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High-dose ionizing radiation is known to induce adverse effects such as inflammation and fibrosis in the heart. Transcriptional regulators PPARα and TGFβ are known to be involved in this radiation response. PPARα, an anti-inflammatory transcription factor controlling cardiac energy metabolism, is inactivated by irradiation. The pro-inflammatory and pro-fibrotic TGFβ is activated by irradiation via SMAD-dependent and SMAD-independent pathways. The goal of this study was to investigate how altering the level of PPARα influences the radiation response of these signaling pathways. For this purpose, we used genetically modified C57Bl/6 mice with wild type (+/+), heterozygous (+/−) or homozygous (−/−) PPARα genotype. Mice were locally irradiated to the heart using doses of 8 or 16 Gy; the controls were sham-irradiated. The heart tissue was investigated using label-free proteomics 20 weeks after the irradiation and the predicted pathways were validated using immunoblotting, ELISA, and immunohistochemistry. The heterozygous PPARα mice showed most radiation-induced changes in the cardiac proteome, whereas the homozygous PPARα mice showed the least changes. Irradiation induced SMAD-dependent TGFβ signaling independently of the PPARα status, but the presence of PPARα was necessary for the activation of the SMAD-independent pathway. These data indicate a central role of PPARα in cardiac response to ionizing radiation.

Neural stem cells are highly susceptible to radiogenic DNA damage, however, little is known about their mechanisms of DNA damage response (DDR) and the long‐term consequences of genotoxic exposure. Patched1heterozygous mice (Ptc1+/−) provide a powerful model of medulloblastoma (MB), a frequent pediatric tumor of the cerebellum. Irradiation of newborn Ptc1+/−mice dramatically increases the frequency and shortens the latency of MB. In this model, we investigated the mechanisms through which multipotent neural progenitors (NSCs) and fate‐restricted progenitor cells (PCs) of the cerebellum respond to DNA damage induced by radiation, and the long‐term developmental and oncogenic consequences. These responses were assessed in mice exposed to low (0.25 Gy) or high (3 Gy) radiation doses at embryonic day 13.5 (E13.5), when NSCs giving rise to the cerebellum are specified but the external granule layer (EGL) has not yet formed, or at E16.5, during the expansion of granule PCs to form the EGL. We found crucial differences in DDR and apoptosis between NSCs and fate‐restricted PCs, including lack of p21 expression in NSCs. NSCs also appear to be resistant to oncogenesis from low‐dose radiation exposure but more vulnerable at higher doses. In addition, the pathway to DNA repair and the pattern of oncogenic alterations were strongly dependent on age at exposure, highlighting a differentiation‐stage specificity of DNA repair pathways in NSCs and PCs. These findings shed light on the mechanisms used by NSCs and PCs to maintain genome integrity during neurogenesis and may have important implications for radiation risk assessment and for development of targeted therapies against brain tumors. StemCells2013;31:2506–2516

The two-stage skin carcinogenesis model of initiation and promotion in Carcinogenesis-susceptible (Car-S) mice has been used to investigate the pathways of promotional activity of 12- O -tetradecanoylphorbol-13-acetate (TPA), a phorbol ester tumor promoter, and benzoyl peroxide (BzPo), a free radical-generating compound. To test whether distinct populations of 9,10-dimethyl-1,2-benzanthracene (DMBA)-initiated epidermal keratinocytes are responsive to the two promoters, tandem experiments were performed. DMBA-initiated Car-S mice were promoted twice weekly with maximal promoting doses of TPA or BzPo. When the number of papillomas/mouse reached a plateau, promotion in the TPA and BzPo groups was switched to BzPo or TPA, respectively, until achievement of a new plateau. Mice promoted with BzPo developed 11.0±1.3 papillomas/mouse and subsequent TPA promotion induced 13.8 additional papillomas, for a total of 24.8±2.1 papillomas/mouse. TPA-promoted mice developed 23.3±1.1 papillomas/mouse, and subsequent BzPo promotion for 91 days did not promote additional papillomas. Our results show a less than additive tumor response after sequential promotion with BzPo and TPA, or vice versa, indicating that the pathways of promotional activity of TPA and BzPo are interacting. While the final papilloma yield was similar at the end of the two tandem promotion experiments independently of promoter sequence, the percentage of mice developing carcinomas was significantly higher in mice that were promoted with BzPo in the first stage. No significant differences in the frequency and type of c-Ha- ras mutations were observed in TPA- and BzPo-promoted tumors, suggesting that promotion of DMBA-initiated cells by BzPo requires introduction of additional molecular alterations compared to TPA.

The herbicide dichlobenil (2,6-dichlorobenzonitrile) is a tissue-specific toxicant inducing necrosis in the olfactory mucosa. Transmission electron microscopy showed vacuolations (1 hr) and necrosis (4 hr) in the Bowman's glands following intraperitoneal injection of dichlobenil (25 mg/kg) in C57B1 mice, whereas no lesions were noted in the olfactory neuroepithelium at these timepoints. Twenty-four hr following injection (25 mg/kg), most of the lamina propria and the olfactory epithelium were severely damaged; the basal lamina, nerves, and blood vessels in the lamina propria, however, remained intact. Following a lower dose (12 mg/kg), the lesions were not as pronounced. The effects of dichlobenil (6, 12, and 25 mg/kg) on cell replication in the olfactory mucosa, as determined by incorporation of 3H-thymidine 3 days later, were more pronounced in the lamina propria than in the neuroepithelium and occurred at a lower dose in the lamina propria than in the neuroepithelium. Together these studies support the previous proposal that dichlobenil induces a primary damage in the Bowman's glands.

Copper is both an essential nutrient required for the activity of several enzymes and a toxic element able to catalyze free radical formation. Trichloroethylene (TCE) is a xenobiotic that generates epoxidic intermediates by bioactivation through the cytochrome P-450 system. In this study, the influence of a dietary copper imbalance on the TCE-induced lung damage was investigated. Weaning mice were fed copper-deficient, copper-sufficient, and copper-excessive diets. After 4 wk, mice were exposed for 30 min to 6,500 ppm of TCE and euthanatized 48 hr later. Lung damage in the TCE-treated mice consisted of vacuolations of Clara cells and was quantitatively evaluated by counting the vacuolated cells per micrometer of basal lamina. At the ultrastructural level, vacuolations appeared as the result of hydropic swelling of the endoplasmic reticulum cisternae. The copper-deficient mice presented the highest number of vacuolated Clara cells. These mice also showed alteration of the capillary endothelium and interstitium and decreased pulmonary copper-zinc-superoxide dismutase activity. Occurrence of oxidative stress in lungs of both copper-sufficient and copper-deficient mice following TCE treatment was indicated by a decrease in reduced glutathione and an increase in its oxidized form.

Pathbase (http://www.pathbase.net) is a web accessible database of histopathological images of laboratory mice, developed as a resource for the coding and archiving of data derived from the analysis of mutant or genetically engineered mice and their background strains. The metadata for the images, which allows retrieval and interoperability with other databases, is derived from a series of orthogonal ontologies and controlled vocabularies. One of these controlled vocabularies, MPATH, was developed by the Pathbase Consortium as a formal description of the content of mouse histopathological images. The database currently has over 1000 images on-line with 2000 more under curation and presents a paradigm for the development of future databases dedicated to aspects of experimental biology.