G through the cortex was observed after 100 cGy radiation as judged by Student’s t-test (p = .0031) (Fig. 5A, B). To begin to assess transport of Ab out of the brain, levels of low-density lipoprotein receptor-related protein 1 (LRP1) were quantified in tissue samples by Western blot. LRP1 is a critical protein involved in binding Ab and trafficking it out of the brain [32] that can be modulated by peripheral inflammatory signals [33]. Even though radiation resulted in increased endothelial activation, we did not observe any difference in LRP1 protein level 6 months after 100 cGy 56Fe particle irradiation (Fig. 5C).DiscussionHere we report that GCR caused enhanced AD plaque pathology. To our knowledge, this is the first report of radiationbeing associated with enhanced plaque pathology in an AD mouse model. In addition to disease acceleration, we observed that low HZE doses are able to cause cognitive impairment as measured by contextual fear conditioning and novel object recognition in APP/ PS1 tg mice (Fig. 1). While contextual fear conditioning and, to a certain extent, novel object recognition are dependent on an intact hippocampus, the cued tone 25331948 freezing response is thought to measure Title Loaded From File hippocampal independent memory [34,35]. The lack of impairment in tone mediated freezing demonstrates that the cognitive dysfunction we observe can be, at least in part, traced to hippocampal mediated memory processes. This is consistent with other reports on the effect of radiation impacting hippocampal dependent memory [7,36]. Because we did not run parallel studies with wild-type control mice, we do not know whether cognitive impairment resulted from radiation alone or represented a synergy between radiation and mutant AD gene expression in these mice. HZE irradiation alone can lead to cognitive deficits in wild-type mice [7]; however, the only report of deficits in contextual fear conditioning or novel object recognition with C57BL/6 mice required 200 or 300 cGy iron [37]. Unfortunately, differences in mouse strain, timing, and radiation beam energy limit our ability to extrapolate from these studies. Multiple possible radiation induced effects might contribute to cognitive dysfunction in our model. One example is a defect inSpace Radiation Promotes Alzheimer PathologyFigure 2. Immunohistochemical staining for Congo red and 6E10 increases after 56Fe particle irradiation. (A, C) Representative images of half male brains stained for Congo red (A) or 6E10 (C) 6 months after 0 cGy or 100 cGy 56Fe particle radiation. Scale bar is 1 mm. (B, D) Quantitative measurement of percent plaque area Stance.Methods Study PopulationThis was a cross-sectional study conducted in the assessed with Congo red (B) and 6E10 (D). In addition, total number of individual 6E10 positive plaques (E) and the average size of plaques (mm2) (F) was determined. Each dot represents a single animal measured as percent area of the cortex and hippocampus combined. Data was analyzed with Student’s t-test for the females and one-way ANOVA with a Bonferroni post test for the males. Data displayed as mean 6 SD, n = 8?4 animals per dose. *P,.05, **P,.01. doi:10.1371/journal.pone.0053275.gneurogenesis, which has been documented in response to traditional radiotherapy [38] as well as exposure to 56Fe particles [5,7,39]. In addition to neuronal proliferation defects, impaired cognition couldalso result from inhibition of long-term potentiation (LTP) [40], an effect which has been reported with 56Fe particle irradiation in the APP23 transgenic mouse model of AD [41].Space R.G through the cortex was observed after 100 cGy radiation as judged by Student’s t-test (p = .0031) (Fig. 5A, B). To begin to assess transport of Ab out of the brain, levels of low-density lipoprotein receptor-related protein 1 (LRP1) were quantified in tissue samples by Western blot. LRP1 is a critical protein involved in binding Ab and trafficking it out of the brain [32] that can be modulated by peripheral inflammatory signals [33]. Even though radiation resulted in increased endothelial activation, we did not observe any difference in LRP1 protein level 6 months after 100 cGy 56Fe particle irradiation (Fig. 5C).DiscussionHere we report that GCR caused enhanced AD plaque pathology. To our knowledge, this is the first report of radiationbeing associated with enhanced plaque pathology in an AD mouse model. In addition to disease acceleration, we observed that low HZE doses are able to cause cognitive impairment as measured by contextual fear conditioning and novel object recognition in APP/ PS1 tg mice (Fig. 1). While contextual fear conditioning and, to a certain extent, novel object recognition are dependent on an intact hippocampus, the cued tone 25331948 freezing response is thought to measure hippocampal independent memory [34,35]. The lack of impairment in tone mediated freezing demonstrates that the cognitive dysfunction we observe can be, at least in part, traced to hippocampal mediated memory processes. This is consistent with other reports on the effect of radiation impacting hippocampal dependent memory [7,36]. Because we did not run parallel studies with wild-type control mice, we do not know whether cognitive impairment resulted from radiation alone or represented a synergy between radiation and mutant AD gene expression in these mice. HZE irradiation alone can lead to cognitive deficits in wild-type mice [7]; however, the only report of deficits in contextual fear conditioning or novel object recognition with C57BL/6 mice required 200 or 300 cGy iron [37]. Unfortunately, differences in mouse strain, timing, and radiation beam energy limit our ability to extrapolate from these studies. Multiple possible radiation induced effects might contribute to cognitive dysfunction in our model. One example is a defect inSpace Radiation Promotes Alzheimer PathologyFigure 2. Immunohistochemical staining for Congo red and 6E10 increases after 56Fe particle irradiation. (A, C) Representative images of half male brains stained for Congo red (A) or 6E10 (C) 6 months after 0 cGy or 100 cGy 56Fe particle radiation. Scale bar is 1 mm. (B, D) Quantitative measurement of percent plaque area assessed with Congo red (B) and 6E10 (D). In addition, total number of individual 6E10 positive plaques (E) and the average size of plaques (mm2) (F) was determined. Each dot represents a single animal measured as percent area of the cortex and hippocampus combined. Data was analyzed with Student’s t-test for the females and one-way ANOVA with a Bonferroni post test for the males. Data displayed as mean 6 SD, n = 8?4 animals per dose. *P,.05, **P,.01. doi:10.1371/journal.pone.0053275.gneurogenesis, which has been documented in response to traditional radiotherapy [38] as well as exposure to 56Fe particles [5,7,39]. In addition to neuronal proliferation defects, impaired cognition couldalso result from inhibition of long-term potentiation (LTP) [40], an effect which has been reported with 56Fe particle irradiation in the APP23 transgenic mouse model of AD [41].Space R.
