5-fluorouracil-induced histopathological changes in the central nervous system of rat fetuses

Time-course changes in 5-fluorouracil-induced neural progenitor cell damages in the developing rat brain

5-Fluorouracil (5-Fu) is a DNA-damaging agent and teratogenic in rodents. This study aimed to investigate its influence on neural progenitor cells (NPCs) in the developing fetal rat brain. Dams were intraperitoneally injected with 5-Fu (50 mg/kg b.w.) on gestation day 13 and its effects on fetal NPCs were observed from 3 to 72 hours after treatment (HAT), via periodic examination at six intervals. In NPCs of the fetal brain, the p53-labeling index (LI%) was markedly elevated at 3 HAT. Pyknosis and cleaved caspase-3-LI% also increased at 3 HAT, reaching peak values at 9 and 12 HAT. These parallel changes suggested the induction of apoptosis through a p53-mediated pathway. Pyknotic NPCs were distributed across the ventricular zone (VZ) of the telencephalic wall until 12 HAT, and became localized in the medial and dorsal layers at 12 and 48 HAT. Significant decreases in the numbers of mitotic NPCs and BrdU-LI% were noted from 3 HAT and 24 HAT, respectively. BrdU-positive NPCs were located in the ventral and middle layer at 24 and 48 HAT. p21-positive cells were detected at 12 and 24 HAT. The present results demonstrated that p53-mediated apoptosis was induced in all phases of the cell cycle of the NPCs in the early stage after 5-FU treatment. Furthermore, apoptosis of NPCs and suppression of cell proliferative activity are the events that take place in parallel leading to prominent reduction in the width of the telencephalic wall.

Ribosomal stress and Tp53-mediated neuronal apoptosis in response to capsid protein of the Zika virus

We report here that in rat and human neuroprogenitor cells as well as rat embryonic cortical neurons Zika virus (ZIKV) infection leads to ribosomal stress that is characterized by structural disruption of the nucleolus. The anti-nucleolar effects were most pronounced in postmitotic neurons. Moreover, in the latter system, nucleolar presence of ZIKV capsid protein (ZIKV-C) was associated with ribosomal stress and apoptosis. Deletion of 22 C-terminal residues of ZIKV-C prevented nucleolar localization, ribosomal stress and apoptosis. Consistent with a casual relationship between ZIKV-C-induced ribosomal stress and apoptosis, ZIKV-C-overexpressing neurons were protected by loss-of-function manipulations targeting the ribosomal stress effector Tp53 or knockdown of the ribosomal stress mediator RPL11. Finally, capsid protein of Dengue virus, but not West Nile virus, induced ribosomal stress and apoptosis. Thus, anti-nucleolar and pro-apoptotic effects of protein C are flavivirus-species specific. In the case of ZIKV, capsid protein-mediated ribosomal stress may contribute to neuronal death, neurodevelopmental disruption and microcephaly.

Comparative neurotoxicity screening in human iPSC-derived neural stem cells, neurons and astrocytes

Induced pluripotent stem cells (iPSC) and their differentiated derivatives offer a unique source of human primary cells for toxicity screens. Here, we report on the comparative cytotoxicity of 80 compounds (neurotoxicants, developmental neurotoxicants, and environmental compounds) in iPSC as well as isogenic iPSC-derived neural stem cells (NSC), neurons, and astrocytes. All compounds were tested over a 24-h period at 10 and 100 μM, in duplicate, with cytotoxicity measured using the MTT assay. Of the 80 compounds tested, 50 induced significant cytotoxicity in at least one cell type; per cell type, 32, 38, 46, and 41 induced significant cytotoxicity in iPSC, NSC, neurons, and astrocytes, respectively. Four compounds (valinomycin, 3,3',5,5'-tetrabromobisphenol, deltamethrin, and triphenyl phosphate) were cytotoxic in all four cell types. Retesting these compounds at 1, 10, and 100 μM using the same exposure protocol yielded consistent results as compared with the primary screen. Using rotenone, we extended the testing to seven additional iPSC lines of both genders; no substantial difference in the extent of cytotoxicity was detected among the cell lines. Finally, the cytotoxicity assay was simplified by measuring luciferase activity using lineage-specific luciferase reporter iPSC lines which were generated from the parental iPSC line. This article is part of a Special Issue entitled SI: PSC and the brain.

Effect of methotrexate on neuroepithelium in the rat fetal brain

Pregnant rats were treated with 30 mg/kg of methotrexate (MTX) on gestation day 13, and fetal brains were examined histopathologically from 6 to 48 hr after the treatment. In the telencephalon of the control group, there were few pyknotic neuroepithelial cells throughout the experimental period. Six hr after MTX treatment, several pyknotic neuroepithelial cells scattered throughout the telencephalic wall. At 12–36 hr, pyknotic neuroepithelial cells increased significantly and were diffusely distributed throughout the telencephalic wall. Neuroepithelial cells were eliminated and showed sparse cell density at 36 hr in the telencephalon. Almost all fetuses died at 48 hr. Most of the pyknotic neuroepithelial cells were positively stained by the TUNEL method and positive for cleaved caspase-3. While mitotic and phospho-histone H3-positive neuroepithelial cells were located along the ventricular layer of telencephalon in the control group, they were rarely observed in the same region at 6–36 hr in the MTX-treated group. MTX induced few pyknotic changes to neuroepithelial cells in the metencephalon, compared to other parts of brain. The distribution of apoptotic neuroepithelial cells and the time-course changes of the indices of apoptotic and mitotic neuroepithelial cells were different from those of other DNA-damaging chemicals reported previously. The difference may reflect the disparity in mechanisms of apoptosis and the inhibition of cell proliferation in neuroepithelial cells induced by MTX. To our knowledge, this is the first report demonstrating histopathological findings of fetal brain damage induced by MTX.

Distribution and sequence of pyknotic cells in rat fetuses exposed to busulfan

Busulfan, an antineoplastic bifunctional-alkylating agent, is known to induce developmental anomalies. In the present study, we examined the distribution and sequence of pyknotic cells in rat fetal tissues exposed to busulfan. Pregnant rats on gestation day 13 were administered intraperitoneally 30 mg/kg of busulfan, and fetal tissues were examined at 6, 12, 24, 36, 48, 72 and 96 hours after treatment (HAT). Pyknosis of component cells was observed markedly in the brain, moderately in the eyes and spinal cord and mildly in the craniofacial tissue, mandible, limb buds, tail bud, ganglions, alimentary tract, lungs, kidneys, pancreas and liver. In the brain, mitotic inhibition was also detected. Most of the pyknotic cells were considered to be apoptotic cells judging from the results of TUNEL staining and electron microscopic examination. Commonly in the above-mentioned tissues, pyknotic cells began to increase at 24 HAT, peaked at 36 or 48 HAT and disappeared at 96 HAT, which is when the histological picture returned to normal in most tissues except for the brain, spinal cord and eyes. The present study clarified the outline of busulfan-induced apoptosis in rat fetuses.