|Zebrafish embryo--Courtesy of Zebrafish Lab|
It was previously thought hairlike projections called stereocilia that form hair bundles are made from cellular scaffolding proteins that do not change or circulate. Recently, though, researchers at Case Western Reserve University School of Medicine have drawn an interesting link between the movement of protein in hair bundles and the signs of the repair and renewal mechanism. These findings, published in Cell Reports, hold promise in furthering our knowledge of the molecular changes in hearing loss, which could lead to new therapies in the clinic.
When sound waves hit hair cells lining the inner ear, energy is converted into electrical signals which provide information to the brain. Experiencing extremely loud noises can permanently damage these hair cells resulting in permanent hearing loss.
By studying the inner ears of baby zebrafish, the researchers tracked protein movement through a microscope, as zebrafish are translucent at this stage of development. They found that proteins in the hair bundles within the inner ear move at a surprising speed.
"We made movies of the secret inner workings of the hair bundle in a live animal, and what is happening in the ear is amazing and unexpected," senior author Brian McDermott said.
In particular a protein called fascin 2b moved at exceptional speed through the hair bundles, as compared to proteins essential for the structural movement of the stereocilia such as actin and myosin. It's thought the speed of fascin 2b movement is to help repair breaks made in the actin or myosin machinery on exposure to loud sounds.
This gives insight into the dynamic internal structure of stereocilia and challenges the conventional view. "It was once thought that most everything within the stereocilia was relatively immobile and static.
"No one has shown that stereocilia heal themselves, so next we will find out if there's a repair mechanism. People go deaf from damage to stereocilia in the inner ear. If we figure out ways of manipulating protein dynamics within stereocilia to heal this damage, we would likely be able to diminish hearing loss in humans," McDermott said.
Continuing with the zebrafish model as their preferred model for studying hearing loss and the inner ear, McDermott and his team hope to discover whether stereocilia has a self-repair mechanism.