Millennial mole rats

Some naked mole rats alive today were born in the late 1980s. Most similar animals their size live for about one or two years, so how are they doing it? Georgia Mills spoke to Cambridge University's Ewan St John Smith...

Ewan - Here we’ve got two colonies of naked mole rats. The naked mole rats are mammals; they’re rodents, but there’ rather unusual because they’re naked. They have some hairs down the sides of their body they use for orientating themselves but, unlike our stereotypical mammal, they’re hairless. The polite thing to say is they look like a cocktail sausage with legs and teeth.

Georgia - Why are naked mole rats of interest to scientists?

Ewan - The first thing that made them of interest to scientists was when it was observed they live in these big colonies headed up by a breeding female. We call this eusocial - they have one breeding animal in a colony, it’s a bit like bees and termites. Then they’re cold blooded, that’s makes them interesting to scientists.

But from a biomedical perspective, what’s really interesting is that these animals live for over 30 years. Based on their size - usually bigger animals live for longer - we’d predict them to live somewhere between three and four years so trying to understand how they live healthily for a long time is what a lot of scientists are interested in.

We have a few ideas about why that is: they’re highly resistant to cancer. It used to be the case if people said mole rats don’t get cancer, but now there’s been one or two incidences. But mice, if you look after them in captivity, usually two thirds or more die of cancer between 18 months and 28 months of age.

So they’re highly resistant to cancer and it also appears that they’re highly resistant to cognitive or neurological impairments. As they get older we don’t notice the animals struggling to negotiate their colonies. There’s not many incidents of them developing neurodegenerative conditions but, that said, there hasn’t been a huge amount of study looking at older animals. The animals that were born in my colonies last week, they’ll naturally die when I retire so looking at ageing in a rodent like this is quite complicated.

Georgia - Do we know how they’re resistant to cancer?

Ewan - There’s some information about how they’re resistant to cancer. It appears their cells have more control on the cell growths so they’re better able to detect how a cell is proliferating and put brakes on how that occurs. But, at the moment, I think we’re a long way off trying to understand how exactly the mole rat manages that.

We have better understanding about some of their other adaptations. We know they’re very resistant to hypoxia, so low levels of oxygen. When a human has a stroke, there’s no oxygen being delivered to the brain and parts of the brain start dying, and that’s what underlies the disabilities that people have as a result of the stroke.

Similarly hypoxia is associated with lots of neurodegenerative conditions such as Alzheimer’s and the mole rat is really resistant to this. So without oxygen they don’t become incapacitated for almost 20 minutes and when they are given oxygen again, it’s as though nothing ever happened, they come back to life perfectly normally. We’ve got quite a good understanding on how their brains keep surviving in this low oxygen environment.

Similarly when it comes to looking at their pain behaviour, naked mole rats respond perfectly normally to thermal stimuli, so hot and cold. They respond normally to mechanical stimuli, but certain chemicals such as acid, they don’t show any response at all. And, again, this probably relates to the fact that they live in this underground environment of high carbon dioxide, low oxygen levels.

Carbon dioxide when it mixed with water produces acid, so these animals live in a very safe environment with few predators but it’s acidic so, presumably, over time they’ve adapted to this environment to prevent acid causing pain. From a clinical perspective it’s quite interesting for us to identify the molecules involved in that acid insensitivity because acidosis is associated with lots of inflammatory pain and also certain forms of cancer.

Georgia - Wow! These guys are like the superheroes of the animal kingdom, they’re just resistant to everything. Why haven’t all animals done this, it seems like a quite useful idea?

Ewan - One answer would be that maybe in order to have those things happen to you you end up looking like a mole rat and other animals are too vain.