Neurotoxic response in astrocytes to acute exposure of simulated microgravity

As extended duration space flights become the next goal in space exploration, a more profound understanding in the biophysiological changes to microgravity remains an important topic to The National Aeronautics and Space Administration (NASA). Astrocytes are the major representative of glial cells found in a 10:1 ratio when compare to neurons and occupying 25% to 50% of brain volume. Even though astrocytes seem to protect the brain from neurotoxic stress and insults, studies directed toward understanding the effects of microgravity on these cells are few in number. To better understand the effects of microgravity and how it may alter key signals that induce toxicity we hypothesize: A) That exposure to simulated microgravity in astrocytes alters key genes involved in neurotoxicity; and B) That CB2 receptors are present in astrocytes and simulated microgravity alters CB2 expression. If microgravity alters or causes adverse effects to the main neuroprotective cells, the consequences and ramifications are important. The results of astrocyte morphology studies show a decreasing number of cells compared to control samples. The microgravityexposed samples show a shrunken or less spread morphology that indicates constraints on cell recovery. DNA damage is evident from tails seen in the Comet Assay with increased time exposure to simulated microgravity. Flow cytometry performed to examine changes to the cell cycle gave results indicating a three-fold increase in DNA fragmentation and no major changes for G1, S, G2 and mitosis phases. Measurements taken of superoxide levels show a two-fold increase in ROS. A neurotoxic gene profile shows 10 genes significantly altered in response to simulated microgravity. Double labeling studies indicated that CB1 and CB2 receptors are co-localized in the same astroglial cell. Western blot analyses corroborated the immunocytochemistry results and showed distinct immunoreactive bands at the same molecular mass as CB1 (62 KDa) and CB2 (42KDa). Pre-incubation with CB2 blocking-peptide, completely abolished the CB2 immunoreactivity. Together, these results indicate that astroglial cells constitutively coexpress CBI and CB2 receptors. Astrocyte receptor subtype CB1 shows an inverse gene expression pattern compared to CB2 after exposure to simulated microgravity. Hence these results demonstrate that simulated microgravity exerts adverse effects in astrocytes and alters expression of key genes involved in modulating neurotoxicity including cannabinoid receptors. The significance of this research resides in the fact that long-term space travel missions might present a risk of development of neurological associated diseases to NASA cosmonauts.