Respiratory Channelopathies Flashcards
What is cystic fibrosis?
Autosomal recessive disease of the epithelial tissue that disrupts electrolyte transport
Which 6 tissues are affected by cystic fibrosis?
1) Airways
2) Liver
3) Pancreas
4) Small intestine
5) Reproductive
6) Skin
How are the airways impacted in CF?
Clogging and infection
How is the liver impacted in CF?
1) Blockage of small bile ducts - pressure build up
2) Liver function problems
How is the pancreas impacted in CF?
1) Blockage of the bile ducts:
- Prevents secretion of digestive enzymes into the small intestine from the pancreas
2) Failure of babies to thrive
How is the small intestine impacted in CF?
1) Obstructions due to thick content in 10% of newborns:
- Thick mucus
- Can’t breakdown milk
- Can’t put weight on
2) Problems with the GI tract in older people
How is the reproductive system impacted in CF?
- Absence of the vas deferens
- 95% of males INFERTILE
- Small number in women also
How is the skin impacted in CF?
Excess secretion of NaCl via sweat sweat glands
What is the condition called where the child’s intestine content is thick and sticky called?
Meconium ileus
How is CF inherited?
Why is it not always inherited in this way?
Via MENDELIAN GENETICS:
1/4 CF
1/4 normal
1/2 carriers
Not always inherited in this way because Mendelian genetics are RANDOM
Describe the protein production differences in carriers and CF patients?
Carriers - 50% of the normal protein produces
CF - 0% of the normal protein produced
Describe the structure of the CF transmembrane conductance regulator (CFTR)
- 12 transmembrane domains
- Cl- ION CHANNEL
- 2 NUCLEAR BINDING DOMAIN (NBDs)
- Regulatory domain
What are the NBDs in CFTR called
NBD1 and NBD
Does the CFTR transport Cl- in or out of the cells?
In OR out, depending on what cell the channel is found in
What do the NBD of the CFTR bind to?
What does this cause?
Bind nucleotides (such as ATP)
Regulatory mechanism - determines if the channel is open or closed
Why is the regulatory domain of CFTR important?
Site for PHOSPHORYLATION:
- When ATP –> ADP, phosphate released binds to this domain
- Important in regulating the opening/closing of the channel
What mutations cause CFTR?
>1900 mutations possible, in the: - Intracellular loops - Extracellular loops - NDB etc.
What is the most common CFTR mutation?
What % of cases this contribute to?
Delta F508 mutation in NBD1
70% of cases
Describe variable penetrance
2 individuals with the SAME mutation profile can have DIFFERENT severities due to environmental and genetic (non-coding regions) reasons
How do environmental influences impact of the phenotype of CF?
More severe disease if LESS affluent
What do mutations in the CFTR impact on?
How?
Protein:
1) PRODUCTION
- mRNA not stable
- Breaks down
- Protein not produced
2) PROCESSING
- Missfolded
- Sent for degradation
- Not processed
3) TRAFFICKING
- Protein made but doesn’t get to the membrane
4) CONDUCTION
- Pore closed
- Doesn’t allow the ions to move through the channel
5) REGULATION
- Protein is made, processed and trafficked but CAN’T CONDUCT
- Channel cannot be opened by ATP binding to the NBD
What is the pathology of the lungs in CF?
1) VISCOUS airway mucus
2) Recurrent BACTERIAL infections
3) Antibiotic RESISTANCE (developed by bacteria in the lungs)
4) INFLAMMATION
5) Tissue degeneration
What does the viscous mucus do in CF?
TRAP bacteria
Why do patient with CF have recurrent bacterial infections?
Struggle to clear the bacteria that traps the bacteria
Bacteria stays in the lungs
Why do CF patients have inflammation?
Triggered by the infection as CFTR found on some IMMUNE cells
Causes over inflammation
Why do CF patients have tissue degeneration?
Damage to the tissues from the inflammation
Lung tissue doesn’t grow back
What is the most common case of death in CF patients?
Poor LUNG function - can’t get oxygen into the airways
What is present in the basolateral membrane of the upper airway epithelial cell?
1) Na+/K+ ATPase
2) K+ channels
3) NKCC1
In the basolateral membrane of the upper airway epithelial cell, what do the Na+/K+ ATPase and K+ channel do?
Set the:
- NEGATIVE membrane potential
AND
- Low INTRACELLULAR Na+ concentration
- -> Provide the driving force for the uptake of Na+ through NKCC1
What does NKCC1 do in the basolateral membrane of the upper airway epithelial cell?
What happens to the ions that are taken up?
Takes Na2+, 2Cl- and K+ INTO the cell
Na+ and K+ are RECYCLED through basolateral membrane channels
Cl- ACCUMULATES inside the cell
What channel is present in the basolateral membrane of the upper airway epithelial cell?
What does this channel usually do?
What does this cause?
The CFTR Cl- channel
Usually:
- Secretes Cl- into the airway mucus liquid layer
- Drives the movement of WATER and Na+ in the SAME DIRECTION (between the cells)
What is the airway mucus liquid layer?
What is the optimum height of this layer?
What is the height of the layer set by?
Layer of liquid with mucus on the top
Optimum heigh - 7microns
Hight set by the secretion of Cl- through the CFTR channel (as Na+ and water follow)
AND
Na+ resorption throguh ENAC
What happens to the airway mucus liquid layer in CF?
Why?
What does this cause?
Layer DECREASES in height
Cl- is NOT secreted through the CFTR channel
Cannot regulate the height of the layer
Liquid layer for cilia movement is not optimum
Struggle to beat and move mucus and bacteria out of the respiratory tract
Describe the relationship between CFTR and ENAC
What happens to this relationship in CF?
What does this cause?
When CFTR is activated - ENAC inhibited
IN CF:
- CTFR is inactive
- ENAC is activated
Causes:
- Enhanced Na+ absorption
- Also causes the layer to DECREASE
- Cilia bend over and cannot beat
How do we know the CFTR channel regulates the height of the mucus liquid layer?
Through IN VITRO studies of BRONCHIAL cells:
Change liquid layer ABOVE optimum and LOWER than optimum
In normal patients - level was brought to the optimum
In CF patients - height of the layer was BELOW optimum
What does the FC08 CF mutation affect?
Trafficking and processing:
- Protein is missfolded and sent for degradation
- Less CFTR in the membrane
What happens if FC08 mutant gets to the membrane?
Works almost NORMALLY
Where is CFTR found, other than the upper airways?
What does it regulated here?
In bottom 2/3 of the crypts in the colon
Regulates water in the faeces
Where are enterotoxins released from?
What do they do?
Released from bacteria
Activate CFTR and cause diarrhoea (increases Cl- and therefore water release into the intestines)
Why is CF so common?
During cholera epidemics, carriers of CF were PROTECTED:
- Only 50% mutated protein
- Only 50% CFTR can be activated by enterotoxins
- Only 50% of water secreted into the gut (less lost)
- Less likely to die
- Carriers increase
What are current treatments for the symptoms CF?
1) Physiotherapy
2) Bronchdilator drugs
3) Antibiotics
4) Steroids
5) Mucolytics
What do steroids do to treat CF?
Reduce inflammation
What are mucolytics and what do they do?
Enzymatic compounds:
- Break down mucus
- Making it easier to remove mucus from the airways and swallow it
- Bacteria doesn’t sit inside the mucus
What does gene therapy do?
Describe this approach
Treat the cause of CF, not the symptoms
- Deliver CFTR DNA to target cells
- DNA –> mRNA
- CFTR protein produced
What are the disadvantages of using gene therapy to treat the cause of CF?
1) Challenging
2) POOR SUCCESS rate (hard to get to the lungs)
3) Expensive
What are the new approaches to treat CF?
CFTR modulators:
1) Read-through agents
2) Correctors
3) Potentiators
What do read-through agents do?
FORCE production of full length CFTR (when premature stop of nonsense mutations)
What do correctors do?
FORCE the mutant CFTR protein to the CELL MEMBRANE
Restoring functional Cl- secretion if the mutant is functional
What do potentiators do?
Increase the phosphorylation of the CFTR channels which must be trafficked normally
How have potentiators been shown to be effective?
Increase the HEIGHT of the liquid layer
HIGHER percentage of the wild-type protein
Increase FEV1
