Program in Membrane Biology, Center for System Biology, Nephrology Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
J Physiol. 2019 Apr;597(7):1957-1973. doi: 10.1113/JP277565. Epub 2019 Feb 28.
In the epididymis, elaborate communication networks between epithelial cells are important with respect to establishing 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. In the present study, 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 P2X4. 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 neighbouring cells.
Cell-cell cross-talk is crucial for the dynamic function of epithelia, although how epithelial cells detect and respond to variations in extracellular stimuli to modulate their environment remains incompletely understood. In the present study, we used the epididymis as a model system to investigate epithelial cell regulation by luminal factors. In the epididymis, elaborate communication networks between the different epithelial cell types are important for establishing 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 the present 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 P2X4 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 P2X4 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, as well as how they communicate with neighbouring cells, might be translatable to other acidifying epithelia.
在附睾中，上皮细胞之间精细的通讯网络对于建立精子成熟和储存所需的最佳酸性管腔环境非常重要，这对于男性生育能力至关重要。附睾透明细胞通过位于其顶膜的质子泵 V-ATPase 分泌质子。在本研究中，我们剖析了透明细胞响应管腔 ATP 和腺苷以通过腺苷受体 ADORA2B 和 pH 敏感 ATP 受体 P2X4 调节其酸化活性的分子机制。我们证明，通过核苷酸酶将 ATP 水解产生腺苷在 V-ATPase 依赖的质子分泌中起关键作用，并且是确保管腔隔室酸化的反馈回路的一部分。这些结果有助于我们更好地理解专业质子分泌细胞如何响应细胞外信号来调节其功能，以及它们如何与邻近细胞进行通讯。
细胞间通讯对于上皮组织的动态功能至关重要，尽管上皮细胞如何检测和响应细胞外刺激的变化以调节其环境仍不完全清楚。在本研究中，我们使用附睾作为模型系统来研究管腔因子对上皮细胞的调节。在附睾中，不同上皮细胞类型之间的精细通讯网络对于为精子的成熟和储存建立最佳酸性管腔环境非常重要。特别是，透明细胞 (CCs) 通过位于其顶膜的质子泵 V-ATPase 将质子分泌到管腔中，该过程被管腔碱化激活。然而，CCs 如何检测管腔 pH 变化以调节其功能仍未被描述。在其他组织中，细胞外 pH 调节上皮转运的嘌呤能调节。在本研究中，体内灌流的小鼠附睾尾的功能分析表明，管腔 ATP 和腺苷通过嘌呤能 ADORA2B 和 P2X4 受体调节 CCs 的酸化活性，并且管腔腺苷含量本身受到管腔 pH 的调节。总之，我们的观察结果说明了 CCs 如何被 pH 敏感的 P2X4 受体和核苷酸酶激活的机制，为维持管腔 pH 提供了反馈机制。这些专业质子分泌细胞响应细胞外信号以调节其功能的新机制，以及它们与邻近细胞的通讯方式，可能适用于其他酸化上皮组织。
