Using genetically engineered mice for radiation research

The laboratory mouse has been used for many decades as a model system for radiation research. Recent advances in genetic engineering now allow scientists to delete genes in specific cell types at different stages of development. The ability to manipulate genes in the mouse with spatial and temporal control opens new opportunities to investigate the role of genes in regulating the response of normal tissues and tumors to radiation. Currently, we are using the Cre-loxP system to delete genes, such as p53, in a cell-type specific manner in mice to study mechanisms of acute radiation injury and late effects of radiation. Our results demonstrate that p53 is required in the gastrointestinal (GI) epithelium to prevent radiation-induced GI syndrome and in endothelial and/or hematopoietic cells to prevent late effects of radiation. We have also used these genetic tools to generate primary tumors in mice to study tumor response to radiation therapy. These advances in genetic engineering provide a powerful model system to dissect both the mechanisms of normal tissue injury after irradiation and the mechanisms by which radiation cures cancer.     

Upregulation and nuclear translocation of testicular ghrelin protects differentiating spermatogonia from ionizing radiation injury

Proper control of apoptotic signaling is important for maintenance of testicular homeostasis after ionizing radiation (IR). Herein, we challenged the hypothesis that ghrelin, a pleiotropic modulator, is potentially involved in IR-induced germ cell injury. Lower body exposure to 2 Gy of IR induced a notable increase of ghrelin expression in the nuclear of differentiating spermatogonia at defined stages, with an impairment in the Leydig cells (LCs)-expressing ghrelin. Unexpectedly, inhibition of the ghrelin pathway by intraperitoneal injection of a specific GHS-R1α antagonist enhanced spermatogonia elimination by apoptosis during the early recovery following IR, and thereafter resulted in impaired male fertility, suggesting that the anti-apoptotic effects of evoked ghrelin, although transient along testicular IR injury, have a profound influence on the post-injury recovery. In addition, inhibition of ghrelin signaling resulted in a significant increase in the intratesticular testosterone (T) level at the end of 21 days after IR, which should stimulate the spermatogenic recovery from surviving spermatogonia to a certain extent during the late stage. We further demonstrated that the upregulation and nuclear trafficking of ghrelin, elaborately regulated by IR-elicited antioxidant system in spermatogonia, may act through a p53-dependent mechanism. The elicitation of ghrelin expression by IR stress, the regulation of ghrelin expression by IR-induced oxidative stress and the interaction between p53 and ghrelin signaling during IR injury were confirmed in cultured spermatogonia. Hence, our results represent the first evidence in support of a radioprotective role of ghrelin in the differentiating spermatogonia. The acutely, delicate regulation of local-produced ghrelin appears to be a fine-tune mechanism modulating the balance between testicular homeostasis and early IR injury.     

Inhibition of Intestinal Epithelial Apoptosis Improves Survival in a Murine Model of Radiation Combined Injury

World conditions place large populations at risk from ionizing radiation (IR) from detonation of dirty bombs or nuclear devices. In a subgroup of patients, ionizing radiation exposure would be followed by a secondary infection. The effects of radiation combined injury are potentially more lethal than either insult in isolation. The purpose of this study was to determine mechanisms of mortality and possible therapeutic targets in radiation combined injury. Mice were exposed to IR with 2.5 Gray (Gy) followed four days later by intratracheal methicillin-resistant Staphylococcus aureus (MRSA). While either IR or MRSA alone yielded 100% survival, animals with radiation combined injury had 53% survival (p = 0.01). Compared to IR or MRSA alone, mice with radiation combined injury had increased gut apoptosis, local and systemic bacterial burden, decreased splenic CD4 T cells, CD8 T cells, B cells, NK cells, and dendritic cells, and increased BAL and systemic IL-6 and G-CSF. In contrast, radiation combined injury did not alter lymphocyte apoptosis, pulmonary injury, or intestinal proliferation compared to IR or MRSA alone. In light of the synergistic increase in gut apoptosis following radiation combined injury, transgenic mice that overexpress Bcl-2 in their intestine and wild type mice were subjected to IR followed by MRSA. Bcl-2 mice had decreased gut apoptosis and improved survival compared to WT mice (92% vs. 42%; p<0.01). These data demonstrate that radiation combined injury results in significantly higher mortality than could be predicted based upon either IR or MRSA infection alone, and that preventing gut apoptosis may be a potential therapeutic target.     

MiR-34a in age and tissue related radio-sensitivity and serum miR-34a as a novel indicator of radiation injury

MiR-34a, a direct target of p53, has shown to exert potent anti-proliferative effects. It has also been found that miR-34a can be induced by irradiation in vitro and in vivo. However, the relationship between miR-34a and radio-sensitivity, and its potential diagnostic significance in radiation biology, remain unclear. This study found that differing responses to ionizing radiation (IR) of young and adult mice were related to miR-34a. First, we found that miR-34a could be induced in many organs by radiation of both young and adult mice. However, the level of miR-34a induced by young mice was much higher when compared to adult mice. Next, we found that miR-34a played a critical role in radio-sensitivity variations of different tissues by enhancing cell apoptosis and decreasing cell viability. We also found that the induction of miR-34a by radiation was in a p53 dependent manner and that one possible downstream target of miR-34a that lead to different radio-sensitivity was the anti-apoptosis molecular Bcl-2. However, over-expression of miR-34a and knockdown of Bcl-2 could significantly enhance the radio-sensitivity of different cells while inhibition of miR-34a could protect cells from radiation injury. Finally, we concluded that miR-34a could be stable in serum after IR and serve as a novel indicator of radiation injury. Taken together, this data strongly suggests that miR-34a may be a novel indicator, mediator and target of radiation injury, radio-sensitivity and radioprotection.     

Induction of genetic instability by ionizing radiation

Evidence is presented to support the hypothesis that radiation may induce a heritable, genome-wide process of instability that leads to an enhanced frequency of genetic changes occurring among the progeny of the original irradiated cell. This instability is transmissible over many generations of cell replication. Mutational instability is induced in a relatively large fraction (approximately 10%) of the cell population, and may be modulated by factors acting in vivo. Thus, it cannot be a targeted event involving a specific gene or set of genes. There is no dose-response relationship in the range 2-12 Gy, suggesting that the instability phenotype may be induced by quite low radiation doses. The molecular mechanisms associated with the genesis of mutations in unstable populations differ from those for direct X-ray-induced mutations. These results suggest that it may not be possible to predict the nature of the dose-response relationship for the ultimate genetic effects of radiation based on a qualitative or quantitative analysis of the original DNA lesions.     

Mutagenic adaptive response to high-LET radiation in human lymphoblastoid cells exposed to low doses of heavy-ion radiation

Adaptive response (AR) and bystander effect are two important phenomena involved in biological responses to low doses of ionizing radiation (IR). Furthermore, there is a strong interest in better understanding the biological effects of high-LET radiation. We previously demonstrated the ability of low doses of X-rays to induce an AR to challenging heavy-ion radiation [8]. In this study, we assessed in vitro the ability of priming low doses (0.01Gy) of heavy-ion radiation to induce a similar AR to a subsequent challenging dose (1-4Gy) of high-LET IR (carbon-ion: 20 and 40keV/μm, neon-ion: 150keV/μm) in TK6, AHH-1 and NH32 cells. Our results showed that low doses of high-LET radiation can induce an AR characterized by lower mutation frequencies at hypoxanthine-guanine phosphoribosyl transferase locus and faster DNA repair kinetics, in cells expressing p53.     

Effects of nonionizing radiation on birds

1. With the ability to fly comes a greater probability of direct irradiation by nonionizing radiation. The effect of nonionizing radiation on birds is, therefore, of environmental significance. 2. Most biological effects of exposure to nonionizing radiation in avian species are a result of radiation-induced temperature increases. 3. The incubating avian egg provides a model to study nonthermal effects of microwave exposure since ambient incubation temperature can be adjusted to compensate for absorbed thermal energy. 4. Some studies have shown that exposure to nonthermal levels of nonionizing radiation affect a bird's ability to recover from acute physiological stressors. 5. Although earlier research indicated that modulated radiofrequency radiation increased calcium-ion efflux in chick forebrain tissue, criticism of experimental techniques and contradictory results between related studies have made final conclusions elusive. 6. Birds have been shown to be able to reliably detect magnetic fields in both the field and laboratory. Some researchers have reported malformations in chicken embryos exposed to a sinusoidal bipolar oscillating magnetic field.     

Essential metalloelement metabolism and radiation protection and recovery.

Understanding the metabolism of essential metalloelements and their role in tissue maintenance and function as well as the roles of essential metalloelement-dependent enzymes in responding to injury offers a new approach to preventing and/or treating radiation injury. This review presents the roles of some essential metalloelement-dependent enzymes in the maintenance and function of tissues and their responses to radiation injury and gives an account of the observed effects of nontoxic doses of essential metalloelement compounds on protection against radiation damage and its recovery. The radiolysis of chemical bonds and free radicals derived from oxygen accounts for the acute and chronic aspects of radiation injury. The recognized biochemical roles of essential metalloelements and their observed pharmacological effects predict the therapeutic usefulness of essential metalloelement complexes in the prevention and/or treatment of radiation injury. Copper complexes have radiation protection and radiation recovery activities and cause rapid recovery of immunocompetence and radiation-induced damage to cells and tissues. Recently, iron, manganese, and zinc complexes have also been found to prevent death in lethally irradiated mice. These pharmacological effects of essential metalloelement complexes can be understood to be due to facilitation of de novo synthesis of essential metalloelement-dependent enzymes which have roles in preventing the accumulation of pathological concentrations of oxygen radicals or repairing damage caused by radiation-induced bond homolysis. Essential metalloelement complexes offer a physiological approach to prevention and/or treatment of radiation injury.     

冠状动脉内放射抑制球囊扩张术后ERK1/2活性及c-fos基因表达

本文旨在观察血管内放射对冠状动脉球囊扩张术后细胞外信号调节激酶１／２（ＥＲＫ１／２）及ｃ－ｆｏｓ基因表达的影响。实验对猪的左冠状动脉前降支或回旋支行球囊行过度扩张术,术后即刻能过血管内放射治疗系统对猪冠状动脉损伤局部给予２０Ｇｙ的放射剂量,分别是在术后３ｄ和３０ｄ处死动物,留取目标血管组织。通过反转录－聚合酶链反应定量检测血管内入射对球囊扩张术后血管组织ｃ－ｆｏｓ ｍＲＮＡ的表达,采用生化方法测定     

Cell cycle arrest determines the intensity of the global transcriptional response of Saccharomyces cerevisiae to ionizing radiation

Whole-genome analysis was performed using DNA microarrays to define the changes in the gene expression patterns occurring in Saccharomyces cerevisiae cells exposed to ionizing radiation. The effects of sublethal dose on wild-type, rad53 (enhanced sensitivity to radiation and impaired in a cell cycle damage checkpoint), and rad6 (enhanced sensitivity to radiation and functional cell cycle block by radiation) mutant backgrounds and of a higher dose on the wild-type and G(2)-phase-arrested cells were analyzed. Several gene pathways were identified as being implicated in the response to radiation. In particular, the cell cycle blockage that occurred in the wild-type strain after a high radiation dose and in the rad6 mutant after a lower dose entailed modifications of defined gene expression patterns, which are described here and are compared with the gene modulation patterns observed in the rad53 strain in the absence of efficient blockage. Loss of the RAD53 function caused a major increase in the number of genes modulated by radiation. Given that Rad53-Sad1p, the protein encoded by RAD53, has functions other than those directly connected to cell cycle arrest, we determined the gene patterns that were modulated upon irradiation of rad53 cells that had been forced to arrest in G(2) phase by nocodazole treatment. These differential whole-genome analyses shed light on the multiplicity of functions of the pivotal Rad53-Sad1p protein. The results obtained describe how the cells respond to different irradiation conditions by modulating important gene classes, including those associated with stress defense, ribosomal proteins, histones, ergosterol and GCR1-controlled sugar metabolism.