Unraveling purinergic regulation in the epididymis: Activation of V-ATPase-dependent acidification by luminal ATP and adenosine.

KEY POINTS: In the epididymis, elaborate communication networks between epithelial cells are important to establish an optimal acidic luminal environment for the maturation and storage of spermatozoa, which is essential for male fertility. Proton secretion by epididymal clear cells is achieved via the proton pumping V-ATPase located in their apical membrane. Here, we dissect the molecular mechanisms by which clear cells respond to luminal ATP and adenosine to modulate their acidifying activity via the adenosine receptor ADORA2B and the pH-sensitive ATP receptor P2 × 4. We demonstrate that the hydrolysis of ATP to produce adenosine by ectonucleotidases plays a key role in V-ATPase-dependent proton secretion, and is part of a feedback loop that ensures acidification of the luminal compartment These results help us better understand how professional proton-secreting cells respond to extracellular cues to modulate their functions, and how they communicate with neighboring cells.

ABSTRACT: Cell-cell crosstalk is crucial for the dynamic function of epithelia, but how epithelial cells detect and respond to variations in extracellular stimuli to modulate their environment remains incompletely understood. Here we used the epididymis as a model system for the study of epithelial cell regulation by luminal factors. In the epididymis, elaborate communication networks between the different epithelial cell types are important to establish an optimal acidic luminal environment for the maturation and storage of spermatozoa. In particular, clear cells (CCs) secrete protons into the lumen via the proton pumping V-ATPase located in their apical membrane, a process that is activated by luminal alkalinization. However, how CCs detect luminal pH variations to modulate their function remains uncharacterized. Purinergic regulation of epithelial transport is modulated by extracellular pH in other tissues. In this study, functional analysis of the mouse cauda epididymis perfused in vivo showed that luminal ATP and adenosine modulate the acidifying activity of CCs via the purinergic ADORA2B and P2 × 4 receptors, and that luminal adenosine content is itself regulated by luminal pH. Altogether, our observations illustrate mechanisms by which CCs are activated by pH sensitive P2 × 4 receptor and ectonucleotidases, providing a feedback mechanism for the maintenance of luminal pH. These novel mechanisms by which professional proton-secreting cells respond to extracellular cues to modulate their functions, and how they communicate with neighboring cells might be translatable to other acidifying epithelia. This article is protected by copyright. All rights reserved.