Fishing for answers on bone loss in space

January 25, 2016

During spaceflight, astronauts lose bone mineral density, but it is not clear exactly what causes this loss. Scientists trying to understand why recently went fishing for answers. They reared small freshwater fish aboard the International Space Station for 56 days and examined the animals' jawbones and teeth for any potential effects from microgravity.

Previous studies suggest that microgravity activates osteoclasts, cells that control the breakdown of bone tissue, and the Medaka fish investigation examined the relationship between this increased osteoclast activity and reduced bone mineral density.

A paper based on the Medaka results was recently published Scientific Reports. Co-author and principal investigator Akira Kudo, a professor in the Graduate School of Bioscience and Biotechnology at Tokyo Institute of Technology, said investigators found increased volume and activity of osteoclasts and significant reduction of bone mineral density in the fish aboard the station. Using electron microscopes, investigators also observed abnormalities in osteoclast mitochondria. Mitochondria are round or rod-shaped organelles inside most of our cells that produce enzymes for converting food to energy.

Genetic analysis also revealed significant increase in activity in two genes that may be involved in mitochondria function, suggesting that osteoclast activation might be linked to the reaction of mitochondria to microgravity.

"If this is also true for astronauts, medicines that target mitochondria dysfunction may restore the bone loss in space," said Kudo.

Additional research will be necessary back on Earth to verify this information in order to take these findings to the next step.

Medaka fish are considered model organisms for life science research, which means they have characteristics that allow them easily to be maintained, reproduced and studied. Previously, these fish were mated successfully in space and the resulting eggs developed and hatched normally. In this investigation, 24 fish were transported to the space station and spent two months in the Aquatic Habitat in the Kibo module. The fish used for this experiment have fluorescent osteoclast cells, which makes them easier to observe.

The fish in space showed normal body growth even though they had decreased mineral density in bones and teeth. The investigators observed the fish regularly and while the Medaka swam normally at first, they tended to become motionless late in the flight. This indicates that microgravity's effect on bone density likely involves changes in mechanical force that lowers overall physical activity and therefore causes osteoclast activation

"It has been difficult to understand the mechanism of age-related bone loss on Earth," Kudo said. "The Medaka experiment finding of new genes affected by microgravity provides a good animal model to clarify this mechanism." The work could advance development of drugs to treat osteoporosis here on Earth in addition to reducing bone loss in astronauts on long-term missions.

Other results from the experiment conducted on Medaka and recently published in a PLOS ONE paper identified 11 genes involved in changes in other tissues, including the brain and intestines. Several of these genes overlapped with those involved in bone loss, making it likely they play a role in sensing microgravity. Researchers plan to test the function of these genes in future space station experiments.

For this Medaka investigation, though, fishing for answers yielded an excellent catch.

NASA/Johnson Space Center

Related Mitochondria Articles from Brightsurf:

Researchers improve neuronal reprogramming by manipulating mitochondria
Researchers at Helmholtz Zentrum M√ľnchen and Ludwig Maximilians University Munich (LMU) have identified a hurdle towards an efficient conversion: the cell metabolism.

Inside mitochondria and their fascinating genome
EPFL scientists have observed -- for the first time in living cells -- the way mitochondria distribute their transcriptome throughout the cell, and it involves RNA granules that turn out to be highly fluid.

'Cheater mitochondria' may profit from cellular stress coping mechanisms
Cheating mitochondria may take advantage of cellular mechanisms for coping with food scarcity in a simple worm to persist, even though this can reduce the worm's wellbeing.

A ribosome odyssey in mitochondria
The ciliate mitoribosome structure provides new insights into the diversity of translation and its evolution.

Fireflies shed light on the function of mitochondria
By making mice bioluminescent, EPFL scientists have found a way to monitor the activity of mitochondria in living organisms.

First successful delivery of mitochondria to liver cells in animals
This experiment marks the first time researchers have ever successfully introduced mitochondria into specific cells in living animals.

Lack of mitochondria causes severe disease in children
Researchers at Karolinska Institutet in Sweden have discovered that excessive degradation of the power plants of our cells plays an important role in the onset of mitochondrial disease in children.

Unexpected insights into the dynamic structure of mitochondria
As power plants and energy stores, mitochondria are essential components of almost all cells in plants, fungi and animals.

Mitochondria are the 'canary in the coal mine' for cellular stress
Mitochondria, tiny structures present in most cells, are known for their energy-generating machinery.

Master regulator in mitochondria is critical for muscle function and repair
New study identifies how loss of mitochondrial protein MICU1 disrupts calcium balance and causes muscle atrophy and weakness.

Read More: Mitochondria News and Mitochondria Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to