Transgenic animals may help resolve a sticky situation in cystic fibrosis

Depletion of Airway Submucosal Glands and TP63+KRT5+ Basal Cells in Obliterative Bronchiolitis

RATIONALE

Obliterative bronchiolitis (OB) is a major cause of mortality after lung transplantation. Depletion of airway stem cells (SCs) may lead to fibrosis in OB.

OBJECTIVES

Two major SC compartments in airways are submucosal glands (SMGs) and surface airway p63 (also known as TP63 [tumor protein 63])-positive/K5 (also known as KRT5 [keratin 5])-positive basal cells (BCs). We hypothesized that depletion of these SC compartments occurs in OB.

METHODS

Ferret orthotopic left lung transplants were used as an experimental model of OB, and findings were corroborated in human lung allografts. Morphometric analysis was performed in ferret and human lungs to evaluate the abundance of SMGs and changes in the expression of phenotypic BC markers in control, lymphocytic bronchiolitis, and OB airways. The abundance and proliferative capacity of proximal and distal airway SCs was assessed using a clonogenic colony-forming efficiency assay.

MEASUREMENTS AND MAIN RESULTS

Ferret allografts revealed significant loss of SMGs with development of OB. A progressive decline in p63+/K5+ and increase in K5+/K14+ and K14+ BC phenotypes correlated with the severity of allograft rejection in large and small ferret airways. The abundance and proliferative capacity of basal SCs in large allograft airways declined with severity of OB, and there was complete ablation of basal SCs in distal OB airways. Human allografts mirrored phenotypic BC changes observed in the ferret model.

CONCLUSIONS

SMGs and basal SC compartments are depleted in large and/or small airways of lung allografts, and basal SC proliferative capacity declines with progression of disease and phenotypic changes. Global airway SC depletion may be a mechanism for pulmonary allograft failure.

Pancreatic pathophysiology in cystic fibrosis

The pancreas is one of the earliest, and most commonly affected, organs in patients with cystic fibrosis (CF). Studying the pathogenesis of pancreatic disease is limited in CF patients, due to its early clinical onset, co-morbidities and lack of tissue samples from the early phases of disease. In recent years, several new CF animal models have been developed that have advanced our understanding of both CF exocrine and endocrine pancreatic disease. Additionally, these models have helped us to better define the influence of pancreatic lesions on CF disease progression in other organs, such as the gastrointestinal tract and lung.

Neural control of submucosal gland and apical membrane secretions in airways

The mechanisms that lay behind the low-level secretions from airway submucosal glands and the surface epithelium in the absence of external innervation have been investigated in small areas (1.0-1.5 cm(2)) of mucosa from sheep tracheas, freshly collected from a local abattoir. Glandular secretion was measured by an optical method while short circuit current was used as a measure of surface secretion. Activation of neurones in the intrinsic nerve net by veratrine alkaloids caused an immediate increase in both glandular secretion and short circuit current, both effects being blocked by the addition of tetrodotoxin. However, agents known to be acting directly on the glands, such as muscarinic agonists (e.g., carbachol) or adenylate cyclase activators (e.g., forskolin) were not influenced by tetrodotoxin. The toxin alone had no discernable effect on the low-level basal secretion shown by unstimulated glands. Calu-3 cell monolayers, generally agreed to be a surrogate for the secretory cells of submucosal glands, showed no sensitivity to veratrine alkaloids, strengthening the view that the veratrine-like drugs acted exclusively on the intrinsic nerve net. The data are discussed in relation way in which transplanted lungs can maintain mucociliary clearance and hence a sterile environment in the absence of external innervation, as in transplanted lungs.

Ferret and pig models of cystic fibrosis: prospects and promise for gene therapy

Large animal models of genetic diseases are rapidly becoming integral to biomedical research as technologies to manipulate the mammalian genome improve. The creation of cystic fibrosis (CF) ferrets and pigs is an example of such progress in animal modeling, with the disease phenotypes in the ferret and pig models more reflective of human CF disease than mouse models. The ferret and pig CF models also provide unique opportunities to develop and assess the effectiveness of gene and cell therapies to treat affected organs. In this review, we examine the organ disease phenotypes in these new CF models and the opportunities to test gene therapies at various stages of disease progression in affected organs. We then discuss the progress in developing recombinant replication-defective adenoviral, adeno-associated viral, and lentiviral vectors to target genes to the lung and pancreas in ferrets and pigs, the two most affected organs in CF. Through this review, we hope to convey the potential of these new animal models for developing CF gene and cell therapies.

Genetically engineered livestock: ethical use for food and medical models

Recent advances in the production of genetically engineered (GE) livestock have resulted in a variety of new transgenic animals with desirable production and composition changes. GE animals have been generated to improve growth efficiency, food composition, and disease resistance in domesticated livestock species. GE animals are also used to produce pharmaceuticals and as medical models for human diseases. The potential use of these food animals for human consumption has prompted an intense debate about food safety and animal welfare concerns with the GE approach. Additionally, public perception and ethical concerns about their use have caused delays in establishing a clear and efficient regulatory approval process. Ethically, there are far-reaching implications of not using genetically engineered livestock, at a detriment to both producers and consumers, as use of this technology can improve both human and animal health and welfare.

Stem cells of the respiratory system: from identification to differentiation into functional epithelium

We review recent progress in the stem cell biology of the respiratory system, and discuss its scientific and translational ramifications. Several studies have defined novel stem cells in postnatal lung and airways and implicated their roles in tissue homeostasis and repair. In addition, significant advances in the generation of respiratory epithelium from pluripotent stem cells (PSCs) now provide a novel and powerful platform for understanding lung development, modeling pulmonary diseases, and implementing drug screening. Finally, breakthroughs have been made in the generation of decellularized lung matrices that can serve as a scaffold for repopulation with respiratory cells derived from either postnatal or PSCs. These studies are a critical step forward towards the still distant goal of stem cell-based regenerative medicine for diseases of lung and airways.

New animal models of cystic fibrosis: what are they teaching us?

PURPOSE OF REVIEW

Cystic fibrosis is the first human genetic disease to benefit from the directed engineering of three different species of animal models (mice, pigs, and ferrets). Recent studies on the cystic fibrosis pig and ferret models are providing new information about the pathophysiology of cystic fibrosis in various organ systems. Additionally, new conditional cystic fibrosis transmembrane conductance regulator (CFTR) knockout mice are teaching unexpected lessons about CFTR function in surprising cellular locations. Comparisons between these animal models and the human condition are key to dissecting the complexities of disease pathophysiology in cystic fibrosis.

RECENT FINDINGS

Cystic fibrosis pigs and ferrets have provided new models to study the spontaneous development of disease in the lung and pancreas, two organs that are largely spared overt spontaneous disease in cystic fibrosis mice. New cystic fibrosis mouse models are now interrogating CFTR functions involved in growth and inflammation at an organ-based level using conditional knockout technology. Together, these models are providing new insights on the human condition.

SUMMARY

Basic and clinical cystic fibrosis research will benefit greatly from the comparative pathophysiology of cystic fibrosis mice, pigs, and ferrets. Both similarities and differences between these three cystic fibrosis models will inform pathophysiologically important mechanisms of CFTR function in humans and aid in the development of both organ-specific and general therapies for cystic fibrosis.