Background. Renal aquaporin-1 (AQP1), a water channel protein,
is known to be secreted into urine, conveyed by nano-sized
extracellular vesicles called exosomes. A previous study has demonstrated
that acetazolamide (AZ), a diuretic that inhibits
carbonic anhydrases, alters the expression level of AQP1 in cultured
cells. Herewe investigated whether AZ alters the release of
urinary exosomal AQP1 in vivo.
Methods. The effect of AZ on urinary exosomal AQP1
secretion was examined in rats and compared with furosemide
(another diuretic), NaHCO3 (an alkalizing agent) and
NH4Cl (an acidifying agent). Urine, blood and kidney
samples were obtained 2 h after each treatment. Urinary
exosomes were isolated by a differential centrifugation technique
and urinary exosomal proteins were analyzed by
immunoblotting.
Results. The release of exosomal AQP1 into urine was markedly
increased after treatment with AZ, accompanied by alkaluria
and metabolic acidosis. Immunohistochemistry clearly
demonstrated that AZ increased the apical membrane expression
of AQP1 in the proximal tubules. AZ did not affect the
release of exosomal marker proteins (tumor susceptibility
gene 101 protein and apoptosis-linked gene 2 interacting
proteinX). Treatmentwith furosemide did not change,whereas
NaHCO3 and NH4Cl decreased the exosomal release of
AQP1.
Conclusion. The present findings indicate that AZ increases the
release of exosomal AQP1 into urine in association with
enhanced apical membrane expression of AQP1. |
