Autism is one of the leading causes of human intellectual disability (ID). More than 1% of the human population has autism spectrum disorders (ASDs), and it has been estimated that over 50% of those with ASDs also have ID. Fragile X syndrome (FXS) is the most common inherited form of mental retardation and is the leading known genetic cause of autism, affecting approximately 1 in 4000 males and 1 in 8000 females. Approximately 30% of boys with FXS will be diagnosed with autism in their later lives. The cause of FXS is through an over-expansion of the CGG trinucleotide repeat located at the 5’ untranslated region of the FMR1 gene, leading to hypermethylation of the surrounding sequence and eventually partially or fully silencing of the gene. Therefore, the protein product of the gene, fragile X mental retardation protein (FMRP), is reduced or missing. As a single-gene disorder, FXS offers a scientifically tractable way to examine the underlying mechanism of the disease and also shed some light on understanding ASD and ID. The mouse model of FXS (Fmr1−/y mice) is widely accepted and used as a good model, offering good structural and face validity. Since a primary deficit of FXS is believed to be altered neuronal communication, in this thesis I examined white matter tract and dendritic spine abnormalities in the mouse model of FXS. Loss of FMRP does not alter the gross morphology of the white matter. However, recent brain imaging studies indicated that loss of FMRP could lead to some minute abnormalities in different major white matter tracts in the human brain. The gross white matter morphology and myelination was unaltered in the Fmr1−/y mice, however, a small but significant increase of axon diameter in the corpus callosum (CC) was found compared to wild-type (WT) controls. Our computation model suggested that the increase of axon diameter in the Fmr1−/y mice could lead to an increase of conduction velocity in these animals. One of the key phenotypes reported previously in the loss of FMRP is the increase of “immature” dendritic spines. The increase of long and thin spines was reported in several brain regions including the somatosensory cortex and visual cortex in both FXS patients and the mouse model of FXS. Although recent studies which employed state-of-the-art microscopy techniques suggested that only minute differences were noticed between the WT and Fmr1−/y mice. In agreement with previous findings, I found an increase of dendritic spine density in the visual cortex in the Fmr1−/y mice, and spine morphology was also different between the two genotypes. We found that the spine head diameter is significantly increased in the CA1 area of the apical dendrites of the Fmr1−/y mice compared to WT controls. Dendritic spine length is also significantly increased in the same region of the Fmr1−/y mice. However, apical spine head size does not alter between the two genotypes in the V1 region of the visual cortex, and spine length is significantly decreased in the Fmr1−/y mice compared to WT animals in this region. Lovastatin, a drug known as one of the 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors, functions as a modulator of the mitogen-activated protein kinases (MAPK) pathway through inhibiting Ras farnesylation, was used in an attempt to rescue the dendritic spine abnormalities in the Fmr1−/y mice. Mice lacking FMRP are susceptible to audiogenic seizure (AGS). Previous work has shown that 48 hr of lovastatin treatment reduced the incidence of AGS in the Fmr1−/y mice. However, chronic lovastatin treatment failed to rescue the spine density and morphology abnormalities in the Fmr1−/y mice. Mouse models are invaluable tools for modelling human diseases. However inter-strain differences have often confounded results between laboratories. In my final Chapter of this thesis, I compared two commonly used C57BL/6 substrains of mice by recording their electrophysiological responses to visual stimuli in vivo. I found a significant increase of high-frequency gamma power in adult C57BL/6JOla mice, and this phenomenon was reduced during the critical period. My results suggested that the C57BL/6JOla substrain has a significant stronger overall inhibitory network activity in the visual cortex than the C57BL/6J substrain. This is in good agreement with previous findings showing a lack of open-eye potentiation to monocular deprivation in the C57BL/6JOla substrain, and highlights the need for appropriate choice of mouse strain when studying neurodevelopmental models. They also give valuable insights into the genetic mechanisms that permit experience-dependent developmental plasticity. In summary, these findings give us a better understanding of the fine structure abnormalities of the Fmr1−/y mice, which in turn can benefit future discoveries of the underlying mechanisms of neurodevelopmental disorders such as ID and ASDs.

A key problem in multiple sclerosis (MS) is the diminished capacity for myelin repair. Although oligodendrocyte (OL) precursors can be seen at the lesion site, their ability to differentiate appears inhibited. MicroRNAs are key regulators of OL differentiation, and have been observed to be misregulated in MS lesions compared to healthy white matter. Thus, aberrant microRNA expression in MS lesions may disrupt the ability of incoming oligodendrocyte progenitor cells (OPC s) to differentiate. Specifically, a microRNA known as miR - 145 is downregulated as OPCs progress to OLs, but is found at unusually high levels in MS lesions. In this study, we investigated how misregulation of miR - 145 affects OL differentiation in vitro. Bioinformatic analysis revealed that putative targets of miR - 145 are significantly enriched for factors which promote actin cytoskeleton organization and myelination. An immortalized OL cell line was transduced with an inducible lentivirus to create stable lines that overexpress miR - 145. These stable lines were characterized while proliferating, early in differentiation and late in differentiation. Immunofluorescence was used to quantify changes in proliferation rate, apoptosis, branching ability and myelin gene expression. qPCR arrays were used to quantify changes in microRNA target expression levels between induced and uninduced cells. Two stable lines were created: ON - 145 - 1 and ON - 145 - 2, which upon induction, over - express miR - 145 ~33 - fold and ~11 - fold, respectively. When proliferating, no significant morphological differences nor target expression differences could be detected between induced and uninduced cells. Proliferation was significantly decreased in ON - 145 - 1 induced cells, but not in ON - 145 - 2. No changes in apoptosis frequency were detected. In contrast, during early and late differentiation, both induced cell lines showed significant morphological defects characterized by a reduction in both iii primary and secondary branching. Further, significant differences in branching ability were observed between induced cells of ON - 145 - 1 and ON - 145 - 2, suggesting a dose - dependent response to miR - 145 overexpression. Expression of MAG, a myelin marker, was also significantly lowered in induced cells of both cell lines. Finally, we found that multiple miR - 145 targets involved in promoting cytoskeletal organization and myelination were significantly decreased both early and late in differentiation. These results suggest that overexpression of miR - 145 during OL differentiation may disrupt actin organization and myelin gene expression required for successful process extension and subsequent myelinating ability. Thus, the increase in miR - 145 in MS lesions may be a significant contributing factor to the loss of myelin repair in MS lesions.

No description available.

The overall focus of this research project was to develop an in vitro tissue-engineered system that accurately reproduced the physiology of the sensory elements of the stretch reflex arc as well as engineer the myelination of neurons in the systems. In order to achieve this goal we hypothesized that myelinating culture systems, intrafusal muscle fibers and the sensory circuit of the stretch reflex arc could be bioengineered using serum-free medium formulations, growth substrate interface design and microfabrication technology. The monosynaptic stretch reflex arc is formed by a direct synapse between motoneurons and sensory neurons and is one of the fundamental circuits involved in motor control. The circuit serves as a proprioceptive feedback system, relaying information about muscle length and stretch to the central nervous system (CNS). It is composed of four elements, which are split into two circuits. The efferent or motor circuit is composed of an [alpha]-motoneuron and the extrafusal skeletal muscle fibers it innervates, while the afferent or sensory circuit is composed of a Ia sensory neuron and a muscle spindle. Structurally, the two muscular units are aligned in parallel, which plays a critical role modulating the system's performance. Functionally, the circuit acts to maintain appropriate muscle length during activities as diverse as eye movement, respiration, locomotion, fine motor control and posture maintenance. Myelination of the axons of the neuronal system is a vertebrate adaptation that enables rapid conduction of action potentials without a commensurate increase in axon diameter. In vitro neuronal systems that reproduce these effects would provide a unique modality to study factors influencing sensory neuronal deficits, neuropathic pain, myelination and diseases associated with myelination. In this dissertation, results for defined in vitro culture conditions resulting in myelination of motoneurons by Schwann cells, pattern controlled myelination of sensory neurons, intrafusal fiber formation, patterned assembly of the mechanosensory complex and integration of the complex on bio-MEMS cantilever devices. Using these systems the stretch sensitive sodium channel BNaC1 and the structural protein PICK1 localized at the sensory neuron terminals associated with the intrafusal fibers was identified as well as the Ca2+ waves associated with sensory neuron electrical activity upon intrafusal fiber stretch on MEMS cantilevers. The knowledge gained through these multi-disciplinary approaches could lead to insights for spasticity inducing diseases like Parkinson's, demyelinating diseases and spinal cord injury repair. These engineered systems also have application in high-throughput drug discovery. Furthermore, the use of biomechanical systems could lead to improved fine motor control for tissue-engineered prosthetic devices.

Primary cilia are nonmotile, hair-shaped organelles that extend from the basal body in the centrosome. The present study is the first investigation of this organelle in the oligodendrocyte lineage in vivo. I used immunohistochemical approaches in normal and cilia-deficient mutant mice to study cilia in relation to oligodendrogenesis and myelination. Primary cilia immunoreactive for Arl13b and ACIII were commonly present in NG2+ oligodendrocyte progenitor cells (OPCs), in which cilia-associated pathways control proliferation, differentiation, and migration. The loss of primary cilia is generally associated with enhanced Wnt/β-catenin signaling, and Wnt/β-catenin signaling has been shown to promote myelin gene expression. I examined whether the lack of cilia in the oligodendrocyte lineage is associated with elevated Wnt/β-catenin activity. I found that absence of a primary cilium was associated with with higher levels of TCF3, and with β-galactosidase in Axin2-lacZ Wnt reporter mice. This evidence supports the proposal that cilia loss in oligodendrocytes leads to enhanced Wnt/β-catenin activity, which promotes myelination. Cilia are dependent on the centrosome, which assembles microtubules for the cilium, the cytoskeleton, and the mitotic spindle. Centrosomes are the organizing center for microtubule assembly in OPCs, but this function is decentralized in oligodendrocytes. I found that the intensity of centrosomal pericentrin was reduced in oligodendrocytes relative to OPCs, and γ-tubulin was evident in centrosomes of OPCs but not in mature oligodendrocytes. These decreases in centrosomal proteins might contribute to functional differences between OPCs and oligodendrocytes. The importance of cilia in the oligodendrocyte lineage was examined in Tg737orpk mice, which have a hypomorphic IFT88 mutation resulting in decreased cilia numbers and lengths. These mice showed marked, differential decreases in numbers of oligodendrocytes and myelin, yet little or no change in OPC populations. It appears that sufficient cells were available for maturation, but lineage progression was stalled. There were no evident effects of the mutation on Wnt/β-catenin. Factors that might contribute to the abnormalities in the oligodendrocyte lineage of Tg737orpk mice include decreased cilia-dependent Shh mitogenic signaling and dysregulation in cilia-associated pathways such as Notch and Wnt/β-catenin.

Multiple Sclerosis (MS) is an inflammatory disease which causes areas of demyelination in the Central Nervous System (CNS) and affects only humans. Current therapies for MS are focused on anti-inflammatory treatment, which reduce the occurrence and clinical relapses of the disease. However, progressive disability of the disease is related to axonal degeneration. After demyelination, remyelination occurs, which helps repair the demyelinated lesions and protects axons from degeneration. However, this endogenous remyelination is inefficient, and currently there are no therapies available to enhance remyelination. The aim of this thesis was to first characterize a fast and reliable model to study CNS remyelination in vitro, and second to investigate the role of semaphorin 3a (Sema3A) and semaphorin 3f (Sema3F) signaling in CNS remyelination. Various in vivo models have been developed to investigate the pathology of multiple sclerosis, and can be used to test remyelination therapies. However, in vivo models are expensive, animal- and time- consuming. Until now, there has been no well-characterized and robust in vitro model for remyelination study. In this thesis, an ex vivo slice culture system with mouse brain and spinal cord was developed, and characterized by immunofluorescent microscopy and transmission electron microscopy, for CNS remyelination study. Automated (re)myelinating quantification by image pro plus software was developed and validated to provide a fast and reliable way for testing factors that change remyelination efficiency. Two such factors are Sema3A and 3F, which were initially identified as axon guidance cues during development. Sema3A (repulsive) and 3F (attractive) were proved to play a role in oligodendrocyte precursor cell (OPC) migration during development, and hypothesized to be important in remyelination. In this thesis, I investigated the effects and mechanisms for this by adding recombinant SEMA3A or SEMA3F or by knockdown their obligatory receptors Neuropilin (Nrp) 1 and 2, using lentivirus induced miRNAi. Slice culture and primary OPC culture were used to determine the effect on OPC survival, migration, proliferation, differentiation and myelination.

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS) characterized by demyelination and loss of oligodendrocytes (OLGs), the CNS myelin-producing cells. Thus, understanding the mechanisms that control OLG development can provide valuable knowledge regarding remyelination therapies for MS. This disease is thought to result from an autoimmune attack towards myelin. FTY720, an immunomodulator under evaluation for MS treatment is a sphingosine-1-phosphate (S1P) analog. We found before that S1P plays a crucial role in the NT-3-mediated survival of OLGs, an observation that led us to investigate whether FTY720 could have any effect on these cells. Our studies demonstrate that FTY720 indeed has a direct effect on OLG progenitors, protecting them from apoptotic death through a mechanism involving ERK1/2 and Akt activation. However, another key finding of our study was that this drug arrested OLG differentiation, an effect counteracted by NT-3 which not only enhanced the survival of OLG progenitors but also stimulated their maturation. Furthermore, NT-3 induced an increase in myelin basic protein (MBP) levels in the absence of effects on MBP gene promoter activation or mRNA expression. These observations suggested that NT-3 up-regulated MBP levels by a posttranscriptional mechanism raising the question of whether this neurotrophin could have a more general positive effect on the expression of other OLG proteins. In agreement with this idea, we found that NT-3 also induced the expression of the myelin proteins MAG and MOG. Additionally, [35S]-Methionine labeling indicated a 50% increase in de novo protein synthesis following only a 15 min exposure to NT-3. Such a rapid increase in protein synthesis reinforced the idea that NT-3 plays a crucial role regulating protein expression by posttranscriptional mechanisms. In support of this possibility, we found that NT-3 stimulated the phosphorylation of the initiation factor eIF4E and its inhibitory partner 4EBP1, both essential players in mediating cap-dependent protein synthesis. This stimulation involved the activation of ERK1/2 and PI3K/mTOR mediated signaling pathways. To our knowledge, this is the first study on the regulation of translation initiation in OLGs and the first report describing the potential role of NT-3 as an activator of initiation.

Myelination of axons in the central and peripheral nervous system (CNS and PNS) is required for saltatory propagation of nerve impulses. Myelinated axons are organized in functionally distinct membrane domains and the correct formation and maintenance of these domains is fundamental for the correct propagation of the electrical impulse; however, the underlying mechanisms by which these domains are specified are just starting to be unravelled. The paranodal junctions (PNJs) have been shown to contribute to node formation in the CNS and to domain maintenance both in the CNS and PNS. In this thesis I have studied the function of the linkage of the PNJs to the axonal cytoskeleton in regulating these processes by using a combination of knock out and transgenic rescue strategies. Further, I have initiated studies on the live imaging of node assembly. I have shown that the link between the PNJ and the axonal cytoskeleton is required for both the correct timing of oligodendrocyte process migration and for clustering nodal proteins at heminodes, before nodes of Ranvier are formed. Failure to correctly regulate these events during development results in shorter internodes in adults. Further, I have shown the importance of the axonal paranodal cytoskeleton in the maintenance of the node of Ranvier, both in CNS and PNS. In the absence of a link between the PNJ and the axonal cytoskeleton, paranodes disassemble, which causes disruption of both nodal and juxtaparanodal domains. Electron microscopy shows that, despite paranodal disruption, transverse bands are preserved when the anchorage of the PNJ to the axonal cytoskeleton is removed. Surprisingly, the preservation of these structures is associated with the amelioration of the neurological defects seen in mice lacking PNJs. In order to study nodal assembly, I have initiated studies on the transport of the nodal proteins Neurofascin186 and β1Nav tagged with fluorescent tags in transgenic mice, in order to analyse axonal transport during development. I have exploited the triangularis muscle explant preparation and have analysed transport of nodal proteins in young and adult mice. I have shown that transport speeds decrease with age and that the two proteins are transported at different speeds in young animals, but these differences do not persist in adults. This suggests that during myelination these proteins are transported in different vesicles and that this may change during development.

Diversos estudos relatam os efeitos da exposição à nicotina nos períodos pré e pós-natal, contudo, pouco se sabe a respeito dos efeitos da fumaça do cigarro na cascata de eventos que caracteriza o desenvolvimento do sistema nervoso central (SNC). Neste contexto, o objetivo deste trabalho foi esclarecer se a exposição à fumaça do cigarro no início do período pós-natal induz prejuízo ao desenvolvimento do SNC na infância, e as possíveis consequências na adolescência e na fase adulta. Camundongos BALB/c foram expostos a uma mistura de fumaça central e lateral do cigarro referência 3R4F (Universidade de Kentucky, EUA), desde o 3° dia de vida pós-natal (P) até P14 por duas horas diárias. Nossos resultados indicam que a exposição à fumaça do cigarro no início do período pós-natal induz prejuízo ao processo de aprendizado e memória e aumento na ansiedade em todas as idades avaliadas, além de induzir diminuição da atividade locomotora na infância e na adolescência. Ainda, observamos diminuição dos níveis de BDNF e das proteínas sinápticas sinapsina e sinaptofisina no hipocampo, cerebelo, córtex pré-frontal e estriado. A fumaça do cigarro também induz diminuição na porcentagem de fibras mielinizadas no nervo óptico e aumento da proteína básica de mielina (PBM) no cerebelo na infância, além de diminuição da PBM no telencéfalo e tronco encefálico na adolescência e no cerebelo na fase adulta. Nossos resultados sugerem que a exposição à fumaça do cigarro no início do período pós-natal causa prejuízo ao desenvolvimento do SNC, sendo que não há reversão dos efeitos observados no aprendizado e memória ou mesmo nos níveis de proteína pré-sináptica na adolescência e na fase adulta. / Several studies show the effects of nicotine exposure during pre- and postnatal period. However, little is known about the effects of environmental tobacco smoke (ETS) in the cascade of events that characterizes the brain development. Thus, the aim of this study was to evaluate the effects of ETS in early brain development. BALB/c mice were exposed to a mixture of mainstream and sidestream of tobacco smoke of reference cigarettes 3R4F (University of Kentucky, EUA) from the 3rd (P3) to the 14th (P14) day of life, during 2h/day. Our results showed that ETS induced impairment in learning and memory and increased anxiety in all the ages evaluated. In addition, there was a decrease in locomotor activity during childhood and adolescence. ETS also induced impairment in synaptic transmission, by a decrease in synapsin, synaptophysin and BDNF in hippocampus, cerebellum and prefrontal cortex as compared to the control group. The percentage of myelinated fibers in the optic nerve in childhood and in myelin basic protein (MBP) in the telencephalon and brainstem were lower in adolescents mice exposed to ETS when compared to the control group. In cerebellum, there was an increase in MBP in infants and a decrease in adults compared to the control group. Taken all together, our results suggest that the exposure to ETS in the early postnatal period induces impairment to the brain development. It is noteworthy that the effects on learning and memory or even in the presynaptic protein levels were not reversed in adolescence and adulthood.

Diversos estudos relatam os efeitos da exposição à nicotina nos períodos pré e pós-natal, contudo, pouco se sabe a respeito dos efeitos da fumaça do cigarro na cascata de eventos que caracteriza o desenvolvimento do sistema nervoso central (SNC). Neste contexto, o objetivo deste trabalho foi esclarecer se a exposição à fumaça do cigarro no início do período pós-natal induz prejuízo ao desenvolvimento do SNC na infância, e as possíveis consequências na adolescência e na fase adulta. Camundongos BALB/c foram expostos a uma mistura de fumaça central e lateral do cigarro referência 3R4F (Universidade de Kentucky, EUA), desde o 3° dia de vida pós-natal (P) até P14 por duas horas diárias. Nossos resultados indicam que a exposição à fumaça do cigarro no início do período pós-natal induz prejuízo ao processo de aprendizado e memória e aumento na ansiedade em todas as idades avaliadas, além de induzir diminuição da atividade locomotora na infância e na adolescência. Ainda, observamos diminuição dos níveis de BDNF e das proteínas sinápticas sinapsina e sinaptofisina no hipocampo, cerebelo, córtex pré-frontal e estriado. A fumaça do cigarro também induz diminuição na porcentagem de fibras mielinizadas no nervo óptico e aumento da proteína básica de mielina (PBM) no cerebelo na infância, além de diminuição da PBM no telencéfalo e tronco encefálico na adolescência e no cerebelo na fase adulta. Nossos resultados sugerem que a exposição à fumaça do cigarro no início do período pós-natal causa prejuízo ao desenvolvimento do SNC, sendo que não há reversão dos efeitos observados no aprendizado e memória ou mesmo nos níveis de proteína pré-sináptica na adolescência e na fase adulta. / Several studies show the effects of nicotine exposure during pre- and postnatal period. However, little is known about the effects of environmental tobacco smoke (ETS) in the cascade of events that characterizes the brain development. Thus, the aim of this study was to evaluate the effects of ETS in early brain development. BALB/c mice were exposed to a mixture of mainstream and sidestream of tobacco smoke of reference cigarettes 3R4F (University of Kentucky, EUA) from the 3rd (P3) to the 14th (P14) day of life, during 2h/day. Our results showed that ETS induced impairment in learning and memory and increased anxiety in all the ages evaluated. In addition, there was a decrease in locomotor activity during childhood and adolescence. ETS also induced impairment in synaptic transmission, by a decrease in synapsin, synaptophysin and BDNF in hippocampus, cerebellum and prefrontal cortex as compared to the control group. The percentage of myelinated fibers in the optic nerve in childhood and in myelin basic protein (MBP) in the telencephalon and brainstem were lower in adolescents mice exposed to ETS when compared to the control group. In cerebellum, there was an increase in MBP in infants and a decrease in adults compared to the control group. Taken all together, our results suggest that the exposure to ETS in the early postnatal period induces impairment to the brain development. It is noteworthy that the effects on learning and memory or even in the presynaptic protein levels were not reversed in adolescence and adulthood.