Although studies have demonstrated that genome instability is accumulated in patients with Alzheimer\'s disease (AD), the specific types of genome instability linked to AD pathogenesis remain poorly understood. Here, we report the first characterization of the age- and sex-related trajectories of telomere length (TL) and micronuclei in APP/PS1 mice model and wild-type (WT) controls (C57BL/6). TL was measured in brain (prefrontal cortex, cerebellum, pituitary gland, and hippocampus), colon and skin, and MN was measured in bone marrow in 6- to 14-month-old mice. Variation in TL was attributable to tissue type, age, genotype and, to a lesser extent, sex. Compared to WT, APP/PS1 had a significantly shorter baseline TL across all examined tissues. TL was inversely associated with age in both genotypes and TL shortening was accelerated in brain of APP/PS1. Age-related increase of micronuclei was observed in both genotypes but was accelerated in APP/PS1. We integrated TL and micronuclei data with data on cognition performance and brain amyloidosis. TL and micronuclei were linearly correlated with cognition performance or Aβ40 and Aβ42 levels in both genotypes but to a greater extent in APP/PS1. These associations in APP/PS1 mice were dominantly driven by females. Together, our findings provide foundational knowledge to infer the TL and micronuclei trajectories in APP/PS1 mice during disease progression, and strongly support that TL attrition and micronucleation are tightly associated with AD pathogenesis in a female-biased manner.

The cytokinesis-block micronucleus assay has proven to be a reliable technique for biological dosimetry. This study aimed to establish the dose-response curve for X-ray-induced micronucleus. Peripheral blood samples from three healthy donors were irradiated with various doses and scoring criteria by the micronuclei (MN) in binucleated cells. The results showed that the frequency of MN increased with the elevation of radiation dose. CABAS and Dose Estimate software were used to fit the MN and dose into a linear quadratic model, and the results were compared. The linear and quadratic coefficients obtained by the two software were basically the same and were comparable with published curves of similar radiation quality and dose rates by other studies. The dose-response curve established in this study can be used as an alternative method for in vitro dose reconstruction and provides a reliable tool for biological dosimetry in accidental or occupational radiation exposures.

Cytokinesis block micronucleus (CBMN) assay is a widely used radiation biological dose estimation method. However, the subjectivity and the time-consuming nature of manual detection limits CBMN for rapid standard assay. The CBMN analysis is combined with a convolutional neural network to create a software for rapid standard automated detection of micronuclei in Giemsa stained binucleated lymphocytes images in this study. Cell acquisition, adhesive cell mass segmentation, cell type identification, and micronucleus counting are the four steps of the software\'s analysis workflow. Even when the cytoplasm is hazy, several micronuclei are joined to each other, or micronuclei are attached to the nucleus, this algorithm can swiftly and efficiently detect binucleated cells and micronuclei in a verification of 2000 images. In a test of 20 slides, the software reached a detection rate of 99.4% of manual detection in terms of binucleated cells, with a false positive rate of 14.7%. In terms of micronuclei detection, the software reached a detection rate of 115.1% of manual detection, with a 26.2% false positive rate. Each image analysis takes roughly 0.3 s, which is an order of magnitude faster than manual detection.

Perturbation of epigenetic regulation is a well-established mechanism for cancer but its role for lead (Pb)-associated toxicity has not been adequately investigated. We aimed to investigate whether occupational Pb exposure is associated with micronuclei (MN) frequency and to further explored the mediating roles of epigenetic gene regulation. All the Pb-exposed workers recruited from a Chinese acid battery factory, blood lead levels (BLLs) and MN frequency in lymphocytes were measured. In addition, methylation levels of seven genes (Line-1, RASSF1A, RUNX3, p16, CYP26C1, hMLH1, p15) were examined among 230 workers. Robust Poisson regression model was used to investigate the association between BLLs and MN frequency. Mediation analysis was used to explore the mediating role of specific DNA methylation. Among total 677 participants, 71% were male, median BLLs was 229.1 μg/L (P25  = 155.5, P75  = 319.3; ranged from 8.9 to 647.7 μg/L), mean MN frequency was 2.5‰ (SD = 1.8‰; ranged from 0 to 9‰). Results from base model, adjusted for age, sex, and body mass index, showed that MN frequency would increase 1.38 (95%confidential interval: 1.34, 1.43) per 100 μg/L increment in BLLs. Using categorized exposure variable analyses, a BLLs dose-response increase in MN frequency was observed: 2.74 (2.13, 3.51), 3.43 (2.73, 4.32), 4.41 (3.89, 5.01) to 6.86 (6.02, 7.81). Mediation analysis indicated that Line-1 methylation significantly mediated 3.6% of the association of BLLs with MN frequency. Occupational Pb exposure induces MN frequency in a dose-response relationship. Part of this association was mediated by Line-1 promotor methylation.

In order to assess the health risk of low-dose radiation to radiation professionals, monitoring is performed through chromosomal aberration analysis and micronuclei (MN) analysis. MN formation has drawbacks for monitoring in the low-dose range. Nucleoplasmic bridge (NPB) analysis, with a lower background level, has good dose-response relationships at both high and relatively low dose ranges. Dicentric and ring chromosomes were analyzed in 199 medical radiation professionals, and NPB/MN yields were analyzed in 205 radiation professionals. The effects of sex, age of donor, types of work, and length of service on these cytogenetic endpoints were also analyzed. The yields of the three cytogenetic endpoints were significantly higher in radiation professionals versus controls. Frequencies of dicentric plus ring chromosomes were affected by length of service. NPB frequencies were influenced by type of work and length of service. MN yields were affected not only by types of work and length of service but also by donor sex and age. In conclusion, dicentric plus ring chromosomes, NPB, and MN can be induced by low-dose radiation in radiation professionals. NPB is a potential biomarker to assess the health risk of occupational low-dose radiation exposure.

Cigarette smoking increases health risks, such as respiratory diseases and heart diseases. Despite the decline in smoking rates in some countries, millions of adults still choose to smoke cigarettes. The use of next-generation nicotine delivery devices, such as tobacco heating products (THPs), may become a potentially safer alternative to smoking. Here, we report on the development of an electrically heated THP, coded as THP COO, with three different flavored tobacco sticks. The purpose of the study was to measure the levels of a list of harmful and potentially harmful constituents (HPHCs) in the total particulate matter (TPM) generated and to conduct a set of toxicological assessments of THP COO as compared with 3R4F reference cigarette. For all 55 HPHCs identified, the levels generated by the THP tobacco sticks were significantly lower in comparison to those in 3R4F TPM. The rate of reduction of HPHCs was between 68.6% and 99.9% under Health Canada Intense (HCI) smoking regimen. Human lung cancer cells (NCI-H292) exposed to 3R4F TPM showed dose-dependent responses for most of the 15 in vitro toxicity endpoints, whereas those exposed to comparable doses of THP COO TPMs did not. Therefore, exclusive use of the THP COO products may reduce the exposure of those tested HPHCs and thus potentially reduce health risk of smoking.

The objective of this research was to explore the dose-effect relationships of dicentric plus ring (dic + r), micronucleus (MN) and nucleoplasmic bridges (NPB) induced by carbon ions in human lymphocytes.
Venous blood samples were collected from three healthy donors. 12C6+ ions beam was used to irradiate the blood samples at the energy of 330 MeV and linear energy transfer (LET) of 50 keV/μm with a dose rate of 1 Gy/min in the spread-out Bragg peak. The irradiated doses were 0 (sham irradiation), 1, 2, 3, 4, 5 and 6 Gy. Dic + r chromosomes aberrations were scored in metaphases. The cytokinesis-block micronucleus cytome (CBMN) was conducted to analyze MN and NPB. The maximum low-dose relative biological effectiveness (RBEM) values of the induction of dic + r, MN and NPB in human lymphocytes for 12C6+ ions irradiation was calculated relative to 60Co γ-rays.
The frequencies of dic + r, MN and NPB showed significantly increases in a dose-depended manner after exposure to 12C6+ ions. The distributions of dic + r and MN exhibited overdispersion, while the distribution of NPB agreed with Poisson distribution at all doses. Linear-quadratic equations were established based on the frequencies of dic + r and MN. The dose-response curves of NPB frequencies followed a linear model. The derived RBEM values for dic + r, MN and NPB in human lymphocytes irradiated with 12C6+ ions were 8.07 ± 2.73, 2.69 ± 0.20 and 4.00 ± 2.69 in comparison with 60Co γ-rays.
The dose-response curves of carbon ions-induced dic + r, MN and NPB were constructed. These results could be helpful to improve radiation risk assessment and dose estimation after exposed to carbon ions irradiation.

1-Methylpyrene (1-MP) is a common environmental pollutant and animal carcinogen. After sequential activation by cytochromes P450 and sulfotransferases, it induced gene mutations and micronuclei in mammalian cells. The type of micronuclei formed, entire chromosomes or fragments, was not analysed. In this study, 1-MP and its primary metabolite, 1-hydroxymethylpyrene (1-HMP), were investigated for the induction of centromere-positive and -negative micronuclei in the human hepatoma cell line HepG2 and its derivative C3A, expressing relevant enzymes at higher levels. Under a short-exposure (9 h)/long-recovery regime (2 cell cycles in total), 1-MP and 1-HMP provided negative test results in HepG2 cells. However, they induced micronuclei in C3A cells, the effect being blocked by 1-aminobenzotriazole (inhibitor of cytochromes P450s) and reduced by pentachlorophenol (inhibitor of sulfotransferases). Immunofluorescence staining of centromere protein B in the micronuclei revealed purely clastogenic effects under this regime. Unexpectedly, 1-MP and 1-HMP at concentrations 1/5-1/4 of that required for micronuclei formation led to mitotic arrest and spindle aberrations, as detected by immunofluorescence staining of β- and γ-tubulin. Following extended exposure (72 h, 2 cell cycles, no recovery), damage to the spindle apparatus and centrosomes was detected at even lower concentrations, with concurrent formation of micronuclei. At low concentrations (1-8 µM 1-MP, 0.25-0.5 µM 1-HMP), the micronuclei induced were unexceptionally centromere-positive. Thus, the chromosome-damaging mechanism of 1-MP was regime and concentration dependent: potently aneugenic under persistent exposure, while clastogenic at higher concentrations following a short-exposure/long-recovery regime. This is a convincing evidence for the existence of metabolic activation-dependent aneugens.

Micronuclei, small spatially-separated, nucleus-like structures, are a common feature of human cancer cells. There are considerable heterogeneities in the sources, structures and genetic activities of micronuclei. Accumulating evidence suggests that micronuclei and main nuclei represent separate entities with respect to DNA replication, DNA damage sensing and repairing capacity because micronuclei are not monitored by the same checkpoints nor covered by the same nuclear envelope as the main nuclei. Thus, micronuclei are spatially restricted \"mutation factories.\" Several large-scale DNA sequencing and bioinformatics studies over the last few years have revealed that most micronuclei display a mutational signature of chromothripsis immediately after their generation and the underlying molecular mechanisms have been dissected extensively. Clonal expansion of the micronucleated cells is context-dependent and is associated with chromothripsis and several other mutational signatures including extrachromosomal circular DNA, kataegis and chromoanasynthesis. These results suggest what was once thought to be merely a passive indicator of chromosomal instability is now being recognized as a strong mutator phenotype that may drive intratumoral genetic heterogeneity. Herein, we revisit the actionable determinants that contribute to the bursts of mutagenesis in micronuclei and present the growing number of evidence which suggests that micronuclei have distinct short- and long-term mutational and functional effects to cancer genomes. We also pose challenges for studying the long-term effects of micronucleation in the upcoming years.

Autophagy has been well documented to play an important role in maintaining genomic stability. However, in addition to directly engulfing and digesting the damaged organelles and chromatin fragments, autophagy can affect many cellular processes including DNA damage response, regulation of redox homeostasis, and cell division; it remains to be determined to what extent each of those processes contributes to the maintenance of genomic stability. We here examined the role of autophagy-dependent redox regulation in the maintenance of genomic stability in two cancer cell lines (HT1080 and U2OS) and mesenchymal stem cells (MSCs) using micronuclei MN, also referred to as cytoplasmic chromatin fragments, as a marker. Our results showed that the spontaneous and genotoxic stress-induced frequencies of MN in cancer cells were significantly reduced by autophagy activators rapamycin and Torin1, and the reduction in MN was accompanied by a reduction in reactive oxygen species (ROS). Increased micronucleation in senescent MSCs, in which autophagic flux is blocked, was also attenuated by rapamycin, together with a reduction in ROS. Inhibition of autophagy by chloroquine (CQ) or ATG5 depletion, on the other hand, resulted in an increased frequency of MN, though a ROS elevation in response to autophagy inhibition was only observed in MSCs. Importantly, the induction of MN by autophagy inhibition in MSCs could be abrogated by antioxidant N-acetylcysteine (NAC). In contrast to the reported impairment of CHK1 activation in Atg7-deficient mouse embryonic fibroblasts, we found that the level of phosphorylated CHK1 was increased by CQ or ATG5 depletion but decreased by rapamycin or Torin1, suggesting that the increased genomic instability by defective autophagy is not caused by insufficient activation of CHK1-homologous recombination cascade. Together, our findings suggest that redox homeostasis regulated by autophagy contributes substantially to the maintenance of genomic stability in certain contexts.