From: Baylor University Newswire
Published December 27, 2007 02:04 PM

Cholesterol fine-tunes hearing

HOUSTON - Levels of cholesterol in the membranes of hair cells in the inner ear can affect your hearing, said a consortium of researchers from Baylor College of Medicine, Rice University and Purdue University in a report in today's print edition of The Journal of Biological Chemistry.

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Dr. William Brownell, professor of otolaryngology at BCM and his colleagues, said that the amount of cholesterol in the outer hair cell membrane found in the inner ear can affect hearing. "We've known for a long time that cholesterol is lower in the outer hair cell membranes than in the other cells of the body," said Brownell, senior author of the report. "What we didn't know was the relationship it had to hearing."

Dr. Lavanya Rajagopalan, postdoctoral fellow in otolaryngology at BCM, led the research team that manipulated the cholesterol levels in outer hair cells of mice. She and her colleagues measured the mice's hearing ability by a technique that uses inaudible sound waves emitted from the ear as it reacts to external sound. There are two types of sensory hair cells in the inner ear called the inner and outer hair cells. It is the outer hair cells that are affected by cholesterol levels and produce the inaudible sounds in the ear canal.

"Depleting the cholesterol resulted in a hearing loss. Adding cholesterol initially increased hearing but later resulted in a hearing loss," Brownell said. "So you can change an animals hearing just by adding or subtracting cholesterol." The fine tuning of the cholesterol happens naturally in development and does not change significantly after birth.

In contrast, cholesterol in the bloodstream can vary with eating habits. That is why avoiding fatty foods can promote a healthy heart. "Will our hearing be affected if we continually eat greasy meals? Right now, we don't see a connection between the two," Brownell said. "The results of the study help us understand the cellular mechanisms for regulating hearing and give us another way to potentially help those with hearing loss."

Others who took part in the study include Drs. Anping Xia, Angela Sturm, John S. Oghalai, Fred A. Pereira, and research assistant Haiying Liu of BCM, Jennifer N. Greeson and Dr. Robert M. Raphael of Rice University and Dr. Amy L. Davidson of Purdue University. This study was supported by grants from the National Institute of Deafness and Other Communication Disorders, the National Science Foundation, the Deafness Research Foundation, the Keck Center for Interdisciplinary Bioscience Training and the Welch Foundation.

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