Combined deficiencies of poly(ADP)ribosyl polymerase 1 (PARP1) and ataxia telangiectasia mutated (ATM) result in synthetic lethality and, in the mouse, early embryonic death. Here, we investigated the genetic requirements for this lethality via analysis of mice deficient for PARP1 and either of two ATM-regulated DNA damage response (DDR) factors: histone H2AX and 53BP1. We found that, like ATM, H2AX is essential for viability in a PARP1-deficient background. In contrast, deficiency for 53BP1 modestly exacerbates phenotypes of growth retardation, genomic instability, and organismal radiosensitivity observed in PARP1-deficient mice. To gain mechanistic insights into these different phenotypes, we examined roles for 53BP1 in the repair of replication-associated double-strand breaks (DSBs) in several cellular contexts. We show that 53BP1 is required for DNA-PKcs-dependent repair of hydroxyurea (HU)-induced DSBs but dispensable for RPA/ RAD51-dependent DSB repair in the same setting. Moreover, repair of mitomycin C (MMC)-induced DSBs and sister chromatid exchanges (SCEs), two RAD51-dependent processes, are 53BP1 independent. Overall, our findings define 53BP1 as a main facilitator of nonhomologous end joining (NHEJ) during the S phase of the cell cycle, beyond highly specialized lymphocyte rearrangements. These findings have important implications for our understanding of the mechanisms whereby ATM-regulated DDR prevents human aging and cancer.DNA double-strand breaks (DSBs) arise constantly in mammalian cells from endogenous and exogenous sources (35). Defective DSB repair leading to cellular senescence or apoptosis, or aberrant repair to form chromosomal rearrangements, has been linked to aging and cancer in humans (22, 31). To prevent these deleterious outcomes, mammalian cells have evolved the DNA damage response (DDR), a network of factors that sense and signal DSBs to promote their repair (29). ataxia telangiectasia mutated (ATM) is a phophoinositide 3-kinase (PI3K)-like kinase that regulates the functions of hundreds of substrates during DDR, including histone H2AX and 53BP1 (41). Ultimately, the DDR restores DNA strand continuity via either of two main DSB repair pathways: homologous recombination (HR), an error-free pathway that operates only during the S/G 2 phases (70), or nonhomologous end joining (NHEJ), a versatile but error-prone pathway that operates throughout the cell cycle (37, 44).Poly(ADP)ribosyl polymerase 1 (PARP1) regulates, among other processes, transcription, cell death, and DNA repair (57). In the last context, PARP1 senses single-strand breaks (SSBs) and promotes their repair via base excision repair (BER) (15). Although PARP1 is not a component of the BER pathway per se, PARP1-deficient cells accumulate SSBs, which become substrates for HR-mediated repair upon replication (10, 21). ATM and other DDR factors may play important roles in DSB recognition and recruitment of the HR machinery in this setting (42). In addition, PARP1 also catalyzes PAR formation at de novo-generated DNA DSBs (28...

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Background: Posterior circulation strokes comprise approximately 20-25% of all strokes of ischemic origin. Strokes affecting this area carry a significantly higher risk for subsequent stroke or death as compared to anterior circulation strokes. Embolic protection device (EPD) use for carotid artery stenosis has translated into percutaneous interventions of proximal vertebral artery (VA) stenosis. However, the use of EPDs when treating intracranial lesions has yet to be studied and may not be feasible as the vessel caliber is frequently smaller than in existing devices. Objective: The aim of this study is to describe a proximal aspiration technique used during the treatment of intracranial VA and basilar artery (BA) atherosclerotic disease. Methods: Proximal embolic protection was utilized during the treatment of intracranial VA/BA stenosis with angioplasty and stenting in patients with medically refractory disease. Results: Three patients with severe symptomatic posterior circulation stenosis refractory to medical management were treated with angioplasty and stenting utilizing proximal aspiration. Pre- and post-treatment angiograms and MRIs were compared. Treated vascular stenoses were significantly improved, without new neurological deficits or ischemic injury identified on imaging. Conclusions: The proposed technique of proximal embolic protection may help overcome the challenge of embolus propagation inherent to the treatment modality that was encountered during the treatment of intracranial VA/BA stenosis.

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Dural arteriovenous fistulae (dAVFs) are vascular anomalies formed by abnormal connections between branches of dural arteries and dural veins or dural venous sinus(es). These pathologic shunts constitute 10%–15% of all intracranial arteriovenous malformations. The hallmark of malignant dAVFs is the presence of cortical venous drainage, a finding that increases the likelihood of nonhemorrhagic neurologic deficit, intracranial hemorrhage, and mortality if left unaddressed. Endovascular approaches have become the primary modality for the treatment of dAVFs. The authors present a case of staged endovascular transarterial embolization of a malignant dAVF running parallel to the left transverse sinus in a patient with headaches and pulsatile tinnitus. The fistula was completely treated using Onyx and n-butyl cyanoacrylate.The video can be found here: https://youtu.be/GSAto_wlC3I.