Microgravity or hypergravity evoked serious thrombotic and
haemorrhagic problems or even fatalities occur commonly in the
world (1–6). In addition to “the Apollo 15 space syndrome” de-
scribed in crewmen in space (1), many reports have documented
the risk of thrombosis or haemorrhage under microgravity or
microgravity-related conditions in human and experimental ani-
mals (1, 2, 7, 8). For example, there was increased formation of
platelet thrombi in the post-capillary venules and capillaries, and
this blockage led to edema and extravasation of red blood cells
after resumption of weight bearing in the COSMOS 2044 rats
which were orbited for 14 days (7). Similar tragedies often
happen to people in altered gravitational environments on the
ground. Depending on incomplete case reports, approximately
four deaths annually in the United States are associated with
roller coasters (3, 4). Except for the external causes related to in-
juries from falls or collisions, more than half of the fatalities have
been found to relate with haemorrhagic and thrombotic prob-
lems (3, 4). Moreover, thrombotic diseases have been reported to
occasionally occur in aircrew members, especially an anterolat-
eral myocardial infarction occurred in a 37-year-old pilot im-
mediately after his high-G centrifuge training profile (5, 6).
Effects of microgravity and hypergravity on platelet functions
Kesheng Dai1; Yuedan Wang2; Rong Yan1; Quanwei Shi1; Zhicheng Wang1; Yanhong Yuan1,3; Hong Cheng1; Suping Li1;
Yubo Fan1; Fengyuan Zhuang1
1Department of Biological Science and Technology, Beijing University of Aeronautics and Astronautics, Beijing, China; 2Department of
Immunology, Peking University, Beijing, China; 3Space Cell and Molecular Biology Laboratory, China Astronaut Research and Training Center,
Many serious thrombotic and haemorrhagic diseases or fatal-
ities have been documented in human being exposed to micro-
gravity or hypergravity environments, such as crewmen in space,
roller coaster riders, and aircrew subjected to high-G training.
Some possible related organs have been examined to explore
the mechanisms underlying these gravity change-related dis-
eases. However, the role of platelets which are the primary
players in both thrombosis and haemostasis is unknown. Here
we show that platelet aggregation induced by ristocetin or col-
lagen and platelet adhesion to von Willebrand factor (VWF)
were significantly decreased after platelets were exposed to
simulated microgravity. Conversely, these platelet functions
were increased after platelets were exposed to hypergravity. The
tail bleeding time in vivo was significantly shortened in mice ex-
posed to high-G force, whereas, was prolonged in hindlimb un-
Platelets, thrombosis, haemorrhage, simulated microgravity, hy-
loaded mice. Furthermore, three of 23 mice died after 15 min-
utes of –8 Gx stress. Platelet thrombi disseminated in the heart
ventricle and blood vessels in the brain, lung, and heart from the
dead mice. Finally, glycoprotein (GP) Ibα surface expression and
its association with the cytoskeleton were significantly de-
creased in platelets exposed to simulated microgravity, and ob-
viously increased in hypergravity-exposed platelets. These data
indicate that the platelet functions are inhibited in microgravity
environments, and activated under high-G conditions, suggesting
a novel mechanism for gravity change-related haemorrhagic and
thrombotic diseases. This mechanism has important implications
for preventing and treating gravity change-related diseases, and
also suggests that special attentions should be paid to human ac-
tions under different gravity conditions.
Thromb Haemost 2009; 101: 902–910
Platelets and Blood Cells
Department of Biological Science and Technology
Beijing University of Aeronautics and Astronautics
37 Xueyuan Road, Haidian district
Beijing 100083, China
Tel.: +86 10 82339862, Fax: +86 10 82127801
This work was supported by grants from National Natural Science Foundation of
China (NSFC 30770795), Program for New Century Excellent Talents in University
(NCET-06–0167), and A Foundation for the Author of National Excellent Doctoral
Dissertation of P.R. China (FANEDD 200560).
Received: November 17, 2008
Accepted after major revision: January 28, 2009
Prepublished online: March 11, 2009
© 2009 Schattauer GmbH, Stuttgart
Dai et al. Effect of gravity on platelet functions
Many efforts have been made to explore the mechanisms
underlying the gravity change related thrombotic and haem-
orrhagic diseases. The decrease in blood volume resulting from
water deficit in the human body while in space has been con-
sidered as a risk factor for thrombotic-ischaemic diseases (1, 2,
9). The abnormalities in the cardiovascular system evoked by
gravity change, such as coronary vasospasm (1), sustained rise in
heart rate (10), and arrhythmia have been also thought to play
roles in the development of the thrombotic and haemorrhagic
diseases (3, 4). However, these risk factors only suggest the
thrombotic and haemorrhagic tendency. On the other hand, the
role of platelets which are the primary players in both thrombo-
sis and haemostasis is still unknown. In addition, while the
causes of some diseases following amusement park rides such as
cerebral haemorrhage and chronic subdural haematoma remain
difficult to be determined (11), a research from three popular
high-G roller coasters indicates that even for a conservative
worst-case scenario, the highest estimated peak head acceler-
ations induced by roller coasters were far below conventional
levels that are predicted for head injuries (12). It appears that the
physiological effects of amusement park rides rather than the di-
rect physical injuries may play important roles in the devel-
opment of haemorrhagic and thrombotic diseases or even fatal-
Platelets play a critical role in thrombosis and haemostasis.
Under high-shear rate flow conditions such as in arteries and
capillaries, the interaction of platelet glycoprotein (GP) Ib-IX
with von Willebrand factor (VWF) exposed at injured vascular
wall initiates platelet adhesion (13, 14). Simultaneously, GPIb-
IX-VWF interaction triggers the intracellular signalling cascade
which leads to the irreversible platelet stable adhesion and aggre-
gation, and consequently results in stopping bleeding or throm-
bus formation (15, 16). VWF–GPIb-IX-V interaction also me-
diates the formation of platelet microaggregates under patho-
logical shear stress (17), or in patients with abnormally large
VWF multimers resulting in thrombotic thrombocytopenic pur-
pura (TTP) (18). In this study we find that platelet functions are
inhibited under simulated microgravity conditions and activated
in high-G environments, suggesting a novel mechanism for grav-
ity change related thrombotic and haemorrhagic diseases. Fur-
thermore, glycoprotein (GP) Ibα surface expression and redis-
tribution data indicated that the varied association of GPIbα with
the cytoskeleton in response to gravity change may play a key
role in gravity-related platelet functional variations.
Materials and methods
Antibodies and reagents
Monoclonal antibodies SZ2 against GPIbα and SZ51 against
P-selectin (GMP-140) were generous gifts of Dr. Changgeng
Ruan (Soochow University, Suzhou, China) (19, 20). Purified
human VWF was generously provided by Dr. Xiaoping Du (Uni-
versity of Illinois, Chicago, IL, USA). Ristocetin, Collagen and
ADP were purchased from Sigma (St. Louis, MO, USA). Poly-
clonal goat anti-mouse P-selectin antibody sc-6941 was pur-
chased from Santa Cruz Biotechnology (Santa Cruz, CA, USA).
Rotary cell culture system
To investigate the effect of microgravity on platelet function, a
National Aeronautics and Space Administration-recommended
and a widely accepted, ground-based, microgravity-simulating
system, the Rotary Cell Culture System (RCCS) (Synthecon,
Houston, TX, USA) was used to simulate microgravity con-
ditions similar to those encountered during spaceflight (21–23).
Platelets were either rotated about a horizontal axis perpendicu-
lar to the gravitational vector to randomise gravitational vectors
across the surface of the platelets and generate microgravity of
about 10–2 G, or rotated about a vertical axis parallel to the gravi-
tational vector to experience normal gravitational forces and
serve as a control (1 G) environment (21–23).
Centrifuge for high-G force
To achieve net hypergravity force, a custom-built slow-speed 30
cm radius centrifuge was used to produce hypergravity stress in
platelet and mice experiments. Platelets or mice were placed on
the plate of the centrifuge. Relatively low hypergravity and short
time were inflicted on the platelets or mice to avoid platelet sedi-
mentation or unwanted physical injury to the mice, respectively.
The tail suspension-hindlimb unloaded model as previously de-
scribed (24–27) was performed on six- to eight-week-old adult
C57 black mice for 24 hours (h) to simulate microgravity.
Briefly, the tail was placed in traction tape, which was attached to
a swivel and crossbar setup that allowed the animals full mobility
in the cage with the forelimbs. The tape should be loose enough
to allow normal blood circulation but tight enough so that the
traction tape will not peel away from the tail. The mice were
maintained at 30° angle, head-down tilt for 24 h. The animals had
ad libitum access to standard mice chow and water. The syn-
chronous 1 G control mice that were matched for weight and
gender were treated in the same way with the tail placed in trac-
tion tape except that the hindlimb unloaded for 24 h. The mice
were anesthetised with intraperitoneal injection of pentobarbital
and were subjected to tail-bleeding time test immediately after
24 h of suspension. For high-G experiments, the mice were anes-
thetised with pentobarbital. –8 Gx and 15 minutes (min) cen-
trifugation was adapted to the mice using 30 cm radius centri-
fuge. The synchronous 1 G control mice were anesthetised and
placed on a plateau with –1 Gx for 15 min. The mice were sub-
jected to tail-bleeding time test immediately after centrifugation.
All procedures performed in this study were approved by the
Peking University Institutional Animal Care and Use Commit-
Platelet preparation and aggregation
Blood was drawn from healthy donors, and anti-coagulated with
1/10 volume of 3.8% trisodium citrate. Platelet-rich plasma
(PRP) was obtained by centrifugation at 300 × g for 20 min and
was incubated at 22°C for 2 h to recover to resting state as pre-
viously described (28, 29). To prepare washed platelets, blood
was anti-coagulated with ACD (85 mM sodium citrate, 111 mM
dextrose, 71 mM citric acid). Platelets were washed with CGS
buffer (12.9 mM sodium citrate, 33.33 mM glucose, and 123.2
mM NaCl, pH7.4) and resuspended in modified Tyrode’s buffer
this model affects platelet function still remains to be investi-
gated. Actually, reports from Riley et al. provided direct evidence
for the effects of gravity on platelet function in vivo (7, 42). Up to
now, while the reason for increased platelet activation in the rats
after resumption of weight bearing is still unknown (7), the ob-
servations in our report indicate that the hypergravity conditions
experienced during launch or reentry might play a key role.
Since the beginning of the Space Era, most attention has been
paid to the cardiovascular system for thrombosis or haemorrhage
episodes. However, the altered platelet function verified in this
paper may play important roles in some space symptoms. Both
the hyper- and micro-gravity environments are commonly ex-
perienced during the aerospace mission. Up to now, though se-
vere platelet-related tragedy has not been reported in crew
members, considering increasing public passion about space
travelling, our study suggests that special attention should be
paid to the effects of micro- and hypergravity on platelet func-
We thank Drs. Changgeng Ruan (Soochow University, Suzhou, China) and
Xiaoping Du (University of Illinois, Chicago, IL, USA) for providing
reagents; and Dr. Chunkui Shao (Sun-Yat Sun University, Guangzhou,
China) for technical help with pathological analysis.
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