Osteoclastogenesis and sphingosine-1-phosphate secretion from human osteoclast precursor monocytes are modulated by the cystic fibrosis transmembrane conductance regulator.

Osteopenia and increased fracture rates are well-recognized in patients with cystic fibrosis (CF) disease. In CF pathology, F508del is the most common CFTR mutation, with more than 85% of patients carrying it on at least one allele. The underlying molecular defect in CFTR caused by the F508del-CFTR mutation in osteoclastogenesis, i.e., on the generation and bone-resorption activity of osteoclasts (OCs) from peripheral blood-derived monocytes (PBMCs) remained unexplored. We therefore investigated whether the F508del mutation could affect the osteoclastogenic capacity of PBMCs collected from 15 adult patients bearing the F508del-CFTR mutation, to modulate their bone-resorptive abilities and the level of sphingosine-1-phosphate (S1P) produced by OCs, a key factor in the bone mineral density and formation. In the present study, a severe, defective differentiation of CF-F508del PBMCs to CF-F508del OCs without any significant difference in nuclei number per OC was found compared to non-CF healthy PBMCs from 13 subjects after 7-14-days culture periods. We observed a reduced number of formed non-CF healthy OCs in the presence of a selective inhibitor of CFTR chloride conductance (CFTR-Inh172). Our data regarding OCs resorptive capabilites revealed that a loss of CFTR chloride activity in OCs led to a marked reduction in their trench-resorption mode. A 7-fold increase of the S1P release by CF-F508del OCs was found compared to non-CF healthy OCs after a 21-days culture period. We hypothesize that defective maturation of F508del-OCs precursor monocytes associated with high S1P production in the bone environment might contribute to low bone mineral density observed in the CF population.

CFTR-deficient pigs display alterations of bone microarchitecture and composition at birth.

BACKGROUND: The lack of cystic fibrosis transmembrane conductance regulator (CFTR) function causes cystic fibrosis (CF), predisposing to severe lung disease, reduced growth and osteopenia. Both reduced bone content and strength are increasingly recognized in infants with CF before the onset of significant lung disease, suggesting a developmental origin and a possible role in bone disease pathogenesis. The role of CFTR in bone metabolism is unclear and studies on humans are not feasible. Deletion of CFTR in pigs (CFTR -/- pigs) displays at birth severe malformations similar to humans in the intestine, respiratory tract, pancreas, liver, and male reproductive tract. METHODS: We compared bone parameters of CFTR -/- male and female pigs with those of their wild-type (WT) littermates at birth. Morphological and microstructural properties of femoral cortical and trabecular bone were evaluated using micro-computed tomography (µCT), and their chemical compositions were examined using Raman microspectroscopy. RESULTS: The integrity of the CFTR -/- bone was altered due to changes in its microstructure and chemical composition in both sexes. Low cortical thickness and high cortical porosity were found in CFTR -/- pigs compared to sex-matched WT littermates. Moreover, an increased chemical composition heterogeneity associated with higher carbonate/phosphate ratio and higher mineral crystallinity was found in CFTR -/- trabecular bone, but not in CFTR -/- cortical bone. CONCLUSIONS: The loss of CFTR directly alters the bone composition and metabolism of newborn pigs. Based on these findings, we speculate that bone defects in patients with CF could be a primary, rather than a secondary consequence of inflammation and infection.

An Optimized Method to Generate Human Active Osteoclasts From Peripheral Blood Monocytes.

Osteoclasts (OCs), the bone-resorbing cells, play a key role in skeletal development and adult bone remodeling. They also participate in the pathogenesis of various bone disorders. One of the major technical difficulties in the generation of OCs, when working on human material, is the ability to achieve large differentiation of mature OCs from human peripheral blood mononuclear cells (PBMCs). Access to a standardized source of active OCs is needed to better analyze the roles of human OCs. The aim of this study was to develop a procedure yielding active and mature OCs from fresh human PBMCs. We therefore examined the differentiation of PBMCs to OCs in different cell culture media, using non-stripped and charcoal-stripped sera in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL). We also studied the effects of vitamin D3 in the differentiation level of PBMCs to OCs. Phalloidin-AlexaFluor®488/DAPI fluorescent stainings and dentin resorption analyses by scanning electron microscopy were used to identify the number and size of differentiated OCs, number of nuclei per cell and resorption activities of OCs for a 7-14-21-day culture period. This study reports an optimized method for an efficient production of human active OCs from a low seeding density of PBMCs, after a 14-day culture period by using a medium containing fetal bovine charcoal-stripped serum in the presence of M-CSF and RANKL, and in the absence of vitamin D3.

Bone demineralization is improved by ivacaftor in patients with cystic fibrosis carrying the p.Gly551Asp mutation.

Low bone mineral density (BMD) is a common problem in adults with cystic fibrosis (CF), the etiology of which is multifactorial. In this study, we provide the first evidence that ivacaftor improves BMD in CF patients carrying the p.Gly551Asp mutation. Consistently, in vitro experiments with TNF-α-stimulated primary F508del-CFTR osteoblasts demonstrated that correction of p.Phe508del-CFTR markedly decreased RANKL protein production, a major factor of bone resorption. These clinical and fundamental observations suggest that rescue of mutated CFTR protein improves bone remodeling and support the link between CFTR and bone cell physiology. These findings represent a step forward in the development of potential new therapies for CF-related bone disease.

Overexpression of RANKL in osteoblasts: a possible mechanism of susceptibility to bone disease in cystic fibrosis.

Bone fragility and loss are a significant cause of morbidity in patients with cystic fibrosis (CF), and the lack of effective therapeutic options means that treatment is more often palliative rather than curative. A deeper understanding of the pathogenesis of CF-related bone disease (CFBD) is necessary to develop new therapies. Defective CF transmembrane conductance regulator (CFTR) protein and chronic inflammation in bone are important components of the CFBD development. The receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) drive the regulation of bone turnover. To investigate their roles in CFBD, we evaluated the involvement of defective CFTR in their production level in CF primary human osteoblasts with and without inflammatory stimulation, in the presence or not of pharmacological correctors of the CFTR. No major difference in cell ultrastructure was noted between cultured CF and non-CF osteoblasts, but a delayed bone matrix mineralization was observed in CF osteoblasts. Strikingly, resting CF osteoblasts exhibited strong production of RANKL protein, which was highly localized at the cell membrane and was enhanced in TNF (TNF-α) or IL-17-stimulated conditions. Under TNF stimulation, a defective response in OPG production was observed in CF osteoblasts in contrast to the elevated OPG production of non-CF osteoblasts, leading to an elevated RANKL-to-OPG protein ratio in CF osteoblasts. Pharmacological inhibition of CFTR chloride channel conductance in non-CF osteoblasts replicated both the decreased OPG production and the enhanced RANKL-to-OPG ratio. Interestingly, using CFTR correctors such as C18, we significantly reduced the production of RANKL by CF osteoblasts, in both resting and TNF-stimulated conditions. In conclusion, the overexpression of RANKL and high membranous RANKL localization in osteoblasts are related to defective CFTR, and may worsen bone resorption, leading to bone loss in patients with CF. Targeting osteoblasts with CFTR correctors may represent an effective strategy to treat CFBD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Enhanced F508del-CFTR channel activity ameliorates bone pathology in murine cystic fibrosis.

In patients with cystic fibrosis (CF), rib and thoracic vertebral fractures can have adverse effects on lung health because the resulting pain and debilitation can impair airway clearance. The F508del mutation in the CF transmembrane conductance regulator (Cftr) gene induces an osteopenic phenotype in humans and mice. N-butyldeoxynojyrimicin (miglustat), an approved drug for treating type 1 Gaucher disease, was found to normalize CFTR-dependent chloride transport in human F508del CFTR lung cells and in nasal mucosa of F508del CF mice. Herein, we investigated whether targeting F508del-CFTR may rescue the skeletal osteopenic phenotype in murine CF. We found that oral administration of low-dose miglustat (120 mg/kg once a day for 28 days) improved bone mass and microarchitecture in the lumbar spine and femur in F508del mice. The increased bone density was associated with an increased bone formation rate and reduced bone resorption. This effect was associated with increased 17ß-estradiol but not with insulin-like growth factor 1 serum levels in miglustat-treated F508del mice. Exposure of primary F508del osteoblasts to miglustat partially restored the deficient CFTR-dependent chloride transport in these bone-forming cells. This study provides evidence that reversal of CFTR-dependent chloride transport in osteoblasts normalizes bone mass and microarchitecture in murine CF. These findings may provide a potential therapeutic strategy to prevent or correct the bone disease in patients with CF.

The F508del mutation in cystic fibrosis transmembrane conductance regulator gene impacts bone formation.

The F508del mutation in the cystic fibrosis transmembrane conductance regulator (Cftr) gene is believed to be an independent risk factor for cystic fibrosis-related bone disease. In this study, we evaluated the bone mineral density as well as the histomorphometric parameters of bone formation and bone mass in both F508del-Cftr homozygous mice (F508del Cftr(tm1Eur)) and Cftr(+/+) littermate controls at 6 (prepubertal), 10 (pubertal), and 14 (young adult) weeks of age in both sexes. The bone architecture of F508del Cftr(tm1Eur) and wild-type (WT) littermate mice was evaluated by bone densitometry, microcomputed tomography, and analysis of the dynamic parameters of bone formation. Serum levels of both insulin-like growth factor 1 and osteocalcin also were determined. Reduced bone mineral density, lower femoral bone mass, and altered trabecular bone architecture were observed in F508del Cftr(tm1Eur) mice compared with controls at 6, 10, and 14 weeks of age. A decrease in the bone formation rate in F508del Cftr(tm1Eur) mice was shown compared with control mice, independently of age and sex. In addition, we found lower insulin-like growth factor 1 levels in F508del Cftr(tm1Eur) mice compared with age-matched controls, whereas osteocalcin levels were normal. Severe osteopenia and altered bone architecture were found in young and mature adult F508del Cftr(tm1Eur) mice. Our findings show that the F508del mutation in CFTR impacts trabecular bone mass by reducing bone formation.

Azithromycin fails to reduce inflammation in cystic fibrosis airway epithelial cells.

Cystic fibrosis is a hereditary disease caused by a mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene that encodes a chloride (Cl(-)) channel. Cystic fibrosis pulmonary pathophysiology is characterised by chronic inflammation and bacterial infections. Azithromycin, a macrolide antibiotic, has shown promising anti-inflammatory properties in some inflammatory pulmonary diseases. Moreover, all clinical studies have presented an improvement of the respiratory condition of cystic fibrosis patients, but the molecular and cellular mechanisms remain unknown. The aim of this study was to investigate, in bronchial epithelial cells, the effects of azithromycin on inflammatory pathways involved in cystic fibrosis. We have analysed the effects of azithromycin on cystic fibrosis and non-cystic fibrosis bronchial epithelial cell lines but also in non-immortalized non-cystic fibrosis human glandular cells. To create an inflammatory context, cells were treated with Tumor Necrosis Factor (TNF)-α or Interleukin (IL)1-ß. Activation of the NF-κB pathway was investigated by luciferase assay, western blotting, and by Förster Resonance Energy Transfer imaging, allowing the detection of the interaction between the transcription factor and its inhibitor in live cells. In all conditions tested, azithromycin did not have an anti-inflammatory effect on the cystic fibrosis human bronchial epithelial cells and on CFTR-inhibited primary human bronchial glandular cells. More, our data showed no effect of azithromycin on IL-1ß- or TNF-α-induced IL-8 secretion and NF-κB pathway activation. Taken together, these data show that azithromycin is unable to decrease in vitro inflammation in cystic fibrosis cells from airways.

Reduced expression of Tis7/IFRD1 protein in murine and human cystic fibrosis airway epithelial cell models homozygous for the F508del-CFTR mutation.

12-O-tetradecanoyl phorbol-13-acetate-induced sequence 7/interferon related development regulator 1 (Tis7/IFRD1) has been recently identified as a modifier gene in lung inflammatory disease severity in patients with cystic fibrosis (CF), based upon its capacity to regulate inflammatory activities in neutrophils. In CF patients, the F508del mutation in the Cftr gene encoding a chloride channel, the CF transmembrane conductance regulator (CFTR) in airway epithelial cells results in an exaggerated inflammatory response of these cells. At present, it is unknown whether the Tis7/IFRD1 gene product is expressed in airway epithelial cells. We therefore investigated the possibility there is an intrinsic alteration in Tis7/IFRD1 protein level in cells lacking CFTR function in tracheal homogenates of F508del-CFTR mice and in a F508del-CFTR human bronchial epithelial cell line (CFBE41o(-) cells). When Tis7/IFRD1 protein was detectable, trachea from F508del-CFTR mice showed a reduction in the level of Tis7/IFRD1 protein compared to wild-type control littermates. A significant reduction of IFRD1 protein level was found in CFBE41o(-) cells compared to normal bronchial epithelial cells 16HBE14o(-). Surprisingly, messenger RNA level of IFRD1 in CFBE41o(-) cells was found elevated. Treating CFBE41o(-) cells with the antioxidant glutathione rescued the IFRD1 protein level closer to control level and also reduced the pro-inflammatory cytokine IL-8 release. This work provides evidence for the first time of reduced level of IFRD1 protein in murine and human F508del-CFTR airway epithelial cell models, possibly mediated in response to oxidative stress which might contribute to the exaggerated inflammatory airway response observed in CF patients homozygous for the F508del mutation.

Bone disease in cystic fibrosis: what's new?

Cystic fibrosis (CF) is the most common autosomal recessive disease among Caucasians. It is due to a mutation in the cftr gene, which encodes the CF transmembrane conductance regulator (CFTR), a chloride channel located in the plasma membrane of mucus-secreting epithelial cells. Numerous other functions of the CFTR protein were identified recently. The survival gains achieved in CF patients over the last 30 years have led to the emergence of delayed complications, one of which is bone disease. The fracture risk is increased from late adolescence onward. Vertebral fractures have an estimated prevalence of 14% among CF patients and can cause severe respiratory complications. Bone mineral density (BMD) is below the age-specific range. Among young adults with CF, 23.5% have BMD values below the cutoff for osteoporosis. Z-scores, which are decreased in children with CF compared to healthy controls, diminish further in adolescence as a result of inadequate peak bone mass accumulation. Studies have shown increased bone resorption, most notably during infectious episodes, and disturbances in bone formation. The numerous pathophysiological mechanisms that contribute to diminish bone strength in CF patients include exocrine pancreatic failure with malabsorption, protein-calorie malnutrition, inflammation related to recurrent infection, and deficiencies in vitamins D and K. In addition, many recent studies support a role for abnormal CFTR function in the osteoblast dysfunction seen in CF. Appropriate diagnostic and therapeutic management of osteoporosis in CF patients is crucial. Risk factors for osteoporosis should be corrected to the extent possible. Oral bisphosphonate therapy may deserve consideration, particularly in adults.

Restoration of chloride efflux by azithromycin in airway epithelial cells of cystic fibrosis patients.

Azithromycin (AZM) has shown promising anti-inflammatory properties in chronic obstructive pulmonary diseases, and clinical studies have presented an improvement in the respiratory condition of cystic fibrosis (CF) patients. The aim of this study was to investigate, in human airway cells, the mechanism by which AZM has beneficial effects in CF. We demonstrated that AZM did not have any anti-inflammatory effect on CF airway cells but restored Cl(-) efflux.

Cystic fibrosis transmembrane conductance regulator (CFTR) regulates the production of osteoprotegerin (OPG) and prostaglandin (PG) E2 in human bone.

Bone loss is an important clinical issue in patients with cystic fibrosis (CF). Whether the cystic fibrosis transmembrane conductance regulator (CFTR) plays a direct role in bone cell function is yet unknown. In this study, we provide evidence that inhibition of CFTR-Cl(-) channel function results in a significant decrease of osteoprotegerin (OPG) secretion accompanied with a concomitant increase of prostaglandin (PG) E(2) secretion of primary human osteoblast cultures (n=5). Our data therefore suggest that in bone cells of CF patients, the loss of CFTR activity may result in an increased inflammation-driven bone resorption (through both the reduced OPG and increased PGE(2) production), and thus might contribute to the early bone loss reported in young children with CF.

Proinflammatory effect of sodium 4-phenylbutyrate in deltaF508-cystic fibrosis transmembrane conductance regulator lung epithelial cells: involvement of extracellular signal-regulated protein kinase 1/2 and c-Jun-NH2-terminal kinase signaling.

Sodium 4-phenylbutyrate (4-PBA) has attracted a great deal of attention in cystic fibrosis (CF) pathology due to its capacity to traffic DeltaF508-cystic fibrosis transmembrane conductance regulator (CFTR) to the cell membrane and restore CFTR chloride function at the plasma membrane of CF lung cells in vitro and in vivo. Using two different DeltaF508-CFTR lung epithelial cell lines (CFBE41o- and IB3-1 cells, characterized with DeltaF508-homozygous and heterozygous genotype, respectively) in vitro, 4-PBA induced an increase of proinflammatory cytokine interleukin (IL)-8 production in a concentration-dependent manner. This 4-PBA-induced IL-8 production was associated with a strong reduction of proteasome and nuclear factor-kappaB transcriptional activities in the two DeltaF508-CFTR lung cells either in a resting state or after tumor necrosis factor-alpha stimulation. In contrast, a strong increase of activator protein-1 transcriptional activity was observed. The inhibition of extracellular signal-regulated protein kinase 1/2 (ERK1/2) by 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene (U0126) and 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059) and c-Jun-NH(2)-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) by anthra[1,9-cd] pyrazol-6 (2H)-one (SP600125), respectively, was associated with a reduction (2-3.5-fold) of IL-8 production in both DeltaF508-CFTR lung cell lines treated with 4-PBA. No significant change of IL-8 production was observed after an inhibition of p38 MAPK with 4-[4-(4-fluorophenyl)-5-(4-pyridinyl)-1H-imidazol-2-yl] phenol (SB202190). Therefore, we suggest that inhibition of both ERK1/2 and JNK signaling may be a means to strongly reduce 4-PBA-induced IL-8 production in combination with 4-PBA treatment to restore CFTR Cl(-) channel function in lung epithelial cells of patients with CF.

Airway epithelial cell inflammatory signalling in cystic fibrosis.

Cystic fibrosis (CF) is the most common lethal monogenic disorder in Caucasians, estimated to affect one out of 2500-4000 new-borns. In patients with CF, lack of CF transmembrane conductance regulator (CFTR) Cl(-) channel function leads to progressive pulmonary damage and ultimately to death. Severe and persistent polymorphonuclear neutrophil-dominated endobronchial inflammation and chronic bacterial infection are characteristic hallmarks of CF lung disease. Whether CFTR dysfunction results directly in an increased predisposition to infection and whether inflammation arises independent of infection remains to be established. The loss of functional CFTR in airway epithelial cells promotes depletion and increased oxidation of the airway surface liquid. Activated neutrophils present in airways produce large amounts of proteases and reactive oxygen species (ROS). Together these changes are associated with diminished mucociliary clearance of bacteria, activation of epithelial cell signalling through multiple pathways, and subsequent hyperinflammatory responses in CF airways. The NF-kappaB pathway and Ca(2+) mobilization in airway epithelial cells are believed to be of key importance for control of lung inflammation through regulated production of mediators such as interleukin-8 that participate in recruitment and activation of neutrophils, modulation of apoptosis, and control of epithelial barrier integrity. In this review, the current understanding of the molecular mechanisms by which airway epithelial cells contribute to abnormal lung inflammation in CF, as well as the anti-inflammatory strategies that can be proposed are discussed.

Cystic fibrosis transmembrane conductance regulator controls lung proteasomal degradation and nuclear factor-kappaB activity in conditions of oxidative stress.

Cystic fibrosis is a lethal inherited disorder caused by mutations in a single gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, resulting in progressive oxidative lung damage. In this study, we evaluated the role of CFTR in the control of ubiquitin-proteasome activity and nuclear factor (NF)-kappaB/IkappaB-alpha signaling after lung oxidative stress. After a 64-hour exposure to hyperoxia-mediated oxidative stress, CFTR-deficient (cftr(-/-)) mice exhibited significantly elevated lung proteasomal activity compared with wild-type (cftr(+/+)) animals. This was accompanied by reduced lung caspase-3 activity and defective degradation of NF-kappaB inhibitor IkappaB-alpha. In vitro, human CFTR-deficient lung cells exposed to oxidative stress exhibited increased proteasomal activity and decreased NF-kappaB-dependent transcriptional activity compared with CFTR-sufficient lung cells. Inhibition of the CFTR Cl(-) channel by CFTR(inh-172) in the normal bronchial immortalized cell line 16HBE14o- increased proteasomal degradation after exposure to oxidative stress. Caspase-3 inhibition by Z-DQMD in CFTR-sufficient lung cells mimicked the response profile of increased proteasomal degradation and reduced NF-kappaB activity observed in CFTR-deficient lung cells exposed to oxidative stress. Taken together, these results suggest that functional CFTR Cl(-) channel activity is crucial for regulation of lung proteasomal degradation and NF-kappaB activity in conditions of oxidative stress.