Researchers have identified tiny molecules that may lead to big breakthroughs in the treatment of hearing loss and deafness.
An international team, including researchers from Tel Aviv University in Israel and Purdue University, found that lack of these molecules causes abnormal development of the inner ear and leads to progressive hearing loss.
Donna Fekete, the Purdue professor of biological sciences involved in the study, said this new information could provide promising leads to treat hearing loss.
"The molecules we identified could be used as a molecular tool delivered directly into the ears of deaf people to induce regeneration of important sensory cells that would improve hearing," she said. "The molecules also could potentially help people with balance disorders related to inner ear function such as Meniere's disease."
The National Institutes of Health National Institute on Deafness and Other Communication Disorders, or NIDCD, reports that 36 million American adults have some degree of hearing loss.
In many cases of non-congenital hearing loss, the cause is degeneration of specialized sensory cells in the inner ear, called hair cells. Hair cells convert sound waves into electrical impulses that can be interpreted by the brain. According to the NIDCD, excessive noise, certain medications, aging and disease can damage or destroy hair cells. Because humans are unable to replace lost hair cells, hearing declines as they are lost.
The international research team identified microRNAs - tiny pieces of the genetic building block ribonucleic acid, or RNA - critical to the survival of hair cells. MicroRNAs regulate genes by selectively preventing certain genes from making proteins.
Karen Avraham, the Tel Aviv University professor who led the study, said this research shows that a loss of certain microRNAs can cause deafness.
"We 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," said Avraham, who is a professor in the Department of Human Molecular Genetics. "Until very recently, science only knew that mutation in protein-coding genes caused deafness. We went a layer deeper and discovered that the loss of microRNAs leads to deafness as well."
In recent separate studies conducted in Spain and the United Kingdom, mutations in a single microRNA were reported to cause deafness in humans and mice, showing the importance of microRNAs in the inner ear and the link to human hearing loss, Avraham said.
Earlier research had shown microRNAs to be involved in ear development, but this study is the first to remove the microRNAs at the time when hair cells are just beginning to form, Fekete said. A paper detailing the work was published in the April 14 issue of the Proceedings of the National Academy of Sciences .
In addition to Avraham and Fekete, co-authors of the paper include assistant research scientist Takunori Satoh and research assistant Deborah J. Biesemeier from Purdue; Lilach Friedman, Amiel Dror, Eyal Mor, Tamar Tenne, Ginat Toren and Noam Shomron from Tel Aviv University; and Eran Hornstein from The Weizmann Institute of Science in Rehovot, Israel.
The first microRNA was discovered in 1993, and the field has taken off within the last eight years, Fekete said.
"In a sense it is a whole new way of looking at gene regulation that we didn't know much about 10 years ago," she said. "Now people all over the world from different fields are trying to figure out the roles microRNAs play and how they can be used to improve human health."