Function of the Membrane Water Channel Aquaporin-5 in the Salivary Gland

Abstract

The process of saliva production in the salivary glands requires transepithelial water transfer from the interstitium to the acinar lumen. There are two transepithelial pathways: the transcellular and paracellular. In the transcellular pathway, the aquaporin water channels induce passive water diffusion across the membrane lipid bilayer. It is well known that aquaporin-5 (AQP5) is expressed in the salivary glands, in which it is mainly localized at the apical membrane of the acinar cells. This suggests the physiological importance of AQP5 in transcellular water transfer. Reduced saliva secretion under pilocarpine stimulation in AQP5-null mice compared with normal mice further indicates the importance of AQP5 in this process, at least in stimulated saliva secretion. Questions remain therefore regarding the role and importance of AQP5 in basal saliva secretion. It has been speculated that there would be some short-term regulation of AQP5 such as a trafficking mechanism to regulate saliva secretion. However, no histochemical evidence of AQP5-trafficking has been found, although some of biochemical analyses suggested that it may occur. There are no reports of human disease caused by AQP5 mutations, but some studies have revealed an abnormal subcellular distribution of AQP5 in patients or animals with xerostomia caused by Sjögren’s syndrome and X-irradiation. These findings suggest the possible pathophysiological importance of AQP5 in the salivary glands.

Transdifferentiation of mouse adipose-derived stromal cells into acinar cells of the submandibular gland using a co-culture system

“…Water permeability is decreased about 65% in parotid ACs and 77% in sublingual ACs in Aqp5-deficient mice [45]. Thus, AQP5 is important in the process of water transfer during saliva secretion from ACs [44]. In the present study, AC-specific markers (Amyl and AQP5) were expressed from Day 14 during the transdifferentiation of ADSCs (Fig.…”

“…AQP5 is mainly expressed in the salivary gland [39,40], respiratory epithelium [41], lacrimal gland [42] and sweat gland [43]. In salivary glands, it is primarily localized at the apical membrane of ACs [44]. Water permeability is decreased about 65% in parotid ACs and 77% in sublingual ACs in Aqp5-deficient mice [45].…”

Biocompatible Tissue Scaffold Compliance Promotes Salivary Gland Morphogenesis and Differentiation

“…32 Saliva production depends on the expression levels and localization of the water channel protein aquaporin 5 (AQP5) by the secretory epithelium [33][34][35][36] and expression of smooth muscle alpha-actin (SM a-actin) by the myoepithelium 37 ; loss of these functional markers is associated with salivary hypofunction. 38,39 Engineering of an artificial salivary gland should thus strive to support both of these cell types.…”

Regulation of Aquaporins by Vasopressin in the Kidney

“…The tissue distributions of the various AQP isoforms in mammals are briefly summarized in Table 1. Details of the tissue distributions have been described in a number of review articles (Matsuzaki et al, 2012Takata et al, 2004). …”