Elsevier

Hearing Research

Volume 283, Issues 1–2, January 2012, Pages 80-88
Hearing Research

Research paper
Genetic background effects on age-related hearing loss associated with Cdh23 variants in mice

https://doi.org/10.1016/j.heares.2011.11.007Get rights and content

Abstract

Inbred strain variants of the Cdh23 gene have been shown to influence the onset and progression of age-related hearing loss (AHL) in mice. In linkage backcrosses, the recessive Cdh23 allele (ahl) of the C57BL/6J strain, when homozygous, confers increased susceptibility to AHL, while the dominant allele (Ahl+) of the CBA/CaJ strain confers resistance. To determine the isolated effects of these alleles on different strain backgrounds, we produced the reciprocal congenic strains B6.CBACa-Cdh23Ahl+ and CBACa.B6-Cdh23ahl and tested 15-30 mice from each for hearing loss progression. ABR thresholds for 8 kHz, 16 kHz, and 32 kHz pure-tone stimuli were measured at 3, 6, 9, 12, 15 and 18 months of age and compared with age-matched mice of the C57BL/6J and CBA/CaJ parental strains. Mice of the C57BL/6N strain, which is the source of embryonic stem cells for the large International Knockout Mouse Consortium, were also tested for comparisons with C57BL/6J mice. Mice of the C57BL/6J and C57BL/6N strains exhibited identical hearing loss profiles: their 32 kHz ABR thresholds were significantly higher than those of CBA/CaJ and congenic strain mice by 6 months of age, and their 16 kHz thresholds were significantly higher by 12 months. Thresholds of the CBA/CaJ, the B6.CBACa-Cdh23Ahl+, and the CBACa.B6-Cdh23ahl strain mice differed little from one another and only slightly increased throughout the 18-month test period. Hearing loss, which corresponded well with cochlear hair cell loss, was most profound in the C57BL/6J and C57BL/6NJ strains. These results indicate that the CBA/CaJ-derived Cdh23Ahl+ allele dramatically lessens hearing loss and hair cell death in an otherwise C57BL/6J genetic background, but that the C57BL/6J-derived Cdh23ahl allele has little effect on hearing loss in an otherwise CBA/CaJ background. We conclude that although Cdh23ahl homozygosity is necessary, it is not by itself sufficient to account for the accelerated hearing loss of C57BL/6J mice.

Highlights

► We investigated auditory effects of Cdh23 variants in both C57BL/6J and CBA/CaJ genetic backgrounds. ► The CBA/CaJ-derived Cdh23 allele lessens hearing loss and decreases hair cell loss in a C57BL/6J genetic background. ► The C57BL/6J-derived Cdh23 allele has no effect on hearing loss or hair cell death in a CBA/CaJ genetic background. ► Deleterious alleles at other loci in addition to Cdh23 must contribute to the accelerated hearing loss of C57BL/6J mice. ► Mice of the C57BL/6J and C57BL/6N substrains have identical hearing loss profiles.

Introduction

Age-related hearing loss (AHL), or presbycusis, poses a serious human health concern as it negatively affects the life of many elderly individuals (Dalton et al., 2003). In a 2003 CDC study, presbycusis was found to be second only to arthritis as a handicapping condition within the elderly segment of our society (Bielefeld et al., 2010). Susceptibility to AHL has a significant genetic component although AHL presents with a complex pathophysiology (DeStefano et al., 2003). A range of environmental factors, including exposure to loud noises or ototoxic drugs, can exacerbate and accelerate AHL. The high degree of genetic complexity in human populations coupled with highly variable environmental factors make it difficult to identify the genetic components underlying AHL in the human population, although some limited success has been achieved (Bared et al., 2010, DeStefano et al., 2003, Friedman et al., 2009, Garringer et al., 2006, Rodriguez-Paris et al., 2008, Unal et al., 2005).

Laboratory mice are more amenable to studies of AHL predisposition because of their well-defined genetics, short life span and the ability of researchers to control for environmental factors. Like humans, many inbred mouse strains express variable degrees of AHL, and at least ten quantitative trait loci associated with AHL have been identified in mice (Latoche et al., 2011, Noben-Trauth and Johnson, 2009). C57BL/6J (B6J) and CBA/CaJ (CBA) are the two most widely used inbred strains in hearing research. The B6J strain has been used extensively as a model of early onset AHL (Henry and Chole, 1980, Hequembourg and Liberman, 2001, Mikaelian, 1979, Wang et al., 2008, Willott, 1986). B6J mice exhibit a high frequency hearing loss by 3–6 months of age that progresses to a profound impairment by 15 months. In contrast, CBA mice remain resistant to AHL until 15 months of age or older and are often used as good hearing controls (Henry and Chole, 1980, Li and Borg, 1991, Zheng et al., 1999). B6J and CBA mice also exhibit dramatically different rates of cochlear hair cell loss (Spongr et al., 1997).

One of the major genetic factors contributing to hearing loss in B6J mice is the ahl locus on Chromosome 10 (Johnson et al., 1997), which has been shown to be a splice variant of the cadherin 23 gene (Cdh23) (Noben-Trauth et al., 2003). The CBA strain does not have this predisposing Cdh23 splice variant, consistent with its much slower rate of hearing loss. Cadherin 23 has been shown to be a component of the tip links of hair cell stereocilia, along with protocadherin 15 (Kazmierczak et al., 2007). Mutations in the genes encoding these two proteins affect tip link formation and stability, which is necessary for normal hair cell mechanotransduction (Alagramam et al., 2011). Mice with an ENU-induced missense mutation in the ectodomain of Cdh23 show a loss of tip links that correlates with a progressive hearing loss that is similar to, but more severe than the hearing loss associated with the ahl splice variant of Cdh23 (Schwander et al., 2009).

Here we report on the characterization of two reciprocal congenic strains that we developed to evaluate the isolated effects of Cdh23 allelic variants when on different strain backgrounds. The CBACa.B6-Cdh23ahl congenic stain (CBA.B6-ahl) is homozygous for the recessive AHL susceptibility allele (ahl) of Cdh23, which we transferred from the B6J strain onto the CBA background. The reciprocal B6.CBACa-Cdh23Ahl+ congenic strain (B6.CBA-Ahl+) is homozygous for the dominant AHL resistance allele (Ahl+) of Cdh23, which we transferred from the CBA strain onto the B6J background. To follow the progression of hearing loss in the congenic strain mice and mice of the B6J and CBA parental strains, auditory brainstem response (ABR) thresholds were measured at 3, 6, 9, 12, 15 and 18 months of age. After the final ABR test, inner ears of mice from each strain were examined for cochlear hair cell loss to determine its correspondence with hearing loss.

We also report on hearing loss in mice of the C57BL/6N strain (B6N), an NIH subline of C57BL/6 separated from B6J in 1951. A complete description of the B6N strain at The Jackson Laboratory (C57BL/6NJ, Stock #005304) and its development is given in the JAX mice database (http://jaxmice.jax.org/strain/005304.html). Like B6J, the B6N strain carries the Cdh23ahl hearing loss susceptibility allele, but it has not previously been assessed for AHL. Because the B6N strain is the source of embryonic stem cells for the International Knockout Mouse Consortium (http://www.knockoutmouse.org/), establishment of a hearing profile for this control strain is important for assessing hearing-related phenotypes of the many knockout mice being generated by this program.

Section snippets

Mice and congenic strain development

All mice examined in this study originated from The Jackson Laboratory (http://www.jax.org/), and all procedures involving their use were approved by the Institutional Animal Care and Use Committee. The Jackson Laboratory is accredited by the American Association for the Accreditation of Laboratory Animal Care.

We use the following abbreviated strain designations throughout the paper, which are followed in parentheses by their corresponding full inbred strain names and Jackson Laboratory Stock

Age-related hearing loss

Hearing assessment by ABR threshold analysis was performed for all five strains at 3, 6, 9, 12, 15 and 18 months of age. Table 1 lists the ABR threshold means for each auditory stimulus, the numbers of mice tested, and threshold variance estimates (standard deviations) for each strain and test age. The changes in ABR thresholds for each strain over time are illustrated graphically in Fig. 1 for each test stimulus. At 3 months of age all of the strains exhibited normal ABR thresholds for all

CAST- and CBA-derived Cdh23 alleles reduce hearing loss in B6 congenic mice

We previously generated and analyzed a B6.CAST-Ahl+ congenic strain (Johnson et al., 1997, Keithley et al., 2004) analogous to the B6.CBA-Ahl+ congenic strain described in this paper, but with the AHL protective allele of the CAST/EiJ (CAST) strain, rather than the CBA strain, transferred to the B6J strain background. Mice of both congenic strains exhibit a much slower rate of hearing loss compared with the B6J host strain mice, demonstrating that both CAST and CBA alleles of Cdh23 can confer

Acknowledgments

We thank Patsy Nishina and David Bergstrom of The Jackson Laboratory for their critical review of this manuscript. We also thank Sandra Gray for her skilled mouse colony management and assistance in the development of the congenic strains. This research was supported by R01 grant DC005827 (KRJ) from the National Institutes of Health (NIH), National Institute on Deafness and Other Communication Disorders (NIDCD). The Jackson Laboratory institutional shared services are supported by NIH National

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