Space radiation induces distinct senescent phenotypes: Implications for space travel [scRNA-Seq]
As Earth's magnetic field and ozone continue to weaken, space radiation begins pose a significant threat to the health of not only space travelers, but the world's population. Space radiation and its high-energy and high-charge ions create distinct clusters of DNA and concentrated macromolecular damage that results in the accumulation of senescent cells (SnCs) known to play a critical role in promoting multimorbidity. Here we demonstrate that human fibroblasts exposed to different forms of space radiation acquire senescence-associated phenotypes including morphological alterations and the accumulation of SA-ßgal+ cells more efficiently than ?-irradiation. Bulk and single cell RNA (scRNAseq) sequencing analysis revealed that space irradiated human fibroblasts up-regulated senescent-like phenotypes to a greater extent than ?-irradiation and enriched pathways associated with chronic activation and adaptation of the integrated stress response and NADPH-coupled redox metabolism. Healthy cells treated with conditioned media from irradiated SnCs manifested pro-inflammatory transcriptional profiles dependent on both radiation and cell type. Finally, treatment with known senotherapeutics demonstrated radiation-specific effects in primary dermal fibroblasts. Our data demonstrate that space radiation differentially induces senescent phenotypes in human cells compared to ?-irradiation that may play a key role in the pathogenic effects of space travel. Overall design: IMR-90 human fibroblasts were obtained from ATCC and cultures in MEM (Gibco), supplemented with 10% FBS, 1% penicillin/streptomycin (Gibco), and non-essential amino acids (Gibco) and sodium pyruvate (Gibco). The cells were maintained at 37°C, 5% CO2 and 20% O2.  All cells were seeded at 50% confluence and replicate cultures were shipped overnight to the National Aeronautics and Space Administration (NASA) Laboratory at Brookhaven National Laboratory. Upon arrival cells were allowed to recover from shipment overnight prior to radiation exposure and irradiation occurred as described previously. Briefly, irradiations occurred using particle beams for Hydrogen (H), Silicon (Si), Iron (Fe) using particle energies of 150, 238 and 600 MeV/n with LET values of 0.5, 79 and 174 ke V/µm respectively. For ?-irradiation, a 137Cs source (JL Shepard and Associates, CA) was used, all cells regardless of types of radiation exposure received final doses of 4.0Gy. Following exposure to space radiation, a media change was preformed, and cells were allowed to rest overnight prior to overnight shipment back to the University of Minnesota where they were allowed to rest another 13 days to allow senescence induction. During senescence induction medium was replaced and collected every 2-3 days and routine passaging was conducted.