Open Access

New World arenaviruses represent an important group of zoonotic pathogens that pose a serious threat to human health. While some virus species cause severe disease, resulting in hemorrhagic fever and neurological symptoms, other closely related family members exhibit little or no pathogenicity. For instance, Junín virus (JUNV) is the causative agent of Argentine hemorrhagic fever, while the closely related Tacaribe virus (TCRV) is avirulent in humans. Little is known about host cell responses to infection, or how they contribute to virulence; however, TCRV strongly induces caspase-dependent apoptosis (i.e. non-inflammatory programmed cell death) in infected cells, whereas JUNV does not. In order to better understand the connection between apoptosis and pathogenesis, we sought to unravel the regulation of pro- and anti-apoptotic signaling in response to arenavirus infection. We demonstrated that apoptosis induced by TCRV proceeds over the mitochondrial-regulated intrinsic pathway and involves activation of p53 (accumulation and phosphorylation), activation of the pro-apoptotic BH3-only factors Puma and Noxa (accumulation), as well as inactivation of another pro-apoptotic factor called Bad (phosphorylation). The regulation of these factors in response to TCRV infection is accompanied by other classical hallmarks of intrinsic apoptosis, such as disorganization of the mitochondrial network, cytochrome c release, PS flipping, caspase cleavage and nuclear condensation. The involvement of the BH3-only factors as key players in regulating TCRV-induced apoptosis could also be validated in knockout cells, which showed either suppressed or increased apoptosis depending on the respective activation (i.e. Puma and Noxa) or inactivation (i.e. Bad) status of the respective BH3 protein. Interestingly, while JUNV does not trigger late stages of apoptosis induction (i.e. caspase activation, nuclear condensation and cell death), we could show that it activates similar upstream pro-apoptotic signaling events including activation of p53, Puma and Noxa. This supports the current hypothesis that JUNV actively evades the induction of apoptosis through the involvement of a mechanism targeting late steps in the apoptotic cascade. Specifically, this model proposes that intrinsic activation is suppressed at the level of caspase activation by JUNV NP, which serves as an alternative substrate for caspase cleavage. Additionally, in order to identify viral factors associated with the induction of apoptosis, a full genome sequencing of TCRV was performed and contributed to the validation and correction of substantial errors reported in existing sequences for TCRV. With the help of this sequence, correct expression plasmids containing the viral genes for NP, GP and Z were constructed and tested for their ability to induce apoptosis in vitro. This revealed that both TCRV and JUNV Z are triggers for apoptosis, which further supports our finding that JUNV also induces activation of pro-apoptotic factors. Again, consistent with a model where JUNV NP blocks caspase activation directly, co-expression of JUNV Z and NP abrogated caspase activation, while simultaneous expression of TCRV NP and Z still resulted in cell death. Finally, identification of the specific apoptotic factors involved in regulating TCRV-induced apoptosis (i.e. Bad, Puma and Noxa) and the generation of the respective knockout cell lines allowed us to investigate what influence apoptosis induction has on virus infection. Interestingly, knockout of these factors showed no direct impact on virus growth in Vero cells. However, TCRV particles produced in cells with the individual pro-apoptotic (i.e. Puma and Noxa) or anti-apoptotic (i.e. Bad) factors knocked out showed altered infectivity in primary human monocytes and macrophages, which represent important target cells for arenaviruses. Since TCRV particles that originate from the different knockout cells would be expected to contain different amounts of PS in their envelope (depending on the level of apoptosis taking place), this suggests a role of apoptosis in facilitating PS-receptor-mediated entry and/or PS-receptor signaling through downstream kinases, either of which could be contributing to successful infection in professional phagocytic cells. In particular, phosphorylation of some of the identified factors involved in regulating TCRV-induced apoptosis indicates the involvement of upstream kinases from diverse signaling pathways, some of which also play a role in regulating cytokine production – another host cell reaction that differs significantly between TCRV- and JUNV-infected monocytes and macrophages. As such, these findings represent an exciting basis for a possible connection between apoptotic responses and the regulation of pro- and anti-inflammatory cytokine responses via their associated upstream signaling processes and provide a starting point for future studies that will help us to better understand how these processes contribute to arenavirus pathogenicity.

Non-thermal atmospheric pressure plasma has drawn more and more attention to the field of wound healing research during the last two decades. It is characterized by a unique composition, which includes amongst others free radicals, ions and electrons. Furthermore, non-thermal plasma exhibits temperatures that are below those inducing thermal cell damage. Next to its well-established anti-bacterial properties, plasma can have lethal as well as stimulating effects on mammalian cells. Therefore, the medical application of non-thermal plasma on chronic wounds seems to be a promising tool to enable healing processes. However, less is known about the plasma-mediated induction of intracellular signaling pathways in human immune cells, which play a leading part in the process of wound recovery and removal of pathogens. Therefore, this thesis examined the cellular effects of a non-thermal atmospheric pressure plasma treatment on human immune cells using the argon plasma jet kinpen 09. Here, the CD4+ T helper cell line Jurkat, the monocyte cell line THP-1 as well as the corresponding primary cells were investigated. First, cell survival and apoptosis induction was assessed in response to non-thermal plasma treatment by growth curves and flow cytometric assays. On the one hand it could be shown that primary cells are more susceptible to plasma treatment than the respective cell lines. On the other hand, monocytes responded less sensitive to plasma exposure than lymphocytes. Furthermore, this thesis outlined the impact of non-thermal plasma treatment on the gene expression level of immune cells. Therefore, DNA microarray analysis was performed with the cell lines Jurkat and THP-1. It became obvious that plasma exposure modulated the expression of several genes in both cell types. Differential expression of distinct target genes was further validated by quantitative PCR in the immune cell lines. Here, elevated gene expression levels of JUN and FOS in Jurkat cells and increased transcription of JUND in THP-1 cells in response to plasma treatment were made visible. JUN, FOS and JUND are components of the transcription factor AP-1, which is involved amongst others in gene expression of IL-8 and HMOX-1. Consequently, transcriptional induction of the inflammatory cytokine IL-8 as well as the enzymes HMOX-1 and GSR was detected in plasma-treated THP-1 cells. In addition, alterations in the protein activation levels were analyzed in plasma-treated Jurkat, THP-1 cells and primary monocytes. Since some of the identified target genes are known to be associated with the MAPK pathways, the regulation of these cascades was further investigated by western blot analysis. In all investigated cell types the pro-proliferative signaling molecules ERK 1/2 and MEK 1/2 as well as the pro-apoptotic signaling proteins p38 MAPK and JNK 1/2 were activated in a plasma treatment time dependent manner. In contrast to Jurkat and primary monocytes, the anti-apoptotic HSP27 was only induced in THP-1 cells in response to plasma exposure. Moreover, modulation of cytokine production and secretion was examined in the different immune cell types and co-cultured THP-1 and HaCaT keratinocytes by ELISA or flow cytometry. While Jurkat cells showed no plasma-mediated regulation of cytokine expression, THP-1 cells revealed an increased IL-8 secretion after long plasma time duration (360 s). Additionally, the intracellular expression levels of IL-6 and IL-8 were modulated in primary monocytes by plasma exposure. While short plasma treatment caused no alteration of the number of cells expressing IL-8 an up-regulation of the intracellular IL-6 level occurred after 30 s of plasma treatment. Long plasma treatment times resulted in a significant decrease of the intracellular IL-8 and IL-6 production levels. Furthermore, co-cultured THP-1 and HaCaT cells as well as mono-cultured THP-1 and HaCaT cells were examined regarding their cytokine secretion profile. Here, cells treated with plasma (180 s) as well as LPS and plasma (180 s and LPS) were compared with untreated cells. IL-6, IL-8 and GM-CSF secretion was induced by both plasma and plasma combined with LPS treatment in mono-cultivated HaCaT cells and co-cultured cells. Though, the highest cytokine secretion levels were reached in the plasma and LPS exposed co-culture. In contrast, mono-cultivated THP-1 cells only showed an increased secretion of IL-6, IL-8 and TNFa after incubation with plasma together with LPS exposed medium. In conclusion, this study revealed for the first time the non-thermal plasma-modulated expression of numerous genes and cytokines and the activation state of various signaling cascades in human immune cells. Thus, it contributes to gain a better understanding of the immune-modulatory impacts of plasma that might promote the wound healing process.

Lungenkrebs ist die weltweit häufigste Ursache eines krebsassoziierten Todes und nimmt weiter stetig in seiner Prävalenz zu. Das Versagen der Standard-Chemotherapie ist besonders im fortgeschrittenen Stadium für viele Todesfälle verantwortlich. Neue Therapiewege werden daher dringend benötigt. Auch die Behandlung von Medulloblastomen stellt sich gerade bei erkrankten Kindern unter 3 Jahren als schwierig dar, auch weil durch die oftmals sehr intensiven Therapieregime mit schwerwiegenden Spätfolgen gerechnet werden muss. Es muß dementsprechend ebenso für diese Erkrankung nach innovativen Behandlungsansätzen gesucht werden. TRAIL verkörpert solch einen neuen, vielversprechenden Ansatz, da es in der Lage ist selektiv in Tumorzellen eine Apoptose zu bewirken. In ersten klinischen Studien hat es bereits seine gute Verträglichkeit bewiesen. Jedoch sind in zahlreichen Tumoren Resistenzen gegenüber TRAIL gefunden worden, welche die therapeutische Nutzung einschränken könnten. Die Proteinkinase C-Familie wurde schon mehrfach mit einer TRAIL-Resistenz in Verbindung gebracht. In dieser Arbeit wurde daher die TRAIL-Resistenz von A549 Lungenkarzinom- und DAOY Medulloblastomzellen in Hinblick auf ihre Beeinflussbarkeit durch die Proteinkinase C (PKC) untersucht. Sowohl in A549, als auch in DAOY Zellen, die zuvor noch nicht in diesem Zusammenhang untersucht wurden, konnte durch eine Inhibition der PKC die TRAIL-Resistenz durchbrochen werden. NPC 15437, ein PKC-Inhibitor, der vor allem die neuen Isoformen der PKC hemmt, verstärkte sehr deutlich den TRAIL-induzierten Zelltod und den Verlust des mitochondrialen Membranpotentials in beiden Zelllinien, ohne selbst wesentlich eine Apoptose auszulösen. Durch den pan-Caspase-Inhibitor z-VAD-fmk war dieser Effekt komplett unterdrückbar. Anschließend wurde versucht die verantwortliche PKC-Isoform zu bestimmen. Die Vorbehandlung mit Phorbol-12-myristat-13-acetat (PMA), Phorbol-12,13-didecanoat (PDD), sowie 12-Deoxyphorbol-13-phenylacetat-20-acetat (dPPA) verminderte den TRAIL-sensibilisierenden Effekt von NPC 15437 signifikant um etwa die Hälfte, während die Vorbehandlung mit Phorbol-13-monoacetat (PA) und Phorbol-12-monomyristat (PMM) keine Wirkung zeigte. Gö6976 und der membrangängige PKCα/β-spezifische Peptidinhibitor myr-ψ-PKC waren zudem nicht in der Lage eine Sensibilisierung für TRAIL zu bewirken. Es ergab sich daraus die Vermutung, dass PKCε eine herausragende Funktion in der TRAIL-Resistenz der Zelllinien ausübt. Der Einsatz von gegen PKCε gerichteter siRNA bestätigte dies und der membrangängige Peptidinhibitor myr-PKCε-V1-2 erfüllte von allen getesteten Substanzen am besten die Funktion eines TRAIL-Wirkungsverstärkers. Außerdem wurde durch Western Blot-Analysen eine mögliche Rolle von cFLIP/CFLAR für die TRAIL-Resistenz von A549 und DAOY Zellen weitestgehend ausgeschlossen. Die vorliegende Arbeit stellt die Proteinkinase C(ε) als einen wichtigen Resistenzfaktor der TRAIL-induzierten Apoptose heraus und zeigt wie deren Hemmung die zukünftige Krebstherapie verbessern könnte.

TNF-alpha und TRAIL representieren interessante Kandidaten für die Behandlung von malignen Tumoren. Verschiedene Krebszellen weisen eine Resistenz gegenüber dem zytotoxischen Effekt von TRAIL und TNF-alpha auf, so dass eine alleinige Tumorbehandlung mit TRAIL und TNF-alpha unzureichend sein kann. In unserer Arbeit erforschten wir die Apoptoseinduktion in der Lungenkarzinomzelllinie A549 nach TRAIL und TNF-alpha-Applikation in Kombination mit der Inhibition der antiapoptotischen Proteine Bcl-xl und PKC-eta. Die Transfektion der A549-Zellen mit chimeren Antisense-ODN ergab eine zeit- und dosisabhängige Suppression von Bcl-xl und PKC-eta, wie sich in der RT-PCR und Western-Blot-Analyse zeigte. Die Suppression von Bcl-xl und PKC-eta führte zu einer verstärkten zytotoxischen Wirkung des TRAIL in Caspase-Aktivitätstests und in der Zellzyklusanalyse. Eine Apoptoseinduktion nach Gabe von TNF-alpha konnten wir in der Zelllinie A549 jedoch nicht erkennen. Unsere Schlussfolgerung ist, das Bcl-xl und die PKC-eta als wesentliche Resistenzfaktoren gegenüber TRAIL agieren und verwertbare Ziele darstellen, um die zytotoxischen Effekte von Apoptose-induzierenden Substanzen wie zum Beispiel TRAIL zu verstärken.

Die Parodontitis stellt eine entzündlich-degenerative Erkrankung aller Bestandteile des Zahnhalteapparates dar. Bis heute sind die Mechanismen des Gewebeabbaus nicht hinreichend geklärt. Ziel dieser Arbeit war es, den Matrixabbau während einer Parodontitis hinsichtlich verschiedener Marker des pathogenetischen Ablaufs und Apoptose zu charakterisieren. Granulationsgewebe und gesunde Gingiva wurden immunhistochemisch auf Elastase (Neutrophilenmarker), IL-1a, MMP-1, MMP-8, Caspase-3 und Caspase-6 untersucht. Zusätzlich wurde eine TUNEL-Untersuchung durchgeführt, um zu überprüfen, ob eine Korrelation zwischen der Expression von Caspasen und dem Nachweis von Apoptose vorliegt. IL-1a und MMP-1 scheinen massiv am Matrixverlust im chronischen Entzündungstadium beteiligt zu sein. Im Granulationsgewebe und in gesunder Gingiva wurde Apoptose nachgewiesen. Apoptose von neutrophilen Granulozyten könnte eine Bedeutung für die Konstanthaltung des zellulären Infiltrates in gesunder Gingiva haben. Wahrscheinlich wird durch Apoptose von Fibroblasten die Reparaturfähigkeit des Bindegewebes während einer Parodontitis eingeschränkt und somit vermehrter Gewebeabbau vermittelt.