As is well-known, space flights bring with them a unique set of
health hazards. That includes bone and muscle deterioration. Loss of
bone density is currently one of the most serious problems for
astronauts. It is similar in nature to osteoporosis, an ailment common
for senior people.
Understanding microgravity and its effects on living
organisms can help find new clinical methods of coping with this issue.
‘What events and genes influence the progress of osteoporosis in medaka fishes in space-like conditions has been elaborated in a Russian-Japenese research.’
The paper appeared in Scientific Reports
. The co-authors from the Russian side are Oleg Gusev (Extreme Biology
Lab, Kazan Federal University) and Vladimir Sychyov (Institute of
Medical and Biological Problems of RAS).
Oleg Gusev explains, "Fishes are one of the test organisms that give
an opportunity to outline space flight effects on one's health. Water
stabilizes overloads and compensates microgravity. What we see in this
research are the results of other factors, possibly space radiation or
other sensitivities to gravity. Medaka fish also grows fast, so that's
another benefit for the testing process. Their genome has been
Soyuz TMA-06M delivered several medakas to the International Space
Station. Its other name - rice fish - indicates its special affinity
for rice paddies. Medakas first visited space in 1994 on Columbia -
they successfully spawned during that flight. This time they will stay
in ISS for several years.
As it turned out, medakas start losing bone density much faster than
humans - almost immediately after arriving. The paper aims to explain
what events and genes influence the progress of osteoporosis in medakas.
These particular fishes have been genetically modified - they have
fluorescent proteins in them (in red and green light). These different
proteins are formed in osteoclasts (bone cells that eliminate the old
bone tissue) and osteoblasts (the ones that create new bone tissue).
Both types of cells started appearing more quickly on the orbit than on
Microgravity leads to different changes in the body, such as
redistribution of liquids, hypertension, and vertigo. Mineralization of
bones decreases, but little is understood about how osteoclasts and
osteoblasts react to these conditions.
The researchers hypothesize about up-regulation of genes osterix,
osteocalcin, TRAP, and MMP9 in microgravity. Specific genes osterix and
osteocalcin can react to gravity shifts because their activity rose
simultaneously during the experiment.
Transcriptomic analysis of fishes' throat bones showed a significant
increase in regulation of 2 genes of osteoblasts and 3 genes of
osteoclasts. More detailed analysis in space showed increases in
activities of the genes c-fos, jun-B-like, pai-1, ddit4, and tsc22d3.
Earlier other researchers have shown that glucocorticoid hormones
increase the activity of transcription factor AP-1 that regulates gene
expression in response to a variety of stimuli, including cytokines,
growth factors, stress, and bacterial and viral infections.
Glucocorticoid receptors may be involved in osteoclast activity
Also, stress is known to elevate blood pressure, which
leads to nitrous oxide (NO) production and in turn - to blood pressure
Glucocorticoid receptors (GCR) and nitrous oxide, as some recent observations
have proved, act in unison through the changes in activities of such
genes as tsc22d3 and ddit4 which react to microgravity.
Thus, the paper suggests the participation of NO - GCR signal pathway in microgravity stress.