Gut microbiota mediate early life stress-induced social dysfunction and anxiety-like behaviors by impairing amino acid transport at the gut.

Early life stress alters gut microbiota and increases the risk of neuropsychiatric disorders, including social deficits and anxiety, in the host. However, the role of gut commensal bacteria in early life stress-induced neurobehavioral abnormalities remains unclear. Using the maternally separated (MS) mice, our research has unveiled a novel aspect of this complex relationship. We discovered that the reduced levels of amino acid transporters in the intestine of MS mice led to low glutamine (Gln) levels in the blood and synaptic dysfunction in the medial prefrontal cortex (mPFC). Abnormally low blood Gln levels limit the brain's availability of Gln, which is required for presynaptic glutamate (Glu) and γ-aminobutyric acid (GABA) replenishment. Furthermore, MS resulted in gut microbiota dysbiosis characterized by a reduction in the relative abundance of Lactobacillus reuteri (L. reuteri). Notably, supplementation with L. reuteri ameliorates neurobehavioral abnormalities in MS mice by increasing intestinal amino acid transport and restoring synaptic transmission in the mPFC. In conclusion, our findings on the role of L. reuteri in regulating intestinal amino acid transport and buffering early life stress-induced behavioral abnormalities provide a novel insight into the microbiota-gut-brain signaling basis for emotional behaviors.

Improvement of plant quality by amino acid transporters: A comprehensive review.

Amino acids serve as the primary means of transport and organic nitrogen carrier in plants, playing an essential role in plant growth and development. Amino acid transporters (AATs) facilitate the movement of amino acids within plants and have been identified and characterised in a number of species. It has been demonstrated that these amino acid transporters exert an influence on the quality attributes of plants, in addition to their primary function of transporting amino acid transport. This paper presents a summary of the role of AATs in plant quality improvement. This encompasses the enhancement of nitrogen utilization efficiency, root development, tiller number and fruit yield. Concurrently, AATs can bolster the resilience of plants to pests, diseases and abiotic stresses, thereby further enhancing the yield and quality of fruit. AATs exhibit a wide range of substrate specificity, which greatly optimizes the use of pesticides and significantly reduces pesticide residues, and reduces the risk of environmental pollution while increasing the safety of fruit. The discovery of AATs function provides new ideas and ways to cultivate high-quality crop and promote changes in agricultural development, and has great potential in the application of plant quality improvement.

A LAT1-Like Amino Acid Transporter Regulates Neuronal Activity in the Drosophila Mushroom Bodies.

The proper functioning of neural circuits that integrate sensory signals is essential for individual adaptation to an ever-changing environment. Many molecules can modulate neuronal activity, including neurotransmitters, receptors, and even amino acids. Here, we ask whether amino acid transporters expressed by neurons can influence neuronal activity. We found that minidiscs (mnd), which encodes a light chain of a heterodimeric amino acid transporter, is expressed in different cell types of the adult Drosophila brain: in mushroom body neurons (MBs) and in glial cells. Using live calcium imaging, we found that MND expressed in α/ß MB neurons is essential for sensitivity to the L-amino acids: Leu, Ile, Asp, Glu, Lys, Thr, and Arg. We found that the Target Of Rapamycin (TOR) pathway but not the Glutamate Dehydrogenase (GDH) pathway is involved in the Leucine-dependent response of α/ß MB neurons. This study strongly supports the key role of MND in regulating MB activity in response to amino acids.

Methionine Source and Level Modulate Gut pH, Amino Acid Transporters and Metabolism Related Genes in Broiler Chickens.

This study determined the effects of two methionine (Met) sources at three total sulfur amino acids (TSAA) to lysine ratios (TSAA/Lys) on gut pH, digestive enzyme activity, amino acid transporter expression, and Met metabolism of broilers. The birds were randomly assigned to a 2 × 3 factorial arrangement with Met sources (dl-Met and dl-2-hydroxy-4-(methylthio)-butanoic acid (OH-Met)) and TSAA/Lys (0.58, 0.73, and 0.88) from 1 to 21 days. The results demonstrated that dl-Met and OH-Met supported the same growth performance, but high TSAA/Lys ratio reduced the feed intake and body weight (P < 0.05). OH-Met reduced the crop chyme pH and enhanced the jejunal lipase activity (P < 0.05). ATB0,+ expression decreased with increased dl-Met levels in the duodenum; the low TSAA/Lys ratio induced a stronger mRNA expression of basolateral Met transporters. OH-Met resulted in an increase of cystathionine ß-synthase expression in the liver and a decrease in serum homocysteine levels at middle TSAA/Lys ratio compared with dl-Met treatment (P < 0.05). In conclusion, two Met sources support the same growth, but OH-Met acidified the crop chyme. The investigated transporter transcripts differed significantly along the small intestine. At the middle TSAA/Lys ratio, OH-Met showed a higher metabolic tendency of the trans-sulfuration pathway compared with dl-Met.

Amino acid permease OsAAP12 negatively regulates rice tillers and grain yield by transporting specific amino acids to affect nitrogen and cytokinin pathways.

Amino acids are necessary nutrients for the growth of Oryza sativa (rice), which can be mediated by amino acid transporter; however, our understanding of these transporters is still limited. This study found that the expression levels of amino acid permease gene OsAAP12 differed between indica and japonica rice. Altered expression of OsAAP12 negatively regulated tillering and yield in transgenic rice lines. Subcellular localization revealed that OsAAP12 was primarily localized to the plasma membrane. Moreover, it was indicated that OsAAP12 transported polar neutral amino acids asparagine (Asn), threonine (Thr), and serine (Ser) through experiments involving yeast heterologous complementation, fluorescence amino acid uptake, and amino acid content determination. Additionally, exogenous application of amino acids Asn, Thr, and Ser suppressed axillary buds outgrowth in OsAAP12 overexpression lines compared with wild-type ZH11. Conversely, the opposite trend was observed in CRISPR mutant lines. RNA-seq analysis showed that the expression patterns of genes involved in the nitrogen and cytokinin pathways were generally altered in OsAAP12 modified lines. Hormone assays indicated that OsAAP12 mutant lines accumulated cytokinins in the basal part of rice, whereas overexpression lines had the opposite effect. In summary, CRISPR mutant of OsAAP12 boosted rice tillering and grain yield by coordinating the content of amino acids and cytokinins, which has potential application value in high-yield rice breeding.

Tryptophan transport gene inactivation promotes the development of antibiotic resistance in Escherichia coli.

Indole serves as a signaling molecule that could regulate different bacterial physiological processes, including antibiotic resistance through biofilm formation and drug efflux pump activity. In Escherichia coli, indole is produced through the tryptophan pathway, which involves three permeases (Mtr, AroP, and TnaB) that can transport the amino acid tryptophan. Although these permeases play distinct roles in the secretion of indole biosynthesis, their impact on multidrug resistance mediated by indole remaines unclear. This study was designed to investigate the connection between the tryptophan transport system and antibiotic resistance by constructing seven gene deletion mutants from E. coli MG1655 (wild type). Our result showed that deletion of the aroP or tnaB gene led to increased antibiotic resistance as evaluated by MICs for different antibiotics. Efflux activity test results revealed that the increased antibiotic resistance was related with the AcrAB-Tolc drug efflux pump in the mutants. The transcriptome analysis further demonstrated that decreased susceptibility to kanamycin and ampicillin in E. coli was accompanied by reduced accumulation of reactive oxygen species and decreased motility. These findings highlight the substantial influence of the tryptophan transport system on antibiotic resistance in E. coli, which is crucial for developing strategies against antibiotic resistance in bacterial infections.

Zinc proteinate with moderate chelation strength enhances zinc absorption by upregulating the expression of zinc and amino acid transporters in primary cultured duodenal epithelial cells of broiler embryos.

Recent study showed that zinc (Zn) and amino acid transporters may be involved in enhancing Zn absorption from Zn proteinate with moderate chelation strength (Zn-Prot M) in the duodenum of broilers. However, the specific mechanisms by which Zn-Prot M promotes the above Zn absorption are unknown. Therefore, in this study, 3 experiments were conducted to investigate specific and direct effects of Zn-Prot M and Zn sulfate (ZnS) on Zn absorption and expression of related transporters in primary duodenal epithelial cells of broiler embryos so as to preliminarily address possible mechanisms. In experiment 1, cells were treated with 100 µmol Zn/L as ZnS or Zn-Prot M for 20, 40, 60, 80, 100, or 120 min. Experiment 2 consisted of 3 sub-experiments. In experiment 2A, cells were treated with a Zn-unsupplemented basal medium (Control) or the basal medium supplemented with 100 or 200 µmol Zn/L as ZnS or Zn-Prot M for 60 min; in experiment 2B, cells were treated with a Zn-unsupplemented basal medium (Control) or the basal medium supplemented with 200 µmol Zn/L of as the ZnS or Zn-Prot M for 120 min; in experiment 2C, cells were treated with a Zn-unsupplemented basal medium (Control) or the basal medium supplemented with 400 or 800 µmol Zn/L as ZnS or Zn-Prot M for 120 min. In experiment 3, cells were treated with a Zn-unsupplemented basal medium (Control) or the basal medium supplemented with 400 µmol Zn/L as ZnS or Zn-Prot M for 120 min. The results of experiment 1 indicated that the minimum incubation time for saturable Zn absorption was determined to be 50.83 min using the best fit line. The results in experiment 2 demonstrated that a Zn concentration of 400 µmol/L and an incubation time of 120 min were suitable to increase the absorption of Zn from Zn-Prot M compared to ZnS. In experiment 3, Zn absorption across cell monolayers was significantly increased by Zn addition (P < 0.05), and was significantly greater with Zn-Prot M than with ZnS (P < 0.05). Compared to the control, Zn addition significantly decreased Zn transporter 10 and peptide-transporter 1 mRNA expression levels and increased y + L-type amino transporter 2 (y + LAT2) protein abundance (P < 0.05). Moreover, protein expression levels of zrt/irt-like protein 3 (ZIP3), zrt-irt-like protein 5 (ZIP5), and y + LAT2 were significantly greater for Zn-Prot M than for ZnS (P < 0.05). These findings suggest that Zn-Prot M promote Zn absorption by increasing ZIP3, ZIP5 and y + LAT2 protein expression levels in primary duodenal epithelial cells.

Our previous studies demonstrated that zinc (Zn) proteinate with moderate chelation strength (Zn-Prot M) exhibited the greatest bioavailability compared to the inorganic Zn sulfate (ZnS) and other organic Zn sources with either weak or strong chelation strength in broilers. Our recent study further showed that Zn and amino acid transporters could be potentially involved in promoting the absorption of Zn as Zn-Prot M in the duodenum of broilers. Nevertheless, further in vitro experiments are required to reveal the specific mechanisms by which Zn-Prot M promotes Zn absorption, where it is necessary first to investigate the specific and direct effect of Zn-Prot M on Zn absorption and the expression of Zn and amino acid transporters compared to that of ZnS. Therefore, we performed an in vitro study and found that Zn-Prot M increased Zn absorption and protein expression levels of the zrt­irt-like protein 3 (ZIP3), zrt­irt-like protein 5 (ZIP5), and y + L-type amino transporter 2 (y + LAT2) compared to ZnS, suggesting that ZIP3, ZIP5, and y + LAT2 might be involved in promoting the absorption of Zn from Zn-Prot M in the primary cultured duodenal epithelial cells of broiler embryos.

CRISPR/Cas9-induced knockout of an amino acid permease gene (AAP6) reduced Arabidopsis thaliana susceptibility to Meloidogyne incognita.

BACKGROUND: Plant-parasitic root-knot nematode (Meloidogyne incognita) causes global yield loss in agri- and horticultural crops. Nematode management options rely on chemical method. However, only a handful of nematicides are commercially available. Resistance breeding efforts are not sustainable because R gene sources are limited and nematodes have developed resistance-breaking populations against the commercially available Mi-1.2 gene-expressing tomatoes. RNAi crops that manage nematode infection are yet to be commercialized because of the regulatory hurdles associated with transgenic crops. The deployment of the CRISPR/Cas9 system to improve nematode tolerance (by knocking out the susceptibility factors) in plants has emerged as a feasible alternative lately. RESULTS: In the present study, a M. incognita-responsive susceptibility (S) gene, amino acid permease (AAP6), was characterized from the model plant Arabidodpsis thaliana by generating the AtAAP6 overexpression line, followed by performing the GUS reporter assay by fusing the promoter of AtAAP6 with the ß-glucuronidase (GUS) gene. Upon challenge inoculation with M. incognita, overexpression lines supported greater nematode multiplication, and AtAAP6 expression was inducible to the early stage of nematode infection. Next, using CRISPR/Cas9, AtAAP6 was selectively knocked out without incurring any growth penalty in the host plant. The 'Cas9-free' homozygous T3 line was challenge inoculated with M. incognita, and CRISPR-edited A. thaliana plants exhibited considerably reduced susceptibility to nematode infection compared to the non-edited plants. Additionally, host defense response genes were unaltered between edited and non-edited plants, implicating the direct role of AtAAP6 towards nematode susceptibility. CONCLUSION: The present findings enrich the existing literature on CRISPR/Cas9 research in plant-nematode interactions, which is quite limited currently while compared with the other plant-pathogen interaction systems.

Fitness landscape of substrate-adaptive mutations in evolved amino acid-polyamine-organocation transporters.

The emergence of new protein functions is crucial for the evolution of organisms. This process has been extensively researched for soluble enzymes, but it is largely unexplored for membrane transporters, even though the ability to acquire new nutrients from a changing environment requires evolvability of transport functions. Here, we demonstrate the importance of environmental pressure in obtaining a new activity or altering a promiscuous activity in members of the amino acid-polyamine-organocation (APC)-type yeast amino acid transporters family. We identify APC members that have broader substrate spectra than previously described. Using in vivo experimental evolution, we evolve two of these transporter genes, AGP1 and PUT4, toward new substrate specificities. Single mutations on these transporters are found to be sufficient for expanding the substrate range of the proteins, while retaining the capacity to transport all original substrates. Nonetheless, each adaptive mutation comes with a distinct effect on the fitness for each of the original substrates, illustrating a trade-off between the ancestral and evolved functions. Collectively, our findings reveal how substrate-adaptive mutations in membrane transporters contribute to fitness and provide insights into how organisms can use transporter evolution to explore new ecological niches.

High Overexpression of SiAAP9 Leads to Growth Inhibition and Protein Ectopic Localization in Transgenic Arabidopsis.

Amino acid permeases (AAPs) transporters are crucial for the long-distance transport of amino acids in plants, from source to sink. While Arabidopsis and rice have been extensively studied, research on foxtail millet is limited. This study identified two transcripts of SiAAP9, both of which were induced by NO3- and showed similar expression patterns. The overexpression of SiAAP9L and SiAAP9S in Arabidopsis inhibited plant growth and seed size, although SiAAP9 was found to transport more amino acids into seeds. Furthermore, SiAAP9-OX transgenic Arabidopsis showed increased tolerance to high concentrations of glutamate (Glu) and histidine (His). The high overexpression level of SiAAP9 suggested its protein was not only located on the plasma membrane but potentially on other organelles, as well. Interestingly, sequence deletion reduced SiAAP9's sensitivity to Brefeldin A (BFA), and SiAAP9 had ectopic localization on the endoplasmic reticulum (ER). Protoplast amino acid uptake experiments indicated that SiAAP9 enhanced Glu transport into foxtail millet cells. Overall, the two transcripts of SiAAP9 have similar functions, but SiAAP9L shows a higher colocalization with BFA compartments compared to SiAAP9S. Our research identifies a potential candidate gene for enhancing the nutritional quality of foxtail millet through breeding.

Role of a novel endoplasmic reticulum-resident glycoprotein Mtc6/Ehg2 in high-pressure growth: stability of tryptophan permease Tat2 in Saccharomyces cerevisiae.

Deep-sea organisms are subjected to extreme conditions; therefore, understanding their adaptive strategies is crucial. We utilize Saccharomyces cerevisiae as a model to investigate pressure-dependent protein regulation and piezo-adaptation. Using yeast deletion library analysis, we identified 6 poorly characterized genes that are crucial for high-pressure growth, forming novel functional modules associated with cell growth. In this study, we aimed to unravel the molecular mechanisms of high-pressure adaptation in S. cerevisiae, focusing on the role of MTC6. MTC6, the gene encoding the novel glycoprotein Mtc6/Ehg2, was found to stabilize tryptophan permease Tat2, ensuring efficient tryptophan uptake and growth under high pressure at 25 MPa. The loss of MTC6 led to promoted vacuolar degradation of Tat2, depending on the Rsp5-Bul1 ubiquitin ligase complex. These findings enhance our understanding of deep-sea adaptations and stress biology, with broad implications for biotechnology, environmental microbiology, and evolutionary insights across species.

Blocking of amino acid transporter OsAAP7 promoted tillering and yield by determining basic and neutral amino acids accumulation in rice.

BACKGROUND: Amino acids are not only the main form of N in rice, but also are vital for its growth and development. These processes are facilitated by amino acid transporters within the plant. Despite their significance, only a few AAP amino acid transporters have been reported. RESULTS: In this study, we observed that there were differences in the expression of amino acid transporter OsAAP7 among 521 wild cultivated rice varieties, and it directly negatively correlated with tillering and grain yield per plant. We revealed that OsAAP7 protein was localized to the endoplasmic reticulum and had absorption and transport affinity for amino acids such as phenylalanine (Phe), lysine (Lys), leucine (Leu), and arginine (Arg) using subcellular localization, yeast substrate testing, fluorescent amino acid uptake, and amino acid content determination. Further hydroponic studies showed that exogenous application of amino acids Phe, Lys and Arg inhibited the growth of axillary buds in the overexpression lines, and promoted the elongation of axillary buds in the mutant lines. Finally, RNA-seq analysis showed that the expression patterns of genes related to nitrogen, auxin and cytokinin pathways were changed in axillary buds of OsAAP7 transgenic plants. CONCLUSIONS: This study revealed the gene function of OsAAP7, and found that blocking of amino acid transporter OsAAP7 with CRISPR/Cas9 technology promoted tillering and yield by determining basic and neutral amino acids accumulation in rice.

Amino acid transporters within the solute carrier superfamily: Underappreciated proteins and novel opportunities for cancer therapy.

BACKGROUND: Solute carrier (SLC) transporters, a diverse family of membrane proteins, are instrumental in orchestrating the intake and efflux of nutrients including amino acids, vitamins, ions, nutrients, etc, across cell membranes. This dynamic process is critical for sustaining the metabolic demands of cancer cells, promoting their survival, proliferation, and adaptation to the tumor microenvironment (TME). Amino acids are fundamental building blocks of cells and play essential roles in protein synthesis, nutrient sensing, and oncogenic signaling pathways. As key transporters of amino acids, SLCs have emerged as crucial players in maintaining cellular amino acid homeostasis, and their dysregulation is implicated in various cancer types. Thus, understanding the intricate connections between amino acids, SLCs, and cancer is pivotal for unraveling novel therapeutic targets and strategies. SCOPE OF REVIEW: In this review, we delve into the significant impact of amino acid carriers of the SLCs family on the growth and progression of cancer and explore the current state of knowledge in this field, shedding light on the molecular mechanisms that underlie these relationships and highlighting potential avenues for future research and clinical interventions. MAJOR CONCLUSIONS: Amino acids transportation by SLCs plays a critical role in tumor progression. However, some studies revealed the tumor suppressor function of SLCs. Although several studies evaluated the function of SLC7A11 and SLC1A5, the role of some SLC proteins in cancer is not studied well. To exert their functions, SLCs mediate metabolic rewiring, regulate the maintenance of redox balance, affect main oncogenic pathways, regulate amino acids bioavailability within the TME, and alter the sensitivity of cancer cells to therapeutics. However, different therapeutic methods that prevent the function of SLCs were able to inhibit tumor progression. This comprehensive review provides insights into a rapidly evolving area of cancer biology by focusing on amino acids and their transporters within the SLC superfamily.

Regulation of placental amino acid transport in health and disease.

Abnormal fetal growth, i.e., intrauterine growth restriction (IUGR) or fetal growth restriction (FGR) and fetal overgrowth, is associated with increased perinatal morbidity and mortality and is strongly linked to the development of metabolic and cardiovascular disease in childhood and later in life. Emerging evidence suggests that changes in placental amino acid transport may contribute to abnormal fetal growth. This review is focused on amino acid transport in the human placenta, however, relevant animal models will be discussed to add mechanistic insights. At least 25 distinct amino acid transporters with different characteristics and substrate preferences have been identified in the human placenta. Of these, System A, transporting neutral nonessential amino acids, and System L, mediating the transport of essential amino acids, have been studied in some detail. Importantly, decreased placental Systems A and L transporter activity is strongly associated with IUGR and increased placental activity of these two amino acid transporters has been linked to fetal overgrowth in human pregnancy. An array of factors in the maternal circulation, including insulin, IGF-1, and adiponectin, and placental signaling pathways such as mTOR, have been identified as key regulators of placental Systems A and L. Studies using trophoblast-specific gene targeting in mice have provided compelling evidence that changes in placental Systems A and L are mechanistically linked to altered fetal growth. It is possible that targeting specific placental amino acid transporters or their upstream regulators represents a novel intervention to alleviate the short- and long-term consequences of abnormal fetal growth in the future.

Amino acid transporters in neurological disorders and neuroprotective effects of cysteine derivatives.

For most diseases and disorders occurring in the brain, the full causes behind them are yet unknown, but many show signs of dysfunction of amino acid transporters or abnormalities in amino acid metabolism. The blood-brain barrier (BBB) plays a key role in supporting the function of the central nervous system (CNS). Because of its unique structure, the BBB can maintain the optimal environment for CNS by controlling the passage of hydrophilic molecules from blood to the brain. Nutrients, such as amino acids, can cross the BBB via specific transporters. Many amino acids are essential for CNS function, and dysfunction of these amino acid transporters can lead to abnormalities in amino acid levels. This has been linked to causes behind certain genetic brain diseases, such as schizophrenia, autism spectrum disorder, and Huntington's disease (HD). One example of crucial amino acids is L-Cys, the rate-limiting factor in the biosynthesis of an important antioxidant, glutathione (GSH). Deficiency of L-Cys and GSH has been linked to oxidative stress and has been shown as a plausible cause behind certain CNS diseases, like schizophrenia and HD. This review presents the current status of potential L-Cys therapies and gives future directions that can be taken to improve amino acid transportation related to distinct CNS diseases.

TFE3-SLC36A1 axis promotes resistance to glucose starvation in kidney cancer cells.

Higher demand for nutrients including glucose is characteristic of cancer. "Starving cancer" has been pursued to curb tumor progression. An intriguing regime is to inhibit glucose transporter GLUT1 in cancer cells. In addition, during cancer progression, cancer cells may suffer from insufficient glucose supply. Yet, cancer cells can somehow tolerate glucose starvation. Uncovering the underlying mechanisms shall shed insight into cancer progression and benefit cancer therapy. TFE3 is a transcription factor known to activate autophagic genes. Physiological TFE3 activity is regulated by phosphorylation-triggered translocation responsive to nutrient status. We recently reported TFE3 constitutively localizes to the cell nucleus and promotes cell proliferation in kidney cancer even under nutrient replete condition. It remains unclear whether and how TFE3 responds to glucose starvation. In this study, we show TFE3 promotes kidney cancer cell resistance to glucose starvation by exposing cells to physiologically relevant glucose concentration. We find glucose starvation triggers TFE3 protein stabilization through increasing its O-GlcNAcylation. Furthermore, through an unbiased functional genomic study, we identify SLC36A1, a lysosomal amino acid transporter, as a TFE3 target gene sensitive to TFE3 protein level. We find SLC36A1 is overexpressed in kidney cancer, which promotes mTOR activity and kidney cancer cell proliferation. Importantly, SLC36A1 level is induced by glucose starvation through TFE3, which enhances cellular resistance to glucose starvation. Suppressing TFE3 or SLC36A1 significantly increases cellular sensitivity to GLUT1 inhibitor in kidney cancer cells. Collectively, we uncover a functional TFE3-SLC36A1 axis that responds to glucose starvation and enhances starvation tolerance in kidney cancer.

Structure and mechanisms of transport of human Asc1/CD98hc amino acid transporter.

Recent cryoEM studies elucidated details of the structural basis for the substrate selectivity and translocation of heteromeric amino acid transporters. However, Asc1/CD98hc is the only neutral heteromeric amino acid transporter that can function through facilitated diffusion, and the only one that efficiently transports glycine and D-serine, and thus has a regulatory role in the central nervous system. Here we use cryoEM, ligand-binding simulations, mutagenesis, transport assays, and molecular dynamics to define human Asc1/CD98hc determinants for substrate specificity and gain insights into the mechanisms that govern substrate translocation by exchange and facilitated diffusion. The cryoEM structure of Asc1/CD98hc is determined at 3.4-3.8 Å resolution, revealing an inward-facing semi-occluded conformation. We find that Ser 246 and Tyr 333 are essential for Asc1/CD98hc substrate selectivity and for the exchange and facilitated diffusion modes of transport. Taken together, these results reveal the structural bases for ligand binding and transport features specific to human Asc1.

Amino acid transporter SLC7A5 regulates cell proliferation and secretary cell differentiation and distribution in the mouse intestine.

The intestine is critical for not only processing nutrients but also protecting the organism from the environment. These functions are mainly carried out by the epithelium, which is constantly being self-renewed. Many genes and pathways can influence intestinal epithelial cell proliferation. Among them is mTORC1, whose activation increases cell proliferation. Here, we report the first intestinal epithelial cell (IEC)-specific knockout (ΔIEC) of an amino acid transporter capable of activating mTORC1. We show that the transporter, SLC7A5, is highly expressed in mouse intestinal crypt and Slc7a5ΔIEC reduces mTORC1 signaling. Surprisingly, adult Slc7a5ΔIEC intestinal crypts have increased cell proliferation but reduced mature Paneth cells. Goblet cells, the other major secretory cell type in the small intestine, are increased in the crypts but reduced in the villi. Analyses with scRNA-seq and electron microscopy have revealed dedifferentiation of Paneth cells in Slc7a5ΔIEC mice, leading to markedly reduced secretory granules with little effect on Paneth cell number. Thus, SLC7A5 likely regulates secretory cell differentiation to affect stem cell niche and indirectly regulate cell proliferation.

Arginine alleviates Clostridium perfringens α toxin-induced intestinal injury in vivo and in vitro via the SLC38A9/mTORC1 pathway.

Introduction: Clostridium perfringens α toxin is a main virulence factor responsible for gut damage in animals. Arginine is a functional amino acid exhibiting significant immunoregulatory activities. However, the effects and immunoregulatory mechanisms of arginine supplementation on α toxin-induced intestinal injury remain unclear. Methods: In vivo, 256 male Arbor Acres chickens were randomly assigned to a 2×2 factorial arrangement, involving diet treatments (with or without 0.3% arginine supplementation) and immunological stress (with or without α toxin challenge). In vitro, IEC-6 cells were treated with or without arginine in the presence or absence of α toxin. Moreover, IEC-6 cells were transfected with siRNA targeting mTOR and SLC38A9 to explore the underlying mechanisms. Results and discussion: The results showed that in vivo, arginine supplementation significantly alleviated the α toxin-induced growth performance impairment, decreases in serum immunoglobulin (Ig)A and IgG levels, and intestinal morphology damage. Arginine supplementation also significantly reduced the α toxin-induced increase in jejunal proinflammatory cytokines interleukin (IL)-1ß, IL-6 and IL-17 mRNA expression. Clostridium perfringens α toxin significantly decreased jejunal mechanistic target of rapamycin (mTOR) and solute carrier family 38 member 9 (SLC38A9) mRNA expression, while arginine supplementation significantly increased mTOR and SLC38A9 mRNA expression. In vitro, arginine pretreatment mitigated the α toxin-induced decrease in cell viability and the increase in cytotoxicity and apoptosis. Arginine pretreatment also alleviated the α toxin-induced upregulation of mRNA expression of inflammation-related cytokines IL-6, C-X-C motif chemokine ligand (CXCL)10, CXCL11 and transforming growth factor-ß (TGF-ß), as well as apoptosis-related genes B-cell lymphoma-2 associated X protein (Bax), B-cell lymphoma-2 (Bcl-2), B-cell lymphoma-extra large (Bcl-XL) and cysteinyl aspartate specific proteinase 3 (Caspase-3) and the ratio of Bax to Bcl-2. Arginine pretreatment significantly increased the α toxin-induced decrease in mTOR, SLC38A9, eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4EBP1) and ribosomal protein S6 kinase (S6K) mRNA expression. Knockdown SLC38A9 and mTOR largely abrogated the positive effects of arginine pretreatment on α toxin-induced intracellular changes. Furthermore, SLC38A9 silencing abolished the increased mTOR mRNA expression caused by arginine pretreatment. In conclusion, arginine administration attenuated α toxin-induced intestinal injury in vivo and in vitro, which could be associated with the downregulation of inflammation via regulating SLC38A9/mTORC1 pathway.

A CRISPRi/a screening platform to study cellular nutrient transport in diverse microenvironments.

Blocking the import of nutrients essential for cancer cell proliferation represents a therapeutic opportunity, but it is unclear which transporters to target. Here we report a CRISPR interference/activation screening platform to systematically interrogate the contribution of nutrient transporters to support cancer cell proliferation in environments ranging from standard culture media to tumours. We applied this platform to identify the transporters of amino acids in leukaemia cells and found that amino acid transport involves high bidirectional flux dependent on the microenvironment composition. While investigating the role of transporters in cystine starved cells, we uncovered a role for serotonin uptake in preventing ferroptosis. Finally, we identified transporters essential for cell proliferation in subcutaneous tumours and found that levels of glucose and amino acids can restrain proliferation in that environment. This study establishes a framework for systematically identifying critical cellular nutrient transporters, characterizing their function and exploring how the tumour microenvironment impacts cancer metabolism.