Hypergravity: cellular life under extreme force

The Large Diameter Centrifuge. Photo credit: ESA-A. Le Floc'h

Team Twistosity are on the case to improve our understanding of how non-specialised cells respond to increased gravity.

This article originally featured in the June edition of RCSU Broadsheet, the magazine that brings together science, society and the arts.

Back in December 2016 Team Twistosity, made up of students Emma Woodcock, Paul Girvan (both Imperial College London) and Julia Eckert (Technische Universität Dresden), found out that their proposal for the annual ‘Spin Your Thesis!’ programme, organised by the European Space Agency’s Education Office, had been successful. The prize: a unique opportunity to carry out their experiment at ESA’s Large Diameter Centrifuge (LDC) in the Netherlands. Over the last few months they have been refining their plans in preparation for their time at the LDC in September 2017, where they will explore the effect of hypergravity on non-specialised cells.

Microgravity v hypergravity

Gravity, the natural phenomenon that keeps us from drifting off into space, can be measured using the unit of acceleration ‘g’. As we go about our lives on the surface of the Earth we experience 1g, known as standard gravity. Conditions lower than 1g are described as microgravity, which is the reason astronauts in orbit in space appear to float weightlessly. On the opposite end of the spectrum sits hypergravity, an environment heavier than Earth’s standard. Paul illuminates: “the fastest accelerating roller-coaster in the UK lets you experience 4.5g for a couple of seconds.” Twistosity will use the LDC to create a series of hypergravitational environments from 1g to 20g, and monitor the effect on cells. To get up to 20 times the force of gravity the outside edge of the LDC travels at 101 km/h.

In order to capture cell reaction to hypergravity Twistosity will use an innovative fluorescence technique, pioneered by one of their supervisors, Dr Marina Kuimova. Small chemical probes, called molecular rotors, will be inserted through the cell membranes; evidence of a reaction will be apparent from the amount of fluorescence given off by the molecular rotors, indicating intercellular viscosity. Paul explains:

“The molecular rotors are made up of two parts joined by an axis, which can spin independently of each other. When they spin very fast they don’t fluoresce, indicating low viscosity, but if their movement is restricted and the spinning slows down, they start to give off light, signifying higher viscosity.”

The team name, Twistosity, was chosen because of its reference to the twisting motion of the molecular rotors. Twistosity hypothesise that it’s a change in viscosity that characterises a non-specialised cell’s response to hypergravity.

What's so special about the LDC?

The LDC was built by ESA to simulate and investigate hypergravity. Four arms extend from the centre of the machine each supporting two boxes, known as gondolas, where the experiments take place. Up to 80kg of equipment can be placed in each gondola. The huge size of this facility, which in total weighs over 5000 kg, presents Twistosity with an exciting opportunity:

“You never get centrifuges this large in a university environment, it’s just not possible. The largest would be 50cm max . The LDC allows us to more realistically judge how gravity effects whatever we put inside it.”

Centrifuge gondola. Credit: ESA

A microscope can be placed directly inside the gondola, allowing Twistosity to record images of the cells in real-time rather than spinning the cells and imaging them afterwards under a lab bench microscope. The team can therefore monitor how quickly the cells respond to changes in stimuli and avoid introducing artefacts into the data when moving the cells from the centrifuge to a microscope, potentially distorting results.

The other problem that the LDC uniquely solves is a mathematical concept called sheer force. If you imagine water flowing over something, the force of the water may induce a dragging motion; in small centrifuges sheer force builds up and instead of squishing the sample, like gravity should, it will drag it, potentially manipulating the results of the experiment:

“When you have gravity and sheer force both acting on a sample it produces confusing results as you don’t know which stimulus the cell is responding to. This problem with small centrifuges is minimised in a large centrifuge.”

The LDC spins at such great speed that Paul admits he had concerns about the logistics of their experiment; “how on earth are we going to put a microscope in this and not totally destroy it!” Aside from protecting the microscope, other risks include problems growing the cells in the first place. The team must try to anticipate possible issues before they even get close to the LDC.

As part of their preparation Emma went for a week of training with ESA Education, which she says allowed her to fully grasp what it meant to be running a multidisciplinary, international project from start to finish. As well as meeting other teams from across Europe, Emma visited the Euro Space Centre, giving her the opportunity to experience ESA training techniques: “the VR moon walk in particular was, as well as educational, hilarious!” She also met Twistosity’s mentor, a leading expert in the area of gravity research, who is helping them to formulate their ideas to obtain the most interesting data possible. Paul highlights the long-term benefits of working with ESA Education:

“These people put things into space, so everything has to be planned step by step, all the contingencies put into place and everything thought about in great detail. One of the things that I’m trying to take away from this [experience] is ESA’s [rigorous] attitude and their preparation techniques…”

Cell exploration

At this stage the team doesn’t know how fast the cells will respond to hypergravity, but their preliminary research leads them to anticipate a response within 3 hours. However, they will remain flexible as “it’s science and science never goes exactly to plan, which is both the fun part and the infuriating part.”

Initially Twistosity were expecting to be given 2.5 days at the LDC, but were delighted to find out that this year’s teams have both been awarded five days each. The additional time will enable them to trial two different prototypal cell types. The first is a human embryonic kidney cell known as HEK-293 used widely in research. The second is a cell that lines the walls of blood vessels:

“[The blood vessel] cells can respond to the sheer force of blood flow; what we’re going to do is see if they respond to gravity in different ways from cells that don’t have anything to do with blood flow, sheer force or anything gravity-related.”

Twistosity will look at the viscosity of both the cell membranes and also the cytoplasm inside the cells.

“ESA see the potential significance and originality of our experiment … the results could be really key to understanding how non-specialist cells respond to gravity.”

Specialised cells have adapted to carry out specific functions. Plant root cells, for example, contain tiny, distinctive organelles, which sense gravity, guiding them down towards sources of water and nutrients. Scientists are finding that non-specialised cells that don’t contain organelles, like skin cells, can also perceive gravity; the question Twistosity are interested in is how?

“I guess as a scientist you should be open minded about what [your experiment] will produce, but what we’d like to see is that under hyper g the cells will become more viscous and that we will be able to detect this.”

As well as keeping our feet firmly on the ground, gravity also has a fundamental effect on our physiology. Microgravity in space contributes to astronaut muscle wastage and decreasing bone density. Twistosity’s experiment aims to broaden our understanding of human cells under hypergravity:

“To truly understand something you need to appreciate it from all angles, in this case, exploring what happens when cells are subjected to more gravity than we’re used to on Earth or in space. We want to build up the picture of how the whole system works, how the body, an organ, a single cell, respond to changes in gravity … and how else would we get the opportunity to do this? We wouldn’t, without ESA’s ‘Spin Your Thesis!’ programme; it’s pretty awesome!”

We look forward to catching up with Emma, Paul and Julia in September!