Age dependency of hepatic response to gamma-rays in B6C3F1 mice.

Background: With a rapid increase in the frequency of medical radiation exposure, radiation effects on the children have become a great concern in recent years. Therefore, firm evidences are required for radiation protection for medical exposure. It has been reported that neonatal B6C3F1 mice had high sensitivity of radiation-induction of liver tumors and life shortening compared with adult mice. However, little is known about the underlying mechanism of its high susceptibility. We hypothesize here that the unique characteristic response of neonatal hepatocytes to radiation may contribute to high susceptibility to radiation hepatocarcinogenesis. In this study, we aimed to investigate the normal development, focusing on proliferative activity of fetal, neonatal and adult livers histologically, and then to analyze the hepatocyte response to radiation in terms of cell cycle arrest and apoptosis. \nMaterials and Methods: For investigation of normal development of liver in B6C3F1 mice, the livers of mice at various ages, from 13-days post-conception (fetus) up to 10-week of age (adult), were analyzed histologically. For investigation of the age dependence of hepatocyte response to radiation, 17 days post-conception, 1-week-old (neonatal), and 7-week-old mice were whole-body irradiated with 4 Gy at a dose rate of gamma-rays from 137Cs. Subsequently, mice were killed at 0 (unirradiated), 1, 3, 6, 12, 24 and 48 hours. Then immunohistochemical analyses, using antibody against p53, Ki67, active caspase3, PCNA, and gamma-H2AX, were performed. BrdU and TUNEL analyses were also performed at 3 to 48h after irradiation.\nResults and Discussion: The liver proliferative status was dramatically changed during development from fetus to adult stage. There were many active proliferaive hepatic cells as well as hematopoietic cells in the fetal livers. Immature bile ducts and hepatic cords were formed at 1 week of age. At 7 weeks of age, matured hepatic cells were morphologically fully developed. We here found that radiation responses, in terms of cell cycle arrest and induction of apoptosis, were different among fetus, neonatal and adult hepatocytes. In fetal hepatocytes, p53 was accumulated soon after irradiation, which was followed by cell cycle arrest and apoptosis. In adult hepatocytes, which are rarely proliferating, there showed few apoptotosis after irradiation. In great contrast, the neonatal hepatocytes showed, surprisingly, the few apoptotosis after irradiation and continued proliferation. The resistance to apoptosis and continued proliferation may contribute to the accumulation of damaged cells, which may lead to high susceptibility to radiation tumorigenesis.The 3rd JCA-AACR Special Joint Conferenc

Radiation exposure enhances hepatocyte proliferation in neonatal mice but not in adult mice

Intuitively, irradiation of an infant organ before it undergoes development-related expansion would be expected to confer greater cancer risk than irradiation of a fully-developed adult tissue, and this is generally observed. However, if tissues also vary in their initial responses to radiation depending on age, the interplay between tissue- and age-dependent risk would potentially be quite complex. We have previously shown opposing age-dependent induction of apoptosis for the intestinal epithelium and hematopoietic cells in mice, but such data are not yet available for the liver. Here, we have examined markers of DNA damage, initiation of DNA damage responses, cell cycle arrest, apoptosis and proliferation, as well as gene expression, in the B6C3F1 mouse liver over the hours and days following irradiation of mice at 1 or 7 weeks of age. We found that induction and resolution of radiation-induced DNA damage is not accompanied by significant changes in these cellular endpoints in the adult liver, while in infant hepatocytes modest induction of p53 accumulation and p21-mediated cell cycle arrest in a small fraction of damaged cells was overshadowed by a further stimulation of proliferation over the relatively high levels already found in the neonatal liver. We observed distinct expression of genes which regulate cell division between the ages which may contribute to the differential responses. These data suggest that the growth factor signaling environment of the infant liver may mediate radiation-induced proliferation and increased liver cancer risk following irradiation during early life

Radiation response and cellular re-population kinetics of thymocytes in neonatal B6C3F1 mice.

Murine thymic lymphoma (TL) is a suitable model for studying the causative genes of human T-cell acute lymphoblastic leukemia (T-ALL) and radiation-lymphomagenesis. Risk of radiation-induced thymic lymphoma is dependent on the age at exposure. Incidence of thymic lymphoma after whole-body irradiation of neonate (one week-old) B6C3F1 mice is higher than that for adults (seven weeks of age). However, the mechanism(s) of susceptibility for neonates is unknown. In this study, we aimed to clarify age-dependent changes in thymocyte re-population kinetics and cellular responses to radiation, to shed light on the age effect for radiation carcinogenesis. After 4 Gy whole-body gamma-irradiation, the total number of thymocytes dramatically decreased and then increased in two waves. Cellular re-population especially CD4-CD8- cells was more immediate after neonate irradiation (day 4-10, day 14-25) than after adult irradiation (day 5-10, day 23-35). Apoptosis was delayed in neonates (6 h after irradiation) compared to adults (3 h), but cell proliferation persisted longer in neonates (6 h) than in adults (3 h). These differences in radiation response and recovery of thymocytes after irradiation may account for in part the higher susceptibility of the neonatal thymus to radiation carcinogenesis.6th International Workshop of Kyoto T Cell Conferenc

Novel Virulent Bacteriophage ΦSG005, Which Infects Streptococcus gordonii, Forms a Distinct Clade among Streptococcus Viruses

Bacteriophages are viruses that specifically infect bacteria and are classified as either virulent phages or temperate phages. Despite virulent phages being promising antimicrobial agents due to their bactericidal effects, the implementation of phage therapy depends on the availability of virulent phages against target bacteria. Notably, virulent phages of Streptococcus gordonii, which resides in the oral cavity and is an opportunistic pathogen that can cause periodontitis and endocarditis have previously never been found. We thus attempted to isolate virulent phages against S. gordonii. In the present study, we report for the first time a virulent bacteriophage against S. gordonii, ΦSG005, discovered from drainage water. ΦSG005 is composed of a short, non-contractile tail and a long head, revealing Podoviridae characteristics via electron microscopic analysis. In turbidity reduction assays, ΦSG005 showed efficient bactericidal effects on S. gordonii. Whole-genome sequencing showed that the virus has a DNA genome of 16,127 bp with 21 coding sequences. We identified no prophage-related elements such as integrase in the ΦSG005 genome, demonstrating that the virus is a virulent phage. Phylogenetic analysis indicated that ΦSG005 forms a distinct clade among the streptococcus viruses and is positioned next to streptococcus virus C1. Molecular characterization revealed the presence of an anti-CRISPR (Acr) IIA5-like protein in the ΦSG005 genome. These findings facilitate our understanding of streptococcus viruses and advance the development of phage therapy against S. gordonii infection

Lifespan shortening after exposure of mice at fetal, childhood and adulthood periods to gamma-rays and carbon ions

Background: There are insufficient data at present on cancer risk after exposure of heavy ions, to the fetal and childhood periods. Using animal models, we studied the age-at-exposure effects of heavy ions on cancer induction and lifespan shortening for radiation protection for fetuses and children. \nMaterials and Methods: Fifty female and male B6C3F1 mice per group were exposed to gamma rays (137Cs) or carbon ions (13 keV/µm) at various ages from fetal to mature adulthood periods. Mouse ages at the time of irradiation included pre-implantation (3 days post-conception (dpc)), major organogenesis (13 dpc), late fetal (17 dpc), neonatal (1 week after birth), infantile (3 weeks), young adulthood (7 weeks) and mature adulthood stages (15 weeks). The doses ranged between 0.2 and 4 Gy for gamma rays and 0.2 and 2 Gy for carbon ions. The mice were observed until moribund and their lifespan and the developed cancers were analyzed.\nResults and Discussion: Our study indicated that female mice appeared to be more susceptible to radiation-induced lifespan shortening than male mice. Effect of gamma-rays on lifespan shortening was more manifested when irradiated at neonatal than adult stage. Surprisingly, irradiation with gamma rays at the late fetal stage had little influence on lifespan shortening compared to infant and adulthood exposures. On the other hand, carbon ions were more potent in reducing lifespan than gamma rays when female neonatal mice were exposed. When carbon ions were exposed, however, fetuses were as susceptible as infants. The results on the lifespan shortening suggest a larger RBE of carbon ions for fetuses than later stages. The RBE of carbon ions for reducing the tumor-free survival rate was ~1.0 for fetuses, suggesting that RBE of 13keV/µm carbon for cancer induction is 1.0 ~ 1.5 irrespective of age-at-exposure.14th International Congress of Radiation Researc

Novel Virulent Bacteriophage ΦSG005, Which Infects Streptococcus gordonii, Forms a Distinct Clade among Streptococcus Viruses

Bacteriophages are viruses that specifically infect bacteria and are classified as either virulent phages or temperate phages. Despite virulent phages being promising antimicrobial agents due to their bactericidal effects, the implementation of phage therapy depends on the availability of virulent phages against target bacteria. Notably, virulent phages of Streptococcus gordonii, which resides in the oral cavity and is an opportunistic pathogen that can cause periodontitis and endocarditis have previously never been found. We thus attempted to isolate virulent phages against S. gordonii. In the present study, we report for the first time a virulent bacteriophage against S. gordonii, ΦSG005, discovered from drainage water. ΦSG005 is composed of a short, non-contractile tail and a long head, revealing Podoviridae characteristics via electron microscopic analysis. In turbidity reduction assays, ΦSG005 showed efficient bactericidal effects on S. gordonii. Whole-genome sequencing showed that the virus has a DNA genome of 16,127 bp with 21 coding sequences. We identified no prophage-related elements such as integrase in the ΦSG005 genome, demonstrating that the virus is a virulent phage. Phylogenetic analysis indicated that ΦSG005 forms a distinct clade among the streptococcus viruses and is positioned next to streptococcus virus C1. Molecular characterization revealed the presence of an anti-CRISPR (Acr) IIA5-like protein in the ΦSG005 genome. These findings facilitate our understanding of streptococcus viruses and advance the development of phage therapy against S. gordonii infection