RESUMO
Chromosome instability (CIN) is frequently observed in many tumors. The breakage-fusion-bridge (BFB) cycle has been proposed to be one of the main drivers of CIN during tumorigenesis and tumor evolution. However, the detailed mechanism for the individual steps of the BFB cycle warrants further investigation. Here, we demonstrate that a nuclease-dead Cas9 (dCas9) coupled with a telomere-specific single-guide RNA (sgTelo) can be used to model the BFB cycle. First, we show that targeting dCas9 to telomeres using sgTelo impedes DNA replication at telomeres and induces a pronounced increase of replication stress and DNA damage. Using Single-Molecule Telomere Assay via Optical Mapping (SMTA-OM), we investigate the genome-wide features of telomeres in the dCas9/sgTelo cells and observe a dramatic increase of chromosome end fusions, including fusion/ITS+ and fusion/ITS-. Consistently, we also observe an increase in the formation of dicentric chromosomes, anaphase bridges, and intercellular telomeric chromosome bridges (ITCBs). Utilizing the dCas9/sgTelo system, we uncover many interesting molecular and structural features of the ITCB and demonstrate that multiple DNA repair pathways are implicated in the formation of ITCBs. Our studies shed new light on the molecular mechanisms of the BFB cycle, which will advance our understanding of tumorigenesis, tumor evolution, and drug resistance.
RESUMO
Chromosome instability (CIN) is frequently observed in many tumors. The breakage-fusion-bridge (BFB) cycle has been proposed to be one of the main drivers of CIN during tumorigenesis and tumor evolution. However, the detailed mechanisms for the individual steps of the BFB cycle warrants further investigation. Here, we demonstrated that a nuclease-dead Cas9 (dCas9) coupled with a telomere-specific single-guide RNA (sgTelo) can be used to model the BFB cycle. First, we showed that targeting dCas9 to telomeres using sgTelo impeded DNA replication at telomeres and induced a pronounced increase of replication stress and DNA damage. Using Single-Molecule Telomere Assay via Optical Mapping (SMTA-OM), we investigated the genome-wide features of telomeres in the dCas9/sgTelo cells and observed a dramatic increase of chromosome end fusions, including fusion/ITS+ and fusion/ITS-.Consistently, we also observed an increase in the formation of dicentric chromosomes, anaphase bridges, and intercellular telomeric chromosome bridges (ITCBs). Utilizing the dCas9/sgTelo system, we uncovered many novel molecular and structural features of the ITCB and demonstrated that multiple DNA repair pathways are implicated in the formation of ITCBs. Our studies shed new light on the molecular mechanisms of the BFB cycle, which will advance our understanding of tumorigenesis, tumor evolution, and drug resistance.
RESUMO
Background: Alcohol and caffeine are the 2 frequently consumed substances in the general population, and the 2 substances are frequently co-consumed. Both substances may increase cardiac arrhythmia risk. However, it is unknown whether alcohol and caffeine co-consumption can synergistically enhance cardiac arrhythmogenesis. Objective: The study sought to investigate whether caffeine and binge drinking synergistically affect cardiac arrhythmogenesis. Methods: A binge drinking rat model (alcohol 2 g/kg, intraperitoneal, every other day for 3 times) was used. Rats (4 months old, both sexes) were randomized into the following 4 groups: binge alcohol-only group (A) (n = 8), nonalcohol, caffeine-only (60 mg/kg, intraperitoneal) group (C) (n = 8), binge alcohol plus caffeine group (A+C) (n = 8), and binge alcohol + caffeine + dantrolene group (A+D) (n = 7, treated with dantrolene 10 mg/kg before each alcohol injection). We also investigated whether alcohol induces Ca2+ sparks and dantrolene treatment attenuates alcohol-induced Ca2+ leak in ventricular myocytes. Results: No arrhythmia was induced with caffeine alone (group C, n = 0 of 8) or alcohol alone (group A, n = 0 of 8). However, alcohol + caffeine induced spontaneous ventricular tachyarrhythmias in all rats (group A+C, n = 8 of 8; P < .001 vs group C or A). Dantrolene prevented ventricular tachyarrhythmia induction in all 7 rats (group A+D, n = 0 of 7; P < .001 vs group A+C). In isolated ventricular myocytes, alcohol significantly increased Ca2+ sparks and dantrolene treatment reduced alcohol-induced Ca2+ sparks. Conclusion: Co-consumption of caffeine and binge drinking synergistically promote spontaneous ventricular tachyarrhythmias in rats. Dantrolene treatment can decrease alcohol-enhanced Ca2+ sparks in vitro and prevented alcohol and caffeine induced ventricular tachyarrhythmias in vivo.
RESUMO
ABSTRACT: Binge drinking is a risk factor for cardiac arrhythmias, known as the holiday heart syndrome. Atrial fibrillation (AF) is the most frequently diagnosed arrhythmia in this condition. Recent reports indicated that cardiac ryanodine receptor (RyR2) dysfunction and Ca 2+ leak contribute to alcohol-enhanced AF. In this study, we investigated whether stabilizing RyR2 with dantrolene treatment can prevent alcohol-enhanced AF in rats. A binge drinking rat model was established with alcohol (2 g /kg, IP) delivered once every other day for 4 times. The study consisted of following 3 groups: control group (n = 9), binge alcohol group (n = 10), and binge alcohol + dantrolene (A+D) group (dantrolene, 10 mg/kg, IP before each alcohol injection, n = 9). Echocardiography, left ventricular hemodynamics, in vivo atrial electrophysiology and AF inducibility test, RyR2 phosphorylation level, and blood norepinephrine level were studied 24 hours after the last injection. Ca 2+ leak in isolated atrial myocytes from control and binge alcohol rats was examined. Binge alcohol significantly increased AF inducibility (1/9 in control vs. 8/9 in binge alcohol group, P < 0.05) and AF duration. Dantrolene treatment significantly reduced both AF inducibility (2/9 in dantrolene group, P < 0.05) and AF duration. Binge alcohol significantly increased Ca 2+ leak in isolated atrial myocytes, which was reduced by dantrolene treatment. Blood norepinephrine,7 RyR2 phosphorylation level, cardiac echocardiography, and left ventricular hemodynamics were not significantly affected 24 hours after binge drinking. In conclusion, stabilizing RyR2 with dantrolene treatment significantly attenuated binge drinking-enhanced AF, suggesting that therapeutic strategies stabilizing RyR2 could be a preventive measure to blunt binge drinking-enhanced AF arrhythmogenesis.