Development of a mito-CRISPR system for generating mitochondrial DNA-deleted strain in Saccharomyces cerevisiae

Mitochondrial dysfunction can occur in a variety of ways, most often due to the deletion or mutation of mitochondrial DNA (mtDNA). The easy generation of yeasts with mtDNA deletion is attractive for analyzing the functions of the mtDNA gene. Treatment of yeasts with ethidium bromide is a well-known method for generating ρ° cells with complete deletion of mtDNA from Saccharomyces cerevisiae. However, the mutagenic effects of ethidium bromide on the nuclear genome cannot be excluded. In this study, we developed a "mito-CRISPR system" that specifically generates ρ° cells of yeasts. This system enabled the specific cleavage of mtDNA by introducing Cas9 fused with the mitochondrial target sequence at the N-terminus and guide RNA into mitochondria, resulting in the specific generation of ρ° cells in yeasts. The mito-CRISPR system provides a concise technology for deleting mtDNA in yeasts.

Health risks of space exploration: targeted and nontargeted oxidative injury by high-charge and high-energy particles

SIGNIFICANCE

During deep space travel, astronauts are often exposed to high atomic number (Z) and high-energy (E) (high charge and high energy [HZE]) particles. On interaction with cells, these particles cause severe oxidative injury and result in unique biological responses. When cell populations are exposed to low fluences of HZE particles, a significant fraction of the cells are not traversed by a primary radiation track, and yet, oxidative stress induced in the targeted cells may spread to nearby bystander cells. The long-term effects are more complex because the oxidative effects persist in progeny of the targeted and affected bystander cells, which promote genomic instability and may increase the risk of age-related cancer and degenerative diseases.

RECENT ADVANCES

Greater understanding of the spatial and temporal features of reactive oxygen species bursts along the tracks of HZE particles, and the availability of facilities that can simulate exposure to space radiations have supported the characterization of oxidative stress from targeted and nontargeted effects.

CRITICAL ISSUES

The significance of secondary radiations generated from the interaction of the primary HZE particles with biological material and the mitigating effects of antioxidants on various cellular injuries are central to understanding nontargeted effects and alleviating tissue injury.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the cellular responses to HZE particles, particularly under reduced gravity and situations of exposure to additional radiations, such as protons, should be useful in reducing the uncertainty associated with current models for predicting long-term health risks of space radiation. These studies are also relevant to hadron therapy of cancer.

Effects of ionizing radiation on mitochondria

The current concept of radiobiology posits that damage to the DNA in the cell nucleus is the primary cause for the detrimental effects of radiation. However, emerging experimental evidence suggests that this theoretical framework is insufficient for describing extranuclear radiation effects, particularly the response of the mitochondria, an important site of extranuclear, coding DNA. Here, we discuss experimental observations of the effects of ionizing radiation on the mitochondria at (1) the DNA and (2) functional levels. The roles of mitochondria in (3) oxidative stress and (4) late radiation effects are discussed. In this review, we summarize the current understanding of targets for ionizing radiation outside the cell nucleus. Available experimental data suggest that an increase in the tumoricidal efficacy of radiation therapy might be achievable by targeting mitochondria. Likewise, more specific protection of mitochondria and its coding DNA should reduce damage to healthy cells exposed to ionizing radiation.

Prognostic value of mitochondrial DNA content and G10398A polymorphism in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer-related mortality worldwide. Mitochondrial dysfunction has been postulated to render cancer cells resistant to apoptosis based on the Warburg hypothesis. However, few studies have investigated the prognostic value of mitochondrial DNA (mtDNA) content and G10398A polymorphism in NSCLC patients. mtDNA copy number and G10398A polymorphism in 128 NSCLC tissue samples were assessed by real-time PCR (RT-PCR) and PCR-RFLP respectively, and their relationship to prognosis were analyzed by survival analysis and Cox proportional hazards model. In vitro, an mtDNA deletion A549 ρ(0) cell model was utilized to assess the function of mtDNA on radiosensitivity. Cell cycle distribution and reactive oxygen species (ROS) were analyzed to elucidate the potential mechanisms. For the whole group, the median follow-up time and overall survival time were 22.5 and 23.4 months, respectively. Patients with high mtDNA content had a marginally longer survival time than patients with low mtDNA content (P=0.053). Moreover, patients with high mtDNA content plus 10398G had a significantly longer overall survival time compared with those having low mtDNA content plus 10398A (47 vs. 27 months, P<0.05). In addition, multivariate analysis showed that stage and low mtDNA content plus 10398A were the two most independent prognostic factors. In vitro, the A549 ρ(0) cells showed more resistance to radiation than ρ(+) cells. Following radiation, ρ(0) cells showed delayed G2 arrest and lower ROS level as compared to ρ(+) cells. In conclusion, the present study suggests that in patients with NSCLC, low mtDNA content plus 10398A could be a marker of poor prognosis which is associated with resistance to anticancer treatment caused by low mtDNA content plus 10398A polymorphism resulting in mitochondrial dysfunction.

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.

Mitochondrial DNA depletion induces radioresistance by suppressing G2 checkpoint activation in human pancreatic cancer cells

We hypothesized that mitochondrial function regulates cell cycle checkpoint activation and radiosensitivity. Human pancreatic tumor cells (MiaPaCa-2, rho(+)) were depleted of mitochondrial DNA (rho degrees ) by culturing cells in the presence of ethidium bromide. Depletion of mitochondrial DNA was verified by PCR amplification of total DNA using primer pairs specific for mitochondrial DNA. Loss of mitochondrial DNA decreased plating efficiency and the percentage of cells in S phase. Exponential cultures were irradiated with 2, 4 and 6 Gy (dose rate: 0.83 Gy/min) of ionizing radiation and harvested for determination of cell viability, growth and cell cycle phase distributions. Rho degrees cells were radioresistant compared to rho(+) cells, with a dose-modifying factor (DMF) of 1.6. Although cell growth was significantly inhibited in irradiated rho(+) cells compared to unirradiated control cells, the inhibition in Rho degrees cells was minimal. In addition, mitochondrial DNA depletion suppressed radiation-induced G(2) checkpoint activation, which was accompanied by increases in both cyclin B1 and CDK1. These results suggest that mitochondrial function may regulate cell cycle checkpoint activation and radiosensitivity in pancreatic cancer cells.

Cytogenetic effects of low-dose radiation with different LET in human peripheral blood lymphocytes

Chromosome damage and the spectrum of aberrations induced by low doses of gamma-irradiation, X-rays and accelerated carbon ions (195 MeV/u, LET 16.6 keV/microm) in peripheral blood lymphocytes of four donors were studied. G0-lymphocytes were exposed to 1-100 cGy, stimulated by PHA, and analyzed for chromosome aberrations at 48 h post-irradiation by the metaphase method. A complex nonlinear dose-effect dependence was observed over the range of 1 to 50 cGy. At 1-7 cGy, the cells showed the highest radiosensitivity per unit dose (hypersensitivity, HRS), which was mainly due to chromatid-type aberration. According to the classical theory of aberration formation, chromatid-type aberrations should not be induced by irradiation of unstimulated lymphocytes. With increasing dose, the frequency of aberrations decreased significantly, and in some cases it even reached the control level. At above 50 cGy the dose-effect curves became linear. In this dose range, the frequency of chromatid aberrations remained at a low constant level, while the chromosome-type aberrations increased linearly with dose. The high yield of chromatid-type aberrations observed in our experiments at low doses confirms the idea that the molecular mechanisms which underlie the HRS phenotype may differ from the classical mechanisms of radiation-induced aberration formation. The data presented, as well as recent literature data on bystander effects and genetic instability expressed as chromatid-type aberrations on a chromosomal level, are discussed with respect to possible common mechanisms underlying all low-dose phenomena.

Hyperinsulinemia, impaired glucose tolerance, and diabetes mellitus in survivors of childhood cancer: prevalence and risk factors

CONTEXT

Hyperinsulinism and its associated metabolic abnormalities, including diabetes mellitus (DM), have been reported in long-term survivors of childhood cancer, mainly after bone marrow transplant (BMT); however, the predisposing factors are unclear, and early markers have not been identified.

METHODS

The prevalence of overweight/obesity, abdominal adiposity and hyperinsulinemia (HI), impaired glucose tolerance (IGT), or DM was examined prospectively in 248 survivors of childhood cancer (36 prepubertal, 88 pubertal, and 124 adult subjects; 67 BMT) at a median of 12.9 yr (2.3-33.6) after diagnosis and compared with healthy controls. Potential risk factors for the development of HI, IGT, or DM were sought.

RESULTS

Overweight/obesity was not increased when comparing subjects with controls; however, the prevalence of abdominal adiposity in prepubertal and pubertal subjects was roughly doubled (P < or = 0.04). Fasting insulin concentrations were higher in prepubertal and pubertal subjects compared with their controls (P < 0.001) and were similar in adult and pubertal subjects. HI, IGT, or DM was detected in 39 of 212 (18%) pubertal or adult subjects (23 BMT). Ten of 88 (11%) pubertal and 14 of 124 (11%) adult subjects had IGT/DM (vs. 0 and 4.9% controls, respectively; P < 0.001). Total body irradiation, untreated hypogonadism, and abdominal adiposity emerged as independent risk factors for the development of HI, IGT, or DM in multivariate regression analysis.

CONCLUSIONS

The risk factors identified suggest the need for reconsideration of BMT protocols and regular screening of survivors. The increased prevalence of abdominal adiposity among prepubertal subjects, none of whom had developed HI/IGT/DM, suggests that a waist to height ratio greater than 0.5 has potential as a clinical screening tool.