T Cell Transcriptomes Are Dynamically Modulated by Microgravity In Vivo Along Core Gene Networks and Key Molecular Pathways

Background: The health of astronauts and success of space missions are contingent on resilience to the cumulative stressors of the space environment, including radiation, isolation, confinement and microgravity. While these factors are known to disrupt physiological function at molecular and cellular levels, the isolated impact of microgravity itself remains poorly defined. Objective: To explore in vivo effects of long-term Simulated MicroGravity (SMG) on T cell transcriptomes by analyzing gene expression changes in peripheral blood T cells of healthy volunteers. Methods: A three-week SMG exposure was completed by ten healthy male participants, during which peripheral blood specimens were harvested at five critical junctures (covering baseline, intra-exposure and recovery stages). Post-collection, T lymphocytes were enriched, and their total RNA was extracted. Transcriptome analysis was performed by RNA-seq, the gold standard for transcriptomics owing to its unbiased approach to gene detection and quantification, which provides genome-wide quantification with global normalization and, through a genome-wide analytical approach, the statistical framework to detect differentially expressed genes with controlled error rates. Following next-generation sequencing, a rigorous bioinformatics framework was employed to analyze and interpret the volunteers’ global gene expression dynamics. Results: Ground-based SMG induces widespread deregulation of gene-regulatory circuitry within T lymphocytes. SMG is associated with transcriptome shifts in several key molecular pathways in vivo including those involved in cell proliferation, cell cycle regulation, maintenance of genome integrity, as well as oncogenic and tumor suppressor gene networks. Corresponding hub genes were differentially expressed in the majority of tested healthy volunteers. Conclusions: SMG perturbs essential intracellular gene-regulatory networks in human T cells in vivo. The mechanical unloading imposed by microgravity, even in the absence of detectable systemic effects, was sufficient to deregulate core gene networks, upset the transcript-level equilibrium of central molecular pathways and alter associated gene expression profiles.