An international team of scientists studied fish that have visited the ISS and discovered the cellular mechanisms that govern bone loss in zero gravity. It turns out that microgravity changes the genes that are responsible for the development of bone tissue cells.
In fact, not only fish skeletons become ill with microgravity. Loss of bone tissue is one of the most serious problems faced by astronauts during and after their shifts on the ISS. The manifestations of loss resemble senile osteoporosis, although astronauts encounter it long before old age - bones become more fragile and brittle, and lose calcium. Changes at the cellular level are noticeable immediately after flying in a dive plane.
The cellular mechanism of bone loss has remained unclear until now. It is known that weightlessness changes a lot in a living organism - for example, the heart gradually loses its skill to accelerate with a sharp change in pressure. Because of this, the astronauts who have returned to Earth faint from sudden movements. Changes also occur at the level of gene expression and were observed during the collection of biomaterials from astronauts.
Containers with laboratory medaka fish arrive at the ISS
To find out what exactly happens in bone and cartilage cells in zero gravity, scientists decided to send Japanese aquarium fish medaka (Oryzias latipes) to the ISS, whose cellular mechanisms for the development of bones and cartilage are very similar to those of mammals. In 2014, genetically modified fish flew aboard the space station, in whose bodies the increased activity of certain genes revealed itself as a bright glow.
It turned out that already on the first day in zero gravity, 105 genes began to work hard in fish, and another 49, on the contrary, were much less active in space than in the bodies of fish from the control group on Earth. Of these genes, 5 are associated with the development of skeletal cells: two regulate the growth of osteoblasts (young bone cells), and three - osteoclasts - giant cells that are involved in dissolving existing bone tissue. All of these genes regulate the production of transcription factors that are involved in the development of osteoblasts and osteoclasts.
Medaka fish
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Under normal conditions, these genes come into operation at different times, but weightlessness has shifted their schedules and led to serious changes in the structure of bone tissue. Scientists have yet to explain exactly how this happens in laboratory fish and in humans.
Even more important are the general conclusions made by the authors of the study: changes in gene activity on the very first day of a change in gravity suggest that the cell has a ready-made defense mechanism against jumps in gravity, which turns on almost instantly. This mechanism significantly changes the entire chromatin structure - the substance of the cell nucleus, which consists of DNA, RNA and proteins necessary for their work, tuning the nucleus in accordance with the change in gravity.
The research results are published in Scientific Reports.