Thesis (Ph.D.)--Ohio University, March, 2009. / Title from PDF t.p. Release of full electronic text on OhioLINK has been delayed until April 1, 2011. Includes bibliographical references (leaves 99-108)

The timing of differentiation underlies the development of any organ system. In neural development, the expression of the transcription factor Hes1 has been shown to be oscillatory in neural progenitors, but at a low steady state in differentiated neurons. This change in the dynamics of expression marks the timing of differentiation. We previously constructed a mathematical model to test the experimental hypothesis that the topology of the miR-9/Hes1 network and specifically the accumulation of the micro-RNA, miR-9, could terminate Hes1 oscillations and account for the timing of neuronal differentiation, using deterministic delay differential equations. However, biochemical reactions are the result of random encounters between discrete numbers of molecules, and some of these molecules may be present at low numbers. The finite number of molecules interacting within the system leads to inherent randomness, and this is known as intrinsic stochasticity. The stochastic model predicts that low molecular number causes the time to differentiation to be distributed, which is in agreement with recent experimental evidence and considered important to generate cell type diversity. For the exact same model, fewer reacting molecules causes a decrease in the average time to differentiation, showing that the number of molecules can systematically change the timing of differentiation. Oscillations are important for a wide range of biological processes, but current methods for discovering oscillatory genes have primarily been designed for measurements performed on a population of cells. We introduce a new approach for analysing biological time series data designed for cases where the underlying dynamics of gene expression is inherently noisy at a single cell level. Our analysis method combines mechanistic stochastic modelling with the powerful methods of Bayesian nonparametric regression, and can distinguish oscillatory expression in single cell data from random fluctuations of nonoscillatory gene expression, despite peak-to-peak variability in period and amplitude of single cell oscillations. Models of gene expression commonly involve delayed biological processes, but the combination of stochasticity, delay and nonlinearity lead to emergent dynamics that are not understood at a theoretical level. We develop a theory to explain these effects, and apply it to a simple model of gene regulation. The new theory can account for long time-scale dynamics and nonlinear character of the system that emerge when the number of interacting molecules becomes low. Both the absolute length and the uncertainty in the delay time are shown to be crucial in controlling the magnitude of nonlinear effects.

Notch signalling is an evolutionary highly conserved signalling pathway. It plays various important roles in the regulation of many fundamental cellular processes such as proliferation, stem cell maintenance and differentiation during embryonic and adult development. Notch signalling has a simple transduction pathway. Upon Notch ligand binding to the receptor, the Notch intracellular domain (NICD) is released into the nucleus. The nuclear NICD interacts with the DNA-binding protein Suppressor of Hairless (Su(H)) to activate the expression of target genes, which are silenced by the Su(H)-corepressor complex in the absence of Notch activity. The functions of Notch are very context-dependent, making it important to identify the Notch regulated genes in different processes. Neural stem cells (NSCs) are cells that can divide and differentiate into all kinds of cells within the brain while they self-renew. Notch signalling is one of the key regulators in maintaining NSCs and performs a similar function in both Drosophila and vertebrate NSCs. Drosophila NSCs serve as an ideal model for studying the relationship between Notch function and stem cell behaviours. Although many target genes, such as the Hes genes, have been identified, they cannot fully account for the diversity of Notch responses. Therefore, further functional study of more potential target genes is needed to gain understanding about Notch-regulated NSC maintenance. In this thesis, a group of potential direct Notch target genes are examined for their responsiveness to Notch regulation and their functions in Drosophila NSCs. Previous genome-wide study in the Bray lab has found a number of potential Notch target genes in the Drosophila larval brain, with the characteristics of Notch transcription factor Su(H) binding and mRNA upregulation by Notch over-activation (Zacharioudaki et al. 2016). I first examined the Notch responsive element (NRE) activity of these potential Notch targets and their regulation by Notch both in vivo and in cell lines. The presented findings validated path, cables and Asph as direct Notch target genes in Drosophila NSCs, while syp, lola and Fer2 do not exhibit characteristics of Notch responsive targets in NSCs. The functional roles of two of the responsive genes, path and cables, were subsequently explored in Drosophila larval brains. Firstly, I found that Path, a potential amino acid transporter, is not only important for protecting NSC proliferation under normal and abnormal conditions through integrating growth pathways, but is also required for protecting brain growth under nutrition deprivation. Secondly, the cables gene was connected to a distal NRE through knocking out the suspected NRE region and the gene itself using the CRISPR/Cas9 technique. Subsequent experiments revealed that cables is also required for NSC proliferation. In summary, a group of direct Notch target genes were validated and as a consequence two genes that are important for protecting NSC proliferation were identified.

京都大学 / 新制・課程博士 / 博士(医科学) / 甲第23424号 / 医科博第129号 / 新制||医科||9(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 林 康紀, 教授 伊佐 正, 教授 高橋 淳 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21656号 / 医博第4462号 / 新制||医||1035(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 髙橋 良輔, 教授 浅野 雅秀, 教授 井上 治久 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Alzheimer's disease (AD), marked by a serious and progressive decline in cognitive abilities, is a severely debilitating disease that is becoming an increasing concern with our aging population. Defects in neurogenesis have been shown to exist in AD and aggravate the neuropathology and cognitive deficits associated with the disease. In this study, I aimed to characterize the cellular and molecular defects of neurogenesis in the triple transgenic mouse model of AD (3xTG). To do so, I first performed a detailed immunohistochemistry characterization using neurogenic markers that were quantified and analyzed in the hippocampus of control and 3xTG mice. This analysis not only revealed an overall decrease in the pool of neural stem and progenitor cells (NSPCs) in 3xTG brains, but also defects in proliferation, differentiation and a loss within the neuroblast, immature neuron and mature neuron populations. Subsequent immunohistochemistry analysis of two molecular targets, Hopx and LPAR1, involved in NSC maintenance and proliferation respectively, revealed their dysregulation in 3xTG brains, providing some indication of molecular defects underlying this loss. The neurosphere assay was next employed to assess cell-autonomous defects and fewer neurospheres were formed from cultured 3xTG NSPCs, suggesting a defect in NSPC pool expansion that is intrinsic to 3xTG NSPC function. Molecular characterization of these cultured NSPCs via qPCR revealed the upregulation of mitochondrial and fatty acid oxidation genes in 3xTG NSPCs, suggesting not only a dysregulation of metabolic functions, but also an acclimation to oxidative stress conditions. Interestingly, 3xTG NSPCs formed larger and more neurospheres when grown in galactose medium - which is used to simulate oxidative stress - relative to the control, confirming an adaptative response to oxidative stress conditions. Further characterization of these cellular defects and underlying molecular mechanisms can reveal novel therapeutic strategies for AD.

Alzheimer's disease (AD) leads to neurodegeneration resulting in cognitive and physical impairments. AD is denoted by accumulation of intracellular neurofibrillary tangles, known as tau, and extracellular plaques of the amyloid beta protein (Aβ). Aβ results from the proteolytic cleavage of the amyloid precursor protein (APP) by β- and gamma-secretases in the amyloidogenic pathway. Although, Aβ has been widely studied for neurodegeneration, the role of APP in both, the healthy and diseased conditions, has not yet been entirely understood. The function that APP has in neural stem cell (NSC) proliferation, differentiation, and migration during adult neurogenesis has been previously studied. Additionally, APP has be shown to be overexpressed after neural damage resulted from conditions, such as AD and traumatic brain injury (TBI). In this study, the role of APP in in vitro damaged neural tissue cells was further investigated by evaluating neural progenitor cell proliferation, migration, and differentiation after a scratch assay. For these purposes, induced pluripotent stem (iPS) cells from AD patients were differentiated into neural progenitor cells to model the disease conditions and later treated with Phenserine to reduce their levels of APP expression. The results suggested that APP may enhance neural progenitor cell proliferation and glial differentiation while inhibiting neural progenitor cell migration and neuronal cell specialization after neural tissue damage.

Cells in multicellular organisms are surrounded by a complex three-dimensional macromolecular extracellular matrix (ECM). This matrix, traditionally thought to uniquely serve a structural function providing support and strength to cells within tissues, is increasingly being recognized to have pleiotropic effects in neurogenesis and regeneration processes such as neocortex folding, stem cell niche maintenance, peripheral nerve regeneration, axonal growth, and many more. ECM mediates these processes via cell-ECM interactions which provide the cells with a wealth of signals including biophysical and mechanical cues in a spatiotemporal manner. Owing to the importance of the surrounding microenvironment, modern neural tissue engineering strategies have focused on the development of engineered biomaterials capable of finely instructing the neuronal response according to their physicochemical characteristics. Neurons and neural stem cells are in fact sensitive to their mechanical and topographical environment, and cell–substrate binding contributes to this sensitivity by activating specific signaling pathways for basic cell function. In addition, the advances in nanotechnology have opened the possibility of introducing decorative nano-motifs that interact with cells at the molecular level. Successful strategies in tissue engineering are driven by not only advances in the synthesis of highly instructive biomaterials but also greatly depend on the right selection of cell sources. As a matter of fact, advances in neural tissue engineering have been strongly hampered by the poor availability of cell sources, considering that primary neurons are the only type of cells that do not proliferate. The discovery of induced pluripotent stem cells (iPSCs) has addressed many of the cell-related limitations in neural tissue engineering, offering the possibility to consistently produce a wide range of neural cell lines. Advances in cell biology have led to the development of iPSCs-derived brain spheroid, which surely represent the most promising tools for several neural tissue engineering applications ranging from in vitro modelling of neurodegenerative diseases (i.e., Parkinson's, Huntington's and Alzheimer's), biomaterials testing and drug screening platforms. The overarching goal of my doctoral work was to engineer biomaterials with instructive physicochemical properties to elicit beneficial cellular responses that are suitable for different neural tissue engineering applications such as nerve regeneration and 3D in vitro modelling. In the first study (Chapter 2), I evaluated the compounded effects of surface stiffness and micro-topography on dorsal root ganglion and human bone-marrow mesenchymal stem cells behavior. To this end, arrays of parallel microchannels of different geometries were introduced on the surface of chitosan films by electrophoretic replica deposition. In addition, a novel chemical crosslinking with citric acid was performed to both enhance the long-term stability of the chitosan films and fine-tune the surface stiffness for the investigation of its role in cell behavior. In the second study (Chapter 3), I developed a novel nanocomposite consisting of a collagen hydrogel decorated with glycine-derived carbon nanodots (Gly-CNDs). After a comprehensive physicochemical characterization of the resulting nanocomposite, I evaluated the effects exerted on neuronal differentiation and electrophysiological maturation of mouse iPSCs-derived brain spheroid. In the third study (Chapter 4), I optimized an alignable collagen-based hydrogel characterized by anisotropically oriented fibers with potential applications in both peripheral and central nervous system repair. I established a protocol that encompasses the introduction in the collagen solution of biodegradable laminin-functionalized magnetic microbeads and the time-controlled application of an external magnetic field. The regenerative potential of the hydrogel was unveiled using mouse iPSCs-derived neural stem cells.

The cannabinoid system exerts functional regulation of neural stem cell (NSC) selfrenewal, proliferation, and differentiation during both homeostatic and pathologic conditions. Recent evidence suggests that cannabinoid signaling is neuroprotective against reduction in NSC proliferation and neurogenesis caused by a multitude of conditions including injury due to HIV-1 associated neurotoxic proteins, neuroinflammation, and stroke. Yet not all effects of cannabinoids or cannabinoid-like compounds on neurogenesis can be attributed to signaling through either of the classical cannabinoid receptors CB1 or CB2. The recently de-orphaned GPR55 is targeted by numerous cannabinoid compounds suggesting GPR55 may be causing these aberrant effects. Activation of GPR55 has shown immune-modulatory effects outside the central nervous system (CNS) and anti-inflammatory actions on microglia, the resident immune cells within the CNS. New evidence has confirmed that both human and murine NSCs express functional levels of GPR55 yet the effects that GPR55 activation has on adult neurogenesis or NSC responses to inflammation has not been elucidated. In the present study we sought to determine the role GPR55 signaling has on NSC proliferation and neurogenesis as well as possible neuroprotective mechanisms within the NSC pool in response to inflammatory insult. Activation of GPR55 increased human NSC proliferation in vitro as assessed by BrdU incorporation and flow cytometry. Neuronal differentiation was also upregulated by signaling through GPR55 under homeostatic conditions in both human and murine NSC samples. Expression of NSC differentiation markers (nestin, sox2, GFAP, S100b, DCX, bIII-tubulin) in vitro was determined by immunohistochemistry, qPCR, and flow cytometry. In vivo, C57BL/6 and GPR55-/- mice were administered the GPR55 agonist O-1602 (4 μg/kg/day) directly into the left hippocampus via stainless steel cannula connected to an osmotic mini-pump for a continuous 14 days. O-1602 treatment increased hippocampal NSC proliferation, survival, and immature neuron formation as compared to vehicle treated animals. These results were determined to be dependent on GPR55 activation as GPR55-/- animals did not show any response to agonist treatment. Interestingly, GPR55-/- mice displayed significantly reduced rates of hippocampal NSC proliferation and neuroblast formation as compared to C57BL/6 animals. Chronic production of inflammatory mediators, such as IL-1b seen in neuroinflammation, to NSCs is known to reduce proliferation rates and attenuate neurogenesis both in vitro and in vivo. Addition of GPR55 agonists to IL-1b (10 ng/mL) treated human and murine NSC samples in vitro protected against reductions in neuron formation as assessed by immunohistochemistry and flow cytometry. Moreover, inflammatory cytokine receptor mRNA expression was down regulated by GPR55 activation in a neuroprotective manner. To determine inflammatory responses in vivo, we treated C57BL/6 and GPR55-/- mice with LPS (0.2 mg/kg/day) continuously for 14 days via osmotic mini-pump. Reductions in NSC survival (as determined by BrdU incorporation), immature neurons, and neuroblast formation due to LPS were attenuated by concurrent direct intrahippocampal administration of the GPR55 agonist, O-1602 (4μg/kg/day) in C57BL/6 mice but not in GPR55-/-mice. Neuroprotection by O-1602 treatment was not found to be microglia dependent as microglia activation was not altered by agonist administration. Molecular analysis of the hippocampal region showed a suppressed ability to regulate immune responses by GPR55-/- animals manifesting in a prolonged inflammatory response (IL-1b, IL-6, TNFa) after chronic, systemic inflammation as compared to C57BL/6 animals. Taken together, these results suggest a neuroprotective role of GPR55 activation on NSCs in vitro and in vivo and that GPR55 provides a novel therapeutic target against negative regulation of hippocampal neurogenesis by inflammatory insult. / Biomedical Sciences

The neuronal differentiation of neural stem cells (NSCs) has received much attention due to its potential for the treatment of neurodegenerative diseases (i.e., Parkinson’s and Alzheimer’s diseases). In this regard, discovering compounds that direct differentiation of NSCs is highly required to facilitate therapeutic applications. In this study, we examined various bioactive compounds (SA1, SA2, LiCl, compound B, and DHED) to induce the neuronal differentiation of human neural stem cells (hNSCs). The study was conducted on the cells grown in three dimensional (3D) hydrogel or two dimensional (2D) environment since 3D hydrogel mimics the extracellular matrix and provides physiologically more relevant environment than 2D cell culture system. Three-dimensional (3D) hydrogel systems in this study involve polysaccharides such as alginate and hyaluronic acid. Neuronal differentiation of hNSCs was monitored in genetic level and protein level by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunocytochemistry (ICC), respectively. This study will show the effect of bioactive compounds on hNSCs differentiation in 2D and 3D culture systems. / Bioengineering