Le développement du système nerveux central fait intervenir de nombreux processus cellulaires comme la prolifération, la différenciation, l'apoptose, la migration neuronale et le guidage axonal. Ces processus sont finement régulés et aboutissent à la formation d'un système nerveux central fonctionnel. Au cours de cette thèse, je me suis principalement intéressé à une molécule chimiotropique, la Nétrine-1 et à ses récepteurs APP (Amyloïd-b Precursor Protein) et DCC (Deleted in Colorectal Cancer). La Nétrine-1 est impliquée à la fois dans le contrôle de la navigation neuronale (ie migration neuronale et guidage axonal) et dans celui de la survie neuronale. Un premier aspect de mon travail a consisté à étudier le rôle d'un nouveau récepteur à la Nétrine-1 : APP. Nous avons donc démontré que APP est un récepteur à la Nétrine-1 impliqué dans le guidage des axones commissuraux. En effet, APP collabore avec DCC afin de stimuler la croissance axonale en réponse à la Nétrine-1. Le second aspect de mon travail a été l'étude du rôle de la Nétrine-1 en tant que facteur de survie neuronale. En effet, son récepteur DCC appartient à la famille des récepteurs à dépendance. En absence de Nétrine-1, DCC ne reste pas inactif, mais déclenche une signalisation pro-apoptotique qui va éliminer la cellule. Nous avons démontré que pendant le développement du système nerveux, la Nétrine-1 inhibe cette signalisation et contrôle la survie des neurones commissuraux. Le contrôle de la signalisation pro-apoptotique de DCC par la Nétrine-1 pourrait ainsi réaliser un contrôle qualité des projections axonales et faciliter l'orientation du cône de croissance lors du guidage du cône de croissance / The development of the central nervous system requires several cellular processes such as proliferation, differentiation, apoptosis, neuronal migration and axon guidance. This whole process is finely regulated and leads to the formation of a functional central nervous system. During my thesis, I have mainly worked on a chemotropic molecule, Netrin-1 and its receptors APP (Amyloid-ß Precursor Protein) and DCC (Deleted in Colorectal Cancer). Netrin-1 is involved in both neuronal navigation (neuronal migration and axonal guidance) and neuronal survival. I have firstly investigated the role of a new Netrin-1 receptor, APP during axonal guidance. We have shown that APP is involved in the guidance of commissural axons. Indeed, APP collaborates with DCC in order to promote axonal outgrowth in response to Netrin-1. Thereafter, I have investigated the role of Netrin-1 as a neuronal survival factor. In fact, the Netrin-1 receptor DCC belongs to the dependence receptor family. In absence of Netrin-1, DCC does not remain inactive, since it triggers a pro-apoptotic signalling pathway. During the development of the central nervous system, we have shown that Netrin-1 blocks the pro-apoptotic signalling pathway and promotes neuronal survival. The Netrin-1 control of DCC pro-apoptotic signalling might carry out a “quality control” of the axonal projection or/and it could promote the steering of the growth cone during axonal guidance

L'Atrophie Musculaire spinale (SMA) est une maladie neurodégénérative causée par des mutations du gène SMN1 et caractérisée par la dégénérescence sélective des motoneurones alpha de la moelle épinière. les mécanismes moléculaires de la SMA ne sont aps clairs. cependant, deux hypothèses ont été retenues:D'une part, que la déficience en SMN entraine une perturbation de la biogenèse des snRNPs spliceosomales individuelles et par conséquent des défauts d'épissage. pendant ma thèse, nous avons montré que la déficience en SMN provoquait une diminution des particules tri-snRNPs majeures amis surtout mineures et que cela avait des conséquences sur l'épissage d'un sous-groupe de pré-ARNm contenant des introns mineurs.D'autre part, que la déficience en SMN entraine des altérations de transport d'ARN dans les axones, essentiels pour la survie des motoneurones. A part l'ARNm de la beta-actine et l'ARNm de cpg15 récemment identifié, ceux qui pourraient être transportés par SMN n'ont pas été décrits. nous avons donc identifié les ARN interagissant avec les isoformes a-SMN et SMN-fl dans des cellules neuronales, et montré que certains de ces ARN cibles colocalisent avec SMN dans les axones, suggérant qu'elle est impliquée dans leur transport. / Spinal Muscular Atrophy is a neurodegenerative disease caused by mutations in SMN1 gene. SMA is characterized by the loss of alpha-motoneurons of the spinal cord. However, the precise molecular mechanisms underlying the disease are still unkown. two hypotheses have been retained to explain SMA pathigenesis:In one hand, the fact that SMN deficiency leads to a perturbation of individual snRNPs biogenesis and consequently splicing defects. During my PhD, we have shown that SMN deficiency alters the levels of major, but mostly, minor tri-snRNPs. And that leads to splicing defects of a subset of pre-mRNA containing minor introns.In the other hand, that SMN deficiency causes alteration of axonal transport of RNAs crucial to motoneurons survival. Except beta-actin mRNA and the recently identified cpg mRNA, the RNA targets of SMN have not been described. We succeed to identify RNA targets of both a-SMN and SMN-fl isoformes in a neuronal cell line and colocalisation data of some of these targets suggested that SMN could be implicated in the transport of these RNAs.

No description available.

Traumatic brain injury (TBI) remains an important cause of morbidity and mortality within society. TBI may result in both focal and diffuse brain injury. Diffuse traumatic axonal injury (TAI) is an important pathological substrate of TBI, and can be associated with a range of clinical states, ranging from concussion through to death, the clinical severity being associated with a number of factors related to the injury. A retrospective study was conducted using 406 cases with TBI, from the archive of the Academic Department of Pathology (Neuropathology) University of Edinburgh, during the period from1982 and 2005. This cohort was sequential and provided a unique description of the range of pathologies associated with fatal TBI within the Edinburgh catchment area. All the data was collected on a proforma and analysed to provide a description of the incidence in the injury patterns among the Edinburgh cohort. This cohort was then used to provide cases to try and critically assess the mechanisms of axonal injury in TBI. A study was undertaken to investigate TAI in an experimental model of non-impact head injury in a gyrencephalic mammalian model (piglet model) and in human autopsy materials using immunohistochemical analysis of a range of antibodies, and to define the distribution of axonal injury with flow and neurofilament markers in TAI. A further objective was to examine the expression of β-APP as an indicator of impaired axonal transport, three neurofilament markers targeting NF-160, NF-200, and the phosphorylated form of the neurofilament heavy chain (NFH), in different anatomical regions of piglet and human brains. The double immunofluorescence labelling method was then employed to investigate the hypothesis of co-localisation between β-APP and each one of the previous neurofilament markers. The animal studies showed significant differences in NF-160 between sham and injured 3-5 days old piglet cases (6 hour survival) and between 3-5 days sham and injured, when stained with SMI-34 antibody. In 4 weeks old piglet cases (6 hour survival), immunoreactivity of β-APP was significantly higher in injured than control. No other significant differences for any of the antibodies were noted, based on age, velocity, and survival time. Human results suggested that the brainstem had a higher level of β-APP and NF-160 than the corpus callosum and internal capsule. Co-localisation of β-APP with NFs was not a consistent feature of TAI in piglet and human brains, suggesting that markers of impaired axonal transport and neurofilament accumulation are sensitive to TAI, but may highlight different populations involved in the evolution of TAI.

Pumilio 2 (PUM2) is a member of the Puf family of mRNA binding proteins and translational regulators which are involved in various processes including embryonic patterning and memory formation. Nevertheless, its functions in the outgrowth of neuronal axons have not been studied. This study shows endogenous expression of PUM2 in neurites of dorsal root ganglia (DRG) neurons and transport of PUM2 along retinal ganglion cell (RGC) axons and their growth cones. Overexpression of PUM2 in DRG neurons resulted in shorter axons when compared to control neurons. Expression of either dominant negative mutation (dnPUM2) or PUM2W349G displayed a reduction in axonal length. PUM2 downregulation with microRNA (miRNA) also caused a reduction in neurite length compared to control neurons. Finally, PUM2 silencing did not alter eye size at E4, which allows investigation of axonal outgrowth in RGC in vivo. These results suggest a novel role for PUM2 in axonal outgrowth.

Introdução: A lesão axonal traumática (LAT) ou lesão axonal difusa (LAD) esta presente em grande parte dos traumatismos crânio-encefálicos (TCE), sendo importante causa de mortalidade e morbidade das suas vítimas. A LAT dispara uma sequência de mudanças neurodegenerativas encefálicas que são, paradoxalmente, acompanhadas por recuperação cognitiva. Objetivo: Avaliar quantitativamente a LAT, através da razão de transferência de magnetização (RTM) e de medidas volumétricas para caracterizar a evolução temporoespacial das mudanças macroscópicas e microscópicas e investigar possível correlação entre elas, auxiliando no entendimento da sua fisiopatologia. Este estudo ainda investigou correlação entre atrofia e dano axonal/mielínico e a evolução funcional. Métodos: Imagens 3D-T1, 3DGE (PRESTO) e de transferência de magnetização (ITM) foram obtidas de 26 pacientes vítimas de TCE moderado e grave e de 26 controles, de idade e sexo semelhantes. Os pacientes foram submetidos a RM com 2 (fase aguda tardia/subaguda), 6 (crônica precoce) e 12 (crônica tardia) meses do TCE. A RM foi realizada nos controles em apenas uma única ocasião. Através de métodos automatizados, calculou-se o volume da substancia cinzenta (SC), da substancia branca (SB) e do encéfalo total (ET), ajustando-os pelo volume intracraniano. A partir de histogramas da RTM obtidos das mesmas regiões, calculou-se a média e os percentis 25, 50 e 75% da RTM. As imagens PRESTO foram usadas na exclusão dos focos hemorrágicos da análise da RTM, nos pacientes. A evolução funcional foi medida pela escala prognostica de Glasgow (EPG), realizada um ano após o TCE. Resultados: A RTM media e o volume foram significativamente diferentes nos pacientes e nos controles. Os pacientes apresentaram RTM media maior (p < 0,05) e volume menor na SC e ET, desde o primeiro exame (fase aguda tardia/subaguda precoce). Na SB, valores menores tanto da RTM media (p=0,02) quanto do volume (p=0,009) foram observados nos pacientes apenas no terceiro exame (fase crônica tardia). Redução progressiva da RTM media dos pacientes foi observada em todos os compartimentos, estimada em 1,14% na SC, 1,38% na SB e 1,40% no ET durante todo o estudo. Houve também redução volumétrica gradual da SB e do ET, com taxa de atrofia total de 3,20% e 1,50%, respectivamente. Não houve relação entre redução da RTM media e atrofia. Nenhum dos parâmetros mostrou valor prognostico nas fases subaguda ou crônica precoce. Conclusões: A LAT resulta numa rarefação axonal/mielínica e redução volumétrica progressiva do tecido encefálico, que se perpetua por até um ano do trauma. As mudanças são mais expressivas e prolongada na SB. A redução do volume e da RTM media se mostraram independentes na LAT. Isso sugere que os dois parâmetros reflitam aspectos complementares da fisiopatologia da LAT, em níveis micro e macroestrutural / Introduction: Traumatic axonal injury (TAI) or diffuse axonal injury (DAI) is a frequent component of traumatic brain injury (TBI) and a major cause of mortality and morbidity in this population. It triggers a sequence of degenerative changes in the brain, that are paradoxically accompanied by cognitive recovery. Purposes: The present study used magnetization transfer ratio (MTR) and volumetric data to appreciate the spatiotemporal evolution of macroscopic and microscopic changes and investigate possible correlation between them, enhancing the knowledge about its pathophysiology. It also investigated correlation between atrophy and axonal/myelin damage and functional outcome. Methods: Volumetric T1-weighted, 3DGE (PRESTO) and magnetization transfer images (MTI) were obtained from 26 patients who experienced moderate to severe TBI and 26 age- and sex-matched controls. Patients were scanned at 2 (late acute/subacute stage), 6 (early chronic) and 12 months (late chronic) postinjury and controls, only once. Whole brain (WB), gray matter (GM) and white matter (WM) volumes were measured using automated technique and adjusted for intracranial volume. Histogram analysis was performed in the same regions, with calculation of the mean MTR and its 25, 50 and 75% percentiles. The PRESTO images were used to exclude the small lesions from the MTR analysis in the patients. Functional outcome was assessed 12 months after injury using the Glasgow Outcome Scale (GOS). Results: Mean MTR and volume were significantly different between patients and controls. Patients presented higher mean MTR values (p < 0,05) and smaller volume (p < 0,05) in the GM and WB, as of the first exam (late acute/subacute stage). In the WM, reduction of both, the mean MTR (p=.02) and volume (p=.009), was observed only in their third exam (late chronic stage). Progressive decrease of patients\' mean MTR was observed in all compartments, with rates of 1.14% for the GM, 1.38% for the WM and 1.40% for the WB across the study. Continuing reduction of the WM and WB volume was also observed, with total atrophy rate of 3.20% and 1.50%, respectively. No correlation between mean MT and the volumetric changes was found. None of the parameters showed prognostic value during the subacute and early chronic stages. Conclusions: TAI results in a progressive axonal/myelinic rarefaction and volumetric brain reduction that continues until a year postinjury. The changes are greater and lasts longer in the WM. The reduction in the volume and mean MTR were independent between them in TAI. This suggests that the two parameters reflect complementary aspects of the TAI pathologic lesion at macro and microstructural levels

No description available.

Reliable biomarkers of axonal damage are urgently needed in neurological diseases. Neurofilaments (Nf) are specific structural elements of neurons composed of at least three subunits: Nf light chain (NfL), Nf medium and Nf heavy chain (NfH). This PhD aimed to characterise NfL levels and their correlation with clinical features in patients with neurological diseases with a different rate of progression and following and under different treatment regimes. An important aim was also to develop a bioassay for NfL measurements in blood. Cerebrospinal fluid (CSF) NfL levels discriminated patients with a clinically isolated syndrome (CIS) (p=0.001) or multiple sclerosis (MS) (p=0.035) from healthy controls more efficiently, and was more sensitive to change after natalizumab therapy (p<0.0001) than CSF NfH (p=0.002). Further, CSF NfL levels decreased in fingolimodtreated MS patients (p=0.001), but not in those receiving placebo (p=0.433). Based on these findings, a sensitive method for the detection of NfL in serum was developed and validated. Patients with neurological diseases had higher serum NfL values than controls. In acute spinal cord injury (SCI), serum NfL levels correlated with injury severity and long-term motor outcome, and Minocycline treatment was associated with decreased NfL levels in complete SCI patients compared to placebo. Finally, I found that serum NfL levels were higher in CIS patients than in healthy controls but did not predict conversion to clinically definite MS (CDMS). Independent predictors of CDMS were instead oligoclonal bands, number of T2 lesions and age at CIS. Lower 25-OHvitamin D levels were associated with CDMS in univariate analysis, but this was attenuated in the multivariate model. In conclusion, NfL proved to be an analytically stable protein which is an important prerequisite for biomarkers. The role of NfL quantification as a surrogate measure of neuroaxonal damage is corroborated by my findings and further supports the usefulness of NfL as a putative biomarker of axonal damage in various neurological diseases.

Axonal degeneration is the major cause of disability in progressive multiple sclerosis (MS). It has been shown that in MS and relevant disease models, demyelinated axons harbor an increased number of mitochondria, which is reflected in bigger stationary sites of mitochondria, increased mitochondrial activity and increased transport speed of mitochondria. This axonal response of mitochondria to demyelination (ARMD) is protective, as there is an increase in energy demand due to the redistribution of sodium channels along the axon following demyelination. However, it remains to be determined how this ARMD is mounted and how mitochondrial dynamics are involved. By using in vivo and in vitro systems we are determined to elucidate the transport and fusion dynamics of the ARMD and where these additional mitochondria come from. Using a cerebellar slice culture system with lysolecithin induced demyelination, we show that the increase in mitochondrial occupancy of the axon already occurs at 24 hours after demyelination and plateaus around 3 to 4 days after demyelination. At 24 hours, there was a steep increase in the mitochondrial numbers inside the axon, which is then followed by an increase in mitochondrial size over the following days. All parameters decrease again over the following days, but remain elevated compared to baseline even 12 days after demyelination. To determine the source of these additional mitochondria and to assess the fusion dynamics within the axon, we used a lentivirus expressing a mitochondrial targeted photoconvertible dye (mEOS2) to label mitochondria in Purkinje cells. The mitochondria that are labelled green in the Purkinje cell axons are then photoconverted to red by illuminating the initial part of the axon with a 405-nm laser and imaged over the following 20 minutes to determine the transport and fusion dynamics. This showed an increased number of mitochondria moving from the cell body into the axon, as well as an increase in retrograde transport of mitochondria in the demyelinated compared to the myelinated axons. Furthermore the size of newly transported mitochondria and their speed was increased in the anterograde direction. Furthermore, the fusion rate of newly transported mitochondria with stationary converted mitochondria was increased in the demyelinated axons compared to myelinated control. These changes can also be observed in unmyelinated axons, as well as axons of cerebellar slices of the dysmyelinating shiverer mutant with or without lysolecithin treatment. The manipulation of mitochondrial dynamics after demyelination with the fission inhibitor mdivi-1 and the ATPase inhibitor oligomycin both showed an increasing or decreasing effect on the mitochondrial parameters after demyelination respectively. The effect on the axonal health after demyelination was detrimental with both of these treatments. Increasing mitochondrial biogenesis with pioglitazone increased axonal mitochondrial parameters, as well as ameliorated axonal damage after demyelination with lysolecithin. As the neuronal cell bodies in MS harbour mitochondrial DNA deletions, which affects their physiology, including energy production efficiency, another aim of this thesis was to model this deficiency in vitro. As it was not possible to model these mitochondrial defects in vitro within the experiments of this thesis, the characterization of a mitochondrial mutant in vivo model was done as a contribution to a greater set of experiments performed by other members of the Mahad lab.

Pumilio 2 (PUM2) is a member of the Puf family of mRNA binding proteins and translational regulators which are involved in various processes including embryonic patterning and memory formation. Nevertheless, its functions in the outgrowth of neuronal axons have not been studied. This study shows endogenous expression of PUM2 in neurites of dorsal root ganglia (DRG) neurons and transport of PUM2 along retinal ganglion cell (RGC) axons and their growth cones. Overexpression of PUM2 in DRG neurons resulted in shorter axons when compared to control neurons. Expression of either dominant negative mutation (dnPUM2) or PUM2W349G displayed a reduction in axonal length. PUM2 downregulation with microRNA (miRNA) also caused a reduction in neurite length compared to control neurons. Finally, PUM2 silencing did not alter eye size at E4, which allows investigation of axonal outgrowth in RGC in vivo. These results suggest a novel role for PUM2 in axonal outgrowth.