Date of Award

9-19-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioinformatics

First Advisor

Rupak Pathak

Abstract

Deep-space missions, such as those planned for the cis-lunar space and Mars, pose unique challenges to astronaut health due to prolonged microgravity (MG) exposure and low-dose chronic irradiation (CIR). Understanding the impact of these stressors on secondary lymphoid tissues, such as the spleen and intestine, is crucial for ensuring crewmembers' well-being, given the impracticality of conducting this research with human samples. Using a ground-based facility, we exposed C57BL/6 female and male mice to CIR (1.74 Gy at a dose rate of 0.0029 Gy/h) and/or simulated MG (SMG) via hind limb unloading (HLU) for one month. Spleen and intestinal tissues were collected at the termination of the experiment to determine the change in immune cells' phenotype by flow cytometry, functional changes in isolated CD4+/CD8+ T cells following activation with CD3/CD28 for 24 h and measurement of TNF-α, IFN-γ and IL-2 by ELISA, and functional changes in B-cells following activation with LPS for 24 h and measurement of IgM and IgA by ELISA. Our findings revealed that CIR and/or SMG altered a greater variety of immune cells in both lymphoid and myeloid lineages in female mice than in male mice, the function of splenic CD4+ T cells, CD8+ T cells and CD19+ B cells altered in a sex specific manner, and the distribution of different immune cells changed based on animal sex. In intestinal tissue, we evaluated immune cell distribution, crypt cell proliferation, protein profile, and microbial landscape from cecal samples using QIIME2 (Quantitative Insights Into Microbial Ecology). We found that SMG influences CIR's effects on intestinal immune cell populations. SMG+CIR resulted in greater suppression of crypt cell proliferation compared to singular treatments. Notably, 59 proteins were significantly changed in the SMG+CIR group, indicating potential involvement in DNA repair, UV response, Kras Signaling, and Xenobiotic metabolism. Functional pathway enrichment analysis using Ingenuity Pathway Analysis (IPA) revealed alterations in pathways and linkage to diseases such as gastrointestinal disease, developmental disorder, and cancer, particularly in the SMG+CIR group compared to Sham. Moreover, CIR and/or SMG significantly altered microbial diversity and the relative abundance of specific bacterial taxa. These results underscore the potential of space-related factors to disrupt immune cell phenotypes, proliferation rates, key biological pathways, and the composition of intestinal microbiota. Developing effective strategies to mitigate these alterations is critical for reducing the specific clinical risks that crewmembers may face during long-term deep-space missions.

Download

Included in

Biology Commons

Share

COinS