Na+/H+ exchangers of mammalian cells

Pathophysiological role of ion channels and transporters in hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) has continued to increase annually worldwide, and HCC has become a common cause of cancer-related death. Despite great progress in understanding the molecular mechanisms underlying HCC development, the treatment of HCC remains a considerable challenge. Thus, the survival and prognosis of HCC patients remain extremely poor. In recent years, the role of ion channels in the pathogenesis of diseases has become a hot topic. In normal liver tissue, ion channels and transporters maintain water and electrolyte balance and acid‒base homeostasis. However, dysfunction of these ion channels and transporters can lead to the development and progression of HCC, and thus these ion channels and transporters are expected to become new therapeutic targets. In this review, ion channels and transporters associated with HCC are reviewed, and potential targets for new and effective therapies are proposed.

GGA1 interacts with the endosomal Na+/H+ Exchanger NHE6 governing localization to the endosome compartment

Mutations in the endosomal Na+/H+ exchanger (NHE6) cause Christianson Syndrome (CS), an X-linked neurological disorder. NHE6 functions in regulation of endosome acidification and maturation in neurons. Using yeast two-hybrid screening with the NHE6 carboxyl-terminus as bait, we identify Golgi-associated, Gamma adaptin ear containing, ARF binding protein 1 (GGA1) as an interacting partner for NHE6. We corroborated the NHE6-GGA1 interaction using: co-immunoprecipitation (co-IP); over-expressed constructs in mammalian cells; and co-IP of endogenously-expressed GGA1 and NHE6 from neuroblastoma cells, as well as from mouse brain. We demonstrate that GGA1 interacts with organellar NHEs (NHE6, NHE7 and NHE9), and that there is significantly less interaction with cell-surface localized NHEs (NHE1 and NHE5). By constructing hybrid NHE1/NHE6 exchangers, we demonstrate that the cytoplasmic tail of NHE6 interacts most strongly with GGA1. We demonstrate the co-localization of NHE6 and GGA1 in cultured, primary hippocampal neurons, using super-resolution microscopy. We test the hypothesis that the interaction of NHE6 and GGA1 functions in the localization of NHE6 to the endosome compartment. Using subcellular fractionation experiments, we show that NHE6 is mis-localized in GGA1 knockout cells, wherein we find less NHE6 in endosomes, but more NHE6 transport to lysosomes, and more Golgi retention of NHE6, with increased exocytosis to the surface plasma membrane. Consistent with NHE6 mis-localization, and Golgi retention, we find the intra-luminal pH in Golgi to be alkalinized in GGA1-null cells. Our study demonstrates a new interaction between NHE6 and GGA1 which functions in the localization of this intra-cellular NHE to the endosome compartment.

GGA1 interacts with the endosomal Na+/H+ Exchanger NHE6 governing localization to the endosome compartment

Mutations in the endosomal Na+/H+ exchanger (NHE6) cause Christianson syndrome (CS), an X-linked neurological disorder. Previous studies have shown that NHE6 functions in regulation of endosome acidification and maturation in neurons. Using yeast two-hybrid screening with the NHE6 carboxyl-terminus as bait, we identify Golgi-associated, Gamma adaptin ear containing, ARF binding protein 1 (GGA1) as an interacting partner for NHE6. We corroborated the NHE6-GGA1 interaction using co-immunoprecipitation (co-IP): using over-expressed constructs in mammalian cells; and co-IP of endogenously-expressed GGA1 and NHE6 from neuroblastoma cells, as well as from mouse brain. We demonstrate that GGA1 interacts with organellar NHEs (NHE6, NHE7 and NHE9) but not with cell-surface localized NHEs (NHE1 and NHE5). By constructing hybrid NHE1/NHE6 exchangers, we demonstrate that the cytoplasmic tail of NHE6 is necessary and sufficient for interactions with GGA1. We demonstrate the co-localization of NHE6 and GGA1 in cultured, primary hippocampal neurons, using super-resolution microscopy. We test the hypothesis that the interaction of NHE6 and GGA1 functions in the localization of NHE6 to the endosome compartment. Using subcellular fractionation experiments, we show that NHE6 is mis-localized in GGA1 knockout cells wherein we find less NHE6 in endosomes but more NHE6 transport to lysosomes, and more Golgi retention of NHE6 with increased exocytosis to the surface plasma membrane. Consistent with NHE6 mis-localization, and Golgi retention, we find the intra-luminal pH in Golgi to be alkalinized. Our study demonstrates a new interaction between NHE6 and GGA1 which functions in the localization of this intra-cellular NHE to the endosome compartment.

A Neanderthal/Denisovan GLI3 variant contributes to anatomical variations in mice

Changes in genomic structures underlie phenotypic diversification in organisms. Amino acid-changing mutations affect pleiotropic functions of proteins, although little is known about how mutated proteins are adapted in existing developmental programs. Here we investigate the biological effects of a variant of the GLI3 transcription factor (GLI3R1537C) carried in Neanderthals and Denisovans, which are extinct hominins close to modern humans. R1537C does not compromise protein stability or GLI3 activator-dependent transcriptional activities. In contrast, R1537C affects the regulation of downstream target genes associated with developmental processes. Furthermore, genome-edited mice carrying the Neanderthal/Denisovan GLI3 mutation exhibited various alterations in skeletal morphology. Our data suggest that an extinct hominin-type GLI3 contributes to species-specific anatomical variations, which were tolerated by relaxed constraint in developmental programs during human evolution.

Polyunsaturated ω3 fatty acids prevent the cardiac hypertrophy in hypertensive rats

It has been demonstrated that supplementation with the two main omega 3 polyunsaturated fatty acids (ω3 FAs), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), leads to modifications in the cardiac physiology. ω3 FAs can affect the membrane's lipid composition, as well as proteins' location and/or function. The Na⁺/H⁺ exchanger (NHE1) is an integral membrane protein involved in the maintenance of intracellular pH and its hyperactivity has been associated with the development of various cardiovascular diseases such as cardiac hypertrophy. Our aim was to determine the effect of ω3 FAs on systolic blood pressure (SBP), lipid profiles, NHE1 activity, and cardiac function in spontaneously hypertensive rats (SHR) using Wistar rats (W) as normotensive control. After weaning, the rats received orally ω3 FAs (200 mg/kg body mass/day/ 4 months). We measured SBP, lipid profiles, and different echocardiography parameters, which were used to calculate cardiac hypertrophy index, systolic function, and ventricular geometry. The rats were sacrificed, and ventricular cardiomyocytes were obtained to measure NHE1 activity. While the treatment with ω3 FAs did not affect the SBP, lipid analysis of plasma revealed a significant decrease in omega-6/omega-3 ratio, correlated with a significant reduction in left ventricular mass index in SHR. The NHE1 activity was significantly higher in SHR compared with W. While in W the NHE1 activity was similar in both groups, a significant decrease in NHE1 activity was detected in SHRs supplemented with ω3 FAs, reaching values comparable with W. Altogether, these findings revealed that diet supplementation with ω3 FAs since early age prevents the development of cardiac hypertrophy in SHR, perhaps by decreasing NHE1 activity, without altering hemodynamic overload.

Depletion of Na+/H+ Exchanger Isoform 1 Increases the Host Cell Resistance to Trypanosoma cruzi Invasion

Na+/H+ exchanger isoform 1 (NHE1), a member of a large family of integral membrane proteins, plays a role in regulating the cortical actin cytoskeleton. Trypanosoma cruzi, the agent of Chagas disease, depends on F-actin rearrangement and lysosome mobilization to invade host cells. To determine the involvement of NHE1 in T. cruzi metacyclic trypomastigote (MT) internalization, the effect of treatment in cells with NHE1 inhibitor amiloride or of NHE1 depletion was examined in human epithelial cells. MT invasion decreased in amiloride-treated and NHE1-depleted cells. The phosphorylation profile of diverse protein kinases, whose activation is associated with remodeling of actin fibers, was analyzed in amiloride-treated and NHE1-depleted cells. In amiloride-treated cells, the phosphorylation levels of protein kinase C (PKC), focal adhesion kinase (FAK) and Akt were similar to those of untreated cells, whereas those of extracellular signal-regulated protein kinases (ERK1/2) increased. In NHE1-deficient cells, with marked alteration in the actin cytoskeleton architecture and in lysosome distribution, the levels of phospho-PKC and phospho-FAK decreased, whereas those of phospho-Akt and phospho-ERK1/2 increased. These data indicate that NHE1 plays a role in MT invasion, by maintaining the activation status of diverse protein kinases in check and preventing the inappropriate F-actin arrangement that affects lysosome distribution.

Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

The Physiological Function and Potential Role of the Ubiquitous Na+/H+ Exchanger Isoform 8 (NHE8): An Overview Data

The Na⁺/H⁺ exchanger transporters (NHE) play an important role in various biologic processes including Na⁺ absorption, intracellular pH homeostasis, cell volume regulation, proliferation, and apoptosis. The wide expression pattern and cellular localization of NHEs make these proteins pivotal players in virtually all human tissues and organs. In addition, recent studies suggest that NHEs may be one of the primeval transport protein forms in the history of life. Among the different isoforms, the most well-characterized NHEs are the Na⁺/H⁺ exchanger isoform 1 (NHE1) and Na⁺/H⁺ exchanger isoform 3 (NHE3). However, Na⁺/H⁺ exchanger isoform 8 (NHE8) has been receiving attention based on its recent discoveries in the gastrointestinal tract. In this review, we will discuss what is known about the physiological function and potential role of NHE8 in the main organ systems, including useful overviews that could inspire new studies on this multifaceted protein.

Inhibition of c-MYC-miRNA 19 Pathway Sensitized CML K562 Cells to Etoposide via NHE1 Upregulation

As a previously discovered target of DNA damage, Na⁺/H⁺ exchanger 1 (NHE1) plays a role in regulation of intracellular pH (pH_i) through the extrusion of intracellular proton (H⁺) in exchange for extracellular sodium (Na⁺). Its abnormal expression and dysfunction have been reported in solid tumor and hematopoietic malignancies. Here, we reported that suppression of NHE1 in BCR-ABL⁺ hematopoietic malignancies' K562 cells treated with Etoposide was manipulated by miR-19 and c-MYC. Inhibition of miR-19 or c-MYC enhanced the expression of NHE1 and sensitized K562 cells to Etoposide in vitro. The in vivo nude mouse transplantation model was also performed to confirm the enhanced sensitivity of K562 cells to Etoposide by inhibiting the miR-19 or c-MYC pathway. TCGA analysis conferred a negative correlation between miR-19 level and leukemia patients' survival. Thus, our results provided a potential management by which the c-MYC-miRNA 19 pathway might have a crucial impact on sensitizing K562 cells to Etoposide in the therapeutic approaches.

Effect of Different Salts on Nutrients Uptake, Gene Expression, Antioxidant, and Growth Pattern of Selected Rice Genotypes

Climate change leads to soil salinization, and the dynamic scarcity of freshwater has negatively affected crop production worldwide, especially Oryza sativa. The association among ion uptake, gene expression, antioxidant, biomass, and root and shoot development under different salt stress are not fully understood. Many studies are related to the effect of NaCl only. This study used two salts (CaCl₂ and MgCl₂) along with NaCl and analyzed their effects on mineral uptake (macronutrients and micronutrients), gene expression, seed germination, antioxidants, plant growth, and biomass in different rice genotypes. CaCl₂ (up to 200 mM) slightly increased the germination percentage and seedling growth, whereas, 150 mM MgCl₂ in the soil increased the root, shoot length, and fresh and dry weight in cultivars IR 28 and Cheongcheong. All agronomic traits among rice genotypes were drastically reduced by NaCl stress compared to other salts. Different salt stress differentially regulated ion uptake in the roots and shoots among different rice genotypes. Under different salt stress, a consistent decrease in Ca²⁺, Mn²⁺, and Fe²⁺ ions was observed in the roots of Cheongcheong, Nagdong, and IR 28. Similarly, under different salts, the stress in the shoots of Cheongcheong (Ca²⁺, Na⁺, and Zn²⁺) and Nagdong (Ca²⁺, Mg²⁺, Na⁺, and Zn²⁺) and the shoots of IR 28 (Ca²⁺ and Mg²⁺) consistently increased. Under different salts, a salt stress-related gene was expressed differentially in the roots of rice genotypes. However, after 6 and 12 h, there was consistent OsHKT1, OsNHX1, and OsSOS1 gene upregulation in the shoots of Nagdong and roots and shoots of the salt-tolerant cultivar Pokkali. Under different salt stress, glutathione (GSH) content increased in the shoot of IR 28 and Nagdong by NaCl, and MgCl₂ salt, whereas, POD activity increased significantly by CaCl₂ and MgCl₂ in cultivar Cheongcheong and IR 28 shoot. Therefore, this study suggested that Pokkali responded well to NaCl stress only, whereas, the plant molecular breeding lab cultivar Nagdong showed more salt tolerance to different salts (NaCl, CaCl₂, and MgCl₂). This can potentially be used by agriculturists to develop the new salt-tolerant cultivar "Nagdong"-like Pokkali.

Microscale thermophoresis and fluorescence polarization assays of calcineurin-peptide interactions

Calcineurin is a Ca²⁺/calmodulin-dependent phosphatase. It is very important to study the affinity between calcineurin and its substrate or other interacting proteins. Two conserved motifs have been reported on the interactive proteins of calcineurin, namely, the PxIxIT motif and the LxVP motif. Here, we used 5(6)-carboxyfluorescein to fluorescently label the N-terminus of the short peptides derived from the two motifs and then determined the affinity between the protein and polypeptides. Microscale thermophoresis (MST) is very suitable for determining calcineurin with peptides containing the LxVP motif. The K_d values of the binding of calcineurin with NFATc1-YLAVP, NHE1-YLTVP, and A238L-FLCVK peptides were 6.72 ± 0.19 μM, 17.14 ± 0.35 μM, and 15.57 ± 0.10 μM, respectively. The GST pull-down results further confirmed the binding trend of the three peptides to calcineurin. However, fluorescently labeled PxIxIT polypeptides are not suitable for MST due to their own aggregation. We determined the binding affinity of the RCAN1-PSVVVH polypeptide to calcineurin by the fluorescence polarization (FP) method. MST and FP assays are fast and accurate in determining the affinity between protein-peptide interactions. Our research laid the foundation for screening the molecules that affect the binding between calcineurin and its substrates in the future.

Astrocytes: The Housekeepers and Guardians of the CNS

Astroglia are a diverse group of cells in the central nervous system. They are of the ectodermal, neuroepithelial origin and vary in morphology and function, yet, they can be collectively defined as cells having principle function to maintain homeostasis of the central nervous system at all levels of organisation, including homeostasis of ions, pH and neurotransmitters; supplying neurones with metabolic substrates; supporting oligodendrocytes and axons; regulating synaptogenesis, neurogenesis, and formation and maintenance of the blood-brain barrier; contributing to operation of the glymphatic system; and regulation of systemic homeostasis being central chemosensors for oxygen, CO₂ and Na⁺. Their basic physiological features show a lack of electrical excitability (inapt to produce action potentials), but display instead a rather active excitability based on variations in cytosolic concentrations of Ca²⁺ and Na⁺. It is expression of neurotransmitter receptors, pumps and transporters at their plasmalemma, along with transports on the endoplasmic reticulum and mitochondria that exquisitely regulate the cytosolic levels of these ions, the fluctuation of which underlies most, if not all, astroglial homeostatic functions.

Effect of a chemical dispersant (Corexit 9500A) on the structure and ion transport function of blue crab (Callinectes sapidus) gills

Chemical dispersants are commercially available mixtures of surfactants and solvents that have become important tools in the remediation of spilled oil. Given the importance of oil to the world economy, the recurring nature of spills, and the prevalence of dispersant use in remediation, there is a critical need to understand potential toxic impacts of dispersants on invertebrate and vertebrate animals. Blue crabs (Callinectes sapidus) play ecologically important roles in the environments they inhabit and support economically important fisheries along the Atlantic Coast and in the Gulf of Mexico. In studies reported here, we assessed the impact of a chemical dispersant, Corexit 9500A, on the structure and ion transport function of blue crab gills. Exposure of blue crabs to Corexit 9500A for 24 h (0-300 ppm in artificial seawater under static conditions) revealed a 24-h lethal concentration 50 (LC₅₀) estimate of 210 ppm. A histological analysis of gills from crabs exposed for 24 h to a sub-lethal concentration of Corexit 9500A (125 ppm) revealed evidence of loss or disruption of cuticle, and an increase in stained amorphous material in the hemolymph spaces of gill lamellae. Quantitative image analysis of stained gill sections revealed the area/length ratio of gill lamellae in crabs exposed to Corexit 9500A (24 h, 125 ppm), was greater than that in gill lamellae from control crabs; the results are consistent with the presence of edematous swelling in gill lamellae from dispersant-exposed crabs. Quantitative PCR was used to measure the relative abundance of transcripts encoding three ion transport proteins (Na⁺/K⁺ ATPase, plasma membrane Ca²⁺ ATPase (PMCA), and sarcoplasmic reticulum/endoplasmic reticulum Ca²⁺ ATPase (SERCA)) in gills from Corexit-exposed and control crabs. In general, the abundance of transcripts encoding each ion transport protein was lower in gills from dispersant-exposed crabs than in gills from control crabs. The combined results are consistent with the hypothesis that 24-h exposure of blue crabs to a sublethal concentration of Corexit 9500A impacts both the structure and ion transport function of gills.

Rice Cultivars Under Salt Stress Show Differential Expression of Genes Related to the Regulation of Na+/K+ Balance

Soil salinity is a major problem in agriculture because high accumulation of Na⁺ ions in plants causes toxicity that can result in yield reduction. Na⁺/K⁺ homeostasis is known to be important for salt tolerance in plants. Na⁺/K⁺ homeostasis in rice (Oryza sativa L.) involves nine high-affinity K⁺ transporter (HKT) encoding Na⁺-K⁺ symporter, five OsNHX Na⁺/H⁺ antiporters, and OsSOS1 Na⁺/K⁺ antiporter genes. In the present study, we investigated various molecular and physiological processes to evaluate germination rate, growth pattern, ion content, and expression of OsHKT, OsNHX, and OsSOS1genes related to Na⁺/K⁺ homeostasis in different rice genotypes under salt stress. We found a significant increase in the germination percentage, plant vigor, Na⁺/K⁺ ratio, and gene expression of the OsHKT family in both the roots and shoots of the Nagdong cultivar and salt-tolerant cultivar Pokkali. In the roots of Cheongcheong and IR28 cultivars, Na⁺ ion concentrations were found to be higher than K⁺ ion concentrations. Similarly, high expression levels of OsHKT1, OsHKT3, and OsHKT6 were observed in Cheongcheong, whereas expression levels of OsHKT9 was high in IR28. The expression patterns of OsNHX and OsSOS1 and regulation of other micronutrients differed in the roots and shoots regions of rice and were generally increased by salt stress. The OsNHX family was also expressed at high levels in the roots of Nagdong and in the roots and shoots of Pokkali; in contrast, comparatively low expression levels were observed in the roots and shoots of Cheongcheong and IR28 (with the exception of high OsNHX1 expression in the roots of IR28). Furthermore, the OsSOS1 gene was highly expressed in the roots of Nagdong and shoots of Cheongcheong. We also observed that salt stress decreases chlorophyll content in IR28 and Pokkali but not in Cheongcheong and Nagdong. This study suggests that under salt stress, cultivar Nagdong has more salt-tolerance than cultivar Cheongcheong.

Intracellular pH regulation and the acid delusion

The hydrogen ion concentration ([H+]) in intracellular cytoplasmic fluid (ICF) must be maintained in a narrow range in all species for normal protein functions. Thus, mechanisms regulating ICF are of fundamental biological importance. Studies on the regulation of ICF [H+] have been hampered by use of pH notation, failure to consider the roles played by differences in the concentration of strong ions (strong ion difference, SID), the conservation of mass, the principle of electrical neutrality, and that [H+] and bicarbonate ions [HCO3-] are dependent variables. This argument is based on the late Peter Stewart's physical-chemical analysis of [H+] regulation reported in this journal nearly forty years ago (Stewart. 1983. Can. J. Physiol. Pharmacol. 61: 1444-1461. Doi:10.1139/y83-207). We start by outlining the principles of Stewart's analysis and then provide a general understanding of its significance for regulation of ICF [H+]. The system may initially appear complex, but it becomes evident that changes in SID dominate regulation of [H+]. The primary strong ions are Na+, K+, and Cl-, and a few organic strong anions. The second independent variable, partial pressure of carbon dioxide (PCO2), can easily be assessed. The third independent variable, the activity of intracellular weak acids ([Atot]), is much more complex but largely plays a modifying role. Attention to these principles will potentially provide new insights into ICF pH regulation.

Renal Handling of Albumin-From Early Findings to Current Concepts

Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.

Cardiomyocyte Na+/H+ Exchanger-1 Activity Is Reduced in Hypoxia

Fully-activated Na⁺/H⁺ exchanger-1 (NHE1) generates the cardiomyocyte's largest trans-membrane extrusion of H⁺ ions for an equimolar influx of Na⁺ ions. This has the desirable effect of clearing excess intracellular acidity, but comes at a large energetic premium because the exchanged Na⁺ ions must ultimately be extruded by the sodium pump, a process that consumes the majority of the heart's non-contractile ATP. We hypothesize that the state of NHE1 activation depends on metabolic resources, which become limiting in periods of myocardial hypoxia. To test this functionally, NHE1 activity was measured in response to in vitro and in vivo hypoxic treatments. NHE1 flux was interrogated as a function of intracellular pH by fluorescence imaging of rodent ventricular myocytes loaded with pH-sensitive dyes BCECF or cSNARF1. Anoxic superfusates promptly inhibited NHE1, tracking the time-course of mitochondrial depolarization. Mass spectrometry of NHE1 immuno-precipitated from Langendorff-perfused anoxic hearts identified Tyr-581 dephosphorylation and Tyr-561 phosphorylation. The latter residue is part of the domain that interacts with phosphatidylinositol 4,5-bisphosphate (PIP₂), a membrane lipid that becomes depleted under metabolic inhibition. Tyr-561 phosphorylation is expected to electrostatically weaken this activatory interaction. To test if a period of hypoxia produces a persistent inhibition of NHE1, measurements under normoxia were performed on myocytes that had been incubated in 2% O₂ for 4 h. NHE1 activity remained inhibited, but the effect was ablated in the presence of Dasatinib, an inhibitor of Abl/Src-family tyrosine kinases. Chronic tissue hypoxia in vivo, attained in a mouse model of anemic hypoxia, also resulted in persistently slower NHE1. In summary, we show that NHE1 responds to oxygen, a physiologically-relevant metabolic regulator, ostensibly to divert ATP for contraction. We describe a novel mechanism of NHE1 inhibition that may be relevant in cardiac disorders featuring altered oxygen metabolism, such as myocardial ischemia and reperfusion injury.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

Lysosomal Biology and Function: Modern View of Cellular Debris Bin

Lysosomes are the main proteolytic compartments of mammalian cells comprising of a battery of hydrolases. Lysosomes dispose and recycle extracellular or intracellular macromolecules by fusing with endosomes or autophagosomes through specific waste clearance processes such as chaperone-mediated autophagy or microautophagy. The proteolytic end product is transported out of lysosomes via transporters or vesicular membrane trafficking. Recent studies have demonstrated lysosomes as a signaling node which sense, adapt and respond to changes in substrate metabolism to maintain cellular function. Lysosomal dysfunction not only influence pathways mediating membrane trafficking that culminate in the lysosome but also govern metabolic and signaling processes regulating protein sorting and targeting. In this review, we describe the current knowledge of lysosome in influencing sorting and nutrient signaling. We further present a mechanistic overview of intra-lysosomal processes, along with extra-lysosomal processes, governing lysosomal fusion and fission, exocytosis, positioning and membrane contact site formation. This review compiles existing knowledge in the field of lysosomal biology by describing various lysosomal events necessary to maintain cellular homeostasis facilitating development of therapies maintaining lysosomal function.

Solution structure of the cytoplasmic domain of NhaP2 a K+/H+ antiporter from Vibrio cholera

NhaP2 is a K⁺/H⁺ antiporter from Vibrio cholerae which consists of a transmembrane domain and a cytoplasmic domain of approximately 200 amino acids, both of which are required for cholera infectivity. Here we present the solution structure for a 165 amino acid minimal cytoplasmic domain (P2MIN) form of the protein. The structure reveals a compact N-terminal domain which resembles a Regulator of Conductance of K⁺ channels (RCK) domain connected to a more open C-terminal domain via a flexible 20 amino acid linker. NMR titration experiments showed that the protein binds ATP through its N-terminal domain, which was further supported by waterLOGSY and Saturation Transfer Difference NMR experiments. The two-domain organisation of the protein was confirmed by BIOSAXS, which also revealed that there are no detectable-ATP-induced conformational changes in the protein structure. Finally, in contrast to all known RCK domain structures solved to date, the current work shows that the protein is a monomer.

Probing Nanoparticle-Cell Interaction Using Micro-Raman Spectroscopy: Silver and Gold Nanoparticle-Induced Stress Effects on Optically Trapped Live Red Blood Cells

Advancements in the field of nanotechnology have resulted in the emergence of a large variety of engineered nanomaterials for innumerable applications. Despite the ubiquitous use of nanomaterials in daily life, concerns regarding the potential toxicity and safety of these materials have also been raised. There is a high demand for assessing the unwanted effects of both gold and silver nanoparticles, which is increasingly being used in biomedical applications. This paper deals with the study of stress due to silver and gold nanoparticles of varying size on red blood cells (RBCs) using Raman tweezers spectroscopy. RBCs were incubated with nanoparticles of size in the 10-100 nm range with the same concentrations, and micro-Raman spectra were recorded by optically trapping the nanoparticle-treated live RBCs. Spectral modifications implicating hemoglobin deoxygenation were observed in all nanoparticle-treated RBCs. One of the probable reason for the deoxygenation trend can be the adhesion of nanoparticles onto the cell surface causing imbalance in cell functioning. Moreover, the higher spectral variations observed for silver nanoparticles indicate that oxidative stress is involved in cell damage. These mechanisms lead to the modification in the hemoglobin structure because of changes in the pH of cytoplasm, which can be detected using Raman spectroscopy.

Na+-dependent transporters: The backbone of astroglial homeostatic function

Astrocytes are the principal homeostatic cells of the central nerves system (CNS) that support the CNS function at all levels of organisation, from molecular to organ. Several fundamental homeostatic functions of astrocytes are mediated through plasmalemmal pumps and transporters; most of which are also regulated by the transplasmalemmal gradient of Na⁺ ions. Neuronal activity as well as mechanical or chemical stimulation of astrocytes trigger plasmalemmal Na⁺ fluxes, which in turn generate spatio-temporally organised transient changes in the cytosolic Na⁺ concentration, which represent the substrate of astroglial Na⁺ signalling. Astroglial Na⁺ signals link and coordinate neuronal activity and CNS homeostatic demands with the astroglial homeostatic response.

Sodium homeostasis in the tumour microenvironment

The concentration of sodium ions (Na+) is raised in solid tumours and can be measured at the cellular, tissue and patient levels. At the cellular level, the Na+ gradient across the membrane powers the transport of H+ ions and essential nutrients for normal activity. The maintenance of the Na+ gradient requires a large proportion of the cell's ATP. Na+ is a major contributor to the osmolarity of the tumour microenvironment, which affects cell volume and metabolism as well as immune function. Here, we review evidence indicating that Na+ handling is altered in tumours, explore our current understanding of the mechanisms that may underlie these alterations and consider the potential consequences for cancer progression. Dysregulated Na+ balance in tumours may open opportunities for new imaging biomarkers and re-purposing of drugs for treatment.

Physiology of Astroglia

Astrocytes are principal cells responsible for maintaining the brain homeostasis. Additionally, these glial cells are also involved in homocellular (astrocyte-astrocyte) and heterocellular (astrocyte-other cell types) signalling and metabolism. These astroglial functions require an expression of the assortment of molecules, be that transporters or pumps, to maintain ion concentration gradients across the plasmalemma and the membrane of the endoplasmic reticulum. Astrocytes sense and balance their neurochemical environment via variety of transmitter receptors and transporters. As they are electrically non-excitable, astrocytes display intracellular calcium and sodium fluctuations, which are not only used for operative signalling but can also affect metabolism. In this chapter we discuss the molecules that achieve ionic gradients and underlie astrocyte signalling.

Mycobacterium tuberculosis sensor kinase DosS modulates the autophagosome in a DosR-independent manner

Dormancy is a key characteristic of the intracellular life-cycle of Mtb. The importance of sensor kinase DosS in mycobacteria are attributed in part to our current findings that DosS is required for both persistence and full virulence of Mtb. Here we show that DosS is also required for optimal replication in macrophages and involved in the suppression of TNF-α and autophagy pathways. Silencing of these pathways during the infection process restored full virulence in MtbΔdosS mutant. Notably, a mutant of the response regulator DosR did not exhibit the attenuation in macrophages, suggesting that DosS can function independently of DosR. We identified four DosS targets in Mtb genome; Rv0440, Rv2859c, Rv0994, and Rv0260c. These genes encode functions related to hypoxia adaptation, which are not directly controlled by DosR, e.g., protein recycling and chaperoning, biosynthesis of molybdenum cofactor and nitrogen metabolism. Our results strongly suggest a DosR-independent role for DosS in Mtb.

Diverse Stakeholders of Tumor Metabolism: An Appraisal of the Emerging Approach of Multifaceted Metabolic Targeting by 3-Bromopyruvate

Malignant cells possess a unique metabolic machinery to endure unobstructed cell survival. It comprises several levels of metabolic networking consisting of 1) upregulated expression of membrane-associated transporter proteins, facilitating unhindered uptake of substrates; 2) upregulated metabolic pathways for efficient substrate utilization; 3) pH and redox homeostasis, conducive for driving metabolism; 4) tumor metabolism-dependent reconstitution of tumor growth promoting the external environment; 5) upregulated expression of receptors and signaling mediators; and 6) distinctive genetic and regulatory makeup to generate and sustain rearranged metabolism. This feat is achieved by a "battery of molecular patrons," which acts in a highly cohesive and mutually coordinated manner to bestow immortality to neoplastic cells. Consequently, it is necessary to develop a multitargeted therapeutic approach to achieve a formidable inhibition of the diverse arrays of tumor metabolism. Among the emerging agents capable of such multifaceted targeting of tumor metabolism, an alkylating agent designated as 3-bromopyruvate (3-BP) has gained immense research focus because of its broad spectrum and specific antineoplastic action. Inhibitory effects of 3-BP are imparted on a variety of metabolic target molecules, including transporters, metabolic enzymes, and several other crucial stakeholders of tumor metabolism. Moreover, 3-BP ushers a reconstitution of the tumor microenvironment, a reversal of tumor acidosis, and recuperative action on vital organs and systems of the tumor-bearing host. Studies have been conducted to identify targets of 3-BP and its derivatives and characterization of target binding for further optimization. This review presents a brief and comprehensive discussion about the current state of knowledge concerning various aspects of tumor metabolism and explores the prospects of 3-BP as a safe and effective antineoplastic agent.

Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

Background

Angiotensin II (Ang II) contributes to the progression of renal diseases associated with proteinuria and glomerulosclerosis mainly by inducing podocyte apoptosis. In the present study, we investigated whether the chronic effects of Ang II via AT1 receptor (AT1R) would result in endoplasmic reticulum (ER) stress/PKC-delta/p38 MAPK stimulation, and consequently podocyte apoptosis.

Methods

Wistar rats were treated with Ang II (200 ng·kg⁻¹·min⁻¹, 42 days) and or losartan (10 mg·kg⁻¹·day⁻¹, 14 days). Immortalized mouse podocyte were treated with 1 μM Ang II and/or losartan (1 μM) or SB203580 (0.1 μM) (AT1 receptor antagonist and p38 MAPK inhibitor) for 24 h. Kidney sections and cultured podocytes were used to evaluate protein expression by immunofluorescence and immunoblotting. Apoptosis was evaluated by flow cytometry and intracellular pH (pHi) was analyzed using microscopy combined with the fluorescent probe BCECF/AM.

Results

Compared with controls, Ang II via AT1R increased chaperone GRP 78/Bip protein expression in rat glomeruli (p < 0.001) as well as in podocyte culture (p < 0.01); increased phosphorylated eIf2-α (p < 0.05), PKC-delta (p < 0.01) and p38 MAPK (p < 0.001) protein expression. Furthermore, Ang II induced p38 MAPK-mediated late apoptosis and increased the Bax/Bcl-2 ratio (p < 0.001). Simultaneously, Ang II via AT1R induced p38 MAPK-NHE1-mediated increase of pHi recovery rate after acid loading.

Conclusion

Together, our results indicate that Ang II-induced podocyte apoptosis is associated with AT1R/ER stress/PKC-delta/p38 MAPK axis and enhanced NHE1-mediated pHi recovery rate.

A polyclonal antibody against extracellular loops 1 of chNHE1 blocks avian leukosis virus subgroup J infection

Avian leukosis virus subgroup J (ALV-J), an oncogenic retrovirus, induces myelocytomas and other various tumors, leading to great economical losses in poultry industry. It is a great challenge to develop effective preventive methods for ALV-J control due to its antigenic variations in the variable regions of envelope. In present study, we generated a mouse polyclonal antibody targeting the first extracellular loop (ECL1) of chicken Na⁺/H⁺ exchanger isoform 1 (chNHE1), the receptor of ALV-J, to block ALV-J infection in vitro and in vivo. In ALV-J infected DF-1 cells, chNHE1 expression and the intracellular pH (pHi) were up-regulated with "wave" pattern, indicating that the disequilibrium of ALV-J infected cells associated with chNHE1. Next, we validated that ALV-J infection was significantly blocked with time dependent after treating with anti-ECL1 antibody and accordingly the pHi value were recovered, indicating the blockage of ALV-J infection did not affect Na⁺/H⁺ exchange. Furthermore, in anti-ECL1 antibody treatment chickens that infected by ALV-J, weight gain and immune organs were recovered, and viral loads were significantly decreased, and the tissue injury and inflammation were reduced significantly from 21 to 35 days of age. The study demonstrated that anti-ECL1 antibody effectively blocks ALV-J infection without affecting Na⁺/H⁺ exchange, and sheds light on a novel strategy for retroviruses control.

Genome-Wide Identification and Analysis of Arabidopsis Sodium Proton Antiporter (NHX) and Human Sodium Proton Exchanger (NHE) Homologs in Sorghum bicolor

Na⁺ transporters play an important role during salt stress and development. The present study is aimed at genome-wide identification, in silico analysis of sodium-proton antiporter (NHX) and sodium-proton exchanger (NHE)-type transporters in Sorghum bicolor and their expression patterns under varied abiotic stress conditions. In Sorghum, seven NHX and nine NHE homologs were identified. Amiloride (a known inhibitor of Na⁺/H⁺ exchanger activity) binding motif was noticed in both types of the transporters. Chromosome 2 was found to be a hotspot region with five sodium transporters. Phylogenetic analysis inferred six ortholog and three paralog groups. To gain an insight into functional divergence of SbNHX/NHE transporters, real-time gene expression was performed under salt, drought, heat, and cold stresses in embryo, root, stem, and leaf tissues. Expression patterns revealed that both SbNHXs and SbNHEs are responsive either to single or multiple abiotic stresses. The predicted protein⁻protein interaction networks revealed that only SbNHX7 is involved in the calcineurin B-like proteins (CBL)- CBL interacting protein kinases (CIPK) pathway. The study provides insights into the functional divergence of SbNHX/NHE transporter genes with tissue specific expressions in Sorghum under different abiotic stress conditions.

Bcl-xL deamidation is regulated by multiple ion transporters and is intramolecularly catalyzed

In susceptible tumor cells, DNA-damaging antineoplastic agents induce an increase in intracellular pH during the premitochondrial stage of apoptosis. The rate of nonenzymatic deamidation of two asparagines in the anti-apoptotic protein Bcl-x_L is accelerated by this increase in pH. Deamidation of these asparagines is a signal for the degradation of Bcl-x_L, which is a component of the apoptotic response to DNA damage. It has previously been shown that the increase in pH is mediated by the ion transporter Na⁺/H⁺ exchanger 1 in some cells. Here we demonstrate that one or more additional ion transporters also have a role in the regulation of Bcl-x_L deamidation in at least some tumor cell lines and fibroblasts. As a second, independent finding, we report that there are histidines in close proximity to the Bcl-x_L deamidation sites that are highly conserved in land-dwelling species and we present evidence that deamidation of human Bcl-x_L is intramolecularly catalyzed in a manner that is dependent upon these histidines. Further, we present evidence that these histidines act as a pH-sensitive switch that enhances the effect of the increase in pH on the rate of Bcl-x_L deamidation. The conservation of such histidines implies that human Bcl-x_L is in essence "designed" to be deamidated, which provides further evidence that deamidation serves as a bona fide regulatory post-translational modification of Bcl-x_L.

NHERF1 Between Promises and Hopes: Overview on Cancer and Prospective Openings

Na+/H+ exchanger regulatory factor 1 (NHERF1) is a scaffold protein, with two tandem PDZ domains and a carboxyl-terminal ezrin-binding (EB) region. This particular sticky structure is responsible for its interaction with different molecules to form multi-complexes that have a pivotal role in a lot of diseases. In particular, its involvement during carcinogenesis and cancer progression has been deeply analyzed in different tumors. The role of NHERF1 is not unique in cancer; its activity is connected to its subcellular localization. The literature data suggest that NHERF1 could be a new prognostic/predictive biomarker from breast cancer to hematological cancers. Furthermore, the high potential of this molecule as therapeutical target in different carcinomas is a new challenge for precision medicine. These evidences are part of a future view to improving patient clinical management, which should allow different tumor phenotypes to be treated with tailored therapies. This article reviews the biology of NHERF1, its engagement in different signal pathways and its involvement in different cancers, with a specific focus on breast cancer. It also considers NHERF1 potential role during inflammation related to most human cancers, designating new perspectives in the study of this "Janus-like" protein.

Inhibition of Na+/H+ Exchanger With EMD 87580 does not Confer Greater Cardioprotection Beyond Preconditioning on Ischemia-Reperfusion Injury in Normal Dogs

Postischemic accumulation of intracellular Na⁺ promotes calcium overload and contributes to cellular necrosis. Cardioprotection afforded by pharmacologic blockade of the sodium-hydrogen exchanger subtype 1 (NHE1) is thought to be more remarkable than that obtained by ischemic conditioning (IC). The window of protection provided by IC pretreatment is maintained even when performed up to 48 hours before ischemia. In addition, the perception exists that combined NHE1 inhibition plus IC produces greater than additive protection against ischemic injury. The current study compared the efficacy of NHE1 blockade by N-[2-methyl-4,5-bis(methylsulfonyl)-benzoyl]-guanidine (EMD 87580 5 mg/kg) combined with first- or second-window IC on ischemic tolerance in dogs subject to 90-minute acute ischemia and 180-minute reperfusion. Infarct size (tetrazolium staining), vascular responses, and myocardial perfusion (microspheres) were assessed. EMD 87580 given before ischemia or before reperfusion did not reduce infarct size (compared to vehicle-treated group). Significant protection against tissue necrosis was obtained by both first- and second-window IC, but additive cardioprotection (ie, greater than that afforded by IC) was not observed by treatment with EMD 87580. Vascular reactivity in the infarct-related artery was not preserved after ischemia-reperfusion in any of the experimental groups. Likewise, either the pharmacologic or the nonpharmacologic interventions did not modify myocardial perfusion. These data demonstrate that EMD 87580 did not protect against ischemia-reperfusion injury regardless of the time of drug administration. Combined EMD 87580 and IC did not antagonize protection that was achieved by either first- or second-window IC alone; no additive protection beyond preconditioning was obtained. Further study is necessary to assess the value of NHE1 blockers as protective agents against myocardial injury.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

A Comprehensive Review of Our Current Understanding of Red Blood Cell (RBC) Glycoproteins

Human red blood cells (RBC), which are the cells most commonly used in the study of biological membranes, have some glycoproteins in their cell membrane. These membrane proteins are band 3 and glycophorins A-D, and some substoichiometric glycoproteins (e.g., CD44, CD47, Lu, Kell, Duffy). The oligosaccharide that band 3 contains has one N-linked oligosaccharide, and glycophorins possess mostly O-linked oligosaccharides. The end of the O-linked oligosaccharide is linked to sialic acid. In humans, this sialic acid is N-acetylneuraminic acid (NeuAc). Another sialic acid, N-glycolylneuraminic acid (NeuGc) is present in red blood cells of non-human origin. While the biological function of band 3 is well known as an anion exchanger, it has been suggested that the oligosaccharide of band 3 does not affect the anion transport function. Although band 3 has been studied in detail, the physiological functions of glycophorins remain unclear. This review mainly describes the sialo-oligosaccharide structures of band 3 and glycophorins, followed by a discussion of the physiological functions that have been reported in the literature to date. Moreover, other glycoproteins in red blood cell membranes of non-human origin are described, and the physiological function of glycophorin in carp red blood cell membranes is discussed with respect to its bacteriostatic activity.

Mechanism of down regulation of Na-H exchanger-2 in experimental colitis

BACKGROUND

The Na-H exchanger [NHE] performs an electroneutral uptake of NaCl and water from the lumen of the gastrointestinal tract. There are several distinct NHE isoforms, some of which show an altered expression in the inflammatory bowel diseases (IBD). In this study, we examined a role of NHE-2 in experimental colitis.

METHODS

Colitis was induced in male Sprague-Dawley rats by intra-rectal administration of trinitrobenzenesulphonic acid (TNBS). On day 6 post-TNBS, the animals were sacrificed, colonic and ileal segments were taken out, cleaned with phosphate buffered saline and used in this study.

RESULTS

There was a significant decrease in the level of NHE-2 protein as measured by ECL western blot analysis and confocal immunofluorescence microscopy. The levels of NHE-2 mRNA and heteronuclear RNA measured by an end-point RT-PCR and a real time PCR were also decreased significantly in the inflamed colon. However, there was no change in the level of NHE-2 protein in response to in vitro TNF-α treatment of uninflamed rat colonic segment. These changes were selective and localized to the colon as actin, an internal control, remained unchanged. Confocal immunofluorescence microscopy revealed co-localization of NHE-2 and NHE-3 in the brush borders of colonic epithelial cells. Inflamed colon showed a significant increase in myeloperoxidase activity and colon hypertrophy. In addition, there was a significant decrease in body weight and goblet cells' mucin staining in the TNBS treated colon. These changes were not conspicuous in the non-inflamed ileum.

CONCLUSIONS

These findings demonstrate suppression of NHE-2 expression on the brush borders in the colonic epithelial cells which is regulated transcriptionally. However a role of TNF-α in the regulation of NHE-2 is discounted in the present model of colitis. This decrease in the NHE-2 expression will lead to a loss of electrolyte and water uptake thus contributing to the symptoms associated with IBD.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Na+/H+ exchanger 3 inhibitor diminishes hepcidin-enhanced duodenal calcium transport in hemizygous β-globin knockout thalassemic mice

Recent investigation has shown that the liver-derived iron-regulating hormone, hepcidin, can potentiate intestinal calcium absorption in hemizygous β-globin knockout thalassemic (BKO) mice. Since the upregulation of Fe²⁺ and H⁺ cotransporter, divalent metal transporter (DMT)-1, has been shown to correlate with thalassemia-induced intestinal calcium absorption impairment, the inhibition of the apical Na⁺/H⁺ exchanger (NHE)-3 that is essential for cytoplasmic pH regulation and transepithelial sodium absorption was hypothesized to negatively affect hepcidin action. Herein, the positive effect of hepcidin on the duodenal calcium transport was evaluated using Ussing chamber technique. The results showed that BKO mice had lower absorptive surface area and duodenal calcium transport than wild-type mice. Besides, paracellular transport of zinc in BKO mice was compromised. Hepcidin administration completely restored calcium transport. Since this hepcidin action was totally abolished by inhibitors of the basolateral calcium transporters, Na⁺/Ca²⁺ exchanger (NCX1) and plasma membrane Ca²⁺-ATPase (PMCA_1b), the enhanced calcium flux potentially occurred through the transcellular pathway rather than paracellular pathway. Interestingly, the selective NHE3 inhibitor, 100 nM tenapanor, markedly inhibited hepcidin-enhanced calcium transport. Accordingly, hepcidin is one of the promising therapeutic agents for calcium malabsorption in β-thalassemia. It mainly stimulates the transcellular calcium transport across the duodenal epithelium in an NHE3-dependent manner.

Efficient acquisition of iron confers greater tolerance to saline-alkaline stress in rice (Oryza sativa L.)

To elucidate the mechanisms underlying tolerance to saline-alkaline stress in two rice genotypes, Dongdao-4 and Jigeng-88, we exposed them to medium supplemented with 10 mM Na2CO3 and 40 mM NaCl (pH 8.5). Dongdao-4 plants displayed higher biomass, chlorophyll content, and photosynthetic rates, and a larger root system than Jigeng-88 under saline-alkaline conditions. Dongdao-4 had a higher shoot Na+/K+ ratio than Jigeng-88 under both control and saline-alkaline conditions. Dongdao-4 exhibited stronger rhizospheric acidification than Jigeng-88 under saline-alkaline conditions, resulting from greater up-regulation of H+-ATPases at the transcriptional level. Moreover, Fe concentrations in shoots and roots of Dongdao-4 were higher than those in Jigeng-88, and a higher rate of phytosiderophore exudation was detected in Dongdao-4 versus Jigeng-88 under saline-alkaline conditions. The Fe-deficiency-responsive genes OsIRO2, OsIRT1, OsNAS1, OsNAS2, OsYSL2, and OsYSL15 were more strongly up-regulated in Dongdao-4 than Jigeng-88 plants in saline-alkaline medium, implying greater tolerance of Dongdao-4 plants to Fe deficiency. To test this hypothesis, we compared the effects of Fe deficiency on the two genotypes, and found that Dongdao-4 was more tolerant to Fe deficiency. Exposure to Fe-deficient medium led to greater rhizospheric acidification and phytosiderophore exudation in Dongdao-4 than Jigeng-88 plants. Expression levels of OsIRO2, OsIRT1, OsNAS1, OsNAS2, OsYSL2, and OsYSL15 were higher in Dongdao-4 than Jigeng-88 plants under Fe-deficient conditions. These results demonstrate that a highly efficient Fe acquisition system together with a large root system may underpin the greater tolerance of Dongdao-4 plants to saline-alkaline stress.

A Histidine Cluster in the Cytoplasmic Domain of the Na-H Exchanger NHE1 Confers pH-sensitive Phospholipid Binding and Regulates Transporter Activity

The Na-H exchanger NHE1 contributes to intracellular pH (pH_i) homeostasis in normal cells and the constitutively increased pH_i in cancer. NHE1 activity is allosterically regulated by intracellular protons, with greater activity at lower pH_i However, the molecular mechanism for pH-dependent NHE1 activity remains incompletely resolved. We report that an evolutionarily conserved cluster of histidine residues located in the C-terminal cytoplasmic domain between two phosphatidylinositol 4,5-bisphosphate binding sites (PI(4,5)P₂) of NHE1 confers pH-dependent PI(4,5)P₂ binding and regulates NHE1 activity. A GST fusion of the wild type C-terminal cytoplasmic domain of NHE1 showed increased maximum PI(4,5)P₂ binding at pH 7.0 compared with pH 7.5. However, pH-sensitive binding is abolished by substitutions of the His-rich cluster to arginine (RXXR3) or alanine (AXXA3), mimicking protonated and neutral histidine residues, respectively, and the RXXR3 mutant had significantly greater PI(4,5)P₂ binding than AXXA3. When expressed in cells, NHE1 activity and pH_i were significantly increased with NHE1-RXXR3 and decreased with NHE1-AXXA3 compared with wild type NHE1. Additionally, fibroblasts expressing NHE1-RXXR3 had significantly more contractile actin filaments and focal adhesions compared with fibroblasts expressing wild type NHE1, consistent with increased pH_i enabling cytoskeletal remodeling. These data identify a molecular mechanism for pH-sensitive PI(4,5)P₂ binding regulating NHE1 activity and suggest that the evolutionarily conserved cluster of four histidines in the proximal cytoplasmic domain of NHE1 may constitute a proton modifier site. Moreover, a constitutively activated NHE1-RXXR3 mutant is a new tool that will be useful for studying how increased pH_i contributes to cell behaviors, most notably the biology of cancer cells.

Elevated intracellular pH appears in aged oocytes and causes oocyte aneuploidy associated with the loss of cohesion in mice

Increases in the aneuploidy rate caused by the deterioration of cohesion with increasing maternal age have been well documented. However, the molecular mechanism for the loss of cohesion in aged oocytes remains unknown. In this study, we found that intracellular pH (pHi) was elevated in aged oocytes, which might disturb the structure of the cohesin ring to induce aneuploidy. We observed for the first time that full-grown germinal vesicle (GV) oocytes displayed an increase in pHi with advancing age in CD1 mice. Furthermore, during the in vitro oocyte maturation process, the pHi was maintained at a high level, up to ∼7.6, in 12-month-old mice. Normal pHi is necessary to maintain protein localization and function. Thus, we put forward a hypothesis that the elevated oocyte pHi might be related to the loss of cohesion and the increased aneuploidy in aged mice. Through the in vitro alkalinization treatment of young oocytes, we observed that the increased pHi caused an increase in the aneuploidy rate and the sister inter-kinetochore (iKT) distance associated with the strength of cohesion and caused a decline in the cohesin subunit SMC3 protein level. Young oocytes with elevated pHi exhibited substantially the increase in chromosome misalignment.

Regulation of lysosomal ion homeostasis by channels and transporters

Lysosomes are the major organelles that carry out degradation functions. They integrate and digest materials compartmentalized by endocytosis, phagocytosis or autophagy. In addition to more than 60 hydrolases residing in the lysosomes, there are also ion channels and transporters that mediate the flux or transport of H⁺, Ca²⁺, Na⁺, K⁺, and Cl⁻ across the lysosomal membranes. Defects in ionic exchange can lead to abnormal lysosome morphology, defective vesicle trafficking, impaired autophagy, and diseases such as neurodegeneration and lysosomal storage disorders. The latter are characterized by incomplete lysosomal digestion and accumulation of toxic materials inside enlarged intracellular vacuoles. In addition to degradation, recent studies have revealed the roles of lysosomes in metabolic pathways through kinases such as mechanistic target of rapamycin (mTOR) and transcriptional regulation through calcium signaling molecules such as transcription factor EB (TFEB) and calcineurin. Owing to the development of new approaches including genetically encoded fluorescence probes and whole endolysosomal patch clamp recording techniques, studies on lysosomal ion channels have made remarkable progress in recent years. In this review, we will focus on the current knowledge of lysosome-resident ion channels and transporters, discuss their roles in maintaining lysosomal function, and evaluate how their dysfunction can result in disease.

Connecting the dots: the effects of macromolecular crowding on cell physiology

The physicochemical properties of cellular environments with a high macromolecular content have been systematically characterized to explain differences observed in the diffusion coefficients, kinetics parameters, and thermodynamic properties of proteins inside and outside of cells. However, much less attention has been given to the effects of macromolecular crowding on cell physiology. Here, we review recent findings that shed some light on the role of crowding in various cellular processes, such as reduction of biochemical activities, structural reorganization of the cytoplasm, cytoplasm fluidity, and cellular dormancy. We conclude by presenting some unresolved problems that require the attention of biophysicists, biochemists, and cell physiologists. Although it is still underappreciated, macromolecular crowding plays a critical role in life as we know it.

Avian leukosis virus subgroup J induces its receptor--chNHE1 up-regulation

Background

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus which causes immunosuppression and neoplasia in meat-type and egg-type chickens. ALV-J infects host cells via specific interaction between the viral Env and the cell surface receptor —chicken sodium hydrogen exchanger type 1 (chNHE1). NHE1 involved in altering the cellular pH and playing a critical role in tumorigenesis. However, little is known about the other relationship between ALV-J and chNHE1.

Methods and results

In ALV-J infected DF-1 cells, the mRNA level of chNHE1 was up-regulated with time-dependent manner tested by real time PCR, and accordingly, intracellular pH was increased tested by spectrofluorometer. In vivo, the mRNA level of chNHE1 was determined by real time PCR in ALV-J infected experimental chickens and field cases. The result showed that the mRNA level of chNHE1 was up-regulated after virus shedding, especially in continuous viremic shedders (CS group). However, no significant difference was found between non-shedding group (NS group) and control group. In field cases, mRNA level of chNHE1 was positively correlated with increasing ALV-J load in tumor bearing and immune tolerance chickens. Furthermore, immunohistochemistry results showed that the protein expression of chNHE1 was up-regulated in different organs of both experimental chickens and tumor bearing chickens compared with the control.

Conclusion

Taken together, we conclude that ALV-J induces chNHE1 up-regulation in viremia and neoplasia chickens.

Time-dependent activity of Na+/H+ exchanger isoform 1 and homeostasis of intracellular pH in astrocytes exposed to CoCl2 treatment

Hypoxia causes injury to the central nervous system during stroke and has significant effects on pH homeostasis. Na+/H+ exchanger isoform 1 (NHE1) is important in the mechanisms of hypoxia and intracellular pH (pHi) homeostasis. As a well-established hypoxia-mimetic agent, CoCl2 stabilizes and increases the expression of hypoxia inducible factor‑1α (HIF-1α), which regulates several genes involved in pH balance, including NHE1. However, it is not fully understood whether NHE1 is activated in astrocytes under CoCl2 treatment. In the current study, pHi and NHE activity were analyzed using the pHi‑sensitive dye BCECF‑AM. Using cariporide (an NHE1‑specific inhibitor) and EIPA (an NHE nonspecific inhibitor), the current study demonstrated that it was NHE1, not the other NHE isoforms, that was important in regulating pHi homeostasis in astrocytes during CoCl2 treatment. Additionally, the present study observed that, during the early period of CoCl2 treatment (the first 2 h), NHE1 activity and pHi dropped immediately, and NHE1 mRNA expression was reduced compared with control levels, whereas expression levels of the NHE1 protein had not yet changed. In the later period of CoCl2 treatment, NHE1 activity and pHi significantly increased compared with the control levels, as did the mRNA and protein expression levels of NHE1. Furthermore, the cell viability and injury of astrocytes was not changed during the initial 8 h of CoCl2 treatment; their deterioration was associated with the higher levels of pHi and NHE1 activity. The current study concluded that NHE1 activity and pHi homeostasis are regulated by CoCl2 treatment in a time-dependent manner in astrocytes, and may be responsible for the changes in cell viability and injury observed under hypoxia-mimetic conditions induced by CoCl2 treatment.

Emerging roles of Na⁺/H⁺ exchangers in epilepsy and developmental brain disorders

Epilepsy is a common central nervous system (CNS) disease characterized by recurrent transient neurological events occurring due to abnormally excessive or synchronous neuronal activity in the brain. The CNS is affected by systemic acid-base disorders, and epileptic seizures are sensitive indicators of underlying imbalances in cellular pH regulation. Na(+)/H(+) exchangers (NHEs) are a family of membrane transporter proteins actively involved in regulating intracellular and organellar pH by extruding H(+) in exchange for Na(+) influx. Altering NHE function significantly influences neuronal excitability and plays a role in epilepsy. This review gives an overview of pH regulatory mechanisms in the brain with a special focus on the NHE family and the relationship between epilepsy and dysfunction of NHE isoforms. We first discuss how cells translocate acids and bases across the membrane and establish pH homeostasis as a result of the concerted effort of enzymes and ion transporters. We focus on the specific roles of the NHE family by detailing how the loss of NHE1 in two NHE mutant mice results in enhanced neuronal excitability in these animals. Furthermore, we highlight new findings on the link between mutations of NHE6 and NHE9 and developmental brain disorders including epilepsy, autism, and attention deficit hyperactivity disorder (ADHD). These studies demonstrate the importance of NHE proteins in maintaining H(+) homeostasis and their intricate roles in the regulation of neuronal function. A better understanding of the mechanisms underlying NHE1, 6, and 9 dysfunctions in epilepsy formation may advance the development of new epilepsy treatment strategies.

Growth of embryo and gene expression of nutrient transporters in the small intestine of the domestic pigeon (Columba livia)

The objective of this study was to investigate the relationship between gene expression of nutrient (amino acid, peptide, sodium and proton) transporters in the small intestine and embryonic growth in domestic pigeons (Columba livia). One hundred and twenty-five fertilized eggs were randomly assigned into five groups and were incubated under optimal conditions (temperature of 38.1 °C and relative humidity of 55%). Twenty embryos/birds from each group were sacrificed by cervical dislocation on embryonic day (E) 9, 11, 13, 15 and day of hatch (DOH). The eggs, embryos (without yolk sac), and organs (head, brain, heart, liver, lungs, kidney, gizzard, small intestine, legs, and thorax) were dissected, cleaned, and weighed. Small intestine samples were collected for RNA isolation. The mRNA abundance of intestinal nutrient transporters was evaluated by real-time reverse transcription-polymerase chain reaction (RT-PCR). We classified these ten organs into four types according to the changes in relative weight during embryonic development. In addition, the gene expression of nutrient transporters was differentially regulated by embryonic day. The mRNA abundances of b(0,+)AT, EAAT3, y(+)LAT2, PepT1, LAT4, NHE2, and NHE3 increased linearly with age, whereas mRNA abundances of CAT1, CAT2, LAT1, EAAT2, SNAT1, and SNAT2 were increased to higher levels on E9 or E11 and then decreased to lower levels until DOH. The results of correlation analysis showed that the gene expressions of b(0,+)AT, EAAT3, PepT1, LAT4, NHE2, NHE3, and y(+)LAT2 had positive correlations with body weight (0.71<correlation coefficient (CC)<0.82, P<0.0001), while CAT1, CAT2, EAAT2, SNAT1, and SNAT2 had negative correlations with body weight (-0.86<CC<-0.64, P<0.0001). The gene expressions of b(0,+)AT, EAAT3, LAT4, PepT1, NHE2, NHE3, and y(+)LAT2 showed positive correlations with intestinal weight (0.80<CC<0.91, P<0.0001), while CAT1, CAT2, and EAAT2 showed negative correlations with intestinal weight (-0.84<CC<-0.67, P<0.0001). It was concluded that the differences between growth trajectories of organs and gene expression of nutrient transporters in small intestine were due to their functional and physiological properties, which provided a comprehensive study of amino acid and peptide transporter mRNA in the small intestine during embryonic growth of pigeons.