Ionizing radiation is a known risk factor for gastrointestinal (GI) pathologies including cancer. Hormones and related signaling crosstalk, which could contribute to radiation-induced persistent pathophysiologic changes in the small intestine and colon, remain to be explored. The current study assessed perturbation of GI homeostasis-related hormones and signaling pathways at the systemic as well as at the tissue level in small intestine and colon. Mice (6-8 week old C57BL/6J) were exposed to 2 Gy γ radiation, serum and tissue samples were collected, and insulin like growth factor 1 (IGF-1) and leptin signaling were assessed two or twelve months after radiation exposure. Serum levels of IGF-1, IGF binding protein 3 (IGFBP3), leptin, and adiponectin were altered at these times after irradiation. Radiation was associated with increased IGF1 receptor (IGF1R) and obesity (leptin) receptor (Ob-R), decreased adiponectin receptor 1 (Adipo-R1) and 2 (Adipo-R2), and increased Ki-67 levels in small intestine and colon at both time points. Immunoblot analysis further showed increased IGF1R and Ob-R, and decreased Adipo-R2. Additionally, upregulation of PI3K/Akt and JAK2 signaling, which are downstream of IGF1 and leptin, was also observed in irradiated samples at both time points. These results when considered along with increased cell proliferation in the small intestine and colon demonstrate for the first time that ionizing radiation can persistently increase IGF1 and leptin and activate downstream proliferative pathways, which may contribute to GI functional alterations and carcinogenesis.
Keywords: colorectal cancer; insulin like growth factor 1; intestinal homeostasis; ionizing radiation; leptin.