Radiation persistently promoted oxidative stress, activated mTOR via PI3K/Akt, and downregulated autophagy pathway in mouse intestine

Abstract

While acute effects of toxic radiation doses on intestine are well established, we are yet to acquire a complete spectrum of sub-lethal radiation-induced chronic intestinal perturbations at the molecular level. We investigated persistent effects of a radiation dose (2 Gy) commonly used as a daily fraction in radiotherapy on oxidants and anti-oxidants, and autophagy pathways, which are interlinked processes affecting intestinal homeostasis. Six to eight weeks old C57BL/6J mice (n=10) were exposed to 2 Gy γ-ray. Mice were euthanized two or twelve months after radiation, intestine surgically removed, and flushed using sterile PBS. Parts of the intestine from jejunal-ilial region were fixed, frozen, or used for intestinal epithelial cell (IEC) isolation. While oxidant levels and mitochondrial status were assessed in isolated IEC, autophagy and oxidative stress related signaling pathways were probed in frozen and fixed samples using PCR-based expression arrays and immunoprobing. Radiation exposure caused significant alterations in the expression level of 26 autophagy and 17 oxidative stress related genes. Immunoblot results showed decreased Beclin1 and LC3-II and increased p62, PI3K/Akt, and mTOR. Flow cytometry data showed increased oxidant production and compromised mitochondrial integrity in irradiated samples. Immunoprobing of intestinal sections showed increased 8-oxo-dG and nuclear PCNA, and decreased autophagosome marker LC3-II in IEC after irradiation. We show that sub-lethal radiation could persistently downregulate anti-oxidants and autophagy signaling, and upregulate oxidant production and proliferative signaling. Radiation-induced promotion of oxidative stress and downregulation of autophagy could work in tandem to alter intestinal functions and have implications for post-radiation chronic gastrointestinal diseases.

Space radiation exposure persistently increased leptin and IGF1 in serum and activated leptin-IGF1 signaling axis in mouse intestine

“…Reduced IGFBP3 along with increased pro-proliferative Ki67 staining in intestine and colon is in agreement with earlier observations reporting anti-proliferative and pro-apoptotic effects of IGFBP37677. Our observations in this study could act as the prelude necessary for future studies on contribution of leptin/IGF1 signaling axis to some of the heavy ion radiation’s long-term consequences such as premature senescence, metabolic alterations, and GI carcinogenesis we have reported previously413577879. The current study performed in wild type mice irradiated with a non-lethal dose of 56 Fe radiation is an initial step towards understanding GI tract related long-term hormonal alterations after heavy ion space radiation exposure especially after low dose exposures.…”

Renoprotective approaches and strategies in acute kidney injury

“…On one hand, mTOR is a key to cell growth and proliferation by promoting protein synthesis. On the other hand, recent work has demonstrated that mTOR is a crucial, negative regulator of autophagy in response to nutritional status, growth factor and stress signals (Jung et al, 2010; Datta et al, 2014). In AKI, the role of mTOR varies according to experimental models.…”

Crosstalk between autophagy and intracellular radiation response (Review)

“…Mitochondria ROS act as essential signaling molecules in the regulation of the mitophagy and tumor development (71,72). Mitophagy is a process of mitochondria-selective autophagy in response to various signals, including oxidative stress, starvation, and modification of mitochondrial proteins (73). It has been shown that degradation of mitochondria and mtDNA can be executed by mitophagy.…”