Do crocodiles hold the key to improving human hearing?

The World Health Organization notes that more than five percent of the world’s population need rehabilitation to address their ‘disabling’ hearing loss – that’s 432 million adults, and 34 million children.

The WHO also estimates that by 2050, one in every ten people will have disabling hearing loss.

People inevitably start losing their hearing as they age, or at a younger age due to other genetic and external factors. 

On the other hand, crocodiles, even though they live almost as long as humans and can live past 70 years, have good hearing throughout their lifetimes.

What do scientists hope to achieve by studying crocodiles?

Scientists from Sweden write that the fact that auditory receptors in several non-mammalian species undergo cell renewal after damage “has raised hope of finding new options to treat human sensorineural deafness.”

In order to check whether hair cells are regenerated, they explored the auditory organ in the crocodile “to validate possible ongoing natural hair cell regeneration.”

One of the reasons why crocodiles have good hearing even as they age is the fact that they can create new hair cells. A research group from Uppsala University in Sweden is researching exactly this. They hope that their research into crocodiles will eventually help people with impaired hearing.

The research team analysed “two male Cuban crocodiles (Crocodylus rhombifer) and an adult male African Dwarf crocodile (Osteolaemus tetraspis) … using transmission electron microscopy and immunohistochemistry using confocal microscopy.”

How do the crocodiles’ hair cells get activated?

“We can see that new hair cells seem to be formed from the activation of so-called support cells, which [are] connected to crocodiles having certain cell structures that humans appear to lack. Our hypothesis is that nerves that carry impulses from the brain, so-called efferent nerves, trigger that regrowth,” says Helge Rask-Andersen, professor of experimental otology at Uppsala University and one of the researchers behind the study.

The study is published in Frontiers in Cell and Developmental Biology.

The scientists conclude that “Crocodilians seem to produce new hair cells during their life span from a range of supporting cells,” and that “Crocodilians seem to restore and sculpt their tectorial membranes throughout their lives.”

Why do humans lose their hearing?

Hundreds of millions of people experience impaired hearing – and as a result, come across significant problems. Their quality of life decreases as well.

The most common cause of hearing impairment is receptors in the ears cease working. These delicate receptors do not regenerate in humans. 

On the other hand, receptors in other animals that are not mammals, such as crocodiles, can regenerate. Crocodiles, for example, can survive more than 70 years, with excellent hearing on land and in water.

What do we know about hair regeneration?

Animals can quickly regenerate the hair cells in their ears if they were to get damaged, but scientists to this day are not sure how they do it. 

Crocodiles, with their precise hearing abilities on land and underwater, are highly attuned to different pitches. Their receptors’ sensitivity to different pitches is affected by external temperature – allowing them to encounter different kinds of dangers in different environments during evolution.

What did Uppsala scientists discover?

Ear researchers at Uppsala University Hospital teamed up with researchers at Uppsala University, utilising electron microscopy and molecular technologies to study the inner ear of the crocodile.

One intriguing discovery was that small cell particles are secreted in the crocodile’s ear. The particles are similar to exosomes and can secrete enzymes that dissolve or form the membrane against which the cilia in the ear rub as sound comes in. The exosomes create small cavities that make it easier for the cilia to bend when sound vibrations arrive at the ear.

“One hypothesis is that this increases sensitivity to sound and hearing improves. Our hope is to learn how crocodiles regenerate their hair cells and to eventually be able to use that on people in the future,” says Helge Rask-Andersen from the Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital.