# Elevated SASP Factors, Reduced Antioxidant Enzymes, and Increased Tumor Susceptibility in Space Radiation-Exposed ApcMin/+ Mice

## TL;DR

Exposure to space radiation increases cancer risk in mice by altering proteins linked to tumor growth and reduced antioxidant defenses.

## Contribution

Identified a serum proteomic signature linked to space radiation-induced tumor susceptibility and cancer-related SASP factors.

## Key findings

- GCR exposure increased gastrointestinal and mammary tumor burden in ApcMin/+ mice.
- Proteomic analysis revealed 194 upregulated and 461 downregulated serum proteins after GCR exposure.
- Elevated TGF-β1, MMP9, and reduced antioxidant activity were observed in GCR-exposed mice.

## Abstract

Human missions into deep space will expose astronauts to the unique and complex radiation environment of galactic cosmic radiation (GCR), a mixed field of high-energy protons and heavy ions predicted to substantially increase long-term cancer risk. To support effective risk stratification, early detection, and mitigation strategies, there is a need to identify biomarkers indicative of GCR-induced cancer risk. Here, we applied a Tandem Mass Tag (TMT)-based quantitative proteomics approach to identify potential biomarkers associated with GCR-induced gastrointestinal (GI) and mammary tumorigenesis using the female ApcMin/+ mouse, a well-established model of human colorectal and breast cancer. Eight- to ten-week-old ApcMin/+ mice were exposed to 75 cGy of simulated GCR and serum and tissue samples were collected 100–110 days post-exposure for molecular and histopathological analyses. Tumor incidence was scored by blinded observers, and serum proteomes exhibiting a fold change > 1.2 or <0.83 with p < 0.05 were considered significantly altered. Bioinformatics analyses, including Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and unsupervised clustering, were employed to delineate GCR-responsive molecular networks. Validation of differentially expressed proteins (DEPs) was performed using immunoblotting, ELISA, and enzyme activity assays. GCR exposure resulted in a significant increase in both GI and mammary tumor burden relative to controls. Proteomic profiling revealed 194 upregulated and 461 downregulated proteins, distinguishing GCR-exposed from control serum proteomes. Functional enrichment analyses highlighted alterations in metabolic processes, PI3K-AKT, HIF-1, and PPAR signaling pathways, alongside the suppression of antioxidant defense mechanisms. Notably, mice exposed to GCR exhibited elevated serum levels of TGF-β1 and MMP9, accompanied by reduced levels and enzymatic activities of key antioxidant defenses. Cross-referencing 36 GCR-induced serum SASP factors with the Human Protein Atlas revealed 11 SASP proteins associated with human breast and colorectal cancers. Together, these findings show that GCR exposure triggers a pro-tumorigenic serum proteomic signature that may serve as a biomarker for assessing cancer risk in astronauts during deep-space missions.