OBJECTIVE: Ocular surface hydration is critical for eye health and its impairment can lead to dry eye disease. Extracellular calcium-sensing receptor (CaSR) is regulator of ion transport in epithelial cells expressing cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. CFTR is also a major ion channel in ocular surface epithelia, however the roles of CaSR in ocular surface are not well studied. This study aims to investigate expression and functional roles of CaSR in ocular surface.
METHODS: CaSR immunostaining was performed in mouse and human cornea and conjunctiva. Ocular surface potential difference (OSPD) and tear fluid volume measurements were performed in mice with topically applied cinacalcet (CaSR activator) and NPS-2143 (CaSR inhibitor).
RESULTS: CaSR is expressed in corneal and conjunctival epithelia of mice and humans. Topically administered CaSR activator cinacalcet inhibits cAMP agonist forskolin-induced Cl- secretion and CFTR activity up to 90 %. CaSR inhibitor NPS-2143 stimulates CFTR-mediated Cl- secretion in mouse ocular surface, after which cAMP agonist forskolin had minimal additional secretory effects. Single dose NPS-2143 treatment (as an eye drop) increases tear fluid volume in mice by ∼60 % compared to vehicle treatment. NPS-2143 effect on tear volume lasts at least 8 h after single dose.
CONCLUSIONS: CaSR is a key regulator of ocular surface ion transport and CaSR inhibition promotes Cl- and tear secretion in the ocular surface. If they are found to be effective in in dry eye models, CaSR inhibitors (currently in clinical development) can potentially be repurposed as novel prosecretory treatments for dry eye disease.

Together with its β-subunit OSTM1, ClC-7 performs 2Cl-/H+ exchange across lysosomal membranes. Pathogenic variants in either gene cause lysosome-related pathologies, including osteopetrosis and lysosomal storage. CLCN7 variants can cause recessive or dominant disease. Different variants entail different sets of symptoms. Loss of ClC-7 causes osteopetrosis and mostly neuronal lysosomal storage. A recently reported de novo CLCN7 mutation (p.Tyr715Cys) causes widespread severe lysosome pathology (hypopigmentation, organomegaly, and delayed myelination and development, \"HOD syndrome\"), but no osteopetrosis. We now describe two additional HOD individuals with the previously described p.Tyr715Cys and a novel p.Lys285Thr mutation, respectively. Both mutations decreased ClC-7 inhibition by PI(3,5)P2 and affected residues lining its binding pocket, and shifted voltage-dependent gating to less positive potentials, an effect partially conferred to WT subunits in WT/mutant heteromers. This shift predicts augmented pH gradient-driven Cl- uptake into vesicles. Overexpressing either mutant induced large lysosome-related vacuoles. This effect depended on Cl-/H+-exchange, as shown using mutants carrying uncoupling mutations. Fibroblasts from the p.Y715C patient also displayed giant vacuoles. This was not observed with p.K285T fibroblasts probably due to residual PI(3,5)P2 sensitivity. The gain of function caused by the shifted voltage-dependence of either mutant likely is the main pathogenic factor. Loss of PI(3,5)P2 inhibition will further increase current amplitudes, but may not be a general feature of HOD. Overactivity of ClC-7 induces pathologically enlarged vacuoles in many tissues, which is distinct from lysosomal storage observed with the loss of ClC-7 function. Osteopetrosis results from a loss of ClC-7, but osteoclasts remain resilient to increased ClC-7 activity.

Mammalian SLC26 proteins are membrane-based anion transporters that belong to the large SLC26/SulP family, and many of their variants are associated with hereditary diseases. Recent structural studies revealed a strikingly similar homodimeric molecular architecture for several SLC26 members, implying a shared molecular principle. Now a new question emerges as to how these structurally similar proteins execute diverse physiological functions. In this study, we sought to identify the common versus distinct molecular mechanism among the SLC26 proteins using both naturally occurring and artificial missense changes introduced to SLC26A4, SLC26A5, and SLC26A9. We found: (i) the basic residue at the anion binding site is essential for both anion antiport of SLC26A4 and motor functions of SLC26A5, and its conversion to a nonpolar residue is crucial but not sufficient for the fast uncoupled anion transport in SLC26A9; (ii) the conserved polar residues in the N- and C-terminal cytosolic domains are likely involved in dynamic hydrogen-bonding networks and are essential for anion antiport of SLC26A4 but not for motor (SLC26A5) and uncoupled anion transport (SLC26A9) functions; (iii) the hydrophobic interaction between each protomer\'s last transmembrane helices, TM14, is not of functional significance in SLC26A9 but crucial for the functions of SLC26A4 and SLC26A5, likely contributing to optimally orient the axis of the relative movements of the core domain with respect to the gate domains within the cell membrane. These findings advance our understanding of the molecular mechanisms underlying the diverse physiological roles of the SLC26 family of proteins.

Coastal regions, home to a significant portion of the world\'s population, confront a formidable challenge: the corrosive impact of chloride-rich environments on vital infrastructure. These areas often host essential transportation systems, such as trains and metros, reliant on pre-existing electrical infrastructure. Unfortunately, complete isolation of this infrastructure is rarely feasible, resulting in the emergence of stray currents and electrical potentials that expedite corrosion processes. When coupled with conducive mediums facilitating chemical electrocell formation, the corrosion of reinforced concrete elements accelerates significantly. To combat this issue, international standards have been established, primarily focusing on augmenting the thickness of reinforcement bar covers and restricting stray voltage between rails and the ground. Nevertheless, these measures only provide partial solutions. When subjected to service loads, these elements develop cracks, especially when exposed to stray currents and chlorides, dramatically increasing corrosion rates. Corrosion products, which expand in volume compared to steel, exert internal forces that widen cracks, hastening the deterioration of structural elements. The study deals with the degradation of reinforced concrete columns under the combined action of loads, chloride-rich environments, and electrical voltage-simulating stray currents. In these conditions, degradation and reduction of load-bearing capacity accelerate compared to unloaded conditions, significantly amplifying the corrosion rate. Astonishingly, even in the absence of mechanical loads, stray currents alone induce tensile stresses in elements due to corrosion product formation, leading to longitudinal cracks parallel to the reinforcement bars.

In nature, ceramides are a class of sphingolipids possessing a unique ability to self-assemble into protein-permeable channels with intriguing concentration-dependent adaptive channel cavities. However, within the realm of artificial ion channels, this interesting phenomenon is scarcely represented. Herein, we report on a novel class of adaptive artificial channels, Pn-TPPs, based on PEGylated cholic acids bearing triphenylphosphonium (TPP) groups as anion binding motifs. Interestingly, the molecules self-assemble into chloride ion channels at low concentrations while transforming into small molecule-permeable nanopores at high concentrations. Moreover, the TPP groups endow the molecules with mitochondria-targeting properties, enabling them to selectively drill holes on the mitochondrial membrane of cancer cells and subsequently trigger the caspase 9 apoptotic pathway. The anticancer efficacies of Pn-TPPs correlate with their abilities to form nanopores. Significantly, the most active ensembles formed by P5-TPP exhibits impressive anticancer activity against human liver cancer cells, with an IC50 value of 3.8 μM. While demonstrating similar anticancer performance to doxorubicin, P5-TPP exhibits a selectivity index surpassing that of doxorubicin by a factor of 16.8.

Chloride transport within concrete is critical for the durability of reinforced concrete structures; however, its diffusion under the coupling action of temperature and humidity has not been fully comprehended. Therefore, in this work, the coupling effects of temperature, relative humidity, and mineral admixtures on chloride transport in concrete were investigated through experimental and numerical simulation work. The results show that the chloride diffusion coefficient decreases with the decreased temperature and growth of relative humidity; however, the chloride concentration on the concrete surface is increased with the growth of temperature and relative humidity. Moreover, compounding about 15% fly ash (FA) and 30% granulated ground blast furnace slag (GGBS) to replace the cement is the most beneficial for improving the antichloride capacity of concrete, considering also the strength. In addition, the numerical simulation considering the coupled effect of temperature and relative humidity of chloride transport in concrete has good agreement with that of experimental results.

ClC is the main family of natural chloride channel proteins that transport Cl- across the cell membrane with high selectivity. The chloride transport and selectivity are determined by the hourglass-shaped pore and the filter located in the central and narrow region of the pore. Artificial unimolecular channel that mimics both the shape and function of the ClC selective pore is attractive, because it could provide simple molecular model to probe the intriguing mechanism and structure-function relevance of ClC. Here we elaborated upon the concept of molecular hourglass plus anion-π interactions for this purpose. The concept was validated by experimental results of molecular hourglasses using shape-persistent 1,3-alternate tetraoxacalix[2]arene[2]triazine as the central macrocyclic skeleton to control the conductance and selectivity, and anion-π interactions as the driving force to facilitate the chloride dehydration and movement along the channel.

Pendrin (SLC26A4) is an anion exchanger from the SLC26 transporter family which is mutated in human patients affected by Pendred syndrome, an autosomal recessive disease characterized by sensoneurinal deafness and hypothyroidism. Pendrin is also expressed in the kidney where it mediates the exchange of internal HCO3- for external Cl- at the apical surface of renal type B and non-A non-B-intercalated cells. Studies using pendrin knockout mice have first revealed that pendrin is essential for renal base excretion. However, subsequent studies have demonstrated that pendrin also controls chloride absorption by the distal nephron and that this mechanism is critical for renal NaCl balance. Furthermore, pendrin has been shown to control vascular volume and ultimately blood pressure. This review summarizes the current knowledge about how pendrin is linking renal acid-base regulation to blood pressure control.

The development of stimuli-responsive artificial H+ /Cl- ion channels, capable of specifically disturbing the intracellular ion homeostasis of cancer cells, presents an intriguing opportunity for achieving high selectivity in cancer therapy. Herein, we describe a novel family of non-covalently stapled self-assembled artificial channels activatable by biocompatible visible light at 442 nm, which enables the co-transport of H+ /Cl- across the membrane with H+ /Cl- transport selectivity of 6.0. Upon photoirradiation of the caged C4F-L for 10 min, 90 % of ion transport efficiency can be restored, giving rise to a 10.5-fold enhancement in cytotoxicity against human colorectal cancer cells (IC50 =8.5 μM). The mechanism underlying cancer cell death mediated by the H+ /Cl- channels involves the activation of the caspase 9 apoptosis pathway as well as the scarcely reported disruption of the autophagic processes. In the absence of photoirradiation, C4F-L exhibits minimal toxicity towards normal intestine cells, even at a concentration of 200 μM.

Endosomes and lysosomes are intracellular vesicular organelles with important roles in cell functions such as protein homeostasis, clearance of extracellular material, and autophagy. Endolysosomes are characterized by an acidic luminal pH that is critical for proper function. Five members of the gene family of voltage-gated ChLoride Channels (CLC proteins) are localized to endolysosomal membranes, carrying out anion/proton exchange activity and thereby regulating pH and chloride concentration. Mutations in these vesicular CLCs cause global developmental delay, intellectual disability, various psychiatric conditions, lysosomal storage diseases, and neurodegeneration, resulting in severe pathologies or even death. Currently, there is no cure for any of these diseases. Here, we review the various diseases in which these proteins are involved and discuss the peculiar biophysical properties of the WT transporter and how these properties are altered in specific neurodegenerative and neurodevelopmental disorders.