Maria Moreno-Villanueva ¹ Luis Jimenez-Chavez ² Stephanie Krieger ³ Lianghao Ding ⁴ Ye Zhang ⁵ Adriana Babiak-Vazquez ³ Mark Berres ⁶ Sandra Splinter ⁶ Kristen E Pauken ⁷ Brian C. Schaefer ⁸ Brian Crucian ⁹ Honglu Wu ^9*

• ¹ University of Konstanz, Konstanz, Baden-Württemberg, Germany
• ² University of Central Florida, Orlando, Florida, United States
• ³ KBRwyle, Houston, Texas, United States
• ⁴ University of Texas Southwestern Medical Center, Dallas, Texas, United States
• ⁵ Kennedy Space Center, National Aeronautics and Space Administration, Washington, DC, Washington, United States
• ⁶ University of Wisconsin-Madison, Madison, Wisconsin, United States
• ⁷ University of Texas MD Anderson Cancer Center, Houston, Texas, United States
• ⁸ Uniformed Services University of the Health Sciences, Bethesda, Maryland, United States
• ⁹ Johnson Space Center, National Aeronautics and Space Administration, Houston, Texas, United States

The impact of spaceflight on the immune system and mitochondria has been investigated for decades. However, the molecular mechanisms underlying spaceflight-induced immune dysregulations are still unclear.Methods: In this study, blood from eleven crewmembers was collected before and during International Space Station (ISS) missions. Transcriptomic analysis was performed in isolated peripheral blood mononuclear cells (PBMCs) using RNA-sequencing. Differentially expresses genes (DEG) in space were determined by comparing of the inflight to the preflight samples. Pathways and statistical analyses of these DEG were performed using the Ingenuity Pathway Analysis (IPA) tool.In comparison to pre-flight, a total of 2030 genes were differentially expressed in PBMC collected between 135 and 210 days in orbit, which included a significant number of surface receptors.The dysregulated genes and pathways were mostly involved in energy and oxygen metabolism, immune responses, cell adhesion/migration and cell death/survival. Discussion: Based on the DEG and the associated pathways and functions, we propose that mitochondria dysfunction was caused by constant modulation of mechano-sensing receptors in microgravity, which triggered a signaling cascade that led to calcium overloading in mitochondria. The response of PBMC in space shares T-cell exhaustion features, likely initiated by microgravity than by infection.Consequences of mitochondria dysfunction included immune dysregulation and prolonged cell survival which potentially explain the reported findings of inhibition of T cell activation and telomere lengthening in astronauts.Our study potentially identifies the upstream cause of mitochondria dysfunction and the downstream consequences in immune cells.