Browsing by Subject "Flow cytometry"
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Item Open Access Alterations in the molecular properties of neural stem cells from aged brains and brain tumors(Bilkent University, 2017-06) Burhan, Özge PelinIt is known that new neuron formation in the brain continues throughout the life of an organism. In the adult human brain, it was proven that neurogenesis in the hippocampus is higher than expected, almost 700 new neurons are formed in a day. The formation of new neurons is supported by the stem cell subpopulation in the brain. With learning and the formation of new memories, the neuron production increases. However, changes in the cognitive abilities with advancing age are thought to be caused by the functional and molecular alterations in the stem cell populations. Molecular changes in neural stem cells throughout aging were found to be deterrents of the increased risk of cancer with age, such as tumor suppressor mechanisms. However, the activation and overlap of tumor suppressing mechanisms result in senescence in stem cells that have accumulated oncogenic mutations, which causes the stem cell pool exhaustion. It is thought that cancer cells acquire stem cell-like properties in order to have the unlimited proliferation and self-renewal properties, which are characteristics of both healthy and cancer stem cells. Neural cancer stem cells have the ability to produce glial and neural cells, like normal stem cells. The cancer stem cell subpopulations are implicated in the growth of tumor tissues. Hence, it is important to identify and characterize cancer stem cells and make a distinction between cancer and non-cancer stem cells. In this project, this issue was addressed by studying the marker expressions of brain tumor tissues obtained from humans, which confirmed that the cancer cells do express stem cell and progenitor cell markers, such as Sox2 and Vimentin. The presence of mature neurons was also established by the mature neuronal marker NeuN. In order to determine whether these stem cells may be different in young and old subjects, a study was also carried out in young and old zebrafish neural stem cells in order to identify the expression differences between the groups. The presence of proliferating stem cells and differentiated cells were identified in cell culture. This analysis of neural stem cells in old and young zebrafish revealed 18 differentially-expressed genes. The results indicated a higher differentiation rate in old zebrafish stem cells, which may be due to the increased loss of neural cells in the old zebrafish brain. The development of markers that could be widely used for the diagnosis of cancer and the identification of cell types is important. For reliable diagnosis and identification of cancer cells, multiple cellular markers are used. Hence the distinction of cell types based on light scattering differences would speed up the process of diagnosis, and the elimination of marker used for the distinction of cell types would be beneficial. The final project mentioned in this thesis involves the analysis of C6 (rat glioma) cell line for scattering properties and cell cycle arrest. A general method for definition of a scatter data interval for C6 cells in different stages was developed and can be applied to other cell types and diseases. These studies show that the proliferation and stem cell markers’ expressions differ between cancer and healthy stem cells, and the expression of neuroprotective genes is differentially upregulated in old zebrafish neural stem cells compared to the young. This data could contribute to the knowledge on normal and cancer stem cell expression differences, as well as how age affects the expression, and supply information required for the development of a cancer stem cell identification and targeting methods.Item Open Access Computational study of scattering from healthy and diseased red blood cells(Society of Photo Optical Instrumentation Engineers, 2010-08-05) Ergül, Özgür; Arslan-Ergül, A.; Gürel, LeventWe present a comparative study of scattering from healthy red blood cells (RBCs) and diseased RBCs with deformed shapes. Scattering problems involving three-dimensional RBCs are formulated accurately with the electric and magnetic current combined-field integral equation and solved efficiently by the multilevel fast multipole algorithm. We compare scattering cross section values obtained for different RBC shapes and different orientations. In this way, we determine strict guidelines to distinguish deformed RBCs from healthy RBCs and to diagnose various diseases using scattering cross section values. The results may be useful for designing new and improved flow cytometry procedures.Item Open Access Development of an experimental image processing tool and flow-cytometry based electromagnetic scattering analysis for medical diagnosis of red blood cell pathology(Bilkent University, 2020-08) Göktaş, PolatThe morphological, biophysical and biochemical properties of biological cells are critical markers for many fields, including life sciences, medical diagnosis, etc. Label-free, high-throughput classification and detection of cellular information at the single-cell level are invaluable for medical diagnostics. In particular, an efficient algorithm for image analytics plays an important role in biomedical research and in vitro diagnostics with grow importance for healthcare. Morphological/biophysical alterations in single biological cells have been associated with hematologic diseases, such as sickle cell disease. Anemia, which has multiple causes, such as iron deficiency, chronic blood loss and hemolysis, is a prevalent health problem affecting an estimated two billion people or 30% of the world’s population. The ability to measure hemoglobin concentration in anemic patients continuously has significant potential to facilitate hemoglobin monitoring, improve the detection of acute anemia, and avoid the complications and expense. Currently, a major challenge in many clinical laboratories, quantification of cellular information at the single-cell level requires complex laboratory sample preparation and data analysis procedures. Here, we demonstrate that the combination of a novel incubation procedure with rapid gas exchange, image-based flow cytometry (IFC) and a computational cell morphology framework, based on the boundary integral equation method (with the use of Muller Boundary Integral Equation Method) is presented to improve the accuracy of classification of red blood cells (RBCs) subtypes (including normal, intermediate and sickled RBCs) as they appear in time under low oxygen. In this dissertation, the results of the following numerical simulations and experiments are presented: We have investigated the changes in time to follow the rate of sickling with IFC as cells undergo deoxygenation. We have proposed a new shape quantification feature criteria as a Sickle Index parameter obtained from a user-defined custom mask in the IFC data to provide better identification of “true” normal, intermediate and sickle cell region boundaries in IFC. Especially, the main merit of the study lies in showing for the first time that the light scattering analysis based on boundary shape structures is correlated with the measured side scattering (SSC-A) pattern realized by IFC to provide the refractive index distribution for each RBC subtypes. Moreover, we applied different ionic strengths and osmolarity conditions to control the ratio of Discocyte/Stomatocyte/Echinocyte (D/S/E) subtypes in murine RBCs. Analysis of samples were performed using conventional and image-based flow cytometry (FC). The predicted cellular information showed good agreement with the expected results of our experimental data extracted from bright-field and dark-field images in IFC. The rich information on the predicted scattering pattern makes our angle-resolved light scattering technique for the purpose of the automatic RBC morphological profile in conventional FC, and discover RBC subpopulation target areas for the label-free analysis of conventional FC data. With this approach, we are able to notably reduce the data analysis procedure to identify RBC subtypes from a cell population in a given experiment through IFC or conventional FC with an angle-resolved light scattering method. Our approach could lead to replacing current manual protocols in the clinical procedure to avoid complex laboratory processes, and manual gating analysis and fluorescent stains in light microscopy or FCs. This study shows that our method has the potential to be used robust and objective characterization, and follow-up care of anemia status, and to provide a rapid action for the conditions that would lead to chronic anemia condition causing to a reduced lifespan, organ damage or painful crisis, and will be useful for the evaluation of anti-sickling agents which are currently proposed or are in clinical trials.Item Open Access Development of viscoelastic particle migration for microfluidic flow cytometry applications(Bilkent University, 2020-04) Serhatlıoğlu, MuratAdvances in cell biology, quantification, and identification procedures are essential to develop novel particle characterization tools on the diagnostics, biotechnology, pharmaceutical industry, and material science. Flow cytometry is a pivotal technology and meets the need for almost a century. Increase in today’s demand for fast, precise, accurate, and low-cost point-of-care diagnostic tools and cell counting technologies necessitate further improvements for state-of-the-art flow cytometry platforms. These improvements are achievable using novel and precise particle focusing techniques, multiple detection methods, integrated fluidic, optical, and electronic units in the same workflow. Thanks to its indisputable advantages in such integrities, microfluidic flow cytometry platforms are attractive and promising tool for the future of next-generation flow cytometry technologies. In this thesis, we developed viscoelastic focusing technique compatible with optical, impedimetric, and imaging-based microfluidic flow cytometry methods. Elastic nature of the viscoelastic fluids induces lateral migration for suspended particles into a single streamline and meets the requirement for central particle focusing on flow cytometry devices. Viscoelastic focusing is a passive particle manipulation technique and eliminates the need for sheath flow or any other active actuation mechanism. Firstly, we developed viscoelastic focusing technique for optical microfluidic flow cytometry in a palm-sized glass capillary device. Optical detection was performed by fiber-coupled laser source and photodetectors. We demonstrated the detection of polystyrene (PS) cytometry calibration beads suspended in three viscoelastic solutions: Polyethylene oxide (PEO), Hyaluronic acid (HA), and Polyvinylpyrrolidone (PVP). Secondly, we investigated the viscoelastic focusing efficiency of PEO-based viscoelastic solutions at varying ionic concentrations to demonstrate their use in impedance-based microfluidic flow cytometry. We performed cytometry measurements using PS beads and human red blood cells (RBCs). We showed that elasto-inertial focusing of PS beads is possible with the combination of inertial and viscoelastic effects for high-throughput flow cytometry applications. Additionally, non-spherical shape RBCs were aligned along the channel centerline in parachute shape, which yielded to decrease the non-spherical shape-based signal variations in impedance cytometry devices consistent impedimetric signals. Our results showed that proposed flow cytometry devices give similar performance to state-of-the-art systems in terms of throughput and measurement accuracy. Optical- and impedance-based flow cytometry applications were demonstrated using only pressure-driven flow. Under the simultaneous use of pressure-driven flow and DC electric field, particles inside microfluidic channels exhibit intricate migration behavior at different particle equilibrium positions. Available experimental and analytical studies fall short in giving a thorough explanation to particle equilibrium states. Also, the understanding is so far limited to the results based on Newtonian and neutral viscoelastic fluids.Thirdly in this thesis study, a holistic approach is taken to elaborate the interplay of governing electrophoretic and slip-induced/elastic/shear gradient lift forces. Experimental studies were carried on particle migration in Newtonian, neutral viscoelastic, and polyelectrolyte viscoelastic media to provide a comprehensive understanding of particle migration. Our experiments with the viscoelastic media led to contradictory results with the existing explanations. Then, we introduced the Electro-Viscoelastic Migration (EVM) theory to provide a unifying explanation for particle migration in Newtonian and viscoelastic solutions. Additionally, we performed confocal imaging experiments with fluorescent-labeled polymer solutions to explore the underlying migration behavior in the EVM technique. We observed the formation of cross-sectionally non-uniform viscoelastic solution would pave the way for undiscovered unique applications in the microfluidic community. In summary, presented devices were emonstrated with straightforward fabrication techniques on a single straight microcapillary or microchannel. It is possible to couple fluidics, optical, and impedimetric detection units into the same workflow. Our approach in microfluidic flow cytometry applications proved that viscoelastic fluids are good candidates for the development of integrated, portable, and cost-efficient next-generation cytometry platforms and low resource settings. Additionally, the unifying EVM technique has a strong potential to precisely focusing and separating cells, polyelectrolytes, DNA fractions, and proteins according to their charge and size with a comparable resolution and measurement time as a replacement for gel electrophoresis or chromatography applications.Item Open Access Femtosecond laser fabrication of fiber based optofluidic platform for flow cytometry applications(SPIE, 2017) Serhatlioglu, Murat; Elbuken, Çağlar; Ortac, Bülend; Solmaz, Mehmet E.Miniaturized optofluidic platforms play an important role in bio-analysis, detection and diagnostic applications. The advantages of such miniaturized devices are extremely low sample requirement, low cost development and rapid analysis capabilities. Fused silica is advantageous for optofluidic systems due to properties such as being chemically inert, mechanically stable, and optically transparent to a wide spectrum of light. As a three dimensional manufacturing method, femtosecond laser scanning followed by chemical etching shows great potential to fabricate glass based optofluidic chips. In this study, we demonstrate fabrication of all-fiber based, optofluidic flow cytometer in fused silica glass by femtosecond laser machining. 3D particle focusing was achieved through a straightforward planar chip design with two separately fabricated fused silica glass slides thermally bonded together. Bioparticles in a fluid stream encounter with optical interrogation region specifically designed to allocate 405nm single mode fiber laser source and two multi-mode collection fibers for forward scattering (FSC) and side scattering (SSC) signals detection. Detected signal data collected with oscilloscope and post processed with MATLAB script file. We were able to count number of events over 4000events/sec, and achieve size distribution for 5.95μm monodisperse polystyrene beads using FSC and SSC signals. Our platform shows promise for optical and fluidic miniaturization of flow cytometry systems. © 2017 SPIE.Item Open Access Integration of glass micropipettes with a 3D printed aligner for microfluidic flow cytometer(Elsevier B.V., 2018) Bayram, A.; Serhatlıoğlu, Murat; Ortaç, Bülend; Demic, S.; Elbüken, Çağlar; Sen, M.; Solmaz, M. E.In this study, a facile strategy for fabricating a microfluidic flow cytometer using two glass micropipettes with different sizes and a 3D printed millifluidic aligner was presented. Particle confinement was achieved by hydrodynamic focusing using a single sample and sheath flow. Device performance was extracted using the forward and side-scattered optical signals obtained using fiber-coupled laser and photodetectors. The 3-D printing assisted glass capillary microfluidic device is ultra-low-cost, not labor-intensive and takes less than 10 min to fabricate. The present device offers a great alternative to conventional benchtop flow cytometers in terms of optofluidic configuration.Item Open Access The prosurvival IKK-related kinase IKKϵ integrates LPS and IL17A signaling cascades to promote Wnt-dependent tumor development in the intestine(American Association for Cancer Research, 2016-05) Göktuna, S. I.; Shostak, K.; Chau, T.-L.; Heukamp, L.C.; Hennuy, B.; Duong, H.-Q.; Ladang, A.; Close, P.; Klevernic, I.; Olivier, F.; Florin, A.; Ehx, G.; Baron, F.; Vandereyken, M.; Rahmouni, S.; Vereecke, L.; Loo, G. V.; Büttner, R.; Greten, F. R.; Chariot, A.Constitutive Wnt signaling promotes intestinal cell proliferation, but signals from the tumor microenvironment are also required to support cancer development. The role that signaling proteins play to establish a tumor microenvironment has not been extensively studied. Therefore, we assessed the role of the proinflammatory Ikk-related kinase Ikkϵ in Wnt-driven tumor development. We found that Ikkϵ was activated in intestinal tumors forming upon loss of the tumor suppressor Apc. Genetic ablation of Ikkϵ in b-catenin-driven models of intestinal cancer reduced tumor incidence and consequently extended survival. Mechanistically, we attributed the tumor-promoting effects of Ikkϵ to limited TNF-dependent apoptosis in transformed intestinal epithelial cells. In addition, Ikkϵ was also required for lipopolysaccharide (LPS) and IL17A-induced activation of Akt, Mek1/2, Erk1/2, and Msk1. Accordingly, genes encoding proinflammatory cytokines, chemokines, and anti-microbial peptides were downregulated in Ikkϵ-deficient tissues, subsequently affecting the recruitment of tumor-associated macrophages and IL17A synthesis. Further studies revealed that IL17A synergized with commensal bacteria to trigger Ikkϵ phosphorylation in transformed intestinal epithelial cells, establishing a positive feedback loop to support tumor development. Therefore, TNF, LPS, and IL17A-dependent signaling pathways converge on Ikkϵ to promote cell survival and to establish an inflammatory tumor microenvironment in the intestine upon constitutive Wnt activation.