Rolling Stones in the Ear♦

♦ See referenced article, J. Biol. Chem. 2010, 285, 21724–21735

Biomineralization occurs in a variety of tissues and is responsible for forming bones, teeth, and components of the ear. However, when this process goes awry it can lead to pathological conditions, most notably the formation of kidney stones (typically calcium oxalate crystals). In this Paper of the Week, Amiel Dror and colleagues show for the first time that calcium oxalate stones can also form in the inner ear. Normally, the vestibular system within the inner ear depends on tiny extracellular calcium carbonate minerals, known as otoconia, for proper mechanical stimulation of the sensory hair cells. Combining a mouse model of hearing loss with imaging and spectroscopy tools, Dror and colleagues found that a missense mutation within the Slc26a4 gene, which abolishes the transport activity of the encoded protein pendrin, produced dramatic changes in mineral composition, size, and shape within the vestibular sensory organs. Specifically in the saccule, a gradual change in mineral composition over time led to the formation and aggregation of calcium oxalate stones in adult mice. This visually arresting study provides insight into the underexplored area related to the biochemistry and genetics of ear function and might also hold therapeutic potential for disorders affecting equilibrium and balance.

Morphology of otoconia from the utricle and saccule of wild-type and Slc26a4 mice across three progressive stages. Minerals extracted from Slc26a4 mice are larger and show altered morphology relative to wild-type; at 10 months crystals found in the saccule of mutant mice (K) resemble calcium oxalate dihydrate (weddellite) instead of the large calcitic crystals observed earlier.