The intrepid tardigrade

The inspiration for this week's article comes not from a new discovery or breakthrough in biotechnology, but from an awesome video I found in Nature’s February 2021 edition of “Sharpest Science Shots of the Month”.

The video was of a tardigrade – an eight-legged microscopic invertebrate creature known affectionately as the water bear or moss piglet due to its characteristic plump shape – doing what can only be described as a microscopic circus act.

Tardigrades are truly remarkable little creatures, ranging from 0.05 to 2.1 mm in length, that can be found everywhere from the depths of the ocean to high mountain tops, and even in the harsh conditions of the Artic and Antarctic.

What makes them so extraordinary is their ability to survive… well… pretty much anything you can throw at them, from extreme temperatures and pressures, radiation, dehydration and starvation, to the vacuum of outer space.

All of which is very interesting, but what does it have to do with biotechnology and medicine?

Well, the answer to that question is that understanding how tardigrades can survive such harsh conditions can help us understand the ability of biological systems to adapt and evolve.This has led to them becoming valuable biological models providing us with clues as to how to deal with things like radiation damage and living in space.

Credits: Penelope Fenton

Tardigrades as model biological systems

Tardigrades have developed some truly amazing properties over their 600 million years of evolution, but what peaked researchers’ interest in them as a model species is that they are small and easy to culture, but at the same time structurally complex, allowing results to be extrapolated to human being and other vertebrates..

Scientific interest in tardigrades goes back to the 1960s, when they became one of the potential model organisms to study development and neurobiology from a genetic perspective. In the end they lost out to another microscopic creature called C. elegans, because scientists decided that the tardigrades had too many neurons.

Still, they have some pretty cool party tricks, one of the most fascinating being their ability to perform cryptobiosis – the nearly complete cessation of all metabolic activity – when no liquid water is available. These desiccated tardigrades, known as tun, can travel the world on the wind, before coming back to life in a matter of minutes when re-exposed to water.

It’s because of this that they are commonly found in the mosses of the Artic, where their ability to freeze rapidly and remain deep frozen helps them get through the long polar winters. The most extreme case to date is the revival of a frozen tardigrade from a moss sample collected in Antarctica in the 1980s and stored at −20 °C for more than 30 years.

But these extreme properties of tardigrades are more than just interesting phenomena; they have applications in both space and medical research.

Tardigrades in space research

The idea that tardigrades could be useful in astrobiology (biological space research) also goes back to the 1960s, but it wasn’t until the 21st century that the idea started to take hold.

In the early 2000s, various space missions included projects like the Tardigrade Resistance to Space Effects Project, which analysed the impact of environmental stress and DNA damage in space, and Tardigrades in Space, which went a step further to look into mechanisms of repairing structural DNA damage caused by space flight stresses.

Future research is likely to focus on cryptobiosis as a means of travelling long cosmic distances, and how long they can survive in the simulated environments of other planets, including the effects of cosmic radiation, low temperature and microgravity on their survival. The first earthly beings to colonise Mars may very well be tardigrades!

Tardigrades in biomedical research

Here on earth, understanding of the tardigrade’s extreme survival abilities has useful applications too. Their resistance to radiation damage and other extreme circumstances have led to a number of studies in the biomedical field.

A publication from 2019 shed light on the mechanism used by tardigrades to protect their DNA from high radiation levels. They demonstrated that a protein called Dsup, a so-called damage-suppressor protein, binds to the tardigrade’s DNA, providing protection against the damage caused by the hydroxyl radicals created when the body is exposed to radiation.

More recent research has shown that Dsup is just one of a range so-called intrinsically disordered proteins – a fairly new class of proteins with properties of great interest in medicine – found exclusively in tardigrades , which help them to resist other abiotic stresses like freezing, high temperatures and desiccation.

Many of these tardigrade proteins have properties that pave the road for novel biomedical and pharmacological applications including the conservation of pharmaceutical products and biomaterials and the creation of entirely new classes of drugs.

A recent advance was the delivery of one of the tardigrade’s damage-suppressor proteins to the healthy tissues of cancer-infected mice undergoing radiotherapy. Using this method, the protein was shown to offer protective effects to the healthy tissue while preserving the efficacy of the radiation therapy.

All in all, tardigrades are a pretty impressive (and very cute) bunch that we are sure to hear a lot more about in medicine in the future.