Aquaporin 1 (AQP1) Expression in Healthy Dog Tears

Barbara Lamagna,Alessandra Pelagalli,Paolo Ciaramella,Arturo Brunetti,Francesco Lamagna,Antonio Di Loria

doi:10.3390/ani10050820

Abstract

Simple SummaryThe characterisation of tear proteins is very important for scientists and clinicians, as it enhances their understanding of ocular physiological phenomena that sometimes evolve into diseases. Recently, ophthalmic research has been focused on aquaporins (AQPs), a family of water channel proteins that are largely ubiquitous in body tissues and are known for their role in water and small solute transport across cell membranes. Based on AQPs’ presumable role in the eye, the aim of the present study was to investigate the expression of aquaporin-1 (AQP1) by Western blot analysis in canine eye tears. To this end, we collected tears from both eyes of 15 healthy dogs by employing two tear collection methods: Schirmer tear strips (STS) and ophthalmic sponges (OS). Moreover, ocular parameters such as Schirmer tear test 1 (STT 1), intraocular pressure (IOP), and tear film break up time (BUT) were measured, and fluorescein and lissamine green staining were performed to uncover possible correlations among the aforementioned parameters. Our results showed that the expression of AQP1 in tears collected by both methods and expressed as multiple bands (measured by densitometry) was higher for the tears collected by OS than for those collected by STS. This work forms the basis of future studies aiming to understand and establish the involvement of AQPs in the production and secretion of tears.Aquaporins (AQPs) are a family of thirteen membrane proteins that play an essential role in the transport of fluids across the cell plasma membrane. Recently, the expression of AQPs in different ocular tissues and their involvement in the pathophysiology of eye diseases, have garnered attention. Considering that literature on AQP expression in the lacrimal glands and their secretion is scarce, we aimed to characterise AQP1 expression in the tears of healthy dogs using two tear collection methods (Schirmer tear strips (STS) and ophthalmic sponges (OS)). Fifteen healthy dogs, free of ophthalmic diseases, were included in the study. Tear collection was performed by using STS in one eye and OS in the other. After the extraction of proteins from the tears, the expression of AQP1 was analysed by Western blotting. AQP1 was expressed as a band of 28 kDa. In addition, differences were observed in the expression of AQP1 and in the correlation between tear volume and protein concentration, in tears collected by the two different methods. Our results suggest that AQP1 has a specific role in tear secretion; further research is required to assess its particular role in the function of the ocular surface in eye physiology and pathology.

Highlights

In the past twenty years, the lacrimal gland of humans and other animal species has been studied extensively in terms of its role in tear fluid composition and secretion [1], in the context of either ocular physiology [2] or pathology [3]
The lacrimal gland produces a tear film of a complex mixture, whose components exhibit a highly variable composition with a predominant aqueous fraction secreted by acinar cells, which play a major role in the high tear fluid volume
It can be hypothesised is distributed throughout the surface of the eye, interacting with the conjunctiva and cornea. These that aquaporin 1 (AQP1) contributes to different functions of lacrimal fluid that is distributed throughout the surface findings suggest the role of AQP1 in controlling the homeostasis of the tear fluid and in its of the eye, interacting with the conjunctiva and cornea. These findings suggest the role of AQP1 in interaction with ocular surface contributing to the ocular controlling the homeostasis of the tear fluid and in its interaction with ocular surface contributing microenvironment (Figure 7)

Summary

Introduction

In the past twenty years, the lacrimal gland of humans and other animal species has been studied extensively in terms of its role in tear fluid composition and secretion [1], in the context of either ocular physiology [2] or pathology (especially dry eye syndrome) [3]. The lacrimal gland produces a tear film of a complex mixture, whose components (mucous, aqueous and lipid layers) exhibit a highly variable composition with a predominant aqueous fraction secreted by acinar cells, which play a major role in the high tear fluid volume. AQPs are a family of thirteen water channel proteins well characterised in terms of their physiological role in the transport of fluids to several tissues of different organisms [7]. The first AQP isolated in the eye was aquaporin-0 (AQP0) [8]

Objectives

Methods

Discussion

Conclusion