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Doxycycline-inducible viral vector systems for selective overexpression of supportive factors to enhance in vitro megakaryocyte and platelet production

Cullmann, Katharina (2020)
Doxycycline-inducible viral vector systems for selective overexpression of supportive factors to enhance in vitro megakaryocyte and platelet production.
Technische Universität Darmstadt
doi: 10.25534/tuprints-00011722
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The generation of platelets and megakaryocytes (MK) in vitro provides a potent strategy to overcome the shortage of today’s platelet transfusions to patients with acute needs. The amount of patients, depending on donations, and in need for transfusions are increasing while platelet donors are not more frequent. Furthermore, the risk of bacterial contamination in platelet products is high due to their storage at room temperature to prevent platelet activation. This also shortens the shelf life of platelet products. After repetitive transfusions, patients can develop refractoriness and immunity adding further complications to the use of platelet therapies. Therefore, alternative sources for platelets are sought for. Platelets can be produced in vitro from MK progenitors, hematopoietic stem cells or pluripotent stem cells. However, production is inefficient, particularly taking in consideration that the tremendous amount 4-5 x 1011 platelets have to be produced for filling one transfusion unit. In this study, we wanted to explore whether the expression of single supporting candidate factors in murine induced pluripotent stem cells (iPSC) could increase platelet production in vitro. We concentrated on the overexpression of major transcription factors of earlyphase megakaryopoiesis (Gata1, Pbx1, and Evi1) and late phase (Nfe2) to enhance MK production platelet release. Furthermore, to support platelet release from MK, we expressed hyperactive variants of the small GTPases RhoA and Cdc42. Gene modifications in iPSC, however, experience major drawbacks because of silencing of ectopic gene expression especially during differentiation. Furthermore, expression of the supportive factors has to be tightly controlled to avoid unwanted interference of the factors with pluripotency and differentiation since the transduction has to be performed in the pluripotent state. To overcome this, a tet-inducible expression system in iPSC was developed which was based on the generation of iPSC containing the reverse tetracycline (rt) transactivator TA-M2 in the Rosa26 safe harbor locus to prevent gene silencing of the (rt)TA-M2 and thereby guaranteeing its robust expression throughout the differentiation process. After verification of pluripotency and differentiation potential of the generated iPSC, the candidate factors were introduced with gammaretroviral vectors containing the respective transgene expressed from a Tet-responsive minimal promoter. In our experiments we found that overexpression of Gata1 elevated production of megakaryocyte progenitors, however, full maturation of the cells was impaired. In contrast, overexpression of Nfe2 elevated numbers of released platelets. In a second approach, we developed a doxycycline (dox)-induced overexpression system that should be transferable to human cells. We improved Tet-inducible all-in-one gammaretroviral vectors by introducing different ubiquitous chromatin opening elements derived from the human HNRPA2B1/CBX3 locus (A2UCOE), previously proven to prevent silencing of constitutive-expressing retroviral vectors in hiPSC. Tet-all-in-one retroviral vectors rely on a persistent expression of the transactivator and good regulation of the tet-responsive promoter. The incorporation of an additional element (with promoter activity) can interfere with the regulation. We incorporated elements of different sizes in sense and antisense transcriptional orientation into Tet-all-in-one gammaretroviral vectors and tested these for the regulation and anti-silencing capacity in different cell lines including murine and human iPSC. The U670 was identified to be the most potent element in preventing silencing which also conferred the strongest expression from the vector in the induced state. Longer fragments also sustained the gene expression but vector titers and induction efficiencies were impaired. Gammaretroviral Tet-all-in-one vectors turned out to be superior to their lentiviral counterparts due to the capability to produce higher titers. Finally, the expression and tight regulation of the thrombopoietin receptor Mpl within Tetinducible gammaretroviral vectors after incorporation of the U670s element was confirmed by cytokine-dependent cell growth. In addition, the PGK promoter could be replaced by the 670bp elements and sustained transgene silencing without interfering with the tight regulation of the vectors. With this part of the study, we found potent gammaretroviral vector candidates which pave the way for future application of overexpression of GATA1 and NFE2 in the human system to increase MK and platelet production in vitro.

Typ des Eintrags: Dissertation
Erschienen: 2020
Autor(en): Cullmann, Katharina
Art des Eintrags: Erstveröffentlichung
Titel: Doxycycline-inducible viral vector systems for selective overexpression of supportive factors to enhance in vitro megakaryocyte and platelet production
Sprache: Englisch
Referenten: Süß, Prof. Dr. Beatrix ; Nuber, Prof. Dr. Ulrike ; Modlich, Prof. Dr. Ute
Publikationsjahr: 2020
Ort: Darmstadt
Datum der mündlichen Prüfung: 3 September 2019
DOI: 10.25534/tuprints-00011722
URL / URN: https://tuprints.ulb.tu-darmstadt.de/11722
Kurzbeschreibung (Abstract):

The generation of platelets and megakaryocytes (MK) in vitro provides a potent strategy to overcome the shortage of today’s platelet transfusions to patients with acute needs. The amount of patients, depending on donations, and in need for transfusions are increasing while platelet donors are not more frequent. Furthermore, the risk of bacterial contamination in platelet products is high due to their storage at room temperature to prevent platelet activation. This also shortens the shelf life of platelet products. After repetitive transfusions, patients can develop refractoriness and immunity adding further complications to the use of platelet therapies. Therefore, alternative sources for platelets are sought for. Platelets can be produced in vitro from MK progenitors, hematopoietic stem cells or pluripotent stem cells. However, production is inefficient, particularly taking in consideration that the tremendous amount 4-5 x 1011 platelets have to be produced for filling one transfusion unit. In this study, we wanted to explore whether the expression of single supporting candidate factors in murine induced pluripotent stem cells (iPSC) could increase platelet production in vitro. We concentrated on the overexpression of major transcription factors of earlyphase megakaryopoiesis (Gata1, Pbx1, and Evi1) and late phase (Nfe2) to enhance MK production platelet release. Furthermore, to support platelet release from MK, we expressed hyperactive variants of the small GTPases RhoA and Cdc42. Gene modifications in iPSC, however, experience major drawbacks because of silencing of ectopic gene expression especially during differentiation. Furthermore, expression of the supportive factors has to be tightly controlled to avoid unwanted interference of the factors with pluripotency and differentiation since the transduction has to be performed in the pluripotent state. To overcome this, a tet-inducible expression system in iPSC was developed which was based on the generation of iPSC containing the reverse tetracycline (rt) transactivator TA-M2 in the Rosa26 safe harbor locus to prevent gene silencing of the (rt)TA-M2 and thereby guaranteeing its robust expression throughout the differentiation process. After verification of pluripotency and differentiation potential of the generated iPSC, the candidate factors were introduced with gammaretroviral vectors containing the respective transgene expressed from a Tet-responsive minimal promoter. In our experiments we found that overexpression of Gata1 elevated production of megakaryocyte progenitors, however, full maturation of the cells was impaired. In contrast, overexpression of Nfe2 elevated numbers of released platelets. In a second approach, we developed a doxycycline (dox)-induced overexpression system that should be transferable to human cells. We improved Tet-inducible all-in-one gammaretroviral vectors by introducing different ubiquitous chromatin opening elements derived from the human HNRPA2B1/CBX3 locus (A2UCOE), previously proven to prevent silencing of constitutive-expressing retroviral vectors in hiPSC. Tet-all-in-one retroviral vectors rely on a persistent expression of the transactivator and good regulation of the tet-responsive promoter. The incorporation of an additional element (with promoter activity) can interfere with the regulation. We incorporated elements of different sizes in sense and antisense transcriptional orientation into Tet-all-in-one gammaretroviral vectors and tested these for the regulation and anti-silencing capacity in different cell lines including murine and human iPSC. The U670 was identified to be the most potent element in preventing silencing which also conferred the strongest expression from the vector in the induced state. Longer fragments also sustained the gene expression but vector titers and induction efficiencies were impaired. Gammaretroviral Tet-all-in-one vectors turned out to be superior to their lentiviral counterparts due to the capability to produce higher titers. Finally, the expression and tight regulation of the thrombopoietin receptor Mpl within Tetinducible gammaretroviral vectors after incorporation of the U670s element was confirmed by cytokine-dependent cell growth. In addition, the PGK promoter could be replaced by the 670bp elements and sustained transgene silencing without interfering with the tight regulation of the vectors. With this part of the study, we found potent gammaretroviral vector candidates which pave the way for future application of overexpression of GATA1 and NFE2 in the human system to increase MK and platelet production in vitro.

Alternatives oder übersetztes Abstract:
Alternatives AbstractSprache

Die Verabreichung von Thrombozyten zur Behandlung von Folgen verschiedener medizinischer Indikationen ist nicht immer komplikationslos. Zum einen steigt die Zahl der Patienten, die diese Therapien benötigen, bei gleichbleibender Zahl von ThrombozytenSpendern, was die Knappheit der Produkte in den nächsten Jahren zur Folge haben könnte. Außerdem erhöht die Aufbewahrung der Thrombozyten-Konzentrate bei Raumtemperatur das Risiko bakterieller Kontaminationen. Somit können die Blutprodukte nur wenige Tage gelagert werden und viele Einheiten müssen unverwendet entsorgt werden. Darüber hinaus reagieren einige Spender mit Immunreaktion auf die erhaltenen Präparate, was zur Refraktärität von Thrombozyten führt. Eine mögliche Lösung hierfür ist die Produktion von patienteneigenen und HLA-kompatiblen Thrombozyten in der Zellkultur aus induzierten pluripotenten Stammzellen (iPSC). Ein großes Hindernis ist dabei die große Menge an Zellen, die hergestellt werden muss (4-5 x 1011) und die mindere Funktionalität der in Kultur hergestellten Thrombozyten im Vergleich zu den gespendeten. In dieser Arbeit haben wir eine Strategie entwickelt, um Ausbeute und Funktionalität der im Labor hergestellten Thrombozyten zu steigern. Dies basiert auf einem induzierbaren gammaretroviralen Vektorsystem. Im ersten Teilprojekt sollen Ausbeute und Funktionalität von in vitro erzeugten Thrombozyten gesteigert werden, indem spezifische Faktoren zu einem bestimmten Zeitpunkt während der Differenzierung überexprimiert werden. Im Fokus standen hierbei die Transkriptionsfaktoren Gata1, Pbx1 und Evi1 die ein frühes Stadium der Megakaryopoese kontrollieren und Nfe2, der die Freisetzung von Thrombozyten steuert. Eine besondere Herausforderung ist die Stilllegung der eingebrachten Gene, insbesondere während der Differenzierung von iPSC. Der PGK Promotor, der in vielen Systemen die Expression des Transaktivators des Tetinduzierbaren Systems steuert, ist davon ganz besonders betroffen durch seine vielen potenziellen Methylierungsstellen. Durch die Erzeugung von murinen iPSC, die den (rt)TA-M2 von einem internen Lokus exprimieren, konnte dessen kontinuierliche Expression gewährleistet werden. Nach Verifizierung der Pluripotenz und des Differenzierungsmusters der generierten iPSC und deren Transduktion mit den einzelnen unterstützenden Faktoren wurde gezeigt, dass die Überexpression von Gata1 zu einem prozentualen Anstieg der Vorläuferzellen führte, die jedoch Defizite in der finalen Ausreifung aufwiesen. Im Gegensatz dazu führte die Überexpression von Nfe2 zu einer gesteigerten Anzahl von freigesetzten Thrombozyten pro Megakaryozyt. Überexpression beider Faktoren in Kombination wäre daher eine vielversprechende Kombination für künftige Studien. Um dieses System auf die Differenzierung von humanen Thrombozyten aus iPSC übertragen zu können, haben wir gammaretrovirale All-in-one-Vektoren optimiert. Hierbei wird die Stilllegung des PGK Promotors durch das Einfügen eines Chromatin-öffnenden-elements (A2UCOE) verhindert. Dieses stammt vom humanen HNRPA2B1/CBX3 Genlokus. Da die Elemente Promotoraktivität besitzen, könnte deren Einbringen die Regulierbarkeit der Vektoren beeinträchtigen. Wir haben Elemente verschiedener Größen und Lokalisationen in jeweils zwei verschiedenen transkriptionellen Orientierungen vor den PGK Promotor eingesetzt. Dabei stellte sich heraus, dass sich das Element U670s besonders eignet, da die Regulierung nicht beeinträchtigt war und die Stilllegung des Transgens in verschiedenen Zelllinien inklusive hiPSC verzögert bzw. verhindert werden konnte. Dabei waren gammaretrovirale Vektoren den lentiviralen überlegen, aufgrund der höheren Titer, die erreicht werden konnten. Die Funktionalität des Vektors wurde durch die regulierte Expression des Thrombopoietinrezeptors Mpl und das daraus relsultierende Cytokin-abhängige Wachstum von transduzierten Zellen bestätigt. Auch der Austausch des PGK Promotors durch das U670 Element konnte die Expression des Transgens weiterhin regulieren. Hiermit haben wir Vektoren hergestellt, um die Faktoren GATA1 und NFE2 auch im humanen System überexprimieren zu können und somit zur Steigerung der Ausbeute generierter Megakaryozyten und Thrombozyten in der Zellkultur auch im humanen System beitragen zu können.

Deutsch
URN: urn:nbn:de:tuda-tuprints-117222
Sachgruppe der Dewey Dezimalklassifikatin (DDC): 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
Fachbereich(e)/-gebiet(e): 10 Fachbereich Biologie
10 Fachbereich Biologie > Stammzell- und Entwicklungsbiologie
10 Fachbereich Biologie > Synthetic RNA biology
Hinterlegungsdatum: 26 Mai 2020 08:39
Letzte Änderung: 25 Jul 2023 08:46
PPN:
Referenten: Süß, Prof. Dr. Beatrix ; Nuber, Prof. Dr. Ulrike ; Modlich, Prof. Dr. Ute
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: 3 September 2019
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