Pannexin 1 deficiency can induce hearing loss

https://doi.org/10.1016/j.bbrc.2015.05.049Get rights and content

Highlights

  • Deletion of Panx1 gap junction gene can induce hearing loss.

  • The hearing loss is progressive, moderate to severe.

  • Active cochlear amplification is reduced in Panx1 KO mice.

  • Panx1 deficiency can activate Caspase-3 pathway causing cell degeneration.

Abstract

Gap junctions play a critical role in hearing. Connexin gap junction gene mutations can induce a high incidence of hearing loss. Pannexin (Panx) gene also encodes gap junction proteins in vertebrates. Panx1 is a predominant pannexin isoform and has extensive expression in the cochlea. Here, we report that deletion of Panx1 in the cochlea could produce a progressive hearing loss. The auditory brainstem response (ABR) recording showed that hearing loss was moderate to severe and severe at high-frequencies. Distortion product otoacoustic emission (DPOAE), which reflects the activity of active cochlear mechanics that can amply acoustic stimulation to enhance hearing sensitivity and frequency selectivity, was also reduced. We further found that Panx1 deficiency could activate Caspase-3 cell apoptotic pathway in the cochlea to cause hair cells and other types of cells degeneration. These data indicate that like connexins Panx1 deficiency can also induce hearing loss. These data also suggest that pannexins play important rather than redundant roles in the cochlea and hearing.

Introduction

As a gene family to encode gap junctional proteins in vertebrates, Pannexin (Panx1) was identified 10 years ago [1], [2]. So far, three pannexin isoforms (Panx1, 2, and 3) have been cloned from the human and mouse genomes [2]. Despite the lack of similar sequences with connexins, pannexin proteins share large similarities at the structural and functional levels [3]. They have been found to play important and critical roles in many physiological and pathological processes, such as ATP release [4], [5], Ca2+ homeostasis [6], [7], release of synaptic neurotransmitters [8], mediation of cell apoptosis [9], [10], and immunological response [11]. However, pannexin functions in vivo still remain largely undetermined.

It has been well-demonstrated that gap junctions play a critical role in hearing. Connexin (Cx) gene mutations can induce a high incidence of hearing loss [12], [13]. Cx26 and Cx30 have extensive expression in the cochlea [14], [15], [16]. Deletion of Cx26 in the cochlea can induce hearing loss [17], [18], [19], [20], [21], [22]. Like connexins, pannexins are also extensively expressed in the inner ear [23]. In particular, high expression of Panx1 was found in the cochlear spiral limbus (SLM), supporting cells in the organ of Corti (OC), and fibrocytes in the cochlear lateral wall [23]. In this study, we used Panx1 deficient mice to examine the function of Panx1 in the cochlea and hearing. We found that deletion of Panx1 in the cochlea can induce hearing loss. This study provides important information about the pannexin function in hearing.

Section snippets

Creation of Panx1 knockout mice

Panx1tm1a(KOMP)Wtsi knockout first mice were purchased from KOMP (Knock Out Mouse Project) and crossed with Pax2-Cre transgenic mouse line (the Mutation Mouse Regional Center, Chapel Hill, NC) to generate Panx1 conditional knockout (KO) in the cochlea. The mouse genotyping was identified by PCR amplification with the following primers: Panx1-Mut1a: 5′-CAC TGC ATT CTA GTT GTG GTT TGT CC-3′, Panx1-Mut2 (gene specific primer): 5′-CTG GCT CTC ATA ATT CTT GCC CTG-3′, Panx1-WF (wildtype-F): 5′-CTG

Deletion of Panx1 in the cochlea

As shown in our previous study [23], Panx1 had strong labeling in the organ of Corti (OC), the spiral limbus (SLM), and the cochlear lateral wall (Fig. 1A). In Panx1 KO mice, Panx1 expression in the SLM was completely deleted (Fig. 1B). Most of Panx1 expression in the cochlea and the cochlear lateral wall were also deleted. Only small, scattered Panx1 labeling was visible. The labeling was also light (Fig. 1B). In addition, the cochlea appeared normal development (Fig. 1B).

Hearing loss in Panx1 KO mice

Fig. 2 shows that

Conflict of interest

There is no conflict of interest.

Acknowledgments

We are grateful to Dr. Gerhard Dahl at Miami University for kindly providing anti-Panx1 antibody. This work was supported by a grant (R01) from the National Institute on Deafness and Other Communication Disorders, DC 05989.

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