Curcumin enhances cystic fibrosis transmembrane regulator expression by down-regulating calreticulin

The biogenesis of potassium transporters: implications of disease-associated mutations

The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.

Therapeutic potential of phytochemicals for cystic fibrosis

The aim of this review was to review and discuss various phytochemicals that exhibit beneficial effects on mutated membrane channels, and hence, improve transmembrane conductance. These therapeutic phytochemicals may have the potential to decrease mortality and morbidity of CF patients. Four databases were searched using keywords. Relevant studies were identified, and related articles were separated. Google Scholar, as well as gray literature (i.e., information that is not produced by commercial publishers), were also checked for related articles to locate/identify additional studies. The relevant databases were searched a second time to ensure that recent studies were included. In conclusion, while curcumin, genistein, and resveratrol have demonstrated effectiveness in this regard, it should be emphasized that coumarins, quercetin, and other herbal medicines also have beneficial effects on transporter function, transmembrane conductivity, and overall channel activity. Additional in vitro and in vivo studies should be conducted on mutant CFTR to unequivocally define the mechanism by which phytochemicals alter transmembrane channel function/activity, since the results of the studies evaluated in this review have a high degree of heterogenicity and discrepancy. Finally, continued research be undertaken to clearly define the mechanism(s) of action and the therapeutic effects that therapeutic phytochemicals have on the symptoms observed in CF patients in an effort to reduce mortality and morbidity.

Therapeutic applications of curcumin nanomedicine formulations in cystic fibrosis

Medicinal applications of turmeric-derived curcumin have been known to mankind for long ages. Its potential in managing "cystic fibrosis" has also been evaluated. This autosomal recessive genetic disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) which involves an impaired secretion of chloride ions and leads to hypersecretion of thick and sticky mucus and serious complications including airway obstruction, chronic lung infection, and inflammatory reactions. This narrative review aims to highlight the available evidence for the efficacy of curcumin nanoformulations in its potential treatment of cystic fibrosis. Recent research has shown that curcumin acts on the localized mutant CFTR ion channel at the plasma membrane. Preclinical studies have also shown that curcumin nanoformulations have promising effects in the treatment of cystic fibrosis. In this context, the purpose of this narrative review is to highlight the general bioactivity of curcumin, the types of formulations and related studies, thus opening new therapeutic perspectives for CF.

The effects of nano-curcumin as a nutritional strategy on clinical and inflammatory factors in children with cystic fibrosis: the study protocol for a randomized controlled trial

BACKGROUND

Cystic fibrosis (CF) is a genetic disorder, which is caused by the CFTR protein defects. Along with CFTR dysfunction, inflammation plays a key role in the disease outcomes. Inflammation may develop due to the internal dysfunction of the CFTR protein or external factors. Curcumin affects the CFTR protein function primarily as a corrector and potentiator and secondary as an anti-inflammatory and antimicrobial agent. The present study aims to assess the impact of nano-curcumin on clinical and inflammatory markers in children with CF.

METHODS

This prospective, double blind control trial will be conducted at the Akbar Children's Hospital in Mashhad, Iran. Children with CF will be enrolled based on the eligibility criteria. Placebo and curcumin with the maximum dose of 80 mg considering the body surface of the patients will be administrated for 3 months. The primary outcome is to evaluate inflammation based on serum interleukin-6, interleukin-10, and hs-CRP, stool calprotectin, and neutrophil count of nasopharyngeal swab. The secondary outcome involved clinical assessment via spirometry, anthropometrics, and quality of life. They will be assessed before and after 3 months.

DISCUSSION

Due to the multifarious effects of curcumin on CF disease, it could be proposed as a nutritional strategy in the treatment of cystic fibrosis.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials IRCT20200705048018N1 . Registered on July 10, 2020.

Effects of curcumin on ion channels and pumps: A review

Curcumin, an orange-yellow lipophilic polyphenolic molecule, is the active component of Curcuma longa, which is extensively used as a spice in most of the Asian countries. This natural compound is able to interact with a large number of molecular structures like proteins, enzymes, lipids, DNA, RNA, transporter molecules, and ion channels. It has been reported to possess several biological effects such as antioxidant, anti-inflammatory, wound healing, antimicrobial, anticancer, antiangiogenic, antimutagenic, and antiplatelet aggregation properties. These beneficial effects of curcumin are because of its extraordinary chemical interactions such as extensive hydrogen and covalent bonding, metal chelation, and so on. Therefore, the aim of this review was to outline the evidence in which curcumin could affect different types of ion channels and ion channel-related diseases, and also to elucidate basic molecular mechanisms behind it. © 2019 IUBMB Life, 2019.

CFTR-regulated MAPK/NF-κB signaling in pulmonary inflammation in thermal inhalation injury

The mechanism underlying pulmonary inflammation in thermal inhalation injury remains elusive. Cystic fibrosis, also hallmarked with pulmonary inflammation, is caused by mutations in CFTR, the expression of which is temperature-sensitive. We investigated whether CFTR is involved in heat-induced pulmonary inflammation. We applied heat-treatment in 16HBE14o- cells with CFTR knockdown or overexpression and heat-inhalation in rats in vivo. Heat-treatment caused significant reduction in CFTR and, reciprocally, increase in COX-2 at early stages both in vitro and in vivo. Activation of ERK/JNK, NF-κB and COX-2/PGE2 were detected in heat-treated cells, which were mimicked by knockdown, and reversed by overexpression of CFTR or VX-809, a reported CFTR mutation corrector. JNK/ERK inhibition reversed heat-/CFTR-knockdown-induced NF-κB activation, whereas NF-κB inhibitor showed no effect on JNK/ERK. IL-8 was augmented by heat-treatment or CFTR-knockdown, which was abolished by inhibition of NF-κB, JNK/ERK or COX-2. Moreover, in vitro or in vivo treatment with curcumin, a natural phenolic compound, significantly enhanced CFTR expression and reversed the heat-induced increases in COX-2/PGE2/IL-8, neutrophil infiltration and tissue damage in the airway. These results have revealed a CFTR-regulated MAPK/NF-κB pathway leading to COX-2/PGE2/IL-8 activation in thermal inhalation injury, and demonstrated therapeutic potential of curcumin for alleviating heat-induced pulmonary inflammation.

Therapeutic options for hydrating airway mucus in cystic fibrosis

BACKGROUND

In cystic fibrosis (CF), genetic mutations in the CF transmembrane conductance regulator (CFTR) gene cause reduced chloride efflux from ciliated airway epithelial cells. This results in a reduction in periciliary liquid (PCL) depth of the airway surface liquid due to associated reduced water efflux. PCL layer dehydration reduces mucociliary clearance (MCC), leading to airway obstruction (reduced airflow and inflammation due to pathogen invasion) with mucus plug formation.

SUMMARY

Rehydrating mucus increases MCC. Mucus hydration can be achieved by direct hydration (administering osmotic agents to set up an osmotic gradient), using CFTR modulators to correct dysfunctional CFTR, or it can be achieved pharmacologically (targeting other ion channels on airway epithelial cells). Key Messages: The molecular mechanisms of several therapies are discussed in the context of pre-clinical and clinical trial studies. Currently, only the osmotic agent 7% hypertonic saline and the CFTR 'potentiator' VX-770 (ivacaftor) are used clinically to hydrate mucus. Emerging therapies include the osmotic agent mannitol (Bronchitol), the intracellular Ca(2+)-raising agent Moli1901/lancovutide, the CFTR potentiator sildenafil [phosphodiesterase type 5 (PDE5) inhibitor] and the CFTR 'corrector' VX-809 (lumacaftor). Other CFTR correctors (e.g. 'chemical chaperones') are also showing pre-clinical promise.

Calreticulin: roles in cell-surface protein expression

In order to perform their designated functions, proteins require precise subcellular localizations. For cell-surface proteins, such as receptors and channels, they are able to transduce signals only when properly targeted to the cell membrane. Calreticulin is a multi-functional chaperone protein involved in protein folding, maturation, and trafficking. However, evidence has been accumulating that calreticulin can also negatively regulate the surface expression of certain receptors and channels. In these instances, depletion of calreticulin enhances cell-surface expression and function. In this review, we discuss the role of calreticulin with a focus on its negative effects on the expression of cell-surface proteins.

Potential for therapeutic manipulation of the UPR in disease

Increased endoplasmic reticulum (ER) stress and the activated unfolded protein response (UPR) signaling associated with it play key roles in physiological processes as well as under pathological conditions. The UPR normally protects cells and re-establishes cellular homeostasis, but prolonged UPR activation can lead to the development of various pathologies. These features make the UPR signaling pathway an attractive target for the treatment of diseases whose pathogenesis is characterized by chronic activation of this pathway. Here, we focus on the molecular signaling pathways of the UPR and suggest possible ways to target this response for therapeutic purposes.

Molecular Chaperones as Targets to Circumvent the CFTR Defect in Cystic Fibrosis

Cystic Fibrosis (CF) is the most common autosomal recessive lethal disorder among Caucasian populations. CF results from mutations and resulting dysfunction of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). CFTR is a cyclic AMP-dependent chloride channel that is localized to the apical membrane in epithelial cells where it plays a key role in salt and water homeostasis. An intricate network of molecular chaperone proteins regulates CFTR’s proper maturation and trafficking to the apical membrane. Understanding and manipulation of this network may lead to therapeutics for CF in cases where mutant CFTR has aberrant trafficking.

Calreticulin chaperones regulate functional expression of vomeronasal type 2 pheromone receptors

A variety of social behaviors like intermale aggression, fear, and mating rituals are important for sustenance of a species. In mice, these behaviors have been implicated to be mediated by peptide pheromones that are sensed by a class of G protein-coupled receptors, vomeronasal receptor type 2 (V2Rs), expressed in the pheromone detecting vomeronasal organ. Matching V2Rs with their cognate ligands is required to learn what receptors the biologically relevant pheromones are acting on. However, this feat has been greatly limited by the unavailability of appropriate heterologous tools commonly used to study ligand receptor specificity, because this family of receptors fails to traffic to the surface of heterologous cells. Here we show that calreticulin, a housekeeping chaperone commonly expressed in most eukaryotic cells, is sparsely expressed in the vomeronasal sensory neurons (VSNs). Correspondingly, knockdown of calreticulin in commonly available cell lines enables V2Rs to efficiently target to the cell membrane. Using this knowledge, we have now been able to successfully surface express receptors and functionally identify cognate ligands. Additionally, calreticulin4, a homolog of calreticulin shows restricted and enriched expression in the VSNs. Interestingly, in heterologous cells, calreticulin4 does not inhibit surface expression of V2Rs and can in part carry out functions of calreticulin. On the basis of our data, we postulate that V2Rs may use a unique trafficking mechanism whereby an important and more commonly expressed chaperone is deleterious for membrane export and is replaced by a functionally equivalent homolog that does not inhibit export while carrying out its functions.

Transit defect of potassium-chloride Co-transporter 3 is a major pathogenic mechanism in hereditary motor and sensory neuropathy with agenesis of the corpus callosum

Missense and protein-truncating mutations of the human potassium-chloride co-transporter 3 gene (KCC3) cause hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), which is a severe neurodegenerative disease characterized by axonal dysfunction and neurodevelopmental defects. We previously reported that KCC3-truncating mutations disrupt brain-type creatine kinase-dependent activation of the co-transporter through the loss of its last 140 amino acids. Here, we report a novel and more distal HMSN/ACC-truncating mutation (3402C → T; R1134X) that eliminates only the last 17 residues of the protein. This small truncation disrupts the interaction with brain-type creatine kinase in mammalian cells but also affects plasma membrane localization of the mutant transporter. Although it is not truncated, the previously reported HMSN/ACC-causing 619C → T (R207C) missense mutation also leads to KCC3 loss of function in Xenopus oocyte flux assay. Immunodetection in Xenopus oocytes and in mammalian cultured cells revealed a decreased amount of R207C at the plasma membrane, with significant retention of the mutant proteins in the endoplasmic reticulum. In mammalian cells, curcumin partially corrected these mutant protein mislocalizations, with more protein reaching the plasma membrane. These findings suggest that mis-trafficking of mutant protein is an important pathophysiological feature of HMSN/ACC causative KCC3 mutations.

CFTR-deficiency renders mice highly susceptible to cutaneous symptoms during mite infestation

Pruritus, also known as itch, is a sensation that causes a desire to scratch. Prolonged scratching exacerbates skin lesions in several skin diseases such as atopic dermatitis. Here, we identify the cystic fibrosis transmembrane conductance regulator (CFTR/Cftr), an integral membrane protein that mediates transepithelial chloride transport, as a determinant factor in mice for the susceptibility to several cutaneous symptoms during mite infestation. Mice that endogenously express dysfunctional Cftr (Cftr(ΔF508/ΔF508)) show significant increase of scratching behavior and skin fibrosis after mite exposure. These phenotypes were due to the increased expression of nerve growth factor (NGF) that augments the sensitization of peripheral nerve fibers. Moreover, protein gene product 9.5 (PGP9.5)-positive neurites were abundant in the epidermis of mite-infested Cftr(ΔF508/ΔF508) mice. Furthermore, mite-infested Cftr(+/+) mice orally administered with a chloride channel inhibitor glibenclamide had higher scratching count and increased level of NGF than vehicle-treated mice. Consistently, mite extract-exposed primary and transformed human keratinocytes, treated with CFTR inhibitor, had significantly higher level of NGF mRNA compared with vehicle-treated, mite extract-exposed cells. These results reveal that CFTR in keratinocytes plays a critical role for the regulation of peripheral nerve function and pruritus sensation, and suggest that Cftr(ΔF508/ΔF508) mice may serve as a novel mouse model that represents NGF-dependent generation of pruritus.

Bcl-2 suppresses sarcoplasmic/endoplasmic reticulum Ca2+-ATPase expression in cystic fibrosis airways: role in oxidant-mediated cell death

RATIONALE

Modulation of the activity of sarcoendoplasmic reticulum calcium ATPase (SERCA) can profoundly affect Ca(2+) homeostasis. Although altered calcium homeostasis is a characteristic of cystic fibrosis (CF), the role of SERCA is unknown.

OBJECTIVES

This study provides a comprehensive investigation of expression and activity of SERCA in CF airway epithelium. A detailed study of the mechanisms underlying SERCA changes and its consequences was also undertaken.

METHODS

Lung tissue samples (bronchus and bronchiole) from subjects with and without CF were evaluated by immunohistochemistry. Protein and mRNA expression in primary non-CF and CF cells was determined by Western and Northern blots.

MEASUREMENTS AND MAIN RESULTS

SERCA2 expression was decreased in bronchial and bronchiolar epithelia of subjects with CF. SERCA2 expression in lysates of polarized tracheobronchial epithelial cells from subjects with CF was decreased by 67% as compared with those from subjects without CF. Several non-CF and CF airway epithelial cell lines were also probed. SERCA2 expression and activity were consistently decreased in CF cell lines. Adenoviral expression of mutant F508 cystic fibrosis transmembrane regulator gene (CFTR), inhibition of CFTR function pharmacologically (CFTR(inh)172), or stable expression of antisense oligonucleotides to inhibit CFTR expression caused decreased SERCA2 expression. In CF cells, SERCA2 interacted with Bcl-2, leading to its displacement from caveolae-related domains of endoplasmic reticulum membranes, as demonstrated in sucrose density gradient centrifugation and immunoprecipitation studies. Knockdown of SERCA2 using siRNA enhanced epithelial cell death due to ozone, hydrogen peroxide, and TNF-alpha.

CONCLUSIONS

Reduced SERCA2 expression may alter calcium signaling and apoptosis in CF. These findings decrease the likelihood of therapeutic benefit of SERCA inhibition in CF.

Role of N-linked oligosaccharides in the biosynthetic processing of the cystic fibrosis membrane conductance regulator

The epithelial chloride channel CFTR is a glycoprotein that is modified by two N-linked oligosaccharides. The most common mutant CFTR protein in patients with cystic fibrosis, DeltaF508, is misfolded and retained by ER quality control. As oligosaccharide moieties of glycoproteins are known to mediate interactions with ER lectin chaperones, we investigated the role of N-linked glycosylation in the processing of wild-type and DeltaF508 CFTR. We found that N-glycosylation and ER lectin interactions are not major determinants of trafficking of wild-type and DeltaF508 from the ER to the plasma membrane. Unglycosylated CFTR, generated by removal of glycosylation sites or treatment of cells with the N-glycosylation inhibitor tunicamycin, did not bind calnexin, but did traffic to the cell surface and exhibited chloride channel activity. Most importantly, unglycosylated DeltaF508 CFTR still could not escape quality control in the early secretory pathway and remained associated with the ER. However, the absence of N-linked oligosaccharides did reduce the stability of wild-type CFTR, causing significantly more-rapid turnover in post-ER compartments. Surprisingly, the individual N-linked carbohydrates do not play equivalent roles and modulate the fate of the wild-type protein in different ways in its early biosynthetic pathway.

Curcumin: preventive and therapeutic properties in laboratory studies and clinical trials

Curcumin is a natural polyphenol used in ancient Asian medicine. Since the first article referring to the use of curcumin to treat human disease was published in The Lancet in 1937, >2,600 research studies using curcumin or turmeric have been published in English language journals. The mechanisms implicated in the inhibition of tumorigenesis by curcumin are diverse and appear to involve a combination of antiinflammatory, antioxidant, immunomodulatory, proapoptotic, and antiangiogenic properties via pleiotropic effects on genes and cell-signaling pathways at multiple levels. The potentially adverse sequelae of curcumin's effects on proapoptotic genes, particularly p53, represent a cause for current debate. When curcumin is combined with some cytotoxic drugs or certain other diet-derived polyphenols, synergistic effects have been demonstrated. Although curcumin's low systemic bioavailability after oral dosing may limit access of sufficient concentrations for pharmacologic effects in tissues outside the gastrointestinal tract, chemical analogues and novel delivery methods are in preclinical development to overcome this barrier. This article provides an overview of the extensive published literature on the use of curcumin as a therapy for malignant and inflammatory diseases and its potential use in the treatment of degenerative neurologic diseases, cystic fibrosis, and cardiovascular diseases. Despite the breadth of the coverage, particular emphasis is placed on the prevention and treatment of human cancers.

Coupling cystic fibrosis to endoplasmic reticulum stress: Differential role of Grp78 and ATF6

Cystic fibrosis (CF) is the most common Caucasian autosomal recessive disease. It is due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding the CFTR protein, which is a chloride (Cl(-)) channel. The most common mutation leads to a missing phenylalanine at position 508 (DeltaF508). The DeltaF508-CFTR protein is misfolded and retained in the endoplasmic reticulum and may trigger the unfolded protein response (UPR). Furthermore, CF is accompanied by inflammation and infection, which are also involved in the UPR. To date, the UPR transducer ATF6 and ER stress sensor Grp78 have been used as UPR markers. Therefore, our aim was to study the activation of ATF6 and Grp78 in transfected human epithelial cells expressing the DeltaF508-CFTR protein, and we showed that they are activated in these cells. We investigated the effect of exogenous UPR inducers thapsigargin (Tg) and tunicamycin (Tu) on Grp78 and ATF6 expression. Whereas the cells reacted to the UPR induction, we show a difference in the electrophoretic pattern of ATF6. The Grp78/ATF6 complex was previously described, but its stability during UPR is controversial. Using co-immunoprecipitation we show that it is stable in DeltaF508-CFTR-expressing cells and is maintained under UPR conditions. Finally, using siRNA, we show that decreased ATF6 expression induces increased cAMP-dependent halide flux through DeltaF508-CFTR due to its increased membrane localization. Therefore, our results suggest that UPR may be triggered in CF and that ATF6 may be a therapeutic target.