The SLC36 family of proton-coupled amino acid transporters and their potential role in drug transport

Cancer SLC6A6-mediated taurine uptake transactivates immune checkpoint genes and induces exhaustion in CD8+ T cells

Taurine is used to bolster immunity, but its effects on antitumor immunity are unclear. Here, we report that cancer-related taurine consumption causes T cell exhaustion and tumor progression. The taurine transporter SLC6A6 is correlated with aggressiveness and poor outcomes in multiple cancers. SLC6A6-mediated taurine uptake promotes the malignant behaviors of tumor cells but also increases the survival and effector function of CD8+ T cells. Tumor cells outcompete CD8+ T cells for taurine by overexpressing SLC6A6, which induces T cell death and malfunction, thereby fueling tumor progression. Mechanistically, taurine deficiency in CD8+ T cells increases ER stress, promoting ATF4 transcription in a PERK-JAK1-STAT3 signaling-dependent manner. Increased ATF4 transactivates multiple immune checkpoint genes and induces T cell exhaustion. In gastric cancer, we identify a chemotherapy-induced SP1-SLC6A6 regulatory axis. Our findings suggest that tumoral-SLC6A6-mediated taurine deficiency promotes immune evasion and that taurine supplementation reinvigorates exhausted CD8+ T cells and increases the efficacy of cancer therapies.

Comprehensive review of amino acid transporters as therapeutic targets

The solute carrier (SLC) family, with more than 400 membrane-bound proteins, facilitates the transport of a wide array of substrates such as nutrients, ions, metabolites, and drugs across biological membranes. Amino acid transporters (AATs) are membrane transport proteins that mediate transfer of amino acids into and out of cells or cellular organelles. AATs participate in many important physiological functions including nutrient supply, metabolic transformation, energy homeostasis, redox regulation, and neurological regulation. Several AATs have been found to significantly impact the progression of human malignancies, and dysregulation of AATs results in metabolic reprogramming affecting tumor growth and progression. However, current clinical therapies that directly target AATs have not been developed. The purpose of this review is to highlight the structural and functional diversity of AATs, the molecular mechanisms in human diseases such as tumors, kidney diseases, and emerging therapeutic strategies for targeting AATs.

Metabolic Signature of Warburg Effect in Cancer: An Effective and Obligatory Interplay between Nutrient Transporters and Catabolic/Anabolic Pathways to Promote Tumor Growth

Aerobic glycolysis in cancer cells, originally observed by Warburg 100 years ago, which involves the production of lactate as the end product of glucose breakdown even in the presence of adequate oxygen, is the foundation for the current interest in the cancer-cell-specific reprograming of metabolic pathways. The renewed interest in cancer cell metabolism has now gone well beyond the original Warburg effect related to glycolysis to other metabolic pathways that include amino acid metabolism, one-carbon metabolism, the pentose phosphate pathway, nucleotide synthesis, antioxidant machinery, etc. Since glucose and amino acids constitute the primary nutrients that fuel the altered metabolic pathways in cancer cells, the transporters that mediate the transfer of these nutrients and their metabolites not only across the plasma membrane but also across the mitochondrial and lysosomal membranes have become an integral component of the expansion of the Warburg effect. In this review, we focus on the interplay between these transporters and metabolic pathways that facilitates metabolic reprogramming, which has become a hallmark of cancer cells. The beneficial outcome of this recent understanding of the unique metabolic signature surrounding the Warburg effect is the identification of novel drug targets for the development of a new generation of therapeutics to treat cancer.

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.

Effects of lncRNA MTC on protein expression in skin fibroblasts of Liaoning Cashmere goat based on iTRAQ technique

Existing experiments have found a new intergenic lncRNA activated by melatonin, which is called lncRNA MTC. However, the regulatory mechanism of lncRNA MTC in Liaoning Cashmere goat skin fibroblasts has not been clarified. Specific knockdown of lncRNA MTC inhibits cell proliferation and increases apoptosis. iTRAQ reagent was used for relative and absolute quantification of proteins in lncRNA MTC-KD and NC groups to evaluate changes in protein expression during dermal fibroblast development following lncRNA MTC deletion. A total of 5931 proteins were found in Liaoning Cashmere goat skin fibroblasts, of which 123 were differentially expressed, including 32 up-regulated proteins and 91 down-regulated proteins. Of the 91 down-regulated proteins, 32 act mainly through related pathways (e.g., cell cycle, mitochondrial function, ribosomal structure, vesicular transport, cytoskeletal components and skin morphogenesis). LncRNA MTC facilitates the proliferation of Liaoning Cashmere goat skin fibroblasts by regulating ITGB5, TlN2, CTSS, POLG, RAP1B, CHAF1A, CDCA8 and other proteins involved in cell proliferation. The results of this study provide some candidate proteins for the in-depth investigation of the molecular mechanism of lncRNA MTC, which facilitates hair growth in cashmere goats and provides more insights into their regulatory networks and biochemical pathways.

Nicotinamide Adenine Dinucleotide Deficiency and Its Impact on Mammalian Development

Significance: Nicotinamide adenine dinucleotide (NAD) is an important molecule synthesized from tryptophan or vitamin B3 and involved in numerous cellular reactions. NAD deficiency during pregnancy causes congenital NAD deficiency disorder (CNDD) characterized by multiple congenital malformations and/or miscarriage. Studies in genetically engineered mice replicating mutations found in human patient cases show that CNDD can be prevented by dietary supplements. Recent Advances: A growing number of patient reports show that biallelic loss-of-function of genes involved in NAD de novo synthesis (KYNU, HAAO, NADSYN1) cause CNDD. Other factors that limit the availability of NAD precursors, for example, limited dietary precursor supply or absorption, can cause or contribute to NAD deficiency and result in CNDD in mice. Molecular flux experiments allow quantitative understanding of NAD precursor concentrations in the circulation and their usage by different cells. Studies of NAD-consuming enzymes and contributors to NAD homeostasis help better understand how perturbed NAD levels are implicated in various diseases and adverse pregnancy outcomes. Critical Issues: NAD deficiency is one of the many known causes of adverse pregnancy outcomes, but its prevalence in the human population and among pregnant women is unknown. Since NAD is involved in hundreds of diverse cellular reactions, determining how NAD deficiency disrupts embryogenesis is an important challenge. Future Directions: Furthering our understanding of the molecular fluxes between the maternal and embryonic circulation during pregnancy, the NAD-dependent pathways active in the developing embryo, and the molecular mechanisms by which NAD deficiency causes adverse pregnancy outcomes will provide direction for future prevention strategies. Antioxid. Redox Signal. 39, 1108-1132.

Betaine-Based and Polyguanidine-Inserted Zwitterionic Micelle as a Promising Platform to Conquer the Intestinal Mucosal Barrier

Developing nanocarriers for oral drug delivery is often hampered by the dilemma of balancing mucus permeation and epithelium absorption, since huge differences in surface properties are required for sequentially overcoming these two processes. Inspired by mucus-penetrating viruses that universally possess a dense charge distribution with equal opposite charges on their surfaces, we rationally designed and constructed a poly(carboxybetaine)-based and polyguanidine-inserted cationic micelle platform (hybrid micelle) for oral drug delivery. The optimized hybrid micelle exhibited a great capacity for sequentially overcoming the mucus and villi barriers. It was demonstrated that a longer zwitterionic chain was favorable for mucus diffusion for hybrid micelles but not conducive to cellular uptake. In addition, the significantly enhanced internalization absorption of hybrid micelles was attributed to the synergistic effect of polyguanidine and proton-assisted amine acid transporter 1 (PAT1). Moreover, the retrograde pathway was mainly involved in the intracellular transport of hybrid micelles and transcytosis delivery. Furthermore, the prominent intestinal mucosa absorption in situ and in vivo liver distribution of the oral hybrid micelle were both detected. The results of this study indicated that the hybrid micelles were capable of conquering the intestinal mucosal barrier, having a great potential for oral application of drugs with poor oral bioavailability.

Co-option of a conserved host glutamine transporter facilitates aphid/Buchnera metabolic integration

Organisms across the tree of life colonize novel environments by partnering with bacterial symbionts. These symbioses are characterized by intimate integration of host/endosymbiont biology at multiple levels, including metabolically. Metabolic integration is particularly important for sap-feeding insects and their symbionts, which supplement nutritionally unbalanced host diets. Many studies reveal parallel evolution of host/endosymbiont metabolic complementarity in amino acid biosynthesis, raising questions about how amino acid metabolism is regulated, how regulatory mechanisms evolve, and the extent to which similar mechanisms evolve in different systems. In the aphid/Buchnera symbiosis, the transporter ApGLNT1 (Acyrthosiphon pisum glutamine transporter 1) supplies glutamine, an amino donor in transamination reactions, to bacteriocytes (where Buchnera reside) and is competitively inhibited by Buchnera-supplied arginine-consistent with a role regulating amino acid metabolism given host demand for Buchnera-produced amino acids. We examined how ApGLNT1 evolved a regulatory role by functionally characterizing orthologs in insects with and without endosymbionts. ApGLNT1 orthologs are functionally similar, and orthology searches coupled with homology modeling revealed that GLNT1 is ancient and structurally conserved across insects. Our results indicate that the ApGLNT1 symbiotic regulatory role is derived from its ancestral role and, in aphids, is likely facilitated by loss of arginine biosynthesis through the urea cycle. Given consistent loss of host arginine biosynthesis and retention of endosymbiont arginine supply, we hypothesize that GLNT1 is a general mechanism regulating amino acid metabolism in sap-feeding insects. This work fills a gap, highlighting the broad importance of co-option of ancestral proteins to novel contexts in the evolution of host/symbiont systems.

Molecular landscapes of glioblastoma cell lines revealed a group of patients that do not benefit from WWOX tumor suppressor expression

Introduction

Glioblastoma (GBM) is notorious for its clinical and molecular heterogeneity, contributing to therapeutic failure and a grim prognosis. WWOX is one of the tumor suppressor genes important in nervous tissue or related pathologies, which was scarcely investigated in GBM for reliable associations with prognosis or disease progression despite known alterations. Recently, we observed a phenotypic heterogeneity between GBM cell lines (U87MG, T98G, U251MG, DBTRG-05MG), among which the anti-GBM activity of WWOX was generally corresponding, but colony growth and formation were inconsistent in DBTRG-05MG. This prompted us to investigate the molecular landscapes of these cell lines, intending to translate them into the clinical context.

Methods

U87MG/T98G/U251MG/DBTRG-05MG were subjected to high-throughput sequencing, and obtained data were explored via weighted gene co-expression network analysis, differential expression analysis, functional annotation, and network building. Following the identification of the most relevant DBTRG-distinguishing driver genes, data from GBM patients were employed for, e.g., differential expression analysis, survival analysis, and principal component analysis.

Results

Although most driver genes were unique for each cell line, some were inversely regulated in DBTRG-05MG. Alongside driver genes, the differentially-expressed genes were used to build a WWOX-related network depicting protein-protein interactions in U87MG/T98G/U251MG/DBTRG-05MG. This network revealed processes distinctly regulated in DBTRG-05MG, e.g., microglia proliferation or neurofibrillary tangle assembly. POLE4 and HSF2BP were selected as DBTRG-discriminating driver genes based on the gene significance, module membership, and fold-change. Alongside WWOX, POLE4 and HSF2BP expression was used to stratify patients into cell lines-resembling groups that differed in, e.g., prognosis and treatment response. Some differences from a WWOX-related network were certified in patients, revealing genes that clarify clinical outcomes. Presumably, WWOX overexpression in DBTRG-05MG resulted in expression profile change resembling that of patients with inferior prognosis and drug response. Among these patients, WWOX may be inaccessible for its partners and does not manifest its anti-cancer activity, which was proposed in the literature but not regarding glioblastoma or concerning POLE4 and HSF2BP.

Conclusion

Cell lines data enabled the identification of patients among which, despite high expression of WWOX tumor suppressor, no advantageous outcomes were noted due to the cancer-promoting profile ensured by other genes.

Fast drosophila enterocyte regrowth after infection involves a reverse metabolic flux driven by an amino acid transporter

Upon exposure to a bacterial pore-forming toxin, enterocytes rapidly purge their apical cytoplasm into the gut lumen, resulting in a thin intestinal epithelium. The enterocytes regain their original shape and thickness within 16 h after the ingestion of the bacteria. Here, we show that the regrowth of Drosophila enterocytes entails an inversion of metabolic fluxes from the organism back toward the intestine. We identify a proton-assisted transporter, Arcus, that is required for the reverse absorption of amino acids and the timely recovery of the intestinal epithelium. Arcus is required for a peak of amino acids appearing in the hemolymph shortly after infection. The regrowth of enterocytes involves the insulin signaling pathway and Myc. The purge decreases Myc mRNA levels, which subsequently remain at low levels in the arcus mutant. Interestingly, the action of arcus and Myc in the intestinal epithelium is not cell-autonomous, suggesting amino acid fluxes within the intestinal epithelium.

The Role of Proton-Coupled Amino Acid Transporter 2 (SLC36A2) in Cold-Induced Thermogenesis of Mice

Brown adipocytes mainly utilize glucose and fatty acids to produce energy, which play key roles in thermogenesis. Furthermore, brown adipocytes also utilize other substrates, such as amino acids, for energy expenditure in various conditions. Here, we report the new physiological roles of proton-coupled amino acid transporters, SLC36A2 and SLC36A3, on global energy metabolism. The relative mRNA expression levels of both Slc36a2 and Slc36a3 were all highest in brown adipose tissue. We then generated global Slc36a2 and Slc36a3 knockout mice to investigate their functions in metabolism. Neither loss of Slc36a2 nor Slc36a3 affected the body weight and body composition of the mice. Slc36a2 knockout mice exhibited increased oxygen consumption during the daytime. After cold treatment, inhibition of Slc36a2 significantly decreased the mass of brown adipose tissue compared to wildtype mice, while it lowered the expression level of Cpt1a. Moreover, the serum lipid levels and liver mass were also decreased in Slc36a2 knockout mice after cold treatment. On the contrary, Slc36a3 knockout impaired glucose tolerance and up-regulated serum LDL-cholesterol concentration. Thus, SLC36A2 and SLC36A3 play central and different roles in the energy metabolism of the mice.

Glycine: The Smallest Anti-Inflammatory Micronutrient

Glycine is a non-essential amino acid with many functions and effects. Glycine can bind to specific receptors and transporters that are expressed in many types of cells throughout an organism to exert its effects. There have been many studies focused on the anti-inflammatory effects of glycine, including its abilities to decrease pro-inflammatory cytokines and the concentration of free fatty acids, to improve the insulin response, and to mediate other changes. However, the mechanism through which glycine acts is not clear. In this review, we emphasize that glycine exerts its anti-inflammatory effects throughout the modulation of the expression of nuclear factor kappa B (NF-κB) in many cells. Although glycine is a non-essential amino acid, we highlight how dietary glycine supplementation is important in avoiding the development of chronic inflammation.

Effect of muscle fibre types and carnosine levels on the expression of carnosine-related genes in pig skeletal muscle

It is generally accepted that carnosine (β-alanyl-L-histidine) content is higher in glycolytic than in oxidative muscle fibres, but the underlying mechanisms responsible for this difference remain to be elucidated. A first study to better understand potential mechanisms involved was undertaken (1) to determine whether differences in the expression of carnosine-related enzymes (CARNS1, CNDP2) and transporters (SLC6A6, SLC15A3, SLC15A4, SLC36A1) exist between oxidative and glycolytic myofibres and (2) to study the effect of carnosine on myoblast proliferative growth and on carnosine-related gene expression in cultured myoblasts isolated from glycolytic and oxidative muscles. Immunohistochemistry analyses were conducted to determine the cellular localization of carnosine-related proteins. Laser-capture microdissection and qPCR analyses were performed to measure the expression of carnosine-related genes in different myofibres isolated from the longissimus dorsi muscle of ten crossbred pigs. Myogenic cells originating from glycolytic and oxidative muscles were cultured to assess the effect of carnosine (0, 10, 25 and 50 mM) on their proliferative growth and on carnosine-related gene expression. The mRNA abundance of CNDP2 and of the studied carnosine transporters was higher in oxidative than in glycolytic myofibres. Since carnosine synthase (CARNS1) mRNA abundance was not affected by either the fibre type or the addition of carnosine to myoblasts, its transcriptional regulation would not be the main process by which carnosine content differences are determined in oxidative and glycolytic muscles. The addition of carnosine to myoblasts leading to a dose-dependent increase in SLC15A3 transcripts, however, suggests a role for this transporter in carnosine uptake and/or efflux to maintain cellular homeostasis.

Lysosomal Ion Channels and Lysosome-Organelle Interactions

Intracellular organelles exchange their luminal contents with each other via both vesicular and non-vesicular mechanisms. By forming membrane contact sites (MCSs) with ER and mitochondria, lysosomes mediate bidirectional transport of metabolites and ions between lysosomes and organelles that regulate lysosomal physiology, movement, membrane remodeling, and membrane repair. In this chapter, we will first summarize the current knowledge of lysosomal ion channels and then discuss the molecular and physiological mechanisms that regulate lysosome-organelle MCS formation and dynamics. We will also discuss the roles of lysosome-ER and lysosome-mitochondria MCSs in signal transduction, lipid transport, Ca ²⁺ transfer, membrane trafficking, and membrane repair, as well as their roles in lysosome-related pathologies.

In situ rearranged multifunctional lipid nanoparticles via synergistic potentiation for oral insulin delivery

Oral administration of therapeutic peptides/proteins (TPPs) is confronted with multiple gastrointestinal (GI) barriers such as mucus and intestinal epithelium, and the first-pass metabolism in the liver is also responsible for low bioavailability. In situ rearranged multifunctional lipid nanoparticles (LNs) were developed to overcome these obstacles via synergistic potentiation for oral insulin delivery. After the reverse micelles of insulin (RMI) containing functional components were gavaged, LNs formed in situ under the hydration effect of GI fluid. The nearly electroneutral surface generated by the rearrangement of sodium deoxycholate (SDC) and chitosan (CS) on the reverse micelle core facilitated LNs (RMI@SDC@SB12-CS) to overcome mucus barrier and the sulfobetaine 12 (SB12) modification further promoted epithelial uptake of LNs. Subsequently, chylomicron-like particles formed by the lipid core in the intestinal epithelium were easily transported to the lymphatic circulation and then into the systemic circulation, thus avoiding hepatic first-pass metabolism. Eventually, RMI@SDC@SB12-CS achieved a high pharmacological bioavailability of 13.7% in diabetic rats. In conclusion, this study provides a versatile platform for enhanced oral insulin delivery.

Tissue-specific effects of exercise as NAD+ -boosting strategy: Current knowledge and future perspectives

Nicotinamide adenine dinucleotide (NAD⁺ ) is an evolutionarily highly conserved coenzyme with multi-faceted cell functions, including energy metabolism, molecular signaling processes, epigenetic regulation, and DNA repair. Since the discovery that lower NAD⁺ levels are a shared characteristic of various diseases and aging per se, several NAD⁺ -boosting strategies have emerged. Other than pharmacological and nutritional approaches, exercise is thought to restore NAD⁺ homeostasis through metabolic adaption to chronically recurring states of increased energy demand. In this review we discuss the impact of acute exercise and exercise training on tissue-specific NAD⁺ metabolism of rodents and humans to highlight the potential value as NAD⁺ -boosting strategy. By interconnecting results from different investigations, we aim to draw attention to tissue-specific alterations in NAD⁺ metabolism and the associated implications for whole-body NAD⁺ homeostasis. Acute exercise led to profound alterations of intracellular NAD⁺ metabolism in various investigations, with the magnitude and direction of changes being strongly dependent on the applied exercise modality, cell type, and investigated animal model or human population. Exercise training elevated NAD⁺ levels and NAD⁺ metabolism enzymes in various tissues. Based on these results, we discuss molecular mechanisms that might connect acute exercise-induced disruptions of NAD⁺ /NADH homeostasis to chronic exercise adaptions in NAD⁺ metabolism. Taking this hypothesis-driven approach, we hope to inspire future research on the molecular mechanisms of exercise as NAD⁺ -modifying lifestyle intervention, thereby elucidating the potential therapeutic value in NAD⁺ -related pathologies.

In Situ Polymerization of Zwitterions on Therapeutic Proteins to Enable Their Effective Oral Delivery

Oral administration of protein drugs has always been challenging owing to various intestinal barriers. Herein, we developed an efficient oral protein delivery strategy by using in situ polymerization of zwitterions to encapsulate proteins, which were then loaded into enteric coated capsules for oral feeding. After oral administration of such capsules, the enteric coating would be degraded once the capsule enters the intestine, releasing polyzwitterion/protein nanocomplexes. With the help of polyzwitterion modification, such nanocomplexes were able to pass through the mucus and cellular barriers, likely by the proton-assisted amino acid transporter 1 (PAT1) pathway. Such a polyzwitterion-based protein encapsulation strategy could allow for effective oral delivery of different proteins, including bovine serum albumin (BSA), insulin, and antibodies. Using this strategy, the oral bioavailabilities of insulin and immunoglobin G (IgG) were measured to be as high as 16.9% and 12.5%, respectively. Notably, oral feeding of polyzwitterion/insulin capsules could effectively lower the blood glucose level of diabetic animals (mice, rats, and pigs). Moreover, polyzwitterion/antiprogramed death-1 (αPD-1) capsules were able to induce efficient antitumor immune responses, showing significant tumor inhibition effects toward B16F10- and 4T1-tumor bearing mouse models after oral administration. No significant toxic effect was observed for such oral protein formulations in the treated animals. Our work presents a strategy for the efficient oral delivery of protein drugs, including those with large molecular weights (e.g., antibodies) that can hardly be orally delivered using existing technologies.

Potential of Nuclear Imaging Techniques to Study the Oral Delivery of Peptides

Peptides are small biomolecules known to stimulate or inhibit important functions in the human body. The clinical use of peptides by oral delivery, however, is very limited due to their sensitive structure and physiological barriers present in the gastrointestinal tract. These barriers can be overcome with chemical and mechanical approaches protease inhibitors, permeation enhancers, and polymeric encapsulation. Studying the success of these approaches pre-clinically with imaging techniques such as fluorescence imaging (IVIS) and optical microscopy is difficult due to the lack of in-depth penetration. In comparison, nuclear imaging provides a better platform to observe the gastrointestinal transit and quantitative distribution of radiolabeled peptides. This review provides a brief background on the oral delivery of peptides and states examples from the literature on how nuclear imaging can help to observe and analyze the gastrointestinal transit of oral peptides. The review connects the fields of peptide delivery and nuclear medicine in an interdisciplinary way to potentially overcome the challenges faced during the study of oral peptide formulations.

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects.

PAT2 regulates vATPase assembly and lysosomal acidification in brown adipocytes

OBJECTIVE

Brown adipocytes play a key role in maintaining body temperature as well as glucose and lipid homeostasis. However, brown adipocytes need to adapt their thermogenic activity and substrate utilization to changes in nutrient availability. Amongst the multiple factors influencing brown adipocyte activity, autophagy is an important regulatory element of thermogenic capacity and activity. Nevertheless, a specific sensing mechanism of extracellular amino acid availability linking autophagy to nutrient availability in brown adipocytes is unknown.

METHODS

To characterize the role of the amino acid transporter PAT2/SLC36A2 in brown adipocytes, loss or gain of function of PAT2 were studied with respect to differentiation, subcellular localization, lysosomal activity and autophagy. Activity of vATPase was evaluated by quenching of EGFP fused to LC3 or FITC-dextran loaded lysosomes in brown adipocytes upon amino acid starvation, whereas the effect of PAT2 on assembly of the vATPase was investigated by Native-PAGE.

RESULTS

We show that PAT2 translocates from the plasma membrane to the lysosome in response to amino acid withdrawal. Loss or overexpression of PAT2 impair lysosomal acidification and starvation induced S6K re-phosphorylation, as PAT2 facilitates the assembly of the lysosomal vATPase, by recruitment of the cytoplasmic V1 subunit to the lysosome.

CONCLUSION

PAT2 is an important sensor of extracellular amino acids and regulator of lysosomal acidification in brown adipocytes.

Impact of Zwitterionic Polymers on the Tumor Permeability of Molecular Bottlebrush-Based Nanoparticles

Biocompatible polymers possessing antifouling properties for biomolecules are necessary to be combined with nanoparticles for cancer chemotherapy to improve their retention in blood and subsequent tumor accumulation. However, these properties simultaneously lead to poor affinity to cells, and low tumor tissue permeability subsequently, which is one of the major barriers in achieving efficient anticancer efficacy. To address this, we try to elucidate the tumor permeability of nanoparticles using molecular bottlebrushes (MBs) as model polymeric nanoparticles composed of various biocompatible polymers. An MB comprising nonionic poly[(ethylene glycol) methyl ether methacrylate] (PEGMA) shows no tumor permeability at all, whereas zwitterionic MBs composed of poly(phosphobetaine methacrylate), poly(sulfobetaine methacrylate), or poly(carboxybetaine methacrylate) penetrate deeply into tumor tissues. The carboxybetaine-based MBs showed an efficient cellular uptake into cancer cells while the other MBs did not, which enable them to penetrate into tumor tissues via the transcytosis pathway. Additionally, their permeability is based on intercellular or intracellular pathways, which might be related to the zwitterionic betaine properties that recognize protein transporters on cancer cells. Surprisingly, incorporating only 10 mol % of the zwitterionic betaine polymers into PEGMA-based MBs significantly enhances their tissue permeability. This platform technology enables us to redesign the PEG-based nanoparticles developed for cancer chemotherapy in clinical applications.

Identification of novel alternative splicing associated with mastitis disease in Holstein dairy cows using large gap read mapping

Background

Mastitis is a very common disease in the dairy industry that producers encounter daily. Transcriptomics, using RNA-Sequencing (RNA - Seq) technology, can be used to study the functional aspect of mastitis resistance to identify animals that have a better immune response to mastitis. When the cow has mastitis, not only genes but also specific mRNA isoforms generated via alternative splicing (AS) could be differentially expressed (DE), leading to the phenotypic variation observed. Therefore, the objective of this study was to use large gap read mapping to identify mRNA isoforms DE between healthy and mastitic milk somatic cell samples (N = 12). These mRNA isoforms were then categorized based on being 1) annotated mRNA isoforms for gene name and length, 2) annotated mRNA isoforms with different transcript length and 3) novel mRNA isoforms of non - annotated genes.

Results

Analysis identified 333 DE transcripts (with at least 2 mRNA isoforms annotated, with at least one being DE) between healthy and mastitic samples corresponding to 303 unique genes. Of these 333 DE transcripts between healthy and mastitic samples, 68 mRNA isoforms are annotated in the bovine genome reference (ARS.UCD.1.2), 249 mRNA isoforms had novel transcript lengths of known genes and 16 were novel transcript lengths of non - annotated genes in the bovine genome reference (ARS.UCD.1.2). Functional analysis including gene ontology, gene network and metabolic pathway analysis was performed on the list of 288 annotated and unique DE mRNA isoforms. In total, 67 significant metabolic pathways were identified including positive regulation of cytokine secretion and immune response. Additionally, numerous DE novel mRNA isoforms showed potential involvement with the immune system or mastitis. Lastly, QTL annotation analysis was performed on coding regions of the DE mRNA isoforms, identifying overlapping QTLs associated with clinical mastitis and somatic cell score.

Conclusion

This study identified novel mRNA isoforms generated via AS that could lead to differences in the immune response of Holstein dairy cows and be potentially implemented in future breeding programs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08430-x.

An attempt to valorize the only black meat chicken breed of India by delineating superior functional attributes of its meat

Kadaknath, the only black chicken indigenous to India, faces the threat of extinction due to declining numbers. Its meat is used in tribal medicine for invigorating and health-promoting properties. Expectations of immune-boosting and therapeutic properties in its meat are creating a buzz these days. Thus, Kadaknath meat was explored and further compared with the commercial Cobb 400 broiler (Cobb) for the functional traits that might be contributing towards proclaimed pharmacological benefits. Birds (n = 20/ group) were raised under similar management conditions and the two primal chicken meat cuts (breast and thigh) were collected at the marketing age. Kadaknath meat was found to be an enriched source of functional biomolecules (carnosine, anserine, creatine). Its breast meat carnosine content was more than double of the Cobb broiler, 6.10 ± 0.13 and 2.73 ± 0.1 mg/ g of wet tissue, respectively. Similarly, the thigh meat of Kadaknath was a significantly (P < 0.05) richer source of carnosine. The genetic background was a key determinant for muscle carnosine content as a significant abundance of CARNS1 and SLC36A1 expression was identified in the Kadaknath breast. The superior functional property of Kadaknath meat was established by the antioxidant capacity established by the Oxygen radical absorbance capacity assay and a stronger ability to inhibit the formation of advanced glycation end products (AGEs). The identification of fairly unknown nutritional and functional advantages of Kadaknath meat could potentially change the paradigm with its meat consumption. It will help in developing a brand name for Kadaknath products that will propel an increase in its market share and ultimately conservation of this unique but endangered poultry germplasm.

Hyperglycinuria: diagnosis in middle age

Isolated hyperglycinuria is a rare disorder that is associated with osteoporosis and renal calculi. We report findings in a middle-aged, black woman who presented for renal function evaluation with a history of transient hypobicarbonataemia associated with topiramate therapy. She displayed the full triad of high urinary glycine, early-onset osteopenia despite normal reproductive hormones, and renal calculus with high urinary oxalate, phosphate and uric acid. Parathyroid hormone and fibroblast growth factor 23 were both normal. Formal genetic testing did not reveal mutations in SLC6A20, SLC6A18, SLC6A19, SLC36A2, the known genes associated with glycinuria; however, black individuals are poorly represented in the genetic databases. It may well be that otherwise unidentified mutations may be present or that topiramate may result in a lingering proximal tubule defect even after cessation of the drug.

Unconventional Functions of Amino Acid Transporters: Role in Macropinocytosis (SLC38A5/SLC38A3) and Diet-Induced Obesity/Metabolic Syndrome (SLC6A19/SLC6A14/SLC6A6)

Amino acid transporters are expressed in mammalian cells not only in the plasma membrane but also in intracellular membranes. The conventional function of these transporters is to transfer their amino acid substrates across the lipid bilayer; the direction of the transfer is dictated by the combined gradients for the amino acid substrates and the co-transported ions (Na⁺, H⁺, K⁺ or Cl⁻) across the membrane. In cases of electrogenic transporters, the membrane potential also contributes to the direction of the amino acid transfer. In addition to this expected traditional function, several unconventional functions are known for some of these amino acid transporters. This includes their role in intracellular signaling, regulation of acid–base balance, and entry of viruses into cells. Such functions expand the biological roles of these transporters beyond the logical amino acid homeostasis. In recent years, two additional unconventional biochemical/metabolic processes regulated by certain amino acid transporters have come to be recognized: macropinocytosis and obesity. This adds to the repertoire of biological processes that are controlled and regulated by amino acid transporters in health and disease. In the present review, we highlight the unusual involvement of selective amino acid transporters in macropinocytosis (SLC38A5/SLC38A3) and diet-induced obesity/metabolic syndrome (SLC6A19/SLC6A14/SLC6A6).

Measuring the oral bioavailability of protein hydrolysates derived from food sources: A critical review of current bioassays

BACKGROUND

Food proteins are a source of hydrolysates with potentially useful biological attributes. Bioactive peptides from food-derived proteins are released from hydrolysates using exogenous industrial processes or endogenous intestinal enzymes. Current in vitro permeability assays have limitations in predicting the oral bioavailability (BA) of bioactive peptides in humans. There are also difficulties in relating the low blood levels of food-derived bioactive peptides detected in preclinical in vivo models to pharmacodynamic read-outs relevant for humans.

SCOPE AND APPROACH

In this review, we describe in vitro assays of digestion, permeation, and metabolism as indirect predictors of the potential oral BA of hydrolysates and their constituent bioactive peptides. We discuss the relationship between industrial hydrolysis processes and the oral BA of hydrolysates and their peptide by-products.

KEY FINDINGS

Hydrolysates are challenging for analytical detection methods due to capacity for enzymatic generation of peptides with novel sequences and also new modifications of these peptides during digestion. Mass spectrometry and peptidomics can improve the capacity to detect individual peptides released from complex hydrolysates in biological milieu.

A Proton-Coupled Transport System for β-Hydroxy-β-Methylbutyrate (HMB) in Blood-Brain Barrier Endothelial Cell Line hCMEC/D3

β-Hydroxy-β-methylbutyrate (HMB), a leucine metabolite, is used as a nutritional ingredient to improve skeletal muscle health. Preclinical studies indicate that this supplement also elicits significant benefits in the brain; it promotes neurite outgrowth and prevents age-related reductions in neuronal dendrites and cognitive performance. As orally administered HMB elicits these effects in the brain, we infer that HMB crosses the blood-brain barrier (BBB). However, there have been no reports detailing the transport mechanism for HMB in BBB. Here we show that HMB is taken up in the human BBB endothelial cell line hCMEC/D3 via H⁺-coupled monocarboxylate transporters that also transport lactate and β-hydroxybutyrate. MCT1 (monocarboxylate transporter 1) and MCT4 (monocarboxylate transporter 4) belonging to the solute carrier gene family SLC16 (solute carrier, gene family 16) are involved, but additional transporters also contribute to the process. HMB uptake in BBB endothelial cells results in intracellular acidification, demonstrating cotransport with H⁺. Since HMB is known to activate mTOR with potential to elicit transcriptomic changes, we examined the influence of HMB on the expression of selective transporters. We found no change in MCT1 and MCT4 expression. Interestingly, the expression of LAT1 (system L amino acid transporter 1), a high-affinity transporter for branched-chain amino acids relevant to neurological disorders such as autism, is induced. This effect is dependent on mTOR (mechanistic target of rapamycine) activation by HMB with no involvement of histone deacetylases. These studies show that HMB in systemic circulation can cross the BBB via carrier-mediated processes, and that it also has a positive influence on the expression of LAT1, an important amino acid transporter in the BBB.

Insights into the Interaction of Lysosomal Amino Acid Transporters SLC38A9 and SLC36A1 Involved in mTORC1 Signaling in C2C12 Cells

Amino acids are critical for mammalian target of rapamycin complex 1 (mTORC1) activation on the lysosomal surface. Amino acid transporters SLC38A9 and SLC36A1 are the members of the lysosomal amino acid sensing machinery that activates mTORC1. The current study aims to clarify the interaction of SLC38A9 and SLC36A1. Here, we discovered that leucine increased expressions of SLC38A9 and SLC36A1, leading to mTORC1 activation. SLC38A9 interacted with SLC36A1 and they enhanced each other's expression levels and locations on the lysosomal surface. Additionally, the interacting proteins of SLC38A9 in C2C12 cells were identified to participate in amino acid sensing mechanism, mTORC1 signaling pathway, and protein synthesis, which provided a resource for future investigations of skeletal muscle mass.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

A pH-Triggered Self-Unpacking Capsule Containing Zwitterionic Hydrogel-Coated MOF Nanoparticles for Efficient Oral Exendin-4 Delivery

Oral peptide or protein delivery is considered a revolutionary alternative to daily subcutaneous injection; however, major challenges remain in terms of impediments of the gastrointestinal environment and the intestinal epithelium consisting of mucus and the epithelial cell layer, leading to low bioavailability. To protect against gastrointestinal degradation and promote penetration across the intestinal mucosa, a pH-triggered self-unpacking capsule encapsulating zwitterionic hydrogel-coated metal-organic framework (MOF) nanoparticles is engineered. The MOF nanoparticles possess a high exendin-4 loading capacity, and the zwitterionic hydrogel layer imparts unique capability of permeation across the mucus layer and effective internalization by epithelial cells to the nano-vehicles. In addition to the gastro-resistant feature, the pH-responsive capsules are dissociated drastically in the intestinal environment due to the rapid generation of abundant CO₂ bubbles, which triggers a sudden release of the nanoparticles. After oral administration of the capsules containing exendin-4-loaded nanoparticles into a diabetes rat model, markedly enhanced plasma exendin-4 levels are achieved for over 8 h, leading to significantly increased endogenous insulin secretion and a remarkable hypoglycemic effect with a relative pharmacological availability of 17.3%. Owing to the low risk of hypoglycemia, this oral exendin-4 strategy will provide a vast potential for daily and facile diabetes treatment.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

Blood-brain barrier alterations in human brain tumors revealed by genome-wide transcriptomic profiling

BACKGROUND

Brain tumors, whether primary or secondary, have limited therapeutic options despite advances in understanding driver gene mutations and heterogeneity within tumor cells. The cellular and molecular composition of brain tumor stroma, an important modifier of tumor growth, has been less investigated to date. Only few studies have focused on the vasculature of human brain tumors despite the fact that the blood-brain barrier (BBB) represents the major obstacle for efficient drug delivery.

METHODS

In this study, we employed RNA sequencing to characterize transcriptional alterations of endothelial cells isolated from primary and secondary human brain tumors. We used an immunoprecipitation approach to enrich for endothelial cells from normal brain, glioblastoma (GBM) and lung cancer brain metastasis (BM).

RESULTS

Analysis of the endothelial transcriptome showed deregulation of genes implicated in cell proliferation, angiogenesis and deposition of extracellular matrix (ECM) in the vasculature of GBM and BM. Deregulation of genes defining the BBB dysfunction module were found in both tumor types. We identified deregulated expression of genes in vessel-associated fibroblasts in GBM.

CONCLUSION

We characterize alterations in BBB genes in GBM and BM vasculature and identify proteins that might be exploited for developing drug delivery platforms. In addition, our analysis on vessel-associated fibroblasts in GBM shows that the cellular composition of brain tumor stroma merits further investigation.

Transcriptional Response of Osmolyte Synthetic Pathways and Membrane Transporters in a Euryhaline Diatom During Long-term Acclimation to a Salinity Gradient

How diatoms respond to fluctuations in osmotic pressure is important from both ecological and applied perspectives. It is well known that osmotic stress affects photosynthesis and can result in the accumulation of compounds desirable in pharmaceutical and alternative fuel industries. Gene expression responses to osmotic stress have been studied in short-term trials, but it is unclear whether the same mechanisms are recruited during long-term acclimation. We used RNA-seq to study the genome-wide transcription patterns in the euryhaline diatom, Cyclotella cryptica, following long-term acclimation to salinity that spanned the natural range of fresh to oceanic water. Long-term acclimated C. cryptica exhibited induced synthesis or repressed degradation of the osmolytes glycine betaine, taurine and dimethylsulfoniopropionate (DMSP). Although changes in proline concentration is one of the main responses in short-term osmotic stress, we did not detect a transcriptional change in proline biosynthetic pathways in our long-term experiment. Expression of membrane transporters showed a general tendency for increased import of potassium and export of sodium, consistent with the electrochemical gradients and dependence on co-transported molecules. Our results show substantial between-genotype differences in growth and gene expression reaction norms and suggest that the regulation of proline synthesis important in short-term osmotic stress might not be maintained in long-term acclimation. Further examination using time-course gene expression experiments, metabolomics and genetic validation of gene functions would reinforce patterns inferred from RNA-seq data.

Effects of lysine and leucine in free and different dipeptide forms on the growth, amino acid profile and transcription of intestinal peptide, and amino acid transporters in turbot (Scophthalmus maximus)

This study was conducted to evaluate the effects of different dipeptides (lysine-leucine, lysine-glycine, and leucine-glycine) and free amino acids (lysine and leucine) on the growth, gene expression of intestinal peptide and amino acid transporters, and serum free amino acid concentrations in turbot. Fish (11.98 ± 0.03 g) were fed four experimental diets supplementing with crystalline amino acids (CAA), lysine-leucine (Lys-Leu), lysine-glycine (Lys-Gly), and leucine-glycine (Gly-Leu). Fish protein hydrolysate (FPH) containing a mixture of free amino acids and small peptides was designed as a positive control diet. There was no significant difference in the growth and feed utilization among three dipeptide diets (Lys-Leu, Lys-Gly, and Gly-Leu). Compared with the CAA group, feed efficiency ratio was significantly higher in the Lys-Leu and Lys-Gly groups, and protein efficiency ratio was significantly higher in the Lys-Leu group. For peptide transporter, oligopeptide transporter 1 (PepT1) mRNA level was not affected by dietary treatments. For amino acid transporters, lower expression of B0 neutral amino acid transporter 1 (B0AT1) and proton-coupled amino acid transporter 1 (PAT1) were observed in fish fed the dipeptide and FPH diets compared with the CAA diet. In conclusion, juvenile turbot fed Lys-Leu, Gly-Leu, and Lys-Gly had a similar growth performance, whereas lysine and leucine in the Lys-Leu form can be utilized more efficiently for feed utilization than those in free amino acid from. In addition, compared to free amino acids, dipeptides and fish protein hydrolysate in diets may down-regulate the expression of amino acid transporters but did not affect the expression of PepT1.

Systemic muscle wasting and coordinated tumour response drive tumourigenesis

Cancer cells demand excess nutrients to support their proliferation, but how tumours exploit extracellular amino acids during systemic metabolic perturbations remain incompletely understood. Here, we use a Drosophila model of high-sugar diet (HSD)-enhanced tumourigenesis to uncover a systemic host-tumour metabolic circuit that supports tumour growth. We demonstrate coordinate induction of systemic muscle wasting with tumour-autonomous Yorkie-mediated SLC36-family amino acid transporter expression as a proline-scavenging programme to drive tumourigenesis. We identify Indole-3-propionic acid as an optimal amino acid derivative to rationally target the proline-dependency of tumour growth. Insights from this whole-animal Drosophila model provide a powerful approach towards the identification and therapeutic exploitation of the amino acid vulnerabilities of tumourigenesis in the context of a perturbed systemic metabolic network.

Suppression of SHROOM1 Improves In Vitro and In Vivo Gene Integration by Promoting Homology-Directed Repair

Homologous recombination (HR) is often used to achieve targeted gene integration because of its higher precision and operability compared with microhomology-mediated end-joining (MMEJ) or non-homologous end-joining (NHEJ). It appears to be inefficient for gene integration in animal cells and embryos due to occurring only during cell division. Here we developed genome-wide high-throughput screening and a subsequently paired crRNA library screening to search for genes suppressing homology-directed repair (HDR). We found that, in the reporter system, HDR cells with knockdown of SHROOM1 were enriched as much as 4.7-fold than those with control. Down regulating SHROOM1 significantly promoted gene integration in human and mouse cells after cleavage by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9), regardless of the donor types. The knock-in efficiency of mouse embryos could also be doubled by the application of SHROOM1 siRNA during micro-injection. The increased HDR efficiency of SHROOM1 deletion in HEK293T cells could be counteracted by YU238259, an HDR inhibitor, but not by an NHEJ inhibitor. These results indicated that SHROOM1 was an HDR-suppressed gene and that the SHROOM1 knockdown strategy may be useful for a variety of applications, including gene editing to generate cell lines and animal models for studying gene function and human diseases.

Involvement of sodium-coupled neutral amino acid transporters (system A) in l-proline transport in the rat retinal pericytes

The retinal pericytes contribute to the supply of collagen to the basement membrane, and thus, form the structural support of the blood-retinal barrier. Since l-proline (L-Pro) is a major component of collagen, the uptake of L-Pro is an important process for the synthesis of collagen. This study was aimed to elucidate L-Pro transport mechanism(s) in the retinal pericytes. The transport of [³H]L-Pro was evaluated in the conditionally immortalized rat retinal pericyte cell line, TR-rPCT1 cells. The expression of the candidate transporter was examined by qualitative/quantitative reverse transcription-polymerase chain reaction, immunoblot analysis, and immunostaining. The [³H]L-Pro uptake by TR-rPCT1 cells showed Na⁺-dependence, Cl^--independence, and concentration-dependence with a K_m of 810 μM. The substrates for system A, such as 2-(methylamino)isobutyric acid (MeAIB), significantly inhibited the L-Pro uptake, suggesting the involvement of system A in the uptake of L-Pro. Among the subtypes of system A, the mRNA expression levels of ATA2 were the highest in TR-rPCT1 cells. Immunostaining analysis of the isolated rat retinal capillaries containing pericytes indicated the protein expression of ATA2 in retinal pericytes. In conclusion, it is suggested that ATA2, at least in part, is involved in the transport of L-Pro in the retinal pericytes.

Role of Taurine Transporter in the Retinal Uptake of Vigabatrin

Vigabatrin (VGB) is a first-line drug used for treatment of infantile spasms. On therapeutic dose, VGB accumulates in the retina causing permanent peripheral visual field constriction. The mechanism involved in retinal accumulation of VGB is ambiguous. In the present study, mechanism of VGB transport into retina was evaluated. VGB uptake into retina was studied in vitro using human adult retinal pigment epithelial (ARPE-19) cells as a model for outer blood retinal barrier. The VGB cell uptake studies demonstrated saturation kinetics with K_m value of 13.1 mM and uptake was significantly increased at pH 7.4 and hyperosmolar conditions indicating involvement of carrier-mediated Na⁺-Cl^--dependent transporter. In the presence of taurine transporter (TauT) substrates (taurine and GABA) and inhibitor guanidinoethyl sulfonate (GES), the uptake of VGB decreased significantly demonstrating contribution of TauT. The VGB retinal levels in rats were decreased by 1.5- and 1.3-folds on chronic administration of GES and taurine, respectively. In conclusion, this study demonstrated the TauT involvement in VGB uptake and accumulation in retina.

Zwitterionic micelles efficiently deliver oral insulin without opening tight junctions

Oral delivery of protein drugs is considered a life-changing solution for patients who require regular needle injections. However, clinical translation of oral protein formulations has been hampered by inefficient penetration of drugs through the intestinal mucus and epithelial cell layer, leading to low absorption and bioavailability, and safety concerns owing to tight junction openings. Here we report a zwitterionic micelle platform featuring a virus-mimetic zwitterionic surface, a betaine side chain and an ultralow critical micelle concentration, enabling drug penetration through the mucus and efficient transporter-mediated epithelial absorption without the need for tight junction opening. This micelle platform was used to fabricate a prototype oral insulin formulation by encapsulating a freeze-dried powder of zwitterionic micelle insulin into an enteric-coated capsule. The biocompatible oral insulin formulation shows a high oral bioavailability of >40%, offers the possibility to fine tune insulin acting profiles and provides long-term safety, enabling the oral delivery of protein drugs.

Transcriptomic analyses reveal a systemic defense role of the uninfested adjacent leaf in tea plant (Camellia sinensis) attacked by tea geometrids (Ectropis obliqua)

To get a more detailed understanding of the interaction between tea plant (Camellia sinensis) and tea geometrids (Ectropis obliqua), transcriptomic profile in undamaged adjacent leaf (TGL) of tea geometrids fed local leaves (LL) was investigated for the first time. Here, approximately 245 million clean reads contained 39.39 Gb of sequence data were obtained from TGL. Further analysis revealed that systemic response was induced in TGL after tea geometrids feeding on LL, although the defense response was weaker than that in LL. The differentially expressed genes (DEGs) identification analysis showed little overlap of DEGs between TGL and LL. Comparative transcriptome analysis suggested that JA signal regulated resistant pathway was induced in LL; whereas primary metabolism pathway was activated in TGL in response to tea geometrids feeding. This study reveals a novel resistance mechanism of TGL to tea geometrids feeding.

New Insights in the Complexity and Functionality of the Neurovascular Unit

The neurovascular unit (NVU) encompasses all brain cells and underlines that neurons, glia and brain vasculature are in intimate physical and functional association. Brain function is dependent on blood flow and local increases in blood flow in response to neural activity - functional hyperaemia takes place at the NVU. Although this is a vital function of the NVU, many studies have demonstrated that the NVU also performs other tasks. Blood vessels in the brain, which are composed of multiple cell types, are essential for correct brain development. They constitute the niche for brain stem cells, sense the environment and communicate changes to neural tissue, and control the immune quiescence of the CNS. In this brief chapter we will discuss new insights into the biology of NVU, which have further revealed the heterogeneity and complexity of the vascular tree and its neurovascular associations.

Lactate/GPR81 signaling and proton motive force in cancer: Role in angiogenesis, immune escape, nutrition, and Warburg phenomenon

Reprogramming of biochemical pathways is a hallmark of cancer cells, and generation of lactic acid from glucose/glutamine represents one of the consequences of such metabolic alterations. Cancer cells export lactic acid out to prevent intracellular acidification, not only increasing lactate levels but also creating an acidic pH in extracellular milieu. Lactate and protons in tumor microenvironment are not innocuous bystander metabolites but have special roles in promoting tumor-cell proliferation and growth. Lactate functions as a signaling molecule by serving as an agonist for the G-protein-coupled receptor GPR81, involving both autocrine and paracrine mechanisms. In the autocrine pathway, cancer cell-generated lactate activates GPR81 on cancer cells; in the paracrine pathway, cancer cell-generated lactate activates GPR81 on immune cells, endothelial cells, and adipocytes present in tumor stroma. The end result of GPR81 activation is promotion of angiogenesis, immune evasion, and chemoresistance. The acidic pH creates an inwardly directed proton gradient across the cancer-cell plasma membrane, which provides driving force for proton-coupled transporters in cancer cells to enhance supply of selective nutrients. There are several molecular targets in the pathways involved in the generation of lactic acid by cancer cells and its role in tumor promotion for potential development of novel anticancer therapeutics.

Proton Control of Transitions in an Amino Acid Transporter

Amino acid transport into the cell is often coupled to the proton electrochemical gradient, as found in the solute carrier 36 family of proton-coupled amino acid transporters. Although no structure of a human proton-coupled amino acid transporter exists, the crystal structure of a related homolog from bacteria, GkApcT, has recently been solved in an inward-occluded state and allows an opportunity to examine how protons are coupled to amino acid transport. Our working hypothesis is that release of the amino acid substrate is facilitated by the deprotonation of a key glutamate residue (E115) located at the bottom of the binding pocket, which forms part of the intracellular gate, allowing the protein to transition from an inward-occluded to an inward-open conformation. During unbiased molecular dynamics simulations, we observed a transition from the inward-occluded state captured in the crystal structure to a much more open state, which we consider likely to be representative of the inward-open state associated with substrate release. To explore this and the role of protons in these transitions, we have used umbrella sampling to demonstrate that the transition from inward occluded to inward open is more energetically favorable when E115 is deprotonated. That E115 is likely to be protonated in the inward-occluded state and deprotonated in the inward-open state is further confirmed via the use of absolute binding free energies. Finally, we also show, via the use of absolute binding free energy calculations, that the affinity of the protein for alanine is very similar regardless of either the conformational state or the protonation of E115, presumably reflecting the fact that all the key interactions are deep within the binding cavity. Together, our results give a detailed picture of the role of protons in driving one of the major transitions in this transporter.

Sex-specific transcriptional and proteomic signatures in schizophrenia

It has remained unclear why schizophrenia typically manifests after adolescence and which neurobiological mechanisms are underlying the cascade leading to the actual onset of the illness. Here we show that the use of induced pluripotent stem cell-derived neurons of monozygotic twins from pairs discordant for schizophrenia enhances disease-specific signal by minimizing genetic heterogeneity. In proteomic and pathway analyses, clinical illness is associated especially with altered glycosaminoglycan, GABAergic synapse, sialylation, and purine metabolism pathways. Although only 12% of all 19,462 genes are expressed differentially between healthy males and females, up to 61% of the illness-related genes are sex specific. These results on sex-specific genes are replicated in another dataset. This implies that the pathophysiology differs between males and females, and may explain why symptoms appear after adolescence when the expression of many sex-specific genes change, and suggests the need for sex-specific treatments.

Trading amino acids at the aphid-Buchnera symbiotic interface

Plant sap-feeding insects thrive despite feeding exclusively on a diet lacking in essential amino acids. This nutritional deficit is countered through endosymbiotic relationships with microbial symbionts. Nonessential amino acids, vital for microbial symbionts, are utilized by symbiont metabolic pathways and yield essential amino acids required by their eukaryotic hosts. Symbionts are completely dependent on their host to meet nutritional requirements. The endosymbionts are surrounded individually by host-derived symbiosomal membranes and are housed within specialized host bacteriocyte cells. The transport capabilities of the symbiosomal membrane remain unknown. Here, we identify a transport system that mediates a crucial step in this metabolic complementarity: a transporter capable of transporting nonessential amino acids across the symbiosomal membrane of the pea aphid Acyrthosiphon pisum.

Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host–symbiont interface. The symbiosomal membrane must be a dynamic and selectively permeable structure to enable bidirectional and differential movement of essential nutrients, metabolites, and biosynthetic intermediates, vital for growth and survival of host and symbiont. However, despite this crucial role, the molecular basis of membrane transport across the symbiosomal membrane remains unresolved in all bacteriocyte-containing insects. A transport protein was immunolocalized to the symbiosomal membrane separating the pea aphid Acyrthosiphon pisum from its intracellular symbiont Buchnera aphidicola. The transporter, A. pisum nonessential amino acid transporter 1, or ApNEAAT1 (gene: ACYPI008971), was characterized functionally following heterologous expression in Xenopus oocytes, and mediates both inward and outward transport of small dipolar amino acids (serine, proline, cysteine, alanine, glycine). Electroneutral ApNEAAT1 transport is driven by amino acid concentration gradients and is not coupled to transmembrane ion gradients. Previous metabolite profiling of hemolymph and bacteriocyte, alongside metabolic pathway analysis in host and symbiont, enable prediction of a physiological role for ApNEAAT1 in bidirectional host–symbiont amino acid transfer, supplying both host and symbiont with indispensable nutrients and biosynthetic precursors to facilitate metabolic complementarity.

FLCN is a novel Rab11A-interacting protein that is involved in the Rab11A-mediated recycling transport

The Birt-Hogg-Dubé (BHD) syndrome related protein FLCN has recently been implicated in the vesicular trafficking processes by interacting with several Rab family GTPases. In the previous studies, we have shown that FLCN could inhibit the binding of overexpressed PAT1, which is a membrane-bound amino acid transporter, to the lysosome in human embryonic kidney 293 cells. This tends to stabilize the lysosomal amino acid pool that is a critical signal to activate the mTORC1 signaling pathway. However, the mechanisms of FLCN during this process remain unexplored. Here we report that FLCN can bind through its C-terminal DENN-like domain to the recycling transport regulator, Rab11A. Suppression of either Rab11A or FLCN facilitated the localization of the overexpressed PAT1 to the lysosome and inhibited its targeting on the plasma membrane. As a consequence, the mTORC1 was down-regulated. The in vitro GEF activity assay does not support FLCN modifies the Rab11A activity directly. Instead, we found FLCN promoted the loading of PAT1 on Rab11A. Our data uncover a function of FLCN in the Rab11A-mediated recycling pathway and might provide new clues to understand BHD.This article has an associated First Person interview with the first author of the paper.