Novel finding of caveolin‐2 in apical membranes of proximal tubule and first detection of caveolin‐2 in urine: A promising biomarker of renal disease

Abstract

Caveolin‐2 (Cav‐2) is expressed in a variety of cell tissue, and it has also been found in renal tissue. The expression of Cav‐2 in proximal tubules is stillunclear. The aim of this study was to carry out a complete evaluation of theexpression pattern of Cav‐2 in rat renal cortex to clarify and deepen theknowledge about the localization of Cav‐2 in the proximal tubules and also toevaluate its presence in urine. Male Wistar rats were used to assess Cav‐2expression by Western blot analysis in homogenates, apical, and basolateralmembranes from kidney cortex, in lysates and total plasma membranes fromrenal cortical cell suspensions, in urine, and in urinary exosomes. Cav‐2 wasclearly expressed in renal cortex homogenates and in both apical andbasolateral membranes isolated from kidney cortex, with a greater expressionon the former membranes. It was also observed in lysates and in plasmamembranes from cortical cell suspensions. Moreover, Cav‐2 was found in urineand in its exosomal fraction. These results confirmed the presence of Cav‐2 inproximal tubule cells in the kidney of healthy rats, and showed for the first time its expression at the apical membrane of these cells and in urine. Besides,urinary exosomal pathway could be involved in Cav‐2 urinary excretion undernormal conditions. We observed an increase in the urinary abundance of Cav‐2in two models of acute kidney injury, and thus we proposed the urinaryexcretion of Cav‐2 as a potential biomarker of kidney injury.