Clonal deletion of T cell repertoires with specific T cell receptor Vβ chains by two endogenous superantigens in NC/Nga mice

<p>Superantigens (SAgs) are powerful T-cell stimulatory proteins. Because an atopic dermatitis (AD) model NC/Nga mice had two endogenous SAgs, namely <i>minor lymphocyte-stimulating locus-1</i>^<i>a</i> <i>(Mls-1</i>^<i>a</i><i>)</i> and <i>mouse mammary tumor virus (MMTV)(SHN)</i>, SAg-responsive T-cells bearing Vβ5.1, Vβ6, Vβ8.1, Vβ8.2, Vβ8.3, Vβ9, and Vβ11 should be endogenously deleted. Here, we discuss that the endogenous SAgs-expression may be involved in AD-sensitivity in NC/Nga mice.</p

The Maximal Protection by DMSO of Mammalian Cells Exposed to Very High LET Radiations

To understand indirect action for high linear energy transfer (LET), we examined the radioprotection effects of dimethylsulfoxide (DMSO) on the cell killing for cells irradiated with very high LET heavy ions. Exponentially growing Chinese hamster V79 cells were exposed to low- and high-LET radiations. We estimated that a maximal protectable fraction from a regression lines in the reciprocal plots degree of radical scavenger against the concentration from the cell survival curves. The contribution of indirect action decreased with increasing LET, but remained at the very high LET region. The contribution of indirect action in the cell killing were 52, 39 and 32% at LET of 797, 1298 and 2106 keV/mm, respectively. When cell survival curves were analyzed by the linear-quadratic equation, dependence of the DMSO concentration on the survival curve parameters were found. The quadratic (b) term depends on DMSO concentration in X-rays, and the linear (a) term depends on that in the very high LET radiation. The results suggest that an indirect action to cell killing results from a double-event mechanism in X-rays, and from a single-event mechanism in the very high LET radiation.13th international Congress of Radiation Researc

Heavy-ion-induced mutations in the gpt delta transgenic mouse: Effect of p53 gene knockout

The influence of the loss of p53 gene on heavy-ion-induced mutations was examined by constructing a new line of transgenic mice, p53 knockout (p53-/-) gpt delta. In this mouse model, deletions in lambda DNA integrated into the mouse genome are preferentially selected as Spi- phages, which can then be subjected to molecular analysis. Mice were exposed to 10 Gy of whole-body carbon-ion irradiation. The carbon ions were accelerated to 135 MeV/u by the RIKEN Ring Cyclotron. The p53 defect markedly enhanced the Spi- mutant frequency (MF) in the kidneys of mice exposed to C-ion irradiation: the Spi- MF increased 4.4- and 2.8-fold over the background level after irradiation in p53-/- and p53+/+ mice, respectively. There was no significant difference in the background Spi- MF between p53-/- and p53+/+ mice. Sequence analysis of the Spi- mutants indicated that the enhancement of kidney Spi- MF in p53-/- mice was primarily due to an increase in complex or rearranged-type deletions. In contrast to the kidney, the p53 defect had no effect on the Spi- MF in liver: Spi- MF increased 3.0- and 2.7-fold after the irradiation in p53-/- and p53+/+ mice, respectively. Our results suggest that p53 suppresses deletion mutations induced by heavy-ion irradiation in an organ-specific manner

Cooperative interaction among BMAL1, HSF1, and p53 protects mammalian cells from UV stress

The circadian clock allows physiological systems to adapt to their changing environment by synchronizing their timings in response to external stimuli. Previously, we reported clock- controlled adaptive responses to heat-shock and oxidative stress and showed how the cir- cadian clock interacts with BMAL1 and HSF1. Here, we present a similar clock-controlled adaptation to UV damage. In response to UV irradiation, HSF1 and tumor suppressor p53 regulate the expression of the clock gene Per2 in a time-dependent manner. UV irradiation first activates the HSF1 pathway, which subsequently activates the p53 pathway. Importantly, BMAL1 regulates both HSF1 and p53 through the BMAL1–HSF1 interaction to synchronize the cellular clock. Based on these findings and transcriptome analysis, we propose that the circadian clock protects cells against the UV stress through sequential and hierarchical interactions between the circadian clock, the heat shock response, and a tumor suppressive mechanism

In vivo TSPO and cannabinoid receptor type 2 availability early in post-stroke neuroinflammation in rats: a positron emission tomography study

Abstract Background Upregulated levels of 18-kDa translocator proteins (TSPO) and type 2 endocannabinoid receptors (CB2) are considered to reflect different aspects of microglia-related neuroinflammatory responses in the brain. Relative to the increase in the TSPO expression that occurs slightly later during neuroinflammation in a proinflammatory fashion, CB2 activation is considered to relate to the neuroprotective responses that occurs predominantly at an early stage of brain disorders. These findings, however, were deduced from studies with different animal samples under different experimental settings. Here, we aimed to examined the differences in TSPO binding and CB2 availability at an early stage of stroke in the same animal using positron emission tomography (PET). Methods We used a total of eight Sprague-Dawley rats that underwent photothrombotic stroke surgery. The binding levels of a TSPO tracer [11C](R)PK11195 and a CB2 tracer [11C]NE40 were measured at 24 h after the surgery in the same animal using PET in combination with immunohistochemistry for CB2 and several other markers. A morphological inspection was also performed with X-ray computed tomography for small animals. Results The levels of [11C]NE40 binding potential (BPND) were significantly higher in the cerebral cortical region on the lesion side than those on the non-lesion side, whereas no difference was found in the levels of [11C](R)PK11195 BPND between hemispheres. The tracer influx index (R1) data were all reduced on the lesion side irrespective of tracers. This increase in [11C]NE40 BPND was concomitant with an elevation in CB2 expression mainly within the microglia in the peri-infarct area, as shown by immunohistochemical examinations with Iba-1, CD11b/c+, and NG2+ staining. Conclusions The present results provide in vivo evidence of different responses of microglia occurring in the acute state of stroke. The use of the CB2 tracer [11C]NE40 allows us to evaluate the roles played by the neuroprotective aspect of microglia in acute neuroinflammatory processes

Contributions of Direct and Indirect Actions in Cell Killing by High-LET Radiations

Biological effects of radiation originate principally in damages to DNA. DNA damages by X-rays as well as heavy ions are induced by a combination of direct and indirect actions. The contribution of indirect action in cell killing can be estimated from the maximum degree of protection by dimethylsulfoxide (DMSO) which suppresses indirect action without affecting the direct one. Exponentially growing Chinese hamster V79 cells were exposed to high LET radiations of 20 to 2106 keV/micrometer in the presence or absence of DMSO and their colony survival was determined. The contribution of indirect action in cell killing decreased with the increase in the LET. However, the contribution did not reach to zero even at very high LETs and was estimated to be 32% at an LET of 2106 keV/micrometer. Therefore, even though the radiochemically estimated G value of OH radicals was nearly zero at an LET of 1000 keV/micrometer, indirect action by OH radicals contributed to a substantial fraction of biological effects of high LET radiations. A RBE determined at a survival level of 10% increased with LET, reaching a maximum value of 2.88 at 200 keV/micrometer, and decreased thereafter. When the RBE was estimated separately for direct action (RBED) and indirect action (RBEI), both of them exhibited a similar LET dependency as the RBE, peaking at 200 keV/micrometer. However, the peak value was much higher for RBED (5.99) than RBEI (1.89). Thus, direct action contributes more to the high RBE of high LET radiations than indirect action does