Chromatin Regulation of DNA Damage Repair and Genome Integrity in the Central Nervous System

With the continued extension of lifespan, aging and age-related diseases have become a major medical challenge to our society. Aging is accompanied by changes in multiple systems. Among these, the aging process in the central nervous system is critically important but very poorly understood. Neurons, as post-mitotic cells, are devoid of replicative associated aging processes, such as senescence and telomere shortening. However, because of the inability to self-replenish, neurons have to withstand challenge from numerous stressors over their lifetime. Many of these stressors can lead to damage of the neurons' DNA. When the accumulation of DNA damage exceeds a neuron's capacity for repair, or when there are deficiencies in DNA repair machinery, genome instability can manifest. The increased mutation load associated with genome instability can lead to neuronal dysfunction and ultimately to neuron degeneration. In this review, we first briefly introduce the sources and types of DNA damage and the relevant repair pathways in the nervous system (summarized in Fig. 1). We then discuss the chromatin regulation of these processes and summarize our understanding of the contribution of genomic instability to neurodegenerative diseases. Abbreviations DDRDNA damage response NHEJnonhomologous end joining HRhomologous recombination BERbase excision repair NERnucleotide excision repair SSBsingle-strand break SSBRsingle-strand break repair DSBRdouble-strand break repair DSBdouble-strand break mtDNAmitochondrial DNA PARpoly(ADP-ribose) HAThistone acetyltransferase HDAChistone deacetylase ATMataxia telangiectasia mutated MMRmismatch repair CNVcopy number variation iPSCinduced pluripotent stem cell HDHuntington's disease ADAlzheimer's disease PDParkinson's disease ALSamyotrophic lateral sclerosis Keywords neurodegenerative diseases DNA repair DNA damage response histone modifications central nervous syste

DNA Damage and Its Links to Neurodegeneration

The integrity of our genetic material is under constant attack from numerous endogenous and exogenous agents. The consequences of a defective DNA damage response are well studied in proliferating cells, especially with regards to the development of cancer, yet its precise roles in the nervous system are relatively poorly understood. Here we attempt to provide a comprehensive overview of the consequences of genomic instability in the nervous system. We highlight the neuropathology of congenital syndromes that result from mutations in DNA repair factors and underscore the importance of the DNA damage response in neural development. In addition, we describe the findings of recent studies, which reveal that a robust DNA damage response is also intimately connected to aging and the manifestation of age-related neurodegenerative disorders such as Alzheimer's disease and amyotrophic lateral sclerosis. Video Abstract: In this Review, Madabhushi etal. summarize the current state of knowledge about how DNA damage and changes to the DNA damage response in neurons might underlie neurodegenerative diseases

Modeling Alzheimer's disease with human induced pluripotent stem (iPS) cells

In the last decade, induced pluripotent stem (iPS) cells have revolutionized the utility of human in vitro models of neurological disease. The iPS-derived and differentiated cells allow researchers to study the impact of a distinct cell type in health and disease as well as performing therapeutic drug screens on a human genetic background. In particular, clinical trials for Alzheimer's disease (AD) have been failing. Two of the potential reasons are first, the species gap involved in proceeding from initial discoveries in rodent models to human studies, and second, an unsatisfying patient stratification, meaning subgrouping patients based on the disease severity due to the lack of phenotypic and genetic markers. iPS cells overcome this obstacles and will improve our understanding of disease subtypes in AD. They allow researchers conducting in depth characterization of neural cells from both familial and sporadic AD patients as well as preclinical screens on human cells.In this review, we briefly outline the status quo of iPS cell research in neurological diseases along with the general advantages and pitfalls of these models. We summarize how genome-editing techniques such as CRISPR/Cas9 will allow researchers to reduce the problem of genomic variability inherent to human studies, followed by recent iPS cell studies relevant to AD. We then focus on current techniques for the differentiation of iPS cells into neural cell types that are relevant to AD research. Finally, we discuss how the generation of three-dimensional cell culture systems will be important for understanding AD phenotypes in a complex cellular milieu, and how both two- and three-dimensional iPS cell models can provide platforms for drug discovery and translational studies into the treatment of AD.National Institutes of Health (U.S.) (Grant R01-AG047661

Cyclin-dependent kinase 5 phosphorylates the N-terminal domain of the postsynaptic density protein PSD-95 in neurons

PSD-95 (postsynaptic density 95) is a postsynaptic scaffolding protein that links NMDA receptors to the cytoskeleton and signaling molecules. The N-terminal domain of PSD-95 is involved in the synaptic targeting and clustering of PSD-95 and in the clustering of NMDA receptors at synapses. The N-terminal domain of PSD-95 contains three consensus phosphorylation sites for cyclin-dependent kinase 5 (cdk5), a proline-directed serine-threonine kinase essential for brain development and implicated in synaptic plasticity, dopamine signaling, cocaine addiction, and neurodegenerative disorders. We report that PSD-95 is phosphorylated in the N-terminal domain by cdk5 in vitro and in vivo, and that this phosphorylation is not detectable in brain lysates of cdk5-/- mice. N-terminal phosphorylated PSD-95 is found in PSD fractions together with cdk5 and its activator, p35, suggesting a role for phosphorylated PSD-95 at synapses. In heterologous cells, coexpression of active cdk5 reduces the ability of PSD-95 to multimerize and to cluster neuronal ion channels, two functions attributed to the N-terminal domain of PSD-95. Consistent with these observations, the lack of cdk5 activity in cultured neurons results in larger clusters of PSD-95. In cdk5-/- cortical neurons, more prominent PSD-95 immunostained clusters are observed than in wild-type neurons. In hippocampal neurons, the expression of DNcdk5 (inactive form of cdk5) or of the triple alanine mutant (T19A, S25A, S35A) full-length PSD-95 results in increased PSD-95 cluster size. These results identify cdk5-dependent phosphorylation of the N-terminal domain of PSD-95 as a novel mechanism for regulating the clustering of PSD-95. Moreover, these observations support the possibility that cdk5-dependent phosphorylation of PSD-95 dynamically regulates the clustering of PSD-95/NMDA receptors at synapses, thus providing a possible mechanism for rapid changes in density and/or number of receptor at synapses

HDAC2 expression in parvalbumin interneurons regulates synaptic plasticity in the mouse visual cortex

An experience-dependent postnatal increase in GABAergic inhibition in the visual cortex is important for the closure of a critical period of enhanced synaptic plasticity. Although maturation of the subclass of parvalbumin (Pv)-expressing GABAergic interneurons is known to contribute to critical period closure, the role of epigenetics on cortical inhibition and synaptic plasticity has not been explored. The transcription regulator, histone deacetylase 2 (HDAC2), has been shown to modulate synaptic plasticity and learning processes in hippocampal excitatory neurons. We found that genetic deletion of HDAC2 specifically from Pv interneurons reduces inhibitory input in the visual cortex of adult mice and coincides with enhanced long-term depression that is more typical of young mice. These findings show that HDAC2 loss in Pv interneurons leads to a delayed closure of the critical period in the visual cortex and supports the hypothesis that HDAC2 is a key negative regulator of synaptic plasticity in the adult brain.National Institute of Neurological Diseases and Stroke (U.S.) (Grant NS078839)National Institute on Aging (Grant NS078839

Forebrain-specific deletion of Cdk5 in pyramidal neurons results in mania-like behavior and cognitive impairment

Cyclin-dependent kinase 5 (Cdk5) is associated with synaptic plasticity and cognitive function. Previous reports have demonstrated that Cdk5 is necessary for memory formation, although others have reported Cdk5 conditional knockout mouse models exhibiting enhanced learning and memory. Furthermore, how Cdk5 acts in specific cell populations to affect behavior and cognitive outcomes remains unclear. Here we conduct a behavioral characterization of a forebrain-specific Cdk5 conditional knockout mouse model under the αCaMKII promoter, in which Cdk5 is ablated in excitatory pyramidal neurons of the forebrain. The Cdk5 conditional knockouts exhibit hyperactivity in the open field, reduced anxiety, and reduced behavioral despair. Moreover, the Cdk5 conditional knockouts also display impaired spatial learning in the Morris water maze and are severely impaired in contextual fear memory, which correspond to deficits in synaptic transmission. Remarkably, the hyperactivity of the Cdk5 conditional knockouts can be ameliorated by the administration of lithium chloride, an inhibitor of GSK3β signaling. Collectively, our data reveal that Cdk5 ablation from forebrain excitatory neurons results in deleterious effects on emotional and cognitive behavior and highlight a key role for Cdk5 in regulating the GSK3β signaling pathway.National Institutes of Health (U.S.) (Grant T32 MH074249)National Institutes of Health (U.S.) (Grant R01 NS051874

L'Ottocento editoriale e le sue radici. Alcune riflessioni su fabbrica, illustrazione, smercio dei libri

Il saggio, pubblicato anche come separatum, è la prefazione di LORETTA DE FRANCESCHI, Pubblicare, divulgare, leggere nell'Ottocento italiano, Manziana, Vecchiarelli, 2013 (collezione di sei saggi, l'ultimo dei quali inedito). Si sottolineano cinque punti: 1) Rapporti fra editoria e preparazione politica del Risorgimento. 2) Editoria di libri e periodici e formazione di un pensiero e di una formazione culturale unitaria. 3) Rapporti fra editori, tipografi e librai e le istituzioni dello Stato nascente. 4) Evoluzione delle morfologie tipografiche. 5) Biblioteche pubbliche e pubblica lettura nei loro rapporti con scuola e università. Si svolge un'ampia riflessione sullo sviluppo dei rapporti fra lettura individuale e libertà personale a partire dalla traduzione della Bibbia di Lutero; con speciale attenzione al ruolo riservato a libro e lettura nell'opera di John Foxe, Book of Martyrs, pubblicata in quattro successive edizioni riccamente illustrate. Il saggio è completato da 29 immagini. Si tratta di 4 edizioni di Machiavelli: Principe (Milano, 1817); Istorie (1796, Filadelfia); edizione pirata di Opere complete, Napoli, 1877 (es. Terni, bct), Der Fürstenspiegel, Der Antimachiavell, Jena 1912 (es. Weimar, Herzogin Anna-Amalia Bibliothek; Berlin, StaBi). Frontespizî di: Roscoes's Italian Novelists, London, Prewett, 1825, nell'es. dell'Harvard College Library. Tesoro dei novellieri italiani, Parigi, Baudry, 1847 (es. Madrid, Universidad Complutense). L'antologia dei prosatori italiani scelta da Panizzie stampata da John Taylor, London, 1828 (Cambridge, University Libr.). Verso del frontespizio di La Fontaine, Fables choisies, Paris, De l'Imprimerie d'Aug. Delalain, 1816 (es. Paris, Bibliothèque de France). Molte tavole dalle varie edizioni del Book of Martyrs, 1563, p. 1571 | 1570, p. 2104 | 1576, p. 1807 | 1583, p. 1911 (Courtesy: TAMO).Illustrazioni di J. E. Millais sa A. Trollope, Orley Farm, London, Chapman & Hall, 1862 (es. Oxford, Bodleian Library). Infine, sono riprodotti alcuni dipinti: P. A. Besnard, Matinée d'été, 1886 (Musée des Beaux-Arts, Reims). Winslow Homer, The New Novel, 1877 (Museum of Fine Arts, Springfield, Massachusetts). E. von Grützner, Lesender Prämonstratensermönch in der Klosterbibliothek, 1925 ca. Edward Hopper (1882-1967), Hotel by a Railroad, 1952 (Hirshhorn Museum and Sculpture Garden, Smithsonian Institution, Washington, DC).The paper, printed also as a an offprint, was originally issued as a Preface to LORETTA DE FRANCESCHI, Pubblicare, divulgare, leggere nell'Ottocento italiano, Manziana, Vecchiarelli, 2013, a collection of six essays, the last one unpublished. The paper underlines five topics: 1) The relations with the politic history of the Italian Risorgimento. 2) The role of books and periodical publishing in the building of national thinking and enculturation. 3) The relations between the rising of the Italian State and publishers, typographers, booksellers. 4) Morphemic features of the printing process during its history. 5) Public libraries and public reading, in their relations both with primary, undergraduate and uppergraduate instruction on the other side. A long review is made about the relations between reading and personal freedom, since Luther's translation of the Bible; special attention is devoted to the place of reading (with evidence about women's reading) in John Foxe's Book of Martyrs, published by John Day in four widely illustrated editions. A gallery of 29 images is appended to the paper, referring to: 4 editions of Machiavelli: Principe (Milano, 1817), Istorie (1796, Filadelfia). Pirate edition of Opere complete, Napoli, 1877 (es. Terni, bct), Der Fürstenspiegel, Der Antimachiavell, Jena 1912 (es. Weimar, Herzogin Anna-Amalia Bibliothek; Berlin, StaBi). Titlepages of: Roscoes's Italian Novelists, London, Prewett, 1825, in the copy belonging to the Harvard College Library. Tesoro dei novellieri italiani, Parigi, Baudry, 1847 (es. Madrid, Universidad Complutense). Panizzi's choice of Italian prose-writers, printed by John Taylor, London, 1828 (Cambridge, University Libr.). Verso of the titlepage of La Fontaine, Fables choisies, Paris, De l'Imprimerie d'Aug. Delalain, 1816 (es. Paris, Bibliothèque de France). Many tables from J. Foxe, Book of Martyrs, ed. 1563, p. 1571 | ed. 1570, p. 2104 | ed. 1576, p. 1807 | ed. 1583, p. 1911 (Courtesy: TAMO). A. Trollope, Orley Farm, London, Chapman & Hall, 1862, ill. by J. E. Millais (es. Oxford, Bodleian Library). Moreover, about the following paintings: P. A. Besnard, Matinée d'été, 1886 (Musée des Beaux-Arts, Reims). Winslow Homer, The New Novel, 1877 (Museum of Fine Arts, Springfield, Massachusetts). E. von Grützner, Lesender Prämonstratensermönch in der Klosterbibliothek, 1925 ca. Edward Hopper (1882-1967), Hotel by a Railroad, 1952 (Hirshhorn Museum and Sculpture Garden, Smithsonian Institution, Washington, DC

Synaptic Deficits Are Rescued in the p25/Cdk5 Model of Neurodegeneration by the Reduction of β-Secretase (BACE1)

Alzheimer's disease (AD) is the most common cause of dementia, and is characterized by memory loss and cognitive decline, as well as amyloid β (Aβ) accumulation, and progressive neurodegeneration. Cdk5 is a proline-directed serine/threonine kinase whose activation by the p25 protein has been implicated in a number of neurodegenerative disorders. The CK-p25 inducible mouse model exhibits progressive neuronal death, elevated Aβ, reduced synaptic plasticity, and impaired learning following p25 overexpression in forebrain neurons. Levels of Aβ, as well as the APP processing enzyme, β-secretase (BACE1), are also increased in CK-p25 mice. It is unknown what role increased Aβ plays in the cognitive and neurodegenerative phenotype of the CK-p25 mouse. In the current work, we restored Aβ levels in the CK-p25 mouse to those of wild-type mice via the partial genetic deletion of BACE1, allowing us to examine the Aβ-independent phenotype of this mouse model. We show that, in the CK-p25 mouse, normalization of Aβ levels led to a rescue of synaptic and cognitive deficits. Conversely, neuronal loss was not ameliorated. Our findings indicate that increases in p25/Cdk5 activity may mediate cognitive and synaptic impairment via an Aβ-dependent pathway in the CK-p25 mouse. These findings explore the impact of targeting Aβ production in a mouse model of neurodegeneration and cognitive impairment, and how this may translate into therapeutic approaches for sporadic AD.National Institutes of Health (U.S.) (Grant NIH R01NS051874)Ruth L. Kirschstein National Research Service Award (Predoctoral Fellowship F31GM80055-03

Amyloid-Independent Mechanisms in Alzheimer's Disease Pathogenesis

Despite the progress of the past two decades, the cause of Alzheimer's disease (AD) and effective treatments against it remain elusive. The hypothesis that amyloid-β (Aβ) peptides are the primary causative agents of AD retains significant support among researchers. Nonetheless, a growing body of evidence shows that Aβ peptides are unlikely to be the sole factor in AD etiology. Evidence that Aβ/amyloid-independent factors, including the actions of AD-related genes, also contribute significantly to AD pathogenesis was presented in a symposium at the 2010 Annual Meeting of the Society for Neuroscience. Here we summarize the studies showing how amyloid-independent mechanisms cause defective endo-lysosomal trafficking, altered intracellular signaling cascades, or impaired neurotransmitter release and contribute to synaptic dysfunction and/or neurodegeneration, leading to dementia in AD. A view of AD pathogenesis that encompasses both the amyloid-dependent and -independent mechanisms will help fill the gaps in our knowledge and reconcile the findings that cannot be explained solely by the amyloid hypothesis.National Institutes of Health (U.S.) (Grant P01-AG027916)National Institutes of Health (U.S.) (Grant R01-NS051874

The cyclin-dependent kinase 5 activators p35 and p39 interact with the alpha-subunit of Ca2+/calmodulin-dependent protein kinase II and alpha-actinin-1 in a calcium-dependent manner

Cyclin-dependent kinase 5 (Cdk5) is a critical regulator of neuronal migration in the developing CNS, and recent studies have revealed a role for Cdk5 in synaptogenesis and regulation of synaptic transmission. Deregulation of Cdk5 has been linked to the pathology of neurodegenerative diseases such as Alzheimer\u27s disease. Activation of Cdk5 requires its association with a regulatory subunit, and two Cdk5 activators, p35 and p39, have been identified. To gain further insight into the functions of Cdk5, we identified proteins that interact with p39 in a yeast two-hybrid screen. In this study we report that alpha-actinin-1 and the alpha-subunit of Ca2+/calmodulin-dependent protein kinase II (CaMKIIalpha), two proteins localized at the postsynaptic density, interact with Cdk5 via their association with p35 and p39. CaMKIIalpha and alpha-actinin-1 bind to distinct regions of p35 and p39 and also can interact with each other. The association of CaMKIIalpha and alpha-actinin-1 to the Cdk5 activators, as well as to each other, is stimulated by calcium. Further, the activation of glutamate receptors increases the association of p35 and p39 with CaMKIIalpha, and the inhibition of CaMKII activation diminishes this effect. The glutamate-mediated increase in association of p35 and CaMKIIalpha is mediated in large part by NMDA receptors, suggesting that cross talk between the Cdk5 and CaMKII signal transduction pathways may be a component of the complex molecular mechanisms contributing to synaptic plasticity, memory, and learning