Martina Wilke

Mouse models of cystic fibrosis: phenotypic analysis and research applications

Genetically modified mice have been studied for more than fifteen years as models of cystic fibrosis (CF). The large amount of experimental data generated illuminates the complex multi-organ pathology of CF and raises new questions relevant to human disease. CF mice have also been used to test experimental therapies prior to clinical trials. This review recapitulates the major phenotypic traits of CF mice and highlights important new findings including aberrant alveolar macrophages, bone and cartilage abnormalities and abnormal bioactive lipid metabolism. Novel data are presented on the intestinal and nasal physiology of F508del-CFTR CF mice backcrossed onto different genetic backgrounds. Caveats, and sources of variability including age, gender and animal husbandry, are discussed. Interspecies differences limit comparison of lung pathology in CF mice to the human disease. The recent development of genetically modified pigs and ferrets heralds the application of more advanced animal models to CF research and drug development.

Rescue of functional delF508-CFTR channels in cystic fibrosis epithelial cells by the α-glucosidase inhibitor miglustat

In the disease cystic fibrosis (CF), the most common mutation delF508 results in endoplasmic reticulum retention of misfolded CF gene proteins (CFTR). We show that the α‐1,2‐glucosidase inhibitor miglustat (N‐butyldeoxynojirimycin, NB‐DNJ) prevents delF508‐CFTR/calnexin interaction and restores cAMP‐activated chloride current in epithelial CF cells. Moreover, miglustat rescues a mature and functional delF508‐CFTR in the intestinal crypts of ileal mucosa from delF508 mice. Since miglustat is an orally active orphan drug (Zavesca®) prescribed for the treatment of Gaucher disease, our findings provide the basis for future clinical evaluation of miglustat in CF patients.

The Hematopoietic System-specific Minor Histocompatibility Antigen HA-1 Shows Aberrant Expression in Epithelial Cancer Cells

Allogeneic stem cell transplantation (SCT) can induce curative graft-versus-tumor reactions in patients with hematological malignancies and solid tumors. The graft-versus-tumor reaction after human histocompatibility leukocyte antigen (HLA)-identical SCT is mediated by alloimmune donor T cells specific for polymorphic minor histocompatibility antigens (mHags). Among these, the mHag HA-1 was found to be restricted to the hematopoietic system. Here, we report on the HA-1 ribonucleic acid expression by microdissected carcinoma tissues and by single disseminated tumor cells isolated from patients with various epithelial tumors. The HA-1 peptide is molecularly defined, as it forms an immunogenic peptide ligand with HLA-A2 on the cell membrane of carcinoma cell lines. HA-1–specific cytotoxic T cells lyse epithelial tumor cell lines in vitro, whereas normal epithelial cells are not recognized. Thus, HA-1–specific immunotherapy combined with HLA-identical allogeneic SCT may now be feasible for patients with HA-1+ carcinomas.

Correction of the ΔPhe508 Cystic Fibrosis Transmembrane Conductance Regulator Trafficking Defect by the Bioavailable Compound Glafenine

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes a cAMP-activated anion channel expressed in epithelial cells. The most common mutation ΔPhe508 leads to protein misfolding, retention by the endoplasmic reticulum, and degradation. One promising therapeutic approach is to identify drugs that have been developed for other indications but that also correct the CFTR trafficking defect, thereby exploiting their known safety and bioavailability in humans and reducing the time required for clinical development. We have screened approved, marketed, and off-patent drugs with known safety and bioavailability using a ΔPhe508-CFTR trafficking assay. Among the confirmed hits was glafenine, an anthranilic acid derivative with analgesic properties. Its ability to correct the misprocessing of CFTR was confirmed by in vitro and in vivo studies using a concentration that is achieved clinically in plasma (10 μM). Glafenine increased the surface expression of ΔPhe508-CFTR in baby hamster kidney (BHK) cells to ∼40% of that observed for wild-type CFTR, comparable with the known CFTR corrector 4-cyclohexyloxy-2-{1-[4-(4-methoxybenzensulfonyl)-piperazin-1-yl]-ethyl}-quinazoline (VRT-325). Partial correction was confirmed by the appearance of mature CFTR in Western blots and by two assays of halide permeability in unpolarized BHK and human embryonic kidney cells. Incubating polarized CFBE41o− monolayers and intestines isolated from ΔPhe508-CFTR mice (treated ex vivo) with glafenine increased the short-circuit current (Isc) response to forskolin + genistein, and this effect was abolished by 10 μM CFTRinh172. In vivo treatment with glafenine also partially restored total salivary secretion. We conclude that the discovery of glafenine as a CFTR corrector validates the approach of investigating existing drugs for the treatment of CF, although localized delivery or further medicinal chemistry may be needed to reduce side effects.

The cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in maturation stage ameloblasts, odontoblasts and bone cells.

Patients with cystic fibrosis (CF) have mild defects in dental enamel. The gene mutated in these patients is CFTR, a Cl(-) channel involved in transepithelial salt and water transport and bicarbonate secretion. We tested the hypothesis that Cftr channels are present and operating in the plasma membranes of mouse ameloblasts. Tissue sections of young mouse jaws and fetal human jaws were immunostained with various anti-Cftr antibodies. Specificity of the antibodies was validated in Cftr-deficient murine and human tissues. Immunostaining for Cftr was obtained in the apical plasma membranes of mouse maturation ameloblasts of both incisor and molar tooth germs. A granular intracellular immunostaining of variable intensity was also noted in bone cells and odontoblasts. In Cftr-deficient mice the incisors were chalky white and eroded much faster than in wild type mice. Histologically, only maturation ameloblasts of incisors were structurally affected in Cftr-deficient mice. Some antibody species gave also a positive cytosolic staining in Cftr-deficient cells. Transcripts of Cftr were found in maturation ameloblasts, odontoblasts and bone cells. Similar data were obtained in forming human dentin and bone. We conclude that Cftr protein locates in the apical plasma membranes of mouse maturation ameloblasts. In mouse incisors Cftr is critical for completion of enamel mineralization and conceivably functions as a regulator of pH during rapid crystal growth. Osteopenia found in CF patients as well as in Cftr-deficient mice is likely associated with defective Cftr operating in bone cells.

Parallel Improvement of Sodium and Chloride Transport Defects by Miglustat (n-Butyldeoxynojyrimicin) in Cystic Fibrosis Epithelial Cells

Cystic fibrosis, an autosomal recessive disease frequently diagnosed in the Caucasian population, is characterized by deficient Cl- transport due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. A second major hall-mark of the disease is Na+ hyperabsorption by the airways, mediated by the epithelial Na+ channel (ENaC). In this study, we report that in human airway epithelial CF15 cells treated with the CFTR corrector miglustat (n-butyldeoxynojyrimicin), whole-cell patch-clamp experiments showed reduced amiloride-sensitive ENaC current in parallel with a rescue of defective CFTR Cl- channel activity activated by forskolin and genistein. Similar results were obtained with cells maintained in culture at 27°C for 24 h before electrophysiology experiments. With monolayers of polarized CF15 cells, short-circuit current (Isc) measurements also show normalization of Na+ and Cl- currents. In excised nasal epithelium of cftrF508del/F508del mice, like with CF15 cells, we found normalization of amiloride-sensitive Isc. Moreover, oral administration of miglustat (6 days) decreased the amiloride-sensitive Isc in cftrF508del/F508del mice but had no effect on cftr-/- mice. Our results thus show that rescuing the trafficking-deficient F508del-CFTR by miglustat down-regulates Na+ absorption. A miglustat-based treatment of CF patients may thus have a beneficial effect both on Cl- and Na+ transports.

Positional mapping of loci in the DiGeorge critical region at chromosome 22q11 using a new marker (D22S183)

The majority of patients with DiGeorge syndrome (DGS) and velo-cardio-facial syndrome (VCFS) and a minority of patients with non-syndromic conotruncal heart defects are hemizygous for a region of chromosome 22q11. The chromosomal region that is commonly deleted is larger than 2 Mb. It has not been possible to narrow the smallest region of overlap (SRO) of the deletions to less than ca 500 kb, which suggests that DGS/VCFS might be a contiguous gene syndrome. The saturation cloning of the SRO is being carried out, and one gene (TUPLE1) has been identified. By using a cosmid probe (M51) and fluorescence in situ hybridization, we show here that the anonymous DNA marker locus D22S183 is within the SRO, between TUPLE1 and D22S75 (probe N25). A second locus with weak homology to D22S183, recognized by cosmid M56, lies immediately outside the common SRO of the DGS and VCFS deletions, but inside the SRO of the DGS deletions. D22S183 sequences are strongly conserved in primates and weaker hybridizing signals are found in DNA of other mammalian species; no transcripts are however detected in polyA+ RNA from various adult human organs. Probe M51 allows fast reliable screening for 22q11 deletions using fluorescence in situ hybridization. A deletion was found in 11 out of 12 DGS patients and in 3 out of 7 VCFS patients. Two patients inherited the deletion from a parent with mild (atypical) symptoms.

Proteomic Analysis of Naphthalene-Induced Airway Epithelial Injury and Repair in a Cystic Fibrosis Mouse Model

Combined results from laser capture microdissection of mouse airway epithelial cells followed by high power (MALDI-FTICR) MS, and fluorescent two-dimensional gel elctrophoresis (2D-DIGE) of the whole lung, allowed us to identify proteins differentially expressed after naphthalene induced airway injury. Further, we discovered several novel aspects of Cystic Fibrosis (CF) lung pathology in an F508del-Cftr mouse model using this approach. The combined MALDI-FTICR-MS and 2D-DIGE data show that lung carbonyl reductase (CBR2), involved in prostaglandin metabolism, converting PGE2 to PGF2alpha, is localized to airway cells and is reduced 2-fold in mutant mice compared to normal, both before and after challenge. Further, we observe a downregulation of two key enzymes of retinoic acid metabolism after injury, which is more pronounced in CF mutant mice. These data show that state-of-the-art proteomics can be used to evaluate airway injury in small cell samples. Further, the results suggest the involvement of prostaglandin and retinoic acid metabolism in the abnormal responses of CF mutant mice to injury.

Spontaneous rescue from cystic fibrosis in a mouse model

BackgroundFrom the original CftrTgH(neoim)Hgumutant mouse model with a divergent genetic background (129P2, C57BL/6, MF1) we have generated two inbred CftrTgH(neoim)Hgumutant strains named CF/1-CftrTgH(neoim)Hguand CF/3-CftrTgH(neoim)Hgu, which are fertile and show normal growth and lifespan. Initial genome wide scan analysis with microsatellite markers indicated that the two inbred strains differed on the genetic level. In order to further investigate whether these genetic differences have an impact on the disease phenotype of cystic fibrosis we characterised the phenotype of the two inbred strains.ResultsReduced amounts, compared to wild type control animals, of correctly spliced Cftr mRNA were detected in the nasal epithelia, lungs and the intestine of both inbred CftrTgH(neoim)Hgustrains, with higher residual amount observed for CF/1-CftrTgH(neoim)Hguthan CF/3-CftrTgH(neoim)Hgufor every investigated tissue. Accordingly the amounts of wild type Cftr protein in the intestine were 9% for CF/1-CftrTgH(neoim)Hguand 4% for CF/3-CftrTgH(neoim)Hgu. Unlike the apparent strain and/or tissue specific regulation of Cftr mRNA splicing, short circuit current measurements in the respiratory and intestinal epithelium revealed that both strains have ameliorated the basic defect of cystic fibrosis with a presentation of a normal electrophysiology in both tissues.ConclusionUnlike the outbred CftrTgH(neoim)Hguinsertional mouse model, which displayed the electrophysiological defect in the gastrointestinal and respiratory tracts characteristic of cystic fibrosis, both inbred CftrTgH(neoim)Hgustrains have ameliorated the electrophysiological defect. On the basis of these findings both CF/1-CftrTgH(neoim)Hguand CF/3-CftrTgH(neoim)Hguoffer an excellent model whereby determination of the minimal levels of protein required for the restoration of the basic defect of cystic fibrosis can be studied, along with the modulating factors which may affect this outcome.

Rescue of Murine F508del CFTR Activity in Native Intestine by Low Temperature and Proteasome Inhibitors

Most patients with Cystic Fibrosis (CF) carry at least one allele with the F508del mutation, resulting in a CFTR chloride channel protein with a processing, gating and stability defect, but with substantial residual activity when correctly sorted to the apical membranes of epithelial cells. New therapies are therefore aimed at improving the folding and trafficking of F508del CFTR, (CFTR correctors) or at enhancing the open probability of the CFTR chloride channel (CFTR potentiators). Preventing premature breakdown of F508del CFTR is an alternative or additional strategy, which is investigated in this study. We established an ex vivo assay for murine F508del CFTR rescue in native intestinal epithelium that can be used as a pre-clinical test for candidate therapeutics. Overnight incubation of muscle stripped ileum in modified Williams E medium at low temperature (26°C), and 4 h or 6 h incubation at 37°C with different proteasome inhibitors (PI: ALLN, MG-132, epoxomicin, PS341/bortezomib) resulted in fifty to hundred percent respectively of the wild type CFTR mediated chloride secretion (forskolin induced short-circuit current). The functional rescue was accompanied by enhanced expression of the murine F508del CFTR protein at the apical surface of intestinal crypts and a gain in the amount of complex-glycosylated CFTR (band C) up to 20% of WT levels. Sustained rescue in the presence of brefeldin A shows the involvement of a post-Golgi compartment in murine F508del CFTR degradation, as was shown earlier for its human counterpart. Our data show that proteasome inhibitors are promising candidate compounds for improving rescue of human F508del CFTR function, in combination with available correctors and potentiators.