Earth's gravity and magnetism have unexpected effects on the human genome and mitochondria – Physics World

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The human genome doesn’t seem to mind being in zero-gravity environments, and in some cases, the mitochondria that produce energy for our cells actually benefit from spending time outside the Earth’s magnetic field. These two findings – which come from separate research groups in the US and the UK – could have important implications for space travel, while the latter hints at a new pathway for treating neurodegenerative conditions such as Parkinson’s disease.
The human genome encodes information in molecules of DNA, and its structure is directly linked to its function. Any changes to this structure can lead to disease. However, while scientists know that mechanical stress can produce such changes, physicist Alexandra Zidovska of New York University in the US says that the role of gravity – a mechanical stressor that is omnipresent on Earth – is poorly understood.
To determine gravity’s effects on the genome, Zidovska and colleagues studied how the system responded when this force was removed. “We did this by building a ‘random positioning machine’ that allows us to simulate zero gravity here on Earth,” she tells Physics World. “This is a device – akin to the larger devices that astronauts use in their training – that can rotate cells in two or three dimensions. It can simulate zero-gravity conditions on timescales shorter than those on which cellular processes occur.”
Although such devices are widely used, Zidovska explains that most previous studies of this type used biochemical assays or immunofluorescence techniques to image fixed cells. In the new work, which appears in Science Advances, Zidovska and colleagues instead imaged live cells using a high-resolution confocal technique. They did this by culturing the cells on a glass-bottomed dish while being very careful to avoid air bubbles, which cause stress for cells and can even kill them.
The team also tuned the speed and 3D rotation path of the random positioning machine in a way that minimizes the effects of fluid flow caused by the rotation. These flow effects can likewise damage cells, and since they do not exist in “real” zero-gravity environments (for example in space), it was important to reduce them as much as possible.
The team’s results show that after 24 hours in the simulated zero-gravity environment, the genome’s organization and dynamics held up unexpectedly well. This result could be important for assessing the cellular-level effects of zero gravity during space travel, though Zidovska acknowledges that these aren’t the only genetic hazards that space travellers face.
“In addition to zero gravity, we are also exposed to cosmic radiation in space, which is known to cause DNA damage,” she says. “Until now, however, it has been difficult to decouple the effects of zero gravity and this radiation in space. In our experiments we are able to simulate zero gravity without this confounding effect.”
Meanwhile, a team at the University of Nottingham in the UK has found that the Earth’s magnetic field appears to play a more complex role in the behaviour of mitochondria. These energy-generating structures are vital for the health and lifespan of all organisms with large, complex cells, including plants and fungi as well as animals.
Like gravity, the Earth’s geomagnetic field is all-pervading, with a strength that varies between 25-60 uT. Much previous research into its biological effects has focused either on its role in shielding organisms from cosmic radiation, or on how magnetoreception helps migrating birds and marine mammals to navigate long distances.
In this study, researchers led by Nottingham biochemist Lisa Chakrabarti examined healthy (wild type) fruit flies alongside flies that have been genetically engineered to carry a defect in the Pink1 B9 gene. These flies act as a biological model that replicates key features of early-onset Parkinson’s disease, including malfunctioning mitochondria; degraded (dopaminergic) neurons; and reduced physical activity and lifespan.
Chakrabarti and colleagues placed these populations of flies inside a chamber surrounded by a barrier that combines four layers of passive μ-metal shielding with nine internal active field-cancelling coils. In this way, they kept the flies’ ambient magnetic field below 5 nT.
The researchers measured the flies’ lifespans by counting the numbers of dead and living flies after a certain period. They also observed the flies’ physical activity by recording the percentage that crossed a marked line every five days. Finally, to further assess the flies’ health, they used a high-resolution respirometer and quantum sensors based on nitrogen-vacancy centres in diamond to monitor levels of superoxide, a highly reactive molecule produced by mitochondria.
The team found that shielding the Pink1 flies from the Earth’s magnetic field increased their lifespan by around 20%, although they became less physically active. Healthy flies, on the other hand, became more physically active, but their lifespan actually decreased.
Early Earth’s magnetic field strength was similar to today’s
The researchers say that these effects stem from changes in energy metabolism in mitochondria through their electron transport system when the magnetic field is reduced. Reporting their work in Aging-US, they suggest that hypomagnetic environments might therefore form the basis of new mitochondrial-targeted therapies for neurodegenerative disease.
“There is also the possibility that (short) periods of time in a magnetically shielded environment might be beneficial for some other medical conditions,” Chakrabarti says. “Another major implication is for astronauts travelling further into space where the geomagnetic field has no influence.” As well as being exposed to additional radiation, Chakrabarti suggests that astronauts “might suffer separate specific effects from the absence of the geomagnetic field”.
The Nottingham researchers now plan to study the molecular and biochemical changes that underlie the effects they have observed. “We also have some data on vertebrates which is very striking, so we will continue to work on that too,” Chakrabarti tells Physics World.
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