Immunohistochemical localization of aquaporins in the human inner ear

Abstract

We report the immunolocalization of aquaporins (AQPs) 1, 4, and 6 in the human auditory and vestibular endorgans. A rapid protocol was applied to audiovestibular endorgans microdissected from postmortem human temporal bones from six subjects (ages ranging from 75 to 97 years) with no history of audiovestibular disease. Temporal bones were fixed in formalin, and the endorgans were immediately microdissected. Cryostat sections were obtained from audiovestibular endorgans and were subjected to double-immunohistochemical staining with antibodies against AQPs and several cellular markers. In the human cochlea, AQP1 immunoreactivity was localized to the fibrocytes of the spiral ligament and the sub-basilar tympanic cells; AQP4 immunoreactivity was localized to the outer sulcus cells, Hensen's cells, and Claudius' cells; AQP6 immunoreactivity was localized to the apical portion of interdental cells in the spiral limbus. In the vestibular endorgans (macula utriculi and cristae), AQP1 was localized to fibrocytes and blood vessels of the underlying stroma and trabecular perilymphatic tissue; AQP4 immunoreactivity was localized to the basal pole of vestibular supporting cells; AQP6 was localized to the apical portion of vestibular supporting cells. Cochlear and vestibular hair cells and nerve fibers were not immunoreactive for any AQP. Supporting cells were identified with antibodies against glial fibrilar acidic protein. Nerve fibers and terminals were identified with antibodies against neurofilaments and Na(+)K(+)ATPase. The high degree of conservation of AQP expression in the human inner ear suggests that AQPs play a critical role in inner ear water homeostasis.

Expression of aquaporins and vasopressin type 2 receptor in the stria vascularis of the cochlea

“…Since the discovery of aquaporin (AQP) water channels (Agre et al, 1993), it has become clear that these channels play a crucial role in water homeostasis not only in the kidney but also in the inner ear. Indeed, expressions of proteins and/or mRNAs of AQPs in the inner ear have already been reported including negative reports (AQP-1: Stankovic et al, 1995;Sawada et al, 2003;AQP2: Kumagami et al, 1998;Beitz et al, 1999;Merves et al, 2000;Mhatre et al, 2002;Sawada et al, 2002;Fukushima et al, 2005;Zhong and Liu, 2003;AQP-3: Beitz et al, 1999;AQP-4: Takumi et al, 1998;Minami et al, 1998;AQP-5: Beitz et al, 1999;Mhatre et al, 1999;Löwenheim and Hirt, 2004;AQP-6: Fukushima et al, 2002;Lopez et al, 2007;Taguchi et al, 2008;AQP-7: Beitz et al, 1999;Huang et al, 2002;AQP-8: Beitz et al, 1999;Huang et al, 2002;and AQP-9: Huang et al, 2002). However, previous reports have had many contradictions.…”

Expression and immunolocalization of aquaporin-6 (Aqp6) in the rat inner ear

“…Although the systemic distribution of Aqp6 has not been extensively examined, Aqp6 mRNA is reported to be expressed in the rat inner ear [9], and the immunolocalization of Aqp6 protein in the human cochlea and vestible has been reported [14]. However, the immunolocalization of Aqp6 protein in the inner ear of experimental animals has not been reported.…”

Hormonal Aspects of Ménière’s Disease on the Basis of Clinical and Experimental Studies

“…AQP2, vasopressin-regulated water channel protein, is well known to be predominantly localized in the kidney [14] and colon [15] . In the inner ear, AQP1, AQP3, AQP4, AQP5, and AQP mRNAs and/or proteins are reported to be expressed [11][12][13][16][17][18][19][20] .…”