Acid Transport Mechanisms Research Articles

Diacylglycerol O-acyltransferase isoforms play a role in peridroplet mitochondrial fatty acid metabolism in bovine liver

Hepatocellular lipid accumulation characterizes fatty liver in dairy cows. Lipid droplets (LD), specialized organelles that store lipids and maintain cellular lipid homeostasis, are responsible for the ectopic storage of lipids associated with several metabolic disorders. In recent years, nonruminant studies have reported that LD-mitochondria interactions play an important role in lipid metabolism. Due to the role of diacylglycerol acyltransferase isoforms (DGAT1 and DGAT2) in LD synthesis, we explored mechanisms of mitochondrial fatty acid transport in ketotic cows using liver biopsies and isolated primary hepatocytes. Compared with healthy cows, cows with fatty liver had massive accumulation of LD and high protein expression of the triglyceride (TAG) synthesis-related enzymes DGAT1 and DGAT2, LD synthesis-related proteins perilipin 2 (PLIN2) and perilipin 5 (PLIN5), and the mitochondrial fragmentation-related proteins dynamin-related protein 1 (DRP1) and fission 1 (FIS1). In contrast, factors associated with fatty acid oxidation, mitochondrial fusion, and mitochondrial electron transport chain complex were lower compared with those in the healthy cows. In addition, transmission electron microscopy revealed significant contacts between LD-mitochondria in liver tissue from cows with fatty liver. Compared with isolated cytoplasmic mitochondria, expression of carnitine palmitoyl transferase 1A (CPT1A) and DRP1 was lower, but mitofusin 2 (MFN2) and mitochondrial electron transport chain complex was greater in isolated peridroplet mitochondria from hepatic tissue of cows with fatty liver. In vitro data indicated that exogenous free fatty acids (FFA) induced hepatocyte LD synthesis and mitochondrial dynamics consistent with in vivo results. Furthermore, DGAT2 inhibitor treatment attenuated the FFA-induced upregulation of PLIN2 and PLIN5 and rescued the impairment of mitochondrial dynamics. Inhibition of DGAT2 also restored mitochondrial membrane potential and reduced hepatocyte reactive oxygen species production. The present in vivo and in vitro results indicated functional differences are present among different types of mitochondria in the liver tissue of dairy cows with ketosis. Activity of DGAT2 may play a key role in maintaining liver mitochondrial function and lipid homeostasis in dairy cows during the transition period.

Layer-specific mechanisms of perfluoroalkyl acid (PFAA) transport and partition in estuarine environments: Unveiling the depth-dependent differences

Understanding of characteristics and transport of perfluoroalkyl acids (PFAAs) in heterogeneous estuarine environments is limited. Furthermore, the role of suspended particles (SPS) in different layers remains unclear. This study explores the multiphase distribution process and mechanism of PFAAs controlled by SPS across surface and bottom layers in five small estuaries. Peaks in PFAA concentrations are consistently observed at strongly stratified sites. Concentrations of the PFAAs in both surface and bottom SPS decreased as the degree of mixing increased from strongly stratified levels to well-mixed levels. The water-SPS partitioning of some short-chain PFAAs (PFBS, PFHxA, and PFHpA) is influenced by environmental factors (pH, depth, temperature, and salinity) due to electrostatic interactions, while the sorption of some long-chain PFAAs (PFOA, PFOS, and PFNA) is controlled by SPS and dissolved organic carbon (OC), driven by hydrophobic interactions. Additionally, SPS dominates OC transport in estuarine systems, except in sandy sediment environments. SPS plays a dominant role in PFAA partitioning in both surface and bottom water-SPS systems (p < 0.05), and salinity only significantly affects PFBS in bottom layer (p < 0.01). These findings are critical for understanding the drivers of PFAA partitioning and the roles of SPS in different layers, underscoring the necessity of considering particle-associated PFAA fractions in future coastal environmental management.

Human Gastric Organoid-Derived Mucus Shares Key Properties with Native Gastric Mucus and Inhibits Motility of Helicobacter pylori

To prevent and treat gastric disease caused by Helicobacter pylori, it is crucial to understand the role of the stomach’s first line of defense: the gastric mucus layer. Gastric mucus is a complex hydrogel that has been studied extensively in animal models, and multiple groups have collected and purified porcine gastric mucus to yield pure solutions of mucin proteins. However, purified mucin—the functional viscoelastic component of mucus—cannot accurately recapitulate the molecular complexity of mucus in its entirety since it lacks salts, lipids, electrolytes, and other proteins. Additionally, access to human samples for functional analyses remains a critical barrier to mucus research. Therefore, the objective of this study was to engineer sterile human gastric mucus in vitro to evaluate its translational potential to native mucus (NM), for further study of interactions between mucus and H. pylori bacteria. In vivo, H. pylori use flagellar motility to traverse the mucus layer and colonize the underlying epithelium. We hypothesize that the microarchitecture and gel-forming capacity of our lab-grown mucus (LGM) significantly restrict H. pylori motility. Inspired by previous studies, we developed and optimized a protocol for the in vitro production of sterile LGM using epithelial monolayers derived from human gastric organoids and cultured at an air-liquid interface. This mucus could be easily harvested and did not require purification or processing. Additionally, mucus production was maintained for over one month, demonstrating the robustness of our culture system. Mass spectrometry and size exclusion chromatography revealed that the LGM has a molecular composition similar to that of native mucus. Further, we have confirmed with cryo-scanning electron microscopy that the LGM has a characteristic honeycomb structure with similar pore size distributions to those found in native mucus. Rheometric frequency sweeps demonstrated comparable, predominantly elastic gel behavior in both LGM and NM samples. Acid flow experiments in a 2D Hele Shaw cell have also demonstrated that LGM enables viscous fingering—a previously studied hydrodynamic phenomenon typical of mucus gels that is thought to be involved in gastric acid transport mechanisms in vivo. Finally, live imaging and particle tracking were used to quantify the motility of H. pylori in the LGM. Compared to liquid media, the LGM caused a significant decrease in H. pylori swimming speed. Overall, our human gastric lab-grown mucus recapitulates key functions of native mucus and will enable future investigations into gastric mucus pathophysiology and H. pylori infection. NIH Grants: R01 GM131408-01 &amp; UL1 TR002319. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Molecular mechanisms of Na+-driven bile acid transport in human NTCP

Human Na+ taurocholate co-transporting protein (hNTCP) is a key bile salt transporter to maintain enterohepatic circulation and is responsible for the recognition of hepatitis B and D viruses. Despite landmark cryoelectron microscopy studies revealing open-pore and inward-facing states of hNTCP stabilized by antibodies, the transport mechanism remains largely unknown. To address this knowledge gap, we used molecular dynamics and enhanced sampling metadynamics simulations to elucidate the intrinsic mechanism of hNTCP-mediated taurocholate acid (TCA) transport driven by Na+ binding. We uncovered three TCA-binding modes, including one that closely matched the limited cryoelectron microscopy density observed in the open-pore hNTCP. We also captured several key hNTCP conformations in the substrate transport cycle, particularly including an outward-facing, substrate-bound state. Furthermore, we provided thermodynamic evidence supporting that changes in the Na+-binding state drive the TCA transport by exploiting the amphiphilic nature of the substrate and modulating the protein environment, thereby enabling the TCA molecule to flip through. Understanding these mechanistic details of Na+-driven bile acid transport may aid in the development of hNTCP-targeted therapies for liver diseases.

Abstract 198: Selective targeting of endothelial mTORC1 reduces transendothelial fatty acid delivery to improve anti-tumor immunity and suppress metastatic outgrowth

Abstract Tumor metastasis requires sufficient nutrients to support outgrowth of disseminated tumor cells. Cancer cells utilize fatty acids as a key source of energy and biomass, but these nutrients impair the cytotoxic activities of T cells, serving to support metastatic progression. Blood is a rich source of fatty acids, but the vascular endothelium serves as a barrier to limit access to the surrounding tumor tissue. However, it is unclear how long-chain fatty acid delivery to early metastatic tumors is regulated. Here, we report that endothelial mTORC1 promotes transport of fatty acids into developing metastatic tumors, leading to reduced anti-tumor immune responses and improved outgrowth. Using a murine model of metastatic outgrowth in the lung, tumor burden was significantly reduced upon targeted deletion of Raptor, an essential component of the mTORC1 complex, in endothelial cells (RptorECKO). We employed a multifaceted approach using metabolomics, transcriptomics, and molecular assays to identify a Raptor/mTORC1-mediated mechanism of transendothelial fatty acid transport via RAB and CLSTN1 cargo trafficking. In vivo uptake of a fluorescent palmitic acid analog in tumor cells and T cells was reduced in RptorECKO lung metastatic tumors, which correlated with improved markers of cytotoxicity. Combination of low-dose RAD001/everolimus, which selectively inhibits mTORC1 in endothelial cells, with anti-PD1 reduces metastatic disease and impairs long-chain fatty acid uptake in T cells, corresponding to improved anti-tumor immunity. These findings describe a novel mechanism of transendothelial fatty acid transportation during metastatic outgrowth, supporting future development of therapeutic strategies to target endothelial mTORC1 activity. Citation Format: Deanna N. Edwards, Shan Wang, Wenqiang Song, Laura C. Kim, Yoonha Hwang, Jin Chen. Selective targeting of endothelial mTORC1 reduces transendothelial fatty acid delivery to improve anti-tumor immunity and suppress metastatic outgrowth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 198.

Types of Membrane Transporters and the Mechanisms of Interaction between Them and Reactive Oxygen Species in Plants.

Membrane transporters are proteins that mediate the entry and exit of substances through the plasma membrane and organellar membranes and are capable of recognizing and binding to specific substances, thereby facilitating substance transport. Membrane transporters are divided into different types, e.g., ion transporters, sugar transporters, amino acid transporters, and aquaporins, based on the substances they transport. These membrane transporters inhibit reactive oxygen species (ROS) generation through ion regulation, sugar and amino acid transport, hormone induction, and other mechanisms. They can also promote enzymatic and nonenzymatic reactions in plants, activate antioxidant enzyme activity, and promote ROS scavenging. Moreover, membrane transporters can transport plant growth regulators, solute proteins, redox potential regulators, and other substances involved in ROS metabolism through corresponding metabolic pathways, ultimately achieving ROS homeostasis in plants. In turn, ROS, as signaling molecules, can affect the activity of membrane transporters under abiotic stress through collaboration with ions and involvement in hormone metabolic pathways. The research described in this review provides a theoretical basis for improving plant stress resistance, promoting plant growth and development, and breeding high-quality plant varieties.

Integrated metabolomic and transcriptomic analyses reveal themolecular mechanism of amino acid transport between source and sink during tea shoot development.

The weighted gene co-expression network analysis and antisense oligonucleotide-mediated transient gene silencing revealed that CsAAP6 plays an important role in amino acid transport during tea shoot development. Nitrogen transport from source to sink is crucial for tea shoot growth and quality formation. Amino acid represents the major transport form of reduced nitrogen in the phloem between source and sink, but the molecular mechanism of amino acid transport from source leaves to new shoots is not yet clear. Therefore, the composition of metabolites in phloem exudates collected by the EDTA-facilitated method was analyzed through widely targeted metabolomics. A total of 326 metabolites were identified in the phloem exudates with the richest variety of amino acids and their derivatives (93), accounting for approximately 39.13% of the total metabolites. Moreover, through targeted metabolomics, it was found that the content of glutamine, glutamic acid, and theanine was the most abundant, and gradually increased with the development of new shoots. Meanwhile, transcriptome analysis suggested that the expression of amino acid transport genes changed significantly. The WGCNA analysis identified that the expression levels of CsAVT1, CsLHTL8, and CsAAP6 genes located in the MEterquoise module were positively correlated with the content of amino acids such as glutamine, glutamic acid, and theanine in phloem exudates. Reducing the CsAAP6 in mature leaves resulted in a significant decrease in the content of glutamic acid, aspartic acid, alanine, leucine, asparagine, glutamine, and arginine in the phloem exudates, indicating that CsAAP6 played an important role in the source to sink transport of amino acids in the phloem. The research results will provide the theoretical basis and genetic resources for the improvement of nitrogen use efficiency and tea quality.

Direct evidence for the electroconvective mechanism of neutral amino acid transport during electrodialysis

For the first time, direct evidence was obtained using laser interferometry and flicker-noise spectroscopy that the main cause of the increase in the transport of amino acids through a sulfonated cation-exchange membrane in intense current modes is electroconvection. The turbulent nature of electroconvective vortices at the solution/membrane interface, acidification of the solution in the demineralization compartment and a substantial intensification of amino acid fluxes under over-limiting current modes were revealed. This indicates the electroconvective destruction of the barrier effect of the solution layer with a high pH value near the cation-exchange membrane.

Evaluation of L-Alanine Metabolism in Bacteria and Whole-Body Distribution with Bacterial Infection Model Mice

The World Health Organization has cautioned that antimicrobial resistance (AMR) will be responsible for an estimated 10 million deaths annually by 2050. To facilitate prompt and accurate diagnosis and treatment of infectious disease, we investigated the potential of amino acids for use as indicators of bacterial growth activity by clarifying which amino acids are taken up by bacteria during the various growth phases. In addition, we examined the amino acid transport mechanisms that are employed by bacteria based on the accumulation of labeled amino acids, Na+ dependence, and inhibitory effects using a specific inhibitor of system A. We found that 3H-L-Ala accurately reflects the proliferative activity of Escherichia coli K-12 and pathogenic EC-14 in vitro. This accumulation in E. coli could be attributed to the amino acid transport systems being different from those found in human tumor cells. Moreover, biological distribution assessed in infection model mice with EC-14 using 3H-L-Ala showed that the ratio of 3H-L-Ala accumulated in infected muscle to that in control muscle was 1.20. By detecting the growth activity of bacteria in the body that occurs during the early stages of infection by nuclear imaging, such detection methods may result in expeditious diagnostic treatments for infectious diseases.

The molecular mechanism of sialic acid transport mediated by Sialin.

Malfunction of the sialic acid transporter caused by various genetic mutations in the SLC17A5 gene encoding Sialin leads to a spectrum of neurodegenerative conditions called free sialic acid storage disorders. Unfortunately, how Sialin transports sialic acid/proton (H+) and how pathogenic mutations impair its function are poorly defined. Here, we present the structure of human Sialin in an inward-facing partially open conformation determined by cryo-electron microscopy, representing the first high-resolution structure of any human SLC17 member. Our analysis reveals two unique features in Sialin: (i) The H+ coupling/sensing requires two highly conserved Glu residues (E171 and E175) instead of one (E175) as implied in previous studies; and (ii) the normal function of Sialin requires the stabilization of a cytosolic helix, which has not been noticed in the literature. By mapping known pathogenic mutations, we provide mechanistic explanations for corresponding functional defects. We propose a structure-based mechanism for sialic acid transport mediated by Sialin.

The oleaginous yeast Starmerella bombicola reveals limitations of Saccharomyces cerevisiae as a model for fatty acid transport studies.

Saccharomyces cerevisiae is the model organism to most yeast researchers, and information obtained from its physiology is generally extrapolated to other yeasts. Studies on fatty acid transport in S. cerevisiae are based on the expression of both native fatty acid export genes as well as heterologous proteins. Starmerella bombicola, on the other hand, is an oleaginous yeast of industrial relevance but its fatty acid transport mechanisms are unknown. In this study, we attempt to use existing knowledge from S. cerevisiae to study fatty acid transport in S. bombicola, but the obtained results differ from those observed in S. cerevisiae. First, we observed that deletion of SbPRY1 in S. bombicola leads to higher fatty acid export, the opposite effect to the one previously observed for the Pry homologues in S. cerevisiae. Second, following reports that human FATP1 could export fatty acids and alcohols in S. cerevisiae, we expressed FATP1 in a fatty acid-accumulating S. bombicola strain. However, FATP1 reduced fatty acid export in S. bombicola, most likely due to its acyl-CoA synthetase activity. These results not only advance knowledge on fatty acid physiology of S. bombicola, but also improve our understanding of S. cerevisiae and its limitations as a model organism.

Structural insights into the HBV receptor and bile acid transporter NTCP

Around 250 million people are infected with hepatitis B virus (HBV) worldwide1, and 15 million may also carry the satellite virus hepatitis D virus (HDV), which confers even greater risk of severe liver disease2. The HBV receptor has been identified as sodium taurocholate co-transporting polypeptide (NTCP), which interacts directly with the first 48 amino acid residues of the N-myristoylated N-terminal preS1 domain of the viral large protein3. Despite the pressing need for therapeutic agents to counter HBV, the structure of NTCP remains unsolved. This 349-residue protein is closely related to human apical sodium-dependent bile acid transporter (ASBT), another member of the solute carrier family SLC10. Crystal structures have been reported of similar bile acid transporters from bacteria4,5, and these models are believed to resemble closely both NTCP and ASBT. Here we have used cryo-electron microscopy to solve the structure of NTCP bound to an antibody, clearly showing that the transporter has no equivalent of the first transmembrane helix found in other SLC10 proteins, and that the N terminus is exposed on the extracellular face. Comparison of our structure with those of related proteins indicates a common mechanism of bile acid transport, but the NTCP structure displays an additional pocket formed by residues that are known to interact with preS1, presenting new opportunities for structure-based drug design.

Chemical characterizations of neurotransmission receptors of human and plant to unfold the evolutionary relationships among them

Vertebrates have very well defined nervous systems. A group of researchers hypothesize that plant also has an alternative sort of sensitive nervous system. They find a close relationship of the neurotransmission mechanism of animal with that of the plant and suspect a close relationship in amino acid transport mechanism among both the organisms. Although the protein structure is conserved more than molecular sequences, but the 3D structure of protein is largely influenced by the amino acid residues in the interior part of it. The constituents of a primary protein sequence have a variety of biochemical information which control the structure, function and stability of the protein. Hence, in this present study it is tried for characterization and comparison of neurotransmission receptors associated with human and plant to unfold the evolutionary relationships among them in bio-molecular level based on the chemical properties of the amino acids. The protein sequences of ionotropic glutamate receptor and GABA receptor of human (from vertebrate) and Arabidopsis thaliana (from plant) are considered as datasets. The 20 standard amino acids are classified into 8 chemical groups and are identified by specific numeric values. Alignment-based methods are used to identify the identical and similar amino acids among the aligned sequences.The common pattern finding procedure finds some conserved regions in the receptor protein sequences of both the species. The proximity between the protein sequences are calculated based on the distribution of each chemical group (in percentage) in them and phylogenetic trees are constructed to show the evolutionary relationships of neurotransmission receptors of both the species. The conventional multiple sequence alignment (MSA) method is also applied on the datasets and the results are compared. The analysis is further extended to structural level to understand the extent to which the animal and plant proteins are similar.

Functional Characterization of Rare Variants in OAT1/SLC22A6 and OAT3/SLC22A8 Urate Transporters Identified in a Gout and Hyperuricemia Cohort.

The OAT1 (SLC22A6) and OAT3 (SLC22A8) urate transporters are located on the basolateral membrane of the proximal renal tubules, where they ensure the uptake of uric acid from the urine back into the body. In a cohort of 150 Czech patients with primary hyperuricemia and gout, we examined the coding regions of both genes using PCR amplification and Sanger sequencing. Variants p.P104L (rs11568627) and p.A190T (rs146282438) were identified in the gene for solute carrier family 22 member 6 (SLC22A6) and variants p.R149C (rs45566039), p.V448I (rs11568486) and p.R513Q (rs145474422) in the gene solute carrier family 22 member 8 (SLC22A8). We performed a functional study of these rare non-synonymous variants using the HEK293T cell line. We found that only p.R149C significantly reduced uric acid transport in vitro. Our results could deepen the understanding of uric acid handling in the kidneys and the molecular mechanism of uric acid transport by the OAT family of organic ion transporters.

Placental adaptation to maternal malnutrition.

Maternal malnutrition gives rise to both short- and long-term consequences for the survival and health of the offspring. As the intermediary between mother and fetus, the placenta has the potential to interpret environmental signals, such as nutrient availability, and adapt to support fetal growth and development. While this potential is present, it is clear that at times placental adaptation fails to occur resulting in poor pregnancy outcomes. This review will focus on placental responses to maternal undernutrition related to changes in placental vascularization and hemodynamics and placental nutrient transport systems across species. While much of the available literature describes placental responses that result in poor fetal outcomes, novel models have been developed to utilize the inherent variation in fetal weight when dams are nutrient restricted to identify placental adaptations that result in normal-weight offspring. Detailed analyses of the spectrum of placental responses to maternal malnutrition point to alternations in placental histoarchitectural and vascular development, amino acid and lipid transport mechanisms, and modulation of immune-related factors. Dietary supplementation with selected nutrients, such as arginine, has the potential to improve placental growth and function through a variety of mechanisms including stimulating cell proliferation, protein synthesis, angiogenesis, vasodilation, and gene regulation. Improved understanding of placental responses to environmental cues is necessary to develop diagnostic and intervention strategies to improve pregnancy outcomes.

Вплив корвітину на склад холатів жовчі самців щурів в умовах хронічного соціального стресу

The creation of universally effective and safe correctors of biliary secretion disorders is becoming more timely. There is an urgent need for scientists to find drugs that would correct blood cholesterol levels and metabolism in liver effectively and without limiting side effects. The purpose of the study was to investigate the possibility of using corvitin to correct stress-induced biliary disorders of the liver of male rats. Materials and methods. The article looks at recent research dealing with changes in the bile acid composition of outbred male rats’ bile under chronic social stress (social defeat in daily male confrontations, 14 days) when using Corvitin (1 mg/kg, intragastrically, 7 days). Chronic social stress was created by daily agonistic interactions between animals. The state of memory and the level of research activity in the object recognition test (cognitive test) were also studied. The main fractions of conjugated bile acids (taurocholic, taurohenodeoxycholic and taurodeoxycholic, glycocholic, glycochenodeoxycholic and glycodeoxycholic and free ones – cholic, chenodeoxycholic and deoxycholic) were determined by the method of thin layer chromatography of bile. Results and discussion. Chronic social stress leads to a slight increase in the overall activity of the experimental animals, but significantly impairs the processes of recognition and memory. Social stress significantly inhibits the processes that ensure the synthesis, biotransformation and transport of bile acids in the bile. Also, chronic social stress causes changes in bile production, which reduce the solubilization properties of bile and increase the risk of lithogenesis. Conclusion. The use of Corvitin simultaneously with the simulation of experimental social stress normalized the biliary secretory function of the liver, which indicates a high potential for the use of Corvitin as a corrective factor in chronic social stress. Corvitin used by us in the conditions of experimental social stress to some extent corrected the content of bile acids in the liver of male rats, which indicates the ability of this drug to interfere with the metabolism of cholate in liver cells, in the mechanisms of bile acid transport. Correction of stress-induced pathologies of liver bile-secretory function by Corvitin requires further thorough experimental studies

Study on the mechanism of reactive acid transport in fractured two-mineral carbonate rocks

Centering on the mechanism of reactive acid transport in fractured two-mineral carbonate rocks, this paper established a two-mineral model for fractured media with the extended finite element method based on the two-scale continuum model. A series of examples are presented with the numerical model, the numerical results show that the variation of volume fraction of dolomite, the surface reaction constant of dolomite as well as the diffusion coefficient can alter the dissolution morphology and dissolution performance. As the volume fraction of dolomite increases or surface reaction constant of dolomite decreases, the dissolution patterns would transform form wormhole to uniform dissolution. And the bedding distribution and porphyritic distribution of dolomite will cause a fragmentation phenomenon for the dissolution morphology. Besides, the bedded dolomite can bring about an increased acid consumption. It can be inferred that the reaction rate difference between limestone and dolomite is the key factor that affects the dissolution morphology, and the retarded acid with a low reaction rate in dolomite rocks does not perform well.

Leaf-derived ABA regulates rice seed development via a transporter-mediated and temperature-sensitive mechanism.

Long-distance transport of the phytohormone abscisic acid (ABA) has been studied for ~50 years, yet its mechanistic basis and biological significance remain very poorly understood. Here, we show that leaf-derived ABA controls rice seed development in a temperature-dependent manner and is regulated by defective grain-filling 1 (DG1), a multidrug and toxic compound extrusion transporter that effluxes ABA at nodes and rachilla. Specifically, ABA is biosynthesized in both WT and dg1 leaves, but only WT caryopses accumulate leaf-derived ABA. Our demonstration that leaf-derived ABA activates starch synthesis genes explains the incompletely filled and floury seed phenotypes in dg1 Both the DG1-mediated long-distance ABA transport efficiency and grain-filling phenotypes are temperature sensitive. Moreover, we extended these mechanistic insights to other cereals by observing similar grain-filling defects in a maize DG1 ortholog mutant. Our study demonstrates that rice uses a leaf-to-caryopsis ABA transport-based mechanism to ensure normal seed development in response to variable temperatures.

The Role of Oxidative Stress in Hyperuricemia and Xanthine Oxidoreductase (XOR) Inhibitors.

Uric acid is the end product of purine metabolism in humans. Hyperuricemia is a metabolic disease caused by the increased formation or reduced excretion of serum uric acid (SUA). Alterations in SUA homeostasis have been linked to a number of diseases, and hyperuricemia is the major etiologic factor of gout and has been correlated with metabolic syndrome, cardiovascular disease, diabetes, hypertension, and renal disease. Oxidative stress is usually defined as an imbalance between free radicals and antioxidants in our body and is considered to be one of the main causes of cell damage and the development of disease. Studies have demonstrated that hyperuricemia is closely related to the generation of reactive oxygen species (ROS). In the human body, xanthine oxidoreductase (XOR) catalyzes the oxidative hydroxylation of hypoxanthine to xanthine to uric acid, with the accompanying production of ROS. Therefore, XOR is considered a drug target for the treatment of hyperuricemia and gout. In this review, we discuss the mechanisms of uric acid transport and the development of hyperuricemia, emphasizing the role of oxidative stress in the occurrence and development of hyperuricemia. We also summarize recent advances and new discoveries in XOR inhibitors.

Structural Insights into the Atomistic Mechanisms of Uric Acid Recognition and Translocation of Human Urate Anion Transporter 1.

Background: Human urate transporter 1 (hURAT1) is the most pivotal therapeutic target for treating hyperuricemia. However, the molecular interactions between uric acid and URAT1 are still unknown due to lack of structural details. Methods: In the present study, several methods (homology modeling, sequence alignment, docking, and mutagenesis) were used to explain the atomistic mechanisms of uric acid transport of hURAT1. Results: Residues W357-F365 in the TMD7 and P484-R487 in the TMD11 present in the hURAT1 have unique roles in both binding to the uric acid and causing subsequent structural changes. These residues, located in the transport tunnel, were found to be related to the structural changes, as demonstrated by the reduced Vmax values and an unaltered expression of protein level. In addition, W357, G361, T363, F365, and R487 residues may confer high affinity for binding to uric acid. An outward-open homology model of hURAT1 revealed a crucial role for these two domains in the conformational changes of hURAT1. F241 and H245 in TMD5, and R477 and R487 in TMD11 may confer high affinity for uric acid, and as the docking analysis suggests, they may also enhance the affinity for the inhibitors. R477 relation to the structural changes was demonstrated by the Vmax values of the mutants and the contribution of positive charge to the uric acid selectivity. Conclusions: W357-F365 in TMD7, P484-R487 in TMD11, and residues F241, H245, and R477 were found to be critical for the translocation and recognition of uric acid.