AQP2

Question 1

Autosomal NDI results from..

Answer 1

Recessive trait in 90% of cases

Question 2

NDI manifests at birth with penetrance..

Answer 2

Equal in male and females

Question 3

Gene for NDI is located on..

Answer 3

Chromosome 12q13

Question 4

AQP2 is..

Answer 4

A water channel found specifically in the principal cells of the collecting duct in the kidney

Question 5

NDI is caused by

Answer 5

Failure to recruit AQP2 to the apical membrane of principal cells

Question 6

NDI symptoms

Answer 6

Polyuria, polydipsia, increase serum osmolality and decrease urine osmolality
Severe risk of dehydration

Question 7

Normal AQP2 protein function occurs..

Answer 7

When the posterior pituitary releases vasopressin (ADH)

Question 8

ADH acts on

Answer 8

Kidney to increase water reabsorption

Question 9

ADH binds to

Answer 9

V2 a G-protein coupled receptor on basolateral membrane of principal cells
Activate adenyl cyclase to produce cAMP as second messenger response
cAMP activated PKA

Question 10

PKA phosphorylates AQP2 at

Answer 10

Serine 256

Question 11

AQP2 travels in vesicles to

Answer 11

Apical membrane associated with dynein

AQP2 is exocytosed to apical membrane where it facilitates the transfer of water

Question 12

Water is transferred through AQP2 ..

Answer 12

In single file by Grotthuss chain mechanism
through signature NPA motif
Asn-Pro-Ala

Question 13

NDI occurs when..

Answer 13

AQP2 is not made

Improper trafficking of AQP2 to the apical membrane of principal cells

Question 14

AQP2 not getting to apical membrane means..

Answer 14

Urine can’t be concentrated

Question 15

Certain mutations in AQP2 cause disease

Most common in..

Answer 15

Pore-forming region of AQP2
Core region
TMD and connecting loops
(Robben et al., 2006)

Question 16

Mutations in AQP2 result in

Answer 16

Misfolding, retention in ER or rapid degradation of the protein

Question 17

Duzehli et al 2012

Answer 17

L137P mutation in TMD causes misfolding in tertiary structure leaving hydrophobic regions exposed

Question 18

Vargas-Poussou et al 1998

Answer 18

R82X resulting in premature stop codon incomplete protein

= not functional

Question 19

Mulders et al 1997

Answer 19

A147T less stable than WT
Decrease water permeability
Exhibited some functionality when tested in xenopus oocytes
Vesicles congregate on basolateral membrane (Asai et al., 2003)

Question 20

KO mice models of NDI have demonstrated ..

Answer 20

Critical role of AQP2 in maintaining water balance

Question 21

Deletion or mutation of several genes can result in..

Answer 21

Severe defects in the ability to concentrate urine and resistance of the kidney to ADH

Question 22

Several models of autosomal recessive NDI have been established..

Answer 22

All with poor viability n

Question 23

Mice are very sensitive to..

Answer 23

Polyuria

Question 24

Rojek et al 2006

Answer 24

Total AQP2 KO mice do not survive postnatally

Question 25

Yang et al 2001

Answer 25

Mimicking human NDI causing mutation T126M in mice leads to early death within 6 days

Question 26

Mice with collecting duct-selective KO of AQP2 are.. (Rojek et al, 2006)

Answer 26

Viable but have severe urinary concentration defect
Findings suggest that the collecting duct is necessary for urine concentration but some compensation may occur via AQP2 in connecting tube

Question 27

Lloyd et al 2005

Answer 27

F240V mutation in mice resulting in rec NDI supports hypothesis that defective targeting of AQP2 is basis for some forms of NDI

Question 28

Yang et al 2009 inducible KO mouse model of NDI

Answer 28

Identify potential therapeutic compounds for NDI in adult mice

Question 29

Yang et al 2009 KO models suggest

Answer 29

Functional channels may be stimulated to reach the membrane by bypassing normal signalling

Question 30

Problem with Yang et al 2009 KO model

Answer 30

Assessing AQP2 function and trafficking in different systems
Species differences arise

Question 31

Conclusions of KO models

Answer 31

Provide ideal tool for studying molecular basis of NDI

Investigate potential therapeutic strategies, large number of different mutations necessitates use of other systems