Wide expression of type I Na+-phosphate cotransporter 3 (NPT3/SLC17A2), a membrane potential-driven organic anion transporter

Alleviating effect of selenium-enriched Lactobacillus plantarum 6076 on dextran sulfate sodium-induced colitis and liver inflammation in mice

The aim of this study is to investigate the alleviating effect of selenium-enriched Lactobacillus plantarum (SL) 6076 on colitis and liver inflammation induced by sodium dextran sulfate (DSS) in mice and its potential molecular mechanisms. Lactobacillus plantarum (LA) was cultured for 3 generations on MRS medium containing sodium selenite to generate SL. LA (3.2 × 1011 CFU mL-1), low selenium Lactobacillus plantarum (LS) (3.9 × 1010 CFU mL-1, 0.35 mg mL-1 Se) and high selenium Lactobacillus plantarum (HS) (2.8 × 1010 CFU mL-1, 0.52 mg mL-1 Se) were continuously fed to mice for 21 d to observe their effects on DSS-induced colitis and liver inflammation in mice. The composition of gut microbiota was detected through high-throughput 16S rRNA sequencing, and inflammatory cytokines, oxidative stress parameters, and serum biochemical indicators were measured in the colon and liver using quantitative polymerase chain reaction (qPCR) and biochemical analysis methods. The results showed that SL alleviated inflammation symptoms in the colon and liver, reduced the expression of inflammatory factors in the colon and liver, regulated oxidative stress responses in the colon, downregulated NF-κB-P65 pathway factors, and altered the composition and structure of the gut microbiota. In summary, DSS-induced colitis may cause liver inflammation, and SL had a significant relieving effect on both colon and liver inflammation. The intervention effect of SL was better than that of LA, while HS was better than LS. SL had a significant alleviating effect on DSS-induced colitis, and may exert its therapeutic effect by downregulating NF-κB-P65 signaling pathways and regulating the structure of intestinal microbiota. This study provides a new approach for the treatment of colitis.

Substrate recognition and proton coupling by a bacterial member of solute carrier family 17

The solute carrier 17 family transports diverse organic anions using two distinct modes of coupling to a source of energy. Transporters that package glutamate and nucleotide into secretory vesicles for regulated release by exocytosis are driven by membrane potential but subject to allosteric regulation by H+ and Cl-. Other solute carrier 17 members including the lysosomal sialic acid exporter couple the flux of organic anion to cotransport of H+. To begin to understand how similar proteins can perform such different functions, we have studied Escherichia coli DgoT, a H+/galactonate cotransporter. A recent structure of DgoT showed many residues contacting D-galactonate, and we now find that they do not tolerate even conservative substitutions. In contrast, the closely related lysosomal H+/sialic acid cotransporter Sialin tolerates similar mutations, consistent with its recognition of diverse substrates with relatively low affinity. We also find that despite coupling to H+, DgoT transports more rapidly but with lower apparent affinity at high pH. Indeed, membrane potential can drive uptake, indicating electrogenic transport and suggesting a H+:galactonate stoichiometry >1. Located in a polar pocket of the N-terminal helical bundle, Asp46 and Glu133 are each required for net flux by DgoT, but the E133Q mutant exhibits robust exchange activity and rescues exchange by D46N, suggesting that these two residues operate in series to translocate protons. E133Q also shifts the pH sensitivity of exchange by DgoT, supporting a central role for the highly conserved TM4 glutamate in H+ coupling by DgoT.

Diversity of function and mechanism in a family of organic anion transporters

Originally identified as transporters for inorganic phosphate, solute carrier 17 (SLC17) family proteins subserve diverse physiological roles. The vesicular glutamate transporters (VGLUTs) package the principal excitatory neurotransmitter glutamate into synaptic vesicles (SVs). In contrast, the closely related sialic acid transporter sialin mediates the flux of sialic acid in the opposite direction, from lysosomes to the cytoplasm. The two proteins couple in different ways to the H⁺ electrochemical gradient driving force, and high-resolution structures of the Escherichia coli homolog d-galactonate transporter (DgoT) and more recently rat VGLUT2 now begin to suggest the mechanisms involved as well as the basis for substrate specificity.

Functional Characterization of the Novel and Specific Thyroid Hormone Transporter SLC17A4

Background: A recent genome-wide association study identified the SLC17A4 locus associated with circulating free thyroxine (T4) concentrations. Human SLC17A4, being widely expressed in the gastrointestinal tract, was characterized as a novel triiodothyronine (T3) and T4 transporter. However, apart from the cellular uptake of T3 and T4, transporter characteristics are currently unknown. In this study, we delineated basic transporter characteristics of this novel thyroid hormone (TH) transporter. Methods: We performed a broad range of well-established TH transport studies in COS-1 cells transiently overexpressing SLC17A4. We studied cellular TH uptake in various incubation buffers, TH efflux, and the inhibitory effects of different TH metabolites and known inhibitors of other TH transporters on SLC17A4-mediated TH transport. Finally, we determined the effect of tunicamycin, a pharmacological inhibitor of N-linked glycosylation, and targeted mutations in Asn residues on SLC17A4 function. Results: SLC17A4 induced the cellular uptake of T3 and T4 by ∼4 times, and of reverse (r)T3 by 1.5 times over control cells. The uptake of T4 by SLC17A4 was Na⁺ and Cl^- independent, stimulated by low extracellular pH, and reduced by various iodothyronines and metabolites thereof, particularly those that contain at least three iodine moieties irrespective of the presence of modification at the alanine side chain. None of the classical TH transporter inhibitors studied attenuated SLC17A4-mediated TH transport. SLC17A4 also facilitates the efflux of T3 and T4, and to a lesser extent of 3,3'-diiodothyronine (T2). Immunoblot studies on lysates of transfected cells cultured in absence or presence of tunicamycin indicated that SLC17A4 is subject to N-linked glycosylation. Complementary mutational studies identified Asn66, Asn75, and Asn90, which are located in extracellular loop 1, as primary targets. Conclusions: Our studies show that SLC17A4 facilitates the transport of T3 and T4, and less efficiently rT3 and 3,3'-T2. Further studies should reveal the physiological role of SLC17A4 in TH regulation.

Vesicular Glutamate Transporters (SLCA17 A6, 7, 8) Control Synaptic Phosphate Levels

Vesicular glutamate transporters (VGLUTs) fill synaptic vesicles with glutamate. VGLUTs were originally identified as sodium-dependent transporters of inorganic phosphate (Pi), but the physiological relevance of this activity remains unclear. Heterologous expression of all three VGLUTs greatly augments intracellular Pi levels. Using neuronal models, we show that translocation of VGLUTs to the plasma membrane during exocytosis results in highly increased Pi uptake. VGLUT-mediated Pi influx is counteracted by Pi efflux. Synaptosomes prepared from perinatal VGLUT2^-/- mice that are virtually free of VGLUTs show drastically reduced cytosolic Pi levels and fail to import Pi. Glutamate partially competes with sodium (Na⁺)/Pi (NaPi)-uptake mediated by VGLUTs but does not appear to be transported. A nanobody that blocks glutamate transport by binding to the cytoplasmic domain of VGLUT1 abolishes Pi transport when co-expressed with VGLUT1. We conclude that VGLUTs have a dual function that is essential for both vesicular glutamate loading and Pi restoration in neurons.

Preparation, characterization, and in vivo evaluation of anti-inflammatory activities of selenium nanoparticles synthesized by Kluyveromyces lactis GG799

Selenium (Se) is an essential micronutrient that has implications in human diseases, including inflammatory bowel disease (IBD), especially with respect to Se deficiencies. Recently, selenium nanoparticles (SeNPs) have attracted significant attention due to their diversity of biological activities and unique advantages including low toxicity and high biological availability. In this study, an eco-friendly, efficient and low-cost method for synthesis of SeNPs by Kluyveromyces lactis GG799 (K. lactis GG799) was established, and the SeNPs were investigated for their physicochemical properties and anti-inflammatory activities in vivo. K. lactis GG799 was able to successfully transform sodium selenite into bright-red SeNPs with particle sizes of 80 and 150 nm and the nanoparticles accumulated intracellularly. Upon isolation, the SeNPs were found to be mainly capped by proteins and polysaccharides by components analysis. Dietary supplementation with 0.6 mg kg-1 Se (in the form of biogenic SeNPs) effectively attenuated dextran sulphate sodium (DSS)-induced ulcerative colitis (UC) in mice by alleviating oxidative stress and intestinal inflammation. These findings suggested that SeNPs synthesized by K. lactis GG799 may be a promising and safe Se supplement for the prevention and treatment of IBD.

Functional characterization and tissue localization of the facilitative glucose transporter GLUT12

Facilitative glucose transporters (GLUTs) play crucial roles in glucose utilization and homeostasis. GLUT12 was initially isolated as a novel GLUT4-like transporter involved in insulin-dependent glucose transport. However, tissue distribution and biochemical properties of GLUT12 are not well understood. In this study, we investigated the basic kinetic properties and tissue distribution of GLUT12. Human GLUT12 and GLUT1 were overexpressed and purified using Ni-NTA column chromatography. Reconstituted proteoliposomes showed time-dependent d-glucose transport activity, which was inhibited by phloretin and dehydroascorbate. Dose dependence of glucose transport revealed a KM and Vmax values of 6.4 mM and 1.2 μmol/mg/min, respectively, indicating that GLUT12 is a high-affinity type GLUT. Glucose transport by GLUT12 was inhibited by ATP and glucose-1-phosphate, glucose-6-phosphate and disaccharides (properties similar to those of GLUT1). Indirect immunohistochemistry revealed the distribution of mouse GLUT12 in the apical region of distal tubules and collecting ducts in the kidney and epithelial cells of the jejunum. In addition to these cells, GLUT12 was present in chromaffin cells in the adrenal medulla, the anterior pituitary lobe, as well as the thyroid and pyloric glands. These tissue distributions suggest a unique function of GLUT12, besides that of an insulin-dependent glucose transport.

Maternal organic selenium supplementation during gestation improves the antioxidant capacity and reduces the inflammation level in the intestine of offspring through the NF-κB and ERK/Beclin-1 pathways

Selenium (Se) is postulated to protect against inflammation in the gut by attenuating oxidative stress. This study was conducted to investigate the effects of maternal 2-hydroxy-4-methylselenobutanoic acid (HMSeBA), an organic Se source, on the intestinal antioxidant capacity and inflammation level of the offspring and its possible mechanism. Forty-three sows were randomly assigned to receive one of the following three diets during gestation: control diet, sodium selenite (Na₂SeO₃) supplemented diet or HMSeBA supplemented diet, respectively. Samples were collected from the offspring at birth and weaning. The results showed that maternal HMSeBA supplementation significantly upregulated ileal GPX2 and SePP1 gene expression compared with the control and Na₂SeO₃ groups, while suppressed the expression of ileal IL-1β, IL-6 and NF-κB genes in newborn piglets compared with the control group. Moreover, maternal HMSeBA supplementation significantly increased the protein of ileal GPX2 and p-mTOR compared with the control and Na₂SeO₃ groups, but decreased the ileal p-NF-κB, Beclin-1 and p-ERK proteins in newborn piglets compared with the control group. The weaned piglets of the HMSeBA group had lower serum IL-1β and IL-6 than the piglets of the control group at 2 h of LPS challenge. In addition, after the LPS challenge, the HMSeBA group had a lower relative abundance of ileal p-NF-κB and Beclin-1 proteins than the control and Na₂SeO₃ groups. In conclusion, maternal HMSeBA supplementation during gestation can improve the offspring's intestinal antioxidant capacity and reduce the inflammation level by suppressing NF-κB and ERK/Beclin-1 signaling.

Functional and Biochemical Consequences of Disease Variants in Neurotransmitter Transporters: A Special Emphasis on Folding and Trafficking Deficits

Neurotransmitters, such as γ-aminobutyric acid, glutamate, acetyl choline, glycine and the monoamines, facilitate the crosstalk within the central nervous system. The designated neurotransmitter transporters (NTTs) both release and take up neurotransmitters to and from the synaptic cleft. NTT dysfunction can lead to severe pathophysiological consequences, e.g. epilepsy, intellectual disability, or Parkinson’s disease. Genetic point mutations in NTTs have recently been associated with the onset of various neurological disorders. Some of these mutations trigger folding defects in the NTT proteins. Correct folding is a prerequisite for the export of NTTs from the endoplasmic reticulum (ER) and the subsequent trafficking to their pertinent site of action, typically at the plasma membrane. Recent studies have uncovered some of the key features in the molecular machinery responsible for transporter protein folding, e.g., the role of heat shock proteins in fine-tuning the ER quality control mechanisms in cells. The therapeutic significance of understanding these events is apparent from the rising number of reports, which directly link different pathological conditions to NTT misfolding. For instance, folding-deficient variants of the human transporters for dopamine or GABA lead to infantile parkinsonism/dystonia and epilepsy, respectively. From a therapeutic point of view, some folding-deficient NTTs are amenable to functional rescue by small molecules, known as chemical and pharmacological chaperones.

Selenium-rich maize modulates the expression of prostaglandin genes in lipopolysaccharide-stimulated RAW264.7 macrophages

Cell signaling is necessary for the organs to co-ordinate with the whole body and it includes response to external stimuli, inflammation, hormonal secretions and other various metabolic functions. In the present study, we have focused on the inflammatory signals modulated by the reactive oxygen and nitrogen species (RONS). Under homeostatic conditions, these species turn on the COX-1-dependent arachidonic acid (AA) pathway towards the release of anti-inflammatory enzymes. However, the excess release of these ions induces negative effects in the form of inflammation by turning on the COX-2-dependent AA pathway to release pro-inflammatory enzymes. In the present study, we observed the shunting of the COX-2-dependent AA pathway towards the release of anti-inflammatory enzymes with the supplementation of organic dietary selenium in the form of seleniferous maize extracts. We observed that 500 nM selenium concentration in Se-maize extracts downregulated the COX-2 and mPGES-1 expressions by 3.8- and 3.2-fold and upregulated the GPx-1 and H-PGDS expressions by 5.0- and 5.4-fold, respectively. To facilitate more availability of Se from the dietary matrices, Se-maize extracts were incubated with rMETase. It was observed that the enzyme-treated cells increased the downregulation of COX-2 and mPGES-1 expressions by 24.8- and 21.0-fold and the upregulation of GPx-1 and H-PGDS expressions by 13.2- and 16.5-fold, respectively.

Tissue-Wide Gene Expression Analysis of Sodium/Phosphate Co-Transporters in Pigs

Sodium/phosphate co-transporters are considered to be important mediators of phosphorus (P) homeostasis. The expression of specific sodium/phosphate co-transporters is routinely used as an immediate response to dietary interventions in different species. However, a general understanding of their tissue-specificity is required to elucidate their particular contribution to P homeostasis. In this study, the tissue-wide gene expression status of all currently annotated sodium/phosphate co-transporters were investigated in two pig trials focusing on a standard commercial diet (trial 1) or divergent P-containing diets (trial 2). A wide range of tissues including the gastrointestinal tract (stomach, duodenum, jejunum, ileum, caecum, and colon), kidney, liver, bone, muscle, lung, and aorta were analyzed. Both trials showed consistent patterns in the overall tissue-specific expression of P transporters. While SLC34A2 was considered as the most important intestinal P transporter in other species including humans, SLC34A3 appeared to be the most prominent intestinal P transporter in pigs. In addition, the P transporters of the SLC17 family showed basal expression in the pig intestine and might have a contribution to P homeostasis. The expression patterns observed in the distal colon provide evidence that the large intestine may also be relevant for intestinal P absorption. A low dietary P supply induced higher expressions of SLC20A1, SLC20A2, SLC34A1, and SLC34A3 in the kidney cortex. The results suggest that the expression of genes encoding transcellular P transporters is tissue-specific and responsive to dietary P supply, while underlying regulatory mechanisms require further analyses.

Selenium deficiency induces splenic growth retardation by deactivating the IGF-1R/PI3K/Akt/mTOR pathway

Selenium (Se) deficiency impairs the development and function of immune system in human beings and animals. We investigated the effect and molecular mechanism of Se deficiency on spleen development in chicken. The concentration of Se in blood and spleen, the spleen weight and splenocyte number, the histological characteristics of spleen, the concentration of growth factors in serum, the transcription level of growth factor receptor gene and the activity of growth and proliferation pathway in spleen were investigated. We found that the growth of the spleen and the splenocyte number were significantly lower in the chicken fed with Se-deficient diet for 21 and 35 days. The ELISA and qRT-PCR results showed that the serum IGF-I concentration and the transcription level of IGF1R gene in spleen were significantly lower in the SD group. The Western blotting and immunohistochemistry results showed that Se deficiency could deactivate the PI3K/Akt/mTOR pathway in spleen. In summary, the results indicated that Se deficiency decreases the growth rate of spleen and the number of splenic lymphocytes by deactivating the IGF-1R/PI3K/Akt/mTOR pathway.

Preparation and characterization of selenium enriched-Bifidobacterium longum DD98, and its repairing effects on antibiotic-induced intestinal dysbacteriosis in mice

The aim of this study was to investigate the characteristics of a novel selenium-enriched Bifidobacterium longum DD98 (Se-B. longum DD98) supplement food and its repairing effects on the intestinal ecology of mammals. We assessed the growth, Se accumulation, and Se biotransformation of B. longum DD98 and its effects on antibiotic-induced intestinal dysbacteriosis in mice. The viable bacterial count at the end of fermentation was not significantly affected by the presence of Se. Bifidobacterium longum DD98 took up inorganic Se from the medium and biotransformed it into Se-containing proteins and selenoamino acids. The dominant Se species was selenomethionine (SeMet), which comprised 87% of the total Se in Se-B. longum DD98. Furthermore, Se-B. longum DD98 showed better regulation of the disrupted intestinal microbiota back to normal levels and repaired damaged colon tissues compared to the natural recovery and B. longum DD98 treatments. These findings suggest that B. longum DD98 efficiently biotransformed inorganic Se into more bioactive organic Se forms and may have therapeutic potential for the restoration of antibiotic-induced intestinal dysbacteriosis.

The SLC22 Transporter Family: A Paradigm for the Impact of Drug Transporters on Metabolic Pathways, Signaling, and Disease

The SLC22 transporter family consists of more than two dozen members, which are expressed in the kidney, the liver, and other tissues. Evolutionary analysis indicates that SLC22 transporters fall into at least six subfamilies: OAT (organic anion transporter), OAT-like, OAT-related, OCT (organic cation transporter), OCTN (organic cation/carnitine transporter), and OCT/OCTN-related. Some-including OAT1 [SLC22A6 or NKT (novel kidney transporter)] and OAT3 (SLC22A8), as well as OCT1 (SLC22A1) and OCT2 (SLC22A2)-are widely studied drug transporters. Nevertheless, analyses of knockout mice and other data indicate that SLC22 transporters regulate key metabolic pathways and levels of signaling molecules (e.g., gut microbiome products, bile acids, tricarboxylic acid cycle intermediates, dietary flavonoids and other nutrients, prostaglandins, vitamins, short-chain fatty acids, urate, and ergothioneine), as well as uremic toxins associated with chronic kidney disease. Certain SLC22 transporters-such as URAT1 (SLC22A12) and OCTN2 (SLC22A5)-are mutated in inherited metabolic diseases. A new systems biology view of transporters is emerging. As proposed in the remote sensing and signaling hypothesis, SLC22 transporters, together with other SLC and ABC transporters, have key roles in interorgan and interorganism small-molecule communication and, together with the neuroendocrine, growth factor-cytokine, and other homeostatic systems, regulate local and whole-body homeostasis.

Link between the unfolded protein response and dysregulation of mitochondrial bioenergetics in Alzheimer's disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder affecting more than 47.5 million people worldwide. Metabolic impairments are common hallmarks of AD, and amyloid-β (Aβ) peptide and hyperphosphorylated tau protein—the two foremost histopathological signs of AD—have been implicated in mitochondrial dysfunction. Many neurodegenerative disorders, including AD, show excessive amounts of mis-/unfolded proteins leading to an activation of the unfolded protein response (UPR). In the present study, we aimed to characterize the link between ER stress and bioenergetics defects under normal condition (human SH-SY5Y neuroblastoma cells: control cells) or under pathological AD condition [SH-SY5Y cells overexpressing either the human amyloid precursor protein (APP) or mutant tau (P301L)]. More specifically, we measured UPR gene expression, cell viability, and bioenergetics parameters, such as ATP production and mitochondrial membrane potential (MMP) in basal condition and after an induced ER stress by thapsigargin. We detected highly activated UPR and dysregulated bioenergetics in basal condition in both AD cellular models. Strikingly, acute-induced ER stress increased the activity of the UPR in both AD cellular models, leading to up-regulation of apoptotic pathways, and further dysregulated mitochondrial function.

Locus 5p13.1 may be associated with the selection of cancer-related HBV core promoter mutations

Background: The basal core promoter (BCP) double mutations (A1762T and G1764A) of hepatitis B virus (HBV) have been reported to be an aetiological factor of hepatocellular carcinoma (HCC). What distinguishes the subset of HBV carriers in whom these mutations are selected? Methods: A genome-wide association study (GWAS) was carried out on 218 asymptomatic HBsAg carriers infected with HBV with BCP double mutations and 191 controls infected with HBV with the wild type BCP. The highest ranking nucleotide polymorphisms (SNPs) were validated with other study subjects, 203 cases and 181 controls. The expression of the gene nearest a SNP found to be significant was examined using RT-PCR. Results: Forty-five candidate SNPs were identified in the GWAS. Three SNPs were found to be associated with the selection of HBV BCP double mutations in the replication stage, including rs7717457 at 5p13.1, rs670011 at 17q21.2, rs2071611 at 6p22.2. Especially, rs7717457 (P= 4.57×10^-5 combined P) reached the potential GWAS significance level. The expression of gene complement component 7 (C7), nearest to SNP rs7717457, differed significantly between the case and control groups (t=2.045, P=0.04), suggesting that SNP rs7717457 was associated with the expression of its nearest gene. Conclusions: SNP rs7717457 is associated with the selection of HBV BCP double mutations, providing an important clue to understanding the mechanisms of oncogenesis of HBV BCP double mutations.

Chemical glycomics enrichment: imaging the recycling of sialic acid in living cells

The development of metabolic oligosaccharide engineering (MOE) over the past two decades enabled the bioimaging studies of glycosylation processes in physio-pathological contexts. Herein, we successfully applied the chemical reporter strategy to image the fate of sialylated glycoconjugates in healthy and sialin-deficient patient fibroblasts. This chemical glycomics enrichment is a powerful tool for tracking sialylated glycoconjugates and probing lysosomal recycling capacities. Thus, such strategies appear fundamental for the characterization of lysosomal storage diseases.

Genetic variants in two pathways influence serum urate levels and gout risk: a systematic pathway analysis

The aims of this study were to identify candidate pathways associated with serum urate and to explore the genetic effect of those pathways on the risk of gout. Pathway analysis of the loci identified in genome-wide association studies (GWASs) showed that the ion transmembrane transporter activity pathway (GO: 0015075) and the secondary active transmembrane transporter activity pathway (GO: 0015291) were both associated with serum urate concentrations, with P_FDR values of 0.004 and 0.007, respectively. In a Chinese population of 4,332 individuals, the two pathways were also found to be associated with serum urate (P_FDR = 1.88E-05 and 3.44E-04, separately). In addition, these two pathways were further associated with the pathogenesis of gout (P_FDR = 1.08E-08 and 2.66E-03, respectively) in the Chinese population and a novel gout-associated gene, SLC17A2, was identified (OR = 0.83, P_FDR = 0.017). The mRNA expression of candidate genes also showed significant differences among different groups at pathway level. The present study identified two transmembrane transporter activity pathways (GO: 0015075 and GO: 0015291) were associations with serum urate concentrations and the risk of gout. SLC17A2 was identified as a novel gene that influenced the risk of gout.

Selenium deficiency induces duodenal villi cell apoptosis via an oxidative stress-induced mitochondrial apoptosis pathway and an inflammatory signaling-induced death receptor pathway

Selenium is an important nutritional trace element possessing antioxidant and anti-apoptotic properties in intestinal.

Clodronate: A Vesicular ATP Release Blocker

Clodronate is a first-generation bisphosphonate used worldwide for antiresorptive therapy for osteoporosis. Although clodronate is analgesic in nature, its mechanism and efficacy were unknown for some time. Recently, clodronate was identified as a selective and potent inhibitor for vesicular nucleotide transporter (VNUT), a transporter responsible for vesicular storage of ATP. Clodronate inhibits vesicular ATP release from neurons and reduces chronic neuropathic and inflammatory pain following blockade of purinergic chemical transmission. Its effectiveness is stronger, faster acting, and longer lasting than that of existing drugs such as pregabalin. Thus, clodronate might be a promising drug for attenuating chronic neuropathic pain and opens a new field of drug discovery as a presynaptic blocker for purinergic chemical transmission.

Vesicular nucleotide transporter (VNUT): appearance of an actress on the stage of purinergic signaling

Vesicular storage of ATP is one of the processes initiating purinergic chemical transmission. Although an active transport mechanism was postulated to be involved in the processes, a transporter(s) responsible for the vesicular storage of ATP remained unidentified for some time. In 2008, SLC17A9, the last identified member of the solute carrier 17 type I inorganic phosphate transporter family, was found to encode the vesicular nucleotide transporter (VNUT) that is responsible for the vesicular storage of ATP. VNUT transports various nucleotides in a membrane potential-dependent fashion and is expressed in the various ATP-secreting cells. Mice with knockout of the VNUT gene lose vesicular storage and release of ATP from neurons and neuroendocrine cells, resulting in blockage of the initiation of purinergic chemical transmission. Thus, VNUT plays an essential role in the vesicular storage and release of ATP. The VNUT knockout mice exhibit resistance for neuropathic pain and a therapeutic effect against diabetes by way of increased insulin sensitivity. Thus, VNUT inhibitors and suppression of VNUT gene expression may be used for therapeutic purposes through suppression of purinergic chemical transmission. This review summarizes the studies to date on VNUT and discusses what we have learned about the relevance of vesicular ATP release as a potential drug target.