Understanding a Pressure Relief Valve in the Inner Ear

By Ian Swinburne, Ph.D.

The inner ear senses sound to order to hear as well as sensing head movements in order to balance. Sounds or body movements create waves in the fluid within the ear. Specialized cells called hair cells, because of their thin hairlike projections, are submerged within this fluid. Hair cells bend in response to these waves, with channels that open in response to the bending. The makeup of the ear’s internal fluid is critical because as it flows through these channels its contents encode the information that becomes a biochemical and then a neural signal. The endolymphatic sac of the inner ear is thought to have important roles in stabilizing this fluid that is necessary for sensing sound and balance.

This study helps unravel how a valve in the inner ear's endolymphatic sac acts to relieve fluid pressure, one key to understanding disorders affected by pressure abnormalities such as Ménière’s disease.

While imaging transparent zebrafish, my team and I found a pressure-sensitive relief valve in the endolymphatic sac that periodically opens to release excess fluid, thus preventing the tearing of tissue. In our paper published in the journal eLife June 19, 2018, we describe how the relief valve is composed of physical barriers that open in response to pressure. The barriers consist of cells adhering to one another and thin overlapping cell projections that are continuously remodeling and periodically separating in response to pressure.

The unexpected discovery of a physical relief valve in the ear emphasizes the need for further study into how organs control fluid pressure, volume, flow, and ion homeostasis (balance of ions) in development and disease. It suggests a new mechanism underlying several hearing and balance disorders characterized by pressure abnormalities, including Ménière’s disease.

Here is a time-lapse video of the endolymphatic sac, with the sac labeled “pressure relief valve” at 0:40.

2017 Ménière’s Disease Grants scientist Ian A. Swinburne, Ph.D., is conducting research at Harvard Medical School. He was also a 2013 Emerging Research Grants recipient.

Ménière's Disease Grantee Featured in Reader's Digest

Credit: Agnieszka Marcinska, Shutterstock

Ian Swinburne, Ph.D., a 2018 Ménière's Disease Grant (MDG) recipient, shared his expertise regarding vertigo with Reader's Digest in an article called "What Causes Vertigo? 15 Things Neurologists Wish You Knew" published in March 2018. 

"The spinning, dizzying loss of balance which earmarks vertigo can come without warning," the article opens. Various professionals provide information about its duration, how it feels, and different types.

HHF-funded Dr. Swinburne notes specifically that the inner ear and balance disorder Ménière's disease can cause vertigo. He explains that "[b]outs of vertigo likely arise in patients with Ménière's disease, because the inner ear's tissue tears from too much fluid pressure—causing the ear's internal environment to become abnormal.'" He is currently pursuing a research project to understand the inner ear stabilizes fluid composition, which he believes will help to identify ways to restore or elevate this function to mitigate or cure Ménière's disease.

View the full article from Reader's Digest, here.

New Grantees Will Advance Understanding of Ménière's Disease

By Lauren McGrath

Hearing Health Foundation's (HHF) newly established Ménière's Disease Grants (MDG) program will significantly advance our understanding of the mechanisms of Ménière's Disease. In 2018, two innovators will have the opportunity to investigate the disorder's diagnosis and treatment.

Ménière's Disease is a disorder of the inner ear that causes episodes of vertigo as a result of fluid that fills the tubes of the inner ear. In addition to dizziness and nausea, Ménière's attacks can cause some loss of hearing in one or both ears and a constant ringing sound. The causes of Ménière's remain unknown and a cure has yet to be identified. The National Institutes of Health estimates that 615,000 individuals in the United States live with the disorder.

Two grants have recently been awarded for 2018 for innovative Ménière's Disease research. Both grantees were also previously funded by HHF’s Emerging Research Grants (ERG) program.

Gail Ishiyama, M.D.

Gail Ishiyama, M.D. of UCLA David Geffen School of Medicine is focusing on cellular and molecular biology of the microvasculature in the macula utricle of patients diagnosed with Ménière’s disease. Her project will provide greater information on the blood labyrinthine barrier and allow for the development of interventions that prevent the progression of hearing loss and stop the disabling vertigo in Ménière’s disease patients.

Ian Swinburne, Ph.D.

Ian Swinburne, Ph.D. of Harvard Medical School is classifying the endolymphatic duct and sac's cell types and their gene sets using high-throughput single-cell transcriptomics. His work will generate a list of endolymphatic sac cell types and the genes governing their function, which will aid in Ménière's diagnosis (which can be delayed due to the range of fluctuating symptoms) and the development of a targeted drug or gene therapy.

HHF is grateful for the opportunity to fund Drs. Ishiyama and Swinburne. If you are interested in naming a research grant in any discipline within the hearing and balance space, please contact development@hhf.org.