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Neuroscience Reviews: DNA Double-Strand Breaks in the Human Brain

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Neuroscience Reviews: DNA Double-Strand Breaks in the Human Brain KOPF® February 2016 Kopf Carrier #86 PUBLISHED BY DAVID KOPF INSTRUMENTS TUJUNGA, CALIFORNIA 10 9 876543210123456 Neuroscience Reviews: DNA Double-Strand Breaks in the Human Brain Mia P. Castiglione1, Judith M. Horowitz2, German Torres1* 1Department of Biomedical Sciences New York Institute of Technology, College of Osteopathic Medicine Old Westbury, New York, 11568, USA 2Department of Psychology The State University of New York at Fredonia Fredonia, New York, 14063, USA *Corresponding Author: German Torres, Ph.D. [email protected] Summary specific DNA mutations or lesions. In this brief review, we discuss recent insights into the DNA damage and mutations occur neurobiology of DNA double-strand breaks in throughout the lifetime of neurons due to their the context of pathogenicity as well as with high rates of oxygen metabolism, post-mitotic respect to molecular functionality. state and long life span. Exquisite molecular mechanisms have evolved to repair this dam- What are DNA age. However, such repair is not always suc- double-strand breaks? cessful and the results can lead to neurode- generative disorders. DNA damage occurs throughout the entire lifetime of neurons due in part to their high Introduction rates of oxygen metabolism, post-mitotic state and relatively long life span (Brochier Despite the fact that nuclear DNA has and Langley, 2013). At different stages of de- evolved exquisite molecular mechanisms to velopment, neurons are susceptible to DNA repair and replicate itself, de novo point mu- damaging factors that invariably impact broad tations often occur. In particular, the human scales of nucleotide sequences (Fig. 1). A brain carries considerable mutations that fraction of these mutations are a source of se- arise during fetal development and through- lective (evolutionary) advantage, but in most out the lifetime of each individual. Indeed, cases, spontaneous occurring mutations can genome-wide scale studies indicate that neu- alter key cellular function contributing to ma- rons exhibit different rates of germline and jor psychiatric and neurodegenerative disor- somatic mutations within and between brain ders (see below). In this context, DNA double- genomes. To compensate for the high rate strand breaks are a type of molecular lesion and spectrum of mutations, several nuclear in which the double helix structure is physi- DNA repair mechanisms have also evolved cally broken at specific genomic loci (Price, in the mammalian nervous system to resolve 2013). This molecular breakage interrupts the normal nucleotide sequence of exonic genes, neuro-pathologies have different behavioral thus limiting the availability of either DNA symptoms, their etiologies might share a con- strand to fully participate in DNA replication spicuous common feature, namely, neural ge- (Schipler, 2013). It should be noted that DNA nome instability. damage in the form of double-strand breaks arise spontaneously in the brain parenchyma What we know as a result of ongoing neuronal activity (McK- innon, 2013; Torres et al., 2015). Thus, neu- Nuclear and mitochondrial DNA mutations rons undergo continuous remodeling cycles are the sources of heritable diseases and evo- of DNA damage and DNA repair; distinct sig- lutionary change. To minimize replicative and naling pathways that are required for neural non-replicative DNA errors, genomes have development. evolved an array of DNA repair pathways in the nervous system. One of these pathways is the so-called non-homologous end-joint (NHEJ) pathway which repairs helix-distort- ing lesions such as those induced by ultra- violet radiation (McKinnon, 2013). If NHEJ is disrupted during neural development, defects might arise in the form of microcephaly and/ or high-grade gliomas (Gilmore and Walsh, Fig. 1. Neurons contain an array of DNA repair path- 2012). Another repairing pathway operating in ways to ensure genome integrity (A). These repair pathways respond to specific types of lesions, such the human nervous system is Ataxia telangi- as DNA double-strand breaks (B). DNA lesions are ectasia, muted (ATM) which responds to DNA then corrected by nucleotide excision repair pathways damage-responsive kinases. Of interest, dis- (C). However, if defects in DNA repair pathways oc- ruption of ATM leads to progressive cerebel- cur during neural development, accumulation of DNA lar ataxia and other neurodegenerative disor- damage may directly lead to progressive disease pathology. ders characterized by widespread signaling dysfunction at the synapse (Suberbielle et al., 2013). The presence of these specific bio- Why it matters? chemical repair pathways highlights the im- While DNA double-strand breaks are portance of maintaining the DNA architecture, widespread events in developing and mature a prerequisite for molecular functionality and nervous system landscapes (Torres et al., evolutionary fitness. 2015), deficiencies in repair of nuclear and Next steps mitochondrial DNA damage have been linked to several neurodegenerative disorders. For DNA damage happens both during devel- example, Xeroderma Pigmentosum, Cock- opment and in the mature human brain (Fig. ayne syndrome, Ataxia telangiectasia and Tri- 2). DNA double-strand breaks also occur dur- cothiodystrophy are disease phenotypes that ing the aging process, in particular, and may result from unavailable repair pathways that contribute to overall cognitive decline. Thus, normally safeguard DNA integrity (Jeppesen understanding how DNA damage promotes et al., 2011; McKinnon, 2013; Madabhushi et pathology in the brain may allow for the de- al., 2014). Along the same lines, a lack of DNA velopment of rational, effective therapies for double-strand break repair system has also DNA repair-deficient syndromes. been linked to Alzheimer’s disease, Parkin- son’s disease and Amyotrophic lateral sclero- sis (Madabhushi et al., 2014). Although these 2 dx.doi.org/10.1016/j.pneurobio.2011.04.013. 2011 Apr 30 [Epub Review] Madabhushi R, Pan L, Tsai LH (2014) DNA damage and its links to neurodegeneration. Neuron 83:266-283. dx.doi.org/10.1016/j. neuron.2014.06.034. 2014 Jul 16. [Epub Re- view] McKinnon PJ (2013) Maintaining genome stability in the nervous system. Nat. Neuro- sci 16(11):1523-1529. dx.doi.org/10/1038/ nn.3537. 2013 Oct 28 [Epub Review] Fig. 2. Representative bright-field images of the Price BD, D’Andrea AD (2013) Chroma- human hypothalamus (B) and inferior colliculus (D) tin remodeling at DNA double-strand breaks. showing the distribution pattern of DNA double-strand breaks. The nuclear distribution of a DNA double- Cell 152:1344-1354. dx.doi.org/10.1016/j. strand break marker (i.e., 53BP1) is widespread cell.2013.02.011 14 March 2013 [Epub Re- throughout the brain landscape. This suggests that view] DNA double-strand breaks are common, ongoing events spontaneously occurring in the normal brain. (A Schipler A, Iliakis G (2013) DNA double- and C) illustrate the anatomical location of the pho- strand-break complexity levels and their pos- tographed areas (arrows). Scale bars = 20 mm in (A) sible contributions to the probability for error- and (C); 100 μm in (B); 50 μm in (D). Adapted from Torres et al., 2015 (Neuroscience 290, 196-2013). prone processing and repair pathway choice. Nucleic Acids Research 41(16) 7589-7605 [Epub 26 Jun 2013] References Suberbielle E, Sanchez PE, Kravitz AV, Brochier C, Langley B (2013) Chromatin Wang X, Ho K, Eilertson K, Devidze N, Kre- modifications associated with DNA double- itzer AC, Mucke L (2013) Physiologic brain strand breaks repair as potential targets for activity causes DNA double-strand breaks in neurological diseases. Neurotherapeutics neurons, with exacerbation by amyloid-β. Nat 10(4):817-830. dx.doi.org/10.1007/s13311- Neurosci 16(5):613-621. dx.doi.org/10.1038/ 013-0210-9. Review nn.3356 [Epub 2013 Mar 24] Gilmore EC, Walsh CA (2012) Genetic Torres G, Leheste JR, Ramos RL (2015) causes of microcephaly and lessons for neu- Immunocytochemical localization of DNA ronal development. Wiley Interdiscip Rev double-strand breaks in human and rat Dev Biol 2(4):461-478. dx.doi.org/10.1002/ brains. Neuroscience 290:196-203. dx.doi. wdev.89. 2012 Oct 4 [Epub Review] org/10.1016/j.neuroscience.2015.01.027. [Epub 2015 Jan 28] Jeppesen DK, Bohr VA, Stevnsner T (2011) DNA Repair deficiency in neurode- generation. Prog Neurobiol 94(2):166-200. 3 Bibliographies Mia P. Castiglione ([email protected]), awarded approximately half a million dollars OMS I, received her B.S. Honors Degree with in grants to study brain diseases such as Distinction in Neuroscience with a minor in schizophrenia, depression and Parkinson’s Biology from University of Delaware in 2013. disease. She is currently working as a student-research assistant in the Biomedical Sciences depart- Dr. German Torres ([email protected]) ment at the New York Institute of Technol- received a Ph.D. from the University of Cali- ogy College of Osteopathic Medicine (NYIT fornia at Santa Barbara and is currently an COM). She anticipates receiving a D.O. de- Associate Professor in the department of bio- gree from the above institution in 2019. medical sciences at the New York Institute of Technology, College of Osteopathic Medicine. Judith M. Horowitz, Ph.D. (horowitz@ His specific research interests are centered fredonia.edu) is an accomplished researcher on the biological basis of brain disorders. in the fields of psychology and neuroscience. Dr. Horowitz has written articles published in peer reviewed journals on brain science and chemical neuroanatomy. She has also been 4 Editor’s Column reaps the financial gains of putting the results of pure research into practical use. This 86th issue of the Carrier is another in However, Myhrvold points out that this is our Neuroscience Re- simply wrong. He and Bill Gates founded Mi- views. Written by Mia crosoft Research, a very large industrial re- P. Castiglione, Judith search laboratory with the clear understand- M. Horowitz, German ing that basic research was not its mission. Torres, it describes the The research done there was to be focused phenomenon of DNA on innovations that could be turned into rev- double strand breaks in human brain cells enue quickly.
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