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Two functional genomics approaches investigating the nervous system: the role of Collagen VI in cognition and the importance of Glucocerebrosidase in myelinating cells
No full textThe central nervous system (CNS) is one of the most fascinating apparatus that scientists ever encountered. This is because it owns a complex and finely regulated structure, allowing to modulate our emotions and behaviours. The mammal brain is organized in different but connected districts that control all our behaviours and needs, from the most basic to the higher ones like abstract reasoning. On a small scale, these districts are made up by cells owning peculiar features, such as conducting electric impulses or sensing dangerous molecules. The functioning of the CNS is still very obscure because of its complexity, making its investigation not trivial. One of the major technological leaps that allowed to better understand the mechanisms occurring in the CNS is the generation of transgenic models, that allowed understanding the role of single genes and their involvement in pathological situations, even in specific cellular subset (conditional knockout) or from a certain life point onward (inducible knockout). In this PhD thesis, I exploited two genetically modified mouse models, targeting the extracellular matrix (ECM) protein Collagen VI, and the enzyme Glucocerebrosidase in myelin-forming cells, respectively. In the first case, the Col6a1-/- mouse, was used in the past as a tool to investigate the pathogenesis of human muscular diseases caused by mutations in Collagen VI genes. However, since this is a total knockout, the role of this protein could be explored also in other districts. During my PhD I studied the function of Collagen VI in the synaptic cleft of the neuromuscular junction (NMJ) and in the CNS. Our findings indicate that Collagen VI is deposited within the NMJ cleft and that its lack impairs the transmission of acetylcholine and alters the post-synaptic apparatus, supporting a role for NMJ defects in contributing to the muscular weakness observed in Collagen VI-related patients. Additionally, I was involved in a project aiming at understanding how lack of Collagen VI affects cognition. Behavioural alterations were indeed observed in our model, and for the first time, cognition was finely assessed in patients with Collagen VI-related myopathies. We detected deficient dopaminergic signalling in mice and suggested the involvement of meninges. These two projects represent a classical approach of in vivo functional genomics, where a transgenic model is used to study the role of a protein in different organs. But beside basic research, we also adopted a collaborative and translational approach to transfer the findings observed in mice to human patients, in view of broadening the understanding of Collagen VI-related diseases beyond the undeniable muscular issues. The other project I was involved during my PhD consisted in investigating the role of Glucocerebrosidase, or GBA1, in myelinating glia exploiting a conditional knockout mouse model. Myelination is carried out by Schwann cells in the peripheral nervous system and oligodendrocytes (OL) in the CNS. Their roles include both axonal insulation and trophic support. GBA1 is involved in the onset of a lysosomal storage disease called Gaucher disease (GD), and is considered a major genetic risk factor for Parkinson’s disease (PD). In both GD and PD, neurodegeneration is observed, but the contribution of oligodendroglial GBA1 has never been investigated: this is the first attempt to understand whether and how the lack of this enzyme impacts on myelinating glia survival (in particular OLs), and in turn on neuronal functionality. Taking advantage of different approaches, we assessed in vitro the possibility that GBA1 inhibition could affect lysosomal functioning and myelination in a line of OLs. Then we exploited the novel conditional mouse model and
detected myelin involvement and neurodegenerative hallmarks, suggesting oligodendroglial GBA1 contribution to the onset of neuropathic features in PD and GD.Il sistema nervoso centrale (SNC) è uno degli apparati più complessi che gli scienziati abbiano mai studiato, perché possiede una struttura complessa e finemente regolata che ci permette di modulare le nostre emozioni e i nostri comportamenti. Il cervello dei mammiferi è organizzato in diverse regioni che controllano tutti i nostri bisogni, dai più semplici ai più complessi, come il ragionamento astratto. Su scala più piccola queste regioni sono formate da cellule con peculiari caratteristiche, come la possibilità di trasmettere impulsi elettrici o di percepire la presenza di molecole dannose. La complessità del SNC ne rende la piena comprensione un’impresa ardua. Uno dei progressi scientifici che maggiormente hanno permesso di comprendere i meccanismi che regolano il funzionamento del SNC è stata la generazione di modelli transgenici, che consentono di studiare il ruolo di singoli geni anche in singoli tipi cellulari (knockout condizionali) o dopo la nascita (knockout inducibili). Durante il mio dottorato, ho utilizzato due modelli transgenici al fine di abolire in un caso la produzione di una proteina della matrice extracellulare (MEC), il collagene VI; nell’ altro caso l’enzima glucocerebrosidasi (GBA1), deleto specificamente nelle cellule della glia mielinizzante, ovvero nelle cellule di Schwann e negli oligodendrociti (OL). Il modello murino Col6a1-/- è uno strumento potente per comprendere la patogenesi delle malattie causate da mutazioni dei geni codificanti il Collagene VI. Essendo un knockout totale, il ruolo di questa proteina è stato esplorato in diversi distretti, tra cui la giunzione neuromuscolare e il SNC. I risultati ottenuti durante il mio dottorato indicano che il Collagene VI è depositato a livello della fessura sinaptica della giunzione, e che la sua assenza altera la trasmissione mediata dall’acetilcolina e l’apparato postsinaptico, indicando che la debolezza muscolare che si osserva nei pazienti con malattie del Collagene VI è anche riconducibile a difetti di trasmissione neuromuscolare. Inoltre, ho lavorato ad un progetto atto a comprendere come l’assenza di Collagene VI possa alterare il comportamento e le abilità cognitive. Questo tipo di alterazioni sono state osservate sia nel modello Col6a1-/- sia per la prima volta in pazienti con malattie
del Collagene VI. Abbiamo identificato una difettiva trasmissione dopaminergica e proposto un meccanismo che coinvolge le meningi. Da un lato questi due progetti rappresentano un classico approccio di genomica funzionale, in cui un modello transgenico viene generato per studiare il ruolo di una proteina in diversi organi. Ma andando oltre la ricerca di base, è stato adottato un approccio traslazionale cercando di validare nei pazienti ciò che era stato osservato nel modello murino, al fine di ampliare le conoscenze relative alle malattie da Collagene VI. L’altro progetto in cui sono stata coinvolta durante il mio dottorato consiste nello studio di GBA1 specificatamente nella glia mielinizzante, in particolare negli OL. I loro ruoli principali consistono nell’assicurare propagazione saltatoria dell’impulso elettrico e supportare i neuroni. GBA1 è coinvolto nell’insorgenza di una malattia da accumulo lisosomiale chiamata malattia di Gaucher, ed è considerato un fattore di rischio per il morbo di Parkinson. In entrambe le malattie, si osserva neurodegenerazione ma il contributo di GBA1 oligodendrogliale non è mai stato investigato: questo progetto è il primo che tenta di capire se e in che modo l’assenza di questo enzima ha un impatto sugli OL e quindi sulla funzionalità neuronale. Usando differenti approcci, abbiamo valutato in vitro gli effetti dell’inibizione di GBA1 nella funzionalità lisosomiale e nella mielinizzazione. Successivamente abbiamo utilizzato la nuova linea condizionale dov’è stato osservato un coinvolgimento della mielina e degenerazione, che suggeriscono per la prima volta il contributo degli OL nella malattia di Gaucher e nel Parkinson
A conditional mouse model and in vitro system to study Gba1 in myelinating glia: novel contribution for Gaucher Disease and Parkinson's Disease
No full textLack of collagen VI promotes neurodegeneration by impairing autophagy and inducing apoptosis during aging
Full text linkCollagen VI is an extracellular matrix (ECM) protein with a broad distribution in different tissues and mostly deposited at the close periphery of the cell surface. Previous studies revealed that collagen VI protects neurons from the toxicity of amyloid-βpeptides and from UV-induced damage. However, the physiological role of this protein in the central nervous system (CNS) remains unknown. Here, we established primary neural cultures from murine cortex and hippocampus, and carried out in vitro and in vivo studies in wild-type and collagen VI null (Col6a1-/-) mice. Col6a1-/- neural cultures displayed an increased incidence of spontaneous apoptosis and higher vulnerability to oxidative stress, accompanied by altered regulation of autophagy with increased p62 protein levels and decreased LC3 lipidation. Analysis of brain sections confirmed increased apoptosis and abnormal regulation of autophagy in the CNS of collagen VI-deficient animals. To investigate the in vivo physiological consequences of these CNS defects, we carried out functional studies and found that motor and memory task performances were impaired in aged Col6a1-/-mice. These findings indicate that lack of collagen VI leads to spontaneous apoptosis and defective autophagy in neural cells, and point at a protective role for this ECM protein in the CNS during physiological aging
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Collagen VI in healthy and diseased nervous system
No full textCollagen VI is a major extracellular matrix protein exerting a number of functions in different tissues, spanning from biomechanical to regulatory signals in the cell survival processes, and playing key roles in maintaining the stemness or determining the differentiation of several types of cells. In the last couple of years, emerging findings on collagen VI have led to increased interest in its role in the nervous system. The role of this protein in the peripheral nervous system was intensely studied and characterized in detail. Collagen VI acts as a regulator of Schwann cell differentiation and is required for preserving peripheral nerve myelination, function and structure, as well as for orchestrating nerve regeneration after injury. Although the role and distribution of collagen VI in the peripheral nervous system is now well established, the role of this distinctive extracellular matrix component in the central nervous system, along with its links to human neurological and neurodegenerative disorders, remains an open field of investigation. In this Review, we summarize and discuss a number of recent findings related to collagen VI in the central and peripheral nervous systems. We further link these findings to different aspects of the protein that are relevant to human diseases in these compartments in order to provide a comprehensive overview of the roles of this key matrix component in the nervous system
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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