Researchers explain why astronauts lose bone mineral density in space

A group of researchers at the Tokyo Institute of Technology studied the reasons behind the loss of bone mineral density experienced by astronauts in a spaceflight. They reared Medaka fish aboard the International Space Station for 56 days and examined their jawbones and teeth to observe any effects of microgravity. To make it easy to study them, osteoclast cells – the cells that control the breakdown of bone tissue – of the fish were tagged fluorescent. While the fishes were active initially, the effect of microgravity became evident when the fishes tended to become motionless. When observed through an electron microscope, it was seen that the mitochondria in osteoclast cells, which are round or rod-shaped organelles in our cells that produce enzymes for converting food to energy, showed abnormalities. This reaction of mitochondria to microgravity is thought to be a result of increased activity in two genes that ultimately leads to osteoclast activation. Thus, the researchers think that medicines that target the dysfunction in mitochondria would help avert the loss of bone density in space. These findings would also be useful in developing novel treatment methods for osteoporosis.

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