The focus of this project falls largely within the realm of investigating the development of brain-cognition relations from a developmental cognitive neuroscience perspective. There were two main goals of this study. First, this study focused on the regional differences in baseline-to-working memory task brain electrical activity and specifically investigated the hypothesis that there would be an increasing specificity of task EEG power between 3½ and 4½ years of age. The second goal of this study was to investigate the sources of variability in working memory function and to specifically examine the contributions of task-related EEG, the regulatory dimensions of temperament, and linguistic ability to the prediction of working memory performance. This second study objective included an investigation of the relation between working memory and each of these variables (1) separately, (2) in conjunction with age, and (3) collectively to examine any multivariate contributions to the explanation of variance in working memory function in early childhood. The results of this study provided some support to the increasing specificity of baseline-to-task EEG power hypothesis. Specifically, an increase in brain electrical activity was found for four scalp regions at age 4 and only two regions at age 4½. These findings coupled with previous work indicating an increase in task brain electrical activity for only one region at age 4½ suggest that cortical specialization is occurring during the early childhood years. With regard to the investigation of sources of variability working memory function, age, brain electrical activity, temperament, and linguistic functioning were all found to be meaningful variables in the explanation of variance in working memory. However, linguistic functioning " and specifically language receptivity " was found to be the strongest and most meaningful associate of working memory function. Additional findings of interest included the differential associations demonstrated between working memory and temperament for each age group and also an increase in the strength of the relation between working memory and language across the three ages. / Ph. D.

The central nervous system (CNS) is protected by a vascular blood-brain barrier that prevents many types of pathogens from entering the brain. Still, some pathogens have evolved mechanisms to traverse this barrier and establish a long-term infection. The apicomplexan parasite, Toxoplasma gondii, is one such pathogen with the ability to infect the CNS in virtually all warm-blooded animals, including humans. Across the globe, an estimated 30% of the human population is infected with Toxoplasma, an infection for which mounting evidence suggests increases the risk for developing neurological and neuropsychiatric disorders, like seizures and schizophrenia. In my dissertation, I investigate the telencephalic neural circuit changes induced by long-term Toxoplasma infection in the mouse brain and the neuroimmune signaling role of the complement system in mediating microglial remodeling of neural circuits following parasitic infection. While there has been keen interest in investigating neural circuit changes in the amygdala – a region of the brain involved in fear response and which Toxoplasma infection alters in many species of infected hosts – the hippocampus and cortex have been less explored. These are brain regions for which Toxoplasma also has tropism, and moreover, are rich with fast-spiking parvalbumin perisomatic synapses, a type of GABAergic synapse whose dysfunction has been implicated in epilepsy and schizophrenia. By employing a range of visualization techniques to assess cell-to-cell connectivity and neuron-glia interactions (including immunohistochemistry, ultrastructural microscopy, and microglia-specific reporter mouse lines), I discovered that longterm Toxoplasma infection causes microglia to target and ensheath neuronal somata in these regions and subsequently phagocytose their perisomatic inhibitory synapses. These findings provide a novel model by which Toxoplasma infection within the brain can lead to seizure susceptibility and a wider range of behavioral and cognitive changes unrelated to fear response. In the Toxoplasma infected brain, microglia, along with monocytes recruited to the brain from the periphery, coordinate a neuroinflammatory response against pathogenic invasion. This is characterized by a widespread activation of these cells and their increased interaction with neurons and their synaptic inputs. Yet, whether T. gondii infection triggers microglia and monocytes (i.e. phagocytes) to target, ensheath, and remove perisomatic inhibitory synapses on neuronal somata indiscriminately, or whether specificity exists in this type of circuit remodeling, remained unclear. Through a comprehensive assessment of phagocyte interactions with cortical neuron subtypes, I demonstrate that phagocytes selectively target and ensheath excitatory pyramidal cells in long-term infection. Moreover, coupling of in situ hybridization with transgenic reporter lines and immunolabeling revealed that in addition to phagocytes, excitatory neurons also express complement component C3 following infection (while inhibitory interneurons do not). Lastly, by employing targeted deletion of complement components, C1q and C3, I show that complement is required for phagocyte ensheathment of excitatory cells and the subsequent removal of perisomatic inhibitory synapses on these cells (albeit not through the classical pathway). Together, these studies highlight a novel role for complement in mediating synapse-type and cell-type specific circuit remodeling in the Toxoplasma infected brain. / Doctor of Philosophy / Parasites are microorganisms that rely on other living organisms (called hosts) for their survival. Although some parasites only live on their hosts, others have developed ways to establish infections and obtain the nutrients that keep them alive from host cells. My Ph.D. research has focused on studying one of these parasites, Toxoplasma gondii (commonly referred to as Toxo), that has evolved the unique ability to establish brain infections in almost all animals around the world, from rodents to humans. Recent discoveries show that brain infection with this parasite can cause seizures, an imbalance in the way that specialized cells of the brain (called neurons) communicate with each other, causing harmful hyperactivity within the brain. Toxo infection can also cause behavioral and cognitive changes in infected animals, making them more susceptible to predation. In humans, infection with Toxo increases their risk for developing different types of mental illness, such as schizophrenia. The focus of my Ph.D. research has been in trying to understand, at the cellular and molecular level, how infection with this parasite can lead to seizures and behavioral changes, by using mice as a model. Mice have a similar brain structure to humans, and over the years, scientists have developed many tools that allow us to visualize and study the connections between neurons (called synapses). I'm interested in understanding how changes in these connections affect how neurons communicate with each other, and ultimately, how we behave and think. I have been studying a type of connection that, if lost or damaged, can lead to seizures and some types of mental illness. These connections are called 'perisomatic inhibitory synapses', and they form on many distinct types of neurons, but specifically on the cell bodies of these neurons. They act as a traffic light, informing neurons when and for how long to 'slow down' their activity. I discovered that after the parasite enters the brain, it causes another type of cell in the brain, called microglia, to extensively interact with neurons in the cortex and hippocampus (areas of your brain important for thinking, executing behavior, and learning). Microglia are immune cells of the brain that inspect the brain for anything damaged or that doesn't belong (like parasites) and removes them from the brain. By performing experiments where I delete individual immune molecules from mice, I found that one immune molecule, called 'complement component C3' acts as cue for microglia to find these cells, wrap around them, and permanently remove these important connections. Surprisingly, however, microglia don't remove these connections from all neurons, indiscriminately, they do so only on one specific cell type called 'excitatory pyramidal neurons,' and as the name implies, they're the ones who drive activity in the brain. My half-a-decade's worth of research helps us understand parasitic infections in the brain in a couple of ways: First, I have discovered one of the mechanisms by which neuronal connections are lost in the Toxo-infected brain (which is a mechanism that leads to loss of neuronal connections in the injured and aging brain as well). This is significant because it might provide insight into why some people who are infected with Toxo develop seizures or mental illness, while others don't. More importantly, Toxo-infection causes changes in the brain that are very specific, in terms of both the type of neuronal connection that is affected and the type of cell that is affected. Why these changes are so specific remain to be uncovered, but it suggests that Toxo can either a) trigger a unique immune response in the brain that leads to very precise changes in neuron-toneuron connections and signaling or b) the parasite, while hiding inside of neurons, may hijack the machinery of certain cell types in a way that helps them survive longer.

Initial studies in this work explored the role of interleukin-6 (IL6) and leukemia inhibitory factor (LIF) in preimplantation bovine embryos. Neither cytokine affected the total percentage of embryos which developed to the blastocyst stage in vitro. However, supplementation of IL6 increased blastocyst inner cell mass (ICM) cell number without affecting trophectoderm (TE) cell number. Additionally, we found that IL6 activated signal transducer and activator of transcription 3 (STAT3) specifically within ICM cells. LIF, however, did not affect ICM cell number or activate STAT3 in ICM cells, and was not pursued further. This increase in ICM cell number by IL6 was largely comprised of hypoblast (GATA6+:NANOG-) cells, and most IL6-responsive cells in day 9 blastocysts were hypoblast cells (as measured by STAT3 activation). However, some epiblast (NANOG+) cells were also IL6-responsive, and IL6 appeared to initially slow epiblast differentiation. Finally, IL6-treated blastocysts also had increased transcripts of hypoblast/primitive endoderm (PE) markers. These results indicate that IL6 may improve pregnancy retention of IVP embryos by improving yolk sac development, but further work is needed to confirm this theory. Activation of STAT3 by IL6 could be blocked with a chemical Janus kinase 2 (JAK2) inhibitor (AZD1480). JAK2 inhibition from day 5 to 8 resulted in blastocyst ICMs with fewer than 10% the normal cell number, regardless of IL6 supplementation. This indicates that STAT3 is critical for bovine ICM development. Further analysis revealed that inhibition of JAK2/STAT did not prevent ICM formation but disrupted its maintenance. Additionally, we assessed the suitability of zinc sulfate and a bovine embryonic stem cell culture media (TeSR) for improving bovine embryo development in vitro. Zinc sulfate increased day 8 blastocyst total and ICM cell number. Therefore, zinc sulfate appears to improve blastocyst quality. The TeSR medium improved embryo development beyond day 8. In normal synthetic oviduct fluid, blastocysts degenerated after day 8, while blastocysts moved to TeSR had greatly increased cell numbers, and even exhibited PE migration out from the ICM, a phenomenon that has not been reported in vitro. This indicates that extended blastocyst culture is possible with TeSR media. / Doctor of Philosophy / Bovine embryos have been produced in vitro for the purpose of being transferred to recipient cattle to produce a calf since the 1980s. This practice allows cattle breeders to increase the number of offspring from their best females each year, and also allows for more rapid progress in generational genetic improvement. However, only approximately 10% of bovine oocytes survive and produce a calf. This poor efficiency of bovine in vitro embryo production negatively impacts the procedure's widespread use. A significant portion of these embryo losses are likely a result of inadequate in vitro culture conditions, particularly of the embryo culture media, the fluid in which embryos are grown. This media is often called "synthetic oviduct fluid," or SOF, because it is designed to mimic the fluid present in the cow's oviduct, where the embryo would normally reside. However, SOF is much simpler in nature than actual cow oviduct fluid, and this leads to reduced embryonic survival of in vitro produced embryos. Unfortunately, we know very little of what molecules control and promote bovine embryo development. Therefore, one major goal of bovine embryo research is to identify these factors and add them to SOF. The goal of this work was to examine the ability of three molecules, interleukin-6 (IL6), leukemia inhibitory factor (LIF), and zinc sulfate, to increase the number and quality of blastocysts produced through in vitro culture techniques. Additionally, I tested the replacement of SOF with a complex cell culture media, known as TeSR. This medium is more complex than SOF, and therefore should better promote embryo development. This work revealed that IL6, but not LIF, improves in vitro produced (IVP) bovine blastocyst quality. Unfortunately, neither IL6 nor LIF affected the percentage of embryos which survived to the blastocyst stage. However, IL6, but not LIF, increased the number of cells in the inner cell mass (ICM) of the blastocysts. ICM cells are the portion of the embryo which will produce the future calf. IVP bovine embryos are known to have fewer cells than normal, in vivo derived, blastocysts, and this issue is believed to cause some embryonic death after embryo transfer. Therefore, treatment with IL6 may increase the percentage of embryos which will survive after transfer and produce a calf. We also found the addition of zinc sulfate to SOF to benefit embryo quality. None of the concentrations of zinc significantly improved the percentage of embryos which survived to the blastocyst stage, but 2 µM zinc did increase ICM cell number. Like IL6, this may improve embryo survival after transfer. The use of the TeSR media as a replacement for SOF had some benefits. Unfortunately, this media is unusable for producing embryos for transfer to recipients, as we discovered early embryos could not survive in the media. However, blastocyst-stage embryos thrived in it, and could be cultured in vitro for a longer period of time as a result. Therefore, this media will be a useful tool for studying bovine embryo development in vitro, however it is unlikely to benefit calf production. In summary, this work provides evidence that zinc sulfate and IL6 are beneficial additions to SOF. However, future work is needed to determine if embryos produced with these factors are more able to produce a calf. Additionally, we discovered that TeSR is a superior extended blastocyst culture medium.

Inhibitory Control (IC), a vital facet of childhood development, involves the ability to suppress a dominant response, as well as the ability to suppress irrelevant thoughts and behaviors. This ability emerges during the first year of life and develops rapidly during the preschool years. A variety of tasks have been developed to measure IC in this age group and, recently, research has demonstrated important differences in task performance according to various distinctions among these tasks. One under-researched distinction is that of whether an IC task requires the child to give a verbal or a motoric response. Therefore, the purpose of this study was to examine, in 4-year-old children, the differences and similarities among IC tasks requiring either a verbal or a motoric response. Differences were explored with respect to the contributions to verbal and motoric IC performance of language, intelligence, temperament, and frontal encephalography, as well as with respect to social and school readiness outcomes. IC was best described by a two-component model, distinguishing verbal and motoric IC. Both baseline and task electrophysiology contributed to task performance in the verbal Yes-No task as well as the motoric IC composite. Language and intelligence, too, were associated with both verbal and motoric IC, although nonverbal intelligence was less strongly correlated with verbal IC than it was with motoric IC. All laboratory measures of IC related to parent report of children’s IC as well as to other parent-reported temperament scales and factors. Children’s verbal and motoric IC were associated, too, with children’s social development, surprisingly showing the most consistent associations with social inhibition. Asocial behavior positively correlated more strongly with motoric IC than with verbal IC. Children’s laboratory IC positively correlated with their school readiness, even when controlling for their intelligence although children’s emergent literacy more positively related to their motoric, rather than verbal, IC. An interaction of intelligence and IC contributed to social variables, but not to school readiness. This research supports the important distinction between verbal and motoric IC, and demonstrates the utility of including an array of measures of both in early childhood research. / Ph. D.

Social cognition is a set of complex processes that mediate much of human behavior. The development of these skills is related to and interdependent on other cognitive processes, particularly inhibitory control, which allows for willful suppression of dominant responses. Many aspects of social behavior rely on inhibitory control to moderate impulsive or socially inappropriate behaviors and process complex perspective-taking. Furthermore, the brain regions associated with inhibitory control and social cognition overlap functionally and structurally. I review neurodevelopmental literature to suggest that social cognition is developmentally dependent on inhibitory control and that the neural foundations of both these skills are measurable in infancy. I tested this model using growth curve and structural equation modeling and show that 10-month, but not 5-month, frontotemporal coherence predicts social cognition in late childhood through preschool inhibitory control. These findings provide insight into the neurodevelopmental trajectory of cognition and suggest that connectivity from frontal regions to other parts of the brain is a foundation for the development of these skills. / Doctor of Philosophy / Social cognition is the ability to understand and interpret another’s thoughts, words, and actions and inhibitory control is the ability to suppress one’s own thoughts, words, and actions. These two types of cognition are similar and use the same brain regions, and I suggest that inhibitory control underlies much of social cognition. In order to test this, I examined children’s inhibitory control and brain connectivity at 5 months, 10 months, 24 months, 48 months, and 9 years and measured social cognition at 9 years. I found that connectivity between the frontal and temporal lobes at 10 months predicted inhibitory control and 48-months, which then predicted social cognition at 9 years. This suggests that infant brain connectivity sets the stage for developing inhibitory control, which is important for later social cognition

Seventy-three children participated in an investigation of inhibitory control (IC) at 3 years of age. Child IC was measured under various conditions in order to determine the impact that nonverbal and/or motivational task demands had on child IC task performance. Furthermore, task performance was examined with respect to measures of language, temperament, and psychophysiology. Tasks showed different patterns of relations to each of these variables. Furthermore, performance on the Hand Game, our measure of nonverbal IC, was explained by frontal EEG activity and, surprisingly, by language abilities. In contrast, performance on two other IC tasks, Day-Night and Less is More, was not related to measures of language or frontal EEG, perhaps because children performed at chance level on these tasks, indicating that these tasks may be too difficult for 3-year-old children. Implications of these findings are discussed. / Master of Science

Les cytokines MIFs (Macrophage Migration Inhibitory Factor) sont des protéines multifonctionnelles qui, chez les mammifères, interviennent dans plusieurs processus majeurs tels que le contrôle du cycle et de la mobilité cellulaire, l’activation de la réponse immunitaire et l’inhibition de l’apoptose. Des travaux récents montrent que les protéines MIFs peuvent également jouer un rôle majeur dans l’immunité des invertébrés, et être utilisées par des organismes parasites d’animaux ou de végétaux pour inhiber les défenses de leurs hôtes respectifs, ce qui soulève la question de leur diversité, de leur histoire évolutive et des potentielles différences fonctionnelles. L’objectif général de ce travail de thèse était d’explorer la diversité et l’histoire évolutive des protéines MIFs à une échelle trans-règne, puis de rechercher leurs éventuelles différences fonctionnelles, en se focalisant sur les systèmes plantes-pathogènes. Nous avons tout d’abord identifié les MIFs chez 803 espèces de plantes, champignons, protistes, et métazoaires, et analysé leur présence/absence et histoire évolutive en fonction des taxa, de l’écologie et du mode de vie (libre ou parasitaire) des espèces. Nous avons montré que l’histoire évolutive des MIFs, chez les eucaryotes, est complexe et implique des duplications ancestrales ainsi que des pertes multiples ou des re-duplications récentes. Les plantes (espèces libres autotrophes) et les parasites de plantes (autres que champignons) possèdent un nombre médian de trois MIFs, alors que les espèces hétérotrophes et les parasites d’animaux ont un nombre de MIF plus faible et/ou plus variable. De plus, les protéines MIFs semblent essentielles et fortement conservées, avec de nombreux résidus sous sélection purifiante, chez certains groupes comme les plantes, alors que dans d’autres groupes, elles semblent facultatives (e.g. champignons) ou présentes en plusieurs copies divergentes (e.g. nématodes, insectes), ce qui suggère de potentielles néofonctionalisations. Nous avons ensuite analysé l’effet des protéines MIFs de plusieurs espèces sur la mort cellulaire en système végétal. Tous les organismes testés (plantes oomycètes, protozoaires, insectes et nématodes), y compris ceux n’ayant pas d’interaction avec les plantes, possèdent au moins une protéine MIF capable d’inhiber cette mort cellulaire. Cela suggère que l’inhibition de la mort cellulaire en plante ne correspond pas à une néofonctionalisation des MIFs de parasites de plantes, mais serait liée à des propriétés structurales et conservées des MIFs. Toutefois, aucun des paramètres étudiés (localisation subcellulaire) ou prédits in silico (présence de motifs, structures 3D, oligomérisation, modifications post-traductionnelles) ne semble lié à cette activité d’inhibition de la mort cellulaire. De futures études fonctionnelles poussées sont nécessaires à l’élucidation des relations structure/fonction de ces protéines complexes. / Macrophage migration inhibitory factors (MIF) are multifunctional proteins regulating major processes in mammals, including control of the cell cycle and migration, activation of innate immune responses, and prevention of p53-mediated apoptosis. MIF proteins also play a role in innate immunity of invertebrate organisms or serve as virulence factors in parasitic organisms, raising the question of their evolutionary history and of a putative differential evolution of structure/function relationships. The general aim of this PhD was to explore the diversity and evolutionary history of MIF proteins accross kingdoms, and to investigate their potential functional differences, with a special emphasis on host-parasite systems. We first performed a broad survey of MIF presence or absence and evolutionary relationships across 803 species of plants, fungi, protists, and animals, and explored a potential relation with the taxonomic status, the ecology, and the lifestyle of individual species. We show that MIF evolutionary history in eukaryotes is complex, involving ancestral duplications, multiple gene losses and recent clade-specific re-duplications. Of note, plants and plant parasites (other than fungi) harbour a median number of three MIFs, while heterotrophic and animal parasite species harbour a lower or/and variable MIF number. Intriguingly, MIFs seem to be essential and highly conserved with many sites under purifying selection in some kingdoms (e.g. plants), while in other kingdoms they appear more dispensable (e.g. in fungi) or present in several diverged variants (e.g. insects, nematodes), suggesting potential neofunctionalizations within the protein superfamily. We then analysed the effect of MIF proteins from selected species on plant cell death. All organisms tested (plant, oomycetes, protozoa, insects, and nematodes) including species that are not in interaction with plants, possess at least one MIF protein showing a significant cell death inhibitory effect. This suggests that plant cell death inhibition does not result from a neofunctionalization of MIF from plant-parasites, and is related to conserved structural features of MIF proteins. However, none of the parameters predicted in silico (sequence motifs, 3D structures, oligomerization, post-traductional modifications) appeared to be related to the cell death inhibitory activity. Future extensive functional studies are necessary to unravel the structure-function relationship of these evolutionarily and functionally complex proteins.

Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology & Toxicology Student: Beáta Repeľová Supervisor: PharmDr. Lukáš Červený, Ph.D. Title of diploma thesis: Study of effects of antiretroviral drugs on transmembrane transport of tenofovir disoproxil fumarate across MDCKII - ABCB1 cell monolayer Tenofovir disoproxil fumarate (TDF) - ester prodrug of tenofovir is considered as one of the most frequently used component of combination antiretroviral therapy. Several ways of application and good patients' tolerability is typical for this compound. TDF is a substrate of dug transporter such as P-glycoprotein (P-gp) therefore its efflux activity may limit the bioavailability after oral administration and distribution of TDF. As many of antiretroviral drugs are also substrates or inhibitors of P-gp, drug - drug interactions with TDF at the level of transmembrane transport could be expected. The aim of the diploma thesis was to describe effects of co-administered antiretroviral drugs on transfer of TDF across MDCKII cell monolayer by using bidirectional transport and concentration equilibrium setups. The results of experiments confirmed that TDF is a substrate of P-gp. High values of efflux ratio describing transmembrane transport of TDF across parental cells have been observed. This...

Für medizinische Anwendungen sind Stammzellen aufgrund ihrer Eigenschaften (Selbsterneuerung, hohe Proliferationsrate und Differenzierungsmöglichkeit in verschiedene Zelltypen) beispielsweise in den Bereichen des regenerativen Gewebeersatzes und der Zelltherapie sehr interessant. In vivo umgibt die Stammzellen eine definierte Mikroumgebung, die sie unterstützt sich zu teilen, ihren undifferenzierten Status aufrecht zu erhalten und Tochterzellen für das Wachstum, die routinemäßige Erneuerung oder den Ersatz von Gewebe zu produzieren. Diese Mikroumgebungen werden als Stammzellnischen bezeichnet. Für die Kultivierung von Stammzellen in vitro muss die in vivo-Situation möglichst getreu nachgestaltet werden. Ziel der Forschung ist die Schaffung einer künstlichen Umgebung, die sowohl die funktionellen Eigenschaften einer Nische besitzt als auch frei von Risiken xenogener Pathogene oder Gewebeunverträglichkeiten für die Anwendung am humanen Organismus eingesetzt werden kann. Einen Ansatz dafür bietet beispielsweise die Kopplung von Faktoren, die für den Erhalt der Stammzelleigenschaften notwendig sind, an synthetische Oberflächen. Ausgehend vom Bedarf an Kultur- oder Modellsystemen für die Expansion von (embryonalen) Stammzellen sollte in dieser Arbeit analysiert werden, ob alternierende Maleinsäureanhydrid (MA)-Copolymere ein geeignetes Trägersystem für die biofunktionelle kovalente Immobilisierung spezifischer Zytokine sind und dadurch unter anderem als künstliche Stammzellnische Anwendung finden können. MA-Copolymere eignen sich aufgrund ihrer spontanen Reaktion mit Aminogruppen für die Immobilisierung von Proteinen. Das Zytokin LIF (Leukemia inhibitory factor) existiert in vivo auch in immobilisierter Form und ist in embryonalen Mausstammzellen (mESC) allein in der Lage, das Stammzellpotential dieser Zellen zu erhalten. Aus diesem Grund ist LIF für die Analyse der Aufgabenstellung geeignet. Nach der Charakterisierung LIF-modifizierter Oberflächen wurde die biologische Verfügbarkeit des kovalent immobilisierten Zytokins mit Hilfe von LIF-sensitiven Fibroblasten und mESC der Linie R1 überprüft. Anschließend wurde im Mausmodell in vivo der Erhalt der Pluripotenz der mESC durch immobilisiertes LIF analysiert. Dafür standen die Oberflächen Poly(ethylen-alt-maleinsäureanhydrid) (PEMA) und Poly(octadecen-alt-maleinsäureanhydrid) (POMA) jeweils ohne und mit Polyethylenglykol (PEG7)-Modifizierung zur Verfügung, an die LIF kovalent gekoppelt wurde. Zusätzlich wurde LIF physisorptiv an einer Kollagen-Fibronektin-Matrix über hydrolysiertem POMA immobilisiert. Mit Hilfe von radioaktiv markiertem LIF konnte gezeigt werden, dass die Gesamtbeladungsmenge mit Zytokin von den Eigenschaften der MA-modifizierten Träger abhing. Auf PEMA konnten mit steigenden Immobilisierungskonzentrationen höhere Belegungsdichten an der Oberfläche erreicht werden, die im analysierten Bereich eine lineare Abhängigkeit zeigten. Aufgrund der starken Quellung in wässrigen Lösungen war eine Einlagerung von LIF-Molekülen in die Polymerschicht möglich und führte bei hohen Immobilisierungskonzentrationen auch nach 3 Tagen Inkubation mit proteinhaltigem Medium noch zur Verdrängung nicht kovalent gebundener Zytokinmoleküle aus PEMA-Oberflächen. Obwohl ein Teil des LIF in die Polymerschicht eindrang, war der Großteil der Moleküle für einen spezifischen Antikörper zugänglich. Hydrophobe Oberflächen mit POMA konnten bei hohen Immobilisierungskonzentrationen weniger LIF binden und zeigten Sättigungsverhalten der Oberflächen bei einer Belegungsdichte von 178 ng/cm^2 LIF. Eine Freisetzung von LIF nach mehr als 3 Tagen konnte nicht beobachtet werden. Gleichzeitig war hier aufgrund der hydrophoben Polymerseitenketten die Antikörperzugänglichkeit deutlich reduziert. Wegen des geringen Quellungsverhaltens von POMA in wässrigen Lösungen konnte eine Einlagerung des immobilisierten Zytokins in die Polymerschicht aber ausgeschlossen werden. Die kovalente LIF-Immobilisierung über PEG7-Spacer führte im Vergleich zu den nicht PEG-modifizierten Oberflächen PEMA und POMA zu jeweils geringeren Belegungsdichten, ohne dabei den Charakter der Abhängigkeit von der Immobilisierungskonzentration zu verändern (linear für PEMA+PEG7, Sättigung für POMA+PEG7). Die schlechte Antikörperzugänglichkeit von immobilisiertem LIF auf POMA konnte durch die Einführung des PEG7-Spacers deutlich verbessert werden und erreichte einen Wert ähnlich dem der hydrophilen PEMA-Oberflächen. Kovalent immobilisiertes LIF zeigte auf den vier MA-Oberflächen homogene und definiert einstellbare Belegungsdichten auf den einzelnen Proben. Die physisorptive Immobilisierung von LIF an extrazelluläre Matrixkomponenten auf hydrolysiertem POMA führte zu inhomogenen und bereits bei geringen Immobilisierungskonzentrationen instabilen Belegungsdichten. Die Einstellung definierter Belegungsdichten und die homogene Verfügbarkeit des Zytokins sind für die spätere Anwendung bei der Kultivierung wichtig, da so allen Zellen die gleiche definierte Zytokindosis unabhängig von der Oberflächencharakteristik präsentiert wird und Populationsunterschiede vermieden werden. LIF-sensitive Mausfibroblasten der Linie NIH3T3 reagierten auf immobilisiertes LIF mit der Aktivierung des Signalwegproteins STAT3. Durch den direkten Vergleich von STAT3-Aktivierungsprofilen nach Stimulation mit gelöstem oder immobilisiertem LIF konnte gezeigt werden, dass durch beide Präsentationsformen innerhalb der ersten 15 Minuten nach Stimulationsbeginn eine starke Aktivierung von STAT3 erfolgt, die anschließend wieder abklingt. Die Profile beider Präsentationsformen unterschieden sich in ihren Intensitäten nur bei der starken STAT3-Aktivierung. Dabei ergaben sich bei gelöstem LIF aufgrund der größeren Kontaktfläche mit Zytokin (gesamte Zelloberfläche) etwas stärkere Aktivierungen. Durch die sehr ähnlichen Aktivierungsprofile konnte nachgewiesen werden, dass das Zytokin LIF für Zellen zugänglich an MA-Copolymere mit und ohne Spacer-Modifizierung immobilisiert werden kann. Dabei lag ein Teil der Moleküle in einer Konformation und Orientierung gebunden vor, die die Funktionalität des Zytokins erhalten konnten. Zwischen den Oberflächen mit kovalenter LIF-Immobilisierung konnten keine wesentlichen Unterschiede in der STAT3-Aktivierung festgestellt werden. LIF war an all diesen Oberflächen für die LIF-sensitiven NIH3T3 Mausfibroblasten biologisch verfügbar. LIF-abhängige embryonale Mausstammzellen (mESC) reagierten nach 72 Stunden LIF-Stimulation mit der Aktivierung von STAT3. Bei Belegungsdichten ab 8 ng/cm^2 kovalent immobilisiertem LIF auf POMA mit und ohne PEG7-Spacer konnten ähnliche Aktivierungen wie durch die Stimulation mit gelöstem LIF festgestellt werden. Dies bestätigte die biofunktionelle LIF-Immobilisierung. Zwischen den POMA-Oberflächen mit und ohne PEG7 war dabei kein deutlicher Unterschied erkennbar. Eine reduzierte Zugänglichkeit des Antikörpers auf POMA beeinflusste demnach die biologische Verfügbarkeit des Zytokins für die mESC nicht. Der Erhalt des Stammzellpotentials durch kovalent an POMA gebundenes LIF konnte in vitro durch die Präsenz von Oct4 im Zellkern der mESC nachgewiesen werden. Durch die instabile Immobilisierung bei physisorptiver Assoziation des Zytokins an Matrixkomponenten über hydrolysiertem POMA reduzierte sich der Erhalt des Stammzellpotentials auf diesen Oberflächen stark. Kovalent immobilisiertes LIF dagegen konnte auch während der Kultur über mehrere Passagen hinweg die Pluripotenz der murinen ESC erhalten. Nach der Fusion mit Blastozysten beteiligten sich diese kultivierten Zellen in vivo erfolgreich an der Bildung von Chimären. Dabei konnten keine Unterschiede der Chimärenhäufigkeit zwischen der Kultivierung der mESC mit gelöstem oder kovalent an POMA immobilisiertem LIF festgestellt werden. Kovalent an MA-Copolymere immobilisiertes LIF ist demnach in der Lage, gelöstes LIF vollständig zu ersetzen und über mehrere Passagen hinweg allein das Stammzellpotential von mESC zu erhalten. Die Experimente zeigten, dass sich MA-Copolymere für die funktionelle kovalente Immobilisierung von Signalmolekülen eignen. Dabei konnten keine starken Unterschiede bei der Reaktion der Zellen auf die Oberflächen PEMA oder POMA festgestellt werden. Auch die Einführung eines zusätzlichen Spacers war für die Signaltransduktion nach Stimulation mit kovalent immobilisiertem LIF nicht notwendig. Für künftige Arbeiten zur kovalenten Immobilisierung von LIF an MA-Copolymeren ist deshalb aus Stabilitäts- und Effizienzgründen die Oberfläche POMA zu bevorzugen. Diese Favorisierung kann jedoch aufgrund der unterschiedlichen Tertiärstruktur anderer Proteine und ihrer verschiedenen Steifigkeiten sowie bei der Verwendung anderer Zelltypen nicht automatisch für ein anderes Modellsystem übernommen werden. Die Verwendung hydrophiler Oberflächen oder die Kopplung über Spacer sollte demnach in Abhängigkeit vom zu immobilisierenden Protein und den auszusiedelnden Zellen geprüft werden. Die vorgestellte Kopplungsmethode umgeht die Modifikation des Proteins sowie Behandlungen zur Vernetzung des Zytokins. Die Immobilisierungsreaktion ist bei Raumtemperatur und Umgebungsdruck sowie unter sterilen Bedingungen durchführbar. Immobilisierte Zytokine werden homogen kovalent an der Oberfläche gebunden und sind dort für die Zellen zugänglich. Außerdem ermöglicht die Einstellung definierter Belegungsdichten die gezielte Applikation von Zytokindosen. MA-Copolymere sind somit nicht nur für die Kultivierung von Stammzellen unter Erhaltung des Stammzellstatus einsetzbar, sondern eignen sich auch für Differenzierungsstudien. Teilergebnisse dieser Arbeit wurden publiziert unter K. Alberti, R.E. Davey, K. Onishi, S. George, K. Salchert, F.P. Seib, M. Bornhäuser, T. Pompe, A. Nagy, C.Werner, and P.W. Zandstra. Functional immobilization of signaling proteins enables control of stem cell fate. Nat Methods, 5(7):645–650, Jul 2008 und T. Pompe, K. Salchert, K. Alberti, P.W. Zandstra, and C. Werner. Immobilization of growth factors on solid supports for the modulation of stem cell fate. Nat Protocols, 5(6):1042–1050, Jun 2010. / In vitro cultivation of (embryonic) stem cells requires a defined environment. Together different properties as cytokine supplement, extracellular matrix composition or topographic design can mimic this stem cell niche in an artificial system. For mouse embryonic stem cells the cytokine leukemia inhibitory factor (LIF) is able to keep those cells in undifferentiated state and to enhance self renewal without the supplement of other factors. In vivo LIF exists in both diffusible and extracellular matrix immobilized form. This work investigates whether LIF can be immobilized covalently to alternating maleic anhydride (MA)-copolymers in a functional manner. When bioavailable, covalently immobilized LIF should be able to interact with specific cytokine receptor subunits and provide information to keep murine embryonic stem cells in a pluripotent state. In aqueous solution with neutral pH (such as phosphate buffered saline, PBS) and ambient temperature and pressure MA-copolymers react spontaneously with aminogroups and therefore represent a useful support for covalent protein immobilization. Depending on the choice of co-monomer, properties of copolymer vary: ethylene results in hydrophilic poly-(ethylene-alt-maleic anhydride) (PEMA), octadecene in more hydrophobic poly-(octadecene-alt-maleic anhydride) (POMA). LIF can be covalently immobilized onto the MA-copolymers as shown by radiolabeling experiments. The amount of cytokine coupled to PEMA increased linear whereas on POMA saturation could be observed for higher concentrations. A subsequent coupling of a polyethylene glycol spacer (PEG7) further modified the properties and led to more hydrophilic surfaces. The amount of LIF per area decreased in comparison to MA-copolymers without the spacer but the graph characteristics remained unaltered (linear for PEMA+PEG7, saturation for POMA+PEG7). During the first three days in buffer solution supplemented with bovine serum albumin, unbound LIF was displaced and the amount of immobilized cytokine remained stable. This Stability after preincubation allowed to immobilize required amounts of LIF per area. Although hydrophilic surfaces with PEMA showed swelling behavior resulting in increased layer thickness after incubation in PBS, accessibility to LIF for an antibody was not impaired. The amounts per area detected by radiolabeling method and using the antibody were similar and indicated that LIF was not covered by copolymers. For cell culture addition of diffusible as well as immobilized growth factors or cytokines requires dosage control. Frequently it is necessary to provide homogeneous distribution of the factor of interest. In the present study analysis by fluorescence microscopy confirmed homogeneity for surfaces with covalently immobilized LIF (iLIF) but not for LIF physisorbed to extracellular matrix components collagen type I and fibronectin. LIF transduces signals via the JAK/STAT pathway. Preliminary experiments with LIF-sensitive fibroblasts showed similar activation of STAT3 after stimulation with immobilized or diffusible LIF. The results of STAT3 activation revealed an activation profile with high intensities within the first 15 minutes for both immobilized and diffusible LIF followed by decrease. STAT3 activation profiles were similar on different surfaces and independent of LIF presentation mode. These results revealed that fibroblasts could recognize covalently immobilized LIF onto MA-copolymers and were able to activate STAT3. In the absence of LIF mESC start to differentiate within 24 to 36 hours and loose their pluripotency. To confirm the functional immobilization of LIF mouse embryonic stem cells (mESC) were cultivated on iLIF-modified POMA or POMA+PEG7 surfaces for 72 hours and stained for activated STAT3. Results showed a dose-dependent activation increasing with the iLIF amount per area. Higher amounts (8 and 75 ng/cm^2) of iLIF activated STAT3 similar to 10 ng/ml diffusible LIF. Introduction of PEG7 spacer did not further increased STAT3 activation. Both, the amount of ESC marker Oct4 and the percentage of Oct4-positive cells increased with higher amounts of iLIF and showed similar results as obtained with 10 ng/ml diffusible LIF. Murine ESC cultivated on LIF physisorbed to matrix components expressed similar amounts of transcription factor Oct4 compared to unstimulated cells. STAT3 activation and Oct4 expression in the absence of diffusible cytokine indicated a functional covalent immobilization of LIF. To confirm the pluripotency, mESC were stimulated for 6 to 8 subcultures only with iLIF, cell aggregates were fused with mouse embryos and implanted in pseudopregnant surrogate mothers. Three weeks after birth the contribution of mESC aggregates to chimera was evaluated. ESC stimulated with iLIF only contributed to chimera formation with around the same frequency as mESC cultivated with 10 ng/ml diffusible LIF. Thus, iLIF maintained pluripotency of mESC during in vitro expansion and could replace diffusible LIF. As shown by the experiments, MA-copolymers provide a support to covalently immobilize cell signaling molecules in a functional manner. This method of coupling does not need any protein modification or cross-linking treatment after protein incubation. Reaction can be carried out under sterile conditions at ambient temperature and pressure. The immobilized ligand is distributed equally on the supporting copolymer and the adjustment of required ligand amounts is possible. These properties characterize MA-copolymers as a suitable support to immobilize cell signaling molecules not only for keeping the stem cell fate but also for differentiation studies. Parts of this work were published: K. Alberti, R.E. Davey, K. Onishi, S. George, K. Salchert, F.P. Seib, M. Bornhäuser, T. Pompe, A. Nagy, C.Werner, and P.W. Zandstra. Functional immobilization of signaling proteins enables control of stem cell fate. Nat Methods, 5(7):645–650, Jul 2008. T. Pompe, K. Salchert, K. Alberti, P.W. Zandstra, and C. Werner. Immobilization of growth factors on solid supports for the modulation of stem cell fate. Nat Protocols, 5(6):1042–1050, Jun 2010.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 86-111).