Abstract
Effects of 3-month exposure to microgravity environment on the expression of genes and proteins in mouse brain were studied. Moreover, responses of neurobiological parameters, nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF), were also evaluated in the cerebellum, hippocampus, cortex, and adrenal glands. Spaceflight-related changes in gene and protein expression were observed. Biological processes of the up-regulated genes were related to the immune response, metabolic process, and/or inflammatory response. Changes of cellular components involving in microsome and vesicular fraction were also noted. Molecular function categories were related to various enzyme activities. The biological processes in the down-regulated genes were related to various metabolic and catabolic processes. Cellular components were related to cytoplasm and mitochondrion. The down-regulated molecular functions were related to catalytic and oxidoreductase activities. Up-regulation of 28 proteins was seen following spaceflight vs. those in ground control. These proteins were related to mitochondrial metabolism, synthesis and hydrolysis of ATP, calcium/calmodulin metabolism, nervous system, and transport of proteins and/or amino acids. Down-regulated proteins were related to mitochondrial metabolism. Expression of NGF in hippocampus, cortex, and adrenal gland of wild type animal tended to decrease following spaceflight. As for pleiotrophin transgenic mice, spaceflight-related reduction of NGF occured only in adrenal gland. Consistent trends between various portions of brain and adrenal gland were not observed in the responses of BDNF to spaceflight. Although exposure to real microgravity influenced the expression of a number of genes and proteins in the brain that have been shown to be involved in a wide spectrum of biological function, it is still unclear how the functional properties of brain were influenced by 3-month exposure to microgravity.
Highlights
Altered gravitational environment represents a unique challenge for biological systems that have evolved against a constant gravitational background and it has been reported that exposure to actual and/or simulated microgravity, as well as to rotationally induced hypergravity, causes various physiological adaptations, including in the central nervous system (CNS) [1,2,3,4] and antigravity muscle [5,6] in mice, rats and humans
Responses of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) Despite the lack of a sufficient number of animals and tissues available for a complete statistical evaluation of the effect of 91day-exposure to space environment, the expression of NGF in hippocampus and cortex of the spaceflight wild type animal tended to be less than ground controls (LC and GC, Fig. 1)
The level in adrenal gland was lower than group laboratory controls (LCs) (p.0.05)
Summary
Altered gravitational environment represents a unique challenge for biological systems that have evolved against a constant gravitational background and it has been reported that exposure to actual and/or simulated microgravity, as well as to rotationally induced hypergravity, causes various physiological adaptations, including in the central nervous system (CNS) [1,2,3,4] and antigravity muscle [5,6] in mice, rats and humans. In terms of the nervous system, the hindlimb suspension, which is often used as the simulation model for exposure to microgravity environment, causes the decrease of electromyogram activity in soleus muscle, afferent neurograms in spinal cord [15], GABAergic neurons in the hindlimb somatosensory cortex [1], and neurogenesis in rats [16]. Exposure to simulated microgravity environments by hindlimb suspension might induce distinct changes specific to the regions of the brain
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