Lecture 8 - Atypical CF

Question 1

Classic CF

Answer 1

severe symptoms with 2 CFTR mutations

Question 2

Atpical CFTR

Answer 2

mild symptoms
one or no CFTR mutations
thought to be due to modifier genes involved in CFTR regulation or affecting how airway cells work

Question 3

Gain of function ENaC mutations

Answer 3

results in lower ASL as there is increased Na+ absorption

Question 4

Gain of function ENac mutation hypothesis

Answer 4

gain of function mutations increase sodium absorption so ASL is depleted resulting in CF-like mutations

Question 5

ENaC mutations

Answer 5

some have no effect on sodium current, therefore do not cause symptoms
some show increased sodium current with enhanced amiloride effects
2 mutations show decreased ENaC function indicating no effect or increase the ASL therefore impacting mucocilliary

Question 6

ENaC mutations show that…

Answer 6

protein levels remains he same, therefore no change in protein number

Question 7

Classic CF nasal potential different results

Answer 7

decreased CFTR function with increased ENaC function

Question 8

Atypical CF nasal potential difference results

Answer 8

chloride is mildly effected, but it is ENaC with the most effect

Question 9

Isotenolol in nasal potential difference experiments

Answer 9

used to stimulate chloride handling

Question 10

aQ493R mutation

Answer 10

EC loop
increased ENaC currents
massively increased current in absence of amiloride
from sodium self inhibition

Question 11

Sodium feedback inhibition

Answer 11

Works to promote ENaC endocytosis, sodium enters cell to increase the IC conc, which promotes ENaC endocytosis in normal individuals

Question 12

Sodium feedback inhibition with low EC sodium

Answer 12

this reduces stimulation of endocytosis

Question 13

Sodium feedback inhibition can be used to…

Answer 13

compare currents in absence and presence of sodium to give an idea of how much endocytosis is occurring

Question 14

Cleaving EnaC results in

Answer 14

increased Po

Question 15

Uncleaved ENaC channels

Answer 15

near silent with a low Po therefore generating smaller ENaC currents

Question 16

Cleaved ENaC channels

Answer 16

very active with a high Po therefore generating large ENaC currents

Question 17

How to determine if mutation is due to issues with ENaC cleavage

Answer 17

adding chymotrypsin and nearing response

WT = increased Po with no activation of near silent channels

Question 18

Sodium self inhibition

Answer 18

Sodium entering cell blocks the channel it entered through

Question 19

BV348M mutation

Answer 19

Gain of function which showed a bigger increase in current when amiloride was removed. Change in Po, not due to channel number

Question 20

Mouse overexpression of BSCNN1b

Answer 20

PCL reduced compared to WT, suggests decreased mucus clearance

Question 21

Results of BSCNN1b MT mice given intra-tracheal bacteria

Answer 21

Some individuals with CF-life symptoms but not 2 CFTR mutations
ENaC mutations observed in patients
GoF explains symptoms observed
some ENaC LoF mutations
Different mutations seem to lead to an increase in current via changes in Po
ENaC B overexpression mouse model highlights impact on the lungs and supports that some atypical CF patients have ENaC MT

Question 22

All forms of Cf are either…

Answer 22

Loss/gain of ENaC function or loss of CFTR function