Molecular physiology of cation-coupled Cl- cotransport: the SLC12 family

A study on the subchronic toxicity of triclocarban to the early-life development of oryzias melastigma and focused on the analysis of osmoregulatory regulation mechanisms

Triclocarban (TCC), a novel antimicrobial agent found in personal care products, has been extensively detected in marine environments. However, research on the toxic effects of TCC on marine organisms remains inadequate. This study delved into the subchronic toxic effects of TCC on the early life stages of marine medaka (Oryzias melastigma, O. melastigma), revealing that TCC could reduce embryo heart rate and hatching rate while diminishing the survival rate of larvae. Biomarker assays indicated that TCC could inflict damage on the embryos' antioxidant and nervous systems. Transcriptomic analysis suggested that TCC could impact cell growth, reproduction, and various life processes, activating cancer signaling pathways, increasing the likelihood of cancer, and exerting toxic effects on the immune and osmoregulatory systems. To validate and enhance our understanding of TCC's unique toxic impact on the osmoregulatory system of O. melastigma, we conducted homology modeling and molecular docking analyses on the protein involved in osmoregulation. The study intuitively revealed the potential binding affinity of TCC to sodium/potassium-transporting ATPase subunit alph (ATP1A1), indicating its ability to disrupt osmotic balance in marine fish by affecting this target protein. In summary, the results of this study will further enhance our comprehension of the potential toxic effects and mechanisms of TCC on the early stages of marine fish, with a specific focus on its unique toxic effects in osmoregulation.

Cross-talk between zinc and calcium regulates ion transport: A role for the zinc receptor, ZnR/GPR39

Zinc is essential for many physiological functions, with a major role in digestive system, skin health, and learning and memory. On the cellular level, zinc is involved in cell proliferation and cell death. A selective zinc sensing receptor, ZnR/GPR39 is a Gq-coupled receptor that acts via the inositol trisphosphate pathway to release intracellular Ca2+. The ZnR/GPR39 serves as a mediator between extracellular changes in Zn2+ concentration and cellular Ca2+ signalling. This signalling pathway regulates ion transporters activity and thereby controls the formation of transepithelial gradients or neuronal membrane potential, which play a fundamental role in the physiological function of these tissues. This review focuses on the role of Ca2+ signalling, and specifically ZnR/GPR39, with respect to the regulation of the Na+/H+ exchanger, NHE1, and of the K+/Cl- cotransporters, KCC1-3, and also describes the physiological implications of this regulation.

Astrocytic chloride regulates brain function in health and disease

Chloride ions (Cl-) play a pivotal role in synaptic inhibition in the central nervous system, primarily mediated through ionotropic mechanisms. A recent breakthrough emphathizes the significant influence of astrocytic intracellular chloride concentration ([Cl-]i) regulation, a field still in its early stages of exploration. Typically, the [Cl-]i in most animal cells is maintained at lower levels than the extracellular chloride [Cl-]o, a critical balance to prevent cell swelling due to osmotic pressure. Various Cl- transporters are expressed differently across cell types, fine-tuning the [Cl-]i, while Cl- gradients are utilised by several families of Cl- channels. Although the passive distribution of ions within cells is governed by basic biophysical principles, astrocytes actively expend energy to sustain [Cl-]i at much higher levels than those achieved passively, and much higher than neuronal [Cl-]i. Beyond the role in volume regulation, astrocytic [Cl-]i is dynamically linked to brain states and influences neuronal signalling in actively behaving animals. As a vital component of brain function, astrocytic [Cl-]i also plays a role in the development of disorders where inhibitory transmission is disrupted. This review synthesises the latest insights into astrocytic [Cl-]i, elucidating its role in modulating brain function and its implications in various pathophysiological conditions.

Cancer Stem Cells of Esophageal Adenocarcinoma are Suppressed by Inhibitors of TRPV2 and SLC12A2

BACKGROUND

The potential of membrane transporters activated in cancer stem cells (CSCs) as new therapeutic targets for cancer is attracting increasing interest. Therefore, the present study examined the expression profiles of ion transport-related molecules in the CSCs of esophageal adenocarcinoma (EAC).

METHODS

Cells that highly expressed aldehyde dehydrogenase 1 family member A1 (ALDH1A1) were separated from OE33 cells, a human Barrett's EAC cell line, by fluorescence-activated cell sorting. CSCs were identified based on the formation of tumorspheres. Gene expression profiles in CSCs were examined by a microarray analysis.

RESULTS

Among OE33 cells, ALDH1A1 messenger RNA levels were higher in CSCs than in non-CSCs. Furthermore, CSCs exhibited resistance to cisplatin and had the capacity to redifferentiate. The results of the microarray analysis of CSCs showed the up-regulated expression of several genes related to ion channels/transporters, such as transient receptor potential vanilloid 2 (TRPV2) and solute carrier family 12 member 2 (SLC12A2). The cytotoxicities of the TRPV2 inhibitor tranilast and the SLC12A2 inhibitor furosemide were higher at lower concentrations in CSCs than in non-CSCs, and both markedly reduced the number of tumorspheres. The cell population among OE33 cells that highly expressed ALDH1A1 also was significantly decreased by these inhibitors.

CONCLUSIONS

Based on the present results, TRPV2 and SLC12A2 are involved in the maintenance of CSCs, and their specific inhibitors, tranilast and furosemide, respectively, have potential as targeted therapeutic agents for EAC.

Life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) causes alterations in antioxidative status, ion regulation and histology of zebrafish gills

Tris (2-chloroethyl) phosphate (TCEP) has been receiving great concerns owing to its ubiquitous occurrence in various environmental compartments and potential risks to wildlife and humans. Gill is structural basis for ion regulation and homeostasis in fish and susceptible to xenobiotics. However, current knowledge on the impacts of long-term exposure to TCEP on the structure and physiological function of fish gills are insufficient. In this work, zebrafish were exposed to environmental realistic concentrations (0.8, 4, 20 and 100 μg/L) of TCEP from 3 h post ferterlization (hpf) till 120 days post ferterlization (dpf). Our results demonstrated that life-cycle exposure to TCEP significantly decreased the activity of glutathione S-transferase (GST), but elevated the activities of antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and increased malondialdehyde (MDA) content in zebrafish gills. Gene transcription analysis implied that the mRNA expressions of antioxidant-related genes (nrf2, cat and nqo1) were induced, while the transcription of gstα1, hmox1, keap1 were down-regulated, indicating that Nrf2-Keap1 pathway might be activated to defend the oxidative stress induced by TCEP. Additionally, the ion homeostasis was disrupted by TCEP exposure, evidenced by reduced activities of Na+/K+-ATPase (NKA), Ca2+-ATPase and Mg2+-ATPase and downregulated transcription levels of ncc, nkcc, cftr and clc-3. Besides, whole-life exposure to TCEP resulted in a series of structural damages to gills, including epithelial lifting, epithelial rupture, telangiectasis, vacuolation, edema and shortened gill lamellae. Overall, our results demonstrated that long-term TCEP exposure could induce oxidative stress, affect ion regulation and cause histological changes in zebrafish gills.

Integrative genome-wide analyses identify novel loci associated with kidney stones and provide insights into its genetic architecture

Kidney stone disease (KSD) is a complex disorder with high heritability and prevalence. We performed a large genome-wide association study (GWAS) meta-analysis for KSD to date, including 720,199 individuals with 17,969 cases in European population. We identified 44 susceptibility loci, including 28 novel loci. Cell type-specific analysis pinpointed the proximal tubule as the most relevant cells where susceptibility variants might act through a tissue-specific fashion. By integrating kidney-specific omics data, we prioritized 223 genes which strengthened the importance of ion homeostasis, including calcium and magnesium in stone formation, and suggested potential target drugs for the treatment. The genitourinary and digestive diseases showed stronger genetic correlations with KSD. In this study, we generate an atlas of candidate genes, tissue and cell types involved in the formation of KSD. In addition, we provide potential drug targets for KSD treatment and insights into shared regulation with other diseases.

SLC12A cryo-EM: analysis of relevant ion binding sites, structural domains, and amino acids

The solute carrier family 12A (SLC12A) superfamily of membrane transporters modulates the movement of cations coupled with chloride across the membrane. In doing so, these cotransporters are involved in numerous aspects of human physiology: cell volume regulation, ion homeostasis, blood pressure regulation, and neurological action potential via intracellular chloride concentration modulation. Their physiological characterization has been largely studied; however, understanding the mechanics of their function and the relevance of structural domains or specific amino acids has been a pending task. In recent years, single-particle cryogenic electron microscopy (cryo-EM) has been successfully applied to members of the SLC12A family including all K+:Cl- cotransporters (KCCs), Na+:K+:2Cl- cotransporter NKCC1, and recently Na+:Cl- cotransporter (NCC); revealing structural elements that play key roles in their function. The present review analyzes the data provided by these cryo-EM reports focusing on structural domains and specific amino acids involved in ion binding, domain interactions, and other important SCL12A structural elements. A comparison of cryo-EM data from NKCC1 and KCCs is presented in the light of the two recent NCC cryo-EM studies, to propose insight into structural elements that might also be found in NCC and are necessary for its proper function. In the final sections, the importance of key coordination residues for substrate specificity and their implication on various pathophysiological conditions and genetic disorders is reviewed, as this could provide the basis to correlate structural elements with the development of novel and selective treatments, as well as mechanistic insight into the function and regulation of cation-coupled chloride cotransporters (CCCs).

Excitatory/inhibitory balance in epilepsies and neurodevelopmental disorders: Depolarizing γ-aminobutyric acid as a common mechanism

Epilepsy is one of the most common neurological disorders. Although many factors contribute to epileptogenesis, seizure generation is mostly linked to hyperexcitability due to alterations in excitatory/inhibitory (E/I) balance. The common hypothesis is that reduced inhibition, increased excitation, or both contribute to the etiology of epilepsy. Increasing evidence shows that this view is oversimplistic, and that increased inhibition through depolarizing γ-aminobutyric acid (GABA) similarly contributes to epileptogenisis. In early development, GABA signaling is depolarizing, inducing outward Cl- currents due to high intracellular Cl- concentrations. During maturation, the mechanisms of GABA action shift from depolarizing to hyperpolarizing, a critical event during brain development. Altered timing of this shift is associated with both neurodevelopmental disorders and epilepsy. Here, we consider the different ways that depolarizing GABA contributes to altered E/I balance and epileptogenesis, and discuss that alterations in depolarizing GABA could be a common denominator underlying seizure generation in neurodevelopmental disorders and epilepsies.

SLC12A9 is a lysosome-detoxifying ammonium - chloride co-transporter

Ammonia is a ubiquitous, toxic by-product of cell metabolism. Its high membrane permeability and proton affinity causes ammonia to accumulate inside acidic lysosomes in its poorly membrane-permeant form: ammonium (NH ₄ ⁺ ). Ammonium buildup compromises lysosomal function, suggesting the existence of mechanisms that protect cells from ammonium toxicity. Here, we identified SLC12A9 as a lysosomal ammonium exporter that preserves lysosomal homeostasis. SLC12A9 knockout cells showed grossly enlarged lysosomes and elevated ammonium content. These phenotypes were reversed upon removal of the metabolic source of ammonium or dissipation of the lysosomal pH gradient. Lysosomal chloride increased in SLC12A9 knockout cells and chloride binding by SLC12A9 was required for ammonium transport. Our data indicate that SLC12A9 is a chloride-driven ammonium co-transporter that is central in an unappreciated, fundamental mechanism of lysosomal physiology that may have special relevance in tissues with elevated ammonia, such as tumors.

Toxicity of perfluorobutanesulfonate on gill functions of marine medaka (Oryzias melastigma): A time course and hypoxia co-exposure study

Perfluorobutanesulfonate (PFBS) is found in hypoxia regions. Results of previous studies have shown that hypoxia was capable of altering the inherent toxicity of PFBS. However, regarding gill functions, hypoxic influences and time course progression of toxic effects of PFBS remain unclear. In this study, with the aim to reveal the interaction behavior between PFBS and hypoxia, adult marine medaka Oryzias melastigma were exposed for 7 days to 0 or 10 μg PFBS/L under normoxic or hypoxic conditions. Subsequently, to explore the time-course transition in gill toxicity, medaka were exposed to PFBS for 21 days. The results showed that hypoxia dramatically increased the respiratory rate of medaka gill, which was further enhanced by exposure to PFBS; although exposure to PFBS under normoxic conditions for 7 days did not alter respiration, exposure to PFBS for 21 days significantly accelerated the respiration rate of female medaka. Concurrently, both hypoxia and PFBS were potent to interrupt the gene transcriptions and Na⁺, K⁺-ATPase enzymatic activity that play pivotal roles in the osmoregulation in gills of marine medaka, consequently disrupting homeostasis of major ions in blood, such as Na⁺, Cl^-, and Ca²⁺. In addition, composition and diversity of the microbiome residing on surfaces of the gill were profiled by using amplicon sequencing. Acute exposure to hypoxia for only 7 days caused a significant decrease in diversity of the bacterial community of gill whatever the presence of PFBS, while PFBS exposure for 21 days increased the diversity of gill microbial community. Principal component analysis revealed that, compared with PFBS, hypoxia was the predominant driver of gill microbiome dysbiosis. Depending on duration of exposure, a divergence was caused in the microbial community of gill. Overall, the current findings underline the interaction between hypoxia and PFBS on gill function and demonstrate the temporal variation in PFBS toxicity.

Quantitative Phosphoproteomics Reveals the Requirement of DYRK1-Mediated Phosphorylation of Ion Transport- and Cell Junction-Related Proteins for Notochord Lumenogenesis in Ascidian

The dual-specificity tyrosine phosphorylation-regulated kinase (DYRK1) phosphorylates diverse substrates involved in various cellular processes. Here, we found that blocking the kinase activity of DYRK1 inhibited notochord development and lumenogenesis in ascidian Ciona savignyi. By performing phosphoproteomics in conjunction with notochord-specific proteomics, we identified 1065 notochord-specific phosphoproteins that were present during lumen inflation, of which 428 differentially phosphorylated proteins (DPPs) were identified after inhibition of DYRK1 kinase activity. These DPPs were significantly enriched in metal ion transmembrane transporter activity, protein transport and localization, and tight junction. We next analyzed the downregulated phosphoproteins and focused on those belonging to the solute carrier (SLC), Ras-related protein (RAB), and tight junction protein (TJP) families. In vivo phospho-deficient study showed that alanine mutations on the phosphosites of these proteins resulted in defects of lumenogenesis during Ciona notochord development, demonstrating the crucial roles of phosphorylation of transmembrane transport-, vesicle trafficking-, and tight junction-related proteins in lumen formation. Overall, our study provides a valuable data resource for investigating notochord lumenogenesis and uncovers the molecular mechanisms of DYRK1-mediated notochord development and lumen inflation.

Na+/Cl- cotransporter 2 is not fish-specific and is widely found in amphibians, non-avian reptiles, and select mammals

Solute carrier 12 (Slc12) is a family of electroneutral cation-coupled chloride (Cl-) cotransporters. Na+/K+/2Cl- (Nkcc) and Na+/Cl- cotransporters (Ncc) belong to the Nkcc/Ncc subfamily. Human and mouse possess one gene for the Na+/Cl- cotransporter (ncc gene: slc12a3), whereas teleost fishes possess multiple ncc genes, slc12a3 (ncc1) and slc12a10 (ncc2), in addition to their species-specific paralogs. Amphibians and squamates have two ncc genes: slc12a3 (ncc1) and ncc3. However, the evolutionary relationship between slc12a10 and ncc3 remains unresolved, and the presence of slc12a10 (ncc2) in mammals has not been clarified. Synteny and phylogenetic analyses of vertebrate genome databases showed that ncc3 is the ortholog of slc12a10, and slc12a10 is present in most ray-finned fishes, coelacanths, amphibians, reptiles, and a few mammals (e.g., platypus and horse) but pseudogenized or deleted in birds, most mammals, and some ray-finned fishes (pufferfishes). This shows that slc12a10 is widely present among bony vertebrates and pseudogenized or deleted independently in multiple lineages. Notably, as compared with some fish that show varied slc12a10 tissue expression profile, spotted gar, African clawed frog, red-eared slider turtle, and horse express slc12a10 in the ovaries or premature gonads. In horse tissues, an unexpectedly large number of splicing variants for Slc12a10 have been cloned, many of which encode truncated forms of Slc12a10, suggesting that the functional constraints of horse slc12a10 are weakened, which may be in the process of becoming a pseudogene. Our results elaborate on the evolution of Nkcc/Ncc subfamily of Slc12 in vertebrates.NEW & NOTEWORTHY slc12a10 is not a fish-specific gene and is present in a few mammals (e.g., platypus and horse), non-avian reptiles, amphibians, but was pseudogenized or deleted in most mammals (e.g., human, mouse, cat, cow, and rhinoceros), birds, and some ray-finned fishes (pufferfishes).

Activation of Swell1 in microglia suppresses neuroinflammation and reduces brain damage in ischemic stroke

Cl^- movement and Cl^--sensitive signal pathways contributes to the survival and switch of inflammatory phenotype of microglia and are believed to play a key role in the inflammatory brain injury after ischemic stroke. Here, we demonstrated an important role of Cl^- transmembrane transporter Swell1, in the survival and M2-like polarization of microglia in ischemic stroke. Knockdown or overexpression of Swell1 in cultured microglia inhibited or increased hypotonic-activated Cl^- currents, respectively, and these changes were completely blocked by the volume-regulated anion channels (VRACs) inhibitor DCPIB. Swell1 conditional knock-in mice promoted microglia survival in ischemic brain region and resulted in significant reductions in neural cell death, infarction volume and neurological deficits following transient middle cerebral artery occlusion (tMCAO). Using gene manipulating technique and pharmacological inhibitors, we further revealed that Swell1 opening led to SGK1 (a Cl^--sensitive kinase)-mediated activation of FOXO3a/CREB as well as WNK1 (another Cl^--sensitive kinase)-mediated SPAK/OSR1-CCCs activation, which promoted microglia survival and M2-like polarization, thereby attenuating neuroinflammation and ischemic brain injury. Taken together, our results demonstrated that Swell1 is an essential component of microglia VRACs and its activation protects against ischemic brain injury through promoting microglia survival and M2-like polarization.

Inhibition mechanism of NKCC1 involves the carboxyl terminus and long-range conformational coupling

The Na-K-2Cl cotransporter-1 (NKCC1) is an electroneutral Na⁺-dependent transporter responsible for simultaneously translocating Na⁺, K⁺, and Cl^- ions into cells. In human tissue, NKCC1 plays a critical role in regulating cytoplasmic volume, fluid intake, chloride homeostasis, and cell polarity. Here, we report four structures of human NKCC1 (hNKCC1), both in the absence and presence of loop diuretic (bumetanide or furosemide), using single-particle cryo-electron microscopy. These structures allow us to directly observe various novel conformations of the hNKCC1 dimer. They also reveal two drug-binding sites located at the transmembrane and cytosolic carboxyl-terminal domains, respectively. Together, our findings enable us to delineate an inhibition mechanism that involves a coupled movement between the cytosolic and transmembrane domains of hNKCC1.

Cryo-EM structure of the human NKCC1 transporter reveals mechanisms of ion coupling and specificity

The sodium-potassium-chloride transporter NKCC1 of the SLC12 family performs Na⁺ -dependent Cl^- - and K⁺ -ion uptake across plasma membranes. NKCC1 is important for regulating cell volume, hearing, blood pressure, and regulation of hyperpolarizing GABAergic and glycinergic signaling in the central nervous system. Here, we present a 2.6 Å resolution cryo-electron microscopy structure of human NKCC1 in the substrate-loaded (Na⁺ , K⁺ , and 2 Cl^- ) and occluded, inward-facing state that has also been observed for the SLC6-type transporters MhsT and LeuT. Cl^- binding at the Cl1 site together with the nearby K⁺ ion provides a crucial bridge between the LeuT-fold scaffold and bundle domains. Cl^- -ion binding at the Cl2 site seems to undertake a structural role similar to conserved glutamate of SLC6 transporters and may allow for Cl^- -sensitive regulation of transport. Supported by functional studies in mammalian cells and computational simulations, we describe a putative Na⁺ release pathway along transmembrane helix 5 coupled to the Cl2 site. The results provide insight into the structure-function relationship of NKCC1 with broader implications for other SLC12 family members.

Molecular Identification of Pro-Excitogenic Receptor and Channel Phenotypes of the Deafferented Lumbar Motoneurons in the Early Phase after SCT in Rats

Spasticity impacts the quality of life of patients suffering spinal cord injury and impedes the recovery of locomotion. At the cellular level, spasticity is considered to be primarily caused by the hyperexcitability of spinal α-motoneurons (MNs) within the spinal stretch reflex circuit. Here, we hypothesized that after a complete spinal cord transection in rats, fast adaptive molecular responses of lumbar MNs develop in return for the loss of inputs. We assumed that early loss of glutamatergic afferents changes the expression of glutamatergic AMPA and NMDA receptor subunits, which may be the forerunners of the developing spasticity of hindlimb muscles. To better understand its molecular underpinnings, concomitant expression of GABA and Glycinergic receptors and serotoninergic and noradrenergic receptors, which regulate the persistent inward currents crucial for sustained discharges in MNs, were examined together with voltage-gated ion channels and cation-chloride cotransporters. Using quantitative real-time PCR, we showed in the tracer-identified MNs innervating extensor and flexor muscles of the ankle joint multiple increases in transcripts coding for AMPAR and 5-HTR subunits, along with a profound decrease in GABAAR, GlyR subunits, and KCC2. Our study demonstrated that both MNs groups similarly adapt to a more excitable state, which may increase the occurrence of extensor and flexor muscle spasms.

Chloride channels in the lung: Challenges and perspectives for viral infections, pulmonary arterial hypertension, and cystic fibrosis

Fine control over chloride homeostasis in the lung is required to maintain membrane excitability, transepithelial transport as well as intra- and extracellular ion and water homeostasis. Over the last decades, a growing number of chloride channels and transporters have been identified in the cells of the pulmonary vasculature and the respiratory tract. The importance of these proteins is underpinned by the fact that impairment of their physiological function is associated with functional dysregulation, structural remodeling, or hereditary diseases of the lung. This paper reviews the field of chloride channels and transporters in the lung and discusses chloride channels in disease processes such as viral infections including SARS-CoV- 2, pulmonary arterial hypertension, cystic fibrosis and asthma. Although chloride channels have become a hot research topic in recent years, remarkably few of them have been targeted by pharmacological agents. As such, we complement the putative pathophysiological role of chloride channels here with a summary of their therapeutic potential.

How Many Cell Types Are in the Kidney and What Do They Do?

The kidney maintains electrolyte, water, and acid-base balance, eliminates foreign and waste compounds, regulates blood pressure, and secretes hormones. There are at least 16 different highly specialized epithelial cell types in the mammalian kidney. The number of specialized endothelial cells, immune cells, and interstitial cell types might even be larger. The concerted interplay between different cell types is critical for kidney function. Traditionally, cells were defined by their function or microscopical morphological appearance. With the advent of new single-cell modalities such as transcriptomics, epigenetics, metabolomics, and proteomics we are entering into a new era of cell type definition. This new technological revolution provides new opportunities to classify cells in the kidney and understand their functions.

Does Plasma Inhibit the Activity of KCl Cotransport in Red Cells From LK Sheep?

Red cells from LK sheep represent an important paradigm for control of KCl cotransport activity, as well as being important to sheep erythroid function. A previous report (Godart et al., 1997) suggested that autologous plasma markedly inhibits red cell KCC activity and identified the presence of the bicarbonate/CO₂ buffer system as the probable cause. Findings were restricted, however, to red cells from patients with sickle cell disease (SCD) swollen anisotonically and carried out at a very high O₂ tension (c.700 mmHg). It was therefore important to investigate the generality of the effect described and whether it was also relevant to the two main stimuli for KCC activity encountered most often by circulating red cells in vivo - low pH in active muscle beds during exercise and high urea concentrations in the renal medulla during antidiuresis. Results confirm that inhibition was significant in response to anisotonic swelling with KCC activity in MOPS-buffered saline (MBS) vs. bicarbonate-buffered saline (BBS) and in MBS vs. plasma both reduced (by about 25 and 50%, respectively). By contrast, however, inhibition was absent at low pH and in high concentrations of urea. These findings suggest therefore that red cell KCC activity represents an important membrane permeability in vivo in red cells suspended in plasma. They are relevant, in particular, to sheep red cells, and may also be important by extension to those of other species and to the abnormal red cells found in human patients with SCD.

The Important Role of Ion Transport System in Cervical Cancer

Cervical cancer is a significant gynecological cancer and causes cancer-related deaths worldwide. Human papillomavirus (HPV) is implicated in the etiology of cervical malignancy. However, much evidence indicates that HPV infection is a necessary but not sufficient cause in cervical carcinogenesis. Therefore, the cellular pathophysiology of cervical cancer is worthy of study. This review summarizes the recent findings concerning the ion transport processes involved in cell volume regulation and intracellular Ca²⁺ homeostasis of epithelial cells and how these transport systems are themselves regulated by the tumor microenvironment. For cell volume regulation, we focused on the volume-sensitive Cl⁻ channels and K⁺-Cl⁻ cotransporter (KCC) family, important regulators for ionic and osmotic homeostasis of epithelial cells. Regarding intracellular Ca²⁺ homeostasis, the Ca²⁺ store sensor STIM molecules and plasma membrane Ca²⁺ channel Orai proteins, the predominant Ca²⁺ entry mechanism in epithelial cells, are discussed. Furthermore, we evaluate the potential of these membrane ion transport systems as diagnostic biomarkers and pharmacological interventions and highlight the challenges.

Perfluorinated compounds disrupted osmoregulation in Oryzias melastigma during acclimation to hypoosmotic environment

Perfluorinated compounds (PFCs) are a type of ubiquitous contaminants spreading in the estuarine and coastal areas. Anadromous fish should deal with hypoosmotic challenge with PFCs stress during their migration from seawater to estuaries. However, few studies have been carried out to investigate the adverse impact of PFCs on fish osmoregulation and the underlying mechanism. In this study, Oryzias melastigma, an euryhaline fish model, were exposed to four representative PFC congeners including perfluorobutane sulfonate (PFBS), perfluorooctane sulfonates (PFOS), perfluorooctanoic acid (PFOA), and perfluorododecanoic acid (PFDoA) separately under both seawater and freshwater conditions. Histopathological changes in gills, ion homeostasis, Na⁺/K⁺-ATPase (NKA) activity, as well as the expression of related genes was detected upon exposure. Results showed that PFCs induced morphological changes in gills, disturbed the levels of major ions (Na⁺, Ca²⁺, Mg²⁺), and inhibited the NKA activity. Transcriptome analysis in fish gills during the acclimation to freshwater revealed that PFCs influenced the osmoregulation mainly by interfering with the endocrine system, signal transduction, as well as cellular community and motility. Validation with qRT-PCR confirmed that the mRNA expressions of osmoregulatory genes encoding hormones and receptors, as well as ion transmembrane transporters were disturbed by PFCs. Longer chain homolog (PFOS) showed a greater impact on osmoregulation than the shorter chain homolog (PFBS). Within the same carbon chain, sulfonic congener (PFOS) induced more serious injury to gills than carboxylic congener (PFOA). The interaction between PFCs and salinity varied in different adverse outcome. These results help to further understand the mechanism of how PFCs influence osmoregulation and elicit the need to assess the ecological risk of PFCs and other pollutants on anadromous migration.

A network embedding framework based on integrating multiplex network for drug combination prediction

Drug combination is a sensible strategy for disease treatment because it improves the treatment efficacy and reduces concomitant side effects. Due to the large number of possible combinations among candidate compounds, exhaustive screening is prohibitive. Currently, a large number of studies have focused on predicting potential drug combinations. However, these methods are not entirely satisfactory in terms of performance and scalability. In this paper, we proposed a Network Embedding frameWork in MultIplex Network (NEWMIN) to predict synthetic drug combinations. Based on a multiplex drug similarity network, we offered alternative methods to integrate useful information from different aspects and to decide the quantitative importance of each network. For drug combination prediction, we found seven novel drug combinations that have been validated by external sources among the top-ranked predictions of our model. To verify the feasibility of NEWMIN, we compared NEWMIN with other five methods, for which it showed better performance than other methods in terms of the area under the precision-recall curve and receiver operating characteristic curve.

High-Resolution Views and Transport Mechanisms of the NKCC1 and KCC Transporters

Cation-chloride cotransporters (CCCs) are responsible for the coupled co-transport of Cl- with K+ and/or Na+ in an electroneutral manner. They play important roles in myriad fundamental physiological processes--from cell volume regulation to transepithelial solute transport and intracellular ion homeostasis--and are targeted by medicines commonly prescribed to treat hypertension and edema. After several decades of studies into the functions and pharmacology of these transporters, there have been several breakthroughs in the structural determination of CCC transporters. The insights provided by these new structures for the Na+/K+/Cl- cotransporter NKCC1 and the K+/Cl- cotransporters KCC1, KCC2, KCC3 and KCC4 have deepened our understanding of their molecular basis and transport function. This focused review discusses recent advances in the structural and mechanistic understanding of CCC transporters, including architecture, dimerization, functional roles of regulatory domains, ion binding sites, and coupled ion transport.

Nonlinear effects of environmental salinity on the gill transcriptome versus proteome of Oreochromis niloticus modulate epithelial cell turnover

A data-independent acquisition (DIA) assay library for targeted quantitation of thousands of Oreochromis niloticus gill proteins using a label- and gel-free workflow was generated and used to compare protein and mRNA abundances. This approach generated complimentary rather than redundant data for 1899 unique genes in gills of tilapia acclimated to freshwater and brackish water. Functional enrichment analyses identified mitochondrial energy metabolism, serine protease and immunity-related functions, and cytoskeleton/ extracellular matrix organization as major processes controlled by salinity in O. niloticus gills. Non-linearity in salinity-dependent transcriptome versus proteome regulation was revealed for specific functional groups of genes. The relationship was more linear for other molecular functions/ cellular processes, suggesting that the salinity-dependent regulation of O. niloticus gill function relies on post-transcriptional mechanisms for some functions/ processes more than others. This integrative systems biology approach can be adopted for other tissues and organisms to study cellular dynamics for many changing ecological contexts.

Increased Endocytosis of Cadmium-Metallothionein through the 24p3 Receptor in an In Vivo Model with Reduced Proximal Tubular Activity

BACKGROUND

The proximal tubule (PT) is the major target of cadmium (Cd2+) nephrotoxicity. Current dogma postulates that Cd2+ complexed to metallothionein (MT) (CdMT) is taken up through receptor-mediated endocytosis (RME) via the PT receptor megalin:cubilin, which is the predominant pathway for reuptake of filtered proteins in the kidney. Nevertheless, there is evidence that the distal parts of the nephron are also sensitive to damage induced by Cd2+. In rodent kidneys, another receptor for protein endocytosis, the 24p3 receptor (24p3R), is exclusively expressed in the apical membranes of distal tubules (DT) and collecting ducts (CD). Cell culture studies have demonstrated that RME and toxicity of CdMT and other (metal ion)-protein complexes in DT and CD cells is mediated by 24p3R. In this study, we evaluated the uptake of labeled CdMT complex through 24p3R after acute kidney injury (AKI) induced by gentamicin (GM) administration that disrupts PT function. Subcutaneous administration of GM at 10 mg/kg/day for seven days did not alter the structural and functional integrity of the kidney's filtration barrier. However, because of PT injury, the concentration of the renal biomarker Kim-1 increased. When CdMT complex coupled to FITC was administered intravenously, both uptake of the CdMT complex and 24p3R expression in DT increased and also colocalized after PT injury induced by GM. Although megalin decreased in PT after GM administration, urinary protein excretion was not changed, which suggests that the increased levels of 24p3R in the distal nephron could be acting as a compensatory mechanism for protein uptake. Altogether, these results suggest that PT damage increases the uptake of the CdMT complex through 24p3R in DT (and possibly CD) and compensate for protein losses associated with AKI.

Increased intracellular Cl- concentration in pulmonary arterial myocytes is associated with chronic hypoxic pulmonary hypertension

Chloride channels play an important role in regulating smooth muscle contraction and proliferation, and contribute to the enhanced constriction of pulmonary arteries (PAs) in pulmonary hypertension (PH). The intracellular Cl^- concentration ([Cl^-]_i), tightly regulated by various Cl^- transporters, determines the driving force for Cl^- conductance, thereby the functional outcome of Cl^- channel activation. This study characterizes for the first time the expression profile of Cl^- transporters/exchangers in PA smooth muscle and provides the first evidence that the intracellular Cl^- homeostasis is altered in PA smooth muscle cells (PASMCs) associated with chronic hypoxic PH (CHPH). Quantitative RT-PCR revealed that the endothelium-denuded intralobar PA of rats expressed Slc12a gene family-encoded Na-K-2Cl cotransporter 1 (NKCC1), K-Cl cotransporters (KCC) 1, 3, and 4, and Slc4a gene family-encoded Na⁺-independent and Na⁺-dependent Cl^-/HCO₃^- exchangers. Exposure of rats to chronic hypoxia (10% O₂, 3 wk) caused CHPH and selectively increased the expression of Cl^--accumulating NKCC1 and reduced the Cl^--extruding KCC4. The intracellular Cl^- concentration ([Cl^-]_i) averaged at 45 mM and 47 mM in normoxic PASMCs as determined by fluorescent indicator MEQ and by gramicidin-perforated patch-clamp technique, respectively. The ([Cl^-]_i was increased by ∼10 mM in PASMCs of rats with CHPH. Future studies are warranted to further establish the hypothesis that the altered intracellular Cl^- homeostasis contributes to the pathogenesis of CHPH.

Membrane Transport Proteins in Osteoclasts: The Ins and Outs

During bone resorption, the osteoclast must sustain an extraordinarily low pH environment, withstand immense ionic pressures, and coordinate nutrient and waste exchange across its membrane to sustain its unique structural and functional polarity. To achieve this, osteoclasts are equipped with an elaborate set of membrane transport proteins (pumps, transporters and channels) that serve as molecular ‘gatekeepers’ to regulate the bilateral exchange of ions, amino acids, metabolites and macromolecules across the ruffled border and basolateral domains. Whereas the importance of the vacuolar-ATPase proton pump and chloride voltage-gated channel 7 in osteoclasts has long been established, comparatively little is known about the contributions of other membrane transport proteins, including those categorized as secondary active transporters. In this Special Issue review, we provide a contemporary update on the ‘ins and outs’ of membrane transport proteins implicated in osteoclast differentiation, function and bone homeostasis and discuss their therapeutic potential for the treatment of metabolic bone diseases.

The structural basis of function and regulation of neuronal cotransporters NKCC1 and KCC2

NKCC and KCC transporters mediate coupled transport of Na++K++Cl- and K++Cl- across the plasma membrane, thus regulating cell Cl- concentration and cell volume and playing critical roles in transepithelial salt and water transport and in neuronal excitability. The function of these transporters has been intensively studied, but a mechanistic understanding has awaited structural studies of the transporters. Here, we present the cryo-electron microscopy (cryo-EM) structures of the two neuronal cation-chloride cotransporters human NKCC1 (SLC12A2) and mouse KCC2 (SLC12A5), along with computational analysis and functional characterization. These structures highlight essential residues in ion transport and allow us to propose mechanisms by which phosphorylation regulates transport activity.

Identification of key modules and hub genes in glioblastoma multiforme based on co-expression network analysis

Glioblastoma multiforme (GBM) is the most malignant primary tumour in the central nervous system, but the molecular mechanisms underlying its pathogenesis remain unclear. In this study, data set GSE50161 was used to construct a co‐expression network for weighted gene co‐expression network analysis. Two modules (dubbed brown and turquoise) were found to have the strongest correlation with GBM. Functional enrichment analysis indicated that the brown module was involved in the cell cycle, DNA replication, and pyrimidine metabolism. The turquoise module was primarily related to circadian rhythm entrainment, glutamatergic synapses, and axonal guidance. Hub genes were screened by survival analysis using The Cancer Genome Atlas and Human Protein Atlas databases and further tested using the GSE4290 and Gene Expression Profiling Interactive Analysis databases. The eight hub genes (NUSAP1, SHCBP1, KNL1, SULT4A1, SLC12A5, NUF2, NAPB, and GARNL3) were verified at both the transcriptional and translational levels, and these gene expression levels were significant based on the World Health Organization classification system. These hub genes may be potential biomarkers and therapeutic targets for the accurate diagnosis and management of GBM.

SLC12A8 plays a key role in bladder cancer progression and EMT

Bladder cancer is the most common malignant tumor of the urinary system. The intention of the present research is to explore the prognostic value and biological function of solute carrier family 12 member 8 (SLC12A8) in bladder cancer. The analysis based on the TCGA and ONCOMINE database revealed that the expression of SLC12A8 in bladder cancer was notably increased compared with the normal group. SLC12A8 expression was notably correlated with the age, pathological stage, T-stage, and lymph node metastasis of bladder cancer patients. Moreover, the patients’ overall survival was notably shorter in the high SLC12A8 group. Compared with the control, SLC12A8 upregulation enhanced the proliferative, invasive, and migratory capacities of bladder cancer cells and promoted the expression of epithelial–mesenchymal transition (EMT) protein markers including β-catenin, vimentin, snail, and slug, while reduced the expression of E-cadherin. In the case of downregulated SLC12A8 expression, the proliferative, invasive, and migratory capacities of bladder cancer cells and the expression of EMT protein markers presented the opposite trend. This study demonstrated that SLC12A8 was highly correlated with oncogenesis and progression of bladder cancer, indicating that SLC12A8 may be a meaningful biomarker for initial diagnosis and early treatment of bladder cancer.

Structures and an activation mechanism of human potassium-chloride cotransporters

Potassium-chloride cotransporters KCC1 to KCC4 mediate the coupled export of potassium and chloride across the plasma membrane and play important roles in cell volume regulation, auditory system function, and γ-aminobutyric acid (GABA) and glycine-mediated inhibitory neurotransmission. Here, we present 2.9- to 3.6-Å resolution structures of full-length human KCC2, KCC3, and KCC4. All three KCCs adopt a similar overall architecture, a domain-swap dimeric assembly, and an inward-facing conformation. The structural and functional studies reveal that one unexpected N-terminal peptide binds at the cytosolic facing cavity and locks KCC2 and KCC4 at an autoinhibition state. The C-terminal domain (CTD) directly interacts with the N-terminal inhibitory peptide, and the relative motions between the CTD and the transmembrane domain (TMD) suggest that CTD regulates KCCs' activities by adjusting the autoinhibitory effect. These structures provide the first glimpse of full-length structures of KCCs and an autoinhibition mechanism among the amino acid-polyamine-organocation transporter superfamily.

Solute carrier family 12 member 8 impacts the biological behaviors of breast carcinoma cells by activating TLR/NLR signaling pathway

This study aimed to understand the expression of solute carrier family 12 member 8 (SLC12A8) in breast carcinoma and its biological functions, as well as its effect on the Toll-like receptor /NOD-like receptor (TLR/NLR) signaling pathway. The expression of SLC12A8 was analyzed using the public RNA sequencing dataset from TCGA database and the two datasets from Oncomine database. The former dataset was also used to evaluate the prognostic value of SLC12A8 in breast carcinoma. Real-time qPCR and western blot were applied to measure relative expression of SLC12A8. Functionally, the effect of SLC12A8 on the cells proliferation and motion was studied using cell counting kit 8 and Transwell assays respectively. Mechanistic studies were conducted using Gene Set Enrichment Analysis (GSEA) and confirmed by western blot. As a result, SLC12A8 was upregulated in breast carcinoma, and high levels of SLC12A8 led to a poorer prognosis and can be regarded as an independent prognosticator for patients with breast carcinoma. Functional experiments demonstrated that SLC12A8-knockdown suppressed while SLC12A8-overexpression elevated the viability, invasiveness and motility of breast carcinoma cells. Furthermore, GSEA indicated that high SLC12A8 was positively correlated with TLR/NLR signaling pathway. Silencing SLC12A8 significantly reduced the protein expression of TLR/NLR-related markers, whereas overexpression of SLC12A8 caused an elevation on the protein expression of these markers. All these data suggested that SLC12A8 plays a promoting effect on the cells viability, invasiveness and motility in breast carcinoma by activating TLR/NLR signaling pathway.

Differential diagnosis of perinatal Bartter, Bartter and Gitelman syndromes

The common finding of hypokalemic alkalosis in several unrelated disorders may confound the early diagnosis of salt-losing tubulopathy (SLT). Antenatal Bartter syndrome (BS) must be considered in idiopathic early-onset polyhydramnios. Fetal megabladder in BS may allow its distinction from third-trimester polyhydramnios that occurs in congenital chloride diarrhea (CCD). Fetal megacolon occurs in CCD while fecal chloride >90 mEq/L in infants is diagnostic. Failure-to-thrive, polydipsia and polyuria in early childhood are the hallmarks of classic BS. Unlike BS, there is low urinary chloride in hypokalemic alkalosis of intractable emesis and cystic fibrosis. Rarely, renal salt wasting may result from cystinosis, Dent disease, disorders of paracellular claudin-10b and Kir4.1 potassium-channel deficiency. Acquired BS may result from calcimimetic up-regulation of a calcium-sensing receptor or autoantibody inactivation of sodium chloride co-transporters in Sjögren syndrome. A relatively common event of heterozygous gene mutations for Gitelman syndrome increases the likelihood of its random occurrence in certain diseases of adult onset. Finally, diuretic abuse is the most common differential diagnosis of SLT. Unlike the persistent elevation in BS, urinary chloride concentration losses waxes and wanes on day-to-day assessment in patients with diuretic misuse.

Role of the Cation-Chloride-Cotransporters in Cardiovascular Disease

The SLC12 family of cation-chloride-cotransporters (CCCs) is comprised of potassium chloride cotransporters (KCCs), which mediate Cl- extrusion and sodium-potassium chloride cotransporters (N[K]CCs), which mediate Cl- loading. The CCCs play vital roles in cell volume regulation and ion homeostasis. The functions of CCCs influence a variety of physiological processes, many of which overlap with the pathophysiology of cardiovascular disease. Although not all of the cotransporters have been linked to Mendelian genetic disorders, recent studies have provided new insights into their functional role in vascular and renal cells in addition to their contribution to cardiovascular diseases. Particularly, an imbalance in potassium levels promotes the pathogenesis of atherosclerosis and disturbances in sodium homeostasis are one of the causes of hypertension. Recent findings suggest hypothalamic signaling as a key signaling pathway in the pathophysiology of hypertension. In this review, we summarize and discuss the role of CCCs in cardiovascular disease with particular emphasis on knowledge gained in recent years on NKCCs and KCCs.

Polarized Expression of Ion Channels and Solute Carrier Family Transporters on Heterogeneous Cultured Human Corneal Endothelial Cells

Purpose

To clarify the expression profiles of ion channels and transporters of metabolic substrates among heterogeneous cultured human corneal endothelial cells (cHCECs) distinct in their effectiveness in reconstituting the corneal endothelium.

Methods

Integrated proteomics for cell lysates by liquid chromatography–tandem mass spectrometry was carried out from three aliquots of cHCECs enriched in either cluster of definition (CD)44^−/+ (mature) cHCECs or CD44^++/+++ cell-state transition (CST) cHCECs. The expression profiles of cations/anions, monocarboxylic acid transporters (MCTs), and solute carrier (SLC) family proteins, as well as carbonic anhydrases (CAs), were investigated.

Results

The polarized expression of cations/anions, MCTs, and SLC family proteins, as well as CAs, was clarified for mature and CST cHCECs. Most SLC4 family members, including SLC4A11 and SLC4A4 (NBCe1), were upregulated in the CST cHCECs, whereas SLC9A1 (Na⁺/H⁺ exchanger isoform one [NHE1]) and CA5B were detected only in the mature cHCECs. In addition, SLC25A42, catalyzing the entry of coenzyme A into the mitochondria, and SLC25A18, functioning as a mitochondrial glutamate carrier 2 (both relevant for providing the substrates for mitochondrial bioenergetics), were selectively expressed in the mature cHCECs.

Conclusions

Our findings may suggest the relevance of qualifying the polarized expression of these ion channels and transporter-like proteins to ensure not only the suitability but also the in vivo biological functionality of cHCECs selected for use in a cell-injection therapy.

Solute Carrier Transporters as Potential Targets for the Treatment of Metabolic Disease

The solute carrier (SLC) superfamily comprises more than 400 transport proteins mediating the influx and efflux of substances such as ions, nucleotides, and sugars across biological membranes. Over 80 SLC transporters have been linked to human diseases, including obesity and type 2 diabetes (T2D). This observation highlights the importance of SLCs for human (patho)physiology. Yet, only a small number of SLC proteins are validated drug targets. The most recent drug class approved for the treatment of T2D targets sodium-glucose cotransporter 2, product of the SLC5A2 gene. There is great interest in identifying other SLC transporters as potential targets for the treatment of metabolic diseases. Finding better treatments will prove essential in future years, given the enormous personal and socioeconomic burden posed by more than 500 million patients with T2D by 2040 worldwide. In this review, we summarize the evidence for SLC transporters as target structures in metabolic disease. To this end, we identified SLC13A5/sodium-coupled citrate transporter, and recent proof-of-concept studies confirm its therapeutic potential in T2D and nonalcoholic fatty liver disease. Further SLC transporters were linked in multiple genome-wide association studies to T2D or related metabolic disorders. In addition to presenting better-characterized potential therapeutic targets, we discuss the likely unnoticed link between other SLC transporters and metabolic disease. Recognition of their potential may promote research on these proteins for future medical management of human metabolic diseases such as obesity, fatty liver disease, and T2D. SIGNIFICANCE STATEMENT: Given the fact that the prevalence of human metabolic diseases such as obesity and type 2 diabetes has dramatically risen, pharmacological intervention will be a key future approach to managing their burden and reducing mortality. In this review, we present the evidence for solute carrier (SLC) genes associated with human metabolic diseases and discuss the potential of SLC transporters as therapeutic target structures.

Liver Transcriptome Responses to Heat Stress and Newcastle Disease Virus Infection in Genetically Distinct Chicken Inbred Lines

Heat stress results in reduced productivity, anorexia, and mortality in chickens. The objective of the study was to identify genes and signal pathways associated with heat stress and Newcastle disease virus (NDV) infection in the liver of chickens through RNA-seq analysis, using two highly inbred chicken lines (Leghorn and Fayoumi). All birds were held in the same environment until 14 days of age. On day 14, half the birds were exposed to 38 °C with 50% relative humidity for 4 h, then 35 °C until the end of the experiment. The remaining birds were kept at 25 °C throughout the experiment. The heat-treated birds were inoculated at 21 days of age with 10⁷ EID₅₀ (One EID₅₀ unit is the amount of virus that will infect 50 percent of inoculated embryos) NDV La Sota strain to investigate the effects of both heat stress and NDV infection. Physiological parameters were recorded as blood phenotypes at three stages: acute heat (AH), chronic heat (CH1), and chronic heat combined with NDV infection (CH&NDV), at 4 h, 7 days, and 10 days post-initiation of heat treatment, respectively. Our previous work revealed that the heat-resilient Fayoumi line maintained a more stable acid-base balance in their blood compared to the Leghorn line. Liver samples were harvested on both AH and CH&NDV to characterize the transcriptome profiles of these two inbred lines. Both genetic lines and treatments had large impact on the liver transcriptome. Fayoumi birds had more differentially expressed genes (DEGs) than Leghorn birds for both treatments. Metabolic and immune-related genes were on the DEG list, with Fayoumi having more immune-related DEGs than Leghorns, which was confirmed by gene functional enrichment analysis. Weighted correlation network analysis (WGCNA) indicated that the driver genes such as Solute Carrier Family genes could be very important for stabilizing the acid-base balance in Fayoumi birds during heat stress. Therefore, candidate genes such solute carrier family genes could be potential genetic targets that are regulated by Fayoumis to maintain physical hemostasis under heat stress. Differential gene expression showed that Leghorns mainly performed metabolic regulation in response to heat stress and NDV infection, while Fayoumis regulated both immune and metabolic functions. This study provides novel insights and enhances our understandings of liver response to heat stress of heat resilient and susceptible inbred chicken lines.

GABAergic mechanisms in the suprachiasmatic nucleus that influence circadian rhythm

The mammalian central circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN contains multiple circadian oscillators which synchronize with each other via several neurotransmitters. Importantly, an inhibitory neurotransmitter, γ-amino butyric acid (GABA), is expressed in almost all SCN neurons. In this review, we discuss how GABA influences circadian rhythms in the SCN. Excitatory and inhibitory effects of GABA may depend on intracellular Cl^- concentration, in which several factors such as day-length, time of day, development, and region in the SCN may be involved. GABA also mediates oscillatory coupling of the circadian rhythms in the SCN. Recent genetic approaches reveal that GABA refines circadian output rhythms, but not circadian oscillations in the SCN. Since several efferent projections of the SCN have been suggested, GABA might work downstream of neuronal pathways from the SCN which regulate the temporal order of physiology and behavior.

Solute carriers in scallop genome: Gene expansion and expression regulation after exposure to toxic dinoflagellate

The solute carriers (SLCs) are membrane proteins that transport many endogenous and exogenous substances such as xenobiotic toxins. Bivalve mollusks, mainly feeding on microalgae, show marked capacity to accumulate paralytic shellfish toxins (PSTs), the most common and hazardous marine biotoxins produced by dinoflagellates. Exploring the SLCs related to PST accumulation in bivalve could benefit our understanding about the mechanisms of PST bioavailability in bivalve and the adaptations of these species. Herein, we provided the first systematic analysis of SLC genes in mollusks, which identified 673 SLCs (PySLCs, 48 subfamilies) in Yesso scallop (Patinopecten yessoensis), 510 (48 subfamilies) in Pacific oyster (Crassostrea gigas), and 350 (47 subfamilies) in gastropod owl limpet (Lottia gigantea). Significant expansion of subfamilies SLC5, SLC6, SLC16, and SLC23 in scallop, and SLC46 subfamily in both scallop and oyster were revealed. Different PySLC members were highly expressed in the developmental stages and adult tissues, and hepatopancreas harboured more specifically expressed PySLCs than other tissues/organs. After feeding the scallops with PST-producing dinoflagellate, 131 PySLCs were regulated and more than half of them were from the expanded subfamilies. The trend of expression fold change in regulated PySLCs was consistent with that of PST changes in hepatopancreas, implying the possible involvement of these PySLCs in PST transport and homeostasis. In addition, the PySLCs from the expanded subfamily were revealed to be under positive selection, which might be related to lineage-specific adaptation to the marine environments with algae derived biotoxins.

Cryo-EM structures of the human cation-chloride cotransporter KCC1

Cation-chloride cotransporters (CCCs) mediate the coupled, electroneutral symport of cations with chloride across the plasma membrane and are vital for cell volume regulation, salt reabsorption in the kidney, and γ-aminobutyric acid (GABA)-mediated modulation in neurons. Here we present cryo-electron microscopy (cryo-EM) structures of human potassium-chloride cotransporter KCC1 in potassium chloride or sodium chloride at 2.9- to 3.5-angstrom resolution. KCC1 exists as a dimer, with both extracellular and transmembrane domains involved in dimerization. The structural and functional analyses, along with computational studies, reveal one potassium site and two chloride sites in KCC1, which are all required for the ion transport activity. KCC1 adopts an inward-facing conformation, with the extracellular gate occluded. The KCC1 structures allow us to model a potential ion transport mechanism in KCCs and provide a blueprint for drug design.

The TWIST1-centered competing endogenous RNA network promotes proliferation, invasion, and migration of lung adenocarcinoma

The proposed competing endogenous RNA (ceRNA) mechanism suggested that diverse RNA species, including protein-coding messenger RNAs and non-coding RNAs such as long non-coding RNAs, pseudogenes and circular RNAs could communicate with each other by competing for binding to shared microRNAs. The ceRNA network (ceRNET) is involved in tumor progression and has become a hot research topic in recent years. To date, more attention has been paid to the role of non-coding RNAs in ceRNA crosstalk. However, coding transcripts are more abundant and powerful than non-coding RNAs and make up the majority of miRNA targets. In this study, we constructed a mRNA-mRNA related ceRNET of lung adenocarcinoma (LUAD) and identified the highlighted TWIST1-centered ceRNET, which recruits SLC12A5 and ZFHX4 as its ceRNAs. We found that TWIST1/SLC12A5/ZFHX4 are all upregulated in LUAD and are associated with poorer prognosis. SLC12A5 and ZFHX4 facilitated proliferation, migration, and invasion in vivo and in vitro, and their effects were reversed by miR-194–3p and miR-514a-3p, respectively. We further verified that SLC12A5 and ZFHX4 affected the function of TWIST1 by acting as ceRNAs. In summary, we constructed a mRNA-mRNA related ceRNET for LUAD and highlighted the well-known oncogene TWIST1. Then we verified that SLC12A5 and ZFHX4 exert their oncogenic function by regulating TWIST1 expression through a ceRNA mechanism.

Overexpression of SLC12A5 is associated with tumor progression and poor survival in ovarian carcinoma

INTRODUCTION

The solute carrier family 12 member 5 (SLC12A5) gene is playing a putative oncogenic role in colorectal carcinoma. However, the status of SLC12A5 amplification and expression in ovarian carcinoma and its potential clinical and/or prognostic significance has not yet been investigated.

METHODS

In the present study, semi-quantitative staining and fluorescence in situ hybridization were used to investigate SLC12A5 protein expression and gene amplification levels. Samples were obtained from archival, formalin-fixed, paraffin-embedded pathological specimens consisting of 30 normal ovaries, 30 ovarian cystadenomas, 30 borderline ovarian tumors, and 147 invasive ovarian carcinomas. SLC12A5 immunohistochemical staining results, pathological parameters, and patient prognosis were then evaluated using various statistical models. Patient survival rate was also assessed using receiver-operator curve analysis.

RESULTS

Our results revealed no SLC12A5 protein overexpression in normal ovaries. However, 7% of cystadenomas had SLC12A5 protein overexpression along with 17% of borderline tumors and 37% of ovarian carcinomas (P<0.01). Amplification of SLC12A5 was detected in 10.3% of ovarian carcinomas. Further correlational analyses showed that SLC12A5 protein overexpression in ovarian carcinomas was significantly associated with ascending histological grade, pT/pN/pM status, as well as FIGO stage (P<0.05). A subsequent univariate survival analysis of our ovarian carcinoma cohorts resulted in a significant association between SLC12A5 protein overexpression and decreased patient survival (44.3 and 85.9 months for high and low SLC12A5 protein expression, respectively; P<0.001). Importantly, additional multivariate analysis revealed that SLC12A5 protein expression was a significant, independent prognostic factor for overall survival in ovarian carcinoma patients (P=0.003).

CONCLUSIONS

Collectively, these findings support the conclusion that SLC12A5 protein overexpression could indicate an invasive and/or aggressive phenotype of ovarian carcinoma. Future work will need to investigate whether SLC12A5 protein can serve as an independent prognostic molecular marker in patients with ovarian carcinoma.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Cervical spinal contusion alters Na+-K+-2Cl- and K+-Cl- cation-chloride cotransporter expression in phrenic motor neurons

Spinal chloride-dependent synaptic inhibition is critical in regulating breathing and requires neuronal chloride gradients established by cation-chloride cotransporters Na+-K+-2Cl- (NKCC1) and K+-Cl- (KCC2). Spinal transection disrupts NKCC1/KCC2 balance, diminishing chloride gradients in neurons below injury, contributing to spasticity and chronic pain. It is not known if similar disruptions in NKCC1/KCC2 balance occur in respiratory motor neurons after incomplete cervical contusion (C2SC). We hypothesized that C2SC disrupts NKCC1/KCC2 balance in phrenic motor neurons. NKCC1 and KCC2 immunoreactivity was assessed in CtB-positive phrenic motor neurons. Five weeks post-C2SC: 1) neither membrane-bound nor cytosolic NKCC1 expression were significantly changed, although the membrane/cytosolic ratio increased, consistent with net chloride influx; and 2) both membrane and cytosolic KCC2 expression increased, although the membrane/cytosolic ratio decreased, consistent with net chloride efflux. Thus, contrary to our original hypothesis, complex shifts in NKCC1/KCC2 balance occur post-C2SC. The functional significance of these changes remains unclear.

Slc12a8 is a nicotinamide mononucleotide transporter

Nicotinamide mononucleotide (NMN) is a biosynthetic precursor of NAD⁺ known to promote cellular NAD⁺ production and counteract age-associated pathologies associated with a decline in tissue NAD⁺ levels. How NMN is taken up into cells has not been entirely clear. Here we show that the Slc12a8 gene encodes a specific NMN transporter. We find that Slc12a8 is highly expressed and regulated by NAD⁺ in the murine small intestine. Slc12a8 knockdown abrogates the uptake of NMN in vitro and in vivo. We further show that Slc12a8 specifically transports NMN, but not nicotinamide riboside, and that NMN transport depends on the presence of sodium ion. Slc12a8 deficiency significantly decreases NAD⁺ levels in the jejunum and ileum, which is associated with reduced NMN uptake as traced by doubly labeled isotopic NMN. Finally, we observe that Slc12a8 expression is upregulated in the aged murine ileum, which contributes to the maintenance of ileal NAD⁺ levels. Our work identifies the first NMN transporter and demonstrates that Slc12a8 has a critical role in regulating intestinal NAD⁺ metabolism.

Role of WNK Kinases in the Modulation of Cell Volume

Ion Transport across the cell membrane is required to maintain cell volume homeostasis. In response to changes in extracellular osmolarity, most cells activate specific metabolic or membrane-transport pathways to respond to cell swelling or shrinkage and return their volume to its normal resting state. This process involves the rapid adjustment of the activities of channels and transporters that mediate flux of K⁺, Na⁺, Cl^-, and small organic osmolytes. Cation chloride cotransporters (CCCs) NKCCs and KCCs are a family of membrane proteins modulated by changes in cell volume and/or in the intracellular chloride concentration ([Cl^-]_i). Cell swelling triggers regulatory volume decrease (RVD), promoting solute and water efflux to restore normal cell volume. Swelling-activated KCCs mediate RVD in most cell types. In contrast, cell shrinkage triggers regulatory volume increase (RVI), which involves the activation of the NKCC1 cotransporter of the CCC family. Regulation of the CCCs during RVI and RVD by protein phosphorylation is a well-characterized mechanism, where WNK kinases and their downstream kinase substrates, SPAK and OSR1 constitute the essential phospho-regulators. WNKs-SPAK/OSR1-CCCs complex is required to regulate cell shrinkage-induced RVI or cell swelling-induced RVD via activating or inhibitory phosphorylation of NKCCs or KCCs, respectively. WNK1 and WNK4 kinases have been established as [Cl^-]_i sensors/regulators, while a role for WNK3 kinase as a cell volume-sensing kinase has emerged and is proposed in this chapter.

Gitelman's Syndrome: characterization of a novel c.1181G>A point mutation and functional classification of the known mutations

We have investigated the mechanisms by which a novel missense point mutation (c.1181G>A) found in two sisters causes Gitelman's syndrome by impairing the sodium chloride co-transporter (NCC, encoded by SLC12A3 gene) function. The cDNA and in vitro transcribed mRNA of either wild-type or mutated SLC12A3 were transfected into HEK293 cells and injected into Xenopus laevis oocytes, respectively. The expression, maturation, trafficking, and function of the mutated and wild-type NCC were assessed by Western blotting, immunohistochemistry and ²²Na⁺ uptake studies. By immunoblotting of lysates from HEK293 cells and oocytes expressing wild-type NCC, two NCC-related bands of approximately 130 kDa and 115 kDa, corresponding to fully and core-glycosylated NCC, respectively, were identified. In contrast, the mutant NCC only showed a single band of approximately 115 kDa, indicating impaired maturation of the protein. Moreover, oocytes injected with wild-type NCC showed thiazide-sensitive ²²Na⁺ uptake, which was absent in those injected with the mutant NCC. The novel mutation was discussed in the context of the functionally characterized NCC mutations causing Gitelman's syndrome, which fit into five classes. In conclusion, the functional characterization of this novel Gly394Asp NCC and its localization on the NCC structure, alongside that of previously known mutations causing Gitelman's syndrome, may provide novel information on the function of the different domains of the human NCC.