Abstract

Exposure to microgravity in low-Earth orbit (LEO) has been shown to affect human cardiovascular, musculoskeletal, and immune systems. Post-flight brain imaging indicates that reports about astronauts and mouse models suggest that microgravity may cause intracranial fluid shifts and possibly alter white and gray matter of the brain [1]. To focus on the effects of microgravity on the brain, we used induced pluripotent stem cells (iPSCs) to produce three-dimensional (3D) human neural organoids as models of the nervous system. We studied iPSCs derived from four individuals, including people with the neurological diseases primary progressive multiple sclerosis (PPMS) and Parkinsons disease (PD) and non-symptomatic controls. We patterned the organoids toward cortical and dopaminergic fates representing regions of the brain affected by MS and PD, respectively. Microglia were generated from the same cell lines and integrated into a portion of the organoids. The organoids were maintained for 30 days in a novel static culture system on the International Space Station (ISS) and live samples were returned to Earth. The post-flight samples were evaluated using histology, transcriptome and secretome analysis. Microglia-specific genes and secreted proteins were detectable in the microglia-containing organoid cultures. The gene expression analyses of individual organoids cultured in LEO and on Earth suggest that cell proliferation was lower and neural cells were more mature in samples that were cultured in LEO. These experiments lay the groundwork for further studies, including long term studies to investigate the effects of microgravity on the brain. With two more missions using similar cells, we are determining whether this effect of microgravity is consistent in separate experiments. Such studies may ultimately aid in developing countermeasures for the effects of microgravity on the nervous systems of astronauts during space exploration and suggest novel therapeutic interventions for neurological diseases on Earth.