310
Cell Growth in Microgravity
Fig. 4
Suborbital Flight. Suborbital
rockets release a research payload at
high altitude and offer 4 to 12 min of
free-fall. Investigators can study cell
movement, signal transduction, and
characterization of fluid dynamics in the
culture environment.
is the moon. Cell cultures can experience
microgravity in space (orbit) or in models
for
simulating
microgravity
on
Earth:
clinostatic culture, parabolic flight (aircraft
or sounding rocket), and drop towers. Drop
towers only provide very short durations
of microgravity (3 to 4 s) and are of
limited use for biological experiments.
Parabolic flight can provide somewhat
longer durations of microgravity (aircraft:
15–35 s, soundingrocket: 7–15 min). Cell
cultures can be maintained in clinostatic
rotation indeFnitely depending on the
culture
system
used.
Thus,
there
are
analog systems that can be used to reFne
hypotheses for spaceflight. Each of these
systems shares some characteristics with
microgravity. It is essential to understand
both the advantages and limitations of
model systems. The main advantage for
cell science is that many experiments
can be modeled for extended periods
on the ground using one or more of
these analogs.
4
Cellular Response to Microgravity
More than 120 experiments have been per-
formed in space during the past 15 years
that demonstrate that microgravity in-
duces changes in single cells. The op-
portunity to conduct experiments using
cells in microgravity and the development
of ground-based models provide
in vitro
models to study adaptation to the condi-
tions in microgravity. Cellular responses to
microgravity are varied, depending on cell
type and species of origin. Lymphocytes
from humans, monkeys, and rodents are
affected by gravitational unloading. The
list spans from the plant kingdom all the
way across the animal phyla. The differ-
ent parameters affecting cells seem to
depend on their size, dynamics, shape,
circadian rhythms, function, location, and
so on. Mammalian cells are especially
susceptible to microgravity-related pertur-
bations. In the immune system, there is
extensive evidence that microgravity sup-
presses the immune function
in vitro
and
possibly
in vivo
. The outcome of the sup-
pressed functions in long duration space
travel is unknown. Nevertheless, it is of
concern that widely accepted parameters
of immune function are compromised
in microgravity. The underlying mecha-
nisms of dysfunction in microgravity are
the subjects of flight and ground-based
experiments.
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