Studies on the International Space Station to assess the effects of microgravity on iPSC-derived neural organoids

Exposure to microgravity in low-Earth orbit (LEO) has been shown to affect human health. Post-flight brain imaging and studies of astronauts and mouse models suggest that microgravity may cause intracranial fluid shifts and possibly alter white and gray matter of the brain. To focus on the effects of microgravity on brain cells, we used induced pluripotent stem cells (iPSCs) to produce three-dimensional (3D) human neural organoids as models of the nervous system. We studied iPSC-derived organoids from four individuals, including people with the neurological diseases primary progressive multiple sclerosis (PPMS) and Parkinson's 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 a month 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 transcriptome analysis. Microglia-specific genes were detectable in the microglia-containing organoid cultures. Differential 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. Overall design: Three dimensional aggregates created from iPSC-derived cortical neurons or dopaminergic neurons were exposed to microgravity for 38 days on the ISS with ground control samples cultured in parallel under normal gravity conditions on earth. Additional experimental variabiles incuded samples with or without iPSC-derived microglia added to the organoids at the start of the experiment. Bulk RNAseq analysis was performed on individual organoids in replicates for each condition.