The glutamate/neutral amino acid transporter family SLC1: molecular, physiological and pharmacological aspects

Satellite glial cell manipulation prior to axotomy enhances developing dorsal root ganglion central branch regrowth into the spinal cord

The central and peripheral nervous systems (CNS and PNS, respectively) exhibit remarkable diversity in the capacity to regenerate following neuronal injury with PNS injuries being much more likely to regenerate than those that occur in the CNS. Glial responses to damage greatly influence the likelihood of regeneration by either promoting or inhibiting axonal regrowth over time. However, despite our understanding of how some glial lineages participate in nerve degeneration and regeneration, less is known about the contributions of peripheral satellite glial cells (SGC) to regeneration failure following central axon branch injury of dorsal root ganglia (DRG) sensory neurons. Here, using in vivo, time-lapse imaging in larval zebrafish coupled with laser axotomy, we investigate the role of SGCs in axonal regeneration. In our studies we show that SGCs respond to injury by relocating their nuclei to the injury site during the same period that DRG neurons produce new central branch neurites. Laser ablation of SGCs prior to axon injury results in more neurite growth attempts and ultimately a higher rate of successful central axon regrowth, implicating SGCs as inhibitors of regeneration. We also demonstrate that this SGC response is mediated in part by ErbB signaling, as chemical inhibition of this receptor results in reduced SGC motility and enhanced central axon regrowth. These findings provide new insights into SGC-neuron interactions under injury conditions and how these interactions influence nervous system repair.

ASCT2 is a major contributor to serine uptake in cancer cells

The non-essential amino acid serine is a critical nutrient for cancer cells due to its diverse biosynthetic functions. While some tumors can synthesize serine de novo, others are auxotrophic and therefore reliant on serine uptake. Importantly, despite several transporters being known to be capable of transporting serine, the transporters that mediate serine uptake in cancer cells are not known. Here, we characterize the amino acid transporter ASCT2 (SLC1A5) as a major contributor to serine uptake in cancer cells. ASCT2 is well known as a glutamine transporter in cancer, and our work demonstrates that serine and glutamine compete for uptake through ASCT2. We further show that ASCT2-mediated serine uptake is essential for purine nucleotide biosynthesis and that estrogen receptor α (ERα) promotes serine uptake by directly activating SLC1A5 transcription. Collectively, our work defines an additional important role for ASCT2 as a serine transporter in cancer and evaluates ASCT2 as a potential therapeutic target.

Amino Acid Transporters Proteins Involved in the Glutamate-Glutamine Cycle and Their Alterations in Murine Models of Alzheimer's Disease

The brain's ability to integrate external stimuli and generate responses is highly complex. While these mechanisms are not completely understood, current evidence suggests that alterations in cellular metabolism and microenvironment are involved in some dysfunctions as complex as Alzheimer's disease. This pathology courses with defects in the establishment of chemical synapses, which is dependent on the production and supply of neurotransmitters like glutamate and its recycling through the glutamate-glutamine cycle. Alterations in the expression and function of the amino acid transporters proteins involved in this cycle have recently been reported in different stages of Alzheimer's disease. Most of these data come from patients in advanced stages of the disease or post-mortem, due to the ethical and technical limitations of human studies. Therefore, genetically modified mouse models have been an excellent tool to analyze metabolic and even behavioral parameters that are very similar to those that develop in Alzheimer's disease, even at presymptomatic stages. Hence, this paper analyzes the role of glutamate metabolism and its intercellular trafficking in excitatory synapses from different approaches using transgenic mouse models; such an analysis will contribute to our present understanding of AD.

Amino acid influx via LAT1 regulates iron demand and sensitivity to PPMX-T003 of aggressive natural killer cell leukemia

Aggressive natural killer cell leukemia (ANKL) is a rare hematological malignancy with a fulminant clinical course. Our previous study revealed that ANKL cells proliferate predominantly in the liver sinusoids and strongly depend on transferrin supplementation. In addition, we demonstrated that liver-resident ANKL cells are sensitive to PPMX-T003, an anti-human transferrin receptor 1 inhibitory antibody, whereas spleen-resident ANKL cells are resistant to transferrin receptor 1 inhibition. However, the microenvironmental factors that regulate the iron dependency of ANKL cells remain unclear. In this study, we first revealed that the anti-neoplastic effect of PPMX-T003 was characterized by DNA double-strand breaks in a DNA replication-dependent manner, similar to conventional cytotoxic agents. We also found that the influx of extracellular amino acids via LAT1 stimulated sensitivity to PPMX-T003. Taken together, we discovered that the amount of extracellular amino acid influx through LAT1 was the key environmental factor determining the iron dependency of ANKL cells via adjustment of their mTOR/Myc activity, which provides a good explanation for the different sensitivity to PPMX-T003 between liver- and spleen-resident ANKL cells, as the liver sinusoid contains abundant amino acids absorbed from the gut.

Co-Expression Network Analysis and Molecular Docking Demonstrate That Diosgenin Inhibits Gastric Cancer Progression via SLC1A5/mTORC1 Pathway

Background

Tumor-Node-Metastasis (TNM) stage of gastric cancer (GC) is one of the main factors affecting clinical outcome. The aim of this study was to explore the targets related to TNM stage of GC, and screening natural bioactive drug.

Methods

RNA sequencing data of the TCGA-STAD cohort were downloaded from UCSC database. Genes associated with TNM staging were identified by weighted gene co-expression network analysis (WGCNA). Univariate Cox regression, least absolute shrinkage and selection operator (LASSO), extreme gradient boosting (Xgboost), random forest (RF) and cytohubba plug-in of cytoscope were applied to screen hub genes. Natural bioactive ingredients were available from the HERB database. Molecular docking was used to evaluate the binding activity of active ingredients to the hub protein. CCK-8, flow cytometry, transwell and Western blot assays were used to analyze the effects of diosgenin on GC cells.

Results

898 TNM-related genes were screened out through WGCNA. Three genes associated with GC progression/prognosis were identified, including nuclear receptor subfamily 3 group C member 2 (NR3C2), solute carrier family 1 member 5 (SLC1A5) and FAT atypical cadherin 1 (FAT1) based on the machine learning algorithms and hub co-expression network analysis. Diosgenin had good binding activity with SLC1A5. SLC1A5 was highly expressed in GC and was closely associated with tumor stage, overall survival and immune infiltration of GC patients. Diosgenin could inhibit cell viability and invasive ability, promote apoptosis and induce cell cycle arrest in G0/G1 phase. In addition, diosgenin promoted cleaved caspase 3 expression and inhibited Ki67, cyclin D1, p-S6K1, and SLC1A5 expression levels, while the mTORC1 activator (MHY1485) reversed this phenomenon.

Conclusion

For the first time, this work reports diosgenin may inhibit the activation of mTORC1 signaling through targeting SLC1A5, thereby inhibiting the malignant behaviors of GC cells.

The Role of Glutamate and Blood-Brain Barrier Disruption as a Mechanistic Link between Epilepsy and Depression

Epilepsy is associated with substantial neuropsychiatric impairments that persist long after the onset of the condition, significantly impacting quality of life. The goal of this review was to uncover how the pathological consequences of epilepsy, such as excessive glutamate release and a disrupted blood-brain barrier (BBB), contribute to the emergence of neuropsychiatric disorders. We hypothesize that epilepsy induces a dysfunctional BBB through hyperexcitation, which then further amplifies post-ictal glutamate levels and, thus, triggers neurodegenerative and neuropsychiatric processes. This review identifies the determinants of glutamate concentration levels in the brain and explores potential therapeutic interventions that restore BBB integrity. Our focus on therapeutic BBB restoration is guided by the premise that it may improve glutamate regulation, consequently mitigating the neurotoxicity that contributes to the onset of neuropsychiatric symptoms.

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.

Transient kinetics reveal the mechanism of competitive inhibition of the neutral amino acid transporter ASCT2

ASCT2 (alanine serine cysteine transporter 2), a member of the solute carrier 1 family, mediates Na+-dependent exchange of small neutral amino acids across cell membranes. ASCT2 was shown to be highly expressed in tumor cells, making it a promising target for anticancer therapies. In this study, we explored the binding mechanism of the high-affinity competitive inhibitor L-cis hydroxyproline biphenyl ester (Lc-BPE) with ASCT2, using electrophysiological and rapid kinetic methods. Our investigations reveal that Lc-BPE binding requires one or two Na+ ions initially bound to the apo-transporter with high affinity, with Na1 site occupancy being more critical for inhibitor binding. In contrast to the amino acid substrate bound form, the final, third Na+ ion cannot bind, due to distortion of its binding site (Na2), thus preventing the formation of a translocation-competent complex. Based on the rapid kinetic analysis, the application of Lc-BPE generated outward transient currents, indicating that despite its net neutral nature, the binding of Lc-BPE in ASCT2 is weakly electrogenic, most likely because of asymmetric charge distribution within the amino acid moiety of the inhibitor. The preincubation with Lc-BPE also led to a decrease of the turnover rate of substrate exchange and a delay in the activation of substrate-induced anion current, indicating relatively slow Lc-BPE dissociation kinetics. Overall, our results provide new insight into the mechanism of binding of a prototypical competitive inhibitor to the ASCT transporters.

Genetic factors underlying host resistance to Rhipicephalus microplus tick infestation in Braford cattle: a systems biology perspective

Approximately 80% of the world's cattle are raised in regions with a high risk of tick-borne diseases, resulting in significant economic losses due to parasitism by Rhipicephalus (Boophilus) microplus. However, the lack of a systemic biology approach hampers a comprehensive understanding of tick-host interactions that mediate tick resistance phenotypes. Here, we conducted a genome-wide association study (GWAS) of 2933 Braford cattle and found 340 single-nucleotide polymorphisms (SNPs) associated with tick counts. Gene expression analyses were performed on skin samples obtained from previously tick-exposed heifers with extremely high or low estimated breeding values for R. microplus counts. Evaluations were performed both before and after artificial infestation with ticks. Differentially expressed genes were found within 1-Mb windows centered at significant SNPs from GWAS. A total of 330 genes were related to the breakdown of homeostasis that was induced by larval attachment to bovine skin. Enrichment analysis pointed to a key role of proteolysis and signal transduction via JAK/STAT, NFKB and WNT/beta catenin signaling pathways. Integrative analysis on matrixEQTL revealed two cis-eQTLs and four significant SNPs in the genes peptidyl arginine deiminase type IV (PADI4) and LOC11449251. The integration of genomic data from QTL maps and transcriptome analyses has identified a set of twelve key genes that show significant associations with tick loads. These genes could be key candidates to improve the accuracy of genomic predictions for tick resistance in Braford cattle.

A Comprehensive Review of Membrane Transporters and MicroRNA Regulation in Alzheimer's Disease

Alzheimer's disease (AD) is a distressing neurodegenerative condition characterized by the accumulation of amyloid-beta (Aβ) plaques and tau tangles within the brain. The interconnectedness between membrane transporters (SLCs) and microRNAs (miRNAs) in AD pathogenesis has gained increasing attention. This review explores the localization, substrates, and functions of SLC transporters in the brain, emphasizing the roles of transporters for glutamate, glucose, nucleosides, and other essential compounds. The examination delves into the significance of SLCs in AD, their potential for drug development, and the intricate realm of miRNAs, encompassing their transcription, processing, functions, and regulation. MiRNAs have emerged as significant players in AD, including those associated with mitochondria and synapses. Furthermore, this review discusses the intriguing nexus of miRNAs targeting SLC transporters and their potential as therapeutic targets in AD. Finally, the review underscores the interaction between SLC transporters and miRNA regulation within the context of Alzheimer's disease, underscoring the need for further research in this area. This comprehensive review aims to shed light on the complex mechanisms underlying the causation of AD and provides insights into potential therapeutic approaches.

Chronic social defeat stress induces the down-regulation of the Nedd4L-GLT-1 ubiquitination pathway in the prefrontal cortex of mice

Stressful life events contribute to the onset of major depressive disorder (MDD). We recently demonstrated abnormalities in ubiquitination in the pathophysiology of MDD. However, the underlying molecular mechanisms remain unclear. We investigated the involvement of the ubiquitination system-mediated glutamatergic dysfunction in social impairment induced by chronic social defeat stress (CSDS). Adult C57BL/6J mice were exposed to aggressor ICR male mice for 10 consecutive days. Social impairment was induced by CSDS in the social interaction test 1 days after the last stress exposure. In terms of brain microdialysis, CSDS reduced depolarization-evoked glutamate release in the prefrontal cortex (PFC), which was reversed by a glutamate transporter 1 (GLT-1) inhibitor. Interestingly, the expression of ubiquitinated, but not total GLT-1, was decreased in the PFC of mice exposed to CSDS. The expression of neural precursor cells expressing developmentally downregulated gene 4-like (Nedd4L: E3 ligase for GLT-1), and ubiquitin-conjugating enzyme E2D2 (Ube2d2: E2 ubiquitin-conjugating enzyme for Nedd4L) was also reduced in CSDS mice. Furthermore, the downregulation of the Nedd4L-GLT-1 ubiquitination pathway decreased SIT ratio, but up-regulation increased it even in non-CSDS mice. Taken together, the decrease in GLT-1 ubiquitination may reduce the release of extracellular glutamate induced by high-potassium stimulation, which may lead to social impairment, while we could not find differences in GLT-1 ubiquitination between susceptible and resistant CSDS mice. In conclusion, GLT-1 ubiquitination could play a crucial role in the pathophysiology of MDD and is an attractive target for the development of novel antidepressants.

A glutamine tug-of-war between cancer and immune cells: recent advances in unraveling the ongoing battle

Glutamine metabolism plays a pivotal role in cancer progression, immune cell function, and the modulation of the tumor microenvironment. Dysregulated glutamine metabolism has been implicated in cancer development and immune responses, supported by mounting evidence. Cancer cells heavily rely on glutamine as a critical nutrient for survival and proliferation, while immune cells require glutamine for activation and proliferation during immune reactions. This metabolic competition creates a dynamic tug-of-war between cancer and immune cells. Targeting glutamine transporters and downstream enzymes involved in glutamine metabolism holds significant promise in enhancing anti-tumor immunity. A comprehensive understanding of the intricate molecular mechanisms underlying this interplay is crucial for developing innovative therapeutic approaches that improve anti-tumor immunity and patient outcomes. In this review, we provide a comprehensive overview of recent advances in unraveling the tug-of-war of glutamine metabolism between cancer and immune cells and explore potential applications of basic science discoveries in the clinical setting. Further investigations into the regulation of glutamine metabolism in cancer and immune cells are expected to yield valuable insights, paving the way for future therapeutic interventions.

Amino acid derivative of probenecid potentiates apoptosis-inducing effects of vinblastine by increasing oxidative stress in a cancer cell-specific manner

Many chemotherapeutic drugs suffer from multidrug resistance (MDR). Efflux transporters, namely ATP-binding cassettes (ABCs), that pump the drugs out of the cancer cells comprise one major reason behind MDR. Therefore, ABC inhibitors have been under development for ages, but unfortunately, without clinical success. In the present study, an l-type amino acid transporter 1 (LAT1)-utilizing derivative of probenecid (PRB) was developed as a cancer cell-targeted efflux inhibitor for P-glycoprotein (P-gp), breast cancer resistant protein (BCRP) and/or several multidrug resistant proteins (MRPs), and its ability to increase vinblastine (VBL) cellular accumulation and apoptosis-inducing effects were explored. The novel amino acid derivative of PRB (2) increased the VBL exposure in triple-negative human breast cancer cells (MDA-MB-231) and human glioma cells (U-87MG) by 10-68 -times and 2-5-times, respectively, but not in estrogen receptor-positive human breast cancer cells (MCF-7). However, the combination therapy had greater cytotoxic effects in MCF-7 compared to MDA-MB-231 cells due to the increased oxidative stress recorded in MCF-7 cells. The metabolomic study also revealed that compound 2, together with VBL, decreased the transport of those amino acids essential for the biosynthesis of endogenous anti-oxidant glutathione (GSH). Moreover, the metabolic differences between the outcomes of the studied breast cancer cell lines were explained by the distinct expression profiles of solute carriers (SLCs) that can be concomitantly inhibited. Therefore, attacking several SLCs simultaneously to change the nutrient environment of cancer cells can serve as an adjuvant therapy to other chemotherapeutics, offering an alternative to ABC inhibitors.

Cranberry Proanthocyanidins Mitigate Reflux-Induced Transporter Dysregulation in an Esophageal Adenocarcinoma Model

We recently reported that cranberry proanthocyanidins (C-PACs) inhibit esophageal adenocarcinoma (EAC) by 83% through reversing reflux-induced bacterial, inflammatory and immune-implicated proteins and genes as well as reducing esophageal bile acids, which drive EAC progression. This study investigated whether C-PACs' mitigation of bile reflux-induced transporter dysregulation mechanistically contributes to EAC prevention. RNA was isolated from water-, C-PAC- and reflux-exposed rat esophagi with and without C-PAC treatment. Differential gene expression was determined by means of RNA sequencing and RT-PCR, followed by protein assessments. The literature, coupled with the publicly available Gene Expression Omnibus dataset GSE26886, was used to assess transporter expression levels in normal and EAC patient biopsies for translational relevance. Significant changes in ATP-binding cassette (ABC) transporters implicated in therapeutic resistance in humans (i.e., Abcb1, Abcb4, Abcc1, Abcc3, Abcc4, Abcc6 and Abcc10) and the transport of drugs, xenobiotics, lipids, and bile were altered in the reflux model with C-PACs' mitigating changes. Additionally, C-PACs restored reflux-induced changes in solute carrier (SLC), aquaporin, proton and cation transporters (i.e., Slc2a1, Slc7a11, Slc9a1, Slco2a1 and Atp6v0c). This research supports the suggestion that transporters merit investigation not only for their roles in metabolism and therapeutic resistance, but as targets for cancer prevention and targeting preventive agents in combination with chemotherapeutics.

ASCT2 is the primary serine transporter in cancer cells

The non-essential amino acid serine is a critical nutrient for cancer cells due to its diverse biosynthetic functions. While some tumors can synthesize serine de novo, others are auxotrophic for serine and therefore reliant on the uptake of exogenous serine. Importantly, however, the transporter(s) that mediate serine uptake in cancer cells are not known. Here, we characterize the amino acid transporter ASCT2 (coded for by the gene SLC1A5) as the primary serine transporter in cancer cells. ASCT2 is well-known as a glutamine transporter in cancer, and our work demonstrates that serine and glutamine compete for uptake through ASCT2. We further show that ASCT2-mediated serine uptake is essential for purine nucleotide biosynthesis and that ERα promotes serine uptake by directly activating SLC1A5 transcription. Together, our work defines an additional important role for ASCT2 as a serine transporter in cancer and evaluates ASCT2 as a potential therapeutic target in serine metabolism.

Analysis of a new therapeutic target and construction of a prognostic model for breast cancer based on ferroptosis genes

Breast cancer, which is the most common malignant tumor among women worldwide and an important cause of death in women. The existing prognostic model for patients with breast cancer is not accurate as breast cancer is resistant to commonly used antitumor drugs. Ferroptosis is a novel mechanism of programmed cell death that depends on iron accumulation and lipid peroxidation. Various studies have confirmed the role of ferroptosis in tumor regulation and ferroptosis is now considered to play an important role in breast cancer development. At present, the association between breast cancer prognosis and ferroptosis-related gene expression remains unclear. Further exploration of this research area may optimize the evaluation and prediction of prognosis of patients with breast cancer and finding of new therapeutic targets. In this study, clinical factors and the expression of multiple genes were evaluated in breast cancer samples from the Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) database database. Eleven prognostication-related genes (TP63, IFNG, MT3, ANO6, FLT3, PTGS2, SLC1A4, JUN, SLC7A5, CHAC1, and TF) were identified from differentially expressed genes to construct a survival prediction model, which showed a good prediction ability. KEGG pathway analysis revealed that immune-related pathways were the primary pathways. ssGSEA analysis showed significant differences in the distribution of certain immune-related cell subsets, such as CD8+T cells and B cells, and in the expression of multiple immune genes, including type II IFN response and APC coinhibition. In addition, 10 immune targets related to ferroptosis in breast cancer were found: CD276, CD80, HHLA2, LILRA2, NCR3LG1, NECTIN3, PVR, SLAMF9,TNFSF4, and BTN1A1. Using TCGA, new ferroptosis genes related to breast cancer prognosis were identified, a new reliable and accurate prognosis model was developed, and 10 new potential therapeutic targets different from the traditional targeted drugs were identified to provide a reference for improving the poor prognosis of patients with breast cancer.

Proteomic alterations in the brain and blood-brain barrier during brain Aβ accumulation in an APP knock-in mouse model of Alzheimer's disease

BACKGROUND

Blood-brain barrier (BBB) dysfunction is supposed to be an early event in the development of Alzheimer's disease (AD). This study aimed to investigate the relationship between BBB alterations and AD progression in terms of amyloid-β peptide (Aβ) accumulation in the brains of humanized amyloid precursor protein knock-in (APP-KI) mice.

METHODS

Brain Aβ accumulation was examined using immunohistochemical analysis. Alterations in differentially expressed proteins were determined using sequential window acquisition of all theoretical fragment ion mass spectroscopy (SWATH-MS)-based quantitative proteomics, and Metascape, STRING, Gene Ontology, and KEGG were used for network analyses of altered biological pathways and processes. Statistical significance was determined using the unpaired two-tailed Student's t-test and Welch's t-test for two groups and one-way analysis of variance followed by Tukey's test for more than two groups. Correlations between two groups were determined using Pearson's correlation analysis.

RESULTS

Brain Aβ accumulation in APP-KI mice was detectable at 2 months, increased significantly at 5 months, and remained elevated at 12 months of age. The levels of differentially expressed proteins in isolated brain capillaries were higher in younger mice, whereas those in the brain were higher in older mice. Network analyses indicated changes in basement membrane-associated and ribosomal proteins in the brain capillaries. There were no significant changes in key proteins involved in drug or Aβ transport at the BBB. In contrast, solute carrier transporter levels in astrocytes, microglia, and neurons were altered in the brain of older mice. Moreover, the levels of the lipid transporters Apoe and Apoj were upregulated in both the brain and isolated brain capillaries after Aβ accumulation.

CONCLUSIONS

Our results suggest that changes in the brain occurred after advanced Aβ accumulation, whereas initial Aβ accumulation was sufficient to cause alterations in the BBB. These findings may help elucidate the role of BBB alterations in AD progression and predict the distribution of drugs across the BBB in the brain of patients with AD.

Transporter-Mediated Drug Delivery

Transmembrane transport of small organic and inorganic molecules is one of the cornerstones of cellular metabolism. Among transmembrane transporters, solute carrier (SLC) proteins form the largest, albeit very diverse, superfamily with over 400 members. It was recognized early on that xenobiotics can directly interact with SLCs and that this interaction can fundamentally determine their efficacy, including bioavailability and intertissue distribution. Apart from the well-established prodrug strategy, the chemical ligation of transporter substrates to nanoparticles of various chemical compositions has recently been used as a means to enhance their targeting and absorption. In this review, we summarize efforts in drug design exploiting interactions with specific SLC transporters to optimize their therapeutic effects. Furthermore, we describe current and future challenges as well as new directions for the advanced development of therapeutics that target SLC transporters.

Segment-Dependent Gene Expression Profiling of the Cartilaginous Fish Nephron Using Laser Microdissection for Functional Characterization of Nephron at Segment Levels

For adaptation to a high salinity marine environment, cartilaginous fishes have evolved a ureosmotic strategy. They have a highly elaborate "four-loop nephron" in the kidney, which is considered to be important for reabsorption of urea from the glomerular filtrate to maintain a high concentration of urea in the body. However, the function and regulation, generally, of the "four-loop nephron" are still largely unknown due to the complicated configuration of the nephron and its many subdivided segments. Laser microdissection (LMD) followed by RNA-sequencing (RNA-seq) analysis is a powerful technique to obtain segment-dependent gene expression profiles. In the present study, using the kidney of cloudy catshark, Scyliorhinus torazame, we tested several formaldehyde-free and formaldehyde-based fixatives to optimize the fixation methods. Fixation by 1% neutral buffered formalin for 15 min resulted in sufficient RNA and structural integrities, which allowed LMD clipping of specific nephron segments and subsequent RNA-seq analysis. RNA-seq from the LMD samples of the second-loop, the fourth-loop, and the five tubular segments in the bundle zone revealed a number of specific membrane transporter genes that can characterize each segment. Among them, we examined expressions of the Na ⁺ -coupled cotransporters abundantly expressed in the second loop samples. Although the proximal II segment of the second loop is known for the elimination of excess solutes, the present results imply that the PII segment is also crucial for reabsorption of valuable solutes. Looking ahead to future studies, the segment-dependent gene expression profiling will be a powerful technique for unraveling the renal mechanisms and regulation in euryhaline elasmobranchs.

Embryonic modulation through thermal manipulation and in ovo feeding to develop heat tolerance in chickens

Healthy chickens are necessary to meet the ever-increasing demand for poultry meat. Birds are subjected to numerous stressful conditions under commercial rearing systems, including variations in the environmental temperature. However, it is difficult to counter the effects of global warming on the livestock industry. High environmental temperature is a stressful condition that has detrimental effects on growth and production performance, resulting in decreased feed intake, retarded growth, compromised gut health, enhanced oxidative stress, and altered immune responses. Traditional approaches include nutritional modification and housing management to mitigate the harmful effects of hot environments. Currently, broiler chickens are more susceptible to heat stress (HS) than layer chickens because of their high muscle mass and metabolic rate. In this review, we explored the possibility of in ovo manipulation to combat HS in broiler chickens. Given their short lifespan from hatching to market age, embryonic life is thought to be one of the critical periods for achieving these objectives. Chicken embryos can be modulated through either temperature treatment or nourishment to improve thermal tolerance during the rearing phase. We first provided a brief overview of the harmful effects of HS on poultry. An in-depth evaluation was then presented for in ovo feeding and thermal manipulation as emerging strategies to combat the negative effects of HS. Finally, we evaluated a combination of the two methods using the available data. Taken together, these investigations suggest that embryonic manipulation has the potential to confer heat resistance in chickens.

Energy metabolism pathways in breast cancer progression: The reprogramming, crosstalk, and potential therapeutic targets

Breast cancer (BC) is a malignant tumor that seriously endangers health in women. BC, like other cancers, is accompanied by metabolic reprogramming. Among energy metabolism-related pathways, BC exhibits enhanced glycolysis, tricarboxylic acid (TCA) cycle, pentose phosphate pathway (PPP), glutamate metabolism, and fatty acid metabolism activities. These pathways facilitate the proliferation, growth and migration of BC cells. The progression of BC is closely related to the alterations in the activity or expression level of several metabolic enzymes, which are regulated by the intrinsic factors such as the key signaling and transcription factors. The metabolic reprogramming in the progression of BC is attributed to the aberrant expression of the signaling and transcription factors associated with the energy metabolism pathways. Understanding the metabolic mechanisms underlying the development of BC will provide a druggable potential for BC treatment and drug discovery.

SLC1A3 facilitates Newcastle disease virus replication by regulating glutamine catabolism

As obligate intracellular parasites, viruses rely completely on host metabolic machinery and hijack host nutrients for viral replication. Newcastle disease virus (NDV) causes acute, highly contagious avian disease and functions as an oncolytic agent. NDV efficiently replicates in both chicken and tumour cells. However, how NDV reprograms host cellular metabolism for its efficient replication is still ill-defined. We previously identified a significantly upregulated glutamate transporter gene, solute carrier family 1 member 3 (SLC1A3), during NDV infection via transcriptome analysis. To investigate the potential role of SLC1A3 during NDV infection, we first confirmed the marked upregulation of SLC1A3 in NDV-infected DF-1 or A549 cells through p53 and NF-κB pathways. Knockdown of SLC1A3 inhibited NDV infection. Western blot analysis further confirmed that glutamine, but not glutamate, asparagine, or aspartate, was required for NDV replication. Metabolic flux data showed that NDV promotes the decomposition of glutamine into the tricarboxylic acid cycle. Importantly, the level of glutamate and glutaminolysis were reduced by SLC1A3 knockdown, indicating that SLC1A3 propelled glutaminolysis for glutamate utilization and NDV replication in host cells. Taken together, our data identify that SLC1A3 serves as an important regulator for glutamine metabolism and is hijacked by NDV for its efficient replication during NDV infection. These results improve our understanding of the interaction between NDV and host cellular metabolism and lay the foundation for further investigation of efficient vaccines.

Expression of nutrient transporter genes in response to dietary rice gluten meal and protease enzyme supplementation and the consequent effects on growth, nutrient digestibility, immunity and jejunum histomorphometry in chicken

The objective of this study was to investigate the effects of feeding rice gluten meal (RGM) as an alternative protein source along with protease enzyme supplementation on growth performance, expression of nutrient transporter genes, nutrient digestibility, immune response and gut histomorphometry of broiler chicken. Proximate analysis of RGM revealed 923 g dry matter (DM), 500 g crude protein (CP), 69.2 g ether extract, 94.7 g crude fiber, 215.4 g nitrogen-free extract, 43.7 g ash, 6.20 g calcium, 7.80 g total phosphorus, 18.99 MJ gross energy and 12.68 MJ metabolizable energy per kg diet. Significant upregulation of nutrient transporter genes (PepT1, EAAT3 and mucin) and better growth performance was observed in the birds fed control diet which was statistically similar to the birds fed 150 g RGM compared to birds fed higher RGM levels. Histomorphometry of jejunum, nutrient digestibility, and immune response of birds did not reveal any significant effect of RGM or protease enzyme supplementation. However, the inclusion of RGM up to 150 g/kg diet resulted in significant decline of feed cost/kg live weight gain, dressed meat yield and eviscerated meat yield by 13.13%, 12.99% and 13.36%, respectively compared to control. Thus, it was concluded that the inclusion of 150 g RGM/kg diet in broiler chicken ration has no adverse effects on the growth pattern of birds and can be used for least-cost feed formulation for chicken.

The Involvement of Long Non-Coding RNAs in Glutamine-Metabolic Reprogramming and Therapeutic Resistance in Cancer

Metabolic alterations that support the supply of biosynthetic molecules necessary for rapid and sustained proliferation are characteristic of cancer. Some cancer cells rely on glutamine to maintain their energy requirements for growth. Glutamine is an important metabolite in cells because it not only links to the tricarboxylic acid cycle by producing α-ketoglutarate by glutaminase and glutamate dehydrogenase but also supplies other non-essential amino acids, fatty acids, and components of nucleotide synthesis. Altered glutamine metabolism is associated with cancer cell survival, proliferation, metastasis, and aggression. Furthermore, altered glutamine metabolism is known to be involved in therapeutic resistance. In recent studies, lncRNAs were shown to act on amino acid transporters and glutamine-metabolic enzymes, resulting in the regulation of glutamine metabolism. The lncRNAs involved in the expression of the transporters include the abhydrolase domain containing 11 antisense RNA 1, LINC00857, plasmacytoma variant translocation 1, Myc-induced long non-coding RNA, and opa interacting protein 5 antisense RNA 1, all of which play oncogenic roles. When it comes to the regulation of glutamine-metabolic enzymes, several lncRNAs, including nuclear paraspeckle assembly transcript 1, XLOC_006390, urothelial cancer associated 1, and thymopoietin antisense RNA 1, show oncogenic activities, and others such as antisense lncRNA of glutaminase, lincRNA-p21, and ataxin 8 opposite strand serve as tumor suppressors. In addition, glutamine-dependent cancer cells with lncRNA dysregulation promote cell survival, proliferation, and metastasis by increasing chemo- and radio-resistance. Therefore, understanding the roles of lncRNAs in glutamine metabolism will be helpful for the establishment of therapeutic strategies for glutamine-dependent cancer patients.

Recent progress of amino acid transporters as a novel antitumor target

Glutamine transporters transport different amino acids for cell growth and metabolism. In tumor cells, glutamine transporters are often highly expressed and play a crucial role in their growth. By inhibiting the amino acid transport of these transporters, the growth of cancer cells can be inhibited. In recent years, more and more attention has been paid to the study of glutamine transporter. In this article, the differences between the ASC system amino acid transporter 2 (ASCT2), L-type amino acid transporter 1 (LAT1), and the cystine–glutamate exchange (xCT) transporters research progress on the mechanism of action and corresponding small molecule inhibitors are summarized. This article introduces 62 related small molecule inhibitors of different transporters of ASCT2, LAT1, and xCT. These novel chemical structures provide ideas for the research and design of targeted inhibitors of glutamine transporters, as well as important references and clues for the design of new anti-tumor drugs.

Glutamatergic pathways in the brains of turtles: A comparative perspective among reptiles, birds, and mammals

Glutamate acts as the main excitatory neurotransmitter in the brain and plays a vital role in physiological and pathological neuronal functions. In mammals, glutamate can cause detrimental excitotoxic effects under anoxic conditions. In contrast, Trachemys scripta, a freshwater turtle, is one of the most anoxia-tolerant animals, being able to survive up to months without oxygen. Therefore, turtles have been investigated to assess the molecular mechanisms of neuroprotective strategies used by them in anoxic conditions, such as maintaining low levels of glutamate, increasing adenosine and GABA, upregulating heat shock proteins, and downregulating KATP channels. These mechanisms of anoxia tolerance of the turtle brain may be applied to finding therapeutics for human glutamatergic neurological disorders such as brain injury or cerebral stroke due to ischemia. Despite the importance of glutamate as a neurotransmitter and of the turtle as an ideal research model, the glutamatergic circuits in the turtle brain remain less described whereas they have been well studied in mammalian and avian brains. In reptiles, particularly in the turtle brain, glutamatergic neurons have been identified by examining the expression of vesicular glutamate transporters (VGLUTs). In certain areas of the brain, some ionotropic glutamate receptors (GluRs) have been immunohistochemically studied, implying that there are glutamatergic target areas. Based on the expression patterns of these glutamate-related molecules and fiber connection data of the turtle brain that is available in the literature, many candidate glutamatergic circuits could be clarified, such as the olfactory circuit, hippocampal–septal pathway, corticostriatal pathway, visual pathway, auditory pathway, and granule cell–Purkinje cell pathway. This review summarizes the probable glutamatergic pathways and the distribution of glutamatergic neurons in the pallium of the turtle brain and compares them with those of avian and mammalian brains. The integrated knowledge of glutamatergic pathways serves as the fundamental basis for further functional studies in the turtle brain, which would provide insights on physiological and pathological mechanisms of glutamate regulation as well as neural circuits in different species.

Identify an innovative ferroptosis-related gene in hepatocellular carcinoma

Background

SLC1A5 has been demonstrated to be associated with the progression of other tumors; however, studies are lacking in hepatocellular carcinoma (HCC). Here, we identify SLC1A5, as a novel ferroptosis factor, for HCC patients.

Methods

The core biomarkers were identified by univariate and multivariate Cox regression analysis, and the genes present in liver cancer were validated using the public database. Then, gene set enrichment analysis (GSEA) was performed to explore the underlying molecular mechanisms. In addition, we explore the relationship between SLC1A5 and clinical factors. Finally, we determine the effect of SLC1A5 on HCC cells using real‐time PCR, cell scratch analysis, transwell analysis, and CCK8 analysis in molecular biology experiments.

Results

Cox regression model shows that SLC1A5 was an independent risk factor for HCC patients. GSEA results indicated high expression of SLC1A5 related to the fatty acid metabolism pathway. Clinical correlation analysis demonstrates that alpha‐fetoprotein (AFP) expression was positively correlated with SLC1A5 (p = 8e−05), and the higher tumor stage means the higher expression of SLC1A5 (p = .02). In addition, SLC1A5 expression was also positively correlated with vascular infiltration of HCC (p = .04). Furthermore, the SLC1A5 function deficiency experiment explored its underlying impact on the biological function of HCC. qPCR, also called quantitative polymerase chain reaction, confirmed that SLC1A5 was highly expressed in liver cancer when compared with normal tissues. Studies have also shown that downregulation of SLC1A5 can inhibit wound healing, invasion, and proliferation of HCC cells.

Conclusion

In conclusion, ferroptosis factor SLC1A5 is a new therapeutic target for hepatocellular carcinoma.

Expression of ferroptosis-related gene correlates with immune microenvironment and predicts prognosis in gastric cancer

The study is to explore the role of ferroptosis-related genes (FRGs) in the occurrence and development of gastric cancer (GC), and to construct a new prognosis signature to predict the prognosis in GC. Clinical information and corresponding RNA data of GC patients were downloaded from TCGA and GEO databases. Consensus clustering was performed to identify new molecular subgroups. ESTIMATE, CIBERSORT, McpCounter and TIMER algorithm were used to analyze the infiltration of immune cells in two molecular subgroups. LASSO algorithm and multivariate Cox analysis were used to construct a prognostic risk signature. Functional analysis was conducted to elucidate the underlying mechanisms. Finally, the FRPGs were verified by Quantitative Real-Time PCR. We obtained 16 FRGs and divided GC patients into two subgroups by consistent clustering. Cluster C1 with a higher abundance of immune cell infiltration but lower probability in response to immunotherapy, it was reasonable to speculate that Cluster C1 was in accordance with the immune rejection type. Functional analysis showed that the biological process of DEGs in training cohort mainly included immune globulin, and human immune response mediated by circulating immune globulin. GSEA analysis showed that compared with Cluster C2, Cluster C1 showed lower expression in lipid metabolism. The nomogram combined with risk signature and clinical features can accurately predict the prognosis of GC patients. We identified two molecular subtypes, Clusters C1 and C2. In Cluster C1, patients with poor prognosis present with a hyperimmune status and low lipid metabolism, and we speculate that Cluster C1 was in accordance with the immune rejection type. The risk model based on FRPGs can accurately predict the prognosis of GC. These results indicated that ferroptosis is associated with TIME, and deserved considerable attention in determining immunotherapy treatment strategy for GC patients.

Strategies for Successful Over-Expression of Human Membrane Transport Systems Using Bacterial Hosts: Future Perspectives

Ten percent of human genes encode for membrane transport systems, which are key components in maintaining cell homeostasis. They are involved in the transport of nutrients, catabolites, vitamins, and ions, allowing the absorption and distribution of these compounds to the various body regions. In addition, roughly 60% of FDA-approved drugs interact with membrane proteins, among which are transporters, often responsible for pharmacokinetics and side effects. Defects of membrane transport systems can cause diseases; however, knowledge of the structure/function relationships of transporters is still limited. Among the expression of hosts that produce human membrane transport systems, E. coli is one of the most favorable for its low cultivation costs, fast growth, handiness, and extensive knowledge of its genetics and molecular mechanisms. However, the expression in E. coli of human membrane proteins is often toxic due to the hydrophobicity of these proteins and the diversity in structure with respect to their bacterial counterparts. Moreover, differences in codon usage between humans and bacteria hamper translation. This review summarizes the many strategies exploited to achieve the expression of human transport systems in bacteria, providing a guide to help people who want to deal with this topic.

Diversity of satellite glia in sympathetic and sensory ganglia

Satellite glia are the major glial type found in sympathetic and sensory ganglia in the peripheral nervous system, and specifically, contact neuronal cell bodies. Sympathetic and sensory neurons differ in morphological, molecular, and electrophysiological properties. However, the molecular diversity of the associated satellite glial cells remains unclear. Here, using single-cell RNA sequencing analysis, we identify five different populations of satellite glia from sympathetic and sensory ganglia. We define three shared populations of satellite glia enriched in immune-response genes, immediate-early genes, and ion channels/ECM-interactors, respectively. Sensory- and sympathetic-specific satellite glia are differentially enriched for modulators of lipid synthesis and metabolism. Sensory glia are also specifically enriched for genes involved in glutamate turnover. Furthermore, satellite glia and Schwann cells can be distinguished by unique transcriptional signatures. This study reveals the remarkable heterogeneity of satellite glia in the peripheral nervous system.

Cysteine 467 of the ASCT2 Amino Acid Transporter Is a Molecular Determinant of the Antiport Mechanism

The plasma membrane transporter ASCT2 is a well-known Na⁺-dependent obligatory antiporter of neutral amino acids. The crucial role of the residue C467 in the recognition and binding of the ASCT2 substrate glutamine, has been highlighted by structure/function relationship studies. The reconstitution in proteoliposomes of the human ASCT2 produced in P. pastoris is here employed to unveil another role of the C467 residue in the transport reaction. Indeed, the site-directed mutant C467A displayed a novel property of the transporter, i.e., the ability of mediating a low but measurable unidirectional transport of [³H]-glutamine. This reaction conforms to the main features of the ASCT2-mediated transport, namely the Na⁺-dependence, the pH dependence, the stimulation by cholesterol included in the proteoliposome membrane, and the specific inhibition by other common substrates of the reconstituted human ASCT2. Interestingly, the WT protein cannot catalyze the unidirectional transport of [³H]-glutamine, demonstrating an unspecific phenomenon. This difference is in favor of a structural conformational change between a WT and C467A mutant that triggers the appearance of the unidirectional flux; this feature has been investigated by comparing the available 3D structures in two different conformations, and two homology models built on the basis of hEAAT1 and GLT_Ph.

Logistic ridge regression to predict bipolar disorder using mRNA expression levels in the N-methyl-D-aspartate receptor genes

BACKGROUND

It is hypothesized that demographic variables and mRNA expression levels in the N-methyl-D-aspartate receptor (NMDAR) genes can be employed as potential biomarkers to predict bipolar disorder using artificial intelligence and machine learning approaches.

METHODS

To determine bipolar status, we established a logistic ridge regression model resulting from the analysis of age, gender, and mRNA expression levels in 7 NMDAR genes in the blood of 51 bipolar patients and 139 unrelated healthy individuals in the Taiwanese population. The NMDAR genes encompasses COMT, GCAT, NRG1, PSAT1, SHMT2, SLC1A4, and SRR. We also compared our approach with various state-of-the-art algorithms such as support vector machine and C4.5 decision tree.

RESULTS

The analysis revealed that the mRNA expression levels of COMT, GCAT, NRG1, PSAT1, SHMT2, SLC1A4, and SRR were associated with bipolar disorder. Moreover, the logistic ridge regression model (area under the receiver operating characteristic curve = 0.922) performed maximally among predictive models to infer the complicated relationship between bipolar disorder and biomarkers. Additionally, the results for the age- and gender-matched cohort were similar to those of the unmatched cohort.

LIMITATIONS

The cross-sectional study design limited the predictive value.

CONCLUSION

This is the first study demonstrating that the mRNA expression levels in the NMDAR genes may be altered in patients with bipolar disorder, thereby supporting the NMDAR hypothesis of bipolar disorder. The study also indicates that the mRNA expression levels in the NMDAR genes could serve as potential biomarkers to distinguish bipolar patients from healthy controls using artificial intelligence and machine learning approaches.

Molecular Characterization and Nutrition Regulation of the Neutral Amino Acid Transporter ASCT2 in Triploid Crucian Carp

AlaSerCys Transporter 2 (ASCT2), encoded by the SLC1A5 gene, plays an important role in the absorption of glutamine. In this study, the full-length cDNA sequence of ASCT2 was cloned from triploid crucian carp. It encodes 539 amino acid residues and a stop codon. Phylogenetic analysis revealed that the sequences of the ASCT2 ORF region in cyprinid fishes shared high sequence homology. Comparing the abundance of ASCT2 in different tissues, we found its expression level in muscle was significantly higher than that in intestine (p < 0.05). In addition, the expression levels of ASCT2 also appeared different in diurnal variation. Then we found the addition of 2.5% glutamate in a feeding diet significantly increased the expression levels of ASCT2 in intestine and muscle (p < 0.05). However, in glutamine experiments, the muscle showed the highest expression level of ASCT2 when fish were fed the diet containing 3.0% glutamine (p < 0.05). In vitro, ASCT2 was sensitive to glutamine and its expression level appeared down-regulated when the addition of glutamine was added to 0.1 mg/mL. Finally, we found that the diet with 29% protein level significantly increased the expression level of ASCT2 in intestine (p < 0.05). Nevertheless, different protein sources (fish meal and soybean meal) had no significant effect on the expression levels of ASCT2 in intestine and muscle (p > 0.05). These results provided data for the study of ASCT2 in triploid crucian carp regulated by feeding nutrition, which had a potential application in improving feed formulation in aquaculture.

Knockdown of circular RNA septin 9 inhibits the malignant progression of breast cancer by reducing the expression of solute carrier family 1 member 5 in a microRNA-149-5p-dependent manner

Breast cancer (BC) is the most frequently diagnosed cancer in women. Increasing evidence suggests that circular RNA (circRNA) exerts critical functions in BC progression. However, the roles of circRNA septin 9 (circSEPT9) in BC development and the underneath mechanism remain largely unclear so far. In this work, the RNA levels of circSEPT9, microRNA-149-5p (miR-149-5p) and solute carrier family 1 member 5 (SLC1A5) were detected by quantitative real-time polymerase chain reaction. Western blot was performed to check protein expression. Glutamine uptake, cell proliferation and cell apoptosis were investigated by glutamine uptake, cell counting kit-8, cell colony formation, 5-Ethynyl-29-deoxyuridine, flow cytometry analysis or DNA content quantitation assay. The interactions of miR-149-5p with circSEPT9 and SLC1A5 were identified by a dual-luciferase reporter assay. Mouse model assay was carried out to analyze the effect of circSEPT9 on tumor formation in vivo. Results showed that circSEPT9 and SLC1A5 expression were significantly upregulated, while miR-149-5p was downregulated in BC tissues and cells as compared with paracancerous normal breast tissues and human normal breast cells. Knockdown of circSEPT9 or SLC1A5 inhibited glutamine uptake and cell proliferation, but induced cell apoptosis in BC cells. SLC1A5 overexpression relieved circSEPT9 silencing-induced repression of BC cell malignancy. In mechanism, circSEPT9 regulated SLC1A5 expression by sponging miR-149-5p. In support, circSEPT9 knockdown led to delayed tumor tumorigenesis in vivo. In summary, these results indicates that circSEPT9 may act an oncogenic role in BC malignant progression by regulating miR-149-5p/SLC1A5 pathway, providing a novel mechanism responsible for BC development.

Development and Validation of a Novel Ferroptosis-Related Gene Signature for Predicting Prognosis and the Immune Microenvironment in Gastric Cancer

Ferroptosis is a mode of regulated cell death that depends on iron and plays pivotal roles in regulating various biological processes in human cancers. However, the role of ferroptosis in gastric cancer (GC) remains unclear. In our study, a total of 2721 differentially expressed genes (DEGs) were filtered based on The Cancer Genome Atlas (TCGA) (n = 375) dataset. Weighted gene coexpression network (WGCNA) analysis was then used and identified 7 modules, of which the blue module with the most significant enrichment result was selected. By taking the intersections of the blue module and ferroptosis-related genes (FRGs), we obtained 23 common genes. Functional analysis was performed to explore the biological function of the genes of interest, and with univariate Cox regression (UCR) analysis, survival genes were screened to construct a prognostic model based on 3 genes (SLC1A5, ANGPTL4, and CGAS), which could play a role in predicting the survival of GC patients. UCR and multivariate Cox regression (MCR) analysis revealed that the prognostic index could be used as an independent prognostic indicator and validated using another GSE84437 dataset. Notably, patients in the high-risk group had higher mutation frequencies, such as TTN and TP53. TIMER analysis demonstrated that the risk score strongly correlated with macrophage and CD4+ T cell infiltration. In addition, the high- and low-risk groups illustrated different distributions of different immune statuses. Furthermore, the low-risk group had a higher immunophenoscore (IPS), which meant a better response to immune checkpoint inhibitors (ICIs). Finally, gene set enrichment analysis (GSEA) revealed several significant pathways involved in GC. In this study, a novel FRG signature was built that could predict GC prognosis and reflect the status of the tumor immune microenvironment.

A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1

The ASCT1 transporter of the SLC1 family is largely involved in equilibration of neutral amino acids' pools across the plasma membrane and plays a prominent role in the transport of both L- and D-isomers of serine, essential for the normal functioning of the central nervous system in mammals. A number of mutations in ASCT1 (E256K, G381R, R457W) have been linked to severe neurodevelopmental disorders, however in the absence of ASCT1 structure it is hard to understand their impact on substrate transport. To ameliorate that we have determined a cryo-EM structure of human ASCT1 at 4.2 Å resolution and performed functional transport assays and molecular dynamics simulations, which revealed that given mutations lead to the diminished transport capability of ASCT1 caused by instability of transporter and impeded transport cycle.

ASCT1 and ASCT2: Brother and Sister?

The SLC1 family includes seven members divided into two groups, namely, EAATs and ASCTs, that share similar 3D architecture; the first one includes high-affinity glutamate transporters, and the second one includes SLC1A4 and SLC1A5, known as ASCT1 and ASCT2, respectively, responsible for the traffic of neutral amino acids across the cell plasma membrane. The physiological role of ASCT1 and ASCT2 has been investigated over the years, revealing different properties in terms of substrate specificities, affinities, and regulation by physiological effectors and posttranslational modifications. Furthermore, ASCT1 and ASCT2 are involved in pathological conditions, such as neurodegenerative disorders and cancer. This has driven research in the pharmaceutical field aimed to find drugs able to target the two proteins.This review focuses on structural, functional, and regulatory aspects of ASCT1 and ASCT2, highlighting similarities and differences.

Host-Endosymbiont Genome Integration in a Deep-Sea Chemosymbiotic Clam

Endosymbiosis with chemosynthetic bacteria has enabled many deep-sea invertebrates to thrive at hydrothermal vents and cold seeps, but most previous studies on this mutualism have focused on the bacteria only. Vesicomyid clams dominate global deep-sea chemosynthesis-based ecosystems. They differ from most deep-sea symbiotic animals in passing their symbionts from parent to offspring, enabling intricate coevolution between the host and the symbiont. Here, we sequenced the genomes of the clam Archivesica marissinica (Bivalvia: Vesicomyidae) and its bacterial symbiont to understand the genomic/metabolic integration behind this symbiosis. At 1.52 Gb, the clam genome encodes 28 genes horizontally transferred from bacteria, a large number of pseudogenes and transposable elements whose massive expansion corresponded to the timing of the rise and subsequent divergence of symbiont-bearing vesicomyids. The genome exhibits gene family expansion in cellular processes that likely facilitate chemoautotrophy, including gas delivery to support energy and carbon production, metabolite exchange with the symbiont, and regulation of the bacteriocyte population. Contraction in cellulase genes is likely adaptive to the shift from phytoplankton-derived to bacteria-based food. It also shows contraction in bacterial recognition gene families, indicative of suppressed immune response to the endosymbiont. The gammaproteobacterium endosymbiont has a reduced genome of 1.03 Mb but retains complete pathways for sulfur oxidation, carbon fixation, and biosynthesis of 20 common amino acids, indicating the host’s high dependence on the symbiont for nutrition. Overall, the host–symbiont genomes show not only tight metabolic complementarity but also distinct signatures of coevolution allowing the vesicomyids to thrive in chemosynthesis-based ecosystems.

Sulforaphane enhances long-term potentiation and ameliorate scopolamine-induced memory impairment

Increases in human life expectancy have led to increases in the prevalence of senile dementia and neurodegenerative diseases. This is a major problem because there are no curative treatments for these diseases, and patients with unmanaged cognitive and neurodegenerative symptoms experience many social problems. Sulforaphane is a type of organosulfur compound known as an isothiocyanate. It is derived from glucoraphanin, a compound found in cruciferous vegetables such as broccoli, brussels sprouts, and cabbages, via an enzymatic reaction that is triggered by plant damage (e.g., chewing). Sulforaphane exhibits activity against cancer, inflammation, depression, and severe cardiac diseases. It can also alleviate oxidative stress and neural dysfunction in the brain. However, there is insufficient knowledge about the electrophysiological and behavioral basis of the effects of sulforaphane on learning and memory. Therefore, we evaluated whether acute sulforaphane administration affected long-term potentiation (LTP) in organotypic cultured rat hippocampal tissues. We also measured the effect of sulforaphane on the performance of three behavioral tests, the Y-maze test, the passive avoidance test, and the Morris water maze, which assess short-term memory, avoidance memory, and short and long-term spatial memory, respectively. We found that sulforaphane increased the total field excitatory postsynaptic potential (fEPSP) in a dose-dependent manner after high frequency stimulation and attenuated scopolamine-induced interference of the fEPSP in the hippocampal CA1 area. Sulforaphane also restored cognitive function and inhibited memory impairment as indicated by the alleviation of the negative neurological effects of scopolamine, i.e, a lowered ratio of spontaneous alternation in the Y-maze, a reduced step-through latency in the passive avoidance test, and an increased navigation time in the Morris water maze. These results indicate that sulforaphane can effectively prevent the attenuation of LTP and cognitive abilities induced by cholinergic and muscarinic receptor blockade. Further research is warranted to explore the potential therapeutic and prophylactic utility of sulforaphane for improving learning and memory, especially in those suffering from neurodegenerative disorders.

Glutamate transporters: Critical components of glutamatergic transmission

Glutamate is the major excitatory neurotransmitter in the vertebrate central nervous system. Once released, it binds to specific membrane receptors and transporters activating a wide variety of signal transduction cascades, as well as its removal from the synaptic cleft in order to avoid its extracellular accumulation and the overstimulation of extra-synaptic receptors that might result in neuronal death through a process known as excitotoxicity. Although neurodegenerative diseases are heterogenous in clinical phenotypes and genetic etiologies, a fundamental mechanism involved in neuronal degeneration is excitotoxicity. Glutamate homeostasis is critical for brain physiology and Glutamate transporters are key players in maintaining low extracellular Glutamate levels. Therefore, the characterization of Glutamate transporters has been an active area of glutamatergic research for the last 40 years. Transporter activity its regulated at different levels: transcriptional and translational control, transporter protein trafficking and membrane mobility, and through extensive post-translational modifications. The elucidation of these mechanisms has emerged as an important piece to shape our current understanding of glutamate actions in the nervous system.

Organic iron absorption and expression of related transporters in the small intestine of broilers

An experiment was conducted to investigate the effect of organic and inorganic Fe sources on Fe absorption and expression of related transporters in the small intestine of broilers. Iron-deficient intact broilers (7-day-old) were fed an Fe-unsupplemented corn-soybean meal basal diet or the basal diet supplemented with 60 mg Fe/kg as Fe sulfate (FeSO₄•7H₂O), Fe-Met with weak chelation strength (Fe-Met W), Fe-proteinate with moderate chelation strength (Fe-Prot M) or Fe-proteinate with extremely strong chelation strength (Fe-Prot ES) for 14 d. The plasma Fe contents were enhanced (P < 0.02) by Fe addition, and greater (P < 0.0002) in Fe-Prot M and Fe-Prot ES groups than in Fe-Met W and FeSO₄ groups. Supplemental Fe decreased (P < 0.03) the divalent metal transporter 1 (DMT1) mRNA levels in the duodenum and jejunum, and ferroportin 1 (FPN1) mRNA levels in the duodenum on d 21, but no differences (P > 0.20) were detected among different Fe sources. Regardless of Fe source, the mRNA levels of DMT1 and FPN1 were higher (P < 0.02) in the duodenum than in the jejunum and ileum, and in the jejunum than in the ileum (P < 0.05). However, Fe addition did not affect (P > 0.10) the mRNA levels of amino acid transporters and protein levels of DMT1 and FPN1 in the small intestine of broilers. These results indicate that organic Fe sources with stronger chelation strength showed higher Fe absorption in broilers in vivo; the mRNA expression of Fe and amino acid transporters varied along with the extension of the small intestine; the absorption of Fe as organic Fe chelates was not mediated by the amino acid transporters in intact chicks in this study.

Targeting SLC1A5 blocks cell proliferation through inhibition of mTORC1 in arsenite-treated human uroepithelial cells

Arsenic is an environmental contaminant, which is widely distributed in soil, air, and water. There is sufficient evidence to indicate that arsenic increases the risk of bladder cancer in humans. However, its underlying mechanisms remain elusive. Glutamine (Gln) has multiple functions that promote carcinogenesis. Indeed, Gln transporters on cancer cells surface are often upregulated. Elevated expression levels of Alanine, serine, cysteine-preferring transporter 2 (ASCT2; SLC1A5) have been reported in many types of human tumors. This study characterized the role of SLC1A5 in cell proliferation in arsenite-treated cells. In short-term experiments, SV-40 immortalized human uroepithelial (SV-HUC-1) cells were treated with Sodium arsenite (NaAsO₂) (0, 0.5, 1, 2, 4, 8 μM) for 24 h. In long-term experiments, SV-HUC-1 cells were exposed to 0.5 μM NaAsO₂ for 40 weeks. In both short-term and long-term experiments, arsenite increased expression of SLC1A5 by 1.89-fold and 2.25-fold, respectively. Arsenite increased Gln consumption of SV-HUC-1 cells, and Gln starvation inhibited cell proliferation in long-term arsenite-treated cells. Importantly, inhibiting SLC1A5 blocked cell proliferation by downregulating mTORC1 in long-term arsenite-treated cells. Moreover, SLC1A5 regulated mTORC1 in an αKG-dependent manner. Our results suggest that SLC1A5 plays an important role in cell proliferation of arsenite-treated SV-HUC-1 cells.

Regulation of gene expression in chickens by heat stress

Abstract

High ambient temperatures are a critical challenge in the poultry industry which is a key producer of the animal-based food. To evaluate heat stress levels, various parameters have been used, including growth rates, blood metabolites, and hormones. The most recent advances have explored expression profiling of genes that may play vital roles under stress. A high ambient temperature adversely affects nutrient uptake and is known to modulate the expression of genes encoding for sodium-dependent glucose transporters, glucose transporters, excitatory amino acid transporters, and fatty acid-binding proteins which are responsible for the absorption of macronutrients in the intestine. Various defensive activities are stimulated to protect the cell of different tissues from the heat-generated stress, including expression of early stress response genes coding for heat shock protein (HSP), c-FOS like protein, brain-derived neurotrophic factor (BDNF), and neuronal nitric oxide synthase (nNOS); antioxidant enzyme genes such as superoxide dismutase (SOD), catalase (CAT), and nicotinamide adenine dinucleotide phosphate oxidase (NOX4); and immune-related genes such as cytokines and toll-like receptors (TLRs). The potential role of HSPs in protecting the cell from stress and their presence in several tissues make them suitable markers to be evaluated under heat stress. BDNF and c-FOS genes expressed in the hypothalamus help cells to adapt to an adverse environment. Heat causes damage to the cell by generating reactive oxygen species (ROS). The NOX4 gene is the inducer of ROS under heat stress, which is in turns controlled by antioxidant enzymes such as SOD and CAT. TLRs are responsible for protecting against pathogenic attacks arising from enhanced membrane permeability, and cytokines help in controlling the pathogen and maintaining homeostasis. Thus, the evaluation of nutrient transporters and defense mechanisms using the latest molecular biology tools has made it possible to shed light on the complex cellular mechanism of heat-stressed chickens. As the impacts of heat stress on the above-mentioned aspects are beyond the extent to which the reduced growth performance could be explained, heat stress has more specific effects on the regulation of these genes than previously thought.

Graphical abstract

Effect of heat exposure on the nutrient transporters, antioxidants, and immune inflammation in chickens. Most of the nutrient transporters were suppressed under heat stress. Increase in the production of reactive oxygen species resulted in enhanced production of antioxidant enzymes. Expression of various proinflammatory cytokines and toll-like receptors were enhanced due to heat stress in chicken.

Association Between the SLC1A1 Glutamate Transporter Gene and Obsessive-Compulsive Disorder in the Chinese Han Population

BACKGROUND

Obsessive-compulsive disorder (OCD) is a common, serious and genetically related mental illness; the etiology of OCD has not yet reached a definitive conclusion. Multiple evidence suggests that the glutamatergic system plays a major role in the pathophysiology of OCD. However, subsequent studies on the glutamate transporter gene are not consistent. OCD is a heterogeneous disease. To resolve the complex genetic basis of OCD, division the disorder into different subphenotypes is an effective method for studying the pathogenesis of OCD.

METHODS

We recruited 438 OCD patients and 465 age- and sex-matched controls from a Chinese Han population. rs10491734, rs3780412, rs301434 and rs3087879 SNPs were genotyped by real-time TaqMan polymerase chain reaction, and the chi-squared test was used to compare allele and genotype frequencies of variants between the two groups.

RESULTS

The genotype of rs301434 was statistically significant in total patients with OCD and the controls. After grouping by age and gender, the genotype of rs301434 was statistically significant in early-onset OCD, late-onset OCD as well as male OCD, the allele and genotype of rs3780412 was associated with late-onset OCD. Haplotype analysis showed that four loci haplotypes (G-A-A-G and G-G-A-G) were associated with total OCD, (G-G-A-G) was associated with female OCD, (G-A-G-G) was associated with male OCD, (G-A-A-G and G-G-A-G) were associated with late-onset OCD.

CONCLUSION

This study provides suggestive evidence that SLC1A1 may be involved in the development of OCD in the Han population. However, these findings require further replication.

Defining compartmentalized stem cell populations with distinct cell division dynamics in the ocular surface epithelium

Adult tissues contain label-retaining cells (LRCs), which are relatively slow-cycling and considered to represent a property of tissue stem cells (SCs). In the ocular surface epithelium, LRCs are present in the limbus and conjunctival fornix; however, the character of these LRCs remains unclear, owing to lack of appropriate molecular markers. Using three CreER transgenic mouse lines, we demonstrate that the ocular surface epithelium accommodates spatially distinct populations with different cell division dynamics. In the limbus, long-lived Slc1a3CreER-labeled SCs either migrate centripetally toward the central cornea or slowly expand their clones laterally within the limbal region. In the central cornea, non-LRCs labeled with Dlx1CreER and K14CreER behave as short-lived progenitor cells. The conjunctival epithelium in the bulbar, fornix and palpebral compartment is regenerated by regionally unique SC populations. Severe damage to the cornea leads to the cancellation of SC compartments and conjunctivalization, whereas milder limbal injury induces a rapid increase of laterally expanding clones in the limbus. Taken together, our work defines compartmentalized multiple SC/progenitor populations of the mouse eye in homeostasis and their behavioral changes in response to injury.

Interaction of the neutral amino acid transporter ASCT2 with basic amino acids

Glutamine transport across cell membranes is performed by a variety of transporters, including the alanine serine cysteine transporter 2 (ASCT2). The substrate-binding site of ASCT2 was proposed to be specific for small amino acids with neutral side chains, excluding basic substrates such as lysine. A series of competitive inhibitors of ASCT2 with low µM affinity were developed previously, on the basis of the 2,4-diaminobutyric acid (DAB) scaffold with a potential positive charge in the side chain. Therefore, we tested whether basic amino acids with side chains shorter than lysine can interact with the ASCT2 binding site. Molecular docking of L-1,3-diaminopropionic acid (L-DAP) and L-DAB suggested that these compounds bind to ASCT2. Consistent with this prediction, L-DAP and L-DAB, but not ornithine, lysine or D-DAP, elicited currents when applied to ASCT2-expressing cells. The currents were carried by anions and showed the hallmark properties of ASCT2 currents induced by transported substrates. The L-DAP response could be eliminated by a competitive ASCT2 inhibitor, suggesting that binding occurs at the substrate binding site. The KM for L-DAP was weakly voltage dependent. Furthermore, the pH dependence of the L-DAP response showed that the compound can bind in several protonation states. Together, these results suggest that the ASCT2 binding site is able to recognize L-amino acids with short, basic side chains, such as the L-DAP derivative β-N-methylamino-l-Alanine (BMAA), a well-studied neurotoxin. Our results expand the substrate specificity of ASCT2 to include amino acid substrates with positively charged side chains.

ACE2 and gut amino acid transport

ACE2 is a type I membrane protein with extracellular carboxypeptidase activity displaying a broad tissue distribution with highest expression levels at the brush border membrane (BBM) of small intestine enterocytes and a lower expression in stomach and colon. In small intestinal mucosa, ACE2 mRNA expression appears to increase with age and to display higher levels in patients taking ACE-inhibitors (ACE-I). There, ACE2 protein heterodimerizes with the neutral amino acid transporter Broad neutral Amino acid Transporter 1 (B0AT1) (SLC6A19) or the imino acid transporter Sodium-dependent Imino Transporter 1 (SIT1) (SLC6A20), associations that are required for the surface expression of these transport proteins. These heterodimers can form quaternary structures able to function as binding sites for SARS-CoV-2 spike glycoproteins. The heterodimerization of the carboxypeptidase ACE2 with B0AT1 is suggested to favor the direct supply of substrate amino acids to the transporter, but whether this association impacts the ability of ACE2 to mediate viral infection is not known. B0AT1 mutations cause Hartnup disorder, a condition characterized by neutral aminoaciduria and, in some cases, pellagra-like symptoms, such as photosensitive rash, diarrhea, and cerebellar ataxia. Correspondingly, the lack of ACE2 and the concurrent absence of B0AT1 expression in small intestine causes a decrease in l-tryptophan absorption, niacin deficiency, decreased intestinal antimicrobial peptide production, and increased susceptibility to inflammatory bowel disease (IBD) in mice. Thus, the abundant expression of ACE2 in small intestine and its association with amino acid transporters appears to play a crucial role for the digestion of peptides and the absorption of amino acids and, thereby, for the maintenance of structural and functional gut integrity.

Genetic Association of Epilepsy and Anti-Epileptic Drugs Treatment in Jordanian Patients

Purpose

The aim of this study was to investigate the possible effects of single-nucleotide polymorphisms (SNPs) within SLC1A1, SLC6A1, FAM131B, GPLD1, F2, GABRG2, GABRA1, and CACNG5 genes on response to anti-epileptic drugs (AEDs) and the genetic predisposition of epilepsy in Jordanian patients.

Patients and Methods

A total of 299 healthy individuals and 296 pediatric patients from the Jordanian population were recruited. Blood samples are collected, and genotyping was performed using a custom platform array analysis.

Results

The SLC1A1 rs10815018 and FAM131B rs4236482 polymorphisms found to be associated with epilepsy susceptibility. Moreover, SLC1A1 rs10815018 and GPLD1 rs1126617 polymorphisms were associated with generalized epilepsy (GE), while FAM131B rs4236482 is associated with the focal phenotype. Regarding the therapeutic response, the genetic polymorphisms of FAM131B rs4236482, GABRA1 rs2279020, and CACNG5 rs740805 are conferred poor response (resistance) to AEDs. There was no linkage of GLPD1 haplotypes to epilepsy, its subtypes, and treatment responsiveness.

Conclusion

Our findings suggested that SLC1A1, FAM131B, and GPLD1 polymorphisms increasing the risk of generating epilepsy, while FAM131B, GABRA1, and CACNG5 variants may play a role in predicting drug response in patients with epilepsy (PWE).

L-Cysteine-mediated modulation of copper trafficking in prostate cancer cells: an in vitro and in vivo investigation with 64Cu and 64Cu-PET

Copper imbalance is implicated in many diseases, including cancer. Copper in blood is mainly transported by carrier proteins but a small fraction is bound to low molecular weight species, possibly amino acids. Their roles in cellular copper delivery are unknown. Our aim was to test whether accumulation of 64Cu into cancer-derived cells can be influenced by copper-binding serum amino acids. In vitro cellular accumulation of 64Cu was measured in Hank's Balanced Salt Solution in the presence of 100 μM l-histidine, l-methionine, l-cysteine and l-threonine. l-Cysteine markedly increased 64Cu accumulation and retention in DU145, PC3 and SK-OV-3 cells, while some other cell lines did not show an effect. This effect was not due to 64Cu delivery in the form of a 64Cu-cysteine complex, nor to reduction of 64Cu(ii) to 64Cu(i) by l-cysteine. Pre-incubation of cells with l-cysteine increased 64Cu accumulation, even if l-cysteine was removed from HBSS before 64Cu was added. The effect of l-cysteine on 64Cu accumulation was not mediated by increased glutathione synthesis. Despite the demonstrable in vitro effect, pre-injection of l-cysteine precursor N-acetyl-cysteine (NAC) in vivo did not enhance 64Cu delivery to DU145 xenografts in mice. Instead, it decreased 64Cu accumulation in the DU145 tumour and in brain, as assessed by PET imaging. We conclude that 64Cu is not delivered to DU145 cancer cells in vitro as a complex with amino acids but its cellular accumulation is enhanced by l-cysteine or NAC influx to cells. The latter effect was not demonstrable in vivo in the DU145 xenograft.

Transport of Amino Acids Across the Blood-Brain Barrier

The blood-brain-barrier (BBB), present in brain capillaries, constitutes an essential barrier mechanism for normal functioning and development of the brain. The presence of tight junctions between adjacent endothelial cells restricts permeability and movement of molecules between extracellular fluid and plasma. The protein complexes that control cell-cell attachment also polarize cellular membrane, so that it can be divided into luminal (blood-facing) and abluminal (brain) sides, and each solute that enters/leaves the brain must cross both membranes. Several amino acid (AA) transport systems with different distributions on both sides of the BBB have been described. In a broad sense, there are at least five different systems of facilitative transporters and all of them are found in the luminal membrane. Some of these transporters are very specific for a small group of substrates and are located exclusively on the luminal side of the BBB. However, the two major facilitative carriers, system L and system y⁺, are located in both membranes, although asymmetrically. The position of these Na⁺-independent transporters ensures AA availability in the brain and also its bidirectional transport across the endothelial cells. On the other hand, there are several Na⁺-dependent transport systems that transport AAs against its concentration gradient together with the movement of Na⁺ ions. The majority of these active transporters are present exclusively at the abluminal membrane and are responsible for AA efflux from the brain into the endothelial cells. Since they are Na⁺-coupled, the sodium pump Na⁺/K⁺-ATPase is also highly expressed on this abluminal side of the BBB. Once inside the cell, the facilitative transporters located in the luminal membranes mediate export from the endothelial cell to the blood. In summary, the polarized distribution of these transport systems between the luminal and abluminal membranes, and the fact that more than one transporter may carry the same substrate, ensures supply and excretion of AAs in and out of the brain, thereby controlling its homeostasis and proper function.