Tel Aviv U research holds out hope for deaf

Researchers have traced deafness to a loss of microRNA molecules.

A new study by Prof. Karen Avraham of the Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine at Tel Aviv University Tel Aviv University has uncovered one of the root causes of deafness.

Prof. Avraham has discovered that microRNAs, tiny molecules that regulate cell functions, help us hear. The molecules are found in “hair” cells of the ear. This discovery opens an entirely new window for possible treatments, and a cure for all types of deafness, age-related or genetic.

“Over the last decade, science has found that microRNAs are involved in heart disease, and in cancer, and for the first time ever, our lab shows that these tiny regulators in all our cells can cause deafness,” says Prof. Avraham, whose groundbreaking work has previously discovered 4 deafness genes and novel mutations in 10 deafness genes, among 46 known ones.

Prof. Avraham’s results were published this month in the Proceedings of the National Academy of Science. They may lead to ways of ameliorating deafness, even in people whose hearing loss has no genetic basis, such as those who have suffered severe injury to the ear. Her recent study investigated mice and zebrafish, but the model holds true for all vertebrates ― including humans, she says.

“We’ve found that ‘hair’ cell microRNAs are regulators involved in the normal development and survival of cells in the inner ear and are necessary for proper hearing,” says Prof. Avraham. “Until now science only knew that mutations in protein-coding genes caused deafness. We went a layer deeper and discovered that the loss of microRNAs leads to deafness as well.”

Doctors still don’t know what causes hearing loss in most people, but they do know where the process starts to break down. For some reason, there is an abnormal development or wearing down of specialized sensory cells, called hair cells located in the inner ear. These cells are responsible for translating sounds to electrical pulses that the brain can interpret. When we lose them, we lose our ability to hear.

In the new study, developed with an international team including Prof. Avraham’s post-doctoral fellow Dr. Lilach M. Friedman, and other researchers from Israel and from Purdue University, the scientists sought to see what would happen if they stopped the formation of all the microRNAs in the ears of a mouse.

They “knocked-down” or blocked the functioning of the microRNA molecules, and as a result, the hair cells degenerated in the mouse ears. A few weeks later the mice became profoundly deaf, suggesting that a lack of normal microRNAs might lead to progressive hearing loss in people that were born with normal hearing, as well, says Prof. Avraham.

MicroRNAs are tiny pieces of RNA, the chemical building blocks that carries genetic information between DNA, to becoming proteins. MicroRNAs control whether or not a protein will actually be made. The important roles of microRNAs in animals have been discovered only during the last decade, and major efforts are being made to develop strategies for inserting these tiny molecules into cells, in order to use them as cures.

If scientists can figure out how microRNAs regulate hair cells, they could be used to rescue the cells that are dying, says Prof. Avraham, who also collaborates with Palestinian researchers to help them understand, and combat, the high incidence of genetic deafness in the Palestinian population.

Published by Globes [online], Israel business news - www.globes.co.il - on April 13, 2009

© Copyright of Globes Publisher Itonut (1983) Ltd. 2009

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