Aquaporin-1 Facilitates Transmesothelial Water Permeability: In Vitro and Ex Vivo Evidence and Possible Implications in Peritoneal Dialysis

Abstract

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.

β3 Adrenergic Receptor Agonist Mirabegron Increases AQP2 and NKCC2 Urinary Excretion in OAB Patients: A Pleiotropic Effect of Interest for Patients with X-Linked Nephrogenic Diabetes Insipidus

“…Nonspecific binding sites were blocked with 1% bovine serum albumin in PBS for 30 min. Sections were then incubated with the primary antibodies rabbit anti-BAR3 (SC-50436, Santa Cruz Biotechnology, Inc., www.scbt.com, accessed on 22 November 2022) with mouse anti-AQP2 antibody [38] (SC-515770, Santa Cruz Biotechnology, Inc., www.scbt.com, accessed on 22 November 2022) or mouse anti-NKCC2 [20] or mouse anti-AQP1 [39,40] (SC-25287, Santa Cruz Biotechnology, Inc., www.scbt.com, accessed on 22 November 2022). Sections were incubated with Alexa Fluor-conjugated secondary antibody.…”

Nutritional and Physiological Properties of Thymbra spicata: In Vitro Study Using Fecal Fermentation and Intestinal Integrity Models

“…The short circuit current (Isc) and the transepithelial resistance (Rt) were measured as previously described [ 31 ].…”

Oxidative Stress-Induced Alterations of Cellular Localization and Expression of Aquaporin 1 Lead to Defected Water Transport upon Peritoneal Fibrosis

“…All these above-mentioned changes in peritoneum permeability are thought to result from the impairment of free water transport and ultrafiltration abilities due to defected water channel protein, aquaporin 1 (AQP1) on both endothelium and mesothelium upon the occurrence of peritoneum fibrosis [15,16]; moreover, Piccapane et al showed functional AQP1 was crucial for transmesothelial water transport. Another study also demonstrated that AQP1-containing exosomes present in peritoneal dialysis effluent may potentially serve as a biomarker for the integrity of the peritoneum, and reflect the water permeability status of the peritoneum; more importantly, detection of those AQP1-containing exosomes may be used to predict ultrafiltration failure in PD patients [17][18][19]; however, although the changes shown on PET and impairment of AQP1 were considered as relevant indications to fibrosis and angiogenesis, the underlying mechanism of these functional changes on peritoneum remains to be elucidated [20][21][22][23].…”