L7 - Respiratory Channelopathies Flashcards
What are the statistics on cystic fibrosis?
Autosomal recessive Disease of electrolyte transport in epithelial tissue 1 in 2,500 births 1 in 20 a carrier 50 years ago survival past 1 year rare
What are the symptoms of cystic fibrosis in the many different tissues affected?
Airways – clogging and infection
Liver – blockage of small bile ducts and problems with liver function in 5%
Pancreas – blockage of the ducts prevents secretion of digestive enzymes in 65%
Small intestine – obstructions due to thick content in 10%
Reproductive tract – absence of vas deferens in 95% males making them infertile
- Small number of infertile women
Skin – excess secretion of NaCl via sweat glands
What are the clinical manifestations of cystic fibrosis?
Meconium ileus – 1 day Pancreatic insufficient – 1 week Distal intestinal obstruction syndrome – 3 weeks Respiratory disease – 1 month Liver disease – 2 years Male infertility – 3 years
What is the inheritance of cystic fibrosis?
Autosomal recessive (both copies don’t require the same mutation)
If two carrier parents
- 2 will be carriers (50% normal CF protein)
- 1 will be normal
- 1 will have CF
What is NBD1/NBD2?
Nucleotide binding domain
Binding of nucleotide regulates whether the ion channels are open or closed
Found in the cystic fibrosis protein
What is the cystic fibrosis protein structure?
NBD1/NBD2
Transmembrane spanning domains and intracellular/extracellular binding loops
- Mutations found throughout these areas
1 protein = 1 functional channel
Where are many cystic fibrosis mutations found?
> 1900 mutations in cystic fibrosis transmembrane conductance regulator (CFTR)
What 5 things do cystic fibrosis mutations impact on?
Conduction – ion channel doesn’t allow Cl ions to move
Regulation – by nucleotides and phosphorylation means it never opens
Trafficking – protein is made but is not transported to membrane
Processing – mutant protein is misfolded so doesn’t get sent to membrane
Production - protein not made
What are some common cystic fibrosis mutations?
F508 (found in NBD1) – 90% allelic frequency
G551 – 15% allelic frequency in the UK
W1282X
G542X
N1303K
Last three - 1-3% allelic frequency
What is the lung pathology of a cystic fibrosis patient?
Viscous airway mucous
Recurrent bacterial infections – due to inability to clear mucus
Antibiotic resistance bacteria
Inflammation – triggered by infections
Tissue degeneration – due to over inflammation
Damage to lung tissue is a common cause of death
What channels are found on the upper airways of the lung on the basolateral membrane?
NKCC1
NaKATPase
K channel
What channels are found on the upper airways of the lung on the apical membrane?
ENaC
CFTR (not present in CF patient)
What does NKCC1 do?
Na and K recycle
Cl builds up in the cell
- Cl moves out the cell across the liquid layer
What does CFTR d0?
Normally when CFTR is active it inhibits ENaC
What happens to CFTR in CF patient?
- Cannot secrete Cl so cannot control the height of the liquid layer
- CFTR does not inhibit ENaC so influx of Na into the cell
- Further reduces the height of the liquid layer
- Cilia bend over and can no longer beat and remove the mucus
What is F508 involved in?
Normal conductance and regulation
Mutations in trafficking, processing and production
How do you get colonic protection from CF?
Bottom two thirds of the crypt contains CFTR - control Cl secretion and H2O follows
- This regulates water content of the faeces
Enterotoxins activate CFTR leading diarrhoea
Not in a carrier – as only 50% of the proteins are affected by enterotoxins
What are the different treatments for CF?
Physiotherapy – move mucus Bronchodilator drugs – open airways Antibiotics Steroids – reduces inflammation Mucolytics – enzymes that break down mucus Gene therapy
How can gene therapy be used to treat CF?
Delivery of CFTR DNA to target cells DNA transcribed to mRNA and protein produced Challenging Poor success rate Expensive
What are some new approaches as ways to treat CF?
CFTR modulators
- Read-through agents
- Correctors
- Potentiators
How can read through agents treat CF?
Force production of full length CFTR when premature stop or nonsense mutations
E.g. aminoglycoside antibiotics
How can correctors treat CF?
Force mutant CFTR protein to the cell membrane
If the mutant is functional then Cl- secretion is restored
E.g. F508
How can potentiators treat CF?
Increase the Po of the CFTR channels, which must be trafficked normally
E.g. G551D mutation is a target for VX-770
What is the impact of potentiators in vitro?
Very expensive
Effective – height of liquid layer increases
Improvement of lung function by 10% after 2 weeks
