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Role of fms-like tyrosine kinase 3 in cardiac health and disease

Della Verde, Giacomo. Role of fms-like tyrosine kinase 3 in cardiac health and disease. 2018, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_12755

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Abstract

The fms-like tyrosine kinase 3 receptor (flt3) and ligand (flt3L) are important regulators of early haematopoiesis (1). Uncontrolled activity of flt3 is associated with acute myeloid leukaemia, making flt3 a major target of receptor tyrosine kinase inhibitors (TKIs) (2). TKIs are currently used in a variety of malignancies and patients have experienced cardiotoxicity under some of them. We recently demonstrated that exogenous activation of flt3 through intramyocardial injection of flt3L is cardioprotective and improves post-myocardial infarction remodeling and function in mice (3).
Based on this background, we wanted to assess how endogenous disruption of flt3-signaling affects the healthy and the injured heart. We also hypothesized that lack of flt3L has an impact on the adult cardiac progenitor cell pool, and, hence, on their contribution to cardiac homeostasis.
We isolated cardiac progenitor cells (CPCs) according to the side population (SP) phenotype (SP-CPCs) from 12 week-old wt and flt3L-/- mice (4) and we further expanded the SP-CPC fraction positive for Sca1 and negative for CD31 in culture (5). Our in vivo findings showed a reduced number of SP-CPCs in flt3L-/- hearts, suggesting an untimely activation of a proportion of this physiologically quiescent population. In line with this finding, transcriptional comparison revealed a reduced CD31- progenitor cell signature in flt3L-/- SP-CPCs, with downregulation of transcripts involved in cell cycle arrest and stemness. Expanded SP-CPCs do express functional flt3 receptor and secrete flt3L allowing for an autocrine and/or paracrine activation of the receptor. SP-CPCs maintained the capacity to differentiate into different cardiac lineages when expanded under progenitor potential-preserving culturing conditions. However, in this context, flt3L-/- SP-CPCs showed enhanced proliferation capacity associated with reduced differentiation potential towards all three major cardiac lineages, i.e., cardiomyocytes, smooth muscle and endothelial cells.
Echocardiography showed that disruption of flt3-signaling leads to significant systolic dysfunction and subtle structural alterations of the heart. Specifically, flt3L-/- hearts are smaller and exhibit reduced microvascularization within the ventricular wall. Together, these findings support that flt3-signaling is important for the maintenance of a functional CPC pool and cardiac homeostasis of the healthy heart. We further investigated the implications of the lack of a functional flt3 system in a model of myocardial infarction. Given the importance of flt3 in cardiomyocyte survival (3) and myocardial microvascularization, we hypothesized that flt3-disruption may aggravate post-infarct myocardial damage and dysfunction. Contrary to this hypothesis, however, flt3L ablation mitigated the functional decline during the acute and post-acute phase after myocardial infarction. This protective effect may involve potential immunomodulatory properties related to flt3-signaling as supported by our most recent RNA sequencing data.
In summary, this thesis work shows that in a context of a potential prospective use of CPCs for cardiac cell therapy, careful adjustments of culturing conditions are pivotal to preserve the CPC potential, and thus the capability for multi-lineage commitment and differentiation, during ex vivo expansion.
Furthermore, this work uncovers a so-far unrecognized role of flt3 signaling in the regulation of adult CPC homeostasis and function. In particular we showed that flt3 contributes to the maintenance of a pool of quiescent, functional cardiac progenitor cells in vivo and their balanced proliferation and differentiation in vitro.
Finally, our most recent data suggest that the systemic inhibition of flt3 may be protective during the early phase post-myocardial infarction. In view of the increasing use of TK targeting cancer therapies, improved understanding of the roles of such TK in cardiac health and disease is important in order to anticipate potential cardiac side effects. This work uncovers so far unknown functions of flt3 signaling in the healthy and injured heart that raise both awareness of potential cardiac toxicity, but also of a possible therapeutic effect of the systemic inhibition of flt3 in the post-acute phase after myocardial infarction.
Advisors:Handschin, Christoph and Kuster, Gabriela M.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Growth & Development > Growth & Development (Handschin)
UniBasel Contributors:Handschin, Christoph
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:12755
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (102 Seiten)
Language:English
Identification Number:
Last Modified:10 Oct 2018 04:30
Deposited On:09 Oct 2018 14:18

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