Aquaporins Flashcards
Discovery of AQP evidence
CHIP28 transfection oocytes- water permeability
Structure of AQP1
Hydrophobicity plot
B and E loops hydrophobic
Cytoplasmic C and N termini
Glycosyl chain on one monomer of 4
Water/ glycerol movement through AQP
Hydrophobic residues promote water movement
AQP6 role in chloride transport
Colocalised with H+ATPase
AQP6 channels most active at acidic pHs e.g. pH4
Fluorescent protein tagging permeabilities to NO3, Cl-, Iodide etc.
AQP1 expression in proximal kidney
Osmotic water movement permeability
AQP1 gold particle expression
-Proximal tubule, Descending Limb, Vasta recta
AQP1 KO effects
AQP1 WT and AQP4 WT vs AQP1KOs
- INCREASE in urine osmolality
- Body Weight
- Lethargy
- Organ morphology unchanged on physiological examination
AQP1 KO water permeability
Schnermann: in vitro proximal tubule microperfusion; in vivo micropuncture of tubules
Near-water isomolar reabsorption
Compensatory decrease in GFR, and an increased osmotic gradient
AQP1 effect on CCM
Evidence of no AQP1 in DTL
AQP1 KOs: lower water permeability in KOs
?no expression of AQP1 in human and rat in short loop thin limbs (90%)
AAV-AQP1 rescue did not produce a rescue
AQP1 in vasa recta
KOs: reduced water permeability
Increased diameter of Vasa recta
AQP1 in peritoneal transport
Sucrose infusion measuring albumin tracer via catheter in mice
decreased in AQP1 KO mice
AQP4 control
AQP1 contributes to
Wang 2015
AQP1 null PKD mice had more, larger PCT cysts
AQP1 reduced growth of cysts in vitro
Pkd1 associated with increased B-catenin pathway activation
Western blot analysis demonstrates that B-catenin phosphorylation is decreased in KOs- may be associated with cyst formation
Water permeability in CCD
Osmotic water permeability in response to ADH
Vasopressin increases water permeability during application
Expression of AQP2 in response to vasopressin
Gold particle staining APM:IV ratio
Increased upon AVP stimulation
Reverse translocation
AVP pathway
Critical role of Ser256 in AQP2 expression
AVP- V2R- PKA- phosphorylates Ser256
Ala (not), Asp (permanently)
Inhibition of PKA with H89- reduced APM:IV ratio
Role of PKC on decreasing AQP2 expression
PMA activates PKC- decreased expression
Ro31-8220 inhibits- increased expression
PMA + forksolin mutate Ser256s
Long term AQP2 expression control
EPAC1
- differential expression in different tubule regions immunohistochemistry
Upregulation of PKA
Reduction in PKC inhibition
AQP2 expression and stimuli
AVP infusion AQP2 expression
Dehydration
Overhydration (induces hyponatraemia)
AQP1 in CSF Production
Light-Perfusion chamber- water transport across choroid
KOs- decreased
Forskolin- drives solute secretion- greater osmolality difference
AQP1 and ICP
AQP1KOs vs WT, AQP3KOs
Gravity increases- reduces expression
AQP1 and prognosis
Cold-induced brain injury
-survival times, ICP
AQP1 in spinal cord
Fluorescent staining C fibres
KOs- nociception, hot plate test
AQP4 Cytotoxic oedema
Mortality
Hemispheric enlargement
Water intoxication
Meningitis model- neurological score
AQP4 Vasogenic oedema
evans blue does not cross BBB- cold induced injury
tumour vasogenic oedma model- neurological score
AQP4 Vasogenic oedema
evans blue does not cross BBB- cold induced injury
tumour vasogenic oedma model- neurological score
AQP4 coexpression with Kir4.1 in astrocytes
Contrasting evidence
Gold particle co-localisation greatest at foot processes
A-Syntrophin KO- gold particle colocalisation
Generalised hyperthermia induced seizures susceptibility
BUT
In hippocampus, AQP4 expressed in CA1 and dentate gyri
KOs of either Kir4.1 or AQP4 does not affect other
Effect may be mediated by an expansion of ECS- increasing tumour susceptibility
AQP4 and plasticity
KOs
Basal transmission unaffected
Affected LTD and LTP in one induction protocol
Object placement memory test
AQP9 expression in ischaemic stroke
Increases
Increased expression of AQP9 in diabetes- may be involved in energy metabolism
- removal of lactate after stroke
AQP1 and 4 in cell migration
Expression in CHO/FRT cell lines
Chemotactic assay and scratch assay
AQP1- tumorigenesis and angiogenesis
Tumour size invasiveness No. blood vessels Necrotic tissue survival
AQP4 migration
Phosphorylation at Serine180 reduces permeability and migration PKC agonist (PMA) PKC antagonist (Chelerythrine)
PLC inhibitor also decreases migration
AQP 1 and foetal development
KOs
-Greater volume of dilute amniotic fluid
-Chorionic plates unable to reabsorb excessive fluid
AQP1 in lung- effects on production
CV disease and AQP1
Rabbits
Increased AQP1 mRNA and protein following MI
Peak at Day 7
KO mice
HR, O2 consumption
LV mass, thickness and diffusion distance
AQP2 in diabetes insipidus
NDI: Kidneys not responsive to AVP- x linked mutation of V2R gene
-inducible by lithium administration- reduces expression of AQP2
dehydration re-increases levels
AQP2 in chronic heart failure- rat studies and treatments
CHF-induced rats AQP2 expression apical membrane- immunoblotting
May be due to increased AVP levels
Could explain water retention -oedema, hyponatraemia
V2R antagonists (Tolvaptan, Satavaptan)
EVEREST trial
No benefits long term prognosis
May improve fluid balance, dyspnoea, oedema in acute exacerbations
