Immunolocalization of water channel aquaporins in the nasal olfactory mucosa

Abstract

Aquaporins (AQPs), membrane water channel proteins expressed in various tissues and organs, serve in the transfer of water and small solutes across the membrane. We raised antibodies to AQPs using isoform-specific synthetic peptides and surveyed their expression in the rat nasal olfactory and respiratory mucosae. AQP1, AQP3, AQP4, and AQP5 were detected by immunohistochemical and immunoblotting analyses. AQP1 was expressed in the endothelial cells of blood vessels and the surrounding connective tissue cells in the olfactory and respiratory mucosae. AQP1 may be involved in water transfer across the blood vessel wall. In the olfactory epithelium, no AQP was detected in the olfactory sensory cells. Instead, AQP3 was abundant in the olfactory epithelium, where it was localized in the supporting cells and basal cells. Expression of AQP3 was mostly restricted to the basal cells in the respiratory epithelium. In marked contrast, AQP4 was abundant in the respiratory epithelium, but its abundance was limited to the basal cells in the olfactory epithelium. In the Bowman's gland, AQP5 was localized in the apical membrane in the secretory acinar cells, whereas AQP3 and AQP4 were found in the basolateral membrane. Similar localization was seen in its duct cells. These results showed a distinct localization pattern for AQPs in the olfactory epithelium. AQP3 and AQP4 in the supporting cells and basal cells may play an important role in generating and maintaining the specific microenvironment around the olfactory sensory cells. AQP3, AQP4, and AQP5 in the Bowman's gland may serve in the secretion to generate the microenvironment at the apical surface of the olfactory dendrites for odorant reception.

Epithelial and endothelial barriers in the olfactory region of the nasal cavity of the rat

“…In the olfactory system, perineural cells around the Wla olfactoria were found to be highly immunoreactive for anti-AQP1 antibodies (Ablimit et al 2006; this study, Fig. 1d), the OECs were immunonegative.…”

“…The concept of the so-called neurovascular unit describing complex interrelationships between neurons, glial cells and microvessels (Iadecola 2004;Simard and Nedergaard 2004) has never been applied to the olfactory system. Recently, several studies have been published focussing on junctional connections in the olfactory epithelium (Menco 1988;Miragall et al 1994;Hussar et al 2002;Rash et al 2005;Ablimit et al 2006), but only little attention has been paid to the cellular system of the olfactory Wla.…”

Epithelial membrane transporters expression in the developing to adult mouse vomeronasal organ and olfactory mucosa

“…The AQP patterns of expression in olfactory and vomeronasal glands were different, AQP3 and AQP4 being expressed in the former, AQP2 in the latter, and AQP5 in both. These findings are supported in part by those of rats showing the presence of several AQPs (AQP1, AQP3, AQP4, and AQP5) in the nasal olfactory mucosa (Ablimit et al, 2006) as well as the vomeronasal organ (Ablimit et al, 2008); a main difference is the absence of AQP4 in olfactory neurons of the VNO in mice. Besides the obvious possibility of speciesrelated difference, this finding is consistent with the lack of AQP4 in sensory cells of the mice OE (confirmed in rats by Ablimit et al, 2006 and in mice by Lu et al, 2008) and the expression of AQP4 in astroglial cells in the central nervous system (Verkman, 2005); moreover, the neuronal marker (PGP9.5) used by Ablimit et al (2008) is less specific to olfactory neurons than OMP.…”

“…The sustentacular cells are thought to play no role in stimulus detection; however, they are involved in, e.g., K + transport (Vogalis et al, 2005) and maintenance of water/salt balance in the NML (Menco et al, 1998;Rochelle et al, 2000) that can contribute to the equilibrium of the perireceptor environment. More recently, epithelial regulatory, secretory, and transport factors have been hypothesized to play a role in chemoreception: the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) and the aquaporins (AQPs) have been involved in olfaction (Ablimit et al, 2006;Grubb et al, 2007), and the Clara cell secretory protein 26 (CC26), a member of the cellular antioxidant system, has been involved in taste (Merigo et al, 2008). The epithelial transporters (CFTR and AQPs) are probably collaborating to regulation of the water and ionic environment at the chemoreceptor surface as well as the intercellular space; CC26 is conceivably involved in maintaining of the proper redox equilibrium in the epithelium.…”

Aquaporins in sperm osmoadaptation: an emerging role for volume regulation

“…Alternatively, we hypothesize that AQP3 may function as a part of the membrane osmosensing/mechanosensing system for the initial sensing of cell swelling and therefore, may "trigger" subsequent RVD events such as solute transport and cytoskeleton reconstruction. This hypothesis is supported by the fact that AQP3 is strongly expressed in many organs, such as the bladder, trachea and esophagus, and in olfactory cells [18,28,29] , where they seem to have no obvious requirements for rapid water movement but need sensitive perception of tension, shear stress and so on. Moreover, this hypothesis is supported by the recent discovery that AQP5 is actively involved in salivary gland cell RVD by coordinating with TRPV4, a volume sensitive calcium channel, to concertedly regulate cell volume under hypotonic stimulation [23] .…”