Abstract
All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.
Highlights
Humans in space live in an unusual environment characterized by many stress factors affecting human health
Cell viability and apoptosis assays validated the data obtained by bioinformatic analyses: Lymphocytes cultured in simulated microgravity conditions exhibited elevated apoptosis and reduced cell proliferation [84]
This study clearly showed the changes in the expression of numerous genes involved in the regulation of the mitochondria-associated apoptotic pathway in spaceflight mice retinal tissues compared with the ground control
Summary
Humans in space live in an unusual environment characterized by many stress factors affecting human health. This review describes the spaceflight options and ground-based techniques suitable for microgravity-based research, the process of programmed cell death, and the current knowledge of apoptosis in small animals, e.g., mice, in space. The mission preparation time is between one and two years, and access to the experimental hardware integrated in the rocket is possible until 1 h prior to launch. The experiment must be rotated, either continuously in one or two axes by means of a two-dimensional (2D)- or 3D-clinostat, or with directional changes by means of a random positioning machine (RPM) [32] These will achieve the so-called simulated functional weightlessness only in a very small volume in the centre of the rotational axes; they are only suited for very small samples like tissue and cell cultures. Many effects of spaceflight on the human body, such as a decrease in bone density, muscle mass, and strength and cephalic fluid shift, are mimicked very well by HDBR [35]
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