Functional interplay between CFTR and pendrin: physiological and pathophysiological relevance

: The transport of chloride and bicarbonate across epithelia controls the pH and volume of the intracellular and luminal fluids, as well as the systemic pH and vascular volume. The anion exchanger pendrin (SLC26A4) and the cystic fibrosis transmembrane conductance regulator (CFTR) channel are expressed in the apical membrane of epithelial cells of various organs and tissues, including the airways, kidney, thyroid, and inner ear. While pendrin drives chloride reabsorption and bicarbonate, thiocyanate or iodide secretion within the apical compartment, CFTR represents a pathway for the apical efflux of chloride, bicarbonate, and possibly iodide. In the airways, pendrin and CFTR seems to be involved in alkalinization of the apical fluid via bicarbonate secretion, especially during inflammation, while CFTR also controls the volume of the apical fluid via a cAMP-dependent chloride secretion, which is stimulated by pendrin. In the kidney, pendrin is expressed in the cortical collecting duct and connecting tubule and co-localizes with CFTR in the apical membrane of β intercalated cells. Bicarbonate secretion occurs via pendrin, which also drives chloride reabsorption. A functional CFTR is required for pendrin activity. Whether CFTR stimulates pendrin via a direct molecular interaction or other mechanisms, or simply provides a pathway for chloride recycling across the apical membrane remains to be established. In the thyroid, CFTR and pendrin might have overlapping functions in driving the apical flux of iodide within the follicular lumen. In other organs, including the inner ear, the possible functional interplay between pendrin and CFTR needs to be explored

EGF stimulates IClswell by a redistribution of proteins involved in cell volume regulation.

Background: ICln is a multifunctional protein involved in the generation of chloride currents activated during regulatory volume decrease (RVD) after cell swelling (IClswell). Growth factor receptors play a key role in different cellular processes and epidermal growth factor (EGF) regulates swelling-activated chloride permeability. Aim: We set out to investigate if the EGF-induced upregulation of IClswell could be explained by a rearrangement of ICln subcellular distribution and interaction with its molecular partners. Methods: NIH-3T3 fibroblasts were serum-deprived for 24 hours and stimulated with EGF (40 ng/ml) for 30 minutes. IClswell activation, ICln distribution and interaction with its molecular partner HSPC038 were assessed by whole cell patch clamp and fluorescence resonance energy transfer (FRET). Results: EGF treatment significantly enhanced the direct molecular interaction between ICln and HSPC038 and also resulted in an increase of ICln and HSPC038 association with the plasma membrane. Importantly, these events are associated with a significant increase of IClswell. Conclusions: The present data indicate that EGF might exert its role in the modulation of volume-sensitive chloride currents in part through activation and translocation of ICln and HSPC038 to the plasma membrane

regulatory volume decrease in isolated nematocytes is affected by crude venom from the jellyfish pelagia noctiluca

Crude venom from nematocysts of the Scyphozoan Pelagia noctiluca possesses hemolytic and cytotoxic power on cultured cells and elicits local and systemic inflammation reactions in vivo. The ability of regulating their volume after exposure to an anisosmotic solution is a fundamental feature common to cells from vertebrates and invertebrates, including Cnidarians. The aim of the present work i s to assay whether crude venom from Pelagia noctiluca may affect the regulatory volume decrease (RVD) of nematocytes isolated from the Anthozoan Aiptasia mutabilis, here employed as a cell model. For this purpose, nematocytes were isolated by 605 mM NaSCN plus 0.01 mM Ca2+ application on acontia of Aiptasia mutabilis, while crude venom was obtained by sonication of a population of, respectively, 10, 25 and 50 nematocysts/µL (n/µL). Isolated nematocytes were pre-treated for 30 min with crude venom, submitted to hypotonic stress and their osmotic response and RVD were measured optically. Our results show that, after exposure to crude venom, nematocytes were morphologically intact, as shown by the Trypan blue exclusion test, but did not exhibit RVD. This effect was dose-dependent and reversed by the ionopho re gramicidin. The last observation suggests an inhibitory effect of venom on cell membrane ion transport mechanisms involved in RVD. Further studies are needed to verify this hypothesis and ascertain if a similar effect could be observed in human cells

oxidative stress affects responsiveness to hypotonicity of renal cells

Oxidative stress plays a critical role in the pathophysiology of several kidney diseases and is the consequence of alterations like ischemic events. The regulatory volume decrease (RVD) is an homeostatic response essential to many cells, including renal cells, to counteract changes in the osmolarity of the external medium. The aim of the present work is to verify whether oxidative stress affects RVD in a model of renal cells (human embryonic kidney cells, HEK 293 Phoenix). To accomplish this aim, the experimental procedure consisted in: i) cell culture preparation and treatment with 200 μM H2O2; and ii) measurement of cell volume changes in isotonic conditions or following hypotonic stress. H2O2 added to the extracellular isotonic solution induced a significant reduction in cell volume, and added to the extracellular hypotonic solution dramatically impaired the expected osmotic cell swelling. Pre-incubation of cells in an extracellular isotonic solution containing H2O2 prevented cell from swelling after hypotonic stress application. In conclusion, H2O2 leads to cell shrinkage in isotonic conditions, inhibits the hypotonicity-induced cell swelling and consequently prevents RVD, hypothetically due to an activation of transport pathways determining ion loss and, in turn, water efflux. Cell shrinkage in isotonic conditions is a hallmark of apoptosis and is known as the apoptotic volume decrease

A FRET-Based Approach for Quantitative Evaluation of Forskolin-Induced Pendrin Trafficking at the Plasma Membrane in Bronchial NCI H292 Cells

Background: Human pendrin (SLC26A4, PDS) is an integral membrane protein acting as an electroneutral anion exchanger. Loss of function mutations in pendrin protein cause Pendred syndrome, a disorder characterized by sensorineural deafness and a partial iodide organification defect that may lead to thyroid goiter. Additionally, pendrin up-regulation could play a role in the pathogenesis of several diseases including bronchial asthma and chronic obstructive pulmonary disease (COPD). Therefore, monitoring the plasma membrane abundance and trafficking of pendrin in the context of a living cell is crucially important. Methods: Trafficking of pendrin to the plasma membrane was monitored by fluorescence resonance energy transfer (FRET), a physical phenomenon occurring between two fluorophores (the FRET donor and acceptor) located in close spatial proximity. Because the efficiency of the energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, FRET is extremely sensitive to small changes in distance between the donor and acceptor and is therefore a powerful tool to determine protein-protein interactions. Results: FRET studies revealed that forskolin-induced cAMP production is associated with a significant increase of pendrin expression at plasma membrane, which is paralleled by a decrease in intracellular pH. Pendrin transposition to the membrane is accompanied with a partial depolymerization of actin cytoskeleton via Rho-GTPase inhibition. Conclusion: Trafficking to the plasma membrane is critical in the regulation of pendrin activity. Therefore, reliable tools for monitoring and quantifying this phenomenon are highly desirable

Editorial: Non-invasive brain stimulation techniques in neurological and neuropsychiatric disorders: Physiological and molecular evidence

[no abstract available

VRAC Channels and the Cellular Redox Balance

Volume-regulated anion channels (VRAC) are mainly involved in the regulated transport of osmolytes such as ions or small organic compounds across the plasma membrane during anisosmotic cell swelling. However, they also play additional roles in various pathophysiological processes, such as the transport of metabolites and drugs, extracellular signal transduction and anti-cancer drug resistance. These channels are formed by heteromers of LRRC8 proteins, of which LRRC8A is the essential subunit that combines with its paralogs LRRC8B–E to form hexameric complexes. Despite the extensive research devoted to the understanding of VRACs functions, different aspects of these channels are still to be characterized in depth. In this chapter, recent findings concerning the involvement of VRAC channels in the cellular redox balance will be summarized. Also, their relevance as potential targets of antioxidant therapies will be discussed

S-CMC-Lys protective effects on human respiratory cells during oxidative stress.

The mucoactive drug S-carbocysteine lysine salt monohydrate (S-CMC-Lys) stimulates glutathione (GSH) efflux from respiratory cells. Since GSH is one of the most important redox regulatory mechanisms, the aim of this study was to evaluate the S-CMC-Lys effects on GSH efflux and intracellular concentration during an oxidative stress induced by the hydroxyl radical (xOH). Experiments were performed on cultured human respiratory WI-26VA4 cells by means of patch-clamp experiments in whole-cell configuration and of fluorimetric analyses at confocal microscope. xOH exposure induced an irreversible inhibition of the GSH and chloride currents that was prevented if the cells were incubated with S-CMC-Lys. In this instance, the currents were inhibited by the specific blocker CFTR(inh)-172. CFT1-C2 cells, which lack a functional CFTR channel, were not responsive to S-CMC-Lys, but the stimulatory effect of the drug was restored in LCFSN-infected CFT1 cells, functionally corrected to express CFTR. Fluorimetric measurements performed on the S-CMC-Lys-incubated cells revealed a significant increase of the GSH concentration that was completely hindered after oxidative stress and abolished by CFTR(inh)-172. The cellular content of reactive oxygen species was significantly lower in the S-CMC-Lys-treated cells either before or after xOH exposure. As a conclusion, S-CMC-Lys could exert a protective function during oxidative stress, therefore preventing or reducing the ROS-mediated inflammatory response

Decellularized silk fibroin scaffold primed with adipose mesenchymal stromal cells improves wound healing in diabetic mice

Introduction: Silk fibroin (SF) scaffolds have been shown to be a suitable substrate for tissue engineering and to improve tissue regeneration when cellularized with mesenchymal stromal cells (MSCs). We here demonstrate, for the first time, that electrospun nanofibrous SF patches, cellularized with human adipose-derived MSCs (Ad-MSCs-SF) or decellularized (D-Ad- MSCs-SF) are effective in the treatment of skin wounds, improving skin regeneration in db/db diabetic mice. Methods: The conformational and structural analyses of SF and D-Ad-MSCs-SF patches were performed by scanning electron microscopy, confocal microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. Wounds were performed by a 5mm punch biopsy tool on the mouse\u2019s back. Ad-MSCs-SF and D-Ad-MSCs-SF patches were transplanted and the efficacy of treatments was assessed by measuring the wound closure area, by histological examination and by gene expression profile. We further investigated the in vitro angiogenic properties of Ad-MSCs-SF and D-Ad-MSCs-SF patches by affecting migration of human umbilical vein endothelial cells (HUVECs), keratinocytes (KCs) and dermal fibroblasts (DFs), through the aortic ring assay and, finally, by evaluating the release of angiogenic factors. Results: We found that Ad-MSCs adhere and grow on SF, maintaining their phenotypic mesenchymal profile and differentiation capacity. Conformational and structural analyses on SF and D-Ad- MSCs-SF samples, showed that sterilization, decellularization, freezing and storing did not affect the SF structure. When grafted in wounds of diabetic mice, both Ad-MSCs-SF and DAd- MSCs-SF significantly improved tissue regeneration, reducing the wound area respectively by 40% and 35%, within three days, completing the process in around 10 days compared to 15-17 days of controls. RT2 gene profile analysis of the wounds treated with Ad- MSCs-SF and D-Ad-MSCs-SF showed an increment of genes involved in angiogenesis and matrix remodelling. Finally, Ad-MSCs-SF and D-Ad-MSCs-SF co-cultured with HUVECs, DFs and KCs, preferentially enhanced the HUVECs\u2019 migration and the release of angiogenic factors stimulating microvessel outgrowth in the aortic ring assay. Conclusions: Our results highlight for the first time that D-Ad-MSCs-SF patches are almost as effective as Ad-MSCs-SF patches in the treatment of diabetic wounds, acting through a complex mechanism that involves stimulation of angiogenesis. Our data suggest a potential use of DAd- MSCs-SF patches in chronic diabetic ulcers in humans