Inside the hair cell, the cuticular plate serves as a foundation that anchors the tuft of vibration-sensing structures called hair bundles. When sound waves (vibrations) enter the cochlea, the fluid inside it moves. When the hair bundles detect this movement, they trigger sound signals in the auditory nerve, which sends the sound information to the brain.
The pioneering research carried out by Jung-Bum Shin and his team at the University of Virginia School of Medicine, sheds light on the function of the cuticular plate, which for the most part has remained unexplored. This has mainly been due to a lack of tools available to scientists to probe its inner workings, but this is starting to change.
The team used a range of techniques to investigate a protein called LIM domain only protein 7, which is encoded by the LM07 gene. They showed that this protein is found inside the cuticular plate.
When the team blocked the activity of the gene in mice, they found:
- the cuticular plate was weaker and much thinner
- there was a reduction in the amount of F- actin (a vital part of the cell’s cytoskeleton) within the cuticular plate
- there were defects in the arrangement of the anchor points of the hair bundle.
These observations suggest that LMO7 protein is a vital component of the cuticular plate, helping to keep the hair bundle stiff and anchored. They also showed that the cochlea’s tuning and sensitivity to vibrations was altered in mice lacking the LMO7 gene, presumably because the hair bundle had lost its stiffness.
Despite the fact that these abnormalities were detectable at a very early age, hearing was not affected until much later, indicating that defects in the cuticular plate could over time give rise to late-onset, progressive hearing loss.
The research was carried out on mice, but LM07 is common to all vertebrates, which suggests that mutations in the human version of the gene could lead to age-related hearing loss in people.
Age-related hearing loss is a complicated condition and it is likely that a number of factors, including other genes and a variety of environmental factors, play a role. The next steps for the team include investigating how genetic risks, such as those posed by LM07, interact with a range of environmental factors. For example, could people with a weakened cuticular plate be more susceptible to the damaging effects of loud noise?
This study, led by Ting-Ting Du, a postdoctoral researcher in the Shin lab, was a collaborative effort with other laboratories at the University of Virginia, the National Institutes of Health and Stanford University. The findings have been published in the journal Nature Communications.