Expression and localisation of aquaporin water channels in human urothelium in situ and in vitro.
BACKGROUND
Urothelium is generally considered to be impermeable to water and constituents of urine. The possibility that human urothelium expresses aquaporin (AQP) water channels as the basis for water and solute transport has not previously been investigated.


OBJECTIVE
To investigate the expression of AQP water channels by human urothelium in situ, in proliferating urothelial cell cultures and in differentiated tissue constructs.


METHODS
AQP expression by human urothelium in situ and cultured urothelial cells was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunolabelling. Expression screening was carried out on samples of freshly isolated urothelia from multiple surgical (bladder and ureteric) specimens and on proliferating and differentiated normal human urothelial (NHU) cells in culture. Urothelial tissue constructs were established and investigated for expression of urothelial differentiation markers and AQPs.


METHODS
Qualitative study.


CONCLUSIONS
Transcripts for AQP3, AQP4, AQP7, AQP9, and AQP11 were expressed consistently by freshly isolated urothelia as well as by cultured NHU cells. AQP0, AQP1, AQP2, AQP5, AQP6, AQP8, AQP10, and AQP12 were not expressed. Immunochemistry confirmed expression of AQP3, AQP4, AQP7, and AQP9 at the protein level. AQP3 was shown to be intensely expressed at cell borders in the basal and intermediate layers in both urothelium in situ and differentiated tissue constructs in vitro.


CONCLUSIONS
This is the first study to demonstrate that AQPs are expressed by human urothelium, suggesting a potential role in transurothelial water and solute transport. Our findings challenge the traditional concept of the urinary tract as an impermeable transit and storage unit and provide a versatile platform for further investigations into the biological and clinical relevance of AQPs in human urothelium.
Rubenwolf
Peter C
PC
Jack Birch Unit for Molecular Carcinogenesis, Department of Biology, University of York, York, UK.
Georgopoulos
Nikolaos T
NT
Clements
Lisa A
LA
Feather
Sally
S
Holland
Philip
P
Thomas
David F M
DF
Southgate
Jennifer
J
D020346:Aquaporins / Q000235:genetics* / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D004847:Epithelial Cells / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D020133:Reverse Transcriptase Polymerase Chain Reaction; D001743:Urinary Bladder / Q000166:cytology / Q000502:physiology*; D019459:Urothelium / Q000166:cytology / Q000502:physiology*; D014867:Water / Q000378:metabolism
D020346:Aquaporins; D014867:Water