Lithium and protein kinase C modulators regulate swelling-activated K-Cl cotransport and reveal a complete phosphatidylinositol cycle in low K sheep erythrocytes

Val-Leu-Leu-Tyr (VLLY) Alleviates Ethanol-Induced Gastric Mucosal Cell Impairment by Improving Mitochondrial Fission

Ethanolic gastric mucosal impairment is one of the most common disorders in the gastrointestinal system. In this study, we investigated the potential alleviating effects of sea cucumber peptides on Ges-1 impairment caused by ethanol and the associated mechanisms. The sea cucumber peptide VLLY could promote the proliferation and migration of healthy Ges-1 cells. After ethanol injury, VLLY peptide treatment could greatly promote the migration of Ges-1 cells, scavenge intracellular and mitochondrial ROS, reverse mitochondrial fission and F-actin depolymerization, and improve mitochondrial respiration. VLLY peptide restored mitochondrial dynamics by downregulating Drp1 and Fis1 and upregulating Mfn2 against excessive mitochondrial fission. In addition, the VLLY peptide maintained the mitochondrial membrane potential, ablated the leakage of cytochrome c to the cytoplasm, upregulated the expression of the antiapoptotic factor Bcl-XL, decreased the expression of the proapoptotic factors of Bax, BAD, and cleaved caspase-3, and finally blocked the mitochondria-related apoptotic pathway. These findings strongly suggested that sea cucumber peptides could promote proliferation and migration of healthy Ges-1 cells and reverse ethanol-induced excess mitochondrial fission and maintain mitochondrial homeostasis through the Fis1/Bax pathway, thereby improving ethanol-induced apoptosis. VLLY offers a new perspective for improving the ethanolic gastric mucosal epithelial cell injury.

Circular Economy and Sustainable Recovery of Taiwanese Tilapia (Oreochromis mossambicus) Byproduct-The Large-Scale Production of Umami-Rich Seasoning Material Application

In this study, umami-rich seasoning powder was produced from the offcuts of Taiwanese tilapia (Oreochromis mossambicus) by cooking concentration and spray drying of granules while yielding an abundance of glutamic acid (0.23 mg/100 g), glycine (0.10 mg/100 g), aspartic acid (0.11 mg/100 g), lysine (0.10 mg/100 g), and 11 other aminic acids. It exhibited water content (3.81%), water activity (0.3), powder yields (68.83%), and a good water solubility index (99.89%), while the particle microstructure was a spherical powder. Additionally, it received the highest overall preference score (7.53) in the consumer-type sensory evaluation compared to commercially available seasonings. This study proves that offcuts may be part of the human diet after proper processing and can be widely used to flavor savory food. The producers involved could increase their economic returns while meeting the environmental challenges. The practical contribution could create incremental value for products to critical stakeholders at each point in the tilapia supply chain with an operational guide for transitioning from inefficient to innovative circular practices.

Reduction of sodium chloride: a review

Sodium chloride (NaCl) is an enjoyable condiment. However, evidence is accumulating to indicate that an excessive intake of Na⁺ in food may lead to an increased risk of cardiovascular and cerebrovascular diseases. Previous systematic reviews have focused on replacing NaCl with other metal salts (e.g. KCl). However, new salty flavor enhancers (yeast extract, taste peptides, and odor compounds) have yet to be reviewed. This systematic review evaluates the methods for, and feasibility, of NaCl reduction. It defines NaCl reduction and considers the methods used for this purpose, especially the use of flavor enhancers (yeast extract, taste peptides, and odor compounds). © 2022 Society of Chemical Industry.

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.

Kinetic studies of K-Cl cotransport in cultured rat vascular smooth muscle cells

During aging, and development of atherosclerosis and cardiovascular disease (CVD), aortic vascular smooth muscle cells (VSMCs) transition from healthy contractile to diseased synthetic phenotypes. K-Cl cotransport (KCC) maintains cell volume and ion homeostasis in growth and differentiation, and hence is important for VSMC proliferation and migration. Therefore, KCC activity may play a role in the contractile-to-synthetic VSMC phenotypic transition. Early, medium, and late synthetic passage VSMCs were tested for specific cytoskeletal protein expression. KCC-mediated ouabain- and bumetanide-insensitive Rb+ (a K+ congener) influx was determined as Cl--dependent Rb+ influx at different external Rb+ and Cl- ion concentrations, [Rb+]o and [Cl-]o. Expressions of the cytoskeletal proteins α-actin, vimentin, and desmin fell from early through late synthetic VSMCs. KCC kinetic parameters, such as maximum velocity ( Vm), and apparent Cl- and Rb+ affinities ( Km), were calculated with Lineweaver-Burk, Hanes-Woolf, and Hill approximations. Vm values of both Rb+- and Cl--dependent influxes were of equal magnitude, commensurate with a KCC stoichiometry of unity, and rose threefold from early to late synthetic VSMCs. Hill coefficients for Rb+ and Cl- correlated with cell passage number, suggesting increased KCC ligand cooperativity. However, Km values for [Cl-]o were strikingly bimodal with 60-80 mM in early, ~20-30 mM in medium, and 60 mM in late passage cells. In contrast, Km values for [Rb+]o remained steady at ~17 mM. Since total KCC isoform expression was similar with cell passage, structure/function changes of the KCC signalosome may accompany the transition of aortic VSMCs from a healthy to a diseased phenotype.

Kinetics of hyperosmotically stimulated Na-K-2Cl cotransporter in Xenopus laevis oocytes

A detailed study of hypertonically stimulated Na-K-2Cl cotransport (NKCC1) in Xenopus laevis oocytes was carried out to better understand the 1 K(+):1 Cl(-) stoichiometry of transport that was previously observed. In this study, we derived the velocity equations for K(+) influx under both rapid equilibrium assumptions and combined equilibrium and steady-state assumptions and demonstrate that the behavior of the equations and curves in Lineweaver-Burke plots are consistent with a model where Cl(-) binds first, followed by Na(+), a second Cl(-), and then K(+). We further demonstrate that stimulation of K(+) movement by K(+) on the trans side is an intrinsic property of a carrier that transports multiple substrates. We also demonstrate that K(+) movement through NKCC1 is strictly dependent upon the presence of external Na(+), even though only a fraction of Na(+) is in fact transported. Finally, we propose that the larger transport of K(+), as compared with Na(+), is a result of the return of partially unloaded carriers, which masks the net 1Na(+):1K(+):2Cl(-) stoichiometry of NKCC1. These data have profound implications for the physiology of Na-K-2Cl cotransport, since transport of K-Cl in some conditions seems to be uncoupled from the transport of Na-Cl.

Lithium-induced suicidal erythrocyte death

Lithium (Li+), an effective drug for treatment of bipolar disorders, is known to alter several Ca²+ transporting systems. Increased cellular Ca²+ has in turn been shown to stimulate eryptosis, the suicidal death of erythrocytes. Eryptosis is characterised by exposure of phosphatidylserine (PS) at the erythrocyte surface and by cell shrinkage. The present experiments explored whether Li+ influences eryptosis. In erythrocytes from healthy volunteers, cytosolic Ca²+ activity (Fluo-3 fluorescence), cell volume (forward scatter) and PS exposure (annexin V binding) were determined by fluorescence-activated cell sorting analysis. Exposure to Li+ (≥ 1 mM) did not significantly modify forward scatter but significantly increased cytosolic Ca²+ activity (within 3 h) and annexin binding (within 48 h). The effect was paralleled by increase of cellular adenosine triphosphate concentration. Glucose depletion (24 h) strongly increased PS exposure, an effect significantly enhanced in the presence of Li+ (≥ 1 mM). In conclusion, Li+ triggers suicidal erythrocyte death, an effect at least partially due to increase of cytosolic Ca²+ activity.

Water permeability through aquaporin-4 is regulated by protein kinase C and becomes rate-limiting for glioma invasion

Glial-derived tumors, gliomas, are highly invasive cancers that invade normal brain through the extracellular space. To navigate the tortuous extracellular spaces, cells undergo dynamic changes in cell volume, which entails water flux across the membrane through aquaporins (AQPs). Two members of this family, AQP1 and AQP4 are highly expressed in primary brain tumor biopsies and both have a consensus phosphorylation site for protein kinase C (PKC), which is a known regulator of glioma cell invasion. AQP4 colocalizes with PKC to the leading edge of invading processes and clustered with chloride channel (ClC2) and K(+)-Cl(-) cotransporter 1 (KCC1), believed to provide the pathways for Cl(-) and K(+) secretion to accomplish volume changes. Using D54MG glioma cells stably transfected with either AQP1 or AQP4, we show that PKC activity regulates water permeability through phosphorylation of AQP4. Activation of PKC with either phorbol 12-myristate 13-acetate or thrombin enhanced AQP4 phosphorylation, reduced water permeability and significantly decreased cell invasion. Conversely, inhibition of PKC activity with chelerythrine reduced AQP4 phosphorylation, enhanced water permeability and significantly enhanced tumor invasion. PKC regulation of AQP4 was lost after mutational inactivation of the consensus PKC phosphorylation site S180A. Interestingly, AQP1 expressing glioma cells, by contrast, were completely unaffected by changes in PKC activity. To demonstrate a role for AQPs in glioma invasion in vivo, cells selectively expressing AQP1, AQP4 or the mutated S180A-AQP4 were implanted intracranially into SCID mice. AQP4 expressing glioma cells showed significantly reduced invasion compared to AQP1 and S180 expressing tumors as determined by quantitative stereology, consistent with a differential role for AQP1 and AQP4 in this process.

Current knowledge about the functional roles of phosphorylative changes of membrane proteins in normal and diseased red cells

With the advent of proteomic techniques the number of known post-translational modifications (PTMs) affecting red cell membrane proteins is rapidly growing but the understanding of their role under physiological and pathological conditions is incompletely established. The wide range of hereditary diseases affecting different red cell membrane functions and the membrane modifications induced by malaria parasite intracellular growth represent a unique opportunity to study PTMs in response to variable cellular stresses. In the present review, some of the major areas of interest in red cell membrane research have been considered as modifications of erythrocyte deformability and maintenance of the surface area, membrane transport alterations, and removal of diseased and senescent red cells. In all mentioned research areas the functional roles of PTMs are prevalently restricted to the phosphorylative changes of the more abundant membrane proteins. The insufficient information about the PTMs occurring in a large majority of the red membrane proteins and the general lack of mass spectrometry data evidence the need of new comprehensive, proteomic approaches to improve the understanding of the red cell membrane physiology.

Lithium fluxes indicate presence of Na-Cl cotransport (NCC) in human lens epithelial cells

During regulatory volume decrease (RVD) of human lens epithelial cells (hLECs) by clotrimazole (CTZ)-sensitive K fluxes, Na-K-2Cl cotransport (NKCC) remains active and K-Cl cotransport (KCC) inactive. To determine whether such an abnormal behavior was caused by RVD-induced cell shrinkage, NKCC was measured in the presence of either CTZ or in high K media to prevent RVD. NKCC transports RbCl + NaCl, and LiCl + KCl; thus ouabain-insensitive, bumetanide-sensitive (BS) or Cl-dependent (ClD) Rb and Li fluxes were determined in hyposmotic high NaCl media with CTZ, or in high KCl media alone, or with sulfamate (Sf) or nitrate as Cl replacement at varying Rb, Li or Cl mol fractions (MF). Unexpectedly, NKCC was inhibited by 80% with CTZ (IC(50) = 31 microM). In isosmotic (300 mOsM) K, Li influx was approximately 1/3 of Rb influx in Na, 50% lower in Sf, and bumetanide-insensitive (BI). In hypotonic (200 mOsM) K, only the ClD but not BS Li fluxes were detected. At Li MFs from 0.1-1, Li fluxes fitted a bell-shaped curve maxing at approximately 0.6 Li MF, with the BS fluxes equaling approximately 1/4 of the ClD-Li influx. The difference, i.e. the BI/ClD Li influx, saturated with increasing Li and Cl MFs, with K(ms) for Li of 11 with, and 7 mM without K, and of approximately 46 mM for Cl. Inhibition of this K-independent Li influx by thiazides was weak whilst furosemide (<100 microM) was ineffective. Reverse transcription polymerase chain reaction and Western blots verified presence of both NKCC1 and Na-Cl cotransport (NCC). In conclusion, in hyposmotic high K media, which prevents CTZ-sensitive K flux-mediated RVD in hLECs, NKCC1, though molecularly expressed, was functionally silent. However, a K-independent and moderately thiazide-sensitive ClD-Li flux, i.e. LiCC, likely occurring through NCC was detected operationally and molecularly.

K-Cl cotransport function and its potential contribution to cardiovascular disease

K-Cl cotransport is the coupled electroneutral movement of K and Cl ions carried out by at least four protein isoforms, KCC1-4. These transporters belong to the SLC12A family of coupled cotransporters and, due to their multiple functions, play an important role in the maintenance of cellular homeostasis. Significant information exists on the overall function of these transporters, but less is known about the role of the specific isoforms. Most functional studies were done on K-Cl cotransport fluxes without knowing the molecular details, and only recently attention has been paid to the isoforms and their individual contribution to the fluxes. This review summarizes briefly and updates the information on the overall functions of this transporter, and offers some ideas on its potential contribution to the pathophysiological basis of cardiovascular disease. By virtue of its properties and the cellular ionic distribution, K-Cl cotransport participates in volume regulation of the nucleated and some enucleated cells studied thus far. One of the hallmarks in cardiovascular disease is the inability of the organism to maintain water and electrolyte balance in effectors and/or target tissues. Oxidative stress is another compounding factor in cardiovascular disease and of great significance in our modern life styles. Several functions of the transporter are modulated by oxidative stress, which in turn may cause the transporter to operate in either "overdrive" with the purpose to counteract homeostatic changes, or not to respond at all, again setting the stage for pathological changes leading to cardiovascular disease. Intracellular Mg, a second messenger, acts as an inhibitor of K-Cl cotransport and plays a crucial role in regulating the activity of protein kinases and phosphatases, which, in turn, regulate a myriad of cellular functions. Although the role of Mg in cardiovascular disease has been dealt with for several decades, this chapter is evolving nowadays at a faster pace and the relationships between Mg, K-Cl cotransport, and cardiovascular disease is an area that awaits further experimentation. We envision that further studies on the role of K-Cl cotransport, and ideally on its specific isoforms, in mammalian cells will add missing links and help to understand the cellular mechanisms involved in the pathophysiology of cardiovascular disease.

Identification of key functional domains in the C terminus of the K+-Cl- cotransporters

The K+-Cl- cotransporter (KCC) isoforms constitute a functionally heterogeneous group of ion carriers. Emerging evidence suggests that the C terminus (Ct) of these proteins is important in conveying isoform-specific traits and that it may harbor interacting sites for 4beta-phorbol 12-myristate 13-acetate (PMA)-induced effectors. In this study, we have generated KCC2-KCC4 chimeras to identify key functional domains in the Ct of these carriers and single point mutations to determine whether canonical protein kinase C sites underlie KCC2-specific behaviors. Functional characterization of wild-type (wt) and mutant carriers in Xenopus laevis oocytes showed for the first time that the KCCs do not exhibit similar sensitivities to changes in osmolality and that this distinguishing feature as well as differences in transport activity under both hypotonic and isotonic conditions are in part determined by the residue composition of the distal Ct. At the same time, several mutations in this domain and in the proximal Ct of the KCCs were found to generate allosteric-like effects, suggesting that the regions analyzed are important in defining conformational ensembles and that isoform-specific structural configurations could thus account for variant functional traits as well. Characterization of the other mutants in this work showed that KCC2 is not inhibited by PMA through phosphorylation of its canonical protein kinase C sites. Intriguingly, however, the substitutions N728S and S940A were seen to alter the PMA effect paradoxically, suggesting again that allosteric changes in the Ct are important determinants of transport activity and, furthermore, that the structural configuration of this domain can convey specific functional traits by defining the accessibility of cotransporter sites to regulatory intermediates such as PMA-induced effectors.

Signal transduction mechanisms of K+-Cl- cotransport regulation and relationship to disease

The K+-Cl- cotransport (COT) regulatory pathways recently uncovered in our laboratory and their implication in disease state are reviewed. Three mechanisms of K+-Cl- COT regulation can be identified in vascular cells: (1) the Li+-sensitive pathway, (2) the platelet-derived growth factor (PDGF)-sensitive pathway and (3) the nitric oxide (NO)-dependent pathway. Ion fluxes, Western blotting, semi-quantitative RT-PCR, immunofluorescence and confocal microscopy were used. Li+, used in the treatment of manic depression, stimulates volume-sensitive K+-Cl- COT of low K+ sheep red blood cells at cellular concentrations <1 mM and inhibits at >3 mM, causes cell swelling, and appears to regulate K+-Cl- COT through a protein kinase C-dependent pathway. PDGF, a potent serum mitogen for vascular smooth muscle cells (VSMCs), regulates membrane transport and is involved in atherosclerosis. PDGF stimulates VSM K+-Cl- COT in a time- and concentration-dependent manner, both acutely and chronically, through the PDGF receptor. The acute effect occurs at the post-translational level whereas the chronic effect may involve regulation through gene expression. Regulation by PDGF involves the signalling molecules phosphoinositides 3-kinase and protein phosphatase-1. Finally, the NO/cGMP/protein kinase G pathway, involved in vasodilation and hence cardiovascular disease, regulates K+-Cl- COT in VSMCs at the mRNA expression and transport levels. A complex and diverse array of mechanisms and effectors regulate K+-Cl- COT and thus cell volume homeostasis, setting the stage for abnormalities at the genetic and/or regulatory level thus effecting or being affected by various pathological conditions.

Erythrocyte signal transduction pathways, their oxygenation dependence and functional significance

Erythrocytes play a key role in human and vertebrate metabolism. Tissue O2 supply is regulated by both hemoglobin (Hb)-O2 affinity and erythrocyte rheology, a key determinant of tissue perfusion. Oxygenation-deoxygenation transitions of Hb may lead to re-organization of the cytoskeleton and signalling pathways activation/deactivation in an O2-dependent manner. Deoxygenated Hb binds to the cytoplasmic domain of the anion exchanger band 3, which is anchored to the cytoskeleton, and is considered a major mechanism underlying the oxygenation-dependence of several erythrocyte functions. This work discusses the multiple modes of Hb-cytoskeleton interactions. In addition, it reviews the effects of Mg2+, 2,3-diphosphoglycerate, NO, shear stress and Ca2+, all factors accompanying the oxygenation-deoxygenation cycle in circulating red cells. Due to the extensive literature on the subject, the data discussed here, pertain mainly to human erythrocytes whose O2 affinity is modulated by 2,3-diphosphoglycerate, ectothermic vertebrate erythrocytes that use ATP, and to bird erythrocytes that use inositol pentaphosphate.

PDGF activates K-Cl cotransport through phosphoinositide 3-kinase and protein phosphatase-1 in primary cultures of vascular smooth muscle cells

K-Cl cotransport (K-Cl COT, KCC) is an electroneutrally coupled movement of K and Cl present in most cells. In this work, we studied the pathways of regulation of K-Cl COT by platelet-derived growth factor (PDGF) in primary cultures of vascular smooth muscle cells (VSMCs). Wortmannin and LY 294002 blocked the PDGF-induced K-Cl COT activation, indicating that the phosphoinositide 3-kinase (PI 3-K) pathway is involved. However, PD 98059 had no effect on K-Cl COT activation by PDGF, suggesting that the mitogen-activated protein kinase pathway is not involved under the experimental conditions tested. Involvement of phosphatases was also examined. Sodium orthovanadate, cyclosporin A and okadaic acid had no effect on PDGF-stimulated K-Cl COT. Calyculin A blocked the PDGF-stimulated K-Cl COT by 60%, suggesting that protein phosphatase-1 (PP-1) is a mediator in the PDGF signaling pathway/s. In conclusion, our results indicate that the PDGF-mediated pathways of K-Cl COT regulation involve the signaling molecules PI 3-K and PP-1.

Regulation of K-Cl cotransport: from function to genes

This review intends to summarize the vast literature on K-Cl cotransport (COT) regulation from a functional and genetic viewpoint. Special attention has been given to the signaling pathways involved in the transporter's regulation found in several tissues and cell types, and more specifically, in vascular smooth muscle cells (VSMCs). The number of publications on K-Cl COT has been steadily increasing since its discovery at the beginning of the 1980s, with red blood cells (RBCs) from different species (human, sheep, dog, rabbit, guinea pig, turkey, duck, frog, rat, mouse, fish, and lamprey) being the most studied model. Other tissues/cell types under study are brain, kidney, epithelia, muscle/smooth muscle, tumor cells, heart, liver, insect cells, endothelial cells, bone, platelets, thymocytes and Leishmania donovani. One of the salient properties of K-Cl-COT is its activation by cell swelling and its participation in the recovery of cell volume, a process known as regulatory volume decrease (RVD). Activation by thiol modification with N-ethylmaleimide (NEM) has spawned investigations on the redox dependence of K-Cl COT, and is used as a positive control for the operation of the system in many tissues and cells. The most accepted model of K-Cl COT regulation proposes protein kinases and phosphatases linked in a chain of phosphorylation/dephosphorylation events. More recent studies include regulatory pathways involving the phosphatidyl inositol/protein kinase C (PKC)-mediated pathway for regulation by lithium (Li) in low-K sheep red blood cells (LK SRBCs), and the nitric oxide (NO)/cGMP/protein kinase G (PKG) pathway as well as the platelet-derived growth factor (PDGF)-mediated mechanism in VSMCs. Studies on VSM transfected cells containing the PKG catalytic domain demonstrated the participation of this enzyme in K-Cl COT regulation. Commonly used vasodilators activate K-Cl COT in a dose-dependent manner through the NO/cGMP/PKG pathway. Interaction between the cotransporter and the cytoskeleton appears to depend on the cellular origin and experimental conditions. Pathophysiologically, K-Cl COT is altered in sickle cell anemia and neuropathies, and it has also been proposed to play a role in blood pressure control. Four closely related human genes code for KCCs (KCC1-4). Although considerable information is accumulating on tissue distribution, function and pathologies associated with the different isoforms, little is known about the genetic regulation of the KCC genes in terms of transcriptional and post-transcriptional regulation. A few reports indicate that the NO/cGMP/PKG signaling pathway regulates KCC1 and KCC3 mRNA expression in VSMCs at the post-transcriptional level. However, the detailed mechanisms of post-transcriptional regulation of KCC genes and of regulation of KCC2 and KCC4 mRNA expression are unknown. The K-Cl COT field is expected to expand further over the next decades, as new isoforms and/or regulatory pathways are discovered and its implication in health and disease is revealed.