EFA6D expression and localization in renal tubules correlate with epithelial cell attenuation and membrane...

In our recent study (Watthanakitphibun et al., 2026), we reported remarkable membrane modifications in the basolateral cell domains of attenuated epithelial cells in dilated distal tubules and collecting ducts in the renal cortex, predominantly in the former, induced by unilateral ureteral obstruction (UUO). These modifications included the disappearance of typical basal infoldings and the appearance of ellipsoidal membrane sacs containing thin cytoplasmic processes along the basolateral cell membranes and within the cellular interior. We thus suggested that they represent a temporal sequence of membrane addition sources to compensate for the increased cell surface area associated with cell attenuation. To support the proposed temporal sequence of these membrane modifications, the present study examined the expression and localization of EFA6D, a molecule that plays a pivotal role in activating Arf6, whose involvement in membrane dynamics is well established, in the renal cortical tubules of adult mice under UUO. While EFA6D was faintly expressed in normal kidneys, western blotting revealed enhanced expression on UUO day 1, with significantly higher levels on days 3 and 5. Double immunofluorescence microscopy showed EFA6D immunoreactivity localized in attenuated cells of dilated distal tubules dominantly and of collecting ducts less dominantly, but not significantly in proximal tubules. In ultrastructure, EFA6D was mainly localized in the ellipsoidal membrane sacs and clusters of small vesicles beneath the apical membranes in the attenuated epithelial cells. Our findings on the expression and cellular interior localization of EFA6D support the proposed temporal sequence of events: disappearance of basal infolding, followed by membrane sac formation, and subsequent membrane addition. This sequence promotes cell surface expansion associated with cell attenuation during tubule/duct dilation induced by UUO.