The Klotho mouse is a recently developed model that exhibits phenotypes 
resembling human aging. We used this model to investigate sensorineural hearing 
loss from the point of view that it may be considered an issue of aging. Using 
reverse transcription-polymerase chain reaction, Western blotting and 
immunohistochemical staining, we were able to confirm klotho gene transcription 
and protein synthesis in the kidney and inner ear. Klotho protein was mainly 
expressed in the stria vascularis and spiral ligament of the inner ear and in 
the distal convoluted tubule of the kidney, likely serving a common function in 
the two organs, i.e., modulating ion transport. The threshold for the auditory 
brainstem response was significantly higher in Klotho mice than in wild-type 
mice, and wave I latencies were prolonged. On the other hand, Klotho mice 
exhibited a normal distribution of I-IV interpeak intervals. No obvious 
morphological abnormalities were detected in Klotho mice, although no expression 
of Klotho protein was detected, and there was an apparent hearing disorder. 
Taken together, these findings suggest that by contributing to the maintenance 
ion homeostasis in the endolymph, Klotho protein serves as a key mediator of 
auditory function.