Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, 70125 Bari, Italy.
Department of Sciences, University of Basilicata, 85100 Potenza, Italy.
Int J Mol Sci. 2021 Nov 21;22(22):12535. doi: 10.3390/ijms222212535.
We previously showed that mesothelial cells in human peritoneum express the water channel aquaporin 1 (AQP1) at the plasma membrane, suggesting that, although in a non-physiological context, it may facilitate osmotic water exchange during peritoneal dialysis (PD). According to the three-pore model that predicts the transport of water during PD, the endothelium of peritoneal capillaries is the major limiting barrier to water transport across peritoneum, assuming the functional role of the mesothelium, as a semipermeable barrier, to be negligible. We hypothesized that an intact mesothelial layer is poorly permeable to water unless AQP1 is expressed at the plasma membrane. To demonstrate that, we characterized an immortalized cell line of human mesothelium (HMC) and measured the osmotically-driven transmesothelial water flux in the absence or in the presence of AQP1. The presence of tight junctions between HMC was investigated by immunofluorescence. Bioelectrical parameters of HMC monolayers were studied by Ussing Chambers and transepithelial water transport was investigated by an electrophysiological approach based on measurements of TEA dilution in the apical bathing solution, through TEA-sensitive microelectrodes. HMCs express Zo-1 and occludin at the tight junctions and a transepithelial vectorial Na transport. Real-time transmesothelial water flux, in response to an increase of osmolarity in the apical solution, indicated that, in the presence of AQP1, the rate of TEA dilution was up to four-fold higher than in its absence. Of note, we confirmed our data in isolated mouse mesentery patches, where we measured an AQP1-dependent transmesothelial osmotic water transport. These results suggest that the mesothelium may represent an additional selective barrier regulating water transport in PD through functional expression of the water channel AQP1.
我们之前曾表明，人腹膜间皮细胞在质膜上表达水通道蛋白 aquaporin 1（AQP1），这表明尽管在非生理环境中，它可能有助于腹膜透析（PD）期间的渗透水分子交换。根据预测 PD 期间水分子转运的三孔模型，假定间皮作为半透性屏障的功能作用可以忽略不计，那么腹膜毛细血管的内皮是水分子跨腹膜转运的主要限制屏障。我们假设完整的间皮层对水分子的通透性较差，除非 AQP1 在质膜上表达。为了证明这一点，我们对人腹膜间皮细胞的永生化细胞系（HMC）进行了特征描述，并在不存在或存在 AQP1 的情况下测量了渗透驱动的跨间皮水分子通量。通过免疫荧光法研究了 HMC 之间是否存在紧密连接。通过 Ussing 室研究了 HMC 单层的生物电学参数，并通过基于测量顶侧浴液中 TEA 稀释的电生理学方法研究了跨上皮水分子转运，通过 TEA 敏感微电极进行测量。HMC 在上皮细胞间紧密连接表达 Zo-1 和封闭蛋白，并具有跨上皮的 Na 向量转运。实时跨间皮水分子通量对顶侧溶液渗透压升高的反应表明，在存在 AQP1 的情况下，TEA 稀释的速率比不存在 AQP1 时高四倍。值得注意的是，我们在分离的小鼠肠系膜斑块中证实了我们的数据，我们在其中测量了依赖于 AQP1 的跨间皮渗透水分子转运。这些结果表明，间皮可能通过功能性表达水通道蛋白 AQP1 代表调节 PD 中水分子转运的另一个选择性屏障。
