Exposing young rats to particles of high energy and charge (HZE particles), a ground-based model for exposure to cosmic rays, enhances indices of oxidative stress and inflammation, disrupts the functioning of neuronal communication, and alters cognitive behaviors. Even though exposure to HZE particles occurs at low fluence rates, the cumulative effects of long-term exposure result in molecular changes similar to those seen in aged animals. In the present study, we assessed markers of autophagy, a dynamic process for intracellular degradation and recycling of toxic proteins and organelles, as well as stress and inflammatory responses, in the brains of Sprague-Dawley rats irradiated at 2 months of age with 5 and 50 cGy and 1 Gy of ionizing oxygen particles (16O) (1000 MeV/n). Compared to nonirradiated controls, exposure to 16O particles significantly inhibited autophagy function in the hippocampus as measured by accumulation of ubiquitin inclusion bodies such as P62/SQSTM1, autophagosome marker microtubule-associated protein 1 beta light chain 3 (MAP1B-LC3), beclin1 and proteins such as mammalian target of rapamycin (mTOR). The molecular changes measured at short (36 h) and long (75 days) intervals after 16O-particle exposure indicate that the loss of autophagy function occurred shortly after exposure but was recovered via inhibition of mTOR. However, HZE-particle radiation caused significant sustained loss of protein kinase C alpha (PKC-α), a key G protein modulator involved in neuronal survival and functions of neuronal trophic factors. Exposure to 16O particles also caused substantial increases in the levels of nuclear factor kappa B (NF-κB) and glial fibrillary acidic protein (GFAP), indicating glial cell activation 75 days after exposure. This is the first report to show the molecular effects of 16O-particle radiation on oxidative stress, inflammation and loss of autophagy in the brain of young rats.

2011
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