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Lung cancer is the main cause of cancer-related deaths worldwide. Despite the availability of several targeted therapies and immunotherapies in the clinics, the prognosis for lung cancer remains poor. A major problem for the low benefit of these therapies is intrinsic and acquired resistance, asking for pre-clinical models for closer investigation of predictive biomarkers for refined personalized medicine and testing of possible combination therapies as well as novel therapeutic approaches to break resistances.
One third of all lung adenocarcinoma harbor mutations in the KRAS gene, of which 39 % are transitions from glycine to cysteine in codon 12 (KRASG12C). Being considered “undruggable” in previous decades, KRASG12C-inhibitors now paved the way into the standard-of-care for lung adenocarcinoma treatment in the clinics. Still, the overall response rates as well as overall survival of patients treated with KRASG12C-inhibitors are sobering. Therefore, 3D KRASG12C-biomarker in vitro models were developed based on a decellularized porcine jejunum (SISmuc) using commercial and PDX-derived cell lines and characterized in regards of epithelial-mesenchymal-transition (EMT), stemness, proliferation, invasion and c-MYC expression as well as the sensitivity towards KRASG12C-inhibiton. The phenotype of lung tumors harboring KRAS mutations together with a c-MYC overexpression described in the literature regarding invasion and proliferation for in vivo models was well represented in the SISmuc models. A higher resistance towards targeted therapies was validated in the 3D models compared to 2D cultures, while reduced viability after treatment with combination therapies were exclusively observed in the 3D models. In the test system neither EMT, stemness nor the c-MYC expression were directly predictive for drug sensitivity. Testing of a panel of combination therapies, a sensitizing effect of the aurora kinase A (AURKA) inhibitor alisertib for the KRASG12C-inhibitor ARS-1620 directly correlating with the level of c-MYC expression in the corresponding 3D models was observed. Thereby, the capability of SISmuc tumor models as an in vitro test system for patient stratification was demonstrated, holding the possibility to reduce animal experiments.
Besides targeted therapies the treatment of NSCLC with oncolytic viruses (OVs) is a promising approach. However, a lack of in vitro models to test novel OVs limits the transfer from bench to bedside. In this study, 3D NSCLC models based on the SISmuc were evaluated for their capability to perform efficacy and risk assessment of oncolytic viruses (OVs) in a pre-clinical setting. Hereby, the infection of cocultures of tumor cells and fibroblasts on the SISmuc with provided viruses demonstrated that in contrast to a wildtype herpes simplex virus 1 (HSV-1) based OV, the attenuated version of the OV exhibited specificity for NSCLC cells with a more advanced and highly proliferative phenotype, while fibroblasts were no longer permissive for infection. This approach introduced SISmuc tumor models as novel test system for in vitro validation of OVs.
Finally, a workflow for validating the efficacy of anti-cancer therapies in 3D tumor spheroids was established for the transfer to an automated platform based on a two-arm-robot system. In a proof-of-concept process, H358 spheroids were characterized and treated with the KRASG12C-inhibitor ARS-1620. A time- and dose-dependent reduction of the spheroid area after treatment was defined together with a live/dead-staining as easy-to-perform and cost-effective assays for automated drug testing that can be readily performed in situ in an automated system.
The unicellular pathogen Trypanosoma brucei is the causative agent of African
trypanosomiasis, an endemic disease prevalent in sub-Saharan Africa. Trypanosoma brucei alternates between a mammalian host and the tsetse fly vector. The extracellular parasite survives in the mammalian bloodstream by periodically exchanging their ˈvariant surface glycoproteinˈ (VSG) coat to evade the host immune response. This antigenic variation is achieved through monoallelic expression of one VSG variant from subtelomeric ˈbloodstream
form expression sitesˈ (BES) at a given timepoint. During the differentiation from the bloodstream form (BSF) to the procyclic form (PCF) in the tsetse fly midgut, the stage specific surface protein is transcriptionally silenced and replaced by procyclins. Due to their subtelomeric localization on the chromosomes, VSG transcription and silencing is partly regulated by homologues of the mammalian telomere complex such as TbTRF, TbTIF2 and TbRAP1 as well as by ˈtelomere-associated proteinsˈ (TelAPs) like TelAP1. To gain more insights into transcription regulation of VSG genes, the identification and characterization of other TelAPs is critical and has not yet been achieved. In a previous study, two biochemical approaches were used to identify other novel TelAPs. By using ˈco-immunoprecipitationˈ (co-IP) to enrich possible interaction partners of TbTRF and by affinity chromatography using telomeric repeat oligonucleotides, a listing of TelAP candidates has been conducted. With this approach TelAP1 was identified as a novel component of the telomere complex, involved in the kinetics of transcriptional BES silencing during BSF to PCF differentiation. To gain further insights into the telomere complex composition, other previously enriched proteins were characterized through a screening process using RNA interference to deplete potential candidates. VSG expression profile changes and overall proteomic changes after depletion were analyzed by mass spectrometry. With this method, one can gain insights into the functions of the proteins and their involvement in VSG expression site regulation. To validate the interaction of proteins enriched by co-IP with TbTRF and TelAP1 and to identify novel interaction proteins, I performed reciprocal affinity purifications of the four most promising candidates (TelAP2, TelAP3, PPL2 and PolIE) and additionally confirmed colocalization of two candidates with TbTRF via immunofluorescence (TelAP2, TelAP3). TelAP3 colocalizes with TbTRF and potentially interacts with TbTRF, TbTIF2, TelAP1 and TelAP2, as well as with two translesion polymerases PPL2 and PolIE in BSF. PPL2 and PolIE seem to be in close contact to each other at the telomeric ends and fulfill different roles as only PolIE is involved in VSG regulation while PPL2 is not. TelAP2 was previously characterized to be associated with telomeres by partially colocalizing with TbTRF and cells show a VSG derepression phenotype when the protein was depleted. Here I show that TelAP2 interacts with the telomere-binding proteins TbTRF and TbTIF2 as well as with the telomere-associated protein TelAP1 in BSF and that TelAP2 depletion results in a loss of TelAP1 colocalization with TbTRF in BSF.
In conclusion, this study demonstrates that characterizing potential TelAPs is effective in gaining insights into the telomeric complex's composition and its role in VSG regulation in Trypanosoma brucei. Understanding these interactions could potentially lead to new therapeutic targets for combatting African trypanosomiasis.
Electrochemical impedance spectroscopy (EIS) is a valuable technique analyzing electrochemical behavior of biological systems such as electrical characterization of cells and biomolecules, drug screening, and biomaterials in biomedical field. In EIS, an alternating current (AC) power signal is applied to the biological system, and the impedance of the system is measured over a range of frequencies.
In vitro culture models of endothelial or epithelial barrier tissue can be achieved by culturing barrier tissue on scaffolds made with synthetic or biological materials that provide separate compartments (apical and basal sides), allowing for further studies on drug transport. EIS is a great candidate for non-invasive and real-time monitoring of the electrical properties that correlate with barrier integrity during the tissue modeling. Although commercially available transendothelial/transepithelial electrical resistance (TEER) measurement devices are widely used, their use is particularly common in static transwell culture. EIS is considered more suitable than TEER measurement devices in bioreactor cultures that involve dynamic fluid flow to obtain accurate and reliable measurements. Furthermore, while TEER measurement devices can only assess resistance at a single frequency, EIS measurements can capture both resistance and capacitance properties of cells, providing additional information about the cellular barrier's characteristics across various frequencies. Incorporating EIS into a bioreactor system requires the careful optimization of electrode integration within the bioreactor setup and measurement parameters to ensure accurate EIS measurements. Since bioreactors vary in size and design depending on the purpose of the study, most studies have reported using an electrode system specifically designed for a particular bioreactor. The aim of this work was to produce multi-applicable electrodes and established methods for automated non-invasive and real-time monitoring using the EIS technique in bioreactor cultures. Key to the electrode material, titanium nitride (TiN) coating was fabricated on different substrates (materials and shape) using physical vapor deposition (PVD) and housed in a polydimethylsiloxane (PDMS) structure to allow the electrodes to function as independent units. Various electrode designs were evaluated for double-layer capacitance and morphology using EIS and scanning electron microscopy (SEM), respectively. The TiN-coated tube electrode was identified as the optimal choice. Furthermore, EIS measurements were performed to examine the impact of influential parameters related to culture conditions on the TiN-coated electrode system. In order to demonstrate the versatility of the electrodes, these electrodes were then integrated into in different types of perfusion bioreactors for monitoring barrier cells. Blood-brain barrier (BBB) cells were cultured in the newly developed dynamic flow bioreactor, while human umblical vascular endothelial cells (HUVECs) and Caco-2 cells were cultured in the miniature hollow fiber bioreactor (HFBR). As a result, the TiN-coated tube electrode system enabled investigation of BBB barrier integrity in long-term bioreactor culture. While EIS measurement could not detect HUVECs electrical properties in miniature HFBR culture, there was the possibility of measuring the barrier integrity of Caco-2 cells, indicating potential usefulness for evaluating their barrier function. Following the bioreactor cultures, the application of the TiN-coated tube electrode was expanded to hemofiltration, based on the hypothesis that the EIS system may be used to monitor clotting or clogging phenomena in hemofiltration. The findings suggest that the EIS monitoring system can track changes in ion concentration of blood before and after hemofiltration in real-time, which may serve as an indicator of clogging of filter membranes. Overall, our research demonstrates the potential of TiN-coated tube electrodes for sensitive and versatile non-invasive monitoring in bioreactor cultures and medical devices.
Barth Syndrome (BTHS) is an inherited X-chromosomal linked disorder, characterized by early development of cardiomyopathy, immune system defects, skeletal muscle myopathy and growth retardation. The disease displays a wide variety of symptoms including heart failure, exercise intolerance and fatigue due to the muscle weakness. The cause of the disease are mutations in the gene encoding for the mitochondrial transacylase Tafazzin (TAZ), which is important for remodeling of the phospholipid cardiolipin (CL). All mutations result in a pronounced decrease of the functional enzyme leading to an increase of monolysocardiolipin (MLCL), the precursor of mature CL, and a decrease in mature CL itself. CL is a hallmark phospholipid of mitochondrial membranes, highly enriched in the inner mitochondrial membrane (IMM). It is not only important for the formation of the cristae structures, but also for the function of different protein complexes associated with the mitochondrial membrane. Reduced levels of mature CL cause remodeling of the respiratory chain supercomplexes, impaired respiration, defects in the Krebs cycle and a loss of mitochondrial calcium uniporter (MCU) protein. The defective Ca2+ handling causes impaired redox homeostasis and energy metabolism resulting in cellular arrhythmias and defective electrical conduction. In an uncompensated situation, blunting mitochondrial Ca2+ uptake provokes increased mitochondrial emission of H2O2 during workload transitions, related to oxidation of NADPH, which is required to regenerate anti-oxidative enzymes. However, in the hearts and cardiac myocytes of mice with a global knock-down of the Taz gene (Taz-KD), no increase in mitochondrial ROS was observed, suggesting that other metabolic pathways may have compensated for reduced Krebs cycle activation.
The healthy heart produces most of its energy by consuming fatty acids. In this study, the fatty acid uptake into mitochondria and their further degradation was investigated, which showed a switch of the metabolism in general in the Taz-KD mouse model. In vivo studies revealed an increase of glucose uptake into the heart and decreased fatty acid uptake and oxidation. Disturbed energy conversion resulted in activation of retrograde signaling pathways, implicating overall changes in the cell metabolism. Upregulated integrated stress response (ISR) was confirmed by increased levels of the downstream target, i.e., the activating transcription factor 4 (ATF4). A Tafazzin knockout mouse embryonal fibroblast cell model (TazKO) was used to inhibit the ISR using siRNA transfection or pharmaceutical inhibition. This verified the central role of
II
the ISR in regulating the metabolism in BTHS. Moreover, an increased metabolic flux into glutathione biosynthesis was observed, which supports redox homeostasis. In vivo PET-CT scans depicted elevated activity of the xCT system in the BTHS mouse heart, which transports essential amino acids for the biosynthesis of glutathione precursors. Furthermore, the stress induced signaling pathway also affected the glutamate metabolism, which fuels into the Krebs cycle via -ketoglutarate and therefore supports energy converting pathways. In summary, this thesis provides novel insights into the energy metabolism and redox homeostasis in Barth syndrome cardiomyopathy and its regulation by the integrated stress response, which plays a central role in the metabolic alterations. The aim of the thesis was to improve the understanding of these metabolic changes and to identify novel targets, which can provide new possibilities for therapeutic intervention in Barth syndrome.
In dieser Arbeit wurde durch das immunhistochemische Anfärben von nodalen (Natriumkanäle, NF), paranodalen (Caspr, NF) und internodalen (MBP) Proteinen der in Fingerhautbiopsien vorhanden Nervenfasern untersucht, ob eine Veränderung der typischen Verteilungsmuster dieser Proteine, eine demyelinisierende Polyneuropathie anzeigen kann. Dazu wurden am Universitätsklinikum Würzburg prospektiv 93 Polyneuropathie-Patienten und 25 Kontrollpersonen rekrutiert. Bei allen Patienten wurden Hautstanzbiospien am Zeigefinger durchgeführt. Bei 35 Patienten mit schweren oder unklaren Verläufen, wurden konsiliarisch Nervus suralis Biopsien durchgeführt. Aus einem Abschnitt von 27 dieser Biopsien, konnten im Rahmen dieser Arbeit Zupfnervenpräparate angefertigt und analog zu den Hautbiopsien ausgewertet werden. Aus der Routinediagnostik der Klinik flossen weiterhin die Ergebnisse der elektrophysiologischen Routinediagnostik und der Histologiebefund der Nervus suralis Biopsien in die Auswertung ein.
Zusammenfassend kamen veränderte Natriumkanalbanden in Fingerhautbiopsien signifikant häufiger bei Patienten mit elektrophysiologisch als demyelinisierend befundeten Polyneuropathien, als bei Patienten mit elektrophysiologisch als axonal befundeten Polyneuropathien vor. Vielfach fanden sich veränderte Natriumkanalbanden inmitten para- und internodal unauffälliger Schnürringe und umgekehrt. Diese Beobachtung stützt die bereits in Vorarbeiten vorgeschlagene und in der aktuellen Leitlinie zur Diagnostik für Polyneuropathien aufgegriffene Entität der Paranodopathien (Uncini, Susuki, & Yuki, 2013). Möglich wäre, dass eine veränderte Verteilung der Natriumkanäle die schnelle Leitfähigkeit beeinträchtigen und somit trotz intakter Bemarkung, elektrophysiologisch das Bild einer demyelinisierenden Neuropathie vermittelt. Ein direkter Zusammenhang zwischen dem Auftreten von doppelten und verlängerten Natriumkanalbanden und einzelnen Messwerten (z.B. Amplituden und Latenzzeiten) fand sich nicht. Auch in den Zupfnervenpräparaten der Nervus suralis Biopsien, konnten o.g. Verteilungsmuster untersucht werden. Deren Vorkommen zeigte sich als unabhängig vom elektrophysiologischen und histologischen Befund, von der Ätiologie der PNP und von den gefundenen Veränderungen in den Hautbiopsien des betreffenden Patienten.
Es zeigte sich, dass die unmittelbare postoperative gesundheitsbezogene Lebensqualität erwartungsgemäß deutlich eingeschränkt, jedoch nach circa sechs Monaten wieder auf dem Ausgangsniveau der präoperativen Ebene angekommen war. Sowohl die Symptomskalen als auch die Funktionsskalen zeigten statistisch signifikante Unterschiede der erhobenen Werte bezüglich des Vergleichs der präoperativen zu den postoperativen Daten, dasselbe ließ sich über die Werte im Rahmen der Verlaufskontrolle nach circa sechs Monaten erheben. Eine kurzfristige Einbuße der Lebensqualität durch einen stationären Krankenhausaufenthalt sowie einer operativen Versorgung erscheint logisch. Für die zukünftige Entscheidung vor allem auch für Personen, welche aufgrund einer benignen Leberraumforderung eine operative Versorgung erhalten sollen, ist zu sagen, dass die globale gesundheitsbezogene Lebensqualität postoperativ nach circa sechs Monaten gleich bzw. etwas gebessert ausfiel und somit eine Rechtfertigung der operativen Versorgung auch bei benignen Erkrankungen darstellen kann.
Ein wesentlicher Aspekt der Arbeit ist, dass gezeigt werden konnte, dass auch bei komplexen Lebereingriffen eine schnelle Rekonvaleszenz - mindestens auf das Niveau vor dem Eingriff - innerhalb der ersten sechs Monate zu erwarten ist. Die systematische Erfassung der Lebensqualität hilft die postoperativen Einschränkungen und die Rekonvaleszenz zu normieren.
Graphs provide a key means to model relationships between entities.
They consist of vertices representing the entities,
and edges representing relationships between pairs of entities.
To make people conceive the structure of a graph,
it is almost inevitable to visualize the graph.
We call such a visualization a graph drawing.
Moreover, we have a straight-line graph drawing
if each vertex is represented as a point
(or a small geometric object, e.g., a rectangle)
and each edge is represented as a line segment between its two vertices.
A polyline is a very simple straight-line graph drawing,
where the vertices form a sequence according to which the vertices are connected by edges.
An example of a polyline in practice is a GPS trajectory.
The underlying road network, in turn, can be modeled as a graph.
This book addresses problems that arise
when working with straight-line graph drawings and polylines.
In particular, we study algorithms
for recognizing certain graphs representable with line segments,
for generating straight-line graph drawings,
and for abstracting polylines.
In the first part, we first examine,
how and in which time we can decide
whether a given graph is a stick graph,
that is, whether its vertices can be represented as
vertical and horizontal line segments on a diagonal line,
which intersect if and only if there is an edge between them.
We then consider the visual complexity of graphs.
Specifically, we investigate, for certain classes of graphs,
how many line segments are necessary for any straight-line graph drawing,
and whether three (or more) different slopes of the line segments
are sufficient to draw all edges.
Last, we study the question,
how to assign (ordered) colors to the vertices of a graph
with both directed and undirected edges
such that no neighboring vertices get the same color
and colors are ascending along directed edges.
Here, the special property of the considered graph is
that the vertices can be represented as intervals
that overlap if and only if there is an edge between them.
The latter problem is motivated by an application
in automated drawing of cable plans with vertical and horizontal line segments,
which we cover in the second part.
We describe an algorithm that
gets the abstract description of a cable plan as input,
and generates a drawing that takes into account
the special properties of these cable plans,
like plugs and groups of wires.
We then experimentally evaluate the quality of the resulting drawings.
In the third part, we study the problem of abstracting (or simplifying)
a single polyline and a bundle of polylines.
In this problem, the objective is to remove as many vertices as possible from the given polyline(s)
while keeping each resulting polyline sufficiently similar to its original course
(according to a given similarity measure).
Anxiety patients overgeneralize fear, also because of an inability to perceptually discriminate threat and safety signals. Therefore, some studies have developed discrimination training that successfully reduced the occurrence of fear generalization. The present work is the first to take a treatment-like approach by using discrimination training after generalization has occurred. Therefore, two studies were conducted with healthy participants using the same fear conditioning and generalization paradigm, with two faces as conditioned stimuli (CSs), and four facial morphs between CSs as generalization stimuli (GSs). Only one face (CS+) was followed by a loud scream (unconditioned stimulus, US). In Study 1, participants underwent either fear-relevant (discriminating faces) or fear-irrelevant discrimination training (discriminating width of lines) or a non-discriminative control training between the two generalization tests, each with or without feedback (n = 20 each). Generalization of US expectancy was reduced more effectively by fear-relevant compared to fear-irrelevant discrimination training. However, neither discrimination training was more effective than non-discriminative control training. Moreover, feedback reduced generalization of US expectancy only in discrimination training. Study 2 was designed to replicate the effects of the discrimination-training conditions in a large sample (N = 244) and examine their benefits in individuals at risk for anxiety disorders. Again, feedback reduced fear generalization particularly well for US expectancy. Fear relevance was not confirmed to be particularly fear-reducing in healthy participants, but may enhance training effects in individuals at risk of anxiety disorder. In summary, this work provides evidence that existing fear generalization can be reduced by discrimination training, likely involving several (higher-level) processes besides perceptual discrimination (e.g., motivational mechanisms in feedback conditions). Its use may be promising as part of individualized therapy for patients with difficulty discriminating similar stimuli.
Sepsis ist ein häufiges und akut lebensbedrohliches Syndrom, das eine Organfunktionsstörung in Folge einer dysregulierten Immunantwort auf eine Infektion beschreibt. Eine frühzeitige Diagnosestellung und Therapieeinleitung sind von zentraler Bedeutung für das Überleben der Patient:innen. In einer Pilotstudie konnte unsere Forschungsgruppe mittels Durchflusszytometrie eine ausgeprägte Hyporeaktivität der Thrombozyten bei Sepsis nachweisen, die einen potenziell neuen Biomarker zur Sepsis-Früherkennung darstellt. Zur Evaluation des Ausmaßes und Entstehungszeitpunktes der detektierten Thrombozytenfunktionsstörung wurden im Rahmen der vorliegenden Arbeit zusätzlich zu Patient:innen mit Sepsis (SOFA-Score ≥ 2; n=13) auch hospitalisierte Patient:innen mit einer Infektion ohne Sepsis (SOFA-Score < 2; n=12) rekrutiert. Beide Kohorten wurden zu zwei Zeitpunkten (t1: <24h; t2: Tag 5-7) im Krankheitsverlauf mittels Durchflusszytometrie und PFA-200 untersucht und mit einer gesunden Kontrollgruppe (n=28) verglichen.
Phänotypische Auffälligkeiten der Thrombozyten bei Sepsis umfassten: (i) eine veränderte Expression verschiedener Untereinheiten des GPIb-IX-V-Rezeptorkomplexes, die auf ein verstärktes Rezeptor-Shedding hindeutet; (ii) ein ausgeprägtes Mepacrin-Beladungsdefizit, das auf eine zunehmend reduzierte Anzahl von δ-Granula entlang des Infektion-Sepsis Kontinuums hinweist; (iii) eine Reduktion endständig gebundener Sialinsäure im Sinne einer verstärkten Desialylierung. Die funktionelle Analyse der Thrombozyten bei Sepsis ergab bei durchflusszytometrischer Messung der Integrin αIIbβ3-Aktivierung (PAC-1-Bindung) eine ausgeprägte generalisierte Hyporeaktivität gegenüber multiplen Agonisten, die abgeschwächt bereits bei Infektion nachweisbar war und gemäß ROC-Analysen gut zwischen Infektion und Sepsis diskriminierte (AUC >0.80 für alle Agonisten). Im Gegensatz dazu zeigten Thrombozyten bei Sepsis und Analyse mittels PFA-200 unter Einfluss physiologischer Scherkräfte eine normale bis gar beschleunigte Aggregation.
Die Reaktivitätsmessung von Thrombozyten mittels Durchflusszytometrie stellt weiterhin einen vielversprechenden Biomarker für die Sepsis-Früherkennung dar. Für weitere Schlussfolgerungen ist jedoch eine größere Kohorte erforderlich. In nachfolgenden Untersuchungen sollten zudem mechanistische Ursachen der beschriebenen phänotypischen und funktionellen Auffälligkeiten von Thrombozyten bei Infektion und Sepsis z.B. mittels Koinkubationsexperimenten untersucht werden.
Die Jahresabschlussprüfung verfolgt das Ziel, die Verlässlichkeit der Rechnungslegung zu bestätigen. Folglich kann sie einen wesentlichen Beitrag zu einem hohen Informationsniveau an den Märkten leisten. Angesichts dieser großen ökonomischen Bedeutung unternimmt der deutsche Gesetzgeber zahlreiche Anstrengungen, um eine hohe Prüfungsqualität sicherzustellen.
Die Sichtung der Wirtschaftsprüferordnung zeigt hierbei, dass regulatorische Maßnahmen ergriffen werden, die am Kern der Jahresabschlussprüfung ansetzen, nämlich an den Berufsangehörigen selbst. So wurde der Zugang zum Berufsstand der vereidigten Buchprüfer mehrmals geschlossen und wiedereröffnet. Des Weiteren sind markante Anpassungen des Niveaus des Wirtschaftsprüfungsexamens im Zeitablauf zu erkennen. Bei der Jahresabschlussprüfung der Unternehmen von öffentlichem Interesse sind außerdem besondere Berufspflichten zu erfüllen. Zum einen ist diesen schweren Eingriffen in die Freiheit der Berufswahl und der Berufsausübung gemein, dass sie allesamt die Qualifikation des Abschlussprüfers adressieren. Zum anderen werden die entsprechenden Gesetzesänderungen mehrheitlich mit einer Stärkung der Prüfungsqualität begründet.
Fraglich ist, inwiefern jene Facetten der Prüferqualifikation tatsächlich einen Einfluss auf die Prüfungsqualität ausüben. Aufgrund mangelnder Evidenz ergibt sich die Notwendigkeit, eine empirische Studie am deutschen Prüfermarkt durchzuführen und somit den Beginn zur Schließung der identifizierten Forschungslücke zu setzen.
Das Ziel der vorliegenden Dissertation besteht folglich darin, den Zusammenhang zwischen der Prüferqualifikation und der Prüfungsqualität mittels Regressionsanalysen zu untersuchen. Dazu wurde ein einzigartiger Datensatz zu deutschen privaten prüfungspflichtigen Kapitalgesellschaften mit unkonsolidierten Finanz- und Prüferinformationen im Zeitraum 2006-2018 mit insgesamt 217.585 grundlegenden Beobachtungen erhoben, bereinigt und aufbereitet. Da die Prüfungsqualität nicht direkt beobachtbar ist, wird zwischen wahrgenommener Prüfungsqualität und tatsächlicher Prüfungsqualität unterschieden. Im Rahmen dieser Dissertation wird die wahrgenommene Prüfungsqualität über Fremdkapitalkosten und die tatsächliche Prüfungsqualität über absolute diskretionäre Periodenabgrenzungen approximiert.
Die Ergebnisse der Hauptregressionen zeigen überwiegend, dass kein Zusammenhang zwischen den Maßgrößen der Prüferqualifikation und der wahrgenommenen und tatsächlichen Prüfungsqualität besteht. Die Zusatz- und Sensitivitätsanalysen unterstützen diesen Befund. So können mit Blick auf die Berufszugangsregelungen keine Qualitätsunterschiede zwischen den Berufsständen der Wirtschaftsprüfer und der vereidigten Buchprüfer nachgewiesen werden. Auch innerhalb des Berufstandes der Wirtschaftsprüfer ergeben sich keine Hinweise auf ein Qualitätsgefälle zwischen den Prüfergruppen, die unterschiedliche Examensanforderungen durchlebt haben. Hinsichtlich der Berufsausübungsregelungen ist zu beobachten, dass die zusätzlichen Anforderungen an die Jahresabschlussprüfung der Unternehmen von öffentlichem Interesse nicht mit einer anderen Prüfungsqualität bei privaten Unternehmen verbunden sind. Die beschriebenen regulatorischen Schritte des Gesetzgebers im Bereich der Prüferqualifikation erscheinen somit im Lichte einer verbesserten Prüfungsqualität nicht zwingend gerechtfertigt.