type E. amylovora, while heat-killed auxotroph cells did not exhibit this effect, suggesting nutritional competition with the virulent strain on flowers. The results of our study suggest that certain nonpathogenic E. amylovora auxotrophs could have utility as fire blight biocontrol agents.IMPORTANCE This study has revealed the availability of a range of host metabolites to E. amylovora cells growing in apple tissues and has examined whether these metabolites are available in sufficient quantities to render bacterial de novo synthesis of these metabolites partially or even completely dispensable for disease development. The metabolomics analysis revealed that auxotrophic E. amylovora mutants have substantial impact on their environment in culture, including those that fail to grow appreciably. The reduced growth of virulent E. amylovora on flowers treated with an arginine auxotroph is consistent with the mutant competing for limiting resources in the flower environment. This information could be useful for novel fire blight management tool development, including the application of nonpathogenic E. amylovora auxotrophs to host flowers as an environmentally friendly biocontrol method. Fire blight management options are currently limited mainly to antibiotic sprays onto open blossoms and pruning of infected branches, so novel management options would be attractive to growers.

Identifying the Components of Acidosis in Patients With Severe Plasmodium falciparum Malaria Using Metabolomics.

BACKGROUND: Acidosis in severe Plasmodium falciparum malaria is associated with high mortality, yet the pathogenesis remains incompletely understood. The aim of this study was to determine the nature and source of metabolic acids contributing to acidosis in patients with severe falciparum malaria. METHODS: A prospective observational study was conducted to characterize circulating acids in adults with P. falciparum malaria (n = 107) and healthy controls (n = 45) from Bangladesh using high-resolution liquid chromatography-mass spectrometry metabolomics. Additional in vitro P. falciparum culture studies were performed to determine if parasites release the acids detected in plasma from patients with severe malaria acidosis. RESULTS: We identified previously unmeasured plasma acids strongly associated with acidosis in severe malaria. Metabolomic analysis of P. falciparum parasites in vitro showed no evidence that these acids are released by the parasite during its life cycle. Instead, 10 of the plasma acids could be mapped to a gut microbial origin. Patients with malaria had low L-citrulline levels, a plasma marker indicating reduced gut barrier integrity. Longitudinal data showed the clearance of these newly identified acids was delayed in fatal cases. CONCLUSIONS: These data suggest that a compromise in intestinal barrier function may contribute significantly to the pathogenesis of life-threatening acidosis in severe falciparum malaria. CLINICAL TRIALS REGISTRATION: NCT02451904.

Metabolomic Profiling of the Malaria Box Reveals Antimalarial Target Pathways.

The threat of widespread drug resistance to frontline antimalarials has renewed the urgency for identifying inexpensive chemotherapeutic compounds that are effective against Plasmodium falciparum, the parasite species responsible for the greatest number of malaria-related deaths worldwide. To aid in the fight against malaria, a recent extensive screening campaign has generated thousands of lead compounds with low micromolar activity against blood stage parasites. A subset of these leads has been compiled by the Medicines for Malaria Venture (MMV) into a collection of structurally diverse compounds known as the MMV Malaria Box. Currently, little is known regarding the activity of these Malaria Box compounds on parasite metabolism during intraerythrocytic development, and a majority of the targets for these drugs have yet to be defined. Here we interrogated the in vitro metabolic effects of 189 drugs (including 169 of the drug-like compounds from the Malaria Box) using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). The resulting metabolic fingerprints provide information on the parasite biochemical pathways affected by pharmacologic intervention and offer a critical blueprint for selecting and advancing lead compounds as next-generation antimalarial drugs. Our results reveal several major classes of metabolic disruption, which allow us to predict the mode of action (MoA) for many of the Malaria Box compounds. We anticipate that future combination therapies will be greatly informed by these results, allowing for the selection of appropriate drug combinations that simultaneously target multiple metabolic pathways, with the aim of eliminating malaria and forestalling the expansion of drug-resistant parasites in the field.

Calcineurin homologous proteins regulate the membrane localization and activity of sodium/proton exchangers in C. elegans.

Calcineurin B homologous proteins (CHP) are N-myristoylated, EF-hand Ca(2+)-binding proteins that bind to and regulate Na(+)/H(+) exchangers, which occurs through a variety of mechanisms whose relative significance is incompletely understood. Like mammals, Caenorhabditis elegans has three CHP paralogs, but unlike mammals, worms can survive CHP loss-of-function. However, mutants for the CHP ortholog PBO-1 are unfit, and PBO-1 has been shown to be required for proton signaling by the basolateral Na(+)/H(+) exchanger NHX-7 and for proton-coupled intestinal nutrient uptake by the apical Na(+)/H(+) exchanger NHX-2. Here, we have used this genetic model organism to interrogate PBO-1's mechanism of action. Using fluorescent tags to monitor Na(+)/H(+) exchanger trafficking and localization, we found that loss of either PBO-1 binding or activity caused NHX-7 to accumulate in late endosomes/lysosomes. In contrast, NHX-2 was stabilized at the apical membrane by a nonfunctional PBO-1 protein and was only internalized following its complete loss. Additionally, two pbo-1 paralogs were identified, and their expression patterns were analyzed. One of these contributed to the function of the excretory cell, which acts like a kidney in worms, establishing an alternative model for testing the role of this protein in membrane transporter trafficking and regulation. These results lead us to conclude that the role of CHP in Na(+)/H(+) exchanger regulation differs between apical and basolateral transporters. This further emphasizes the importance of proper targeting of Na(+)/H(+) exchangers and the critical role of CHP family proteins in this process.

Anthranilate fluorescence marks a calcium-propagated necrotic wave that promotes organismal death in C. elegans.

For cells the passage from life to death can involve a regulated, programmed transition. In contrast to cell death, the mechanisms of systemic collapse underlying organismal death remain poorly understood. Here we present evidence of a cascade of cell death involving the calpain-cathepsin necrosis pathway that can drive organismal death in Caenorhabditis elegans. We report that organismal death is accompanied by a burst of intense blue fluorescence, generated within intestinal cells by the necrotic cell death pathway. Such death fluorescence marks an anterior to posterior wave of intestinal cell death that is accompanied by cytosolic acidosis. This wave is propagated via the innexin INX-16, likely by calcium influx. Notably, inhibition of systemic necrosis can delay stress-induced death. We also identify the source of the blue fluorescence, initially present in intestinal lysosome-related organelles (gut granules), as anthranilic acid glucosyl esters--not, as previously surmised, the damage product lipofuscin. Anthranilic acid is derived from tryptophan by action of the kynurenine pathway. These findings reveal a central mechanism of organismal death in C. elegans that is related to necrotic propagation in mammals--e.g., in excitotoxicity and ischemia-induced neurodegeneration. Endogenous anthranilate fluorescence renders visible the spatio-temporal dynamics of C. elegans organismal death.

Analysis of Ca2+ signaling motifs that regulate proton signaling through the Na+/H+ exchanger NHX-7 during a rhythmic behavior in Caenorhabditis elegans.

Membrane proton transporters contribute to pH homeostasis but have also been shown to transmit information between cells in close proximity through regulated proton secretion. For example, the nematode intestinal Na(+)/H(+) exchanger NHX-7 causes adjacent muscle cells to contract by transiently acidifying the extracellular space between the intestine and muscle. NHX-7 operates during a Ca(2+)-dependent rhythmic behavior and contains several conserved motifs for regulation by Ca(2+) input, including motifs for calmodulin and phosphatidylinositol 4,5-bisphosphate binding, protein kinase C- and calmodulin-dependent protein kinase type II phosphorylation, and a binding site for calcineurin homologous protein. Here, we tested the idea that Ca(2+) input differentiates proton signaling from pH housekeeping activity. Each of these motifs was mutated, and their contribution to NHX-7 function was assessed. These functions included pH recovery from acidification in cells in culture expressing recombinant NHX-7, extracellular acidification measured during behavior in live moving worms, and muscle contraction strength as a result of this acidification. Our data suggest that multiple levels of Ca(2+) input regulate NHX-7, whose transport capacity normally exceeds the minimum necessary to cause muscle contraction. Furthermore, extracellular acidification limits NHX-7 proton transport through feedback inhibition, likely to prevent metabolic acidosis from occurring. Our findings are consistent with an integrated network whereby both Ca(2+) and pH contribute to proton signaling. Finally, our results obtained by expressing rat NHE1 in Caenorhabditis elegans suggest that a conserved mechanism of regulation may contribute to cell-cell communication or proton signaling by Na(+)/H(+) exchangers in mammals.

miR-786 regulation of a fatty-acid elongase contributes to rhythmic calcium-wave initiation in C. elegans.

BACKGROUND: Rhythmic behaviors are ubiquitous phenomena in animals. In C. elegans, defecation is an ultradian rhythmic behavior: every ∼50 s a calcium wave initiating in the posterior intestinal cells triggers the defecation motor program that comprises three sequential muscle contractions. Oscillatory calcium signaling is central to the periodicity of defecation. The posteriormost intestinal cells function as the pacemaker for this rhythmic behavior, although it is unclear how the supremacy of these cells for calcium-wave initiation is controlled. RESULTS: We describe how the loss of the mir-240/786 microRNA cluster, which results in arrhythmic defecation, causes ectopic intestinal calcium-wave initiation. mir-240/786 expression in the intestine is restricted to the posterior cells that function as the defecation pacemaker. Genetic data indicate that mir-240/786 functions upstream of the inositol 1,4,5-trisphosphate (IP(3)) receptor. Through rescue analysis, it was determined that miR-786 functions to regulate defecation. Furthermore, we identified elo-2, a fatty-acid elongase with a known role in defecation cycling, as a direct target for miR-786. We propose that the regulation of palmitate levels through repression of elo-2 activity is the likely mechanistic link to defecation. CONCLUSIONS: Together, these data indicate that miR-786 confers pacemaker status on posterior intestinal cells for the control of calcium-wave initiation through the regulation of elo-2 and, subsequently, palmitate levels. We propose that a difference in fatty-acid composition in the posterior intestinal cells may alter the activities of membrane proteins, such as IP(3)-receptor or TRPM channels, that control pacemaker activity in the C. elegans intestine.