Comprehensive Study of the Influence of Altered Gravity on the Oxidative Burst of Mussel (Mytilus edulis) Hemocytes

Abstract

Microgravity induces alterations in the functioning of immune cell; however, the underlying mechanisms have not yet been identified. In this study, hemocytes (blood cells) of the blue mussel Mytilus edulis were investigated under altered gravity conditions. The study was conducted on the ground in preparation for the BIOLAB TripleLux-B experiment, which will be performed on the International Space Station (ISS). On-line kinetic measurements of reactive oxygen species (ROS) production during the oxidative burst and thus cellular activity of isolated hemocytes were performed in a photomultiplier (PMT)-clinostat (simulated microgravity) and in the 1g operation mode of the clinostat in hypergravity on the Short-Arm Human Centrifuge (SAHC) as well as during parabolic flights. In addition to studies with isolated hemocytes, the effect of altered gravity conditions on whole animals was investigated. For this purpose, whole mussels were exposed to hypergravity (1.8 g) on a multi-sample incubator centrifuge (MuSIC) or to simulated microgravity in a submersed clinostat. After exposure for 48 h, hemocytes were taken from the mussels and ROS production was measured under 1 g conditions. The results from the parabolic flights and clinostat studies indicate that mussel hemocytes respond to altered gravity in a fast and reversible manner. Hemocytes (after cryo-conservation) exposed to simulated microgravity (μg), as well as fresh hemocytes from clinorotated animals, showed a decrease in ROS production. Measurements during a permanent exposure of hemocytes to hypergravity (SAHC) show a decrease in ROS production. Hemocytes of mussels measured after the centrifugation of whole mussels did not show an influence to the ROS response at all. Hypergravity during parabolic flights led to a decrease but also to an increase in ROS production in isolated hemocytes, whereas the centrifugation of whole mussels did not influence the ROS response at all. This study is a good example how ground-based facility experiments can be used to prepare for an upcoming ISS experiment, in this case the TRIPLE LUX B experiment.