Improvement of chloride transport defect by gonadotropin-releasing hormone (GnRH) in cystic fibrosis epithelial cells

Evaluation of aminopyrrolidine amide to improve chloride transport in CFTR-defective cells

The aminopyrrolidine amide PF-429242 is a specific inhibitor of the Site-1 Protease which is responsible for the cleavage, and thus the activation of the Activating Transcription Factor6 that down regulates many genes, during the Unfolded Protein Response. We hypothesized that PF-429242 could be used to prevent the ATF6-dependent down regulation of some genes. We chose the CFTR gene encoding the CFTR chloride channel as a model because it is down-regulated by ATF6 in Cystic Fibrosis. We evaluated the action of PF-429242 in human bronchial cells expressing the most frequent mutation of CFTR (p.Phe508del) found in patients. We observed that PF-429242 increases the synthesis of the mRNA and the protein encoded by the CFTR gene harbouring the mutation. We also observed that PF-429242 alleviates the defects of the p.Phe508del-CFTR channel in human Cystic Fibrosis cells. Our results suggest that aminopyrrolidine amide is a potential therapeutic target for Cystic Fibrosis that could also have beneficial effects in other diseases involving CFTR, such as the Chronic Obstructive Pulmonary Disease.

A novel role for CFTR interaction with LH and FGF in azoospermia and epididymal maldevelopment caused by cryptorchidism

Cryptorchidism occurs frequently in children with cystic fibrosis. Among boys with cryptorchidism and abrogated mini-puberty, the development of the epididymis and the vas deferens is frequently impaired. This finding suggests that a common cause underlies the abnormal development of Ad spermatogonia and the epididymis. The cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-binding cassette transporter protein that acts as a chloride channel. The CFTR gene has been associated with spermatogenesis and male fertility. In boys with cryptorchidism, prepubertal hypogonadotropic hypogonadism induces suboptimal expression of the ankyrin-like protein gene, ASZ1, the P-element induced wimpy testis-like gene, PIWIL, and CFTR. The abrogated expression of these gene leads to transposon reactivation, and ultimately, infertility. Curative gonadotropin-releasing hormone agonist (GnRHa) treatment stimulates the expression of CFTR and PIWIL3, which play important roles in the development of Ad spermatogonia and fertility. Furthermore, GnRHa stimulates the expression of the epididymal androgen-sensitive genes, CRISP1, WFDC8, SPINK13, and PAX2, which thereby promotes epididymal development. This review focuses on molecular evidence that favors a role for CFTR in cryptorchidism-induced infertility. Based on information available in the literature, we interpreted our RNA-Seq expression data obtained from samples before and after randomized GnRHa treatment in boys with bilateral cryptorchidism. We propose that, in boys with cryptorchidism, CFTR expression is controlled by luteinizing hormone and testosterone. Moreover, CFTR regulates the activities of genes that are important for fertility and Wolffian duct differentiation.

Buserelin alleviates chloride transport defect in human cystic fibrosis nasal epithelial cells

Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) chloride (Cl-) channel regulated by protein kinases, phosphatases, divalent cations and by protein-protein interactions. Among protein-protein interactions, we previously showed that Annexin A5 (AnxA5) binds to CFTR and is involved in the channel localization within membranes and in its Cl- channel function. The deletion of phenylalanine at position 508 (F508del) is the most common mutation in CF which leads to an altered protein (F508del-CFTR) folding with a nascent protein retained within the ER and is quickly degraded. We previously showed that AnxA5 binds to F508del-CFTR and that its increased expression due to a Gonadoliberin (GnRH) augments Cl- efflux in cells expressing F508del-CFTR. The aim of the present work was to use the GnRH analog buserelin which is already used in medicine. Human nasal epithelial cells from controls and CF patients (F508del/F508del) were treated with buserelin and we show here that the treatment alleviates Cl- channel defects in CF cells. Using proteomics we highlighted some proteins explaining this result. Finally, we propose that buserelin is a potential new pharmaceutical compound that can be used in CF and that bronchus can be targeted since we show here that they express GnRH-R.

Function and regulation of TRPM7, as well as intracellular magnesium content, are altered in cells expressing ΔF508-CFTR and G551D-CFTR

Cystic fibrosis (CF), one of the most common fatal hereditary disorders, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene product is a multidomain adenosine triphosphate-binding cassette (ABC) protein that functions as a chloride (Cl(-)) channel that is regulated by intracellular magnesium [Mg(2+)]i. The most common mutations in CFTR are a deletion of a phenylalanine residue at position 508 (ΔF508-CFTR, 70-80 % of CF phenotypes) and a Gly551Asp substitution (G551D-CFTR, 4-5 % of alleles), which lead to decreased or almost abolished Cl(-) channel function, respectively. Magnesium ions have to be finely regulated within cells for optimal expression and function of CFTR. Therefore, the melastatin-like transient receptor potential cation channel, subfamily M, member 7 (TRPM7), which is responsible for Mg(2+) entry, was studies and [Mg(2+)]i measured in cells stably expressing wildtype CFTR, and two mutant proteins (ΔF508-CFTR and G551D-CFTR). This study shows for the first time that [Mg(2+)]i is decreased in cells expressing ΔF508-CFTR and G551D-CFTR mutated proteins. It was also observed that the expression of the TRPM7 protein is increased; however, membrane localization was altered for both ΔF508del-CFTR and G551D-CFTR. Furthermore, both the function and regulation of the TRPM7 channel regarding Mg(2+) is decreased in the cells expressing the mutated CFTR. Ca(2+) influx via TRPM7 were also modified in cells expressing a mutated CFTR. Therefore, there appears to be a direct involvement of TRPM7 in CF physiopathology. Finally, we propose that the TRPM7 activator Naltriben is a new potentiator for G551D-CFTR as the function of this mutant increases upon activation of TRPM7 by Naltriben.

Gonadotropin-releasing hormone stimulates biliary proliferation by paracrine/autocrine mechanisms

During cholestatic liver disease, there is dysregulation in the balance between biliary growth and loss in bile duct-ligated (BDL) rats modulated by neuroendocrine peptides via autocrine/paracrine pathways. Gonadotropin-releasing hormone (GnRH) is a trophic peptide hormone that modulates reproductive function and proliferation in many cell types. We evaluated the autocrine role of GnRH in the regulation of cholangiocyte proliferation. The expression of GnRH receptors was assessed in a normal mouse cholangiocyte cell line (NMC), sham, and BDL rats. The effect of GnRH administration was evaluated in normal rats and in NMC. GnRH-induced biliary proliferation was evaluated by changes in intrahepatic bile duct mass and the expression of proliferation and function markers. The expression and secretion of GnRH in NMC and isolated cholangiocytes was assessed. GnRH receptor subtypes GnRHR1 and GnRHR2 were expressed in cholangiocytes. Treatment with GnRH increased intrahepatic bile duct mass as well as proliferation and function markers in cholangiocytes. Transient knockdown and pharmacologic inhibition of GnRHR1 in NMC decreased proliferation. BDL cholangiocytes had increased expression of GnRH compared with normal rats, accompanied by increased GnRH secretion. In vivo and in vitro knockdown of GnRH decreased intrahepatic bile duct mass/cholangiocyte proliferation and fibrosis. GnRH secreted by cholangiocytes promotes biliary proliferation via an autocrine pathway. Disruption of GnRH/GnRHR signaling may be important for the management of cholestatic liver diseases.

G551D-CFTR needs more bound actin than wild-type CFTR to maintain its presence in plasma membranes

Cystic Fibrosis is due to mutations in the CFTR gene. The missense mutation G551D (approx. 5% of cases) encodes a CFTR chloride channel with normal cell surface expression but with an altered chloride channel activity, leading to a severe phenotype. Our aim was to identify specific interacting proteins of G551D-CFTR which could explain the channel defect. Wild-type CFTR (Wt-CFTR) was co-immunoprecipitated from stably transfected HeLa cells and resolved by 2D gel electrophoresis. Among the detected spots, one was expressed at a high level. Mass Spectrometry revealed that it corresponded to actin which is known to be involved in the CFTR's channel function. To assess whether actin could be involved in the altered G551D-CFTR function, its basal expression was studied. Because actin expression was the same in wt- and in G551D-CFTR expressing cells, its interaction with both wt- and G551D-CFTR was studied by co-immunoprecipitation, and we found that a higher amount of actin was bound onto G551D-CFTR than onto Wt-CFTR. The role of actin upon wt- and G551D-CFTR function was further studied by patch-clamp experiments after cytochalasin D treatment of the cells. We found a decrease of the very weak currents in G551D-CFTR expressing cells. Because a higher amount of actin is bound onto G551D-CFTR than onto Wt-CFTR, it is likely to be not involved in the mutated CFTR's defect. Nevertheless, because actin is necessary to maintain the very weak global currents observed in G551D-CFTR expressing HeLa cells, we conclude that more actin is necessary to maintain G551D-CFTR in the plasma membrane than for Wt-CFTR.