Acceleration of astrocytic differentiation in neural stem cells surviving X-irradiation

Transgenerational effects of gamma radiation dose and dose rate on Drosophila flies irradiated at an early embryonal stage

Ionizing radiation (IR) kills cells mainly through induction of DNA damages and the surviving cells may suffer from mutations. Transgenerational effects of IR are well documented, but the exact mechanisms underlying them are less well understood; they include induction of mutations in germ cells and epigenetic inheritance. Previously, effects in the offspring of mice and zebrafish exposed to IR have been reported. A few studies also showed indications of transgenerational effects of radiation in humans, particularly in nuclear power workers. In the present project, short- and long-term effects of low-dose-rate (LDR; 50 and 97 mGy/h) and high-dose-rate (HDR; 23.4, 47.1 and 495 Gy/h) IR in Drosophila embryos were investigated. The embryos were irradiated at different doses and dose rates and radiosensitivity at different developmental stages was investigated. Also, the survival of larvae, pupae and adults developed from embryos irradiated at an early stage (30 min after egg laying) were studied. The larval crawling and pupation height assays were applied to investigate radiation effects on larval locomotion and pupation behavior, respectively. In parallel, the offspring from 3 Gy irradiated early-stage embryos were followed up to 12 generations and abnormal phenotypes were studied. Acute exposure of embryos at different stages of development showed that the early stage embryo is the most sensitive. The effects on larval locomotion showed no significant differences between the dose rates but a significant decrease of locomotion activity above 7 Gy was observed. The results indicate that embryos exposed to the low dose rates have shorter eclosion times. At the same cumulative dose (1 up to 7 Gy), HDR is more embryotoxic than LDR. We also found a radiation-induced depigmentation on males (A5 segment of the dorsal abdomen, A5pig^-) that can be transmitted up to 12 generations. The phenomenon does not follow the classical Mendelian laws of segregation.

Species-specific developmental timing is maintained by pluripotent stem cells ex utero

How species-specific developmental timing is controlled is largely unknown. By following human embryonic stem (ES) cell and mouse epiblast stem (EpiS) cell differentiation through detailed RNA-sequencing time courses, here we show that pluripotent stem cells closely retain in vivo species-specific developmental timing in vitro. In identical neural differentiation conditions in vitro, gene expression profiles are accelerated in mouse EpiS cells compared to human ES cells with relative rates of differentiation closely reflecting the rates of progression through the Carnegie stages in utero. Dynamic Time Warping analysis identified 3389 genes that were regulated more quickly in mouse EpiS cells and identified none that were regulated more quickly in human ES cells. Interestingly, we also find that human ES cells differentiated in teratomas maintain the same rate of differentiation observed in vitro in spite of being grown in a mouse host. These results suggest the existence of a cell autonomous, species-specific developmental clock that pluripotent stem cells maintain even out of context of an intact embryo.

Dose-dependent short- and long-term effects of ionizing irradiation on neural stem cells in murine hippocampal tissue cultures: neuroprotective potential of resveratrol

INTRODUCTION

Radiation therapy plays an essential role in the treatment of brain tumors, but neurocognitive deficits remain a significant risk, especially in pediatric patients. In recent trials, hippocampal sparing techniques are applied to reduce these adverse effects. Here, we investigate dose-dependent effects of ionizing radiation (IR) on juvenile hippocampal neurogenesis. Additionally, we evaluate the radioprotective potential of resveratrol, a plant polyphenol recognized for its bifunctional tumor-preventive and anticancer effects.

METHODS

Organotypic entorhinal-hippocampal slice cultures from transgenic nestin-CFPnuc C57BL/J6 mice, postnatal days 3-6, were irradiated on a X-ray machine (4.5, 8, 12, and 16 Gy, single doses) after about 2 weeks. Nestin-positive neural stem cells were counted at a confocal live imaging microscope 0, 2, 4, 14, 25, and 42 days after IR. Resveratrol (15 μmol/L) was added 2 hr before and 24 hr after IR. Proliferation and cell death were assessed by BrdU pulse label, 48 hr after and by propidium iodide staining 96 hr after IR. GFAP- and NeuN-positive cells were counted 42 days after IR in cryosectioned immunofluorescence-stained slices.

RESULTS

The observed age-related changes of nestin-positive stem cells in the organotypic slice culture model resembled the reduction of neural stem cells in vivo. IR (4.5-16 Gy) led to a dose-dependent damage of the neural stem cell pool in the dentate gyrus. No recovery was seen within 42 days after doses from 4.5 Gy onward. The decline of nestin-positive cells was paralleled by increased cell death and decreased proliferation. The number of GFAP-positive cells was significantly enhanced. No significant change was detected in the overall NeuN-positive cell population, whereas the number of newborn, NeuN/BrdU double-positive neurons was reduced. Resveratrol treatment reversed the irradiation-induced decline of neural stem cells.

CONCLUSION

The neuroprotective action of resveratrol on irradiated hippocampal tissue warrants further investigation as a possible supplement to hippocampal sparing procedures.

Effect of Lycium bararum polysaccharides on methylmercury-induced abnormal differentiation of hippocampal stem cells

The aim of the present study was to observe the effects of a general extract of Lycium bararum polysaccharides (LBPs) on methylmercury (MeHg)-induced damage in hippocampus neural stem cells (hNSCs). The hippocampal tissues of embryonic day 16 Sprague-Dawley rats were extracted for the isolation, purification and cloning of hNSCs. Following passage and proliferation for 10 days, the cells were allocated at random into the following groups: Control, LBPs, MeHg and MeHg + LBPs. MTT and microtubule-associated protein 2 (MAP-2)/glial fibrillary acidic protein/Hoechst immunofluorescence tests were performed to detect the differentiation and growth of hNSCs in the various groups. The differentiation rate of MeHg-treated hNSCs and the perimeter of MAP-2-positive neurons were 3.632±0.63% and 62.36±5.58 µm, respectively, significantly lower compared with the control group values of 6.500±0.81% and 166±8.16 µm (P<0.05). Furthermore, the differentiation rate and the perimeter of MAP-2-positive neurons in LBPs groups cells was 7.75±0.59% and 253.3±11.21 µm, respectively, significantly higher compared with the control group (P<0.05). The same parameters in the MeHg + LBPs group were 5.92±0.98% and 111.9±6.07 µm, respectively, significantly higher than the MeHg group (P<0.05). The astrocyte differentiation rates in the MeHg and MeHg + LBPs group were 41.19±2.14 and 34.58±1.70, respectively (P<0.05). These results suggest that LBPs may promote the generation and development of new neurons and inhibit the MeHg-induced abnormal differentiation of astrocytes. Thus, LBPs may be considered to be a potential new treatment for MeHg-induced neurotoxicity in hNSCs.

Ionizing Radiation Induces Altered Neuronal Differentiation by mGluR1 through PI3K-STAT3 Signaling in C17.2 Mouse Neural Stem-Like Cells

Most studies of IR effects on neural cells and tissues in the brain are still focused on loss of neural stem cells. On the other hand, the effects of IR on neuronal differentiation and its implication in IR-induced brain damage are not well defined. To investigate the effects of IR on C17.2 mouse neural stem-like cells and mouse primary neural stem cells, neurite outgrowth and expression of neuronal markers and neuronal function-related genes were examined. To understand this process, the signaling pathways including PI3K, STAT3, metabotrophic glutamate receptor 1 (mGluR1) and p53 were investigated. In C17.2 cells, irradiation significantly increased the neurite outgrowth, a morphological hallmark of neuronal differentiation, in a dose-dependent manner. Also, the expression levels of neuronal marker proteins, β-III tubulin were increased by IR. To investigate whether IR-induced differentiation is normal, the expression of neuronal function-related genes including synaptophysin, a synaptic vesicle forming proteins, synaptotagmin1, a calcium ion sensor, γ-aminobutyric acid (GABA) receptors, inhibitory neurotransmitter receptors and glutamate receptors, excitatory neurotransmitter receptors was examined and compared to that of neurotrophin-stimulated differentiation. IR increased the expression of synaptophysin, synaptotagmin1 and GABA receptors mRNA similarly to normal differentiation by stimulation of neurotrophin. Interestingly, the overall expression of glutamate receptors was significantly higher in irradiated group than normal differentiation group, suggesting that the IR-induced neuronal differentiation may cause altered neuronal function in C17.2 cells. Next, the molecular mechanism of the altered neuronal differentiation induced by IR was studied by investigating signaling pathways including p53, mGluR1, STAT3 and PI3K. Increases of neurite outgrowth, neuronal marker and neuronal function-related gene expressions by IR were abolished by inhibition of p53, mGluR-1, STAT3 or PI3K. The inhibition of PI3K blocked both p53 signaling and STAT3-mGluR1 signaling but inhibition of p53 did not affect STAT3-mGluR1 signaling in irradiated C17.2 cells. Finally, these results of the IR-induced altered differentiation in C17.2 cells were verified in ex vivo experiments using mouse primary neural stem cells. In conclusion, the results of this study demonstrated that IR is able to trigger the altered neuronal differentiation in undifferentiated neural stem-like cells through PI3K-STAT3-mGluR1 and PI3K-p53 signaling. It is suggested that the IR-induced altered neuronal differentiation may play a role in the brain dysfunction caused by IR.

CD99 regulates neural differentiation of Ewing sarcoma cells through miR-34a-Notch-mediated control of NF-κB signaling

Sarcomas are mesenchymal tumors characterized by blocked differentiation process. In Ewing sarcoma (EWS) both CD99 and EWS-FLI1 concur to oncogenesis and inhibition of differentiation. Here, we demonstrate that uncoupling CD99 from EWS-FLI1 by silencing the former, nuclear factor-κB (NF-κB) signaling is inhibited and the neural differentiation program is re-established. NF-κB inhibition passes through miR-34a-mediated repression of Notch pathway. CD99 counteracts EWS-FLI1 in controlling NF-κB signaling through the miR-34a, which is increased and secreted into exosomes released by CD99-silenced EWS cells. Delivery of exosomes from CD99-silenced cells was sufficient to induce neural differentiation in recipient EWS cells through miR-34a inhibition of Notch-NF-κB signaling. Notably, even the partial delivery of CD99 small interfering RNA may have a broad effect on the entire tumor cell population owing to the spread operated by their miR-34a-enriched exosomes, a feature opening to a new therapeutic option.

Radiation responses of stem cells: targeted and non-targeted effects

Stem cells are fundamental to the development of any tissue or organism via their ability to self-renew, which is aided by their unlimited proliferative capacity and their ability to produce fully differentiated offspring, often from multiple lineages. Stems cells are long lived and have the potential to accumulate mutations, including in response to radiation exposure. It is thought that stem cells have the potential to be induced into a cancer stem cell phenotype and that these may play an important role in resistance to radiotherapy. For radiation-induced carcinogenesis, the role of targeted and non-targeted effects is unclear with tissue or origin being important. Studies of genomic instability and bystander responses have shown consistent effects in haematopoietic models. Several models of radiation have predicted that stem cells play an important role in tumour initiation and that bystander responses could play a role in proliferation and self-renewal.

The cognitive defects of neonatally irradiated mice are accompanied by changed synaptic plasticity, adult neurogenesis and neuroinflammation

Background/purpose of the study

Epidemiological evidence suggests that low doses of ionising radiation (≤1.0 Gy) produce persistent alterations in cognition if the exposure occurs at a young age. The mechanisms underlying such alterations are unknown. We investigated the long-term effects of low doses of total body gamma radiation on neonatally exposed NMRI mice on the molecular and cellular level to elucidate neurodegeneration.

Results

Significant alterations in spontaneous behaviour were observed at 2 and 4 months following a single 0.5 or 1.0 Gy exposure. Alterations in the brain proteome, transcriptome, and several miRNAs were analysed 6–7 months post-irradiation in the hippocampus, dentate gyrus (DG) and cortex. Signalling pathways related to synaptic actin remodelling such as the Rac1-Cofilin pathway were altered in the cortex and hippocampus. Further, synaptic proteins MAP-2 and PSD-95 were increased in the DG and hippocampus (1.0 Gy). The expression of synaptic plasticity genes Arc, c-Fos and CREB was persistently reduced at 1.0 Gy in the hippocampus and cortex. These changes were coupled to epigenetic modulation via increased levels of microRNAs (miR-132/miR-212, miR-134). Astrogliosis, activation of insulin-growth factor/insulin signalling and increased level of microglial cytokine TNFα indicated radiation-induced neuroinflammation. In addition, adult neurogenesis within the DG was persistently negatively affected after irradiation, particularly at 1.0 Gy.

Conclusion

These data suggest that neurocognitive disorders may be induced in adults when exposed at a young age to low and moderate cranial doses of radiation. This raises concerns about radiation safety standards and regulatory practices.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-57) contains supplementary material, which is available to authorized users.

Hematopoietic stem cell injury induced by ionizing radiation

SIGNIFICANCE

Exposure to ionizing radiation (IR) as the result of nuclear accidents or terrorist attacks is a significant threat and a major medical concern. Hematopoietic stem cell (HSC) injury is the primary cause of death after accidental or intentional exposure to a moderate or high dose of IR. Protecting HSCs from IR should be a primary goal in the development of novel medical countermeasures against radiation.

RECENT ADVANCES

Significant progress has been made in our understanding of the mechanisms by which IR causes HSC damage. The mechanisms include (i) induction of HSC apoptosis via the p53-Puma pathway; (ii) promotion of HSC differentiation via the activation of the G-CSF/Stat3/BATF-dependent differentiation checkpoint; (iii) induction of HSC senescence via the ROS-p38 pathway; and (iv) damage to the HSC niche.

CRITICAL ISSUES

Induction of apoptosis in HSCs and hematopoietic progenitor cells is primarily responsible for IR-induced acute bone marrow (BM) injury. Long-term BM suppression caused by IR is mainly attributable to the induction of HSC senescence. However, the promotion of HSC differentiation and damage to the HSC niche can contribute to both the acute and long-term effects of IR on the hematopoietic system.

FUTURE DIRECTIONS

In this review, we have summarized a number of recent findings that provide new insights into the mechanisms whereby IR damages HSCs. These findings will provide new opportunities for developing a mechanism-based strategy to prevent and/or mitigate IR-induced BM suppression. Antioxid.

Smac mimetic promotes glioblastoma cancer stem-like cell differentiation by activating NF-κB

Recently, a broader role of inhibitor of apoptosis (IAP) proteins besides their antiapoptotic functions has been described. Therefore, we investigated the effect of non-toxic concentrations of the small-molecule Smac mimetic BV6, which antagonizes IAP proteins, on differentiation of cancer stem-like cells (CSLCs) derived from primary glioblastoma (GBM) specimens. Here, we identify a novel function of BV6 in regulating differentiation of GBM CSLCs by activating NF-κB. BV6 at non-lethal doses stimulates morphological changes associated with the differentiation of GBM CSLCs. BV6 increases transcriptional activity, mRNA and protein levels of the astrocytic marker GFAP without altering expression of the neuronal marker β-III-tubulin, indicating that BV6 induces astrocytic differentiation of GBM CSLCs. Molecular studies reveal that BV6 triggers processing of the NF-κB subunit p100 to p52, nuclear translocation of p52 and p50 and increased NF-κB DNA-binding. Intriguingly, inhibition of NF-κB by overexpression of dominant-negative IκBα super-repressor (IκBα-SR) blocks the BV6-stimulated increase in GFAP and differentiation. Interestingly, this BV6-stimulated differentiation is associated with reduced expression of stemness markers such as CD133, Nanog and Sox2 in GBM CSLCs. In contrast, BV6 does not alter cell morphology, differentiation and expression of stemness markers in non-malignant neural stem cells. Importantly, BV6 treatment reduces clonogenicity of GBM CSLCs in vitro and in vivo, suppresses their tumorigenicity in orthotopic and subcutaneous mouse models and significantly increases the survival of mice. By identifying a novel role of BV6 in promoting differentiation of GBM CSLCs, these findings provide new insights into Smac mimetic-regulated non-apoptotic functions with important implications for targeting GBM CSLCs.

Radiation-Induced Bystander Response: Mechanism and Clinical Implications

Significance: Absorption of energy from ionizing radiation (IR) to the genetic material in the cell gives rise to damage to DNA in a dose-dependent manner. There are two types of DNA damage; by a high dose (causing acute or deterministic effects) and by a low dose (related to chronic or stochastic effects), both of which induce different health effects. Among radiation effects, acute cutaneous radiation syndrome results from cell killing as a consequence of high-dose exposure. Recent advances: Recent advances in radiation biology and oncology have demonstrated that bystander effects, which are emerged in cells that have never been exposed, but neighboring irradiated cells, are also involved in radiation effects. Bystander effects are now recognized as an indispensable component of tissue response related to deleterious effects of IR. Critical issues: Evidence has indicated that nonapoptotic premature senescence is commonly observed in various tissues and organs. Senesced cells were found to secrete various proteins, including cytokines, chemokines, and growth factors, most of which are equivalent to those identified as bystander factors. Secreted factors could trigger cell proliferation, angiogenesis, cell migration, inflammatory response, etc., which provide a tissue microenvironment assisting tissue repair and remodeling. Future directions: Understandings of the mechanisms and physiological relevance of radiation-induced bystander effects are quite essential for the beneficial control of wound healing and care. Further studies should extend our knowledge of the mechanisms of bystander effects and mode of cell death in response to IR.

FTY720, sphingosine 1-phosphate receptor modulator, selectively radioprotects hippocampal neural stem cells

Cranial irradiation is an effective treatment modality for both primary and metastatic brain tumors, yet it induces cognitive decline in a substantial number of patients. At present, there are no established methods for neuroprotection. Recent investigations have revealed a link between radiation-induced cognitive dysfunction and the loss of neural precursor cells in the hippocampus. Hence, identifying pharmacological agents, capable of protecting this cell population, is of interest. FTY720 (fingolimod), an FDA-approved oral drug for the treatment of multiple sclerosis, has been shown to promote the survival and differentiation of neural progenitors, as well as remyelination and repair after brain injury. In this study, we show that FTY720, used at nanomolar concentrations, is capable of increasing the viability and neurogenicity of irradiated neural stem cells from the hippocampus. In contrast, it does not provide radioprotection in a human breast cancer cell line and two glioma cell lines. These results suggest a potential therapeutic role for FTY720 as a neuroprotector during cranial irradiation. Further preclinical studies are warranted to evaluate this possibility.