Meet the Ugly Naked Guys

This plump sausage with teeth is actually a naked mole-rat.

It makes a noise like a tweeting bird, eats poo, and is the only known mammal to be cold-blooded.

Scientists at the University of Cambridge are fascinated by this weirdness - in particular the facts that:

Naked mole-rats age healthily,

they very rarely get cancer, and

acid doesn’t cause them pain.

In trying to work out why and how these things are true, a team led by Professor Ewan St. John Smith hopes to gain insights that could help to prevent and better treat human illnesses.

Unusual pain sensitivity

“Our research identified a genetic variation in naked mole-rats that means acid acts like an anaesthetic to their nerves,” says Smith, Director of the Naked Mole Rat Initiative in the University of Cambridge’s Department of Pharmacology and Fellow at Corpus Christi College.

“We think it’s because in the wild, these animals live in large colonies underground where their exhaled carbon-dioxide builds up and reacts with moisture to make carbonic acid. This caused them to evolve so that acid doesn’t cause them pain and they can stay safe in their burrows.”

Many human conditions involving inflammation – such as arthritis – can create localised acidity. Understanding how naked mole-rats don’t feel acid could help researchers understand how acid usually causes pain, and develop new drugs to stop it.

Cancer resistance

Only a few cases of cancer have ever been found in naked mole-rats. In contrast, one in two humans are likely to get cancer in their lifetime.

In collaboration with Dr Walid Khaled in the University’s Department of Pharmacology/Wellcome-MRC Stem Cell Institute, Smith’s team is trying to work out why naked mole-rats are resistant to cancer, so the knowledge can be used to prevent cancer or better treat it in humans. While the majority of cancer research in animals uses mice and rats, he believes that naked mole-rats are another important avenue to explore.

“We found that naked mole-rat cells transform from healthy to cancerous in the same way mouse cells (our model human) do. So the puzzle remains as to why cases of cancer are far rarer in naked mole-rats than mice or humans," he says. A collaboration with researchers at the Wellcome Sanger Institute found that mutations in naked mole-rat DNA occur at a slower rate than in mouse DNA, and it could also be that naked mole-rats have an ultra-good immune system that spots cells with cancer and kills them off.

Healthy ageing

Broadly speaking, the bigger the animal the longer it lives. Based on their mouse-like size, naked mole-rats would be expected to live around three to five years. But their maximum lifespan is over 30 years, and current record holder is a 39-year old. They age healthily too, making it difficult for researchers to tell the difference between a three-year-old and a 30-year-old by eye alone.

“I met a 37-year old naked mole-rat when I was 38,” says Smith. “I had flashes of grey in my hair and wrinkles in my face, but the mole-rat looked great!”

As you get older, your chance of dying increases because more things start going wrong – but naked mole-rats don’t have this age-related risk of death. They usually die because another animal kills them in a fight.

“It’s great that medicine can now help people live longer, but unfortunately we can’t deal very well with ageing-related illnesses like dementia. If we can understand why the naked mole-rats don’t really get these problems, there’s an awful lot to be learned,” he says.

In collaboration with Dr Gabriel Balmus in the University’s Department of Clinical Neurosciences/UK Dementia Research Institute, Smith is trying to discover how the cellular profile of the naked mole-rat brain changes with age, to understand what mechanisms exist to support healthy ageing in the naked mole-rat.

Smith keeps five colonies of naked mole-rats in Cambridge for his research.

Each animal is microchipped so he and the team can tell them apart.

The animals are cold-blooded so they can’t generate their own body heat – they rely on the environment, and their behaviour, to stay warm. In the lab this means they have to be kept at 30oC with heat cables running under certain cages - which the animals usually choose to sleep together in a ball on top of, to conserve heat.

Naked mole-rats running on a wheel. Film credit: Hayley Forest

Naked mole-rats running on a wheel. Film credit: Hayley Forest

The lab also has to be kept humid, otherwise naked mole-rat skin gets flaky. And to mimic their wild burrows, they need to be kept in cages under red light and connected by tunnels - which requires plenty of space.

“We want to track the naked mole-rats over time, so we need microchips to know who’s who. It is possible to study them in a lab environment, but they are an unusual species and not every university is set up to look after them. So, we try to facilitate collaborations in the UK and beyond.”

A leading expert on these strange animals, Smith is keen to set up research collaborations with scientists at other institutions so that much more can be learned about them. He says:

“There are so many things we still don’t understand about naked mole-rats. We can see they have many weird features, and we’re trying to work out the underpinning genetic or physiological basis for these.

“Once we understand more, we can transfer that knowledge across to helping companion animals or humans with problems such as inflammatory pain, arthritis and cancer.”

Fast facts

- The Latin name for naked mole-rats is Heterocephalus glaber – which essentially means 'different headed bald thing'.

- They come from Ethiopia, Kenya and Somalia.

- They're not completely naked: the lines of hairs down the sides of the body act as mechanical sensors so the naked mole-rats can orient themselves in their burrows.

- They’re ‘eusocial’, that is, they live in colonies headed by a single breeding female called the queen.

- There are over 30 species of African mole-rat – and all the others are warm-blooded and furry. This makes naked mole-rats unusual even compared to their closest relatives.

Learn more in Smith's series of animations, funded by the Dunhill Medical Trust

Episode 1: What can the naked mole rat teach us about living longer?

Episode 2: The naked mole rat's weird biology can help us develop ways to combat painful human conditions like osteoarthritis.

Episode 3: Did you know that naked mole rats are almost impervious to cancer?

Published 6 September 2022

The text in this work is licensed under a Creative Commons Attribution 4.0 International License