A therosclerosis, a progressive, chronic, inflammatory disease with specific, localized manifestations in the arterial wall, is a major health burden and is predicted to become the leading cause of mortality and morbidity worldwide. 1,2 Complications of atherosclerosis, such as myocardial infarction (MI), which is the largest single cause of death in developed countries, are caused by inflammation-driven rupture of atherosclerotic plaques. 3A major hurdle in research on mechanisms of plaque rupture is the lack of appropriate mouse models which exhibit plaque rupture and lesion characteristics of vulnerable, unstable, and thus rupture-prone plaques as found in humans.4 Such characteristics most importantly include a thin and ruptured fibrous cap, plaque inflammation, neovascularization within the plaque (vasa vasorum), plaque hemorrhage, and intravascular (often occlusive) thrombus formation. 2,3,[5][6][7] In addition, an animal model of plaque instability/rupture should include responsiveness to pharmacological agents known to reduce the risk of plaque rupture in humans. 8,9 Currently discussed animal models of atherosclerosis typically represent a few but not the full combination of the characteristics seen in human unstable/ruptured plaques. [10][11][12][13][14] An animal model of New Methods in Cardiovascular Biology© 2013 American Heart Association, Inc. Rationale: The high morbidity/mortality of atherosclerosis is typically precipitated by plaque rupture and consequent thrombosis. However, research on underlying mechanisms and therapeutic approaches is limited by the lack of animal models that reproduce plaque instability observed in humans.Objective: Development and use of a mouse model of plaque rupture that reflects the end stage of human atherosclerosis. Methods and Results:On the basis of flow measurements and computational fluid dynamics, we applied a tandem stenosis to the carotid artery of apolipoprotein E-deficient mice on high-fat diet. At 7 weeks postoperatively, we observed intraplaque hemorrhage in ≈50% of mice, as well as disruption of fibrous caps, intraluminal thrombosis, neovascularization, and further characteristics typically seen in human unstable plaques. Administration of atorvastatin was associated with plaque stabilization and downregulation of monocyte chemoattractant protein-1 and ubiquitin. Microarray profiling of mRNA and microRNA (miR) and, in particular, its combined analysis demonstrated major differences in the hierarchical clustering of genes and miRs among nonatherosclerotic arteries, stable, and unstable plaques and allows the identification of distinct genes/miRs, potentially representing novel therapeutic targets for plaque stabilization. The feasibility of the described animal model as a discovery tool was established in a pilot approach, identifying a disintegrin and metalloprotease with thrombospondin motifs 4 (ADAMTS4) and miR-322 as potential pathogenic factors of plaque instability in mice and validated in human plaques. Conclusions:The newly described mouse mod...

RNA polymerase I (Pol I)-mediated transcription of the ribosomal RNA genes (rDNA) is confined to the nucleolus and is a rate-limiting step for cell growth and proliferation. Inhibition of Pol I by CX-5461 can selectively induce p53-mediated apoptosis of tumour cells in vivo. Currently, CX-5461 is in clinical trial for patients with advanced haematological malignancies (Peter Mac, Melbourne).Here we demonstrate that CX-5461 also induces p53-independent cell cycle checkpoints mediated by ATM/ATR signaling in the absence of DNA damage. Further, our data demonstrate that the combination of drugs targeting ATM/ATR signaling and CX-5461 leads to enhanced therapeutic benefit in treating p53-null tumours in vivo, which are normally refractory to each drug alone. Mechanistically, we show that CX-5461 induces an unusual chromatin structure in which transcriptionally competent relaxed rDNA repeats are devoid of transcribing Pol I leading to activation of ATM signaling within the nucleoli. Thus, we propose that acute inhibition of Pol transcription initiation by CX-5461 induces a novel nucleolar stress response that can be targeted to improve therapeutic efficacy.