A Review: Expression of Aquaporins in Otitis Media

Abstract

Otitis media (OM) refers to inflammatory diseases of the middle ear (ME), regardless of cause or pathological mechanism. Among the molecular biological studies assessing the pathology of OM are investigations of the expression of aquaporins (AQPs) in the ME and Eustachian tube (ET). To date, fifteen studies have evaluated AQPs expression in the ME and ET. Although the expression of individual AQPs varies by species and model, eleven types of AQP, AQP1 to AQP11, were found to be expressed in mammalian ME and ET. The review showed that: (1) various types of AQPs are expressed in the ME and ET; (2) AQP expression may vary by species; and (3) the distribution and levels of expression of AQPs may depend on the presence or absence of inflammation, with variations even in the same species and same tissue. Fluid accumulation in the ME and ET is a common pathological mechanism for all types of OM, causing edema in the tissue and inducing inflammation, thereby possibly involving various AQPs. The expression patterns of several AQPs, especially AQP1, 4 and 5, were found to be altered in response to inflammatory stimuli, including lipopolysaccharide (LPS), suggesting that AQPs may have immunological functions in OM.

Keywords: aquaporin; human middle ear; otitis media; transmembrane permeability; water channel.

Figure 1

Phylogenetic leaf of the human aquaporin gene family. Water permeable aquaporins are shown in bold (AQP0, 1, 2, 4, 5, 6, 8, AqpZ). Glycerol permeable aquaglyceroporins are in italics (AQP3, 7, 9, 10, GlpF). E. coli homologues are AqpZ and GlpF. The unclassified subfamily comprising AQP11 and 12 is on the bottom right. The scale bar represents genetic distance between homologues.