Involvement of the intracellular ion channel CLIC1 in microglia-mediated beta-amyloid-induced neurotoxicity

CLIC1 and IFITM2 expression in brain tissue correlates with cognitive impairment via immune dysregulation in sepsis and Alzheimer's disease

BACKGROUND

Sepsis, a life-threatening condition driven by dysregulated host responses to infection, is associated with long-term cognitive impairments resembling Alzheimer's disease (AD). However, the molecular mechanisms linking sepsis-induced cognitive dysfunction and AD remain unclear. We hypothesized that shared genetic pathways underlie cognitive deficits in both conditions.

METHODS

Cecal ligation and puncture (CLP) in C57BL/6 J mice modeled sepsis-induced cognitive decline and amyloid pathology. Brain tissue datasets (GSE33000 for AD; GSE135838 for sepsis) were analyzed via Weighted Gene Co-expression Network Analysis (WGCNA), machine learning, and functional enrichment. Key genes were validated through ROC analysis, immune infiltration profiling, and in vivo/in vitro experiments.

RESULTS

Sepsis accelerated cognitive decline and AD-like pathology in mice. Bioinformatics identified CLIC1 and IFITM2 as co-diagnostic genes linked to immune dysregulation in both sepsis and AD. Immune infiltration revealed reduced neutrophils/NK cells, M1 macrophage polarization, and naïve-to-memory B cell shifts in sepsis versus AD. CLIC1 and IFITM2 were upregulated in CLP mice and cytokine-stimulated human cerebral endothelial cells, aligning with bioinformatics predictions.

CONCLUSION

CLIC1 and IFITM2, pivotal in immune cell activation, emerged as shared biomarkers of sepsis-related cognitive impairment and AD. These findings highlight immune-driven molecular intersections in cognitive deficits, offering novel targets for mechanistic research and therapeutic development.

CLICs Inhibitor IAA94 Alleviates Inflammation and Injury in Septic Liver by Preventing Pyroptosis in Macrophages

Macrophage pyroptosis represents a pivotal mechanism underlying acute liver injury during sepsis. Chloride intracellular channel proteins (CLICs) have been linked to inflammatory reflexes, with IAA94 serving as an inhibitor of channel formation characteristic of CLICs. In a mouse model, IAA94 demonstrated efficacy in reducing pro-inflammatory cytokines in liver tissues, decreasing macrophage in the liver, inhibiting the development of the pro-fibrosis phenotype, and alleviating tissue injury. Additionally, IAA94 exhibited inhibitory effects on the activation of NLRP3 inflammasome, leading to the suppression of pyroptosis in J774A.1 cells and the liver. Additionally, IAA94 was observed to impede the interaction between NEK7 and NLRP3. Furthermore, it was observed that the conditioned medium of pyroptotic macrophages treated with IAA94 induced an attenuated inflammatory response in hepatocytes in comparison to that induced by the conditioned medium of pyroptotic macrophages. However, NLRP3 overexpression impeded the beneficial effects of IAA94. In conclusion, IAA94 has the capacity to impede NLRP3 inflammasome formation-mediated pyroptosis by blocking CLICs-mediated chloride efflux and the inhibition of NEK7-NLRP3 interactions, thereby establishing CLICs as a promising therapeutic target against liver inflammation.

Chloride intracellular channel (CLIC) protein function in S1P-induced Rac1 activation requires membrane localization of the C-terminus, but not thiol-transferase nor ion channel activities

We have established a novel and evolutionarily-conserved function for chloride intracellular channel proteins (CLICs) in regulating Rho/Rac GTPases downstream of G protein-coupled receptors (GPCRs). Endothelial CLIC1 and CLIC4 are rapidly and transiently re-localized from the cytoplasm to the plasma membrane in response to the GPCR ligand sphingosine-1-phosphate (S1P), and both CLICs are required to activate Rac1 in response to S1P, but how they perform this function remains unknown. Biochemical studies suggest that CLICs act as non-specific ion channels and/or as glutathione-S-transferases, dependent on N-terminal features, in vitro. Here we investigate CLIC functional domains and membrane localization requirements for their function in S1P-mediated Rac1 signaling. Structure-function analyses of CLIC function in endothelial cells demonstrate that CLIC1 and CLIC4-specific functions reside at their C-termini, and that the CLIC4 N-terminus encodes determinants required for S1P-induced re-localization to the plasma membrane but is dispensable for S1P-induced Rac1 activation when the C-terminus is localized to the plasma membrane via a heterologous signal. Our results demonstrate that the postulated ion channel and thiol-transferase activities of CLICs are not required for Rac1 activation and suggests that sequences in the CLIC C-termini are critical for this function. Given the importance of S1P signaling in vascular biology and disease, our work establishes a platform to further our understanding of the membrane-localized proteins required to link GPCR activity to Rho/Rac regulation.

Circular RNA APP contributes to Alzheimer's disease pathogenesis by modulating microglial polarization via miR-1906/CLIC1 axis

BACKGROUND

Abnormal microglial polarization phenotypes contribute to the pathogenesis of Alzheimer's disease (AD). Circular RNAs (circRNAs) have garnered increasing attention due to their significant roles in human diseases. Although research has demonstrated differential expression of circRNAs in AD, their specific functions in AD pathogenesis remain largely unexplored.

METHODS

CircRNA microarray was performed to identify differentially expressed circRNAs in the hippocampus of APP/PS1 and WT mice. The stability of circAPP was assessed via RNase R treatment assay. CircAPP downstream targets miR-1906 and chloride intracellular channel 1 (CLIC1) were identified using bioinformatics and proteomics, respectively. RT-PCR assay was conducted to detect the expression of circAPP, miR-1906 and CLIC1. Morris water maze (MWM) test, passive avoidance test and novel object recognition task were used to detect cognitive function of APP/PS1 mice. Microglial M1/M2 polarization and AD pathology were assessed using Western blot, flow cytometry and Golgi staining assays. CLIC1 expression and channel activity were evaluated using Western blot and functional chloride channel assays, respectively. The subcellular location of circAPP was assessed via FISH and RT-PCR assays. RNA pull-down assay was performed to detect the interaction of miR-1906 with circAPP and 3' untranslated region (3'UTR) of CLIC1 mRNA.

RESULTS

In this study, we identified a novel circRNA, named circAPP, that is encoded by amyloid precursor protein (APP) and is implicated in AD. CircAPP is a stable circRNA that was upregulated in Aβ-treated microglial cells and the hippocampus of APP/PS1 mice. Downregulation of circAPP or CLIC1, or overexpression of miR-1906 in microglia modulated microglial M1/M2 polarization in Aβ-treated microglial cells and the hippocampus of APP/PS1 mice, and improved AD pathology and the cognitive function of APP/PS1 mice. Further results revealed that circAPP was mainly distributed in the cytoplasm, and circAPP could regulate CLIC1 expression and channel activity by interacting with miR-1906 and affecting miR-1906 expression, thereby regulating microglial polarization in AD.

CONCLUSIONS

Taken together, our study elucidates the regulatory role of circAPP in AD microglial polarization via miR-1906/CLIC1 axis, and suggests that circAPP may act as a critical player in AD pathogenesis and represent a promising therapeutic target for AD.

Chloride intracellular channel (CLIC) protein function in S1P-induced Rac1 activation requires membrane localization of the C-terminus, but not thiol-transferase nor ion channel activities

We have established a novel and evolutionarily-conserved function for chloride intracellular channel proteins (CLICs) in regulating Rho/Rac GTPases downstream of G protein-coupled receptors (GPCRs). Endothelial CLIC1 and CLIC4 are rapidly and transiently re-localized from the cytoplasm to the plasma membrane in response to the GPCR ligand sphingosine-1-phosphate (S1P), and both CLICs are required to activate Rac1 in response to S1P, but how they perform this function remains unknown. Biochemical studies suggest that CLICs act as non-specific ion channels and/or as glutathione-S-transferases, dependent on N-terminal features, in vitro. Here we investigate CLIC functional domains and membrane localization requirements for their function in S1P-mediated Rac1 signaling. Structure-function analyses of CLIC function in endothelial cells demonstrate that CLIC1 and CLIC4-specific functions reside at their C-termini, and that the CLIC4 N-terminus encodes determinants required for S1P-induced re-localization to the plasma membrane but is dispensable for S1P-induced Rac1 activation when the C-terminus is localized to the plasma membrane via a heterologous signal. Our results demonstrate that the postulated ion channel and thiol-transferase activities of CLICs are not required for Rac1 activation and suggests that sequences in the CLIC C-termini are critical for this function. Given the importance of S1P signaling in vascular biology and disease, our work establishes a platform to further our understanding of the membrane-localized proteins required to link GPCR activity to Rho/Rac regulation.

Physiology of neuroglia of the central nervous system

Neuroglia of the central nervous system (CNS) are a diverse and highly heterogeneous population of cells of ectodermal, neuroepithelial origin (macroglia, that includes astroglia and oligodendroglia) and mesodermal, myeloid origin (microglia). Neuroglia are primary homeostatic cells of the CNS, responsible for the support, defense, and protection of the nervous tissue. The extended class of astroglia (which includes numerous parenchymal astrocytes, such as protoplasmic, fibrous, velate, marginal, etc., radial astrocytes such as Bergmann glia, Muller glia, etc., and ependymoglia lining the walls of brain ventricles and central canal of the spinal cord) is primarily responsible for overall homeostasis of the nervous tissue. Astroglial cells control homeostasis of ions, neurotransmitters, hormones, metabolites, and are responsible for neuroprotection and defense of the CNS. Oligodendroglia provide for myelination of axons, hence supporting and sustaining CNS connectome. Microglia are tissue macrophages adapted to the CNS environment which contribute to the host of physiologic functions including regulation of synaptic connectivity through synaptic pruning, regulation of neurogenesis, and even modifying neuronal excitability. Neuroglial cells express numerous receptors, transporters, and channels that allow neuroglia to perceive and follow neuronal activity. Activation of these receptors triggers intracellular ionic signals that govern various homeostatic cascades underlying glial supportive and defensive capabilities. Ionic signaling therefore represents the substrate of glial excitability.

Advancements in Targeting Ion Channels for the Treatment of Neurodegenerative Diseases

Ion channels are integral membrane proteins embedded in biological membranes, and they comprise specific proteins that control the flow of ion transporters in and out of cells, playing crucial roles in the biological functions of different cells. They maintain the homeostasis of water and ion metabolism by facilitating ion transport and participate in the physiological processes of neurons and glial cells by regulating signaling pathways. Neurodegenerative diseases are a group of disorders characterized by the progressive loss of neurons in the central nervous system (CNS) or peripheral nervous system (PNS). Despite significant progress in understanding the pathophysiological processes of various neurological diseases in recent years, effective treatments for mitigating the damage caused by these diseases remain inadequate. Increasing evidence suggests that ion channels are closely associated with neuroinflammation; oxidative stress; and the characteristic proteins in neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Therefore, studying the pathogenic mechanisms closely related to ion channels in neurodegenerative diseases can help identify more effective therapeutic targets for treating neurodegenerative diseases. Here, we discuss the progress of research on ion channels in different neurodegenerative diseases and emphasize the feasibility and potential of treating such diseases from the perspective of ion channels.

Identification of an ionic mechanism for ERα-mediated rapid excitation in neurons

The major female ovarian hormone, 17β-estradiol (E2), can alter neuronal excitability within milliseconds to regulate a variety of physiological processes. Estrogen receptor-α (ERα), classically known as a nuclear receptor, exists as a membrane-bound receptor to mediate this rapid action of E2, but the ionic mechanisms remain unclear. Here, we show that a membrane channel protein, chloride intracellular channel protein-1 (Clic1), can physically interact with ERα with a preference to the membrane-bound ERα. Clic1-mediated currents can be enhanced by E2 and reduced by its depletion. In addition, Clic1 currents are required to mediate the E2-induced rapid excitations in multiple brain ERα populations. Further, genetic disruption of Clic1 in hypothalamic ERα neurons blunts the regulations of E2 on female body weight balance. In conclusion, we identified the Clic1 chloride channel as a key mediator for E2-induced rapid neuronal excitation, which may have a broad impact on multiple neurobiological processes regulated by E2.

Identification of immune infiltration and PANoptosis-related molecular clusters and predictive model in Alzheimer's disease based on transcriptome analysis

This study aims to explore the expression profile of PANoptosis-related genes (PRGs) and immune infiltration in Alzheimer's disease (AD). Based on the Gene Expression Omnibus database, this study investigated the differentially expressed PRGs and immune cell infiltration in AD and explored related molecular clusters. Gene set variation analysis (GSVA) was used to analyze the expression of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes in different clusters. Weighted gene co-expression network analysis was utilized to find co-expressed gene modules and core genes in the network. By analyzing the intersection genes in random forest, support vector machine, generalized linear model, and extreme gradient boosting (XGB), the XGB model was determined. Eventually, the first five genes (Signal Transducer and Activator of Transcription 3, Tumor Necrosis Factor (TNF) Receptor Superfamily Member 1B, Interleukin 4 Receptor, Chloride Intracellular Channel 1, TNF Receptor Superfamily Member 10B) in XGB model were selected as predictive genes. This research explored the relationship between PANoptosis and AD and established an XGB learning model to evaluate and screen key genes. At the same time, immune infiltration analysis showed that there were different immune infiltration expression profiles in AD.

Chloride ions in health and disease

Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in differential regulation of cellular functions such as transcription and translation, post-translation modifications, cell cycle and proliferation, cell volume, and pH levels. In intracellular compartments, Cl- modulates the function of lysosomes, mitochondria, endosomes, phagosomes, the nucleus, and the endoplasmic reticulum. In extracellular fluid (ECF), Cl- is present in blood/plasma and interstitial fluid compartments. A reduction in Cl- levels in ECF can result in cell volume contraction. Cl- is the key physiological anion and is a principal compensatory ion for the movement of the major cations such as Na+, K+, and Ca2+. Over the past 25 years, we have increased our understanding of cellular signaling mediated by Cl-, which has helped in understanding the molecular and metabolic changes observed in pathologies with altered Cl- levels. Here, we review the concentration of Cl- in various organs and cellular compartments, ion channels responsible for its transportation, and recent information on its physiological roles.

Integrins as the pivotal regulators of cisplatin response in tumor cells

Cisplatin (CDDP) is a widely used first-line chemotherapeutic drug in various cancers. However, CDDP resistance is frequently observed in cancer patients. Therefore, it is required to evaluate the molecular mechanisms associated with CDDP resistance to improve prognosis among cancer patients. Integrins are critical factors involved in tumor metastasis that regulate cell-matrix and cell-cell interactions. They modulate several cellular mechanisms including proliferation, invasion, angiogenesis, polarity, and chemo resistance. Modification of integrin expression levels can be associated with both tumor progression and inhibition. Integrins are also involved in drug resistance of various solid tumors through modulation of the tumor cell interactions with interstitial matrix and extracellular matrix (ECM). Therefore, in the present review we discussed the role of integrin protein family in regulation of CDDP response in tumor cells. It has been reported that integrins mainly promoted the CDDP resistance through interaction with PI3K/AKT, MAPK, and WNT signaling pathways. They also regulated the CDDP mediated apoptosis in tumor cells. This review paves the way to suggest the integrins as the reliable therapeutic targets to improve CDDP response in tumor cells.

Chloride intracellular channel (CLIC) proteins function as fusogens

Chloride Intracellular Channel (CLIC) family members uniquely transition between soluble and membrane-associated conformations. Despite decades of extensive functional and structural studies, CLICs' function as ion channels remains debated, rendering our understanding of their physiological role incomplete. Here, we expose the function of CLIC5 as a fusogen. We demonstrate that purified CLIC5 directly interacts with the membrane and induces fusion, as reflected by increased liposomal diameter and lipid and content mixing between liposomes. Moreover, we show that this activity is facilitated by acidic pH, a known trigger for CLICs' transition to a membrane-associated conformation, and that increased exposure of the hydrophobic inter-domain interface is crucial for this process. Finally, mutation of a conserved hydrophobic interfacial residue diminishes the fusogenic activity of CLIC5 in vitro and impairs excretory canal extension in C. elegans in vivo. Together, our results unravel the long-sought physiological role of these enigmatic proteins.

The Cl- transporter ClC-7 is essential for phagocytic clearance by microglia

Microglia, professional phagocytic cells of the brain, rely upon the appropriate activation of lysosomes to execute their immune and clearance functions. Lysosomal activity is, in turn, modulated by a complex network of over 200 membrane and accessory proteins that relay extracellular cues to these key degradation centers. The ClC-7 chloride (Cl-)-proton (H+) antiporter (also known as CLCN7) is localized to the endolysosomal compartments and mutations in CLCN7 lead to osteopetrosis and neurodegeneration. Although the functions of ClC-7 have been extensively investigated in osteoclasts and neurons, its role in microglia in vivo remains largely unexamined. Here, we show that microglia and embryonic macrophages in zebrafish clcn7 mutants cannot effectively process extracellular debris in the form of apoptotic cells and β-amyloid. Despite these functional defects, microglia develop normally in clcn7 mutants and display normal expression of endosomal and lysosomal markers. We also find that mutants for ostm1, which encodes the β-subunit of ClC-7, have a phenotype that is strikingly similar to that of clcn7 mutants. Together, our observations uncover a previously unappreciated role of ClC-7 in microglia and contribute to the understanding of the neurodegenerative phenotypes that accompany mutations in this channel.

Reducing branched-chain amino acids improves cardiac stress response in mice by decreasing histone H3K23 propionylation

Identification of branched-chain amino acid (BCAA) oxidation enzymes in the nucleus led us to predict that they are a source of the propionyl-CoA that is utilized for histone propionylation and, thereby, regulate gene expression. To investigate the effects of BCAAs on the development of cardiac hypertrophy and failure, we applied pressure overload on the heart in mice maintained on a diet with standard levels of BCAAs (BCAA control) versus a BCAA-free diet. The former was associated with an increase in histone H3K23-propionyl (H3K23Pr) at the promoters of upregulated genes (e.g., cell signaling and extracellular matrix genes) and a decrease at the promoters of downregulated genes (e.g., electron transfer complex [ETC I-V] and metabolic genes). Intriguingly, the BCAA-free diet tempered the increases in promoter H3K23Pr, thus reducing collagen gene expression and fibrosis during cardiac hypertrophy. Conversely, the BCAA-free diet inhibited the reductions in promoter H3K23Pr and abolished the downregulation of ETC I-V subunits, enhanced mitochondrial respiration, and curbed the progression of cardiac hypertrophy. Thus, lowering the intake of BCAAs reduced pressure overload-induced changes in histone propionylation-dependent gene expression in the heart, which retarded the development of cardiomyopathy.

Biophysical characterization of chloride intracellular channel 6 (CLIC6)

Chloride intracellular channels (CLICs) are a family of proteins that exist in soluble and transmembrane forms. The newest discovered member of the family CLIC6 is implicated in breast, ovarian, lung gastric, and pancreatic cancers and is also known to interact with dopamine-(D(2)-like) receptors. The soluble structure of the channel has been resolved, but the exact physiological role of CLIC6, biophysical characterization, and the membrane structure remain unknown. Here, we aimed to characterize the biophysical properties of this channel using a patch-clamp approach. To determine the biophysical properties of CLIC6, we expressed CLIC6 in HEK-293 cells. On ectopic expression, CLIC6 localizes to the plasma membrane of HEK-293 cells. We established the biophysical properties of CLIC6 by using electrophysiological approaches. Using various anions and potassium (K+) solutions, we determined that CLIC6 is more permeable to chloride-(Cl-) as compared to bromide-(Br-), fluoride-(F-), and K+ ions. In the whole-cell configuration, the CLIC6 currents were inhibited after the addition of 10 μM of IAA-94 (CLIC-specific blocker). CLIC6 was also found to be regulated by pH and redox potential. We demonstrate that the histidine residue at 648 (H648) in the C terminus and cysteine residue in the N terminus (C487) are directly involved in the pH-induced conformational change and redox regulation of CLIC6, respectively. Using qRT-PCR, we identified that CLIC6 is most abundant in the lung and brain, and we recorded the CLIC6 current in mouse lung epithelial cells. Overall, we have determined the biophysical properties of CLIC6 and established it as a Cl- channel.

Targeting Clic1 for the treatment of obesity: A novel therapeutic strategy to reduce food intake and body weight

OBJECTIVE

Despite great advances in obesity therapeutics in recent years, there is still a need to identify additional therapeutic targets for the treatment of this disease. We previously discovered a signature of genes, including Chloride intracellular channel 1 (Clic1), whose expression was associated with drug-induced weight gain, and in these studies, we assess the effect of Clic1 inhibition on food intake and body weight in mice.

METHODS

We studied the impact of Clic1 inhibition in mouse models of binge-eating, diet-induced obese mice and genetic models of obesity (Magel2 KO mice).

RESULTS

Clic1 knockout (KO) mice ate significantly less and had a lower body weight than WT littermates when either fed chow or high fat diet. Furthermore, pharmacological inhibition of Clic1 in diet-induced obese mice resulted in suppression of food intake and promoted highly efficacious weight loss. Clic1 inhibition also reduced food intake in binge-eating models and hyperphagic Magel2 KO mice. We observed that chronic obesity resulted in a significant change in subcellular localization of Clic1 with an increased ratio of Clic1 in the membrane in the obese state. These observations provide a novel therapeutic strategy to block Clic1 translocation as a potential mechanism to reduce food intake and lower body weight.

CONCLUSIONS

These studies attribute a novel role of Clic1 as a driver of food intake and overconsumption. In summary, we have identified hypothalamic expression of Clic1 plays a key role in food intake, providing a novel therapeutic target to treat overconsumption that is the root cause of modern obesity.

Immunological characterization and diagnostic models of RNA N6-methyladenosine regulators in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, and it displays both clinical and molecular variability. RNA N6-methyladenosine (m6A) regulators are involved in a wide range of essential cellular processes. In this study, we aimed to identify molecular signatures associated with m6A in Alzheimer's disease and use those signatures to develop a predictive model. We examined the expression patterns of m6A regulators and immune features in Alzheimer's disease using the GSE33000 dataset. We examined the immune cell infiltration and molecular groups based on m6A-related genes in 310 Alzheimer's disease samples. The WGCNA algorithm was utilized to determine differently expressed genes within each cluster. After evaluating the strengths and weaknesses of the random forest model, the support vector machine model, the generalized linear model, and eXtreme Gradient Boosting, the best machine model was selected. Methods such as nomograms, calibration curves, judgment curve analysis, and the use of independent data sets were used to verify the accuracy of the predictions made. Alzheimer's disease and non-disease Alzheimer's groups were compared to identify dysregulated m6A-related genes and activated immune responses. In Alzheimer's disease, two molecular clusters linked to m6A were identified. Immune infiltration analysis indicated substantial variation in protection between groups. Cluster 1 included processes like the Toll-like receptor signaling cascade, positive regulation of chromatin binding, and numerous malignancies; cluster 2 included processes like the cell cycle, mRNA transport, and ubiquitin-mediated proteolysis. With a lower residual and root mean square error and a larger area under the curve (AUC = 0.951), the Random forest machine model showed the greatest discriminative performance. The resulting random forest model was based on five genes, and it performed well (AUC = 0.894) on external validation datasets. Accuracy in predicting Alzheimer's disease subgroups was also shown by analyses of nomograms, calibration curves, and decision curves. In this research, we methodically outlined the tangled web of connections between m6A and AD and created a promising prediction model for gauging the correlation between m6A subtype risk and AD pathology.

Intracellular chloride channel 1 and tumor

As the major intracellular anion, chloride plays an important role in maintaining intracellular and extracellular ion homeostasis, osmotic pressure, and cell volume. Intracellular chloride channel 1, which has the physiological role of forming membrane proteins in the lipid bilayer and playing ion channels, is a hot research topic in recent years. It has been found that CLIC1 does not only act as an ion channel but also participates in cell cycle regulation, apoptosis, and intracellular oxidation; thus, it participates in the proliferation, invasion, and migration of various tumor cells in various systems throughout the body. At the same time, CLIC1 is highly expressed in tumor cells and is associated with malignancy and a poor prognosis. This paper reviews the pathological mechanisms of CLIC1 in systemic diseases, which is important for the early diagnosis, treatment, and prognosis of systemic diseases associated with CLIC1 expression.

Plant dehydroascorbate reductase moonlights as membrane integrated ion channel

Plant dehydroascorbate reductases (DHARs) are only known as soluble antioxidant enzymes of the ascorbate-glutathione pathway. They recycle ascorbate from dehydroascorbate, thereby protecting plants from oxidative stress and the resulting cellular damage. DHARs share structural GST fold with human chloride intracellular channels (HsCLICs) which are dimorphic proteins that exists in soluble enzymatic and membrane integrated ion channel forms. While the soluble form of DHAR has been extensively studied, the existence of a membrane integrated form remains unknown. We demonstrate for the first time using biochemistry, immunofluorescence confocal microscopy, and bilayer electrophysiology that Pennisetum glaucum DHAR (PgDHAR) is dimorphic and is localized to the plant plasma membrane. In addition, membrane translocation increases under induced oxidative stress. Similarly, HsCLIC1 translocates more into peripheral blood mononuclear cells (PBMCs) plasma membrane under induced oxidative stress conditions. Moreover, purified soluble PgDHAR spontaneously inserts and conducts ions in reconstituted lipid bilayers, and the addition of detergent facilitates insertion. In addition to the well-known soluble enzymatic form, our data provides conclusive evidence that plant DHAR also exists in a novel membrane-integrated form. Thus, the structure of DHAR ion channel form will help gain deeper insights into its function across various life forms.

Rab11A Depletion in Microglia-Derived Extracellular Vesicle Proteome upon Beta-Amyloid Treatment

Microglia, the macrophage-like glial cells, behave as sentinels against exogenous pathogens invading the neural tissue. Their commitment is not only confined to the defensive function, but they also perform balancing trophic activities such as neuronal postnatal development, remodeling and pruning of synapses. Likewise, microglia-derived extracellular vesicles (EVs) can play strategic roles in maintaining a healthy brain by modulating neuronal activity and by controlling neurite outgrowth as well as innate immune response. Nevertheless, strong evidence also points to their role in the development of neurodegenerative pathologies such as Alzheimer's disease (AD). Here, we explored EV protein content released by BV2 microglial cells in a resting state and after stimulation with beta-amyloid peptides (Aβ), mimicking conditions occurring in AD. In the resting BV2 cells, we extended the list of proteins present in mouse microglia EV cargo with respect to those reported in the Vesiclepedia exosome database while, in amyloid-triggered microglia, we highlighted a pronounced drop in EV protein content. Focusing on Rab11A, a key factor in the recycling routes of amyloid species, we observed a dramatic decrease of this protein in Aβ-treated microglia EV cargo with respect to the EVs from the untreated sample. This decrease might affect the delivery of Rab11A to neurons thus increasing the harmful amyloid burden in neuronal cells that eventually may lead to their death. We tentatively proposed that alterations observed in EVs derived from Aβ-treated microglia may represent molecular features that, among others, shape the disease-associated microglial phenotype, a recently proposed subset of microglial population, present in neurodegenerative pathologies.

Sterol Structural Features' Impact on the Spontaneous Membrane Insertion of CLIC1 into Artificial Lipid Membranes

Background: A membrane protein interaction with lipids shows distinct specificity in terms of the sterol structure. The structure of the sterol's polar headgroup, steroidal rings, and aliphatic side chains have all been shown to influence protein membrane interactions, including the initial binding and subsequent oligomerization to form functional channels. Previous studies have provided some insights into the regulatory role that cholesterol plays in the spontaneous membrane insertion of the chloride intracellular ion channel protein, CLIC1. However, the manner in which cholesterol interacts with CLIC1 is yet largely unknown. Method: In this study, the CLIC1 interaction with different lipid:sterol monolayers was studied using the Langmuir trough and neutron reflectometry in order to investigate the structural features of cholesterol essential for the spontaneous membrane insertion of the CLIC1 protein. Molecular docking simulations were also performed to study the binding affinities between CLIC1 and the different sterol molecules. Results: This study, for the first time, highlights the vital role of the free sterol 3β-OH group as an essential structural requirement for the interaction of CLIC1 with cholesterol. Furthermore, the presence of additional hydroxyl groups, methylation of the sterol skeleton, and the structure of the sterol alkyl side chain have also been shown to modulate the magnitude of CLIC1 interaction with sterols and hence their spontaneous membrane insertion. This study also reports the ability of CLIC1 to interact with other naturally existing sterol molecules. General Significance: Like the sterol molecules, CLIC proteins are evolutionarily conserved with almost all vertebrates expressing six CLIC proteins (CLIC1-6), and CLIC-like proteins are also present in invertebrates and have also been reported in plants. This discovery of CLIC1 protein interaction with other natural sterols and the sterol structural requirements for CLIC membrane insertion provide key information to explore the feasibility of exploiting these properties for therapeutic and prophylactic purposes.

Pharmacological modulation of chloride channels as a therapeutic strategy for neurological disorders

Chloride homeostasis is critical in the physiological functions of the central nervous system (CNS). Its concentration is precisely regulated by multiple ion-transporting proteins such as chloride channels and transporters that are widely distributed in the brain cells, including neurons and glia. Unlike ion transporters, chloride channels provide rapid responses to efficiently regulate ion flux. Some of chloride channels are also permeable to selected organic anions such as glutamate and γ-aminobutyric acid, suggesting neuroexcitatory and neuroinhibitory functions while gating. Dysregulated chloride channels are implicated in neurological disorders, e.g., ischemia and neuroinflammation. Modulation of chloride homeostasis through chloride channels has been suggested as a potential therapeutic approach for neurological disorders. The drug design for CNS diseases is challenging because it requires the therapeutics to traverse the blood-brain-barrier. Small molecules are a well-established modality with better cell permeability due to their lower molecular weight and flexibility for structure optimization compared to biologics. In this article, we describe the important roles of chloride homeostasis in each type of brain cells and introduce selected chloride channels identified in the CNS. We then discuss the contribution of their dysregulations towards the pathogenesis of neurological disorders, emphasizing the potential of targeting chloride channels as a therapeutic strategy for CNS disease treatment. Along with this literature survey, we summarize the small molecules that modulate chloride channels and propose the potential strategy of optimizing existing drugs to brain-penetrants to support future CNS drug discovery.

Chloride Intracellular Channel Protein 2 Promotes Microglial Invasion: A Link to Microgliosis in the Parkinson's Disease Brain

Activated microglia potentially cause neurodegeneration in Parkinson's disease (PD). Matrix metalloproteinase (MMP)-9 plays a crucial role in the pathogenesis of PD, but the modulator of microglial release of MMP-9 remains obscure. Given the modulatory effect of chloride intracellular channel protein 2 (CLIC2) on MMPs, we aimed to determine the role of CLIC2 in regulating microglial MMP expression and activation. We found that CLIC2 is expressed in microglia and neurons in rat brain tissue and focused on the function of CLIC2 in primary cultured microglia. Exposure to recombinant CLIC2 protein enhanced microglial invasion activity, and its knockdown abolished this activity. Moreover, increased activation of MMP-9 was confirmed by the addition of the CLIC2 protein, and CLIC2 knockdown eliminated this activation. Additionally, increased expression of CLIC2 was observed in PD-modeled tissue. In conclusion, CLIC2 increases MMP-9 activity in the microglia, which are involved in PD pathogenesis.

The amyloid plaque proteome in early onset Alzheimer's disease and Down syndrome

Amyloid plaques contain many proteins in addition to beta amyloid (Aβ). Previous studies examining plaque-associated proteins have shown these additional proteins are important; they provide insight into the factors that drive amyloid plaque development and are potential biomarkers or therapeutic targets for Alzheimer's disease (AD). The aim of this study was to comprehensively identify proteins that are enriched in amyloid plaques using unbiased proteomics in two subtypes of early onset AD: sporadic early onset AD (EOAD) and Down Syndrome (DS) with AD. We focused our study on early onset AD as the drivers of the more aggressive pathology development in these cases is unknown and it is unclear whether amyloid-plaque enriched proteins differ between subtypes of early onset AD. Amyloid plaques and neighbouring non-plaque tissue were microdissected from human brain sections using laser capture microdissection and label-free LC-MS was used to quantify the proteins present. 48 proteins were consistently enriched in amyloid plaques in EOAD and DS. Many of these proteins were more significantly enriched in amyloid plaques than Aβ. The most enriched proteins in amyloid plaques in both EOAD and DS were: COL25A1, SMOC1, MDK, NTN1, OLFML3 and HTRA1. Endosomal/lysosomal proteins were particularly highly enriched in amyloid plaques. Fluorescent immunohistochemistry was used to validate the enrichment of four proteins in amyloid plaques (moesin, ezrin, ARL8B and SMOC1) and to compare the amount of total Aβ, Aβ40, Aβ42, phosphorylated Aβ, pyroglutamate Aβ species and oligomeric species in EOAD and DS. These studies showed that phosphorylated Aβ, pyroglutamate Aβ species and SMOC1 were significantly higher in DS plaques, while oligomers were significantly higher in EOAD. Overall, we observed that amyloid plaques in EOAD and DS largely contained the same proteins, however the amount of enrichment of some proteins was different in EOAD and DS. Our study highlights the significant enrichment of many proteins in amyloid plaques, many of which may be potential therapeutic targets and/or biomarkers for AD.

Transmembrane Chloride Intracellular Channel 1 (tmCLIC1) as a Potential Biomarker for Personalized Medicine

Identification of potential pathological biomarkers has proved to be essential for understanding complex and fatal diseases, such as cancer and neurodegenerative diseases. Ion channels are involved in the maintenance of cellular homeostasis. Moreover, loss of function and aberrant expression of ion channels and transporters have been linked to various cancers, and to neurodegeneration. The Chloride Intracellular Channel 1 (CLIC1), CLIC1 is a metamorphic protein belonging to a partially unexplored protein superfamily, the CLICs. In homeostatic conditions, CLIC1 protein is expressed in cells as a cytosolic monomer. In pathological states, CLIC1 is specifically expressed as transmembrane chloride channel. In the following review, we trace the involvement of CLIC1 protein functions in physiological and in pathological conditions and assess its functionally active isoform as a potential target for future therapeutic strategies.

Mutant Presenilin 1 Dysregulates Exosomal Proteome Cargo Produced by Human-Induced Pluripotent Stem Cell Neurons

The accumulation and propagation of hyperphosphorylated tau (p-Tau) is a neuropathological hallmark occurring with neurodegeneration of Alzheimer's disease (AD). Extracellular vesicles, exosomes, have been shown to initiate tau propagation in the brain. Notably, exosomes from human-induced pluripotent stem cell (iPSC) neurons expressing the AD familial A246E mutant form of presenilin 1 (mPS1) are capable of inducing tau deposits in the mouse brain after in vivo injection. To gain insights into the exosome proteome cargo that participates in propagating tau pathology, this study conducted proteomic analysis of exosomes produced by human iPSC neurons expressing A246E mPS1. Significantly, mPS1 altered the profile of exosome cargo proteins to result in (1) proteins present only in mPS1 exosomes and not in controls, (2) the absence of proteins in the mPS1 exosomes which were present only in controls, and (3) shared proteins which were upregulated or downregulated in the mPS1 exosomes compared to controls. These results show that mPS1 dysregulates the proteome cargo of exosomes to result in the acquisition of proteins involved in the extracellular matrix and protease functions, deletion of proteins involved in RNA and protein translation systems along with proteasome and related functions, combined with the upregulation and downregulation of shared proteins, including the upregulation of amyloid precursor protein. Notably, mPS1 neuron-derived exosomes displayed altered profiles of protein phosphatases and kinases involved in regulating the status of p-tau. The dysregulation of exosome cargo proteins by mPS1 may be associated with the ability of mPS1 neuron-derived exosomes to propagate tau pathology.

Acetylation-stabilized chloride intracellular channel 1 exerts a tumor-promoting effect on cervical cancer cells by activating NF-κB

PURPOSE

Cervical cancer remains a major cause of cancer-related death in women, especially in developing countries. Previously, we found that the acetylation levels of chloride intracellular channel 1 (CLIC1) at lysine 131 were increased in cervical cancer tissues using a label-free proteomics approach. The aim of this study was to further determine the role of CLIC1 expression and its acetylation in cervical cancer.

METHODS

CLIC1 expression and its implications for the prognosis of cervical cancer were analyzed using primary patient samples and cells, and the Gene Expression Profiling Interactive Analysis (GEPIA) database (gepia.cancer-pku.cn). The effect of CLIC1 on cervical cancer cells was evaluated using Cell Counting Kit (CCK)-8, flow cytometry, scratch wound healing, transwell, Western blotting and co-immunoprecipitation (Co-IP) assays. In vivo tumor growth was assessed using mouse xenograft models.

RESULTS

We found that CLIC1 expression was increased in cervical cancer tissues and cells and that patients with a high CLIC1 expression tended to have a shorter overall survival time. Knockdown of CLIC1 significantly reduced in vitro cervical cancer cell proliferation, migration and invasion, and in vivo tumorigenesis. At the molecular level, we found that nuclear factor kappa B (NF-κB) activity was positively regulated by CLIC1. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB, attenuated the tumor-promoting effect of CLIC1. Moreover, we found that CLIC1 acetylation at K131 was upregulated in cervical cancer cells, which stabilized CLIC1 by inhibiting its ubiquitynation. Substitution of K131 inhibited CLIC1 ubiquitynation and promoted in vitro cervical cancer cell proliferation, migration and invasion, and in vivo tumor growth. In addition, we found that acetyltransferase HAT1 was responsible for CLIC1 acetylation at K131.

CONCLUSION

Our data indicate that CLIC1 acts as a tumor promoter in cervical cancer, suggesting a potential treatment strategy for cervical cancer by regulating CLIC1 expression and/or acetylation.

Chloride intracellular channel 1 cooperates with potassium channel EAG2 to promote medulloblastoma growth

Ion channels represent a large class of drug targets, but their role in brain cancer is underexplored. Here, we identify that chloride intracellular channel 1 (CLIC1) is overexpressed in human central nervous system malignancies, including medulloblastoma, a common pediatric brain cancer. While global knockout does not overtly affect mouse development, genetic deletion of CLIC1 suppresses medulloblastoma growth in xenograft and genetically engineered mouse models. Mechanistically, CLIC1 enriches to the plasma membrane during mitosis and cooperates with potassium channel EAG2 at lipid rafts to regulate cell volume homeostasis. CLIC1 deficiency is associated with elevation of cell/nuclear volume ratio, uncoupling between RNA biosynthesis and cell size increase, and activation of the p38 MAPK pathway that suppresses proliferation. Concurrent knockdown of CLIC1/EAG2 and their evolutionarily conserved channels synergistically suppressed the growth of human medulloblastoma cells and Drosophila melanogaster brain tumors, respectively. These findings establish CLIC1 as a molecular dependency in rapidly dividing medulloblastoma cells, provide insights into the mechanism by which CLIC1 regulates tumorigenesis, and reveal that targeting CLIC1 and its functionally cooperative potassium channel is a disease-intervention strategy.

Chloride intracellular channel 4 participate in the protective effect of Ginkgolide B in MPP+ injured MN9D cells: insight from proteomic analysis

Background

Ginkgolide B (GB), the extract of G. biloba leaves, has been shown to be protective against many neurological disorders, including Parkinson’s disease (PD). Efforts have been made to synthesized ginkgolides analogs and derivatives with more targeted and smaller molecular weight. In the present study, four GB derivatives (GBHC-1-GBHC-4) were synthesized, and their protective roles in N-methyl-4-phenylpyridinium (MPP +) injured MN9D dopaminergic neuronal cell line were evaluated. Also, cell response mechanisms upon these GB derivatives treatment were analyzed by iTRAQ proteomics.

Methods

MN9D cells were treated with MPP + to induce in vitro cell models of PD. Four GB derivatives (GBHC-1-GBHC-4) were synthesized, and their protective roles on cell viability and apoptosis in in vitro PD model cells were evaluated by CCK8 assay, fluorescence-activated cell sorting and DAPI staining, respectively. The proteomic profiles of MPP+ injured MN9D cells pretreated with or without GB and GB derivatives were detected using the isobaric tags for relative and absolute quantification (iTRAQ) labeling technique.

Results

Pretreatment with GBHC-1-GBHC-4 noticeably increased cell viability and attenuated cell apoptosis in MPP+ -injured MN9D cells. Using proteomic analysis, we identified differentially expressed proteins upon GB and GB derivatives treatment. Chloride intracellular channel 4 (CLIC4) and “protein processing in endoplasmic reticulum” pathways participated in the protective roles of GB and GBHC-4. GB and GBHC-4 pretreatment could significantly reverse MPP+ -induced CLIC4 expression and translocation from cytoplasm to nucleus of MN9D cells.

Conclusions

Quantitative comparative proteomic analysis identified differentially expressed proteins associated with GB and GB derivatives. We further verified the expression of CLIC4 by western blotting and immunocytochemistry assay. This bio-information on the identified pathways and differentially expressed proteins such as CLIC4 provide more targeted directions for the synthesis of more effective and targeted GB derivatives for the treatment of neurological disorders.

CLIC2α Chloride Channel Orchestrates Immunomodulation of Hemocyte Phagocytosis and Bactericidal Activity in Crassostrea gigas

Chloride ion plays critical roles in modulating immunological interactions. Herein, we demonstrated that the anion channel CLIC2α mediates Cl⁻ flux to regulate hemocytes functions in the Pacific oyster (Crassostrea gigas). Specifically, during infection by Vibrio parahemolyticus, chloride influx was activated following onset of phagocytosis. Phosphorylation of Akt was stimulated by Cl⁻ ions entering host cells, further contributing to signal transduction regulating internalization of bacteria through the PI3K/Akt signaling pathway. Concomitantly, Cl⁻ entered phagosomes, promoted the acidification and maturation of phagosomes, and contributed to production of HOCl to eradicate engulfed bacteria. Finally, genomic screening reveals CLIC2α as a major Cl⁻ channel gene responsible for regulating Cl⁻ influx in oysters. Knockdown of CLIC2α predictably impeded phagosome acidification and restricted bacterial killing in oysters. In conclusion, our work has established CLIC2α as a prominent regulator of Cl⁻ influx and thus Cl⁻ function in C. gigas in bacterial infection contexts.

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Influx of chloride ions is switched on during phagocytosis in oyster hemocytes

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PI3K/Akt signaling pathway mediates chloride-dependent activation of phagocytosis

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Cl⁻ promotes phagosomal acidification and HOCl production

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CLIC2α is the principal chloride channel encoding gene within oyster genome

Predicting Clinical Dementia Rating Using Blood RNA Levels

The Clinical Dementia Rating (CDR) is commonly used to assess cognitive decline in Alzheimer's disease patients and is included in the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. We divided 741 ADNI participants with blood microarray data into three groups based on their most recent CDR assessment: cognitive normal (CDR = 0), mild cognitive impairment (CDR = 0.5), and probable Alzheimer's disease (CDR ≥ 1.0). We then used machine learning to predict cognitive status using only blood RNA levels. Only one probe for chloride intracellular channel 1 (CLIC1) was significant after correction. However, by combining individually nonsignificant probes with p-values less than 0.1, we averaged 87.87% (s = 1.02) predictive accuracy for classifying the three groups, compared to a 55.46% baseline for this study due to unequal group sizes. The best model had an overall precision of 0.902, recall of 0.895, and a receiver operating characteristic (ROC) curve area of 0.904. Although we identified one significant probe in CLIC1, CLIC1 levels alone were not sufficient to predict dementia status and cannot be used alone in a clinical setting. Additional analyses combining individually suggestive, but nonsignificant, blood RNA levels were significantly predictive and may improve diagnostic accuracy for Alzheimer's disease. Therefore, we propose that patient features that do not individually predict cognitive status might still contribute to overall cognitive decline through interactions that can be elucidated through machine learning.

CLIC1 Protein Accumulates in Circulating Monocyte Membrane during Neurodegeneration

Pathologies that lead to neurodegeneration in the central nervous system (CNS) represent a major contemporary medical challenge. Neurodegenerative processes, like those that occur in Alzheimer’s disease (AD) are progressive, and at the moment, they are unstoppable. Not only is an adequate therapy missing but diagnosis is also extremely complicated. The most reliable method is the measurement of beta amyloid and tau peptides concentration in the cerebrospinal fluid (CSF). However, collecting liquid samples from the CNS is an invasive procedure, thus it is not suitable for a large-scale prevention program. Ideally, blood testing is the most manageable and appropriate diagnostic procedure for a massive population screening. Recently, a few candidates, including proteins or microRNAs present in plasma/serum have been identified. The aim of the present work is to propose the chloride intracellular channel 1 (CLIC1) protein as a potential marker of neurodegenerative processes. CLIC1 protein accumulates in peripheral blood mononuclear cells (PBMCs), and increases drastically when the CNS is in a chronic inflammatory state. In AD patients, both immunolocalization and mRNA quantification are able to show the behavior of CLIC1 during a persistent inflammatory state of the CNS. In particular, confocal microscopy analysis and electrophysiological measurements highlight the significant presence of transmembrane CLIC1 (tmCLIC1) in PBMCs from AD patients. Recent investigations suggest that tmCLIC1 has a very specific role. This provides an opportunity to use blood tests and conventional technologies to discriminate between healthy individuals and patients with ongoing neurodegenerative processes.

Intracellular Chloride Channels: Novel Biomarkers in Diseases

Ion channels are integral membrane proteins present on the plasma membrane as well as intracellular membranes. In the human genome, there are more than 400 known genes encoding ion channel proteins. Ion channels are known to regulate several cellular, organellar, and physiological processes. Any mutation or disruption in their function can result in pathological disorders, both common or rare. Ion channels present on the plasma membrane are widely acknowledged for their role in various biological processes, but in recent years, several studies have pointed out the importance of ion channels located in intracellular organelles. However, ion channels located in intracellular organelles are not well-understood in the context of physiological conditions, such as the generation of cellular excitability and ionic homeostasis. Due to the lack of information regarding their molecular identity and technical limitations of studying them, intracellular organelle ion channels have thus far been overlooked as potential therapeutic targets. In this review, we focus on a novel class of intracellular organelle ion channels, Chloride Intracellular Ion Channels (CLICs), mainly documented for their role in cardiovascular, neurophysiology, and tumor biology. CLICs have a single transmembrane domain, and in cells, they exist in cytosolic as well as membranous forms. They are predominantly present in intracellular organelles and have recently been shown to be localized to cardiomyocyte mitochondria as well as exosomes. In fact, a member of this family, CLIC5, is the first mitochondrial chloride channel to be identified on the molecular level in the inner mitochondrial membrane, while another member, CLIC4, is located predominantly in the outer mitochondrial membrane. In this review, we discuss this unique class of intracellular chloride channels, their role in pathologies, such as cardiovascular, cancer, and neurodegenerative diseases, and the recent developments concerning their usage as theraputic targets.

Longitudinal transcriptomic analysis of altered pathways in a CHMP2Bintron5-based model of ALS-FTD

Amyotrophic lateral sclerosis and frontotemporal dementia are two neurodegenerative diseases with currently no cure. These two diseases share a clinical continuum with overlapping genetic causes. Mutations in the CHMP2B gene are found in patients with ALS, FTD and ALS-FTD. To highlight deregulated mechanisms occurring in ALS-FTD linked to the CHMP2B gene, we performed a whole transcriptomic study on lumbar spinal cord from CHMP2B^intron5 mice, a model that develops progressive motor alterations associated with dementia symptoms reminiscent of both ALS and FTD. To gain insight into the transcriptomic changes taking place during disease progression this study was performed at three stages: asymptomatic, symptomatic and end stage. We showed that before appearance of motor symptoms, the major disrupted mechanisms were linked with the immune system/inflammatory response and lipid metabolism. These processes were progressively replaced by alterations of neuronal electric activity as motor symptoms appeared, alterations that could lead to motor neuron dysfunction. To investigate overlapping alterations in gene expression between two ALS-causing genes, we then compared the transcriptome of symptomatic CHMP2B^intron5 mice with the one of symptomatic SOD1^G86R mice and found the same families deregulated providing further insights into common underlying dysfunction of biological pathways, disrupted or disturbed in ALS. Altogether, this study provides a database to explore potential new candidate genes involved in the CHMP2B^intron5-based pathogenesis of ALS, and provides molecular clues to further understand the functional consequences that diseased neurons expressing CHMP2B mutant may have on their neighbor cells.

Repurposed Biguanide Drugs in Glioblastoma Exert Antiproliferative Effects via the Inhibition of Intracellular Chloride Channel 1 Activity

The lack of in-depth knowledge about the molecular determinants of glioblastoma (GBM) occurrence and progression, combined with few effective and BBB crossing-targeted compounds represents a major challenge for the discovery of novel and efficacious drugs for GBM. Among relevant molecular factors controlling the aggressive behavior of GBM, chloride intracellular channel 1 (CLIC1) represents an emerging prognostic and predictive biomarker, as well as a promising therapeutic target. CLIC1 is a metamorphic protein, co-existing as both soluble cytoplasmic and membrane-associated conformers, with the latter acting as chloride selective ion channel. CLIC1 is involved in several physiological cell functions and its abnormal expression triggers tumor development, favoring tumor cell proliferation, invasion, and metastasis. CLIC1 overexpression is associated with aggressive features of various human solid tumors, including GBM, in which its expression level is correlated with poor prognosis. Moreover, increasing evidence shows that modification of microglia ion channel activity, and CLIC1 in particular, contributes to the development of different neuropathological states and brain tumors. Intriguingly, CLIC1 is constitutively active within cancer stem cells (CSCs), while it seems less relevant for the survival of non-CSC GBM subpopulations and for normal cells. CSCs represent GBM development and progression driving force, being endowed with stem cell-like properties (self-renewal and differentiation), ability to survive therapies, to expand and differentiate, causing tumor recurrence. Downregulation of CLIC1 results in drastic inhibition of GBM CSC proliferation in vitro and in vivo, making the control of the activity this of channel a possible innovative pharmacological target. Recently, drugs belonging to the biguanide class (including metformin) were reported to selectively inhibit CLIC1 activity in CSCs, impairing their viability and invasiveness, but sparing normal stem cells, thus representing potential novel antitumor drugs with a safe toxicological profile. On these premises, we review the most recent insights into the biological role of CLIC1 as a potential selective pharmacological target in GBM. Moreover, we examine old and new drugs able to functionally target CLIC1 activity, discussing the challenges and potential development of CLIC1-targeted therapies.

CLIC1 promotes the progression of oral squamous cell carcinoma via integrins/ERK pathways

Chloride intracellular channel 1 (CLIC1), a member of the chloride channel protein family, acts as a promoter in many malignancies, but its role in oral cancer remains unclear. Hence, this research aimed to explore the effects of CLIC1 on the progression of oral cancer cells in vitro, and we assessed its role in cell proliferation, apoptosis, migration, invasion, angiogenesis, and chemosensitivity to cisplatin and possible signaling pathways. The results demonstrated that CLIC1 depletion inhibited the proliferation, invasion, migration and angiogenesis of oral squamous cell carcinoma (OSCC) cells in vitro, but promoted cell apoptosis and increased the drug susceptibility to cisplatin. In contrast, CLIC1 upregulation was positively correlated with cell proliferation, invasion and migration and angiogenesis. Mechanistically, CLIC1 silencing decreased the levels of ITGαv, ITGβ1, p-ERK, vimentin, MMP2 and MMP9, and increased the levels of p-p38, E-cadherin, caspase3 and caspase9. CLIC1 overexpression enhanced the ITGαv, ITGβ1, p-ERK, vimentin, MMP2 and MMP9 levels and decreased E-cadherin expression. Overall, these results indicated that CLIC1 promotes the progression of OSCC, and we speculated that its potential mechanism may be related to the regulation of ITGαv and ITGβ1, which led to activation of the MAPK/ERK and MAPK/p38 signal pathways.

Pharmacological modulation of mitochondrial ion channels

The field of mitochondrial ion channels has undergone a rapid development during the last three decades, due to the molecular identification of some of the channels residing in the outer and inner membranes. Relevant information about the function of these channels in physiological and pathological settings was gained thanks to genetic models for a few, mitochondria-specific channels. However, many ion channels have multiple localizations within the cell, hampering a clear-cut determination of their function by pharmacological means. The present review summarizes our current knowledge about the ins and outs of mitochondrial ion channels, with special focus on the channels that have received much attention in recent years, namely, the voltage-dependent anion channels, the permeability transition pore (also called mitochondrial megachannel), the mitochondrial calcium uniporter and some of the inner membrane-located potassium channels. In addition, possible strategies to overcome the difficulties of specifically targeting mitochondrial channels versus their counterparts active in other membranes are discussed, as well as the possibilities of modulating channel function by small peptides that compete for binding with protein interacting partners. Altogether, these promising tools along with large-scale chemical screenings set up to identify new, specific channel modulators will hopefully allow us to pinpoint the actual function of most mitochondrial ion channels in the near future and to pharmacologically affect important pathologies in which they are involved, such as neurodegeneration, ischaemic damage and cancer. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Pharmacodynamic and urinary metabolomics studies on the mechanism of Schisandra polysaccharide in the treatment of Alzheimer's disease

This study was designed to investigate the antagonism of SCP in Aβ25–35-induced AD rats by intervening in neurotransmitters and metabolites.

Calcium Signaling Deficits in Glia and Autophagic Pathways Contributing to Neurodegenerative Disease

SIGNIFICANCE

Numerous cellular processes and signaling mechanisms have been identified that contribute to Alzheimer's disease (AD) pathology; however, a comprehensive or unifying pathway that binds together the major disease features remains elusive. As an upstream mechanism, altered calcium (Ca²⁺) signaling is a common driving force for many pathophysiological events that emerge during normal aging and development of neurodegenerative disease. Recent Advances: Over the previous three decades, accumulated evidence has validated the concept that intracellular Ca²⁺ dysregulation is centrally involved in AD pathogenesis, including the aggregation of pathogenic β-amyloid (Aβ) and phospho-τ species, synapse loss and dysfunction, cognitive impairment, and neurotoxicity.

CRITICAL ISSUES

Although neuronal Ca²⁺ signaling within the cytosol and endoplasmic reticulum (ER) has been well studied, other critical central nervous system-resident cell types affected by aberrant Ca²⁺ signaling, such as astrocytes and microglia, have not been considered as thoroughly. In addition, certain intracellular Ca²⁺-harboring organelles have been well studied, such as the ER and mitochondria; however other critical Ca²⁺-regulated organelles, such as lysosomes and autophagosomes, have only more recently been investigated. In this review, we examine Ca²⁺ dysregulation in microglia and astrocytes, as well as key intracellular organelles important for cellular maintenance and protein handling. Ca²⁺ dysregulation within these non-neuronal cells and organelles is hypothesized to disrupt the effective clearance of misaggregated proteins and cellular signaling pathways needed for memory networks.

FUTURE DIRECTIONS

Overall, we aim to explore how these disrupted mechanisms could be involved in AD pathology and consider their role as potential therapeutic targets. Antioxid. Redox Signal. 29, 1158-1175.

Microglia in Alzheimer's Disease: A Role for Ion Channels

Alzheimer's disease is the most common form of dementia, it is estimated to affect over 40 million people worldwide. Classically, the disease has been characterized by the neuropathological hallmarks of aggregated extracellular amyloid-β and intracellular paired helical filaments of hyperphosphorylated tau. A wealth of evidence indicates a pivotal role for the innate immune system, such as microglia, and inflammation in the pathology of Alzheimer's disease. The over production and aggregation of Alzheimer's associated proteins results in chronic inflammation and disrupts microglial clearance of these depositions. Despite being non-excitable, microglia express a diverse array of ion channels which shape their physiological functions. In support of this, there is a growing body of evidence pointing to the involvement of microglial ion channels contributing to neurodegenerative diseases such as Alzheimer's disease. In this review, we discuss the evidence for an array of microglia ion channels and their importance in modulating microglial homeostasis and how this process could be disrupted in Alzheimer's disease. One promising avenue for assessing the role that microglia play in the initiation and progression of Alzheimer's disease is through using induced pluripotent stem cell derived microglia. Here, we examine what is already understood in terms of the molecular underpinnings of inflammation in Alzheimer's disease, and the utility that inducible pluripotent stem cell derived microglia may have to advance this knowledge. We outline the variability that occurs between the use of animal and human models with regards to the importance of microglial ion channels in generating a relevant functional model of brain inflammation. Overcoming these hurdles will be pivotal in order to develop new drug targets and progress our understanding of the pathological mechanisms involved in Alzheimer's disease.

Mutual Influence of ROS, pH, and CLIC1 Membrane Protein in the Regulation of G1-S Phase Progression in Human Glioblastoma Stem Cells

Glioblastoma (GB) is the most lethal, aggressive, and diffuse brain tumor. The main challenge for successful treatment is targeting the cancer stem cell (CSC) subpopulation responsible for tumor origin, progression, and recurrence. Chloride Intracellular Channel 1 (CLIC1), highly expressed in CSCs, is constitutively present in the plasma membrane where it is associated with chloride ion permeability. In vitro, CLIC1 inhibition leads to a significant arrest of GB CSCs in G₁ phase of the cell cycle. Furthermore, CLIC1 knockdown impairs tumor growth in vivo Here, we demonstrate that CLIC1 membrane localization and function is specific for GB CSCs. Mesenchymal stem cells (MSC) do not show CLIC1-associated chloride permeability, and inhibition of CLIC1 protein function has no influence on MSC cell-cycle progression. Investigation of the basic functions of GB CSCs reveals a constitutive state of oxidative stress and cytoplasmic alkalinization compared with MSCs. Both intracellular oxidation and cytoplasmic pH changes have been reported to affect CLIC1 membrane functional expression. We now report that in CSCs these three elements are temporally linked during CSC G₁-S transition. Impeding CLIC1-mediated chloride current prevents both intracellular ROS accumulation and pH changes. CLIC1 membrane functional impairment results in GB CSCs resetting from an allostatic tumorigenic condition to a homeostatic steady state. In contrast, inhibiting NADPH oxidase and NHE1 proton pump results in cell death of both GB CSCs and MSCs. Our results show that CLIC1 membrane protein is crucial and specific for GB CSC proliferation, and is a promising pharmacologic target for successful brain tumor therapies. Mol Cancer Ther; 17(11); 2451-61. ©2018 AACR.

Protective effects of Erigeron breviscapus Hand.- Mazz. (EBHM) extract in retinal neurodegeneration models

PURPOSE

To investigate the neuroprotective effects of scutellarin, an active component of the multifunctional traditional Chinese herb Erigeron breviscapus (vant.) Hand.-Mazz. (EBHM), which has been used as a neuroprotective therapy for cerebrovascular diseases. We performed the experiments using in vitro and in vivo models of retinal neurodegeneration.

METHODS

In the in vitro experiments, we exposed BV-2 cells to low oxygen levels in an incubator for 24 and 48 h to generate hypoxia models. We then treated these cells with scutellarin at concentrations of 2, 10, and 50 µM. Cell viability was measured using an enzyme-linked immunosorbent assay (ELISA). The levels of the components of the nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3 (NLRP3) inflammasome signaling pathway, including NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), cleaved caspase-1, interleukin-18 (IL-18), and IL-1β were analyzed using western blots and ELISAs. In the in vivo study, we raised the intraocular pressure of Brown Norway rats to 60 mmHg for 30 min to generate a high intraocular pressure (HIOP) model, that is, an acute glaucoma model. The rats were then treated with scutellarin via oral gavage for 2 consecutive weeks. The relevant components of the NLRP3 inflammasome signaling pathway were analyzed with western blots and ELISAs. Retinal ganglion cells (RGCs) were retrogradely labeled using 4% Fluoro-Gold, and then the numbers of cells were calculated. Retinal microglial cells were labeled using immunofluorescence, and then the morphological changes were observed.

RESULTS

In the in vitro cell viability experiments, 50 µM scutellarin statistically significantly enhanced the viability rate when compared to 2 µM and 10 µM scutellarin (hypoxia + 50 µM EBHM group: 94.01±2.130% and 86.02±2.520% after 24 and 48 h, respectively; hypoxia model group: 74.98±3.860% and 64.41±4.890% after 24 and 48 h, respectively; for all when compared to normal control, p<0.001). Scutellarin inhibited the expression of NLRP3 in vitro (the hypoxia + EBHM group/normal control group ratio versus the hypoxia model group/normal control group ratio: 2.30±0.12 versus 4.06±0.19, p<0.01) and in vivo (the HIOP + EBHM group/normal control group ratio versus the HIOP model group/normal control ratio: 3.39±0.42 versus 6.07±0.22, p<0.01). Scutellarin administration also reduced the upregulation of ASC, cleaved caspase-1, IL-18, and IL-1β in vitro and in vivo. In the in vivo study, the RGC survival rate was statistically significantly improved following scutellarin administration (p<0.001 versus the HIOP group), and the number of impaired retinal microglial cells was statistically significantly reduced following scutellarin treatment when compared with the HIOP model group.

CONCLUSIONS

EBHM extract scutellarin exhibits protective effects in retinal hypoxia models by inhibiting NLRP3 inflammasome-mediated inflammatory reactions. Thus, EBHM extract scutellarin may be an appropriate therapeutic option for disorders related to retinal neurodegeneration, such as glaucoma.

Three Decades of Chloride Intracellular Channel Proteins: From Organelle to Organ Physiology

Intracellular organelles are membranous structures central for maintaining cellular physiology and the overall health of the cell. To maintain cellular function, intracellular organelles are required to tightly regulate their ionic homeostasis. Any imbalance in ionic concentrations can disrupt energy production (mitochondria), protein degradation (lysosomes), DNA replication (nucleus), or cellular signaling (endoplasmic reticulum). Ionic homeostasis is also important for volume regulation of intracellular organelles and is maintained by cation and anion channels as well as transporters. One of the major classes of ion channels predominantly localized to intracellular membranes is chloride intracellular channel proteins (CLICs). They are non-canonical ion channels with six homologs in mammals, existing as either soluble or integral membrane protein forms, with dual functions as enzymes and channels. Provided in this overview is a brief introduction to CLICs, and a summary of recent information on their localization, biophysical properties, and physiological roles. © 2018 by John Wiley & Sons, Inc.

Plasma Membrane Protein Profiling in Beta-Amyloid-Treated Microglia Cell Line

In the responsiveness of microglia to toxic stimuli, plasma membrane proteins play a key role. In this study we treated with a synthetic beta amyloid peptide murine microglial cells metabolically differently labelled with stable isotope amino acids (SILAC). The plasma membrane was selectively enriched by a multi-stage aqueous two-phase partition system. We were able to identify by 1D-LC-MS/MS analyses 1577 proteins, most of them are plasma membrane proteins according to the Gene Ontology annotation. An unchanged level of amyloid receptors in this data set suggests that microglia preserve their responsiveness capability to the environment even after 24-h challenge with amyloid peptides. On the other hand, 14 proteins were observed to change their plasma membrane abundance to a statistically significant extent. Among these, we proposed as reliable biomarkers of the inflammatory microglia phenotype in AD damaged tissues MAP/microtubule affinity-regulating kinase 3 (MARK3), Interferon-induced transmembrane protein 3 (IFITM3), Annexins A5 and A7 (ANXA5, ANXA7) and Neuropilin-1 (NRP1), all proteins known to be involved in the inflammation processes and in microtubule network assembly rate.

Tilapia and human CLIC2 structures are highly conserved

Chloride intracellular channels (CLICs) exist in soluble and membrane bound forms. We have determined the crystal structure of soluble Clic2 from the euryhaline teleost fish Oreochromis mossambicus. Structural comparison of tilapia and human CLIC2 with other CLICs shows that these proteins are highly conserved. We have also compared the expression levels of clic2 in selected osmoregulatory organs of tilapia, acclimated to freshwater, seawater and hypersaline water. Structural conservation of vertebrate CLICs implies that they might play conserved roles. Also, tissue-specific responsiveness of clic2 suggests that it might be involved in iono-osmoregulation under extreme conditions in tilapia.

Rhinacanthin C Alleviates Amyloid-β Fibrils' Toxicity on Neurons and Attenuates Neuroinflammation Triggered by LPS, Amyloid-β, and Interferon-γ in Glial Cells

Neuroinflammation plays a central role in the pathophysiology of Alzheimer's disease (AD). Compounds that suppress neuroinflammation have been identified as potential therapeutic targets for AD. Rhinacanthin C (RC), a naphthoquinone ester found in Rhinacanthus nasutus Kurz (Acanthaceae), is currently proposed as an effective molecule against inflammation. However, the exact role of RC on neuroinflammation remains to be elucidated. In the present study, we investigated RC effect on modulating lipopolysaccharides (LPS), amyloid-β peptide (Aβ), or interferon-γ- (IFN-γ-) evoked pathological events in neurons and glia. Our findings demonstrated that RC prevented Aβ-induced toxicity in rat hippocampal neurons and attenuated LPS-activated nitric oxide (NO) production, inducible nitric oxide synthase (iNOS) expression, and NF-κB signaling in rat glia. Likewise, RC suppressed LPS-induced neuroinflammation by reducing NO production and iNOS, IL-1β, CCL-2, and CCL-5 mRNA levels in rat microglia. Further studies using BV-2 microglia revealed that RC inhibited LPS-, Aβ-, and IFN-γ-stimulated IL-6 and TNF-α secretion. Of note, NF-κB and ERK activation was abrogated by RC in BV-2 cell response to Aβ or IFN-γ. Moreover, RC protected neurons from Aβ-stimulated microglial conditioned media-dependent toxicity. Collectively, these data highlight the beneficial effects of RC on neuroprotection and support the therapeutic implications of RC to neuroinflammation-mediated conditions.

Tanshinone IIA Sodium sulfonate regulates antioxidant system, inflammation, and endothelial dysfunction in atherosclerosis by downregulation of CLIC1

BACKGROUND

Tanshinone IIA Sodium sulfonate (STS) is clinically used for treating cardiovascular diseases in Traditional Chinese Medicine due to its antioxidation and anti-inflammation activities. Intracellular chloride channel 1 (CLIC1) participates in the regulation of oxidative stress and inflammation. This study investigates whether CLIC1 mediates the cardioprotective effects of STS.

METHODS

STS were used to treat atherosclerosis (AS) induced by feeding Apolipoprotein E-deficient (ApoE^-/-) mice with a high-fat, cholesterol-rich diet. In addition, normal and CLIC1^-/- human umbilical vein endothelial cells were treated with STS after exposure to H₂O₂ for 12h. The oxidative status was determined by analyzing reactive oxygen species(ROS) and malondialdehyde (MDA) levels. ELISA, qRT-PCR and Western blot were used to determine the levels of TNF-α, IL-6, ICAM-1 and VCAM-1. CLIC1 cellular localization was examined by immunofluorescence. Chloride ion concentration was detected with chloride ion quenchers (MQAE).

RESULTS

STS treatment decreased atherosclerotic lesion area by 3.5 times (P = 0.001) in vivo. Meanwhile, STS reduced MDA production (13.6%, P = 0.008), increased SOD activity (113.6%, P = 0.008), decreased TNF-α (38.6%, P = 0.008) and IL-6 (43.0%, P = 0.03) levels, and downregulated the expression of CLIC1, ICAM-1, and VCAM-1 in the atherosclerotic mice. The dose-dependent anti-oxidative and anti-inflammatory effects of STS were further confirmed in vitro. Furthermore, CLIC1 depletion abolished the STS-mediated decrease of ROS and MDA production in HUVEC cells. Additionally, STS inhibited both CLIC1 membrane translocation and chloride ion concentration.

CONCLUSION

The anti-oxidant, and anti-inflammation properties of STS in preventing AS is mediated by its inhibition of CLIC1 expression and membrane translocation.

Identification and Characterization of a Bacterial Homolog of Chloride Intracellular Channel (CLIC) Protein

Chloride intracellular channels (CLIC) are non-classical ion channels lacking a signal sequence for membrane targeting. In eukaryotes, they are implicated in cell volume regulation, acidification, and cell cycle. CLICs resemble the omega class of Glutathione S-transferases (GST), yet differ from them in their ability to form ion channels. They are ubiquitously found in eukaryotes but no prokaryotic homolog has been characterized. We found that indanyloxyacetic acid-94 (IAA-94), a blocker of CLICs, delays the growth of Escherichia coli. In silico analysis showed that the E. coli stringent starvation protein A (SspA) shares sequence and structural homology with CLICs. Similar to CLICs, SspA lacks a signal sequence but contains an omega GST fold. Electrophysiological analysis revealed that SspA auto-inserts into lipid bilayers and forms IAA-94-sensitive ion channels. Substituting the ubiquitously conserved residue leucine 29 to alanine in the pore-forming region increased its single-channel conductance. SspA is essential for cell survival during acid-induced stress, and we found that acidic pH increases the open probability of SspA. Further, IAA-94 delayed the growth of wild-type but not sspA null mutant E. coli. Our results for the first time show that CLIC-like proteins exist in bacteria in the form of SspA, forming functional ion channels.

Emerging biological roles of Cl- intracellular channel proteins

Cl^- intracellular channels (CLICs) are a family of six evolutionary conserved cytosolic proteins that exist in both soluble and membrane-associated forms; however, their functions have long been elusive. Soluble CLICs adopt a glutathione S-transferase (GST)-fold, can induce ion currents in artificial membranes and show oxidoreductase activity in vitro, but there is no convincing evidence of CLICs having such activities in vivo. Recent studies have revealed a role for CLIC proteins in Rho-regulated cortical actin dynamics as well as vesicular trafficking and integrin recycling, the latter of which are under the control of Rab GTPases. In this Commentary, we discuss the emerging roles of CLIC proteins in these processes and the lessons learned from gene-targeting studies. We also highlight outstanding questions regarding the molecular function(s) of these important but still poorly understood proteins.

Changes in phagocytosis and potassium channel activity in microglia of 5xFAD mice indicate alterations in purinergic signaling in a mouse model of Alzheimer's disease

As the immunocompetent cells of the central nervous system, microglia accumulate at amyloid beta plaques in Alzheimer's disease (AD) and acquire a morphological phenotype of activated microglia. Recent functional studies, however, indicate that in mouse models of amyloidosis and AD, these cells are rather dysfunctional indicated by a reduced phagocytic activity. Here, we report that this reduction in phagocytic activity is associated with perturbed purinergic receptor signaling, since phagocytosis could be stimulated by P2Y₆ receptor activation in control, but not in 5xFAD transgenic animals, an animal model of amyloid deposition. Impaired phagocytosis is not innate, and develops only at later stages of amyloidosis. Furthermore, we show that membrane currents induced by uridine diphosphate, a ligand activating P2Y₆ receptors, are altered in response rate and amplitude in microglia in close vicinity to plaques, but not in plaque-free areas of 5xFAD animals. These changes were accompanied by changes in membrane properties and potassium channel activity of plaque-associated microglia in early and late stages of amyloidosis. As a conclusion, the physiological properties of plaque-associated microglia are altered with a strong impact on purinergic signaling.