Bone turnover in wild type and pleiotrophin-transgenic mice housed for 3 months in the
International Space Station
One of the major goals of the MDS experiment was to investigate bone alterations in 3 Wt and
3 PTN-Tg male mice (2 months old at the time of launch) after 3-month permanence aboard the
ISS.
The study revealed bone loss during spaceflight in the weight-bearing bones of both strains.
For both PTN-Tg and Wt mice a decrease of the trabecular number as well as an increase of the
mean trabecular separation was observed after the flight, whereas trabecular thickness did not
show any significant change.
Non weight-bearing bones were not affected. The PTN-Tg mice exposed to normal gravity
presented a poorer trabecular organization then Wt mice, but interestingly, the expression of
the PTN transgene during flight resulted in some protection against microgravity’s negative
effects. Moreover, osteocytes of the Wt mice, but not of PTN-Tg mice, acquired a round shape,
thus showing for the first time osteocyte space-related morphological alterations in vivo. The
analysis of specific bone formation and resorption marker expression suggested that the
microgravity-induced bone loss was due to both an increased bone resorption and decreased
bone deposition. Apparently, the PTN-Tg protection was the result of higher osteoblast activity
in the flight mice (Travella 2012).
Effects of long-term spaceflight on erythrocytes and oxidative stress of Rodents
Several hematological modifications in humans were observed after microgravity exposure such
as depression of T-cell lymphocyte activation and of our ability to fight infectious
microorganisms. Moreover erythrocyte (red blood cell) hemolysis (breakdown) and hemoglobin
loss was also observed after space missions. In addition, space radiations can induce generation
of hydroxyl radicals, very reactive at the site of their formation, which can initiate a chain of
reactions leading to lipid peroxidation (causing cell damage).
In the MDS mice, after landing, blood cell parameter showed a higher erythrocyte
concentration (RBC) and RDW% with a hematocrit near or above 50%. Platelets were increased
in both Wt and TG mice after flight, while hemoglobin content remained constant. These data
are partially in accordance with human data after space mission and could probably be the
consequence of body fluid shift and altered renal function.
After spaceflight, both Wt and Tg mice underwent oxidative stress and an increase of by-
products of lipid peroxidation concentration. In parallel antioxidant and enzymes involved in
the elimination of hydroperoxides from lipids were also enhanced with higher levels in Tg. After
the MDS mission, mice erythrocytes presented modifications in the cell membrane composition
and an increase of lipid peroxidation products. Despite their cellular activation, antioxidant
defenses were not sufficient to prevent damages caused by oxidative stress (Rizzo 2012).