What have we learned from mouse models for cystic fibrosis?

CFTR-beyond the airways: Recent findings on the role of the CFTR channel in the pancreas, the intestine and the kidneys

With increased longevity of patients suffering from cystic fibrosis, and widespread lung transplantation facilities, the sequelae of defective CFTR in other organs than the airways come to the fore. This minireview highlights recent scientific progress in the understanding of CFTR function in the pancreas, the intestine and the kidney, and explores potential therapeutic strategies to combat defective CFTR function in these organs.

SPX-101 Is a Novel Epithelial Sodium Channel-targeted Therapeutic for Cystic Fibrosis That Restores Mucus Transport

RATIONALE

Cystic fibrosis (CF) lung disease is caused by the loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) combined with hyperactivation of the epithelial sodium channel (ENaC). In the lung, ENaC is responsible for movement of sodium. Hyperactivation of ENaC, which creates an osmotic gradient that pulls fluid out of the airway, contributes to reduced airway hydration, causing mucus dehydration, decreased mucociliary clearance, and recurrent acute bacterial infections. ENaC represents a therapeutic target to treat all patients with CF independent of their underlying CFTR mutation.

OBJECTIVES

To investigate the in vitro and in vivo efficacy of SPX-101, a peptide mimetic of the natural regulation of ENaC activity by short palate, lung, and nasal epithelial clone 1, known as SPLUNC1.

METHODS

ENaC internalization by SPX-101 in primary human bronchial epithelial cells from healthy and CF donors was assessed by surface biotinylation and subsequent Western blot analysis. SPX-101's in vivo therapeutic effect was assessed by survival of β-ENaC-transgenic mice, mucus transport in these mice, and mucus transport in a sheep model of CF.

MEASUREMENTS AND MAIN RESULTS

SPX-101 binds selectively to ENaC and promotes internalization of the α-, β-, and γ-subunits. Removing ENaC from the membrane with SPX-101 causes a significant decrease in amiloride-sensitive current. The peptide increases survival of β-ENaC-transgenic mice to greater than 90% with once-daily dosing by inhalation. SPX-101 increased mucus transport in the β-ENaC mouse model as well as the sheep model of CF.

CONCLUSIONS

These data demonstrate that SPX-101 promotes durable reduction of ENaC membrane concentration, leading to significant improvements in mucus transport.

Characterization of primary rat nasal epithelial cultures in CFTR knockout rats as a model for CF sinus disease

OBJECTIVE

The objectives of the current experiments were to develop and characterize primary rat nasal epithelial cultures and evaluate their usefulness as a model of cystic fibrosis (CF) sinonasal transepithelial transport and CF transmembrane conductance regulator (CFTR) function.

STUDY DESIGN

Laboratory in vitro and animal studies.

METHODS

CFTR^+/+ and CFTR^-/- rat nasal septal epithelia (RNSE) were cultured on semipermeable supports at an air-liquid interface to confluence and full differentiation. Monolayers were mounted in Ussing chambers for pharmacologic manipulation of ion transport and compared to similar filters containing murine (MNSE) and human (HSNE) epithelia. Histology and scanning electron microscopy (SEM) were completed. Real-time polymerase chain reaction of CFTR^+/+ RNSE, MNSE, and HSNE was performed to evaluate relative CFTR gene expression.

RESULTS

Forskolin-stimulated anion transport (ΔIsc in μA/cm² ) was significantly greater in epithelia derived from CFTR^+/+ when compared to CFTR^-/- animals (100.9 ± 3.7 vs. 10.5 ± 0.9; P < 0.0001). Amiloride-sensitive I_SC was equivalent (-42.3 ± 2.8 vs. -46.1 ± 2.3; P = 0.524). No inhibition of CFTR-mediated chloride (Cl^- ) secretion was exhibited in CFTR^-/- epithelia with the addition of the specific CFTR inhibitor, CFTR_Inh -172. However, calcium-activated Cl^- secretion (UTP) was significantly increased in CFTR^-/- RNSE (CFTR^-/- -106.8 ± 1.6 vs. CFTR^+/+ -32.2 ± 3.1; P < 0.0001). All responses were larger in RNSE when compared to CFTR^+/+ and CFTR^-/- (or F508del/F508del) murine and human cells (P < 0.0001). Scanning electron microscopy demonstrated 80% to 90% ciliation in all RNSE cultures. There was no evidence of infection in CFTR^-/- rats at 4 months. CFTR expression was similar among species.

CONCLUSION

The successful development of the CFTR^-/- rat enables improved evaluation of CF sinus disease based on characteristic abnormalities of ion transport.

LEVEL OF EVIDENCE

NA. Laryngoscope, 127:E384-E391, 2017.

Genome editing and genetic engineering in livestock for advancing agricultural and biomedical applications

Genetic modification of livestock has a longstanding and successful history, starting with domestication several thousand years ago. Modern animal breeding strategies predominantly based on marker-assisted and genomic selection, artificial insemination, and embryo transfer have led to significant improvement in the performance of domestic animals, and are the basis for regular supply of high quality animal derived food. However, the current strategy of breeding animals over multiple generations to introduce novel traits is not realistic in responding to the unprecedented challenges such as changing climate, pandemic diseases, and feeding an anticipated 3 billion increase in global population in the next three decades. Consequently, sophisticated genetic modifications that allow for seamless introgression of novel alleles or traits and introduction of precise modifications without affecting the overall genetic merit of the animal are required for addressing these pressing challenges. The requirement for precise modifications is especially important in the context of modeling human diseases for the development of therapeutic interventions. The animal science community envisions the genome editors as essential tools in addressing these critical priorities in agriculture and biomedicine, and for advancing livestock genetic engineering for agriculture, biomedical as well as "dual purpose" applications.

Sinus hypoplasia in the cystic fibrosis rat resolves in the absence of chronic infection

BACKGROUND

Sinus hypoplasia is a hallmark characteristic in cystic fibrosis (CF). Chronic rhinosinusitis (CRS) is nearly universal from a young age, impaired sinus development could be secondary to loss of the cystic fibrosis transmembrane conductance regulator (CFTR) or consequences of chronic infection during maturation. The objective of this study was to assess sinus development relative to overall growth in a novel CF animal model.

METHODS

Sinus development was evaluated in CFTR^-/- and CFTR^+/+ rats at 3 stages of development: newborn; 3 weeks; and 16 weeks. Microcomputed tomography (microCT) scanning, cultures, and histology were performed. Three-dimensional sinus and skull volumes were quantified.

RESULTS

At birth, sinus volumes were decreased in CFTR^-/- rats compared with wild-type rats (mean ± SEM: 11.3 ± 0.85 mm³ vs 14.5 ± 0.73 mm³ ; p < 0.05), despite similar weights (8.4 ± 0.46 gm vs 8.3 ± 0.51 gm; p = 0.86). CF rat weights declined by 16 weeks (378.4 ± 10.6 gm vs 447.4 ± 15.9 gm; p < 0.05), sinus volume increased similar to wild-type rats (201.1 ± 3.77 gm vs 203.4 ± 7.13 gm; p = 0.8). The ratio of sinus volume to body weight indicates hypoplasia present at birth (1.37 ± 0.12 vs 1.78 ± 0.11; p < 0.05) and showed an increase compared with CFTR^+/+ animals by 16 weeks (0.53 ± 0.02 vs 0.46 ± 0.02; p < 0.05). Rats did not develop histologic evidence of chronic infection.

CONCLUSION

CF rat sinuses are smaller at birth, but develop volumes similar to wild-type rats with maturation. This suggests that loss of CFTR may confer sinus hypoplasia at birth, but normal development ensues without chronic sinus infection.

Targeted gene knock-in by CRISPR/Cas ribonucleoproteins in porcine zygotes

The domestic pig is an important “dual purpose” animal model for agricultural and biomedical applications. There is an emerging consensus in the biomedical community for the use of large animal models such as pigs to either serve as an alternative, or complement investigations from the mouse. However, the use of pig has not proven popular due to technical difficulties and time required in generating models with desired genetic modifications. In this regard, the ability to directly modify the genome in the zygote and generate edited animals is highly desirable. This report demonstrates for the first time, the generation of gene targeted animals by direct injection of Cas9 ribonucleoprotein complex and short stretches of DNA sequences into porcine zygotes. The Cas9 protein from Streptococcus pyogenes was pre-complexed with a single guide RNA targeting downstream of the ubiquitously expressed COL1A gene, and co-injected with a single-stranded repair template into porcine zygotes. Using this approach a line of pigs that carry pseudo attP sites within the COL1A locus to enable phiC31 integrase mediated introduction of transgenes has been generated. This new route for genome engineering in pigs via zygote injection should greatly enhance applications in both agriculture and biomedicine.

Somatic Cell Nuclear Transfer Followed by CRIPSR/Cas9 Microinjection Results in Highly Efficient Genome Editing in Cloned Pigs

The domestic pig is an ideal "dual purpose" animal model for agricultural and biomedical research. With the availability of genome editing tools such as clustered regularly interspaced short palindromic repeat (CRISPR) and associated nuclease Cas9 (CRISPR/Cas9), it is now possible to perform site-specific alterations with relative ease, and will likely help realize the potential of this valuable model. In this article, we investigated for the first time a combination of somatic cell nuclear transfer (SCNT) and direct injection of CRISPR/Cas ribonucleoprotein complex targeting GRB10 into the reconstituted oocytes to generate GRB10 ablated Ossabaw fetuses. This strategy resulted in highly efficient (100%) generation of biallelic modifications in cloned fetuses. By combining SCNT with CRISPR/Cas9 microinjection, genome edited animals can now be produced without the need to manage a founder herd, while simultaneously eliminating the need for laborious in vitro culture and screening. Our approach utilizes standard cloning techniques while simultaneously performing genome editing in the cloned zygotes of a large animal model for agriculture and biomedical applications.

Targeted Gene Knockin in Porcine Somatic Cells Using CRISPR/Cas Ribonucleoproteins

The pig is an ideal large animal model for genetic engineering applications. A relatively short gestation interval and large litter size makes the pig a conducive model for generating and propagating genetic modifications. The domestic pig also shares close similarity in anatomy, physiology, size, and life expectancy, making it an ideal animal for modeling human diseases. Often, however, the technical difficulties in generating desired genetic modifications such as targeted knockin of short stretches of sequences or transgenes have impeded progress in this field. In this study, we have investigated and compared the relative efficiency of CRISPR/Cas ribonucleoproteins in engineering targeted knockin of pseudo attP sites downstream of a ubiquitously expressed COL1A gene in porcine somatic cells and generated live fetuses by somatic cell nuclear transfer (SCNT). By leveraging these knockin pseudo attP sites, we have demonstrated subsequent phiC31 integrase mediated integration of green fluorescent protein (GFP) transgene into the site. This work for the first time created an optimized protocol for CRISPR/Cas mediated knockin in porcine somatic cells, while simultaneously creating a stable platform for future transgene integration and generating transgenic animals.

Engineering large animal models of human disease

The recent development of gene editing tools and methodology for use in livestock enables the production of new animal disease models. These tools facilitate site‐specific mutation of the genome, allowing animals carrying known human disease mutations to be produced. In this review, we describe the various gene editing tools and how they can be used for a range of large animal models of diseases. This genomic technology is in its infancy but the expectation is that through the use of gene editing tools we will see a dramatic increase in animal model resources available for both the study of human disease and the translation of this knowledge into the clinic. Comparative pathology will be central to the productive use of these animal models and the successful translation of new therapeutic strategies. © 2015 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Characterization of defects in ion transport and tissue development in cystic fibrosis transmembrane conductance regulator (CFTR)-knockout rats

Animal models for cystic fibrosis (CF) have contributed significantly to our understanding of disease pathogenesis. Here we describe development and characterization of the first cystic fibrosis rat, in which the cystic fibrosis transmembrane conductance regulator gene (CFTR) was knocked out using a pair of zinc finger endonucleases (ZFN). The disrupted Cftr gene carries a 16 base pair deletion in exon 3, resulting in loss of CFTR protein expression. Breeding of heterozygous (CFTR^+/−) rats resulted in Mendelian distribution of wild-type, heterozygous, and homozygous (CFTR^−/−) pups. Nasal potential difference and transepithelial short circuit current measurements established a robust CF bioelectric phenotype, similar in many respects to that seen in CF patients. Young CFTR^−/− rats exhibited histological abnormalities in the ileum and increased intracellular mucus in the proximal nasal septa. By six weeks of age, CFTR^−/− males lacked the vas deferens bilaterally. Airway surface liquid and periciliary liquid depth were reduced, and submucosal gland size was abnormal in CFTR^−/− animals. Use of ZFN based gene disruption successfully generated a CF animal model that recapitulates many aspects of human disease, and may be useful for modeling other CF genotypes, including CFTR processing defects, premature truncation alleles, and channel gating abnormalities.

Proteomics uncovering possible key players in F508del-CFTR processing and trafficking

The achievement and maintenance of a protein native conformation is a very complex cellular process involving a multitude of key factors whose contribution to a successful folding remains to be elucidated. On top of this, it is known that correct folding is crucial for proteins to play their normal role and, consequently, for the maintenance of cellular homeostasis or proteostasis. If the folding process is affected, the protein is unable to achieve its native conformation, compromising its life and function, and a pathological condition may arise. Protein-misfolding diseases are characterized by either formation of protein aggregates that are toxic to the cell (gain-of-toxic-function diseases) or by an incorrect processing of proteins, which leads to a deficiency in protein activity (loss-of-function diseases). In this article we have focused on proteomics advances in the molecular knowledge of protein-misfolding diseases with direct impact on possible key players in F508del-CFTR processing and trafficking.

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.

Knockout mouse models for intestinal electrolyte transporters and regulatory PDZ adaptors: new insights into cystic fibrosis, secretory diarrhoea and fructose-induced hypertension

Knockout mouse models have provided key insights into the physiological significance of many intestinal electrolyte transporters. This review has selected three examples to highlight the importance of knockout mouse technology in unravelling complex regulatory relationships important for the understanding of human diseases. Genetic ablation of the cystic fibrosis transmembrane conductance regulator (CFTR) has created one of the most useful mouse models for understanding intestinal transport. Recent work has provided an understanding of the key role of the CFTR anion channel in the regulation of HCO(3)(-) secretion, and the important consequences that a defect in HCO(3)(-) output may have on the viscoelastic properties of mucus, on lipid absorption and on male and female reproductive function. The regulation of CFTR activity, and also that of the intestinal salt absorptive transporter NHE3, occurs via the formation of PSD95-Drosophila homologue Discs-large-tight junction protein ZO-1 (PDZ) adaptor protein-mediated multiprotein complexes. The recent generation of knockout mice for three members of the sodium-hydrogen regulatory factor (NHERF) family of PDZ adaptor proteins, namely NHERF1 (EBP50), NHERF2 (E3KARP) and NHERF3 (PDZK1), has helped to explain why NHERF1 is essential for both normal and mutant CFTR function. In addition, they have provided new insight into the molecular mechanisms of secretory diarrhoeas. Genetic ablation of members of the recently discovered Slc26 anion transporter gene family not only reproduced the phenotype of the genetic diseases that led to the discovery of the gene family, but also resulted in new insights into complex human diseases such as secretory diarrhoea, fructose-induced hypertension and urolithiasis.

Animal models for target diseases in gene therapy--using DNA and siRNA delivery strategies

Nanoparticles, including lipopolyamines leading to lipoplexes, liposomes, and polyplexes are targeted drug carrier systems in the current search for a successful delivery system for polynucleic acids. This review is focused on the impact of gene and siRNA delivery for studies of efficacy, pharmacodynamics, and pharmacokinetics within the setting of the wide variety of in vivo animal models now used. This critical appraisal of the recent literature sets out the different models that are currently being investigated to bridge from studies in cell lines through towards clinical reality. Whilst many scientists will be familiar with rodent (murine, fecine, cricetine, and musteline) models, few probably think of fish as a clinically relevant animal model, but zebrafish, madake, and rainbow trout are all being used. Larger animal models include rabbit, cat, dog, and cow. Pig is used both for the prevention of foot-and-mouth disease and human diseases, sheep is a model for corneal transplantation, and the horse naturally develops arthritis. Non-human primate models (macaque, common marmoset, owl monkey) are used for preclinical gene vector safety and efficacy trials to bridge the gap prior to clinical studies. We aim for the safe development of clinically effective delivery systems for DNA and RNAi technologies.