AQP2 Flashcards
Autosomal NDI results from..
Recessive trait in 90% of cases
NDI manifests at birth with penetrance..
Equal in male and females
Gene for NDI is located on..
Chromosome 12q13
AQP2 is..
A water channel found specifically in the principal cells of the collecting duct in the kidney
NDI is caused by
Failure to recruit AQP2 to the apical membrane of principal cells
NDI symptoms
Polyuria, polydipsia, increase serum osmolality and decrease urine osmolality
Severe risk of dehydration
Normal AQP2 protein function occurs..
When the posterior pituitary releases vasopressin (ADH)
ADH acts on
Kidney to increase water reabsorption
ADH binds to
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
PKA phosphorylates AQP2 at
Serine 256
AQP2 travels in vesicles to
Apical membrane associated with dynein
AQP2 is exocytosed to apical membrane where it facilitates the transfer of water
Water is transferred through AQP2 ..
In single file by Grotthuss chain mechanism
through signature NPA motif
Asn-Pro-Ala
NDI occurs when..
AQP2 is not made
Improper trafficking of AQP2 to the apical membrane of principal cells
AQP2 not getting to apical membrane means..
Urine can’t be concentrated
Certain mutations in AQP2 cause disease
Most common in..
Pore-forming region of AQP2
Core region
TMD and connecting loops
(Robben et al., 2006)
Mutations in AQP2 result in
Misfolding, retention in ER or rapid degradation of the protein
Duzehli et al 2012
L137P mutation in TMD causes misfolding in tertiary structure leaving hydrophobic regions exposed
Vargas-Poussou et al 1998
R82X resulting in premature stop codon incomplete protein
= not functional
Mulders et al 1997
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)
KO mice models of NDI have demonstrated ..
Critical role of AQP2 in maintaining water balance
Deletion or mutation of several genes can result in..
Severe defects in the ability to concentrate urine and resistance of the kidney to ADH
Several models of autosomal recessive NDI have been established..
All with poor viability n
Mice are very sensitive to..
Polyuria
Rojek et al 2006
Total AQP2 KO mice do not survive postnatally
Yang et al 2001
Mimicking human NDI causing mutation T126M in mice leads to early death within 6 days
Mice with collecting duct-selective KO of AQP2 are.. (Rojek et al, 2006)
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
Lloyd et al 2005
F240V mutation in mice resulting in rec NDI supports hypothesis that defective targeting of AQP2 is basis for some forms of NDI
Yang et al 2009 inducible KO mouse model of NDI
Identify potential therapeutic compounds for NDI in adult mice
Yang et al 2009 KO models suggest
Functional channels may be stimulated to reach the membrane by bypassing normal signalling
Problem with Yang et al 2009 KO model
Assessing AQP2 function and trafficking in different systems
Species differences arise
Conclusions of KO models
Provide ideal tool for studying molecular basis of NDI
Investigate potential therapeutic strategies, large number of different mutations necessitates use of other systems
