Generation and characterization of a delta F508 cystic fibrosis mouse model

Effects of CFTR gene silencing by siRNA or the luminal application of a CFTR activator on fluid secretion from guinea-pig pancreatic duct cells

AIMS

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP regulated chloride channel expressed in the apical plasma membrane of pancreatic duct cells where it plays an important role in fluid secretion. The purpose of this study was to elucidate the role of the CFTR chloride channel on ion and fluid secretion from the guinea-pig pancreas by manipulating the expression of CFTR by RNA interference or by luminal application of a CFTR selective activator, MPB91, in isolated cultured pancreatic ducts.

MATERIALS AND METHODS

Using cDNA isolated from the guinea-pig small intestine, fragments of the CFTR gene were generated by polymerase chain reaction and directly sequenced. Two different RNA duplexes for small interference RNA (siRNA) were designed from the sequence obtained. Fluid secretion from the isolated guinea-pig pancreatic ducts was measured using video-microscopy. The amount of CFTR chloride channel or AQP1 water channel expressed in pancreatic ducts was examined by immunoblotting with antibodies against CFTR or AQP1, respectively.

RESULTS

Guinea-pig CFTR consists of 1481 amino acid residues. An additional glutamine residue was found to be inserted between amino acid residues 403 and 404 of human CFTR. Forskolin-stimulated fluid secretion from intact pancreatic ducts was significantly higher in the presence of MPB91 compared to fluid secretion in the absence of MPB91. Both basal and forskolin-stimulated fluid secretion in pancreatic ducts transfected with CFTR specific siRNAs were reduced by ∼50% compared to fluid secretion from ducts transfected with scrambled negative control dsRNAs. The amount of CFTR and AQP1 proteins was reduced to 34% and 45% of control, respectively.

CONCLUSIONS

The activity of the CFTR chloride channel or the amount of CFTR protein expressed determines the rate of fluid secretion from the isolated guinea-pig pancreatic ducts.

Role of CFTR expressed by neutrophils in modulating acute lung inflammation and injury in mice

Objective and design

Cystic fibrosis transmembrane conductance regulator (CFTR) regulates infection and inflammation. In this study, we investigated whether a lack of functional CFTR in neutrophils would promote lipopolysaccharide (LPS)-induced lung inflammation and injury.

Materials and methods

CFTR-inhibited or F508del-CFTR-mutated neutrophils were stimulated with LPS and cultured to evaluate production of cytokines and NF-κB activation. Wild-type mice were reconstituted with F508del neutrophils or bone marrow and then intratracheally challenged with LPS to observe lung inflammatory response.

Results

Pharmacologic inhibition and genetic mutation of CFTR in neutrophils activated NF-κB and facilitated macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor-α (TNF-α) production. Wild-type mice reconstituted with F508del neutrophils and bone marrow had more severe lung inflammation and injury after LPS challenge compared to wild-type mice receiving wild-type neutrophils or bone marrow reconstitution.

Conclusions

Lack of functional CFTR in neutrophils can promote LPS-induced acute lung inflammation and injury.

Comparative biology of cystic fibrosis animal models

Animal models of human diseases are critical for dissecting mechanisms of pathophysiology and developing therapies. In the context of cystic fibrosis (CF), mouse models have been the dominant species by which to study CF disease processes in vivo for the past two decades. Although much has been learned through these CF mouse models, limitations in the ability of this species to recapitulate spontaneous lung disease and several other organ abnormalities seen in CF humans have created a need for additional species on which to study CF. To this end, pig and ferret CF models have been generated by somatic cell nuclear transfer and are currently being characterized. These new larger animal models have phenotypes that appear to closely resemble human CF disease seen in newborns, and efforts to characterize their adult phenotypes are ongoing. This chapter will review current knowledge about comparative lung cell biology and cystic fibrosis transmembrane conductance regulator (CFTR) biology among mice, pigs, and ferrets that has implications for CF disease modeling in these species. We will focus on methods used to compare the biology and function of CFTR between these species and their relevance to phenotypes seen in the animal models. These cross-species comparisons and the development of both the pig and the ferret CF models may help elucidate pathophysiologic mechanisms of CF lung disease and lead to new therapeutic approaches.

Small intestinal glucose absorption in cystic fibrosis: a study in human and transgenic ΔF508 cystic fibrosis mouse tissues

Intestinal transport is disturbed in cystic fibrosis (CF), with both defective Cl− secretion and changes in absorption being reported. We have examined the effects of the disease on Na+-dependent glucose absorption by the small intestine. Active glucose absorption was monitored as changes in short-circuit current (SCC) in intact and stripped intestinal sheets from normal (Swiss) and transgenic CF (Cftrtm 1 Eur and Cftrtm 2 Cam) mice with the ΔF508 mutation, and in jejunal biopsies from children with CF and normal controls. Na+-dependent glucose uptake at the luminal membrane was measured in brush-border membrane vesicles (BBMVs). Intact and stripped sheets of jejunum and midintestine from Swiss mice exhibited a concentration-dependent increase in SCC with glucose. Apparent Km values were similar in the two preparations, but the apparent Vmax was greater in stripped sheets. This difference was not due to a loss of neural activity in stripped sheets as tetrodotoxin did not influence the glucose-induced SCC in intact sheets. Similar results were observed in stripped sheets of jejunum and mid-intestine from wild-type Cftrtm 1 Eur mice, but in tissues from CF mice the apparent Vmax value was reduced significantly. A lower Vmax was also obtained in intact sheets of mid-intestine from CF (Cftrtm 2 Cam) mice. Jejunal biopsies from CF patients however, exhibited an enhanced glucose-dependent rise in SCC. Na+-dependent uptake by BBMVs from CF (Cftrtm 1 Eur) mice was not reduced compared with wild-type and Swiss BBMVs. It was concluded that, in contrast to human intestine, intestinal glucose absorption was reduced in transgenic mouse models of CF with the ΔF508 mutation, but that this could not be detected in an isolated preparation of brush-border membranes. Transgenic mouse models of CF may not accurately reflect all aspects of intestinal dysfunction in the human disease.

Ducts isolated from the pancreas of CFTR-null mice secrete fluid

The pancreatic pathology in cystic fibrosis (CF) is normally attributed to the failure of ductal fluid secretion resulting from the lack of functional CF transmembrane conductance regulator (CFTR). However, murine models of CF show little or no pancreatic pathology. To resolve this dichotomy we analysed the transport mechanisms involved in fluid and electrolyte secretion by pancreatic ducts isolated from CFTR-null mice. Experiments were performed on cultured interlobular duct segments isolated from the pancreas of the Cftr(tm1Cam) strain of CFTR-null mouse. Fluid secretion to the closed luminal space was measured by video microscopy. The secretory response of ducts isolated from CF mice to cAMP-elevating agonists forskolin and secretin was significantly reduced compared with wild type but not abolished. The Cl(-)- and HCO(3) (-) -dependent components of the ductal secretion were affected equally by the absence of CFTR. The secretory response to carbachol stimulation was unaltered in CF ducts. Loading the ductal cells with the Ca2+ chelator BAPTA completely abolished carbachol-evoked secretion, but did not affect forskolin-evoked secretion in CF or wild-type ducts. We conclude that pancreatic duct cells from CF mice can secrete a significant amount of water and electrolytes by a cAMP-stimulated mechanism that is independent of CFTR and cannot be ascribed to the activation of calcium-activated chloride channels.

Impaired estrogen feedback and infertility in female mice with pituitary-specific deletion of estrogen receptor alpha (ESR1)

Mice lacking estrogen receptor alpha in the pituitary gonadotroph (PitEsr1KO) were generated to determine the physiologic role of pituitary estrogen signaling in the reproductive axis. PitEsr1KO female mice are subfertile or infertile and have elevated levels of serum luteinizing hormone (LH) and LH beta subunit gene expression, reflecting a lack of estrogen negative feedback effect on the gonadotroph. While serum LH values are elevated in PitEsr1KO mice, the degree of elevation is much less than that observed in ESR1-null mice, indicating that the hypothalamus must also have an important role in estrogen negative feedback. PitEsr1KO mice also demonstrate a defect in estrogen positive feedback, as surge LH values and estrous cyclicity are absent in these mice. Although sex steroid feedback in the reproductive axis is thought to involve discrete anatomic regions that mediate either a positive or negative estrogen effect, PitEsr1KO mice demonstrate novel evidence that localizes both estrogen positive feedback and estrogen negative feedback to the gonadotroph, which suggests that they may be mechanistically related.

Airway delivery of low-dose miglustat normalizes nasal potential difference in F508del cystic fibrosis mice

RATIONALE

N-butyldeoxynojyrimicin (NB-DNJ, miglustat [Zavesca]) an approved drug for treating Gaucher disease, was reported to be able to correct the defective trafficking of the F508del-CFTR protein.

OBJECTIVES

To evaluate the efficacy of in vivo airway delivery of miglustat for restoring ion transport in cystic fibrosis (CF).

METHODS

We used nasal transepithelial potential difference (PD) as a measure of sodium and chloride transport. The effect of nasal instillation of a single dose of miglustat was investigated in F508del, cftr knockout and normal homozygous mice. The galactose iminosugar analog N-butyldeoxygalactonojirimycin (NB-DGJ) was used as a placebo.

MEASUREMENTS AND MAIN RESULTS

In F508del mice, sodium conductance (evaluated by basal hyperpolarization) and chloride conductance (evaluated by perfusing the nasal mucosa with chloride-free solution in the presence of amiloride and forskolin) were normalized 1 hour after an intranasal dose of 50 picomoles of miglustat. Chloride conductance in the presence of 200 microM 4-4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of alternative chloride channels, was much higher after miglustat than after placebo. In cftr knockout mice, a normalizing effect was observed on sodium but not on chloride conductance.

CONCLUSIONS

Our results provide clear evidence that nasal delivery of miglustat, at picomolar doses, normalizes sodium and Cftr-dependent chloride transport in F508del transgenic mice; they highlight the potential of topical miglustat as a therapy for CF.

Generation and characterization of a complete null estrogen receptor alpha mouse using Cre/LoxP technology

Conventional estrogen receptor alpha knockout (neo-ERalphaKO, neo-ERalpha(-/-)) mice contain a truncated and chimeric ERalpha fusion protein that retains 35% estrogen-dependent transactivation activity, and therefore the in vivo ERalpha function is difficult to study thoroughly. Furthermore, these neo-ERalpha(-/-) mice cannot be used for tissue and temporal specific ERalpha deletion. Therefore, there is a clear need to establish a floxed ERalpha mouse line that can knockout ERalpha specifically and completely in each selected cell type. Here we generated floxed ERalpha mice using a self-excising ACN (tACE-Cre/Neo) cassette. Mating the floxed ERalpha mice with ACTB-Cre mice produces a deletion of the floxed allele disrupting the reading frame of the ERalpha transcript so that no ERalpha protein is detected in the ACTB-Cre/ERalpha(-/-) mice. Expression of ERalpha target genes, such as G-6-PD and lactoferrin, is diminished by over 90% in the ACTB-Cre/ERalpha(-/-) uterus, but not in the neo-ERalpha(-/-) uterus. Furthermore, we also validated that ACTB-Cre/ERalpha(-/-) females have a hypoplastic internal genital tract, polycystic ovaries with hemorrhagic follicles, infertility, and higher body weight. Together, our data clearly demonstrate that the newly established floxed ERalpha mouse is a reliable mouse model for future studies of ERalpha roles in vivo in the selective estrogen target tissues. The complete knockout of ERalpha in the ACTB-Cre/ERalpha(-/-) mice will also provide an improved mouse model to study the role of ERalpha in vivo.

Generation of a conditional null allele for Cftr in mice

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes a cAMP-regulated chloride channel that is important in controlling the exchange of fluid and electrolytes across epithelial cells. Mutation of CFTR can lead to cystic fibrosis (CF), the most common lethal genetic disease in Caucasians. CF is a systemic illness with multiple organ systems affected including pulmonary, gastrointestinal, pancreatic, immune, endocrine, and reproductive systems. To understand the role of CFTR in the various tissues in which it is expressed, we generated a murine conditional null allele of Cftr (Cftr(fl10)) in which loxP sites were inserted around exon 10 of the Cftr gene. The Cftr(fl10) allele was validated by generating constitutive Cftr null (Cftr(Delta10)) mice using the protamine-cre system. The Cftr(Delta10/Delta10) mice displayed almost identical phenotypes to previously published CF mouse models, including poor growth, decreased survival, intestinal obstruction, and loss of Cftr function as assessed by electrophysiology measurements on gut and nasal epithelium. Mice containing the conditional null Cftr allele will be useful in future studies to understand the role of Cftr in specific tissues and developmental time points and lead to a better understanding of CF disease.

Animal models of chronic lung infection with Pseudomonas aeruginosa: useful tools for cystic fibrosis studies

Cystic fibrosis (CF) is caused by a defect in the transmembrane conductance regulator (CFTR) protein that functions as a chloride channel. Dysfunction of the CFTR protein results in salty sweat, pancreatic insufficiency, intestinal obstruction, male infertility and severe pulmonary disease. In most patients with CF life expectancy is limited due to a progressive loss of functional lung tissue. Early in life a persistent neutrophylic inflammation can be demonstrated in the airways. The cause of this inflammation, the role of CFTR and the cause of lung morbidity by different CF-specific bacteria, mostly Pseudomonas aeruginosa, are not well understood. The lack of an appropriate animal model with multi-organ pathology having the characteristics of the human form of CF has hampered our understanding of the pathobiology and chronic lung infections of the disease for many years. This review summarizes the main characteristics of CF and focuses on several available animal models that have been frequently used in CF research. A better understanding of the chronic lung infection caused particularly by P. aeruginosa, the pathophysiology of lung inflammation and the pathogenesis of lung disease necessitates animal models to understand CF, and to develop and improve treatment.

Role of cilia, mucus, and airway surface liquid in mucociliary dysfunction: lessons from mouse models

Mucociliary clearance is an important primary innate defense mechanism that protects the lungs from deleterious effects of inhaled pollutants, allergens, and pathogens. Mucociliary dysfunction is a common feature of chronic airway diseases in humans. The mucociliary apparatus consists of three functional compartments, that is, the cilia, a protective mucus layer, and an airway surface liquid (ASL) layer, which work in concert to remove inhaled particles from the lung. A synopsis of clinical and pathological observations in patients with cystic fibrosis, primary ciliary dyskinesia, asthma, and chronic bronchitis indicates that abnormalities in each compartment of the mucociliary system can compromise mucus clearance and cause chronic airway disease. However, the mechanisms that lead to deficient mucus clearance are still incompletely understood. Genetically engineered mice with defects in individual elements of the mucociliary apparatus are powerful tools to study the pathogenesis of mucociliary dysfunction in vivo. In this concise review, I assess the pulmonary phenotypes of mouse models with genetically defined abnormalities in ciliary structure/function, mucus production, and ASL regulation, and discuss the results of these animal studies in the context of current pathogenetic hypotheses for mucociliary dysfunction. Recent data driven from these animal studies point to a critical role of ASL dehydration in the pathogenesis of mucociliary dysfunction and chronic airway disease. In mice with airway-specific overexpression of epithelial Na(+) channels (ENaC), which constitute a rate limiting pathway for absorption of salt and water from airway surfaces, ASL depletion caused reduced mucus clearance, and a spontaneous chronic airway disease with mucus obstruction, goblet cell metaplasia, chronic inflammation, reduced bacterial clearance, and high pulmonary mortality. This mouse model of mucociliary dysfunction will allow an in vivo evaluation of novel therapeutic strategies designed to improve mucociliary clearance, and will aid the preclinical development of novel therapies for chronic airway diseases.

Pathophysiological basis of liver disease in cystic fibrosis employing a DeltaF508 mouse model

The molecular pathogenesis of cystic fibrosis (CF) liver disease is unknown. This study investigates its earliest pathophysiological manifestations employing a mouse model carrying DeltaF508, the commonest human CF mutation. We hypothesized that, if increased bile salt spillage into the colon occurs as in the human disease, then this should lead to a hydrophobic bile salt profile and to "hyperbilirubinbilia" because of induced enterohepatic cycling of unconjugated bilirubin. Hyperbilirubinbilia may then lead to an increased bile salt-to-phospholipid ratio in bile and, following hydrolysis, precipitation of divalent metal salts of unconjugated bilirubin. We document in CF mice elevated fecal bile acid excretion and biliary secretion of more hydrophobic bile salts compared with control wild-type mice. Biliary secretion rates of bilirubin monoglucuronosides, bile salts, phospholipids, and cholesterol are increased significantly with an augmented bile salt-to-phospholipid ratio. Quantitative histopathology of CF livers displays mild early cholangiopathy in approximately 53% of mice and multifocal divalent metal salt deposition in cholangiocytes. We conclude that increased fecal bile acid loss leads to more hydrophobic bile salts in hepatic bile and to hyperbilirubinbilia, a major contributor in augmenting the bile salt-to-phospholipid ratio and endogenous beta-glucuronidase hydrolysis of bilirubin glucuronosides. The confluence of these perturbations damages intrahepatic bile ducts and facilitates entrance of unconjugated bilirubin into cholangiocytes. This study of the earliest stages of CF liver disease provides a framework for investigating the molecular pathophysiology of more advanced disease in murine models and in humans with CF.

Production of CFTR-null and CFTR-DeltaF508 heterozygous pigs by adeno-associated virus-mediated gene targeting and somatic cell nuclear transfer

Progress toward understanding the pathogenesis of cystic fibrosis (CF) and developing effective therapies has been hampered by lack of a relevant animal model. CF mice fail to develop the lung and pancreatic disease that cause most of the morbidity and mortality in patients with CF. Pigs may be better animals than mice in which to model human genetic diseases because their anatomy, biochemistry, physiology, size, and genetics are more similar to those of humans. However, to date, gene-targeted mammalian models of human genetic disease have not been reported for any species other than mice. Here we describe the first steps toward the generation of a pig model of CF. We used recombinant adeno-associated virus (rAAV) vectors to deliver genetic constructs targeting the CF transmembrane conductance receptor (CFTR) gene to pig fetal fibroblasts. We generated cells with the CFTR gene either disrupted or containing the most common CF-associated mutation (DeltaF508). These cells were used as nuclear donors for somatic cell nuclear transfer to porcine oocytes. We thereby generated heterozygote male piglets with each mutation. These pigs should be of value in producing new models of CF. In addition, because gene-modified mice often fail to replicate human diseases, this approach could be used to generate models of other human genetic diseases in species other than mice.

Defective formation of PKA/CnA-dependent annexin 2-S100A10/CFTR complex in DeltaF508 cystic fibrosis cells

Cystic fibrosis (CF) is characterised by impaired epithelial ion transport and is caused by mutations in the cystic fibrosis conductance regulator protein (CFTR), a cAMP/PKA and ATP-regulated chloride channel. We recently demonstrated a cAMP/PKA/calcineurin (CnA)-driven association between annexin 2 (anx 2), its cognate partner -S100A10 and cell surface CFTR. The complex is required for CFTR and outwardly rectifying chloride channel function in epithelia. Since the cAMP/PKA-induced Cl(-) current is absent in CF epithelia, we hypothesized that the anx 2-S100A10/CFTR complex may be defective in CFBE41o cells expressing the commonest F508del-CFTR (DeltaF-CFTR) mutation. Here, we demonstrate that, despite the presence of cell surface DeltaF-CFTR, cAMP/PKA fails to induce anx 2-S100A10/CFTR complex formation in CFBE41o- cells homozygous for F508del-CFTR. Mechanistically, PKA-dependent serine phosphorylation of CnA, CnA-anx 2 complex formation and CnA-dependent dephosphorylation of anx 2 are all defective in CFBE41o- cells. Immunohistochemical analysis confirms an abnormal cellular distribution of anx 2 in human and CF mouse epithelia. Thus, we demonstrate that cAMP/PKA/CnA signaling pathway is defective in CF cells and suggest that loss of anx 2-S100A10/CFTR complex formation may contribute to defective cAMP/PKA-dependent CFTR channel function.

The role of the UPS in cystic fibrosis

CF is an inherited autosomal recessive disease whose lethality arises from malfunction of CFTR, a single chloride (Cl^-) ion channel protein. CF patients harbor mutations in the CFTR gene that lead to misfolding of the resulting CFTR protein, rendering it inactive and mislocalized. Hundreds of CF-related mutations have been identified, many of which abrogate CFTR folding in the endoplasmic reticulum (ER). More than 70% of patients harbor the ΔF508 CFTR mutation that causes misfolding of the CFTR proteins. Consequently, mutant CFTR is unable to reach the apical plasma membrane of epithelial cells that line the lungs and gut, and is instead targeted for degradation by the UPS. Proteins located in both the cytoplasm and ER membrane are believed to identify misfolded CFTR for UPS-mediated degradation. The aberrantly folded CFTR protein then undergoes polyubiquitylation, carried out by an E1-E2-E3 ubiquitin ligase system, leading to degradation by the 26S proteasome. This ubiquitin-dependent loss of misfolded CFTR protein can be inhibited by the application of ‘corrector’ drugs that aid CFTR folding, shielding it from the UPS machinery. Corrector molecules elevate cellular CFTR protein levels by protecting the protein from degradation and aiding folding, promoting its maturation and localization to the apical plasma membrane. Combinatory application of corrector drugs with activator molecules that enhance CFTR Cl^- ion channel activity offers significant potential for treatment of CF patients.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

Preclinical evidence that sildenafil and vardenafil activate chloride transport in cystic fibrosis

RATIONALE

Sildenafil has been implicated in the activation of cystic fibrosis transmembrane conductance regulator (CFTR) protein. The effect was observed in vitro and in the presence of doses roughly 300 times larger than those commonly used for treating erectile dysfunction.

OBJECTIVES

To evaluate in vivo the therapeutic efficacy of clinical doses of sildenafil and vardenafil, two clinically approved phosphodiesterase 5 inhibitors, for activating ion transport in cystic fibrosis.

METHODS

We used transepithelial potential difference in vivo across the nasal mucosa as a measure of sodium and chloride transport. The effect of a single intraperitoneal injection of sildenafil (0.7 mg/kg) or vardenafil (0.14 mg/kg) was investigated in F508del, cftr knockout and normal homozygous mice.

MEASUREMENTS AND MAIN RESULTS

In F508del mice, but not in cftr knockout mice, the chloride conductance, evaluated by perfusing the nasal mucosa with a chloride-free solution in the presence of amiloride and with forskolin, was corrected 1 hour after sildenafil administration. A more prolonged effect, persisting for at least 24 hours, was observed with vardenafil. The forskolin response was increased after sildenafil and vardenafil in both normal and F508del mutant animals. In F508del mice, the chloride conductance in the presence of 200 microM 4-4'-diisothiocyanostilbene-2,2'-disulphonic acid, an inhibitor of alternative chloride channels, was much higher after sildenafil injection than after placebo treatment. No effect on the sodium conductance was detected in any group of animals.

CONCLUSIONS

Our results provide preclinical evidence that both drugs stimulate chloride transport activity of F508del-CFTR protein.

What have we learned from mouse models for cystic fibrosis?

Genetically modified mouse strains are important research tools for the study of numerous human diseases. These models provide us with differentiated tissues, which are not often available from human sources. Furthermore, they allow for testing the effects of genetic manipulation and experimental therapeutics on physiology and pathology. Their importance relies on the assumption that biological processes in the mouse very closely resemble those in humans. Cystic fibrosis (CF) is the most common lethal genetic disease in the Caucasian population. CF is a monogenic disease whose phenotype variability is also attributed to genetic variation in other genes, the so-called modifier genes. Modulation of such modifier genes could be a therapeutic strategy to treat CF. CF mice models have been essential not only for understanding the disease better, but also for the discovery of modifier genes and testing of chemical compounds developed to repair the main protein dysfunction in CF, the CF transmembrane conductance regulator. Mice were also indispensable in gene therapy trials and for the study of CF and non-CF lung response to bacterial infections and inflammation challenges, although no spontaneous lung disease is developed in these mice. In this review, mouse models and their most important contribution to the understanding and management of CF will be presented and discussed.

Processing and function of CFTR-DeltaF508 are species-dependent

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The most common mutation, a deletion of the phenylalanine at position 508 (DeltaF508), disrupts processing of the protein. Nearly all human CFTR-DeltaF508 is retained in the endoplasmic reticulum and degraded, preventing maturation to the plasma membrane. In addition, the F508 deletion reduces the activity of single CFTR channels. Human CFTR-DeltaF508 has been extensively studied to better understand its defects. Here, we adopted a cross-species comparative approach, examining human, pig, and mouse CFTR-DeltaF508. As with human CFTR-DeltaF508, the DeltaF508 mutation reduced the single-channel activity of the pig and mouse channels. However, the mutant pig and mouse proteins were at least partially processed like their wild-type counterparts. Moreover, pig and mouse CFTR-DeltaF508 partially restored transepithelial Cl(-) transport to CF airway epithelia. Our data, combined with earlier work, suggest that there is a gradient in the severity of the CFTR-DeltaF508 processing defect, with human more severe than pig or mouse. These findings may explain some previously puzzling observations in CF mice, they have important implications for evaluation of potential therapeutics, and they suggest new strategies for discovering the mechanisms that disrupt processing of human CFTR-DeltaF508.

Long-term docosahexaenoic acid therapy in a congenic murine model of cystic fibrosis

We used a congenic C57Bl/6J cystic fibrosis transmembrane conductance regulator (Cftr)(-/-) mouse model, which develops cystic fibrosis (CF)-like pathology in all organs, to evaluate the short- and long-term therapeutic effects of dietary docosahexaenoic acid (DHA). Thirty-day-old Cftr(-/-) mice and wild-type littermates were randomized to receive a liquid diet with or without DHA (40 mg/day). Animals were killed for histological and lipid analysis after 7, 30, and 60 days of therapy. DHA had no significant therapeutic or harmful effect on the lung, pancreas, or ileum of the Cftr(-/-) mice or their wild-type littermates. In contrast, dietary DHA resulted in highly significant amelioration of the severity of liver disease in the Cftr(-/-) mice, primarily a reduction in the degree of peri-portal inflammation. Additionally, these detailed measurements confirm our previous findings that Cftr(-/-) mice have significant alterations in the pancreas (except external acinar diameter), ileum, liver, lung, and salivary (except sublingual) glands at all ages compared with their age-matched wild-type littermates. In conclusion, inhibition of cytokines and/or eicosanoid metabolism and release of endogenous inhibitors of inflammation by DHA may account for the anti-inflammatory effects in the liver of this congenic murine model of CF. The potential therapeutic benefits of DHA in severe CF-associated liver disease remain to be explored.

Manipulating the mouse genome to engineer precise functional syntenic replacements with human sequence

We have devised a strategy (called recombinase-mediated genomic replacement, RMGR) to allow the replacement of large segments (>100 kb) of the mouse genome with the equivalent human syntenic region. The technique involves modifying a mouse ES cell chromosome and a human BAC by inserting heterotypic lox sites to flank the proposed exchange interval and then using Cre recombinase to achieve segmental exchange. We have demonstrated the feasibility of this approach by replacing the mouse alpha globin regulatory domain with the human syntenic region and generating homozygous mice that produce only human alpha globin chains. Furthermore, modified ES cells can be used iteratively for functional studies, and here, as an example, we have used RMGR to produce an accurate mouse model of human alpha thalassemia. RMGR has general applicability and will overcome limitations inherent in current transgenic technology when studying the expression of human genes and modeling human genetic diseases.

Cystic Fibrosis Mouse Models

Animal models of cystic fibrosis (CF) are powerful tools that enable the study of the mechanisms and complexities of human disease. Murine models have several intrinsic advantages compared with other animal models, including lower cost, maintenance, and rapid reproduction rate. Mice can be easily genetically manipulated by making transgenic or knockout mice, or by backcrossing to well-defined inbred strains in a reasonably short period of time. However, anatomic and immunologic differences between mice and humans mean that murine models have inherent limitations that must be considered when interpreting the results obtained from experimental models and applying these to the pathogenesis of CF disease in humans. This review will focus on the different CF mouse models available that represent diverse phenotypes observed in humans with CF and that can help researchers elucidate the diverse functions of the CFTR protein.

Azithromycin reduces spontaneous and induced inflammation in DeltaF508 cystic fibrosis mice

Background

Inflammation plays a critical role in lung disease development and progression in cystic fibrosis. Azithromycin is used for the treatment of cystic fibrosis lung disease, although its mechanisms of action are poorly understood. We tested the hypothesis that azithromycin modulates lung inflammation in cystic fibrosis mice.

Methods

We monitored cellular and molecular inflammatory markers in lungs of cystic fibrosis mutant mice homozygous for the ΔF508 mutation and their littermate controls, either in baseline conditions or after induction of acute inflammation by intratracheal instillation of lipopolysaccharide from Pseudomonas aeruginosa, which would be independent of interactions of bacteria with epithelial cells. The effect of azithromycin pretreatment (10 mg/kg/day) given by oral administration for 4 weeks was evaluated.

Results

In naive cystic fibrosis mice, a spontaneous lung inflammation was observed, characterized by macrophage and neutrophil infiltration, and increased intra-luminal content of the pro-inflammatory cytokine macrophage inflammatory protein-2. After induced inflammation, cystic fibrosis mice combined exaggerated cellular infiltration and lower anti-inflammatory interleukin-10 production. In cystic fibrosis mice, azithromycin attenuated cellular infiltration in both baseline and induced inflammatory condition, and inhibited cytokine (tumor necrosis factor-α and macrophage inflammatory protein-2) release in lipopolysaccharide-induced inflammation.

Conclusion

Our findings further support the concept that inflammatory responses are upregulated in cystic fibrosis. Azithromycin reduces some lung inflammation outcome measures in cystic fibrosis mice. We postulate that some of the benefits of azithromycin treatment in cystic fibrosis patients are due to modulation of lung inflammation.

Regulation of chemokine expression by NaCl occurs independently of cystic fibrosis transmembrane conductance regulator in macrophages

Chronic pulmonary inflammation and infection are the leading causes of morbidity and mortality in cystic fibrosis (CF). While the effect of mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) on airways remains controversial, some groups have demonstrated increases in Na(+) and Cl(-) in CF airway surface liquid compared to normal airways. We investigated the consequences of NaCl on pro-inflammatory chemokine and cytokine production by macrophages. Stimulation of mouse macrophages with increasing amounts of NaCl induced macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor-alpha (TNF-alpha) production. Further, co-incubation of macrophages with NaCl in the presence of either lipopolysaccharide (LPS) or TNF-alpha synergistically increased MIP-2 production. Both the NaCl and NaCl plus LPS responses were partially dependent on endogenous production and autocrine signaling by TNF-alpha. To investigate the role of CFTR in MIP-2 production, we compared the responses of wild-type and DeltaF508 CF mouse macrophages to NaCl and LPS. The responses of macrophages from both strains were indistinguishable. In addition, CFTR mRNA was not expressed in macrophages. Taken together, these findings suggest that NaCl stimulates MIP-2 production by macrophages through a mechanism that is partially dependent on TNF-alpha but independent of macrophage CFTR expression.

Distinct pattern of lung gene expression in theCftr-KO mice developing spontaneous lung disease compared with their littermate controls

Cystic fibrosis (CF) is caused by a defect in the CF transmembrane conductance regulator (CFTR) protein that functions as a chloride channel. Dysfunction of the CFTR protein results in salty sweat, pancreatic insufficiency, intestinal obstruction, male infertility, and severe pulmonary disease. Most of the morbidity and mortality of CF patients results from pulmonary complications. Differences in susceptibility to bacterial infection and variable degree of CF lung disease among CF patients remain unexplained. Many phenotypic expressions of the disease do not directly correlate with the type of mutation in the Cftr gene. Using a unique CF mouse model that mimics aspects of human CF lung disease, we analyzed the differential gene expression pattern between the normal lungs of wild-type mice (WT) and the affected lungs of CFTR knockout mice (KO). Using microarray analysis followed by quantitation of candidate gene mRNA and protein expression, we identified many interesting genes involved in the development of CF lung disease in mice. These findings point to distinct mechanisms of gene expression regulation between mice with CF and control mice.

Commercial applications of nuclear transfer cloning: three examples

Potential applications of cloning go well beyond the popularly envisioned replication of valuable animals. This is because targeted genetic modifications can be made in donor cells before nuclear transfer. Applications that are currently being pursued include therapeutic protein production in the milk and blood of transgenic cloned animals, the use of cells, tissues and organs from gene-modified animals for transplantation into humans and genetically modified livestock that produce healthier and safer products in an environmentally friendly manner. Commercial and social acceptance of one or more of these early cloning applications will lead to yet unimagined applications of nuclear transfer technology. The present paper summarises progress on three additional applications of nuclear transfer, namely the development of male livestock that produce single-sex sperm, the transfer of immune responses from animals to their clones to permit the production of unlimited supplies of unique polyclonal antibodies, and the generation of genetically modified animals that accurately mimic human diseases for the purpose of developing new therapies. However, the myriad applications of cloning will require appropriate safeguards to ensure safe, humane and responsible outcomes of the technology.

Culture of murine nasal epithelia: model for cystic fibrosis

The ion transport defects reported for human cystic fibrosis (CF) airways are reproduced in nasal epithelia of the CF mouse. Although this tissue has been studied in vivo using the nasal potential difference technique and as a native tissue mounted in the Ussing chamber, little information is available on cultured murine nasal epithelia. We have developed a polarized cell culture model of primary murine nasal epithelia in which the CF tissue exhibits not only a defect in cAMP-mediated Cl- secretion but also the Na+ hyperabsorption and upregulation of the Ca2+-activated Cl- conductance observed in human airways. Both the wild-type and CF cultures were constituted predominantly of undifferentiated cuboidal columnar cells, with most cultures exhibiting a small number of ciliated cells. Although no goblet cells were observed, RT-PCR demonstrated the expression of Muc5ac RNA after approximately 22 days in culture. The CF tissue exhibited an adherent layer of mucus similar to the mucus plaques reported in the distal airways of human CF patients. Furthermore, we found that treatment of CF preparations with a Na+ channel blocker for 7 days prevented formation of mucus adherent to epithelial surfaces. The cultured murine nasal epithelial preparation should be an excellent model tissue for gene transfer studies and pharmacological studies of Na+ channel blockers and mucolytic agents as well as for further characterization of CF ion transport defects. Culture of nasal epithelia from DeltaF508 mice will be particularly useful in testing drugs that allow DeltaF508 CFTR to traffic to the membrane.

Calcium-activated chloride channels

Calcium-activated chloride channels (CaCCs) play important roles in cellular physiology, including epithelial secretion of electrolytes and water, sensory transduction, regulation of neuronal and cardiac excitability, and regulation of vascular tone. This review discusses the physiological roles of these channels, their mechanisms of regulation and activation, and the mechanisms of anion selectivity and conduction. Despite the fact that CaCCs are so broadly expressed in cells and play such important functions, understanding these channels has been limited by the absence of specific blockers and the fact that the molecular identities of CaCCs remains in question. Recent status of the pharmacology and molecular identification of CaCCs is evaluated.

K+ secretion activated by luminal P2Y2 and P2Y4 receptors in mouse colon

Extracellular nucleotides are important regulators of epithelial ion transport, frequently exerting their action from the luminal side. Luminal P2Y receptors have previously been identified in rat distal colonic mucosa. Their activation by UTP and ATP stimulates K+ secretion. The aim of this study was to clarify which of the P2Y receptor subtypes are responsible for the stimulated K+ secretion. To this end P2Y2 and P2Y4 knock-out mice were used to measure distal colonic ion transport in an Ussing chamber. In mouse (NMRI) distal colonic mucosa, luminal UTP and ATP with similar potency induced a rapid and transient increase of the transepithelial voltage (V(te)) (UTP: from -0.81 +/- 0.23 to 3.11 +/- 0.61 mV, n = 24), an increase of equivalent short circuit current (I(sc)) by 166.9 +/- 22.8 microA cm(-2) and a decrease of transepithelial resistance (R(te)) from 29.4 +/- 2.4 to 23.5 +/- 2.0 Omega cm2. This effect was completely inhibited by luminal Ba2+ (5 mm, n = 5) and iberiotoxin (240 nm, n = 6), indicating UTP/ATP-stimulated K+ secretion. RT-PCR analysis of isolated colonic crypts revealed P2Y2, P2Y4 and P2Y6 specific transcripts. The luminal UTP-stimulated K+ secretion was still present in P2Y2 receptor knock-out mice, but significantly reduced (DeltaV(te): 0.83 +/- 0.26 mV) compared to wild-type littermates (DeltaV(te): 2.08 +/- 0.52 mV, n = 9). In P2Y4 receptor knock-out mice the UTP-induced K+ secretion was similarly reduced. Luminal UTP-stimulated K+ secretion was completely absent in P2Y2/P2Y4 double receptor KO mice. Basolateral UTP showed no effect. In summary, these results indicate that both the P2Y2 and P2Y4 receptors are present in the luminal membrane of mouse distal colonic mucosa, and stimulation of these receptors leads to K+ secretion.

Evidence against the Rescue of Defective ΔF508-CFTR Cellular Processing by Curcumin in Cell Culture and Mouse Models

Curcumin, the yellow colored component of the spice turmeric, has been reported to rescue defective DeltaF508-cystic fibrosis transmembrane conductance regulator (CFTR) cellular processing in homozygous mutant mice, restoring nasal potential differences and improving survival (Egan, M. E., Pearson, M., Weiner, S. A., Rajendran, V., Rubin, D., Glockner-Pagel, J., Canny, S., Du, K., Lukacs, G. L., and Caplan, M. J. (2004) Science 304, 600-602). Because of the implied potential use of curcumin or similar compounds in the therapy of cystic fibrosis caused by the DeltaF508 mutation, we tried to reproduce and extend the pre-clinical data of Egan et al. Fluorometric measurements of iodide influx in Fischer rat thyroid cells expressing DeltaF508-CFTR showed no effect of curcumin (1-40 microm) when added for up to 24 h prior to assay in cells grown at 37 degrees C. Controls, including 27 degrees C rescue and 4 mm phenylbutyrate at 37 degrees C, were strongly positive. Also, curcumin did not increase short circuit current in primary cultures of a human airway epithelium homozygous for DeltaF508-CFTR with a 27 degrees C rescue-positive control. Nasal potential differences in mice were measured in response to topical perfusion with serial solutions containing amiloride, low Cl-, and forskolin. Robust low Cl- and forskolin-induced hyperpolarization of 22 +/- 3 mV was found in wild type mice, with 2.1 +/- 0.4 mV hyperpolarization in DeltaF508 homozygous mutant mice. No significant increase in Cl-/forskolin hyperpolarization was seen in any of the 22 DeltaF508 mice studied using different curcumin preparations and administration regimens, including that used by Egan et al. Assay of serum curcumin by ethyl acetate extraction followed by liquid chromatography/mass spectrometry indicated a maximum serum concentration of 60 nm, well below that of 5-15 microm, where cellular effects by sarcoplasmic/endoplasmic reticulum calcium pump inhibition are proposed to occur. Our results do not support further evaluation of curcumin for cystic fibrosis therapy.

Absorption of taurocholic acid by the ileum of normal and transgenic DeltaF508 cystic fibrosis mice

Changes in intestinal transport in cystic fibrosis (CF) include both defective Cl(-) secretion and alterations in absorption. This study focused on the effects of CF on the active re-absorption of bile acids in the ileum of normal and transgenic CF mice. Taurocholic acid absorption was monitored as changes in short-circuit current (SCC) in intact and stripped ileal sheets from normal (Swiss) and transgenic CF (Cftr(tm2Cam)) mice with the DeltaF508 mutation. Taurocholic acid uptake was measured directly in everted ileal sacs and in brush-border membrane vesicles (BBMVs) using radiolabelled bile acid. Taurocholic acid caused a biphasic increase in SCC in both intact and stripped ileal sheets from Swiss mice. The initial phase of the response was associated with active bile acid absorption as it was inhibited by a low mucosal Na(+) concentration, but unaffected by Cl(-)-free conditions, serosal furosemide or mucosal diphenylamine-2-carboxylic acid (DPC). The first phase was concentration-dependent and was reduced in the presence of other actively transported bile acids. Intact ileal sheets from wild-type Cftr(tm2Cam) mice also exhibited a biphasic SCC response to taurocholic acid, but in CF tissues the initial phase was reduced and the second phase was absent. Taurocholic acid was actively taken up by everted ileal sacs from Swiss mice. This process was inhibited by a low mucosal Na(+) concentration or the presence of other actively transported bile acids. A similar taurocholic acid uptake was observed in ileal sacs from wild-type mice, but in those from CF mice transport of the bile acid was significantly reduced. However, taurocholic acid uptake was similar in BBMVs from wildtype and CF ilea. Active absorption of taurocholic acid occurs in mouse ileum and this process is reduced in transgenic mouse models of CF with the DeltaF508 mutation. However, this difference cannot be detected in an isolated preparation of brush-border membranes.

Animal models of cystic fibrosis

Animal models of cystic fibrosis, in particular several different mutant mouse strains obtained by homologous recombination, have contributed considerably to our understanding of CF pathology. In this review, we describe and compare the main phenotypic features of these models. Recent and possible future developments in this field are discussed.

Hepatic iodothyronine deiodinase type 1 activity is decreased in two ΔF508 cystic fibrosis mouse models

BACKGROUND

Abnormal thyroid status has been reported in cystic fibrosis (CF) patients, and this can possibly be correlated to neuromuscular symptoms. Iodothyronine deiodinase type 1 (D1) activity is an important determinant of thyroid status, and we chose to investigate D1 activity in CF liver.

METHODS

We have measured hepatic D1 activities in two DeltaF508 CF mouse models.

RESULTS

Hepatic D1 activity was significantly reduced by 31% to 48% in homozygous DeltaF508 mice compared with wild-type genotypes.

CONCLUSIONS

A decreased hepatic D1 activity could be the biochemical basis of some of the abnormal thyroid parameters observed in cystic fibrosis patients.

Characteristic multiorgan pathology of cystic fibrosis in a long-living cystic fibrosis transmembrane regulator knockout murine model

The lack of an appropriate animal model with multiorgan pathology characteristic of the human form of cystic fibrosis has hampered our understanding of the pathobiology of the disease. We evaluated multiple organs of congenic C57BL/6J cystic fibrosis transmembrane regulator (Cftr)(-/-) and Cftr(+/+) mice maintained from weaning on a liquid diet then sacrificed between 1 and 24 months of age. The lungs of the Cftr(-/-) animals showed patchy alveolar overdistention, interstitial thickening, and fibrosis, with progression up to 6 months of age. The proximal and distal airway surface was encased with mucus-like material but lacked overt evidence of chronic bacterial infections or inflammation. All Cftr(-/-) animals showed progressive liver disease, with hepatosteatosis, focal cholangitis, inspissated secretions, and bile duct proliferation; after 1 year of age there was progression to focal biliary cirrhosis. The intercalated, intralobular and interlobular ducts and acinar lumina of the exocrine pancreas, the parotid and submaxillary glands of the Cftr(-/-) animals were dilated and filled with inspissated material, as well as mild inflammation and acinar cell drop out. Quantitative measurements of the pancreas showed significant acinar atrophy and increased acinar volume in comparison with age-matched Cftr(+/+) littermates. The ileal lumen and crypts were filled with adherent fibrillar material. After 3 months of age the vas deferens of the Cftr(-/-) animals could not be identified. None of the aforementioned pathological changes were observed in the Cftr(+/+) littermates fed the same liquid diet. We show, for the first time, that long-lived C578L/6J Cftr(-/-) mice develop manifestations of cystic fibrosis-like disease in all pathologically affected organs in the human form of cystic fibrosis.

Instability of the insertional mutation in CftrTgH(neoim)Hgu cystic fibrosis mouse model

Background

A major boost to the cystic fibrosis disease research was given by the generation of various mouse models using gene targeting in embryonal stem cells. Moreover, the introduction of the same mutation on different inbred strains generating congenic strains facilitated the search for modifier genes. From the original Cftr^{TgH(neoim)Hgu} CF mouse model we have generated using strict brother × sister mating two inbred Cftr^{TgH(neoim)Hgu} mouse lines (CF/1 and CF/3). Thereafter, the insertional mutation was introgressed from CF/3 into three inbred backgrounds (C57BL/6, BALB/c, DBA/2J) generating congenic animals. In every backcross cycle germline transmission of the insertional mutation was monitored by direct probing the insertion via Southern RFLP. In order to bypass this time consuming procedure we devised an alternative PCR based protocol whereby mouse strains are differentiated at the Cftr locus by Cftr intragenic microsatellite genotypes that are tightly linked to the disrupted locus.

Results

Using this method we were able to identify animals carrying the insertional mutation based upon the differential haplotypic backgrounds of the three inbred strains and the mutant Cftr^{TgH(neoim)Hgu} at the Cftr locus. Moreover, this method facilitated the identification of the precise vector excision from the disrupted Cftr locus in two out of 57 typed animals. This reversion to wild type status took place without any loss of sequence revealing the instability of insertional mutations during the production of congenic animals.

Conclusions

We present intragenic microsatellite markers as a tool for fast and efficient identification of the introgressed locus of interest in the recipient strain during congenic animal breeding. Moreover, the same genotyping method allowed the identification of a vector excision event, posing questions on the stability of insertional mutations in mice.

Evaluation of gene targeting by homologous recombination in ovine somatic cells

Mouse models for some human genetic diseases are limited in their applications since they do not accurately reproduce the phenotype of the human disease. It has been suggested that larger animals, for example sheep, might produce more useful models, as some aspects of sheep physiology and anatomy are more similar to those of humans. The development of methods to clone animals from somatic cells provides a potential novel route to generate such large animal models following gene targeting. Here, we assess targeting of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in ovine somatic cells using homologous recombination (HR) of targeting constructs with extensive (>11 kb) homology. Electroporation of these constructs into ovine fetal and post-natal fibroblasts generated G418-resistant clones, but none analyzed had undergone HR, suggesting that at least for this locus, it is an extremely inefficient process. Karyotyping of targeted ovine fetal fibroblasts showed them to be less chromosomally stable than post-natal fibroblasts, and, moreover, extended culture periods caused them to senesce, adversely affecting their viability for use as nuclear transfer donor cells. These data stress the importance of donor cell choice in somatic cell cloning and suggest that culture time be kept to a minimum prior to nuclear transfer in order to maximize cell viability.

Modulation of Ca2+-activated Cl- secretion by basolateral K+ channels in human normal and cystic fibrosis airway epithelia

Human airway epithelia express Ca2+-activated Cl- channels (CaCC) that are activated by extracellular nucleotides (ATP and UTP). CaCC is preserved and seems to be up-regulated in the airways of cystic fibrosis (CF) patients. In the present study, we examined the role of basolateral K+ channels in CaCC-mediated Cl- secretion in native nasal tissues from normal individuals and CF patients by measuring ion transport in perfused micro Ussing chambers. In the presence of amiloride, UTP-mediated peak secretory responses were increased in CF compared with normal nasal tissues. Activation of the cAMP pathway further increased CaCC-mediated secretion in CF but not in normal nasal mucosa. CaCC-dependent ion transport was inhibited by the chromanol 293B, an inhibitor of cAMP-activated hKvLQT1 K+ channels, and by clotrimazole, an inhibitor of Ca2+-activated hSK4 K+ channels. The K+ channel opener 1-ethyl-2-benzimidazolinone further increased CaCC-mediated Cl- secretion in normal and CF tissues. Expression of hSK4 as well as hCACC-2 and hCACC-3 but not hCACC-1 was demonstrated by reverse transcriptase PCR on native nasal tissues. We conclude that Ca2+-activated Cl- secretion in native human airway epithelia requires activation of Ca2+-dependent basolateral K+ channels (hSK4). Co-activation of hKvLQT1 improves CaCC-mediated Cl- secretion in native CF airway epithelia, and may have a therapeutic effect in the treatment of CF lung disease.

Hypersusceptibility of cystic fibrosis mice to chronic Pseudomonas aeruginosa oropharyngeal colonization and lung infection

No transgenic cystic fibrosis (CF) mouse model developed to date mimics the major clinical phenotype found in humans with CF, chronic Pseudomonas aeruginosa lung infection. In a transgenic CF transmembrane conductance regulator (cftr) mouse colony, we found WT, heterozygous, and homozygous CF mice housed in the same cage became chronically colonized in the oropharynx with environmental P. aeruginosa when the bacterium was present in drinking water. Elimination of P. aeruginosa from drinking water resulted in clearance in most WT and CF heterozygous, but not homozygous mice. For experimental evaluation, a combination of specific animal husbandry techniques and an oral infection route showed cftr(-/-) mice but not WT mice can be chronically colonized by P. aeruginosa with subsequent lung translocation, yielding a pathologic picture indicative of chronic lung infection. In some instances, mucoid isolates of P. aeruginosa were recovered from lungs, indicating conditions were present for conversion to mucoidy. Overexpression of human CFTR in the lungs of WT mice markedly accelerated the clearance rate of P. aeruginosa, demonstrating that lung levels of CFTR play an important role in defense against infection. P. aeruginosa mutants unable to express the surface polysaccharide alginate or the global regulator GacA were deficient in their ability to colonize the mice. CF mice made potent immune responses to P. aeruginosa outer membrane antigens. Overall, we found that under the proper conditions, transgenic CF mice are hypersusceptible to P. aeruginosa colonization and infection and can be used for evaluations of lung pathophysiology, bacterial virulence, and development of therapies aimed at treating CF lung disease.

Loci of intestinal distress in cystic fibrosis knockout mice

The strain-dependent survival of cystic fibrosis (CF) knockout mice has been used to map a modifier of CF, Cfm1, in mice and, subsequently, in humans. To identify additional modifiers of the CF phenotype, in this study, the survival of F2 CF mice derived from a cross between congenic C57BL/6J CF and BALB/cJ CF heterozygotes was followed up to 12 wk of age. A genome-wide linkage scan completed in F2 CF mice revealed a chromosome 10 locus (P = 1.2 x 10(-4)) to predict for intestinal distress in CF male mice. An X chromosome locus for which non-Mendelian inheritance favoring B6 alleles in the surviving CF mice and BALB alleles in mice of a control population, was identified. The survival of female mice, both F2 CF and F2 control, was linked to loci on chromosomes 3 and 5. The identification of additional putative CF modifier loci may permit further genetic dissection of the complex CF phenotype.

Chloride channels in the kidney: lessons learned from knockout animals

Cl- channels are involved in a range of functions, including regulation of cell volume and/or intracellular pH, acidification of intracellular vesicles, and vectorial transport of NaCl across many epithelia. Numerous Cl- channels have been identified in the kidney, based on single-channel properties such as conductance, anion selectivity, gating, and response to inhibitors. The molecular counterpart of many of these Cl- channels is still not known. This review will focus on gene-targeted mouse models disrupting two structural classes of Cl- channels that are relevant for the kidney: the CLC family of voltage-gated Cl- channels and the CFTR. Disruption of several members of the CLC family in the mouse provided useful models for various inherited diseases of the kidney, including Dent's disease and diabetes insipidus. Mice with disrupted CFTR are valuable models for cystic fibrosis (CF), the most common autosomal recessive, lethal disease in Caucasians. Although CFTR is expressed in various nephron segments, there is no overt renal phenotype in CF. Analysis of CF mice has been useful to identify the role and potential interactions of CFTR in the kidney. Furthermore, observations made in CF mice are potentially relevant to all other models of Cl- channel knockouts because they emphasize the importance of alternative Cl- pathways in such models.

Disease genes: flattery and deception

Completion of the human genome project raises the possibility of genetically based treatments for a multitude of human diseases. As yet only a handful of patients have benefited clinically from this approach. Why gene transfer is such a complex issue is discussed in this article. Theoretically, the easiest diseases to treat are single gene recessive diseases, where, presumably, gene delivery to somatic cells is all that is required. Two prime candidates for gene therapy are severe combined immunodeficiency disease (SCID) and cystic fibrosis (CF). Attempts to treat both of these diseases by gene therapy commenced in the late 1980s. Some clinical benefit has been recorded with SCID, but none, as yet, has been recorded with CF.

Mutations in the nucleotide binding domain 1 signature motif region rescue processing and functional defects of cystic fibrosis transmembrane conductance regulator delta f508

The gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), an ATP binding cassette (ABC) transporter that functions as a phosphorylation- and nucleotide-regulated chloride channel, is mutated in cystic fibrosis (CF) patients. Deletion of a phenylalanine at amino acid position 508 (DeltaF508) in the first nucleotide binding domain (NBD1) is the most prevalent CF-causing mutation and results in defective protein processing and reduced CFTR function, leading to chloride impermeability in CF epithelia and heterologous systems. Using a STE6/CFTRDeltaF508 chimera system in yeast, we isolated two novel DeltaF508 revertant mutations, I539T and G550E, proximal to and within the conserved ABC signature motif of NBD1, respectively. Western blot and functional analysis in mammalian cells indicate that mutations I539T and G550E each partially rescue the CFTRDeltaF508 defect. Furthermore, a combination of both revertant mutations resulted in a 38-fold increase in CFTRDeltaF508-mediated chloride current, representing 29% of wild type channel activity. The G550E mutation increased the sensitivity of CFTRDeltaF508 and wild type CFTR to activation by cAMP agonists and blocked the enhancement of CFTRDeltaF508 channel activity by 2 mm 3-isobutyl-1-methylxanthine. The data show that the DeltaF508 defect can be significantly rescued by second-site mutations in the nucleotide binding domain 1 region, that includes the LSGGQ consensus motif.

The mousetrap: what we can learn when the mouse model does not mimic the human disease

In recent years, mouse models for human metabolic diseases have become commonplace because the information gained from in vivo study of biochemical pathways is invaluable, and many metabolic diseases are relatively easy to recreate in mice through gene knockout technology in embryonic stem cells. In certain cases, however, the knockout mice may reproduce only some of the human disease phenotype, may be more severely affected than human cases, or may have no clinical phenotype at all. Under these circumstances, the disease pathology can become more complex, causing the researcher to evaluate basic differences in mouse and human biology as well as questions of genetic background, alternate pathways, and possible gene interactions. This review is a brief analysis of gene knockout models for Lesch-Nyhan syndrome, Lowe syndrome, X-linked adrenoleukodystrophy, Fabry disease, galactosemia, glycogen storage disease type II, metachromatic leukodystrophy, and Tay-Sachs disease, which produce a biochemical model of disease but often do not reproduce clinical symptoms. These mice may be useful for studying the biochemical and physiological pathways in which certain metabolites function toward embryonic and fetal development, as well as specific functions in various organs, and they may provide an inexpensive and useful model system for development of new therapeutic techniques.

Novel role for CFTR in fluid absorption from the distal airspaces of the lung

The active absorption of fluid from the airspaces of the lung is important for the resolution of clinical pulmonary edema. Although ENaC channels provide a major route for Na(+) absorption, the route of Cl(-) transport has been unclear. We applied a series of complementary approaches to define the role of Cl(-) transport in fluid clearance in the distal airspaces of the intact mouse lung, using wild-type and cystic fibrosis Delta F508 mice. Initial studies in wild-type mice showed marked inhibition of fluid clearance by Cl(-) channel inhibitors and Cl(-) ion substitution, providing evidence for a transcellular route for Cl(-) transport. In response to cAMP stimulation by isoproterenol, clearance was inhibited by the CFTR inhibitor glibenclamide in both wild-type mice and the normal human lung. Although isoproterenol markedly increased fluid absorption in wild-type mice, there was no effect in Delta F508 mice. Radioisotopic clearance studies done at 23 degrees C (to block active fluid absorption) showed approximately 20% clearance of (22)Na in 30 min both without and with isoproterenol. However, the clearance of (36)Cl was increased by 47% by isoproterenol in wild-type mice but was not changed in Delta F508 mice, providing independent evidence for involvement of CFTR in cAMP-stimulated Cl(-) transport. Further, CFTR played a major role in fluid clearance in a mouse model of acute volume-overload pulmonary edema. After infusion of saline (40% body weight), the lung wet-to-dry weight ratio increased by 28% in wild-type versus 64% in Delta F508 mice. These results provide direct evidence for a functionally important role for CFTR in the distal airspaces of the lung.

DeltaF508-CFTR causes constitutive NF-kappaB activation through an ER-overload response in cystic fibrosis lungs

The clinical course of Cystic Fibrosis is characterized by recurrent pulmonary infections which ultimately lead to death by respiratory failure. The most common CF causing mutation, deltaF508-CFTR, produces an incorrectly folded protein, which accumulates within the endoplasmic reticulum. However, the molecular mechanism by which the deltaF508-CFTR protein facilitates pulmonary infection and inflammation remains unclear. Here we show that the expression of deltaF508-CFTR causes a constitutive activation of the pro-inflammatory transcription factor NF-kappaB by eliciting an ER stress reaction, the ER-overload response. This endogenous NF-kappaB activation stimulates the transcription of pro-inflammatory cytokines thereby commencing an inflammatory cascade within the CF lung.

Electrolyte transport in the mammalian colon: mechanisms and implications for disease

The colonic epithelium has both absorptive and secretory functions. The transport is characterized by a net absorption of NaCl, short-chain fatty acids (SCFA), and water, allowing extrusion of a feces with very little water and salt content. In addition, the epithelium does secret mucus, bicarbonate, and KCl. Polarized distribution of transport proteins in both luminal and basolateral membranes enables efficient salt transport in both directions, probably even within an individual cell. Meanwhile, most of the participating transport proteins have been identified, and their function has been studied in detail. Absorption of NaCl is a rather steady process that is controlled by steroid hormones regulating the expression of epithelial Na(+) channels (ENaC), the Na(+)-K(+)-ATPase, and additional modulating factors such as the serum- and glucocorticoid-regulated kinase SGK. Acute regulation of absorption may occur by a Na(+) feedback mechanism and the cystic fibrosis transmembrane conductance regulator (CFTR). Cl(-) secretion in the adult colon relies on luminal CFTR, which is a cAMP-regulated Cl(-) channel and a regulator of other transport proteins. As a consequence, mutations in CFTR result in both impaired Cl(-) secretion and enhanced Na(+) absorption in the colon of cystic fibrosis (CF) patients. Ca(2+)- and cAMP-activated basolateral K(+) channels support both secretion and absorption of electrolytes and work in concert with additional regulatory proteins, which determine their functional and pharmacological profile. Knowledge of the mechanisms of electrolyte transport in the colon enables the development of new strategies for the treatment of CF and secretory diarrhea. It will also lead to a better understanding of the pathophysiological events during inflammatory bowel disease and development of colonic carcinoma.

Trafficking of GFP-tagged DeltaF508-CFTR to the plasma membrane in a polarized epithelial cell line

The DeltaF508 mutation reduces the amount of cystic fibrosis transmembrane conductance regulator (CFTR) expressed in the plasma membrane of epithelial cells. However, a reduced temperature, butyrate compounds, and "chemical chaperones" allow DeltaF508-CFTR to traffic to the plasma membrane and increase Cl(-) permeability in heterologous and nonpolarized cells. Because trafficking is affected by the polarized state of epithelial cells and is cell-type dependent, our goal was to determine whether these maneuvers induce DeltaF508-CFTR trafficking to the apical plasma membrane in polarized epithelial cells. To this end, we generated and characterized a line of polarized Madin-Darby canine kidney (MDCK) cells stably expressing DeltaF508-CFTR tagged with green fluorescent protein (GFP). A reduced temperature, glycerol, butyrate, or DMSO had no effect on 8-(4-chlorophenylthio)-cAMP (CPT-cAMP)-stimulated transepithelial Cl(-) secretion across polarized monolayers. However, when the basolateral membrane was permeabilized, butyrate, but not the other experimental maneuvers, increased the CPT-cAMP-stimulated Cl(-) current across the apical plasma membrane. Thus butyrate increased the amount of functional DeltaF508-CFTR in the apical plasma membrane. Butyrate failed to stimulate transepithelial Cl(-) secretion because of inhibitory effects on Cl(-) uptake across the basolateral membrane. These observations suggest that studies on heterologous and nonpolarized cells should be interpreted cautiously. The GFP tag on DeltaF508-CFTR will allow investigation of DeltaF508-CFTR trafficking in living, polarized MDCK epithelial cells in real time.

Ursodeoxycholic acid action on the transport function of the small intestine in normal and cystic fibrosis mice

Ursodeoxycholic acid possesses choleretic and cytoprotective properties and in cystic fibrosis (CF) it is used to treat the hepatobiliary symptoms of the disease. This study investigated the effects of this bile acid on the transport function of the small intestine in normal and CF mice. The effects of ursodeoxycholic acid were monitored as changes in short-circuit current (SCC) in stripped sheets of small intestine from normal (Swiss MF1) and transgenic CF (Cftr(tm2Cam)) mice. In ileal sheets from Swiss MF1 mice, mucosal ursodeoxycholic acid caused a biphasic increase in SCC. The first phase was reduced by lowering the mucosal Na+ concentration, while the second phase was inhibited by (Cl-)-free conditions, serosal furosemide or mucosal diphenylamine-2-carboxylic acid (DPC), suggesting an initial Na+-dependent bile acid absorption followed by a stimulation of electrogenic Cl- secretion. Serosal application of ursodeoxycholic acid to the ileum and mucosal or serosal application to the mid-intestine and jejunum elicited a secretory response only. Secretion was Ca2+-dependent, but did not involve neural mechanisms. Mucosal mast cells, histamine and serotonin (5-HT) were implicated in the secretory response. Responses in tissues from transgenic wild-type mice were similar to those obtained with Swiss MF1 mice, but the secretory response to mucosal or serosal application of the bile acid was impaired in CF tissues. In ilea from CF mice the initial absorptive phase of the response to mucosal ursodeoxycholic acid was still observed. It is concluded that ursodeoxycholic acid induces secretion throughout the murine small intestine by a mechanism that involves degranulation of mucosal mast cells. In the ileum Na+-dependent absorption can also be detected. The secretory response is defective in CF intestine, but the absorptive effect is still present.