Non-obstructive vas deferens and epididymis loss in cystic fibrosis rats

"Shifting sands in cystic fibrosis": impacts of CFTR modulators on reproductive health in people with cystic fibrosis and challenges related to in utero exposure

INTRODUCTION

Mutation-specific disease modifying drugs such as the triple combination Elexacaftor/Tezacaftor/Ivacaftor (ETI), are associated with significant improvements in physical health. Reproductive health and a pursuit of parenthood are of increased relevance; a dramatic increase in childbirth rates for females with CF has already been observed.

AREAS COVERED

Fertility in males and females with CF, and any subsequent impact of CFTR modulator therapy, is reviewed. The potential impacts of maternal use of CFTR modulator drugs on offspring health are considered, as constituent components have been found in fetal circulation in animals and humans, and the implications for maternal continuation or cessation of treatment. Clinical data are reassuring, although cases of lens opacities, and missed CF diagnoses due to false negative newborn screening results have been reported.

EXPERT OPINION

More research and high-quality evidence are needed to characterize maternal, fetal and long-term offspring outcomes following CFTR modulator therapy use during pregnancy and breastfeeding. There is a potential therapeutic impact of targeting CFTR-related organ dysfunction in CF-fetuses via maternal-administration of CFTR modulators. Additionally, any consequences of CFTR-modulation in heterozygote carrier infant warrants urgent and collective consensus regarding ethical and clinical research programs to evaluate this discrete population.

Sexual and Reproductive Health Among Men With Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Due to the distribution of the CFTR protein, CF presents with a heterogeneous phenotype. Men with CF may present with infertility due to congenital abnormalities of the vas deferens. In addition, they may experience testosterone deficiency. Today, they can father biological children with assisted reproductive technologies. We reviewed the current literature on the pathophysiology of these conditions, describe interventions that allow men with CF to conceive biological children, and provide recommendations for management of CF patients with reproductive health concerns.

Role of innate immunity and systemic inflammation in cystic fibrosis disease progression

Pathophysiological manifestations of cystic fibrosis (CF) result from a functional defect in the cystic fibrosis transmembrane conductance regulator (CFTR) paving way for mucus obstruction and pathogen colonization. The role of CFTR in modulating immune cell function and vascular integrity, irrespective of mucus thickening, in determining the host cell response to pathogens/allergens and causing systemic inflammation is least appreciated. Since CFTR plays a key role in the conductance of anions like Cl-, loss of CFTR function could affect various basic cellular processes, such as cellular homeostasis, lysosome acidification, and redox balance. CFTR aids in endotoxin tolerance by regulating Toll-like receptor-mediated signaling resulting in uncontrolled activation of innate immune cells. Although leukocytes of CF patients are hyperactivated, they exhibit compromised phagosome activity thus favouring the orchestration of sepsis from defective pathogen clearance. This review will emphasize the importance of innate immunity and systemic inflammatory response in the development of CF and other CFTR-associated pathologies.

Congenital absence of the vas deferens: Cystic fibrosis transmembrane regulatory gene mutations

Congenital absence of the vas deferens (CAVD) is a rare genetic condition first discovered in the mid-18th century related to mutations in the cystic fibrosis transmembrane regulatory genes. The condition is typically found during work-up of male infertility, and the majority of cases can be diagnosed with complete history and physical examination and pertinent investigations. The condition can be separated into three subcategories, and genetic advances have led to a much better understanding behind the disease, its pathogenesis, and options for treatment. In this review, we discuss the genetics, pathogenesis, embryology, and diagnosis of treatment of CAVD. Future work in this area likely will aim to better understand the epigenetic factors that influence the development of the condition in order to identify potential upstream therapeutic targets.

Ivacaftor Reverses Airway Mucus Abnormalities in a Rat Model Harboring a Humanized G551D-CFTR

Rationale: Animal models have been highly informative for understanding the characteristics, onset, and progression of cystic fibrosis (CF) lung disease. In particular, the CFTR-/- rat has revealed insights into the airway mucus defect characteristic of CF but does not replicate a human-relevant CFTR (cystic fibrosis transmembrane conductance regulator) variant.Objectives: We hypothesized that a rat expressing a humanized version of CFTR and harboring the ivacaftor-sensitive variant G551D could be used to test the impact of CFTR modulators on pathophysiologic development and correction.Methods: In this study, we describe a humanized-CFTR rat expressing the G551D variant obtained by zinc finger nuclease editing of a human complementary DNA superexon, spanning exon 2-27, with a 5' insertion site into the rat gene just beyond intron 1. This targeted insertion takes advantage of the endogenous rat promoter, resulting in appropriate expression compared with wild-type animals.Measurements and Main Results: The bioelectric phenotype of the epithelia recapitulates the expected absence of CFTR activity, which was restored with ivacaftor. Large airway defects, including depleted airway surface liquid and periciliary layers, delayed mucus transport rates, and increased mucus viscosity, were normalized after the administration of ivacaftor.Conclusions: This model is useful to understand the mechanisms of disease and the extent of pathology reversal with CFTR modulators.

Genetics of the congenital absence of the vas deferens

Congenital absence of the vas deferens (CAVD) may have various clinical presentations depending on whether it is bilateral (CBAVD) or unilateral (CUAVD), complete or partial, and associated or not with other abnormalities of the male urogenital tract. CBAVD is usually discovered in adult men either during the systematic assessment of cystic fibrosis or other CFTR-related conditions, or during the exploration of isolated infertility with obstructive azoospermia. The prevalence of CAVDs in men is reported to be approximately 0.1%. However, this figure is probably underestimated, because unilateral forms of CAVD in asymptomatic fertile men are not usually diagnosed. The diagnosis of CAVDs is based on clinical, ultrasound, and sperm examinations. The majority of subjects with CAVD carry at least one cystic fibrosis-causing mutation that warrants CFTR testing and in case of a positive result, genetic counseling prior to conception. Approximately 2% of the cases of CAVD are hemizygous for a loss-of-function mutation in the ADGRG2 gene that may cause a familial form of X-linked infertility. However, despite this recent finding, 10–20% of CBAVDs and 60–70% of CUAVDs remain without a genetic diagnosis. An important proportion of these unexplained CAVDs coexist with a solitary kidney suggesting an early organogenesis disorder (Wolffian duct), unlike CAVDs related to CFTR or ADGRG2 mutations, which might be the result of progressive degeneration that begins later in fetal life and probably continues after birth. How the dysfunction of CFTR, ADGRG2, or other genes such as SLC29A3 leads to this involution is the subject of various pathophysiological hypotheses that are discussed in this review.

Characterization of two rat models of cystic fibrosis-KO and F508del CFTR-Generated by Crispr-Cas9

BACKGROUND

Genetically engineered animals are essential for gaining a proper understanding of the disease mechanisms of cystic fibrosis (CF). The rat is a relevant laboratory model for CF because of its zootechnical capacity, size, and airway characteristics, including the presence of submucosal glands.

METHODS

We describe the generation of a CF rat model (F508del) homozygous for the p.Phe508del mutation in the transmembrane conductance regulator (Cftr) gene. This model was compared to new Cftr -/- rats (CFTR KO). Target organs in CF were examined by histological staining of tissue sections and tooth enamel was quantified by micro-computed tomography. The activity of CFTR was evaluated by nasal potential difference (NPD) and short-circuit current measurements. The effect of VX-809 and VX-770 was analyzed on nasal epithelial primary cell cultures from F508del rats.

RESULTS

Both newborn F508del and Knock out (KO) animals developed intestinal obstruction that could be partly compensated by special diet combined with an osmotic laxative. The two rat models exhibited CF phenotypic anomalies such as vas deferens agenesis and tooth enamel defects. Histology of the intestine, pancreas, liver, and lungs was normal. Absence of CFTR function in KO rats was confirmed ex vivo by short-circuit current measurements on colon mucosae and in vivo by NPD, whereas residual CFTR activity was observed in F508del rats. Exposure of F508del CFTR nasal primary cultures to a combination of VX-809 and VX-770 improved CFTR-mediated Cl- transport.

CONCLUSIONS

The F508del rats reproduce the phenotypes observed in CFTR KO animals and represent a novel resource to advance the development of CF therapeutics.