Zebrafish study could aid human hearing

By Carlos Mayorga

Hearing rarely returns once a human loses the ability to hear.

However, when lower vertebrates such as birds, reptiles, fish and amphibians lose the ability to hear, they are able to regenerate hearing cells, called hair cells, and regain their hearing.

The cells are called hair cells because they are tiny, hair-like projections found in the inner ear which enable humans and animals to hear. Scientists don’t know why certain animals can regenerate hearing cells while higher vertebrates such as humans cannot. For more than a year, U neurobiologist Tatjana Piotrowski has been researching why certain creatures have lost the ability to regenerate these cells.

“The main focus is to understand what genes you need for hair cell regeneration,” Piotrowski said. “Once we understand that, we can go back and see why mammals lost the ability to regenerate hair cells.”

The National Organization for Hearing Research Foundation awarded Piotrowski a $200,000, two-year grant to conduct the study.

For about a year, Piotrowski has been studying genetic mutations in zebrafish — small minnows found in freshwater streams throughout Southeast Asia which are also popular aquarium fish worldwide.

Zebrafish have the same hearing cells as humans but are able to regenerate their cells, which makes them prime models for understanding hair cell regeneration.

“It is remarkable how hair cells in fish die but come back days later,” said Alejandro Sanchez-Alvarado, a professor in neurobiology and anatomy and co-investigator for the study. “The question we ask is, ‘How do fish do this?'”

Hair cells in human ears convert vibrations and sounds into signals the brain can decipher, allowing people to hear. But if cells are exposed to too much vibration or loud noise, they die.

Humans have hundreds of hair cells in the ear, and they don’t all die at once. But over the years, the number of lost cells

can add up, resulting in gradual hearing loss.

Hair cells in zebrafish operate the same way: predators moving close to the zebrafish displace water, which sends vibrations that are picked up by hair cells on zebrafish. The sensory vibrations transmit to the brain and cause the fish to flee from danger.

The hair cells on zebrafish are located on the outside of the skin in various places along the length of the body, making it easier for researchers to study the cells.

Piotrowski randomly disables genes in the fish to identify individual genes that affect hair cell regeneration. Antibiotics are administered to the fish in large doses to kill the hair cells. Once the cells grow back, researchers can isolate those cells and see which genes were turned on in the process.

Piotrowski said the goal of the study is to identify which genes are turned on to regenerate a dead cell. Once researchers can identify the genes, they will be able to look at these genes in humans and investigate why these genes don’t activate.

“The nice thing about fish is that you can modify one gene at a time to see the consequence,” Sanchez-Alvarado said. “These genes are not fish-specific but are similar to what genes are like in humans.”

[email protected]