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Holding out hope of a cure for deafness

Posted By ISRAEL21c Staff On April 14, 2009 @ 7:00 am In | No Comments

An Israeli researcher has discovered that microRNAs in the ‘hair’ cells of our ears are a major cause of deafness, holding out the promise of a potential new cure.

 

An Israeli hearing loss expert has discovered one of the root causes of deafness, opening up the potential for a whole new range of treatments, and even possibly a cure for both genetic and age-related deafness.

In a landmark study, Prof. Karen Avraham of Tel Aviv University has revealed that microRNAs – tiny molecules that regulate cell functions found in the ‘hair’ cells of the ear – help us to hear.

Deafness continues to be a significant problem in medicine today. For all the progress made in the last years, still one in 1,000 US babies are born deaf. The numbers increase as the population grows older, with more than 50 percent of pensioners in America experiencing some form of hearing loss, making it the most common disability in humans.

Despite this, doctors still don’t know what causes hearing loss in most people, but they do know where the process starts to break down.

Lose the cells, and we lose our hearing

For some reason, there is an abnormal development or wearing down of specialized sensory cells, called hair cells located in the inner ear. Responsible for translating sounds to electrical pulses that the brain can interpret, when we lose these cells, we lose our ability to hear.

Avraham, a world-renowned geneticist, whose groundbreaking work has previously discovered four deafness genes and novel mutations in 10 deafness genes, among 46 known ones, looked to microRNA’s for the answer.

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 new drugs and potential cures.

“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 Avraham, who works in the university’s Department of Human Molecular Genetics and Biochemistry.

Working with an international team of researchers, including Avraham’s post-doctoral fellow Dr. Lilach M. Friedman, and scientists from Purdue University, Avraham discovered 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.

Going a layer deeper

“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,” says Avraham, who also collaborates with Palestinian researchers to help them understand, and combat, the high incidence of genetic deafness within the Palestinian population.

In Avraham’s study, which was published this month in the journal the Proceedings of the National Academy of Science, 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-out” 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 Avraham, who adds that the model holds true for all vertebrates – including humans.

If scientists can figure out how microRNAs regulate hair cells, they could be used to rescue the cells that are dying, says Avraham, who believes that this knowledge will have both diagnostic and therapeutic applications on hearing loss in the near future, even in people where the hearing loss has no genetic basis, like after a major injury to the ear.


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