Cystic fibrosis (CF) remains a devastating genetic disease, affecting tens of thousands worldwide with no cure in sight. With over 85% of patients carrying the F508del mutation, the need for precise and reliable preclinical models has never been greater. Cyagen's newly developed B6-hCFTR*F508del humanized mouse model offers a groundbreaking solution—accurately replicating CF pathology for accelerated drug discovery and therapeutic breakthroughs.

Discover how this innovative model is set to transform CF research and bring us closer to better treatments. Read on to explore its unique capabilities.

Introduction to Cystic Fibrosis (CF)

Cystic fibrosis (CF) is a progressive, genetically inherited, and life-threatening disorder that primarily affects Caucasian populations. The disease severely impairs respiratory and digestive systems due to abnormally thick mucus caused by mutations in the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene. CF significantly reduces the quality of life for patients as the resulting abnormally thick mucus obstructs the airways and pancreatic ducts, leading to symptoms such as difficulty breathing, recurrent lung infections, pancreatic insufficiency, and malnutrition.

While advancements in therapies have extended patient life expectancy, CF remains a chronic disease with no definitive cure, requiring long-term treatment and management. Therefore, developing more effective therapies aimed at curing CF is crucial. Over 85% of CF patients carry the F508del mutation, making it a key target for therapeutic development.

Figure 1. Key disease symptoms of cystic fibrosis (CF).[1]

Cystic Fibrosis Transmembrane Conductance Regulator: A Critical Ion Channel Protein

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a critical transmembrane ion channel protein that plays an important role in maintaining the salt and water balance in epithelial tissues in various organs of the body, such as the lungs, pancreas, and sweat glands. The primary function of CFTR is as a chloride ion channel, regulating the transport of chloride and bicarbonate ions across epithelial cell membranes, thereby maintaining tissue fluid balance and pH. This process relies on ATP hydrolysis and can also regulate the activity of other ion channels and transporters.[2] 

Mutations in the CFTR gene, including the F508del variant, lead to abnormal chloride ion channel function, causing a range of diseases, including cystic fibrosis. The disease is particularly prevalent among Caucasians, with an estimated incidence of 1 in 2,500–1 in 1,800 live births and a global patient population of approximately 90,000.[2] The typical phenotypic characteristics of CF include abnormally thick mucus in the lungs, frequent respiratory infections, pancreatic insufficiency, and male infertility (typically associated with vas deferens obstruction).

Figure 2. Conformational changes of the CFTR gated channel are key to its physiological and pharmacological regulation.[3]

The F508del (ΔF508) Pathogenic Mutation

F508del (c.1521_1523delCTT), a.k.a. F508del-CFTR, is the most common pathogenic mutation in cystic fibrosis, with over 85% of patients carrying at least one allele containing this mutation, and approximately 40% being homozygous for it.[4-5] CFTR protein undergoes complex domain assembly during its biosynthesis and folding, and the F508del mutation results in the deletion of the amino acid phenylalanine (F508) in the first nucleotide-binding domain (NBD1) of the CFTR protein, leading to misfolding. The newly synthesized CFTR protein is categorized for degradation through the endoplasmic reticulum-associated degradation (ERAD) pathway before leaving the endoplasmic reticulum and is degraded by the ubiquitin-proteasome system (UPS). This results in abnormal chloride ion channel function, causing chronic pulmonary symptoms.[6] As a result, F508del has become one of the main targets for CF drug development.

Figure 3. Over 85% of CF patients carry at least one copy of the F508del mutant gene.[5]

For example, CFTR modulators developed by Vertex Pharma have demonstrated efficacy in enhancing the conformational stability of the F508del-CFTR mutant protein, reducing its degradation and improving its cell surface expression and function. This improvement in CFTR protein function helps alleviate the disease phenotype in patients.[7-8] However, continued research is critical to refine treatments and address limitations in existing therapies.

Figure 4. Structure of wild-type CFTR protein and F508del-CFTR mutant protein, and the mechanism of action of CFTR modulators.[9]

Cyagen's Novel Humanized CFTR and Humanized Point Mutation Models

The humanized point mutation mouse model significantly improves the accuracy of preclinical in vivo evaluations for CF-targeted therapies. To advance Cystic Fibrosis research, Cyagen has developed B6-hCFTR and B6-hCFTR*F508del humanized mouse models. These mice exhibit CF-related disease characteristics, providing a robust platform for studying CF mechanisms and evaluating therapies targeting the CFTRF508del mutation.

Key Features:

  • B6-hCFTR Mouse Model (Product Number: I001132): Expresses human CFTR without endogenous mouse Cftr gene expression.
  • B6-hCFTR*F508del Mouse Model (Product Number: I001226): Carries the F508del mutation, exhibiting phenotypes consistent with CF pathology.

Validation of Humanized CFTR Gene & Protein Expression

Studies confirm that both the B6-hCFTR and B6-hCFTR*F508del models express humanized CFTR mRNA across critical tissues, including the liver, intestines, and lungs, with no endogenous mouse Cftr gene expression.

Figure 5. Gene expression of CFTR humanized mice in vivo.


CFTR Protein Expression Levels

Both B6-hCFTR and B6-hCFTR*F508del mice successfully expressed human CFTR protein, but the expression level in the latter was significantly lower than that in the former. Notably, the CFTR expression levels in B6-hCFTR*F508del mice being lower than in B6-hCFTR mice mirrors the pathological effects of the F508del mutation.

Figure 6. Comparison of CFTR protein expression in mice in vivo.

Intestinal Histopathological Features & Phenotype Analysis

B6-hCFTR*F508del mice exhibited significant hallmark pathological features of CF, including goblet cell hyperplasia, mucus accumulation, and intestinal wall thickening. In contrast, B6-hCFTR mice showed only mild tissue pathological changes, while wild-type mice had normal tissue. These phenotypes validate the model's utility in studying CF mechanisms and therapeutic approaches.

Figure 7. Comparison of intestinal histopathological features in mice.

Summary

The B6-hCFTR mice (product number: I001132) and B6-hCFTRF508del mice (product number: I001226) successfully express the human CFTR gene and protein, with no expression of endogenous mouse Cftr gene. Notable advantages of these humanized mouse models for CF research include:

  • Expression Patterns: Significantly lower human CFTR expression in B6-hCFTRF508del mice than in B6-hCFTR mice, consistent with the expression characteristics caused by the human F508del mutation.
  • Phenotype: B6-hCFTRF508del mice display significant pathological features, including goblet cell hyperplasia, mucus accumulation, and increased intestinal wall thickness


This indicates that both B6-hCFTR and B6-hCFTRF508del mice show significant advantages in human CFTR gene and protein expression, efficiently simulating the human cystic fibrosis disease characteristics. These ideal models for several research applications:

  • Investigating CFTR protein function
  • Screening and validating CFTR-targeted drugs
  • Advancing preclinical research for CF treatment


Cyagen has also developed a range of fully humanized and humanized point mutation disease models to meet the diverse needs of scientists across numerous research fields, including neurology, metabolism, and rare diseases.


References
[1]Endres TM, Konstan MW. What Is Cystic Fibrosis? JAMA. 2022;327(2):191.
[2]Grasemann H, Ratjen F. Cystic Fibrosis. N Engl J Med. 2023 Nov 2;389(18):1693-1707.
[3]Levring J, Terry DS, Kilic Z, Fitzgerald G, Blanchard SC, Chen J. CFTR function, pathology and pharmacology at single-molecule resolution. Nature. 2023 Apr;616(7957):606-614.
[4]Ong T, Ramsey BW. Cystic Fibrosis: A Review. JAMA. 2023 Jun 6;329(21):1859-1871.
[5]Cystic Fibrosis Foundation. (2021). 2021 Patient Registry Annual Data Report. Retrieved December 12, 2024, from https://www.cff.org/sites/default/files/2021-11/Patient-Registry-Annual-Data-Report.pdf
[6]McDonald EF, Woods H, Smith ST, Kim M, Schoeder CT, Plate L, Meiler J. Structural Comparative Modeling of Multi-Domain F508del CFTR. Biomolecules. 2022 Mar 18;12(3):471.
[7]Carnovale V, Scialò F, Gelzo M, Iacotucci P, Amato F, Zarrilli F, Celardo A, Castaldo G, Corso G. Cystic Fibrosis Patients with F508del/Minimal Function Genotype: Laboratory and Nutritional Evaluations after One Year of Elexacaftor/Tezacaftor/Ivacaftor Treatment. J Clin Med. 2022 Nov 22;11(23):6900.
[8]Riepe C, Wąchalska M, Deol KK, Amaya AK, Porteus MH, Olzmann JA, Kopito RR. Small-molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states. Mol Biol Cell. 2024 Feb 1;35(2):ar15.
[9]Mall MA, Burgel PR, Castellani C, Davies JC, Salathe M, Taylor-Cousar JL. Cystic fibrosis. Nat Rev Dis Primers. 2024 Aug 8;10(1):53.

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